bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron gun beam current control for improved stability
Authors: Kulka C.
Published: July 2002

Stability of the exciting electron beam is critical in spectrometries such as Auger electron spectrometry when, for example, line-shaped studies or quantitative analysis is performed. The beam from an electron gun can be stabilized by feedback control referenced directly to the beam current at the operating acceleration potential. This is accomplished by measuring the beam current and providing to the electron gun a voltage proportional to the current in such a manner as to oppose any change in the beam current. A system employing this method has been constructed and tested with an Auger electron spectrometer using a retarding-grid energy analyzer. A considerable improvement in beam stability was achieved permitting long data acquisition periods necessary to improve signal−to −noise of spectra for Auger analysis. This method of beam control has proven to be superior to conventional systems employing constant grid current or grid voltage regulation.
Fifteen-centimeter-diameter UHV transfer system for remote plasma-wall interaction experiments
Authors: Clausing R. E. , Emerson L. C. , Heatherly L. , Domm T. C. , Simpkins J. E. , Langley R. A.
Published: July 2002

A versatile UHV apparatus is described which permits large (up to 10×10 cm) sample arrays or entire experiments to be inserted from air into an operating tokamak. This can be accomplished without perturbing the tokamak vacuum. Samples or experiments may be exposed in the tokamak for studies of plasma-wall interactions and removed at any time without requiring tokamak shutdown. Samples or experiments may be accurately positioned in the region between the vacuum wall and the plasma limiter remotely. The apparatus provides up to 20 electrical connections for thermocouples, heaters, and signal leads. It also provides linear and rotary mechanical motion for operating experiments sychronized to tokamak discharges. Experiments or samples may be prepared off site and loaded into the transfer system under vacuum. A surface analysis station integral with the transfer system permits individual sample preparation, characterization, and analysis before and after plasma exposures.
Modification of an SSMS ion source to reduce residual gas effects
Authors: Dugger Donald L. , Oblas Daniel W.
Published: July 2002

A simple modification to the spark shield of the ion source of a spark source mass spectrograph is discussed. This helps to maintain a low partial pressure of residual gases during sparking of reactive materials. A grid is placed over the viewing slit to prevent energetic neutrals and ions from striking the walls of the source chamber, thereby desorbing unwanted gases into the ion source chamber. The results show a reduction of an order of magnitude in the total pressure during sparking over the conventional spark shield.
Proposed method for degassing metals for extreme low pressures
Authors: Moore Boude C.
Published: July 2002

Metal outgassing currently limits the pressures attained in vacuum chambers. The dominant residual gas in a carefully degassed metal system is usually hydrogen. The atomic hydrogen within bulk metals could be removed by diffusion processes if surface effects did not interfere. It is proposed that removing the surface hydrogen during vacuum bakeout by continuous electron bombardment (or similar irradiation) would allow the diffusion to proceed and lead to lower outgassing rates and operating pressures.
The use of teflon rope as a vacuum sealing material
Authors: Magee Frank J.
Published: July 2002

The use of Teflon and TFE florocarbon rope material as a means of sealing flanges for vacuum systems is described. A clean vacuum-tight seal can be produced, no outgassing problems exist, the gasket is impervious to most chemicals, never hardens, and is completely inert.
Compositional dependence of Schottky barrier heights for Au on chemically etched InxGa1−xP surfaces
Authors: Kuech T. F. , McCaldin J. O.
Published: July 2002

Measurements of the Au Schottky barrier height were carried out on thin films of n-InxGa1−xP, of various compositions epitaxially grown on n-GaAs substrates. Conventional C–V, I–V, and photo response techniques were used. The junction was formed by evaporating Au in an ion-pumped vacuum system onto a InxGa1−xP surface which had been chemically etched (5H2SO4:1H2O2:1H2O at 40 °C for 90 s). Barrier heights determined from the I–V and photoresponse were found to be in good agreement while the C–V measurement encountered difficulties. The Au barrier, φp, to p-InxGa1−xP was found to be independent of composition. The barrier, φp, was determined by the relation φp+φn=φg where φg is the bandgap energy and φn is the measured barrier to n-InxGa1−xP. It has been observed that the Au barrier height to p-type material for most compound semiconductors is determined by the anion, thus p-InP and p-GaP have the same Au barrier, about 0.76 eV. This dependence on the anion of the compound has now been seen to extend to the alloy system InxGa1−xP measured here. While chemically etched specimens yielded diodes with reproducible barrier heights, diodes formed on surfaces which were untreated or cleaned only with organic solvents were of poor quality with varying barrier heights or even ohmic contacts.
Time-of-flight measurements with a CMA for simultaneous energy and mass determinations of desorbed ions
Authors: Traum M. M. , Woodruff D. P.
Published: July 2002

Using a commercial double-pass cylindrical mirror analyzer (CMA) we have made mass, energy, and angle-resolved measurements of positively charged ions emitted from a surface by electron-stimulated desorption. Because the dispersive character of the CMA selects the ion energy, the mass can be uniquely and simultaneously determined from the flight time in the analyzer. We show that this can be achieved with relatively simple additional electronics, and unity mass resolution is possible up to at least mass 20. Some of the principles, limitations, and capabilities of the technique are described and illustrated by measurements of H+, O+, F+ and Cl+ desorption from a W{100} surface.
SnO2+Al2O3 continuous dynode electron-multiplier
Authors: Mahajan P. W. , Bhoraskar S. V.
Published: July 2002

