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NBSIR 86-3304

Technical Activities 1985

Surface Science Division

C.J. Powell, Chief

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Center for Chemical Physics

Surface Science Division

Gaithersburg, MD 20899

December 1985

Issued January 1986

Prepared for: U.S. DEPARTMENT OF COMMERCE

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ithersburg, MD 20899

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NBSIR 86-3304

» • m TECHNICAL ACTIVITIES 1985

SURFACE SCIENCE DIVISION

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C.J. Powell, Chief

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Center for Chemical Physics

Surface Science Division

Gaithersburg, MD 20899

December 1985

Issued January 1986

Prepared for: U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

ABSTRACT

This report summarizes technical activities of the NBS Surface Science

Division during Fiscal Year 1985. These activities include surface-standards

work, experimental and theoretical research in surface science, the

development of improved measurement methods, and applications to important

scientific and national problems. A listing is given of publications, talks,

professional committee participation, and professional interactions by the

Division staff.

Key words: surface chemistry; surface physics; surface science; surface

standards
FOREWORD

This report is a summary of the technical activities of the NBS Surface

Science Division for the period October 1, 1984 to September 30, 1985. The

report was prepared as part of the Annual Report of the Center for Chemical

Physics within the National Measurement Laboratory of NBS.

The technical work of the Division is separated formally into a task for

the Development of Measurement Methods for Surface Properties and a Surface

Competence task, as outlined briefly in the Introduction. The former task

has two principal activities, a Surface Standards Program and a Surface

Measurement Program. Work performed for these two programs is reported in

Sections 2 and 3. respectively, of the report while work performed for the

competence task is reported in Section 4. There are a number of separate

technical projects for each activity. Information is given on project

objectives, results obtained during the past year, and the nature of planned

activities

.

Sections 5 and 6 of the report contain listings of papers published,

papers submitted for publication, and talks presented during the year. Talks

presented at the Division's seminars at NBS are given in Section 7. The

involvement of Division staff on professional committees is shown in Section

8 while internal and external scientific collaborations are described in

Section 9. Visiting scientists who have worked in the Division during the

year are identified in Section 10 and the Division staff is listed in Section

1

1

.

Further information on the activities of the Division can be obtained by

contacting the scientists identified in each project report or by writing

Dr. C. J. Powell, Chemistry B-248, National Bureau of Standards,

Gaithersburg, MD 20899 (telephone, 301-921-2188).

li
TABLE OF CONTENTS

ABSTRACT i

FOREWORD ii

1 . Introduction 1

A. Background 1

B. Goal, Objectives and Division Program 2

C. Technical Output and Professional Interactions 3

2.

Surface Standards Program 4

A. Reference Data 4

1 . Sputtering Yield Data Compilation 4

2. Characterization of the Imaging Properties

of a Double-Pass Cylindrical-Mirror Analyzer 5

3. Energy Dependence of Electron Attenuation Lengths 6

4. Atomic Layer-by-Layer Analysis of the Source of

Angular Anisotropies in XPS and AES 8

5. Measurement of Core-Level Binding Energies 9

6. Reference Data for X-ray Photoelectron Spectroscopy

and Auger-Electron Spectroscopy 11

7. Algorithm for Fitting Sputter-Depth-Profiles

of Interfaces 12

8. Needs for Reference Data 12
B. Reference Materials . 15

1 . Development and Production of Standard Reference

Materials for Sputter-Depth Profiling ..... 15

2. Quantitative Sputter Depth Profiling of Interfaces ..... IT

3. Needs for Reference Materials 18

C. Review Articles and Books 20

1 . Review Articles 20

2. Review Articles in Publication 25

3. Books 28

D. Standards-Committee Activities 29

1. ASTM Committee E-42 on Surface Analysis 29

2. Surface Chemical Analysis Working Party of the

Versailles Project on Advanced Materials and

Standards (VAMAS) 30

3. ASTM Committee D~32 on Catalysts 34

3. Surface Measurements Program 35

A. Reaction Kinetics at High Pressures over Single

Crystal Catalysts 35

1. Ethane Hydrogenolysis Catalyzed by W( 1 00 ) 35

2. Thin Pt Films on Model Alkane Hydrogenolysis Catalysts ... 35

3. Effect of S on Catalytic Methanation 36

B. Molecular Structure and Reactivity on Surfaces as Studied

Using ESDI AD and HREELS 37

1 . Evidence for Reorientation of CO when Co-adsorbed with

K on Ru(001) 38

2. Structure and Reactivity of NH^ on Clean and Modified

Fe(100) 38
3. Structure of the Surface Hydration Shell of Bromine

on Ag(100) 38

4. CO Chemisorption on Cr (1 10): Evidence for a Precursor to

Dissociation 39

C. Inelastic Neutron Scattering Studies of Adsorption and

Reaction on Catalysts 40

1. Interaction of Vibrating H atoms on Pt Particles 40

2. Hydrogen Adsorption and Interaction with Oxygen on Pt ... 41

3. Neutron Scattering Study of Zeolite Rho 41

D. Surface Characterization Using Synchrotron Radiation 42

1. Electronic Structure of Molecules Adsorbed on Surfaces:

Relation to Geometric Structure 42

2. Electron and Photon-Stimulated Desorption of Ions from

Oxide Surfaces 44

3. New Beam Line at SURF- II 47

4. Construction of Angle-Resolving Display Analyzer 48

5. Experiments at the Brookhaven National Synchrotron

Light Source 48

6. Theory of Stimulated Desorption 49

E. Dynamical Effects Associated with Core-Level Ionization .... 49

1. NSLS X-24A Soft X-Ray Beamline (800 eV - 7 k eV) 49

2. Photon-Excited Multi-Electron Core-Level Excitations

Using Synchrotron Radiation 50

F. Production and Characterization of Ultrasmooth Surfaces . . . . 5 1

G. Laser Diagnostics of Surface Dynamics 52

1 . Laser-Excited Fluorescence as a Probe of the Dynamics

of Thermal Desorption 5 :
2.

Laser-Induced Desorption 53

3. Time-Resolved Measurements of Vibrational Energy Transfer . 54

4. High-Resolution Infrared Reflection-Absorption

Spectroscopy and Picosecond/Femtosecond Measurements .... 56

H. Spin Polarization in Secondary-Electron Cascades in

Ferromagnets 56

I. Theory of Dynamical Molecular Processes at Surfaces 58

4. Surface Competence Program 64

A. Novel Two-Dimension Materials 64

1 . Surface and Interface Chemical Physics of Ultrathin

Films 65

2. Microcomposition and Microstructure of Thin Films 68

3. Theory of the Quantum Hall Effect 69

4. Dynamical Diffraction of X-ray From Crystal Surfaces at

Glancing Incidence 71

B. State Characterization of Energetic Species Ejected

from Surfaces 74

1 . Energy States of Neutral Species Sputtered from

Surfaces 74

2. Electron- and Photon-Stimulated Desorption of Neutral

Species Using Laser Detection Techniques 76

3. Angular and Energy Distributions of Desorbed Ionic Species . 77

5. Publications 79

A. Publications of Past Year 79

B. Publications in Progress 85

C. Recent Publications of New Staff Members 89

6 . Talks 90
7. Surface Science Division Seminars 98

8. Technical and Professional Committee Participation and

Leadership 101

9. Professional Interactions, Consulting and Advisory Services .... 103

10. Visiting Scientists 110

11. Surface Science Division Staff 112

SURFACE SCIENCE DIVISION

C. J. Powell, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1985

1 . INTRODUCTION

A. Background

Over the last ten years, there has been a dramatic growth of surface

science and its applications. At the national and local meetings of many

professional societies, there are typically multiple sessions of papers

concerned with the physical and chemical properties of surfaces.

Similarly, many current professional journals and books are devoted in

whole or in part to similar reports of recent advances in this field.

These advances result from investigations of basic properties (such as composition, atomic structure, electronic structure) of surfaces and the

dependence of many complex surface processes (such as molecular sticking,

dissociation, diffusion, reaction, and desorption) on the basic properties

and other variables relevant to catalysis, corrosion, thin-film systems,

microelectronics, computer elements, and communications applications.

Investigations of this type range from fundamental studies, at an atomic

and molecular level, on clean single-crystal surfaces to similar studies

on appropriately modified surfaces or structures and lead not only to the

development of surface science but also to new materials, devices, and

processes. Similar investigations, principally measurements of surface

composition and of other needed properties, are frequently made of a large

variety of materials (e.g., metals, polymers, semiconductors, oxides,

glasses, etc.) after fabrication and at various time during their service

life for quality control, process optimization, and failure analysis. The

growth of surface science and its multidisciplinary impact on many

important technologies have been documented in a recent article by H. D. Hagstrum [Frontiers in Science and Technology, W. H. Freeman and Co., New

York (1983), pp. 113-134].

A large number of techniques are utilized for surface characterization. A choice of one or more techniques is made typically on the basis

of the property to be measured, the specimen material, and the specific

needs (e.g., spatial resolution, chemical information, sensitivity, degree

of difficulty, and cost). The most common type of surface measurement is

the determination of surface composition. Most surface analyses now are qualitative but there is a growing demand for quantitative analyses with

improved accuracy. At the present time, there are very few standard

procedures and limited reference data and reference materials. A variety

of techniques is employed for the determination of surface atomic

1
structures, surface electronic structure, and for investigations of

surface processes such as reactions, diffusion, segregation, etc.

Theories of the measurement process need to be developed for the newer techniques. For all techniques, there is a need for relevant procedures,

tests to establish measurement reliability, and applicable reference data.

In most cases, the measurement science needs to be developed since

knowledge of the key concepts and parameters is often extremely limited.

The techniques utilized in surface science have generally been

applied to characterize surfaces in an ultrahigh vacuum environment. The

solution of many scientific and technical problems often requires removal

of liquid- or gas-phase material prior to surface examination and/or the

removal of solid-phase material to expose a region of interest. While

this approach has often been successful, artifacts of many different types

can arise during the removal of one or more phases. There is therefore a growing need for improved measurement methods that can be used for the in

situ characterization of solid-solid, solid-liquid and solid-gas

interfaces with the sensitivity, elemental specificity, and spatial

resolution comparable to those attained with the current

surface-characterization methods

B. Goal, Objectives and Division Program

The goal of the Surface Science Division is to improve the quality of

existing surface-characterization measurements and to extend the present

capability. Specific objectives of the Division are:

(1) Perform experimental and theoretical research in surface

science to provide a scientific base for surface-measurement

methodology;

(2) Develop measurement methods and provide properties data for the

physical and chemical characterization of surfaces and surface

processes to meet identified needs of industry, government, and

other groups;

( 3 ) Develop standard procedures, calibration data, and reference

materials in cooperation with national and international

standards organizations; and

(4) Develop expertise in selected new areas of science in order that

NBS can provide measurement services where needs are anticipated

in the near future.

Objectives (1) through (3) are met organizationally through an NBS

task titled "Development of Measurement Methods for Surface Properties"

(Task 15502). The Division's program for this task is divided into two

principal activities, a Surface Standards Program and a Surface

Measurements Program. Work performed during the year in these two areas

is reported in Sections 2 and 3 . respectively. This work is supported by

2
NBS resources (including some funds transferred through the Office of

Standard Reference Data) and by contracts with two Federal agencies

(Department of Energy and Office of Naval Research).

Objective (4) is met through the Surface Competence Program (Task

26117). This task was established in October, 1984 and represents a new

focus by the Division in two areas, "Novel Two-Dimensional Materials" and

"State Characterization of Energetic Species Ejected from Surfaces". A

separate report on these activities is given in Section 4.

C. Technical Output and Professional Interactions

Sections 5 and 6 of this report contain listings of the publications

and talks, respectively, for the past year by Surface Science Division

staff and for projects supported by the Division.

Many members of the Division staff hold leadership positions in

professional societies and groups, as listed in Section 8. These

interactions not only reflect the professional esteem in which these staff

members are held but provide useful mechanisms for both disseminating the

results of NBS work and for learning of significant measurement problems

being faced by those using surface-characterization equipment.

Interest in surface science and surface characterization at NBS

continues to grow. The Division has had an active Seminar program, as indicated in Section 7, and these seminars have been attended by other NBS

staff. The Division staff also participates in an informal weekly lunch

meeting, attended by scientists from a number of NBS organizational units,

at which developments in surface science are discussed. Members of the

Division staff are frequently consulted on a wide range of NBS problems.

Much of the Division’s work is carried out in collaboration with

other scientists within NBS, within the U.S.A., and internationally. The

nature of these collaborations is shown in Section 9. These collaborations are considered important because they enable a relatively small

Division staff to work synergistically with other experts, they enable us

to have access to unique facilities or expertise, and they enable our expertise to be extended to a larger range of important scientific and

technical problems.

The Division has been fortunate in having thirteen visiting

scientists work at NBS for varying periods during the past year, as indicated in Section 10. These scientists enrich our staff and our projects. A further enrichment of our programs comes from Postdoctoral

Research Associates who hold 1- to 2-year appointments; four Postdoctoral

Research Associates worked in the Division during FY 1985.

3
2 . SURFACE STANDARDS PROGRAM

G. P. Chambers, W. F. Egelhoff, Jr., N. E. Erickson

J. Fine, Y. Hashiguchi, R. D. Kelley, C. J. Powell

The term "surface standards" is intended to cover a broad range of

activities that are directed to improving the quality of surfacecharacterization measurements through: (1) development of needed reference

data and standard reference materials; (2) leadership in standardscommittee activities, the development of standard practices, and other

actions to improve the accuracy and reliability of surface-analysis

measurements; and (3) publication of review articles and books that enable

scientists to make surface-characterization measurements of the needed

quality

A. Reference Data

We describe here results of projects in which needed reference data

are being generated. Section 2.C includes recent review articles by

Division staff that summarize and evaluate data required in a number of

surface spectroscopies.

1. Sputtering Yield Data Compilation

(J. Fine and G. P. Chambers)

Sputtering techniques for depth-profile analysis are presently

being used in conjunction with a number of surface analytical methods to

analyze compositional changes of materials at surfaces and at interfaces.

Many of these techniques have now progressed to the point of being able to

provide quantitative sputter-depth-profile information yet the necessary

sputtering yield data is not readily available in easy-to-use, evaluated

form.

We are preparing a compilation of evaluated sputtering-yield data for

those parameters that will have specific use in surface analysis and depth

profiling. This work is supported by the NBS Office of Standard Reference

Data. Our compilation will be in tabular form for those ion species (Ne,

Ar, Kr, Xe , 0

2

, N

2

, Cs) and energies (0.5 to 20 keV) and angles of

incidence used in surface characterization. The compilation will contain

sputtering yields for elemental targets only.

The HP-1000 Data System in the Center for Chemical Physics is being

used for the data compilation. Dr. D. Neumann and members of his group

have provided guidance as well as technical assistance with the software

development

Two interactive data-base management programs were developed this

past year to handle the specific needs of the data compilation. The

structure developed allows easy data entry into one of these data bases;

4
information can then be transferred to the second data base for rapid

access and searching. Additional software has been written to sort and

tabulate the searched data in a format suitable for publication.

Sputtering yield papers are being compiled; data has been abstracted

and entered into the data-base system. Initial tests indicate that the

system is operating properly. Work also is progressing on our on-line

abstract searching capability so that we can collect and enter additional

references and data directly from the computer search into our data base.

In the coming year we intend to complete the data searching and data

entry, to evaluate the data set, and to compile sputtering-yield data of

interest to the surface-analysis and sputter-depth-profiling community on elemental targets.

2. Characterization of the Imaging Properties of a Double-Pass

Cyclindrical-Mirror Analyzer.

(N. E. Erickson, C. J. Powell)

Knowledge of the specimen area being analyzed is important in

surface analysis by Auger-electron spectroscopy (AES) and x-ray

photoelectron spectroscopy (XPS) , particularly when inhomogeneous

specimens are being examined and experimental conditions are being varied.

We have characterized the imaging properties of a commercial double-pass

cylindrical-mirror analyzer (CMA) used for AES and XPS with extensions of

a method developed elsewhere. These extensions have yielded more

quantitative analyzer characterization than was possible previously. This

work was motivated also by the need to evaluate the analyzer imaging

properties on the binding-energy measurements described in Section 2. A.

below.

The electron beam from the coaxial electron gun of the CMA was rastered across a test surface and the intensity of elastically scattered

electrons detected by the analyzer was stored in a computer as a function

of beam position on the specimen and other experimental parameters. The

intensity data could be later plotted to give " three-dimensional" images

that showed clearly the imaging properties of the CMA. Elastic-peak

images have been obtained for a typical specimen orientation (in our case

at an angle of 60° to the CMA axis) and for typical measurement conditions

(electron energies of 100, 500, and 1000 eV ; analyzer pass energies of 25,

50, and 100 eV ; selection of small or large apertures intended for AES or XPS measurements, respectively; and for selected analysis energies ranging

between 1.5 eV above the incident energy and up to 5 eV below the

incident energy). We have investigated how the images were modified as the

specimen was translated along the CMA axis about its optimum position.

Finally, we have obtained absorbed-current images to ensure that the test

specimen was sufficiently smooth to prevent significant artifacts occurring

in the elastic-peak images.

5
Figure 1 shows examples of elastic-peak images recorded with the

specimen at its optimum position and with use of the AES aperture. Figure

1(a) shows images at a fixed pass energy of 50 eV and for incident

energies of 100, 500, and 1000 eV ; Figure 1(b) shows images for an incident

energy of 500 eV and pass energies of 25, 50, and 100 eV. It is clear

that the specimen area contributing to the detected signal is changing as these operating parameters are varied.

Comparisons have been made of observed image widths for particular

operating conditions with those expected from a simple analysis.

Semi -quantitative agreement has been obtained although there are differences in trends (as a function of electron energy or analyzer pass

energy) that can be associated with non-uniformities of grids on the

inner-cylinder apertures, with lack of sphericity of the retarding grids,

and with simplifications of the analysis. Asymmetries in the measured

images, for example at high retardation ratios or when the specimen is

moved from its optimum position, are due to specific imperfections in our instrument.

Substantial changes are seen in the elastic-peak image shapes as the

specimen is translated along the analyzer axis to simulate accidental

misalignments. Similar changes are obtained in the image shapes as an offset voltage is applied to the electron gun so that the analyzer detects

electrons on the high-energy side of the elastic peak or electrons that

have been inelastically scattered in the specimen. The latter changes can

be qualitatively interpreted in terms of the known coupling between

detected signal and source position, angle of emission, and electron

energy. These results indicate that sharp peaks in an energy distribution

come from a smaller specimen area than for broad peaks or for

inelastically scattered electrons.

We have also measured changes in the posiiton of the elastic peak as the incident beam is deflected to representative points on the specimen in

the field of view of the analyzer. Changes of up to ±0.15 eV in peak

position were found and these were not symmetrical about the vertical as would be expected for an ideal instrument.

It is planned to draft a Recommended Practice for Characterization of

the Imaging Properties of Electron Energy Analyzers for ASTM Committee

E-42 on Surface Analysis based on the above methods.

3. Energy Dependence of Electron Attention Lengths

(C. J. Powell)

The attenuation length (AL) of low-energy electrons in solids

is an important parameter in surface analysis by Auger-electron

spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). The AL

determines the surface sensitivity of AES and XPS (and other

electron-spectroscopic techniques of surface characterization) and is

required for quantitative surface analysis by AES and XPS. Accurate AL

6
Fig. 1 Elastic-peak images recorded with a double-pass cylindrical-mirror

analyzer, the AES aperture, and a test specimen at its optimum

position. Left: Images recorded with an analyzer pass energy of

50 eV and incident energies of 100 eV (top), 500 eV (center., and

1000 eV (bottom). Right: Images recorded with an incident energy

of 500 eV and analyzer pass energies of 25 eV (top), 50 eV

(center, and 100 eV (bottom). The horizontal (bottom left to

right) distance scanned by the electron beam on the specimen :s "

mm and the vertical distance is 15 mm.

7
measurements are difficult in the electron energy range of practical

interest but relative AL measurements are useful since they give the AL

energy-dependence which is needed in one method of quantitative analysis.

The Bethe theory of inelastic electron scattering in matter has been

very successful and it was thought useful to test whether it was valid

also for AL data in solids. According to the Bethe theory, AL values A would be given the by formula, X = AE/bln(cE/AE) , where E is the electron

energy, AE the most probable excitation energy for the material, A a term

containing material and other constants, and b and c parameters of order

unity.

AL measurements for Al, Au, Si, Ge, AI 2 O

3

, SiC> 2 , NaF, NaCl, and KI

have been successfully fitted to the Bethe formula for E typically between

100 and 1500 eV. The quality of these fits was generally superior and the

electron energy range greater than for earlier fits to an empirical

formula. It was found, however, that the parameter b was higher and the

parameter c much lower than the values expected from theory. These

deviations are similar to those found in other tests of the Bethe theory

where the electron energies were not high enough for the parameter values

to reach their asymptotic values. Nevertheless, it is useful empirically

that the Bethe equation adequately describe those AL data which exist for

a representative group of materials over a substantial energy range.

Although the derived values of the parameters are material-dependent, good

estimates of the ratios of ALs at different electron energies can be

obtained from the Bethe equation using the average value of c = 0.4 and

the average value of AE = 20 eV.

A separate investigation has shown that electron inelastic mean free

paths (IMFPs) can be calculated from experimental dielectric data. IMFPs

calculated for eight materials agreed reasonably (within 5016 ) with

available AL measurements (which had been obtained with a model in which

elastic electron scattering was assumed to be insignificant). Since it is

difficult to measure ALs with accuracies much better than about 5016, it is

useful to obtain IMFP data from another base of experimental data. It is

planned to extend these calculations using optical data for additional

materials

4. Atomic Layer-by-Layer Analysis of the Source of Angular

Anisotropies in XPS and AES

(W. F. Egelhof f , Jr.)

Attenuation lengths of low-energy electrons in solids, important

for quantitative surface analysis by Auger-electron spectroscopy (AES) and

x-ray photoelectron spectroscopy (XPS) , have been frequently measured from

the characteristic decay or growth of an AES and XPS signal as a film of

increasing thickness is deposited on a substrate. A fundamental

complication for such measurements is the enhancement of an AES or XPS peak

intensity along crystal axes in single-crystal samples. These

enhancements along nearest-neighbor directions are due to forward

8
scattering of the emitted electrons by lattice atoms. An example of the

angular anisotropy is shown in Figure 2(a) for epitaxial Cu layers on Ni(100)

In order to deepen the understanding of the depth dependence of this

forward-scattering phenomenon, single-scattering electron-diffraction

calculations have been performed in collaboration with Dr. R. A. Armstrong

of the National Research Council, Ottawa. Figure 2(b) shows an example of

these calculations for conditions appropriate to the data in Figure 2(a).

The comparison between the calculations and the data reveal several

important points.

(1) Since all observed peaks are accounted for in the calculations,

single-scattering events must be the dominant mechanism for the observed

peaks

(2) The observed thickness at which each of the four peaks first

appears is in accordance with predictions of the calculations. This

result confirms the original interpretation, namely that the intensity of

the peaks is due mainly to constructive interference in the forward

scattering direction by nearest-neighbor and next-nearest-neighbor atoms

in the lattice.

(3) The calculated enhancement in the peak intensities continues to

grow for Cu thicknesses greater than 3 ML whereas in the data there is very

little increase beyond a thickness of 3-3 ML. (Compare, for example, the

peak at 45° in Figures. 2(a) and (b).) This comparison reveals an important

result. The first (single) scattering event enhances the intensity along

a nearest-neighbor direction (e.g. at 45° in Figure 2(c)) but subsequent

(multiple) scattering events wash out this enhancement. The

single-scattering calculations thus predict a continued growth in the

peaks which is not observed experimentally. As a consequence, the

measured peaks are due more to short-range order, or nearest-neighbor

axes, than originally thought.

This combined theoretical and experimental analysis has deepened the

understanding of the phenomena involved in electron attenuation-length

measurements with single-crystal materials. Such measurements will have to

be made in the future for specific angles of electron emission.

5. Measurement of Core-Level Binding Energies

(N. E. Erickson and C. J. Powell)

Accurate reference values of the binding energies of core-level

electrons are needed for the commonly used technique of x-ray

photoelectron spectroscopy (XPS) and for other surface-characterization

methods. These values are needed for the calibration of instrumental

energy scales. For this application, data are required for a limited

number of pure materials that adequately cover the range of common

measur ements

9
EPITAXIAL Cu ON Ni(IOO)

Fig. 2. (a) Measured intensities of the x-ray- induced Cu L^VV Auger

intensity as a function of polar angle of emission for various

thicknesses (in monolayers) of Cu on Ni(100). (b) Corresponding

calculated intensities. (c) Schematic illustration of the

surface profile.

10
We have made measurements earlier of the core-level binding energies

by XPS for the principal peaks of Ni, Cu, Ag, and Au. The accuracy of

these measurement, however, was limited severely by voltage drifts in our

XPS system. To improve the accuracy and precision of the measurements, we

have installed programmable power supplies and digital multimeters for the

control and measurement of the voltages applied to the cylindrical-mirror

analyzer. The experimental measurements are under computer control.

Programs have been written to set and step the analyzer voltage suppliers

and to read the multimeters. Least-squares peak-fitting routines have

been evaluated for determining peak positions. These tests have shown

that fits using a quadratic or a quartic to the top 20-50 % of a peak are

about equally satisfactory.

Stability checks have been made to assess the short-term (several

hours) and long-term (ca. 1 month) stability of the upgraded system. The

short-term reproducibility in the location of peaks is now about 4 meV and

is limited by the counting statistics of typical scans. The long-term

stability is approximately 10 meV and is within the instrumental

specifications for electronic drift.

A certified calibration of the voltage-measuring instruments is

scheduled to be made shortly. We will then make new high-accuracy

measurements of the Ni, Cu, Ag, and Au XPS peaks and compare these with

recent independent measurements at the U.K. National Physical Laboratory

(NPL) . We will initially use a beam of elastically scattered electrons

from a gun with a thermionic cathode as an energy reference, as we have

in our preliminary measurements. We will then use a gun with a field-emission cathode to compare results from the two types of electron

sources and to resolve an apparent discrepancy in a recent measurement of

the Au 4fy/2 binding energy made using a field-emission reference source. After completion of these XPS binding-energy measurements, we will make

similar measurements of the kinetic energies of Auger electrons from Cu,

Ag , and Au and compare these results with similar measurements now in

progress at NPL.

6. Reference Data for X-ray Photoelectron Spectroscopy and

Auger-Electron Spectroscopy

(C. J. Powell and N. E. Erickson)

A project was initiated in FY 82 with funding by the NBS Office

of Standard Reference Data to prepare compilations and evaluations of

core-electron binding energies and of the kinetic energies of selected

Auger electrons for a wide range of elements and compounds. In

particular, data are being compiled of the "chemical shifts" that can give

useful information on the chemical state of a particular element. Data of

this type are now scattered throughout the scientific literature but there

is a need both for a convenient single source and for evaluation of the

sometimes conflicting data. The reference data are being compiled by Dr.

C. D. Wagner, a contractor to NBS, and the Surface Science Division is

providing technical review. Dr. Wagner has currently generated over "!D500

data entries in his files from 600 papers and the compilation is
approximately half-completed. During the past year, progress has been

significantly delayed by illness but it is expected that the project

should be completed next year. The reference data will be included in a report for the Journal of Physical and Chemical Reference Data.

7. Algorithm for Fitting Sputter-Depth-Profiles at Interfaces

(J. Fine, G. P. Chambers, and Y. Hashiguchi)

The determination of interface widths from sputter-depth-profiles is

presently accomplished by means of graphical methods. Since the shapes of

such interface profiles are generally not symmetric and since there is no accepted method of measuring interface widths, accurate width

determination as well as intercomparison of results is often difficult to

accomplish. One solution to this problem is to fit numerically the

interface profile shape to an appropriate analytical expression from which

one can obtain a factor proportional to different definitions of the

interface width.

In collaboration with Dr. W. H. Kirchhoff of the NBS Chemical

Thermodynamics Division, a fitting analysis for Auger-electron

sputter-depth profiles has been developed using a logistic function of the

form:

I = [A + a (T-T 0

) ]/ ( 1 + e + [B + b(T-T 0 )]/(1 e

fc )

where I is the peak intensity of the Auger spectrum of the sputtered atom

as a function of time T. A is the intensity from a totally covered

surface, B is the background intensity from a completely uncovered surface,

and a and b empirical parameters which can account for additional time

dependence of instrumental effects. T

Q is the apparent midpoint of the

transition region and t is a dimensionless, reduced time defined as (T-T )/D. The scaling factor, D, is the characteristic time for

sputtering through the interface region. Asymmetry in the depth profile

can be accommodated by allowing D to vary with time.

A least-squares fitting program has been written which fits the

measured Auger spectral intensities to the above equation within

measurement error. All currently used measures of the interface width are proportional to D. The statistics associated with the least squares fit

allow confidence limits to be placed on the measured widths of interface

regions and on the widths of surface layers of dissimilar materials.

8. Needs for Reference Data

The growth of surface science and its applications has led to

needs for expanded reference data. These needs can be summarized in the

following three categories.

12
(a) Surface Analysis

Four techniques are now in common use for surface analysis:

Auger-electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS),

secondary- ion mass spectroscopy (SIMS) , and ion-scattering spectroscopy

(ISS). With each technique, there is need for the following reference

data:

evaluation of spectra from pure elements for common

conditions of measurement

evaluation of chemical or matrix effects on spectra

benchmark data for the calibration of the energy and

intensity scales of instruments

reference data on line positions in compounds

reference data for key parameters in quantitative analysis

(e.g., ionization cross sections (AES, XPS), ion scattering

cross sections (ISS), electron inelastic mean free paths

and attenuation lengths (AES, XPS), electron backscattering

(AES), ion neutralization cross sections (SIMS, ISS), and

multiple ionization (SIMS)

algorithms for data analysis (e.g., determination of

background due to multiple scattering (AES, XPS, ISS) and

fragments (SIMS, ISS), deconvolution to obtain source

lineshape (AES, XPS, ISS), inelastic scattering (AES, XPS),

and double scattering (ISS))

data for ion sputtering yields in elements, alloys, and

compounds as a function of ion type, ion energy, and

bombardment geometry

data for radiation damage rates during analysis, including

cross sections for desorption from surfaces and

decomposition of surface layers.

