bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of the Desorbed Ion Current in Bayard–Alpert Gauges
Authors: Pittaway L. G.
Published: July 2002

The modulation characteristics of a Bayard–Alpert gauge have been investigated in the presence of a large residual current of desorbed ions, following exposure of the gauge to oxygen. Having observed an increase in the collector current on modulation, when the gas phase ion current was relatively small, modulation factors were measured for the desorbed ion current and were found to vary in magnitude up to 0.2. A sharp peak, which increased the amplitude of the mean residual current by approximately 30%, was also found in the modulation curve between Vmg=−10 and −35 V. Computed potential distributions and ion trajectories have shown that this peak can be attributed to the focussing action of the electrostatic field on energetic ions desorbed from the modulator. Experimental verification of this hypothesis was obtained by selective cleaning of the grid and modulator using electron bombardment. The presence of such a peak would produce errors in the proposed alternative modes of modulation in which a modulator-to-grid potential of −20 V is used.
Influence of Source Parameters on the Properties of an Ion Beam
Authors: Wittmaack K. , Schulz F.
Published: July 2002

Beam profile measurements have been carried out to study the influence of the length of the ion source outlet, the source pressure, and the source magnetic field on the properties of an ion beam. From a variation of the outlet length conditions can be deduced for optimum design with respect to gas efficiency and profile shape. The profile width is found to decrease with increasing source pressure and decreasing magnetic field. This effect is attributed to a corresponding change in the energy distribution of the ions. Profile distortions occurring at high source pressure are likely to be due to ion scattering in the extraction region.
Catalysis and surfaces
Authors: Fischer T. E.
Published: July 2002

Modern developments in the field of catalysis proceed in various directions to which surface science is directly relevant. Alloy catalysts possess interesting properties. The addition of as little as 5% copper to a nickel catalyst, for example, changes the activity for various reactions by several orders of magnitude and completely modifies the selectivity of the catalyst. Such phenomena raise the question of surface composition and electronic structure of alloys and of the degree of localization of chemisorption forces. Most practical catalysts are prepared in the form of highly dispersed metal onto a high surface-area insulator. Both components possess catalytic activity, which leads to the concept of a bifunctional catalyst. Metal catalysts are responsible mostly for hydrogenation, dehydrogenation, and hydrogenolysis of hydrocarbons, while acid sites on insulators are mostly involved in cracking and isomerization of organic molecules. The high dispersion of metal catalysts represents a novel state of matter, the very small particle, whose properties are different from those of a gas, of a conventional solid, or of a liquid. Little is known about the morphology, structure, thermodynamic properties, and alloying behavior of these particles. In addition to the above problems, we discuss two investigations of surfaces and their connection with the problem of catalyst poisoning and the development of a novel fuel cell.
Structural characterization of polycrystalline Cd–Te–In films
Authors: Zapata-Torres M. , Castro-Rodrı́guez R. , Martel A. , Mascarenhas Y. P. , Guevara J. , Melendez-Lira M. , Peña J. L.
Published: July 2002

Polycrystalline Cd–Te–In films have been grown on glass substrates by close-spaced vapor transport combined with a free evaporation technique and the stoichiometric, structural and electrical properties were investigated as functions of In2Te3 concentration added in solid solution into the CdTe structure during In incorporation. Indium was introduced by evaporation during film preparation and the incorporation was controlled by the temperature of the In source. The composition of the films was investigated by Auger electron spectroscopy, showing that, when In concentration increases the Cd concentration decreases they have a similar value (≈22 at. %) at about 750 °C In source temperature. The dark resistivity decreased monotonically four orders of magnitude with the In2Te3 concentration and reached a minimum point. From the structural characterization employed it was shown that the In atoms are incorporated in two ways: (I) for as low-In concentration, the In atoms substitute the Cd atoms, decreasing the resistivity; and (II) for high-In concentration, the In atoms form with the CdTe a solid solution like (CdTe)1−x(In2Te3)x. The x-ray spectra were calculated for In source temperatures of 550 and 750 °C using structure refinement by the Rietveld method and general structure analysis system software. A good agreement between experimental and calculated spectra was found for both temperatures.
Study on the atomic configuration for low-energy electron diffraction analysis on ZrO/W(100)
Authors: Kawata Satoru , Nakane Hideaki , Adachi Hiroshi
Published: July 2002

The ZrO/W(100) surface has remarkably low work function, and shows a peculiar c(4×2) low-energy electron diffraction (LEED) pattern. The I–V (intensity versus voltage) method is adopted to analyze the LEED pattern as widely used. The direction of Zr–O dipole has been expected vertical to the surface, because the vertical dipole most effectively reduces the surface potential. However, the analysis says that atomic arrangement including only the vertical dipole is not good enough for getting the highly reliable I–V curve, thus, horizontal dipole must be considered.
Field emission current cleaning and annealing of microfabricated cold cathodes
Authors: Schwoebel P. R. , Spindt C. A. , Holland C. E. , Panitz J. A.
Published: July 2002

Thermal cleaning and annealing by the extracted field emission current has been used to achieve and maintain stable emission characteristics with microfabricated cold field emission cathodes. Our studies show that the cathode tip surface can be smoothed, recrystallized, and at least partially cleaned of surface adsorbates. The result is a significant decrease in emission current noise and recovery of the initial current–voltage characteristics of the cathode following surface contamination.
Electrically operated hydrogen and oxygen vacuum leaks using ceramic high-temperature ionic conductors
Authors: Schober T. , Meuffels P.
Published: July 2002

