i

Materials Science and

Engineering Laboratory

Nanometrology

FY 2004/2005 Projects

MSEL

Clare Allocca

Senior Scientific Advisor to the Director, MSEL

Stephen Freiman

Deputy Director, MSEL

NISTIR 7130

April 2005

National Institute of

Standards and Technology

Hratch G. Semerjian

Acting Director

Technology

Administration

Phillip J. Bond

Undersecretary of

Commerce for Technology

U.S. Department

of Commerce

Carlos M. Gutierrez

Secretary
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Certain commercial entities, equipment, or materials may be identified in this document

in order to describe an experimental procedure or concept adequately. Such identification

is not intended to imply recommendation or endorsement by the National Institute of

Standards and Technology, nor is it intended to imply that the entities, materials,

or equipment are necessarily the best available for the purpose.
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Table of Contents

Table of Contents

Executive Summary ............................................................................................... 1

Projects in Nanometrology

Nanomechanics

Quantitative Nanomechanical Properties ..................................................................... 2

Mechanical Metrology for Small-Scale Structures ........................................................ 4

Nanoindentation Methods and Standards ................................................................... 5

Nanotribology and Surface Properties ......................................................................... 6

Nanomechanics: Coupling Modeling with Experiments ................................................ 7

Friction Scaling Artifact .............................................................................................. 8

Metrology for Nanoscale Properties: Brillouin Light Scattering .................................. 10

Physical Properties of Thin Films and Nanostructures:

Green’s-Function Methods ....................................................................................... 11

Combinatorial Adhesion and Mechanical Properties:

Axisymmetric Adhesion Testing ................................................................................. 12

Combinatorial Adhesion and Mechanical Properties:

Innovative Approaches to Peel Tests ......................................................................... 13

Nanocharacterization

Thermochemistry and Metrology of Interfacial Interactions ......................................... 14

Chemistry and Structure of Nanomaterials ................................................................ 15

Metrology for Nanoscale Properties: X-ray Methods ................................................. 16

Physical Properties of Thin Films and Nanostructures:

Grain Size Effects on Actuator Fatigue ...................................................................... 17

Physical Properties of Thin Films and Nanostructures:

Nanoporous Low-κ Dielectric Films ......................................................................... 18

Nanoscale Characterization by Electron Microscopy ................................................... 19

Gradient Reference Specimens for Advanced

Scanned Probe Microscopy ...................................................................................... 20

Characterization of Counterion Association with

Polyelectrolytes: Novel Flexible Template Behavior ................................................... 21
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Table of Contents

Nanofabrication and Processing

Grand Challenges in Nanomagnetics: High Coercivity FePt

Alloys for Future Perpendicular Magnetic Data Storage ............................................. 22

On-Chip Interconnects:

Extending Performance of Sub-100 nm Lines ........................................................... 24

Particle Metrology and Nanoassembly ....................................................................... 26

Nanostructure Fabrication Processes:

Patterned Electrodeposition by Surfactant-Mediated Growth ..................................... 27

Nanostructure Fabrication Processes:

Thin Film Stress Measurements ............................................................................... 28

Wet Nanomanufacturing ........................................................................................... 29

2nd Joint Workshop on Measurement Issues in Single-Wall

Carbon Nanotubes: Purity and Dispersion, Part II .................................................... 30

Extraordinary Transport Properties of Nanotube/Polymer Nanocomposites ................. 32

Applications of Carbon Nanotubes:

Carbon Nanotubes and Nanotube Contacts ............................................................... 34

Applications of Carbon Nanotubes:

Cell Viability in Contact with Carbon Nanotubes ......................................................... 35

Applications of Carbon Nanotubes:

Electrochemical Characterization of In-Vivo Neuronal Probes ...................................... 36

Organizational Charts ................................................................................................ 37
1

Executive Summary

Executive Summary

The burgeoning field of nanomaterials extends

across the full range of traditional material classes,

including all forms of metals, polymers, and ceramics.

No previous materials technology has shown concurrent

advances in research and industry as does the field

of nanomaterials in mechanical devices, electronic,

magnetic, and optical components, quantum computing,

biotechnology, and as-yet unanticipated exploitations

of as-yet undiscovered novel properties of assemblies.

There is growing excitement surrounding the ability

of some molecules or particles to self-assemble at

the nanoscale to form new materials with unusual

properties. Nanometrology, i.e., the ability to conduct

measurements at these dimensions, to characterize

the materials, and to elucidate the structure and nature

of these new and novel assemblies, is a requisite and

fundamental cornerstone that must be established

securely if this technology is to flourish.

NIST is uniquely positioned to lead the development

of the measurement methods, instrumentation,

standards, and reference materials that together

will form the metrological infrastructure essential

to the success of nanotechnology.

The MSEL Nanometrology Program incorporates

basic measurement metrologies to determine material

properties, process monitoring at the nanoscale,

nanomanufacturing and fabrication techniques, and

structural characterization and analysis techniques

such as advanced imaging and multiscale modeling.

The Program comprises projects in the Ceramics,

Materials Reliability, Metallurgy, and Polymers

Divisions, and includes structural characterization

using neutron scattering at the NIST Center for

Neutron Research (NCNR). The projects cover a

wide range of measurement and characterization

methods grouped into the areas of mechanical property

measurement, chemical and structural characterization

and imaging, fabrication and monitoring of nanoprocesses

and events, and modeling of nanoscale properties.

In each area, we work to advance basic measurement

capabilities and lead the intercomparison, standardization,

and calibration of test methods. The newly completed

Advanced Measurement Laboratory at the NIST

Gaithersburg site provides an incomparable

environment for accurate nanoscale metrology.

In the area of nanomechanics, we are developing

and standardizing techniques for determining

nanoscale elastic properties (elastic moduli, Poisson’s

ratio, and internal stress), plastic deformation, density,

adhesion, friction, stiction, and tribological behavior.

Work in nanoindentation, used extensively in

determining mechanical properties of thin films and

nanostructures, focuses on developing traceable

calibration methodologies and standard test methods.

We also use atomic force acoustic microscopy,

surface acoustic wave spectroscopy, and Brillouin

light scattering to measure the mechanical properties

of thin films. In addition, we are developing microand nano-scale structures and test methods to measure

strength and fracture behavior of interfaces and

materials having very small volumes. Experimental

studies are accompanied by efforts in the theory,

modeling, and prediction of material properties and

behavior extending from nanoscale to macroscale

dimensions. Modeling efforts include large-scale finite

element methods, multiscale Green’s-function methods,

classical atomistic simulations, and first principles,

quantum mechanical calculations using density

functional theory.

Nanocharacterization utilizes neutron and x-ray

beam lines at three facilities: the NCNR; the National

Synchrotron Light Source at Brookhaven National

Laboratory; and the Advanced Photon Source at

Argonne National Laboratory. Innovative scattering

and spectroscopy methods are advancing our ability

to obtain a wide range of chemical and structural

information at the nanoscale, including chemical bond

identification and orientation, polyelectrolyte dynamics,

and equilibrium structures. In collaboration with three

other NIST laboratories, we are developing electron

microscopy and spectroscopy instrumentation for

quantitative, 3D chemical imaging at the nanoscale.

Other characterization projects include work on

gradient reference specimens for the calibration of

advanced scanning probe microscopy, and the

application of carbon nanotubes as physical probes

of cell membranes.

Efforts in the nanofabrication and processing include

the study of electrochemical and microfluidic methods

for fabricating nanostructures, novel approaches to

nanocalorimetry for the study of interfacial reactions,

and in situ observations of nanoparticle and nanotube

dispersion and alignment. A second joint NASA–NIST

Workshop was held in order to establish the measurement

needs for determination of purity and dispersion of

single-wall carbon nanotubes. The results of this

workshop will be captured in “NIST Recommended

Practice Guides.”
2

Nanomechanics

We are developing AFM-based metrology for

rapid, nondestructive measurement of mechanical

properties with true nanoscale spatial resolution.

Atomic force acoustic microscopy methods enable

elastic-modulus measurements at either a single

point or as a map of local property variations.

Complementary information obtained with

scanning electron microscopy provides insight

into structure-property relations and helps to

interpret nanoscale contact-mechanics behavior.

The information obtained furthers our understanding

of the nanomechanical properties of surfaces,

thin films, and nanoscale structures.

Donna C. Hurley

New measurement solutions are required to address

the rapidly burgeoning field of nanotechnology.

In particular, information about mechanical properties on

the nanoscale is needed. Knowledge of properties like

elastic modulus and interfacial quality (defects, strain,

adhesion, etc.) is critical to successful development of

new films and nanoscale assemblies. Such information

could also assess integrity or reliability in applications

from microelectronics to biotechnology. Existing

methods for mechanical-property measurements have

drawbacks: they are destructive, limited to specialized

test specimens, or not quantitative. Instrumented or

“nano-” indentation (NI), a current industry workhorse,

will have limited value as scales shrink well below

1 μm, and softer materials are more frequently used.

To meet this need, we are developing tools that

exploit the spatial resolution of atomic force microscopy

(AFM). Our approach, called atomic force acoustic

microscopy (AFAM), involves the vibrational resonance

of an AFM cantilever when its tip is in contact with a

sample. By comparing the cantilever’s contact-resonance

frequencies for an unknown material to those for a

reference sample with known properties, the indentation

modulus M of the unknown material can be determined.

[For an isotropic material M = E/(1–ν2), where E is

Young’s modulus and ν is Poisson’s ratio.] The small

tip radius (~5–50 nm) means that we can obtain in-situ

elastic stiffness images with nanoscale spatial resolution.

In FY04, we extended our quantitative AFAM

techniques in a variety of ways. In one effort, the

effect of film thickness on measurement accuracy

was investigated. We measured M for three nickel

(Ni) films approximately 50, 200 and 800 nm thick.

The values of M ranged from 220 GPa to 223 GPa,

significantly lower than that expected for bulk

Quantitative Nanomechanical Properties

polycrystalline Ni. Scanning electron microscopy (SEM)

revealed that the films were nanocrystalline (grain diameter

< 30 nm). The observed reduction in M may be attributed

to an increased volume fraction of grain boundaries in the

nanocrystalline films. More importantly, the average values

of M for all three films were the same within measurement

uncertainty (~10 %). Thus the AFAM results were not

influenced by the elastic properties of the silicon substrate,

even for a 50 nm film. This behavior is due to the fact

that the AFAM stress field extends less than 100 nm into

the sample and decreases rapidly with depth due to the

small applied static loads (0.3–3 μN) and small radius of

contact (5–25 nm). Our result contrasts sharply with

nanoindentation, in which substrate properties must be

included to accurately measure submicrometer films.

The elastic properties of the 800 nm Ni film were also

measured using NI, microtensile testing, and surface

acoustic wave spectroscopy (SAWS). Both AFAM and

NI measure the film’s out-of-plane indentation modulus.

The results were in excellent agreement, validating AFAM

as a quantitative method in spite of its relative newness.

Microtensile testing values for the in-plane Young’s

modulus of the film were not consistent with the AFAM

and NI results if the film was assumed to be elastically

isotropic. The apparently contradictory results were

reconciled by use of a transversely anisotropic model for

the film’s elastic properties. This model is consistent with

the strong <111> film texture observed by x-ray diffraction.

When analyzed with the same model, the SAWS results

indicated that the film density was only slightly lower

(< 5 %) than the bulk value. These results illustrate a

relatively straightforward way to interpret mechanicalproperty measurements of thin films that is based on a

more physically realistic model than the simple assumption

of elastic isotropy.

Another effort investigated the effects of relative

humidity (RH) on AFAM measurements. AFAM contact

Figure 1: a) AFM tapping-mode topography and b) AFAM

relative-stiffness images of Si with n-octyldimethylchlorosilane SAM.
3

Nanomechanics

stiffness measurements may be affected by a variable

water layer between the tip and sample, at least in some

cases. By refining our data analysis methods to include

the effects of such a layer, apparent correlations between

the measured values of M and the ambient RH were

eliminated. This year we also developed a RH-controlled

AFM chamber in order to systematically study

these effects. Samples for the experiments were

provided by the Polymers Division and consisted

of patterned self-assembled monolayers (SAM) of

n-octyldimethylchloro-silane on Si substrates.

Through controlled ultraviolet-ozone exposure, the

relative hydrophobic/hydrophilic nature of the SAM

was adjusted in different sample regions. Figure 1

shows an AFM topography image and an AFAM

relative-stiffness image for a SAM/Si sample. The

SAM stripes are virtually invisible in the topography

image, even at very high resolution (10 nm full scale

height). However, the AFAM image clearly reveals the

hydrophobic SAM stripes. The regions covered by the

SAM appear more compliant (lower contact stiffness)

due to AFAM’s sensitivity to local variations in the

tip-sample adhesion. We are currently performing

further experiments on similar samples in order to

quantify how humidity and adhesion effects can be

distinguished from true mechanical-property variations.

measurements were done at relatively low static loads;

the load was then successively increased up to several

micronewtons to try to break and/or plastically deform

the tip. High-magnification SEM images were obtained

before and after each AFAM measurement. As can be

seen in Figure 2, R increased with use, indicating tip

wear. Values of R measured from the SEM images

were compared to the values obtained from AFAM

data using a Hertzian contact-mechanics model.

The AFAM values of R were consistently smaller than

the SEM values. Further data analysis and additional

experiments are planned to clarify this issue. The

knowledge gained in this way will help us to refine

our understanding of AFAM contact mechanics,

beyond the Hertz approximation, in order to improve

measurement accuracy and repeatability.

In related work, we are performing finite-element

studies of the AFM cantilever. The finite-element mesh

is based on actual cantilever dimensions from SEM

images and includes elastic anisotropy. The predicted

free-space resonant frequencies are in excellent

agreement with those observed experimentally.

Work is underway to predict the vibrational behavior

in contact. These results will allow us to refine

our data analysis models and thus improve

measurement accuracy.

The research described above involves either

quantitative single-point measurements, or qualitative

imaging of relative stiffness. In FY04, we worked to

realize our ultimate goal of quantitative nanomechanical

mapping. Critical to our success is a new frequency

tracking circuit that can determine the contact-resonance

frequencies at each image pixel. The circuit is based on

digital signal processing architecture that enables rapid

data acquisition (typically < 30 min. for a 256 × 256

image). We have begun to obtain resonance-frequency

images for a variety of materials. Recent enhancements

to our AFM mean that we can acquire images from not

only the flexural modes, but also the torsional modes of

the cantilever. By combining information from flexural

and torsional images, it may be possible to determine

simultaneously both Young’s modulus and Poisson’s

ratio for an isotropic material. Work in upcoming

months will focus on issues related to quantitative

image interpretation such as calibration procedures,

cantilever selection, tip wear, and choice of

contact-mechanics model. Each of these elements

plays a role in attaining our goal of truly quantitative

nanomechanical imaging.

For More Information on this Topic

D.C. Hurley (Materials Reliability Division, NIST)

Figure 2: SEM images of AFM cantilever tip a) before use and

b) after repeated AFAM contact experiments. The circled regions

indicate the tip wear that occurred through use.