The use of a new combination of tin oxide and aluminium oxide films as electron multiplier dynodes is reported. The tin oxide serves as a semiconducting material whose resistivity is increased due to the presence of the aluminium oxide which acts as a secondary emitter.(AIP)
Impurity contamination of the SiO2 layer on Si wafers during ion etching
Authors: Hosaka S. , Kawamoto Y. , Hashimoto S.
Published: July 2002

Impurity contamination of the surface layer takes place during 1 keV argon ion bombardment even when etching is only several hundred Å deep. The causes of contamination of the SiO2 layer on Si wafers are investigated using a conventional etching system. The contamination is found to be due to redeposition of sputtered materials on the wafer, impurity ion drift through the SiO2 layer caused by the electric field, and thermal diffusion. It is necessary to avoid using materials containing impurity atoms near the ion-bombarded area, to neutralize surface charges during etching, and to keep the substrate temperature close to room temperature. Under the above conditions, we obtained etched SiO2 layers with mobile ion concentrations less than 1011 e/cm−2 after annealing and BT(bias temperature) treatments.
Bandgap radiation induced photodesorption from V2O5 powder and vanadium oxide surfaces
Authors: Hieu N. Van , Lichtman D.
Published: July 2002

A mass-spectrometric analysis of photodesorption from V2O5 power and oxidized vanadium surfaces shows that carbon dioxide is the only desorbing species under UV irradiation. The threshold wavelength for this process for V2O5 powder is about 520 nm, which corresponds to a photon energy of 2.35 eV. The experimental data also indicates that, (1) the thermal induced and photon-induced desorptions of CO2 from the oxidized vanadium sample behave quite differently, (2) carbon concentration on the sample surface was found to decrease under prolonged exposure to UV radiation, and (3) the CO2 desorption signal depends linearly on the incident photon intensity. This linearity further supports the bandgap photon-induced desorption model, which requires electron-hole pair production as the initiating step.
Detection of a ScD2 film decomposition by AES
Authors: Malinowski M. E.
Published: July 2002

It is shown that there is a linear relation between the amount of ScD2 decomposition as the result of step heating and the Auger peak-to-peak height. (AIP)
Molecular beam apparatus for gas surface studies
Authors: Cavanna E. , Gussoni A. , Mattera L. , Terreni S. , Tommasini F. , Valbusa U. , Salvo C.
Published: July 2002

An experimental apparatus has been designed to study elastic and inelastic scattering of gas atoms from crystal surfaces coupling molecular beam, secondary ion mass spectrometry (SIMS), and cryogenic ultrahigh vacuum (UHV) techniques. The apparatus uses a rotatable quadrupole mass spectrometer to measure angular and time-of-flight (TOF) distributions of the scattered particles. Data of 20Ne and 22Ne scattered by the (001) LiF surface at 80 K are presented. To test the apparatus, the angular distribution of 20Ne for an incident angle of 50° is compared with that carried out with a different method by Boato, Cantini, and Mattera.a) First, inelastic scattering data of Ne from a (001) face of LiF are presented, showing the high sensitivity of the time-of-flight system. The apparatus can be used to perform scattering experiments with atomic hydrogen. It couples a radio frequency (rf) atomic hydrogen source with a magnetic velocity selector and a high sensitivity bolometer detector. An angular distribution of deuterium scattered by a (0001) graphite surface is reported.
Geometry of the abrupt (110) Ge/GaAs interface
Authors: Swarts C. A. , Goddard W. A. , McGill T. C.
Published: July 2002

We have studied the structure relaxation at the abrupt (110) Ge/GaAs interface by applying quantum chemical methods to clusters modeling this interface. Application of this model to bulk Ge and to bulk GaAs leads to theoretical Ge–Ge and Ga–As bond distances of 2.452 and 2.451 Å, respectively, in good agreement with the experimental values of 2.450 and 2.448 Å, respectively. Application of the model to the Ge/GaAs (110) interface indicates that this interface is nearly ideal. We find a very slight reconstruction at the interface leading to a Ge–Ga bond distance which is 0.04 Å longer than the Ge–As bond distance of 2.430 Å. The calculated spacing of the interface layer is 2.3% greater than that of bulk Ge or bulk GaAs.
Kinetics of hydrogen dissolution by titanium, A-digital simulation
Authors: Laser D.
Published: July 2002

The process of hydridization of titanium is described and quantitatively simulated. The process consists of the dissociative adsorption of hydrogen on titanium, its transfer across the surface to form dissolved H atoms and the diffusion of the later inside the Ti bulk. The interrelation between these stages results in a mixed kinetic control in which the dissociative adsorption of hydrogen depends on the available adsorption sites which in turn are released due to the diffusion of hydrogen from the surface region. The adsorption of hydrogen is characterized by a ’’Temkin’’ type isotherm which is constructed here for the first time while the description of the transport of hydrogen in titanium takes into account the possible existence of the three solid phases of the Ti/H system with different solubility and diffusion coefficient of hydrogen. The model predicts the hydrogen dissolution with time, the rate of the hydride decomposition, and the effect of surface inhibition. By comparison with experimental results, the sticking coefficient of hydrogen on a bare titanium surface can be estimated.
Comparison of APS and FRESCA core level binding energy measurements
Authors: Anderson C. R. , Lee R. N. , Morar J. F. , Park R. L.
Published: July 2002

