bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Isotherms for Physical Adsorption at Pressures below 10−10 Torr
Authors: Hobson J. P.
Published: July 2002

Theoretical isotherms for the physical adsorption of argon, nitrogen, and helium on a heterogeneous surface in the pressure range from 10−10 Torr down to pressures indefinitely low are presented. The calculations are based on adding a single assumption to a model that was successful in correlating experimental data for argon, nitrogen, and helium over a wide range of adsorbents, temperatures and pressures above 10−10 Torr. The results are compared with an alternative model that postulates a homogeneous surface and are found to be significantly different. It is concluded that experiments should be possible to establish which, if either, of these approaches is useful.
Cryosorption Pumping of Helium at 4.2 °K
Authors: Grenier G. E. , Stern S. A.
Published: July 2002

The cryosorption pumping of helium gas by means of Molecular Sieve 5A cryosorption panels has been studied at 4.2 °K and in the pressure range from 10−7 to 10−8 Torr. The sticking coefficient of the gas was found to vary from about 0.70 to 0.91 at these pressures, respectively, corresponding to the high pumping speeds of 20000 to 27000 liter/sec/ft2 of panel. The absorptive capacity for helium was also high down to 10−8 Torr, but the pumping speed decreased with increasing surface coverage. It is concluded that helium can be pumped effectively in the high-vacuum region with cryosorption panels refrigerated to 4.2 °K.
Role of Hydrogen in the Sputtering of Nickel–Chromium Films
Authors: Stern E. , Caswell H. L.
Published: July 2002

Mass-spectrometer analysis of the gases in a sputtering apparatus has demonstrated that: (1) Under normal sputtering conditions, copious quantities of hydrogen are evolved from the dissociation of adsorbed water vapor, and (2) hydrogen partial pressures as low as 5 × 10−7 Torr can measurably reduce sputtering rates in an argon discharge. These results have been used to develop a novel approach to thickness control of sputtered thin films. The techniques has been applied to the deposition of nickel–chromium films with a control on thickness of ±1%.
Mass Spectrometric Sampling of Glow Discharges
Authors: Sullivan John J. , Buser Rudolf G.
Published: July 2002

Continuous mass spectrometric sampling of the transient behavior of various gas species from a dc glow discharge originally filled with CO2, and mixtures of CO2-H2, (pressure range 50–1000 μ, discharge current 50–200 mA) have been studied by means of a specially constructed mass spectrometer (90° magnetic deflection) gas-sampling system. The sampling technique employed differential pumping of the mass spectrometer by a constricted ion-getter pump using a variable entrance aperture (valve) to the sampling system. The response of the system to time-varying concentrations is derived and the realization of optimum conditions discussed. This work is part of a program to investigate the gaseous electronics aspect of sealed CO2 laser operation.
Inert Gas Ion Pumping Using Differential Sputter Yield Cathodes
Authors: Tom T. , James B. D.
Published: July 2002

A method to eliminate “argon instability” in a Penning cold-cathode ion pump is proposed. This method involves the use of a metal having a high sputtering yield coefficient as one of the cathodes. The results obtained using titanium and tantalum as cathodes are described. This combination has eliminated the pressure fluctuations while pumping inert gases. The performance characteristics on gases such as air, nitrogen, hydrogen, argon, and helium are also given.
Influence of substrate temperature and deposition rate on structure of thick sputtered Cu coatings
Authors: Thornton John A.
Published: July 2002

Thick [1–10 mil (25.4–254.0 μm)] OFHC copper coatings were deposited on copper, tantalum, and stainless-steel substrates maintained at temperatures (T) in the 50 °–950 °C range, at rates of from 200 to 18 000 Å/min, using primarily hollow and also post-type cathode sputtering apparatuses at argon pressures of 1 and 30 mTorr. Coating structures were examined by preparing metallographic cross sections. Surface topographies and fracture cross sections were examined by scanning electron microscopy. Crystallographic orientations were determined by x-ray diffraction. No significant deposition rate influence was found on the low-temperature structure zones reported previously [J. A. Thornton, J. Vac. Sci. Technol. 11, 666 (1974)] or on the columnar nature of coatings formed at elevated T. Truly equiaxed grain structures were generally not observed with hollow cathodes. Annealing twins were found within the grains for T≳350 °C. Evidence of extensive recrystallization and grain growth was seen for T∠900 °C. Coatings deposited at low rates and T≳400 °C on Cu substrates exhibited epitaxial effects; those on dissimilar substrates showed evidence of agglomeration.
Abstract: Transparent conducting films
Authors: Vossen J. L.
Published: July 2002

Transparent conductors are becoming of increasing importance because of increased interest in the interactions of light with electrically or electronically active materials, and for their high ir reflectivity which is useful for solar energy applications. The information in this presentation is largely organized by film deposition process rather than the film material because, ostensibly, the same material deposited by two different deposition techniques ordinarily yields two widely varying sets of physical properties. This is not surprising because of the complex physics and chemistry of the materials used for this purpose. Broadly speaking, there are two classes of materials: semiconducting oxides and very thin metals. The properties of the oxides depend critically upon their oxidation state and the nature and quantity of impurities trapped in the film. The properties of the thin metals depend upon nucleation and early coalescence phenomena and impurities. Both the electrical and optical properties of both classes depend strongly on the nature of the substrate used (impurities that can diffuse from the substrate into the film and the refractive index of the substrate).