 AFAM contact-resonance frequencies depend not

only on elastic properties, but also on the value of the

tip radius R. Thus knowledge of R and how it changes

over time is essential for accurate measurements of

elastic properties. To address this issue, we performed

AFAM experiments with different AFM cantilevers

on a sample with known elastic properties. The first
4

Nanomechanics

Myriad industrial and biological systems are

composed of small-scale structures for which the

mechanical behavior is not accurately known.

Optimizing the performance and reliability of

these systems requires either mechanical property

measurements on specimens of these structures

harvested from the appropriate phases or

interfaces of the system, or the ability to test these

structures in situ. We are developing standardized

testing configurations and methodologies for

localized measurements of strength and fracture

toughness of materials and interfaces at the

micro- to nanometer-length scale.

Edwin R. Fuller, Jr. and George D. Quinn

This project aims to: (1) measure mechanical

properties of microstructures for myriad industrial

and biological systems that cannot be fabricated in bulk

samples; (2) study small-scale phenomena that may

be controlled by surface effects, e.g., the influence of

surface stresses on crack nucleation and extension; and

(3) obtain quantitative mechanical property data of materials

and interfaces for designing small-scale structures and

components and for assessing their mechanical reliability.

To address these goals, well-characterized testing

configurations must be developed for small-scale

measurements of strength and crack extension. We are

pursuing four tasks: (1) configuration design and finite

element analysis; (2) specimen fabrication; (3) mechanical

testing and fracture analysis (fractography); and (4) length

and force metrology. Work in the Ceramics Division

this year has focused on the first and third areas. Two

collaborations were established in the fabrication task:

one with James A. Beall of the Quantum Electrical

Metrology Division (817) in NIST Boulder, and one with

Northwestern University. Work in the fourth task will

Mechanical Metrology for Small-Scale Structures

come in subsequent years, most likely in collaboration

with the Manufacturing Engineering Laboratory.

Significant progress has been made in the design of a

compressively loaded test configuration with a welldefined, tensile gage section. Such a specimen can be

loaded using a depth-sensing nanoindenter as a universal

testing machine, thereby giving a record of both applied

load and load-point displacement. One of these specimens,

fabricated by James Beall from a silicon wafer by

deep reactive ion etching, is shown in the right-side of

Figure 1. The configuration is similar to a theta specimen,

except that the geometry is hexagonal. When a load

(per unit thickness) is applied to the top beam, a uniform

uniaxial tensile stress results in the middle gage section.

Finite element analysis gives (horizontal) gage section

stresses on the order of 1.25 GPa for 50 mN/μm of applied

load. For a 2 N applied load, these 100 mm-thick

specimens generate 500 MPa of tensile stress in the gage

section. The left-side of Figure 1 shows a reconstructed

failed specimen. The insert shows the fracture surface

of the gage section, and the two [111] cleavage facets

that were formed. Alternate geometries, including a

round theta specimen, are also being considered.

Figure 1: Prototype specimen design.

To extend this technique to a wide variety of

materials and systems, general fabrication procedures

need to be developed. Towards this objective, focusedion-beam (FIB) milling is being explored in collaboration

with Northwestern University. Figure 2 shows our first

attempt at producing a hexagonal theta specimen by

FIBing. It has been scaled-down by about a factor

of 10, and is fabricated from a lamellar directionally

solidified eutectic of Ni0.5Co0.5O and ZrO2.

Contributors and Collaborators

D. Xiang, D.T. Smith (Ceramics Division, NIST);

A. Jillavenkatesa (Standards Services Division, NIST);

J.A. Beall (Quantum Electrical Metrology Division,

NIST); N. Alem, V.P. Dravid (Northwestern University)

Figure 2: Hexagonal theta specimen by FIBing.
5

Nanomechanics

Nanoindentation has rapidly become the method of

choice for quantitative determination of mechanical

properties of thin films and small volumes of material,

but standardization efforts have lagged far

behind the application of the technique in industrial

research and development. Over 1000 commercial

nanoindentation instruments from a variety of

manufacturers are currently in use, with no traceable

force calibration and an extremely limited choice of

standardized test methods. We work with standards

groups and National Measurement Institutes around

the world to develop standard reference materials

(SRMs), traceable calibration transducers, and

robust, reliable methods for obtaining and analyzing

nanoindentation data, so that nanoindentation

results can be used with confidence in product design

and specification.

Douglas T. Smith

Nanoindentation is the most commonly used method

for determining hardness and elastic properties of

small volumes of materials. In this technique, a diamond

indenter is pushed into a specimen surface, and the force

on and displacement into the surface are recorded. The

technique is capable of providing information on the elastic

and plastic deformation of a specimen for indentations as

shallow as 5 nm to 10 nm, and requires minimal specimen

preparation effort. It is routinely used to measure the

mechanical properties of thin films. However, there

are only a very limited number of accepted test methods

available, and no means to traceably calibrate or verify

the performance of nanoindentation instruments.

This leads to large interlaboratory variations in results,

particularly for hard, high modulus materials, and prevents

the use of nanoindentation in thin film or coating

product specifications.

In many mechanical test methods, including

nanoindentation, a force is applied to a specimen, and

some displacement is measured. Traceable displacement

measurement by interferometry is well established. Force

measurement is more problematic, however, because the

SI unit for force is still based on an artifact kilogram mass.

The Microforce Competence Program at NIST has

developed a primary realization of force, traceable to

electronic and length SI units, for force calibration in

the range 1 mN to 10 nN. As part of this program,

transfer force cells are being developed that will allow

force calibration, traceable to NIST, for commercial

nanomechanical test equipment such as nanoindentation

machines and atomic force microscopes. One such

Figure 1: The error in the force applied to a specimen by a

commercial nanoindentation instrument, as referenced to a

traceably calibrated NIST force cell.

Nanoindentation Methods and Standards

transfer force cell was calibrated against the NIST primary

force balance to an uncertainty less than 0.5 % for forces

in the range 0.05 mN to 5.0 mN. That cell was then

mounted, as if it were a specimen, in a popular commercial

nanoindentation instrument that had been recently

calibrated by its manufacturer using their recommended

force calibration procedure. The figure shows the error

in the nanoindentation force recorded by the instrument,

relative to the traceable force cell reading. For forces

above 2 mN, the recorded force is within the 1 %

uncertainty required by most draft standards for

nanoindentation machines. However, for lower applied

force, the error increases dramatically, and at 0.05 mN,

the recorded force is almost 18 % below the actual

applied force.

We are also working with both ASTM (E28.06.11)

and ISO (TC 164/SC 3) on a wide range of standard

test methods for nanoindentation, and an ISO document

for the one method has now been approved (ISO

14577). In addition, the Ceramics and Materials

Reliability Divisions at NIST are working with the

Bundesanstalt für Materialforschung und–prüfung

(BAM) in Germany to develop joint thin film SRMs

(CRMs, or Certified Reference Materials, in Europe)

for use in nanoindentation machine verification.

Contributors and Collaborators

D. Xiang, B. Hockey, G. Quinn (Ceramics Division,

NIST); R. Machado (INMETRO, Brazil); J. Pratt

(Manufacturing Engineering Laboratory, NIST);

D. Hurley (Materials Reliability Division, NIST);

U. Beck (BAM, Germany)
6

Nanomechanics

Accurate adhesion and friction measurements

at the nanoscale are emerging as critical issues

in device industries and nanotechnology.

Measurements characterizing nanometer-thick

molecular assemblies and surface textures to

control surface properties and to ensure reliability

and durability are also needed. Working with

device and magnetic storage industries and other

agencies, we have designed and built instruments

to meet these needs. These instruments are housed

in NIST’s new Advanced Measurement Laboratory.

The facility features vibration isolation, class 1000

clean room standards, and temperature control.

Stephen M. Hsu

The nanotribology and surface properties project

was initiated as a part of the MSEL Nanotechnology

Initiative. The project aims to develop measurement

capability for adhesion, friction, and surface forces

at the nanoscale. We interact extensively with many

industries and research centers in the U.S. and around

the world to promote advances in measurement

science and seek consensus standard harmonization

in three areas: nanocontacts, nanolubrication, and

surface texturing.

Nanocontacts

Adhesion and friction measurements at nanocontacts

require accurate detection of normal and lateral forces

at nanonewton levels. Scanning probe microscopes

use sensitive cantilevers and laser diodes to detect these

forces, but this approach introduces rotation of the tips

and crosstalk among the xyz planes. To understand

the influence of surface forces, many of which are

functions of contact area, attention must be focused

on determining the real area of contact.

To resolve some of the instrumental challenges,

we have engaged instrument makers, such as

Hysitron, Veeco, and others, to solicit their inputs and

collaborations. At the same time, we have established

our own capability in tip fabrication, cantilever spring

constant calibration, and tip characterization. Three

new instruments were successfully installed as a result

of these collaborations: the NIST–Hysitron multiscale

friction tester, the NIST nanoadhesion apparatus, and

the first prototype of an interferometer microscope

from Veeco. We are continuing to work with our

partners to develop next-generation instruments as

suggested by the Nanometrology Grand Challenges

Workshop (NIST, January 2004).

Nanotribology and Surface Properties

The overall objective of the nanocontacts activity

is to develop the constitutive equation of adhesion

and friction including the various components

of surface forces. With our new adhesion and

nanofriction apparatus, we are quantifying the effects

of plowing and electrostatic charge on measurements.

We continue to work with our external academic

partners (UC Berkeley, UC Davis, and Ohio State U)

under the Nanotechnology Extramural Initiative to

develop friction measurement via three approaches:

friction measuring MEMS devices, AFM methods,

and ultrahigh vacuum friction measurement. These

efforts have been successful, and we have gained

considerable understanding of how meniscus forces

and electrostatic forces can exert significant effects on

nanofriction measurements. A NIST special publication

summarizing these findings is under preparation.

Nanolubrication

Molecular assemblies can be organized to impart

hydrophobicity, anti-adhesion, and friction control

characteristics on device surfaces. Supported by other

agencies and the magnetic storage industry, this activity

focuses on how to measure the effects of controlled

composition and spacing on properties of nanometerthick films. An ultrahigh vacuum scanning tunneling

microscope-atomic force microscope was installed in

May 2004 to provide imaging capability at the molecular

level. A micro-tribometer was also developed to measure

the durability of these films. The synchrotron facility

operated by the Division’s Characterization Methods

Group at Brookhaven National Laboratory continues to

be vital in characterizing these complex molecular mixtures.

Surface Texturing

Surface texture increasingly is being considered as

a tool to control surface energy, polarity, adhesion, and

friction. Supported by other agencies and industries,

we are pioneering the use of specific surface features

such as dimples, triangles, and ellipses at microand nanoscale dimensions to supplement molecular

assemblies to control surface properties of surfaces.

An international cooperative study under the auspices

of International Energy Agency (IEA) is underway.

Contributors and Collaborators

C. Ying, R. Gates, J. Chuang, J. Larson–Basse,

L. Ives, D. Fischer (Ceramics Division, NIST); B. Bhushan

(Ohio State U.); K. Komoupoulas (UC Berkeley);

G. Liu (UC Davis); Y.T. Hsia (Seagate); J. Sengers

(U. of Maryland); O. Warren (Hysitron); C. Su (Veeco)
7

Nanomechanics

Knowledge of mechanical behavior is critical

when designing for device performance and

reliability, even for “non-mechanical” systems.

However, nanoscale mechanical behavior

(including failure) is inherently difficult to measure

accurately, and existing modeling tools are only

qualitative at best. We are developing modeling

techniques that provide quantitative predictions

and are validating these results experimentally.

Lyle E. Levine and Anne M. Chaka (838)

Mechanics at the nanoscale is inherently difficult to

model accurately. Finite element modeling (FEM)

can effectively capture the elastic behavior of macroscopic

structures but includes no accurate failure criteria

since this depends upon atomic-scale behavior.

Classical atomistic simulations can handle enough atoms

(millions to billions) to model such events, but these

potentials become inaccurate for large strains and they

cannot effectively handle chemistry. Quantum-mechanicsbased simulations using density functional theory (DFT)

are extremely accurate and handle the chemistry exactly,

but such simulations are so CPU intensive that they

can handle only a few hundred atoms. A combination

of all three modeling techniques is required to

accurately model device behavior at the nanoscale.

the predicted elastic displacement fields to generate

boundary conditions and initial atom positions for

an atomistic simulation using classical potentials.

The use of classical potentials in a large simulation cell

allows the correct propagation of the long-range stresses

to the critical regions where bond distortions are large or

where chemistry effects need to be explored. In these

critical regions, the techniques embed a DFT simulation.

Iteratively, the critical region is relaxed using DFT, and

the classical cell is relaxed using a Monte-Carlo algorithm.

The first application of this hybrid technique was to

determine the vacancy formation energy in aluminum as

a function of distance (at a fixed angle) away from an

edge dislocation. The simulation geometry is shown in

Figure 2. The boundary conditions and initial atomic

positions were calculated from the known elastic

displacement field of an edge dislocation.

Nanomechanics: Coupling Modeling with Experiments

Figure 1: FEM model of a rigid 100 nm diameter sphere

indenting an Al sample to a depth of 10 nm.

Over the past year, we have developed techniques

to handle such multiscale modeling for quasistatic

applications. At the macroscale, FEM is used to simulate

the elastic behavior of a nanomechanical system. Figure 1

shows an example in which an Al sample is being indented

by a rigid 100 nm diameter sphere. The indenter and

three of the sample quadrants have been removed to

highlight the resulting Von Mises stress distribution after

indenting 10 nm. The FEM mesh is fine enough to use

Figure 2: Diagram of a hybrid simulation for obtaining the

vacancy formation energy at different positions relative to an

edge dislocation. The large box represents the EAM cell in

which the DFT region containing the vacancy was embedded.

After an initial dislocation nucleation event,

nanoindentation progresses through the complex

evolution of dislocation structures. For example, the

raised lip around the indent is produced by large

numbers of dislocations exiting the surface. We are

working on modeling the early stages of this process

using 3D dislocation dynamics and assuming a random

distribution of dislocation sources in the sample.

Finally, connection to experimental measurements

requires careful force calibration of the indenter and

calibrated atomic force microscopy measurements (AFM)

of the indenter tip. These calibrations are mostly complete,

and the AFM data will be used to generate a FEM mesh

for the simulations. Bulk single-crystal copper samples

are being cut and polished using non-contact chemical

methods to minimize the dislocation density.

Contributors and Collaborators

S.M. Khan, G. Levi, L. Ma, F. Tavazza (Metallurgy

Division, NIST); B. Hockey, R. Machado, D. Smith,

R. Wagner, D. Xiang (Ceramics Division, NIST)
8

Nanomechanics

Nanofrictional forces are an important factor

in the design of nanodevices and assemblies of

nanoparticles. Literature data on nanofriction,

however, exhibit many discrepancies and

have a wide range of scatter. In a series of

well-controlled experiments, we have discovered

that a significant portion of this discrepancy may

actually be attributed to an unintended scratching

of the surface by the sharp tips used in making

the measurements themselves. Deviation of tip

shape from the “ideal” spherical shape is another

contributor to the disagreements found among the

literature data. This work sheds important insight

into the nature of nanoscale friction measurement.