Ceramic high-temperature proton conductor tubes (BaZr0.9Y0.1O3−x, CaZr0.9In0.1O3−x and Ba3Ca1.18Nb1.82O9−x) were found to be suited for introducing hydrogen into a vacuum system. Leak rates below 10−8 mbar l/s for the assembly, consisting of an active and an 8YSZ support tube, were achieved. The partial pressure of hydrogen in the vacuum system increased linearly with the electric current J flowing through the proton conductor. The other relevant partial pressures were not affected. Measuring the throughput during operation of the hydrogen source showed that within experimental error the total current is used to transport protons to the cathode (transport number tH≈1). The number of moles of H2 pumped into the system per second is given by J/2F. Thus, the device can be used to precisely introduce high purity H2 under current control, and with a response time of a few seconds only, into the vacuum. Similarly, 8YSZ tubes are suitable for the pumping of high purity O2 into a system with a rate given by J/4F moles of O2/s. Since the amount of H2 or O2 introduced is precisely known, the present devices can be used for pressure calibration when the local effective pumping speed is known, or else to measure pumping speeds or conductances when accurate pressure measurements are available.
Surface segregation of hexagonal boron nitride and its surface properties
Authors: Kim Y. S. , Lee K. S. , Lee J. , Tosa M. , Kasahara A. , Yosihara K.
Published: July 2002

The synthesis of uniform hexagonal boron nitride (h-BN) layer has been successfully achieved by a surface segregation method using a helicon wave plasma enhanced radio frequency magnetron sputtering system followed by in situ annealing in an ultrahigh vacuum. Auger electron spectroscopy and x-ray photoelectron spectroscopy revealed that the surface of codeposited Cu/B/N was covered by the segregated h-BN. Atomic force microscopy and scanning tunnel microscopy indicates that the attractive force on the surface segregated h-BN layer is uniformly distributed to an extent of less than 1 nN and exhibited a good insulating property. This result suggests that the surface segregation of h-BN is an effective method to make a template layer for tribological coating, electric microdevices and nanostructured devices.
GaN ablation etching by simultaneous irradiation with F2 laser and KrF excimer laser
Authors: Akane Toshimitsu , Sugioka Koji , Hammura Kiyotaka , Aoyagi Yoshinobu , Midorikawa Katsumi , Obata Kotaro , Toyoda Koichi , Nomura Shintaro
Published: July 2002

GaN (0001)/c- Al 2 O 3 is etched by simultaneous irradiation with an F2 laser and a KrF excimer laser. The use of an F2 laser in addition to a KrF excimer laser reduces the roughness of the GaN surface compared with the case of KrF irradiation etching. An F2 laser, below the etching threshold, simultaneously irradiated with a KrF excimer laser, decreases the etching rate due to an increase in the absorption coefficient of the sample surface against the KrF excimer laser. A very sharp etching sidewall and flat surface are obtained when the etching depth reaches the Al2O3 substrate.
Characterization of high-K dielectric ZrO2 films annealed by rapid thermal processing
Authors: Hu Yao-Zhi , Tay Sing-Pin
Published: July 2002

In this investigation, two kinds of ZrO2 samples were prepared. The ZrO2 films of about 150 Å by PVD were used for physical characterization and the ultrathin ZrO2 films of about 40 Å by RTCVD were used for electrical characterization of MOS capacitors. The samples were annealed in a rapid thermal processing (RTP) system at temperatures of 400–1050 °C in various gas ambients, including O2, N2, forming gas (H2/Ar), wet H2 (15% H2O in H2), and wet O2 (15% H2O in O2). Spectroscopic ellipsometry (SE) with a two layer BEMA optical model was used to characterize the ZrO2 thickness and evaluate the microstructure. A wet etch rate test of ZrO2 films in 1:100 HF solution using SE indicated two distinct etch rates, with a slower initial rate followed by a faster rate. The measured etch rates are dependent of temperature, indicating 4.85 and 38.9 Å/min at 25 and 45 °C, respectively. The RTP annealing temperature and gas ambients have a significant effect on the ZrO2 film etch rate. Rutherford backscattering spectrometry (RBS) and x-ray photoelectron spectroscopy depth profile were used to characterize the films. Three ZrO2 samples were measured by both cross section transmission electron microscopy and SE, indicating that the thickness difference between two techniques is only 1 Å. A mercury probe was used to characterize the electrical properties of the physical vapor deposition dielectric films. The electrical characterization of ultrathin ZrO2 films show that the gas ambients in postdeposition anneal affect the equivalent oxide thickness (EOT) and leakage current significantly. The lowest EOT achieved in this study is 10.9 Å for the sample spike annealed in N2. The RTP effect on electrical properties of ultrathin ZrO2 was also discussed.
Etching technique for ruthenium with a high etch rate and high selectivity using ozone gas
Authors: Nakahara M. , Tsunekawa S. , Watanabe K. , Arai T. , Yunogami T. , Kuroki K.
Published: July 2002

