bluuebunny/crossref_metadata_2025 huggingface dataset:
Summary Abstract: Influence of ion irradiation on surface reactivity
Authors: Miranda R. , Rojo J. M. , Salmerón M.
Published: July 2002

Changes in chemisorption stage of O2/Pt (111) and NO on NiO following argon ion bombardment are reported. A systematic discussion of the mechanisms involved in ion bombardment induced changes in surface reactivity, for a number of systems including the above, is presented.
Titanium gettering in Doublet III
Authors: deGrassie J. S. , Callis R. , Campbell G. , Garcia J. , Ledin E. , Meyer C. , Miller J. , Petersen P. , Smith J. , Stav R. , Taylor T. , Group the Doublet III , Nagami M. , Group the Jaeri
Published: July 2002

The application of mild titanium gettering in the Doublet III tokamak has led to a significant improvement in the obtainable operating regimes and discharge parameters for all of the many plasma cross-sectional shapes studied. With gettering, low-Z impurities and radiated power are greatly reduced. The maximum line average electron density has increased 50% (?emax ∠1×1020/m3), corresponding to a Murakami coefficient of nearly six.
Technical and commercial aspects of plasma heat applications in primary melting, secondary remelting and refining operations
Authors: Bhat G. K.
Published: July 2002

The principles of plasma heat generation, conditions for plasma arc stabilization, and plasma torch designs and operation are reviewed from both engineering principles and practical applications viewpoints. The various types of plasma heat devices available are described and classified in terms of their design and operational features. Manipulation of the plasma torch operating parameters for the control of temperature, heat flux, and efficiency are considered in mathematical and practical details. Coverage is given to the present state of the technology and industrial size systems used abroad for plasma primary melting, secondary remelting, scrap consolidation, refinement, and casting. Economic aspects of certain plasma heat processing of metallic concentrates and materials are discussed. Also, comparative merits of plasma and conventional melting and refining of high alloy steels have been examined. A forecast is provided on the future potentials of plasma heat applications in the specialty metals industry.
E-beam deposition characteristics of reactively evaporated Ta2O5 for optical interference coatings
Authors: Herrmann W. C.
Published: July 2002

Experiments with Ta2O5 as a starting material were undertaken to produce nonabsorbing Ta2O5 as a thin film material for multilayer dielectric coatings. The dependence of refractive index on oxygen pressure, on substrate temperature, and on deposition rate was measured. An interesting relationship was discovered between the evaporation rate and the rate of outgassing of the chemically bound oxygen from the Ta2O5 melt. A condition for nonabsorbing Ta2O5 films, regulated O2 being held at a constant pressure, is indicated when the outgassing rate of oxygen from the melt follows the deposition rate in a linear fashion increasing with increasing deposition rate and remaining constant with constant deposition rate. When this condition is met the maximum rate for nonabsorbing films can be realized, i.e., when the deposition rate is increased beyond a critical limit the outgassing ceases to follow linearly but degenerates and the film becomes absorbing. Automatic rise, soak, and deposit cycles enabled 40%, 35 g, of the starting material to be deposited as nonabsorbing films from the same 15 cc crucible. Ta2O5/SiO2 multilayer structures were fabricated with theoretical stop and pass bands being obtained.
Application of ESCA to corrosion studies of glasses containing simulated nuclear wastes
Authors: Pederson L. R. , Thomas M. T. , McVay G. L.
Published: July 2002

ESCA, in combination with ion sputtering, was used to obtain compositional depth profiles of complex glasses which had been leached in DI water. The earliest and most obvious feature of aqueous attack was alkali depletion from the near surface regions of the glasses. Further corrosion was slowed by a surface buildup of various elements, which included aluminum, iron, nickel, titanium, zirconium, cerium, and neodymium. Elemental releases were calculated from the ESCA results, which were corrected for variations in the sputter rate through the reaction layer, and were compared to those measured directly by ICP solution analysis. The degree of agreement between the two methods was used to assess the importance of matrix dissolution in addition to selective component leaching in the aqueous corrosion of the glasses.
Atomic structure of laser annealed Si(111)–(1×1)
Authors: Zehner D. M. , Noonan J. R. , Davis H. L. , White C. W.
Published: July 2002