Z. Charles Ying and Stephen M. Hsu

Accurate measurement of nanofriction is emerging

 as one of the critical issues in nanotechnology.

Manipulation of molecules, clusters, and nanoparticles

across surfaces to form a functional entity relies on the

ability to overcome the resistance of the particles to

motion across the surface. Further, reliable operation

of micro- and nano-devices often depends on an

accurate estimate of lateral loading. Literature data

on nanofriction, however, have shown wide ranges

of values depending on the length scale of the device.

Silicon friction, e.g., shows an order of magnitude

variation from 0.03 to 0.25. Such results have led to

speculations that there might be an intrinsic scaling

effect such that different friction levels would occur

across the nano-, micro-, and macro-scales. If proven

true, well established friction laws would be invalidated

for nanomaterials.

Given the broad technological significance of this

issue, we have undertaken a detailed investigation of

the nature of this discrepancy. Friction measurements

between non-adhering surfaces were carried out in both

elastic and plastic deformation regions. Diamond tips

of various sizes were used to measure nanofriction

forces on well-characterized substrates such as single

crystal silicon, silicon dioxide, and calcium fluoride.

Experiments were performed using a specially designed

multiscale friction tester developed jointly by NIST and

Hysitron Incorporated based on a capacitance probe

force transducer. In each experiment, the environment

was carefully controlled, and the tip penetration into the

substrate during sliding was continuously measured.

The size and shape of each tip were characterized

using a newly developed “replica technique.” Tips

were imprinted into a soft material, and the imprints

were scanned by AFM and digitally inverted to

Friction Scaling Artifact

Figure 1: 3D profiles, obtained using the replica technique, of the

tips used in the friction measurements.

“reconstruct” the tip in three-dimensional details.

Figure 1 shows images of two of the diamond tips

used in the experiments. The tip shown in Figure 1(a)

is spherical in shape with a 1.2 μm tip radius while

Figure 1(b) shows an ellipsoidal shape with nominal

radius of 4 μm. The detailed dimensional data are

crucial in determining the apparent contact areas and

isolating the influence of surface forces.

Figure 2: Coefficient of friction between Si (100) surface and a

diamond tip with radius R = 1.2 μm, as a function of mechanical

loading force.

Figure 2 shows the coefficient of friction (COF)

between a Si (100) surface and a diamond tip with tip

radius R = 1.2 μm.
9

Nanomechanics

path. Numerical integration of actual tip size and shape

over the sliding path is required. For the hypothesis of

“elastic plowing,” the calculation shows that the friction

force in this regime should be proportional to the projected

cross-sectional area in the direction of sliding. Figure 5

confirms this hypothesis for all three tips.

Figure 3: Image of the silicon surface after friction

measurements, showing scratches at 2.5 mN and higher load.

Figure 4: Coefficient of friction between Si (100) surface and

three diamond tips used in the experiments, as a function of mean

contact pressure.

Figure 5: Friction force as a function of projected cross-section

area in the direction of tip sliding.

Two distinct regions can be seen. Initially, the COF

is constant up to a load of 2.0 mN. For loads above

2.5 mN, the COF increases with load. This friction

transition is contrary to Amoton’s law. Subsequent

investigation revealed that this change in COF is caused

by unintended plowing of the tip into the substrate.

Atomic force microscopy, using a sharp tip on the

surface, suggests that the COF increase coincides with

the first appearance of plastic grooving. In the case

of silicon, a groove 5 Å deep and 2000 Å wide was

detected on the surface at a load of 2.5 mN (Figure 3).

This observation was repeated for different tips and

different substrates. At higher loads, deeper and wider

grooves were observed. These results suggested that

unintended scratching of the surfaces by the sharp tips

used in the friction measurements contributed to the

discrepancies among friction data in the literature.

The initiation of plastic grooving can be quantified in

terms of contact pressure. By determining the apparent

contact area using the digitally inverted tip method, the

transition contact pressures could be calculated for all

of the observed cases. All the results corresponded to

12 GPa which is approximately the hardness of silicon.

Elastic Plowing

Figure 4 shows the friction data for three tips in the

elastic region (no plastic grooving). The data for the two

spherical tips with radii R = 0.5 μm and 1.2 μm exhibit a

common value for the COF. However, a higher friction

value was observed for the 4 μm radius tip.

To explain this discrepancy, we tested the various

contact mechanics models which require the accurate

determination of the real contact areas. Considering a tip

plowing through an elastic substrate, the real area of

contact is the projected cross-section area of the tip in

the direction of sliding. This can be determined from the

tip geometry and “penetration depths” across the sliding

This work shows clearly that nanoscale friction, in

practice, is a complex result of both elastic and inelastic

strains and deformations, and accurate nanofriction

measurement will require careful accounting of all the

forces contributing to the phenomenon. The methodology

established in this work provides a substantial step towards

the data and understanding needed by industry.

For More Information on this Topic

Z.C. Ying, S.M. Hsu (Ceramics Division, NIST)
10

Nanomechanics

Brillouin light scattering is being employed to

provide information on acoustic and magnetic

waves at gigahertz frequencies in thin-film

materials. Measurements and modeling in FY04

have focused primarily on interactions of spin

waves in ferromagnetic films, elastic constants of

nanoporous low-κ dielectrics, and propagation

of acoustic waves in nanopatterned polymers.

Ward Johnson, Sudook Kim, and

Colm Flannery

Technical Description

Brillouin light scattering (BLS) is an experimental

technique that measures the intensity of spectral

components of light that is inelastically scattered

by vibrational waves (phonons) or spin waves

(magnons) in a material. Fabry–Perot interferometric

techniques are used to acquire accumulated spectra

through repeated mechanical sweeping of the

etalon spacing.

BLS is the only laboratory technique that is

currently available for detecting magnons of finite

wavenumber. Because of this capability and because

of innovations in interferometric techniques, BLS has

been increasingly applied to problems in magnetics

over the past couple of decades.

For characterization of phonons in thin films,

BLS offers several advantages over other techniques.

Since it detects phonons in the gigahertz range, elastic

constants can be determined in films of submicron

thickness without the complication of vibrational

energy penetrating significantly into the substrate.

Modes localized in submicron structures can be

characterized. Spatial variations in elastic properties

and vibrational patterns can be measured with a lateral

resolution equal to the size of the laser focal spot on

the specimen (typically, ~50 micrometers).

In this division, techniques are being developed

for characterizing interactions of magnons in metallic

ferromagnetic thin films. Such interactions limit

the speed of magnetic-storage devices, spin-valve

sensors, and other thin-film magnetic devices.

BLS measurements and modeling of vibrational

modes are being pursued in several thin-film systems,

including nanoporous low-dielectric-constant (low-κ)

dielectrics, nanopatterned polymers, and arrays of

molecular rotors.

Metrology for Nanoscale Properties: Brillouin Light Scattering

Accomplishments

During FY04, we developed and applied methods

for measuring magnons that arise directly or indirectly

from microwave pumping of metallic ferromagnetic

films in a static magnetic field (Figure 1). BLS

spectra were studied as a function of scattering

angle, microwave power, and laser power to provide

information on magnon–magnon interactions in

Ni81Fe19. The results demonstrate, for the first time,

detection of nonzero-wavevector magnons arising

from the decay of pumped uniform-precession

magnons in metallic thin films.

Young’s modulus and Poisson’s ratio in

nanoporous low-κ dielectric films were measured

using conventional backscattering techniques. This

research is described elsewhere in this annual report.

Measurements and modeling of vibrational modes in

nanoimprinted polymers were pursued in collaboration

with the University of Akron and the NIST Polymers

Division. In addition to bulk and surface modes,

low-frequency modes were detected and found to

be consistent with vibrational localization in the

imprinted lines. This result suggests the possibility

of characterizing elastic properties on a scale of

tens of nanometers.

Contributors and Collaborators

P. Kabos (Radio-Frequency Technology Division,

NIST); S. Russek (Magnetic Technology Division,

NIST); A. Slavin (Oakland Univ.); J. Michl (Univ.

of Colorado, Chemistry Dept.); R. Horansky (Univ. of

Colorado, Physics Dept.); C. Soles (Polymers Division,

NIST); R.H. Hartschuh, A. Kisliuk, and A. Sokolov

(Univ. of Akron)

Figure 1: Scattering of light off waves in a thin film.
11

Nanomechanics

In the continuum model, we simulate free surfaces

and interfaces by applying the usual boundary conditions.

Accomplishments

We have carried out a detailed analysis of SAW

measurements in a thin TiN film on Si, calculated

stresses in a wide range of solids, and modeled Ge

clusters in Si containing a free surface and a vacancy.

The work is reported in six papers. A library of GFs

is available at www.ctcms.nist.gov/gf, which contains

downloadable teaching and tutorial material on

GFs and computer codes for calculation of GFs.

A GF group of about 50 international users has been

formed at CTCMS.

Contributors and Collaborators

D. Hurley, D.T. Read (Materials Reliability

Division, NIST); L. Bartlolo (Kent State University);

A. Powell (M.I.T.)

Precise knowledge of atomistic configuration

and strains in nanomaterials is needed for their

characterization and development of new devices.

We have developed computationally efficient

Green’s-function methods for calculation of lattice

distortion, elastic strains and displacements in

a variety of material systems. Our work is useful

for interpretation of data obtained by AFAM,

nanoindentation, and SAW experiments.

Vinod K. Tewary and Bo Yang

Technical Description

Green’s function (GF) provides a computationally

efficient tool for interpretation of data obtained by

nanoindentation and atomic force acoustic microscopy

(AFAM) which is useful for elastic characterization of

nanomaterials. The dynamic GF is used for modeling

propagation of surface acoustic waves (SAWs) in

solids and their phonon properties. The GF accounts

for interfaces and free surfaces in the solid and its

elastic anisotropy, which play relatively important roles

in the elastic response of nanomaterials as compared

to ordinary solids. We use GF to calculate the elastic

displacement fields, interaction energy between the

embedded nanostructure and other defects and free

surfaces. The displacement field, due to a force at

the surface, is used for interpretation of AFAM and

nanoindentation measurements. The interaction

energy of the nanostructures is an important factor

in the stability and growth of the nanostructure.

We have developed GF methods both at the discrete

atomistic and macro continuum scales. For a lattice

model containing N atoms, the GF is given by:

G = Φ–1

where G and Φ are 3N × 3N matrices of GF and

force constants respectively. The matrix inversion

is carried out by using the discrete Fourier transform

for a perfect lattice or numerically by computer

simulation for a model crystallite as in molecular

dynamics.

In order to model an embedded nanostructure

in a host solid, or a thin film on a substrate, we

define an initial GF for the host and the final GF.

The final GF is related to the initial GF through the

Dyson equation.

Physical Properties of Thin Films and Nanostructures:

Green’s-Function Methods

Figure 1: Stress distribution in Si due to a surface load.

Figure 2: Interaction energy of a cluster of 147 Ge atoms

with a vacancy and free surface in Si.
12

Nanomechanics

Axisymmetric adhesion tests promise a powerful

means to quantify adhesive performance with

the simultaneous ability to visualize debonding

mechanisms. However, industrial adoption of

these techniques has been slow, since traditional

axisymmetric testing equipment does not allow

rapid assessment of product performance

over a large parameter space. In response,

we are developing instruments that permit

high-throughput (and high value) measurements

of adhesion across combinatorial libraries.

Aaron M. Forster and Seung-ho Moon

Adhesion is governed by surface interactions

 and the mechanical properties of the adhesive.

Axisymmetric adhesion (ASA) measurements, such as

JKR[1] methods and “probe tack” tests, provide powerful

means for quantifying these contributions to adhesion,

while providing visual insight into the mechanisms by

which adhesives fail. However, current ASA instruments

are geared towards serial testing of single specimens.

This “one-at-a-time” paradigm is incompatible with

industry research, which increasingly requires methods

to rapidly and thoroughly measure large numbers of

adhesive formulations. Our objective is to produce

ASA measurement instruments that operate in a

high-throughput manner, while retaining the high-value

data these methods produce. These tools enable the

rapid identification of structure–property relationships

critical for adhesive performance, thereby assisting

industry in developing new adhesive formulations.

This report describes two of the high-throughput ASA

instruments that have been built to address these issues.

The JKR method employs a hemispherical lens that

is pressed into a specimen. Tracking the lens/specimen

contact area versus load or lens displacement yields

the work of adhesion. Our instrument, the Multilens

Combinatorial Adhesion Test (MCAT) employs an array

Combinatorial Adhesion and Mechanical Properties:

Axisymmetric Adhesion Testing

Figure 1: a) Contact area map of MCAT lens array. Each circle

represents data for a separate measurement. b) Contact area vs.

displacement data for a single lens array element. The red line is

the fit to JKR theory, which yields the work of adhesion.

of microlenses to conduct multiple JKR-type adhesion

tests in parallel. By simultaneously tracking the

contact radii of each element of the lens array, up

to 400 measurements of the work of adhesion are collected

in the time required for a single traditional JKR test

(see Figure 1). When MCAT is used in conjunction

with gradient combinatorial specimen libraries, each

lens measures a different adhesive system. We recently

benchmarked MCAT measurements of the work of

adhesion between glass and silicone against single lens

JKR tests, with excellent agreement.

Figure 2: a) Schematic of CPT adhesion test instrument.

b) Adhesion energy (W) of a model PSA vs. temperature. Inset:

Image of probe/sample contact shows debonding of the PSA.

The adhesion of viscoelastic materials, such as pressure

sensitive adhesives (PSAs), is not described well by

JKR-type tests. Probe tack tests provide quantitative

adhesion measurements for viscoelastic systems with

simultaneous visualization of debonding events. We

developed a new combinatorial probe tack (CPT) test

for the measurement of PSA formulation performance

(Figure 2). A key feature of the instrument, a gradient

hot-stage, enables rapid assessment of temperature effects.

Temperature is an important processing parameter and

environmental factor for PSAs. Our CPT testing of PSAs

(Figure 2) rapidly provides quantitative adhesion energy

data and debonding images as a function of temperature.

The device design significantly reduces experimental

uncertainties associated with fabrication of multiple

samples, and reduces the overall measurement time

significantly, while maintaining high-quality, rich datasets.

We are currently refining the CPT instrument and testing

its use towards a variety of applications such as UV-cured

PSAs and epoxy systems.

Reference

1. K.L. Johnson, K. Kendall, and A.D. Roberts,

Proceedings of the Royal Society of London A:

Materials 324, 301 (1971).

