bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure–composition variation in rf-sputtered films of Ge caused by process parameter changes
Authors: Messier Russell , Takamori Takeshi , Roy Rustum
Published: July 2002

It has been shown that noncrystalline Ge-sputtered films prepared under a range of conditions display a wide variation in structure, composition, and film properties depending on the sputtering process parameters. Data are presented in which optical absorption edge, stress, density, argon and oxygen contents, and other film properties can be varied continuously as a function of preparation parameters. The range of changes which can be brought about in these properties is enormous: changes of 20% in density, 500% in Ar content, and positive to negative in macroscopic stress are achieved within ’’normal’’ operating conditions. The data demonstrate unequivocally that the term ’’sputtered film’’ can refer to only a specific sample, not a reproducible material.
Surface crystallization of glassy vapor-deposited selenium films in controlled atmospheres
Authors: Brower W. E. , Capo D. J.
Published: July 2002

Surface crystallization kinetics are measured for pure selenium 60-μm vapor-deposited films. Xerographic lifetimes of selenium photoreceptors are shown to be limited by the overall transformation level of top surface crystallization. The temperature dependence of the overall top surface transformation rate may be plotted in an Arrhenius fashion yielding an activation energy of 26 kcal/mol. Top surface crystallization kinetics for thermal aging of 60-μm films in argon and dry air are similar, both being faster than bulk kinetics.
Sputtered metal carbide solar-selective absorbing surfaces
Authors: Harding G. L.
Published: July 2002

A range of sputtered metal carbide interference filters has been prepared on copper substrates. These show promise as high-temperature-stable selective surfaces for solar energy photothermal conversion. Solar absorptances of 75%–80% and room temperature emittances of about 2% can be obtained at 300 K for single layer metal carbide films on bulk copper. The emittance of an iron carbide film on copper increased to 7% at 600°C. The solar absorptance of the same film was temperature independent up to 500°C. Absorptances of 80%–90% and room temperature emittances of about 4% can be obtained for two-layer interference filters on copper. The coating of both glass and metal surfaces is discussed.
Influence of biased magnetron deposition parameters on amorphous Gd–Co–Cu properties
Authors: Albert P. A. , Guarnieri C. Richard
Published: July 2002

Biased magnetron sputtering has been used to deposit amorphous GdCoCu films from a Gd15Co38Cu47 target. The effects of target current, sputtering pressure, and substrate-bias voltage have been determined. The uniaxial anisotropy energy Ku may be varied from 0.07 × 105 erg/cm3 to 4.0 × 105 erg/cm3 while the quality factor Q=Ku/(2πM2) may be varied from 0.6 to 7.9. In varying these parameters the film compositions are maintained at approximately the target composition, while similar parameter variations in diode sputtering engender compositional changes far greater. Thus, it is shown that magnetron sputtering offers a control of film properties that is unattainable with other deposition techniques.
Chemical implantation of 10-keV H+ and D+ in rutile
Authors: Siskind B. , Gruen D. M. , Varma R.
Published: July 2002

Rutile (TiO2) implanted with 10-keV H+ and D+ exhibits broad ir absorption bands at 3400 and 2505 cm−1, respectively. The D+ implantation also induces a sharp band at 2438 cm−1. This 2438-cm−1 band corresponds to the sharp hydroxyl absorption peak at 3277 cm−1 typically present in flame-grown rutile crystals. In addition the bombardment induces a broad absorption at 900 nm, which is attributed to delocalized electrons resulting from direct chemical reduction of the rutile by the implanted hydrogen or deuterium, and which is similar to the well-known 1500-nm free-carrier absorption in rutile heated in a reducing atmosphere. The absence of such an absorption after 10-keV He+ or Ar+ bombardment implies that reduction by preferential sputtering does not significantly contribute to this band. Evidence is adduced to support the view that the 900-nm absorption, which appears to the eye as a blue color, is associated with chemically implanted D+. Using projected ranges for 10-keV D+ and experimentally determined transition moments for O–D stretch intensities leads to a value for the oscillator strength of the ’’blue’’ band of ∠0.1. The large f value supports the assignment of the ’’blue’’ band to free-carrier absorption rather than to a d–d transition localized at a Ti3+ site.
Highly electronegative contacts to compound semiconductors
Authors: Scranton R. A. , Best J. S. , McCaldin J. O.
Published: July 2002

Gold contacts to most III–V and II–VI compounds position the Fermi level at the interface well into the energy gaps of the semiconductors. To position the Fermi level closer to a conduction-band edge, particularly in the more ionic semiconductors, one may substitute a more electropositive element like Al for the Au contact. To position the Fermi level closer to a valence-band edge, however, there are no further possibilities among the elemental metals, since Au is the most electronegative of these. Two contact materials, (SN)x and HgSe, which overcome this limitation have recently been reported. Barriers produced by these contacts on many compound semiconductors will be reported and shown to exhibit the well-known ionic–covalent transition. Device use and suggestions for further research are mentioned.
Possible selective solar photothermal absorber: Ni dendrites formed on Al surfaces by the CVD of Ni (CO)4
Authors: Grimmer D. P. , Herr K. C. , McCreary W. J.
Published: July 2002

