bluuebunny/crossref_metadata_2025 huggingface dataset:
Room-temperature evolution of vacancy-type damage created by 2 keV B+ implantation of Si
Authors: Gwilliam R. M. , Knights A. P. , Burrows C. P. , Coleman P. G.
Published: July 2002

Beam-based positron annihilation spectroscopy has been applied to the study of near-surface vacancies created by 2 keV B+ ions implanted into Cz Si. The use of a controllable-energy positron beam means that the probe can be tuned to maximize the response to the subsurface damage. Time-dependent changes have been observed in the near-surface vacancy concentration profile. For example, after one week at room temperature, exposure of an implanted sample to white light for 1 h resulted in the migration of ∼95% of the measurable damage to sinks—primarily, it is assumed, to the surface. The relative importance of temperature, air, and light has been investigated.
Molecular beam epitaxy growth of GaAsN layers with high luminescence efficiency
Authors: Kovsh A. R. , Wang J. S. , Wei L. , Shiao R. S. , Chi J. Y. , Volovik B. V. , Tsatsul’nikov A. F. , Ustinov V. M.
Published: July 2002

(In)GaAsN bulk layers and quantum wells usually demonstrate lower photoluminescence intensity than the nitrogen-free compositions. In the present work we have carefully optimized both conductance and operation of a nitrogen plasma source as well as growth parameters of GaAsN layers. We found conditions when incorporation of nitrogen did not lead to formation of additional nonradiative recombination. There is some minimum growth rate to obtain good crystal and optical quality of GaAsN. At growth rates below this value the pattern of reflection high energy electron diffraction turns spotty and the growth proceeds in a three-dimensional mode. This leads to a steep decrease in luminescence efficiency of the grown layer. The minimum value of growth rate depends on nitrogen content and growth temperature. Defects caused by low temperature growth are removed by post-growth annealing. We achieved the same radiative efficiency of GaAsN samples with nitrogen content up to about 1.5% grown at 520 °C as that of a reference layer of GaAs grown at 600 °C. Compositional fluctuation in the GaAsN layers leads to the S-shape temperature dependence of photoluminescence peak position. Post-growth annealing reduces compositional fluctuation.
Angular dependence of uv photoelectron distributions for oxygen adsorbed on W(100)
Authors: Waclawski B. J. , Vorburger T. V. , Stein R. J.
Published: July 2002

Recent theoretical work has suggested the possibility of determining chemisorption bond geometry by the use of uv photoemission. This possibility is being investigated experimentally in an apparatus developed at NBS. The apparatus is described, and preliminary results are presented which show energy distributions as a function of emission angle for electrons photoemitted from W(100), both clean and with adsorbed oxygen. The results obtained at hν = 21.2 eV for several emission angles indicate substantial angular dependence of the photoelectron distributions, not only for the clean (100) surface, but also, more dramatically, with an oxygen adlayer.
Kinetics of compound formation in thin film couples of Al and transition metals
Authors: Howard J. K. , Lever R. F. , Smith P. J. , Ho P. S.
Published: July 2002

Intermetallic coumpound formation at metal–metal interfaces was observed for thin film couples of Al and transition metals such as Cr, Ti, Hf, Zr, Co, Ta, Pd, and Pt. The Al–Cr system was investigated in some detail using a conductance method and nuclear backscattering for reaction-rate measurements. The compounds CrAl7 and Cr2Al11 were identified and their growth was found to be diffusion controlled. The temperature dependence of the rate constant for CrAl7 obeyed an Arrhenius plot from 300° to 450 °C with an activation energy of 1.91±0.1 eV. The Al-rich phases of the remaining transition metals were investigated; the compounds either exhibited a planar interface with parabolic growth kinetics or an irregular interface with nonparabolic growth. An empirical relationship involving the melting point and stability of the compounds was proposed to explain the different growth kinetics.
N
V
V Auger spectra from W(100)
Authors: Withrow S. P. , Luscher P. E. , Propst F. M. , Weinberg W. H.
Published: July 2002

The NVV Auger spectrum from a clean W(100) surface has been measured in the second derivative, d2N (E)/dE2, mode to enhance fine structure. This measurement is compared with spectra generated from both the self-convolution of the tungsten valence-band bulk density of states (obtained from a relativistic APW energy band calculation) and a ’’restricted convolution’’ in which only transitions involving electrons from the same valence energy are allowed. The restricted convolution for a model of the Auger process in which both N6VV and N7VV transitions contribute offers the best match of theory and experiment. No distinct evidence of Auger emission involving the surface resonance present on W(100) is observed. Effects of H2 and O2 adsorption on the Auger spectrum of the W(100) surface are reported.
Ultraviolet photoemission studies of formaldehyde and related molecules adsorbed on Ru(110)
Authors: Fisher Galen B. , Madey Theodore E. , Yates John T.
Published: July 2002

The adsorption of formaldehyde (H2CO), hydrogen, and carbon monoxide on Ru(110) has been studied using angle-integrated ultraviolet photoemission spectroscopy (UPS) and temperature programmed desorption (TPD). The UPS spectra for low exposures of H2CO at 80 K indicate that H2CO dissociates to a substantial degree. These spectra are compared with UPS spectra for the sequential adsorption of hydrogen and CO. Whereas there are similarities between these spectra, the differences in the UPS, work function change, and TPD results are sufficient to suggest that a portion of the dissociated H2CO may exist as a surface molecular complex containing H and CO. This is apparently the first reported example, based on a UPS study, of an oxygen-containing organic molecule which dissociates upon adsorption on a metal surface at 80 K. For high exposures at 80 K, adsorption of a condensed layer of molecular H2CO is observed.
Turbomolecular pump vacuum system for the Princeton Large Torus
Authors: Dylla H. Frederick
Published: July 2002

