bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and chemistry of aluminide coating of Ni–Cr and Ni–Co–Cr alloys
Authors: Jackson M. R. , Rairden J. R.
Published: July 2002

Alloys of composition Ni–20Cr, Ni–35Cr, Ni–50Cr, Co–35Cr, Ni–5Co–20Cr, and Ni–20Co–20Cr have been aluminided by pack cementation. Morphology of the coatings varies considerably among the different alloys. The most striking differences are the avoidance of formation of Kirkendall-type voids in the Ni–Co–Cr alloys, and the degree of continuity of the α-Cr layer formed. Both features need to be controlled to avoid coating loss by cracking and spallation. From the appropriate phase diagrams, the sequence of morphologies formed by aluminization can be rationalized. The relation of total aluminum deposition to alloy composition results from phase equilibria and phase solubilities, and phase diagrams can be used to rationalize this relation as well.
Intercomparison of vacuum standards of countries within the European community in the range 8×10−5 to 8×10−2 Pa.
Authors: Poulter K. F. , Calcatelli A. , Choumoff P. S. , Iapteff B. , Messer G. , Grosse G.
Published: July 2002

A comparison of the vacuum standard maintained by four laboratories within the European Community (Istituto di Metrologia ’’G Colonetti’’ Turin, Italy; Laboratoire de Metrologie, Leybold–Heraeus–Sogev, Valence, France; National Physical Labortory, Teddington, Great Britain and Physikalisch–Technische Bundesanstalt, Berlin, Federal Republic of Germany) has been made in the pressure range 8×10−5Pa to 8×10−2Pa using a JHP high pressure ionization gauge. Three gauges were circulated around the participating labortories, each laboratory carefully following a detailed procedure for the preparation and operation of the gauge so as to minimize random variations in the sensitivity coefficient of the gauge. The gauges were calibrated up to nine times at each pressure by all the laboratories, the measurements in each laboratory taking place over a period of three days. A statistical analysis has been performed which shows that the standard of each of the labortories does not differ from the weighted mean of all the standards by more than ±2%. The results also show that when the three JHP gauges were used in the carefully controlled manner described in this paper, the ionization gauge coefficient did not change from its initial value by more than ±1.7% over an 18 month period.
XPS study of the chemical structure of the nickel/silicon interface
Authors: Grunthaner P. J. , Grunthaner F. J. , Mayer J. W.
Published: July 2002

The chemical nature of the Ni/Si, Ni/Ni2Si and Si/Ni2Si interfaces have been investigated using x-ray photoelectron spectroscopy. Peak position, line shapes, and envelope intensities are used to probe the compositional structure of these systems. Two approaches have been employed: one approach examines the advancing planar silicide front by dynamically monitoring the in situ formation of Ni2Si. This has the advantage of allowing examination of a realistic interface which is bounded on either side by an extended solid. The second approach follows the development of the Si/Ni interface using UHV depositions of thin layers of Ni on Si <100≳. 4He+ backscattering is used to follow the progression of the thin film reaction and to provide quantitative information on atomic composition. These experiments demonstrate that the Ni/Ni2Si interface consists of a Ni-rich silicide transitional phase while the Si/Ni2Si interface shows a transitional structure which is correspondingly Si-rich. Intensity analysis indicates that these interfacial regions are at least 22 Å wide for α-Si substrates and 9–14 Å wide for crystalline Si. The as-deposited Ni/Si interface cannot be described as a unique single-phase, but rather as a chemically graded transitional region showing a composition which varies from Si-rich to Ni-rich silicides.
Plasma polymerization of fluorocarbons in rf capacitively coupled diode system
Authors: Kay E. , Dilks A.
Published: July 2002

Work is reviewed which deals with the interrelationship between plasma etching and plasma polymerization, with emphasis on the plasma-surface interactions leading to polymerization. Particular reference is made to work done in this laboratory relating to the synthesis of metal containing fluoropolymers by simultaneous plasma etching and polymerization in the same system. The polymer deposition rate, at the grounded electrode in a rf capacitively coupled diode reactor configuration, is shown to be strongly dependent on the excitation electrode material, as well as the fluorine/carbon stoichiometry of the injected fluorocarbon. Addition of oxygen to a fluorocarbon plasma enhances etching and reduces polymerization, thus increasing the metal content of the polymer films. Addition of hydrogen on the other hand has the opposite effect. In all cases discussions are presented of the film structures as well as the most likely precursors in the gas phase which lead to polymerization.
An inorganic resist for ion beam microfabrication
Authors: Balasubramanyam K. , Karapiperis L. , Lee C. A. , Ruoff A. L.
Published: July 2002

We report the properties of an inorganic material as a positive ion-beam resist. The ion beam (H+) exposure characteristics of g–GexSe1−x chalcogenide amorphous glass films were investigated. These films exhibit higher sensitivity as ion-beam resists than they do as positive photo- and electron-beam resists. Pattern replication and delineation with this resist material is demonstrated with a conformal gold mask.
Partial dislocations, columnar growth, clustering, and pinhole formation in ultrathin film semiconductor heterostructures
Authors: Phillips J. C.
Published: July 2002

