bluuebunny/crossref_metadata_2025 huggingface dataset:
Intervalley transitions in inversion layers
Authors: Döhler G. H.
Published: July 2002

Transitions between sub-band systems deriving from valleys with different effective mass in the direction of surface quantization involve large momentum transfer. As a consequence the probabilities for impurity-induced transitions between the respective sub-band systems are low. The corresponding transitions by phonon emission are energetically forbidden if the sub-band splitting does not exceed the energy of acoustic phonons near the zone boundary. The transfer of carriers into a sub-band system with lower mobility provides an explanation of the experimentally observed negative photoconductivity and of the extremely long photoresponse times in n-type Si<100≳ inversion layers. The dependence of the photoconductive response on the band splitting provides information about the relative position of the electric sub-bands in different sub-band systems. Relaxation losses from transitions between different sub-band systems also imply a possibility for measuring the sub-band energies if the system is no longer in the electric quantum limit.
Rapid growth of Si by solid-phase epitaxy, including comparisons to conventional Si crystal growth
Authors: Boatright R. L. , McCaldin J. O.
Published: July 2002

A recent development in solid-phase epitaxy is discussed, namely, that Si can be rapidly grown back into a dissolved pit in a (111) Si substrate to just exactly fill the pit, at which time growth ceases. This growth process is driven by the nearby dissolution of amorphous Si and, unlike most conventional growth processes, is not a near-equilibrium process. Also the solid-state growth is strongly affected by volume changes occurring during growth.
Vacuum preparation of pure cesium by electrolysis of glass
Authors: Klemperer Derek F. , Mackenzie Ian
Published: July 2002

A method is described for metering up to about 10 mg of pure Cs into a vacuum system. The Cs is electrolyzed out of a Cs2O-containing glass in contact with molten CsNO3. Experimental evidence shows that less than 1% of the Cs lost from the glass is replaced by diffusion from the salt melt. However, in absence of the melt, Cs ion currents rapidly decay. Using melt, the glass shatters after about 20% of its Cs content has been electrolyzed away. The conduction process is characterised by 137Cs tracer experiments and current–temperature data involving a number of alkali salts. The salt, which does not have to be molten, probably supplies alkali cations to the surface region of the glass, where negative charges on silicate groups accumulate under influence of the electric field. Some decomposition of the glass occurs during electrolysis with the formation of silica.
Molecular fractionation and jet stills
Authors: Maa Jer Ru
Published: July 2002

Working equations are derived for the quantitative design of stills for molecular distillation. The distillation rates and the separation efficiencies in the molecular stills are correlated to the exposure time and the renewal rate of the evaporating surface. A method of interconnecting a number of jet stills to form a molecular fractionator and an example of step-by-step design procedure are also presented.
Orbiting molecular-beam laboratory
Authors: Outlaw R. A. , Brock F. J.
Published: July 2002

The composition of the atmosphere within the planned orbital envelope of the Space Shuttle (200–1000 km) and the velocity necessary to maintain a stable orbit within that envelope (∠8 km s−1) provide unique conditions for forming a high-purity, moderate energy beam (∠5 eV) of atomic oxygen. At 500 km for example, atomic oxygen comprises approximately 90% of the atmosphere with the remaining 10% being primarily helium. Since the mean thermal speed of the ambient atomic oxygen is substantially less than the orbital speed, a high-purity beam can be generated by sweeping through the gas with a series of beam-forming truncated conical shells. Further, molecular shielding provides a low-density background inside the conical shells (∠103 cm−3) within which the beam is formed. The characteristics of the beam, including energy distribution, flux, and purity variation with orbital altitude and methods for lowering the mean energy, are presented. The approach to forming the beam, the planned apparatus, modes of deployment (attached to the Shuttle or as a free flyer), operational capabilities, measurement capabilities, and attitude control requirements, are also discussed. Finally, a number of gas–surface interaction experiments that have been proposed for this laboratory are discussed.
Orientation dependence of surface segregation in a dilute Ni–Au alloy
Authors: Johnson W. C. , Chavka N. G. , Ku R. , Bomback J. L. , Wynblatt P. P.
Published: July 2002

Surface segregation theory admits that the degree of surface enrichment depends on surface orientation through the anisotropy of surface properties such as surface energy. This prediction was tested by determining the surface composition of several grains of different surface orientation in a polycrystalline Ni–Au alloy foil. A scanning Auger microprobe provided Auger point analyses which were used to determine the surface segregation characteristics of individual (randomly oriented) grains, while selected area electron channeling patterns, obtained with a scanning electron microscope, allowed the surface orientation of each grain to be determined. A strong anisotropy of gold surface enrichment was observed; for example,the gold surface concentration at 700°C varied by as much as an order of magnitude over the range of surface orientations investigated. A plot of the variation in surface composition within the standard stereographic triangle showed trends that are comparable with the known anisotropy of surface energy in fcc metals. It is concluded that the coupling of the above experimental techniques provides a powerful tool for the study of such phenomena.
Some effects of anisotropic vibrations in LEED
Authors: Úlehla M. , Davis H. L.
Published: July 2002