A selective solar photothermal absorber can be created by the formation of suitably spaced metallic dendrites. Spacings of around a micron achieve absorption of visible light through multiple internal reflections in a geometric maze effect while retaining the low emissivity properties of the metal at longer wavelengths. Recent experiments elsewhere on the chemical vapor deposition (CVD) of W dendrites on various substrates demonstrated the feasibility of this approach to produce a selective solar photothermal absorber. W dendrite coatings, however, may be too expensive to find a practical application in solar collectors. Ni dendrites, on the other hand, appear to be a potential low-cost selective solar photothermal absorber. Dendrites are formed by the CVD of Ni from Ni carbonyl, Ni (CO)4. This paper presents the physical and optical results of experiments with CVD Ni dendrites on Al substrates. The preparation of the aluminum substrates, the CVD experimental apparatus and methods, and the optical measurement techniques of solar absorptivity (αs) and thermal infrared emissivity (ε) are discussed. The results are described in terms of scanning electron microscope (SEM) photographs of dendritic coatings, and the measured optical properties.
Interface states at the Ga–GaAs interface
Authors: Bachrach R. Z. , Bianconi A.
Published: July 2002

A variable-excitation energy photoemission study has been made of the occupied states near the Ga–GaAs (110) interface as the interface is formed. Using a combination of valence and core-level spectroscopy, new aspects of the interface electronic structure have been deduced. Using valence-band spectroscopy, interface states are found to appear as the Ga film is built up. Using core-level spectroscopy, one finds chemical shifts in both the Ga and As 3d levels. The As shift indicates that surface charge redistribution from the As to the Ga occurs at the interface.
Combined low-energy ion scattering and x-ray photoelectron spectroscopy study of Ta2O5 bombarded by 500–3000-eV He ions
Authors: Nelson G. C.
Published: July 2002

The low-energy ion backscattering spectra of Ta2O5 obtained with He as the probe gas exhibit a pronounced low-energy tail on the metal peak and a strong incident ion energy dependence of the oxygen to tantalum peak intensity ratio. To determine the effect differential scattering cross sections, ion neutralization, and sample reduction have on these spectral features, a combined ISS–XPS study has been carried out. The data indicate that the sample is not reduced by the He ion beam and that a resonant-type neutralization plays a dominant role both in tailing and in the variation of the oxygen to tantalum peak intensity ratio.
Mass artifacts using a Cahn-RG microbalance in water vapor
Authors: Vasofsky R. , Czanderna A. W.
Published: July 2002

Corrections for a ’’mass gain’’ artifact by the weighing mechanism have been found necessary when exposing a Cahn-RG-UHV microbalance in water vapor up to 1.3×103-Pa water vapor. The effect varies linearly with load from 0.2 to 0.9 g and amounts to an apparent mass gain of 27 μg per 100 mg of load at 1.3×103 Pa and 22° C. About two hours were required to reach equilibrium after exposure to water vapor at pressures between 1.3 and 2.4×103 Pa. Similar equilibration times are required in comparable pressure decrements, except that times ranging to as high as 33 h are necessary during final evacuation. Thus, the artifact depends on time, pressure, and load. The mass defect is tentatively ascribed to sorption by the polymer used for insulating the torque motor. Recoating the windings in the torque motor, which was done by the Cahn Division of Ventron, reduced the effect to 12.2 μg at a 100-mg load and 1.3×103 Pa, but the time, pressure, and load dependence of the artifact remained.
Theoretical studies of Si and GaAs surfaces and initial steps in the oxidation
Authors: Goddard III William A. , Barton John J. , Redondo Antonio , McGill T. C.
Published: July 2002

Using ab initio quantum chemical methods (generalized valence bond), we examine (i) the electronic states of Si (111) and GaAs (110) surface, (ii) the relaxation of the Si (111) surface, (iii) the reconstruction of the GaAs surface, (iv) the initial steps in the chemisorption of O2 on Si (111), and (v) the bonding of O atom to Ga and As centers.
Perspectives on III–V compound MIS structures
Authors: Wieder H. H.
Published: July 2002

An overview and assessment is provided of some aspects of the physics and technology of InP, GaAs, InAs, and InSb MIS structures with homomorphic and heteromorphic dielectric layers. Experimental measurements made on such InP and InSb MIS structures are interpreted in the context of the experimental and theoretical framework developed for the Si–SiOx MOS system. GaAs and InAs MIS structure exhibit anomalies attributed principally to pinning of the Fermi level by extrinsic surface states near midgap for GaAs and within the conduction band for InAs. Microwave power gain can be obtained from InP and GaAs MIS field effect transistors irrespective of the density of fast surface states present in them; the surface states cannot respond to the μ-wave signals applied to the MISFET gates.
Effects of neutron radiation on 4.2-K cryocondensation panels
Authors: Chou T. S. , Halama H. J.
Published: July 2002

Thick deuterium films were condensed on an aluminum cryopanel and bombarded with both fast and thermal neutrons. (AIP)
An upper bound to the pressure (outgassing rate) in a dynamic vacuum system (1) Uniform wall bombardment
Authors: Edwards D.
Published: July 2002

It is shown theoretically that the upper bounds of the outgassing rate of a vacuum system under bombardment is independent of the type of bombarding particle as well as the wall material. (AIP)
Interface composition and adhesion of glow-discharge-formed organo–tin polymers
Authors: Kny Erich , Levenson Leonard L. , James William J. , Auerbach Robert A.
Published: July 2002

