bluuebunny/crossref_metadata_2025 huggingface dataset:
The room-temperature oxidation of Cu/Si(100) and Cu/Si(111) interfaces studied by Auger electron spectroscopy, electron energy-loss spectroscopy, and high-resolution electron energy-loss spectroscopy
Authors: Mo/ller Preben J. , He Jian-wei
Published: July 2002

A study by integrated Auger electron spectroscopy, electron energy-loss spectroscopy (EELS), and high-resolution low-energy electron energy loss spectroscopy (HREELS) has been performed on the oxidation of copper silicides, which had been formed by electron beam vapor deposition of Cu onto Si(100) and Si(111) surfaces at 293 K. The splitting of the 92-eV (L2,3VV) silicon Auger intensity peak during increasing copper coverage and with oxidation at 295 K is analyzed in detail. The oxidation process is furthermore investigated by EELS and HREELS through an analysis of the changes in the fine-structure electron energy-loss spectra. An enhanced oxidation due to a catalytic interaction of Cu upon the surface electronic structure is found apparently to be due to an increased production of surface SiO species at the initial stages. No Cu–O bond was detected.
Mechanical high-vacuum pumps with an oil-free swept volume
Authors: Wycliffe H.
Published: July 2002

In both corrosive and clean duties the widely used oil lubricated rotary pump has certain disadvantages. In corrosive applications aggressive vapors and/or abrasive particles tend to contaminate the lubricant of the pump, which shortens its service life, while in clean applications the lubricant may cause contamination of the vacuum process. To overcome these problems a new multistage pump has been developed to work from atmospheric pressure to 0.01 mbar without any lubricant within its pumping chamber. The pump is a multistage positive displacement rotary machine in which a number of intermeshing rotor pairs of different profiles mounted on common shafts are held in correct phase relation without contact by a pair of timing gears. The construction is robust designed for industrial as well as for clean vacuum processes which can benefit by the exclusion of lubricant, sealing, or working fluid from the swept volume of the pump. Handling of condensable vapors or dust laden gas is assisted by gas ballast and versatile orientation of pump mounting. Pump sizes of 80 and 180 m3 h−1 displacement have been developed. The paper explains the reasoning that led to the choice of different mechanisms which have been combined in the pump, its performance and construction.
Increased reliability when pumping reactive gases, due to monitoring of vacuum pump and accessories
Authors: Berges Hanns-Peter
Published: July 2002

Modern standard forepumps are designed for versatile uses. In recent years such applications have increased in importance, for example, in semiconductor production, where reactive gases have to be pumped. In the forepump, these gases are compressed against atmosphere causing not only high pressures, but high temperatures and increased concentrations. This could lead to problems which could make the pump unreliable. The demands made on the vacuum pump, the sealing fluid, and accessories to prevent such problems are described. The design and function of such a forevacuum system is explained, using an example. Monitoring and supervision of the backing system is necessary to increase the reliability. Modular accessories make possible not only optimum adaptation to the different processes, but also central monitoring which can be extended to include automation using a computer. This monitoring system gives warning not only of possible defects, but also of service work that must be carried out. Thus the maintenance work can be effected at a more suitable time, production is not affected, and the operation reliability of the pump system is increased. Even if there is a failure, the charge can usually be completed.
The principle of He enrichment in a counterflow leak detector with a turbomolecular pump with two inlets
Authors: Reich G.
Published: July 2002

The pumping time required to render helium leak detectors operational can be greatly reduced by increasing the He concentration in the gas flow entering the detector. Since this gas flow is composed chiefly of water vapor, a cold trap with liquid nitrogen is a very effective method for concentration. Because the procurement and handling of liquid nitrogen can be difficult, the counterflow principle was proposed and introduced as an alternative many years ago. The tester takes advantage of the fact that the compression ratio of diffusion pumps and turbomolecular pumps for heavy gases is far greater than for light gases. Hence by allowing gas to enter on the forevacuum side it is possible to greatly concentrate light gases such as helium on the high-vacuum side. The sensitivity is then no longer based on the pumping speed of the high-vacuum pump (as with customary leak detectors) but instead on the product obtained by multiplying the compression ratio for He by the pumping speed of the backing pump. As far back as 1967, Becker suggested placing a second high-vacuum pump in the inlet to avoid the relatively long response time arising due to the low pumping speed of the backing pump. Because of the expense entailed, this improvement has not yet been implemented. The problem can be solved at little cost by employing a turbomolecular pump featuring two opposing rotors on a single axle. In this manner one obtains high sensitivity with high pumping speed and no hydrocarbons at the inlet.
Vacuum tightness down to the 10−15 mbar l s−1 range, measured with a spinning rotor viscosity gauge
Authors: Šetina Janez , Zavašnik Rastislav , Nemanič Vinko
Published: July 2002

The pressure rise in small systems (∼10 cm3) evacuated and baked before sealing was measured. The intention was to measure the tightness of glass and ceramic to metal seals, below 10−12 mbar l s−1, that is, below the lowest detectable leak rate of commercial helium leak detectors. Different influences on measurements, like outgassing rate after bakeout, penetration of helium through glass, and environmental conditions like temperature, were evaluated. We determined the lowest pressure rise rate, during a week, including outgassing and all possible leaks, in the 10−15 mbar l s−1 range at total pressure of ∼1.10−6 mbar. The advantages of pressure rise leak detection using the spinning rotor gauge are (1) no gas evolution, (2) no gas pumping, (3) isothermic measurement at 25 °C, and (4) small dead volume and high sensitivity.
Accurate sorption isotherms using a computer-aided microgravimetric method
Authors: Thompson K. A. , Fuller E. L.
Published: July 2002