A formalism is presented which enables effects of certain types of vibrational anisotropy to be included in LEED calculations. Results from a demonstration calculation are presented and compared with a similar calculation where no anisotropy was present.
New sputtering system for manufacturing ZnO thin-film SAW Devices
Authors: Ohji Kenzo , Yamazaki Osamu , Wasa Kiyotaka , Hayakawa Shigeru
Published: July 2002

An improved rf sputtering system for manufacturing ZnO thin-film devices is described. The system consists of a hemispherical electrode geometry with a ZnO center cathode and provides c axis highly oriented ZnO films onto 60 sheets of glass substrate wafers of 25 mm square in one sputtering run. The growth rate of ZnO films is 0.3–0.7 μm/h. The film thickness variations in these wafers are within ±1%. The electrical resistivity of the films ρ?106–107 Ω cm, dielectric constant ε*?8.5, the electromechanical coupling in a longitudinal mode kt?0.23–0.24, in a Rayleigh mode keff?0.07–0.085 for the ZnO film thickness of 3% of the wavelength. The present system enables the manufacture of the ZnO thin-film SAW filter with a frequency accuracy, better than ±0.1%, and a temperature stability, better than −10 ppm/°C.
Temperature dependence of electron spin polarization in low-energy electron diffraction from W(001)
Authors: Riddle T. W. , Mahan A. H. , Dunning F. B. , Walters G. K.
Published: July 2002

The temperature dependence of electron spin polarization and intensity in low-energy electron diffraction (LEED) from a clean W(001) surface has been measured over the range 1000°–300°C. The effect of temperature on polarization is found to be greatest at energies for which the intensity is low and the polarization, and rate of change of polarization with energy, is large. The present results may be interpreted in terms of a shift of polarization features toward lower energies as a result of thermal expansion when the crystal is heated.
Ion-excited Auger electron emission from silicon
Authors: Powell R. A.
Published: July 2002

Auger electron emission from Si excited by ion bombardment with He+, Ne+, Ar+, and Xe+ are reported for ion energies in the range of 1 to 3 keV. The data supports the view that symmetric collisions between Si atoms in the sample are responsible for the observed Auger emission. The relative strength of atomiclike L2,3MM and bulk L2,3VV Auger features in the measured spectra were independent of both ion species and ion energy employed in this study.
Observations of changes in residual gas and surface composition with discharge cleaning in PLT
Authors: Dylla H. F. , Bol K. , Cohen S. A. , Hawryluk R. J. , Meservey E. B. , Rossnagel S. M.
Published: July 2002

Hydrogen discharge cleaning of the PLT vacuum vessel has been studied by mass spectroscopy of desorbed gases and surface analysis of exposed samples. Several modes of vessel conditioning have been studied to date: (1) a high-power discharge cleaning (PDC) mode, with a peak power density to the vessel wall Ps∠0.6 W/cm2 and a peak electron temperature Te∠100 eV; (2) low-power (Taylor-type) discharge cleaning (TDC) with Ps∠0.05 W/cm2 and Te?5 eV. The predominant residual gases produced during PDC are CH4 (1–5×10−6 Torr) and CO (1–10×10−7 Torr), whereas TDC produced primarily H2O (1–2×10−6 Torr) and CH4 (1-10×10−7 Torr). The transient behavior of the residual gases is not simply related to pumping time constants, and provides evidence for the role of surface chemical reactions and diffusion on the formation of these gases. In situ surface analysis of hydrocarbon-covered stainless steel has shown significant decreases in carbon coverage occurring after 103–104 pulses of either cleaning mode. Observed changes in oxygen coverage are more difficult to interpret because of the presence of the passivation oxide layer on the stainless-steel substrates.
High speed CMOS/SOS IC’s fabricated using x-ray lithography
Authors: Stover H. L. , Hause F. L. , McGreivy D.
Published: July 2002

High-speed CMOS/SOS IC’s with 1 μm design rules have been fabricated using x-ray lithography and the negative resist COP at eight mask levels. The fabrication processes four ion-implantation steps and two plasma etching steps. The CMOS/SOS LSI test chip contains ring oscillators with gate lengths of 1, 2, 3, 4, 5, and 7.5 μm. Speed–power data from the ring oscillators are presented; time delay per stage as low as 185 ps was measured for the devices with 1 μm gate lengths. The x-ray source design and the mask technology are reviewed. Scanning electron micrographs of resist patterns and replicated thin-film patterns are presented to show characteristic edge definition and stop coverage of narrow lines. Preliminary reliability testing of finished IC’s is reported; data from thermal stress tests (105 rads from a 60Co source) are compared to similar data from devices fabricated using photolithography. We conclude that x-ray lithography is a viable technology for fineline LSI.
Distortion correction and deflection calibration by means of laser interferometry in an electron-beam exposure system
Authors: Asai Shojiro , Inomata Hiroyuki , Yanagisawa Akira , Takeda Eiji , Miwa Ichiro , Fukinami Minpei
Published: July 2002