A turbomolecular pump vacuum system has been designed and installed on the Princeton Large Torus (PLT). Four vertical shaft, oil-bearing, 1500-l/s turbomolecular pumps have been interfaced to the 6400-l PLT vacuum vessel to provide a net pumping speed of 3000 l/s for H2. The particular requirements and problems of tokamak vacuum systems are enumerated. A vacuum control system is described which protects the vacuum vessel from contamination and protects the turbomolecular pumps from damage under a variety of possible failure modes. The performance of the vacuum system is presented in terms of pumping speed mesurements and residual gas behavior.
The nitrogen pressure in a vacuum system
Authors: Edwards D.
Published: July 2002

Since the N2 outgassing rate from walls of a vacuum system is generally recognized to be very small, the presence of an N2 pressure in the system is a useful indication of the presence of real leaks to the atmosphere. A technique of thermal desorption mass spectrometry is introduced which allows the N2 pressure in the background gas of a baked system to be separated from a CH4 background to a minimum level of N2 detectability of ∠1% of the CO background pressure. In typical baked systems (of which an example is given), it is possible to determine the sum of all real N2 leaks from atmosphere at a level of ∠10−11 Torr l/s. This feature makes the technique ideally suited to large complex systems since the leak rate can be evaluated before detailed leak-finding procedures are initiated.
Glow discharge processing versus bakeout for aluminum storage ring vacuum chambers
Authors: Dean N. R. , Hoyt E. W. , Palrang M. T. , Walker B. G.
Published: July 2002

Experiments were carried out on laboratory and prototype scale systems in order to establish the feasibility of argon discharge processing the PEP storage ring aluminum vacuum chambers. Electron-induced desorption rates showed significant reductions following bakeout and/or argon glow discharge treatment (≳1019 ions cm−1). Data are presented and discussed in relation to advantages and problems associated with: water removal, argon trapping and subsequent release, electron energy dependence, discharge distribution, and surface plasma chemical effects.
Precursor adsorption of O2 on tin and the activation energy for chemisorption
Authors: Chottiner G. , Glover R. E.
Published: July 2002

Condensation of a thick layer of O2 on Sn at 5 K causes an increase in resistance corresponding to a loss of metallic conductivity by less than 0.1 Å of Sn. The small magnitude must mean that oxygen is initially adsorbed in a molecular physisorbed state since tying up even one Sn conduction electron per surface atom in chemical bonds would cause a resistance increase more than 10 times that observed. When warmed above 13 K the resistance of the oxygen-covered Sn films increases irreversibly with time, a change we attribute to chemisorption. The rate increases with increasing temperature and decreases as a total change corresponding to removal of 11 Å of Sn is approached. Analysis of the data for oxidation thicknesses between 1.5 and 8 Å gives consistent values for an activation energy of 0.035 eV.
Electronic orbitals of Se bonded to Ni(100)
Authors: Froitzheim H. , Hagstrum H. D.
Published: July 2002

New angle-integrated UPS spectra are presented at different angles of light incidence for NeI radiation on Ni(100) c (2×2)Se. These spectra show that a Se-derived orbital lies in the energy range of the Ni d band as suggested by Fisher. The corresponding INS spectrum is also given and discussed. It is shown that the present Ni sample produces a two-domain c (2×5)Se structure at one-quarter monolayer as opposed to the p (2×4)Se structure observed on earlier samples.
Subsurface atomic displacements at the GaAs(110) surface
Authors: Kahn A. , So E. , Mark P. , Duke C. B.
Published: July 2002

LEED IS (intensity–momentum transfer) data has been used to verify atomic displacements in the first subsurface layer of GaAs(110). IS profiles averaged over a range of incidence (ϑ) and azimuthal (φ) angles, subject to constant S, data for selected values of ϑ and φ, and similar IS profiles computed from kinematical calculations are intercompared to assess the relative importance of inadequate data averaging and variations of geometric parameters. Preferred atomic position parameters in the terminating region of the lattice are given.
Temperature effects in polarized low-energy electron scattering from solids and liquids
Authors: Unertl W. N.
Published: July 2002

The effects of temperature on the polarization of low-energy electrons scattered from surfaces of liquids, polycrystals, and single crystals are discussed. The polarization of the single scattering component of the intensity is shown to be independent of temperature, whereas that of the multiple scattering intensity is temperature dependent. Differences between polarizations observed for electron scattering from free atoms and from polycrystals and liquids are qualitatively explained and a quantitative theory is outlined. The implications for polarized low-energy electron diffraction from single-crystal surfaces are also discussed.
LEED analysis of a Cu(110) surface
Authors: Noonan J. R. , Davis H. L. , Jenkins L. H.
Published: July 2002

Experimental and calculated I–V profiles for the (0l̄) diffraction beam from a Cu(110) surface are presented and compared. Preliminary results of this comparison suggest that the outermost atomic layer is contracted by ∠10% relative to the bulk interlayer spacing, and there is some evidence that the second-third layer spacing may be slightly contracted. In order to demonstrate the reproducibility of the data obtained in this investigation, degeneracies of beams related by symmetry are also illustrated.
Force measurement in chemical analysis
Authors: Schubart B. , Poulis J. A. , Gast Th.
Published: July 2002

