bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of reordered (001) Au surfaces by positive−ion−channeling spectroscopy, LEED, and AES
Authors: Zehner D. M. , Appleton B. R. , Noggle T. S. , Miller J. W. , Barrett J. H. , Jenkins L. H. , Schow O. E.
Published: July 2002

An extensive investigation of the atomic arrangement on the (001) Au surface has been performed using the techniques of positive−ion−channeling spectroscopy (PICS), LEED, and AES. Both the normal surface in which the Au atoms are ordered in a square array and the reordered surface where it is proposed that the topmost layer of Au atoms are ordered in a hexagonal array have been examined. LEED and AES have been used in determining that the normal atomic arrangement producing the (1×1) LEED pattern is observed only when contamination is present, while the reordered surface producing the complex (5×20) LEED pattern is observed on surfaces which are atomically clean. The yield and energy distributions of 1 MeV 4He+ ions scattered from the oriented Au crystals have been used to determine the number of effective monolayers constituting the normal and reordered surfaces. Single alignment surface peaks and minimum yields have been determined, and experimental data are compared with predictions made by computer simulation calculations. It is found that the surface peak from the reordered surface is larger by an amount corresponding to ? 1 monolayer; this implies that only one extra hexagonal layer of atoms exists on the clean surface.
Abstract: Structure of platimum films deposited on calcite substrates
Authors: Walker Darrel D. , Joebstl Johann A.
Published: July 2002

Single crystal films between 200 and 800 Å thick were prepared by vacuum evaporation of platinum onto cleaved surfaces of calcite. The morphology and structure of the films were studied by transmission electron microscopy and diffraction. (100) and (110) oriented films were observed with the particular orientation dependent on the temperature of the substrate during the deposition process. The temperature ranges and temperatures of maximum ordering in each orientation, effects of substrate pretreatment, and possible reasons for the observed differences in the expitaxial growth of platinum and palladium films will be discussed.
Adsorption of tellurium on Ni(100)
Authors: Becker G. E. , Hagstrum H. D.
Published: July 2002

Four different ordered structures have been observed with the adsorption of Te on Ni(100). The only ordered structure formed at room temperature was the c (2×2) at which the work function went through a minimum as a function of coverage. A well−ordered c (2×4) structure was formed by heating to 900°C when the coverage was 1/4 monolayer or greater. This structure has not been observed with the other chalcogens on Ni(100) for which the p (2×2) structure is observed at 1/4−monolayer coverage. Heating of the sample when it was covered with 1/2 monolayer or more of Te to a critical temperature near 550°C produced a completely faceted surface which was stable at temperatures up to 700°C. An ordered multilayer structure was formed by heating the sample when it was covered with several layers of Te to temperatures in the range from 200 to 500°C.
Energy transfer in adsorption
Authors: Steinbrüchel Ch. , Schmidt L. D.
Published: July 2002

Measurements of the angle−dependent sticking coefficient S (φ) are reported for H2, D2, N2, CO, and CO2 on W(100) and W(110). Towards grazing incidence S (φ) in general increases slightly, but decreases markedly for H2 and D2 on W(110). The results for the heavier gases are interpretable in terms of a simple classical model of condensation via momentum transfer to the substrate lattice. A decrease in S towards grazing incidence implies that a threshold exists for energy transfer. It is shown that models involving a potential barrier at the surface or quantization of lattice excitations can qualitatively explain these results. However, the exact mechanism responsible for condensation of H2 and D2 remains unclear.
Abstract: Computer analysis of FIM diffusion studies
Authors: Reed D. A. , Ehrlich Gert
Published: July 2002

Field ion microscopy has made it possible to observe the diffusion of single atoms or atom clusters at a surface and to examine the interactions between individual atoms. There are two main problems associated with such studies: (1) Only a small number of adatom positions can be recorded per observation, so that statistical fluctuations have a profound effect on the data. (2) The available planes are no larger than 100 Å in diameter, and the effects of the plane boundaries may be significant.

We have performed computer simulations1 of the diffusion of one and two adatoms over a surface, both to determine the magnitude of the statistical errors in such experiments and to ascertain the optimal conditions for data collection. In the usual expression for the diffusion coefficient, D= D0 exp(−VD/kT), the activation energy VD can be obtained to ±8%, and the prefactor D0 to an order of magnitude, provided M, the number of diffusion intervals in the Arrhenius plot, amounts to 300. The statistical error in VD can be reduced to 5% with 750 measurements; the error in the prefactor is similarly lowered to a factor of 5. Further increases in M yield only minimal reductions of the statistical error.

Simulations were also carried out in order to determine corrections to compensate for the presence of boundaries. The effect of boundaries on the measured values of the mean-square displacement 〈R2〉 is generally approximated by the expression

〈R2〉=2Dτ[1−(4/3a) (4Dτ/π)1/2],

which relates the mean-square displacement, executed during an interval τ on a line of length a, to the diffusion coefficient. This is found to be adequate, unless displacements of only one or two steps per diffusion interval predominate. On a plane bounded by a circle of diameter d, this relation becomes