We have studied the characteristics of ruthenium etching reactions and the etch selectivity of Ru to photoresist in ozone gas. The Ru was etched at a maximum etch rate of 950 nm/min at between 100 and 150  °C by the formation of a volatile product, RuO4. However, the etch rate decreased at temperatures above 150 °C, since the formation of RuO2 on the Ru surface hindered the etching reaction. A comparison between the etching reaction of Ru and that of photoresist revealed that Ru was etched predominantly by ozone, whereas the photoresist was etched predominantly by atomic oxygen. This difference in etching behavior enables us to control the etch selectivity between Ru and photoresist. Below 150 °C, the Ru/photoresist selectivity was higher than 40 due to a small amount of atomic oxygen. Conversely, above 300 °C, the selectivity of photoresist/Ru was higher than 40 due to RuO2 formation. Therefore, a high degree of selectivity was achieved by manipulating the temperature.
Stencil reticle cleaning using an Ar aerosol cleaning technique
Authors: Okada Masashi , Kawata Shintaro , Sonoda Yuzuru
Published: July 2002

Reticle cleaning is one of the important issues in all next-generation lithography (NGL) systems. In this article, an Ar aerosol cleaning technique, which is a cryogenic cleaning technique, is described for cleaning a stencil-type reticle for an electron beam stepper. The cleaning efficiency and the redeposition rate depend on the pressure of the process chamber of cleaning. The Al2O3 particles of average size 0.1 μm on the reticle surface and inside the through-hole pattern were effectively removed. The gas flow conditions for damage-free cleaning were limited by the size of the stencil pattern. In the reticle made of a silicon-on-insulator (SOI) wafer, the thermal distortion of the reticle in the cleaning at low temperature was expected. However, after cleaning, the distortion measurement results did not show residual distortion of the reticle.
Enhancement of the film growth rate by promoting iodine adsorption in the catalyst-enhanced chemical vapor deposition of Cu
Authors: Kwon Oh-Kyum , Lee Hyun-Bae , Kang Sang-Won , Park Hyung-Sang
Published: July 2002

The effect of H2 plasma pretreatment on the growth rate of films in the catalyst-enhanced chemical vapor deposition of Cu is presented. Cu(I) hexafluoroacetylacetonate-vinyltrimethylsilane [Cu(I)(hfac)(vtms)] and ethyl iodide (C2H5I) were used as a Cu precursor and a chemical source of iodine, respectively. Before adsorbing iodine onto the sputtered Cu seed layer, a pretreatment with H2 plasma promoted the adsorption of iodine. In addition, the Cu film growth rate was almost linearly enhanced with the surface concentration of the iodine adatom. The increment of the surface concentration of the iodine adatom was confirmed by secondary ion mass spectroscopy analysis. The iodine adatoms were not buried during the Cu deposition, but most of them continuously floated out to the film surface. Thus, the iodine on the surface of the Cu seed layer retained its catalytic effect until the film deposition finished. As a result, the H2 plasma pretreatment performed on the Cu seed layer prior to adsorbing iodine enhances the Cu film growth rate and improves the film qualities, such as electrical resistivity and surface smoothness, by promoting iodine adsorption.
Current-Induced Gas Evolution from Electron Multipliers
Authors: Kendall B. R. F.
Published: July 2002

Electron multipliers are capable of emitting significant volumes of various gases while they are in operation at low pressures. Errors in ultrahigh-vacuum measurements may result. Experiments are described which show that, in a typical case, most of the evolved gas comes from the dynode and collector surfaces as a result of electron bombardment. Additional gas evolution may occur as a result of dynode resistor heating, if internal resistors are used. It appears that gas may also be released from some kinds of insulators when voltage is applied. Methods of minimizing these effects are discussed.
An Inverted Magnetron Helium Leak Detector
Authors: Barrington A. E. , Herzog R. F. K. , Poschenrieder W. P.
Published: July 2002

Ions produced in the cold-cathode discharge of an inverted magnetron and passing through an aperture in the cathode into an ion collector are separated by the magnetic field according to their mass. Under appropriate conditions of applied potential, magnetic field, electrode geometry, and gas density, a mass spectrometer of this type exhibits high sensitivity and resolution for gases of low atomic mass. It is, therefore, exceptionally well suited for helium leak detection. Simultaneously, it serves as an ionization gauge indicating total pressure. Compared with conventional leak detector mass spectrometers, it has the advantage of operating without a hot filament; it is inexpensive, small, rugged, and bakeable; and the associated electronic circuitry is equally simple. In order to enhance its sensitivity, it can be combined with a selective zeolite pump which does not pump helium but provides a low-background pressure of high stability. A simple leak detection system of this type is described with optimum performance in the pressure range below 10−4 Torr, where leaks as small as 10−13 standard cc/sec of air can be detected.
Small Cryopump with Integral Refrigerator
Authors: Turner F. T. , Hogan W. H.
Published: July 2002