In the cooperation between the Technological University of Eindhoven, the Technical University of Berlin, and the Application Laboratory of Sartorius Werke Göttingen, research has been performed on the application of ponderomatic measurements for the detection of fluids in liquid chromatography and other fields of chemical analysis. For this research a special balance has been developed, which in future might be used under vacuum conditions. The apparatus has been described at the Salford VMT conference last year; in the present paper we present experimental results. For the comparison of these results with those of other measurements we shall have to go into some detail about the choice of the frequency of the electric voltage used.
System for transferring samples between chambers in UHV
Authors: Fleisch T. , Shepard A. T. , Ridley T. Y. , Vaughn W. E. , Winograd N. , Baitinger W. E. , Ott G. L. , Delgass W. N.
Published: July 2002

This system provides right angle or end-on transfer of a sample holder from one chamber to another at ultrahigh-vacuum conditions. A convenient mechanical coupling and uncoupling device and magnetically driven transfer rods allow movement of the sample-holder assembly over distances up to 150 cm. The room-temperature holder accommodates two samples. The heatable assembly includes contacts for resistive heating of the sample to temperatures above 1800 K and thermocouple reading of sample temperatures.
Adsorption of water on copper and cuprous oxide
Authors: Sharma S. P.
Published: July 2002

Water adsorption and desorption isotherms are reported for evaporated Cu and Cu2O using a quartz crystal oscillator method with an ultimate sensitivity of 10−8 g cm−2. Cu2O adsorbs more water than Cu at a given relative humidity (RH). Higher adsorbed water content on Cu2O a a given RH partly accounts for the breakdown of its passivity against sulfidation at elevated RH as reported earlier by the author. Isotherms are fitted to a BET-type (type II) model. From the BET parameters, the monolayer capacity and the heat of adsorption have been computed.
Preparation of x-ray lithography masks with 0.1 μm structures
Authors: Parrens P. , Tabouret E. , Tacussel M. C.
Published: July 2002

A process for fabricating x-ray lithography masks having structures as small as 0.1 μm is described in detail. The patterns are made by electron-beam lithography in PMMA resist laid on 1-μm-thick polyimide membrane. The fact we use a very thin substrate strongly reduces the influence of electron backscattering on the resolution. That way it is possible to transfer 0.1 μm lines and spaces in 0.25-μm-thick PMMA resist. Gold absorber patterns are formed using electroplating, this technique being able to reproduce the smallest details of the lithography. On the other hand it allows high-aspect ratios because electroplated gold may be as high as the resist layer. Examples of 0.25 μm lines with 0.05 μm spaces in 0.25-μm-thick gold and 0.2 μm spatial period gratings in 0.15-μm-thick gold are given.
Hemispherical retarding type energy analyzer for IC testing by electron beam
Authors: Goto Y. , Ito A. , Furukawa Y. , Inagaki T.
Published: July 2002

This paper describes an improved hemispherical retarding type energy analyzer for IC testing using an electron beam. A hemispherical retarding type analyzer has been proposed for IC testing but it produces a voltage measurement error of more than 10% even for an optimum slice level. The deficiencies of the analyzer and our improved arrangement are investigated by an analysis of the potential distribution using a high resistance film. A control grid and buffer grid are introduced in the new analyzer to generate a high spherical extraction field. In addition, an electron detector is arranged to give a high collection field outside the retarding grid. The improved hemispherical retarding type energy analyzer produces only a 2% voltage measurement error for a specimen voltage range of −14 to 20 V. This level of performance is ensured for a slice level margin within a 75% range of the output amplitude.
Guidelines for construction of low-pressure gas manifolds
Authors: Paulick T. C.
Published: July 2002

Expressions are obtained for the outflow pattern from the orifices of a gas manifold in the molecular flow regime. The example considered in detail is a section of tubing with identical holes equally spaced along the tube. The manifold is characterized by k, the number of holes, and n, a conductance ratio. Example of outflow patterns for various values of n and k are given. The quantity kn−1/2 emerges as a figure of merit for uniform discharge. A simple experiment supports the usefulness of the model used.
TFTR prototype electrostatic-calorimeter probe head
Authors: Manos D. M. , Budny R. V. , Cohen S. A.
Published: July 2002

Power loading of the limiters in TFTR is a major concern because of problems of impurity generation and thermal stresses. To diagnose this edge plasma we have prepared a prototype electrostatic-calorimeter probe and tested it on the PDX and PLT tokamaks. The probe provides time-resolved measurements of heat flux Q and Langmuir (I–V) characteristics on each of its opposing active elements. The present design, employing carbon shields and tantalum elements, is able to withstand ≊5 kW/cm2 for ≊10 ms or 1 kW/cm2 for 500 ms and provides 5–10 ms time resolution of heat flux. This allows simultaneous estimation of time-resolved radial profiles of ne, Te, and Ti. By fitting the probe with narrow slit apertures and rotating the probe head, the device provides discrimination between particles having different values of Larmor radius and/or ratios of perpendicular to parallel velocities. Calculations required to interpret the results of probe head rotation are also discussed. This information is of interest in the study of fast ion losses during neutral beam, ICRF, and LH auxiliary heating.
Influence of the sputtering gas pressure on deposition profiles
Authors: González-Díaz G. , Mártil I. , Sánchez-Quesada F. , Rodríguez-Vidal M. , Gras-Martí A. , Vallés-Abarca J. A.
Published: July 2002