In order to assure accuracy in an electron-beam exposure system, it is necessary to correct for deflection distortion relative to the standard axes of the system. Distortion up to the third order is measured and corrected on-line in a vector-scan system, which uses a laser interferometry positioned stage, a fiducial mark, and a digital–analog correction circuit. The programmed precedure involves moving the stage to positions which form 5×5 or 9×9 lattice points in a region about 2 mm square. At each stage position, the beam is scanned to find the fiducial mark at a position in the scan field, by detecting backscattered electrons. Mark searching is done twice at each position, with two, predetermined, linearly independent settings of the correction circuit. A set of linear equations is solved using the least-square method, to find out the distortion coefficient as well as the correction setting to compensate for the distortion. The above routine takes about 2–3 min including the stage motion, mark search, and calculation. It has been proven that distortion can be corrected to within ±0.1 μm ensuring the field stitching accuracy. It has also turned out that this method is useful in investigating the nature of the deflection subsystem.
Fast computation method for exposure intensity and pattern correction in electron-beam lithography
Authors: Kikuchi Atsushi , Kanamaru Akio , Okazaki Nobumichi , Nakane Yasuaki , Tsuboi Kunihiko
Published: July 2002

A fast computation method to correct for the proximity effect in electron-beam lithography is studied for practical uses. Formerly, to compute the proximity effect a double integral of two Gaussian distribution functions was applied. To save computation time and memory size, a simplified computation using the error function is discussed. In this solution the proximity effect correction is determined by two real multiplications, four subtractions and one addition. Not only beam intensity but also a pattern element size is considered in every pattern. A large pattern is divided into small sections. In this method, the computation time is proportional to the number of elements. It takes 105 minutes to compute 10 000 test pattern elements with a minicomputer. The experiment proves that the corrected pattern can be exposed as designed. This procedure has proven effective to design VLSI by using a minicomputer.
Cumms 11: An electron-beam-fabricating machine with accurate registration for direct fabrication and mask making
Authors: Jones G. A. C. , Ahmed H.
Published: July 2002

A scanning electron-beam lithograph machine (CUMMS 11) is described, which utilizes a novel back wafer registration technique (BWR). The registration method uses two axially coincident electron beams—one of which addresses the back of the wafer and is used for registration, the other addresses the top chip surface and is used for pattern writing. By reading a matrix array of BWR marks the system recognizes wafer distortions and provides compensation in subsequent pattern writing. An extension of this process allows stitching of subfields for writing large area chips. Since the system is symmetrical with the writing and registration occurrring on the same axis, temperature drifts are insignificant. Also several electronic drifts are self-compensating. Also several electronic drifts are self-compensating. The BWR method is ideally suited to use with shaped electron beam writing optics and may also be used for registration in ion-beam writing or selected area electron-beam annealing systems.
Monomolecular resists—A new approach to high resolution electron beam microlithography
Authors: Barraud A. , Rosilio C. , Ruaudel-Teixier A.
Published: July 2002

The resist specific properties of ultrathin, very regular films made of monomolecular layers are described. Very high resolution can be achieved in electron beam microlithography, on condition that the resist film is thin enough and the pair thickness-voltage is properly chosen. The contrast of the resin is then unimportant. Ultrathin layers can be achieved by superimposing monomolecular layers, each 30 Å thick. This technique yields compact, uniform, reliable films in the range 30–1000 Å. In these organized crystallized films, polymerization is lattice controlled and stress-limited, and this leads to automatically low-dispersed polymers. This low dispersity gives rise to high contrast. This situation is illustrated by the results obtained from a family of three amphiphilic molecules, one (ω-tricosenoic acid) leading to a linear polymer, and two derivatives of it leading to cross-linked polymers. The exposure curves for these three molecules are given. The position of the funcional groups in the molecules have been chosen in such a way that sensitivity and contrast can be adjusted independently. A sensitivity of 30 μC/cm2 at 5kV together with a contrast value γ of 1.5 have been achieved. Resolution tests have been carried out with the simplest of these molecules. Since its contrast is low (γ=0.7), it has been chosen as an example to show that high resolution can be achieved without high contrast, provided the accelerating voltage is properly adapted to film thinness. Best resolution (600 Å) is obtained at 5 kV, although the spot size is the largest at that voltage. At higher voltages, thickness modulation is no longer 100%. The compactness and the inertness of these films together with their fair protective properties make these ultrathin films suited to electron beam microlithography. This new class of electron resists might bring a new lease of life to microlithography, in the domains500–3000 Å, in the next few years.
GaAs transferred electron devices and field effect transistors in monolithic integrated circuits
Authors: Mills Thomas G.
Published: July 2002

Analog-to-digital conversion is being extended to data rates of up to a few giga-samples per second, by advancements in materials, device and process technology. Specific improvements in the material are the result of improved substrate qualification procedures. The primary process improvements include improved annealing and capping for repeatability in ion implantation and selective implantation for reduced contact resistance in ohmic regions. Further, selective ion implant and isolation implants have shown promise for planar processing. TRW has combined the technological developments to fabricate high frequency mesa and planar circuits using transferred electron devices (TED’s) and metal–semiconductor field effect transistors (MESFET’s) as the principal circuit elements.
Reproducibility of the performance of Pirani gauges
Authors: Poulter K. F. , Rodgers Mary-Jo , Ashcroft K. W.
Published: July 2002