Performance characteristics of a compact, self-contained cryopump are described. Inputs required are electrical power and liquid nitrogen. A chevron-shielded 1000-cm2 cryopanel cooled to below 30 °K by a modified Taconis-cycle refrigerator had a pumping speed of 3200 liter/sec for air at pressures below 5×10−4 Torr. The speed for argon was 2200 liter/sec. Calculations of typical heat loads show that a 1-W refrigerator should be capable of supporting nitrogen-pumping speeds as high as 10000 liter/sec. Pumpdowns on an unbaked, 150-liter-volume stainless steel chamber yielded short-term ultimates of 4×10−9 Torr with use of a 50-liter/sec auxiliary sputter-ion pump for noncondensables. By subliming titanium onto liquid-nitrogen-chilled surfaces, ultimates of ∼2×10−10 Torr were observed.
Pressure Equations for the Residual Gases in an Ultrahigh Vacuum System
Authors: Hobson J. P. , Earnshaw J. W.
Published: July 2002

The conventional first-order linear differential equation for the partial pressures of the residual gases in an ultrahigh vacuum system has been tested experimentally and found to be satisfactory for He, CH4, N2, and Ar but unsatisfactory for H2 and CO. Two simultaneous first-order linear differential equations, based upon a model postulating a surface phase obeying Henry’s Law, are suggested for H2 and CO. The solutions to these simultaneous equations yield greatly improved but not complete agreement with experiment. Qualitative suggestions are made for further improvement of the model. Literature concerning quantitative measurements of H2 and CO in ultrahigh vacuum systems and based upon the conventional pressure equation is reexamined critically in terms of the new system of equations.
Gold Wire Seals for Ultrahigh Vacuum
Authors: Hawrylak Roman A.
Published: July 2002

Advantages of gold as sealing material for ultrahigh vacuum are discussed. A new configuration of unpolarized rotatable uhv flanges, sealed with a gold wire gasket, is described. Use of gold wire for sealing irregularly shaped openings, glass windows, and thin foils in vacuum systems is also discussed.
Design of Thermal Manipulators for Ultrahigh Vacuum
Authors: Crawford C. K.
Published: July 2002

Small, rugged, low-cost thermal manipulators have been developed for use in ultrahigh vacuum. When driven by a simple feedback loop using a thermocouple position sensor, they can provide accurate positioning along with response times of less than one sec. It is shown from thermodynamic considerations, however, that the work output for reasonable input energy is limited by the nature of the working substance, is fundamentally low, and that there is little hope of achieving significant improvement. Thus, the manipulators are useful only in applications where small forces are required, such as scanning a beam, orienting a sample, or moving a shutter.
Hydrogen Impurity Removal from Closed Noble-Gas Discharge Systems
Authors: Sullivan John J. , Buser Rudolf G.
Published: July 2002

The removal of hydrogen, considered as an impurity gas, from a closed, noble-gas (helium) discharge system is studied using the techniques of (1) hydrogen pumping through a heated palladium membrane and (2) hydrogen gettering by a titanium film deposited on a water-cooled stainless steel surface. Mass spectrometric and optical measurements are presented which show the effect of helium background (pressure range 10−9 to 10−1 Torr) on hydrogen-removal rate. Experimental results of hydrogen gettering on titanium agree with theory, and not only support, but extend earlier work of other investigators. Removal of hydrogen by the palladium membrane is about equally effective for the geometry employed. In addition, the dependence of deposition rate and film thickness of titanium on helium background pressure and source temperature are discussed.
Monte Carlo Study of Vacuum Vane Gauge Design Criteria
Authors: Thomas Allan M.
Published: July 2002

The force on a movable vane which covers the exit of a tube is related to the pressure at the tube entrance. This principle can be utilized in the construction of a “vane” gauge. The gauge could become an absolute measuring instrument if the correlation between the force on the vane and the pressure at the tube inlet were known. The Monte Carlo method was used to determine this correlation in the free molecular flow regime for a co-axial vane placed at various distances from the end of the tube. Calculations are made of the ratio of the force on the vane to the force on a hypothetical disk replacing the tube entrance. This study revealed that, for short, thin-walled tubes and for a large vane, the force on the vane is fairly insensitive to the amount of separation between the vane and the tube as long as this separation is less than about one half a tube radius. However, for longer tubes, the force on the vane falls off quite rapidly as the vane is moved away from the tube end. The opposite effect was found for tubes with thicker walls, that is, the force ratio increases as the vane is first moved away from the tube and reaches a maximum which may be greater than twice the original value. The method used here is applicable to other geometries.
Causes and Consequences of Nonuniform Gas Distributions in Vacuum Systems
Authors: Moore Boude C.
Published: July 2002

The term “nonuiform gas distributions” refers to the variation of flux, density, and pressure with position in a vacuum system. Six common causes of nonuniformity are listed. Diffuse reflections cannot always be assumed. An approximate analysis of cylindrical systems is presented, based on iteration of Clausing’s flux patterns for open-ended tubes. The method allows rapid comparison of flux uniformity for alternate geometries. The disturbances in the patterns caused by orifice inlets and by orifice pumps are estimated. Spherical geometries are contrasted with cylindrical; the flux being not only uniform over a sphere, but calculated with greater certainty.
Ultrastable system for rf sputtering with rf-induced substrate bias
Authors: Vossen J. L. , O’Neill J. J.
Published: July 2002