Following a brief review of the physics of conductivity and transparency in these materials, detailed analysis of the following film deposition processes are given: hydrolysis of chlorides, pyrolysis, evaporation and sputtering of thin metals (with and without nucleation modifying layers), reactive evaporation and sputtering, and sputtering of oxide targets. The important process-control parameters that affect the electrical and optical properties of transparent conducting films are discussed.
Self-sputtering phenomena in high-rate coaxial cylindrical magnetron sputtering
Authors: Hosokawa N. , Tsukada T. , Misumi T.
Published: July 2002

In order to increase the deposition rate in magnetron sputtering, end plates were attached to both ends of cylindrical target. A current density of 0.1 A/cm2 was obtained with relatively low target voltage from 300 to 800 V. Deposition rates of Al and Cu were measured as functions of target voltage and current. From a discrepancy between measured and calculated values based on sputtering yield data, it is considered that sputtered Al atoms were ionized in a high density argon plasma and that the target was bombarded not only with argon ions but also with aluminum ions. Ionized Al atoms are estimated as about 18% of all the total ion current. Sputtering of Al and Cu in Kr and He were also examined. The same experiment was performed with another configuration of the electrode in which permanent magnet cores were placed inside the cylindrical target so that a spatially alternating magnetic field was applied along the axis. Discharge and sputtering characteristics were similar to the first one, although the shape of plasma and electron current to the substrate were much different.
Anomalous behavior of Meissner coils in high-vacuum applications
Authors: Siebert J. F. , Omori M.
Published: July 2002

The performance of different configurations of a Meissner liquid nitrogen trap operating in the main chamber of a high-vacuum system have been measured. Temperature fluctuations of the cryosurface and corresponding fluctuations in the chamber pressure were monitored for a variety of different chamber base pressures and liquid nitrogen flow conditions. Large fluctuations in the chamber pressure, observed with a high flow resistance, and low heat capacity configuration, clearly illustrate the importance of the thermal stability of the cryosurface in the presence of a condensible gas, such as CO2, that has a vapor pressure at liquid nitrogen temperature comparable to the system base pressure. These experiments indicate that a Meissner trap placed in the main chamber of a conventional 10−6 Torr vacuum system will be fully effective only if designed and operated so that the cryosurface is thermally stable to better than 0.1 K. The design, operation, and performance of such a configuration are presented.
Clean and contaminated TiD2 films: Fabrication and Auger spectra
Authors: Malinowski M. E.
Published: July 2002

Clean and intentionally contaminated stoichiometric TiD2 thin films have been formed under controlled conditions and the surface compositions of the films measured using Auger electron spectroscopy. The unique ultrahigh vacuum system used to fabricate the films is described in detail. In addition, the Auger spectra of clean and CO- and CO2-contaminated films, before and after deuteriding, are presented. The MVV and LMV peaks in the differential spectrum of TiD2 are significantly different from the corresponding peaks in the Ti spectrum, presumably a result of the deuteride formation. Films intentionally contaminated with CO and CO2 have Auger spectra with oxygen peaks and carbide-like carbon peaks. The C and O peak heights and shapes for Ti exposed to CO and CO2 do not change upon formation of TiD2. In addition, for each of these gases, a definite ratio of C/O peak heights was observed: For CO, the C/O ratio was ∠1.3, while for CO2 it was ∠0.58. Both ratios were independent of gas exposures up to ∠1 Torr s.
Precision molecular flow measurement and control for single and multigas systems
Authors: Kiesling Robert A. , Sullivan John J. , Santeler Donald J.
Published: July 2002

This paper presents recent advances in precision molecular flow measurement and control for single backfill gases as well as describing the important factors to be considered in multigas flow and ratio control of several gases at pressures above 0.0133 Pa. A comprehensive theoretical analysis is given describing the variables to be considered in practical systems. Theoretical and experimental data are presented on a new design of molecular flow element specifically designed for vacuum flow applications of any gas, including corrosive types. Single and multigas measurement and control applications using the new flow element with electronic manometer measurement and control instrumentation include reactive sputtering, reactive ion etching, and plasma reactor deposition and etching systems.
A theoretical study of Al overlayers on Si(111)
Authors: Zhang H. I. , Schlüter M.
Published: July 2002

The surface system Si(111) with chemisorbed monolayers of Al is investigated theoretically. Within the self-consistent pseudopotential scheme several different structural models for chemisorption are studied and spectroscopic results are compared to recent experimental photoemission and electron energy loss data obtained on similar systems. It is found that chemical bonds between substrate and metal are formed yielding states in the semiconductor gap which stabilize the Fermi level. From the detailed analysis of several strong spectroscopic features it follows that the interface may structurally be modelled by Al atoms sitting in threefold coordinated positions either above the Si(111) surface or replacing the outermost silicon layer, (i.e., Lander’s substitutional model).
New and unified model for Schottky barrier and III–V insulator interface states formation
Authors: Spicer W. E. , Chye P. W. , Skeath P. R. , Su C. Y. , Lindau I.
Published: July 2002