Contributors and Collaborators

A. Chiche, C.M. Stafford, W.L. Wu, W. Zhang

(Polymers Division, NIST)
13

Nanomechanics

Combinatorial Adhesion and Mechanical Properties:

Innovative Approaches to Peel Tests

Figure 1: Master adhesion map delineating critical surface

energy conditions for adhesion vs. a reduced time-temperature

function, at.

as a function of substrate surface energy, annealing time,

and annealing temperature (see Figure 1). This defines

an operating window of temperature, time, and surface

energy to ensure proper adhesion of a thin polymer film

to the material of interest.

Peel testing is the primary tool industry uses to

gauge adhesive performance, but current peel

test methods involve “one-at-a-time” analysis of

single specimens. Our research aims to accelerate

adhesive performance testing by developing

devices and measurement strategies that meld

the peel test construct with combinatorial and

high-throughput (C&HT) methods.

Christopher M. Stafford and Martin Y.M. Chiang

As part of the mission of the NIST Combinatorial

 Methods Center (NCMC), we are developing

C&HT peel-test methods that enable rapid assessment

of adhesion within the large parameter space associated

with adhesive formulation and processing. This report

describes two milestones we have met in this endeavor.

Our first achievement involves a NIST-developed

experiment design for measuring adhesion of a polymer

layer to an underlying substrate in a combinatorial manner.

This test method utilizes the peel-test geometry to

investigate the interfacial failure between a thin polymer

film and a silicon substrate as a function of annealing time

and temperature, as well as the substrate surface energy.

Combinatorial libraries are generated by using the existing

NCMC gradient toolkits: a polymer film is coated onto

a substrate containing a surface energy gradient, and

this sample is subsequently exposed to an orthogonal

temperature gradient.[1] To further extend the parameter

space available in this study, we incorporated annealing

time as a third dimension. This requires fabricating

multiple identical samples and successively annealing each

sample for longer times. By applying the Williams–Landel–

Ferry (WLF) time-temperature superposition, we can

construct a master curve (failure map) detailing the

transition from adhesion (bonded) to failure (debonded)

Figure 2: a) Force vs. distance curve for a typical peel test; and

b) distribution curve of the force data.

Our second achievement addresses a challenge

in applying the peel test to combinatorial specimens:

the lack of ample statistical information that is the

foundation of this type of measurement. For example,

a conventional peel test conducted under constant

conditions results in a fluctuating force to be averaged.

Applying a continuous gradient of sample properties

or test conditions in the peel direction implies that each

data point (force) corresponds to a given test condition,

thus prohibiting the average force to be calculated

for a given condition. To address this issue, we have

developed a simple statistical treatment that allows

a relationship between the uncertainty of the force

and the domain size to be established. This treatment

ultimately will dictate the number of data points required

to obtain acceptable uncertainties in the measurement.

These studies demonstrate how combinatorial

approaches can be applied to characterize adhesion

using a peel test blueprint. In doing so, we have

designed a new statistical tool to assist in defining the

gradient step size (discrete gradients) or gradient

steepness (continuous gradients) that allows ample

statistical information to be obtained.

Reference

1. For details, see A. Seghal, et al., Microscopy Today

11 (6), 26–29 (2003).

Contributors and Collaborators

A. Chiche, R. Song, A. Karim (Polymers Division,

NIST); J. Filliben (Statistical Engineering Division, NIST)
14

Nanocharacterization

Reactions occurring at interfaces during the

high-temperature processing of complex electronic

materials involve diverse chemical compositions.

To optimize the design and control of these

interfaces, we are developing a generic

thermodynamic/kinetic model for interfacial

interactions. The model includes modification

of bulk reaction and mass transport parameters

to accommodate nanoscale observations.

Lawrence P. Cook, Winnie Wong-Ng,

and Igor Levin

State-of-the-art electronic devices contain complex

materials with chemical constituents ranging widely

over the periodic table; furthermore, new materials are

continually being added. Many electronic packaging

materials consist of metals, ceramics, and semiconductors,

with bi-phasic interfaces of several types. Processing

temperatures may extend up to 900 oC where diffusion

and reaction can be significant. Two principal

problems arise in the treatment of such interactions:

1) the application of equilibrium thermodynamic data

to the non-equilibrium growth of interfacial reaction

zones, and 2) the transition from micro-scale (bulk

dominated), to nanoscale (surface dominated) phenomena.

To address these issues, we have instituted a combined

thermodynamic/kinetic approach to investigate the model

system Ag-Bi2O3-Nb2O5-O, as outlined in Figure 1.

Thermochemistry and Metrology of Interfacial Interactions

Progress includes determination of a preliminary

phase diagram at 850 oC, and development of a

provisional thermodynamic model. Subsequent

construction of a chemical potential diagram has

allowed us to predict alternative diffusion and reaction

paths. Observations on Ag/BiNb5O14 reaction couples

(Figure 2) confirm the relatively high thermodynamic

mobility of Ag. Thermogravimetric data on the

interfacial reaction require more than a simple parabolic

rate law, due to the rapid initial spread of Ag along

reaction site surfaces. By comparison with particulate

interfacial systems, a two-step reaction model is

proposed, for which rate constants can be obtained.

Data for the model system are of direct interest

to the electronics community because Ag is an

important metallization component in many dielectric

ceramics. It is anticipated that continued work

on Ag-Bi2O3-Nb2O5-O will lead to the goal of a

comprehensive thermodynamic/kinetic model.

The model will be tested, iteratively refined, and

extended to other systems.

Contributors and Collaborators

M.D. Vaudin, P.K. Schenck, T. Vanderah, M. Green

(Ceramics Division, NIST); W. Luecke (Metallurgy

Division, NIST); C. Randall, M. Lanagan (Center for

Dielectric Studies, Pennsylvania State University)

Figure 2: Ag Lα X-ray map of Ag/BiNb5O14 reaction zone

(≈ 80 μm wide) produced by annealing in air for 10 h at 850 oC,

with an applied uniaxial compression of ≈ 1 MPa.

Figure 1: Flow chart for development of interfacial model based

on Ag-Bi2O3-Nb2O5-O.
15

Nanocharacterization

Chemistry and Structure of Nanomaterials

Successful nanoscale materials fabrication is

empowered by a detailed knowledge of the chemistry

and structure of surface bound molecules; e.g.,

the optimization of self-assembled monolayers,

molecular templates, micro-electro-mechanical

system lubricants, and functionalized nanotubes.

Near-Edge X-ray Absorption Fine Structure

(NEXAFS) spectroscopy is ideally suited to measure

non-destructively chemical bond concentration,

rehybrization, and orientation with sub-monolayer

molecular sensitivity in diverse nanoscale materials.

Furthermore, NEXAFS can distinguish chemical

bonding in the light elements, measure the orientation

of interfacial molecules, and separately measure

surface versus bulk chemistry simultaneously.

Daniel A. Fischer

Materials having low energy surfaces are used in

many applications, for example, in non-wetting

surfaces or fouling resistant marine coatings. We have

produced a photo-responsive polymer surface by

combining the reversible photo-switching nature of

azobenzene with the self-assembly nature and low

surface energy properties of semi-fluorinated segments,

to create a fluoroazobenzene molecule surface.

Upon UV exposure, this surface reorients between

hydrophobic and less hydrophobic states, as shown

in Figure 1 (left upper and lower panels). For such

surfaces, one could imagine applications ranging from

low cost surface patterning to polymer surfaces that

would adsorb biological macromolecules on cue.

Figure 1: UV light reorients fluorobenzene semi-fluorinated

segments (green) downwards, i.e., to a less hydrophobic state.

We have utilized NEXAFS to observe, verify, and

quantify the reversible cis-trans molecular conformation

transformation from hydrophobic to less hydrophobic

states. The right panels of Figure 1 (upper and lower)

show polarization dependent NEXAFS anisotropy

behavior of the C–F and C–C peaks which reverse with

in situ UV light exposure highlighting the reorientation

of the semi-fluorinated segments.

Figure 2: Carbon NEXAFS of oxidized/functionalized nanotubes.

Figure 3: Model of peroxide functionalization of nanotubes.

Application of NEXAFS spectroscopy to the study of

electronic structure and chemical composition is illustrated

in Figure 2 for various chemically functionalized, singlewalled, carbon nanotubes. Upon peroxide functionalization,

the C=C ring resonance is greatly diminished on extensive

sidewall functionalization indicating loss of extended

conjugation and disruption of nanotube electronic

structure. The C= O peak intensity is greatest for peroxide

chemistry. NEXAFS spectroscopy supports a model

of peroxide funtionalization, shown in Figure 3.

Contributors and Collaborators

S. Samabasivan (Ceramics Division, NIST);

X. Li, C.K. Ober (Cornell); A. Hexemer, E.J. Kramer

(UCSB); S. Banerjee, T. Benny, S.S. Wong (SUSB);

J.A. Misewich (BNL)
16

Metrology for Nanoscale Properties: X-ray Methods

Texture has a large influence on many properties

of thin films. XRD was the primary method for the

characterization of texture for many years. Recently,

alternative local techniques have been developed to

bring the measurements to the nanoscale. This year,

we compared measurements taken with conventional

XRD and EBSD on two thin films: sputtered aluminum

and electroplated copper. Both films had a thickness

of about 1 μm and were grown on [100] silicon

wafers. The inverse pole figures for both samples and

techniques are shown in Figure 1. It is obvious that

the agreement between XRD and EBSD in case of

aluminum film is very good, whereas it is rather poor

for copper film. This is a consequence of different

penetration depths of electrons and x-rays; while the

aluminum sample is homogeneous through the film

thickness, copper film is not. After sample preparation,

electroplated copper is likely to undergo self-annealing

at room temperature. This well-known phenomenon

yields a difference in grain size and orientation

between the surface and the bulk of the sample.

Contributors and Collaborators

Adriana Lita, Jens Müller, Roy H. Geiss,

Dave T. Read, M. Kopycinska–Müller, Robert Keller

(NIST); Laurna Kaatz, Amitendra Chaudhuri

(University of Denver)

Figure 1: EBSD (left) and XRD (right) inverse pole figures of

aluminum (top) and copper (bottom) thin films.

of the {321} lattice spacings (sin2ψ method) yielded the

total residual stress at ambient temperature. The values

obtained are about 0.7 GPa and higher, where the bulk

of the stress is due to the intrinsic (growth) component.

Nanocharacterization

Macroscopic properties of technologically

interesting materials originate from their

underlying micro-structure. To design and

understand improved materials, it is necessary

to characterize the microstructure and correlate

its changes to the macroscopic properties of

interest. We especially focus on x-ray diffraction

studies of biomedical, ferroelectric, optoelectronic,

photovoltaic, semi-conducting, and other materials

relevant to the health and microelectronics

industries. In particular, studies of microstructural

properties, such as strain and stress, crystalline

defects, and texture, complement the information

obtained by other techniques.

Thomas A. Siewert and Davor Balzar

I

n this report, we focus on two topics: the studies of

superconducting tungsten thin films and comparison

of the thin-film texture, as obtained by Electron Back

Scatter Diffraction (EBSD) and x-ray diffraction

(XRD). Tungsten superconducting transition-edge

sensors (TES) are used in different astrophysics and

astronomy applications, and as single-photon detectors

for the quantum computing experiments. Such

detectors comprise thin tungsten films and operate at

temperatures close to absolute zero and to the critical

superconducting transition temperature (Tc) of

tungsten. Thin films, in general, contain both hightemperature α-W phase (with Tc = 15 mK) and β-W

(A15 cubic structure with Tc = 1–4 K). Close to the

Tc, very small thermal changes, such as the absorption

of a single photon, increase the film electrical

resistance. The result is the production of an electrical

output signal that corresponds directly to the detection

of the absorbed photon energy. In general, residual

stress can influence the Tc of the thin film both directly

and by inducing the β→α phase transformation. Thus,

in order to control the Tc, it is necessary to measure

and control both the phase composition and residual

stresses. Residual stresses in films depend on the

preparation conditions, the thickness of the film, and

the difference in thermal expansion coefficient between

the film and the substrate. The total residual stress

results from both the intrinsic (growth) stress and

thermal stress. We measured the stress by XRD

at both ambient and cryogenic temperatures.

The sample was held in a continuous flow cryostat

that was capable of achieving temperatures as low

as 8 K. The cryostat was mounted on a goniometer

to enable the angle-dispersive XRD measurements.

The shift of the α-W {110} Bragg reflection was used

to estimate stress at 8 K, and directional measurement
17

Nanocharacterization

Several materials are now produced commercially

with particle sizes on the order of 10–100 nm.

The availability of ceramic materials in this size

classification is particularly important for the

electronic component industry. Nanopowders

can enable significant decreases in internal layer

thickness (for multilayer devices), minimize the

size and prevalence of processing defects, and

boost the overall performance of components

ranging from capacitors to resistive gas sensors.

Quantifying these performance enhancements

and their dependence on microstructure is a key

objective in the Materials Reliability Division.

Stephanie A. Hooker

Many multilayer ceramic devices can benefit from

the use of ultra-fine powders, including passive

electronic components, gas sensors, and miniature

actuators. However, fabrication issues associated

with processing these high-surface-area powders

have hindered their commercialization. Key challenges

have included nanopowder reproducibility, optimization

of processing slurries, and control of sintering

profiles to produce the desired micro/nanostructure

characteristics. Moreover, in many cases, predicting

the optimum microstructure features for maximum

performance is quite difficult, and extensive

experimentation remains necessary.

One specific component that can benefit from the

use of nanopowders is the multilayer piezoelectric

actuator. These devices generate precise, controlled

motion for translating optics, damping vibrations,

redirecting air flow, and dispensing fluids. Each

component consists of many active layers, the

thickness of which determines the device’s power

requirements. Layer thickness is typically on the

order of several hundred microns for conventional

actuators and is driven by the need for many individual

piezoelectric grains to span the active layer, thereby

reducing the chance for electrical failure. Reducing

grain sizes from micrometer to submicrometer scales

enables dramatic decreases in layer thickness, reducing

power needs and increasing applicability.

However, at issue is the piezoelectric response and,

in particular, the long-term fatigue resistance. Fatigue is

the change in polarization or displacement over time and

is a recognized problem for state-of-the-art actuators.

Because processing-induced defects tend to be on the

scale of the starting powder, nanopowders can improve

mechanical durability. However, a corresponding

Physical Properties of Thin Films and Nanostructures:

Grain Size Effects on Actuator Fatigue

decrease in ferroelectric response is also anticipated

as grain size reduces. Fatigue is affected by both

the mechanical and electrical responses, making its

prediction quite difficult for fine-grained components.

In FY04, we investigated the fatigue behavior of

14 microstructures obtained by controlled sintering

of 80-nm PZT-5A powders. The devices tested were

1206-sized (0.30 cm × 0.15 cm, or 0.12 ́ ́ × 0.06 ́ ́)

chips, each with 10 active layers (50 μm thick).

Characterization included dielectric, impedance, and

ferroelectric properties, as well as short- (< 1 million

cycles) and long-term (1–100 million cycles) degradation

under combined electrical and mechanical influences.

Figure 1: Effect of sintering temperature on ferroelectric fatigue.