The highly accurate core level binding energies measured by Fermi-level Referenced ESCA (FRESCA) have been compared with those of Auger Electron APS (AEAPS) and XPS. The FRESCA and AEAPS measurements directly measured energies with respect to the Fermi-level and are not subject to the instrumental uncertainties characteristic of XPS. Absolute total energies of photoelectrons relative to the Fermi level are measured to an accuracy of 0.12 eV and the energy of photoelectron peaks is measured to 0.17 eV by FRESCA. The accuracy of the binding energy measurements by AEAPS is about 0.35 eV. These accuracies permit the first meaningful opportunity to compare appearance potential and photoelectron binding energies as a test of possible fundamental differences in the two types of measurement. For the 3d transition metal series 2p3/2 binding energies no differences within the uncertainties are found for Ti, V, and Cr, while a significant difference exists for Mn, Fe, Co, and Ni.
Electronic structure of the π-bonded chain model and the nonbuckled antiferromagnetic insulator model for the Si(111) surface
Authors: Northrup John E. , Cohen Marvin L.
Published: July 2002

The electronic structure of the Si(111) surface is investigated with the pseudopotential method and the local density functional formalism. The π-bonded chain model proposed by Pandey is found to be more stable than the nonbuckled antiferromagnetic insulating surface by 0.15 eV/ (surface atom).
Localization of surface excitations and stimulated desorption
Authors: Jennison D. R. , Emin David
Published: July 2002

We recently proposed that delocalized surface electronic excitations may localize by inducing lattice distortions, analogous to small-polaron formation in bulk materials. Here we explain this idea and argue that such localization is a necessary condition for desorption via electronic excitations. The idea of a small polaron is briefly reviewed and the similarity to the desorption problem is explored. It is shown that multihole excitations in which the holes hop together move slowly and are coupled strongly to the lattice motion; as a result they rapidly localize. Moreover, single holes or excitonlike states may also localize depending upon the strength of the coupling to the atomic positions and the local lifetime against hopping. A qualitative understanding of the phenomenon is provided and predictive methods explained, illustrated using the results of ab initio calculations on hydrogen: silicon. Future experimental and theortical work is suggested.
Threshold electron excitation of Auger-electron and x-ray emissions in Ce
Authors: Chamberlain M. B. , Burr A. F. , Liefeld R. J.
Published: July 2002

The intensities of the M5O3 characteristic x-ray line and the M5N4.5N4.5 Auger-electron line from metallic Ce were measured as a function of the electron excitation energy near the M5 ionization energy. The excitation curve of both emissions contained a peak about 3 eV above threshold. The full-width at half-maximum (3.3±0.2 eV) and relative height (4×) of this peak were the same in excitation curves of both these emissions; however, they were different than the respective values (4.1±0.2 eV and 70×) we previously measured for a resonant bremsstrahlung emission observed when the electron excitation energy was near the M5 ionization energy. We also measured excitation curves for the M3N4.5 and M2N4 characteristic x-ray lines. The results support our earlier proposal that two distinct states are excited for near threshold, electron excitation of the Ce M5 level: The 3d 94f1 state which decays via the M5-series characteristic x-ray and Auger-electron emission channels, and the 3d 94f3 intermediate bound state which appears to decay by only a single channel—the emission of a resonant x ray with photon energy of 879.7±1.0 eV. These results may be evidence of a closed channel resonance in the electron scattering cross section in metallic Ce, similar to those reported by Simpson, Mielczarek, and Cooper in neon.
Photoemission studies of the effect of temperature on the Au–GaAs(110) interface
Authors: Petro W. G. , Babalola I. A. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: July 2002

We have performed soft x-ray photoemission spectroscopy (SXPS) measurements, using synchrotron radiation as the excitation source, to study cleaved n-type GaAs(110) surfaces covered with Au overlayers ranging in thickness from 0.3 monolayer (ML) to 80 ML. At room temperature our results show both band-bending effects and significant Au intermixing, with a continuous, monotonic shift of the Au 4f core levels toward their bulk positions with increasing Au coverage. Observation of the Ga 3d and As 3d core levels indicates a preferential As segregation to the surface at the highest Au coverages. The effect of heating (up to 500 °C) on a relatively thick (15 ML) Au overlayer has been studied using valence band as well as core level emission. These results indicate an increase in the Ga and As concentrations with evidence of metallic Ga formation. These findings have an important bearing on our understanding of Schottky barrier formation as well as the particular behavior of the Au–GaAs interface.
Charge transfer at surfaces: A model for ionization in SIMS
Authors: Lin J.-H. , Garrison B. J.
Published: July 2002

A microscopic model is presented to describe the probability of charge transfer for the desorption of ions from surfaces. Results from this model study provide a theoretical basis for understanding the ionization process in SIMS and ESD experiments. Predictions of the model that have a direct bearing on the interpretation of experimental data are emphasized in this study. We examine the effect of angle of ejection, both polar and azimuthal, and the nonconstant velocity during desorption due to a surface binding energy on the ionization probability.
The use of an arc plasma rotating in a magnetic field for metal coating glass substrates
Authors: Vukanovic V. , Butler S. , Kapur Sh. , Krakower E. , Allston T. , Belfield K. , Gibson G.
Published: July 2002