A study has been made of the reproducibility of the calibration of a number of Pirani gauges operating in both the constant temperature and constant voltage modes under clean vacuum conditions within the pressure range 10−3 to 10 Torr (0.133 to 1.33×103 Pa). The calibrations were performed using nitrogen and argon at various times during a six-month period. It was found that the constant temperature version was reproducible to within±6% over the pressure range 10−2 to 10 Torr (1.33 to 1.33×103 Pa) and the constant voltage version had a similar reproducibility over the range 10−3 to 1.0 Torr (0.133 to 133 Pa). This study included measurements to investigate the effects of storage conditions and temperature on the calibration of the gauges, and by generating the pressures in a rising and falling sequence it was also possible to check for any hysteresis effects. It is concluded that these gauges, when used under well defined conditions, may be used as reference gauges for the routine checking of other gauges of this type used on industrial vacuum systems.
Versatile sample transfer mechanism
Authors: Polizzotti R. S. , Schwarz J. A.
Published: July 2002

This paper describes a versatile sample transfer mechanism that allows a prepared sample to be moved rapidly (in seconds) 16 in. under ultrahigh vacuum conditions without unwanted contamination of the sample. Some of the unique features of this motion assembly are: isolation of the internal volume of the bellows from the mating system; precise translational positioning along the axis of translation; 360° continuous rotation of the sample mount; rapid sample changing; and sample temperature range from 77 K to temperatures ≳1500 K.
Micromachining applications for ICF target fabrication
Authors: Deckman H. W.
Published: July 2002

Micromachining techniques used in Inertial Confinement Fusion (ICF) target fabrication encompass laser drilling, single point diamond turning, and plasma as well as chemical etching. These techniques have been developed by several laboratories to produce target components with tolerances and surface finishes in the micron to submicron regime. Some of the spherical target components produced by micromachining techniques include free standing hemispherical shells (diameters 50–500 μm), micron-sized holes in thin glass shells, and plastic-coated glass microballons with surfaces which have been smoothly machined to remove a mounting stalk. Planar targets and components produced by these techniques include small disks and washers of thin brittle materials. Micromachining techniques are also used to fabricate diagnostic instruments such as x-ray mirrors and zone plates. This paper will examine micromachining techniques used to produce target components and diagnostic instruments. The relationship of each micromachining technique to presently used target configurations will also be discussed.
Mechanical boosters on clean or corrosive applications
Authors: Dennis N. T. M. , Budgen L. J. , Laurenson L.
Published: July 2002

This paper discusses in detail the methods that are adopted to either reduce contamination of the oil in the coupling and gears from corrosive vapors in the system, or conversely ensure that the oil vapors cannot reach the high vacuum system. The method of sealing the mechanical booster pump interior from the oil boxes is described and the alternative ways of pumping these boxes are shown. The vacuum that can be achieved above a mechanical booster taking these precautions is given and the level of organic vapors determined by using both a quadrupole mass spectrometer and a quartz crystal microbalance.
Effect of ion implantation on CdSe thin film transistors
Authors: Shepherd F. R. , Westwood W. D. , Scanlon P. J. , Levinson J. , Mitchell I. V. , Plattner H.
Published: July 2002

Thin film transistors have been fabricated by implanting 50 keV Cr, 50 keV Al, and 15 keV B ions into high resistivity (≳105Ωcm), polycrystalline CdSe deposited by thermal evaporation. The implants were made at room temperature into inverted transistor structures fabricated by photoengraving. Both the Cr and Al implants cause a maximum decrease of approximately 1.5% in the c-axis lattice spacing of CdSe, and enhance the (00.1) texture of the grains. Similar but smaller changes in c were observed in B implanted samples. For a fixed CdSe film thickness of ∠800 Å, the drain current, ID, increases rapidly with implant dose above the unimplanted value (∠10 nA). At a dose of 5×1015cm−2, ID was approximately 200 μA (VD = 10 V, VG = 10 V) for the Cr and B implants but was much higher for Al; ID was 1.9 mA at VD = 0.5 V for the same VG. The current-dose dependence is interpreted in terms of filling of grain boundary traps by implanted donors, with the intergrain potential barrier height determined by the implant dose.
Ion beam characterization of the GaAs–GaAs oxide interface for plasma and anodic oxides
Authors: Maggiore C. J. , Wagner R. S.
Published: July 2002

Ion beam channeling has been used to measure the effects of oxide growth and annealing on the substrate at the GaAs–GaAs oxide interface. Plasma and anodic oxides have been grown on 〈100〉 GaAs substrates, and the oxides were removed with an etch in hydrofluoric acid. The substrates were then examined with a beam of 1.5 MeV 3He particles channeled down the 〈100〉 axis. The resultant Ga and As surface peaks can be resolved with Rutherford backscattering and are a measure of the Ga and As at the substrate–oxide interface. Anodic oxides grown by the constant-current method (50 μA) show no change from virgin material at the interface; however, annealing of the oxide prior to its removal results in As enhancement at the surface (?2.0 monolayers). Plasma oxides grown by direct immersion in an rf plasma show As enhancement at the interface without annealing. When grown in a fluorinated plasma, the data show an enhanced Ga surface peak consistent with a thicker interface and modified composition of the substrate. The differential measurements were made with a precision of ±0.2 monolayer.
Photoelectron spectroscopy of II–VI semiconductors under cooperative UV and visible excitation
Authors: Williams R. T. , Rife J. C. , Royt T. R. , Kabler M. N.
Published: July 2002