(b) Surface Science

Many techniques are in common use for the determination of

surface properties and processes. Data are needed in the following areas:

reference data on vibrational energies and intensities for

molecular species on surfaces (as measured by electron

energy-loss spectroscopy, infrared spectroscopy, Raman

scattering, neutron inelastic scattering)

13
reference data for determination of surface structures by

low-energy electron diffraction and other techniques (e.g.,

library of basic data, algorithms to compute surface

structure

)

reference data for absolute determination of surface

coverages (atoms/cm2

) on surfaces of different structure and

atomic composition

reference data for surface processes (kinetic data for

catalytic and surface reactions, desorption, diffusion,

segregation)

Ion-surface interactions are of importance in sputtering

and ion scattering spectroscopy. Reference data are needed

to characterize the electron and photon spectroscopy of

scattered and sputtered ions, as well as of excited neutral

species leaving the surface.

(c) Interface Science

There is rapid development now of techniques that can be

used for the _in situ characterization of solid-solid, solid-gas, and

solid-liquid interfaces. A variety of techniques (e.g., Rutherford

backscattering spectroscopy, infrared spectroscopy, Raman spectroscopy,

extended x-ray absorption fine structure, neutron inelastic scattering,

particle- induced x-ray emission) are being utilized and reference data and

algorithms will be required for their effective application.

The Division is providing reference data to meet some of the

above-mentioned needs through the projects described in this Section and

through the publication of the review articles listed in Section 2.C.

Other current Division projects, not described in detail in this report,

are:

comparison of core-level excitation energies by different

spectroscopic techniques

calculation of electron inelastic mean free paths from

experimental optical data

measurement of electron attenuation lengths in condensed

molecular films

The Division will coordinate its efforts with the data activities that

have been initiated recently through the Surface Chemical Analysis

activity of the Versailles Project on Advanced Materials and Standards

(VAMAS) , as described in Section 2.D.2. There will also be coordination

with the NBS Office of Standard Reference Data and the Standard Reference

Data Subcommittee of ASTM Committee E-42 on Surface Analysis.
B. Reference Materials

1 . Development and Production of Standard Reference Materials for

Sputter-Depth Profiling

(J. Fine)

The objective of this project is to develop standard reference

materials (SRM's) that will allow convenient determinations of ion-beam

sputter-removal rates in commonly used surface-analysis instrumentation.

Thin-film reference materials of known thickness will be used to calibrate

ion-gun current densities for particular operating conditions. This

information together with sputtering-yield data for a range of materials

will establish depth scales in the measurement of depth profiles.

Prototype thin-film structures were initially fabricated in order to

evaluate their usefulness as depth profiling SRM's and to develop

appropriate characterization techniques. These structures were made by

sputter deposition as part of a joint US/Yugoslavia program between NBS and

Dr. B. Navinsek at the J. Stefan Institute in Ljubljana. Analyses of

these prototype materials at NBS and by members of ASTM Committee E-42 on Surface Analysis were done using Auger-electron spectroscopy, x-ray

fluorescence, secondary-ion mass spectroscopy, Rutherford backscattering

spectroscopy, and proton-induced x-ray emission. The results were satisfactory and a stock of similar thin-film SRM's were fabricated in

1982 using the sputter deposition facility at the J. Stefan Institute in

Ljubljana. Production and characterization of the Ni-Cr thin-film SRM was supported by the NBS Office of Standard Reference Materials.

The preliminary analyses obtained on the nickel-chromium multilayered

thin-film structures indicate that this material should be of considerable

benefit as a depth-profiling SRM. Work on its characterization and

calibration has now been completed. We have determined the uniformity and

periodicity of the thin-film layers, absolute film thicknesses, sputtered

interface depth resolution, and structural stability. Measurement methods

used to characterize this Ni-Cr SRM include N(E) Auger sputter profiling,

Rutherford backscattering spectroscopy (RBS), and neutron activation

analysis (NAA) . These measurements have resulted in the following

certified values for this Ni/Cr structure that has recently been issued as NBS Standard Reference Material 2135.

(a) Total Cr and total Ni thicknesses

The total thickness of the five Cr layers and the total

thickness of the four Ni layers were determined by NAA using a gravimetrically calibrated reference and are given below.

Element Total Thickness Uncertainty

Cr 191 yg/cm2 ± 8 yg/cm 2 Ni 235 yg/cm 2

± 9 yg/cm 2

15
The uncertainty stated is based on our best judgement of all factors

involved and corresponds to about two standard deviations of the average.

(b) Individual layer uniformity and Ni+Cr bilayer uniformity

(periodicity)

Layer thickness uniformity was determined by measuring the

ion bombardment time required to sputter-remove a single layer. This time

was obtained by monitoring the surface composition by Auger spectroscopy

during sputter erosion. The uniformity of Ni+Cr bilayer removal also was determined in a similar way.

Type of Layer

Relative Layer

thickness

uncertainty*

Number of profile

me asurements

(9 layers each)

Single Cr layer

Single Ni layer

Bilayer of Ni and Cr

±4.8*

± 4.6$

±3-0$

6

6

6

*This uncertainty is two relative standard deviations.

(c) Individual layer thicknesses

The average thickness for a single layer of a given element

was obtained from the total layer thickness for that element and the

number of layers present. The relative uncertainty of this average layer

thickness was determined by combining the uncertainties in the total

thickness and in the single layer uniformity for that element.

Element

Cr

Ni

*This uncertainty is

Single layer

thickness

38.2 ug/cm2

58.8 ug/cm2

standard deviations

Relative layer

thickness

uncertainty*

±2.3 mg/ cm 2 ±3-5 ug/cm2

The following additional information has been provided about SRM

2135 ; this information is uncertified.

(a) Layer thicknesses in units of length

The certified layer thicknesses could be converted into

units of length (nm) if the densities of the layers were known. As these

densities are not known, an approximate thickness in nm can be derived by

using the known bulk densities for Cr (7.19 g crrT^) and Ni (8.9 g cm~3);

the values so obtained are 53 nm for Cr and 66 nm for Ni.

16
(b) Layer thickness and uniformity

Measurements of SRM 2135 using RBS give information on the

single-layer thickness and uniformity of each of the Cr and Ni layers.

RBS measurements of the single-layer uniformity confirm the uncertainties

obtained from the sputter removal times for single layers. Layer

thickness measurements obtained by RBS depend on the value of the stopping

power used to calculate thickness. A 5 to 10$ uncertainty in thickness

can result from the uncertainty in currently available stopping-power data

and can limit the accuracy of this technique. Single-layer thickness

determined by RBS confirm the values certified, providing that a 5 to 1 0$

uncertainty is assumed in the RBS measurements. The RBS result obtained

for the average thickness of a single Cr layer is 8.5$ smaller than its

certified value, while the RBS single Ni value is 5.4$ smaller than that

certified

(c) Relative sputtering rates and yields of Ni and Cr using

argon ion bombardment

Ion Energy Ni/Cr Rate Ni/Cr Yield

(keV)

1.0 1 .03 1.12

2.0 1 .07 1.17

3.0 1 .09 1 .20

4.5 1 .09 1 .20

Rate is expressed in units of length/time.

Yield is given as number of atoms sputtered per incident ion.

Future work includes characterizing and certifying additional Ni/Cr

structures similar to SRM 2135 as well as a "marker" layer- type sputter

depth profile SRM which we have recently fabricated in production

quantities. This material also was fabricated in Dr. Navinsek's

laboratory and consists of eight Cr layers (- 40 nm each) separated by

about 2 monolayers of C^O^.

2. Quantitative Sputter Depth Profiling of Interfaces

(J. Fine, Y. Hashiguchi)

Determination of composi tion-versus-depth at virgin solid/solid

interfaces is at present difficult to achieve with sputter-depth-profiling

techniques. This is due, to a large extent, to a lack of understanding

of bombardment conditions (i.e., ion beam energy, species, angle of

incidence, current density, and sputtered depth). A careful evaluation

of such factors which affect interface resolution is not available for any

given interface system. A consistent set of such measurements obtained for

various ion beam parameters, all done on the same material, would

significantly enhance our ability to assess the abruptness of interfaces

before sputter-profile analysis took place and would be of value in

determining optimum sputter-prof ile conditions.

17
Our development of the Ni-Cr thin-film depth-profile SRM 2135 with

known layer thickness and periodicity (as described above) makes it both

possible and practical to examine systematically the dependence of

interface resolution on ion beam parameters. Use of the computer

controlled, sequential-mode N(E) Auger data system which has been

previously developed allows us to obtain reliable and accurate

measurements of the interface depth resolution for the Ni-Cr material.

In collaboration with Dr. P. A. Lindfors of the Perkin Elmer

Corporation, Physical Electronics Division and Dr. D. F. Mitchell of the

National Research Council of Canada, Ottawa, we have examined the

dependence of Ni-Cr interface broadening an ion beam energy, ion current

density, and angle of incidence, all as a function of sputtered depth.

Our results indicate that much narrower interfaces are observed when

profiling with low-energy ions; for example, the interface widths with 1 keV argon ion bombardment at a particular ion-beam angle of incidence are about half those for 3 keV bombardment. We also find that narrower

interfaces can be obtained by bombarding at more oblique (grazing) angles.

Our narrowest interfaces (- 5 nm) resulted when the ion beam was incident

at 70° with respect to the surface normal.

Preliminary measurements of interface-width dependence on ion-beam

current density indicate this this parameter may affect interface

resolution. We plan to explore this dependence by examining the

relationship between ion current density and ion energy.

3. Needs for Reference Materials

The following needs for additional reference materials have been

identified

(a) Depth-Profiling SRM’s

Surface analysis is frequently combined with ion sputtering

to measure composition versus depth and to investigate solid-solid

interfaces. It is believed that sputter-depth-prof il ing applications will

continue to grow and, with the development of new techniques for deposition

of materials (e.g., molecular-beam epitaxy), the development of better

depth-profiling techniques, and demands for better accuracy, use of new materials, and desire for sharper interfaces, there will be an increased

demand for suitable SRM's to ensure the reliability of the relevant

measurement system.

NBS has recently developed a multi-layer periodically-modulated SRM

consisting of alternate layers of Ni and Cr (Section 2.B.1). Similar

structures consisting of Ni/Ag and Cr/Cr2 0^ have been fabricated but

remain to be characteri zed . We have also fabricated films of Ta2 0^ on Ta

and these also have to be characterized

18
There are needs for similar SRM's involving other types of materials

in high-technology industries, for example, Si0 2 on Si, epitaxial

modulated- thickness films of GaAs/GaA2,As , thin layers of metals on semiconductors (Schottky barriers), and polymer films on metal substrates.

(b) Calibration of Surface Analysis Instruments

There is a growing need for the characterization and

calibration of surface-analysis instrumentation, particularly since the newer computer-controlled instruments require greater system stability and

reproducibility than before. Until recently, most surface analyses have

been qualitative but there is increasing demand for quantitative analyses

of defined accuracy. These developments require SRM's for instrument

calibration (e.g., of the instrument transmission functions for

Auger-electron spectrometers (AES) and x-ray photoelectron spectrometers

(XPS) and for the determination of instrument performance (e.g., the

detection of trace constituents).

Pure elemental and multicomponent materials can be utilized for

calibration of the energy and intensity scales (and instrument

transmission functions) of AES and XPS instruments. A suite of pure

elements (e.g., Cu, Ag

,

and Au) could be used for both purposes. Liquid

alloys (e.g., Ga-Sn or Ga-In) can be cleaned readily to generate

two-component surfaces of known composition for checks of instruments and

algorithms for analyses. Multicomponent materials with known quantities of

trace elements are needed for determining the ability of an instrument to

detect trace species. Suitable materials could include ion- implanted

impurities in silicon (with a specified depth distribution and maximum

concentration) and multi-component liquid alloys (with homogeneous

compositions or with segregation of trace species at the surface)

(c) Surface Science

There is a need for SRM's that would lead, with the user following a prescription, to surfaces of known composition (e.g., to known

coverage of a chemisorbed layer of molecules on a metal substrate or to a monatomic layer of a metal on a substrate). A single-crystal SRM (e.g.,

Ni) could be cleaned and exposed to different gases (e.g., 0

2 , N

2

, H2 , CO,

H

2 S) to establish known surface coverages of such gases. Such an SRM would

enable calibration of AES and XPS equipment now used for measurements of

surface coverages. Another use of the SRM could be through the deposition

of several monolayers of a metal (e.g., Ag)

,

again after cleaning, with

appropriate thermal treatment to remove all but a monolayer of the

deposit. This process could also be used for the calibration of AES and

XPS equipment used for investigations of novel properties of ultrathin

metal films.

The Division will coordinate its activities to produce and

characterize SRM's with related efforts that have been initiated in other

countries through the Community Bureau of Reference of the Commission of

the European Communities and, more recently, the Surface Chemical Analysis

19
activity of the Versailles Project on Advanced Materials and Standards

(VAMAS), as described in Section 2.D.2. Plans for producing additional

SRM’ s at NBS will also depend on sales of SRM 2135 (Section 2.B.1) and the

results of a needs survey of the ASTM Committee E-42 on Surface Analysis.

C. Review Articles and Books

1 . Review Articles

The Division staff authors many review articles and book

chapters that provide information on measurement methods, relevant

reference data, reference materials, theories of the measurement process

for many surface spectroscopies, and surface standards.

Division staff members have authored 24 review articles recently.

The titles and abstracts of review articles published since 1984 are listed below:

(a) "Instrumentation for Photon Stimulated Desorption,"

R. Stockbauer, Nucl . Instr. Meth. 222 , 284 (1984).

Photon stimulated desorption (PSD) refers to the ejection

of ions, atoms or molecular fragments from a surface initiated by the

absorption of single photons; to date, most studies have concentrated on detection of ions. The properties of PSD which make it attractive as a surface characterization tool are its extreme surface sensitivity, the

ions being ejected only from the topmost layer and the rapidity with which

the ions are ejected. Since the desorption is fast (~10

-1 s), with

respect to molecular vibrations (~10 -1 ^ s), the ion trajectory reflects

the initial bonding geometry of the particle to the surface.

To study the ion desorption process, one would like to know the mass,

kinetic energy distribution, angular distribution and the yield

(desorption rate vs. photon energy) of the desorbing ions. Time-of-flight

(TOF) analyzers are used where the time between the light pulses from the

synchrotron light source is on the same order as the flight time of the

ion from the surface to the detector. One can measure easily ion mass and

yield but not kinetic energy or angular distributions with this class of

analyzer. Electrostatic deflection analyzers are used to measure ion

yields and kinetic energy distributions and, in some instruments, ion

angular distributions. In general, they are useful where the time

structure of the synchrotron light is too short to allow TOF analysis.

Optical methods have recently been applied to the detection of excited

states of neutral Li seen in PSD of LiF.

20
(b) "Inelastic Scattering of Electrons in Solids," C. J. Powell, in Electron Beam Interactions with Solids for

Microscopy , Microanalysis , and Microlithography , D. F. Kyser, H. Niedrig, D. E. Newbury and R. Shimizu, eds. (SEM

Inc., Chicago), 19-31 ( 198-4) .

The principal mechanisms and available data for the

inelastic scattering of electrons in solids are reviewed. The processes

relevant for electron-probe microanalysis, electron

energy-loss-spectroscopy, Auger-electron spectroscopy, and x-ray

photoelectron spectroscopy are described and examples of relevant electron

energy-loss data are shown. The discussion is based on the dielectric

description of inelastic scattering and treats processes important in the

excitation of both core electrons and valence electrons. Information is

given on the cross sections for ionization of core levels, inelastic mean

free paths of Auger electrons and photoelectrons in solids, and radiation

damage

(c) "Non-adiabatic Effects in Elementary Surface Reactions:

State-to-State Molecular Beam Experiments as a Probe," J. W. Gadzuk, in Many -Body Phenomena at Surfaces , D. Langreth

and H. Suhl , eds. (Academic Press, N.Y.), 517 (1984).

A theory of elementary chemical reactions at solid surfaces

is described in terms of surface-induced diabatic transitions between

"reactant" and "product" potential curves, it is then shown how the

internal vibrational state distribution of a diatomic molecule scattered

from a surface could provide unique dynamical information required as input

to the diabatic transition theory.

(d) Early Applications of Vacuum, from Aristotle to Langmuir,"

T. E. Madey, J. Vac. Sci. Tech. A2, 110 (1984).

Highlights of the development of vacuum science and

technology from ancient times to the early twentieth century are reviewed.

The view of the Greek philosophers that vacuum was an impossibility

hampered understanding of the basic principles of vacuum until the mid

17th century. Verifiable vacua were first produced in Italy by Berti and

Toricelli; von Guericke's dramatic experiments vividly demonstrated

atmospheric pressure. Piston-like "air pumps" were widely used in England

and the European continent through the 18th and early 19th centuries to

produce and characterize the properties of vacuum (lack of sound

transmission, inability to support life, gas discharges, etc.). The

Industrial Revolution was made possible through the genius of Newcomen,

who designed huge atmospheric engines (based on condensation of steam to

form a vacuum beneath a piston, which was then driven by the pressure of

the atmosphere). A system of "atmospheric railways" propelled by vacuum

pistons was built in England in the mid 19th century. Serious scientific

developments of the 19th century which necessitated vacuum included

Crooke's and Faraday's gaseous discharge measurements, the first

sputtering experiments by Grove, and isolation of the rare gases by

21
Ramsey, the standards work of Miller, the discovery of the electron by

Thomson and of X-rays by Rdntgen. The development of the incandescent

light by Edison provided a background for the remarkable achievements of

Langmuir in vacuum and surface science at the dawn of the 20th century.

An appendix is included which lists museums containing vacuum-related

exhibits

(e) "Laser Studies of Surface Chemical Reactions," R. R. Cavanagh and D. S. King, Chemistry and Physics of Solid

Surfaces V , Springer-Verlag Series in Chemical Physics 35,

1 41 (1984).

A review of laser studies of surface chemical dynamics with

emphasis on thermal desorption processes is presented. The correlation of

gas-phase and liquid- molecular dynamics with analogous surface processes

is demonstrated with primary emphasis on experimental techniques for

monitoring relevant quantum state populations. Recent results for the

desorption of NO from Ru(001) and NO from oxidized Ru crystals are compared in terms of rotational populations, and velocity and angular flux

distributions

(f) "Characterization of Surfaces Using Electron and Photon

Stimulated Desorption," T. E. Madey, D. E. Ramaker, and R. Stockbauer, Ann. Rev. Phys. Chem. 35., 21 5 ( 1984).

We review various mechanisms of electron- and photonstimulated desorption of ions and neutrals from surfaces. Examples

include desorption from ionic surfaces, from covalent adsorbates on metal

surfaces, and from layers of physically adsorbed atoms. The use of the

electron stimulated desorption ion angular distribution (ESDIAD) method

for determining local structures of surface molecules is described.

(g) "Inelastic Mean Free Paths and Attenuation Lengths of

Low-Energy Electrons in Solids," C. J. Powell, Scanning

Electron Microscopy/1984, IV, 1649 (1984).

A review is given of calculations of inelastic mean free

paths and measurements of attenuation lengths of low-energy electrons in

solids. The emphasis of the review is on the systematics of the

dependence of these quantities on material and electron energy.

Calculations of inelastic mean free paths from experimental dielectric

data indicate that different dependences on electron energy occur in

different materials and that deviations from simple theoretical or empirical expressions are to be expected.

(h) "On Vibrational Lineshapes of Adsorbed Molecules", J. W.

Gadzuk and A. C. Luntz, Surf. Science 1 44, 429 (1984).

The possible information content in lineshapes observed in

vibrational spectroscopy of molecules adsorbed on surface is considered by

drawing analogies with similar situations in other spectroscopic areas

22
where the systematics are more completely understood. When possible,

simple physical models are introduced which illustrate the points to be

stressed. Particular emphasis is placed on the relative roles of T

1 (dissipative decay) vs. T

2

’ (pure dephasing) processes in determining

linewidths, on the roles of substrate electron-hole pairs, phonons, and

photons in T

1 processes, and possible ways to establish which broadening

mechanism is operative in a given situation. A particular kind of

dephasing that is important for vibrational lineshapes in molecular

crystals, so called exchange-coupling, is suggested as playing a significant role for molecular adsorbates as well. Some recent

experimental studies are analyzed in the light of concepts introduced in

this paper.

(i) "The Thermal Desorption of Adsorbed Species," J. T. Yates,

in Methods of Experimental Physics , Vol. 22, Solid State

Physics : Surfaces , R. L. Park and M. G. Lagally, eds.

(Academic Press, N.Y.), 425 (1985).

The experimental and theoretical basis of thermal

desorption spectroscopy as a tool for surface characterization is

described. Methods of analysis of thermal desorption spectra to obtain

kinetic information (desorption energies, desorption order, coverages of

adsorbed species) are included, together with numerous examples of

desorption of small molecules from single-crystal metal surfaces.

(j ) "Experimental Methods in Electron and Photon Stimulated

Desorption," T. E. Madey and R. Stockbauer, in Methods of

Experimental Physics , Vol. 22, Solid State Physics : Surfaces , R. L. Park and M. G. Lagally, eds. (Academic

Press, N.Y.1985), 465 (1985).

We review experimental techniques and applications of

electron stimulated desorption (ESD) and photon stimulated desorption

OPSD) of atomic, molecular, and ionic species from surfaces. The physical

principles of these methods, as well as details of experimental measurements

and data analysis are discussed. We close with a discussion of beam damage

in surface analysis.

(k) "Innershell Ionization Cross Sections," C. J. Powell in

Electron Impact Ionization , T. D. Mark and G. H. Dunn,

eds. (Springer-Verlag, N.Y.), 198 (1985).

A review is presented of cross sections for the ionization

of inner-shell electrons by electron impact. Calculations, measurements,

and empirical formulas are described and compared. Recommendations are given for the selection of cross-Section data. Finally, applications of

inner-shell ionization cross-Section data to materials and surface analysis

problems are described.

23
(l) "The Coordinated Development of Standards for Surface

Chemical Analysis", M. P. Seah and C. J. Powell, NBS

Internal Report NBSIR 85-3120 (March, 1985).

This report is based on a proposal to the Steering

Committee of the Versailles Project on Advanced Materials and Standards

(VAMAS) for the coordinated development amongst the VAMAS member states of

standards for surface chemical analysis. VAMAS was established following

a meeting of the Heads of State or government at Versailles, France in

1982 that agreed on a number of projects relating to technology, growth,

and employment. Specifically, VAMAS was organized to promote

international coordination in the development of standards in a wide range

of advanced material sectors. Surface chemical analysis was approved as

a VAMAS Technical Working Area in June, 1984.

The report describes the growth and diversity of surface analysis in

the development of advanced materials in modern technologies and the use

of surface analysis for improved films and coatings. The principal

techniques of surface analysis in common use are identified and the

technical limitations to accurate surface analyses pointed out. Accurate

surface analyses require: (i) knowledge of the principles of the measurement method, (ii) knowledge of the behavior of the measuring instrument,

and (iii) correct interpretation and expression of the final measured

result. Standards for the measurement of surface composition with known

accuracy and for the reliable determination of chemical state require:

(a) a base of principles, definitions of terms, and suitable equations,

(b) reference procedures for the measurement of intensities and spectral

features, (c) procedures and data for instrument calibrations, (d)

reference data for material parameters such as elemental sensitivity

factors, matrix terms, chemical state spectra, ion sputtering rates, etc;

and (e) standard methods for specifying an analysis. Specific needs are identified for the common methods of surface analysis, Auger-electron

spectroscopy, x-ray photoelectron spectroscopy, and secondary- ion mass spectroscopy together with the needs for ion sputtering which is used to

obtain composition versus depth information in films and coatings.

Existing standards activities in the member countries of VAMAS are reviewed and suggestions are made for additional standards for surface

chemical analysis.

(m) "Surface Harpooning", J. W. Gadzuk, Comments on Atomic an Molecular Physics, J_6, 219 (1985).

The principles involved in charge transf er/harpooning

collisions between atoms or molecules and surfaces are presented in terms

of concepts drawn from gas-phase atomic and molecular collision theory.

As specific examples, the charge state of atoms and the vibrational

excitation or dissociation of molecules which have experience harpooning

while scattering from a surface are considered.

24
(n) "The Uses and Limitations of ESDIAD for Determining the

Structure of Surface Molecules", T. E. Madey, in The

Struc ture of Surfaces , Springer Series in Surface Science

2, M. A. van Hove and S. Y. Tong, Eds. (Springer-Verlag

,

N.Y.), 264 (1985).

The principles and mechanisms of electron-stimulated

desorption (ESD) and photon-stimulated desorption (PSD), as well as the

utility of the electron stimulated desorption ion angular distributions

(ESDIAD) method as a tool for determining the structure of surface

molecules, have been described in a recent book and several review

articles. The present short paper is intended to provide a guide to the

relevant literature, and to describe briefly some recent work relating to

the uses and limitations of ESDIAD for determining the structure of surface

molecules

2. Review Articles in publication

We list below the titles and abstracts of review articles in the

course of publication.

(a) "The Chemisorption of Carbon Monoxide by the Transition

Metals," J. T. Yates, Jr., T. E. Madey, and J. C.

Campuszano, The Chemical Physics of Solid Surfaces and

Heterogeneous Catalysis , D. A. King and D. P. Woodruff,

eds. (Elsevier).

A comprehensive review of the adsorption of carbon monoxide

by transition and noble metals is presented. The systematics of CO

adsorption and dissociation are discussed, along with detailed

examinations of the surface structures, electronic and vibrational

spectra, and kinetic behavior of adsorbed CO.

(b) "Final-State Resolved Studies of Molecule-Surface

Interactions," D. S. King and R. R. Cavanagh in New Laser

and Optical Investigations of Chemistry and Structures at

Interfaces , Verlag Chemie.

Quantum state-specific diagnostics as applied to surface

dynamics are discussed. The NO molecule is used as an illustration of the

experimental determination of gas-surface interactions. Topics reviewed

included beam-surface scattering thermal desorption, vibrational

accommodation, Doppler profiles, and Fourier- transform infrared emission

spectroscopy

(c) "Core-Level Binding-Energy Shifts in Solids at Surfaces,"

W. F. Egelhoff, Jr., Surface Sci. Reports.

This review presents an overview of the theory and of

various successful approaches to the interpretation of core-level

binding-energy shifts observed in photoelectron spectroscopy. The

25
theoretical background is presented at a level readily accessible to the

general reader. Particular attention is paid to relative merits of the

two basically different conceptual frameworks for interpreting core-level

binding-energy shifts, the initial-state—final-state approach and the

equivalent-core-Born-Haber-cycle approach

(d) "Recent Advances Using ESDIAD: Applications to Surface

Chemistry", T. E. Madey, C. Benndorf, N. D. Shinn, Z. Miskovic, and J. Vukanic, Proceedings of DIET-II

Symposium (Desorption Induced by Electronic Transitions),

in Springer Series in Chemical Physics.

Recent applications of ESDIAD (electron stimulated

desorption ion angular distributions) to surface chemistry are described.

Examples include the influence of catalytic promoters and poisons on surface structure and reactivity, the evidence for a new structural form

for adsorbed H

2 0 (i.e., H2 O dimers on Ni(1 10)) , and the characterization

of a new bonding mode for CO on Cr(110). Calculations of the perturbing

influence of image force and reneutralization effects in ESDIAD are described

(e) "Excitation Mechanisms in Vibrational Spectroscopy of

Molecules on Surfaces", J. W. Gadzuk, in V ibrational

Spectroscopy of Molecules on Surfaces , J. T. Yates, Jr.,

and T. E. Madey, eds., Vol. 4 of Methods of Surface

Characterization (Plenum, NY).

An introduction to the theoretical basis of vibrational

excitation mechanisms and processes relevant to vibrational spectroscopy

of adsorbed molecules is presented.

(f) "Neutron Inelastic Scattering: Vibrational Spectroscopy of

Adsorbed Molecules on Surfaces", R. R. Cavanagh, J. J.

Rush, and R. D. Kelley, in Vibrational Spectroscopy of

Molecules on Surfaces , J. T. Yates, Jr. and T. E. Madey,

eds., Vol. 4 of Methods of Surface Charac terization

(Plenum, NY)

An introduction to neutron scattering as a probe of

adsorbates at surfaces is presented. Emphasis is placed on experimental

aspects of triple axis and time-of-fl ight techniques along with a single-phonon model for the spectral features. Wilson FG methods for

constructing molecular force fields relevant to the molecular modes of the

adsorbate are presented. The applicability of neutron scattering for

exploring rotational diffusion and adsorbate torsions is also examined.

26
(g) "Recent Developments in Quantitative Surface Analysis by

Electron Spectroscopy", C. J. Powell, J. Vac. Sci. Tech.

An overview is given of recent developments in quantitative

surface analysis by x-ray photoelectron spectroscopy and Auger-electron

spectroscopy. The two major tasks of an analysis are the identification

of the surface phases that are present and the determination of the

concentrations of particular elements or compounds. Methods for

accomplishing both tasks will be described together with the pitfalls and

problems that remain. Particular attention is given to the following

topics: identification of surface phases and reference data for the

calibration of instrumental energy scales; reference data on inelastic mean

free paths and attenuation lengths; effects of specimen crystallinity;

intensity measurements; measurement of the imaging properties of electron

energy analyzers; and the intensity-energy response functions of different

instruments

(h) "Surface Chemical Analysis - Report on the VAMAS Project,"

C. J. Powell and M. P. Seah, Surf. Interface Anal.

The VAMAS project on surface chemical analysis is a multi-national cooperation for the provision of standards data and

materials for surface chemical analysis measurement and for the provision

of the basic understanding necessary for these activities. This project

is one of a rapidly growing suite of projects initiated as a result of

decisions following the 1982 Versailles Summit Meeting of the Heads of

State or Government of Canada, France, Germany, Italy, Japan, UK, USA and

the Representatives of the Commission of the European Community. During

the past year national representatives to this VAMAS project have been

appointed and national committees established. This article summarizes

the philosophy, scope, and organization of the project and describes

specific activities that have been initiated. Information is given on how

individuals, both within and outside the group of member states, may

participate

(i) "Dynamics of Molecular Processes at Surfaces: Vibrational

Lineshapes and Spectra", J. W. Gadzuk, J. Electron

Spectroscopy

Extremely useful connections exist between the dynamics of

adsorbed molecule vibrations, as revealed in spectroscopic lineshapes, and

the dynamics of molecular processes at surfaces because in both cases, the

constituent atoms of a molecule, solid, or combination of the two execute

multi-dimensional motion over the same potential energy surfaces,

undoubtedly sampling different regions of it.