Island growth of partially ionic semiconductor films (such as GaAs or CuBr) on covalent substrates (such as Ge) may produce not only misfit dislocations but also partial dislocations and antiphase boundaries because of randomization of the translational diatomic phase registry of the ionic phase during multiple island nucleation. It is suggested that such partial dislocations may play an important role in the asymmetry of epitaxial crystal growth of Ge on GaAs compared to GaAs on Ge observed in recent MBE experiments, and may explain nontransitivity of band-edge discontinuities.
Germanium selenide: A resist for low-energy ion beam lithography
Authors: Wagner A. , Barr D. , Venkatesan T. , Crane W. S. , Lamberti V. E. , Tai K. L. , Vadimsky R. G.
Published: July 2002

A negative resist consisting of a layer of germanium selenide ∠1800 Å thick with a surface layer of silver selenide ∠100 Å thick was irradiated with 10 to 38 keV He, N, Ar, and Xe ions. While polymer resists require an incident ion to pass through the entire thickness of the resist film for exposure, germanium selenide films can be exposed with ions which penetrate only the ∠100 Å thick silver selenide surface layer. Thus, germanium selenide is an attractive resist system for low energy focused ion beam lithography. Resist sensitivities of ∠1013 to 1015 ions/cm2 were measured. Both nuclear and electronic stopping contribute to exposing the resist. Submicron lines have been produced in germanium selenide with a 20 keV finely focused ion beam.
Gold transmission gratings with submicrometer periods and thicknesses ≳0.5 μm
Authors: Hawryluk A. M. , Ceglio N. M. , Price Robert H. , Melngailis J. , Smith Henry I.
Published: July 2002

Gold gratings with spatial periods of 0.3 and 0.2 μm have been fabricated in thicknesses of 0.6 and 0.25 μm, respectively, and used in x-ray spectroscopy and spatial-period-division. Fabrication techniques included: holographic lithography, shadowing, x-ray lithography, and gold microplating. Control of linewidth to tolerance of the order of 10 nm has been demonstrated for gratings of 0.2 μm period. A high resolution imaging spectrometer, composed of a 22× Wolter x-ray microscope in conjunction with a gold transmission grating, was tested. At a wavelength of 0.69 nm, a resolving power, λ/Δλ, of 200 was demonstrated. Resolution in this case was source-size limited. Gratings of 99.5 nm period were exposed in PMMA by x-ray (λ = 4.5 nm) spatial-period-division.
Importance of chain reactions in the plasma deposition of hydrogenated amorphous silicon
Authors: Haller Ivan
Published: July 2002

Insight on the deposition mechanism of hydrogenated amorphous silicon (a-Si:H) can be gained by inspecting the consumption rates of SiH4 by various species in the plasma since essentially all the silicon in the silane consumed is incorporated in the solid. Chemical chain reactions eliminating H2 are thermodynamically allowed as the replacement of two Si–H bonds with H–H and Si–Si bonds is thermoneutral or exothermic. In the case where the chain carriers are positive ions, the chain reaction is known to proceed at collisional rates. The relative rate of SiH4 removal by electron impact induced fragmentation can be estimated for various plasma conditions by making appropriate assumptions for the distribution function, mean electron energy, and fragmentation cross section. It is found that under most conditions used for the deposition of a-Si:H, the species arising from chain reactions are more important in silicon transport than fragments directly formed in electron impact.
Chemical sputtering of carbon by sub-eV atomic hydrogen: New results and a critical comparison with previous data relevant to fusion applications
Authors: Stangeby P. C. , Auciello O. , Haasz A. A.
Published: July 2002

The production of methane on carbon (papyex) surfaces under sub-eV atomic hydrogen bombardment has been measured in an ultrahigh vacuum system subjected to special cleaning procedures. These results and previously published methane yield results are compared and their applicability to fusion technology is assessed. A critical analysis of the available data leads to the following conclusions: (i) The inconsistent methane yields spanning four orders of magnitude are most likely due to different experimental procedures. (ii) The monotonically decreasing methane yield as a function of sample temperature, obtained by some groups, is most probably due to the fact that deactivated surfaces were exposed to hydrogen bombardment. (iii) The methane yields which present a maximum at a certain temperature in the range 700–850 K resulted from bombardment of activated surfaces; and (iv) the shift in temperature at which the methane yield maximum occurs in the different studies may be due to temperature nonuniformities over the exposed surfaces and/or different states of activation.
Study of the discharge cleaning process in JIPP T-II torus by residual gas analyzer
Authors: Noda N. , Hirokura S. , Taniguchi Y. , Tanahashi S.
Published: July 2002

After several hours of discharge cleaning, it has been observed that the decay time of the water-vapor partial pressure changes from one well defined value to another. A long decay time observed in the later phase can be interpreted as a result of a slow deoxidization rate of chromium oxide, which may dominate the cleaning process in this phase. Optimization of the electron density for the cleaning is discussed, comparing the experimental results on density dependence of the water-vapor partial pressure with a result based on a zero-dimensional calculation for particle balance. One of the essential points for effective cleaning is found to be raising the electron density of the plasma high enough that the dissociation loss rate of H2O is as large as the sticking loss rate. A density as high as 1011 cm−3 is required for a clean surface condition where sticking probability is presumed to be around 0.5.
Electron inelastic mean free path (IMFP) in single crystal BeO by Rutherford backscattering (RBS) and Auger electron spectroscopy (AES)
Authors: Fowler D. E. , Gyulai J. , Palmstrom C.
Published: July 2002