The interface composition and bonding of thin organo–tin polymers, plasma-deposited on Al, are determined by AES, ESCA, and pull testing. A tin oxide species is formed between the bulk organo–tin polymer and the Al surface within an interfacial region of about 10 nm. This is evidenced by the change in the profile of the Sn-MNN Auger signal and by the energy shift of the Sn 3d3/2 and 3d5/2 peaks in the ESCA spectrum. No tin oxide formation is observed at the interface of organo–tin films deposited under similar conditions on stainless steel. The composition at the interface is also shown to depend on the position of the sample in the glow discharge during film deposition.
Diagnostic test for ion implantation dosimetry
Authors: Matteson S. , Tonn D. G. , Nicolet M.-A.
Published: July 2002

A diagnostic technique is discussed and illustrated by experiment, which reveals sources of error in current integration dosimetry. The technique uses simple, specially prepared samples and an oscilloscope display of the measured current versus time.
Interface studies of AlxGa1–xAs–GaAs heterojunctions
Authors: Garner C. M. , Su C. Y. , Spicer W. E.
Published: July 2002

Ion depth profiling with Auger electron spectroscopy has been used to measure the interface width of AlxGa1–xAs–GaAs heterojunctions grown by molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), and vapor phase epitaxy. By profiling the MBE structures with 250 eV Ar+ ions, it was possible to experimentally measure an interface width (10%–90% Al p–p height) of ∠15 Å. The measured interface width of VPE and LPE AlxGa1–x As–GaAs interfaces was found to be ∠20 and 100 Å, respectively. Additional electrical measurements were made on n–nAlxGa1–xAs–GaAs heterojunctions and these showed the heterojunctions to be ohmic in agreement with previous studies. Thus, the absence of rectification of n–n heterojunctions cannot be explained by compositional grading but must be due to some other material related problem which is at this time unknown.
Study on voltage contrast in SEM
Authors: Lin Y. C. , Everhart T. E.
Published: July 2002

Voltage contrast in the SEM is a contactless technique for the study of potentials and potential distributions. Its applications include the examination of static and dynamic voltage signals on semiconductor devices, the direct observation of grain boundaries on polycrystalline semiconductors, and the detection of acoustic wave signals on a piezoelectric material. The quality of a recorded micrograph and the minimum detectable voltage are both limited by the noise level associated with the electron–beam and the detector system. In general, the electron–beam current must be increased to apoint at which the noise level in the collected signal is acceptable. A relationship between the minimum detectable voltage and the beam current has been established for any specific recording condition. The theory assumes a Maxwellian energy distribution of the secondary electrons. Furthermore, the collector system is assumed to act like a simple energy filter which accepts only secondary electrons having an energy higher than Ef. The theoretical results also indicate that the highest detection sensitivity can be achieved when the collector system is designed so tht Ef is around 2.6 eV for an ’’average’’ metal. A relationship between the electron beam current and the expanded SNR caused by a voltage difference has been obtained experimentally. There was a satisfactory agreement between theoretical predictions and experimental results. The experiment was conducted in an SEM which is equipped with a standard scintillator–photomultiplier detector.
Matrix effect in SIMS analysis using an O2+ primary beam
Authors: Yu Ming L. , Reuter Wilhad
Published: July 2002

We have observed large matrix effects in the secondary ion emission from alloys when bombarded with an O+2 beam. Binary alloys of Ni with Cr, Fe, and Cu were studied. Chromium, which reacted most strongly with oxygen, induced the largest enhancement of the Ni+ ionization probability. Iron enhanced the Ni+ ionization probability to a lesser extent, whereas copper resulted in a decrease of the Ni+ ionization probability. Ni also induced a small enhancement of the ionization probability of Cr. We find a strong correlation of the mean free energy of formation of the metal-oxide bond with the observed trends in the ionization probabilities. These matrix effects can cause artifacts in the depth profiling of metal film structures where interdiffusion at the interface leads to the formation of alloys or intermetallic compounds. This is indeed observed when interfaces of Ni–Fe and Ni–Cr films are studied by SIMS.
Effect of thermal annealing on thin film transistors processed by photoengraving
Authors: Shepherd F. R. , Nentwich H. , Westwood W. D. , Ingrey S. J.
Published: July 2002

Thin film transistors (TFTs) are of current interest for addressing large-area flat panel displays. In most cases, in-vacuum mechanical masking and successive evaporations in a single pumpdown have been used to define the necessary patterns. While this has the advantage of minimizing contamination of the film interfaces, complex and expensive equipment is needed to fabricate high resolution patterns over large areas. We have, therefore, investigated the use of conventional vacuum deposition and photoengraving processes, similar to those used in silicon integrated circuit technology, and have successfully fabricated CdSe TFTs in which the gate and source-drain levels have been defined by photoengraving. Al and Cr metallizations and Al2O3 dielectric layers have been used. Well-saturated transistors with switching ratios of ∠104 and electron mobilities of ∠50 cm2 V−1 s−1 are achieved only after the fabricated structure is thermally annealed. Since some thermal annealing appears to be essential in all of the reported TFT processes, the physical significance of thermal annealing has been investigated. A model involving activated diffusion is presented and the effect of different annealing conditions on transistor characteristics discussed.
Investigation of the semiconductor–oxide electrolyte interface in GaAs utilizing electrolyte electroreflectance
Authors: Silberstein R. P. , Pollak F. H.
Published: July 2002