〈R2〉=4Dτ[1−(16/3πd) (4Dτ/π)1/2]. Interactions between adatoms can be deduced from the distribution function governing the distance between two atoms on a surface. Accurate distance measurements on two-dimensional surfaces are difficult. However, for atoms in adjacent one-dimensional channels no such limitation operates. From Monte Carlo simulations it appears that interaction energies can be derived with a standard error of kT/4 provided ?50 pairs per distance are available over the distance range of interest. The most important factor in such measurements is adequate equilibration between observations; atoms should make at least 5 jumps between determinations of interatomic distances to insure meaningful results. These estimates are applied to an analysis of experimental measurements on diffusion and interaction of W2,3 and Ir adatoms4 on the (211) plane of W.
Chemical identification of individual surface atoms in the atom probe
Authors: Chambers Robert S. , Ehrlich Gert
Published: July 2002

The ability to unequivocally identify the chemical nature of specified adatoms with the atom-probe field-ion microscope is demonstrated for the first time. Design features essential to this capability are discussed together with the underlying experimental techniques. The He ions used to image a given atom at a surface follow a path different from that of the field-evaporated surface atom itself. This results in an aiming error, which has been measured in our surface atom probe. Experiments with Rh atoms adsorbed on the (110) plane of W indicate that the atom probe is capable of identifying individual adatoms with a spatial resolution as good as, or better than, the resolution of the field-ion microscope.
Measurement and modification of first-wall surface composition in the Oak Ridge tokamak (ORMAK)
Authors: Clausing R. E. , Emerson L. C. , Heatherly L. , Colchin R. J. , Twichell J. C.
Published: July 2002

Impurities coming into the plasma from the walls of present-day toroidal plasma confinement devices modify plasma behavior substantially. Small fractions of high-Z ions in the plasma greatly decrease plasma temperatures and increase plasma energy losses. We are attempting to identify and control the sources of impurities from the ’’first-wall’’ in ORMAK. Auger electron spectroscopy, soft x-ray appearance-potential spectroscopy, and other surface-sensitive techniques have been used to characterize the surface composition of the first wall and to develop methods to remove carbon and oxygen. Oxygen glow-discharge cleaning has been shown, in the laboratory, to be an effective way of removing carbon from gold films (simulated ORMAK liner material) and the use of oxygen-discharge cleaning in ORMAK has resulted in a decrease in plasma contamination, a 50% increase in plasma current, and an accompanying increase in plasma temperature. In spite of these improvements the walls of ORMAK are far from clean. Substantial amounts of carbon, oxygen, iron, and other elements remain.
Beam effects in Auger electron spectroscopy analysis of titanium oxide films
Authors: Mathieu H. J. , Mathieu J. B. , McClure D. E. , Landolt D.
Published: July 2002

Auger spectra of TiO2,Ti2O3, TiO, and Ti were determined as a function of sputter time to study ion-beam and electron-beam effects in AES depth profile analysis of titanium oxides. The value of the oxygen–titanium peak amplitude ratio for a given titanium oxide depends on ion-beam energy, electron-beam current density, and oxide composition. Both ion and electron beam give rise to an apparent reduction effect and their combined action stimulates the formation of carbide at the sample surface. The latter effect is more pronounced at an ion-beam energy of 0.5 keV than at 2 keV. Depth resolution characterized by the width of the transition region between oxide and metal decreases with increasing ion-beam energy and with increasing thickness of the sputtered layer.
Isotope effect in the pumping of hydrogen by titanium thin films
Authors: Malinowski M. E.
Published: July 2002

The hydrogen and deuterium pumping speeds at ∠20 mTorr (2.66 Pa) and 300 K of 1000-Å-thick titanium films deposited at 300 K at a rate of ∠3 Å s−1 have been measured. These speeds are approximately constant for H (or D)/Ti loading ratios between 0.3 and 1.3 and are different for each isotope. For deuterium the pumping speed is ∠0.13 l s−1 cm−2, while for hydrogen the speed is essentially two times the deuterium speed, i.e. ∠0.18 l s−1 cm−2. Pumping speed data taken at ∠5 mTorr (0.665 Pa) indicate that agreement of the isotope data with a surface-sticking limited model requires a pressure-dependent, hydrogen isotope-independent sticking coefficient.
Carbon layer formation on the Pt (111) surface as a function of temperature
Authors: Hamilton J. C. , Blakely J. M.
Published: July 2002

The (111) surfaces of carbon-doped Pt single crystals were studied using LEED and Auger spectroscopy to determine the characteristics of carbon segregation of platinum. Carbon was observed to appear on the surface reversibly when the crystals were cooled. Observations of coverage versus temperature, carbon Auger peak shapes, and LEED patterns indicate that the appearance of carbon on Pt(111) can be explained solely by precipitation and that segregation of carbon does not occur on this surface to within the limit of detectability. The fact that no detectable segregation is observed indicates that single carbon atoms are not appreciably more strongly bound on the Pt(111) surface than in the interior of the crystal and that the bonding of a single graphite layer to the Pt(111) surface is weaker than the interlayer bonding of carbon in bulk graphite.
Structure and epitaxy of evaporated cadmium selenide films
Authors: Naguib H. M. , Nentwich H. , Westwood W. D.
Published: July 2002