Radio-frequency sputtering with rf-induced substrate bias has been shown to be extremely valuable in tailoring the properties of many thin films. The use of this process has been inhibited by the lack of availability of simple equipment to implement it. We have designed a system which (1) is very rugged and reliable; (2) has no sensitive or critical tuning controls; (3) is insensitive to phase relationships; (4) is insensitive to fluctuations in gas discharge impedance; (5) is extremely stable, reproducible, and repeatable for long periods of time under a variety of sputtering conditions; and (6) can be operated, literally, in ’’push-button’’ fashion.
Automatic stabilization of an electron-probe forming system
Authors: Doran S. , Perkins M. , Stickel W.
Published: July 2002

Our electron-probe forming system for pattern generation is based on the concept of projecting a demagnified image of a physical object on a target. A complex, automatic probe stabilization method was developed, which does not interfere with system operation. The stabilization system consists of five closed-loop control circuits, activated during beam-off periods and a dynamic, correction-function generator to compensate for deflection astigmatism and field curvature. Probe current is stabilized within 5%; resolution is well within the depth-of-focus range over the lifetime of a cathode. The stabilization can be continuously operated automatically over many cathode life spans by supplementing the circuitry and by adding control software.
A pattern generation technique for serial electron-beam microfabrication systems
Authors: Ozdemir F. S. , Buckey C. R. , Wolf E. D.
Published: July 2002

A hybrid electron-beam pattern generation technique is described which utilizes both digital point-by-point high resolution pattern definition and an analog ramp low resolution pattern fill-in. The analog ramp endpoints are set by the digital-to-analog converters and are thereby self-registered to the digital point-by-point exposure. This dual approach to pattern exposure allows tradeoffs to be made in the performance required of the individual components which make up the pattern generator. Examples of these tradeoffs are discussed. An overall system throughput model was developed and applied to a specific system based on this hybrid pattern generator. The results of applying this model to the 0.1–1.0-μm-linewidth range shows that throughput is strongly influenced by line broadening effects such as electron scattering and processing in the 0.4–1.0-μm-line resolution range and that alignment times (mechanical stage and electron beam) become dominant in the 0.4–1.0-μm range.
Comparison of the properties of different materials used as masks for ion-beam etching
Authors: Cantagrel M.
Published: July 2002

The different parameters used to describe the evolution of a step under ion-beam etching are first defined. Then the properties of three different classes of masking materials are compared. It is concluded that the resists are not a useful high-definition mask. Titanium and vanadium etched in an oxygen partial pressure give best results. Carbon is proposed as a third very interesting masking material due to the fact that its etching rate is high when bombarded with oxygen ions but low when bombarded with argon ions. The last part deals with the influence of ion-beam incidence on the effective masking properties. Two examples are given: low periodicity gratings and overetching suppression at the bottom of steep edges.
High-spatial-resolution scanning Auger spectroscopy applied to analysis of X-band diode burnout
Authors: Weisenberger W. H. , Christou A. , Anand Y.
Published: July 2002

Low-noise-figure Schottky-barrier mixer diodes for use at X-band and above have small active areas and are thus susceptible to burnout or degradation from high rf power levels. As part of a program to improve burnout resistance of mixer diodes for a Navy system, metal diffusion couples were studied and diodes were fabricated, burned out, and analyzed. The microspot Auger analysis technique in the Auger-spot mode provided the required submicron identification of the interdiffusion phenomena in the failed regions of the mixer diodes. For cw-failed diodes, interdiffusion between the various diffusion couples found in both Pt–Ti–Mo–Au and Ti–Mo–Au diodes has been identified as the primary failure mode. In the pulsed case the lack of interdiffusion as made evident in the analysis of edge-burned-out sites indicates the existence of an alternate failure mode.
Abstract: Positive photoresist masking properties of high energy, high dose phosphorous-ion implants and their influence on MOS FET device characteristics
Authors: Mayone J. M. , Oleszek G. M. , Spencer O. S.
Published: July 2002

The use of a positive photoresist (PR) as a phosphorus-ion implant mask for defining the source and drain of a MOS FET suffers from outgassing and deformation of the resist when high energy ions (150 keV) and a high dose (5×1015 P+/cm2) are involved. This deformation affects the dose uniformity and MOS FET channel length. Here we compare PR masks with those made up of a baked mixture of photoresist and a thermal free radical (PR+TFR) as suggested by Kluge and Elie.1 During the preimplant bake the thermoplastic deformation of the PR+TFR mask is significantly lower than that of the PR mask, but there is no significant difference between the deformation of the two masks during implantation providing the preimplantation bakes are the same. We have made MOS FET’s with channel length as defined by the mask (Lmask) varying from 0.15 to 1.600 mil(3.8 to 4 μm) and have visually measured Lmask following the preimplantation bake. By measuring the MOS FET characteristics (in the linear region) we can determine the effective channel length and compare this with Lmask over a wide range of values. The deformation of the resist can be reduced by using thinner resist and be made negligible by substituting low temperature vacuum baking (prior to implantation) for the conventional high temperature air bake.
Scattering of helium and deuterium from single−crystal Pt(111) compared from two different laboratories
Authors: Bernasek Steven L. , Somorjai Gabor A. , Merrill Robert P.
Published: July 2002

The angular distrubutions of scattered beams of helium and deuterium from platinum (111) surfaces which are obtained by two different laboratories using different techniques are compared. A basis for quantitative comparison of such inter−laboratory results is proposed.(AIP)
Electron microscope study of electrodeposited Ni films in the 0.1–50 μ range
Authors: Gündiler I. , Murr L. E.
Published: July 2002