In this paper, recent insights and advances in surface dynamics will

be applied to the problem of vibrational lineshapes. Classical particle

and semi-classical wavepacket dynamics will be used to address the issues

of energy decay (T^

)

vs. pure dephasing (

2

* ) overtones, and non-linear

dynamics as they apply to lineshape analysis.

27
(j) "Field Emission Microscopy - Trends and Perspectives," A.

J. Melmed, Chemistry and Physics of Solid Surfaces VI,

Springer-Verlag

The author's view of the role of surface microscopies, in

particular the field emission microscopies, is given. Brief outlines of

the historical development and nature of field-electron emission

microscopy (FEEM) and field-ion microscopy (FIM) are given and selected

examples are presented to illustrate the scope of research in FEEM and

FIM. Research trends are described and some projections for the future

are made.

3. Books

(C. J. Powell, T. E. Madey)

While there are many books and review articles on different

aspects of surface science and its applications, there is a dearth of

information on how to make reliable surface-characterization measurements.

There is, in essence, a large information gap between review articles in

which the latest scientific advances are discussed and manufacturers'

handbooks in which the operation of a commonly used surface-characterization equipment is described. Arrangements have been made with a commercial publisher to produce a series of books, "Methods of Surface

Characterization," which will address this need. Two Division staff

members (Powell and Madey) and three other scientists (A. W. Czanderna at

the Solar Energy Research Institute; D. M. Hercules and J. T. Yates at the

University of Pittsburgh) constitute an editorial board that will oversee

the production. A series of four volumes in currently planned which will

describe the principles, techniques, and methods considered important for

surface characterization. It is intended to describe how important

surface-characterization measurements are made and how to ensure that the

measurements and interpretations are satisfactory (to the greatest extent

possible). The approach of the series will be pedagogical or tutorial.

Volumes 1 and 2 of the book series will describe the techniques and

methods for electron spectroscopy and ion spectroscopy, respectively,

which are in widespread use for surface analysis. These volumes will be

concerned largely with techniques for which commercial instrumentation is

available. It is hoped that writing for both volumes will be completed

shortly

Volume 3 will describe techniques for specimen handling and depth

profiling. For specimen handling and treatment, this volume will provide

a compilation of methods that have proven useful. This volume will also

address the common artifacts and problems associated with the bombardment

of solid surfaces by electrons and ions. Finally, a description will be

given of methods for depth profiling. Preparation of this volume should

be completed in 1986.

28
Volume 4 will bring together a description of methods for vibrational

spectroscopy of molecules on surfaces. Most of the techniques are currently under active development; commercial instrumentation is

available for some techniques but this situation could change in the next

few years. The current state-of-the-art of each technique will be

described as will the relative capabilities. An important component of

the volume will be the summary of the relevant theory. This volume is

essentially complete.

D. Standards-Committee Activities

Three staff members of the Division hold offices on two ASTM

Committees, the E-42 Committee on Surface Analysis and the D-32 Committee

on Catalysts, and on the recently established Surface Chemical Analysis

Working Party organized under the auspices of the Versailles Project on Advanced Materials and Standards. Participation in the activities of

these groups provides an opportunity for leadership, for dissemination of

NBS expertise, and to learn of significant measurement problems in

relevant areas.

1. ASTM Committee E-42 on Surface Analysis

(C. J. Powell, J. Fine)

The ASTM Committee E-42 on Surface Analysis, founded in 1976, now has some 120 members; in addition, a large number of non-members, both

within the U.S. and throughout the world, participate in Committee

activities. The purpose of the Committee is to advance the field of

surface analysis and the quality of surface analyses through the

development of appropriate standards, standard practices, reference data,

reference materials, round robins, symposia, workshops, and publications.

Committee activities of the past year have included development of

the following documentary standards (which are at varying stages of

approval )

- Additional definitions of terms for AES, XPS, SIMS, and Energetic

Ion Analysis

Guide to Depth Profiling in Auger Electron Spectroscopy

- Guide for Specimen Handling in AES and XPS

Practice for Reporting Spectra in XPS

- Method for Calculating Data-Gathering Speed in XPS

Guide to Steady-State Charge-Referencing Techniques in XPS

- Practice for Reporting Sputter Depth Profile Data in SIMS

(secondary- ion mass spectroscopy)

- Guide to Determine the Depth Resolution in SIMS

Guide for Specification of Ion Beams for Use in Surface Analysis

Procedure for Sample Positioning with Cylindrical Mirror Analyzers

in ISS (ion-scattering spectroscopy)

- Procedure for Approximate Energy Scale Calibration with

Cylindrical Mirror Analyzers Used in ISS

- Proposed Guide for Data Reporting in ISS

29
The Standard Reference Data Subcommittee is conducting a survey of

needs for reference data and of format requirements. A survey of the E-42

membership is being made to determine needs for new types of reference

materials. Finally, a report has been submitted for publication recently

of an ISS round robin involving comparisons of peak-position and

peak-width measurements on a Cu-Ag-Au ternary alloy using seven cylindrical-mirror analyzers from the same manufacturer. This round robin

showed that much of the spread in reported peak positions was associated with incorrect positioning of the specimen with respect to the

analyzer.

The Committee has sponsored two symposia each year, one at the annual

Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy in

the spring and the other at the National Symposium of the American Vacuum

Society (AVS) in the fall. Papers presented at these symposia are published. After 1985, arrangements for the AVS Symposium will be made by

the recently formed AVS Applied Surface Science Division. A workshop is

held at each meeting to discuss particular measurement problems. At the

1984 AVS Symposium the topic was "Data Reduction for Quantification in

Surface Analysis", and the topic at the 1985 Pittsburgh Conference was "Solving Industrial Problems with Surface Analysis".

The Committee is planning to prepare a booklet of E-42 surface

analysis standards which will be published by ASTM. It is believed that

many users of surface-analysis equipment will find the booklet to be a convenient compilation of terminology, guides, and recommended practices.

The booklet will be updated roughly every two years and should be an effective means of disseminating E-42 standards.

2. Surface Chemical Analysis Working Party of the Versailles

Project on Advanced Materials and Standards (VAMAS)

(C. J. Powell)

The "Versailles Agreement" arose from a meeting of the Heads of

State or Government (Economic Summit) of industrialized nations at

Versailles in 1982. The participants represented Canada, Federal Republic

of Germany, France, Italy, Japan, United Kingdom, United States of

America, and the Commission of the European Communities (CEC). A Summit

Working Group on Technology, Growth, and Employment was established

consisting of government science advisers. This group has established

Working Groups in areas such as photovoltaic solar energy, food

technology, advanced robotics, biotechnology, high speed trains, remote

sensing from space, and advanced materials and standards. A summary of

developments resulting from the Versailles Agreement was published as a News and Comment article recently in Science 228 , 827 (1985).

The Versailles Project on Advanced Materials and Standards (VAMAS)

consists of a Steering Committee with respresentati ves from the seven nations above and the CEC. The overall aim of the project is to encourage

international trade. This objective will result from international

30
agreement on codes of practice and performance standards and from

multilateral research aimed at providing the scientific and technological

base necessary to achieve agreement on standards. The project is

essentially a scheme for stimulating the introduction of advanced

materials into high technology products and engineering structures. The

ubiquity of surface analysis through all sectors of high-technology

industry has been demonstrated in recent surveys, and a proposal to

establish a Surface Chemical Analysis (SCA) Working Party won early

approval from the VAMAS Steering Committee. This SCA Working Party is now one of nine such groups that have been approved.

The main objective of the SCA working party is to produce, by

coordinated effort, the reference procedures, data, and materials necessary

to establish standards for surface chemical analysis. This effort is

expected to lead to the international coordination of standards-related

activities before national standards are adopted and to the development of

standards on an international level.

National representatives to the SCA Working Party have been appointed

with C. J. Powell as Chairman for a three-year period. The most urgent

needs for surface analysis pertain to the use of Auger-electron

spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) , secondary-ion

mass spectroscopy (SIMS), and sputter-depth profiling (SDP). As projects

in these areas become established and as other techniques come into greater

use, it is expected that the project will broaden.

Qualitative and quantitative surface analyses require consideration

of the following three items:

(i) the physical principles of the measurement method;

(ii) the behavior of the measuring instrument; and

(iii) the interpretation and expression of the final result.

The basic principles of the physics of the various techniques and the

selected analytical methods are vital since they lead to the working

formulae which are used for quantitative analysis. Agreement must be

obtained on these formulae and their regimes of applicability when working

to certain accuracies for particular types of specimens and for particular

techniques and methods. These formulae involve the measurement of

intensities by the instrument which are then related to the composition at

the surface by functions of the specimen material and the particular

measurement process and by functions of the measuring instrument.

Tabulations are needed of particular materials properties relevant to the

various techniques and information is needed on instrument properties.

Additionally, surface analyses can give chemical- state information, the

interpretation of which requires a similar hierarchy of understanding,

data, and reference procedures. The analyst therefore requires:

(1) an agreed base of principles, definitions of terms, and equations

to relate the techniques and procedures to the measurement;

31
(2) reference procedures specifying how to measure intensities and

spectral features;

(3) reference procedures, reference data, and reference materials for

calibrating instruments, determining instrument functions, and

inter- relating instruments of different designs;

(4) reference data of elemental sensitivity factors, matrix terms,

information depths, libraries of chemical-state spectra,

information on ion-sputtering rates, radation damage, etc.; and

(5) standard methods of specifying an analysis.

Details of specific needs for AES, XPS, SIMS, and SDP have been

identified.

Suitable infrastructures have been developed in most VAMAS states for

the SCA project. In the U.S., the ASTM Committee E-42 on Surface Analysis

has agreed to participate and cooperate in VAMAS SCA projects. Standards

already developed by the E-42 Committee will be disseminated to the other

VAMAS states; standards developed later in the other states will be

considered for adoption by the E-42 Committee. Suitable projects at NBS

and other U.S. laboratories also contribute to the VAMAS SCA activity.

Since January, 1985, a large number of technical projects have been

started in the VAMAS states, many largely as a result of the VAMAS

initiative. These projects are largely national activities, as is to be

expected since it is necessary that national needs, opportunities, and

priorities be established prior to the development of more extensive

bi-national or multi-national projects. The first meeting of the national

representatives to the VAMAS SCA Working Party took place in October, 1985

during a conference in The Netherlands. A number of cooperative projects

were discussed and it was agreed that the following should be implemented.

(a) Development of thin oxide films as reference materials. It

is planned to produce thin films of transition-metal oxides

(Fe20^, NiO, and C^O^) with thicknesses of about 25 nm on metal substrates in Canada. Films of similar thickness of

Si02 on silicon will be produced in Italy. These films

will be characterized by sputter-depth profiling at a number of laboratories in Canada and Italy. The ion

sputtering yields of these oxide films under common conditions of sputter-depth profiling will be compared with

similar measurements on existing Ta2 05 and Ni/Cr reference

materials at NPL and NBS.

(b) Development of calibration data for the energy scales of

Auger-electron spectrometers . Current projects exist at

both NBS and NPL for the independent measurement of the

kinetic energies of the principal Auger-electron

transitions of copper, silver, and gold to be used as

32
calibration data in the energy range 50-2000 eV. After

intercomparison , the calibration data will be utilized in

an interlaboratory comparison of Auger-electron

measurements to be organized by NPL.

(c) Procedures for quantitative x-ray photoelectron

spectroscopy (XPS). It is planned to investigate at NBS

the suitability of recently fabricated Ta2 05 films on silicon and, if necessary, the oxide films prepared in

project (a) as test materials for an interlaboratory

comparison of angle-dependent XPS measurements. If these

films can be cleaned adequately with minimal ion

sputtering, NBS will organize the comparison of XPS

measurements to give information on film thickness and film

stoichiometry

Two additional cooperative projects were discussed and it is likely

that these will be initiated following the preparation of more definite

plans. The first such project is the development of alumina reference

materials with known concentrations of oxygen vacancies. These materials

will be used as reference materials for problems in materials science such

as wetting, adhesion, and electrical breakdown as well as for

determining conditions for radiation damage. The second project is the

development of reference procedures for high-resolution scanning

Auger-electron microscopy so that the effects of topography, specimen

crystallinity, and angle of emission can be minimized.

Plans are being developed for two workshops on surface chemical

analysis for which VAMAS will be a co-sponsor. The first workshop is

planned for October 24, 1986 at NBS and will precede the Tenth

International Vacuum Congress and Sixth International Conference on Solid

Surfaces to be held in Baltimore, October 27—3 1 > 1986. The second

workshop is planned for November 17, 1986 at NPL and will precede the

fourth Conference on Quantitative Surface Analysis at NPL on November

18-20, 1986. These workshops will publicize VAMAS activities, disseminate

results of recent work on quantitative surface analysis, and promote the

development of new cooperative VAMAS projects. Specific attention will be

given at both workshops to needs for reference data, needs for reference

materials, methods of instrument calibration, and analytical methodology.

The VAMAS Surface Chemical Analysis Working Party has aroused a considerable amount of interest and enthusiasm in many of the VAMAS

states. Many scientists believe that VAMAS has already provided and will

continue to provide a considerable stimulus to the development of

standards for surface chemical analysis in each state. Furthermore,

through cooperation via VAMAS, national standards will be developed more efficiently and, it is hoped, without conflicts. The specific areas where

international cooperation through VAMAS will be most effective are believed to be: (1) the development of data banks and preferred data

formats; (2) the development of reference materials; (3) the development

33
of documentary standards for instrument operation and calibration; and

(4) the development of recommended procedures for data acquisition, data

reduction, and expression of final results.

3. ASTM Committee D-32 on Catalysts

(R. A. Haines and R. D. Kelley)

The activities of the ASTM Committee D-32 on Catalysts are concerned with the physical and chemical properties of commercial

catalysts and with developing suitable procedures for catalytic activity

measurements. The membership of the Committee numbers approximately 130.

Semi-annual meetings are attended by between 60-90 percent of the

membership which includes a significant international component. In the

past year, the expansion of Committee activities has continued. These

activities involve four sub-committees: Physical/Chemical Properties - 6 task groups; Physical/Mechanical Properties - 6 task groups; Chemical

Analysis - 2 task groups; Catalytic Properties - 5 task groups. In

general, this expansion has moved into areas that involve complex and

often controversial measurements. Examples of these are the measurement

of catalyst acidity, of the sensitivity of cracking catalysts to metallic

impurities, and of multi-element chemical analysis by atomic absorption.

The Subcommittee on Chemical Analysis is chaired by R. D. Kelley.

This Sub-Committee is involved in finishing the test method

for analysis of platinum in fresh reforming catalysts. A "final" round

robin is presently under way. The effort to analyze palladium in

catalysts has progressed to the round robin stage. Standardization of

x-ray fluorescence analytical procedures and of procedures for the

chemical analysis of spent catalysts are being discussed. In the basemetals task group, the primary emphasis is on the development of a satisfactory test method for determining several base metals by optical

atomic spectroscopy.

The NBS Office of Standard Reference Materials (OSRM) will soon distribute special reference materials for catalysts. As a member of

D-32, Dr. Ruth Haines, Deputy Director of the Center for Chemical Physics,

is preparing the documentation required for NBS acceptance of materials

used by D-32 in various round robin tests. Five years ago the Committee

recognized the need to preserve the catalysts, catalyst carriers and feed

stock used in their round robins. D-32 sought a private sector

distributor but none was found. The OSRM can distribute the materials at

cost but NBS will not certify them. Initially, samples will be available

for physical properties such as surface area and particle size

distribution; mechanical properties such as crush strength; chemical

analysis of supported metals; and reactivity via gas oil conversion

microactivity tests. A series of zeolites will also be available for

which diffraction intensity, unit cell dimensions and zeolite areas have

been determined. All the materials should be available within the next

six months. We can then judge the desirability of producing more standards based on the extent to which these samples are requested.

34
3. SURFACE MEASUREMENTS PROGRAM

C. Benndorf, D. R. Burgess, Jr., R. R. Cavanagh, A. Flodstrora,

J. W. Gadzuk, S. M. Girvin, T. J. Jach, R. D. Kelley, R. L. Kurtz,

T. E. Madey, D. E. Ramaker, N. D. Shinn, R. Stockbauer, P. D. Szuromi

,

T J. Udovic, M. J. Wax

The Division undertakes a number of projects directed to the improved

physical and chemical characterization of surfaces and surface processes.

These projects meet Division objectives through the development of new measurement techniques, improvement of existing techniques, development of

theories of the measurement process, applications to important scientific

and national problems, development of measurement procedures, tests of the

measurement system, development of new concepts, and provision of needed

data.

A. Reaction Kinetics at High Pressures over Single Crystal Catalysts

(P. D. Szuromi, M. J. Wax, T. J. Udovic, R. D. Kelley, T. E. Madey)

The overall objective of this research is to provide a molecular

understanding of heterogeneous catalytic chemistry on well-characterized

single-crystal surfaces. Among the areas studied are the catalytic

synthesis of hydrocarbons from carbon monoxide and hydrogen on metal

surfaces, the mechanism of catalytic poisoning and promotion, and the

reforming of alkanes over model supported Pt catalysts. The apparatus

employed for these studies contains high pressure reactors contiguous to

ultrahigh vacuum surface analysis chambers. The work is supported, in

part, by the Division of Basic Energy Science of the Department of Energy.

Progress during the last year included studies of the hydrogenation

activity of single-crystal W catalysts, as well as the poisoning effect of

adsorbed S and the promoter effect of Pt thin films on the W substrates.

1. Ethane Hydrogenolysis Catalyzed by W ( 1 00

)

Although W is not ordinarily considered a good catalyst, we have

found that the W(100) surface is very effective in catalyzing ethane

hydrogenolysis (p - 100 Torr, 550 < T < 620 K) . A carbidic overlayer

forms rapidly in the early stages of reaction; this surface carbide is the

"true” catalyst for the hydrogenolysis which proceeds with an activation energy of 27 kcal/mole. This is different from the activation

energy for catalytic methanation over W(100), 1 M kcal/mole, suggesting

that methanation and hydrogenation do not share a rate-limiting step.

2. Thin Pt Films as Model Alkane Hydrogenolysis Catalysts

Vapor deposition of Pt onto a W(100) substrate in ultrahigh

vacuum has been used to prepare model supported Pt catalysts which are free of extraneous promoters and poisons. Various Pt loadings (from

fractional monolayer to multilayer) have been achieved reproducibly .

35
Although pure Pt is less active than W for ethane hydrogenolysi s , the

fractional monolayer Pt films catalyze hydrogenoiysis at a rate

significantly greater than the ini tially-clean W(100) surface.

3. Effect of S on Catalytic Methanation

The effect of adsorbed sulfur on the rate of catalytic

methanation over a W(110) crystal has been studied as a function of sulfur

coverage and crystal temperature. As in the case of the initially clean,

non-sulfur-covered surface, carbidic carbon is formed during the course of

the reaction. In Figure 3. the relative rate of reaction as a function of

0) 03 GC

C

o

o

CO0) GC

0) J>

jo

Q) GC

1.0

0.8

0.6

0.4

0.2

0.0

r 0 750 K -—Reaction Temperatures

a 700 K P u = 100 Torr h

2 i

•\

1 V

600 K p co

= 1 To,r

\ A

inhibition of Methanation

• V over W (110) by Adsorbed

A

t) Sulfur

1

i1

°\

s 8

\

\

x Similar Data for Ni (100)

1 i

600 K P = 96 Torr

/

/ h2

i \ P co

= 24 Torr

i O \

N. —

i 8

\ X

\ _

j

X

_L i T Z

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Sulfur Coverage

Fig. 3. Relative Reaction Rate for Catalytic Methanation over W ( 1 10) as a function of sulfur coverage (in fractions of a monolayer).

Similar data for a Ni(100) are shown for comparison.

sulfur coverage (as determined by Auger-electron spectroscopy) is plotted

for several reaction temperatures (together with similar data for Ni(100).

The Arrhenius energy of reaction, 56 kcal/mole, does not change

substantially with sulfur coverage, as can be inferred from the similar

inhibition of the rate of reaction for each temperature at a given

coverage. Although the inhibition at low sulfur coverages is not as

36
dramatic as that seen previously for this reaction over nickel surfaces,

the overall rate of reaction does drop about an order of magnitude at high

coverages of sulfur.

We plan next year to complete both the methanation studies of W ( 1 10)

and the effect of Pt films on hydrogenolysis. The role of Pt films in the

thickness range 1-2 monolayers on W(100) will be characterized for the

hydrogenolysis reaction.

We plan also to initiate a new project to study partial oxidation

catalysts. This important class of reactions has received little

attention from surface scientists, and we propose to probe the mechanism

of the catalytic oxidation of propylene to acrolein over Cu2 0 :

H

2 C = CH-CH 3 + 02

CU

|° H2 C = CH-C^°

Initially, the dehydrogenation of alcohols will be examined on a pure

copper crystal. These reactions will be examined using apparatus which

combines both a high-pressure reactor (2 atmospheres) with an ultrahigh

vacuum surface analysis chamber; the surface over which the catalytic

reactions occur will be probed both before and after reaction. Several

aspects of the oxidation reaction are not well understood: the effect of

the surface geometry of the oxide; the electronic state of the catalyst,

both the oxidation state of copper and the surface valence band structure;

the influence of electronegative species (S, Se , halogens) as promoters;

and the Arrhenius parameters for the overall rate of reaction. These

questions can be addressed by employing: single-crystal oxide surfaces to

control geometric effects; post-reaction analysis by electron

spectroscopies (AES, XPS and UPS); preparation of clean surfaces in

ultrahigh vacuum and of promoted samples of known surface concentration;

and measurement of rate data over a wide range of temperatures, pressures

and reactant ratios.

B. Molecular Structure and Reactivity on Surfaces as Studied Using

ESDIAD and HREELS

(T. E. Madey, N. D. Shinn, and C. Benndorf)

A major challenge in surface science continues to be the

determination of the structures of molecules on surfaces, particularly in

the absence of long-range order. The goals of this project are to provide

a direcdetermination of the structures of adsorbed molecules using the

electron stimulated desorption ion angular distribution (ESDIAD) method,

and to characterize the structures and reactivity of surface species using

high resolution electron energy loss spectroscopy (HREELS). These

techniques, both singly and in combination, are powerful tools for surface

structural characterization.

The present thrusts of this project are (a) to determine the

influence of surface additives (e.g., catalyst promoters and poisons) on

the local structure and reactivity of small molecules (CO, NHq , H2 0) on

37
surfaces, and (b) to determine the structures of those molecules on

ini tially-clean surfaces, particularly in controversial cases. The work

has been supported in part by the Division of Basic Energy Sciences of the

Department of Energy.

During the last year, progress has been made in the following areas.

1. Evidence for Reorientation of CO when co-adsorbed with K on

Ru(001

)

We have used ESDIAD to address a current controversy concerning

the influence of K on the structure of adsorbed CO: does CO "stand up" or "lie down" adjacent to K on Ru(001)? In the absence of K, CO is bonded

with its molecular axis perpendicular to Ru(001 ) at all coverages. Upon

coadsorption with low coverages of K, ESDIAD measurements provide evidence

for a strong local interaction between CO and K, which appears to result

in a reorientation of the CO to an "inclined" or lying-down bonding

configuration. Moreover, complementary thermal desorption and low-energy

electron diffraction measurements suggest the formation of ordered surface

species having K

x (C0)2X stoichiometry. The question of CO bonding

geometry is a major area of current interest in the surface science

community, and the present measurements and models provide new insights

into the CO + K surface chemistry.

2. Structure and Reactivity of NH^ on Clean and Modified Fe(100)

Iron is an excellent catalyst in NH? synthesis, and adsorbed K

is known to "promote" the reaction by increasing the rate. In an attempt

to understand at the molecular level how K influences the bonding geometry

of NH^ to Fe, we used ESDIAD to examine the structure and reactivity of NH3 on clean Fe(100), and on K-dosed Fe(100). On clean Fe(100), adsorption of

NH~ occurs at step sites up to etNH^) - 0.02. For higher coverages, up to

saturation of the first layer (e(NHo) - 0.3*0 , ESDIAD is dominated by a "halo" H

+ pattern indicating that NH^ is bonded via the N atom and the H

atoms (with no azimuthal ordering) are pointed away from the surface. The

ESDIAD data correlate well with thermal desorption data, where different

binding states due to fractional monolayer, second layer, and multilayer

adsorption are observed. Only a small fraction (0 < 0.02) of NHo

dissociates upon heating. When NH^ is coadsorbed with K, the ESDIAD and

thermal desorption data indicate an interaction in which the NH^ molecular

axis is tilted and the binding energy to the substrate is decreased. In

contrast, the interaction between NH^ and 0 does not lead to structural

changes or azimuthal ordering of NH^ as reported previously on Ru(0001)

and N i ( 1 1 1 ) surfaces. This indicates that the NH^ - 0 distance is not

optimal for attractive hydrogen bonding.

3. Structure of the Surface Hydration Shell of Bromide on Ag(110)

Surface science has been a valuable source of inspiration to

electrochemists in recent years, particularly in studies of the

interaction of water and other electrolytes with clean, well-characterized

38
electrode surfaces. In one such study, we have attempted to synthesize an electrochemical double layer in vacuum by examining the interaction of H

2 0

and bromine on an Ag (110) surface using ESDIAD, LEED (low-energy electron

diffraction) and TDS (thermal desorption spectroscopy). Water adsorbed on

clean Ag(110) formed a disordered, hydrogen-bonded overlayer. In the

presence of adsorbed bromine, the adsorbed water was characterized by a higher binding energy and pronounced orientational order. The mixed

adlayers resulting from this surface hydration of bromide also exhibited

long range order. The surface hydration number (nH20/Br ) was two for 0Br < 0.25, and decreased to a few tenths at the Br saturation coverage, 0g r

= 0.75. The present results have important implications for experiments

in which investigators attempt to transfer electrodes from solution to a vacuum environment: neither water on the clean surface nor the hydration

water remain adsorbed in vacuum at roan temperature, and would be lost in

a transfer experiment.

4. CO Chemisorption on Cr(1 10) : Evidence for a Precursor to

Dissociation

HREELS and ESDIAD studies of the chemisorption of CO on Cr(110)

have provided fascinating insights into the structure and kinetics of

molecular dissociation on a metal surface. At 120 K, two molecular

binding modes of CO are sequentially populated. The first, a-jCO, is a novel binding mode for a clean metal surface in which the molecules are bound with the C-0 axis nearly parallel to the Cr(110) surface. Annealing

experiments demonstrate that the a-j binding mode is the precursor to

dissoc iation on Cr(110). At higher CO coverages, 0. 25<9qq<0. 35, the a-|C0

overlayer is disordered by the addition of the second binding mode, a2 C0.

The c^CO species are terminally bound molecules adsorbed at a- top and

bridge sites and aligned approximately perpendicular to the surface.

Annealing studies of CO or 0/C0 adlayers provide evidence for a surface

reaction in addition to direct dissociation at about 170 K. In contrast,

adsorption at 300 K leads to direct dissociative chemisorption with no detectable intermediate molecular adsorbate. The implications of these

results to catalytic reactions of CO have been considered and comparisons

to CO adsorption on clean and "promoted" transition metal been made.

We plan next year to extend the ESDIAD method to the detection of

negative ions; all ESDIAD measurements to date have involved positive

ions. We believe that these challenging measurements will provide new insights into the structure and surface chemistry of a class of molecules

(particularly those containing halogens and other electronegative

groups) for which studies have not been possible previously. A new digital

video system will be constructed for these measurements. This system will

be used to acquire and process data for ion current versus emission angle.

We expect that the digital system will be more sensitive and give more accurate information than the currently used analog system. A later phase

of this work will involve characterization of similar molecules using

39
HREELS and synchrotron methods. The new measurements will be an exciting

complement to our present studies of the influence of surface additives on

the structure and chemistry of adsorbed species.

We will use ESDIAD and HREELS to address a fundamental question in

hyrocarbon surface chemistry, namely, the structure of C

2 h2 on a Cu ( 1 10)

surface. Different models have been proposed involving rehybridized

carbon species with the C-C bond vector either parallel or perpendicular

to the Cu atom rows. ESDIAD may be able to provide a unique insight into

the local bonding geometry of this site.

Despite the extensive interest in the chemistry of H

2 o on transition

metal surfaces, there are no definitive spectroscopic studies of the

adsorption and decomposition of H

2 o in the temperature range 77-300K on

any metal having a high heat of M-0 bond formation where dissociation is

likely to occur. We propose to study in detail the structure and kinetics

of H

2 o adsorption and decomposition on C r ( 1 10) using ESDIAD and HREELS;

the goal will be to identify the fundamental steps in this important

surface reaction.

We will continue to probe the role of both electropositive and

electronegative additives on the structure and chemistry of small adsorbed

molecules. Of particular interest are the major differences in the

"activity" of oxygen in promoting hydrogen abstraction on different

surfaces

C. Inelastic Neutron Scattering Studies of Adsorption and Reaction

on Catalysts

(R. D. Kelley, R. R. Cavanagh, M. J. Wax, T. J. Udovic)

Inelastic incoherent neutron scattering (IINS) studies of

adsorbates on catalyst surfaces are providing new insights into the

vibrational spectroscopy of hydrogen and hydrogen-containing species

adsorbed at the surfaces of high-area catalysts. NBS is ideally suited

for these studies, having a unique combination of neutron physicists and

surface chemists with an interest in catalysis. During the last year,

advances have been made in characterization of both metal and zeolite

catalysts using IINS at the NBS Reactor in collaboration with Dr. J. J. Rush of the Reactor Radiation Division. The work has been supported in

part by the Division of Basic Energy Sciences of the Department of Energy.

1. Interaction of Vibrating H atoms on Pt particles

The dynamical interactions between vibrating hydrogen atoms on the surface of small Pt particles (Pt black) have been studied using IINS

together with isotopic dilution (comparing pure H ada with H ada + D ada ).

The data revealed direct information on the bonding state and dynamical

non-bonded (as opposed to chemical) interactions of these species. Shifts

and broadening of hydrogen vibrational features were accounted for in terms

of mode dispersion due to strong H-H coupling.