We have investigated the electrolyte electroreflectance (EER) spectra of N–GaAs in the vicinity of the Eo transition (direct gap at k↘=0). A pronounced interference phenomenon sensitive to the dc bias electric field has been observed which we identify with an exciton quenching effect within the semiconductor space–charge region (SCR). We have utilized this excitonic feature to interferometrically probe the dynamic and steady-state properties of the SCR during electrochemical anodization procedures. The same EER spectra also exhibit Franz–Keldysh oscillations, the period of which is explicitly dependent on the ac electric field. Using these phenomena we have shown that the interfacial and oxide electric fields under steady-state conditions are just sufficient to continue growing the oxide in compensation for slow dissolution. If the dc bias voltage is suddenly reduced, the SCR temporarily collapses due to transient effects which we attribute to very slow interface states in the oxide. These techniques are applicable to the study of the SCR in a variety of semiconductor–electrolyte systems as well as in the Schottky barrier configuration.
Soft x-ray appearance potential studies of 59Pr, 65Tb, 67Ho, and 68Er
Authors: Chopra D. , Martin G. , Naraghi H. , Martinez L.
Published: July 2002

Soft x-ray appearance potential spectroscopy (SXAPS) investigations of rare-earth metals have been recently conducted by various researchers. Among these studies is one just published, Hua et al., in which it is claimed that no rare-earth metals with an even number of 4f electrons (e.g., 59Pr, 65Tb, 67Ho) has yielded any characteristic appearance potential spectrum. Contrary to this assertion, our data reveals significant results for M4,5 spectra of these metals. Also, the intensity of APS peaks in rare earths is shown to depend on the total number of 4f electrons rather than their odd or even character. Furthermore, the M5/M4 intensity ratios have been systematically investigated.
Comment on ’’Practical way to calculate molecular conductances of pipes with constant annular cross section’’
Authors: Steckelmacher W.
Published: July 2002

An approximation to the molecular flow conductance of an annular pipe given recently by onusic is corrected to make clear the likely errors involved and to show the effect of the cross sectional shape.(AIP)
Metallic coating of microspheres
Authors: Meyer S. F.
Published: July 2002

Extremely smooth, uniform metal coatings of micrometer thicknesses on microscopic glass spheres (microspheres) are often needed as targets for inertial confinement fusion (ICF) experiments. The first part of this paper reviews those methods used successfully to provide metal coated microspheres for ICF targets, including magnetron sputtering with microsphere bouncer and gas levitator, electro- and electroless plating, and chemical vapor deposition with fluidized bed. The second part of this paper discusses some of the critical aspects of magnetron sputter coating of microspheres, including substrate requirements, the sticking of microspheres during coating (preventing uniform coating), and the difficulties in growing the desired dense, smooth, uniform microstructure on continuously moving spherical substrates.
An improved controller for mercury diffusion pumps
Authors: Coplen T. B. , Wildman J.
Published: July 2002

A mercury diffusion pump and rotary pump controller has been constructed to minimize the hazards associated with such pumps. The controller removes power from the diffusion pump when (1) cooling water flow is insufficient, and (2) pressure in the vacuum system is higher than a process control set point. To prevent problems associated with breaks in the vacuum line or breakage of the rotary pump V-belt, the power to both the diffusion pump and rotary pump is removed and an audio alarm sounded if the system pressure exceeds process control set point for more than approximately 50 s.
A cryosorption pumped rapid cycle UHV system
Authors: Visser J. , Scheer J. J.
Published: July 2002

A non-baked v.h.v. system with practical industrial applications is described. (AIP)
Ideal vacancy induced band gap levels in lattice matched thin superlattices: The GaAs–AlAs(100) and GaSb–InAs(100) systems
Authors: Sarma S. Das , Madhukar A.
Published: July 2002

Results of the ideal cation and anion vacancy induced deep levels in thin GaAs–AlAs(100) and GaSb–InAs(100) superlattices are reported. The deep levels are obtained as a function of (a) the spatial location of the vacancy with respect to the interface and (b) the magnitude of the appropriate band edge discontinuity characterizing these superlattices. The theoretical method employed is the Koster–Slater Green’s function technique combined with a LCAO-tight binding description of the electronic structure of perfect superlattices. The tight binding matrix elements, up to second nearest neighbors, are obtained via fitting to the band structure of individual bulk materials involved with the added requirement of reproducing the photothreshold which ensures a correct qualitative ordering of their ionicity. In an attempt to gain an estimate of the importance of self-consistency in the determination of vacancy induced levels, results are also obtained for inequivalent values of the diagonal tight binding energies for As atoms corresponding to the two normally equivalent As interfaces characteristic of GaAs–AlAs(100) superlattice. The effect is estimated to be about 10%. It is argued that these results also provide a simulation of and insight into the possible presence of local potential fluctuations and inequivalent band edge discontinuities at the two interfaces arising from the nature of superlattice growth.
Ohmic contacts to n-GaAs using graded band gap layers of Ga1−xInxAs grown by molecular beam epitaxy
Authors: Woodall J. M. , Freeouf J. L. , Pettit G. D. , Jackson T. , Kirchner P.
Published: July 2002