For n- and p-doped III–V compounds, Fermi-level pinning and accompanying phenomena of the (110) cleavage surface have been studied carefully using photoemission at hν≲300 eV (so that core as well as valence band levels could be studied). Both the clean surfaces and the changes produced, as metals or oxygen are added to those surfaces in submonolayer quantities, have been examined. It is found that, in general, the Fermi level stabilizes after a small fraction of a monolayer of either metal or oxygen atoms have been placed on the surface. Most strikingly, Fermi-level pinning produced on a given semiconductor by metals and oxygen are similar. However, there is a strong difference in these pinning positions depending on the semiconductor: The pinning position is near (1) the conduction band maximum (CBM) for InP, (2) midgap for GaAs, and (3) the valence band maximum (VBM) for GaSb. The similarity in the pinning position on a given semiconductor produced by both metals and oxygen suggests that the states responsible for the pinning resulted from interaction between the adatoms and the semiconductor. Support for formation of defect levels in the semiconductor at or near the surface is found in the appearance of semiconductor atoms in the metal and in disorder in the valence band with a few percent of oxygen. Based on the available information on Fermi energy pinning, a model is developed for each semiconductor with two different electronic levels which are produced by removal of anions or cations from their normal positions in the surface region of the semiconductors. The pinning levels have the following locations, with respect to the VBM: GaAs, 0.75 and 0.5 eV; InP, 0.9 and 1.2 eV (all levels + 0.1 eV). The first energy given is assocaited with a missing anion and the second with a missing cation. For GaSb, only an acceptor due to a missing Sb has been located at 0.1 eV. Our work is found to correlate well with that on practical Schottky barriers. A detailed comparison is made with interface state positions and densities found by others on practical MIS structures, and it is suggested that the large density of these states on III–V’s as compared to Si is due to extrinsic interface states created by stoichiometric deficits of the III–V semiconductor. For GaAs, the dominant state is found at 0.7 eV and is associated with an As deficit. For InP, the major interface level is about 0.1 eV below the CBM. These positions are in good agreement with the existing data obtained from a wide variety of samples.
Direct (TEM) observation of the catalytic oxidation of amorphous carbon by Pd particles
Authors: Moorhead R. D. , Poppa H. , Heinemann K.
Published: July 2002

The catalytic oxidation of amorphous carbon substrates by Pd particles is observed by in situ transmission electron microscopy. Various modes of selective attack of the carbon substrate in the immediate neighborhood of Pd particles are observed, which can be correlated with different degrees of particle mobility. Using amorphous substrates we have been able to demonstrate that the particle-substrate interaction is influenced by the structure of the particle. This has not previously been noted.
Sulfur and oxygen chemistry at free surfaces and grain boundaries of iron alloys
Authors: Thomas M. T. , Baer D. R. , Jones R. H. , Bruemmer S. M.
Published: July 2002

This paper reports a study of grain boundary and free surface segregation in iron alloys. Scanning Auger electron spectroscopy has been used to analyze the extent and spatial distribution of the segregants. It is found that there is a similarity between free surface and grain boundary segregation for vacuum-melted (vm) and zone-refined (zr) materials. S and O are the primary segregants to grain boundaries for vm samples, while N is the predominant segregant for zr material. When O and S are the primary segregated elements, a site competition between them is observed on both the free surface and at grain boundaries. On the free surface the site competition is dependent on grain orientation.
Design and operational characteristics of the cryopump high-vacuum system for the 25 000-l target chamber of the Helios Laser Facility
Authors: Wilson N. G. , Watts Keith N.
Published: July 2002

A vacuum system utilizing two 25 000 l/s (H2O) two-stage (20 and 70 K) helium refrigerator (cold gas) cryopumps and a 1500 l/s turbomolecular pump has been provided for a 25 000-l-volume stainless steel chamber as a part of the Helios Laser Facility. Design goals for the performance of the vacuum system are to produce a chamber pressure of less than 1.33×10−4 Pa after two hours pumping from atmospheric pressure. Details of the vacuum system configuration, and typical operating conditions are described. Observations made during operation indicate the cryopumps utilized initially produce expected pumping performance followed by variable performance (pumping speed and ultimate pressure) depending upon pumping history. The turbomolecular pump utilized has demonstrated reproducible pump speed and ultimate pressure. Both pumps produce some vibration which can cause interference with critical components in the target chamber; vibration damping/attenuation has been successfully employed for the turbomolecular pump with similar techniques being studied for use with the cryopumps. Reliability of the machines utilized has been excellent with only routine maintenance required in the first year of operation. Considerable instability in ionization gauges (Bayard–Alpert type) has been experienced where the expected gauge sensitivity of 10 per Torr has been observed to vary from 7.5 to ≳11.
Low-energy ion erosion studies of machine faceted stainless steel
Authors: Panitz J. K. G. , Sharp D. J.
Published: July 2002

Type 304 annealed stainless-steel substrates with a variety of machine faceted surface finishes have been eroded by low-energy (250–1000 eV) hydrogen, and argon ion beams. The dimensions of the machine faceted features studied range from that of the annealed crystalline grain size (approximately 0.0125 cm) to 0.25-cm macrostructures. Relative erosion rates have been measured and analyzed as a separable function of angular dependent sputtered particle emission and particle recapture. It was found that the formation of a faceted topography on the surface of components exposed to low-energy, light-ion erosion can significantly reduce the effective ion erosion yield.
Surface structures of GaAs(110)
Authors: Kai-Ming Zhang , Ling Yeh
Published: July 2002