First results are reported about deposition of metals on glass substrate using a low current arc plasma source at atmospheric pressure. The arc source consists of a graphite cathode rod placed on the axis of a graphite anode cylinder aligned in a magnetic field. The carrier gas is argon. The deposition material, zinc or gold, is evaporated from a reservoir in the cathode. Depositions on flat substrates positioned on the periphery of the rotating plasma within the anode tube and in a jet outside the anode have been investigated. The investigations are planned to lead towards laser fusion target pusher layer fabrication. This fabrication would be facilitated by a high pressure deposition process where target levitation is readily performed.
Auger line shape studies of carbon species on Rh and Ni surfaces
Authors: Houston J. E. , Peebles D. E. , Goodman D. W.
Published: July 2002

Surface carbon species are known to play an important role in catalytic reactions, in particular, those associated with the conversion of CO to hydrocarbons. Two distinct surface C species have been noted on single crystals of Ni and Ru used as catalysts for the methanation reaction, and these have been associated through their Auger fingerprints with active ‘‘carbidic’’ and inactive ‘‘graphitic’’ forms. In the present paper, we discuss the results of a more detailed study of the Auger line shapes of various C species on Ni(100), Ni(111), and Rh(111) surfaces which include line shape corrections for loss effects. We compare our results with spectra which act as models of the local C environment. We present data which support a multiply coordinated C adsorption site and demonstrates a facile transformation from carbidic to graphitic carbon forms on the Rh surface under thermal annealing. This transformation is shown to manifest itself in the CO2/H2 reaction by a low temperature deactivation of the catalyst surface.
The American Vacuum Society—1973 to 1983
Authors: Vossen J. L. , Hammond Nancy L.
Published: July 2002

On the occasion of the 30th anniversary of the founding of the American Vacuum Society, we have prepared a history of the past decade which is intended to update a history of the first 20 years of the Society published in 1973. Included is information on growth in all areas and changes in administration and operations intended to poise the Society to better serve the technical community. Also recounted are data related to membership, symposia, publications, education, awards, scholarships, international activities, and interactions with various elements of the U.S. Government.
Developments in the transmission for mechanical booster pumps
Authors: Budgen L. J.
Published: July 2002

The standard direct method of driving mechanical boosters has a number of drawbacks, and to overcome these the hydrokinetic drive was developed. Direct and hydrokinetic drives are reviewed and their performances compared. The use of synthetic lubricants in mechanical boosters and their effect on performance is discussed. The main disadvantage when using direct or hydrokinetic drive and pumping corrosive or dangerous gases is the possible leakage of the shaft seal required to seal the input drive shaft of the mechanical booster. To overcome this problem while still retaining the advantages of hydrokinetic drive a magnetic drive system has been developed. A mechanical booster provided with magnetic drive is described and details of its performance given. The performance and limitations of the various drive arrangements are compared.
Computer uses in vacuum equipment and processes
Authors: Kline F. M.
Published: July 2002

Complex ultrahigh vacuum processing systems for manufacturing applications at the Neutron Devices Department dictated the need for sophisticated computer-based designs. Equipment requirements involved data acquisition, instrument control and interactive operation interfacing for a single system incorporating automatic and manual vacuum valves, vacuum ionization gauges, mass spectrometers, thermocouple gauges, capacitance manometers, ion pumps, specialized heaters, and other electronics. By way of example, a design criterion is established and the major technical aspects of computer interfacing are discussed. The significance of the design is that the considerations given to the computer utilization are generally applicable to similar systems and exploits late technologies in electronic interfacing, CRT displays, speech output, and other human interface subsystems. Such systems have been successfully implemented at the Neutron Devices Department from which many general system design philosophies have emanated.
Molecular beam mass spectrometric studies of energy transfer and chemical reactions on heated surfaces
Authors: Foner S. N. , Hudson R. L.
Published: July 2002

A modulated molecular beam mass spectrometer incorporating time-of-flight and threshold ionization capabilities has been used to measure translational and internal energy transfer to polyatomic molecules in collisions with heated surfaces and to observe the production of free radicals and vibrationally excited molecules in catalytic chemical reactions. In chemical reactions on a heated platinum surface, we have observed OH radicals produced in the reaction of H2 and O2, N2H3 radicals in the thermal decomposition of N2H4, vibrationally excited CO2 in the oxidation of CO, and highly vibrationally excited N2 in the thermal decomposition of NH3. The results are compared with other work on these systems.
Edge measurements of T
e,T
i,n,Er on the DITE tokamak using a biased power bolometer
Authors: Stangeby P. C. , McCracken G. M. , Erents S. K. , Vince J. E. , Wilden R.
Published: July 2002

A new edge probe, the biased power bolometer or combined heat flux/Langmuir probe, has been used on the DITE tokamak to obtain detailed spatial and temporal information on plasma density, electron and ion temperature (separately), and radial electric field. The radial electric field is of a magnitude and direction to result in local ambipolar flow to each part of a large equipotential surface such as a limiter.
Seals for large ports on the Tokamak Fusion Test Reactor
Authors: Mullaney D. H. , Mozeleski M. A. , Fleming R. B.
Published: July 2002