Ohmic contacts were studied on structures which utilize the fact that for InAs surfaces Fermi level pinning occurs at or in the conduction band. It was found that an epitaxial layer of n-Ga1−xInxAs grown by molecular beam epitaxy on n-GaAs which is graded in composition from x = 0 at the GaAs interface to 0.8?x?1.0 at the surface will produce a structure with a nearly zero Schottky barrier height for the metal–Ga1−xInxAs interface and hence a low resistance ohmic contact. A transmission line measurement of non-alloyed contact resistance of 5×10−7<Rc<5×10−6 ohm cm2 was obtained for a Ag/n-Ga1−xInxAs/n-GaAs MESFET structure.
A high-current, high speed electron beam lithography column
Authors: Kelly J. , Groves T. , Kuo H. P.
Published: July 2002

The design of a high speed electron-beam lithography column is described. Designed for use with a high speed raster scan system, the column produces a beam current of 600 nA in an 0.5 μm round spot, and has a deflection field of 5 mm2. The column uses a zirconiated thermal field emission cathode, two magnetic lenses, with an intermediate cross-over for blanking purposes, and a two-stage electrostatic deflection system, producing both speed and precision. The column is compatible with a 300 MHz pixel exposure rate and has an accuracy of better than ±0.125 μm (2σ).
A new conformal dry-etch technique for submicrometer structuresa)
Authors: Jun-Ru Ma , Kuo-Hsiung Shen , Wolf E. D. , Everhart T. E.
Published: July 2002

A new microlithographic pattern transfer technique that does not require resist development has been studied. The technique involves the diffusion of gaseous HF and water vapor through the exposed resist and the selective etching of the underlying SiO2. Etching is found to proceed only when the resist is in contact with the SiO2 underneath. The ratio of the etch rate of SiO2 beneath exposed and unexposed resist can be essentially infinity and this very high selectivity was used for etching high resolution SiO2 patterns without development. Variations of etch rate with substrate temperature (100° to 250°C), exposure dose (0−54 J/cm2 for UV, and 0−3.2 mC/cm2 for e-beam at 20 keV) HF vapor flow and resist thickness (1600 to 4000 Å) are presented. This new microlithographic etch process for patterning SiO2 does not require resist development and therefore reduces the three key steps in microlithography—exposure, development, and etching to two. As a result it eliminates the problems introduced during the development stage such as pinholes and loss of pattern fidelity. The process is capable of resolution down to at least 0.7 μm linewidths in silicon dioxide and in principle can be applied to other materials with volatile reaction products.
Prospects for high-brightness x-ray sources for lithography
Authors: Economou N. P. , Flanders D. C.
Published: July 2002

The x-ray source is a critical part of any x-ray lithography system since the source characteristics directly affect resolution, alignment, and throughput. Conventional electron bombardment sources, using either stationary or rotating anodes, are now in wide use. However their poor efficiency, low brightness, and uncollimated nature makes them doubtful candidates for high throughput lithographic systems. Several possible alternative sources have been discussed in recent years. They fall into two broad categories: accelerated charged particle beams and high temperature plasmas. The first category includes the synchrotron and related devices such as wigglers. Although these are large and costly installations, they are excellent sources of soft x-rays and have many advantages as lithographic sources. The second category contains many different systems capable of producing dense, high temperature plasmas. Some of these have been shown to have promise as compact, efficient, high brightness x-ray sources. Devices in each of these two categories will be discussed and the relative advantages and disadvantages of each as a source for x-ray lithography will be outlined.
An automated VLSI-mask inspection system
Authors: Migitaka M. , Mizukami K. , Hisamoto Y. , Wada Y.
Published: July 2002

A fully automated electron beam VLSI-mask inspection system using an electron beam as a probe has been developed. The high resolution of the electron probe, as well as its ease of positioning, permits accurate and rapid inspection. The system can measure 10 000 pattern widths pere hour with a measurement repeatability of 0.3 μm (3 σ standard deviation). The system can also measure the position of patterns in a deflection field with the same measurement repeatability. In the case of chip position measurement, the measurement repeatability is 0.2 μm (3 σ), which is attributable to the low repeatability of an X–Y moving table. Moreover, the system can inspect pattern defects through the use of additional electronic equipment.
A report from the AVS Standards Committee: Comparison of ion gauge calibrations by several standards laboratories
Authors: Warshawsky I.
Published: July 2002

Calibrations by four U.S. laboratories of four hot-cathode ion gauges, in the range 0.07–13 mPa, showed systematic differences among laboratories that were much larger than the expected error of any one calibration. They also suggested that any of the four gauges tested, if properly packaged and shipped, was able to serve as a transfer standard with probable error of 2%. A second comparison was made of the calibrations by two U.S. laboratories of some other gauges that had also been calibrated by the National Physical Laboratory, England. Results did not permit conclusive determination of whether differences were due to the laboratories or to changes in the gauges.
Spray deposition and characterization of cadmium stannate films for solar cells
Authors: Ortiz R Armando
Published: July 2002