The rotational relaxation of the GaAs(110) surface is considered. A cluster model is used fo simulating the crystal surface, and some quasi-atoms are added in order to saturate the dangling bonds in the cluster boundary. The stable relaxation geometry of the GaAs(110) surface is determined by minimizing the total energy of the cluster calculated by the Extended Hückel Method. According to the calculation, a value of 18° for the tilted angle of the surface bond is suggested which is in fairly good agreement with that given by the partial yield photoelectron spectroscopy. The density of states for the cluster is also calculated, it is shown that for this relaxation model there are no empty cation states existing within the band gap.
Solid surfaces, surface processes, and solid/gas interactions
Authors: Czanderna A. W.
Published: July 2002

An overview of the topical coverage of a one-semester, three-hour course on solid surfaces, surface processes, and the solid/gas interface is presented. The main topical areas embracing the nature of the surface phase include topography, shape, depth, composition, purity, and structure, and the methods used to elucidate these parameters. The various theoretical and experimental categories for understanding adsorbate–adsorbent interactions are considered with particular attention focused on physical and chemical adsorption, desorption, and thermal desorption. Surface processes include surface diffusion and chemisorption as a precursor to oxidation and catalysis. The general emphasis of the course is on the experimental aspects of studying surfaces and the harmonious blending of backgrounds in physics, chemistry, materials, mathematics, and engineering for applied and fundamental surface science. The course is designed for graduate students and well qualified seniors majoring in science or engineering, or the equivalent, and has been taught several times.
Study of the initial stages of pack aluminization
Authors: Rairden J. R. , Jackson M. R.
Published: July 2002

The kinetics of the pack aluminizing of René 80 have been studied with emphasis on the early stages of the process. NH4F activated packs containing 2% Al and 5% Ni–40 Al were evaluated. It was found that for the 2% Al (high activity) pack that a weight gain of ∠5.6 mg/cm2 was reached during the initial 10 min of processing; thereafter, there was essentially no further weight gain. In contrast, the 5% Ni–40 Al (low activity) pack showed a gradual weight gain to ∠3.0 mg/cm2 during the 185 min process. Electron microprobe analyses of the coatings were used to characterize the composition profiles of the coatings formed in the two packs. The outer region of coatings formed in a 2% Al pack are of relatively uniform composition for the elements measured: Ni, Co, Cr, and Al. In contrast, the coatings formed in a 5% Ni–40 pack showed sharp compositional gradients in the outer region.
Plasma etching of III–V compound semiconductor materials and their oxides
Authors: Smolinsky G. , Chang R. P. , Mayer T. M.
Published: July 2002

Sixteen reagents were investigated for their ability to etch either GaAs, GaAs–oxide, or both. Except for CCl2F2, fluorine containing reagents such as HF, C2F6, CF3Cl, and CHF3 did not etch. In addition, no etching occurred with the six compounds C2Cl4, CBr2Cl2, CHCl3, PH3, H2 or H2O. Both GaAs and its oxide were etched by CCl4, CCl2F2, PCl3, and HCl; while Cl2 and COCl2 etched only GaAs. Chlorine etched GaAs five times faster than HCl did. Addition of 40% H2 to HCl reduced the etch-rate ratio of GaAs to oxide by 1/8, from 400:1 to 50:1. A 42% H2/58% CCl2F2 plasma etched GaAs only 12 times faster than it etched oxide; this is 1/33 the ratio found for neat HCl and 1/200 the rate of etching GaAs with Cl2. A Cl2 plasma readily etched both GaP and GaSb but not the corresponding oxides. An HCl plasma etched GaP and GaSb and their oxides but did not etch InP or its oxide. The chemistry of these systems is discussed and a model for selective etching of GaAs–oxide over GaAs is proposed.
Morphology of thin superconducting Nb films
Authors: Alessandrini E. I. , Laibowitz R. B. , Viggiano J. M.
Published: July 2002

Experimental results are presented that show correlations between the superconducting transition temperatures (Tc) and the crystalline morphology in very thin Nb films (∠60 nm thick). Variations of vapor deposition rates, substrate temperatures, and pressure during electron beam evaporation lead to different film morphology and grain sizes. Using transmission electron microscopy, diffraction and Tc measurements, it was possible to follow some of the changes in superconducting characteristics effected by the resulting different grain sizes. Broader superconducting transitions and lower Tc’s were generally found for films with average grain sizes ≲10 nm. Average grain sizes of less than 10 nm appear to give lower Tc and a broader transition. Single crystal Nb films showed, in general, a sharp superconducting transition at 9.1 K, the expected value for bulk Nb.
Initial oxidation of CuInSe2
Authors: Kazmerski L. L. , Jamjoum O. , Ireland P. J. , Deb S. K. , Mickelsen R. A. , Chen W.
Published: July 2002