40
2 . Hydrogen Adsorption and Interaction with Oxygen on Pt

1 1 NS was utilized to probe the nature of adsorbed hydrogen and

its interaction with oxygen on platinum black. The vibrational spectra of

adsorbed hydrogen at 80 K were found to be in agreement with the results of

other reported IINS studies. The interaction of oxygen with adsorbed

hydrogen provided vibrational spectra corroborating the existence of at

least two distinct hydrogen-adsorption sites. In addition, hydrogen and

oxygen adsorption on the platinum black blank both yielded spectral

information concerning the chemical state of the platinum surface.

Comparison of the present IINS data to published electron energy-loss

spectroscopy results suggests that oxygen reacted with hydrogen over platinum black to product adsorbed hydroxyl (OH) species.

3. Neutron Scattering Study of Zeolite Rho

Incoherent inelastic neutron scattering has been used to examine

the bonding of framework hydrogen to the faujasite zeolite rho in

collaboration with Drs. G. D. Stucky, L. Abrams, and D. R. Corbin of

Dupont. Vibrational spectra obtained from 160 to 1 600 cm

-1 are consistent

with the existence of planar, symmetric A10(H)Si units in the acid form of

rho at room temperature. As the zeolite undergoes a slight change in

structure on heating, an accompanying transfer of hydrogen atoms occurs to some new bonding site of unknown nature which is characterized by an unusually large- amplitude , low-energy vibration. Quasielastic neutron

scattering data have allowed an upper limit (4x10”° cm2

s _1 at 673 K) to

be set for the rate of diffusion of hydrogen on the framework of partially

dehyaroxylated rho, a result consistent with diffusion measurements by

macroscopic methods.

We plan next year to extend the applications of IINS to the

characterization of adsorbates on the internal and external surfaces of

zeolite catalysts. The new measurements will build upon our recent

studies of the bonding and of diffusion rates of framework hydrogen of

zeolite rho, and will include both adsorbate structures and diffusive

motion of adsorbates in various zeolites. One example will be the

dynamics of NH? interactions in zeolite rho. Quasielastic neutron

scattering will complement the IINS measurements, and will be used to

derive the rates and nature of diffusional motion.

We will use IINS to probe the interactions of hydrogen on and in Pd

black. The main effort will be devoted to cleaning and characterizing the

sample before hydrogen adsorption, followed by a study of both surface and

bulk hydrogen in Pd. This effort is expected to answer long-standing

questions regarding the communication between surface and bulk species.

There have been few studies of adsorption and reactions on supported

catalysts using IINS. Our studies to date have involved the adsorption of

H

2 and small hydrocarbons on unsupported metals (Ni,Pt). We plan to extend

these studies to supported metal catalysts for which there is a vast

literature concerning preparation, cleaning, adsorption and reaction. In

41
collaboration with workers experienced in noble-metal catalyst

preparation, we will choose, prepare and initiate neutron-scattering

studies on prototype catalysts.

D. Surface Characterization Using Synchrotron Radiation

(R. Stockbauer, R. L. Kurtz, N. D. Shinn, D. E. Ramaker

,

A. Flodstrom, and T. E. Madey)

Major goals of this effort are (a) to determine the electronic

structure of surfaces and adsorbates using variable-wavelength synchrotron

radiation and ultraviolet photoelectron spectroscopy (UPS), and (b) to

identify the electronic excitations which result in the photon-stimulated

desorption (PSD) of ions from molecules adsorbed on surfaces as well as from

condensed molecular films. When possible, PSD ion yields are correlated

with UPS of both valence states and core-electronic states of the surface

species. These measurements provide tests of recent theoretical models of

electron- and photon-stimulated desorption, and provide new insights into

the bond-breaking processes induced by ionizing radiation incident on surfaces. The work has been supported in part by the Office of Naval

Research.

Accomplishments during the past year were in six areas:

(1) electronic structure of molecules adsorbed on surfaces; (2) electronstimulated desorption (ESD) and PSD of oxide surfaces; (3) instrumentation

of a new beamline at the NBS synchrotron radiation facility SURF -II;

(4) construction of a new display analyzer; (5) progress at the Brookhaven

National Synchrotron Light Source (NSLS); and (6) theory of stimulated

desorption.

1. Electronic Structure of Molecules Adsorbed on Surfaces:

Relation to Geometric Structure

Synchrotron photoemission studies of the bonding of CO to the

Cr (110) surface at low temperatures have identified differences in the

electronic structure of the molecularly adsorbed CO that are correlated to

the molecular binding configuration. At low coverages (0 < 0.25), only

the c^CO binding state is populated; in this binding state the molecules

are "lying down" on the metal surface. Ultraviolet photoemission measure- ments reveal a unique Cr:C0 4a bonding interaction; this result is

evidence for Cr:C0 bonding substantially different from the conventional

Blyholder model of synergistic CO 5 a+ metal charge donation and metal -* CO

lit backdonation . In contrast, the terminally-bonded ci^CO binding mode, seen at high surface coverage (0 > 0.25), is well described by this

conventional model.

Figure 4 illustrates typical UPS data obtained at 40 eV photon energy

in an experimental configuration which is most sensitive to photoelectron

detection along the [110] surface normal direction. A spectrum for the

clean Cr(110) surface, Figure 4(a), can be compared to those with only a

1 CO

adsorbed, Figure 4(b), and with both a-, CO and a2 C0 adsorbed at high

coverage, Figure 4(c). The spectral differences associated with the two
Cr( 1 1 0)/CO UPS data

ELECTRON BINDING ENERGY (eV)

Fig. 4. Ultraviolet photoemission spectroscopy (UPS) data for CO on a Cr (110) surface; evidence for two different bonding configurations

are presented. Curve (a) is the clean surface spectrum and curve

(b) corresponds to the a-| state of CO (the "lying-down" mode).

Curve (c) is the spectrum which includes the a2 state of CO (the

"standing-up" mode).

binding modes are unmistakable; a weak CO 4a peak at 11.6 eV binding

energy is seen in Figure 4(b) whereas an intense a

2 C0 4o peak at 10.8 eV is

observed in Figure 4(c). Both the binding energy and intensity differences

are strong evidence for the radically different CO binding geometries and

resulting bonding variations.

Angular and photon-energy dependent data provide additional support

for the CO-binding mode models developed from our previous HREELS/ESDIAD

studies (Section 3*B.4). Further studies probing the dissociation of

adsorbed CO and C0:02 interactions on Cr(110) have been performed. As

first seen in the earlier vibrational studies, adsorbate interactions

between co-adsorbed CO and oxygen result in the reorientation of the

lying-down carbon monoxide to a terminally-bonded configuration; this

mode conversion is manifested in the UPS data by the expected changes in

the CO 4a region of the spectra.

43
Preliminary data have been obtained for molecular nitrogen, an isoelectronic non-polar analog to CO, adsorbed on the Cr (110) surface.

These results will be combined with subsequent vibrational data to

determine whether a molecular "lying down" N

2 (ads) species, analogous to

a-|C0, is present.

2. Electron and Photon-Stimulated Desorption of Ions from Oxide

Surfaces

As part of our continuing effort to understand the mechanisms

involved in stimulated desorption of ions from surfaces, we have made

measurements on single-crystal oxides that have forced a re-evaluation of

currently accepted theories. Much of the previous work in stimulated

desorption involves correlation of photon energies for producing

desorption with photon spectroscopic data for atomic excitations. Such

work originally gave rise to fundamentally new ideas about the types of

atomic transitions that could produce desorbing ions. These mechanisms,

however, are incomplete in several aspects and in particular they neglect

the influence of local bonding geometries and surface structure. The

experimental program presently underway is aimed at studying the influence

of surface structure and is giving rise to a broader understanding of the

mechanisms underlying the desorption process.

The surfaces studied to date include the (001) and (110) surfaces of

Ti02

. This material is particularly important since it is the model

system for the Knotek-Feibelman (KF) mechanism of desorption. This model

describes the inter-atomic Auger process that can occur in a maximal- valent material such as Ti02 when a core hole is produced in the

cation by electron or photon impact. This hole is unstable and can decay

by an inter-atomic Auger process involving charge transfer from the 0 2_

ligands. This results in a positively charged 0-ligand which then desorbs

due to the strongly repulsive Madelung potential. This model predicts

that excitation of the Ti 3p level should produce desorption. It also

predicts that any population of Ti 3d-electron states (i.e. no longer a maximal-valent surface) should strongly reduce the probability of the

inter-atomic decay, favoring an intra-atomic decay. This would result in

a much reduced ion yield.

Figure 5(b) shows the oxygen ion yield versus incident photon energy

from a 700°C annealed Ti02 (001) surface; this is a maximal- valent surface.

At the excitation energy of the Ti 3p level, 38 eV, there is an onset in

the ion yield. It peaks at 47 eV and decays rapidly, following the decay

of the excitation probability of the Ti 3p level. In Figure 5(a), we show

the 0 eV constant-final-state spectrum, essentially the photoabsorption

spectrum of this surface. By comparison of this and other

electron-excitation spectra with the ion emission spectra, we hope to

unravel the specifics of the electronic excitations that product

desorption. Thus, in agreement with the predictions of the KF mechanism,

we observe desorption due to the excitation of the Ti 3p level. This

agreement ends, however, when we compare the magnitudes of these yield

curves for the different surfaces studied.

44
Desorption from Ti0 2 (001)

Fig. 5. Photon-stimulated desorption (PSD) of oxygen ions from an annealed

TiC>2 (001) surface showing the role of core-hole excitations, (a)

0 eV constant-final-state intensity (proportional to

photoabsorption cross section) versus photon energy, (b) ion

yield versus photon energy.

The unexpected behavior that we have observed occurs when surface

species are intentionally made non-maximal- valent (Ti 3d-electron states

now populated) by the introduction of defects (by 500 eV Ar

+ -ion

bombardment); the magnitude of the ion yield does not always decrease as the KF mechanism would predict. It has been observed that the ion yield

can even increase with such treatment, the opposite of the behavior that

would be predicted by the KF mechanism. The source of this conflict can

be resolved, however, when one considers the influence of surface

structure and the local site geometries on the process.

It is known that surface geometric structure is drastically modified

by Ar

+ -ion bombardment; however, the details of the atomic rearrangements

that the bombardment produces are not known. In order to compare the ion

emission from surfaces with different geometries, we have resorted to

45
studying two different surfaces of Ti02 , namely the (001) and the (110).

The (001) surface is known to facet on annealing to (011) planes while the

(110) surface is flat. The electron stimulated desorption ion angular

distributions (ESDIAD) that we observe from the (001) surface are consistent with such a faceting; we observe emission from the faces and

the edges of facets. The ESDIAD patterns from the (110) surface, on the

other hand, give only a normal emission spot. Comparison of the

magnitudes of the ion yields from these surfaces, however, indicates that

increased ligand coordination of the Ti cations (such as is expected to be

the case for a flat surface) produces decreased probability of ion

desorption. The origin of this decreased probability could be an enhanced

reneutralization probability or a decrease in the probability of initial

excitation. There is also the possibility that surface dynamics may

strongly influence the ion escape by lattice polarization and recapture.

Our interest in the relative influences of these additional processes in

desorption is to understand not only the initial excitation but also the

decay of this excitation and the subsequent surface dynamics that lead to

ion and neutral desorption.

In order to better understand the structure of complicated surfaces

such as those of Ti02 , a graphics package has been written in FORTRAN that

allows the display of ball-model crystal surfaces. This routine allows

one to define a basis for a lattice, create a bulk crystal of specified

size, and cut planes through this crystal to expose arbitrary surfaces.

These surfaces can be rotated to be viewed from any perspective and

surface vacancies can be introduced interactively. One such crystal ball

model is shown in Figure 6 where the facet believed to be formed on

Ti02 (001) after annealing to 700°C is shown. This modeling of surface

structures will be associated with planned molecular dynamics calculations

to be done in conjunction with our experimental efforts; we hope to better

understand the variety of processes that influence desorption. Such

calculations could allow us to predict site-specific desorption

probabilities and to model desorption trajectories (perhaps even predict

ESDIAD patterns). It is expected that such a feedback between calculation

and experiment will also result in a better understanding of the structure

of both perfect and defective surfaces.

During the next year, we plan to continue to study the mechanisms of

ion desorption from solid oxide surfaces with both experimental studies

and model calculations. Oxides have been shown to be unique systems that

allow investigation of the relation between desorption mechanisms and the

electronic and geometric structure. We will investigate further

desorption from various surfaces of Ti02

. The recent studies of

desorption from the (001) and the (110) surfaces of Ti02 have promoted

interest in the comparative study of Ti02 (011) and Ti 2 0^ (1012). Their

similar surface geometric structures should permit isolation of the

influence of their different electronic structures on the core-hole decay

processes that lead to desorption. In addition, we intend to investigate

the influence of the local-site environment in ion desorption from other

surface such as Mg0(100) and faceted MgO.

46
Fig. 6. Computer-generated model of faceted Ti02 (001) surface.

We plan to make a molecular-dynamics calculation of the lattice

response to a desorption process. An investigation will first be made of

the often complicated geometric structure of oxide surfaces using software

that can produce ball-model drawings of idealized surfaces. This software

will be combined with the molecular-dynamics calculation in which the

initial excitation and decay are assumed to occur rapidly; the subsequent

charge reversal of a ligand then results in the motion of both the ligand

and the rest of the lattice. The calculation should reveal information

about the specifics of the sites that result in desorption and their

angular distributions.

3. New Beam Line at SURF-II

The Surface Science Division has established a new beam line at

the NBS synchrotron light source SURF-II. This will replace the existing

beam line which we have used for the past 5 years. The heart of the new beam line is a toroidal grating monochromator designed by us to deliver

high photon flux to investigate ion emission from surfaces with low ion

yield. The monochromator has been calibrated and characterized and

delivers IxlO 10 photons per second per milliamp of ring current at a wavelength resolution of 4 A. With SURF-II routinely operating in the

47
100 mA range, we will have -1

1

photons per second on the sample at the same resolution. The useful energy range is from IT to 90 eV. A new

laminar grating is being manufactured which will decrease the amount of

second order light being transmitted, and a second new grating will extend

the range of the monochromator to 180 eV.

4. Construction of Angle-Resolving Display Analyzer

A new ellipsoidal-mirror angle- resolving electron- and

ion-energy analyzer is nearing completion. This outstanding instrument

was designed at NBS (based on an instrument constructed at IBM by D.

Eastman) and is being constructed here. It is ideally suited for

angle- resolved PSD, and will be the only such analyzer in North America

used for the measurements. Details and scientific plans are given in

Section 4.B.3.

5. Experiments at the Brookhaven National Synchrotron Light Source

A major effort during the last several years has been the

initiation of an NBS-Naval Research Laboratory collaboration to establish

four beamlines at the Brookhaven National Synchrotron Light Source (NSLS).

We are providing surface science instrumentation to be used on one of the

beamlines at the x-ray ring. The planned experiments have been delayed

due to machine problems but these now appear to be largely overcome.

Our planned research will be an extension of the experiments

performed at the NBS SURF-II facility (see above) to the higher-photon

energies and more intense light available at the NSLS. Light from a unique, extended- range monochromator (5-5000 eV) will be used to study

surface electronic structure and surface bonding of molecules.

Experimental probes will include photoemission spectroscopy, surface

extended x-ray absorption fine structure, and photon-stimulated

desorption.

The main experimental chamber has been installed at NSLS and a sample

preparation chamber has been acquired. The first experiments using the

limited range of the monochromator presently available (20-200 eV) will

involve measurements of electron attenuation lengths as a function of

electron kinetic energy for condensed thin films of molecular solids. The

synchrotron-based method for these measurements was developed and tested

at SURF-II. These measurements will provide benchmark data for electron

transport through organic materials in an energy range near the minimum

value of the attenuation length. When the monochromator energy range is

extended to -1000 eV, we will undertake detailed studies of the roles of

both core-level and valence excitation in the photon-stimulated desorption

of ions from covalently bonded molecules on surface.

48
6. Theory of Stimulated Desorption

Work continued on the elucidation of the mechanisms that can

give rise to electron- and photon-stimulated desorption of ions from

adsorbates on surfaces as well as from single crystals. During this year,

attention was given to the role of secondary electrons in photonstimulated desorption and the extent to which these effects distort the

ion yield spectra. Our studies suggest that these effects are not as dramatic as indicated in the literature. Work was also begun on understanding the mechanisms for negative-ion desorption from surfaces under

electron bombardment and the role these mechanisms may play in negativeion ESDIAD. Our understanding of the role of secondary electrons and the

mechanisms for negative-ion desorption are important for planned future

experiments (Section 3«B).

E. Dynamical Effects Associated with Core-Level Ionization

(T. J. Jach)

The NBS Quantum Metrology Group under the direction of Dr. R. D. Deslattes is developing an experiment to study electronic effects

associated with core-level ionization in atoms, molecules, and at

surfaces. Specific effects to be studied include dynamical effects in

inner-shell vacancy production, relaxation of the extra-atomic

environment, and production of multiple vacancies with or without

ionization. One member of the Surface Science Division staff has been

assigned to work half-time on this project.

During the past year, experimental work involving synchrotron

radiation was pursued with two particular goals in mind. First, the

long-awaited routine operation of the x-ray ring of the Brookhaven

National Synchrotron Light Source (NSLS) became a reality. We aligned and

corrected problems in our tunable focussed soft x-ray beamline (X-24A) to

the point where it is the most intense source of photons in the 2-7 keV

photons available in the world (-10 11 photons/ sec at 3 keV with <0.4 eV

resolution). Second, we initiated experiments to study multi-electron

core-level excitations in atoms and at surfaces.

1. NSLS X-24A Soft X-Ray Beamline (800 eV-7 keV)

The development of the NSLS X-24A beamline at Brookhaven

officially came to fruition in September with the production of a stable,

focussed, tunable x-ray beam in the energy range 2-7 keV. Using a nickel-coated aluminum collecting mirror (which also acts as a low-pass

filter), a double- crystal monochromator, and a nickel-coated focussing

mirror, we obtained a focussed spot 2 mm high by 1 mm wide with the flux

mentioned above. The entire system is in ultra-high vacuum (uhv) with no windows whatsoever (it is contiguous with the main ring vacuum) and

operates stably and comfortably at the highest intensity conditions

reached by the x-ray ring so far (125 mA stored current at 2.5 GeV) . The

system is entirely computer controlled. The flux at this time exceeds all

other tuned sources including the LBL/Exxon 54-pole wiggler at the Stanford

49
Synchrotron Research Laboratory over the energy range described above.

Although an active program of experiments has already begun, we are actively soliciting other potential users.

2. Photon-Excited Multi-Electron Core-Level Excitations Using

Synchrotron Radiation

We have begun a series of experiments aimed at the better

understanding of multi-electron excitations which are photoexcited. Such

effects as the threshold behavior of x-ray resonant Raman fluorescence,

the energy shift due to post-collisional interactions, and the couplings

between different decay channels from multi-electron excited states are

all topics of importance in a number of surface spectroscopies. In

collaboration with the NBS Quantum Metrology Group, we have initiated a three-step program: first, to observe x-ray fluorescence and

Auger-electron decay in monatomic gases; second, to observe these decays

in multi-atom gases; and finally, to observe the decays from solid

surfaces of transition metals. All of these measurements are to be made

as a function of photon energy in the vicinity of the threshold energies

for core-level ionization. Data such as line widths, energy shifts, and

threshold behavior will be used to understand multi-electron excited

states and the dynamics of the decay process.

During the past year we have taken preliminary data on two systems.

We observed K-shell x-ray fluorescence from argon gas using a windowed gas

cell and a uhv bent-crystal (Si) x-ray spectrometer. This work was the

first experiment on the x-24A beamline at NSLS described above. The

incorporation of ion chambers into the gas cell allowed us to tune

precisely the incident beam energy anywhere in the vicinity of the argon

K-edge (including the 4p "white line") and permitted precise tuning of

both the input and output photons.

The second system used an argon gas jet in vacuum and a cyl indrical-mirror electron energy analyzer to observe K-shell

photoemission and KVV Auger-electron decay. This system was put into

operation on the 54-pole wiggler beam line at the Stanford Synchrotron

Research Laboratory. The wiggler was operated as an indulator for the

first time and once again ion chambers monitoring absorption of the photons

in argon gas were used to tune the incident beam.

Both experimental systems yielded spectra with count rates lower than

expected. The coming year will be devoted to system modifications which

are intended to give higher count rates and eliminate other problems which

showed up in the first runs. The same systems will, of course, be used to

take data on monatomic and more complex gases.

A surface-science chamber which has been designed to perform uhv

studies on the x-24a beamline or elsewhere is presently being constructed.

It will permit us to perform the second phase of the multi-electron

excitation work using thin films and single crystals of transition metals.

The lower energy limit of this bearaline (-800 eV) was intentionally chosen

50
to allow study of the L-shell excitations in nickel and copper. We have

previously studied the Auger-electron spectra of these metals with

near- threshold electron excitation and believe that experiments with

near- threshold photon excitation will help resolve uncertainties in

interpretation. We expect to measure x-ray fluorescence, photoemission,

and Auger-electron spectra in the new experiments. Our new chamber will

incorporate a precision goniometer, allowing added surface sensitivity to

be obtained by orienting the sample at glancing incidence.

F. Production and Characterization of Ultrasmooth Surfaces

(T. J. Jach)

Previous surface science experiments have indicated a need for

surfaces which are extremely flat and smooth on an atomic 3cale. An

example of this need is the desire to study photoemission from a metallic

thin film at grazing incidence to obtain maximum surface sensitivity.

There are also obvious reasons for wanting to make smooth defect-free

substrates and thin films such as in the semiconductor industry where

device widths of 100A are being approached. We have initiated an effort

to (a) characterize substrates and thin films for roughness down to a scale of 3A; and (b) push the limit of surface smoothness attainable to 1 OA

or better for a variety of materials.

Reflection electron microscopy (REM) has been used to measure the

roughness of metal surfaces. In collaboration with Drs. G. Hembree of

the NBS Mechanical Production Metrology Division and L. B. Holdeman of

Comsat, a series of thin gold films were deposited on float glass

substrates at a range of temperatures between 30°C to 430°C. We have been

able to photograph structure on the film surfaces with a resolution of

about 10A. The study indicated that gold films deposited at room temperature are far rougher ( 1 00A rms or greater) than previously

thought; other standard techniques such as stylus or scanning electron

microscopy photos failed to reveal this roughness. REM should be capable

of directly detecting step dislocations or other such features on gold

films down to a height of one atom; such a resolution is almost as good as scanning tunneling microscopy. The methods are complementary, however,

since REM is better at looking at large areas rather than small ones. We

have also determined that the roughness is due to initial surface

nucleation and whisker growth which varies in a complex way with

temperature.

During the following year, we will be extending the reflection

electron microscopy technique to examine GaAs substrates as well as continuing work on the gold films. We hope that the success we have had

in characterizing gold films can be used to determine the polishing and

etching methods that produce the smoothest GaAs substrates.

51
G. Laser Diagnostics of Surface Dynamics

(D. R. Burgess, Jr. and R. R. Cavanagh)

The pathways and rates of energy transfer at surfaces remain the key

unresolved issues for understanding chemical reactions at interfaces.

Such information has eluded experiments which rely on conventional

surface-characterization techniques. A variety of laser-based techniques,

however, have recently demonstrated their utility in probing such

molecular dynamics in both the gaseous and liquid states. In this

program, the focus is on exploiting similar laser-based techniques for

addressing the issues of energy transfer at surfaces. The program

utilizes both the temporal and spectral characteristics available in

state-of-the-art lasers. Strong collaborations with Drs. M. P. Casassa,

E. J. Heilweil, D. S. King, D. A. Mantell and J. C. Stephenson of the NBS

Molecular Spectroscopy Division play a vital role in these efforts.

1. Laser-Excited Fluorescence .as a Probe of the Dynamics of Thermal

Desorption

Thermally activated desorption remains a key step in a wide

variety of reactions at surfaces. While it is frequently assumed that the

desorbed species can be accurately viewed as being in equilibrium with the

surface, there have been no direct tests of this assumption. For instance,

the potential for developing surface chemistries which exploit

non-equilibrium reactions of excited-state species will depend on the

efficiency of the accommodation process.

We have studied the thermal desorption of NO from P t ( 1 1 1 ) using

laser-excited fluorescence. The rotational-state distribution have been

examined as a function of NO coverage (0 = 0.1 to 1.0 of saturation) and

we have found that the internal energy of the desorbed NO can be described

by a Boltzmann distribution with T int = (0.95 ± 0.05) T surf (see Figure 7).

We have also examined the influence of coadsorbed CO. While the

adsorption sequence can change the desorption rate of the NO, resulting in

temperatures for the maximum desorption rate being lowered by 25J, the

internal energy is still found to be distributed in a Boltzmann manner,

with T int = T 3urf’ Additional experiments to probe the extent of

rotational alignment of the desorbed NO have indicated that there is no preferred spatial orientation of the rotational angular momentum.

Experiments to measure the kinetic energy in individual rotational states

are presently in progress. It is anticipated that the degree of accommo- dation found for the N0/Pt(111) system will make it an excellent

"benchmark" in future studies of rapid desorption processes (see Sections

2 and 4 below). Future plans include the extension of the NO /P t ( 1 1 1

)

measurements to the N0/Pt(110) system in order to probe the influence of

competition from step-induced NO dissociation with the molecular NO

desorption channel. This work is supported in part by the Department of

Energy

52
Fig. 7. Rotational temperature of NO thermally desorbed from Pt(111),

determined by laser-excited fluorescence, as a function of surface

temperature

2. Laser-Induced Desorption

Lasers have recently become popular tools for inducing

desorption from surfaces. The majority of the work in this area has

focused on the removal of near-monolayer quantities of adsorbed species

within the region illuminated by the laser. From the gas-phase species

which are generated, one can identify and measure concentration gradients

of adsorbates and probe adsorbate diffusion by monitoring the relaxation

of the laser- induced concentration gradient. We have recently begun a series of experiments aimed at using laser-excited fluorescence to measure

the internal-energy distribution as a result of desorption induced by a laser pulse.

In the past year we have been able to assemble a vacuum system for

these studies. It is anticipated that this system will permit us to use laser-excited fluorescence and multi-photon ionization as state-specific

probes of the laser-induced desorption process. We have already successfully used a quadrupole mass spectrometer to probe the desorption of H

2

, CO, and NO from a polycrystalline platinum foil upon irradiation with the

second harmonic from a frequency-doubled NdYAG laser. The laser53
desorption yield has been monitored both as a function of the surfacetemperature rise (laser pulse energy) and as a function of surface

coverage. In all cases, the desorption yield was non-linear in laser

intensity and there was a minimum energy density below which no detectable

desorption was observed. Furthermore, this threshold decreased with

increasing coverage, consistent with the shift to lower temperatures

observed in standard thermal desorption experiments.

A major concern in all experiments where a laser is used to heat a surface is the accurate determination of the surface temperature.

Classical heat conduction equations have been employed to establish the

surface temperature in the past, and are currently being used to analyze

the desorption yields obtained in this laboratory. However, experimental

efforts to validate the surface temperature actually achieved due to laser

heating are sparse. A direct measure of the laser perturbation of the

surface properties would offer the most satisfactory probe of the heating

effects. At this time we are examining the utility of blackbody radiation

as a signature of the extent and the reproducibility of laser-surface

heating. It is anticipated that state-specific detection will be

incorporated into this experiment in the coming year in order to determine

the degree to which laser heating is manifest in the internal and

translational energies of the desorbed molecules. This work is supported in

part by the Department of Energy.

3. Time resolved measurements of vibrational energy transfer

Direct characterization of the time scales and mechanisms for

relaxation and dephasing of vibrational excitation in adsorbed layers is

the aim of this work. Such measurements can provide a quantitative

understanding of a substrate's ability to quench the energy released upon

chemisorption, reaction, or irradiation.

Following our report last year of the first measurements of

vibrational relaxation on surfaces (OH on colloidal Si02 ), the technique

has been extended to self-supporting pressed discs of the same material.

A longer T

1 time for population decay was observed (220 ± 20 ps) than in

any of the measurements where a solvent was also present. Chemical

treatment of the Si02 surfaces has generated BOH, NH2 , and OCH^ adsorbates

which have been probed. The temperature dependence of the vibrational

relaxation rate for both OH and 0D on Si02 has been measured and each is

found to fit a multiphonon model for the thermally-enhanced relaxation

(see Figure 8). These experiments provide a first test of the pathways

involved in vibrational relaxation at surfaces. They also demonstrate

that over the temperature range employed by most industrial reactors, the

relaxation mechanisms on this model catalytic support can be generally

accounted for by a simple multiphonon model of the relaxation process.

Additional work has extended the technique to relaxation measurements of

the OH groups on the zeolite ZSM-5 and of both OH groups and free carriers

on ZnO.

54
Fig. 8. Vibrational relaxation rates (1/T-j) for OH and OD as a function of

temperature. For each isotope, the rates have been normalized to

the rates observed at room temperature. The solid curves represent the temperature dependence of the relaxation rate

predicted by a multiphonon relaxation model, where n is the number

of phonons involved in the relaxation process.

Future work is planned on a range of zeolites in an effort to measure

the differences between the vibrational relaxation rates for OH groups

bound at silica sites as compared to alumina sites. It has long been

postulated that these two sites have distinctly different catalytic

activity and thus it is reasonable to expect that they will have

distinctly different vibrational relaxation rates. By comparing a range

of samples with known catalytic activity, it will be possible to ascertain

the degree of correlation between the observed relaxation rates and the

catalytic activity. We also anticipate that the existing laser system can

be extended into the absorption range of the adsorbed carbon monoxide

fundamental. With this advance in picosecond laser technology, we will be

able to explore the T

1 times for CO bound to small supported

transition-metal particles. This project is supported in part by the Air'

Force Office of Scientific Research.

55
4. High-Resolution Infrared Reflection-Absorption Spectroscopy and

Picosecond/Femtosecond Measurements

To date, we have been able to contribute to a more detailed

picture of the relevant steps in energy transfer at surfaces. While there

remains a great deal still to be done with the techniques which we have

developed, it is becoming clear that several major advances will be

required before direct measurements of vibrational relaxation at wellcharacterized single-crystal surfaces will be possible. The four major

technical issues which must be addressed are: i) Extension of the tuning

range down to 5 ym in order to probe oscillators with large absorption

cross sections such as CO and NO. ii) Increased time resolution to the

range of < 2 ps in order to follow the faster relaxation rates

anticipated for systems which can couple to electron-hole pairs, iii) A high-resolution (=0.1 cm

-1

) reflection-absorption spectrometer to measure

the shape, cross section, and spectral position of the infrared absorption

feature, iv) An optical detection scheme with increased dynamic range in

order to measure changes on the order of 1 part in 10^ in the two

polarization components in an individual laser shot.