A new technique, resonant multiphoton photoelectron spectroscopy, has been used to investigate cleaved samples of ZnTe and CdTe. The simplest application of this technique involves excitation of electrons from the valence band to empty conduction or surface states below the vacuum level and subsequent excitation to states above vacuum by a second photon generally of higher energy. We have detected this and other related processes by measuring spectra of the resultant external photoelectrons. The most striking feature of these spectra is a very sharp primary photoelectron peak corresponding to an intermediate state near the bottom of the conduction band, which has been transiently populated to a density of order 1019 cm−3 by a pulse of 2.33 eV photons. The secondary electron spectrum is also due entirely to multiple photon excitations. Three-photon as well as two-photon excitation processes have been demonstrated.
Summary Abstract: Surface core excitons in III–V semiconductors
Authors: Daw M. S. , Smith D. L. , McGill T. C.
Published: July 2002

Surface core excitons in III–V semiconductors is considered. (AIP)
Chlorine chemisorption on Si(111), Ge(111), and GaAs(110) surfaces
Authors: Zhang K. , Yeh L.
Published: July 2002

In the present work the cluster model and the charge self-consistent extended Hückel method are used to determine the configurations of Cl chemisorption of the Si(111), Ge(111), and GaAs(110) surfaces. According to the calculation, the Cl adatom sits on the top of the silicon surface in a covalent site, which agrees quite well with the photoemission experiments, while on the germanium surface the Cl might sit on both the top site and the interstitial threefold site. Concerning the chemisorption on the GaAs(110) surface, the calculation shows that the Cl adatom adsorbs on the relaxed GaAs(110) surface and is bonded with the surface As atom. The density of states calculated from this configuration seems to agree well with the existing experimental results.
Temperature dependence of helium release from erbium tritide films
Authors: Mitchell D.J. , Patrick R.C.
Published: July 2002

The rates of helium release from ErT2 films were measured during constant temperature storage (ranging from 77–500 K) and following abrupt temperature changes. Large changes in helium release rates were measured immediately following the temperature changes; however, the helium release rates were only slightly temperature dependent following the initial transient response. The helium concentration which corresponds to the onset of accelerated release is found to be a function of temperature for ErT2 films. It is also shown that an ErT2 film that is in accelerated release can be made to release helium at a low rate after decreasing the helium concentration by means of a high-temperature cycle.
Channeling analysis of MBE InAlAs/InGaAs interfaces
Authors: Morgan D. V. , Wood C. E. C. , Ohno H. , Eastman L. F.
Published: July 2002

In this paper we discuss how the Rutherford backscattering/channeling techniques may be used to study the interfaces between InAlAs/InGaAs epitaxial layers.
Proximity corrections in a raster scan electron lithography machine
Authors: Ma S. K. S. , Parikh M. , Ward W.
Published: July 2002

A method to correct proximity effects has been applied to a raster scan electron lithography machine. Since it is very difficult to vary the exposure level of a raster scan machine while it is writing, a multiple pass algorithm has been developed to achieve a maximum number of exposure levels for a given number of passes. Scanning electron micrographs of experimental patterns before and after proximity corrections are presented for comparison. The corrected results show an excellent improvement for lines and gaps at 3/4 μm, although proximity corrections may be needed for lines and gaps even at 1 1/2 μm.
Ion beam joining technique
Authors: Harper J. M. E. , Yeh H. L. , Grebe K. R.
Published: July 2002

Solders of various compositions are used in the electronics industry to interconnect components. To obtain proper reflow of the solder pads to be joined, surface oxides must be removed using an appropriate chemical flux. In this paper, we describe an alternative fluxless joining technique in which an ion beam is used to simultaneously sputter clean and melt solder pads prior to joining, and can also provide the heat needed to perform the joining step itself. Using a Si circuit chip with solder pads of 95% Pb, 5% Sn, the melting temperature of the solder (312 °C) is reached within 25 s in an argon ion beam of 1000 eV, 1.0 mA/cm2. The solder pads are etched about 500 Å during this time, and reflow into clean spherical shapes suitable for joining. Electron microprobe analysis shows that the Pb and Sn are uniformly distributed through the solder pad after reflow. Chips have been sucessfully joined to metalized ceramic substrates using either auxiliary heating or using the heat from a focused ion beam. Pull tests show that ion beam reflowed joints are as strong as those obtained by the standard flux joining process.
The influence of surface oxygen contamination on elemental analysis using photon emission from sputtered atoms (Nb-V alloys)
Authors: Loxton C. M. , Martin P. J. , MacDonald R. J.
Published: July 2002

Quantitative analyses of a series of Nb–V alloys has been made using the photons emitted by atoms sputtered from the surface during medium energy Ar+ bombardment. Analyses were made under UHV and oxygen exposure conditions sufficient to saturate the Nb i yield from one of the alloys. The analyses obtained under UHV conditions were consistent with the bulk concentrations. Results obtained with oxygen exposure (to enhance the signals) varied with the exposure used and were not internally consistent. The influence of oxygen exposure on the Nb i and V i yields has been investigated and the discrepancy between these analyses is related to the enhancements of the Nb i and V i signals changing with the Nb concentration of the alloy. An interpretation of the oxygen induced enhancement curves is discussed, assuming that the surface oxygen coverage changes with the alloy concentration.
Sputter yield measurements on simulated adventitious carbonaceous contamination
Authors: Tompkins H. G. , Frank R. A. , Allara D. L.
Published: July 2002