The oxidation of p-type single-crystal and thin-film polycrystalline CuInSe2 is investigated using complementary Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and x-ray photoelectron spectroscopy (XPS). The compositions of the thermally-grown oxides over the 150 °–300 °C temperature range are found to be primarily In2O3, with some SeO2, estimated to be less than 10% by quantitative AES and XPS. The interface between the oxide and CuInSe2 is examined using AES and SIMS depth-compositional profiling in conjunction with XPS. CuxSe is found to form at the interface. Angular-resolved XPS with an in situ oxidation process is utilized to evaluate the initial oxidation of this Cu-ternary semiconductor. These studies confirm that CuxSe forms during oxide growth.
Electron beam array lithography
Authors: Smith D. O. , Harte K. J.
Published: July 2002

Electron-beam array lithography (EBAL) uses array optics to expose 108 to 1010 resolution elements without mechanical motion. The array optics are based on the use of a first stage of deflection (coarse deflection) which selects one of an array of lenslets. The lenslet array is followed by a second stage of deflection (fine deflection) which selects the final spot position. In order to maximize exposure rate and also minimize mechanical motion, it is proposed to use a 3×3 array of array optics channels to expose a 100 mm wafer. As a numerical example of the projected throughput of such a system consider a 20 MHz stepping rate per channel and 0.5 μm pixels. Then (3×1010 pixels)/(9×2×107 pixels per s) ≊170 s. Now if variable spot sizes and vector writing are used such that only 10% of the pattern is exposed using the smallest feature (pixel), the exposure time is reduced to ∠20 s. Consistent with these calculations, EBAL systems are presently under development with engineering goals of 0.5 μm smallest features, 100 mm wafers, and throughputs of 50 wafers/h. The electron optics of these systems are all electrostatic, and use either thermionic (e.g., LaB6) or field-emission (e.g., W/Zr) cathodes. EBAL systems require that patterns be ’’stitched’’ across the boundaries of the lenslet fields in the array lens. This can be accomplished by the use of a standard calibration plate having fiducial marks at the corners and sides of lenslets. Measurement of the positions of these fiducials provides data from which to calculate a set of stitching constants for each lenslet of each electron-beam channel. Overlay between different pattern levels on a wafer is accomplished by a similar process using data from fiducial marks at the corners of each chip which is being written on a wafer. By these means any pattern level on any wafer can be exposed in any EBAL exposure station.
Computer simulations of resist profiles in x-ray lithography
Authors: Heinrich K. , Betz H. , Heuberger A. , Pongratz S.
Published: July 2002

This paper presents a detailed study on computer simulations of resist profiles obtained in x-ray lithography for exposures made either with synchrotron radiation or with an Al–Kα source. It is assumed, for purposes of the calculations, that the vacuum windows consist of kapton and that silicon is used as the mask material. The influence of edge shape and mask absorber thickness upon the resist structure is of special interest. The other parameters affecting resist profiles, such as Fresnel diffraction (especially in the case of semitransparent absorbers) and photoelectron range, are taken into consideration. In the case of the x-ray tube, the penumbral blur caused by the finite dimensions of the source spot leads to an additional deterioration of the edge sharpness. For the calculations, the intensity distribution over the spot area was assumed to be uniform (with Gaussian-shaped edges). The influence of the photoelectron range upon the resist profiles is calculated, using the simple depth-dose relationship of Gruen. The calculated resist profiles are compared with typical experimental results.
The spectroscopic observation of water formation
Authors: Fisher G. B. , Gland J. L. , Schmieg S. J.
Published: July 2002

The formation of water from atomic oxygen and atomic hydrogen coadsorbed on the Pt(111) surface has been characterized by x-ray photoemission (XPS) and temperature programmed reaction (TPR). These studies were performed between 100 and 155 K, which is below the desorption temperature for adsorbed water on the Pt(111) surface. Only adsorbed atomic oxygen and atomic hydrogen were present on the surface prior to reaction. At 100 K no reaction occurs; however, at 120 K the reaction goes to completion even in the absence of gas phase hydrogen. Therefore, water formation on the Pt(111) surface has a low activation energy with an upper limit of 8 kcal/mol (34 kJ/mol). Although previous work has shown that hydroxyl groups are stable near 150 K on the Pt(111) surface, no significant surface concentration of OH species was detected during these reaction studies. The reaction mechanism most consistent with all of the data is the sequential addition of atomic hydrogen to oxygen and then to hydroxyl groups to form the water product. A low surface concentration of OH groups is expected within this mechanism if OH formation is the rate-limiting reaction step.
Surface structure determination using ion scattering spectroscopy
Authors: Williams R. S.
Published: July 2002

Ion scattering spectroscopy (ISS) using low (<10 keV) energy noble gas ion beams [also known as low energy ion scattering (LEIS)] has been used for nearly a decade and a half in the study of surface composition and structure. Recent advances in both the technology associated with ISS and in the understanding of scattering from solids demonstrate that ISS is about to mature as a spectrometric technique and join LEED as an established tool for surface structure determination. The primary difficulty with ISS analysis has been bombardment damage to surfaces, which can be reduced to undetectable levels by using time-of-flight energy analysis or by monitoring the total (energy-integrated or partially filtered) yield of backscattered particles. Present technology is illustrated with an example of a shadow and blocking cone analysis of time-of-flight ISS data from a GaSb (001) surface. Near-future developments in ISS are anticipated by a computer simulation of a total-yield blocking cone analysis of scattering from a Cu (001) surface.
Plasma etching of niobium with CF4/O2 gases
Authors: Chen Mao-Min , Wang Run Han
Published: July 2002