Experimental thickness profiles of thin films deposited on substrates perpendicular to the target being sputtered show maxima whose position depends on the sputtering gas pressure. A simple model of particle slowing down in the transport stage accounts for this fact. The influence of diffusional transport on thin film profiles deposited on substrates both parallel and perpendicular to the target, can be estimated comparing experimental data with model predictions.
Reaction rates of D2+T2 mixtures at 295 K
Authors: McConville G. T. , Menke D. A. , Ellefson R. E.
Published: July 2002

Reaction rates for the production of DT from D2+T2 mixtures are reported as a function of pressure, initial T2 concentration, and concentration of the impurity of CT4. The reactions took place in a specially constructed stainless steel container. The reactions are reproducible and can be explained in terms of the ion–molecule chain model of Thompson and Schaeffer. The presence of T2O as an impurity has no measurable effect at the measured concentration.
A system for i
n s
i
t
u studies of plasma–surface interactions using x-ray photoelectron spectroscopy
Authors: Vossen J. L. , Thomas J. H. , Maa J.-S. , Mesker O. R. , Fowler G. O.
Published: July 2002

A system is described in which plasma/surface treatments can be performed and the substrates can be analyzed by x-ray photoelectron spectroscopy by transferring them via a load lock into the analytic chamber. Also described are some plasma etching experiments that demonstrate the utility of this apparatus. The system emulates larger systems in which plasma treatments are performed at pressures, voltages, and power densities similar to those employed in large commercial systems.
A simple and efficient internal heater for baking vacuum systems
Authors: LeGrand A. D. , Greene E. F.
Published: July 2002

A simple and convenient method for baking a vacuum system is described which requires less power and shorter bakeout time as compared to conventional baking methods.
Neutral beams for mirrors
Authors: Fink J. H.
Published: July 2002

An important demonstration of negative ion technology is proposed for FY92 when negative ions will be used to form the neutral beams that generate ‘‘sloshing ions’’ in MFTF α+T, an upgrade of the Mirror Fusion Test Facility at Lawrence Livermore National Laboratory. Three different 200 keV beam lines are being considered for this application; I discuss their advantages and disadvantages.
Surface phases for sulfur and oxygen coadsorbed on Ni60Fe40(100)
Authors: Lad R. J. , Schrott A. G. , Blakely J. M.
Published: July 2002

The adsorption of oxygen on a clean Ni60Fe40(100) alloy surface yields a c(2×2)O LEED pattern near half-monolayer coverage; this is accompanied by Fe segregation. The intensity of this pattern decreases (reversibly) near 525 °C with no change in oxygen coverage; this is due to an order–disorder transition in the O overlayer. Sulfur was deposited using a beam of S2 molecules from an electrochemical cell. S-dosed, annealed samples showed negligible alloy segregation and exhibited p(2×2)S or c(2×2)S LEED patterns with varying degrees of surface order, depending on sulfur coverage. Upon exposure to O2 gas, a p(2×2)S pattern was gradually replaced by a c(2×2). The brightest c(2×2) pattern occurred at a total S+O coverage of 0.5 monolayers. LEED studies of the c(2×2) patterns for several S–O compositions at fixed half-monolayer coverage suggest that metastable O-rich and S-rich c(2×2) domains are formed during coadsorption and become partially miscible with temperature cycling.
Finite size effects on reconstruction domains of tungsten(001) surfaces
Authors: Wendelken J. F. , Wang G.-C.
Published: July 2002

The size of reconstruction domains on low-temperature, clean W(001) and also hydrogen-covered W(001) have been studied for both planar and stepped surfaces through analysis of LEED intensities and beam shapes. The stepped surface with step edges parallel to the [110] has an average terrace width of ∼28 Å. For the low temperature, clean, planar surface the average equilibrium reconstruction domain size is ∼130 Å. On the stepped surface, ‘‘zig–zag’’ orientational domains with atomic displacements perpendicular to the steps are preferred and the domain size perpendicular to the steps is limited by the terrace width, while the size parallel to the steps is nearly the same as on the planar surface. Hydrogen-induced reconstruction domains for the commensurate phase are similar in size to the clean surface domains on the planar surface. On the stepped surface, the ‘‘dimer’’ domains are also limited by the terrace width perpendicular to the steps and are additionally limited parallel to the steps to approximately half their planar surface dimension. With increasing hydrogen exposure and the development of the incommensurate phase, the domain dimensions are observed to shrink to less than 12 Å before the transition to the (1×1)-H structure occurs on both planar and stepped surfaces.
A study of the electric field dependence of subthreshold photoemission
Authors: Reifenberger R. , Egert C. M. , Haavig D. L.
Published: July 2002