Quantitative studies of oxidation kinetics by electron spectroscopies require knowledge of the IMFP of electrons in the oxide. In general, IMFP data for oxides are not available. A method is presented for the determination of the IMFP in beryllium oxide using RBS to determine the oxide thickness and AES to measure the chemically shifted Be Auger electron intensity from the BeO-covered surface and the unshifted signal from the Be substrate. Using the normal exponential attenuation relationship between material thickness and the AES signal passing through the material, an IMFP of 6.0±0.8 monolayers is determined for ∼100 eV electrons in BeO. In these experiments the oxide was grown at a temperature (∼700 K) which ensured a good single crystal epitaxy on the substrate. Because of this good structural characterization, the IMFP can be presented equally well in units of monolayers or in units of length. The accuracy of the method and its general applicability to other materials is discussed.
Chemical bonding at the polyimide surface
Authors: Hahn P. O. , Rubloff G. W. , Ho P. S.
Published: July 2002

Surface spectroscopy techniques (UPS and XPS) have been combined with theoretical calculations to investigate the chemical bonding characteristics of the high-temperature polymer polyimide. Both valence and core electronic structure of the intrinsic (‘‘clean’’) polyimide surface as observed in UPS and XPS are well described by the results of the self-consistent-field molecular orbital calculations. Even though the polyimide is already fully cured to complete the imidization reaction and form the final molecular structure of the polymer chains, the valence electronic structure of such as-prepared surfaces changes significantly upon in situ annealing at temperatures above ∼195 °C but well below those which decompose the polymer (≥400 °C). This annealing causes desorption of gas phase H2O and produces the intrinsic polyimide surface. The sorption/desorption of H2O is reversible and thermally activated, and it seems to play an important role in the chemical properties of the polyimide surface. These changes upon annealing and H2O exposure appear primarily in the valence electronic structure as observed by UPS, but corresponding alterations of the core level spectra seen by XPS are considerably smaller.
Energy analysis of microwave ion sources
Authors: Tokiguchi K. , Sakudo N. , Koike H.
Published: July 2002

Energy spreads of Ar+ beams extracted from a microwave ion source are investigated using a high resolution, cylindrical-sector energy analyzer. The energy spread, measured from the spectrum width at half value of the peak, is about 5 eV, and is almost independent of microwave power, gas pressure, and extraction voltage. The excess energy of Ar+ beam due to plasma floating potential is from about 10 to 20 eV, depending on gas pressure and microwave power. Comparison with other sources showed the microwave ion source to be suitable for obtaining high current beams of narrow energy spread.
Phonon inelastic scattering of He atoms from single crystal surfaces
Authors: Toennies J. Peter
Published: July 2002

The inelastic scattering of He atoms provides a direct method for studying the surface phonon dispersion curves of single crystal surfaces. A highly monochromatic intense beam of atoms with a velocity spread Δv/v≲1% at typically 20 meV kinetic energy is scattered from the clean surface prepared and analyzed in an UHV chamber. The time-of-flight distributions reveal up to six sharp maxima which can be attributed to the annihilation or creation of single surface phonons. From the measured energy loss and the scattering angles the frequency and wave number of the interacting surface phonons are determined. Using this technique the Rayleigh mode dispersion curves of LiF, NaF, NaCl, and KCl have been measured out to the zone boundary in recent years. Here we report on new measurements at higher energies (100 meV) which reveal the optical mode S2 and the Lucas mode S4 in NaF. We also present the first measurements on a semiconductor (GaSe), which also yield dispersion curves for an optical mode as well as for the Rayleigh mode. Finally, recent measurements for metal surfaces will be described. For Ag(111) the Rayleigh mode agrees with theory but another observed dispersion curve, attributed to a longitudinally polarized acoustical mode, lies 35% lower than predicted by theory. Some preliminary results for Ni(100) are reported and compared with recent EELS measurements.
Metal clusters in plasma polymerized fluorocarbon films: Cobalt–aluminum
Authors: Kay Eric , Hecq M.
Published: July 2002

Plasma processes are described which lead to the dispersion of metal containing clusters in dielectric film matrices. In contrast to Au clusters dispersed in a polymer film matrix as reported earlier [E. Kay and M. Hecq, J. Appl. Phys. 55, 370 (1984)], this report deals with reactive metals such as Al and Co dispersed in metal fluoride and/or fluorocarbon matrices depending on the composition of the plasma. Optical emission data of the plasma together with film deposition rate and composition measurements for films produced at different substrate temperatures indicate that the adsorption step of (CF2)n polymerization precursors is the rate limiting process in the overall polymerization. Electrical conductivity shows 16 orders of magnitude changes in films made just above and below a critical fluorocarbon/argon gas mixture in the plasma resulting in a critical metal cluster volume fraction in the films. These film characteristics are associated with percolation phenomena. In the case of Al evidence is given that granular Al is obtained by these plasma processes and that associated changes in superconducting transition temperatures Tc are not exclusively related to metal cluster size [M. Hecq, P. Ziemann, and E. Kay, J. Vac. Sci. Technol 1, 364 (1983).]
Spatially resolved surface analysis using optical microreflectometry
Authors: Ruzakowski P. , Holloway P. H. , Remond G.
Published: July 2002