Cadmium stannate films were deposited by spray pryolysis into pyrex glass, starting from an aqueous solution of CdCl2 plus SnCl4 without doping. Structural, optical, and electrical properties were investigated. The films show high optical transparency and an electrical conductivity up to 1.1×102 Ω−1 cm−1. The effect of postdeposition heat treatment under hydrogen was investigated.
Insulator to metal bonding for rf sputtering applications
Authors: Pressman L. D. , Zydzik G.
Published: July 2002

Methods of joining an insulating target to a metal cathole for sputtering applications are described. It is shown that suitable wetting of glass by indium can be obtained using a hot plate and an ultrasonic soldering iron. Glasses so coated are easily joined to the cathode in a vacuum furnace or in air using a hot plate. Targets made by either method have been tested successfully during rf sputtering at power densities up to 16 W/cm2.
Sputter depth profiles of Ni/Cr thin-film structures obtained from the emission of Auger electrons and x rays
Authors: Fine Joseph , Navinsek B. , Davarya F. , Andreadis T. D.
Published: July 2002

Multilayered thin-film Ni/Cr/Ni/Cr. . .  structures, prepared by sputter deposition, were depth profiled by argon ion sputtering at energies of both 1 and 3 keV. Compositional depth profiles were obtained by simultaneously detecting the characteristic emission of Auger electrons and x rays that results from bombardment with 5-keV primary electrons. An ultra-thin windowed energy-dispersive Si (Li) detector was used to monitor the emitted Lα x rays of Ni(0.85 keV) and Cr(0.57 keV). Due to the use of a near-grazing take off angle for x rays, the x-ray ’’probe depth’’ for 5-keV primary electrons is somewhat greater than the thickness of an individual thin film (∠70 nm) and results in an x-ray profile generated by the amount and type of material contained in such a layer thickness. Both Auger and x-ray measurements indicate that each sputtered film is completely resolved, that little degradation in the interface widths is observed in sputtering through all nine layers of the structure, and that determinations of sputtering times based on Ni/Cr periodicity as well as on single film removal are remarkably consistent. The well-defined repetitive profiles indicate that this multilayered material may be well suited for use in sputter depth calibration. In combining x-ray analysis with Auger spectroscopy, the additional information obtained can be very effective in thin-film analysis.
X-ray standing wave analysis for bromine chemisorbed on silicon
Authors: Bedzyk M. J. , Gibson W. M. , Golovchenko J. A.
Published: July 2002

X-ray standing wave measurements on single crystals of silicon are used to determine the coverage and position of chemisorbed bromine. Detailed analysis of the position information leads to the conclusion that silicon surface atoms bonded to adsorbed bromine atoms are in extrapolated bulk-line positions. Direct measurement of the desorption of correlated bromine in air demonstrates the high stability of the Br/Si surface interface.
Calibration of secondary standard ionization gauges
Authors: Hirata M. , Ono M. , Hojo H. , Nakayama K.
Published: July 2002

A McLeod gauge, designed, built and maintained by us, serves as the primary vacuum standard of Japan. We measure the sensitivities for nitrogen of the secondary standard ionization gauges (VS–1) with an accuracy of ±3% with the McLeod gauge in the pressure range from 0.01 to 0.3 Pa. The VS–1 gauge is a triode type that shows constant sensitivity from 1×10−4 to 0.3 Pa. 258 VS–1 gauges were calibrated since 1964. The average value of the sensitivities is 0.137 Pa−1. About 85% of the gauges have sensitivities with less than ±10% deviation from the average. The main reason for the spread of sensitivities was the electrode displacement. We discuss the technical problems connected with the use of the VS–1 gauge as a transfer gauge for international comparison of vacuum standards.
Photoemission and other photoexcitations as probes of the solid–liquid interface
Authors: Buchholz J. C.
Published: July 2002

Two ways of determining information about solid–liquid electrochemical interfaces on an atomic scale are in situ studies generally involving an optical probe and ex situ studies of electrodes transferred to vacuum. In situ photocurrent spectroscopy provides an approach bridging the gap between in situ optical spectroscopy and conventional electron spectroscopy measured ex situ. The method is sensitive to adsorbates, as shown by the observation of adsorption of a precursor to the electrochemical oxidation of Pt and Zn. In addition, bandgap, and band position information has been obtained for multilayer film formation in the electrochemical growth of oxides on Pt, Zn, and Ni. Coupling of these measurements with photoelectron spectroscopy provides a novel way of exploring the electronic structure of electrochemical interfaces.
Alternate method of measuring ion-beam-irradiated areas
Authors: Bhalla A. S. , Tongson L. L.
Published: July 2002

A decoration technique is suggested for measuring the shape and size of ion beam spots. The method is tested for 4He+ incident on Gd2(MoO4)3.
Angle-resolved measurements of the secondary-electron emission spectrum of Cu(100)
Authors: Graham G. W.
Published: July 2002

Angle-resolved measurements of the secondary-electron emission spectrum of the Cu(100) surface have been performed in order to investigate the nature of the temperature dependent peaks observed in the 100–300 eV range of the angle-integrated spectrum. Spectra obtained for emission along directions in the (010) and (011̄) planes show that the peaks result from a superposition of structure in the energy distribution which varies rapidly as a function of emission angle. The interpretation of the peaks in the angle-integrated spectrum in terms of diffraction phenomena is discussed in light of the angle-resolved data.
Measurement of the recombination rate coefficient of a tokamak vacuum vessel wall
Authors: Howe H. , Langley R.
Published: July 2002