Sorption isotherms are routinely acquired for surface area and porosity measurements, but often with less detail than desired for accurate determinations, to measure kinetics, or to compare to new theories. More care is needed to reduce errors and to increase the number of acquisition points. The gravimetric method has the versatility to measure mass, pressure, and temperature directly and independently. The method also has direct accountability; that is, not dependent upon previous measurements (compared to the volumetric method). To obtain more detailed sorption isotherms, a high-vacuum microbalance was designed and interfaced with a minicomputer that controlled all aspects of the data acquisition, which includes mass, pressure, and temperature readings, and storage as well as pressure and temperature control (and filling the bath, if required). The system was successfully tested by initially acquiring nitrogen and argon sorption isotherms for a commercially available alumina catalyst using both gases in condensed form for the sample bath. The nitrogen sorption isotherm compared favorably with data acquired volumetrically. Although nitrogen at 77 K has become the favored standard, argon at 88 K would seem to have some advantages, particularly being monoatomic and having no quadrupolar moment. Other comparisons are given, and the merits of the automated high-vacuum microbalance become quite evident when nonroutine, detailed exploratory studies are required.
Practical in-line reactive sputtering
Authors: Johanson Robert G. , Carruthers William G.
Published: July 2002

This paper presents an overview study of oxide and nitride films produced by reactive dc magnetron sputtering of metallic targets in oxygen–argon and nitrogen–argon atmospheres, using production in-line equipment. The metals investigated are tungsten, titanium, tantalum, nickel, and aluminum. Process parameters, such as deposition rate, sputtering pressure, gas partial pressures, and target power, are discussed relative to optical and electrical film properties. System modifications, such as gas manifolding, and process initiation procedures are detailed.
Mass spectrometric gas analysis as a versatile diagnostic on plasma experiments in fusion research
Authors: Poschenrieder W.
Published: July 2002

The use of mass spectrometers on fusion research devices dates back more than two decades. Still, application is mostly restricted to such more trivial tasks as assessment of the residual gas composition, leak detection, and optimization of discharge cleaning procedures. Proper instrumentation provided, however, mass spectrometry can also serve as a powerful diagnostic for the plasma discharge itself. This application is associated with some not so usual rarified gas dynamics. In a sense the plasma can be visualized as a gigantic ion pump. The complexity of the physics involved presents some formidable problems for data interpretation. Nevertheless, many insights into the details of recycling, e.g., plasma pumping, wall adsorption, and outgassing are obtained. The capability of the method to study aspects of impurity transport and retention will also be demonstrated. The utilization of short pulses of a probing gas, a hydrogen isotope or a rare gas for instance, into the established plasma and the analysis of the subsequent response plays a central role in such studies. The consequent application of gas dynamics also affords the determination of mass resolved ion fluxes ‖‖Bt in the plasma edge. The presentation will preferentially focus on results obtained on ASDEX, owing to the specific advantages offered by a divertor experiment.
Practical Langmuir probe measurements in deposition plasmas
Authors: Felts J. , Lopata E.
Published: July 2002

The use of Langmuir probes in deposition plasmas is briefly reviewed. Electron temperature and plasma density of different depositing plasmas were measured as functions of power, pressure, and flow by double floating cylindrical-type electrostatic probes and calculated using Laframboise’s theory (J. G. Laframboise, University of Toronto Institute for Aerospace Studies Report No. 100, 1966). A description of the cylindrical double-floating probes and the electrical configuration is given. The probes are a useful tool for characterizing sputtering and polymer-forming plasmas.
Vacuum chambers in composite material
Authors: Engelmann G. , Genet M. , Wahl W.
Published: July 2002

Vacuum chambers and windows required for colliding beam experiments in elementary particle physics research should be as transparent as possible for the secondary particles produced in the collisions. Until now, very thin wall chambers were made of stainless steel, aluminum alloys, titanium, or beryllium. Beryllium was the best for transparency but by far the most expensive. To provide an alternative method with good transparency at low cost, CERN has developed a new generation of chambers, made of composite materials and intended primarily for the proton–antiproton mode of operation of the Super Proton Synchrotron. These chambers consist of very thin metallic pipes for vacuum, reinforced by a carbon fiber structure for mechanical stability and clad with a second metallic layer to give electromagnetic screening. Chamber elements have been made by industry and tested extensively at CERN. These elements are up to 1.8 m in length with circular cross-section diameters of 50 to 150 mm and have 0.5–1.5 mm thick walls of carbon fiber/epoxy composite. The combined metallic layers have only 70–120 μm total thickness which is sufficient to meet the requirements regarding gas desorption in ultrahigh vacuum and electromagnetic shielding of the collider detector arrays from the circulating bunched beam. The chambers are bakable up to 130 °C, have a global leak rate over a typical 10-m section of less than 1×10−10 mbar l/s and an outgassing rate of about 10−12 mbar l/s cm2. They are almost as transparent as Be chambers but cost only about 15% as much. A set of carbon fiber vacuum chambers was glued together to a total length of 13 m and successfully tested.
Effect of oxygen contamination on the deposition of hydrogenated amorphous silicon films by tetrode radio frequency sputtering
Authors: Gekka Yasuo , Fukuda Tadashi , Yasumura Yoh-ichi , Kezuka Hiroshi , Akimoto Makio
Published: July 2002