Optical microreflectometry is an analytical technique capable of nondestructively detecting the presence of thin films over diameters as small as 10 μm at atmospheric pressure and room temperature. The technique consists of measuring the percent reflectance of visible light from a flat surface as a function of wavelength and position on a specimen. Applications of optical microreflectometry are given which illustrate that the technique is sensitive to films as thin as 10 Å, sensitive to the chemical state of a compound, and can analyze multiple spots in color bands only 25 μm wide. X-ray photoelectron and Auger electron spectroscopies enable complementary use of optical microreflectometry to be both more useful and quantitative.
Interface depth resolution of Auger sputter profiled Ni/Cr interfaces: Dependence on ion bombardment parameters
Authors: Fine Joseph , Lindfors P. A. , Gorman M. E. , Gerlach R. L. , Navinšek B. , Mitchell D. F. , Chambers G. P.
Published: July 2002

Interface broadening which often results as a consequence of sputter profiling can make it difficult to assess the structure of an original interface. There are a number of factors involved in this broadening which are associated with the parameters of the ion bombardment and which have not previously been evaluated. Sputter profile measurements obtained on a set of similarly fabricated Ni/Cr multilayered thin-film structures have shown that it is practical to systematically examine this interface broadening dependence on ion beam energy, ion current density, and angle of incidence, all as a function of sputtered depth. Results are presented of such a set of Auger sputter depth profile measurements and indicate that there can be dramatic changes in sputtered interface widths depending on the ion bombardment parameters used.
A study of oxidized Nb–Al alloys using Auger electron spectroscopy and photoemission spectroscopy
Authors: Oshima Masaharu , Pate Bradford B.
Published: July 2002

The oxidation properties of Nb–Al alloys have been studied using Auger electron spectroscopy and x-ray photoelectron spectroscopy. Al in the alloy is found to be preferentially sputtered during argon-ion bombardment and to be preferentially oxidized in Nb–Al alloys. Oxidation increases the Al concentration in the oxide layer, which is seen even in the initial stages of oxidation with photoemission spectroscopy using synchrotron radiation. Auger peak shifts of 5×1011 L oxygen-exposed surfaces of Al, Nb, and Nb–Al alloys are found to be due to Auger transitions involving chemically shifted core levels caused by an alloying effect.
Permeability of common elastomers for gases over a range of temperatures
Authors: Laurenson L. , Dennis N. T. M.
Published: July 2002

For elastomers to be used in vacuum applications, their permeability should be low. Elastomers that are now, or likely to be, used in vacuum have been studied. The permeability of copolymers of fluoroelastomers and PTFE propylene (AFLAS) and a homopolymer of epichlorohydrin have been measured for hydrogen, helium, argon, nitrogen, carbon dioxide, and water vapor in the temperature range 20 to 120 °C. The test apparatus consisted of a restrained elastomer diaphragm with a pressure differential across it of normally 1 atm. The gas permeating is detected by a quadrupole mass spectrometer. The results obtained agree with already published values when they exist. The work further shows that for a given elastomer the temperature/permeability relation differs from gas to gas. The correlating of the measured permeability to the practical case of O-ring gaskets used in a vacuum system is discussed.
Status of point defects in HgCdTe
Authors: Jones C. E. , James K. , Merz J. , Braunstein R. , Burd M. , Eetemadi M. , Hutton S. , Drumheller J.
Published: July 2002

This paper reviews the status of point defect studies in HgCdTe and presents new data on the characterization of impurities in CdTe, on shallow and deep acceptors in arsenic-doped HgCdTe, and on the ability of electron paramagnetic resonance (EPR) to detect defects in HgCdTe. Point defects are important in controlling carrier concentrations, minority-carrier lifetimes, and noise in HgCdTe. Shallow impurities from dopants are fairly well understood and their effects follow what is expected from the periodic table. Intrinsic defects such as the mercury vacancy, which is believed to act as a shallow acceptor, are less well understood and suffer from a lack of characterization techniques that can identify individual defects. Deep-level defects are present with concentrations proportional to the shallow acceptor concentrations. These centers often control lifetime and noise. Many of these have been electrically characterized, but not identified. Theoretical work by several groups to calculate defect levels has begun. At present, the errors in this work are larger than the HgCdTe band gaps, but the calculated trends are important. Experimental data on identified deep levels are needed both for guiding material improvement and for improving the theoretical modeling.
AES analysis of the growth mechanism of metal layers on metal surfaces
Authors: Ossicini Stefano , Memeo Rossella , Ciccacci Franco
Published: July 2002