The recombination rate coefficient of the ISX-B vacuum vessel wall has been measured by observing the rate of decrease of gas pressure in the vesssel during a glow discharge. A simple analytic expression which relates the rate of change of the pressure to the recombination rate is derived and verified by comparison with a complete numerical simulation. Comparison of the recombination coefficient measured in ISX-B with previous laboratory measurements shows that the measured value is typical for a stainless steel surface covered with an oxide layer.
Calculation of the pumping speed of turbomolecular vacuum pumps by means of simple mechanical data
Authors: Bernhardt K.-H.
Published: July 2002

A formula for simple calculation of a turbomolecular pump’s pumping speed is developed. The formula includes only mechanical data and a statistical factor k<1. The maximum limiting value of the pumping speed is obtained putting k=1. For this case pumping speed data are easy to calculate and to compare with those given by the manufacturer of a pump. With the aid of the kinetic theory of gases, values for k are computed for a usual case of blade shape and blade speed for different gases. The theoretical results for nitrogen are confirmed by measurements on single flow pumps. It is shown, that for light gases the arrangement of the disks with different shaped blades is of great importance. Results have shown that a high compression ratio does not guarantee a high pumping speed for hydrogen. Measurements on two new pumps confirm this relation.
A system for vacuum gauge calibration using the comparison technique
Authors: Nash P. J. , Thompson T. J.
Published: July 2002

A system for calibrating vacuum gauges in the range 10−4 to 102 Pa with an estimated uncertainty of ±8% is described. The factors affecting the design of the calibration vessel are discussed and the performance of the system enumerated. The reference gauges used are triode ionization gauges and a capacitance manometer. The reproducibilities of the reference gauges are estimated together with the other factors which contribute to the total uncertainty attached to a calibration performed on the system.
Application of a microcomputer to automatic testing of production rotary vane pumps
Authors: Balfour D. , Livesey R. G. , Salmon A. , Snell E. J.
Published: July 2002

Although the tests normally made to assess the performance of newly assembled pumps are thorough, they provide only individual checks against performance specifications. By employing a microcomputer it is possible to conduct repetitive testing of batches of pumps over a wide range of operating conditions to obtain a more meaningful assessment of pump quality. Thus, for example, the power drawn on starting and running at different operating temperatures and pressures can be monitored for different values of mains voltage or frequency. Such measurements, when examined in conjunction with statistical analysis of dimensions of appropriate components, produce invaluable detailed information which can be utilized to provide further improvements in quality. The paper describes a particular automatic test system with details of the computer program, the transducers employed, and the collection and utilization of the data.
The Fermilab Tevatron: Vacuum for a superconducting storage ring
Authors: Bartelson C. L. , Jöstlein H. , Lee G. M. , Limon P. J. , Sauer L. D.
Published: July 2002

A description of the vacuum system of the Fermilab Tevatron, a 1000-GeV accelerator/storage ring, is presented. One-eighth of the ring has been operated for five months at cryogenic temperatures, and with power to the magnets. Results from those tests relevant to the vacuum system are presented.
Vacuum system design for a neutral beam injection system
Authors: Tanabe J.
Published: July 2002

A conceptual design study of neutral beam lines to deliver up to 25 MW of 160 keV neutral deuterium to the proposed West German tokamak, ZEPHYR, was performed at LBL. The study included predicted vacuum behavior of a neutral beam line module, proposed cryopanel design, and a suggested topology for the cryogenic flow distribution system. The cryopanel features an all tubular structure, designed for maximum mechanical flexibility without the use of the bellows in the flow volume. The structure will be insensitive to thermal shock and can withstand large pressure excursions. The distribution system is designed for forced flow cryogenic fluid delivery in two circuits, each feeding three neutral beam lines in hydraulic series. The requirements for balancing a large number of parallel circuits and for long transfer lines are thus avoided by this simple distribution system. Although the plans for ZEPHYR construction were cancelled, the vacuum calculations, the cryopanel, and distribution system design are relevant for the future design of netural beam lines required for plasma heating of the next generation of magnetic fusion devices.
The (changing) MFTF vacuum environment
Authors: Margolies David , Valby Lawrence
Published: July 2002

The mirror fusion test facility (MFTF) vacuum vessel will be about 60 m long and 10 m in diameter at the widest point. The allowable operating densities range from 2×109 to 5×1010 particles per cm3. The maximum leak rate of 10−6 Torrπl/s is dominated during operation by the deliberately injected cold gas of 250 Torrπl/s. This gas is pumped by over 1000 m2 of cryopanels, external sorbtion pumps, and getters. The design and requirements have changed radically over the past several years, and they are still not in final form. The vacuum system design has also changed, but more slowly and less radically. This paper discusses the engineering effort necessary to meet these stringent and changing requirements. Much of the analysis of the internal systems has been carried out using a three-dimensional Monte Carlo computer code, which can estimate time-dependent operational pressures. This code and its use will also be described.
A continuous cryopump for steady state mirror fusion reactors
Authors: Batzer Thomas H. , Call Wayne R.
Published: July 2002