Hydrogenated amorphous silicon films were deposited using the tetrode rf sputtering method by changing the hydrogen partial pressure ratio ξ to argon in atomospheric gas H2/Ar, under the following conditions: one is the oxygen contaminated condition and the other is the condition which prevents the oxygen contamination with gas filtration and Ar-plasma cleaning. The effect of oxygen incorporated in the films on the optical and electrical properties of deposited films was studied comparing the properties of the films deposited under both conditions. From the experimental results, we found that (1) in the dependence of the properties of the oxygen contaminated films on ξ, an irreversible phase transition with respect to ξ observed at ξ>10% is a phenomenon which is assisted by oxygen incorporated in the films. (2) The strong infrared absorption at 650 cm−1 observed in the oxygen contaminated films is one of vibration mode of –Si–O–Si–H bonds formed by oxygen incorporated in the films.
Thermodynamic and kinetic parameters of molecular nitrogen adsorption on Fe{111}
Authors: Grunze M. , Strasser G. , Golze M. , Hirschwald W.
Published: July 2002

We describe thermal desorption experiments and their computer simulations together with thermodynamic equilibrium measurements for molecular nitrogen adsorption on an Fe{111} surface. Three distinct nitrogen adsorption states, labeled δ, γ, and α with increasing desorption temperature, are detected and it is found that adsorption into the π-bonded α state occurs via the δ and γ states at low substrate temperatures. The δ state can act as a precursor for the γ state at T <100 K, but at higher temperatures the direct channel from the gas phase into the γ state predominates the adsorption/desorption kinetics. The activation energy of desorption for γ-N2 is found to be ∼10% lower than the isosteric heat of adsorption indicating the possibility of dynamical effects in the desorption process into vacuum. It was also observed that preadsorbed α-N2 increases the heat of adsorption for γ-N2 which is evidence for a mutually attractive interaction between those two states.
Vapor phase transfer at vacuum chromizing of iron
Authors: Jenko M. , Kansky E.
Published: July 2002

The formation of chromium rich α-FeCr layers on iron samples, buried into chromium granulate and heated in vacuum, is studied. There are two possible processes of supplying an iron surface with the chromium atoms, by surface diffusion and with transfer through the vapor phase. Parallel experiments were performed using either iron samples, buried in chromium, or iron samples, placed 2 mm above the granulate surface. The iron surface temperature is kept in the range from 1000 to 1150 °C. The achieved chromized layer depth is equal for both specimens. That way it is shown that the dominant process in vacuum chromizing is the vapor phase transfer of chromium atoms. Those experimental results enabled the quantitative interpretation of the linear, and parabolic, growth of the chromized layer depth. The chromium evaporation rate and the chromium, and iron, interdiffusion rate in the α-FeCr phase were determined experimentally.
The sputtering and redeposition behavior of VBe12 compound and of Ti–Cu–Li composites within a fusion tokamak environment
Authors: DeWald A. Bruce , Brooks J. N. , Krauss A. R. , Gruen D. M.
Published: July 2002

VBe12 compound and porous titanium composites infiltrated with a lithium bearing copper alloy have been investigated as a means of reducing fusion plasma impurities and sputter erosion associated with fusion tokamak limiter and divertor surfaces. These materials possess high-temperature strength and melt-layer stability properties in conjunction with the self-sustainment of a low-Z overlayer that inhibits erosion of the underlying structural substrate. The sputter erosion and redeposition properties of these materials have been analyzed by calculating the sputtering coefficients via TRIM, which are subsequently used in the REDEP code to evaluate their performance for various plasma-edge temperature regimes. The results have been compared to elemental beryllium, tungsten, and graphite on the basis of minimizing plasma impurities and material erosion, suppressing runaway self-sputtering, and/or enhancing thermal properties.
Graphoepitaxy of Bi, In, and Sn
Authors: Klews P.-M. , Anton R. , Harsdorff M.
Published: July 2002

Experiments were carried out in order to clarify the mechanisms governing graphoepitaxy. Low-melting-point metals were evaporated onto thin, amorphous substrates with a well-defined surface grating microstructure followed by melting and recrystallization in situ in a transmission electron microscope. This resulted in a graphoepitaxial alignment only when the substrate coverage exceeded a certain minimum value. The deposition parameters (substrate temperature, rate) were only found of importance as they influence the substrate coverage. Furthermore, smaller grating periods and/or higher modulation depths were found to increase the range of metal layer thicknesses for which alignment could be obtained. A further improvement was achieved by deposition of an additional carbon layer on top of the metal films prior to annealing. This was found to prevent bead up of thicker films to some extent.
Morphology and electrical properties of In doped CdS thin films
Authors: Dhere Neelkanth G. , Moutinho Helio R. , Dhere Ramesh G.
Published: July 2002