Niobium may be used as an electrode and wiring material in Josephson junction technology. For edge coverage of lines patterned in these films, it is critical to produce a controlled, tapered edge profile. Reactive etching is one of the feasible techniques to accomplish this goal. Plasma etching of niobium in a CF4/O2 gas plasma was studied using an anodically coupled parallel plate reactor. The edge angle was found to be dependent mainly on the etching rate ratio (ERR) of the photoresist to the underlying Nb. Factors which affect the etch rates of Nb and photoresist (thus ERR) such as Nb surface area, temperature of the substrate table, and oxygen concentration in CF4 will be discussed. Parametric studies on the effects of total gas flow rate and chamber pressure will also be reported.
Low-stress diamondlike carbon films
Authors: Zelez Joseph
Published: July 2002

Diamondlike amorphous C films with exceptionally low stress (<108 dyn/cm2) have been prepared by a hybrid process involving bias sputtering with ultrapure C electrodes and plasma decomposition of normal butane. The low stress is believed to be related to the H2 content of the films (<1 at.%). The films have a high density (2.8 g/cm3) and are resistant to wear and abrasion. The films are good dielectrics (ε′=8.8; Q=130; ζ=1.5×1014 Ω ⋅ cm; Ed=3.5×107 V/cm). They are transparent in the visible spectrum and have properties in the infrared that lend themselves to the production of good antireflection coatings. The band gap of the films is about 3.0 eV.
Magnetron sputtering system equipped with a versatile substrate table
Authors: Huggins H. A. , Gurvitch M.
Published: July 2002

A three target dc magnetron sputtering system has been constructed. The main feature of the system is a unique rotating substrate table which permits deposition onto continuously heated or cooled substrates while they are rotating. With this setup, Nb-based tunnel junctions with thin Al overlayers, multilayered materials, and a variety of alloys have been prepared.
Depolarization of D–T plasmas by recycling in material walls
Authors: Greenside H. S. , Budny R. V. , Post D. E.
Published: July 2002

The feasibility of using polarized deuterium (D) and tritium (T) plasmas in fusion reactors may be seriously affected by recycling in material walls. Theoretical and experimental results are reviewed which show how the depolarization rates of absorbed D and T depend on first wall parameters such as the temperature, the bulk and surface diffusivities, the density of electronic states at the Fermi surface, the spectral density of microscopic fluctuating electric field gradients, and the concentration of paramagnetic impurities. Nuclear magnetic resonance (NMR) spectroscopy of hydrogenated and deuterated amorphous semiconductors suggests that low-Z nonmetallic materials may provide a satisfactory first wall or limiter coating under reactor conditions with characteristic depolarization times of several seconds. Experiments are proposed to test the consequences of our analysis.
The evaporation and condensation behavior of As2Se3-like materials
Authors: Jansen Frank , Melnyk Andrew R.
Published: July 2002

The effects of the crucible temperature and the substrate temperature on the deposition efficiency and the film compositon of As2Se3-like materials are analyzed. It is shown that the deposition efficiency increases with increasing deposition rate and decreases with increasing substrate temperature. These results are explained in terms of a model which takes the reevaporation of species from the substrate into account. This model is substantiated by the observed effects of the substrate temperature on the sticking fraction and the arsenic concentration in the film. These compositional changes can be explained by the different vapor pressures of Se-rich and As-rich vapor species, as indeed observed in mass spectrometry measurements of the equilibrium As2Se3-vapor by others.
Using the modulating ion current gauge for total pressure measurements below 10−10 Torr without errors caused by electron-stimulated ion desorption
Authors: Watanabe F. , Hiramatsu S. , Ishimaru H.
Published: July 2002

Total pressure measurements below 10−10 Torr, in an active residual gas, were made using a special hot-cathode ionization gauge, without errors caused by electron-stimulated ion desorption. The gauge can separate the two ion signals, i.e., the signal created from gas phase molecules and that from electron-stimulated ion desorption, by using a new modulation and amplification system. In order to verify this separation effect, experiments were made with oxygen and nitrogen introduction in the 10−10 Torr range.
Electron beam column for a 50×50 mm2 deflection area
Authors: Kuroda Katsuhiro
Published: July 2002

An electron beam column was designed and was used in experiments for a 50×50 mm2 deflection area. The column consists of a condenser lens, a combined focusing and double deflection system, and dynamic focus and astigmatism coils. The system successfully reduced deflective coma and transverse chromatic aberrations that could not be dynamically corrected. The dynamic coils adroitly corrected not only inherent aberrations in the column but also irregular ones produced by misalignment of the beam, column manufacturing error, and so forth. A LaB6 electron gun was employed at a brightness of 5×105A/cm2sr at 20 kV beam energy. After correction, the Gaussian beam diameter was less than 1.5 μm at 100 nA beam current in the deflection area. Test patterns including 4 μm minimum linewidths were exposed onto PMMA resist to demonstrate beam performance. Standard deviations (3σ) of the linewidths were 0.56 and 0.42 μm in the x and y directions, respectively.
All-aluminum-alloy ultrahigh vacuum system for a large-scale electron–positron collider
Authors: Ishimaru Hajime
Published: July 2002