The Tokamak Fusion Test Reactor (TFTR) is a large fusion device being constructed at the Plasma Physics Laboratory of Princeton University. This unit is designed for bakeout at 250 °C, and for a base pressure of 10−8 Torr. The machine has a total of 57 large ports that are removable and are sealed with ‘‘Helicoflex’’ metallic gaskets. There are two seals on each port, a primary and a secondary, with flange bolts between seals. This arrangement balances the load on either side of the bolts, eliminating flange roll that could result from the high sealing forces. The dual seal arrangement also aids in leak detection and permits recovery from a failed primary seal by pumping between seals. All of the large ports have been leak-checked with a helium mass spectrometer leak detector, and all primary seals have been found to be leak tight.
Ion plating in a system with a hot cathode
Authors: Tańcula M. , Oleszkiewicz W. , Zdanowski J.
Published: July 2002

The plating material was heated and evaporated by an electron stream extracted from plasma. The substrate was continuously bombarded by ions extracted from plasma. It was stated that the boundary bias voltage of the crucible exists (e.g., 60 V for Cr) which initiates additional discharge between plasma and crucible. Vapor was intensively ionized in the plasma region. In the case of a grounded or floating substrate, the constant potential difference of 30–150 V between plasma and substrate was observed. Thus, no rf bias of a dielectric substrate was necessary. In the case of a conducting substrate, the effect of bombardment may be enhanced by a negative substrate bias voltage up to 500 V. The layers of Cu, Au, Pt, and Cr were deposited on alumina, silica glass, steel, and brass in Ar (4×10−2 Pa). The deposition rates were 1.2 μm/min for Cu, 0.4 μm/min for Pt, and 0.48 μm/min for Cr at 2 kW power dissipated in the crucible. The adhesion of obtained layers was good and their structure was columnar modified due to ion bombardment. The Cr layers showed structure A15 which is rather rarely obtained.
Electric conduction in metallic Ag particles—Cs2O semiconductor thin films
Authors: Wu Quan-De , Liu Xi-Qing
Published: July 2002

Granular metal films were discussed and reviewed by Abeles et al. Here we discuss the electric conduction in thin films of silver particles dispersed in a matrix of Cs2O. It is a typical system of metallic particles dispersed in a semiconductor. A thin film of Cs2O several hundred Å thick was prepared on a glass substrate with silver electrodes on both sides in a vacuum tube. An amount of silver was deposited onto the film, then its photoemission was monitored during heat treatment to obtain thin film of silver particles dispersed in Cs2O. These procedures were repeated about ten times. Curves of log 1/R vs 1/T were plotted from measurements after each heat treatment. A preliminary explanation is presented in this paper.
Effects of Bi2O3 dissociation on the electrical properties of thermally evaporated films of bismuth oxide
Authors: Dharmadhikari Vineet S. , Goswami A.
Published: July 2002

Bismuth oxide films have been evaporated in an oil diffusion pump system at pressures of ∼0.50 mPa onto glass substrates held near room temperature. The films have been characterized by x-ray photoelectron spectroscopy (XPS), electron and x-ray diffraction, and measurements of the electrical properties. Whereas the as-evaporated films are found to contain a lower suboxide of bismuth and metallic bismuth, the oxidation of these films by heating in air results in bismuth (III) oxide. A capacitance density of ∼2.0 mF/m2 is observed for films as-evaporated. These films at room temperature show a thickness dependent dielectric constant and strong frequency and temperature dependence. In contrast, the oxidized films have a capacitance density of ∼1.0 mF/m2, a thickness independent dielectric constant, and show little dependence on frequency and temperature. In general, as-evaporated films compared to oxidized films have a high dielectric dissipation factor, temperature coefficient of capacitance, percentage variation in capacitance, and the defect density.
Information management data base for fusion target fabrication processes
Authors: Reynolds J.
Published: July 2002

A computer-based data management system has been developed to handle data associated with target fabrication processes including glass microballoon characterization, gas filling, materials coating, and storage locations. The system provides automatic data storage and computation, flexible data entry procedures, fast access, automated report generation, and secure data transfer. It resides on a CDC CYBER 175 computer and is compatible with the CDC data base language Query Update, but is based on custom fortran software interacting directly with the CYBER’s file management system. The described data base maintains detailed, accurate, and readily available records of fusion targets information.
Structure analysis of Ir(100) 1×1 by LEED (100–500 eV)
Authors: Besold G. , Heinz K. , Lang E. , Müller K.
Published: July 2002

LEED intensity measurements and dynamical calculations have been performed for the nonreconstructed Ir(100) surface. They were compared with each other using the Zanazzi–Jona r factor for different energy ranges of the spectra, i.e., 100–250, 250–500, and 100–500 eV. It turns out that the surface relaxation is always nearly the same, at least within the error of the fit, Δd/d=−2%±2%. However, it appears that the r factors are definitely lower for the high energy region accompanied by a slight increase of the precision with which Δd/d can be extracted. The Zanazzi–Jona r factor of the total energy range cannot be interpreted as a linearly weighted average of those of the subranges.
Carbon segregation to the Pd(111) single crystal surface as seen in carbon monoxide thermal desorption spectra
Authors: Ratajczykowa I.
Published: July 2002