The effect of In doping, used to reduce the high resistivities of CdS films deposited at substrate temperatures above 300 °C, on film structure and morphology was studied because of their importance as an appropriate n-type window layer in several types of heterojunction solar cells. Doping with In, even at the lowest doping levels utilized, resulted in the desired reduction in the resistivities from 105 to 10−2 Ω cm. The films were n type with electron concentration of 1018 to 1019 cm−3 and mobility of 14 to 75 cm2 V−1 s−1. At low doping levels, the CdS films remained compact, maintaining their columnar growth, with grain diameters ∼4 μm and the columns mostly along the c axis of the wurtzite phase of CdS being aligned normal to the substrate surface. With higher In incorporation, a slow transformation to much smaller elongated grains, with c axis along the substrate surface was observed. This has been attributed to the segregatino of In at the grain boundaries as CdIn2S4.
Study of the Ti/Si interface using x-ray photoelectron and Auger electron appearance potential spectroscopies
Authors: Chopra D. R. , Chourasia A. R. , Dillingham T. R. , Peterson Keith L. , Gnade B.
Published: July 2002

Thin films of titanium silicide have been grown by evaporative deposition of high-purity Ti on a Si 〈111〉 substrate under high-vacuum conditions and annealing at ∼300 °C for 15 min. The growth of TiSi2 on the top 1000 Å of Si was studied for its stoichiometry as a function of thickness by x-ray photoelectron spectroscopy (XPS) and Auger electron appearance potential spectroscopy (AEAPS). A sputter profiling technique using Ar ions was employed to determine the composition of the overlayer as a function of depth. Results of the study indicate the presence of both TiO2 and SiO2 on the top layers in addition to Ti and Si (which may be bonded to each other). The concentrations of TiO2 and SiO2 are found to decrease with depth, the former decreasing much more rapidly than the latter. The atomic percentage composition measurements indicate the formation of TiSi2 in the Ti overlayer. However, no appreciable shift is observed in the core binding energies of the Ti 2p3/2 and Si 2p peaks. AEAPS, which probes the local density of conduction band states, should be more sensitive to the chemical shift. The AEAPS measurements indeed show a positive shift of approximately 3 eV for the Ti 2p3/2 peak in Ti/Si. Moreover, this peak exhibits a broadening as compared to that of elemental Ti. These results are indicative of the bonding between Ti and Si in the TiSi2. The formation of TiSi2 at 300 °C is corroborated by x-ray diffraction measurements.
Homogenization of tantalum pentoxide reference materials and the establishment of a reference standard for sputtering fluxes and for cross section measurements in nuclear instruments
Authors: Seah M. P. , Holbourn M. W. , Davies J. A. , Ortega C.
Published: July 2002

Tantalum pentoxide films grown anodically on tantalum foil have been used as reference materials for a variety of purposes. For both the calibration of depth resolution in sputter-depth profiling instruments using Auger electron spectroscopy, and for calibrating the sputtering rate in these instruments, the certified reference material BCR 261 has been developed at NPL. Tantalum pentoxide reference materials have also been developed in Paris and at Chalk River with considerable characterization. Here we bring these separate standards to one common absolute calibration, show all to be of identical composition, and show that the sputtering rate is constant with depth. This establishes the NPL/BCR material for determining sputtering flux densities, and hence for calibrating Faraday cups, and also for calibrating nuclear scattering instruments for absolute measurements.
Automatic process control for artificially layered structures
Authors: Gogol C. A. , Deutschman R. A. , Bean J. C.
Published: July 2002

There is an increasing interest in exploiting the properties of thin-film structures that are inherently complex and precise in the repetition and/or variation of their compositions. This is particularly true in the area of molecular-beam epitaxy. This technology is dependent on the control of evaporation sources to provide the precision necessary to fabricate these structures. At best, the Knudsen cell produces fluxes that have a nonlinear dependence on the controlling parameter, temperature, as well as an annoying dependence on the material level within the cell. At worst, the fluxes from electron beam evaporators are not only nonlinear but nonreproducible functions of their control parameter, power. A laboratory or small-system controller is described that combines a miniature ultrahigh vacuum (UHV) compatible, species selective deposition sensor with a software program that runs on a personal computer. It integrates composition control to 0.1 Å/s with the analog control of substrate temperatures, doping levels, and simpler functions such as shutters. This system has been running for 1 1/2 yr and has produced not only complex superlattice structures, but also novel nonlinear profiles such as parabolic composition grading in Ge–Si strained layer heterostructures in a reproducible, operator-independent mode.
Reactive sputter sectioning: A tool for polymer film analysis
Authors: McClure D. J. , Muller C. L. , Tabar R. J.
Published: July 2002

Reactive sputter etching has been used to create thinned ‘‘sections’’ of polymer films for use in microstructural analysis. This paper emphasizes the features of the sputter etching process which must be controlled to permit efficient sectioning without the introduction of artifacts, such as microstructural changes induced by heating and surface texture which might obscure subsequent analysis. Sample mounting techniques which allow oxygen sputter etching rates of 20 μm/h without heating of the film above 50 °C and simple electrode surface design rules which allow etching for long periods with very low levels of surface texturing are described. The minimum oxygen flow rates which must be supplied to prevent a depletion of the oxygen reactant and a concomitant reduction in the etch rate are noted. The utility of the technique is demonstrated with results from a study of the microstructure of a cast polypropylene film as a function of depth through the film.
Infrared total internal reflection spectroscopy of dimethylcadmium on silicon
Authors: Sanchez Esaul , Shaw Ping , O’Neill James A. , Osgood Richard M.
Published: July 2002