An all-aluminum-alloy vacuum system for the TRISTAN ring (30 GeV) is now under construction. Ordinary stainless steel components and stainless steel–aluminum transitions have been eliminated as much as possible from the TRISTAN design. Suitable aluminum-alloy vacuum chambers, elliptical bellows, fittings, flange/gasket/bolt, nut and washer combinations, feedthroughs, gauges, optical windows, sputter ion pumps, turbomolecular pumps, all-metal valves, and related aluminum-alloy vacuum components have been developed. The beam chambers of the dipole and quadrupole magnets, all-metal gate valves, ceramic chambers, and the seamless bellows are directly joined by a fully automatic welding machine, i.e., without using flanges. For demountable joints, a new Conflat-type seal, which consists of Cr2N-coated superalloy flanges, is used. The outgassing rate after baking 24 h at 150 °C is several times 10−14 Torr 1/s cm2 for specially extruded beam ducts. The sputter ion pump, which is made of aluminum alloy, has an extremely short pumpdown time to ultrahigh vacuum, on the order of 10−9 Torr after only 24 h of initial operation, and on the order of 10−10 Torr after a 150 °C, 24 h, initial bakeout procedure.
The measurement of vacuum pressures
Authors: Redhead P. A.
Published: July 2002

A historical review of the science and technology of pressure measurement, in the vacuum range, is given from the first measurement of a subatmospheric pressure in the 1650’s until 1945. The modern period (from 1945 to the present) is reviewed with emphasis on the elucidation of the processes limiting the performance of various vacuum gauges (both total and partial pressure) and the practical solutions to these limitations. A comparison of the performance of modern vacuum gauges is presented.
Use of discharge intensity for evaluation of pumping characteristics of a sputter ion pump
Authors: Pierini M.
Published: July 2002

The pressure dependence of current in sputter ion pump has been investigated. Results may be fitted by a relationship I=kpn. The pumping speed after saturation, has been measured as a function of pressure. The proportionality between pumping speed and discharge intensity I/p has been verified. The exponent in the previous relationship is slightly larger than unity and it is expected that the pumping speed will increase with pressure. Experimental results are in good agreement with expectation, within a wide range of pressure. Measurement of the discharge intensity is therefore a good method to evaluate the pressure dependence of pumping speed for sputter ion pumps. With this method various sputter ion pump element structures have been tested.
Effect of an intermediate tungsten layer on thermal properties of TiC coatings ion plated onto molybdenum
Authors: Fukutomi M. , Fujitsuka M. , Shikama T. , Okada M.
Published: July 2002

Among the various low-Z coating-substrate systems proposed for fusion reactor first-wall applications, molybdenum coated with titanium carbide is considered very promising since it has a good capability of receiving heat from the plasma. The thermal stabilities of TiC layers ion plated onto the molybdenum substrate are discussed with particular reference to the interfacial reaction between the TiC coating and molybdenum. The deposition of an intermediate tungsten layer was found to be very effective in suppressing the formation of reaction layers, resulting in a marked improvement in thermal stabilities of TiC–Mo systems. Thermal shock test using a pulsed electron beam showed that the TiC coatings remained adherent to the molybdenum substrates during energy depositions high enough to melt the substrates within the area of beam deposition. The melt area of the TiC coatings apparently decreased when a tungsten intermediate layer was applied.
Role of dispersed oxides in reducing substrate/coating interdiffusion
Authors: Luthra Krishan L.
Published: July 2002

Theoretical calculations have been performed to evaluate the usefulness of dispersed oxides in a barrier layer in reducing substrate/coating interdiffusion. The important variables influencing interdiffusion are (1) the ratio of the thickness of the barrier layer to the total coating, (2) the volume fraction of oxides in the barrier layer, and (3) a tortuosity factor that depends on the distribution of oxides in the barrier layer. The results of calculations suggest that it may be possible to increase the operating life by a factor of up to about 2.5 or increase the operating temperature by a maximum of about 75 °C in systems where life is limited by substrate/coating interdiffusion.
On plasma sprayed WSi2 and Cr3C2–Ni coatings
Authors: Knotek O. , Elsing R. , Heintz H.-R.
Published: July 2002

WSi2 and Cr3C2–Ni composite powders were applied to AISI 321 and 347, and Nimonic 80 A substrates by the plasma spray process in a nontransferred arc mode. The adhesive shearing strength, the adhesive tensile strength, and the fatigue resistance of the coatings were evaluated. The wear properties of the two coatings on AISI 347 and pin-on-disk tests were compared. Corrosion resistance of the two coatings was determined in 1n-H2SO4 by current density-potential diagrams.
The effect of substrate temperature on topography related defect formation in evaporated aluminum based thin films
Authors: Ryan James G. , Douse Richard , Hahn Loren , Luciano Michael
Published: July 2002