A discussion on the growth of thin metal films on metal substrates on the basis of the Auger technique is presented. Within a simple model the characteristics of the different growths are related to the adsorbate and substrate Auger peak-to-peak intensity ratios. The behavior of these ratios as a function of the number of deposited atoms is studied in the case of the Frank–van der Merwe, Volmer–Weber, and Stranski–Krastanov growth mechanism. A comparison between our calculations and reported measurements is discussed in detail for the Pd/W(110), Au/Pt(100), and Pt/Au(100) systems.
Microstructure and electrical conductivity of plasma deposited gold/fluorocarbon composite films
Authors: Perrin J. , Despax B. , Hanchett V. , Kay E.
Published: July 2002

Gold containing plasma polymerized fluorocarbon films have been deposited at room temperature by reactive rf sputtering. The dc electrical conductivity of the films has been measured as a function of gold volume fraction and changes drastically after annealing at about 180 °C. Two phenomena can be distinguished: (1) a contraction of the cross-linked polymer phase in the film due to internal relaxations which results in relative increase of gold volume fraction; and (2) a change of the gold cluster sizes and shapes observed by transmission electron microscopy (TEM). The latter effect is best interpreted by using the effective medium theory of Sheng which accounts for the influence of particle shape on the percolation threshold and the variation of conductivity of a composite material. Before annealing, the films can be described as a statistical mixture of spherical gold particle coated with polymer and very flat platelets (oblate spheroids) of polymer coated with gold, randomly oriented. The effect of annealing can be accounted for by reduction of oblateness of the gold coated polymer inclusions as confirmed by TEM observations.
Liquid-amorphous and liquid-crystalline phase transformation and impurity segregation phenomena in silicon during pulsed dye laser irradiation
Authors: Narayan J.
Published: July 2002

We have studied microstructural changes and impurity segregation phenomena associated with liquid-amorphous (l-α) and liquid-crystalline (l-c) phase transformations as a function of pulse energy density across a laser spot in indium implanted silicon. The specimens were irradiated with a dye laser pulse (wavelength 0.485 μm, energy density 0.7 J cm−2, pulse duration 9×10−9 s). At an energy density (0.2 J cm−2), we observed a liquid to amorphous phase transformation and concomitant segregation of indium due to interface motion from the bulk and the surface, resulting in a band of indium below the surface. At a higher energy density, explosive recrystallization from the surface is triggered, where a thin layer of liquid moves from the surface resulting in a band of indium at the end of the crystallized front. At a still higher energy density, epitaxial (liquid to crystalline) crystallization occurs below the surface followed by liquid to amorphous phase transformation near the surface. At the highest energy density near the center of the laser spot, epitaxial layer followed by the formation of constitutional/supercooling cells in the top region is observed as a result of interfacial instability of the planar crystallizing interface.
Review of the status of quantum 1/ f  noise in n+–p HgCdTe photodetectors and other devices
Authors: van der Ziel A. , Handel P. H. , Wu X. L. , Anderson J. B.
Published: July 2002

The results of our 1/ f  noise calculations in n+–p HgCdTe diodes and other devices, performed on the basis of the quantum 1/ f  noise theory, are presented and compared with measurements at temperatures of 77, 193, and 300 K, as well as with other experimental data. A more general review of the status of the quantum 1/ f  noise theory in semiconductor devices is also included, with references to previous work. Although the calculations do not contain adjustable parameters, and in spite of uncertainty in some parameters such as the electron lifetime, an encouraging correspondence between theory and experiment and a unified first principles description of 1/ f  noise contributions from scattering, tunneling, or surface and bulk recombination cross sections are obtained both in general and in the case of n+–p HgCdTe diodes. For the latter we suggest some ways in which the quantum 1/ f  noise could be reduced.
An ion scattering spectroscopy and temperature-programed desorption study of the interaction of N2 with Si(111)
Authors: Corallo Cheryl F. , Hoflund Gar B.
Published: July 2002

Ion scattering spectroscopy (ISS) and temperature-programed desorption (TPD) were used to study the interaction between N2 and a Si(111)(7×7) surface at room temperature. No adsorbed nitrogen is detected using Auger electron spectroscopy for doses as high as 3000 L. However, ISS easily detects adsorbed nitrogen following doses as low as 2 L and indicates that a saturation dose is approximately 75 L. Using TPD, evidence of at least two chemisorbed states of nitrogen is found. Hydrogen, which originates from the bulk of the sample, is found to associate with the surface nitrogen. Low-energy electron diffraction was used to monitor surface structure throughout N2 adsorption and during subsequent heating, but no features due to the (8×8) nor the quadruplet pattern observed in previous studies were observed under the exposure conditions used in this study.
Performance characteristics of single-stage centrifugal vacuum pumps at rough vacuum
Authors: Ota M. , Hirayama N.
Published: July 2002

Performance measurement of centrifugal turbopumps has been made in continuum flows in order to demonstrate new mechanical pumps for dry processes with higher pressure ratios per stage and greater throughputs operating at a rough vacuum range. In a closed-loop, pump-test facility, a radial-flow impeller with vaned diffusers or a vaneless diffuser was driven by an air turbine. The influence of intake pressures of the pumps, rotating speeds of the impeller, and geometric configurations of the diffusers, such as the ratios of a vane inlet diameter to an impeller tip diameter, the number of the vanes, and so forth, are discussed on volumetric pumping rates, throughputs, and pressure ratios. The throughput of these pumps is greater than that of an oil-sealed rotary pump with the same intake area. Furthermore, the pumps operating at Mach number 0.94, tip speed of the impeller 324 m/s, Reynolds number 3.9×104, and intake pressure 1.2 kPa have the peak pressure ratio 1.95.
Investigation of InAs and GaSb by high-resolution electron energy-loss spectroscopy
Authors: Thiry P. A. , Longueville J. L. , Pireaux J. J. , Caudano R. , Munekata H. , Liehr M.
Published: July 2002