The characteristics of mirror fusion reactors, i.e., steady state operation, a low neutral gas density, and a large gas throughput require unique vacuum pumping capabilities. One approach that appears to meet these requirements is a liquid helium-cooled cryopump system in which a fixed portion can be isolated and degassed while the remainder continues to pump. The time to degas a rotating, fixed portion of the pumping area and the ratio of that area to the total area fixes the gas inventory in the chamber. It follows that the active pump area maintains the required neutral gas density and the time-averaged degassing rate equals the gas throughput. We have built such a cryopump whereby the gas condensed (deuterium) on the liquid helium-cooled panel can be transferred to a collector pump and subsequently to an exterior mechanical pump and exhausted. At panel loadings as high as 0.55 Torr-/ℓcm2 the gas leakage during degassing is less than 8% and the degassing time is less than 10 min. Scaling to reactor size appears to be feasible.
The leak-checking and testing of the first yin–yang magnet for the Mirror Fusion Test Facility (MFTF)
Authors: Kozman T. A. , Lathrop G. H. , Podesta D. L.
Published: July 2002

Leak-testing and leak-reporting techniques used on the MFTF yin–yang magnet for the world’s largest superconducting coil are reported. Based on this experience, techniques will be developed for leak-testing techniques to be employed on the 24 MFTF-B coils. Additional information is presented on MFTF magnet operation after the completion of these tests. Also described are the leak-hunting techniques and their results when applied to the two liquid-helium circuits (the coil bundle and guard vacuum: both require helium flow for magnet cooldown), their associated piping, liquid-nitrogen radiation shield, and piping. Leak hunting and repair was started in July 1981, when the installation of the magnet liner radiation shields was completed and continued until acceptable leak-rate requirements were met in December 1981. Cooldown and acceptance testing of the magnet was accomplished in January and February 1982.
Calculations of gas density in a closely packed multichannel electrostatic quadrupole (MESQ) array
Authors: Burrell C. F. , Goldberg D. A.
Published: July 2002

As a part of our program for developing new accelerators for high-energy negative ion neutral beam lines, we have studied the pumping properties of a MESQ array such as might be interposed between the ion–source/preaccelerator and a MESQ accelerator. The studies were performed using a 2 1/2 -dimensional Monte Carlo code under the assumption of molecular flow, with pumping to be provided by cryopanels on either side of the array. The basic unit treated by the code was a unit cell which could be translated laterally or longitudinally to reproduce the full array. We have studied the behavior of the system as a function of electrode geometry, array size, and cryopanel position. It was found necessary to insert lateral baffles periodically to prevent downstream migration of the gas in the region between the outer edge of the MESQ array and the cryopanels.
Use of vibration-isolated cryopumps to improve electron microscopes and electron beam lithography units
Authors: Venuti Guy S.
Published: July 2002

Improved vacuum systems and the elimination of hydrocarbon contaminants are essential elements of todays e-beam instruments. Electron microscope manufacturers have made great progress in the reduction of contamination and etching, but the need for continued improvement and additional research still remains. Current advances in vacuum technology and the advent of the vibration-free closed cycle cryopump are contributing to this scientific progression.
Surface properties of attapulgite
Authors: Mikhail R. Sh. , Guindy N. M. , Hanafi S.
Published: July 2002

The adsorption of nitrogen at −196 °C and of water and cyclohexane vapors at 35 °C, was measured on attapulgite samples prepared by heating the clay mineral at various temperatures between 30 and 1000 °C for 5 h in (10−5 Torr.). Specific surface areas were estimated from both the BET method (SBET) and the cumulative values obtained from pore structure analysis (Scum). The results obtained show that for the low temperature samples, the areas measured by water, N2, and cyclohexane are in the following ratio, 4:2:1, attributed to the ability of water to penetrate into the channels of the mineral. As for the high temperature samples, SBET (water)≂SBET (nitrogen) due to the closing of the channels of the mineral and the subsequent disappearence of the water adsorbing property. Heats of immersion were also measured in water and cyclohexane and were correlated with the fraction of wide pores.
Fluorescers and filters of unusual chemical composition for low-energy x-ray measurements
Authors: Jorgensen B. , Liepins R. , Geanangel R. A. , Komm R.
Published: July 2002

The preparation of fluorescers and filters of high oxygen and high nitrogen (53 and 52 wt.%, respectively) for low-energy x-ray measurements is described. The thin films of high oxygen content were fabricated from 50:50 wt.% mixture of Celcon■ and Delrin■, whereas the films of high nitrogen content were synthesized from ammonia–borane on a polyacrylonitrile substrate.
Methane formation and surface modification of TiC coating by hydrogen ion bombardment
Authors: Sukenobu S. , Gomay Y.
Published: July 2002

Methane formation and surface composition change of a TiC coating are studied under hydrogen ion bombardment by means of residual gas analysis and Auger electron spectroscopy. Hydrogen ion energy is between 500 and 3 keV and the target temperature ranges from room temperature to 1000 °C. The methane emission yield is minimum (2–4)×10−3 molecules/ion, near 500 °C and is increased by a factor of 2–3 in room temperature and 1000 °C. The surface composition during hydrogen ion bombardment is quite dependent on both the target temperature and the ion energy. Concerning the temperature effect, the ratio of carbon to titanium atoms of the TiC surface after ion bombardment at room temperature is lower than that at 590 °C. Concerning the energy effect, the C/Ti ratio decreases with lower bombardment energies.