Cadmium selendide films were thermally evaporated onto Corning 7059 glass and (110) KC1 single crystals at temperatures between 25° and 300°C. Films between 0.05 and 1.0 μm thick were deposited at rates between 1.7 and 32 Å/s and their microstructure investigated by transmission electron microscopy, reflection electron diffraction, and x-ray diffraction. The würtzite-hexagonal phase of CdSe was always observed at substrate temperatures up to 200°C but, in the case of KCl, it co-existed with the sphalerite-cubic phase. The crystallite size and the degree of ordering of CdSe increased with increasing substrate temperature and film thickness. For example, the ratio of x-ray intensities from (00.2) and (10.0) planes in films deposited on glass substrates increased by more than two orders of magnitude as film thickness increased from 0.05 to 1 μm. At glass substrate temperatures greater than 200°C, Cd3Se4O11 was also formed. The structure of films deposited on KCl changed from a polycrystalline mixture of cubic and hexagonal phases to a single crystalline (111) cubic phase with increasing thickness. This effect can be attributed to recrystallization caused by thermal stresses induced by the difference in thermal expansion of film and substrate.
H+ and D+ sputtering of thin tantalum films in the energy range of 0.6 to 15 keV
Authors: Meyer Charles H. , Smith Joe N.
Published: July 2002

The sputtering yield for H+ and D+ incident on Ta is measured using simultaneous and coincident Auger analysis and sputter etching of thin Ta films on Cu substrates. The maximum yield is found to be 4.5×10−3 atoms/ion for H+ and 1×10−2 atoms/ion for D+ at an energy of ∠4 keV. Throughout the energy range studied, the data agree well with a semiempirical formula devised earlier for use in determining sputter yields for fusion reactor first wall materials [D. L. Smith, J. Nucl. Mater. 75, 20 (1978)].
Adhesion of thin films of evaporated titanium–copper after electroplating
Authors: Kemmerer C. T. , Mills R. H.
Published: July 2002

Titanium–palladium–gold is a highly reliable multilayer metallization for thin-film integrated circuits. Efforts to reduce the amount of Au and hence the cost of the circuits have led to development of a Ti–Cu–Ni–Au metallization. This system is fabricated by selectively electroplating Cu–Ni–Au onto evaporated Ti–Cu. During the introduction of the new metallization into manufacture, it was observed that evaporated Cu frequently delaminated from evaporated Ti after Cu–Ni–Au plating. The factors investigated were the nature of the substrate surface, residual gas pressure during evaporation of the Ti and/or Cu, thickness of the evaporated Cu, various combinations of plated films and postplating heat treatment. Adherence was evaluated by a tape test, thermocompression bonding and pull testing of leads, and by a simple substrate break-and-peel test. In-depth profiles of the evaporated TiCu interface were obtained by sputter removal and Auger electron spectroscopy techniques. Oxidation of the evaporated Ti layer at pressures greater than 2.7×10−4 Pa prior to evaporation of the Cu layer was found to be a significant factor leading to subsequent delamination after electroplating. Solutions to the delamination problem include optimization of the evaporation equipment, use of a thin layer (∠150 Å) of Pd between the Ti and Cu, elimination of a distinct interface between the Ti and Cu by coevaporation techniques to produce a graded film, or sputtering of the films rather than evaporation.
Function stress testing in large-scale optical multifilm manufacturing
Authors: Leece Steven H.
Published: July 2002

Large-scale optical thin-film production requires rapid feedback of film quality information for process development and control. Postdeposition functional tests which reflect stress in thin films and which emulate long-term use conditions are described. Process parameters for SiO2 evaporation generated through functional testing information are discussed for an illustrative example.
Apparatus for Mössbauer effect emission and AES study of free surfaces
Authors: Anderson C. R. , Richards B. G. , Hoffman R. W.
Published: July 2002

A UHV system has been built for the study of single-crystal surfaces by Mössbauer effect emission spectroscopy (MEES) and AES. The sample temperature range extends from 1500–20 K. Ion sputtering and sample heating allow surface cleaning. The evaporation, by electron bombardment of 57Co electroplated onto a W wire tip, of several 0.001 monolayer (ML) of 57Co onto the surface is carried out at tempertures low enough to insure no surface diffusion. MEES data is then collected through a Be window with surface monitoring by AES. The MEES spectrum of a Ni(111) surface covered by one monolayer of contaminants is a broad, unresolved resonance. The 57Co sits at many different surface sites, many having large hyperfine fields. The MEES spectrum of 57Co on the surface of three or four layers of carbon on a polycrystalline Cu substrate displays a large quadrupole splitting with broadened linewidths.
LEED analysis of the reconstructed Au(110) surface
Authors: Noonan J. R. , Davis H. L.
Published: July 2002

The LEED I–V profiles for six inequivalent nonspecular diffraction beams from a Au(110) - (1×2) surface have been measured, with the incident beam at normal incidence, and compared with model calculations. The experimental curves are compared with theoretical calculations for a model in which every other close-packed, 〈110〉-type row is removed, i.e., the ’’missing row’’ model. The analysis provides little agreement between measured profiles and the calculations for this particular model; e.g., the R factor as defined by Zannazzi and Jona is always greater than 0.6 for changes of both structural and nonstructural model parameters.
Diffraction features in secondary electron emission
Authors: Thapliyal H. V. , Unertl W. N.
Published: July 2002

Prominent features observed for energies between 100 and 600 eV in the secondary electron spectrum of stepped nickel surfaces are shown to have a strong dependence on the degree of surface disorder. Absorbed overlayers also strongly alter these structures. The effects of temperature and primary electron beam incident angle have been studied. Correlation between these features and structures in the integrated elastic intensity support an earlier suggestion that these features are caused by diffraction effects; a simple pseudokinematic scattering theory is used to further examine this suggestion. We have observed these diffraction features on a number of other materials. Their intensity is often as large as prominent Auger peaks so that caution must be exercised in the analysis of Auger peak shapes.
Abstract: Desorption kinetics of one- and two-step mechanisms
Authors: Steinbrüchel Christoph
Published: July 2002