The surface chemistry of dimethylcadmium (DMCd) on silicon surfaces is monitored through changes in the infrared spectra of both chemically and physically adsorbed molecules. A technique involving total internal reflection of the IR probe beam was employed to isolate the surface-molecule signal from that due to ambient gas-phase molecules. Fourier-transformed infrared spectra of DMCd on silicon were recorded in the region from 2.0 to 5.0 μm, where the CH vibrational modes of the molecule occur. Excimer laser irradiation of the molecules at 248 nm under conditions appropriate for Cd film deposition resulted in changes in the observed spectra due to dissociation of both surface and gas-phase molecules.
Atomic and molecular states of oxygen chemisorbed on tungsten(112)
Authors: Wendelken J. F.
Published: July 2002

High-resolution electron energy-loss spectroscopy, x-ray photoemission spectroscopy, and low-energy electron diffraction have been used to characterize the adsorption of oxygen on tungsten(112) as a function of temperature and coverage. Two atomic adsorption sites are observed at 300 K, while at 100 K a molecular state is also observed. Coverage-dependent shifts in the vibrational spectra suggest that atoms in the first adsorption site both strongly influence and are strongly influenced by a lateral shift surface reconstruction while atoms adsorbed in the second site have only a limited relation to the reconstruction. Molecular adsorption is blocked by the atoms in the second site, but occurs only after population of the first site.
High-resolution electron energy-loss studies of space-charge layers on doped GaAs(110) surfaces
Authors: Chen Yu , Lapeyre G. J. , Xu Yabo
Published: July 2002

High-resolution electron energy-loss spectroscopy is used to study heavily doped n-GaAs(110) (4×1018 cm−3). The surface optical phonons and plasmons due to conduction band free carriers are measured. Surface Fermi level pinning is induced with atomic hydrogen adsorption which forms a depletion layer and shifts the plasmon loss. The shifts are calculated in the framework of a two-layer model.
Elastic electron fine structure: Application to the study of local order
Authors: Lin B. Y. , Kahn A.
Published: July 2002

Oscillations are found in the integrated intensity of elastic electrons scattered from amorphous Si. These oscillations are attributed to the multiple scattering of elastic waves between a central atom and its neighbors, an effect which is similar to but more general than that found in extended x-ray absorption fine structure and related phenomena. The Fourier analysis of the signal obtained with amorphous Si produces a dominant peak which closely corresponds to twice the nearest-neighbor distance. The result of a first-principle multiple-scattering calculation reproduces remarkably well in the experiment and clearly demonstrates the physical processes responsible for these oscillations.
Apparatus for verification of beta heating driven layer uniformity in solid deuterium–tritium
Authors: Mruzek M. T. , Ankney J. S. , Decker D. N.
Published: July 2002

A solid deuterium–tritium fuel layer within a spherical inertial confinement fusion target will be driven uniform by β-decay energy if the target is held in an isothermal environment. The apparatus we constructed to verify this process provides an isothermal and radiation-tight environment. Heat exchange between the target (≂20 K) and the environment (4.2 K) is regulated by controlling the helium exchange gas through a specially constructed manifold. A unique optical system maintained at low temperatures allows direct observation of the fuel layer uniformity. Tritium containment in the event of a target failure is assured by tungsten–inert gas welding of the stainless-steel structure. This system conveniently fits a standard vendor supplied 100-l Dewar, and is designed to minimize boiloff and cooldown losses by means of an efficient helium vapor counterflow system. We have also incorporated a vibration isolation system to permit holographic interferometry imaging and evaluation of the fuel layers.
Fabrication of ultrathin unsupported foils
Authors: Graper Edward B.
Published: July 2002

The fabrication of self-supporting unbacked foils of 200-Å gold, 500-Å chromium and titanium, and 1000-Å aluminum oxide, titanium oxide, and zirconium oxide by electron beam evaporation is described. This technology is presented in sufficient detail to permit duplication and general procedures useful in predicting the minimum possible foil thickness are presented.
Atomic force microscopy using optical interferometry
Authors: Erlandsson R. , McClelland G. M. , Mate C. M. , Chiang S.
Published: July 2002

An atomic force microscope using optical interferometry as the lever detection method is presented. Topographic images of graphite with 50-Å lateral resolution have been obtained using repulsive contact forces. Images of the graphite surface showing the atomic periodicity were also recorded; in this case, the image contrast does not represent surface topography, but rather variations in the lateral frictional force on the tip. Images using attractive electrostatic forces to map topographic features are shown. The instrument has also been operated as a scanning tunneling microscope while simultaneously measuring the contact force between the tip and a graphite surface.
Room-temperature growth of ultrathin Ni films on Si(111)
Authors: Porter T. L. , Chang C. S. , Knipping U. , Tsong I. S. T.
Published: July 2002

Ni layers ranging in thickness from 0.1 to 34 Å are deposited onto a clean Si(111) surface in ultrahigh vacuum. The composition and structure of the surface layer is monitored by impact collision ion scattering spectrometry during depositions. Results indicate that at extremely low coverages, Ni atoms diffuse into the Si substrate to form regions of predominantly type-B NiSi2. Further Ni deposition results in lateral growth of silicide islands enriched with surface Si. At 12-Å coverage the islands coalesce and then grow in thickness until 30 Å of Ni has deposited, at which point pure Ni overlayers form.
Measurement of plasma potential using collecting and emitting probes
Authors: Hershkowitz N. , Cho M. H.
Published: July 2002