Although the stable surface structure of a clean, thermally annealed Si(111) is a (7 × 7) at room temperature, a metastable (1 × 1) structure can be obtained by irradiating the crystal with the output of a pulsed ruby laser. The structural determination of this atomically clean (1 × 1) arrangement is important since it may subsequently be used as a basis for the eventual understanding of the (7 × 7) reconstruction. A LEED analysis of the (1 × 1) structure is reported in which I–V profile data for the six lowest indexed nonspecular beams have been collected with the incident electron beam normal to the surface. These experimental profiles have been compared with the results of dynamical calculations, in which the first and second interlayer spacings of the truncated bulk model were varied. Also, nonstructural parameters have been varied in the calculations. The results suggest a bulklike layer termination exhibiting no ordered lateral reconstruction with the first interlayer spacing contracted by 25.5±2.5% and the second expanded by 3.2±1.5% with respect to bulk values. The best comparison between calculated and experimental I–V profiles has produced a six-beam Zanazzi and Jona R-factor of 0.115.
Binding state perturbations in the silicon oxide–tungsten system
Authors: Wu O. K. T. , Burns Richard P.
Published: July 2002

Thin films of silicon dioxide are widely used in present day microelectronic devices. In this study we investigate the model system silicon oxide adsorbed on clean and oxidized polycrystalline tungsten. The adsorbed silicon oxide is formed by means of an SiO molecular beam, and the adsorbate-surface interactions are studied by means of Auger Electron Spectroscopy and Flash Desorption Mass Spectrometry. We find that the binding state of SiO on a W surface can be perturbed by electron beam irradiation and also by oxygen coadsorption. The electron beam desorbs oxygen from the SiO+W system, but Si is not desorbed. After electron bombardment and annealing at 613 K, the single binding state of SiO on W(oxidized) is converted into two states. One state is characteristic of SiO on W(clean), while the other is characteristic of SiO on W(oxidized). In addition, oxygen coadsorption induces changes in the flash desorption spectrum of SiO. An analysis of the desorption spectrum indicates that the coadsorption process leads to attractive interactions between adsorbate and adsorbate. Thus, we conclude that the binding between the silicon oxide and the metal substrate is very sensitive to the film stoichiometry.
Semiconducting behavior in antimony-doped bismuth films
Authors: Damodara Das V. , Jagadeesh M. S.
Published: July 2002

The electric resistivity and Hall effect were studied for the vacuum evaporated and annealed ∠1 at.% Sb-doped bismuth alloy films of various thickness (350–3500 Å) in the temperature range of 77–510 K. Contrary to the behavior of bulk BiSb alloy, where the alloy becomes semiconducting only at about 4 at.% of Sb and above (A.L. Jain, 1959), it is found that thin films of 1% Sb-doped Bi alloy are semiconducting. Moreover, this semiconducting trend begins at about room temperature unlike in bulk BiSb alloys where it is observed only at temperatures below about 180 K. The present type of behavior has been predicted and observed by some earlier workers (Ivanov et al. 1963, 1964). The intercrystalline barrier activation energies determined for various film thicknesses deposited at different substrate temperatures (257 K, 300 K, 373 K) were found to vary with thickness and substrate temperature, activation energy decreasing with increasing thickness and substrate temperature. These observations have been attributed to the film nature of the polycrystalline films (Slater 1956, Espevik 1971, Okuyama 1976, Bednarczyk 1976).
Properties of solar absorbing films produced by an in-line sputter coating plant
Authors: McKenzie D. R.
Published: July 2002

The properties of solar selective films produced by an in-line coating plant are described. The coating plant employs dc sputtering using two hollow cathode magnetrons to apply a two layer copper and metal carbide coating to tubular substrates for evacuated collectors. The absorptance is found to be 0.88 and the emittance 0.035 at room temperature. The film is shown to be of the graded-index type with a structure analogous to the AMA coatings previously described. The grading is inherent in the coating process.
Chemical composition and formation of thermal and anodic oxide/III–V compound semiconductor interfaces
Authors: Wilmsen C. W.
Published: July 2002