Desoption kinetics may be described alternatively as a one-step or two-step process. Two-step kinetics can be well fitted over the entire coverage range by a one-step expression where the activation energy is a linear function of coverage. (AIP)
Shiva and Argus target diagnostics vacuum systems
Authors: Glaros S. S. , Mayo S. E. , Campbell D. , Holeman D.
Published: July 2002

In normal operation Lawrence Livermore Laboratory’s Argus and Shiva laser irraddiation facilities demand a main vacuum system for the target chamber and a separate local vacuum system for each of the larger appendage diagnostics. This paper will describe the Argus and Shiva main vacuum systems, their respective auxiliary vacuum systems, and the individual diagnostics with their respective special vacuum requirements and subsequent vacuum systems. Our latest approach to automatic computer-controlled vacuum systems will be presented.
Tracer slug leak detection
Authors: Moore B. C. , Walker J. A.
Published: July 2002

One of the most difficult tasks in operating and maintaining a space chamber is the leak checking of the liquid nitrogen/liquid helium shroud system. The shroud system is especially susceptible to forming leaks because of the high thermal stresses encountered in the handling of cryogenic liquids, yet it is very difficult to pinpoint the location of a leak as it may only be of significant size at very low temperatures. Shroud systems can often be very long and complex, containing hundreds of meters of piping, and numerous bends and elbows. A method is reported for determining a leak location by using a tracer slug of helium inserted in the stream of a nitrogen carrier gas. This method was applied to a shroud system known to have a leak but whose location was not known. The location was successfully pinpointed by the tracer slug method and verified by conventional methods. In addition to isolating the leak location it was found that the tracer slug method could also give an estimate of leak size.
UHV system for the ultramicrogravimetric study of samples loaded in a controlled environment
Authors: Vasofsky R. , Czanderna A. W. , Thomas R. W.
Published: July 2002

A stainless-steel UHV system which includes a bakable automated vacuum ultramicrobalance and a quadrupole residual gas analyzer, has been designed to permit loading samples onto the balance from a controlled environment. The 20-g load capability of the ultramicrobalance permits using rugged hangdown suspensions. The line-of-sight positioning and high sensitivity of the mass filter allows direct analysis of the outgassing products and permits eliminating the complications of secondary surface reactions. A linear motion feedthrough with a bellows assembly is used to uncouple and raise part of the sample hangdown suspension from the furnace region to an access port above the furnace region. After backfilling the vacuum system with an inert gas, the access port is opened into the controlled atmosphere of a dry box. The unloading and taring of the balance is accomplished by operating a micromanipulator with rubber gloves. A vacuum bakeout oven is used for processing samples prior to storage in the dry box. Representative data concerned with water vapor adsorption and outgassing by a solder sealing glass are presented and discussed.
Synchrotron-radiation-induced heating effects in the PEP storage ring vacuum system
Authors: Martin T. W.
Published: July 2002

The advent of large high-energy storage rings has facilitated the need for more detailed analysis of synchrotron radiation interactions and related thermal effects. In the PEP storage ring, a maximum of 5 MW of synchrotron radiation with a critical energy of 44 keV will interact with 2200 m of vacuum hardware. A Monte Carlo based computer code, EGS, was employed to follow electromagnetic reactions of the synchrotron radiation through various computerized models of the vacuum system. The computer simulated structures with hundreds of discrete regions and varying materials. Results showed that typically 70% of the synchrotron power was absorbed in incident surfaces and 20% was scattered outside the vacuum vessel. The remaining power was deposited in varied vacuum components. Sensitive PEP ring components, particularly distributed ion pumps, were subsequently designed to minimize power absorption and to maximize cooling effects. Other thermal calculations were employed to design for minimal wall temperatures in areas of direct synchrotron radiation incidence.
Physics of compound semiconductor interfaces: A historical perspective
Authors: Bauer Robert S.
Published: July 2002

What started five years ago as a small workshop on compound semiconductor electronics now has grown to an international conference focusing on fundamental aspects of semiconductor interfaces and surfaces. A discussion is presented of the changing emphases, experimental techniques, and technological trends in the field as reflected by the evolution of this conference series. The novel meeting format of PCSI-6 is described which allowed ample discussion of a large number of related papers while minimizing the ’’second class feeling’’ of poster presentations. A survey of participants critically
Theory of exciton effects in semiconductor surface spectroscopy
Authors: Altarelli M. , Bachelet G. , Del Sole R.
Published: July 2002

Electronic excited states at the 〈001〉 and 〈111〉 surfaces of a simple cubic solid are investigated, with inclusion of a contact electron–core hole interaction. Contributions of bulk and surface bands to bound and resonant excitons are derived without approximations. The resulting spectrum dramatically depends on the nature and energy of empty surface states. A large increase of the exciton binding energy near the surface is obtained in some situations, while in others binding is suppressed altogether in the first few planes, and a ’’dead layer’’ results. Limiting cases relevant to the discussion of recent observations of surface excitons in semiconductors and insulators are identified.
Reduction of surface recombination current with an oxygen-doped Al0.5Ga0.5As surface layer on n-type GaAs
Authors: Casey H. C. , Cho A. Y. , Foy P. W.
Published: July 2002