Each of the four technical issues mentioned above would have a substantial impact on the existing program, i.e. new adsorbates could be

studied, faster processes could be followed, damage which accompanies

laser- induced heating could be characterized, and smaller population

changes could be seen. However, if all four objectives can be achieved,

it will then be possible to measure vibrational relaxation rates at the

surfaces of single- crystal metal surfaces. Our efforts to date in the

four areas can be summarized as follows: i) We are currently exploring

several methods for extending the tuning range available to the present

laser system. We have generated = 1 0% of the required tunable infrared

energy in the 5ym region by mixing the output of the existing optical

parametric amplifier. A dye laser based on the Nd +

^ YAG is being

constructed to permit difference-frequency generation in LilO^. ii) A shorter duration (= 2 ps FWHM) synchronously- pumped tunable dye laser is

being amplified in order to generate sufficiently intense pulses for

mixing in nonlinear crystals, iii) The feasibility of a high-resolution

(= 0.1 cm

-1 resolution) infrared ref lection- absorption spectrometer based on a 20 ns Nd^YAG pumped difference-frequency generator is being

explored, iv) In collaboration with Dr. A. Luntz of IBM, optical

detection techniques with improved dynamic range (yet suitable for use in

pulsed-laser experiments) are being explored.

H. Spin Polarization in Secondary-Electron Cascades in Ferromagnets

(S. M. Girvin)

Recent experimental progress in the production and detection of

spin-polarized, low-energy electrons is opening up new avenues of research

in the study of both bulk and surface magnetism. One of the key

requirements for a proper interpretation of many experimental measurements

is an understanding of inelastic scattering and the production of secondary

56
electrons. In collaboration with Drs. D. R. Penn and S. P. Apell of the

MBS Electron Physics Group, a theory has been developed of spin

polarization in secondary-electron cascades in f errcmagnets . We have

found that measurement of the secondary polarization versus kinetic energy

provides useful information about the inelastic scattering which cannot

be obtained from traditional measurements of secondary intensity versus

kinetic energy. In particular, we have found that the ratio of

majority- to minority-spin inelastic lifetimes at an energy E is well

approximated by the simple relation

t + (E)/t + (E)

1-Pb 1+P(E)

1+P B 1-P(E)

where P(E) is the measured secondary-electron polarization at energy E and

Pg is the bulk polarization.

The lifetime ratios deduced from experimental measurements on Ni and

Fe are shown in Figure 9. The rise in the ratio at low energies is due to

the ability of minority electrons to scatter into the empty minority

d-band states which arise form the bulk magnetization.

These results will prove useful in interpretation of photoemission

and inverse-photoemission spectra and of polarized low-energy electron

diffraction data. They also provide a testing ground for microscopic

theories of inelastic and exchange scattering in f err omagnets

Fig. 9. Ratio of spin-up to spin-down lifetimes as a function of energy

for Ni and Fe.

57
I. Theory of Dynamical Molecular Processes at Surfaces

(J. W. Gadzuk)

This project is part of a continuing effort directed to understanding

both the static and dynamic behavior of atoms, molecules, solids,

surfaces, radiation and their mutual interactions. This understanding

comes from consideration of the microscope atomic-scale properties of

individual entities as well as from larger-scale statistical properties of

ensembles. Based upon our studies, phenomenological model theories are constructed which relate to the chemical physics and statistical

mechanical behavior and to the intrinsic properties of relevant

physico-chemical systems. In addition, a significant effort is invested

in the study of the role of an actual measurement process in determining

observed quantities in different surface spectroscopies. Ways in which

measurement-process-specific quantities such as line shapes, satellite

structures, etc. provide additional information on system dynamics are of

considerable interest.

A large-scale theoretical effort has been underway aimed at the

modeling of reaction dynamics at metallic surfaces and at interfaces of

electro-chemical signficance. Major focus in the past has been on the

role of internal degrees of freedom (vibrational, rotational, and

electronic) of molecules in determining energy flow and redistribution

occurring in elementary molecular processes at surfaces.

Work has remained focused on the role of intra- molecular vibrational

degrees of freedom in reactive surface dynamics. In these situations,

energy must be directed in order to break bonds or be extracted to

stabilize highly vibrationally excited species formed for instance at curve crossings where electronic rearrangement takes place. There has

been significant progress in several different directions in the application of an analytic model (developed in collaboration with Dr. S. Holloway

of Liverpool University) for obtaining classical trajectories of a diatomic molecular beam incident upon a surface and in which chargetransf er/curve-crossing events take place.

In collaboration with Dr. Holloway and Ms. M. Karikorpi of Liverpool

University, calculations have been made of the multi-dimensional

Landau-Zener probabilities for a two-state molecule/ surf ace scattering

event. We have obtained the correct branching ratios between scattered

vibrationally-hot neutral molecules and negative-molecular ions. This is

believed to be the first molecular-scattering calculation involving a physical surface which properly includes non- adiabatic coupling between

electronic states of the molecule.

Computer codes have been constructed to calculate the classical

trajectories of molecules over arbitrary potential-energy surfaces (PES)

with emphasis again on those PES which include a curve crossing/ seam. The

example shown in Figure 10 represents a vibrationally cold I p molecule, with

its molecular axis p in an orientation parallel to the physical surface,

normally incident upon the surface with center-of-mass translational

58
energy - leV. Near the surface, I 2

~ can form and this is characterized by an intra-molecular potential with large equilibrium separation and also by

stronger bonding to the surface. The grill work structure at the top of

Figure 10 is the PES. Contours of constant potential have been projected

IODINE

Fig. 10. A proposed potential energy surface (top) for an iodine molecule

incident upon a physical surface in which dissociative adsorption

is possible in the potential well at the surface for the

molecule-surface separation z = 1A along the intra-molecular

coordinate p. Contour plot (bottom) of the PES in the (p,z)

plane and a trajectory for a scattering event in which

translational- to-vibrational energy redistribution occurs.

onto the (p,z) plane (bottom of Figure 10) where the trajectory is also

shown. Note that the incident molecule becomes trapped for several

oscillations as a negative-molecular ion before scattering, in this case

with - 0.7 eV translational energy. Amongst other things, we have

calculated the probability for dissociative scattering as a function of

incident kinetic energy, treating parametrically the well depth of the

I 2 ~/surface bond (the depth of the far left potential vs. z curve in

Figure 10). Results are shown in Figure 11 together with experimental

observations of Kolodney and Amirav. The significant point here is that,

in both our theory and in the experiments, the dissociative scattering

probability

59
o

Fig. 11. Normalized probability for dissociative scattering of I 2 from a surface as a function of the kinetic energy of the incident I 2

molecular beam, treating the adsorption energy of I 2

_ (in eV)

parametrically. The points are reported results of Kolodney and

Amiray for I 2 scattering from a MgO surface.

rises from zero at threshold to a saturation value over a kinetic energy

range of - 4-6 eV. On the basis of the similarity between experiment and

theory, it is believed that the charge- transfer mechanism is important in

molecule- surf ace interactions.

We have developed further the " traj ectori zed wave-packet theory"

reported last year to a point where it now satisfies microscopic

reversibil ity and energy conservation (significant and ubiquitous flaws in

most previous " imposed- trajectory" theories). At the request of the editor

of "Comments on Atomic and Molecular Physics", a review article on

"Surface Harpooning" was written. The principles of chargetransf er/curve-cr ossing collisions were sequentially developed for

atom-atom, atom-molecule, atom-surface, and finally molecule-surface

collisions. By working up in order of complexity, it was easy to see how

one could use and adapt the results obtained in less complex collisional

events

Considerable progress has been made in the area of surface

vibrational spectroscopy, at least in part because of the intimate

connection between atom trajectories and vibrational spectra. A major

60
review article was written on "Excitation Mechanisms in Vibrational

Spectroscopy of Molecules on Surfaces" in which the physics of the

excitation process involved in the five most prevalent experimental

techniques was developed from a single, unified point of view.

Further work on shape-resonances in electron scattering from molecules

demonstrated how a shape-resonance/temporary-negative-molecular ion,

created in an electron energy-loss experiment, not only leads to overtone

enhancement in the intra-molecular excitations but also for any modes

which have a component normal to the surface.

Finally, vibrational lineshapes and spectra of adsorbed molecules

have been studied in terms of the quasi-periodic trajectories over multi-dimensional PES. This is a particularly prudent way to include the

anharmonic effects which lead to dynamically interesting lineshapes

because one can "see" what the oscillator is doing to acquire the lineshape. The lineshape or vibrational spectrum of an excited oscillator is

Koj) =

12 IT

1 im 1 T -*-00 2T

< 2T

/ Y(t)

o

irnt dt *>

where y(t) is the oscillator displacement as a function of time after

initial excitation. As an example, the trajectory of an initially excited

"harmonic" oscillator in the y direction (Y in = 0.1, X in = 0.01), which is

anharmonically coupled to an x-oscillator with half the frequency is shown

in the top of Figure 12. A number of well-defined y oscillations occur prior to a swing into the large- amplitude low-frequency oscillator and

then return to y. This is a characteristic Fermi resonance and the

vibrational spectrum shown in the bottom left of Figure 1 2 is a typical

slightly-split doublet (Am/w-0.1 here). Increasing the initial

displacement, hence anharmonicity , leads to a breakdown of

quasiperiodicity. Thus chaotic motion prevails, as indicated in the

spectrum shown in the bottom right of Figure 12 (Y in = 0.13, X in = 0.01).

The main peak is very much reduced in height, broadened, and an erratic

background appears. We are applying this methodology for determining

vibrational spectra to current problems of active interest in the surface

vibrational- spectroscopy communi ty

We plan to continue work in the area of surface reaction dynamics

with near-term emphasis on the determination of self-consistent reaction

trajectories, realistic electron-hole pair coupling constants, determination of energy-redistribution patterns amongst translational, vibrational, rotational, and electronic degrees of freedom of "reactant"

molecules and electron and phonon modes of surfaces. Analyses are made

for controllable dynamic and reactive conditions with synthesis of the

various components of the elementary reaction theories into theories of

experimentally realizable processes. Special emphasis will be placed on

the phenomenon of dissociative surface processes and on the role of

non-linear dynamics.

61
X10

- ’

Fig. 12. Initial trajectory (top) for an excited oscillator oriented along

the Y axis but anharmonically coupled to an X-oriented oscillator

with half the frequency. Also shown are constant

potential-energy contours. Vibrational spectra (bottom), I(oj) vs

a) (arbitrary units), accompanying such an excitation for initial

excitation below (left) and above (right) the chaotic threshold.

Note the scale change between the two spectra.

62
In addition, analysis will be made, whenever possible, of novel

experimental results. Current interest includes laser- assisted surface

processes and state- to-state analysis, high- resolution surface vibrational

spectroscopy, neutron spectroscopy of metal hydrides, and other

experimental probes of non-adiabatic effects.

63
4. SURFACE COMPETENCE PROGRAM

W. F. Egelhoff, Jr., J. Fine, S. M. Girvin, T. J. Jach

R. Klein, T. E. Madey, A. J. Melmed, R. Stockbauer

The Surface Competence Program is a part of the NBS "Competence

Program." The NBS program was introduced to provide long-term support of

the establishment and maintenance of areas of excellence in science and

technology contributing to the NBS mission and the projected needs of the

NBS clientele.

The Surface Competence Program (NBS Task 26117) was established

October, 1984 with two principal components, "Novel Two-Dimensional

Materials" and "State Characterization of Energetic Species Ejected from

Surfaces". The initiation of this program represents a new focus on these

topics. Each program component consists of several technical projects; some of these projects are extensions of activities in the Division that

had existed prior to the start of this Competence Program while others

have been launched this year. The principal objectives of each program

component are described in the following two main Sections together with

reports of the individual projects.

A. Novel Two-Dimensional Materials

In recent years an increasing awareness has developed of the

important modifications in physical properties which occur in materials as they approach the ultra-thin two-dimensional limit. Some examples of

unusual behavior discovered in such systems include the enhanced catalytic

properties of a gold surface with two monolayers of platinum compared to

bulk platinum, superconductivity of a silver monolayer on germanium, the

quantum Hall effect, the enhanced magnetism in alternating monolayers of

iron and cobalt, the electrical properties of metal- semiconductor

junctions (Schottky barriers), and multiple quantum-well systems for

optical logic devices. These examples suggest a whole new range of

scientifically and technically important chemical and physical properties

waiting to be explored in the two-dimensional regime. Concepts and

methods developed in surface and interface science have been particularly

valuable in many areas of application, and it is believed that these

concepts and methods can be further developed and extended to twodimensional systems with component thicknesses from one to one hundred

atomic layers.

There exist major gaps in current understanding of the fundamental

principles which govern the chemical and physical properties of layered

structures in the two-dimensional limit. In this component of the

program, it is planned to synthesize and determine the fundamental

chemical and physical properties of ultrathin layered materials with

layers so thin (a few atoms thickness) that they exhibit two-dimensional

behavior. Knowledge of the factors influencing the growth and properties

64
of ultrathin layered systems is expected to allow optimization of desired

chemical and physical characteristics and will thus benefit a number of

scientific fields ranging from catalysis to novel semiconductor devices.

We are performing work in four project areas. First, we are planning

to develop the techniques needed to synthesize, by alternating monolayer

deposition, a new class of materials: non-equilibrium ordered alloys.

The structural properties of these materials as grown and during thermal

processing will be investigated by x-ray and electron diffraction. The

chemical reactivity, catalytic activities, and magnetic properties of

these materials will also be investigated. Second, we plan to determine

the microstructure and microcomposition of candidate layered structures by

atom-probe and field-ion microscopy methods with emphasis on the interface

region. These techniques provide composition and structure data with

near-atomic spatial resolution. Third, we will apply modern many-body

theoretical techniques to the study of the quantum Hall effect, magnetism,

and other electronic properties of layered structures. Finally, we are planning to develop techniques for the study of the growth and morphology

of modulated structures using glancing- incidence diffraction of x-rays

from a synchrotron source and other extensions of modern surface methods.

1. Surface and Interface Chemical Physics of Ultrathin Films

(W. F. Egelhof f , Jr.)

Interest in ultrathin metal films (down to the two-dimensional

limit of one atomic layer) on the part of the surface-science community has

greatly increased in the past several years as it has become clear that an understanding of such structures will contribute to solving a wide range

of problems in surface science. Among these are an understanding of the

differences between surface and bulk electronic structure, the changes of

surface electronic structure associated with chemisorption, the basis of

surface magnetism, the modification of surface-layer properties by the

substrate, the relationship between electronic structure and epitaxial

growth, and the surface properties of alloys. The experimental program

presently underway is using an integrated approach to study single-crystal

surfaces, alloys and ultrathin films to contribute to an understanding of

all of the above problems.

We reported last year on the discovery of a new aspect of x-ray

photoelectron spectroscopy (XPS) and Auger-electron spectroscopy (AES) and

have termed it the "searchlight effect". The searchlight effect is

manifested in single-crystal samples by enhanced XPS and AES peak

intensities along nearest- neighbor and next-nearest-neighbor directions in

the lattice.

The searchlight effect is a powerful, new probe of short-range order

and is ideally suited for studying a variety of problems associated with

ultrathin films, surfaces, and interfaces. We now have the opportunity to

perform real-time studies of surface morphological and compositional

dynamics such as clustering of overlayers, surface segregation, and

surface alloying or interdiffusion at interfaces. Although these

65
phenomena are interesting in their own right, we are planning to

investigate them in association with our current primary objective of

synthesizing a new class of materials, non-equilibrium ordered alloys, by

epitaxial growth of alternating metal monolayers. This work has the

potential for opening up a whole new area of materials science. The XPS

searchlight effect is a near-perfect tool for diagnosing, in real time,

any growth processes that interfere with the desired synthesis and should

thus aid greatly in recognizing and overcoming barriers. We anticipate the

capability of producing novel material properties by tailor-making the

lattice structure. Later, we expect to characterize the materials with

x-ray diffraction and electron microscopy and to study their chemical

reactivity, catalytic activity, and magnetic properties.

We are in the process of improving our XPS instrument to carry out

the work just described. Changes in electron optics and detection will

provide substantially better operating characteristics. These changes

will, in part, permit application of the XPS searchlight effect to higher

electron energies than the conventional XPS range where it should have

increased diagnostic power. We are also designing a system of

ul trahigh- vacuum ovens to provide the sources with constant metal vapor

flux that are needed to grow high-quality films with alternating

monolayers by molecular- be am epitaxy.

The source of the angular anisotropies of electron emission in XPS

and AES that give rise to the searchlight effect have been investigated

using single-scattering calculations. These calculations, performed for

copper films as a function of thickness, demonstrate that the enhancements

are associated with forward scattering by nearest- neighbor and

next-nearest-neighbor atoms in the lattice. The searchlight effect can thus be used with confidence as a structural probe. The effect, however,

is a serious complication in the conventional method of measuring (and

using) electron attenuation lengths with single- crystal specimens.

Further details of this analysis are given in Section 2. A. 4.

Work has continued on the development of the equivalent-core approximation (ECA) as an interpretative tool for analyzing core-level

binding-energy shifts. Figure 13(a) shows how the Ni 2p^/2 core-level

shift induced by the adsorption of CO is governed by total-energy

considerations that can readily be understood with the ECA. In the final

state, a fully-screened core hole on Ni becomes (by the ECA) the chemical

equivalent of Cu. We consider the difference between final states with

clean or CO-covered Cu , as in Figure 13(a). Since there is a choice in

the final state between CO on a Ni atom and CO on the Cu atom, we can immediately use the greater Ni-CO bond strength to predict that the final

state leaving Cu clean will have the lower total energy. The Ni 2p^/2

core-level binding energy is just the energy to get from the initial state

to the indicated final states. We therefore deduce that the clean Ni must

exhibit the smaller binding energy and the CO-induced shift must be to

larger binding energy. Figure 13(b) shows the use of the ECA in

66
a)

TOTAL EMEPGY RULE QOVERMNG

SURFACE CORE-LEVEL SHFTS

b) HEAT OF Cu SURFACE SEGREGATION

WTTH ADSORBED CO

iom tot« anargy

h—,o, “”r9y ^

S66695b

\

653.01 «V 0 • *Cu* \

0 -« ?

FNAL

STATES

/

M2.34 «V / MT1AL

STATE

Fig. 13. (a) Illustration of how total energy considerations govern the

CO”induced surface core-level shift in Ni(100). (b) Illustration

of how the bulk- to- surface core-level shift can predict the heat

of CU surface segregation to a surface site with adsorbed CO.

determining from the bulk- to- surf ace Ni 2p^ /2 core-level shift that Cu

segregation to a CO-covered surface site is an endothermic process by 0.24

eV (5.5 kcal/mole). This result is in sharp contrast to the case of Cu

segregation to a clean Ni surface which is 0.43 eV (10 kcal/mole)

exothermic. The adsorption of CO will therefore drive Cu into bulk Ni.

Finally, a major invited article titled "Core-Level Binding-Energy

Shifts at Surfaces and in Solids" has been completed for Surface Science

Reports. This review article will, as it appears, be approximately 200

pages long and contain over a thousand references. The article consists

of a review of the theoretical principles of core-level shifts and a selection of the most illustrative, experimental case studies. The

theoretical principles section is written with the experimentalist in mind

and explains the essential concepts such as core eigenvalues, initialstate contributions, total energy differences, charge- transfer screening,

and polarization and dielectric screening without resorting to the usual,

opaque mathematics. Particular attention is paid to the principles of the

reference-level problem since many important fine points have often been

glossed over in previous descriptions. The section on experimental case studies contains selected results which illustrate, in the most clear-cut

manner possible, the basic mechanisms governing core-level shifts. The

topics include atomic coordination number, charge transfer, Madelung

potentials, cluster size, surface work function, image-charge and chargetransfer screening, band bending, and sample charging. In this section,

particular attention is paid to the relative merits of the two basic

conceptual frameworks for interpreting core-level shifts, the equivalentcore-energy-cycle framework and the initial-state--f inal-state framework.

67
2. Microcomposition and Microstructure of Thin Films

(A. J. Melmed and R. Klein)

This effort is directed to the measurement of microcomposition

in relation to microstructure of thin layers on well-characterized solid

substrates and the determination of interfacial diffusion. The methods of

investigation for these purposes are field-ion microscopy (FIM) , capable

of qualitative atomic structural determination, and atom-probe analysis

for compositional depth-probing on an atomic scale. Both _in situ and ex situ specimen preparation will be used in order to vary widely the

layer-formation procese parameters.

During this reporting period, the unique capability of FIM to

characterize the microstructure of novel materials was demonstrated. One of

the recently discovered class of rapidly solidifed aluminum-based alloys,

which appeared by electron diffraction in the transmission electron

microscope (TEM) to have icosahedral long-range order and no translational

symmetry, was made available to us. A considerable amount of theoretical

work has been done to explain and predict the relevant atomic structure.

Thus far, several theoretical models have predicted correctly most of the

observed diffraction features, but no complete description of atomic

positions has been given. The alloy, approximately AlgMn, was provided to

us in the form of pieces of very brittle ribbon, a few millimeters on a side and some 0.040-0.050 mm thick, and presented some complications in

specimen preparation. However, we succeeded in obtaining reproducible FIM

images which clearly showed that the material has a phase in real space

with structure consistent with icosohedral long-range order; that is,

appropriate two-, three- and five-fold symmetries are present, over a lateral distance of about 200 nm, and no translational symmetry is

evident. Also, we found no evidence for multiple twinning, the major

counter-viewpoint to the acceptance of real icosohedral symmetry. In

those regards, the FIM results clearly agree with the TEM results.

Additionally, the FIM images showed that the microstructure is replete with

micro-defects. Atomic dissection of the material by field evaporation

clearly showed that these features prevailed through a depth of at least

300 nm. Further microscopy remains to be done in an effort to determine

the details of atomic packing in this complex material.

The construction of our energy-corrected atom-probe (ECAP) , which

will be used for determining composition profiles through thin layers and

layer/ substrate interfaces, has been recently completed. All features of

the ECAP have been tested and found to function qualitatively as expected.

Initial quantitative evaluation has indicated that the mass resolution is

better than anticipated in the lower-resolution Section of the ECAP; that

is, M/AM appears to be at least - 250 and possibly is as high as 500

(compared to an expected value of about 150). Quantitative evaluation of

the high- resolution Section has been thwarted so far by a mechanical

misalignment introduced during the ECAP fabrication.

68
We have found it increasingly useful to combine our atcm-probe

analyses with the imaging capability of TEM (in collaboration with

colleagues in the NBS Metallurgy Division). The atom-probe-FIM—TEM

combination is extremely powerful in providing microscopy with a wider

range of contrast and magnification than available to the separate

techniques. For this purpose, we have developed a specimen holder which

allows us to shuttle specimens between the atom-probe FIM and the TEM.

Using this extended capability, we have begun microcomposition and

mi crostructure analyses of nickel-based superalloys (of interest as turbine-blade materials) and of a newly developed class of Al-Li-Cu

alloys

During the next year, it is planned to complete the quantitative

evaluation of the ECAP and to bring the associated electronics to a convenient working arrangement. Presently, the ECAP is operated using the

timing electronics of the general-purpose atom-probe FIM developed earlier

which is awkward for the user. A more appropriate system is partially

developed

Further microscopy and possibly atom-probe analysis of the

icosohedral-symmetry alloys and related materials are planned. Atom-probe

analyses of nickel-based and aluminum-based alloys will also be done. It

is hoped that an ultra- high- vacuum FIM can be assembled specifically for

in situ thin-layer deposition and microstructure characterization.

After full evaluation of the ECAP performance, a program of

depth- probe analyses of thin-layer/ substrate combinations will be

undertaken. Metal/metal systems prepared by alternate-layer vapor

deposition will be investigated in order to characterize the interfacial

composition and to determine the extent of intermixing. Appropriate

choices of elemental metals and preparation parameters will be made in

concert with other related experiments (e.g., Section 4.A.1 above).

3. Theory of the Quantum Hall Effect

(S. M. Girvin)

Artificial semiconductor superlattices (heterostructur es or multi-quantum wells) consisting of alternating atomically smooth layers of

GaAs and GaAlAs are among the most novel and successful two-dimensional

materials. By suitable doping one can create at the GaAs-GaAlAs interface

a two-dimensional electron gas which exhibits many interesting effects.

One of the most remarkable phenomena which has been observed in the

GaAs-GaAlAs system is the quantum Hall effect. At very high magnetic

fields (-10 T) and low temperature (< 4 K) , the Hall resistance of the

two-dimensional electron gas takes on universal quantized values of the

form h/e^i where h is Planck’s constant and e is the elementary charge.

The quantum number i is an integer or simple rational fraction. Associated with this quantization is the existence of persistent nearly

69
dissipationless currents similar to those occurring in superconductors and

superfluids. These unexpected findings have stimulated considerable

experimental and theoretical work at many laboratories.

In collaboration with Drs. A. H. MacDonald (National Research

Council, Ottawa) and P. M. Platzman (AT&T, Bell Laboratories, Murray Hill)

a "magneto-roton" theory has been developed of the collective excitations

in these fractional quantum- number states. This theory is closely

analogous to the Feynman theory of superfluid helium and provides new

insight into the physics underlying the persistence of currents.

The collective modes at long wavelength are predicted to be phonons

(density waves) and magneto- rot ons analogous to the roton excitations in

superfluid helium. The predicted mode spectrum is shown in Figure 14.

Independent numerical calculations on model systems by Dr. F. D. M.

Haldane of AT&T Bell Laboratories have shown that this magneto-roton

theory is remarkably accurate. Figure 14 illustrates the good agreement

between the predicted mode energy and Haldane's numerical results. One of

the advantages of our theory is its analytic simplicity which allows one for the first time to compute quite easily experimentally relevant and

Fig. 14. Collective excitation energy A versus wave vector for v = 1/3,

1/5, and 1/7. The solid lines are analytic results of the

magneto-roton theory. The circles and triangles are from

numerical calculations for v = 1/3 on small spherical and

hexagonal systems by Haldane and Rezayi. Arrows indicate

position of reciprocal lattice vectors of the Wigner crystal at

the appropriate densities.

70
previously inaccessible quantities such as the dielectric response.

Experimental attempts to observe the predicted magneto-roton excitations

via the dielectric response are currently under way in two separate groups

at AT&T Bell Laboratories.

This magneto-roton theory nicely complements earlier work we have

done on the Wigner crystallization transition. As the magnetic field is

increased, the magneto-roton mode goes "soft” at the wave vector

corresponding to the Wigner-crystal reciprocal-lattice vector. The

critical field at which the magneto-roton softening makes the liquid state

unstable agrees quite well with our previous predictions for the field at

which the Wigner crystal becomes stable. Hence the combination of these

two theories gives us a much deeper and more complete understanding of the

liquid-solid transition in this system.

Future work in this area will address questions of the finitetemperature statistical mechanics of the quantum Hall effect and the

effects of disorder. Another project which will take place in the coming

year is the organization of a quantum Hall effect lecture series at the

University of Maryland. In collaboration with Professor R. E. Prange,

plans are being made to edit and publish the lecture notes of the invited

speakers as a Springer-Verlag book. This book is intended to be a tutorial introduction to this rapidly expanding field for both

experimentalists and theorists.

Another area of planned future work concerns the field of metallic

superlattices. Dr. Michael DeWeert will be joining the Division as an NRC

postdoctoral fellow. His area of expertise is superconductivity,

proximity effects, and related phenomena in metallic superlattices. Close

interaction is expected with the superlattice experiments in the Division

and with the proximity effect work in the NBS Temperature and Pressure

Division.

4. Dynamical Diffraction of X-Rays from Crystal Surfaces at

Glancing Incidence

(T. J. Jach)

The structure and registry of adsorbed atoms with respect to the

underlying crystal lattice remains one of the major concerns of surface

science. Diffraction techniques such as low-energy electron diffraction

provide some of this information, but some foreknowledge of potential

sites of the atom and extensive calculation are usually required. We

have developed a new technique using the dynamical diffraction of x-rays

in a glancing- incidence geometry to provide the same type of information.

The technique is surface sensitive but could be employed at interfaces as well

Although the theory for dynamical x-ray diffraction has been

developed previously, it had not been tested experimentally since the

necessary experiments require an intense source of monochromatized x-rays

(e.g., from a synchrotron source), a well-collimated beam, and a specimen

71
crystal with a smooth, defect-free surface. In collaboration with Drs. P. Cowan and S. Brennan of the NBS Quantum Metrology Group and Drs. M.

Bedzyk and G. Materlik of the Deutsches Elektronen Synchrotron (DESY)

at Hamburg, an experiment was conducted last fall at DESY to test the

theory. We observed surface diffraction from Ge(220) planes normal to

the (111) surface at 8 keV with angles of incidence as low as 1 milliradian. X-ray beam collimation at the Bragg angle was about 5 microradians (Figure 15). This extreme collimation, possible only on a synchrotron light source, allowed us to obtain data which turned out to

fit the theory very well.

0

Nal SPECULAR BEAM

Fig. 15. Experimental set-up for grazing- incidence x-ray diffraction.

During the past year we have done considerable data analysis which

gave us a great deal of insight into surface dynamical diffraction theory.

Because we are able to diffract an x-ray beam from a crystal at incidence

angles less than the critical angle for total reflection (- 4 milliradians) , the x-rays inside the crystal are only evanescent

(exponentially-decaying) waves. There are two waves, however, and their

linear combination at the crystal surface forms an x-ray standing wave.

72
Slight changes in the angle of incidence or deviations from the Bragg

angle translate this standing wave back and forth on the surface,

selectively exciting surface atoms whose fluorescence was observed. The

interference process which makes this possible is illustrated in Fig.

16 (a) where the specularly reflected beam is shown to have either a strong

absorption or a maximum at the Bragg condition depending on the angle of

Incidence

Fig. 16 Intensities of (a) specular beam and (b ) diffracted beam as a function of deviation from the ideal Bragg angle 0B for various

fixed angles of incidence <j>. Curves 2, 3. and 5 are experimental

results and curves 1, 4, and 6 are results from dynamical

diffraction theory. The measurements and calculations are for

three angles of incidence: <p = 4.74 mill iradians , less than the

critical angle for total reflection (curves 1 and 2) ;

<j> = 5.55

milliradians , at the critical angle (curves 3 and 4); and <p = 6.35 milliradians, greater than the critical angle (curves 5 and

6 ).