Recently developed plasma potential diagnostic techniques which employ emissive probes are discussed. Using these techniques it is shown that it is possible to determine the plasma potential in plasma densities of <104 to 1013 cm−3, neutral pressures of <10−6 to 1 Torr, ion temperature ranging from 0.1 eV to 1 keV, and electron temperature from 0.1 to 150 eV. The techniques include measurements of the inflection point of the probe’s I–V characteristic in the limit of zero electron emission, differential emissive probes in which a feedback circuit compares two probes with different emission, self-emissive probes in which plasma bombardment provides the probe heating, secondary emissive capacitive probes for which secondary electron emission coefficients are greater than 1.0, and current biased probes.
Depth of origin of sputtered atoms: Experimental and theoretical study of Cu/Ru(0001)
Authors: Burnett J. W. , Biersack J. P. , Gruen D. M. , Jo/rgensen B. , Krauss A. R. , Pellin M. J. , Schweitzer E. L. , Yates J. T. , Young C. E.
Published: July 2002

The depth of origin of sputtered atoms is a subject of considerable interest. The surface sensitivity of analytical techniques such as secondary ion mass spectrometry and surface analysis by resonance ionization of sputtered atoms (SARISA), and the sputtering properties of strongly segregating alloy systems, are critically dependent on the sputtering depth of origin. A significant discrepancy exists between the predictions of existing analytical sputtering theories and computer sputtering models; in general, the computer models predict a much shallower depth of origin. The existing experimental evidence suggests that most of the sputtered atoms originate in the topmost atomic layer, but until recently, the results have not been definitive. We have experimentally determined the depth of origin of atoms sputtered from surfaces consisting of Cu films of <2 monolayers on a Ru(0001) substrate. The Cu/Ru target was statically sputtered using 3.6-keV Ar+. The sputtered neutrals were nonresonantly laser ionized and detected using SARISA. The Cu/Ru sputtering yield ratio and the suppression of the Ru sputtering yield were determined for various Cu coverages. The results indicate that the majority of the sputtered atoms originate in the topmost atomic layer. The Cu/Ru system is also modeled using a modified transport of ions in matter (trim) code. It was found that trim c does not correctly treat the first atomic layer, resulting in a serious underestimate of the number of sputtered atoms which originate in this layer. The corrected version adequately describes the results, predicting that for the experimental conditions roughly two-thirds of the sputtered atoms originate in the first atomic layer. These results are significantly greater than the analytical theory estimate of >40%.
E
F
pinning at the Sn/GaAs(110) interface
Authors: Stiles K. , Kahn A. , Kilday D. , McKinley J. , Margaritondo G.
Published: July 2002

In this study, Sn/GaAs interfaces are studied at both room temperature (RT) and low temperature (LT) (70–100 K) using soft x-ray and ultraviolet photoemission spectroscopies and low-energy electron diffraction. The movement of the Fermi level EF on the RT surface as a function of Sn coverage is initially slow on n-GaAs and fast on p-GaAs. This asymmetry is typically found only at LT for other metal/GaAs interfaces, where it is related to the delayed onset of metallic behavior of the overlayer. In contrast to these other systems, however, Sn/GaAs gives a classic example of Stranski–Krastanov growth at RT. The first two-dimensional layer does not bring EF close to its final position on n-GaAs. At the onset of three-dimensional nucleation (3–4 Å), EF drops abruptly to its final position on n-GaAs. This drop is delayed to ∼5 Å at LT. As for Ag and Au/GaAs, this relatively sharp change in the position of EF appears to be related to the formation of clusters and the appearance of the metallic behavior of the overlayer.
Fundamental characteristics of built-in high-frequency coil-type sputtering apparatus
Authors: Yamashita M.
Published: July 2002

A high-rate sputtering apparatus designed for ion-based film formation was made on an experimental basis. A dense plasma of the order of 1012 cm−3 was generated between the target and the substrate of a dc diode sputtering apparatus by means of an L-coupled high-frequency discharge. When a Cu target was used, the Cu+ ion current in the mass spectrum of the extracted ion beam increased with the Ar gas pressure, and had a maximum value about ten times that of an Ar+ ion current, at a pressure of ∼1×10−1 Torr (1.3×101 Pa). The plasma potential varied continuously from +20 to +200 V when the bias resistance for the high-frequency coil was changed from 10 kΩ to 0. The energy of the ions impinging on the substrate was changed greatly by the change in the plasma potential. The fine structure of the film formed was markedly influenced by the discharge gas pressure and/or the plasma potential. Even ferromagnetic material could be sputtered at a high rate.
Surface composition of gas-covered alloys
Authors: Khanra B. C. , Modak S.
Published: July 2002

We review the recent works of the surface segregation in Ni1−xCux alloys in the presence of hydrogen adatoms. The segregation behavior of the alloy in the whole composition range 0≤x≤1 has been analyzed. The analysis shows that for powdered alloy systems the presence of hydrogen adatoms causes the Ni atoms to segregate to the surface; while for crystalline alloy systems the presence of adatoms reduces the amount of Cu segregation that otherwise takes place in a clean Cu–Ni surface. It has been shown that besides the standard experimental methods like Auger electron spectroscopy and low-energy ion scattering, this segregation behavior may be studied by measuring the adsorbate Knight shifts, the surface core-level binding-energy shifts, and the amount of gas adsorbed by the alloy systems.
A model of dynamic damping in surface and interfacial kinetics
Authors: Erickson J. W.
Published: July 2002