The surface recombination current of GaAs p–n junctions has been reduced by the use of a high resistivity O-doped Al0.5Ga0.5As layer on the n-type layer. A top layer of insulating silicon nitride provides protection from the environment so that this combination meets the requirements of a GaAs surface passivation. Reduction of the surface recombination current results in domination of the kT bulk diffusion current for current densities in excess of 5×10−3 A/cm2. Analysis of the forward I–V characteristics permits assignment of several parameters for these planar p–n junctions. The intrinsic surface recombination velocity–surface diffusion length product soLs was reduced from 3.7 to 0.3 cm2/s by the O–Al0.5Ga0.5As layer. The hole diffusion length Lp was found to be 3.2 μm and the internal quantum efficiency ηq=28%. The product of the space–charge region recombination center concentration NB, the capture-cross section ?, and the thermal velocity ? was NB??=4×107s−1.
Structure and composition of the Si/SiO2 interfacial region on TCE/O2 and CCl4/O2 oxidized silicon
Authors: Frenzel H. , Balk P.
Published: July 2002

SiO2 layers thermically grown at 900°, 1000°, 1100°C on Si in O2 with and without Cl additives were studied with SIMS, AES, and high frequency C–V measurements. With SIMS, a lateral inhomogeneity due to new Cl-rich phase was observed. This phase is probably responsible for Na+ passivation. AES depth profiles show a Si signal that we attribute to SiOx (0<x<2). A correlation between fixed oxide charge and film composition could not be established.
Influence of end-effects on optimum injection condition for electrons in an orbitron device
Authors: Feidt M. , Prulmier D.
Published: July 2002

Optimum ionizing efficiency in an orbitron is strongly dependant on end-effects; they disturb the radial electrostatic field, affect the sensitivity of the device and, at the same time, the optimum positioning of the electron emitter. The ionizing efficiency also depends on space charge effects. The influence of end-effects in an orbitron varies considerably with the electronic current: it is relatively important for small current (for instance in an ionization gauge for ultrahigh vacuum), and less important at high electronic current (as in an ionic pump).
Evidence for grain boundary passivation by oxidation in polycrystalline GaAs solar cells
Authors: Kazmerski L. L. , Ireland P. J.
Published: July 2002

The chemistry and composition of grain boundaries in polycrystalline GaAs grown by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) are examined using complementary Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and x-ray photoelectron spectroscopy (XPS). The effects of an unintentional residual-oxygen partial pressure during LPE growth are investigated in terms of grain boundary passivation. Depth-compositional data verify the grain boundary localization of oxides using an in situ, UHV fracturing technique. Indications of distributions of these oxides over the grain boundary are presented. The performances of Au Schottky barrier solar cells fabricated from the polycrystalline LPE and MBE GaAs are compared and differences are explained in terms of grain boundary activity.
Advanced limiters for ISX
Authors: Mioduszewski P. K. , Edmonds P. H. , Sheffield J.
Published: July 2002

Continuous removal of heat and particles becomes a vital necessity in future steady-state fusion devices. The pump limiter seems to be an attractive concept to combine these two tasks. On ISX, various schemes of pump limiters are being explored with the final goal to furnish the ISX–C device with a pump limiter to handle heat removal and particle control in steady state. The emphasis of the present paper is on pump limiters based on ballistic particle collection. If this concept turns out to be successful in supplying sufficient pumping efficiency, it may be possible to design pump limiters without a leading edge. Analytical calculations of the particle collection efficiency are given for various limiter configurations. Pumping efficiencies of approximately 4–10%, depending on the specific configuration, seem to be feasible and should be sufficient for steady-state operation. Initial experimental results on pump limiter studies in ISX–B confirm the calculated collection efficiencies. By measuring the ion saturation current to the limiter blade and the pressure buildup simultaneously, we found a correlation between the incident particle flux and the pressure rise that agrees well with a simple model.
The L1L23V and L1L23M1 Coster–Kronig transitions in hydrogenated amorphous silicon
Authors: Madden H. H.
Published: July 2002

Electron−excited silicon L1L23V and L1L23M1 Coster−Kronig signals from hydrogenated amorphous silicon surfaces have been measured and compared with corresponding signals from both crystalline and amorphous silicon surfaces. The amorphous surfaces were produced by direct ion bombardment of a single crystal sample. Changes due to hydrogen on these low energy signals were not detectable. These results are in agreement with one set of published results and in contradiction with a second set. Large characteristic-loss-type structure was observed in the spectral range from 5—20 eV. This structure was found to be independent of the production of silicon L1 core holes but dependent on the direction of incidence of the primary electron beam.
Effect of gas composition on vacuum measurement
Authors: Poulter K. F.
Published: July 2002

Accurate pressure measurement with most types of vacuum gauges is critically dependent on a knowledge of the composition of the gas being measured. This paper will discuss the gas dependence of measurement with a number of commonly used types of vacuum gauges. Particular emphasis will be placed on recent work in the author’s laboratory which has shown how the accuracy of capacitance manometers can be affected if the possibility of thermal transpiration is ignored. Methods have been derived and proven for applying corrections when capacitance manometers are used with a wide variety of gases. The dependence of other types of vacuum measuring equipment on gas composition will also be discussed and recent investigations with spinning rotar gauges and ionization gauges will be reviewed. In the paper the potential of small mass spectrometers for quantitative gas analysis will be discussed. The most recent results on the evaluation of these instruments will be given for both small quadrupoles and magnetic sector instruments. The various methods of calibrating these instruments will be discussed with particular emphasis on the requirements of process industries and the monitoring of environmental pollutants.
Investigation of underlayer formation by oxygen on Al(111) and Ti(0001)
Authors: Strong R. L. , Erskine J. L.
Published: July 2002