The severe topography of high density integrated circuits has always caused step coverage problems for metallization layers. A technique has been developed to reveal the presence of Al2O3 in steep step regions for aluminum based metallization layers. This Al2O3 defect may increase the susceptibility of metallization layers to metal step opens. Aluminum oxide formation was studied as a function of substrate temperature, AlCu evaporation rate and slope angle. Al 1% Cu (1.0 μm thick) with a 0.1 μm thick titanium underlayer and 1.0 μm thick Al 1.4% Cu films were evaporated on substrates containing slope angles from 40° to 100° using substrate temperatures of approximately 30 to 200 °C. For Al 1% Cu with a Ti underlayer, the Al2O3 formation angle increases from 61° for the film evaporated at ambient substrate temperature (∼30 °C) to 91° for the film evaporated at 200 °C. Increasing the Al 1% Cu evaporation rate from 0.5 to 9.2 nm/s increased the Al2O3 formation angle from 71° to 92°. No effects on Al2O3 formation were observed due to step height or the presence of a titanium underlayer.
All aluminum alloy, 800-mm-inner diameter gate valve using dual flat-face seals together with differential pumping
Authors: Ishimaru H. , Kuroda T. , Kaneko O. , Oka Y. , Sakurai K.
Published: July 2002

Large metal gate valves are required in the neutral beam injector (NBI) of the R-Tokamak [Ref. 1: The second phase design of R-Tokamak (low radioactivity design), Institute of Plasma Physics, Nagoya University, Nagoya, 464, Japan, Dec. 1983.] at the Institute of Plasma Physics, Nagoya University. The R-Tokamak is designed using aluminum alloys because of the low residual radioactivity. Therefore, the gate valve for the NBI should also be made of aluminum alloys. By relying on differential pumping between dual flat-face seals [Ref. 2: H. Ishimaru, J. Vac. Sci. Technol. A 2, 1170 (1984).], we developed a large gate valve which have no gasket or knife edge.
Calculations of the surface temperature rise and desorption temperature in laser-induced thermal desorption
Authors: Burgess D. , Stair P. C. , Weitz E.
Published: July 2002

The laser-induced thermal desorption (LITD) process is discussed with reference to measurements of the translational energies (temperatures) of desorbed molecules. We present simple expressions which predict both the surface temperature rise for a laser-heated surface and the desorption temperature in LITD. We show that these approximations are excellent descriptions of the laser heating and LITD processes. These expressions are convenient alternatives to numerical solutions of the heat conduction and desorption rate equations using the actual shape of a laser pulse and specific combinations of kinetic parameters.
Dry etching of β-SiC in CF4 and CF4+O2 mixtures
Authors: Palmour J. W. , Davis R. F. , Wallett T. M. , Bhasin K. B.
Published: July 2002

Dry etching of cubic (100)β-SiC single crystal thin films produced via chemical vapor deposition (CVD) has been performed in CF4 and CF4+O2 mixtures, in both the reactive ion etching (RIE) and plasma etching modes. The latter process yielded measurable etch rates, but produced a dark surface layer which appears, from the results of secondary ion mass spectrometry, to be residual SiC. The RIE samples had no residual layer, but Auger electron spectroscopy did reveal a C-rich surface. The optimal RIE conditions were obtained with 10 sccm of pure CF4 at 40 mTorr and a power density of 0.548 W/cm2, giving an etch rate of 23.3 nm/min. Neither the increase of temperature between 293 and 573 K, nor the incremental addition of O2 to CF4 to 50%, produced any strong effect on the etch rates of SiC during RIE. Pictorial evidence of fine line structures produced by RIE of β-SiC films are also presented.
New concepts in molecular gas flow
Authors: Santeler Donald J.
Published: July 2002

This paper will outline several new concepts dealing with molecular flow calculations. One is a simple equation for calculating the ‘‘Clausing’’ transmission probability through circular tubes. A technique will also be demonstrated for developing similar expressions for the short-tube probability of other tube cross sections. Tube conductance will then be compared to transmission probabilities in terms of exit losses, entrance losses, and changes from random gas flow to fully developed tube flow. A format will be presented which assists in converting between short-tube conductance and probabilities. Finally, a correction term is added to Oatley’s probability combining equation to compensate for ‘‘beaming’’ effects. This term reduces the normal maximum error for circular tube calculations from 3.7% to 0.28%.
A note on flow rate and leak rate units
Authors: Ehrlich Charles D.
Published: July 2002

The confusion in the literature and in the laboratory surrounding the terminology and units of gas flow rates, particularly as applied to calibrated leak artifacts, has prompted this discussion of leak rate units. Special attention is paid to conflicting usages of the term ‘‘throughput,’’ and how this frequently leads to the loss of crucial information about the gas temperature and hence the true gas flow rate. The advantages of expressing leak rates in ‘‘mol/s,’’ avoiding the complications of both the explicit mention of temperature in the unit and the need for agreement on ‘‘standard’’ temperature and pressure, are also discussed.
Pulsed gas injection for on-line calibration of residual gas analyzers
Authors: Kendall B. R. F.
Published: July 2002

Pulsed gas injection valves have been developed which deliver highly repeatable single bursts of gas in the 10−7–1 Torr l range. Although originally intended for studying dynamic vacuum phenomena, these valves appear to have interesting possibilities for on-line checking of residual gas analyzer calibration. The work chamber is pumped continuously during calibration. The almost instantaneous and predictable pressure increase in a chamber of known volume allows direct sensitivity measurements to be made provided the analyzer has a sufficiently fast response. Experimental results showing reproducibility and pressure waveforms for a manually triggered valve are summarized. An outline is given of a calibration procedure using pulses of noble gases of differing molecular weights. Preliminary results obtained with a simple electromagnetic valve capable of up to 100 pulses s−1 are also discussed.