The results clearly demonstrate the dependence of

fatigue on microstructure. Figure 1 compares changes

in remanent (i.e., permanent) polarization over time

when devices were cycled using a 35 Hz sinusoidal

wave with an amplitude of +/–75 V. The average

decrease in polarization for the finest-grained materials

(sintered at 1175 °C) was less than 20 % after

0.5 million cycles, compared to nearly 50 % for

larger-grained components.

In FY05, we will expand on this work and examine

the corresponding effects on displacement and domain

reorientation for devices with even thinner internal

layers. The resulting data will then be used to validate

the suitability of these components for biomedical and

smart structures applications, both of which demand

high performance and long operational lifetimes.

Contributors and Collaborators

R. Geiss (Materials Reliability Division, NIST);

C. Kostelecky, D. Deininger, K. Womer (Synkera

Technologies)
18

Nanoporous low-dielectric-constant (low-κ) films

present considerable implementation challenges for

the microelectronics industry and also raise new

scientific questions. We apply optical methods to

these films to evaluate such critical properties as

density/porosity, Young’s modulus, and Poisson’s

ratio. Our techniques allow measurement of

properties that are otherwise difficult to determine

and shed light on how the mechanical properties

depend on porosity.

Colm Flannery and Donna C. Hurley

Current miniaturization trends in microelectronics

require faster device switching. This need can be at

least partially met by lowering the resistance-capacitance

factor of the dielectric materials. One promising solution

is to introduce nanometer-sized pores that reduce the

dielectric constant κ. Unfortunately, introduction of

porosity may lead to a drastic reduction in stiffness

(Young’s modulus), adversely affecting the material’s

chances of surviving the fabrication process. In addition

to predicting and ensuring process reliability, accurate

values of a film’s mechanical properties are needed

to model the mechanical behavior of the resulting

microelectronics device. New tools are needed to

characterize these relevant thin-film properties

(e.g., Young’s modulus and Poisson’s ratio ν), as

well as to better define their dependence on porosity.

In FY04, we evaluated Poisson’s ratio ν in

methylsilsesquioxane (MSSQ) polymer films of varying

porosity with Brillouin light scattering. In this technique,

a Fabry–Perot interferometer detects frequency-shifted

photons scattered by ambient thermal phonons in

the material. The frequency shift of the photons is

characteristic of the acoustic phonon modes in the film.

Values of ν were determined from measurements of both

longitudinal and surface acoustic wave modes. Figure 1

reveals that ν decreases as porosity increases. The results

Physical Properties of Thin Films and Nanostructures:

Nanoporous Low-κ Dielectric Films

Figure 1: Measured Poisson’s ratio vs. porosity for MSSQ films.

Figure 2: Predicted dependence of Poisson’s ratio on porosity.

of an existing finite-element model, shown in Figure 2,

predict that ν will either decrease or increase depending

on the initial ν of the matrix material. In addition, ν tends

towards a constant value of 0.2 for all materials at high

porosity. Our measurements are consistent with the

model. However, they show a much larger rate of decrease

in ν, probably because a percolation threshold had

been reached. Quantitative results like these will prove

valuable for modeling of structures involving low-κ

films. The results also yield insight into the porosity

dependence of ν, about which very little is known.

A second method to determine thin-film properties

involves the frequency-dependent dispersion of lasergenerated surface acoustic waves (SAWs). In FY04,

efforts concentrated mainly on the development of a

standard SAW data analysis procedure. With careful

signal processing that minimizes sensitivity to noise and

maximizes the frequency range of the measured signals,

we can extend the frequency range of our measurements

by 20 %. The result is a significant reduction in the

uncertainty of the extracted film properties. The method

lends itself to automatation and has allowed us to inspect

films less than 300 nm thick. (Previously, films less than

500 nm thick were challenging.)

The improved measurement procedure, combined

with new multilayer Green’s function analysis software,

has allowed us to inspect multilayer structures.

With these capabilities, we have extracted properties

of thin (50–100 nm) capping layers of stiffer materials

on top of more compliant functional films. In addition,

the Young’s modulus, density, and thickness of

the underlying dielectric films were evaluated.

Contributors and Collaborators

S. Kim, V. Tewary (Materials Reliability Division,

NIST); Y. Liu (International Sematech); J. Wetzel

(Tokyo Electron America)

Nanocharacterization
19

Nanocharacterization

Electron microscopy is used to characterize the

structure and composition of materials at the

nanometer scale to better understand and improve

their properties. New measurement techniques in

electron microscopy are being developed and

applied to materials science research. The MSEL

Electron Microscopy Facility primarily serves the

Metallurgy, Ceramics, and Polymers Divisions as

well as other NIST staff and outside collaborative

research efforts.

John E. Bonevich

Atomic-scale structure and compositional

 characterization of materials can lend crucial

insights to the control of their properties. For instance,

direct observation of local structures by transmission

electron microscopy (TEM) provides important

feedback to the optimization of crystal growth and

processing techniques. Various characteristics may be

observed such as crystal structure and orientation, grain

size and morphology, defects such as stacking faults,

twins, grain boundaries and second phase particles.

Structure, composition and internal defect structures,

as well as the atomic structure of surfaces and

interfaces, can provide powerful knowledge for

engineering and understanding materials.

The MSEL Electron Microscopy Facility consists of

two transmission electron microscopes, three scanning

electron microscopes, a specimen preparation laboratory,

and an image analysis/computational laboratory. The

JEM3010 TEM can resolve atomic structures and employs

an energy selecting imaging filter (IF) and X-ray detector

(EDS) for analytical characterization of thin foil specimens.

The S-4700-II FE-SEM employs electron backscattered

diffraction/phase identification (EBSD) and EDS systems

to characterize the crystallographic texture and

composition of materials.

Nanoscale Characterization by Electron Microscopy

Figure 1: MgO cubes with surfaces decorated by small gold

particles. These particle ensembles are used in model studies of

3D chemical imaging at the nanoscale (electron tomography).

Figure 2: Confined Si single electron transistor device.

Highlights from the EM Facility for FY2004 include:

■ A new, high-sensitivity EBSD CCD camera

which acquires in excess of 70 patterns/second,

was installed on the FE-SEM.

■ 3D Chemical Imaging at the Nanoscale, a collaborative

project with CSTL and PL on tomographic

characterization of materials, was initiated (Figure 1).

■ Research collaboration with the Semiconductor

Electronics and Electricity Divisions (EEEL) has

characterized quantum effects in confined Si devices

(Figure 2).

■ Sub-100 nm Ag interconnects formed by

superconformal electrochemical deposition was

characterized.

Contributors and Collaborators

D. Josell, T. Moffat, L. Bendersky (Metallurgy

Division, NIST); I. Levin, B. Hockey (Ceramics Division,

NIST); J.H.J. Scott (Surfaces & Microanalysis Science

Division, NIST); Z. Levine (Optoelectronics Division,

NIST); E. Vogel (Semiconductor Electronics Division,

NIST)
20

Nanocharacterization

Engineering of nanomaterials, biomaterials,

and nano-electromechanical systems hinges on

techniques for imaging complex nano-structures.

In this respect, new Scanned Probe Microscopy

(SPM) methods promise nano-scale mapping of

chemical, mechanical, and electro-optical properties,

but these techniques generally only offer qualitative

information. Through a suite of reference specimens

fabricated with a combinatorial design, we aim to

calibrate image data from emerging SPM methods,

thereby advancing these nanometrology tools.

Michael J. Fasolka and Duangrut Julthongpiput

Recent years have seen the development of a new

generation of SPM techniques, which intend to

measure chemical, mechanical, and electro–optical

properties on the nanoscale. However, contrast in new

SPM images is difficult to quantify since probe fabrication

can be inconsistent and probe/sample interactions are not

understood. Our research at the NIST Combinatorial

Methods Center (NCMC) aims to provide a suite of

reference specimens for the quantification of next

generation SPM data. By design, our specimens will gauge

the quality of custom-made SPM probes, calibrate SPM

image contrast through “traditional” surface measurements

(e.g., spectroscopy, contact angle) and provide information

for understanding complex probe/sample interactions. Our

specimens are produced with bench-top microfabrication

routes and combinatorial gradient methods developed

by the NCMC. Here, combinatorial methods are key

since they enable the fabrication of specimens that vary

properties that govern SPM image contrast in a systematic,

independent manner. Moreover, as opposed to traditional

reference specimens, combinatorial samples provide not

one, but a multitude of calibration conditions.

Figure 1 illustrates principles of our specimen design

through a specific case useful for quantifying chemically

sensitive SPM techniques such as friction-force SPM,

Gradient Reference Specimens for Advanced

Scanned Probe Microscopy

Figure 1: Schematic illustration of our gradient reference

specimen for chemically sensitive SPM techniques.

Figure 2: Preliminary calibration curve relating friction force SPM

image contrast to differences in surface energy (γ ), as determined

from a single gradient reference specimen. The minimum contrast

point (red arrow) illuminates the sensitivity of the probe.

or Chemical Force Microscopy, which employs a

custom-made probe. The crux of this specimen is

a “gradient micropattern” (∇-μp): a series of micronscale lines that continuously change in their chemical

properties (e.g., surface energy) compared to a constant

matrix. Two “calibration fields” adjacent to the ∇-μp

directly reflect the chemistry of the lines and the matrix.

Thus, traditional measurements (e.g., contact angle)

along the calibration fields (1) gauge local chemical

differences in the ∇-μp and thereby (2) calibrate

contrast in SPM images acquired along the ∇-μp.

Figure 2 demonstrates use of this specimen for

calibrating friction force SPM image contrast. We

fabricate this specimen via microcontact printing of a

chlorosilane self-assembled monolayer (SAM) on a SiO2

matrix. The chemical gradient is achieved via a graded

UV-ozonolysis of the SAM. The plot abscissa gives the

difference in friction force (contrast) between the lines

and matrix for SPM images collected along the ∇-μp.

The ordinate expresses the corresponding surface energy

(γ) data (from contact angle measurements) collected

along the calibration fields. Thus, from a single specimen

we create a comprehensive calibration curve that relates

SPM friction force to differences in surface energy.

Moreover, the plot neatly illuminates the smallest

γ difference sensed by the probe (red arrow), which is

useful for gauging the quality of custom-made probes.

Currently, we are refining this reference specimen

design, and we are developing similar designs for other

advanced SPM methods.

Contributors and Collaborators

K. Beers (Polymers Division, NIST);

D. Hurley (Materials Reliability Division, NIST);

T. Nguyen (Materials and Construction Research

Division, BFRL); S. Magonov (Veeco/Digital

Instruments)
21

Nanocharacterization

Polyelectrolytes differ in chain dynamics and

equilibrium structure from neutral polymers due to

long-range electrostatic interactions. This manifests

into strongly interacting solutions for both synthetic

and biopolymers, as observed by associative

behavior and multi-mode relaxations. Origins

of these relaxations require new experimental

methods probing the local structure and dynamics.

Vivek M. Prabhu and Eric J. Amis

Polymeric templates are found throughout nature

most commonly in the nucleic acid base-pairing

of DNA. This special hydrogen bond template

has currently been explored for design of novel

nanostructured materials. New routes to self-assembled

or template-assisted assembly using externally supplied

fields such as electric, flow, magnetic, and patterned

substrates must overcome Brownian motion as well as

structural correlations between and among molecules.

For polyelectrolytes, such as DNA, the long-ranged

electrostatic interactions also contribute to the solution

structure in addition to the local and directional hydrogen

bond associations. The distribution and dynamics of

the counterion species about a polyelectrolyte serve as

a starting point to understand the interactions governing

controlled assembly and complement the often-studied

polymer structure point-of-view.

We have established, using neutron scattering

experiments performed at the NIST Center for

Neutron Research (NCNR), the remarkable ability for

counterions to essentially conform to linear flexible

polyelectrolytes. This was accomplished by direct

measure of the counterion partial static and dynamic

structure factor highlighting the coupled polymer and

counterion association for model synthetic materials

shown below.

Characterization of Counterion Association with

Polyelectrolytes: Novel Flexible Template Behavior

An example of the counterion correlations is shown

by the SANS structural peak in Figure 1. The peak

illustrates the counterion correlations mediated by

the chain. By tuning the range of the electrostatic

interactions with added NaCl, an “invisible” salt,

the influence is two-fold: (1) the electrostatics are

screened, and the solution returns to neutral-like

behavior; and (2) at higher salt concentrations, the

Na+ displace the visible h-TMA+ counterions as shown

in the accompanying schematic. Although the polymer

template is no longer observed, its influence is still

observed with a “visible” salt.

The counterion dynamics are length scale

dependent and slow down near the correlation peak.

This behavior illustrates that the polyion-counterion

motions are coupled at the nanoscale. Hence, the

role of counterions also serves as a design criteria in

assembling structures. Unique labeling has provided

a new viewpoint of charged polymer solution structure

and dynamics. This project aims to characterize the

role of charged polymer topology with branched

materials, networks, and gels on the coupled dynamics

to assess the parameters governing template-assisted

assembly. Modern simulation and theoretical insight

will assist in understanding these challenges for

nanoscale assembly.

Contributors and Collaborators

D. Bossev, N. Rosov (NIST Center for Neutron

Research)

Small-angle neutron scattering (SANS) was used to

characterize the equilibrium structure, while neutron

spin echo (NSE) spectroscopy was used to examine the

dynamics occurring at length scales between (60 and 3)

nm and time scales between 45 ps to 100 ns.

Figure 1: “Visible” organic counterions associate with the negatively

charged chain at low salt and are displaced by added “invisible”

sodium ions for fixed polymer concentration of 24.9 gL–1.
22

Nanofabrication and Processing

The magnetic data storage industry is seeking

to sustain the 30-year trend of exponentially

increasing storage density. This must be achieved

at the same time as maintaining the stability of the

recorded data. The Metallurgy Division at NIST

is collaborating with Seagate Technology to

develop the processes required to produce

patterned media of high-magnetic coercivity

that will meet this challenge.

Jonathan J. Mallett, Thomas P. Moffat, and

William F. Egelhoff, Jr.

Conventional magnetic data storage media are based

on granular films in which many fine grains are

used to define each magnetic bit. The minimum

number of grains per bit is limited by the irregularity

of the shape and spacing of the grains, which produces

irregular boundaries between bits. This irregularity

results in noise in the read signal and can only be

constrained at an acceptable level by maintaining a

fixed minimum number of grains per bit. The natural

approach to increasing data storage density has been

to reduce the grain size, while maintaining the same

number of grains per bit. The limit to this approach

occurs when the magnetic energy barrier to the reversal

of magnetization of each grain approaches the energy of

random thermal fluctuations. At this point, the medium

is no longer stable against spontaneous magnetization

reversal and consequential data loss.

The grain size at which this limit occurs depends

on the magnetocrystalline anisotropy energy of the

Grand Challenges in Nanomagnetics: High Coercivity FePt

Alloys for Future Perpendicular Magnetic Data Storage

magnetic material. FePt in its L10 phase has a

sufficiently large anisotropy energy to allow

magnetically stable grains of 5 nm diameter (Figure 1).