In defect analysis of electrical contacts using surface techniques such as AES or XPS, the first material encountered is invariably a thick or thin layer of adventitious carbonaceous contamination. In this work we use poly (isobutylene) as a model material to simulate the carbonaceous layer. Poly (isobutylene) was chosen because it degrades by random chain scission rather than by unzipping. Films several hundred angstroms thick were deposited on silicon by spin coating and the thickness was measured by ellipsometry. Several of these films of known thickness were sputtered with an ion beam of argon and the sputtering yield calculated. A yield of 1.25 CH2 groups per incoming argon ion at 1.0 kV was measured.
Chemisorption of CO on particulate deposits of platinum
Authors: Doering D. L. , Poppa H. , Dickinson J. T.
Published: July 2002

The morphology and CO chemisorption properties of particulate Pt films have been studied as a function of particle size. The Pt films were vapor deposited onto UHV-cleaved and heat treated mica surfaces at a 200 °C substrate temperature. The average particle sizes ranged from 1.5 to 4.0 nm in diameter as measured by TEM. The particles were found to be irregular in shape and randomly oriented except for larger particles which were more epitaxial. After CO adsorption at 60 °C, two desorption peaks were observed; one at 120 °C (α) attributed to smooth particle surfaces, and another at about 175 °C (β) attributed to particle edges and steps. The ratio of areas under these peaks varied significantly with particle size. The β peak from small particles was a large fraction of the total CO desorption flux, but for a continuous film it was only a minor contributor. With successive desorptions the area under the β peak slowly decreased. TEM showed that major changes in the particle morphology occur during adsorption–desorption cycling. Thus, the decrease in the CO desorption flux is interpreted as due to particle restructuring rather than contamination by CO decomposition as in the case of Ni or Pd on mica. AES measurements corroborate the lack of CO decomposition, even for very small Pt particles.
Performance of the INTOR poloidal divertor
Authors: Post D. E. , Petravic M. , Schmidt J. A. , Heifetz D.
Published: July 2002

The next generation of large tokamak experiments is expected to have large particle and heat outfluxes (∠1023 particles/s and 80 MW). These outfluxes must be controlled to provide adequate pumping of the helium ’’ash’’ and to minimize the sputtering erosion of the vacuum vessel walls, limiters, and neutralizer plates. A poloidal divertor design to solve these problems for INTOR has been done using a two-dimensional code which models the plasma as a fluid and solves equations for the flow of particles, momentum and energy, and calculates the neutral gas transport with Monte-Carlo techniques. These calculations show that there is a regime of operation where the density in the divertor is high and the temperature is low, thus easing the heat load and erosion problems. The neutral pressure at the plate is high, resulting in high gas throughputs with modest pumping speeds.
A group of terminal-flow UHV gauges
Authors: Hua Z. Y. , Yang X. L. , Qiu S. Y. , Chen J. Z. , Tang J. Y. , Sun Q. D.
Published: July 2002

An ionization gauge structure, designated as the ’’terminal-flow’’ type, with the filament and collector plate located on opposite ends of a helical grid, has been designed for a group of nonmagnetic UHV gauges with good sensitivity. Four typical designs, a high sensitivity gauge, a shunt gauge, a suppressor gauge, and a shielding gauge, the characteristics of which have been studied experimentally, are described. The electrodes in each gauge are quite simple; therefore the gauges are easy to degas and can be used on general purpose UHV systems.
Physical measurements of inertial fusion targets
Authors: Weinstein B. W.
Published: July 2002

Measurement of inertial fusion targets has stimulated the development of many new techniques and instruments. This paper reviews the basis for target measurement requirements and the development of optical interferometry, optical scattering, microradiography, and scanning electron microscopy as applied to target measurement. We summarize the resolution and speed which have been achieved to date, and describe several systems in which these are traded off to fill specific measurement applications. We point out the extent to which present capabilities meet the requirements for target measurement and the key problems which remain to be solved.
Power plant design for inertial confinement fusion: Implications for pellets
Authors: Frank T. G. , Pendergrass J. H. , Cook D. L. , Pitts J. H.
Published: July 2002

Potential commercial applications of inertial fusion include the production of electricity and fissile and chemical fuels. In all these applications, a significant amount of high-temperature heat will be produced and converted to electricity. Most of the implications for fusion pellets are common to all applications; the emphasis in this discussion is on central station electric power plants. The requirements and constraints on fusion pellets for power plant applications include: survivability in hostile reaction chamber environments, the ability to withstand large acceleration forces encountered in high-velocity injection, sufficiently large energy releases for economic power production, and high-rate automated manufacture at costs whch are not a large fraction of the value of the fusion energy released.
AES and SEM studies of oxide and sulfide scales formed on sputter-deposited 304 stainless steel at 800 and 950 °C
Authors: Baer D. R. , Prater J. T.
Published: July 2002