High-resolution electron energy loss spectroscopy is used to investigate the initial stage of oxide formation on Al(111) and Ti(0001) surfaces. Analysis of the O/Al(111) vibrational data based on lattice dynamical slab calculations confirms underlayer formation as a precursor to oxidation. These results help account for some of the novel properties associated with oxygen chemisorption on Al(111) and Ti(0001) surfaces and also illustrate the ability of vibrational spectroscopy to provide surface structure information which complements results of other structure sensitive techniques.
Growth of large diameter (Hg,Cd)Te crystals by incremental quenching
Authors: Colombo Luigi , Syllaios A. J. , Perlaky R. W. , Brau M. J.
Published: July 2002

The growth of large (20 mm diam by 50 mm length) Hg1−xCdxTe crystals by incremental quenching of large volume Hg1−xCdxTe alloy melts was demonstrated. This method is based on the sequential freezing of shallow melts that have large surface to volume ratios onto a large diameter growing ingot. The resulting homogeneous polycrystalline ingots were annealed at 665 °C to promote grain growth. Grain sizes ranging from 25 to 35 mm were obtained after annealing at 665 °C for 28 days. In addition, the crystals showed very little substructure and had dislocation densities of 1.25±0.6×105 cm−2. Hall effect measurements on wafers annealed at temperatures below 300 °C show an n-type behavior with carrier concentrations ranging from 3.3×1014 to 4.8×1014 cm−3 and majority carrier mobilities ranging from 1.69×105 to 2.29×105 cm2/V s at 77 K for a composition x=0.225. The compositional variation Δx in the radial and axial direction was measured by several techniques and was found to range from 0.005 to 0.01.
Thermal outgassing from aluminum alloy vacuum chambers
Authors: Chen J. R. , Narushima K. , Ishimaru H.
Published: July 2002

A special aluminum alloy tube, primarily A6063 alloy clad inside with A1050 al pumpdown at room temperature and ∼1×10−13 Torr⋅l/s cm2 10 h after a 1 day bakeout at 150 °C. When the tube was vented to air for 1 day, the vacuum performance was not degraded. Outgassing rates for another type of tube, made of A6063 alloy but using a special extrusion method, were measured for several cases: (1) after exposure to air for about 1.5 years, (2) after partially filled with water for 1 day, and (3) after partially filled with water for 1 week. The outgasssing rate 10 h after baking was ∼1.5×10−13 Torr⋅l/s cm2 for case (2) and <5×10−13 Torr⋅l/s cm2 for case (3). Some surface parameters, adsorption isotherms, surface coverages, mean residence times, and adsorption energies were calculated to describe the surface conditions for all the above cases.
Barium titanate thin-film humidity sensitive capacitor
Authors: Chen S. N. , Ramakrishnan E. S. , Grannemann W. W.
Published: July 2002

A humidity-sensitive capacitor using thin films of BaTiO3 have been successfully deposited on silicon substrates by rf sputtering in an O2/Ar atmosphere. The capacitance of these devices are sensitive to changes in relative humidity, substrate temperature, and postdeposition annealing temperature. Typically, a 300% increase was observed when the relative humidity (RH) was changed from 27 to 90% at a testing frequency of 1 MHz. The capacitance–voltage, current–voltage, and the temperature and frequency effects on the sensor characteristics are presented.
Direct observation of atomic steps and atomic structures in the reconstruction of Pt and Ir surfaces
Authors: Gao Q. J. , Tsong T. T.
Published: July 2002

Atomic steps and atomic structures in the reconstruction of Pt and Ir surfaces, induced by nanosecond pulsed-laser heating, have been studied in field ion microscopy. Pt and Ir (110) planes reconstruct from the (1×1) to the (1×2) by breaking of the [110] atom rows into fragments of two to several atoms and by lateral and cross-channel jumps of these fragments. Jumps of single atoms are rare. The (1×2) structure we have observed is consistent with the ‘‘simple’’ missing row model. The hexagonal structure of the Ir(001) (1×5) reconstructed surface has been directly observed for the first time. The image structure appears to be consistent with the models proposed from low-energy electron diffraction studies although the detail buckling may depend on the size of the plane.
Filled and empty states of H:GaAs(110) through electron energy-loss and photoemission spectroscopies
Authors: Nannarone S. , Astaldi C. , Sorba L. , Colavita E. , Calandra C.
Published: July 2002

The energy distribution of filled and empty states of H:GaAs (100) surface is reported. The results have been obtained by the combined analysis of photoemission and energy-loss spectra (ELS). The main emphasis is devoted to the ELS interpretation of interface plasmon losses of the H:GaAs (110) surface layer. New excitations are found at the vacuum–H:GaAs (110)–GaAs interface and the energy difference between filled and empty states is determined. Starting from filled electronic states as localized by photoemission measurements, empty states of the surface layer are located.
Data processing for scanning tunneling microscopy
Authors: Rosenthaler L. , Hidber H.-R. , Tonin A. , Eng L. , Staufer U. , Wiesendanger R. , Güntherodt H.-J.
Published: July 2002