Structural changes in the thin film–thick film transition of Ni, electrodeposited onto polycrystalline copper substrates, were observed. Nickel was plated onto electropolished substrates from a Watts bath held at 50 °C at a current density of 1 mA/cm2. The Cu substrates, chemically stripped from the thick Ni deposits, were subsequently electrolytically thinned to prepare transmission electron microscope (TEM) specimens. Scanning electron microscope (SEM) observations were made on the Ni deposits before stripping. Epitaxial growth was observed in deposits of 0.1-μ thickness, with traces of polycrystallinity. Deposits acquired a relatively uniform polycrystalline grain structure at about 5-μ thickness, and only slight increases in grain size were observed with increased thickness above 5 μ.
Ellipsometry: Technique for characterization of surfaces and interfaces in light-transmitting ambients
Authors: Bashara N. M. , Azzam R. M. A.
Published: July 2002

An introduction to ellipsometry is presented. Applications to the characterization of isotropic and anisotropic surfaces and films, structural homogeneity, and spectroscopy are discussed. Seventy references provide a representative documentation of the field.
Research in optical films for the applications of integrated optics
Authors: Tien P. K. , Ballman A. A.
Published: July 2002

Because of the need for thin-film devices in integrated optics, the research of optical films has been greatly expanded in the past few years. We review formation of amorphous optical films by vacuum evaporation, reactive sputtering, solution deposition, and gas-discharge polymerization. We also discuss growth of single-crystal optical films by diffusion, melting, chemical vapor deposition, and liquid phase epitaxy. While most of the films available today are still far from perfect, we hope that this review will stimulate new ideas and new efforts in this important area of research.
Optical waveguides and devices
Authors: Cheo P. K.
Published: July 2002

A variety of practical or potential uses of low-optical-loss waveguides and devices for light modulation, deflection, and switching are reviewed. Emphasis is given to those that most likely will become necessary replacements of the bulk for systems involving signal processing, imaging radar, and optical communications. Both the optical properties and structural characteristics of these waveguides suitable for active and passive device applications will be detailed.
Measurement of Ga and Al in a molecular-beam epitaxy chamber by atomic absorption spectrometry (AAS)
Authors: Kometani T. Y. , Wiegmann W.
Published: July 2002

The feasibility of using atomic absorption spectrometry (AAS) to monitor aluminum and gallium atoms in a molecular beam of a system designed for growing epitaxial layers of GaAs and AlxGa1−xAs was investigated. Results are reported to demonstrate the effectiveness of the method for monitoring the flux emitted from source ovens during molecular-beam epitaxial deposition. Absorption by atoms was found to be directly correlated with the temperature of the oven and vapor pressure of the metal. No chemical interaction of atomic vapors of Ga, Al, and As was detected in the molecular beam. Atomic absorption spectrometry compared favorably with mass spectrometry for monitoring Ga.
Relaxation energies in chemisorption spectroscopy
Authors: Gadzuk J. W.
Published: July 2002

The upward shift in atomic energy levels (or decrease in electron binding energies) which occurs upon sorption of an atom on a metal surface due to polarization of the valence band electrons, is considered. The polarization shift or extra−atomic relaxation energy is treated within the framework established by Hedin, Johansson, and Lundqvist and the results are related to image potential shifts which have been previously discussed in chemisorption theories.
Surface photoelectric effect and surface orbital geometry on silicon (111)
Authors: Rowe J. E. , Christman S. B.
Published: July 2002

Photoelectron energy distributions have been measured as a function of photon angle of incidence, ϑi, in the range 28°?ϑi?80°. A resonance lamp with photon energies of 11.7, 16.8, and 21.2 eV was used with a double−pass cylindrical mirror analyzer. Three different surface orbitals were studied: intrinsic surface states, chemisorption orbitals of Cl, and nonbonding orbitals of implanted Ar. All three types of orbitals exhibited a similar dependence of intensity with ϑi which was approximately the same as the net electric field intensity 〈E2z〉z = 0. This implies that the surface photoeffect for silicon (111) is probably not closely related to the detailed surface bond geometry, but is determined by the optical properties of the silicon.
Introduction to tribology
Authors: Jamison W. E.
Published: July 2002

The science of tribology is the study of the interaction of engineering surfaces. Although the name implies interfacial sliding (tribology derives from the Greek word for rubbing), the discipline considers static contact as well. Lubrication to reduce friction and wear has been intimately involved with the empirical development of machinery through the ages. Tribology, therefore, has been basically a ’’catch-up’’ science; trying to explain physical phenomena which were known phenomenogically for decades. The pervasive concept in all tribology is the elastoplastic interaction at the microscopic irregularities on engineering surfaces. Some of the major advances in tribology in the past ten years have been the definition of engineering surfaces on this microscopic scale and the analysis of the thermo-mechanical situation which develops when such surfaces are slid against each other under load. This paper identifies the important parameters of mechanical surface interactions on both macro and micro scales in dry contact and under elastohydrodynamic lubrication.
Recoil phenomena on water evaporating rapidly
Authors: Hickman Kenneth
Published: July 2002