High temperature (800–950 °C) corrosion studies of fine-grained sputter-deposited 304 stainless steel have been conducted at low pressures (<10−2 Pa) in an Auger electron spectroscopy (AES) UHV chamber and compared with studies performed in an environment of mixed gases containing O and S. In situ surface analysis performed at low gas pressures has provided a detailed examination of the diffusion processes that occur during alloy corrosion. Oxide scales formed at 10−2 Pa O2 on sputter-deposited fine-grained 304 stainless steel have been found to closely resemble those formed in mixed-gas environments at atmospheric pressure, suggesting that the same mechanisms are active in both situations. During initial oxidation at 10−2 Pa of Y-doped samples, a silicon oxide was observed by AES to form and then to be covered by a growing chromium oxide. This relates well to the silicon-rich oxide subscale found on similar samples following 24 h in the mixed-gas environment and suggests that the presence of Y affects Si mobility. In addition, the oxide scales on some samples exposed to the mixed gas were observed to be covered by FeS. In the AES system, exposure of oxidized samples to H2S caused a sulfur layer to build on the surface which drew iron onto the oxide-scale surface faster than sulfur diffused into the oxide. This result implies that an FeS layer can form on the surface at an earlier stage of attack than previously thought and can be a significant aspect of the corrosion process.
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u Mössbauer studies of passive films on iron
Authors: Eldridge J. , Kordesch M. E. , Hoffman R. W.
Published: July 2002

Mössbauer effect spectroscopy is applied to the analysis of the passive film on iron with the aim of supplying local site information. High count rate transmission experiments have been performed to examine the passive film in situ under a variety of potentials. When electroplated, Fe-57 enriched iron films are cathodically reduced at −350 mV RHE for over 1 h and then passivated at a potential of 1350 mV in a buffered borate solution pH 8.4, an isomer shift of 0.64±0.01 mm/s vs SNP and a quadrupole splitting of 1.14±0.09 mm/s for the passive layer are obtained. The isomer shift indicates iron present in the Fe+3 valence state. The quadrupole splitting is larger than for bulk crystalline iron oxides, suggesting a disordered structure. MES data of cathodically reduced passive films show only pure iron, demonstrating complete reduction of the passive film. Spectra taken of a natural iron film passivated in an Fe-57 containing borate solution indicate no contribution from iron precipitated from the solution. The resonant area associated with the passive film is observed to depend on specimen preparation, in particular, the amount of time spent during cathodic reduction prior to passivation. The isomer shift and quadrupole splitting are not greatly affected by changes in the passivating potential in the range from 1050 to 1550 mV RHE.
Investigation of GaAs field-effect transistor interfaces using pulsed electron beam excitation
Authors: Flesner L. D. , Nedoluha A. K. , Wieder H. H.
Published: July 2002

Electron-beam pulses applied to various regions of an operating GaAs field-effect transistor (FET) produce both fast and slow changes in gate and drain currents. These effects provide information regarding transient phenomena occurring at the top and bottom interfaces which define the FET channel. In particular, large changes observed in the drain current reflect the kinetics of charge carrier trapping and recombination at the interfaces. Additional information is obtained from changes which result when the gate and drain bias are varied, and from comparison of different device structures, for example, devices with and without gates. Data are presented for a junction FET (JFET) and an analogous device without a gate. The gate bias dependence observed suggests that the trapping phenomena are occurring below the FET channel. A rapid transient response which is observed in the JFET that is absent in devices without a gate indicates enhanced recombination due to the p-n junction.
Studies on silicon-based CdS and ZnS hybrid systems for the utility of these films in solar cells
Authors: Abou-elfotouh F. , Abdelhalim A. S.
Published: July 2002

Sputtered CdS/Si and (Znx–Cd1−x)S/Si heterojunctions have been investigated. After high- temperature annealing (?600 °C) of (Znx–Cd1−x)S films for long periods (?1 h) the values obtained for the electrical resistivity ρ, electron mobility, carrier concentration, and grain size were 15 ohm cm, 80 cm2/V-sec, 8×1016 cm−3 2200 Å, respectively. These are in the range of values required for efficient (7.5%) solar cell heterojunctions. The effect of sulfur diffusion into Si on the cell performance is discussed.
Electron optical column for high-speed electron beam delineator: VL-R2
Authors: Nakasuji M. , Wada H. , Sano S.
Published: July 2002

An electron optical column for a raster scan electron beam delineator with a continuously moving workstage was developed. The electron optical column consists of an electron gun using a single crystal LaB6 cathode, five magnetic lenses, and four electrostatic deflectors, which enable high-speed and hysteresisless deflection. 80-A/cm2 current density with better than 0.3 μm beam resolution and maximum beam size of 0.5×4 μm were obtained. Deflection distortion is less than 0.1 μm, and beam resolution is less than 0.3 μm without dynamic focus or astigmatism correction within 350×250 μm field size. Beam position drift is less than 0.04 μm/2H. Beam intensity instability is less than 1.0% within 36 h. The cathode lifetime was 2700 h.
Fermi level position and density of states of intrinsic, phosphorus-doped, and boron-doped a-Si:H deposited on stainless steel
Authors: Nielsen Paul , Gredin Robert
Published: July 2002