Experiments that detect electrons photoemitted from W(110) at energies below the vacuum level are reported. The data are obtained by performing energy resolved measurements of the electrons photoemitted from a tungsten field emission tip that is illuminated by focused UV lines from an argon–ion laser. Data on the final state energy distributions are analyzed by a theory that includes the transmission probability for an electron escaping from a metal–vacuum interface at energies below threshold. Data on the subthreshold photocurrent integrated over all final state energies reveal an oscillatory contribution when measured as a function of electric field. Fourier analysis of this data gives a frequency of (10.3±0.9)×104 (V/cm)1/2, a result that is in close agreement with previous measurements. The origin of this oscillatory structure has still not been conclusively established.
The use of ion beam sputtered optical coatings as protective overcoats
Authors: Cole B. E. , Moravec T. J. , Ahonen R. G. , Ehlert L. B.
Published: July 2002

Diamond turned aluminium mirrors are being used more often in forward looking infrared (FLIR) imaging systems (operating in the 8–12 μm region) because they provide high optical performance at low cost. The original high reflectivity of these surfaces must be maintained through military standard humidity/temperature cycling tests. We have developed ion beam sputtered Y2O3 as a protective coating that meets all optical and environmental requirements. Data are presented that show that ion beam sputtered optical coatings are much less permeable to water than electron-beam coatings while retaining many of the desirable features of e-beam coatings. The deposition process and the properties of the coatings will be presented. Thin protective coatings of Y2O3 that exhibit very little angular dependence in reflectivity on aluminum have been prepared by ion beam sputtering.
Platinum aluminide coating structural effects on hot corrosion resistance at 900 °C
Authors: Deb P. , Boone D. H. , Streiff R.
Published: July 2002

Studies have shown that platinum modified aluminide coatings can exhibit a range of structural variations depending on initial platinum thickness, prealuminizing heat treatment, aluminizing cycle, and postcoating heat treatment. It had been speculated earlier that such structural variation could account at least in part for some of the reported variation of performance of these coatings. A series of archetype structures was prepared on IN738 by two aluminizing processes: (i) low aluminum activity and (ii) high aluminum activity; and tested at 900 °C under conditions producing so called Type I high temperature hot corrosion. The results of the present investigation showed that the addition of platinum greatly improved the hot corrosion resistance. It is observed that the low aluminum activity process has better corrosion resistance than that of the high aluminum activity process. It is also found that the surface degradation of both aluminizing processes is quite severe when the specimens were given prolonged prealuminizing diffusion heat treatment. Microstructural observation revealed a significant difference in coating thickness in both the processes and it depends on prealuminizing diffusion and the subsequent aluminizing treatment employed.
Diamondlike amorphous carbon films prepared by magnetron sputtering of graphite
Authors: Savvides N. , Window B.
Published: July 2002

Amorphous carbon films, a-C, were prepared by employing dc magnetron sputtering of a graphite target in an argon plasma. A series of a-C films were deposited as a function of sputtering power. The power was varied in the range 5–500 W and the target effective sputtering area was about 20 cm2. The physical and optical properties of the a-C films show a dependence on the sputtering power. The films, although unhydrogenated, possess diamondlike properties such as high hardness, HV=1200–2400 kgf mm−2, and are transparent in the infrared (IR) region with optical gap Eopt =0.40–0.74 eV. We observe a systematic variation of film properties with increasing sputtering power which suggest a transition from fourfold (diamondlike) to threefold (graphitic) coordination of the carbon atoms. For films prepared at low sputtering power about 3/4 of the carbon atoms have tetrahedral coordination and 1/4 have trigonal coordination. At the highest sputtering power the a-C films consist of equal mixtures of tetrahedrally and trigonally bonded carbon atoms.
A core-level binding-energy shift analysis of CO, H, and O adsorption on Cu–Ni surfaces
Authors: Egelhoff W. F.
Published: July 2002

The equivalent core approximation (Z+1) is used with a Born–Haber cycle analysis to analyze the Ni 2p3/2 surface core-level binding-energy shifts which occur upon adsorption of CO, H, and O on Ni(100). The analysis gives values for the heats of desorption of these gases from Cu–Ni alloy surfaces. Perhaps more importantly, it also provides a quantitative determination of how chemisorption of CO, H, and O modify the heats of surface segregation for Cu–Ni surfaces.
X-ray microradiography of inertial fusion targets using a laser-produced plasma as an x-ray source
Authors: Kim Hyo-gun , Wittman Mark D.
Published: July 2002

Optically opaque and multilayered inertial fusion targets can be characterized by x-ray microradiography. A major factor controlling the resolution of this process is the x-ray source size. We have developed an x-ray radiographic method which uses a laser-produced plasma as an x-ray source. Such a source has several advantages over conventional x-ray sources: very small size (≲100 μm in diameter), a pulsed exposure for a duration of less than 1 ns, and an almost unrestricted choice of target materials, thus enabling a wide range of photon energies available. The resulting radiographs show a higher spatial resolution and contrast as compared to those obtained using a conventional x-ray source. These properties may also be enhanced by optimizing the photon energy utilized and by proper choice of x-ray filters.
Neutral beam injector oxygen impurity measurements and concentration reduction via gettering processes
Authors: Kane R. J. , Hsu W. L. , Kerr R. G. , Mills B. E. , Poulsen P. , Hibbs S.
Published: July 2002