Carbon monoxide adsorption was studied on the Pd(111) surface with submonolayer carbon coverages. It is shown that the carbon monoxide desportion spectrum can be used in the detection of a carbon coverage much below the detectability level of AES. Although the estimation of the absolute carbon coverage is subjected to quite a bit uncertainty it seems that a few percent of a monolayer of carbon manifests clearly in the desorption spectrum at low carbon monoxide coverages. With the aid of CO desorption spectra the temperature dependence of the surface segregation of carbon was investigated at temperatures from 450 to 1300 K with the mean C/Pd atomic ratio in the bulk ranging from 1×10−6 to 7×10−6. At any temperature below 835 K carbon does not appear on the surface. At higher temperatures carbon segregates at the surface very quickly and within a temperature range depending on the C/Pd ratio. Carbon that has been segregated on the surface can be easily redissolved even at temperature as low as 450 K. The behavior of carbon is explained in terms of formation and decomposition of the carbon-rich palladium phase PdC0.13. Some implications for cleaning Pd(111) crystals are also shortly discussed.
Rarefied gas flow in a cylindrical annulus
Authors: Lo S. S. , Loyalka S. K. , Storvick T. S.
Published: July 2002

The Hansen–Morse model of the linearized Wang Chang–Uhlenbeck equation is used to study the thermal transpiration and mechanocaloric effects for rarefied polyatomic gases in a cylindrical annulus, where boundary conditions are characterized by diffuse reflection. Phenomenological coefficients at all degrees of rarefaction are reported for physical parameters that represent helium, hydrogen, carbon dioxide, and air. Comparisons with isothermal flow data are given.
Resistor network simulation method for a vacuum system in a molecular flow region
Authors: Ohta Susumu , Yoshimura Nagamitsu , Hirano Haruo
Published: July 2002

A simulation method to obtain the pressure distribution in a complex vacuum system has been proposed. The method introduces a new concept with regard to the function of each component of the vacuum system. The vacuum pump is regarded as a ‘‘vacuum resistor’’ connected at one side to the perfect vacuum. The gas source is regarded as a pressure generator connected to the vacuum. The conducting pipe is regarded as a vacuum resistor between the above elements. The vacuum sides of the pump element and the gas source element are assumed to be connected together by an imaginary route, and thus the vacuum system can be regarded as a closed vacuum circuit network. Such a vacuum circuit network may be replaced by an electric circuit network of a simulator for the vacuum system. The simulator was employed for the high vacuum system of an electron microscope in order to obtain the pressure distribution. The results obtained were in good agreement with the actually measured pressure distribution.
Inverse photoemission from Ni(100) and Ni(111) with oriented oxygen overlayers
Authors: Dose V. , Glöbl M. , Scheidt H.
Published: July 2002

Bremsstrahlung isochromat spectra have been recorded at ℏω0=9.7 eV for clean- and oxygen-covered Ni(100) and Ni(111) surfaces. Angle-integrated and normal incidence angle-resolved spectra are presented. In angle-integrated spectra, ordered c(2×2) and p(2×2) oxygen overlayers on Ni(100) and Ni(111), respectively, cause strong emission enhancement just above the Fermi level. This is attributed to adsorbate-induced antibonding empty electronic states. Energetic position and width of these states is different on the two crystal faces. Normal incidence spectra behave similarly upon oxygen adsorption but are more complicated due to extra emission from strong direct interband transitions.
The role of the professional society in scientific and technological discovery
Authors: Thornton John
Published: July 2002

This paper examines the mechanisms of discovery and invention and the role that a professional society such as the American Vacuum Society can play in promoting scientific and technological advancement. It is argued that discoveries are not, in general, the work of one individual, but that they arise from the combination of many different persons and circumstances, and that the Society can play a vital role in bringing such combinations together.
The design and fabrication of a 30 s pulsed plasma generator
Authors: Biagi L. A. , Ehlers K. W. , Lietzke A. F. , Matuk C. A. , Maruyama Y. , Paterson J. A. , Tanabe J. T.
Published: July 2002

The design and fabrication techniques for a large hybrid magnetic cusp plasma generator developed for 30 s pulse length are described. Included are the magnetic cusp geometry features, water cooling characteristics, filament structures, and the high energy density actively cooled anode and electron dump employed.
Performance of Zr–Al getter pumps under transient load conditions
Authors: Emerson L. C. , Mioduszewski P. K. , Simpkins J. E.
Published: July 2002

Testing of the pump limiter concept in the Impurity Study Experiment (ISX-B) tokamak will involve the use of Zr–Al nonevaporable getter pumps capable of handling intermittent pulses of hydrogen and/or deuterium in the presence of carbon and oxygen impurity concentrations of several percent. To study the pumping characteristics under these conditions we have installed a Zr–Al cartridge pump in a vacuum chamber equipped with a fast gas puff feed system, a quadrupole residual gas analyzer, and a high speed ion gauge for transient pressure measurements. In this paper we report on the performance of the pump over a wide range of gas loads up to that sufficient to provide tens of monolayers of coverage of the getter surface. With flow rates up to 13 Torr l/s, pumping speeds for hydrogen were measured to be 1200–1500 l/s at pressures up to 10 mTorr. The measurements were carried out with gas pulses ranging in length from 50 ms to over 1 s and under conditions that provided a constant pumping speed for impurity species.
A simple bearing for horizontal rotation of heavy equipment in UHV
Authors: Stocker W. , Rieder K. H.
Published: July 2002