We have made photoemission, Auger spectroscopy, and surface photovoltage measurements on a-Si:H films prepared by rf plasma decomposition of SiH4 and doped SiH4 onto substrates at 270 °C. The density of gap states of intrinsic films, determined by photoemission, is less than 1019 eV−1 cm−3. 2.8% P doping produced an additional 2.8×1019 states cm−3. Reducing the P concentration to 0.2% only reduces the excess density to 2×1019 states cm−3. The surface Fermi energy is 0.4 eV from the nearest band edge in both P- and B-doped a-Si:H, but thermopower and conductivity activation energy indicate the bulk EF is about 0.25 eV from the nearest band edge. The variation with thickness of the surface EF in intrinsic films deposited on P- and B-doped films indicates the existence of surface states above the equilibrium EF at a density of about 2.6×1012 eV−1 cm−2, and possibly states below EF at a density of 8.6×1011 eV−1 cm−2. These surface state densities explain the difference between bulk and surface EF in doped films.
Performance characterization of pneumatic single pellet injection system
Authors: Schuresko D. D. , Milora S. L. , Hogan J. T. , Foster C. A. , Combs S. K.
Published: July 2002

The Oak Ridge National Laboratory single-shot pellet injector, which has been used in plasma fueling experiments on ISX and PDX, has been upgraded and extensively instrumented in order to study the gas dyamics of pneumatic pellet injection. An improved pellet transport line was developed which utilizes a 0.3-cm-diam by 100-cm-long guide tube. Pellet gun performance was characterized by measurements of breech and muzzle dynamic pressures and by pellet velocity and mass determinations. Velocities of up to 1.4 km/s were achieved for intact hydrogen pellets using hydrogen propellant at 5-MPa breech pressure. These data have been compared with new pellet acceleration calculations which include the effects of propellant friction, heat transfer, time-dependent boundary conditions, and finite gun geometry. These results provide a basis for the extrapolation of present-day pneumatic injection system performance to velocities in excess of 2 km/s.
Surface and interface analysis of GaAs–oxyfluorides
Authors: Ireland P. J. , Jamjoum O. , Kazmerski L. L. , Ahrenkiel R. K. , Russell P. E. , Stanchina W. , Wager J. F.
Published: July 2002

AES, XPS, and SIMS analysis of the plasma grown oxyfluorides on GaAs are presented. These data indicate that the films are composed of three basic layers. Region 1 is a mixed As2O3, Ga2O3 glass with low concentrations of fluorine. In the second region, fluorine concentrations increase and a shoulder on the As-3d and Ga-3d peaks are observed. As2O3 and Ga2O3 are still the major constituents of the film. At the interface between the oxyfluoride glass and the substrate is a thin metallic As region. The difference between pure oxides and this oxyfluoride is the incorporation of fluorine in the films and lower concentrations of metallic As at the interface.
Initial wall conditioning in Doublet III
Authors: Jackson G. L. , Clausing R. E. , Lietzke A. F. , Ejima S. , Emerson L. C. , Heatherly L.
Published: July 2002

The first year of operation of Doublet III, a large noncircular tokamak (R=1.43 m, a=0.45 m, BT ≤2.6 T), was highlighted by the achievement of a plasma current in excess of 2 MA. This is partially attributed to the low Zeff discharges made possible by wall conditioning using low temperature, low power discharge cleaning, accompanied by preconditioning of the wall and by baking. Approximately 500 h of hydrogen discharge cleaning and 25 h of oxygen discharge cleaning combined with tokamak plasma operations were required to obtain these low Zeff tokamak discharges. During the initial cleanup of the wall, copious quantities (>100 monolayers) of carbon were removed, ultimately with greatest efficiency by oxygen discharge cleaning. During the conditioning process, monitoring the impurity removal rate with the residual gas analyzer (RGA) provided the most understandable measure of the rate of the cleanup, while an in situ Auger analysis surface diagnostic supplied and operated by ORNL was most useful in identifying the presence of heavy hydrocarbons (oil), carbides, and oxygen on the wall and monitoring the transport of limiter materials.
Modifications to the electrical properties of PbTe by low-energy ion bombardment—interpretation in terms of differential sputtering and atomic mixing
Authors: Kubiak R. A. , Parker E. H. C. , King R. M. , Wittmaack K.
Published: July 2002

Investigations are reported into the effect of 350 eV He+, Ar+ and Xe+ bombardment of PbTe. The studies were made on surfaces of thin films prepared by molecular beam deposition under UHV conditions. The modifications to the films were monitored by measurements of the films’ carrier transport properties. Bombardment-induced areal densities of carriers (electrons) up to 6×1013 cm−2 with near-bulk mobilities were observed for ion fluences up 1016 ions/cm2. The results are discussed in terms of preferential sputtering of Te in combination with beam-induced mixing. It is concluded that the induced damage is located very close to the film surface. Whereas in the case of Ar+ and Xe+ bombardment the altered layer appears to extend over a depth commensurate with the ion range, the results for He+ bombardment suggest that only the very surface is depleted of Te. There is evidence that ion-induced desorption of weakly bound surface species contributes significantly to the observed changes in the areal density of carriers.