A body of water is fluid-dynamically stabilized with a vertical temperature gradient by evaporative supercooling of the surface under gradually reduced pressures. Comparative morphology is described of surface ice crystallizing above −5 °C and ice crystallizing below −8 °C. At the lower temperatures, craters are produced by recoil from the rapid emission of vapor generated by latent heat of solidification. The craters, frozen into the surface, present unfamiliar and informative aspects of ice nucleation.
Methanation of CO over Ni catalyst: A theoretical study
Authors: Goddard William A. , Walch Stephen P. , Rappé Anthony K. , Upton Thomas H. , Melius Carl F.
Published: July 2002

Theoretical methods (generalized valence-bond calculations) were used to examine the bond energies and geometries of numerous species chemisorbed onto Ni clusters representing Ni surface. These results were used to obtain thermochemical information and to examine various mechanisms for the methanation of CO over Ni: CO+3H2 →(Ni) CH4+H2O. It is found that chemisorbed formyl radicals (Ni–CHO) lead to a favorably appearing chain reaction that is consistent with current experimental results. In addition, we find a chemisorbed C2 species that may be the catalytically active Cad formed from dissociation of CO.
An upper bound to the outgassing rate of metal surfaces
Authors: Edwards D.
Published: July 2002

An upper bound to the outgassing rate of low-surface-area metal surfaces after an atmospheric exposure is deduced from a recently derived model. The result is Qmax=1.72×10−5/t (Torr l)/(s cm2) where t is in seconds. Comparisons of outgassing data with this estimate are made for (1) various low-surface-area materials, (2) a given surface at elevated temperatures, and (3) a variation in the real pumping speed for a particular surface. Qmax has been found to be an upper bound to the outgassing data under a variation of the above parameters provided that the material is operated at ≲100°C for times between 15 min and 7 days.
Determination of adsorbate bond geometry using photoemission
Authors: Davenport J. W.
Published: July 2002

It has been known for some time that angle-resolved photoemission can give in principle a great deal of information about the valence states of adsorbed species. Recently this technique has been used to determine the orientation of CO on Ni, and Cu and NO on Ni. The reasons for this success are three: (1) a tunable, polarized light source, (2) an energy analyzer which could be positioned arbitrarily with respect to the sample and the light source, and (3) a theory of photoemission which is sufficiently accurate that the variations in intensity with molecular orientation could be predicted. In this paper I discuss the theoretical aspects, and in particular, assess the likelihood that similar experiments can be analyzed for other molecules to yield geometry. Certain results which follow from symmetry are given and multiple scattering calculations on CO and NiCO are compared with data.
LEED structure analysis of a p (2×2) chemisorbed layer of CO on Ti(0001)
Authors: Shih H. D. , Jona F. , Jepsen D. W. , Marcus P. M.
Published: July 2002

Exposure of a clean Ti(0001) surface to CO gas gives rise to the formation of first a p (2×2) and then a 1×1 LEED pattern. An intensity analysis of the p (2×2) phase has been carried out using six integral-order and four fractional-order spectra. Several models involving the CO molecule with axis normal to the surface have been tested with negative results. Fair agreement between observed and calculated intensities has been obtained for models involving C and O atoms (both 1/4 monolayer) in the same plane parallel to the surface and either both in the ’’fcc’’ or both in the ’’hcp’’ threefold symmetrical hollows. The former model is better than the latter, but for neither is the agreement wholly satisfactory. Experience with the N/Ti system suggests that the ’’correct’’ model may involve formation of an underlayer. This model, however, cannot be tested with our computer programs at the present time.
Highly stable single-crystal LaB6 cathode for conventional electron microprobe instruments
Authors: Shimizu R. , Shinike T. , Ichimura S. , Kawaii S. , Tanaka T.
Published: July 2002

The performance of single-crystal LaB6 cathode was examined by measuring the brightness and current stability under the same conditions as for the conventional W hairpin cathode. The LaB6 cathode was mounted in Vogel-type electron gun assembly of an electron probe microanalyser JAX-3 specifically modified for this purpose. The result shows that the present LaB6 cathode provides not only high brightness of 2×105 A/cm2 str. at 20 kV, but also high-current stability better than 1×10−3 Ah−1 in standard operation without any specific aid for current stabilization. Thus an order of magnitude increase in both the brightness and service lifetime can easily be obtained provided that the vacuum of the system is adequate, namely better than 1×10−5 Torr (1.33×10−3 Pa). This substantial improvement of the present single-crystal LaB6 cathode over the conventional W hairpin was also confirmed in a practical way by use in a commercial-type scanning Auger electron microscope, JAMP III.
rf induction technique for sample heating in surface science experiments
Authors: Winters Harold F. , Schlaegel Joe , Horne Don
Published: July 2002

An rf induction technique, which can be used to heat most samples used in surface science experiments, is described in detail. It is shown that the technique (1) can rapidly produce high temperature (2500 K), (2) produces uniform temperature over the surface, (3) produces minimal outgassing, (4) is independent of sample shape, (5) is mechanically simple, (6) is ideal for sequentially heating a number of samples, and (7) is compatible with the types of vacuum systems often used by investigators in the field of surface science. Design and construction techniques are described with special emphasis placed on potential problems.
Helium pumping at 4.2 K by molecular sieve 5A
Authors: Fisher P. W. , Watson J. S.
Published: July 2002