73
These initial experiments were carried out in helium at atmospheric

pressure and we are building a chamber to continue the work in ultra-high

vacuum. We intend to measure position-dependent fluorescence,

photoemission, and Auger-electron decay from surface atoms. To this end, we have already built a new bent-crystal ultrahigh vacuum (uhv) x-ray

spectrometer. The principal task during the coming year will be to design

and build a uhv crystal goniometer which will be accurate to a few seconds

of arc. The equipment is designed to be used on our new focussed x-ray

beam line, X-24A, at the Brookhaven National Synchrotron Light Source.

B. State Characterization of Energetic Species Ejected from Surfaces

Specific state characterization of desorbed and ejected species from

surfaces, whether induced by sputtering or by electron and photon

bombardment, is still rare. It is now possible to address such dynamical

surface interactions using laser techniques to determine the energy state,

velocity, and angular distributions of all the ejected species —especially

the neutrals which are the most abundant. Such studies can provide

detailed microscopic information concerning energy transfer in these

excitation/interaction processes.

The objective in this component of the program is to understand the

excitation dynamics by which atoms and molecules are desorbed from surfaces

in ion- sputtering processes as well as in electron- and photon-stimulated

processes. Detailed characterization of the internal energy, kinetic

energy, and desorption thresholds of desorbed species will provide a microscopic understanding of the nature of the electronic excitations

leading to desorption due to collisions with electrons, photons, and ions.

Angular distributions will provide direct structural information

concerning the surface geometry, as well as information concerning energy

transfer during the collisonal interaction.

We are combining ul trahigh- vacuum surf ace- sci ence techniques with

state-of-the-art laser spectroscopy in several experiments involving

electron-stimulated desorption (ESD), photon- stimulated desorption (PSD),

and ion sputtering. Specifically, we propose to use multiphoton

ionization and other laser-spectroscopic techniques to detect and analyze

neutral species released from crystalline surfaces by electron, photon,

and ion bombardment. These measurements will provide unique insights into

the mechanisms of desorption induced by both electronic transitions and by

direct momentum transfer. Measurements of neutral angular distributions

will be compared directly with ion angular distributions using a new two-dimensional display analyzer, thus providing a detailed description of

competing desorption pathways.

We are performing work in three project areas. First, we are designing an experiment in which laser-spectroscopic techniques will be

used to determine the energy states of neutral atoms and molecules

sputtered from surfaces by ion bombardment. Second, we are collaborating

with scientists at Vanderbilt University on a similar experiment in which

74
neutral species desorbed from surfaces by electron or photon excitation

will be detected and characterized. This experiment may lead later to

similar work at NBS. Finally, we are constructing a new type of display

analyzer to measure angular and energy distributions of neutral species

desorbed from surfaces by electrons or photons to obtain surface-geometry

information and to test theories of ejection mechanisms. Close contact is

made with the related experimental and theoretical projects in the

Division described in Sections 3-B, 3-D, 3*G and 3.1.

1 . Energy States of Neutral Species Sputtered from Surfaces

(J. Fine)

Energetic ion-surface collisions generate extensive near-surface

collision cascades in a solid. The energy transfer and atomic excitations

that take place as a result of such collisions are not well understood in

part because, until rather recently, the primary method for monitoring

these collision phenomena was to measure macroscopic effects such as the

total sputtering yield. The collision cascade causes the ejection of

atoms, ions, electrons, and photons from the surface but it has only been

in the past few years that measurements of the ejected particles or radiation have been utilized to obtain detailed information of specific

atomic collisions that take place in condensed materials.

In recent experiments in which aluminum or silicon targets were bombarded by argon ions, we have shown that the Auger decay of

collisonally excited A1 or Si atoms can take place outside the solid

depending on the distance from the surface (within the material) at which

the excitation occurred, the atom's velocity, and the lifetime of the

atomic excitation. As a result of our Monte-Carlo calculation to analyze

these experiments, we expect that such sputtered atoms will have rather

high kinetic energies - extending up to hundreds of electron volts.

Collisions capable of transferring this much energy and creating

inner-shell (2p) excitation can generate sputtered atoms (ions) which are

in highly excited states. Such energy- transfer and excitation mechanisms

are basic to our enhanced understanding of collisional processes in

condensed materials. Information is required of those atomic processes

which lead to electron promotion, excitation and ionization, and particle

ejection. It is now possible to obtain this type of information by: (1)

probing specific ejected (sputtered) atoms via resonant, multiphoton laser

techniques; (2) monitoring the Auger-electron de-excitation of ejected

atoms as well as those which decay inside the solid; (3) analyzing the

emitted secondary-electron energy distributions. Progress made during the

first year of this project in each of these areas is described below.

(a) Laser Spectroscopy of Sputtered Atoms and Ions

In collaboration with Drs. L. J. Moore (NBS Inorganic

Analytical Research Division) and T. B. Lucatorto (NBS Radiation Physics

Division) , a new series of experiments has been planned and designed to

determine the kinetic energy distributions of specific sputtered atoms

(ions) and their states of excitation. Resonance multiphoton

75
laser- ionization schemes have been developed to detect sputtered atoms in

specific excited states and time- of- flight techniques will be used to

measure their kinetic energy distributions. Pulse timing and gating

sequences have been designed and estimates made of signal intensity

indicate that such measurements are feasible. A new apparatus has been

designed for this experiment and consists of an ultrahigh vacuum chamber

(that allows ion-beam-angle-dependent measurements to be made) connected to

a time-of-flight analyzer. This chamber, which is under construction,

will be coupled to two ultraviolet pulsed-laser systems. We plan to

investigate atoms (ions) sputtered from surfaces of magnesium, aluminum,

and silicon and to determine their charge state, excitation state, and

kinetic energy distributions.

(b ) Auger-Electron De-Excitation of Sputtered Atoms

In collaboration with Drs. C. Le Gressus and J. P. Durand

(Centre d* etudes Nucleaires de Saclay, France), a new series of

measurements were begun to investigate the Auger-electron emission from

ion-bombarded single- crystal aluminum surfaces. Aluminum (100) and (111)

surfaces were bombarded with argon ions and the dependence of atomic-like

and band-like Auger-electron emission was monitored as the crystals were rotated about an axis normal to the surface. Preliminary results indicate

a very marked change in Auger-electron emission intensity as a function of

rotation angle. Intensity minima correspond to geometrical conditions

where the incident ion beam is aligned with a string of atoms (i.e., there

is a shadowing of underlying atoms by the outermost surface atom of a given string). Measurements of this phenomena are still in progress in

Saclay; we anticipate extending this investigation of collisional

excitation processes in single- crystal solids at NBS.

(c) Secondary-Electron Energy Distributions Due to Ion

Bombardment

In collaboration with Dr. I. Terzic (Boris Kidric Institute,

Belgrade, Yugoslavia), an experiment has been designed to study the

secondary-electron energy distributions that result from Ga

+ -Ga collision

at ion energies from 20 to 60 keV. Previous measurements at NBS indicate

that collisional excitation may account for the high energy (> 100 eV)

emitted electrons observed. An apparatus is presently under construction

in Belgrade which will enable us to examine inner-shell excitation

thresholds in this system.

2. Electron- and Photon-Stimulated Desorption of Neutral Species

Using Laser Detection Techniques

(T. E. Madey)

In a collaborative effort with Prof. N. Tolk at Vanderbilt

University, we have initiated measurements to characterize the mechanisms

by which neutral species are excited and desorbed from surfaces using

electron- and photon-stimulated desorption (ESD/PSD).

76
The majority of species removed from surfaces via ESD and PSD are neutral atoms and molecules. However, virtually all measurements of the

energy and angular distributions of desorbing species have been of the

more-easily-detected minority ionic species; only recently have laser

techniques been applied to the detection of neutral species. The few

measurements made to date have concentrated on desorption from poorly

characterized surfaces, or radiation- induced decomposition of bulk solids

(e.g., alkali halides).

Our experiments are designed to search for and characterize the ESD

of both ground-state and excited Li and Na atoms desorbed from

fractional-monolayer films of Li and Na adsorbed on both clean and

oxygen-covered W ( 1 00 ) surfaces. We will employ laser-induced fluorescence

to detect the ground-state neutrals, and light emission following

metastable deexcitation to detect excited neutral species. A later stage

of the measurements will involve the use of synchrotron radiation to

determine the threshold energies for desorption via photon-stimulated • desorption. The choice of experimental systems for these first studies

(Na, Li on 0/W(100)) is based on previous related experiments and the

theoretical interest in these conditions.

2. Angular and Energy Distributions of Desorbed Ionic Species

(R. Stockbauer and T. E. Madey)

We have designed a special analyzer to measure simultaneously

the angular, energy, and mass distributions of ions desorbed from

surfaces. The analyzer will in addition be used for angle- resolved

photoemission.

The construction of a new angle-resolving, display-type ion and

electron energy analyzer is nearing completion. This instrument is based

on the IBM design of Dr. D. Eastman. After completion of the analyzer and

assembly, the analyzer will undergo initial testing in the laboratory using

an electron impact source. The video processing software which will

display the two-dimensional data in an appropriate form will be developed

during this initial testing. This same software will be used to process

similar two-dimensional data from a video system to be installed for our ESDIAD project (Section 3*B).

The initial test experiments using the new analyzer will be a series

of quantitative ESDIAD (Electron Stimulated Desorption-Ion Angular

Distributions) studies of small molecules adsorbed on metal surfaces. The

test systems will include NH^ and H

2 0 on Ni(111), as well as the

coadsorption of each of these molecules with electronegative (0, S, Br

)

and electropositive (K, Na) additives. Some of these systems have been

studied previously but a number of longstanding and important

fundamental questions remain for which the new analyzer can provide

quantitative answers. Experiments are planned to address the following

questions

77
o What are the angular profiles of the ion beams?

o Is there quantitative structural information in individual ESDIAD

beam shapes?

o How do the angular profiles of individual ion beams vary with

adsorption coverage and the presence of co-adsorbates?

o How do the ESDIAD patterns vary as a function of electron

excitation energy?

o Are the ion energy distributions a function of desorption angle?

o How do measured ion trajectories compare with theory?

In later experiments at the NBS synchrotron radiation source SURF -II,

the analyzer will be used in angle- resolved photon-stimulated desorption

studies of clean and adsorbate-covered oxide surfaces. Desorption

thresholds and energy dependences will be correlated with angle- resolved

electron spectroscopic measurements (ultraviolet photoelectron

spectroscopy, constant-initial-state, constant-final-state measurements).

These measurements will be the first detailed, angle- resolved mechanistic

studies of photon- induced bond-breaking processes at surfaces.

78
5. PUBLICATIONS

(a) Publications of Past Year

Armstrong, R. A. and Egelhoff, Jr., W. F., "An Analysis of Angular Dependent

XPS Peak Intensities," Surf. Sci. 1 54 , L225 (1985).

Bange, K., Madey, T. E. and Sass, J. K., "The Adsorption of Oxygen on

Ag (110): A New View of Structure and Bonding," Chem. Phys. Lett. 113 . 56 (1985).

Bange, K. , Madey, T. E. and Sass, J. K. , "Characterization of OH(ad)

Formation by Reaction Between H

20 and 0(ad) on Ag(110)," Surf. Sci.

152/153 . 550 (1985).

Bertel, E., Ramaker, D. E., Kurtz, R. L., Stockbauer, R. and Madey, T. E.,

"Photon Stimulated Desorption of H

+ Ions From OH on Ti and Cr:

Comparison with Bulk Solid H

2o," Phys. Rev. B Rapid Commun. 3J_, 6840

(1985).

Bertel, E., Stockbauer, R., Kurtz, R. L., Madey, T. E. and Ramaker, D. E.,

"The Decay Channels of the 3p Resonance in the 3d Transition Metals and

Their Relevance to the Mechanisms of Electron and Photon Stimulated Ion

Desorption," Surf. Sci. 1 52 , 776 (1985).

Bertel, E., Stockbauer, R., Kurtz, R. L., Madey, T. E. and Ramaker, D. E.,

"3p-Core Hole State Sensitivity in Ion Desorption from Oxidized Cr," in

Desorption Induced by Electronic Transitions, II , eds. W. Brenig and D. Menzel, Springer Series in Surface Sciences, Vol. 4 (Springer-Verlag,

Heidelberg), 84 (1985).

Bertel, E., Stockbauer, R., Kurtz, R. L., Ramaker, D. E. and Madey, T. E.,

"Resonant Photoeraission and the Mechanism of Photon Stimulated Ion

Desorption in a Transition Metal Oxide," Phys. Rev. B 31 . 5580 (1985).

Bozso, F., Yates, Jr., J. T., Arias, J., Metiu, H. and Martin, R. M. , "A

Surface Penning Ionization Study of the CO/N i ( 1 1 1 ) System," J. Chem.

Phys. 28, 4256 (1983).

Butler, J. J., Holland, D. M. P., Parr, A. C. and Stockbauer, R., "A

Threshold Photoelectron-Photoion Coincidence Spectrometr ic Study of

Dimethylether (CHoOCHn)," Int. J. Mass. Spectro. Ion. Phys. 58, 1 (1984).

° ~~

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. and Cavanagh, R. R.,

"Time-Resolved Measurements of Vibrational Relaxation of Molecules on Surfaces: Hydroxyl Groups on Silica Surfaces," J. Vac. Sci. Tech. A3_.

1655 (1985).

Cavanagh, R. R. and King, D. S., "Laser Studies of Surface Chemical

Reactions," in Chemistry and Physics of Solid Surfaces V , Springer

Series in Chemical Physics 35 (Springer-Verlag, New York), 141 (1984;.

79
Ceyer, S., Melmed, A. J., Carroll, J. J. and Graham, W. R., "On the Atomic

Structure and Optical Constants of (001) Tantalum," Surf. Sci. 144, L444

(1984).

Ceyer, S. and Yates, Jr., J. T., "Ammonia Adsorption on the Ag (311) Surface,"

Surf. Sci. 155, 584 (1985).

Ceyer, S. and Yates, Jr., J. T., "Orientation of CH^NC Adsorbed on Ag (311 )

,

J. Phys. Chem. 89, 3842 (1985).

Ciszewski, A. and Melmed, A. J., "Epitaxial Growth and Some Properties of

Samarium Crystals on Tungsten," J. de Physique _45, C9 (1984).

Ciszewski, A. and Melmed, A. J., "Epitaxial Crystal Growth of Gadolinium on Tungsten," Surf. Sci. _1_45, L471 (1984).

Ciszewski, A. and Melmed, A. J., "Surface Self-Diffusion of Dysprosium and

Gadolinium," Surf. Sci. 145, L509 (1984).

Ciszewski, A. and Melmed, A. J., "Epitaxial Crystal Growth of HCP Metals on

BCC Metals: Dysprosium on Tungsten," J. Crystal Growth _69., 253 (1984).

Cox, D. F., Semancik, S. and Szuromi, P. D., "The Interaction of Water Vapor

with Tin Oxide," Proceedings of the International Conference on Solid-State Sensors and Actuators-Transducers , Boston, MA, 385,

(1985).

Doering, D. L. and Semancik, S., "Orientational Ordering in a Strongly

Chemisorbed System: Na on Ru(001)," Phys. Rev. Lett. _53, 66 (1984).

Egelhoff, Jr., W. F., "A Core-Level Binding- Energy Shift Analysis of CO, H,

and 0 Adsorption on Cu-Ni Surfaces," J. Vac. Sci. Tech. A3_, 1305

(1985).

Egelhoff, Jr. W. F., "A New Tool for Studying Epitaxy and Interfaces: The

XPS Searchlight Effect," J. Vac. Sci. Tech. A3., 151 1 (1985).

Egelhoff, Jr., W. F., "Angle Resolved XPS of the Epitaxial Growth of Cu on Ni(110)," in The Structure of Surfaces , M. A. Van Hove and S. T. Tong,

eds., (Springer, Berlin), 199 (1985).

Egelhoff, Jr., W. F., "The XPS Searchlight Effect: A New Analytical Tool for

Layered Structures, Epitaxy, and Interfaces," in Layered Structures,

Epitaxy and Interfaces , MRS Proceedings, Vol. 37, J. M. Gibson, ed.

(Materials Research Society, PA), 443 (1985).

Fine, J., Lindfors, P. A. Gorman, M. E., Gerlach, R. L., Navinsek, B.,

Mitchell, D. F. and Chambers, G. P., "Interface Depth Resolution of

Auger Sputter Profiled Ni/Cr Interfaces: Dependence on Ion Bombardment

Parameters," J. Vac. Sci. Tech. A_3, 1 41 3 (1985).

Fine, J. and Navinsek, B., "Characterization of NBS Standard Reference

Material 2135 for Sputter Depth Profile Analysis," J. Vac. Sci. Tech.

A3, 1408 (1985).

80
Gadzuk, J. W. f "Surface Harpooning," Comments on Atomic and Molecular

Physics, _1_6» 219 (1985).

Gadzuk, J. W. , "Resonance Vibrational Excitation in Electron-Energy Loss

Spectroscopy of Adsorbed Molecules," Phys. Rev. 3 _31_, 6789 (1985).

Gadzuk, J. W. and Holloway, S., "On the Dissociation of Diatomic Molecules at

Metal Surfaces," Chem. Phys. Lett. 114 , 314 (1985).

Gadzuk, J. W. and Luntz , A. C., "On Vibrational Lineshapes of Adsorbed

Molecules," Surf. Sci. 1 44 , 429 (1984).

Gadzuk, J. W. and Nrirskov, J. K. , "Vibrational Excitation, Harpooning and

Sticking in Molecule-Surface Collisions," J. Chem. Phys. 81 , 2828

(1984).

Girvin, S. M. , MacDonald, A. H. and Platzman, ?. M. , "Collective Excitation

Gap in the Quantum Hall Effect," Phys. Rev. Lett. 54 , 581 (1985).

Glick, A. J. and Bryant, G. W. , "Effect of Anisotropy on the Optical

Absorption Spectrum of Polyacetylene," Phys. Rev. 3. _28_, 4295 (1983).

Goodman, D. W. and Yates, Jr., J. T. , "CO Isotopic Mixing Measurements in

Nickel: Evidence for Irreversibility of CO Dissociation," J. Catalysis

82, 255 (1983).

Heilweil, E. J., Casassa, M. P. Cavanagh, R. R. and Stephenson, J. C.

,

"Vibrational Energy Relaxation of Adsorbates on Surfaces," in Ultrashort

Pulse Spectroscopy and Applications, SPIE Voi. 533 (Society of

Photo-Optical Instrumentation Engineers, WA), 15 (1985).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R., and Stephenon, J. C.

,

"Picosecond Vibrational Energy Relaxation of Surface Hydroxyl Groups on Colloidal Silica," J. Chem. Phys. _81_, 2856 (1984).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R. and Stephenson, J. C.,

"Temperature Dependence of the Vibrational Population Lifetime of

0H(v=1) in Fused Silica," Chem. Phys. iett. 117, 185 (1985).

Heilweil, E. J., Casassa, M. ?., Cavanagh, R. R. and Stephenson, J. C.,

"Vibrational Deactivation of Surface OH Chemisorbed on Si02: Solvent

Effects," J. Chem. Phys. 82, 5216 (1985).

Heinonen, 0., Taylor, P. L. and Girvin, S. M. , "Electron-Phonon Interactions

and the Breakdown of the Dissipationiess Quantum Hail Effect," Pnys.

Rev. 3. 30, 3016 (1984).

Holloway, S. and Gadzuk, J. W. , "Energy Redistribution and Dissociation in

Molecule-Surface Collisions Involving Charge Transf er/Surf ace Hopping,

Surf. Sci. 152 , 838 (1985).

Holloway, S. and Gadzuk, J. W. , "Charge Transfer, Vibrational Excitation, an: Dissociative Adsorption in Molecular-Surface Collisions: Class'.cai

Trajectory Theory," J. Chem. Phys. 82, 5203 (1985).

81
Kelley, R. D., Cavanagh, R. R. f Rush, J. J. and Madey, T. E. , "Neutron

Spectroscopic Studies of the Adsorption and Decomposition of C

2H 2 and

C

2Hu on Raney Nickel," Surf. Sci. 155 , 480 (1985).

King, D. S., Mantell, D. A. and Cavanagh, R. R., "NO Thermally Desorbed From

a Saturation Coverage on Pt (111): Internal State Distributions," J.

Chem. Phys. 82, 1046 (1985).

Kurtz, R. L., Stockbauer, R. and Madey, T. E., "Site Specificity in Stimulated

Desorption from TiO ?

,» in Desorption Induced by Electronic

Transitions II , eds. W. Brenig'and D. Menzel, Springer Series in Surface

Sciences, Vol. 4 (Springer-Verlag, Heidelberg), 89 (1985).

Landman, U., Kleiman, G. G. , Cleveland, C. L., Kuster, E., Barnett, R. N.,

and Gadzuk, J. W. , "Hindered and Modulated Rotations of Adsorbed

Diatomic Molecules: States and Spectra," Phys. Rev. B. _29, 4313 (1984).

Madey, T. E., "The U3es and Limitations of ESDIAD for Determining the

Structure of Surface Molecules," in The Structure of Surfaces , Springer

Series in Surface Science 2, eds. M. A. Van Hove and S. Y. Tong

(Springer-Verlag, New York), 264 (1985).

Madey, T. E. and Benndorf, C., "Influence of Surface Additives (Na and 0) on

the Adsorption and Structure of NH^ on Ni(110)," Surf. Sci. 152/153, 587

(1985).

Madey, T. E., Benndorf, C., Shinn, N. D., Miskovic, Z. and Vukanic, J.,

"Recent Advances using ESDIAD: Applications to Surface Chemistry," in

Desorption Induced by Electronic Transitions II, eds. W. Brenig and D.

Menzel, Springer Series in Surface Sciences, Vol. 4 (Springer-Verlag,

Heidelberg), 104 (1985).

Madey, T. E., Ramaker, D. E. and Stockbauer, R., "Characterization of

Surfaces Using Electron and Photon Stimulated Desorption," Ann. Rev.

Phys. Chem. 35, 215 (1984).

Madey, T. E. and Stockbauer, R., "Experimental Methods in Electron and Photon

Stimulated Desorption," in Methods of Experimental Physics , Vol. 22,

Solid State Physics: Surfaces , R. L. Park and M. G. Lagally, eds.

(Academic Press, N.Y.), 465 (1985).

Matthew, J. A. D., "Comparison of Vibrational Broadening in Auger and

Photoelectron Spectroscopy," Phys. Rev. B 29, 3031 (1984).

Matthew, J. A. D., "Auger Spectroscopy of Solid Surfaces: Electron Versus

Ion Excitation," Phys. Scripts. T_6, 79 (1983).

Melmed, A. J. and Carroll, J. J., "An Approach to Realism in Field Ion

Microscopy via Zone Electropolishing," J. Vac. Sci. Tech. k2_, 1388

(1984).

Melmed, A. J., Maurice, V., Frank, 0. and Block, J. H., "Rare-Earth Crystal

Growth from the Vapor: Eu/Re and Eu/W," J. de Physique 45, C9 (1984).

82
Melmed, A. J., Twigg, M. E., Klein, R., Kaufman, M. J. and Fraser, H. L.,

"The Complementary Use of Atom Probe Field Ion Microscopy and Analytical

Transmission Electron Microscopy for the Study of a Ni-Base Superalloy,"

J. de Physique _45_, C9 (1984).

Navinsek, B., Panjan, P., Zabkar, A. and Fine, J., "A Comparison of Sputtered

Ni/Cr Interface Depth Resolution as Obtained by the Quartz Crystal

Microbalance Mass-Loss Method and Auger Spectroscopy," J. Vac. Sci.

Tech. A3, 671 (1985).

Ni5bl, C., Benndorf , C. and Madey, T. E., "H 2o Adsorption on Ni (110):

Evidence for Oriented Water Dimers," Surf. Sci. 1 57 , 29 (1985).

Penn, D. R., Apell, S. P. and Girvin, S. M., "Theory of Spin-Polarized

Secondary Electrons in Transition Metals," Phys. Rev. Lett. _55, 518

(1985).

Powell, C. J., "Inelastic Mean Free Paths and Attenuation Length of

Low-Energy Electrons in Solids," Scanning Electron Microscopy/ 1 984,

1649 (1984).

Powell, C. J., "Energy and Material Dependence of the Inelastic Mean Free

Path of Low-Energy Electrons in Solids," J. Vac. Sci. Tech. A3, 1 388

(1985).

Powell, C. J., "Innershell Ionization Cross Sections," in Electron Impact

Ionization , edited by T. D. Mark and G. H. Dunn (Springer-Verlag,

New York), 198 (1985).

Powell, C. J. (editor), "Technical Activites 1984 - Surface Science Division,"

NBSIR 84-2994 (1985).

Rendell, R. W. and Girvin, S. M. , "Quantum Hall Effect: Role of Inversion

Layer Geometry and Random Impurity Potential" in Precision Measurements

and Fundamental Constants II , eds. B. N. Taylor and W. D. Phillips,

National Bureau of Standards Spec. Publ. 617, 557 (1984).

Schmidt-May, J., Senf, F., Voss, J., Kunz, C, FlodstrOm, A., Nyholm, R.

and Stockbauer, R., "Resonant Photoemission and PSD of Rare Earth

Oxides," Desorption Induced by Electronic Transitions II , eds. W. Brenig

and D. Menzel, Springer Series in Surface Sciences (Springer-Verlag,

Heidelberg), 94 (1985).

Seah, M. P. and Powell, C. J., "The Coordinated Development of Standards for

Surface Chemical Analysis," NBSIR 85-3120 (1985).

Shinn, N. D. and Madey, T. E., "Unusual C-0 Bond Weakening on a Clean Metal

Surface: CO on Cr(110)," Phys. Rev. Lett. _53, 2481 ( 1984).

Shinn, N. D. and Madey, T. E., "Oxygen-Induced CO Reorientation on Cr(110),"

J. Vac. Sci. Tech. A3, 1673 (1985).

Twigg, M. E., "The Effect of Bremsstrahlung-Produced Fluorescence in X-Ray

Microanalysis in the Analytical Transmission Electron Microscope," J.

Electron Microsc. 134, 2 (1984).

83
Twigg, M. E., Melmed, A. J., Klein, R., Kaufman, M. J. and Fraser, H. L., "A

Microanalytical Study of Secondary Precipitation in RSR143 using Atom

Probe Field Ion Microscopy and Analytical Transmission Electron

Microscopy,” Superalloys 6 3 1 (1984).

Udovic, T. J., Kelley, R. D. and Madey, T. E., "The Methanation Activity of

W(110),” Surf. Sci. 150 , L71 (1985).

Yates, Jr., J. T., ”The Thermal Desorption of Adsorbed Species,” in Methods

of Experimental Physics , Vol. 22, Solid State Physics: Surfaces , R. L.

Park and M,. G. Lagally, eds, (Academic Press, N.Y.), 425 (1985).

Yates, Jr., J. T. and Haller, G. L., ”The Interaction of Physisorbed Species

with Chemisorbed Species as Studied by Infrared Spectroscopy,” J. Phys.

Chera. 88,4660 (1984).

84
(b) Publications in Progress

Bange, K. , Madey, T. E. and Sass, J. K. , "The Structure of the Surface

Hydration Shell of Bromide on Ag(110)," Surf. Sci. (in press).

Brennan, S., Cowan, P. L., Jach, T. , Lavilla, R., Perera, R. C. C. and

Winick, H., "Optical and Spectral Characteristics of an Insertion Device

Used Both as a Wiggler and an Undulator," Nucl. Instr. and Meth.

(in press).

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. and Cavanagh, R. R.,

"Time-Resolved Measurements of Vibrational Relaxation at Surfaces," J.

Elect. Spectroscopy (in press).

Cavanagh, R. R., Rush, J. J. and Kelley, R. D., "Neutron Inelastic

Scattering: Vibrational Spectroscopy of Adsorbed Molecules on Surfaces"

in Vibrational Spectroscopy of Molecules on Surfaces edited by J.T.

Yates, Jr. and T. E. Madey, Vol. 4 of Methods of Surface

Characterization , Plenum Press Publishing Co., New York, (in press).

Cowan, P. L., Brennan, S., Deslattes, R. D., Henius, A., Jach, T. and

Kessler, E. G. , "A High Energy Resolution X-Ray Spectroscopy Synchrotron

Radiation Beamline for the Energy Range 800 eV to 5000 eV," Nucl. Inst,

and Meth. (accepted).

Cowan, P. L., Brennan, S., Jach, T., Bedzyk, M. and Materlik, G.

,

"Observations of the Diffraction of Evanescent X-Rays at a Crystal

Surface," Phys. Rev. Lett, (submitted).

Cox, D. F., Semancik, S. and Szuromi , P. D., "Summary Abstract: Structural

and Electronic Properties of Clean and Water-Dosed Sn0 2 (110)," J. Vac.

Sci. Tech, (submitted).

Egelhoff, Jr., W. F., "Core-Level Binding-Energy Shifts in Solids at

Surfaces," Surf. Sci. Reports (submitted).

Erickson, N. E., "Modified Structural Proposal for the Si( 1 1 1 )-(7x7)

Reconstruction Based on an Analysis of Chemisorption Data," Phys. Rev.

B. (submitted).

Erickson, N. E. and Powell, C. J., "Characterization of the Imaging

Properties of a Double-Pass Cylindrical-Mirror Analyzer," Surf.

Interface Anal, (submitted).

Erickson, N. E. and Powell, C. J., "Imaging Properties and Energy Aberrations

of a Double-Pass Cylindrical-Mirror Electron Energy Analyzer," J. Vac.

Sci. Tech, (submitted).

Gadzuk, J. W. , "Excitation Mechanisms in Vibrational Spectroscopy of

Molecules on Surfaces," in " Vibrational Spectroscopy of

Molecules on Surfaces" edited by J. T. Yates, Jr. and T. E. Madey, Vol.

4 of Methods of Surface Characterization , Plenum Press Publishing Co.,

New York (in press).