This contribution deals with the data processing system for our scanning tunneling microscope (STM). Since several collaborators should have access to our STM data, we have decided to separate between data acquisition and data processing. The data acquisition system based on a cheap 8-bit microcomputer controls all aspects of the scanning process, stores the data on disk, and transmits them to the data processing system. Image processing and computer graphics have become more important in scanning tunneling microscopy. We use two μVAX II’s which are connected by a network, one as a storage device (527-MByte disk), the other as a graphic processor (256 colors). We have developed a highly interactive software package which allows manipulating and displaying the STM data. This package includes utilities to fit a plane or a hyperbolic paraboloid and subtract it from the image. The line plots of topography and the local barrier height can be viewed from different point of view. Top-view images can be displayed both in color with different color lookup tables, which can be chosen interactively, and in gray scale. The images can be displayed at higher resolution by a bilinear interpolation. Light sources illuminate the surface to get flat and Gouraud shading. The shading can be combined with perspective or parallel projection and hidden surface removal. There is also a fast Fourier transformation algorithm and a utility for interactive digital filter design implemented. There are utilities to create stereoscopic pictures. Significant examples of the application to images of graphite and of nanometer scale structure images are presented.
Gas injection system for the Advanced Toroidal Facility
Authors: Langley R. A. , Halliwell J. W. , Dyer G. R. , Yarber J. L.
Published: July 2002

A gas injection system that provides three independent gas sources has been developed for the Advanced Toroidal Facility (ATF). Each of the three gas injection lines can supply hydrogen gas at flow rates of 1 to 100 Torr l/s (nitrogen at flow rates of 1.5 to 15 Torr l/s). A feedback control system allows gas injection pulse shaping, with a flow rate rise-time response of <3 ms and a fall-time response of <15 ms. In addition, an autozeroing system removes long-term (>500 ms) temperature drifts in the feedback sensor and reduces effects caused by changes in the magnetic field. A pressure-measuring system provides an absolute measurement of the amount of gas injected into the ATF vacuum vessel as a function of time. The components used in the gas injection lines are discussed, and compromises are elucidated. Flow limits, time constants, and other pertinent points are presented.
New ordered phases and multicriticality of Te/Ni(111): Model calculations and comparisons with experiment
Authors: Thevuthasan S. , McKay S. R. , Unertl W. N.
Published: July 2002

The chemisorbed system tellurium on Ni(111) has been studied using a lattice gas model with pair interactions as long range as sixth neighbor. We discover three distinct (2√3×2√3)R30 phases: low coverage (θ= (1)/(12) ), centered (θ= (1)/(6) ), and high coverage (θ= (1)/(4) ), when interactions are adjusted to match qualitatively the other features of the experimental phase diagram. Each pair of neighboring ordered phases is separated by a coexistence region at low temperatures. The low-coverage 2√3 phase disorders via a first-order transition at higher temperature. At higher coverage, a (√3×√3)R30 phase occurs at intermediate temperature. This phase melts by a first-order transition at low coverages and a continuous, three-state Potts transition at higher coverages. Thus, the simulations suggest that this chemisorbed system may provide an experimental realization of Potts tricritical behavior. Alternate sets of interactions in this long-range lattice gas model produce the (√7×√7)R19, (3×3), and (2×2) phases, which have been reported for other chemisorbed systems on triangular lattices.
Site exchange of atoms across atomically sharp Ag–Au interfaces
Authors: Niemantsverdriet J. W. , Markert K. , Dolle P. , Wandelt K.
Published: July 2002

The thermally activated site exchange between Ag/Au and Au/Ag double layers on a Ru(001) substrate has been studied with photoemission of adsorbed xenon (PAX). The Au/Ag interface is less stable than the Ag/Au interface on Ru, penetration of Au atoms in a Ag underlayer occurs at lower temperatures than penetration of Ag atoms in a Au underlayer. The work serves as a model for other metal–metal interfaces and illustrates the usefulness of PAX in the characterization of surfaces on a subnanometer scale.
Column 1B metal adsorption on Ge(111): The growth mode of Cu
Authors: Hansen J. C. , Knapp B. J. , de Souza-Machado R. , Wagner M. K. , Tobin J. G.
Published: July 2002

Cu was deposited via evaporation onto Ge(111), under ultrahigh vacuum conditions. The resulting surfaces were probed with angle-resolved photoelectron spectroscopy (ARPES), K-resolved inverse photoelectron spectroscopy, low-energy electron diffraction, and Auger electron spectroscopy. The ARPES investigations include valence-band and core level measurements performed using synchrotron radiation. Two parallel studies were pursued: in one, the substrate was kept at room temperature; while in the other, the substrate temperature was raised to ∼200 °C during the evaporations. These measurements indicate subtle but significant differences between the growth modes at the two different temperatures. Both the room temperature and hot surfaces exhibit an ordered ‘‘(5×5)R30° ’’ structure at low coverages. The development of a Cu(111)-like ordering and evidence that some Ge is floating in or on the Cu were observed at higher coverages with room-temperature samples.
Scanning tunneling microscopy of biopolymers: Conditions for microtubule stabilization
Authors: Hameroff Stuart R. , Simić-Krstić Jovana , Kelley Murray F. , Voelker Mark A. , He Jackson D. , Dereniak Eustace L. , McCuskey Robert S. , Schneiker Conrad W.
Published: July 2002