Crystalline InAs and GaSb layers grown by molecular-beam epitaxy have been studied with high-resolution electron energy-loss spectroscopy (HREELS). From the observation of optical surface phonons, resonance frequencies ωTO and oscillator strengths Δε could be determined. The values found for InAs(ωTO=219 cm−1 and Δε=2.9) are in agreement with optically derived data from the literature. As for GaSb, the resonance frequency and the oscillator strength determined by HREELS are at variance with published values. Preliminary results on InAs–GaSb superlattices are presented.
Controls for the vacuum system of LEP
Authors: Strubin P. M.
Published: July 2002

The very large size (27-km circumference) of  LEP (CERN Large Electron Positron storage ring) makes it mandatory to provide extensive remote control for installation, commissioning, and operation. The control facilities will be available both at fixed locations and in the form of mobile consoles which will follow the installation teams. All operations must be accessible to vacuum technicians, who may have little or no computing knowledge. Therefore, menu driven consoles, using a screen and light pen, will be made available to the operators. The large number of pumps, gauges, and valves makes it necessary to find solutions to reduce the cabling costs. An original way of powering the sputter ion pumps uses a single power supply and cable for up to eight pumps, yet allows individual current monitoring for each pump. An ionization gauge power supply for eight heads is economical and saves rack space by multiplexing the ion currents while powering and regulating continuously all filaments. All power supplies must be integrated in the general control system of the LEP machine. This is done by using so-called intelligent equipment controllers, which exchange messages with the main control room by a network of multidrop buses. A sophisticated data base management system is required in order to keep track of the numerous items connected to the vacuum system.
Centrifugal electroslag casting and electroslag permanent mold casting: A new generation in electroslag technology
Authors: Medovar B. I.
Published: July 2002

The E. O. Paton Electric Welding Institute has already developed the equipment and technology for producing 20–500 kg mass billets of structural and tool steels and copper by the centrifugal electroslag casting (CEC) and electroslag permanent mold casting (EPC) methods, which find wide application in industry. By using CEC and EPC it is possible to reclaim metal wastes, to avoid the expansion of forging production capabilities, to decrease the needed amount of machining, and to minimize metal chipping losses when manufacturing the components.
Ultrahigh vacuum studies of Pd metal/insulator/semiconductor diode H2 sensors
Authors: Rye R. R. , Ricco A. J.
Published: July 2002

Hydrogen sensitive Pd metal/insulator/semiconductor diodes provide an ambient temperature, low-power electronic sensor for hydrogen as a result of hydrogen trapping at the Pd/insulator interface. We have obtained both steady-state and kinetic results for diodes with clean Pd surfaces over hydrogen pressures ranging from 10−10 to 10−1 Torr. The sensitivity limit (equivalent to <1011 total H2 impacts/cm2 at the Pd surface) is at least 7 orders of magnitude greater than that obtained for devices with contaminated surfaces, revealing that the kinetic and sensitivity limitations normally reported for such devices are a result of surface contamination. Analysis of the steady-state results is consistent with two binding states (9 and 6.8 kcal/mol of H relative to H2(g)) for H at the Pd/SiO2 interface. The kinetics of the diode response to H2 are consistent with a ‘‘precursor’’ mechanism in which the initial step is adsorption into a weakly bound precursor state from which branching steps populate both strongly bound chemisorbed surface states and bulk states.
History of the International Union for Vacuum Science, Technique, and Applications
Authors: Lafferty J. M.
Published: July 2002

The 30th anniversary of the International Union for Vacuum Science, Technique, and Applications (IUVSTA) will be celebrated during its 1986–1989 triennium. The Union had its beginning on 13 June 1958 in Namur, Belgium, at the First International Congress on Vacuum Technology. This meeting, organized under the leadership of Émile Thomas, was the first large international meeting of vacuists with over 500 participants from 26 countries. The meeting met with much enthusiasm and Medard W. Welch suggested the creation of an international committee to organize future such congresses in different countries. This led to the formation of the International Organization for Vacuum Science and Technology (IOVST) with Professor Thomas serving as President. At that time only three or four countries had their own national vacuum society, and consequently the IOVST was able to attract individuals and corporate members from many countries that had no other platform for the exchange of information on vacuum science. The IOVST was successful in encouraging the creation of additional national vacuum societies. On 8 December 1962 the IOVST revised its statutes to exclude private membership and became an international confederation of national vacuum organizations with ten founder members and changed its name to the International Union for Vacuum Science, Technique, and Applications. The Union maintained the legal status which had been granted to the IOVST under Belgian laws and continued to maintain its Secretariat in Brussels. This paper describes the organizational structure of the IUVSTA and the development of its scientific divisions. Historical background is given for a number of the Union’s activities including the Welch International Scholarship, News Bulletin, Visual Aids Project, and International Vacuum Congresses. A more detailed history of the IUVSTA by the author is available from the Union’s Secretary General.
Time dependence of the infrared spectrum of N2 adsorbed at low coverage on the Ni(110) surface
Authors: Brubaker Mary E. , Malik Igor J. , Trenary Michael
Published: July 2002