We have measured the reduction of oxygen impurity levels by means of gettering within the arc chambers of the TMX-U neutral-beam injectors using the TMX-U neutral-beam test stand. Our analysis incorporated silicon surface-probe measurements and optical Doppler-shift measurements of the hydrogen alpha spectra of deuterium atoms with energies appropriate for D2O parentage. Without gettering, the Auger electron spectroscopy analysis of an exposed silicon sample showed a large oxygen peak below the surface peak with a concentration equivalence of approximately 2% for an accelerated beam. After gettering, with either titanium or chromium getters, optical monochromator data indicated a reduction in the oxygen concentration of at least a factor of 10, whereas Auger spectroscopy data showed at least a factor of 8 reduction. Other metallic impurities remained below the level of detection even after gettering. Additional effects observed during this study include a change in the accelerated deuterium species concentrations, loss of gettering activity, loss of arc operation, and a change in arc performance due to arc chamber gas absorption during operation.
Measurement of beam energy spectrum and impurity content in high-power neutral beam injectors
Authors: Langley R. A. , Ryan P. M. , Tsai C. C. , Menon M. M. , Botnick E. M. , Magee C. W.
Published: July 2002

The energy spectrum and impurity content of a high-power neutral beam are measured by implanting the beam into high-purity silicon crystals. The depth distribution of the beam particles is then measured by secondary ion mass spectrometry (SIMS); the penetration depth is a function of the incident particle energy. This is one of the few measurement techniques that can determine neutral beam energy components directly. From the results, percentages of atomic and molecular ions in the source plasma can be inferred. Use of deuterium as the source gas provides insight into the role of residual hydrogen in the ion source and accelerating grids and in the SIMS analysis. The principal impurities are carbon and oxygen. Preliminary data indicate that carbon can originate from both methane and carbon monoxide, while oxygen can come from molecular oxygen, carbon monoxide, and water. Results are given and future plans are discussed.
A nonmonotonic concentration depth profile of Pt–Rh alloys: A surface segregation study using the atom-probe field ion microscope
Authors: Ahmad M. , Tsong T. T.
Published: July 2002

Equilibrium concentration depth profiles with true single atomic layer depth resolution have been obtained for the surface segregation of Pt–Rh alloys using a time-of-flight atom-probe field ion microscope. The depth profiles obtained for the (001) plane of Pt–Rh alloys of five different bulk composition all show an enrichment of Rh to the top surface layer. It is also observed that there is a significant Rh depletion in the second layer. An additional feature of cosegregated sulfur impurity and overlayer formation is observed. The question of the possible nonequilibrium depth profiles has been resolved by a careful experimental testing. The surface segregation of Rh is consistent with several theoretical models, whereas the nonmonotonic concentration profile may indicate an oscillatory structure in the potential of single ions in the near surface layers.
Characterization of Pt/TiO2 surfaces by means of photoelectron spectroscopy of adsorbed xenon
Authors: Dolle P. , Markert K. , Heichler W. , Armstrong N. R. , Wandelt K. , Kim K. S. , Fiato R. A.
Published: July 2002

Photoelectron spectroscopy of adsorbed Xe (PAX) was used to characterize various Pt/TiO2 (100) surfaces on an atomic scale. The PAX data provide useful information on both geometrical and electronic states of various surface sites. For example, both Ar ion sputtering and high temperature annealing (850 °C) in vacuum produce a distribution of (high charge density) surface defect sites, most likely Ti3+ and Ti2+, whose local surface potentials are higher than on a stoichiometric TiO2 surface by 0.5 and 1 eV, respectively. Submonolayer deposits of Pt on a stoichiometric TiO2 exhibits much lower local surface potentials (0.5–1 eV) than sputter-roughened bulk Pt, suggesting modified charge densities at these sites.
Two-dimensional gas–solid phase transition of xenon adsorbed on different metal substrates
Authors: Jablonski A. , Eder S. , Markert K. , Wandelt K.
Published: July 2002

Coexisting two-dimensional (2D) gas and 2D solid phases of Xe adsorbed on Ag(111), Cu(111), and Ru(001) can be distinguished by means of their Xe(5p) photoemission. The relative equilibrium concentrations (at a given temperature) are substrate dependent and correlate with the xenon–metal interaction strength. Namely, the maximum gas concentration just before 2D phase separation grows with increasing Xe adsorption energy as well as adsorption induced xenon dipole moment in the order Ag(111)<Cu(111)<Ru(001).
Surface thermography
Authors: Ulrickson M.
Published: July 2002

The temperature sensitivity of many plasma materials interactions in both fusion plasmas and process plasmas requires the determination of the surface temperature of the material in contact with the plasma. The determination of the surface temperature is made difficult by the presence of the plasma, the large electrical potentials that may be present, and the need to not contaminate the surface. Radiation thermography permits determination of the surface temperature while overcoming the difficulties listed above. This paper briefly discusses thermal radiation, Planck’s Law, and the selection of the best wavelength band for a given temperature range. Both one and two color pyrometry are discussed. Several considerations that are necessary for practical applications are discussed. Some examples of the use of radiation thermometry in fusion applications between 350 and 3000 °C are presented. Surface heat flux has also been determined from the time variation of the surface temperature.
Interdiffusion in HgTe–CdTe superlattices
Authors: Arch David K. , Faurie J. P. , Staudenmann J.-L. , Hibbs-Brenner Mary , Chow Peter
Published: July 2002