Helium pumping speeds measured for the Excalibur model CVR 1106 cryosorption pump fall into two regimes depending on the feed rate. At feed rates below 6.2×10−6 Torr l s−1 cm−2, pumping speeds decrease with loading from 2.2 l s−1 cm−2 to 0.3 l s−1 cm−2. At feed rates higher than 6.2×10−6 Torr l s−1 cm−2, the speed varies periodically with loading. A typical cycle begins with pumping speeds near 1.7 l s−1 cm−2; speeds decline from this value to about 0.6 Torr l s−1 cm−2 at which time the pump goes through a rapid transition that reverts it back to its original high pumping speed. During the transition, the system reaches presures greater than 10−2 Torr, and rapid boiling occurs in the liquid helium reservoir. At the end of the transition, the system pressure decreases rapidly to the initial low operating pressure, liquid helium boil-off declines, and the pump operates normally for a definite period. The length of each cycle depends on the feed rate.
Reactant supply in reactive ion etching
Authors: Mauer John L. , Logan Joseph S.
Published: July 2002

In reactive ion etching, the etch rate may be reactant limited, so that a measurement of reactant supply is neccessary to understand the details of the etching process. A quantitative determination of reactant supply can be obtained by measuring the total dissociation of the etching gas. In particular, this paper reports the total dissociation of CF4 as a function of input power and pressure in a diode system. A quadrupole mass spectrometer measuring the CF3+ peak indicates the presence of CF4 as well as other molecules containing the (CF3) radical. A transient technique is used to separate the contributions of the other molecules from CF4 so that the total CF4 number density can be calculated. The production of reactant by the dissociation of Cf4 causes etching of silicon and SiO2 on the cathode of the system. Possible reaction sequences of these etching processes are modelled by using the known supply of reactant. The partial pressures of the etching products are calculated and correlated with the etch rates and the rise in total pressure.
Adsorption and decomposition of methanol on aluminum
Authors: Rogers J. W. , White J. M.
Published: July 2002

The adsorption and thermal decomposition of CH3OH on clean polycrystalline Al has been studied using UPS, XPS, and thermal desorption techniques in the temperature range 110–773 K. Molecular adsorption of CH3OH occurs at 110 K; heating leads to a surface intermediate at ∠150 K which persists until 525 K. Beginning at 525 K CH4, CO, CO2, and H2 are evolved and by 773 K the surface is oxidized. The nature of the surface intermediate is discussed.
Particle ejection from ion-bombarded clean and reacted single-crystal surfaces
Authors: Winograd N. , Garrison B. J. , Fleisch T. , Delgass W. N. , Harrison D. E.
Published: July 2002

A model based on a classical dynamical calculation of the impact of a 600-eV Ar+ ion into a single crystal has been developed to the point where it compares quantitatively to a wide variety of experimental observables. Here, we make direct comparisons between experiment and theory for relative sputtering yields, energy and angular distributions of the ejected atoms, and multimer yields. The model is also extended from clean single-crystal surfaces to include adsorbate atoms and molecules. These results are compared to experimental SIMS studies aimed at sorting out the structure-sensitive factors that contribute to the cluster ion yield. In oxygen chemisorption on Ni(100), for example, the O2−/O− yield is four times larger for a c (2×2) coverage than for a p (2×2) coverage, a value also predicted by the calculations. In molecular CO chemisorption, the ejection of CO is found to occur molecularly in both the experiments and in the calculations. In comparison to the calculations, a high value of Ni2CO+/NiCO+ is consistent with a bridge-bonded CO structure at low coverage.
Chemisorption and phase changes on W(100) and Mo(100)
Authors: Estrup Peder J.
Published: July 2002

The surface ’’phases’’ observed by LEED and other techniques in adsorption studies are usually ascribed to pairwise interactions between the adsorbate and the substrate, and between the adsorbed species themselves. However, in the case of chemisorbed hydrogen — and probably other overlayers — on W(100) and Mo(100) the phase changes appear to involve an adsorbate-induced reconstruction of the substrate. The structures are similar to those observed on the clean substrates at low temperture and they are characterized by a periodic lattice distortion whose wave vector depends on the adsorbate density and the temperature. Presumably the driving mechanism involves a lowering of the surface electronic energy and the periodicity may therefore reflect the geometry of the two-dimensional Fermi surface.
Contemporary pseudopotentials—Simple reliability criteria
Authors: Zunger Alex
Published: July 2002

Simple tests are presented that gauge the accuracy of some of the pseudopotentials currently used in the literature to calculate within the density–functional approach the electronic properties of molecules, solids and surfaces. These include the local ’’soft-core’’ and ’’hard-core’’ potentials as well as the nonlocal first principles (’’hard-core’’) potentials. A discussion of common misconceptions regarding pseudopotentials is included.
Design of a metal-seal valve for high radiation use
Authors: Stone Roger R. , Scully Ronald
Published: July 2002

A 457-mm, metal-seal gate valve has recently been developed for the high vacuum, high radiation conditions encountered in the Tokamak Fusion Test Reactor. Air pressure inside an expandable bellows provides the sealing surface by pushing replaceable steel knife edges into an indium ring. The bellows pressure can be increased with every cycle to maintain the seal. After a 2000-cycle test, the valve’s leak rate was 1.8 nTorr l s−1.