Applications of scanning tunneling microscopy (STM) to biological materials have been limited by poor conductivity and instability of biomolecules. We have used STM to probe three different biopolymer materials in air on graphite surfaces: collagen protein, phospholipid membranes, and microtubule protein assemblies. In the case of microtubules, we evaluated parameters for fixation and stabilization for STM imaging and found conditions which resulted in stable, reproducible images. STM of collagen showed linear strands ∼ 1.5 nanometers (nm) in diam. Periodicity of ∼ 3 nm was accentuated by ‘‘spikes’’ which appear to match pyrrolidine ring structures in amino acids proline and hydroxyproline. STM of Langmuir diphosphatidyl ethanolamine phospholipid membranes showed a lattice periodicity (0.4 to 0.5 nm) which appears to match the spacing of phospholipid molecules in membranes. Preparation of microtubules for STM which consistently resulted in reproducible and stable images includes a specific salt and magnesium containing buffer, glutaraldehyde fixation and 0.8 M glycerol. Freeze drying was also utilized, however stable images were also obtained without freeze drying. STM imaging of microtubules in several magnifications showed linear structures of appropriate (≊25 nm) width comprised of 4 nm wide protofilaments. Microtubules often appeared ‘‘buckled’’ and flattened and shaded images (not shown) demonstrated individual ‘‘tubulin’’ subunits. Evidence of tip interaction with the biopolymers was seen with collagen and phospholipid membranes. We feel STM and related technologies have great promise for the study of biomolecular surfaces.
Plasma polymerization by magnetron glow discharge. III. Effect of magnetic field on sputtering characteristics of electrode materials
Authors: Cho D. L. , Yeh Y.-S. , Yasuda H.
Published: July 2002

The sputtering of metal in a magnetron glow discharge polymerization reactor system is investigated as a function of magnetic field. A pair of planar electrodes with circular arrangement of permanent magnets is used with a 10-kHz electric power source. The sputtering of metal from the electrode is investigated for argon (nonpolymer-forming gas) and methane (polymer-forming gas) plasmas. In the case of the argon plasma, the sputtering rate is measured by the rate of deposition of metal upon the surface of quartz crystal. In the case of the methane plasma, the sputtering rate is estimated from the polymer deposition rate and the metal content in the deposited polymer determined by electron spectroscopy for chemical analysis (ESCA). In both cases, no appreciable deposition of metal (Cu or Al used as the electrode) is observed if the maximum parallel component of the magnetic field (with respect to the electric field) is <100 G. The sputtering rate by argon plasma is much greater than methane plasma, and the rate increases with the magnetic field strength of a magnetron. The sputtering rate in a methane plasma is related to the deposition of polymer on the electrode surfaces.
Chemical vapor deposition of boron and boron nitride from decaborane(14)
Authors: Kim Yoon Gi , Dowben P. A. , Spencer J. T. , Ramseyer G. O.
Published: July 2002

We have investigated photoassisted, plasma enhanced chemical vapor deposition and pyrolytic deposition of boron from decaborane (B10H14) and boron nitride from decaborane combined with nitrogen or ammonia. The use of decaborane for depositing boron and boron nitride thin films is seen as a viable alternative to diborane or boron halides.
Initial results for ion-induced release of hydrogen and deuterium from AXF-5Q graphite by hydrogen and deuterium
Authors: Langley R. A.
Published: July 2002

The ion-induced release of hydrogen and deuterium from AXF-5Q graphite has been measured for hydrogen and deuterium ions with energies near 200 eV. The experimental data obtained are analyzed to determine the ion-induced release cross section and the location and release of the additional retained hydrogen (i.e., that not retained in the surface layer). Two different approaches were used to model the release of the additional hydrogen. The model that treats the additional retained hydrogen (deuterium) as having migrated deeper into the graphite on grain surfaces produces results that are consistent with experimental data, whereas the model that treats the additional retained hydrogen as being trapped in a codeposited layer produces results that are inconsistent with experimental data. The ion-induced release cross section is determined to be in the range (1–2)×10−17 cm2.
Carbon deposition in the gaps between tiles: Data from the Tokamak Fusion Test Reactor and laboratory simulation studies
Authors: Hsu W. L. , Mills B. E. , Ehrhardt A. B. , Sun Y. C.
Published: July 2002

The bumper limiter in the Tokamak Fusion Test Reactor (TFTR) is lined with graphite tiles. Between the tiles are gaps of width ∼3 mm. Interaction of the hydrogen plasma with the graphite tiles is known to lead to the deposition of hydrogen-rich carbon layers on low-flux regions of the tiles. When these tiles were disassembled for examination, thick carbon deposits were found to penetrate ∼2 cm down the side faces of the gaps. These deposits were several microns thick, at a depth ∼5 mm below the plasma-facing surface. Experiments were performed in the plasma simulator Laser-Material-Plasma Experiment (LAMPE) to study the mechanism of carbon deposition in narrow gaps. In conjunction with calculations using the neutral transport code DEGAS, the results show that sputtered carbon can be transported deep down the gap by multiple reflections off the faces of the gap. This understanding should be taken into account in the design of tiles for future fusion reactors to minimize codeposition buildup in these nearly inaccessible regions.