The literature on the chemical composition and growth of thermal and anodic oxides of the Ga and In III–V compounds is reviewed and discussed. Emphasis is placed on the questions ’’what is the chemical composition of the oxide/III–V interface’’ and ’’how and why did it get that way’’. It is apparent that much is known about these interfaces but knowledge of a number of important growth, thermodynamic, and structural parameters is lacking.
A pattern recognition technique using sequences of marks for registration in electron beam lithography
Authors: Holburn D. M. , Jones G. A. C. , Ahmed H.
Published: July 2002

A pattern recognition technique is described for precise registration in electron beam lithography. The usual simple mark on the substrate is replaced by a symbol of carefully chosen configuration, based on a pseudorandom binary sequence. The registration symbol obtained by rapidly scanning the electron beam in the region of the symbol is then cross correlated with a stored replica of the registration symbol, either by special purpose hardware or by programmed instructions. It is shown that with this method, registration symbols may be detected accurately even when heavily contaminated with noise, the signal-to-noise ratio being reduced to less than 0.25. The method also allows for the presence of unrelated artefacts in the vicinity of the symbol.
Twenty-five nm features patterned with trilevel e-beam resist
Authors: Tennant D. M. , Jackel L. D. , Howard R. E. , Hu E. L. , Grabbe P. , Capik R. J. , Schneider B. S.
Published: July 2002

We describe a trilevel e-beam resist process based on the high resolution resist PMMA. This process has been used to form metal features 25 nm wide on thick Si substrates by liftoff. Ni–Cr films patterned in this way have been used as masks for reactive ion etching of Si. The resulting structures were arrays of fins ∠ 30 nm wide and 330 nm high on 95 nm centers with a total length of 3 μm. We also discuss the resolution improvement obtained in a trilevel process based on a higher speed resist, P (MMA/MAA).
Neutral density measurements in doublet III
Authors: deGrassie J. S. , DeBoo J. C. , Mahdavi M. A. , Ohyabu N. , Shimada M.
Published: July 2002

In the Doublet III tokamak a variety of cross-sectionally-shaped plasmas has been investigated. Simple magnetically-shielded ionization gauges monitoring the working gas pressure show a striking dependence upon plasma shape. Average neutral density varies over two orders of magnitude. In the exteme cases of the simplified poloidal divertor shapes, the pressure exceeds 10−3 Torr.
Computation of the performance of mechanical boosters with various fore pumps
Authors: Livesey R. G. , Budgen L. J.
Published: July 2002

The large number of possible combinations of mechanical boosters and fore pumps makes it desirable to be able to quickly compute the performance of various combinations using previously measured data. Accurate calculation is important in order to ensure that the combination size and therefore cost and energy usage are kept to a minimum. This paper describes the computation, using a microcomputer, of the speed curves of combinations from data on the zero flow compression ratio characteristics. It is shown that taking the booster inlet impedances into account gives calculated values which are in good agreement with experimental results.
Laboratory study of the PDX/PLT laser blow-off trace element injectors
Authors: Manos D. , Ruzic D. , Moore R. , Cohen S.
Published: July 2002

A laboratory study of the beams produced by laser blow-off trace element injectors used on the PDX and PLT tokamaks has been conducted. Eight target materials were studied, in the form of thin films on glass substrates: Al, Si, Sc, Cr, Fe, Ni, Cu, and Mo. Beam detectors included a quadrupole mass spectrometer, gridded retarding field analyzer, and beam collector plates. The collector plates were later analyzed by optical and electron microscopy and Auger spectroscopy. The results show that the injection produces the following species, in the usual order of decreasing velocity: free electrons, plasma, free ions, highly excited neutral atoms, unexcited neutral atoms, and metal clusters having diameters ranging up to several microns. The percentages of the various species, as well as their distributions of velocities, were found to be strong functions of the metal used, the film thickness, and the laser power density. Monoatomic species are generally contained within a half angle of ∠12°, while clusters are within ∠5°. Models of the production mechanism and implications for the use of the device as a tokamak diagnostic are discussed.
The fabrication of laser-seal-welded targets for particle beam fusion experiments
Authors: Armstrong S. , Flick F. F. , Perry F.
Published: July 2002