The time dependence of the N–N stretching band of N2 chemisorbed on the Ni(110) surface at a coverage of 0.1 monolayer at temperatures of 81, 105, 115, and 125 K was studied with the technique of Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). Spectra requiring 31 s of signal averaging were obtained every 5 min over a period of 45 min. The N–N stretching band initially at 2196 cm−1 splits with time into two components at 2194 and 2199 cm−1 at 105 K while at 81 K no splitting of the band occurs. A similar splitting of the band is observed at 115 and 125 K. After 2 h, hydrogen adsorption from the background results in reforming a single band at 2205 cm−1 at both 105 and 115 K with a full width of 7 cm−1 compared to a bandwidth of 12 cm−1 on the clean surface. These results illustrate the advantages of the high sensitivity, high resolution, and fast data acquisition times available with FT-IRAS. The fact that the band splits only at temperatures at or above 105 K indicates that the process is thermally activated. Several possible sources for the band splitting are discussed.
The interaction of O2 and CO with polycrystalline Zr
Authors: Hoflund Gar B. , Corallo Gregory R. , Asbury Douglas A. , Gilbert Richard E.
Published: July 2002

This study examines (1) the production of a clean polycrystalline surface, (2) oxygen adsorption as a function of room-temperature exposure using ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES), and electron spectroscopy for chemical analysis (ESCA), and (3) CO adsorption. S and Cl are typical contaminants which modify the chemisorption properties of a Zr surface. However, they are difficult to detect using AES or ESCA but are readily observed using ISS. Sputtering a hot Zr surface provides an excellent method for producing a contaminant-free surface. The adsorption of oxygen proceeds in a stepwise fashion by rapidly populating sites in the outermost surface layer, filling subsurface sites and then forming a multilayer oxide film even at room temperature and low O2 pressure (10−6 Torr). CO adsorbs dissociatively on Zr at room temperature. An oxide overlayer is formed which contains no C. The C lies beneath the oxide layer in a chemisorbed or interstitial form. Heating converts this C into a carbidic form and causes segregation of surface oxygen into the bulk Zr.
An x-ray photoelectron spectroscopy investigation of the incorporation of surface oxides into bulk zirconium
Authors: West Paul E. , George Patricia M.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy have been used to investigate the mechanism by which a thin ZrO2 film formed at the surface of polycrystalline zirconium dissolves into the bulk zirconium at 400 °C under nonoxidizing conditions. In addition to ZrO2, a zirconium suboxide is directly observed in the XPS spectra taken after oxidation. On heating the oxidized Zr the intensity of both the Zr 3d5/2 associated with ZrO2 and the O 1s decay linearly with time. A concomitant linear increase is observed in the summed intensities of the Zr 3d5/2 band associated with Zr metal and the suboxide ZrxO. A model is proposed to explain these observations which involves oxygen ion transport from the ZrO2 to the metal interface where formation of a suboxide intermediate appears to be the rate-controlling step. The postulated suboxide at this temperature is ZrxO with x>1.
High vacuum measured by the spinning rotor gauge: Status report of the Bureau International des Poids et Mesures intercomparison
Authors: Messer G. , Röhl P. , Grosse G. , Jitschin W.
Published: July 2002

The spinning rotor gauge is used as a transfer gauge in an international intercomparison of vacuum pressures in the range 5×10−4 to 1 Pa. Results for the stability of the transfer gauge as well as for the vacuum standards in the various laboratories are now available. Several years of experience prove the high stability of this type of gauge; calibrations against a primary pressure standard yield long-term reproducibility within ±0.5%. However, experience also reveals that improper handling of the rotor balls may cause irreversible changes by as much as several percent. In the intercomparison the majority of participating laboratories have performed calibrations so far. Most data lie within an interval of ±1% and never deviate by more than ±3% from the mean. Thus the international standard of high vacuum pressures is very reasonable.
Angular distribution of flux at the exit of cylindrical tubes
Authors: Krasuski P.
Published: July 2002

Integration of elementary fluxes of molecules crossing the entrance and scattered from tube walls in molecular flow was undertaken. Results, which were verified with Monte Carlo simulation procedure, show variation of angular distribution in an exit, i.e., the shapes of distribution curves are no longer the same in different zones of the exit surface. These results characterize the cylindrical tube as a molecular source better than results from previous papers calculated for targets placed at some distance from the exit of the tube.
High-resolution electron energy-loss spectroscopy measurements on hydrophilic silicon (100) wafers: Temperature and aging effects
Authors: Grundner M.
Published: July 2002