Furthermore, FePt deposited by a variety of means

typically forms grains approaching this size.

Unfortunately, the annealing treatment required to

transform the as-deposited A1-structured FePt to

the desirable L10 phase is widely found to result

in an increase in grain size to 100 nm. Current

efforts at NIST focus on developing a method of

electrochemically depositing FePt into a regular

patterned template, circumventing the problem of grain

growth. Simultaneously, the imposed regularity of the

magnetic cells opens the possibility of addressing single

cells (i.e., of using one “grain” per bit). The estimated

achievable density from such an approach is 7 Tbits

per square inch, which is 100 times higher than current

storage densities. Electrodeposition is an obvious

choice for deposition into high aspect ratio templates,

since it does not suffer from the shadowing effect

that characterizes vacuum deposition techniques.

Figure 2: The double cell, designed to minimize the concentration

of Fe3+ and dissolved O2 in the FePt plating solution.

Figure 1: The dependence of storage density on magnetocrystalline

anisotropy energy. The most promising materials are FePt

and CoPt.

Electrodeposition of FePt from aqueous solutions

presents many challenges. The double cell shown in

Figure 2 has been developed to address the problem of

the instability of Fe2+ solutions, which readily oxidize

to produce insoluble Fe(OH)3. The plating solution,

containing FeCl2 and PtCl4 (left) is separated from the

anode by a cation selective membrane, preventing the

oxidation of Fe2+ to Fe3+ that would otherwise occur

at the anode. Fe3+ formation by oxidation with air is

also minimized by blanketing the cell in nitrogen, and

residual Fe3+ is reduced to Fe2+ by an auxiliary

platinum grid electrode.
23

Nanofabrication and Processing

The alloy composition of 300 nm thick films

deposited from this solution was found to depend

mainly on the applied potential and to be insensitive

to the concentration of the solution components.

A thermodynamic regular solution model was used

to describe the dependence of film composition on

applied potential. The comparison of theory to

experimental data can be seen in Figure 3.

The deposited films were found to be remarkably

smooth, with RMS roughness values less than 5 nm

for micron-thick deposits. This was surprising given

the large platinum overpotential (supersaturation),

which usually results in growth instabilities and

consequent roughening.

The control of crystal orientation is an essential

consideration for high-density recording applications.

A transition in the recording industry is currently in

progress to perpendicular media, in which the bits are

magnetized perpendicular to the plane of the medium.

Maximum advantage can be derived from L10 FePt as a

perpendicular medium when it is correctly aligned with

its magnetic easy-axis perpendicular to the substrate

plane. A careful choice of substrate and annealing

parameters is required to recrystallize the as-deposited

random fcc alloy to appropriately oriented L10.

Figure 3: The theoretical and experimental dependence of

composition on the applied potential.

FePt electrodeposited onto a Cu (001) substrate

has recently shown great promise. X-ray diffraction

revealed the transition to L10 upon annealing, and X-ray

pole figures indicated favorable orientations. Figure 4

shows FePt L10 (001) and (110) pole figures. The

(001) figure indicates perpendicular orientation of the

magnetic easy-axis (the c-axis), while the (110) figure

indicates an in-plane texture. The in-plane texture is an

added advantage, as it results in a narrower switching

field distribution.

Copper additions to the alloy have been found to

lower the A1/L10 phase transition temperature by up

to 90 oC. It may be speculated that interdiffusion of

copper from the substrate during the anneal allowed the

recrystallization to proceed from the interface with the

substrate. It is likely that this would allow the film to

replicate the orientation of the substrate.

Figure 4: X-ray pole figures showing favorably oriented FePt L10 .

Figure 5: Magnetic hysteresis measurements showing a 10 kOe

coercivity.

 Magnetic hysteresis measurements performed

using a Kerr magnetometer are shown in Figure 5.

The magnetic coercivity of 10 kOe is comparable to

figures quoted in the literature for vacuum-deposited

FePt. It is believed to be the highest value reported

for an electrodeposited film.

Current efforts focus on controlling the

interdiffusion between substrate and film to minimize

loss of magnetization in the alloy, and on moving

from planar films to through-mask deposited arrays

of FePt pillars.

For More Information on this Topic

W.F. Egelhoff, Jr. (Metallurgy Division, NIST);

E.B. Svedberg (Seagate Research, Pittsburgh)
24

Nanofabrication and Processing

Conductors in on-chip metallizations are now

reaching dimensions so small that defective

seed layers are impacting manufacturing yields,

and electron scattering on surfaces and grain

boundaries is reducing electrical transport in

the buried wires. Our goal is to provide tools

to overcome these barriers. Recent efforts have

quantified sources of the increased resistivity in

wires made of silver, the most conductive of all

metals, demonstrated seedless processing routes

for copper wires, and improved understanding

and modeling of the superfill fabrication process.

Daniel Josell and Thomas P. Moffat

The steady reduction of transistor dimensions in

integrated circuits has been accompanied by similar

size reductions of the on-chip interconnects that carry

electrical signals, pushing the industrial technology for

copper seed deposition close to its limit for defect-free

sidewall coverage. Defects in seed layers, which

arise from limitations in existing sputter technology,

lead to voiding during electrodeposition of the

copper metallization.

Additionally, with the dimensions of the copper

wires in these metallizations now approaching the

intrinsic mean-free-path length of the conduction

electrons, scattering on the wire surfaces has begun

to significantly reduce electron transport and, thus,

the associated electrical conductance of the wires.

With grains in these conductors similarly sized, a

reduction is also to be expected from grain boundary

scattering. While the penalty for both effects is

increased power dissipation and reduced clock speed,

the appropriate approach for mitigation requires

quantitative determination of the relative sizes of

the contributions.

On-Chip Interconnects:

Extending Performance of Sub-100 nm Lines

Technical Details

A tri-layer titanium, palladium and silver seed

(Figure 1) was shown to yield smooth, conductive

surfaces for the electrodeposition of silver wires for

the electrical properties study. The poor seed coverage

that is visible toward the bottom of the smallest

trench (Figure 1c) is a technical challenge noted in the

International Technology Roadmap for Semiconductors.

Such seed defects motivated the “seedless” ruthenium

barrier-based process detailed in last year’s report and

continued by this year’s demonstration of seedless

copper superfill in trenches with ruthenium or iridium

barriers (Figure 2) deposited by perfectly conformal

atomic layer deposition (ALD).

Figure 1: Ti/Pd/Ag seed layer in sub-100 nm deep trenches.

Figure 2: Trenches containing copper that was electrodeposited

directly on an ALD iridium barrier (thin bright layer).

Figure 3: Cross-section views of silver wires fabricated by

electrodeposition in the seeded trenches followed by removal of the

metal from the field (transmission electron microscope).
25

Nanofabrication and Processing

Figure 4: Electrical resistivities of 300 nm tall silver wires

compared to predictions that account for surface scattering with

varying amounts of grain boundary scattering. Resistivities for

wires less than 100 nm wide are impacted by defects.

For the electrical studies, silver wires (Figure 3) were

fabricated by silver electrodeposition on the tri-layer seeds

(Figure 1), using a superfill process developed in the

Metallurgy Division, followed by removal of the metal

in the field adjacent to the wires through chemical–

mechanical planarization and ion polishing.

The wires were studied in a standard four-point probe

geometry that permitted measurement of wire resistances.

Resistivities, obtained from the resistances using measured

wire dimensions, increased significantly with decreasing

wire width (Figure 4). To assess the origin of the resistivity

increase, the Fuchs–Sondheimer analysis for diffuse

scattering of electrons on surfaces was extended to

permit analysis in the presence of both specular and

diffuse scattering. The resulting equations, along with

a previously published equation for grain boundary

scattering, permitted quantitative evaluation of the

experimental data. Significantly, modeling of the data

showed that the increase of resistivity with decrease

of wire size arises as much from scattering on grain

boundaries as from scattering on the wire surfaces.

This indicates that efforts to mitigate size effects must

increase grain size as well as surface specularity if

they expect to be more than modestly successful.

The continuing industrial need for predictive

simulation of feature filling spurred experiment and

modeling of the superfill process itself. Consumption

of adsorbed accelerator, a detrimental deviation from

the surface segregation behavior that is responsible for

the superfill process, was measured. Inclusion of such

consumption in our Curvature Enhanced Accelerator

Coverage (CEAC) model and computer code have made

the filling predictions even more accurate.

This research has continued to impact industry,

indicated by requests for our superfill code from Intel,

Applied Materials, ST Microelectronics, and ATMI;

an invited article on superfill in the IBM Journal of

Research and Development; and invited presentations

given at Cookson–Enthone, in addition to publications

and presentations at conferences.

Selected Project Publications

for FY2004

T.P. Moffat, D. Wheeler, M. Edelstein and D. Josell,

“Superconformal Film Growth: Mechanism and

Quantification,” IBM J. Res. and Dev., in press.

D. Josell, C. Burkhard, Y. Li, Y.-W. Cheng, R.R. Keller,

C.A. Witt, D. Kelley, J.E. Bonevich, B.C. Baker,

T.P. Moffat, “Electrical Properties of Superfilled

Sub-Micrometer Silver Metallizations,” J. Appl. Phys.

96 (1), 759–768, (2004).

D. Wheeler, T.P. Moffat, G.B. McFadden, S. Coriell

and D. Josell, “Influence of Catalytic Surfactant

on Roughness Evolution During Film Growth,”

J. Electrochem. Soc. 151 (8), C538–C544, (2004).

T.P. Moffat, D. Wheeler, and D. Josell,

“Electrodeposition of Copper in the SPS-PEG-Cl Additive

System: I. Kinetic Measurements: Influence of SPS,”

J. Electrochem. Soc. 151 (4), C262–C271, (2004).

W.J. Evans, D.G. Giarikos, D. Josell, and J.W. Ziller,

“Synthesis and Structure of Polymeric Networks of

Silver Hexafluoroacetylacetonate Complexes of THF,

Toluene, and Vinyltrimethylsilane,” Inorg. Chem. 42,

8255–8261, (2003).

For More Information on this Topic

D. Josell, T.P. Moffat (Metallurgy Division, NIST);

G. McFadden (Mathematical and Computational Sciences

Division, NIST); R.R. Keller, Y.-W. Cheng (Materials

Reliability Division, NIST); C. Witt (Cookson–Enthone);

C. Burkhard, Y. Li (Clarkson University); D. Wheeler

(University of Maryland); T.K. Aaltonen, M. Ritala,

M. Leskelä (University of Helsinki, Finland)

Figure 5: Simulations of superconformal feature filling now

account for consumption (incorporation) of adsorbed catalyst.
26

Nanofabrication and Processing

As technology migrates toward smaller physical

dimensions, new analytical approaches are

required to characterize material properties and

to investigate critical issues. Our primary focus is

the application of metrology and the development

of new methods and standards for measuring the

physical and surface properties of nanostructured

particle systems. Applications include functional

materials and devices for catalysis, power

generation, and microelectronic, pharmaceutical,

and biotechnology industries.

Vince Hackley

Nanocrystalline oxides of alkaline-earth cations

produced by a supercritical drying process exhibit

unique and highly reactive surface chemistries. As a

result, these materials have been studied extensively as

destructive adsorbents, catalysts, and bioactive agents.

Investigations were concluded regarding the role of

cation size on the evolution of microstructure in these

materials and on the dispersion properties in aqueous

NaCl solution. A series of small-angle neutron

scattering (SANS) experiments were performed at

the NIST reactor in collaboration with researchers

at Kansas State University. These results indicate a

complex picture for structure formation during the

drying and annealing processes, with string-like gel

morphology giving way to fractally rough particulate

assemblies of compacted nanocrystals.

Particle Metrology and Nanoassembly

Figure 1: Maximum entropy fit to SANS data for annealed

MgO aerogel.

Data were analyzed using the Unified Model of

Beaucage and the maximum entropy method (see

Figure 1). The scale of the finest structural features

increases with increasing cation size for the annealed

product. Analysis indicates the absence of mass fractal

structures but the presence of surface fractal-like

objects. A broad correlation peak in the data for

heat-treated Mg and Ca oxides gives evidence for

some local ordering of the nanocrystals. This data

will help provide a more complete understanding of

the structural development in this complex and

technologically important system.

Figure 2: Schematic diagram of capillary flow cell.

A capillary flow-cell (Figure 2) was developed and

commissioned for the ultra-small-angle x-ray scattering

(USAXS) instrument on the UNICAT beam line at the

Advanced Photon Source. This new capability will

permit in situ investigations of complex multiphase

particulate systems under controlled flow conditions.

Initial applications include the dispersion of single-wall

carbon nanotubes in collaboration with Rice University

and depletion effects in binary colloidal suspensions.

Contributors and Collaborators

A. Allen, L. Lum (Ceramics Division, NIST);

D. Ho (NIST Center for Neutron Research);

K. Klabunde (Kansas State University); M. Pasquali

(Rice University); P. Jemian (University of Illinois)
27

Nanofabrication and Processing

Novel structures and devices can be formed

through template electrodeposition. The ultimate

pattern resolution is determined by the size and

packing of molecules that comprise the template

and their ability to inhibit or catalyze various

electrochemical reactions. In the past year, the

effect of molecular functionality on the metal

deposition process has been explored.

Thomas P. Moffat and Michael J. Fasolka

Over the last decade, electrochemical processing

 has been undergoing a renaissance with the

fabrication of new materials and novel microstructures.

The development of new measurement techniques and

metrological tools for studying controlled growth at

fine length scales is the primary objective of this effort.

2. The role of molecular functionality of the surfactant

and robust design rules; and

3. The anisotropy induced in the electrocrystallization

reaction rate for a given surfactant.

As an example, an alkanethiol monolayer film can

either block or accelerate metal deposition depending

on the molecular functionality of its terminal group.

A dynamic range spanning several orders of magnitude

is possible depending on the system in question (Figures

1 and 2). Based on these measurements, selective metal

deposition may be obtained by patterning a substrate

with the appropriate molecule.

Nanostructure Fabrication Processes:

Patterned Electrodeposition by Surfactant-Mediated Growth

Figure 1: Influence of small changes in molecular structure,

i.e., SO3

– vs. CH3, on the rate of copper deposition.

Figure 3: Spatially patterned monolayer films used to control

nucleation and anisotropic growth of copper crystals.

Through contact printing, higher resolution patterning

is possible, along with some interesting opportunities for

high-throughput combinatorial research. By varying the

surface chemistry, growth of isotropic or faceted crystals

has been shown to be possible (Figure 3).

Contributors and Collaborators

D. Josell, J. Mallett, W.F. Egelhoff (Metallurgy

Division, NIST); M. Walker, L. Richter (CSTL, NIST)

Figure 2: Copper deposition on an alknethiol derivatized gold

substrate only occurs in regions bearing –SO3

– terminated

molecules.