Proposed Sandia particle beam fusion targets require seamless spheres filled with high pressure deuterium-tritium gas. Conventional fill techniques utilizing small diameter fill tubes produce perturbations upon implosion. These perturbations may cause instabilities and jetting of target material into the fuel core, resulting in a low target yield. At Los Alamos, a fabrication technique was developed to eliminate the need for fill tubes. This technique uses a laser to seal-weld a small fill hole in the target wall, while in a high pressure gas environment. This paper will discuss in detail the fabrication parameters for processing simulated laser-seal-welded targets. These steps include electroplating, micromachining and laser welding. The fabricated laser- seal-welded cylindrical targets will be subjected to hydrodynamic experiments at Sandia to determine the effect of the laser seal weld upon implosion.
Improved nonconcentricity characterization of transparent laser fusion targets by interferometry
Authors: Powers T. F.
Published: July 2002

Interference microscopy is an important method of characterizing inertial fusion targets. This paper reviews the current method used for measuring nonconcentricity of optically transparent target shells and describes an improvement that is obtained when the target shell is filled with gas. Experimental verification of this improvement is presented for targets filled with gas through capillary mounting stalks.
Light ion beams as the driver for inertial confinement fusion
Authors: Bieg K. W. , Kuswa G. W.
Published: July 2002

Because of the high costs associated with producing the ≳1 MJ, 10 ns pulse required to initiate a pellet, the efficiency and relatively low cost of pulse power driven ion beams makes this approach particularly attractive both for proof-of-principle and for reactors in the future. Although pulse power technology for producing multimegavolt and multimegampere electric pulses is well-established, the coupling of this energy into ion beams focused onto targets requires further work. During the last six years, focused ion beam intensity has been improved more than five orders of magnitude to a value of ∠1012 W/cm2. An additional factor of 40 in focused power density will be required; this will be provided by the PBFA II accelerator now being designed and scheduled for completion in 1985. This paper will briefly describe how pulse power systems deliver energy to ion sources, how beams are generated and focused, and a few examples of target irradiation experiments. Finally, a concept for delivering beams to pellets in the center of a reactor wall will be described.
Reactive magnetron sputtering of titanium and its oxides
Authors: Nyaiesh A. R. , Holland L.
Published: July 2002

Ti and TiOx films have been made by vacuum and reactive evaporation, respectively, using electron beam heating. However, magnetron sputtering of Ti and its oxides is of interest because of the system’s simplicity and possible applications in the semiconductor and metallurgical industries. An investigation has been made into the discharge and deposition characteristics of a planar magnetron. Using a water-cooled Ti target operated at up to 1200 W in Ar and Ar+O2 mixtures, the results obtained show that V/I curves fall into two groups. Thus a high operating voltage is needed at either a low input power or high O2-gas content which is the characteristic mode for high oxidized film growth. High power inputs (even in the presence of a 25% O2 content) or low O2 content resulted in a low operating voltage and the growth of substantially metallic films. The effects of O2 on the discharge characteristic are briefly considered. Deposition rate curves as a function of power input for different gas mixtures are presented for these two growth modes. Also ’’phase diagrams’’ for both dc and rf power inputs are given which roughly classify the conditions needed to produce deposits tending to the metallic or oxide states. The film growth conditions for rf and dc magnetrons were similar but generally with rf a higher power input was needed to obtain metallic films and this was attributed to the reduced deposition efficiency of the rf system.
Picosecond time-resolved photoelectron spectroscopy of ZnTe
Authors: Williams R. T. , Royt T. R. , Rife J. C. , Long J. P. , Kabler M. N.
Published: July 2002

We describe a new time-resolved probe of excited electronic states near surfaces of semiconductors, as applied to cleaved crystals of ZnTe. Electrons photoexcited to the conduction band by a 5-ps laser pulse are re-excited by a second pulse to states above vacuum energy. Analysis of the photoelectrons resulting from this resonant two-photon process yields data on energy distributions and relaxation times of electrons in the intermediate states. Preliminary evidence for persistent (∠150 ps) occupation of states up to 1.6 eV above the conduction band minimum in ZnTe is presented.
Energy spectra of donors in GaAs–Ga1−xAlxAs quantum well structures in the effective mass approximation
Authors: Mailhiot C. , Chang Yia-Chung , McGill T. C.
Published: July 2002