Three metal carbide spheres located approximately equidistant on a support with a V-shaped circular groove allow easy horizontal rotation of a heavy mass in UHV via a turntable residing on the three spheres with vertical axis in the center of the support.
Many-electron effects in the photoelectron spectra of condensed nitric oxide
Authors: Kao C. M. , Caves T. C. , Messmer R. P.
Published: July 2002

The valence and core level photoelectron spectra of NO condensed on various substrates as obtained by Tonner et al. can be successfully explained using an NO dimer model in which the two NO molecules form a weak N–N bond via the 2π orbitals of the monomers, resulting in a nearly square geometry. In both the O(1s) and N(1s) regions of the x-ray spectrum there are two intense peaks separated by 3.4 eV. From generalized-valence-bond calculations we find for the N(1s) case, that the peak with the smaller electron binding energy arises from an intermolecular charge transfer from one NO monomer to the other, while the second peak arises from intramolecular screening. The first two peaks in the valence region, which have the smallest binding energies and are separated by 2.6 eV, arise from final states which have 2A1 and 2B2 symmetries, respectively. The 2π orbitals of the monomers combine in-phase and out-of-phase to form a1 and b2 orbitals of the dimer. The resulting two final states of the dimer depend upon which orbital is occupied by the unpaired electron.
Chemical reaction and silicide formation at the Pt/Si interface
Authors: Matz R. , Purtell R. J. , Yokota Y. , Rubloff G. W. , Ho P. S.
Published: July 2002

Surface spectroscopy (UPS and AES) and transmission electron microscopy (TEM) techniques have been used to study the chemical behavior of interfaces formed by Pt deposition (∼0.1–100 Å) on atomically clean Si(111) and Si(100) surfaces prepared by sputter/annealing. As shown by the annealing behavior of a thicker (∼100 Å) overlayer, growth of an intermixed phase begins only at ∼200–300 °C and leads to formation of a product which is stable to 500 °C. TEM observations show this product to be single-phase PtSi. The UPS spectrum for PtSi is dominated by two distinct peaks at −3.7 and −6.2 eV, while the Si L2,3VV AES spectrum also show features characteristic of silicidelike bonding. With annealing above ∼400 °C, excess Si segregates to the top surface of the PtSi overlayer. Upon 25 °C deposition, both UPS and AES show clear indications of strong Pt/Si intermixing across the interface from the submonolayer range to ∼40 Å. In the low (submonolayer to few monolayer) coverage range at temperatures ≤300 °C, the new chemical bonds formed are similar but not identical to those for the PtSi. With increasing coverage the UPS peaks shift toward the Fermi energy as expected for a more Pt-rich environment. For these thin layers (∼5–30 Å), TEM shows the presence of both Pt and silicide. Upon annealing to ∼300–400 °C, a mixture of PtSi with some Pt2Si is observed and the UPS and AES features become typical of PtSi; these features remain unchanged with higher temperature annealing until the Si surface segregation becomes appreciable.
Cobalt–samarium magnets sealed for high vacuum applications
Authors: Delmore J. E.
Published: July 2002

A carefully packaged Co–Sm magnet is described for use in an electron capture ion source.
Initial conditioning of the TFTR vacuum vessel
Authors: Dylla H. F. , Blanchard W. R. , Krawchuk R. B. , Hawryluk R. J. , Owens D. K.
Published: July 2002

We report on the initial conditioning of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel prior to the initiation of first plasma discharges, and during subsequent operation with high power Ohmically heated plasmas. Following evacuation of the 86-m3 vessel with the 104 1/s high vacuum pumping system, the vessel was conditioned by a 15-A dc glow discharge in H2 at a pressure of 5 mTorr. Rapid-pulse discharge cleaning was used subsequently to preferentially condition the graphite plasma limiters. The effectiveness of the discharge cleaning was monitored by measuring the exhaust rates of the primary discharge products (CO/C2H4, CH4, and H2O). After 175 h of glow discharge treatment, the equivalent of 50 monolayers of C and O was removed from the vessel, and the partial pressures of impurity gases were reduced to the range of 10−9–10−10 Torr.
Evaluation of the colliding beam accelerator first string full cell vacuum system
Authors: Foerster C. L. , Briggs J. , Christianson C. , Stattel P.
Published: July 2002

The CBA (colliding beam accelerator, formerly know as ISABELLE) full cell magnet system consisting of six superconducting dipole magnets and two superconducting quadrupole magnets requires two separate vacuum systems. One, known as beam vacuum, operates below 3×10−11 Torr and the other, known as insulating vacuum, operates at less than 10−7 Torr to isolate cryocircuits from atmosphere and from the UHV beam tubes. The UHV bore tube is isolated from the 4.0 K magnet by 36 layers of superinsulation and insulating vacuum. Heat load measurements on the bore tube have been completed and found to agree with data obtained in smaller controlled experiments. Measurements of helium, accumulated on cryogenic pumped charcoal panels over many weeks, have verified sensitive helium mass spectrometer leak detection methods for vacuum integrity, proving sound design of the welded complex. The full cell was assembled and operated under conditions that would exist in the completed machine. Pressures below 2×10−11 Torr beam vacuum requirement and below 1×10−7 Torr insulating vacuum, were routinely achieved during all phases of the full cell operation and support systems testing.
Hydrogen interaction with Al(110) studied by high resolution electron energy loss spectroscopy
Authors: Thiry P. A. , Pireaux J. J. , Liehr M. , Caudano R.
Published: July 2002