The three key metrology issues addressed are:

1. The rate differentiation accessible via surfactant

mediated metal film growth;
28

Nanofabrication and Processing

The microelectronics community uses

electrodeposition to produce solderable surface

finishes, magnetic recording media, and copper

interconnections in printed circuit boards and

integrated circuits. These films tend to develop

sizable mechanical stresses that can lead to loss of

adhesion and the generation of bulk and surface

defects. This project focuses on the measurement

of these stresses which should enable the

development of effective mitigation strategies.

Gery R. Stafford and Ole Kongstein

Electrodeposited films tend to develop sizable

mechanical stresses during deposition due to the

nucleation and growth process or solution additives and

alloying elements. We have established an optical bench

dedicated to the in situ measurement of growth and

residual stress during electrodeposition using the wafer

curvature method. In one approach, a substrate of

borosilicate glass is evaporated with 250 nm of gold.

The force exerted on the cantilever by the electrodeposit

causes curvature of the cantilever, which is monitored

during electrodeposition. Forces on the order of

0.03 N/m can be resolved during film deposition.

negative deposition potentials. As the deposit thickens,

the average film stress decreases and becomes

compressive in deposits formed at small deposition

overpotentials. In the physical vapor deposition literature,

this compressive stress has been attributed to the

non-equilibrium concentration of mobile ad-atoms on

the surface that are driven into the grain boundaries.

Nanostructure Fabrication Processes:

Thin Film Stress Measurements

Figure 1: Average film stress during copper deposition.

Figure 1 shows the average in-plane stress associated

with the deposition of copper from an additive-free sulfate

electrolyte. The rapid rise in tensile stress (within the

first 20 nm) and its dependence on deposition potential

are consistent with nuclei coalescence and grain boundary

formation. The highest tensile stresses are associated

with high nucleation densities which are obtained at more

Figure 2: Force/width exerted on the cantilever during the

electrochemical processing of Sn on Cu.

We have also examined the force exerted onto a copper

cantilever electrode during the deposition of matte tin (Sn),

Figure 2. This is a particularly important system since

the growth of tin whiskers, known to produce electrical

short circuits and device failure, has been attributed to

both the residual stress in the electrodeposit as well as

that generated from intermetallic formation at the Sn-Cu

interface. The force curves show the following features:

a tensile to compressive transition during deposition, a

significant tensile relaxation when plating is discontinued,

the development of tensile stress while the deposit is at

open circuit, and a residual tensile stress after the deposit

is electrochemically dissolved. The two latter features

are attributed to the formation of the Cu6Sn5 intermetallic

(IMC) at the Sn-Cu interface. A tensile stress is generated

since the IMC has approximately 6 % smaller volume than

a rule of mixture combination of the Sn and Cu reactants.

Calculating the IMC thickness from the difference in Sn

deposited and stripped, a nominal stress in the intermetallic

was estimated to be 1.2 GPa after only one hour. Future

work will focus on determining to what degree this

increases the compressive stress in the Sn electrodeposit.

Contributors and Collaborators

W. Boettinger, U. Bertocci (Metallurgy Division, NIST)
29

Nanofabrication and Processing

Wet nanomanufacturing is the generation of

novel nanostructures and the control of chemical

reactions (and signals) in a fluid environment;

this requires effective techniques and efficient

material measurements. Therefore, we aim to

develop sophisticated fluid-handling devices for

directing material assembly, controlling material

transport, and measuring material properties.

Steven D. Hudson

Flow control is essential for fluid measurement and

manufacturing applications. The type and strength of

flow are often crucial for producing the desired structure

and properties when assembling advanced materials. Using

recent advances in microfluidic technology, we have

developed a miniature tool without moving parts that

mimics the function of a four-roll mill, a rheological and

processing instrument.[1] Several microchannels converge

to the measurement zone, where micro-particle-image

velocimetry was used to map the flow field. By adjusting

the relative flow rates, the full range of planar linear flows

could be produced. This includes simple shear, which

is inaccessible in the four-roll mill.

Wet Nanomanufacturing

Figure 1: Carbon nanotube clusters suspended in the microfluidic

trap in extensional flow in the horizontal direction. The cluster at

right has fractured from the main one. Also, an individual tube

that has broken from the cluster is visible at the far left (arrow).

Individual tubes have also been trapped and examined in flow.

Most importantly, this new device works as a trap,

so that particles and other objects can be examined in

flow. Using this and related devices, clusters of carbon

nanotubes suspended in fluids have been examined

(Figure 1). In addition, extension and alignment of

individual wormlike micelles has been measured as a

function of flow strength and duration.

To achieve certain flow characteristics for particular

measurement applications, other microchannel geometries

have been and are being developed. Specifically, a

device for measuring cell and tissue viability, and

mechanical response, is being assembled. Also, a new

instrument system for measuring interfacial tension

has been developed.

Although microchannels are effective for these

important functions, reaching a smaller scale efficiently,

requires a new approach. Miniaturization towards

nanochannels is usually not practical, because it

necessitates very high pressures. At these smaller

scales, membranes mediated by pores (as found in

living systems) are likely to be efficient means to

control the transport of material in metrological and

nanomanufacturing processes.

Figure 2: Molecular model of the artificial membrane pore

viewed from: a) the side, b) top, and c) in cross section.

One such membrane pore (Figure 2) assembled

by supramolecular chemistry has been characterized

recently.[2] Determination of Fourier components

(amplitude and phase) by transmission electron

microscopy demonstrated that the supramolecular

assemblies are tubular, with an inner diameter of 1.4 nm.

Proton conduction through these channels has been

measured to be comparable to the transmembrane

protein channel gramacidin. Directed assembly of

other artificial transmembrane channels will be explored.

References

1. Hudson, et al., Applied Physics Letters 85, (2004).

2. Percec, et al., Nature, in press (2004).

Contributors and Collaborators

F. Phelan Jr., K. Migler, P. Start, P. Stone, J. Taboas,

E. Hobbie, E. Amis, J. Cabral, K. Beers, J. Douglas,

J. Pathak (Polymers Division, NIST); J. Kasianowicz

(Biotechnology Division, NIST); V. Percec, D. Discher

(University of Pennsylvania); R. Tuan (NIH)
30

Second Joint Workshop on Measurement Issues in Single-Wall

Carbon Nanotubes: Purity and Dispersion, Part II

Presentations

There were two Keynote Presentations. The first

was given by Dr. Robert Haddon, from the University of

California at Riverside, who presented the latest findings

regarding the use of Near IR Spectroscopy (NIR) as a

primary means of assigning a quantitative value to the

purity of a SWCNT-containing sample. Significant

progress has been made in the use of this technique since

it was discussed at the first workshop. There was general

agreement that NIR may be a viable technique to quantify

purity, but there are several questions remaining, including

affects of tube diameter and type of processing.

The second Keynote Address was given by

Mr. James Von Ehr, the founder and president of Zyvex

Corporation, who focused on the potential commercial

applications for carbon nanotubes in a number of different

areas. He called attention to the need for measurement

techniques that would lead to improved qualification

procedures for nanotubes from a given supplier.

The remainder of the first day was devoted to a

number of plenary presentations on the topic of purity

measurement, followed by breakout sessions whose goal

was to identify the critical measurement issues relative to

the determination of nanotube purity. A poster session

with 25 posters was held in the evening to allow workshop

participants to present their latest findings and to hold

informal discussions with their colleagues.

The primary topic on the second day of the workshop

was the measurement of nanotube dispersion. There were

also several presentations on the characterization of isolated

nanotubes. The end of the second day consisted of

breakout sessions devoted to dispersion measurements.

 The following sections provide some details of the

important issues relative to measurement of purity and

dispersion as discussed during the meeting.

Purity

The purity of single-wall carbon nanotubes was

loosely defined by the attendees at the first workshop

as the quantity of SWCNTs relative to other carbon-like

materials present (amorphous, graphitic, and C60

carbons) as well as metal impurities. The point was

made however that not all producers or users employed

this definition in a way that allows for a quantitative

assessment of the quality of a sample. A number of

measurement techniques used for purity determination

were discussed with the general consensus that no

single technique can describe the quality of a sample

Nanofabrication and Processing

The 2nd Joint Workshop on Measurement Issues in

Single-Wall Carbon Nanotubes, organized by the

National Aeronautics and Space Administration,

Lyndon B. Johnson Space Center (NASA-JSC) and

the National Institute of Standards and Technology

(NIST), was held January 26–28, 2005, at NIST

in Gaithersburg, MD. In attendance were over

80 participants, representing private corporations,

universities, and government laboratories. The

primary purpose of the workshop was to bring

together technical and business leaders in the

field of single-wall carbon nanotubes (SWCNTs)

to discuss measurement priorities and aid in the

development of measurement protocols. The primary

output of the meeting will be “NIST Recommended

Practice Guides,” authored by workshop participants

and edited and published by NIST, for use by

scientists and engineers involved in R&D,

processing, and the production of nanotube

containing products. These “Practice Guides”

will contain measurement protocols that will help

harmonize sample preparation, measurement

procedures, data analysis, and reporting among the

nanotube manufacturers, researchers and end users.

I

t was decided to revisit the topics of purity and

 dispersion, which were the subjects of the first

NASA/NIST workshop held in May 2003. While progress

in these measurements has been made, improvements are

still needed to accurately measure and describe the quality

of nanotube-containing materials and the dispersion

of nanotubes in liquids or polymers, both of which are

considered crucial for the continued growth of applications

incorporating SWCNTs. The organizers recognized that

there remains considerable confusion and ambiguity

regarding which techniques to use for a particular purpose

and the relative accuracy which one should expect to

achieve. Significant differences in both methodology and

interpretation continue to exist from one measurement

laboratory to another. For this reason, comparison

and specification of the quality of SWCNT materials is

extremely difficult, as noted in Nature, 16th Dec. 2004.

To address these challenges, the organizing committee

invited 23 speakers and developed an agenda that

encouraged active participation from attendees. Breakout

sessions addressing both workshop topics were held to

foster open discussion and to invite consensus regarding

best techniques and measurement methods. A half-day

open discussion led to a consensus on those measurements

for which protocols were most urgently needed.
31

of nanotubes. After much discussion it was agreed

that the most extensively utilized techniques are

thermogravimetric analysis (TGA), scanning electron

microscopy (SEM), transmission electron microscopy

(TEM), Raman spectroscopy, and near infrared

spectroscopy. The need for rapid, inexpensive

measurement methods was emphasized.

Both TEM and SEM are used extensively for

qualitative analysis of a sample containing SWCNTs.

There was general accord that a TEM image demonstrating

the existence of a significant quantity of SWCNTs is

an important measure of the quality of the material.

For quantitative estimation, a combination of TGA,

Raman, NIR, and ICP methods was recommended.

Dispersion

Dispersion was divided into two categories,

macrodispersion, defined as the distribution of nanotube

bundles, and nanodispersion, the splitting of the bundles

into individual tubes. In macrodispersion the primary issue

is the agglomeration of SWCNTs in solvents or polymers,

while in nanodispersion the focus is on eliminating

SWCNT ropes. The question of dispersion stability

over time was also viewed as important.

It was agreed that it is critical to have a consistent

sample preparation for all the dispersion characterization

methods. The technique of choice to determine the

degree of macrodispersion appears to be optical

microscopy. However, there is lack of agreement

on what constitutes good versus poor dispersion.

It was suggested that Raman mapping techniques,

SEM, and scanned probe microscopy (SPM) may be

useful complements to optical microscopy. Small angle

scattering (neutron and X-ray) was put forward as a

possible fundamental method to quantify dispersion.

Conclusions

The final session of the workshop was devoted to

presentations of the synopses of each of the breakout

sessions on the topics of purity and dispersion, and

a general discussion and debate regarding priority

needs for measurements. There was consensus that

protocols for measurement techniques would be

valuable even if they are incomplete.

On the topic of purity, the strengths, limitations,

and research needs for a number of measurement

techniques were discussed. A matrix showing techniques

on one axis and the item measured on the other axis

was used to reach a consensus for the most critical

techniques to be addressed in the “Practice Guide.” It

was eventually agreed that chapters would be written on

four primary procedures, TGA, TEM/SEM/SPM, Raman

spectroscopy, and NIR, and two secondary techniques,

inductively coupled plasma (ICP) and x-ray fluorescence.

Volunteer authors were found for each of the chapters.

The attendees agreed that the topic of dispersion

needed a separate “Practice Guide” from that of purity.

The chapters for this “Practice Guide” were divided

into the topics of macro- and nano-dispersion, and

authors were found to write them. There was also a

general agreement that one of the needs was an agreed

upon terminology, which will be included in the “Practice

Guide.” The chapter on macrodispersion would be

primarily devoted to microscopy procedures, while that

on nanodispersion would include mention of a wide

variety of techniques including small-angle-neutron

and x-ray scattering, atomic force microscopy, etc.

A discussion was held regarding the need for

reference materials. While there was consensus

that such materials would be useful, it was felt that

production of such materials should be delayed until

the protocols for the measurement procedures are

more firmly established. A number of participants also

commented that inter-laboratory tests could be quite

useful in establishing laboratory-to-laboratory

correlations on measurements.

Finally, the question was raised regarding the

need for future workshops of this kind. There was a

general sense that future workshops would be valuable,

but there was not consensus on the particular topic.

However, nanotube dimension measurements and

determination of chirality both received strong support.

Nanofabrication and Processing

Figure 1: TEM image of a SWCNT rope observed at NIST.

The presence of impurities, mixtures of single and multi-walled

nanotubes, defects, and tube bundling, coupled with the ultra-small

dimensions, continue to complicate the characterization of these

unique materials.
32

Nanofabrication and Processing

Extraordinary Transport Properties of Nanotube/Polymer

Nanocomposites

Figure 1: Optical microscopy image of 1 % by volume MWNT/PP

nanocomposite (obtained using a 100x objective) demonstrates

good dispersion of the MWNT and reveals a polydispersity in

nanotube length and shape. The MWNT volume fraction in this

figure equals φ = 0.01, which is close to the geometrical percolation

concentration where the CNT network first forms and where the

conductivity and stiffness of the nanocomposite increases by

orders of magnitude (see Figure 2).

the polymer matrix creates additional contributions to

nanocomposite viscoelasticity that can have a radical

effect on the processing characteristics of these materials.

In Figure 2, we characterize the large changes

in viscoelasticity and conductivity for which

polymer composites containing CNT are well known.

Simultaneous measurements of σ and the shear moduli

(G ́, G ́ ́) characterize the elastic and viscous properties

of our composites. G ́ can be thought of as a measure

of “stiffness” and G ́ ́ provides a measurement of

viscous resistance to deformation. The ratio (G ́/G ́ ́)

or “loss tangent” (tan δ ), is a measure of the composite

“firmness,” and we compare this basic quantity to σ.

We observe that both (G ́/G ́ ́) and σ increase with

φ and that this variation becomes rapid for MWNT

volume fraction φ in the range from 0.0025 to 0.01.

We see that adding MWNT to the PP matrix increases

the conductivity by an impressive seven orders of

magnitude as a percolating network structure forms.