We present the results of a study of the energy spectrum of the ground state for shallow donors in quantum well structures, consisting of a single slab of GaAs sandwiched between two semi- infinite layers of Ga1−xAlxAs. The effect of the position of the impurity atom within the central GaAs slab is investigated for different slab thicknesses and alloy compositions. Two limiting cases are presented: One in which the impurity atom is located at the center of the quantum well (on- center impurity), the other in which the impurity atom is located at the edge of the quantum well (on-edge impurity). Both the on-center and the on-edge donor ground state are bound for all values of GaAs slab thicknesses and alloy compositions. The alloy composition x is varied between 0.1 and 0.4. In this composition range, Ga1−xAlxAs is direct and the single-valley effective mass theory is a valid technique for treating shallow donor states. Calculations are carried out in the case of finite potential barriers determined by realistic conduction band offsets.
Physics and chemistry of semiconductor interfaces: Some future directions
Authors: Herman Frank
Published: July 2002

In this paper we will discuss some semiconductor interface problems which we expect will receive increasing attention during the next few years. In particular, we will consider interfaces between crystalline and amorphous semiconductors, interfaces between semiconductor polytypes such as cubic and hexagonal ZnS, and compositionally modulated semiconductor superlattices involving GeSi alloys, as well as transport measurements of interface roughness in GaAs/Ge/GaAs heterostructures.
Study of grain boundary diffusion of potassium in gold films using a clean, controlled, and localized source of alkali atoms
Authors: Farías M. H. , Peña J. L. , Sánchez-Sinencio F.
Published: July 2002

Grain boundary diffusion of K in polycrystalline Au films has been studied by the Auger surface accumulation method. A novel diffusant source which is clean, controlled, and localized was used. The Au film was deposited on a KCl substrate and an electron beam was sent through the Au film. K was then generated by electron impact dissociation of KCl. The value of the diffusion constant obtained is (K′δ/δ′)Db = (1.6±1.1)×10−13 cm2 s−1.
Influence of a multiple-energy ion beam on the equilibrium profile of a binary alloy
Authors: Roush M. L. , Davarya F. , Andreadis T. D. , Goktepe O. F.
Published: July 2002

Ion-bombardment-induced sputtering of a multielement solid results in a preferential movement of the constituents, producing a composition profile which is dependent upon the beam energy. Recent studies have demonstrated transient changes in surface composition of such samples when the bombarding energy is abruptly changed. It is important to be able to treat multiple-energy ion beams since most sputtering systems have a contaminant of multiply charged ions with higher energy than the principal component. We have studied the various competing processes that result in the equilibrium profile in order to develop the capability to predict the equilibrium profile which will result, once the parameters of the bombardment have been specified. We find that the equilibrium profile produced by a beam containing two energies cannot be obtained simply by interpolating between the two profiles that would result from the ion components individually. Interpolation is possible only in the near surface region.
An AES–ELEED study of the Al/GaP(110) interface
Authors: Bonapace C. R. , Kahn A.
Published: July 2002

The Al/GaP(110) interface, formed by evaporating Al on a clean, well-ordered, sputter-annealed GaP(110) surface was studied with ELEED and AES. Evidence for island formation, when Al is evaporated on the room-temperature substrate, comes from the slow decrease of the Ga and P AES peaks and the persistence of the substrate ELEED pattern for up to 75 ML (monolayer) of Al. Limited substrate decomposition was also observed for higher rates of Al evaporation. Upon annealing at moderate temperature, Al undergoes a metal–cation replacement reaction whereby Al–P bonds are formed and metallic Ga appears at the surface of the system. With an initial Al coverage of more than 8 ML and a 690 °C annealing cycle, a few layers of AlP are formed.
Atomic geometries of compound semiconductor surfaces and interfaces
Authors: Kahn A.
Published: July 2002