The interaction of atomic hydrogen with the Al(110) surface in a glow discharge results in the formation of an Al–H species identified by its stretching vibrational band at 1900 cm−1. This band is also detected during early oxidation of Al single crystal surfaces. It is demonstrated that this species is localized at the interface between the metallic substrate and the surface oxide layer. The HREELS results are in total agreement with recent IETS work on Al/Al–oxide/metal tunneling junctions.
Why the close-packed Ni(111) surface dissociatively chemisorbs oxygen and nucleates oxide faster than the more open Ni(100) surface
Authors: Brundle C. R.
Published: July 2002

The 300 K kinetics of dissociative chemisorption and oxide island nucleation and growth are compared for Ni(100) and Ni(111). We conclude that the behavior of oxygen sticking probability as a function of coverage can be understood in terms of direct Langmuir adsorption (no molecular diffusion) and the availability of active empty clusters of adsorption sites of certain sizes and configurations.
Adsorbate–surface and adsorbate–adsorbate interactions and their role in surface reactions
Authors: No/rskov J. K. , Holloway S. , Lang N. D.
Published: July 2002

By studying trends in the interaction energies of atoms and molecules with metal surfaces as the metal is changed or the surface is modified by adsorbed impurities, two important surface properties affecting the adsorption or catalytic activity have been uncovered. The first is the degree of filling of the transition metal d band, which determines the trends in the interaction energies along the transition metal series. The ‘‘volcano curve’’ relating catalytic activity with position in the transition metal series for a large number of reactions can be understood on this basis. The second is the electrostatic potential changes induced by steps or adsorbed electropositive or electronegative atoms. The promoting effect of the alkalis and the poisoning effect of the electronegative atoms on the adsorption of molecules like H2, CO, N2, and O2 can be explained by the sign of the electrostatic interaction between these molecules and the preadsorbed atoms. The relative strength of the influence of the alkalis and the electronegative atoms is discussed on the same basis. Finally, the peculiar effect preadsorbed atoms have on the adsorption of NH3 and H2O are ascribed to the large intramolecular charge transfer in these molecules.
1/f noise in ion-implanted and double-layer epitaxial HgCdTe photodiodes
Authors: Radford W. A. , Jones C. E.
Published: July 2002

1/f noise in Hg0.7Cd0.3Te photodiodes has been measured as a function of temperature, junction area, diode voltage, and gate bias in order to identify the dominant noise mechanisms. The p-n junctions were formed both by ion implantation and by growth of double-layer epitaxial structures. The LPE base layers were doped with arsenic and the devices were passivated with photochemically deposited SiO2. Two leakage current mechanisms were identified as sources of 1/f noise. Under optimized surface potentials, the 1/f noise was proportional to the depletion-region GR current generated at the surface. This was observed in both double-layer devices in which the leakage current was primarily generated at the depletion-region surface, and in ion-implanted devices in which the leakage current had a bulk depletion-region origin. For nonoptimized gate voltages, where tunneling currents were the dominant leakage mechanism, the noise current was proportional to the tunneling current. Surface, bulk, and photogenerated diffusion currents were not accompanied by significant amounts of 1/f noise. The proportionality factor between the noise current and the depletion-region leakage current for the devices passivated with SiO2 was found to range from one to ten times lower than the values previously reported for ZnS-passivated devices. The results are discussed terms of Handel’s bremsstrahlung model, Kleinpenning’s mobility fluctuation model, and the McWhorter–Anderson–Hoffman surface potential fluctuation model.
Current characteristics of a high voltage 60 Hz crossed-field discharge
Authors: Ames Elizabeth E. , Silevitch Michael B. , Graneau Peter
Published: July 2002

This paper deals with the continuation of research on vacuum pumping with 60 Hz ac voltages and permanent magnets arranged to form a crossed-field configuration. It is well known that dc voltages in a crossed-field discharge and in the presence of a titanium cathode will cause a decrease in residual gas pressure. In our previous research it was demonstrated that this result could also be achieved with 60 Hz ac voltages. Before applying this knowledge to commercial vacuum pumps it is important to gain an understanding of the underlying physical mechanisms. Of particular interest are the initiation and maintenance of the discharge under ac conditions. Results reported in this paper deal with a radial magnetic field in the butt-gap between parallel disk electrodes. In this particular crossed-field arrangement, it was found that the electron space charge is unstable, but ion production is more or less continuous with both dc and ac excitation. The pumping yield per ion was found to be low, but could probably be increased by replacing the glass tube with a metallic vessel so that fewer of the sputtered titanium atoms combine in situ with adsorbed gas molecules on the glass wall.
Gas concentration nonuniformity and kinetic anisotropy in high vacuum
Authors: Horodeński Andrzej
Published: July 2002

In a high vacuum particle wall, collisions occur much more frequently than in mutual elastic ones, therefore, chaotization (Maxwellization) does not take place. Hence, the gas-phase state is determined by boundary conditions, i.e., surface scattering processes. In this paper, steady-state equations of low-density (molecular regime) gas, based on probability distribution functions of adsorption, desorption, and reflection, have been derived. Calculations performed for spherical and planar symmetry show that rarefied gas can be strongly nonuniform and anisotropic; deviations from homogeneity can reach one order of magnitude. The idea of experimental verification has been proposed. off