G ́ and G ́ ́ become frequency independent as φ is

varied through the “gelation concentration,” φc ≈ 0.01.

In order to manufacture MWNT nanocomposites

into usable shapes, we must understand how the

network structure acts to influence their processing

behavior. The linear rheological and electrical transport

properties (Figure 2) are strongly altered by flow, as

There has been intense interest in composites of

polymers and carbon nanotubes (CNT) because

of the large transport property (conductivity,

elasticity, viscosity, thermal conductivity) changes

exhibited by these additives for relative low

CNT concentrations (≈ 1 % volume fraction).

NIST’s experience in the area of dielectric and

rheological measurement, in conjunction with

expertise in modeling, puts it in a unique position

to lead the development of new processing

concepts required by industry to utilize this

important new class of materials.

Kalman B. Migler and Jack F. Douglas

The combination of extended shape, rigidity and

deformability allows carbon nanotubes (CNT) to

be mechanically dispersed in polymer matrices in the

form of disordered network structures exhibiting a

gel-like rheology. Our measurements on representative

network-forming multi-wall carbon nanotube (MWNT)

dispersions in polypropylene (PP) indicate that these

materials exhibit extraordinary flow-induced property

changes. Specifically, electrical conductivity σ and

steady shear viscosity η both decrease strongly with

increasing shear rate γ& , and these nanocomposites

exhibit impressively large and negative normal stress

differences, a rarely reported phenomenon in

soft condensed matter. We illustrate the practical

implications of these non-linear transport properties

by showing that MWNTs eliminate die swell in our

nanocomposites, an effect crucial for their processing.

The strong interest in CNT “nanocomposites”

stems from their ability to affect thermal, electrical and

rheological properties for relatively small concentrations

of this type of additive. These additives have found

manufacturing applications in electrostatic painting,

protective coatings for electronic components, and

flammability reduction. Utilization of CNT for

more complex applications, however, requires an

understanding of how processing conditions (mixing,

molding, extrusion) influence nanocomposite properties.

Despite the high elastic modulus of CNT, their small

cross-sectional dimensions and large aspect ratio allows

them to bend substantially in response to inter-tube

interactions under processing conditions. This bending

leads to the formation of a disordered “web-like” structure

(see Figure 1) of substantial mechanical integrity.

The presence of a nanotube network interpenetrating
33

Nanofabrication and Processing

Figure 3 indicates. Notably, both the conductivity

and the viscosity η(γ& ) exhibit a strong thinning.

The viscosity decreases over the full range of shear

explored here, whereas the conductivity shows a

plateau region at low shear. Moreover, a positive

normal force ∆N is observed in our nanocomposite for

φ < φc , where the matrix dominates the rheological

response (Figure 3), but ∆N becomes large and

negative for φ ≥ φc , compensating the large ∆N

exhibited by the matrix polymer. (A negative ∆N in

nanotube dispersions was reported by Lin–Gibson,

et al.) This has significant processing consequences.

Figure 2: Characterization of conductivity and viscolelasticity

of MWNT/PP nanocomposites (φ = 0.025; T = 200 °C).

Inset: Shear modulus as a function of frequency for a range

of nanotube concentrations.

Figure 3: Normal stress measurements showing slightly positive

normal stress for pure PP and increasingly negative normal

stress as the MWNT fraction increases. Inset: Conductivity and

viscosity as a function of shear rate for (φ = 0.025; T = 200 °C).

Figure 4: Comparison of PP extrudate with (A) and without (B)

added nanotubes. The red dashed lines correspond to the die size.

Since the extrusion of the nanocomposite is a basic

processing operation for which normal forces are

known to be important, we extruded a nanocomposite

sample (φ = 0.025) and found that the cross-section

actually shrinks upon extrusion (Figure 4). This

striking effect is contrasted with the extrusion of pure

PP where a nearly 6-fold increase in cross-sectional

area is observed. Evidently, the CNT change the

qualitative nature of the polymer flow.

The suppression of die swell of extruded polymers

by adding a relatively small amount of MWNT (φ ≈ 0.01)

offers a powerful tool for controlling dimensional

characteristics and surface distortion in manufacturing

composites. Our observations of strongly non-linear

rheology under flow (shear thinning and large, negative

normal stresses) imply that these fluids should exhibit

other “anomalous” flow characteristics (e.g., droplet

distortion and thread break-up) that are quite unlike

Newtonian fluids. Understanding these flow

characteristics is crucial for their processing.

For More Information on this Topic

S. Kharchenko, J. Obrzut, E. Hobbie (Polymers

Division, NIST)

S. Lin–Gibson, J.A. Pathak, E.A. Grulke, H. Wang,

and E.K. Hobbie, “Elastic Flow Instability in Nanotube

Suspensions,” Physical Review Letters 92, 048302-(1-4)

(2004).

S.B. Kharchenko, J.F. Douglas, J. Obrzut,

E.A. Grulke, and K.B. Migler, “Extraordinary Flow

Characteristics of Nanotube-Filled Polymer Materials,”

Nature Materials, in press.
34

Applications of Carbon Nanotubes:

Carbon Nanotubes and Nanotube Contacts

A critical requirement for developing carbon

nanotube based electronics is determining the

mechanical and electrical characteristics of

the connection between the carbon nanotube

and its electrode. On this scale (nanometers),

the properties of both the nanotube and

the contact are not scaleable from larger

measurements. To address this issue we are

exploring a technique commonly used to

manipulate the nanotubes and attach them

to substrates inside the scanning electron

microscope. We are subsequently developing

the techniques to measure the small electrical

currents and test the small mechanical strength

associated with the contacts and nanotubes.

Paul Rice

We are developing techniques to measure the

mechanical and electrical properties of carbon

nanotube-based devices and also to image the

nanometer-scale structure within the nanotube and

their electrical contact. Shown in Figure 1 is a

test device that we have fabricated to measure the

electrical characteristics of an individual multiwalled

carbon nanotube. The nanotube was attached,

or welded, to the device in the scanning electron

microscope (SEM) using an accepted technique called

electron beam deposition (EBD). In this example,

a single tube extends from one electrode to another.

Understanding the mechanical properties of the weld

requires visualizing its structure on the atomic scale if

possible. Using high-resolution microscopy techniques

available within the division, we have seen some

interesting new structures of the weld. Previously,

it was assumed that the weld was a uniform material

composed of amorphous carbon. However, we have

seen, using atomic force microscopy (AFM) as well

as transmission electron microscopy (TEM), spurious

deposits of carbon far outside the weld. Figure 2

shows a nanotube welded to a chromium film.

The residual carbon is seen as a surface texture that

covers almost everything including the nanotube.

Figure 1: SEM image of carbon nanotube test device for

electrical measurements. The nanotube extends across a 2 μm

gap. A second accidental tube is hanging on the side and is not

connected to the electrodes.

Figure 2: AFM image of a multiwalled carbon nanotube welded

to a chromium film. The orange peel texture is residual carbon

left behind from the weld process.

This work is beginning to shed some light on the

properties and structure of these very small devices.

A paper has been submitted entitled, “Electron Beam

Deposition Welding: A Practical Application to Building

Carbon Nanotube Devices,” by P. Rice, R.H. Geiss,

S.E. Russek, A. Hartman and D. Finch, to the Journal

of Vacuum Science and Technology B. Further work is

planned to measure contact resistance within the weld

and resistance changes due to distortions caused by the

weld process.

Demonstrating the need for better standards for

nanotube device characterization, a new standards

committee was recently formed by IEEE, on which NIST

currently serves as a contributing member. Furthermore,

presentations have been given to the American Vacuum

Society, NASA Johnson Space Center, and the engineering

department of the University of Colorado.

Contributors and Collaborators

R. Geiss (Materials Reliability Division, NIST);

S.E. Russek, P. Kabos (EEEL, NIST); D. Finch,

A.B. Hartman (University of Colorado)

Nanofabrication and Processing
35

Nanofabrication and Processing

With the recent excitement about carbon

nanotubes and their biological applications,

preliminary studies are underway to determine the

biocompatibility of nanotubes with cell cultures

using our vascular smooth-muscle cell line. The

response of these cells will help us understand the

effects of cell proliferation or degradation due

to direct contact with nanotube mats or clusters.

Paul Rice and Tammy Oreskovic

Carbon nanotubes (CNTs) have great potential for

nanometer scale electronics, superior strength

composites, biological implants, and many other

applications where a well-organized nanometer scale

material is needed. One possible application is using

nanotubes as scaffold materials to support the growth

of transplanted cells and establish proper orientation to

grow artificial tissue. NASA has recently demonstrated

growing retinal cells on nanotube mats. Other possible

applications include sensors and probes for miniature

biological devices, and electrodes for detecting

biomolecules in solutions. However, many issues

still remain in assessing the biocompatibility of these

nanomaterial biosystems for in vivo applications.

In FY04, we explored the viability and proliferation

of cells in contact with carbon nanotubes and

dispersion techniques for compatible surfactants in

cellular environments. In preliminary experiments,

smooth muscle cells were exposed to both entangled

mats and suspensions of multi-walled CNTs by use of

surfactants for dispersion (Figure 1). Results of the

proliferation assay indicate that there is a reduction in

growth and metabolic activity for cells grown directly

on the nanotubes as compared to the controls. These

results indicate that cell attachment may not be as

strong in regions of high CNT density. However, if

the nanotubes are coated with a biologically compatible

surfactant and suspended in media, there appears

to be little effect when compared to the controls.

Figure 2 shows preliminary results of an Alamar

blue proliferation assay.

In FY05, we will continue to explore the

interactions of structure and the effects of clumping

of CNTs on cell growth and orientation. Other possible

directions may include surface modification to promote

cell adhesion and growth, tomography, and size

distribution of CNTs.

Contributors and Collaborators

Dr. N. Varaksa contributed the work on the

surfactant chemistry; Dr. E. Gruelky (University of

Kentucky) supplied carbon nanotubes.

Applications of Carbon Nanotubes:

Cell Viability in Contact with Carbon Nanotubes

Figure 1: Vascular smooth muscle cell growing on a cluster

of multiwalled carbon nanotubes on a glass substrate.

Figure 2: Alamar blue assay, test for cell growth and

proliferation. As the cells grow and divide they metabolize

the Alamar blue compound, changing the medium in which the

cells are growing from a blue color to clear.
36

Instruments for in-vivo recording of neural activity

are critical for ongoing and future research aimed

at Alzheimer’s, Parkinson’s, epilepsy, stroke, and

spinal cord injuries. In addition, the development

of a human-brain-machine interface (HBMI) relies

on improved recording and processing of neuronal

signals. Future recording electrodes must be

small, stable, biocompatible, and robust. More

rugged test procedures are also needed for

evaluating and qualifying new electrode materials.

Stephanie A. Hooker and Dudley Finch

New tools are needed to better image and measure

signal transfer inside live cells. One conventional

approach to electrical measurements in cellular materials

involves a two-electrode glass micropipette that clamps

the cell membrane. The discovery of this device,

referred to as a patch clamp, in 1972 had widespread

impact, leading to a Nobel Prize in 1991. However, the

patch clamp is too large for many of today’s desired

measurements in neurobiology, due to the extent of

physical damage caused during its insertion and use.

Recently, silicon-based MEMS technology has been

explored as a method to produce smaller probes for

neuronal research. These devices typically consist of a

silicon shank (several hundred micrometers long) with

an array of microelectrode recording sites located along

its surface. In this manner, multiple neurons can be

studied simultaneously with a single insertion point.

While these devices show considerable promise,

many biologists continue to employ individual metallic

wires as their primary recording electrodes. These

wires are similar to those used inside the patch clamps

but are inserted directly into the brain. Polymer coatings

are often applied to increase impedance, enable better

handling, and improve biocompatibility. The wires are

typically tungsten or stainless steel with diameters on

the order of 50–100 microns. To date, few studies have

attempted to optimize the wire material, the coating,

or the insertion technique (applied force, speed, etc.).

In collaboration with the University of Colorado’s

Health Sciences Center and the Departments of

Chemistry, Electrical Engineering, and Mechanical

Engineering at the University of Colorado at Boulder,

we are developing measurements to help improve and

optimize in-vivo probes. In FY04, we completed

preliminary studies of wires (25 μm in diameter) coated

with thin (~ 60 nm) layers of aluminum oxide, Al2O3.

Atomic layer deposition (ALD) was used to precisely

Applications of Carbon Nanotubes:

Electrochemical Characterization of In-Vivo Neuronal Probes

control coating thickness, and seven different wires were

compared to determine metal effects on performance.

Figure 1: Electrochemical impedance of ALD-coated microwires

in Ringer’s solution as a function of applied voltage at 100 Hz.

A two-electrode configuration was used for testing

in a Ringer’s buffer solution. Several procedural

variables were evaluated, including the type and size

of the reference wire, the solution temperature and pH,

and the electrode placement. Impedance was measured

as a function of frequency, voltage (Figure 1), and time.

The latter indicates the stability and reliability during

extended recordings, a key requirement for long-term

studies. Stability measurements will continue during

the upcoming months in order to ensure that the ALD

coating is not degraded either chemically (by the

solution) or electrically (by the measurement itself).

However, it should be noted that 25 μm wires are still

too large for subcellular studies. As a result, we plan

to evaluate carbon nanotube (CNT) probes in FY05.

CNT-based AFM probes have already been developed

by other researchers in the Materials Reliability Division

for studying microelectronic films. Moreover, dielectric

coatings have recently been applied to individual tubes

(via ALD) to further enhance signal transfer. If successful

electrochemical measurements can be demonstrated,

CNT based in-vivo probes could have a significant impact

on neuroscience due to their small size (0.1 μm or less)

and anticipated long-term stability.

Contributors and Collaborators

D. Restrepo, A. Sharp (University of Colorado

Health Sciences Center); R. Artale, K. Gall, S. George,

R. Zane (University of Colorado at Boulder)

Nanofabrication and Processing
37

Organizational Charts

Organizational Charts

Materials Science and Engineering Laboratory

Polymers

E.J. Amis, Chief

C.R. Snyder, Deputy

Metallurgy

C.A. Handwerker, Chief

F.W. Gayle, Deputy

Ceramics

D.L. Kaiser, Chief

R.G. Munro, Deputy

Materials Reliability

T.A. Siewert, Acting Chief

NIST Center for

Neutron Research

P.D. Gallagher, Director

Director

Deputy Director

National Institute of Standards and Technology

Director

Boulder Laboratories

Baldrige National Quality

Program

Director for

Administration

& Chief Financial

Officer

Technology

Services

Advanced

Technology

Program

Manufacturing

Extension

Partnership

Manufacturing

Engineering

Laboratory

Chemical Science

and Technology

Laboratory

Materials Science

and Engineering

Laboratory

Electronics and

Electrical Engineering

Laboratory

Information

Technology

Laboratory

Physics

Laboratory

Building and

Fire Research

Laboratory

L.E. Smith, Director

S.W. Freiman, Deputy Director
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