' ~ ~

85
Gadzuk, J. W. and Holloway, S., '’Charge Transfer and Vibrational Excitation

in Molecule-Surface Collisions: Trajectorized Quantum Theory," Physica

Scripta (in press).

Gadzuk, J. W. and Holloway, S., "Collision Induced Dissociation of Diatomic

Molecules on Surfaces: A Charge Transfer Mechanism," J. Chem. Phys. (in

press)

Gadzuk, J. W. , "Dynamics of Molecular Processes at Surfaces: Vibrational

Lineshapes and Spectra," J. Elect. Spectroscopy (in press).

Girvin, S. M., MacDonald, A. H. and Platzman, P. M. , "Fractional Quantum Hall

Effect Superfluidity, Magneto-Rotons , and Fractionally Charged

Vortices," J. of Mag. & Mag. Mat. (in press).

Girvin, S. M., MacDonald, A. H. and Platzman, P. M. , "Magneto-Roton Theory of

Collective Excitations in the Fractional Quantum Hall Effect," Phys.

Rev B (submitted)

Karikorpi, M. , Holloway, S. and Gadzuk, J. W. , "A Classical Trajectory

Surface Hopping Approach to Non-Adiabatic Molecule-Surface Processes,"

J. Elect. Spectroscopy (in press).

King, D. S. and Cavanagh, R. R., "Final-State Resolved Studies of

Molecule-Surface Interactions," New Laser and Optical Investigations of

Chemistry and Structures at Interfaces , Verlag-Chemie (in press).

Kurtz, R. L., "The Influence of Surface Structure on Ion Emission from Ti0 2

,"

J. Vac. Sci. Tech. A (submitted).

Kurtz, R. L., Stockbauer, R. and Madey, T. E., "Angular Distributions of Ions

Desorbing from Ti0

2

," Nucl. Instr. & Meth. B. (submitted).

Kurtz, R. L., Usuki, N., Stockbauer, R. and Madey, T. E., "Measurements of

Electron Attenuation Lengths in Condensed Molecular Solids," J. Elect.

Spect. Rel. Phn. (submitted).

Madey, T. E., "Mechanisms and Applications of Electron Stimulated Desorption

in Surface Science," Vacuum (in press).

Madey, T. E. and Benndorf, C., "Evidence for Molecualar Orientations in

Coadsorption of CO and K on Ru(001)," Surf. Sci. (in press).

Mantell, D. A., Cavanagh, R. R. and King, D. S., "Internal States

Distributions of NO Thermally Desorbed from Pt (111): Dependence on Coverage and Co-adsorbed CO," J. Chem. Phys. (submitted).

MacDonald, A. H. and Girvin, S. M. , "Collective Excitations of Fractional

Hall States in Higher Landau Levels," Phys. Rev. B. Rapid Commun.

(submitted)

MacDonald, A. H. and Girvin, S. M. , "Quasi-Particle States and the Fractional

Quantum Hall Effect," Phys. Rev. Lett, (submitted).

86
MacDonald, A. H., Liu, K. L. and Girvin, S. M. , "Disorder and the Fractional

Quantum Hall Effect: Activation Energies and the Collapse of the Gap,"

Phys. Rev. B. (submitted).

MacDonald, A. H., 0j i , H. C. A. and Girvin, S. M. , "Magnetoplasmon

Excitations from Partially Filled Landau Levels," Phys. Rev. Lett,

(submitted)

MiSkovic, Z., Vukani6, J. and Madey, T. E., "Calculations of

Reneutralization Effects in ESDIAD," Surf. Sci. (submitted).

Penn, D. R., Apell, S. P. and Girvin, S. M. , "Spin Polarization of Secondary

Electrons in Transition Metals: Theory," Phys. Rev. B (submitted).

Platzman, P. M. , Girvin, S. M. and MacDonald, A. H., "Conductivity in the

Fractionally Quantized Hall Effect," Phys. Rev. Lett, (submitted).

Powell, C. J., "Calculations of Electron Inelastic Mean Free Paths from

Experimental Optical Data," Surf. Interface Anal, (in press).

Powell, C. J., "The Energy Dependence of Electron Attenuation Lengths,"

Surf. Interface Anal, (in press).

Powell, C. J., "Recent Developments in Quantitative Surface Analysis by

Electron Spectroscopy," J. Vac. Sci. Tech, (submitted).

Powell, C. J. and Seah, M. P., "Surface Chemical Analysis-Report on the VAMAS

Project," Surf. Interface Anal, (submitted).

Rush, J. J., Cavanagh, R. R., Kelley, R. D. and Rowe, J. M. , "Interaction of

Vibrating H Atoms on the Surface of Platinum Particles by Isotope

Dilution Neutron Spectroscopy," J. Chem. Phys. (in press).

Shinn, N. D., "Synchrotron Photoemission Evidence for 'Lying-Down' CO on Cr(110)," J. Vac. Sci. Tech, (submitted).

Shinn, N. D. and Madey, T. E., "CO Chemisorption on Cr(110): Evidence for a Precursor to Dissociation," J. Chem. Phys. (in press).

Shinn, N. D. and Madey, T. E., "Observation of a Metal: CO 4o Bonding

Interaction for Chemisorbed CO on Cr(110)," Phys. Rev. B (submitted).

Shinn, N. D. and Madey, T. E., "Chemisorption and Dissociation of 0 o on

Cr ( 1 1 0) : An EELS/ESDIAD Study," Nucl. Instr. & Meth. B. (in press).

Stockbauer, R., Kurtz, R. L., Usuki, N. and Madey, T. E. , "The Use of

Synchrotron Radiation to Measure Electron Attenuation Lengths in

Condensed Molecular Solids," Nucl. Instr. & Meth. 3. (submitted).

Twigg, M. E., Melmed, A. J., Klein, R., Kaufman, M. J. and Fraser, H. L., " A Microanalytical Study of Secondary Precipitation in a Nickel-Base

Superalloy with use of Atom Probe Field Ion Microscopy and Analytical

Electron Microscopy," Proc. Fifth Int. Symposium on Superalloys (in

press )

87
Wang, F. W. , Lowry, R. E. and Cavanagh, R. R., "Picosecond Excimer

Fluorescence Spectroscopy: Applications to Local Motions of Polymers

and Polymerization Monitoring," Polymer (submitted).

Wax, M. J., Cavanagh, R. R., Rush, J. R., Stucky, G. D., Abrams, L. and

Corbin, D. R., "A Neutron Scattering Study of Zeolite Rho," J. Phys.

Chem. (submitted).

Wax, M. J., Kelley, R. D. and Madey, T. E., "Ethane Hydrogenolysis Catalyzed

by W(110)," J. Catalysis, (submitted).

Yates, Jr., J. T., Madey, T. E. and Campuszano, J. C., "The Chemisorption of

Carbon Monoxide by the Transition Metals," The Chemical Physics of Solid

Surfaces and Heterogeneous Catalysis , D. A. King and D. P. Woodruff, eds.,

Elsevier (in press).

88
c) Recent Publications of New Staff Members (Burgess and Szuromi

)

Burgess, Jr., D. R., Hussla, I., Stair, P. C., Viswanthan, R., and Weitz, E.,

’’Pulsed Laser-Induced Thermal Desorption from Surfaces: Instrumentation

and Procuedures , " Rev. Sci. Instrum. 55 , 1771 (1984).

Szuromi, P. D., Engstrom, J. R. and Weinberg, W. H., "The Reaction of

Saturated and Unsaturated Hydrocarbons with the (110)— (1 x2 ) and (111)

Surfaces of Iridium,” J. Chem. Phys. 80., 508 (1 984).

Szuromi, P. D., Engstrom, J. R. and Weinberg, W. H. , ”Adsorption and Reaction

of N-Alkanes on the Pt(1 1 0)-( 1 x2) Surface,” J. Phys. Chem. 89 , 2497

(1985).

Szuromi , P. D. and Weinberg, W. H., "The Adsorption and Reaction of Normal

Alkanes on the the Ir ( 1 1 0)-( 1 x2) Surface,” Surf. Sci. 1 49, 226 (1 985).

89
6 TALKS

Cavanagh, R. R., "Energy Transfer at Surfaces: Pump-Probe Measurements of

Vibrational Relaxation," Department of Chemistry, California Institute

of Technology, Pasadena, CA, November 26, 1984.

Cavanagh, R. R., "Energy Transfer at Surfaces: Pump-Probe Measurements of

Vibrational Relaxation," Department of Chemistry, University of Irvine,

Irvine, CA, November 27, 1984.

Cavanagh, R. R., "Laser Diagnostics of Gas/Surface Interactions," American

Institute of Chemical Engineers, San Francisco, CA, November 28, 1984.

Cavanagh, R. R., "Energy Transfer at Surfaces: Pump-Probe Measurements of

Vibrational Relaxation," Department of Chemical Physics, IBM, San Jose,

CA, November 29, 1984.

Cavanagh, R. R., "Picosecond Pump-Probe Measurements of Vibrational

Relaxation at Surfaces," Department of Chemistry, Rutgers University,

Piscataway, NJ, April 1, 1985.

Cavanagh, R. R., "Energy Transfer at Surfaces: Laser Based Measurements,"

Local Section of American Vacuum Society, University of Minnesota,

Minneapolis, MN, May 16, 1985.

Cavanagh, R. R., "Energy Transfer at Surfaces: Laser Based Measurements,"

Physical Chemistry Department, General Motors Company, Detroit, MI, May

24, 1985.

Cavanagh, R. R., "Nitric Oxide Thermally Desorbed from Pt (111): A Microscopic Test of Transition State Theory," Physical Electronics

Conference, University of Wisconsin, Milwaukee, WI , June 17, 1985.

Cavanagh, R. R., "Hydrogen on Small Metal Particles: Structure and Dynamics

from Neutron Scattering," Gordon Research Conference on Metal Hydrides,

Tilton, NH, July 15, 1985.

Cavanagh, R. R., "Vibrational Relaxation at Surfaces: Time Resolved Results,"

Gordon Research Conference on the Dynamics of Gas-Surface Interactions,

New London, NH, July 29, 1985.

Cavanagh, R. R., "Picosecond Pump Measurements of Vibrational Relaxation at

Surfaces," Vibrations at Surfaces IV Conference, Bowness-on-Windermere

,

England, September 17, 1985.

Cavanagh, R. R., "Inelastic Incoherent Neutron Scattering: Vibrational

Spectroscopy of Hydrogen on Platinum Black," Vibrations at Surfaces IV

Conference, Bowness-on-Windermere , England, September 18, 1985.

Egelhoff, W. F. , Jr., "X-Ray Photoelectron Forward Scattering: A New Tool for

Studying Epitaxy and Interfaces," Materials Research Society Meeting,

Boston, MA, November 29, 1984.

90
Egelhoff, W. F . , Jr., "Heats of Adsorption of H and 0 on Cu-Ni Alloy Surfaces

from XPS Data," 31st National Symposium of the American Vacuum Society,

Reno, NV, December 5, 1984.

Egelhoff, W. F., Jr., "Role of Forward Scattering in Angular Dependent XPS,"

31st National Symposium of the American Vacuum Society, Reno, NV,

December 5, 1984.

Egelhoff, W. F., Jr., "New Applications for Angle Resolved XPS," American

Vacuum Society Chapter Meeting, Tampa, FL, February 6, 1985.

Egelhoff, W. F. Jr., "The XPS Searchlight Effect: A New Analytical Tool for

Layered Structure, Epitaxy and Interfaces," American Physical Society

Meeting, Baltimore Convention Center, Baltimore, MD, March 25, 1985.

Egelhoff, W. F. Jr., "A Core-Level Binding-Energy Shift Analysis of CO, H,

and 0 Adsorption on Cu-Ni Surfaces," American Physical Society Meeting,

Baltimore, MD, March 28, 1985.

Egelhoff, W. F., Jr., "Forward Scattering in XPS: A Structural Tool for

Surfaces, Interfaces and Epitaxy," Chemistry Department, University of

California, Berkeley, CA, April 25, 1985.

Egelhoff, W. F., Jr., "Forward Scattering in XPS: A Structural Tool for

Surfaces, Interfaces and Epitaxy," Applied Physics Department, Stanford

University, Stanford, CA, April 26, 1985.

Erickson, N. E., "Characterization of the Imaging Properties of a Double-Pass

Cylindrical-Mirror Analyzer," 6th Symposium on Applied Surface Analysis,

University of Maryland, College Park, MD, May 15, 1985.

Fine, J., "Ion-Beam Mixing and Radiation-Induced Segregation During Sputter

Profiling of Nickel/Silver Interfaces," Condensed Matter and Radiation

Sciences Division Seminar, Naval Research Laboratory, Washington, D.C.,

November 1, 1984.

Fine, J., "Characterization of NBS Standard Reference Material 2135 for

Sputter Depth Profile Analysis," 31st National Symposium of the American

Vacuum Society, Reno, NV, December 4, 1984.

Fine, J., "A Comparison of Sputtered Ni/Cr Interface Depth Resolution as Obtained by the Quartz Crystal Microbalance Mass-Loss Method and Auger

Spectroscopy," 31st National Symposium of the American Vacuum Society,

Reno, NV, December 5, 1984.

Fine, J., "Interface Depth Resolution of Auger Sputter Profiled Ni/Cr

Interfaces: Dependence on Ion Beam Parameters," 31st National Symposium

of the American Vacuum Society, Reno, NV, December 7, 1984.

Fine, J., "Sputter Profile Shapes and Widths of Ni/Cr Interfaces: Their

Dependence on Ion Bombardment Parameters," Seventh International

Conference on Ion Beam Analysis, Hahn Meitner Institute, Berlin, W.

Germany, July 9, 1985.

91
Gadzuk, J. W. , "Molecular Scattering, Energy Redistribution, and Dissociative

Adsorption at Surfaces," Surface Science Seminar, Imperial College,

London, England, September 24, 1984.

Gadzuk, J. W. , "Intra-Molecular Wavepacket Dynamics in Molecule-Surface

Scattering," Workshop on Interactions of Molecular Beams with Solid

Surfaces, St. John's College, Cambridge, England, September 27, 1984.

Gadzuk, J. W. , "Vibrational Lineshapes of Adsorbed Molecules," Department of

Physical Chemistry Seminar, University of Liverpool, Liverpool, England,

October 1, 1984.

Gadzuk, J. W. , "Dynamic Effects in Electronic Excitation and Molecular

Scattering from Surfaces," Department de Medecine Nucleaire and

Radiobiologie, Centre Hospitalie-Universitarire , Sherbrooke, Quebec,

Canada, January 21, 1985.

Gadzuk, J. W. , "Recent Advances in Vibrational Spectroscopy at Surfaces,"

Department de Medecine Nucleaire and Radiobiologie, Centre

Hosptialie-Universitaire, Sherbrooke, Quebec, Canada, January 22, 1985.

Gadzuk, J. W. , "Molecular Dynamics at Surfaces: Harpooning, Vibrational

Excitation, and Dissociative Adsorption," Physics Department Colloquium,

University of Waterloo, Waterloo, Ontario, Canada, January 25, 1985.

Gadzuk, J. W. , "Dissociation Dynamics in Molecule-Surface Collisions,"

American Physical Society Meeting, Baltimore Convention Center,

Baltimore, MD, March 25, 1985.

Gadzuk, J. W. , "Collision Induced Dissociation of Diatomic Molecules on Surfaces," Physical Electronics Conference, University of Wisconsin,

Milwaukee, WI , June 17, 1985.

Gadzuk, J. W., "A Classical Trajectory Surface Hopping Approach to

Non-Adiabatic Processes Occurring During Diatom-Surface Scattering,"

1985 Conf. on the Dynamics of Molecular Collisions, Snowbird Resort,

Snowbird, UT, July 16, 1985.

Gadzuk, J. W. , "A Trajectorized Quantum Model for Surface Harpooning

Processes Occurring in Diatom-Surface Scattering," 1985 Conf. on the

Dynamics of Molecular Collisions, Snowbird Resort, Snowbird, UT, July

17, 1985.

Gadzuk, J. W. , "The Vibrational Lineshapes of Adsorbed Molecules," Vibrations

at Surfaces IV Conference, Bowness-on-Windermere , England, September 17,

1985.

Girvin, S. M. , "Collective Excitation Gap in the Fractional Quantum Hall

Effect," AT&T Bell Laboratory, Murray Hill, NJ, October 31, 1984.

Girvin, S. M. , "The Quantum Hall Effect," Solid State Theory Seminar, Oak

Ridge National Laboratory, Oak Ridge, TN, November 2, 1984.

92
Girvin, S. M. , "Rotons in Superfluid Helium and the Fractional Quantum Hall

Effect," Center for Basic Standards Colloquium, National Bureau of

Standards, Gaithersburg, MD, January 9, 1985.

Girvin, S. M., "Introduction to the Quantum Hall Effect," James Franck

Institute Colloquium, University of Chicago, Chicago, IL, January 15,

1985.

Girvin, S. M. , "Rotons in Superfluid Helium and the Fractional Quantum Hall

Effect," Department of Physics, University of Chicago, Chicago, IL,

January 16, 1985.

Girvin, S. M. , "The Quantum Hall Effect," Department of Physics, Catholic

University, Washington, D.C., February 21, 1985.

Girvin, S. M. , "Rotons in Superfluid Helium and the Fractional Quantum Hall

Effect," Physics Department, Princeton University, Princeton, NJ, March

6, 1985.

Girvin, S. M. , "Rotons and Vortices in Superfluid Helium and the Fractional

Quantum Hall Effect," Physics Department, University of Maryland,

College Park, MD, March 11, 1985.

Girvin, S. M., "Collective Excitation Gap in the Fractional Quantum Hall

Effect," American Physical Society Meeting, Baltimore Convention Center

Baltimore, MD, March 26, 1985.

Girvin, S. M. , "Rotons and Vortices in Superfluid Helium and the Fractional

Quantum Hall Effect," Physics Department, SUNY, Stony Brook, NY, April

26, 1985.

Girvin, S. M. , "Rotons and Vortices in Superfluid Helium and the Fractional

Quantum Hall Effect," Physics Department, University of Minnesota,

Minneapolis, MN, May 6, 1985.

Girvin, S. M. , "Introduction to the Quantum Hall Effect with Applications to

GaAs Heterostructures," Center for Microelectronics and Information

Science, University of Minnesota, Minneapolis, MN, May 7, 1985.

Girvin, S. M. , "Rotons, Vortices and Superfluidity in the Fractional Quantum

Hall Effect," Institute of Theoretical Physics, University of

California, Santa Barbara, CA, June 4, 1985.

Girvin, S. M. , "Introduction to the Quantum Hall Effect," Department of

Materials Science, Harry Diamond Laboratories, Adelphi, MD, August 12,

1 985.

Girvin, S. M. , "Fractional Quantum Hall Effect: Superfluidity,

Magneto-Rotons and Fractionally Charged Vortices," International

Conference on Magnetism and Magnetic Materials, San Francisco, CA,

August 30, 1985.

Girvin, S. M. , "Introduction to the Quantum Hall Effect," Physics Department,

Texas A&M University, September 26, 1985.

93
Jach, T., ’’Observations of Dynamical X-Ray Diffraction from a Crystal Surface

at Glancing Incidence,” American Physical Society, Baltimore Convention

Center, Baltimore, MD, March 26, 1985.

Jach, T., ’’Dynamical X-Ray Diffraction at Glancing Incidence: A New Tool for

Surface Science," Physical Electronics Conference, University of

Wisconsin, Milwaukee, Wi , June 18, 1985.

Kelley, R. D., "Catalytic Activity of Single Crystal Tungsten and Tungsten

Carbide Surfaces," Symposium on Advances in Catalytic Chemistry III",

Hotel Utah, Salt Lake City, UT, May 22, 1985.

Kurtz, R. L., "Site Specificity in Stimulated Desorption from Ti0 2

," 2nd

International Workshop on Desorption Induced by Electronic Transitions,

Elmau, Germany, October 15, 1984.

Kurtz, R. L., "Surface Studies of the Oxides of Titanium: Electronic

Structure, Chemisorption, and Desorption from Ti 203 and Ti0 2 ," IBM

Thomas J. Watson Research Laboratories, Yorktown Heights, NY, November

8, 1984.

Kurtz, R. L., "Surface Studies of the Oxides of Titanium: Electronic

Structure, Chemisorption and Desorption from Ti 20o and Ti0 2

," Applied

Physics Division, Harry Diamond Laboratories, Adelphi , MD, November 20,

1984.

Kurtz, R. L., "Site Specificity in Stimulated Desorption from Ti0

2 ," 31 st

National Symposium of the American Vacuum Society, MGM Grand Hotel,

Reno, NV, December 6, 1984.

Kurtz, R. L., "Influence of Local Environment in Stimulated Desorption from

Ti0 2

," American Physical Society, Baltimore Convention Center, Baltimore,

MD, March 27, 1985.

Kurtz, R. L. , "Application of Surface Analytical Techniques to the

Characterization of Adsorption and Desorption from Solids," Physics

Department Colloquium, Brandeis University, Waltham, MA, April 30,

1 985.

Kurtz, R. L., "Surface Science Applications of Residual Gas Analyzers,"

Residual Gas Analyzer Calibration Workshop, National Bureau of

Standards, Gaithersburg, MD, May 7, 1985.

Madey, T. E., "Uses and Limitations of ESDIAD for Determining the Structures

of Surfaces Molecules," 2nd International Workshop on Desorption Induced

by Electronic Transitions, Garmisch, W. Germany, October 16, 1984.

Madey, T. E., "Desorption Induced by Electronic Transitions," Pittsburgh

Surface Science Center Symposium, University of Pittsburgh, Pittsburgh,

PA, October 30, 1984.

Madey, T. E., "Use of ESDIAD in Surface Chemistry," Department of Chemistry,

Iowa State University, Ames, IA, November 27, 1984.

94
Powell, C. J., "Energy and Material Dependence of the Inelastic Mean Free

Path of Low-Energy Electrons in Solids," 31st National Symposium of the

American Vacuum Society, MGM Grand Hotel, Reno, NV, December 6, 1984.

Powell, C. J., "Physics —What Physicists Do," Career Awareness Day, Walt

Whitman High School, Bethesda, MD, December 10, 1984.

Powell, C. J., "Techniques for Surface Analysis," Analytical Topical Group of

the New York Section of the American Chemical Society, New York, NY,

April 4, 1985.

Powell, C. J., "Developments in Quantitative Surface Analysis by Electron

Spectroscopy," Eastern Electron Spectroscopy Society Mtg., General

Electric R&D Center, Schenectady, NY, June 7, 1985.

Powell, C. J., "Chemical Bonding Studies at the Solid/Gas Interface with

Techniques Using Detected Electrons," Fifth Internat. Conf. on Surface

and Colloid Science and 59th Colloid and Surface Science Symposium,

Clarkson University, Potsdam, NY, June 25, 1985.

Shinn, N. D., "Oxygen-Induced CO Reorientation on Cr (110)," 31 3t National

Symposium of the American Vacuum Society, MGM Grand Hotel, Reno, NV,

December 7, 1984.

Shinn, N. D., "Chemisorption on Cr (110): Uncommon Results for 0

2 and CO,"

Surface Physics Group, Sandia National Laboratory, Livermore, CA,

December 10, 1984.

Shinn, N. D., "Recent Results and Realistic Goals of Silicon-Fluorine

Chemisorption Studies," Surface Physics Group, Hughes Research

Laboratory, Malibu, CA, December 12, 1984.

Shinn, N. D., "Novel 0^ and CO Chemisorption on Cr (110) as Revealed by

Stimulated Desorption and Surface Spectroscopies," Los Alamos National

Laboratory, Los Alamos, NM, March 12, 1985.

Shinn, N. D., "CO Chemistry on the Cr (110) Surface: Insights from Unexpected

Results," Sandia National Laboratory, Albuquerque, NM, March 14, 1985.

Shinn, N. D., "A Molecular Precursor to CO Dissociation on Cr (110): The a-.C0

Binding Mode," Americal Physical Society Meeting, Baltimore Convention

Center, Baltimore, MD, March 27, 1985.

Shinn, N. D., "Synchrotron Photoemission Study of Chemisorbed a-jCO and a 2 C0 on Cr(110)," Physical Electronics Conference, University of Wisconsin,

Milwaukee, WI , June 17, 1985.

Shinn, N. D., "C0:0 2 Interactions on Cr (110): Insights into Surface

Poisoning by Electronegative Adatoms," Department of Physics, Cornell

University, Ithaca, NY, August 14, 1985.

Stockbauer, R., "Photon and Electron Stimulated Desorption of Ions from

Surfaces: Mechanisms and Applications," Physics Department Colloquium,

University of Nebraska, Lincoln, NE, April 4, 1985.

95
Madey, T. E., "Mechanisms and Applications of Electron and Photon Stimulated

Desorption," 1985 Symposium on Surface Science (3S'85),

Bundessportschule Obertraun, Obertraun, Austria, January 29, 1985.

Madey, T. E., "Early Applications of Vacuum, From Aristotle to Langmuir,"

National Bureau of Standards Colloquium, Gaithersburg, MD, February 8,

1985.

Madey, T. E., "The Structures of Molecules on Surfaces as Determined Using

Electron Stimulated Desorption," Department of Chemistry, University of

Montreal, Montreal, Canada, February 27, 1985.

Madey, T. E., "The Structures of Molecules on Surfaces as Determined Using

Electron Stimulated Desorption," Department of Chemistry, Howard

University, March 8, 1985.

Madey, T. E., "Characterization of Surfaces Using Electron Stimulated

Desorption," Ceremonial Symposium Honoring the Retirement of Homer

Hagstrum, AT&T Bell Laboratories, Murray Hill, NJ, March 22, 1985.

Madey, T. E. , "Evidence for Molecular Reorientations in Coadsorption of CO

and K on Ru(001)," American Physical Society, Baltimore Convention

Center, Baltimore, MD, March 28, 1985.

Madey, T. E. , "Adsorption and Orientation of NH^ on Clean and Modified

Fe(100)," 7th European Conference on Surface Science, Aix-en-Provence,

France, April 3, 1985.

Madey, T. E. , "Mechanisms and Applications of Electron Stimulated

Desorption," Department of Physics, Vanderbilt University, Nashville,

TN, April 26, 1985.

Madey, T. E., "Electron and Photon Stimulated Desorption of Adsorbed Metals:

An Overview," Department of Physics, Vanderbilt University, Nashville,

TN, June 21 , 1985.

Madey, T. E. , "The Structure and Chemistry of H

20 on Silver Surfaces,"

Department of Chemistry, Iowa State University, Ames, IA, June 26,

1 985.

Madey, T. E. , "Influence of Surface Additive Atoms on the Structure and

Chemistry of H

20 on Ag(110)," American Chemical Society Meeting,

Americana Congress Hotel, Chicago, IL, September 9, 1985.

Melmed, A. J., "Long-Range Orientational Order and Icosahedral Symmetry in a Metallic Phase Observed by Field Ion Microscopy," American Physical

Society, Baltimore Convention Center, Baltimore, MD, March 28, 1985.

Melmed, A. J., "Field Emission Microscopy- Trends and Perspectives," 3rd

International Field Emission Symposium, Wheeling, W.Va., July 17, 1985.

Melmed, A. J., "Field Emission Microscopy- Trends and Perspectives," Seventh

International Summer Institute in Surface Science, University of

Wisconsin, Milwaukee, WI , July 23, 1985.

96
Stockbauer, R., "Photon and Electron Stimulated Desorption of Ions from

Surfaces: Mechanisms and Applications," Rice University, Houston, TX,

June 1985.

Stockbauer, R., "The Use of Synchrotron Radiation to Measure Electron

Attenuation Lengths in Condensed Molecular Solids," Synchrotron

Radiation Instrumentation Conference, Stanford University Conference

Center, Stanford, CA, August 1, 1985.

Szuromi , P. D., "UHV Studies of Alkane Activation on Iridium and Platinum

Surfaces," Department of Physics and Astronomy, University of Maryland,

College Park, MD , February 1, 1985.

Szuromi, P. D., "Site Specificity of Dissociative Alkane Adsorption on Platinum and Iridium Surfaces," Physical Electronics Conference,

University of Wisconsin, Milwaukee, WI, June 18, 1985.

Szuromi, P. D., "The Effect of Adsorbed Sulfur on the Hydrogenation of of CO over W ( 1 10)" American Chemical Society Meeting, Americana Congress

Hotel, Chicago, IL, September 10, 1985.

Szuromi, P. D., "Comparative Studies of Alkane Activation by Low Index

Surfaces of Platinum and Iridium," American Chemical Society, Americana

Congress Hotel, Chicago, IL, September 10, 1985.

Twigg, M. E., "An Atom Probe Study of Superalloy Microstructure," 5th Annual

Symposium on Superalloys, Seven Springs Mountain Resort, Champion, PA,

October 9, 1984.

Wax, M. J., "Neutron Scattering Studies of Zeolite Rho," 189th National

Meeting of the American Chemical Society, Miami Beach Convention Center,

Miami, FL, April 29, 1985.

Wax, M. J., "Thin Platinum Films as Model Alkane Reforming Catalysts," 189th

National Meeting of the American Chemical Society, Eden Roc Hotel,

Miami, FL, May 2, 1985.

Wax, M. J., "Thin Platinum Films as Model Alkane Reforming Catalysts,"

Symposium on Applied Surface Analysis, University of Maryland, College

Park, MD, May 16, 1985.

Wax, M. J., "Reforming Reactions of Ultrathin Film Model Catalysts," American

Chemical Society, Chicago, IL, September 10, 1985.

97
7. SEMINARS

Bennett, J. M., Naval Weapons Center, China Lake, CA, "Optical Evaluation

Techniques for Films and Surfaces," November 21, 1984.

Bishop, H. E., Materials Development Division, AERE Harwell, England,

"Electron Channeling Effects in Auger Electron Spectroscopy and

Secondary Electron Emission," September 26, 1985.

Cavanagh, R. R., National Bureau of Standards, Gaithersburg, MD, "Temporal

and Spectral Probes of Surfaces Processes: New Opportunities with Laser

Diagnostics," May 21, 1985.

Egelhoff, W. F., Jr., National Bureau of Standards, Gaithersburg, MD, "The

XPS Searchlight Effect: A New Analytical Tool for Layered Structures,

Epitaxy, and Interfaces," February 11, 1985.

Einstein, T., University of Maryland, College Park, MD, "How and Why to Study

Critical Properties of Surfaces and Adsorbates," October 11, 1984.