The commonly used wet chemical surface treatment of Si wafers before processing generates a hydrophilic surface. This surface is characterized by the presence of singular and associated OH groups and an asymmetric Si–O–Si vibration at 1150 cm−1. It exhibits temperature and aging effects. Freshly prepared surfaces show prevalently singular OH groups. A decline in the OH vibrational signal intensity occurs largely in the first hours of storage. Annealing in UHV showed the OH groups to vanish around 720 K on fresh surfaces and around 570 K on aged surfaces. Hydrocarbons could be detected up to 570 K irrespective of aging. The thin oxide films (about 1 nm) exhibited differences in decomposition behavior depending on storage time. Fresh films disappeared between 1020 and 1070 K and aged films between 1120 and 1170 K. The chemistry of the dissolution process appears to be such that islands of Si emerge in the oxide. This is concluded from dissociative water adsorption from the residual gas on patches of Si in the SiO2 film, leading to Si–H and Si–OH groups on Si.
Primary vacuum pumps for the fusion reactor fuel cycle
Authors: Hemmerich J. L.
Published: July 2002

The primary vacuum system for a tokamak-type controlled thermonuclear reactor with 1-GW thermal output is analyzed. The need for recovery, purification, and recycling of deuterium–tritium (D–T) fuel to the reactor leads to the following basic requirements for vacuum pumps at the reactor exhaust: effective pumping speed ∼250 m3 s−1; inlet pressure ∼0.1 Pa; outlet pressure ≥10 Pa (at full flow rate of ∼25 Pa m3 s−2); compatibility with tritium, nuclear radiation, static and dynamic magnetic fields, mechanical shock, and up-to-air accidents; and no contamination of pumped gases (primarily D–T and 4He) by vacuum pump media such as lubricants, operating fluids (vapors), or gases other than D–T and 4He. Based on present experience, the turbomolecular pump appears suitable. It would, however, require a substantial development effort both in technology and unit size to meet the requirements. There remains some doubt about its compatibility with mechanical shock, radiation, magnetic fields, and sudden up-to-air accidents, etc. Therefore, alternative pumping principles are proposed, all shown to work at least in laboratory size models: thermodynamic pumps for transport pumping to replace turbomolecular pumps and selective storage pumps for effluent processing in situ. The proposed systems require development efforts similar to the turbomolecular pump, but are shown to meet all requirements without the need for large protective valves. Selective pumps, pumping none of the hydrogen isotopes (but helium and impurities such as DTO, CO2, methane) or combinations of thermodynamic transport pumps, and regenerable volume getter pumps are shown to perform the major processing task, i.e., purification and recycling of DT, directly at the reactor exhaust.
Effects of residual gas control in relationship with sputtered aluminum film morphology and electromigration properties in fine-line very large scale integrated structures
Authors: Rocke M. J.
Published: July 2002

To understand the effects that the vacuum environment has on the morphology of sputtered aluminum alloys and electromigration, a quantitative study was made down to the parts per million level of the residual gases that are present in a high-rate magnetron sputter system. While previous work has stressed the importance of residual gas control, this work correlates wafer level electromigration results to film morphology and the low-level vacuum contaminants that are present in modern vacuum systems. These low-level residual gases play important parts in determining activation energy, void formation, silicon recrystallization, grain size homogeneity, and hence greatly affect electromigration mean time to failure and sigma. The necessity of controlling the vacuum environment to a much finer degree is demonstrated.
Optical emission in magnetrons: Nonlinear aspects
Authors: Rossnagel S. M. , Saenger K. L.
Published: July 2002

Optical emission measurements have been made on the plasmas generated in conventional, planar magnetrons used for high-rate sputtering of metals. The measurements were made as a function of distance from the 20-cm-diam cathode for Al, Cu, and Ti cathodes in Ne, Ar, and Kr plasmas. The emission from the plasma was coupled through a movable collimator and window assembly to a monochromator and diode array detector. The emission intensity was strongly peaked near the sheath, a few millimeters from the cathode. The intensity of the emission of the neutral rare-gas atoms was approximately linear with discharge current at low discharge power, and proportional to the square root of current at high power. This is consistent with previously observed gas rarefaction effects caused by heating by the sputtered atoms. The emission intensity from the sputtered atoms depended on discharge current to approximately the second power at low discharge current, falling to the 1.4 power in some cases at high power levels. The emission intensity for the ionized, sputtered atoms was observed to depend on the discharge power to the 2.6–3.0 power. These latter observations are consistent with a simple model of excitation dependent on the species density and the electron density, coupled with predicted changes in the electron density and temperature as a function of increasing discharge power.
The mechanical field effect transistor: A new force sensor
Authors: Steinbrüchel Christoph
Published: July 2002

A new force and pressure sensor is proposed, based on a field effect transistor (FET) structure with a movable gate. The sensor consists of a micromachined single-crystal-silicon diaphragm attached to a single-crystal-silicon base plate. The base plate contains the source, channel, and drain of a FET, whereas part of the diaphragm acts as the gate of the FET. An external force applied to the diaphragm changes the distance between the gate and the channel and thus modulates the source–drain current. The sensitivity of the device is predicted to be better than that for conventional capacitive sensors. Furthermore, by combining two devices in a special sensor–reference configuration, a transducer can be formed that is temperature compensated and generates an output signal of several volts requiring minimal signal processing. The design of this type of sensor is discussed in detail, and problems of fabrication are addressed.