Semiconductor superlattices comprised of alternating HgTe and CdTe layers have been proposed as a tunable narrow band gap semiconductor for long wavelength optoelectronic applications. Growth of this novel superlattice material has been reported by several laboratories. Its usefulness as a narrow band gap optical material, however, has not been established. A main issue of concern is the interdiffusion of the constituent Hg, Cd, and Te atoms across the heterointerfaces of the superlattice structure. To determine the extent of this interdiffusion we have carried out, for the first time, temperature dependent x-ray diffraction measurements on HgTe–CdTe superlattices. Peak intensities of the superlattice satellites were monitored as a function of annealing temperature and time to yield estimates of the interdiffusion coefficient D(T). Our results indicate there is appreciable intermixing of the HgTe and CdTe layers at temperatures as low as 110 °C. Such results have serious implications for the use of this material in optoelectronic devices.
Far-infrared magnetospectroscopy of HgTe and Hg1−xMnxTe epilayers grown by molecular-beam epitaxy
Authors: Luo H. , Dobrowolska M. , Yang Z. , Furdyna J. K. , Harris K. A. , Cook J. W. , Schetzina J. F.
Published: July 2002

Far-infrared magnetotransmission experiments were performed on HgTe and Hg1−xMnxTe epilayers grown by molecular-beam epitaxy. The measurements were carried out in the Faraday and Voigt geometries, at fixed photon energies between 2.5 and 12.8 meV, in the temperature range 1.6 K<T<200 K, in magnetic fields up to 6 T. The results were analyzed in terms of the Pidgeon–Brown model, with the spin–spin exchange interaction included for the case of Hg1−xMnxTe . It is found that both HgTe and Hg1−xMnxTe epilayers have excellent electronic properties, which compare favorably with the best quality intrinsic bulk crystals, and which show no effects of strain due to the lattice mismatch with the substrate.
The pumping character of the magnetic suspension-type turbomolecular pump of high flow rate
Authors: Ishizawa Tadao , Miki Masaharu , Urano Chiaki , Kawashima Toshiaki , Yamamoto Masayuki , Masubuchi Noriaki
Published: July 2002

The pumping characteristics of the suspension-type turbomolecular pump with a high flow rate, which is operable within a pressure range of 102 Pa or below required for the semiconductor production system (physical vapor deposition, chemical vapor deposition, etc.), are described below. Conventional turbomolecular pumps are available with the operation pressure only up to a molecular flow range of 10−8 to 10−1 Pa. After trial manufacture of various rotor profiles, the rotor which would make the pump operable up to a transition flow range of 102 Pa was reviewed in this experiment. As a result of the experiment, a rotor which could achieve a flow rate of 2900 standard cm3/min (sccm) (6×102 Pa) at a pumping speed of 600 1/s (N2: 10−1 Pa or less) could be obtained. It was also found that the flow rate characteristics differed according to the rotor profile and working pressure range. Also reviewed in this paper is the surface treatment method for protection of the rotor (Al alloy) from reactive gases (Cl, F, and Ga) used in the semiconductor production systems.
Reliable, low-profile banding of electrical leads in high-vacuum systems
Authors: Fowler G. L.
Published: July 2002

This article describes a very reliable method of securely banding electrical leads to the circumference of a substrate for ultrahigh vacuum applications in which mechanical support and/or electrical insulation are necessary. Its minimal increase to the overall diameter of the substrate (low profile) makes it very convenient to use in confined places.
High-throughput continuous cryopump
Authors: Foster C. A.
Published: July 2002

A cryopump with a unique method of regeneration which allows continuous operation at high throughput has been constructed and tested. Deuterium was pumped continuously at a throughput of 30 Torr l/s at a speed of 2000 l/s and a compression ratio of 200. Argon was pumped at a throughput of 60 Torr l/s at a speed of 1275 l/s. To produce continuous operation of the pump, a method of regeneration that does not thermally cycle the pump is employed. A small chamber (the ‘‘snail’’) passes over the pumping surface and removes the frost from it either by mechanical action with a scraper or by local heating. The material removed is topologically in a secondary vacuum system with low conductance into the primary vacuum; thus, the exhaust can be pumped at pressures up to an effective compression ratio determined by the ratio of the pumping speed to the leakage conductance of the snail. The pump, which is all-metal sealed and dry and which regenerates every 60 s, would be an ideal system for pumping tritium. Potential fusion applications are for pump limiters, for repeating pneumatic pellet injection lines, and for the centrifuge pellet injector spin tank, all of which will require pumping tritium at high throughput. Industrial applications requiring ultraclean pumping of corrosive gases at high throughput, such as the reactive ion etch semiconductor process, may also be feasible.
Resonant tunneling through a HgTe/Hg1−xCdxTe double-barrier, single-quantum-well heterostructure
Authors: Reed M. A. , Koestner R. J. , Goodwin M. W. , Schaake H. F.
Published: July 2002

Resonant tunneling has been demonstrated through a double-barrier, single-quantum-well HgTe/Hg1−xCdxTe heterostructure for the first time. Negative differential resistance is observable at room temperature, exhibiting a 1.4:1 peak-to-valley tunnel current ratio. The observation provides direct evidence for the existence of the proposed intrinsic interface state.
Theoretical studies of ion bombardment: Many-body interactions
Authors: Lo Davy Y. , Tombrello Tom A. , Shapiro Mark H. , Garrison Barbara J. , Winograd Nicholas , Harrison Don E.
Published: July 2002