Surface phenomena such as linear free energy relations, dephasing, and damping are not included in simple adaptations of gas phase reaction dynamics to surface kinetics. A qualitative model of reaction dynamics which incorporates some of the physics of these phenomena is described, in terms of potential manifolds and trajectories. The model predicts effects such as the existence of one-way activation energy barriers and non-Arrhenius behavior. Specific tests of the predictions are proposed, and the importance of appropriate error analysis for surface kinetic data is emphasized.
Band structure of InGaAs
Authors: Stampfl A. , Kemister G. , Leckey R. C. G. , Riley J. D. , Hillebrecht F. U. , Ehlers D. H. , Ley L.
Published: July 2002

The valence-band structure of unstrained In0.27Ga0.73As grown as a 4000-Å-thick overlayer on GaAs, has been determined in the (001) direction from angle-resolved photoemission data. The InGaAs bands lie between the bands of InAs and GaAs but the differences depend on k. The potential in the alloy is therefore not a simple average of that of the constituent compounds.
Interface properties of (Cd,Zn)S/CuInSe2 single-crystal solar cells
Authors: Abou-Elfotouh F. A. , Kazmerski L. L. , Coutts T. J. , Matson R. J. , Asher S. E. , Nelson A. J. , Swartzlander-Franz A. B.
Published: July 2002

Metal contacts to p-type CuInSe2 and heterojunctions of the form n-(CdZn)S/p-CuInSe2 have been prepared, to investigate the electrical behavior and chemical composition of the resulting interfaces and to correlate the results with the composition and corresponding electrical properties of CuInSe2 . The results indicate that the observed variability of the back contacts and front junctions of different CuInSe2 samples can be attributed to the variable initial equilibrium concentration of the intrinsic defect states which dominate the crystals. The type and concentration of the dominant defects can be changed by thermal treatments and by interface induced effects due to the junction electric field and the chemical potential gradients. Diffusion into or out of the CuInSe2 crystals was not detected. More over, no composition or other chemical variation due to the deposition of the sulfide layer was observed.
Interaction of Cu overlayers with W(001) studied by low-energy alkali ion scattering
Authors: Overbury S. H. , Mullins D. R.
Published: July 2002

Low-energy alkali ion scattering, Auger electron spectroscopy, and low-energy electron diffraction have been used to study the structure of ultrathin Cu overlayers on W(100). Incident polar and azimuthal angular scans of the Cu and W single-scattering intensity have been obtained as a function of Cu coverage and annealing temperature, and are used to evaluate various models for the surface structure. Dosing submonolayer amounts of Cu near room temperature results in two-dimensional islands of Cu bonded in fourfold hollows and some dispersed Cu atoms. Annealing at 1000 K causes irreversible displacement of first-layer W atoms and Cu incorporation, as indicated by a pronounced shift in the Li+/W low-angle shadowing edge, and the changes in the shape of the Li+/Cu edge. This result is interesting in view of the immiscibility of Cu and W. Analysis of contour plots of the Li+/Cu single scattering support a growth of up to two pseudomorphic layers of Cu on W(001); although there is Cu and W mixing at the interface.
Alkoxysilane adsorption on metal oxide substrates
Authors: Ramsier R. D. , Zhuang G. R. , Henriksen P. N.
Published: July 2002

Reflection–absorption infrared and inelastic electron tunneling spectroscopies have been used to study adsorption of liquid phase mono-, di-, and trialkoxysilanes on evaporated Al and Cu substrates. Spectral evidence shows that substrate properties influence the chemical and physical nature of trialkoxysilane films, and that silane functionality plays a role in molecular orientation. Results show that dialkoxysilane films contain structural gradients, with adsorption at the monomolecular level influenced by surface morphology, and with organofunctionality and dosing procedure affecting the formation of thicker films. Evidence is presented that monoalkoxysilanes react with alumina surfaces, and a broad, multipeaked band from 1600 to 1900 cm−1 has been interpreted as characteristic of the silylated AlOx/Pb interface.
A mixed Cu–Ni bridge site for CO adsorption
Authors: Garfunkel Eric , Yu Mingren , Yang Shu , Feng Xinghong
Published: July 2002

High-resolution electron energy-loss spectroscopy (HREELS) has been used to study carbon monoxide adsorption on mixed overlayers of Cu on Ni(111) and Ni on Cu(111). The mixed CuNi layers are formed by controlling deposition and annealing temperatures, and metal overlayer coverage. HREELS shows top and bridge CO adsorption on sites which resemble CO on pure Cu and Ni(111) surfaces. We also observe a new mixed bridging site species in which CO is bridge bonded between Cu and Ni atoms. The mixed bridging species is only observed at high CO coverages and low temperatures (<130 K), and appears coincident with a decrease in Ni–CO top site occupancy. A thermodynamic model is proposed to explain the CO transfer from the Ni top to the mixed NiCu bridge sites.
Formation of a platinum oxide during the thermal oxidation of noble-metal alloys
Authors: Graham G. W. , Potter T. J. , Weber W. H.
Published: July 2002