Ekardt, W., Fritz Haber Institute, Berlin, W. Germany, "Size Dependent

Photoabsorption and Photoemission From Small Metal Particles," April 18,

1 985.

Flodstrdm, A., Lund University, Lund, Sweden, "Angle Resolved Photoemission

Studies of Semiconductor Surfaces: Mostly Silicon and Germanium," June

13, 1985.

Freeman, R., AT&T Bell Laboratories, Murray Hill, NJ, "Picosecond Time

Resolved Photoemission from Surfaces of Semiconductors," (cosponsored

with NBS Radiation Physics Division) January 31, 1985.

Gurney, B. A., Cornell University, Ithaca, NY, "Adsorption and Desorption of

CO on Ni ( 1 1 0) , " December 17, 1985.

Heiland, W., Vanderbilt University, Nashville, TN, "Polarized Light Emission

from Grazing Incidence He + Ni ( 1 1 1 ) Interactions," September 13, 1985.

Hicks, R., WR Grace & Company, Columbia, MD, "The Effects of Metal-Support

Interactions on Palladium: Methanol Synthesis Catalysts," April 25,

1985.

Israelachvili , J. N., Australian National University, Canberra, Australia,

"Forces Between Surfaces," (cosponsored with NBS Inorganic Materials and

Thermophysics Divisions) July 1, 1985.

Johnson, A. L., University of California, Berkeley, CA, "Orientation of

Molecules by NEXAFS (Near Edge X-Ray Absorption Fine Structure)," April 12,

1985.

Karikorpi, M. , University of Liverpool, Liverpool, England, "Interaction of

H

2 with Metal Surfaces: Dynamics," July 10, 1985.

98
Klein, R., National Bureau of Standards, Gaithersburg, MD, "Weighty

Considerations on the Micro-Mass- Analysis of Alloys with the Atom

Probe," April 19, 1985.

Kurtz, R. L., National Bureau of Standards, Gaithersburg, MD, "Implications

of Recent Results on Photon-Stimulated Desorption," November 15, 1984.

McKay, J. M. , Yale University, New Haven, CT, "Electronic Structure of

NiO-CO, 0

2 , and H 2O Surface Interactions," June 12, 1985.

Myers, H. P., Chambers University of Technology, Goteborg, Sweden, "Mixed

Valence in Sm Over layers on Al(001) and Cu(001) Surfaces," January 14,

1985.

Paal, Z., Hungarian Academy of Sciences, Budapest, Hungary, "Activity,

Surface Structure and Composition of Pt-Black," September 19, 1984.

Pearlstine, K., Harvard University, Cambridge, MA, "Hydrocarbon Chemistry on Modified Tungsten Surfaces: C-H and C-C Bond Activation," March 4,

1985.

Renouprez, A., Institut de Recherches sur la Catalyse, Villeurbanne Cedex,

France, "EXAFS Study of the Structure of Pd Microaggregates. A

Combined EXAFS and Neutron Study of Hydride Formation," July 23,

1985.

Rys, F., Fritz Haber Institute, Berlin, W. Germany, "Surface Roughening and

Small-Particle Faceting-With Epitaxial Overtones," April 2, 1985.

Sass, J., Fritz Haber Institute, Berlin, W. Germany, "Surface Science Model

Studies of the Electrochemical Interface," January 17, 1985.

Sawatzky, G. , University of Groningen, Groningen, The Netherlands, "The

Electronic Structure, Bandgap, and Spectroscopic Properties of Transition

Metal Compounds," (cosponsored with Electron Physics Group) August 20,

1985.

Schwalke, U., California Institute of Technology, Pasadena, CA, "Vibrational

Spectra of Chemisorbed N0 2 and Condensed N 2

C>4 on the Ru(001) Surface,"

July 26, 1985.

Seah, M., National Physical Laboratory, Teddington, Middlesex, England,

"Electron Spectrometer Intensity Transmission Functions for ESCA,"

November 29, 1984.

Steigerwald, D., Carnegie-Mellon University, Pittsburgh, PA, "Surface

Segregation in NiAu Alloys," March 20, 1985.

Stockbauer, R., National Bureau of Standards, Gaithersburg, MD, "Studies of

Electron Transport and Radiation Damage in Condensed Molecular Films

Using Synchrotron Radiation," February 14, 1985.

Strasser, G. , University of Maine, Orono, ME, "Nitrogen Adsorption on Fe(1l 1 from the Extrinic Precursor to Atomic Nitrogen," September 16 , 1985 .

99
Szuromi , P. D., National Bureau of Standards, Gaithersburg, MD, "Alkane

Activation of Low Index Surfaces of Iridium and Platinum: Comparative

Studies," March 13. 1985.

Szymonski, M., Jagellonian University, Krakow, Poland, "Electron Stimulated

Desorption of Neutrals from Alkali Halide Surfaces," January 16, 1985.

Tomanek, D., Free University of Berlin, Berlin, Germany, "Calculation of

Potential Energy Surfaces for CO and N

2 Dissociation on Transition

Metals," May 28, 1985.

Trenary, M. , University of Illinois, Chicago, IL, "Infrared

Ref lection-Absorption Spectroscopy of CO on Clean and Sulfided Ni(111),"

November 28, 1984.

Yarmoff, J. , University of California, Los Angeles, CA, "Low Energy Ion

Backscattering Spectroscopies Applied to the Determination of Surface

Structure," March 20, 1985.

100
8. TECHNICAL AND PROFESSIONAL COMMITTEE

PARTICIPATION AND LEADERSHIP

Cavanagh, R. R.

Surface Science Division Safety Officer

Treasurer, General Committee of the Physical Electronics Conference

(from 7/85)

Erickson, N. E. Member, ASTM Committee E-42 on Surface Analysis

Fine, J.

Chairman, Subcommittee E-42. 09 on Standard Reference Materials of ASTM

Committee E-42 on Surface Analysis

Member, Program Committee, 11th Conference on Atomic Collisions in

Solids, Washington, D.C., August, 1985.

Gadzuk, J. W.

Treasurer, General Committee of the Physical Electronics Conference

(through 6/85)

Member, Editorial Advisory Board, "Progress in Surface Science"

Kelley, R. D.

Chairman, Subcommittee D-32.03 on Chemical Analysis of ASTM Committee

D -32 on Catalysts

Madey, T. E. Member, Executive Committee of the Governing Board of the American

Institute of Physics (through 3/85); member of AIP Committee on Corporate Associates, and member of AIP Subcommittee on Electronic

Publishing

U.S. Representative to Surface Science Division of the International

Union of Vacuum Science, Technique and Applications (IUVSTA) and

Secretary of Committee

Member, International Advisory Committee, Second International Conference

on the Structure of Surfaces, Amsterdam, The Netherlands, June, 1987

Program Chairman, International Vacuum Congress and International

Conference on Solid Surfaces, Baltimore, MD, October, 1986

Member, Organizing Committee, 11th Conference on Atomic Collisions in

Solids, Washington, D.C., August, 1985

Member, International Advisory Committee, Second Workshop on Desorption

Induced by Electronic Transitions, Garmisch, W. Germany, October, 198 ^

Member, Program Advisory Commitee for the Synchrotron Radiation Center

of the University of Wisconsin, Madison, Wisconsin

101
Member, Advisory Committee for Laboratory of Surface Science and

Technology at the University of Maine, Orono, ME

Member, Davisson-Germer Prize Committee of the American Physical Society

Chairman, Committee for Foreign Interactions, American Vacuum Society

Co-Editor, "History of Vacuum Science and Technology", a monograph to

commemorate the 30th Anniversary of the American Vacuum Society

(published 11/84)

Member, ASTM Committee E-42 on Surface Analysis

Member, Editorial Board, "Methods of Surface Characterization";

co-editor of two volumes in series

Member, Editorial Board, "Journal of Vacuum Science and Technology"

Melmed, A. J.

Secretary, Steering Committee, International Field Emission Symposium

Powell, C. J.

Chairman, ASTM Committee E-42 on Surface Analysis

Chairman, Surface Chemical Analysis Working Party, Versailles Project on Advanced Materials and Sandards

Member, Board of Trustees, Gordon Research Conferences; Vice-Chairman of

Board and Chairman of Selection and Scheduling Committee

Chairman, American Vacuum Society Surface Science Division (through

11/84)

Trustee, American Vacuum Society Scholarships and Awards Committee

Instructor, American Vacuum Society Short Course: "Surface Analysis by

Electron Spectroscopy"

Chairman, Study Group to Examine AVS-ASTM E-42 Interactions

Chairman, Local Committee, Meeting of American Physical Society,

Baltimore, MD, March 1985

Member, Editorial Board, "Applications of Surface Science"

Member, Editorial Board, "Surface and Interface Analysis"

Member, Editorial Board, "Methods of Surface Characterization"

co-editor of one volume in series

Stockbauer, R.

Assistant Program Chairman, International Vacuum Congress and

International Conference on Solid Surface, Baltimore, MD, October,

1986 .

102
9. PROFESSIONAL INTERACTIONS, CONSULTING

AND ADVISORY SERVICES

Cavanagh, R.R.

Collaborating with Dr. D. S. King of the NBS Molecular Spectroscopy

Division on state-specific diagnostics of molecular desorption processes

Collaborating with Drs. M. P. Casassa, E. J. Heilweil and J. C.

Stephenson of the NBS Molecular Spectroscopy Division on real time

measurements of vibrational relaxation processes at surfaces

Collaborating (with R. D. Kelley and M. J. Wax) with Drs. T. J. Udovic

and J. J. Rush of the NBS Reactor Radiation Division on neutron inelastic

scattering studies of adsorbates on high- surf ace- area transition metals

Collaborating with Dr. J. J. Rush of the NBS Reactor Radiation Division,

Dr. G. D. Stucky of du Pont, and Dr. M. J. Wax on vibration and

diffusion properties of hydrogen and ammonia in zeolite H-rho

Collaborating with Drs. T. J. Udovic and J. J. Rush of the NBS Reactor

Radiation Division and Dr. B. J. Tatarchuk of Auburn University on neutron inelastic scattering measurements from adsorbates on dispersed

ruthenium catalysts

Egelhoff, Jr., W. F.

Collaborating with Dr. R. A. Armstrong of the National Research Council,

Ottawa on a theoretical analysis of the basic physics of the XPS

searchlight effect for the purpose of defining and extending its range

of applicability as an analytical tool for surfaces and interfaces.

Fine, J.

Collaborating with Prof. B. Navinsek of the J. Stefan Institute,

Ljubljana, Yugoslavia on the effect of surface topography on measurements of sputtering yields, on depth resolution at interfaces,

and on the fabrication and characterization of standard reference

materials for surface analysis. This collaboration is conducted under

the auspices of the U.S. -Yugoslavia Agreement for Cooperation in Science

and Technology.

Collaborating with Dr. I. Terzic of the Boris Kidric Institute,

Belgrade, Yugoslavia on electronic excitation and electron emission for

ion-bombarded surfaces. This collaboration is conducted under the

auspices of the U.S. -Yugoslavia Agreement for Cooperation in Science

and Technology.

Collaborating with Drs. L. and N. Tanovic of the University of Sarajevo,

Yugoslavia on characterizing surface topography changes that result from

ion bombardment. This collaboration is conducted under the auspices of

the U.S-Yugoslavia Agreement for Cooperation in Science and Technology.

103
Collaborating with Dr. T. Nevadovic of the Boris Kidric Institute,

Belgrade, Yugoslavia on the surface-topography effect of both particle

and laser-beam interactions with thin solid films. This collaboration is

conducted under the auspices of the U.S. -Yugoslavia Agreement for

Cooperation in Science and Technology.

Collaborating with Dr. L. J. Moore of the NBS Inorganic Analytical

Research Division and Dr. T. Lucatorto of the NBS Radiation Physics

Division on the use of laser multiphoton ionization techniques to

identify sputtered atoms and to determine their kinetic energies.

Collaborating with Dr. W. Kirchhoff of the NBS Chemical Thermodynamics

Division on a data analysis procedure for sputter-depth-profile

interface characterization.

Collaborating with Dr. R. F. Fleming of the NBS Inorganic Analytical

Research Division on thin-film thickness measurements of standard

reference materials for surface analysis.

Collaborating with Dr. P. A. Lindfors of the Physical Electronics

Division of Perkin-Elmer Corp. on the interface depth resolution of

sputter-profiled Ni/Cr interfaces.

Collaborating with Drs. C. Le Gressus and J. P. Duraud of the Centre

d' Etudes Nucleaires de Saclay, France on the collisional excitation and

electron decay of atoms at single-crystal surfaces.

Gadzuk, J. W.

Collaborating with Prof. M. Sunjic of the Rudnor Boskovic Institute and

the University of Zagreb, Yugoslavia on theories of electron

spectroscopies and dynamics of molecular processes at surfaces. This

collaboration is conducted under the auspices of the U.S. -Yugoslavia

Agreement for Cooperation in Science and Technology.

Collaborating with Prof. U. Landman of the Georgia Institute of

Technology on theoretical modeling of non-linear and stochastic

molecular processes at surfaces.

Collaborating with Dr. S. Holloway and Ms. M. Karikorpi, University of

Liverpool, England on classical trajectory theories of molecular

processes at surfaces. This collaboration is assisted by a grant from

the NATO Scientific Affairs Division.

Collaborating with Dr. E. Hood, California Institute of Technology, on a theory of polarized-metastable-helium de-excitation spectroscopy at

magnetic surfaces and on electron-transf er probabilities.

Invited lecturer and participant at the Fourth Electrochemistry Study

Group, Fritz-Haber-Institute , Berlin, September 22- 27 , 1985 .

Girvin, S. M.

Collaborating with Drs. A. H. McDonald of the National Research Council

of Canada, Ottawa and P. M. Platzman of AT&T Bell Laboratories , Murray

Hill on developing a new theory of collective excitations in the

fractional quantum Hall effect.

104
Collaborating with Dr. M. Jonson of Chalmers University of Technology,

Gothenburg, Sweden on the theory of the thermoelectric effect in

disordered quantum Hall systems.

Collaborating with Drs . D. R. Penn and S. P. Apell of the NBS Radiation

Physics Division on a theory of spin polarization in secondary cascades

in f erromagnets

Collaborating with Prof. R. E. Prange of the University of Maryland in

the organization of a lecture series on the quantum Hall effect during

fall, 1985. It is planned to publish the lectures as a book.

Visited the Institute of Theoretical Physics at Santa Barbara during

June 3-8, 1985 at the invitation of Prof. J. R. Schrieffer.

Visited AT&T Bell Laboratories, Murray Hill during July 2-12, 1985 at

the invitation of Dr. D. S. Fisher.

Jach, T. J. Collaborating with Drs. P. Cowan and S. Brennan of the NBS Quantum

Metrology Group on the development of a beamline at the National

Synchrotron Light Source, Brookhaven and on experiments to study

electronic effects associated with core-level ionization in atoms,

molecules, and solids.

Collaborating with Drs. P. Cowan and S. Brennan of the NBS Quantum

Metrology Group and with Drs. G. Materlik and M. Bedzik of the German

Electron Synchrotron Laboratory DESY, Hamburg on surface and interface

x-ray diffraction experiments at DESY using glancing incidence.

Collaborating with Drs. G. G. Hembree of the NBS Mechanical Production

Metrology Division and L. B. Holdeman of COMSAT on the fabrication and

characterization of ultra-smooth surfaces and thin films.

Collaborating with Dr. P. Cowan of the NBS Quantum Metrology Group on glancing incidence x-ray excitation of surface atoms to measure surface

core-level binding-energy shifts.

Collaborating with Dr. R. Perera of Lawrence Berkeley Laboratory on an experiment to measure Auger-electron spectra of argon for near-threshold

excitation at the Stanford Synchrotron Radiation Laboratory.

Collaborated with Dr. H. Winick of the Stanford Synchrotron Radiation

Laboratory to improve undulator efficiency.

Kelley, R. D.

Collaborating (with R. R. Cavanagh and M. J. Wax) with Drs. T. J. Udovic and J. J. Rush of the NBS Reactor Division on neutron inelastic

scattering measurements of adsorbates on optically opaque

high-surf ace- area transition metals.

Working on detail as a Program Manager with the Department of Energy

Office of Energy Research, Division of Chemical Sciences. This detail

is on a 70$ part-time basis for a two-year period beginning May, 1985.

105
Kurtz, R. L. Collaborating with Prof. V. E. Henrich of Yale University on studies of

the chemisorption of molecules of catalytic interest on transition-metal

oxide surfaces.

Collaborating (with R. Stockbauer) with Drs. C. Kunz and J. Schmidt-May

of the German Synchrotron Laboratory DESY, Hamburg and Dr. A. Flodstrdm of Lund University, Sweden in studies of the mechanisms of

the photon-stimulated desorption of ions from surfaces.

Collaborating (with R. Stockbauer) with Dr. A. Flodstrdm of Lund

University, Sweden on experiments at the NBS synchrotron radiation

facility of SURF-II to investigate (1) mechanisms of photon-stimulated

desorption of ions from a non-maximal- valent oxide and (2) angular

distributions (ESDIAD) of ions desorbing from adsorbates on semiconductors

Collaborating (with R. Stockbauer) with Dr. V. Bermudez of the Naval

Research Laboratory on studies at the NBS SURF-II facility of the

influence of adsorbates in promoting phase transitions in the surface

conductivity of oxides.

Collaborating (with T. E. Madey and R. Stockbauer) with Drs. W. R.

Hunter, J. Rife, and M. Kabler of the Naval Research Laboratory and with

Dr. R. Williams of Wake Forest College on the design and instrumentation

for a bearaline and chamber at the Brookhaven National Synchrotron Light

Source to study chemisorbed molecules on clean metal surfaces,

mechanisms of photon-stimulated desorption of ions, and electron

attenuation lengths in condensed molecular solids.

Collaborating (with R. Stockbauer) with Mr. J. Jimenez of Yale

University, Prof. D. Caldwell of the University of Florida, and Dr.

D. L. Ederer of the NBS Radiation Physics Division on measurements of

the angular distribution of fluorescence from molecules excited by

synchrotron radiation from the NBS SURF-II facility.

Collaborating with Dr. J. Pena of the University of Mexico, Mexico City

on the preparation of TiC^ samples suitable both for photon-stimulated

desorption experiments at NBS and for secondary-ion mass spectroscopy

experiments in Mexico.

Madey, T. E. Collaborating with Drs. I. Terzi6, J. Vukanid and Z. Mi3kovi6 of the Boris Kidrid Institute, Belgrade, under the

auspices of the U.S. -Yugoslav Agreement for Cooperation in Science and

Technology, on theoretical and experimental studies of electronstimulated desorption and scattering of alkali ions from surfaces.

106
Collaborating (with R. L. Kurtz and R. Stockbauer) with Drs. W. R.

Hunter, J. Rife and M. Kabler of the Naval Research Laboratory and with

Dr. R. Williams of Wake Forest College on the design and instrumentation

for a beamline and chamber at the Brookhaven National Synchrotron Light

Source to study chemisorbed molecules on clean metal surfaces,

mechanisms of photon-stimulated desorption of ions, and electron

attenuation lengths in condensed molecular solids.

Collaborating with Drs. J. Sass and K. Bange of the

Fritz-Haber-Institute, Berlin, and with Dr. E. Stuve of the University

of Washington on fundamental studies of electrochemical phenomena with

emphasis on the interaction between water and surfaces.

Collaborating with Dr. N. Tolk of Vanderbilt University on studies of

electron-stimulated desorption of excited-alkali neutral atoms from

surfaces

Collaborating with Dr. C. Benndorf of the University of Hamburg, under

the auspices of a NATO grant, on studies of the influence of surface

additives on local molecular structure.

Collaborating with Prof. P. A. Thiel of the Dept, of Chemistry, Iowa

State University in writing a comprehensive review article on the

interaction of water with solid surfaces.

Melmed, A. J.

Collaborating as a co-principal investigator with Prof. W. R. Graham of

the University of Pennsylvania on studies of atomic reconstruction of

metal and semiconductor surfaces.

Collaborating with Dr. W. A. Schmidt and Prof. J. H. Block of the

Fritz-Haber-Institute, Berlin on properties of semiconductors in

electric fields and effects due to metallic overlayers.

Collaborating with Dr. B. Rioja of the Aluminum Corporation of America

to determine feasibility of atom-probe analysis of a newly developed

class of Al-Li-Cu alloys.

Collaborating with Dr. R.D. Arollia of the General Electric Company and

Prof. H. Fraser of the University of Illinois to investigate atomic

structure and chemical microcomposition for a series of nickel-based

superalloys.

Collaborating with Mr. J. Smith and Prof. H. Fraser of the University of

Illinois on studies of three related nickel-based superalloys using

field ion microscopy, transmission electron microscopy, and atom probe

analysis

Collaborating with Dr. M. J. Kaufman of the NBS Metallurgy Division on comparative studies with atom-probe field-ion microscopy and

transmission electron microscopy of nickel-based superalloys and a series of Al-Li-Cu alloys.

107
Collaborating with Dr. J. W. Cahn of the NBS Institute for Materials

Science and Engineering on investigations of the atomic structure in

rapidly solidified Al-Mn alloy ribbons exhibiting icosahedral long-range

order by electron diffraction.

Consulted with Dr. R. D. Young of the NBS Mechanical Production

Metrology Division and Mr. S. R. Mielczarek of the NBS Radiation Physics

Division on probe preparation techniques for scanning tunneling

microscopy.

Powell, C. J.

Member of Solid State Physics Review Panel for Office of Naval Research.

Collaborating with Dr. M. P. Seah of the National Physical Laboratory,

London on the development of plans and programs for the Surface Chemical

Analysis Working Party of the Versailles Project on Advanced Materials

and Standards

Stockbauer, R.

Collaborating (with R. L. Kurtz) with Drs. C. Kunz and J.

Schmidt-May of the German Synchrotron Laboratory DESY, Hamburg and Dr.

A. Flodstrdm of Lund University, Sweden in studies of the mechanisms

of the photon-stimulated desorption of ions from surfaces.

Collaborating (with R. L. Kurtz) with Dr. A. Flodstrdm of Lund

University, Sweden on experiments at the NBS synchrotron radiation

facility SURF-II to investigate (1) mechanisms of photon-stimulated

desorption of ions from a non-maximal-valent oxide and (2) angular

distributions ( ESDIAD ) of ions desorbing from adsorbates on semiconductors

Collaborating (with R. L. Kurtz) with Dr. V. Bermudez of the Naval

Research Laboratory on studies at the NBS SURF-II facility of the

influence of adsorbates in promoting phase transitions in the surface

conductivity of oxides.

Collaborating (with R. L. Kurtz and T. E. Madey ) with Drs. W. R. Hunter, J. Rife, and M. Kabler of the Naval Research Laboratory and with

Dr. R. Williams of Wake Forest College on the design and instrumentation

for a beamline and chamber at the Brookhaven National Synchrotron Light

Source to study chemisorbed molecules on clean metal surfaces,

mechanisms of photon-stimulated desorption of ions, and electron

attenuation lengths in condensed molecular solids.

Collaborating (with R. L. Kurtz) with Mr. J. Jiraemez of Yale University,

Prof. D. Caldwell of the University of Florida, and Dr. D. L. Ederer of

the NBS Radiation Physics Division on measurements of the angular

distribution of fluorescence from molecules excited by synchrotron

radiation from the NBS SURF-II facility.

Collaborating with Dr. A. C. Parr of the NBS Radiation Physics Division

and with Dr. D. Holland of Daresbury Laboratory, England on measurements of the fragmentation of molecules using photoelectronphotoion coincidence techniques.

108
Interacting with Drs. A. C. Parr, H. Hardis, and D. L. Ederer of the NBS

Radiation Physics Division, Dr. J. L. Dehmer of Argonne National

Laboratory, and Drs. J. B. West and D. Holland of Daresbury Laboratory,

England on measurements of photoelectron angular distributions as a function of photon energy in gas-phase molecules.

Szurorni, P. Collaborating with Drs. S. Semancik and D. F. Cox of the NBS Chemical

Process Metrology Division in an investigation of the surface properties

of semiconducting oxide surfaces used in gas sensing applications

using ultraviolet photoemission spectroscopy. The interaction of H

2o with tin oxide (a widely used sensor material) has been studied.

Udovic, T. J.

Collaborating (with R. R. Cavanagh, R. D. Kelley, and M. J. Wax) with

Dr. J. J. Rush of the NBS Reactor Radiation Division on neutron

inelastic scattering studies of adsorbed molecules on catalyst

materials

Collaborating (with R. R. Cavanagh) with Dr. J. J. Rush of the NBS

Reactor Radiation Division and with Dr. B. J. Tatarchuk of Auburn

University on neutron inelastic scattering measurements of the

adsorptive behavior of hydrodesulf erization catalysts.

Wax, M. J.

Collaborated (with R. R. Cavanagh) with Dr. J. J. Rush of the NBS

Reactor Radiation Division and Dr. G. D. Stucky of du Pont on the

application of inelastic incoherent neutron scattering to study

diffusional motion of hydrogen in zeolite rho.

Collaborated (with R. R. Cavanagh, R. D. Kelley, and T. J. Udovic) with

Dr. J. J. Rush of the NBS Reactor Radiation Division on neutron

inelastic scattering studies of adsorbed molecules on catalyst

materials

109
10. VISITING SCIENTISTS

The Surface Science Division has been host during the past year to a number of scientists who have worked with the Division staff on problems of

mutual interest.

Barak, D., Head of the Electronic Design Department of the Israeli Nuclear

Research Center-Negev, is working at NBS for one year beginning August,

1985. He is helping to design, construct and test improvements in the

angle-resolved x-ray photoelectron spectrometer (XPS) consisting of a new electron lens system and a position-sensitive electron detection

system.

Benndorf, C., of the University of Hamburg, W. Germany spent two months at

NBS in early autumn 1984 initiating measurements of the structure and

chemistry of ammonia on both clean and alkali-promoted Fe(1 00).

Chambers, G. P., a graduate student at the University of Maryland, has worked

at NBS this past year under a cooperative agreement. He has been

involved in the development of a data base system for the compilation of

evaluated sputtering yield data.

Clinton, W. L., of the Department of Physics of Georgetown University is

spending five months at NBS beginning September, 1985 to perform

theoretical studies relating to electron- and photon-stimulated

desorption of ions and neutral species from surfaces.

Flodstrdm, A., of Lund University, Sweden worked at NBS between May and

August, 1985. He initiated a study of adsorbate structures on semiconductor surfaces using ESDIAD, participated in photon-stimulated

desorption measurements from non-maximal-valent oxides, and cooperated

in the set up and calibration of a new toroidal grating monochromator at

SURF-II.

Hashiguchi, Y., of the Nippon Steel Corporation, Japan has worked at NBS

since March, 1985 on a one- year assignment. He is studying the

interface-width dependence on ion bombardment parameters as well as collisional excitation and laser ionization of sputtered atoms.

Holloway, S. , of the University of Liverpool visited NBS for two weeks during

the summer of 1985 to work on theoretical modeling of reactive molecular

processes at surfaces.

Jansen, W. R., a graduate student of the Twente University of Enschede, The

Netherlands worked at NBS for three months in the fall of 1985. He

extended the existing computer software for automated XPS measurements

to permit operation in a timesharing mode, completed the interfacing of

the computer to the XPS sweep supply, and extended the data reduction

software.

Jimenez, J., a graduate student of Yale University, used the surface science

beam line at SURF-II for three months during the fall of 1985 to study

the angular distributions of fluorescence from gas-phase molecules.

110
Karikorpi, M., a graduate student of the University of Liverpool visited NBS

for two weeks during the summer of 1985 to work on theoretical

modeling of reactive molecular processes at surfaces.

Roovers, A. D. f a graduate student of the Twente University of Technology,

Enschede, The Netherlands, worked at NBS for three months in the fall of

1984. He wrote the basis system software to automate the angle-resolved

XPS instrument with a minicomputer as well as basic software for data

reduction.

Shinn, N. D., of Sandia National Laboratory, Albuquerque, NM, is spending

four months at NBS during the fall of 1985 studying adsorbed molecules

on metal surfaces using high-resolution electron energy-loss

spectroscopy.

Tanuma, S. , of the Nippon Mining Company is working at NBS on a two-year

assignment beginning August, 1985. He will be participating in

measurements of core-level binding energies by different

electron-spectroscopic methods and in calculations of electron inelastic

mean free paths in solids.

Ill
1 Surface Science Division Staff

.

As of September 30, 1985 the Surface Science Division was staffed as follows

C. J. Powell, Chief

L. M. Johnson, Secretary

D. R. F. Burgess, Jr.

R. R. Cavanagh

W. F. Egelhoff, Jr.

N. E. Erickson

J. Fine

J. W. Gadzuk

S. M. Girvin

T. J. Jach

*

U. Landman^

A. J. Melmed

Surface Structure and Kinetics Group

T. E. Madey, Group Leader

G. Reyna, Secretary

P. M. Connelly^

R. D. Kelley

R. L. King+

R. L. Kurtz

E. 0. Neitzel^

A. Pararas

+ + a D. E. Ramaker c R. L. Stockbauer

P. D. Szuromi

NBS-NRC Postdoctoral Research Associate

@ Expert, Part-Time

# Engineering Technician

Electronics Technician

++ Contractor

# * Half time with Quantum Metrology Group

112
N8S-114A 'REV. 2-60

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 86-330U

2. Performing Organ. Report No. 3. Publication Date

FEBRUARY 1986

4. TITLE AND SUBTITLE

Technical Activities 1985

Surface Science Division

5. AUTHOR(S)

C . J . Powell

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Coverea

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

10. SUPPLEMENTARY NOTES

- Document describes a computer program; SF-185, FIPS Software Summary, is attached

11. ABSTRACT (A 200-word or less factual summary of most significant information. I f document includes a significant

bi bliography or literature survey, mention it here)

This report summarizes technical activities of the NBS Surface Science

Division during Fiscal Year 1985 . These activities include surface-standards

work, experimental and theoretical research in surface science, the development

of improved measurement methods, and applications to important scientific and

national problems. A listing is given of publications, talks, professional

committee participation, and professional interactions by the Division staff.

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words : ,

•••• surface chemistry; surface physics; surface science; surface standards

13. AVAILABILITY

fp Unlimited For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D C ^ 20402.

2Q3 O rcl er From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

122

15. Price

J 1 A QC

jSCOmm.QC 4041>oi
3 Vs