Many-body forces obtained by the embedded-atom method are incorporated into the description of low-energy collisions and surface ejection processes in molecular dynamics simulations of sputtering from metal targets. Bombardment of small, single-crystal Cu targets (400–500 atoms) in three different orientations ({100}, {110}, {111}) by 5-keV Ar+ ions have been simulated. The results are compared to simulations using purely pairwise additive interactions. Significant differences in the spectra of ejected atoms are found.
Icosahedral alloys studied by scanning tunneling microscopy
Authors: Wiesendanger R. , Rosenthaler L. , Hidber H.-R. , Eng L. , Staufer U. , Güntherodt H.-J. , Düggelin M. , Guggenheim R.
Published: July 2002

We have used scanning tunneling microscopy (STM) under ultrahigh vacuum conditions in order to study the morphology and chemical structure of several icosahedral samples directly in real space with a lateral and vertical resolution on a subnanometer scale. For the interpretation of the STM images it was necessary also to perform scanning electron microscopy studies on the same samples. A hierarchy of structural units is found with pentagonal-shaped structures on a variety of length scales.
Current–voltage characteristics of metal/vacuum/metal tunneling
Authors: Bryant P. J. , Kim H. S. , Yang R. , Zheng Y. C. , Miller R.
Published: July 2002

The relationship between the quantum-mechanical tunneling of electrons and the separation between electrodes is of fundamental importance to the interpretation of scanning tunneling microscopy data. Two notable experiments in metal/vacuum/metal (MVM) tunneling have been reported recently for silver, lead, and gold electrode sets. We report data here for current–voltage characteristics in MVM tunneling between tungsten–platinum, tungsten–graphite, and tungsten–gold electrodes. The W–C system data are particularly relevant to the large body of scanning tunneling microscopy data from graphite.
Proposal for a sensitive leak test telescope
Authors: Blanchard W. R. , Hemmerich J. L. , Winkel T. , Reiter D.
Published: July 2002

A proposal for an in-vessel movable leak sensor, called a leak test telescope, is described for leak localization inside two of the largest thermonuclear fusion devices (TFTR and JET). To improve sensitivity and source identification beyond the present state of the art, a differential sensor head employing two actively pumping collimators, a continuously rotating shutter, and a quadrupole mass spectrometer as sensor is proposed. With the use of phase-lock signal processing this detector should be capable of detecting a leak of 1×10−6 Torr l/s from a distance of 0.5 m in a typical fusion environment with backgrounds >1×10−7 Torr deuterium–tritium.
Fabrication of a cryogenic foam target for inertial confinement fusion experiments
Authors: Norimatsu T. , Katayama H. , Mano T. , Takagi M. , Kodama R. , Tanaka K. A. , Kato Y. , Yamanaka T. , Nakai S. , Nishino Y. , Nakai M. , Yamanaka C.
Published: July 2002

The first successful fabrication of a cryogenic foam target is reported. Detailed techniques to ensure accurate fuel loading in the foam shell are described. This target has been used for implosion experiments with the Gekko XII glass laser.
Scanning tunneling microscopy of compact disk surfaces
Authors: Sexton B. A. , Cotterill G. F.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to study the surfaces of both the nickel-master disks and the stamped polycarbonate replicas produced during manufacture of compact disks (CD’s). Tunneling directly onto the nickel-master disk in air reveals the three-dimensional shapes and heights of the pits. The quantitative surface roughness of the tops and bases of the pits can be accurately gauged during high-magnification scans. Thin-sputtered gold films (< 20 nm) on the polycarbonate replicas allow direct measurement of the depth of the pits on the mass produced disks. We discuss the requirements for producing high-quality STM images on these types of surfaces with particular reference to the effects of the tip radius r.
Electronic structure of an ordered overlayer on a semiconductor: Bi/GaAs(110)
Authors: Joyce J. J. , Anderson J. , Nelson M. M. , Yu C. , Lapeyre G. J.
Published: July 2002

This paper reports an investigation of the Bi/GaAs interface using low-energy electron diffraction (LEED), Auger, angle resolved photoemission, and high-resolution core level photoemission. The LEED results for Bi overlayers show a 1×1 pattern with the same orientation and lattice spacing as the GaAs(110) cleavage face, while the core level attenuation profiles show an ideal layer-by-layer growth mode for at least 2.5 monolayers (ML). Quantitative analysis of the core level data for 1 ML of Bi on n-type GaAs shows 660 meV of band bending and two bonding sites for the Bi on the GaAs surface. The two bonding sites are determined to be Bi–As and Bi–Ga bonding configurations. A zig–zag chain model is proposed for the first monolayer of Bi atoms on the GaAs surface. The Bi overlayers exhibit a density of states up to the Fermi level which is ∼0.7 eV above the GaAs valence-band maximum. For temperatures between 250 and 350 °C all but the last monolayer of Bi is desorbed from the surface, and above 350 °C the remaining Bi is rapidly lost from the surface. Comparison to the Sb/GaAs interface indicates the importance of stuctural as well as electronic properties of the interface materials in ordered overlayer growth.
Resonant photoemission from the Ni–GaAs(110) interface
Authors: Kendelewicz T. , Cao R. , Miyano K. , Lindau I. , Spicer W. E.
Published: July 2002

The resonant photoemission at the 3p photoabsorption threshold has been studied for room-temperature grown and annealed Ni/GaAs interfaces and vacuum fractured NiAs crystals. For all samples studied strong resonance in the satellite line and an interference dip in the main photoemission line have been observed. Although, core level studies indicate complicated evolution of the interface with distinct new reaction phases, the line shape of resonances proves to be very insensitive to the details of reactivity.