Foils of Pt–35Pd were heated in a 20% O2–Ar mixture at atmospheric pressure, and their surfaces were then examined by Auger electron, x-ray photoelectron, and Raman spectroscopy. It was found that an oxide layer of order 100 Å thick formed within 4 h at 873 K, and two well-defined sets of Pt 4f core levels separated by ∼1 eV were observed, the set at lower binding energy corresponding to platinum metal. The set at higher binding energy apparently originates from a platinum oxide which is thermally more stable and forms more readily than the simple oxides in platinum. Of the two other Pt alloys studied, Pt–10Rh and Pt–45Pd–10Rh, only the latter yields this platinum oxide. Since the surfaces of both of the oxidized Pd-containing alloys are comprised predominantly of PdO, it is suggested that the platinum oxide may be a PtO-like phase whose formation is related to the presence of the isostructural PdO.
Two-point pressure method for measuring the outgassing rate
Authors: Yoshimura Nagamitsu , Hirano Haruo
Published: July 2002

The two-point pressure method for measuring the outgassing rate of a solid material has been introduced, in which the pressures at two points in a pipe are measured. This method was applied to measuring the outgassing rates of two kinds of SUS304 plates, belt-polished plates, and buff-polished plates. The outgassing rates were measured under a pressure as low as that expected in the actual high-vacuum system. Additionally, the one-point pressure method has been introduced, whose validity was ascertained using measured pressures in the experimental setup. The outgassing rates for the same kinds of SUS304 plates were again measured by the conventional orifice method for comparison.
Crystallographic and optical study of ZrO2 partially and totally stabilized with Y2O3
Authors: Mesbah M. , Boyer A. , Groubert E. , Martin L.
Published: July 2002

We have studied the effects of the O2 concentration in the argon sputtering gas and the substrate temperature on the structural and optical properties of the totally stabilized zircone (TSZ) and partially stabilized zircone (PSZ) materials comparatively. In the TSZ material, the presence of molecules of the Y2O3 dopant reduces the effect of different deposition conditions on the film structure in regard to the PSZ material.
Low-energy electron diffraction observations of the thermal evolution of 0.5–3.0 ML Pt/Ni(111)
Authors: Barnard John A. , Ehrhardt Jean Jacques
Published: July 2002

The near-surface geometric structure of the system 0.5–3.0 ML Pt/Ni(111) has been monitored with low-energy electron diffraction (LEED) as a function of annealing treatment. In this coverage range a variety of structures are documented. Evidence is presented for commensurate submonolayer Pt (despite the large misfit) and incommensurate (but aligned) second and third layer Pt, at low temperatures. The second and third layers of Pt yield (111)-type LEED patterns but with spacing at an intermediate value between Ni(111) and Pt(111). In a very narrow range of coverage and annealing treatment (1.5–2 ML PT and 673–773 K) a hexagonal satellite appears around each primary beam. These satellites are interpreted as evidence for partially rotated incommensurate second layer Pt domains. Annealing at 873 K or above of even the thickest deposits (3 ML) produces diffraction spots indistinguishable from Ni(111). Structural evidence is correlated with the thermal evolution of the surface electronic structure in the same system (using photoemission for local and macroscopic work function measurements). The photoemission results complement the LEED information and together they provide evidence for complex diffusional rearrangements even at low temperatures in this system.
Electron excited M-region resonant x-ray excitation spectra from cerium and oxidized cerium
Authors: Mason Bryan E. , Liefeld Robert J.
Published: July 2002

Electron excited M-region x-ray resonances in cerium and cerium oxide were investigated with an instrument which permits simultaneous recording of x-ray emissions and electron spectra from samples prepared in an ultrahigh vacuum. X-ray intensities were recorded as a function of incident electron energy from 850 to 930 eV. This range encompasses the binding energies of the M5 and M4 shell electrons in cerium and the associated x-ray continuum resonances. The x-ray excitation spectra obtained in this study show large resonances for incident electron energies near the M5 and M4 shell ionization energies, but the electron spectra show no corresponding features. The spectra of resonant x rays from cerium oxide show almost no ‘‘chemical shift’’ relative to those from the pure metal but exhibit large increases in the intensity of the resonances. No explanation as to why the oxidized sample x-ray yields are higher is offered. An estimate of the maximum x-ray photon yield per incident electron for cerium and cerium oxide via the resonance effect is 2×10−6 (M5 ) and 9×10−7 (M4 ) for cerium and 6×10−6 (M5 ) and 4×10−6 (M4 ) for cerium oxide.
Surface segregation of Pt–Rh alloys
Authors: Sano N. , Sakurai T.
Published: July 2002

An atom-probe field ion microscope (APFIM) has been employed to determine the surface composition and depth profiles of the (100) plane of Pt–20, 40 wt. % (32.1, 55.8 at. %) Rh alloys. The enrichment of Pt at the top surface layer on annealing at 700 °C (∼1000 K) was observed, agreeing with previous studies by Auger electron spectroscopy, ion scattering spectroscopy, and APFIM. On annealing below 600 °C, however, a reversed surface segregation, Rh enrichment at the first surface, has been observed even without any impurity atoms such as S and P. Upon annealing up to 700 °C in the presence of oxygen, we found no appreciable oxidation of the alloy samples, instead, there appeared chemisorbed oxygen forming an overlayer.