The recent determination of the atomic structure of CdTe(110) and GaSb(110), and of GaAs(110)-In, GaAs(110)-Sb, and GaP(110)-Al has triggered a reevaluation of the atomic structures of compound semiconductor surfaces and interfaces. The atomic geometries of the (110) surfaces are dominated by a top bilayer bond rotation and a small contraction of the bilayer toward the substrate. The magnitude of the rotation angle approximately correlates with the lattice constant of the crystal. No simple correlation can be found between the surface relaxation and the ionicity of the crystal. The long range atomic structure of column III and V elements adsorbed on GaAs(110) and GaP(110) is evaluated, before and after annealing, in terms of adatom electronic configuration and interface reactivity. Column III elements form disordered overlayers whereas column V elements form ordered structures and modify the substrate relaxation. Annealing reactive interfaces (Al on GaAs and GaP) leads to a metal–cation replacement reaction and to the crystallization of a new compound. For unreactive interfaces (In and Sb on GaAs), annealing leads to the desorption of the column III metal (weak bonding) but demonstrates the strong bonding of Sb to the substrate. As expected, no replacement reaction is observed in these latter cases.
Laser fluorescence measurements of hydrogen and metal densities in the Doublet III tokamak
Authors: Muller C. H. , Eames D. R. , Burrell K. H.
Published: July 2002

A general overview of the Doublet III laser spectroscopy program is presented. This program includes tokamak diagnostic experiments and laboratory development work. Measurements of titanium and deuterium in Doublet III are presented along with recent laboratory results. Sputtering of the vacuum walls by energetic charge-exchange neutrals from the plasma center appears to be responsible for the observed Ti impurities in Doublet III. Resonance fluorescence scattering from deuterium atoms near the plasma center has been observed using a broadband dye laser and a narrow band detector. The feasibility of determining ion temperatures using this technique is discussed. Using the measured deuterium densities we have calculated a local electron particle confinement time. Laboratory measurements of carbon and oxygen densities using two-photon laser excitation and of Fe i speed distributions (temperatures) using a laser double-pulse excitation technique are shown to be applicable to the tokamak conditions of Doublet III.
Electrical, structural, and bonding changes induced in silicon by H, Ar, and Kr ion-beam etching
Authors: Singh Ranbir , Fonash S. J. , Ashok S. , Caplan P.J. , Shappirio J. , Hage-Ali M. , Ponpon J.
Published: July 2002

A study to elucidate the role of processing-induced changes in Si, subjected to ion-beam etching has been made. It is shown that these changes can be related to the primary ion beam used in ion-beam etching. Using ESR, trivalently bonded Si has been shown to be present. Fe and Cr have been found to be the main contaminants. An annealing study revealed that the damage can be annealed out at relatively high temperatures.
EBIC characterization of electrically active defects in (Hg,Cd)Te
Authors: Moore T. M. , Schaake H. F.
Published: July 2002

A comparison of low temperature electron beam induced current imaging in the scanning electron microscope and surface defect etch studies has identified subgrain boundaries and isolated dislocations as electrically active recombination centers in p-type solid state recrystallized (Hg1−X,CdX)Te with X=0.3. The ‘‘spotty’’ appearance of these images is attributed to enhanced recombination at Te-rich precipitates decorating dislocations in the subgrain boundaries.
A review of the stainless steel surface
Authors: Adams R. O.
Published: July 2002

The characteristics of the surface of various stainless steels are reviewed. The property of these alloys that makes them stainless is the formation of Cr2O3 on the surface. It has been found that this protective layer can be modified relatively easily by heating, abrading, chemical treatment, or ion bombardment. Modification can be changes in the chemical composition of the surface layer or the formation of a layer of segregated material on the surface. These changes may alter the protective nature of the surface films. The outgassing characteristics of stainless steel surfaces also vary depending upon the treatment these surfaces receive.
The thermalization of energetic atoms during the sputtering process
Authors: Somekh R. E.
Published: July 2002

We consider the sputter deposition process and present a calculation of the rate of energy loss of sputtered atoms and reflected neutrals due to elastic collisions with the sputtering gas atoms. Compared to previous calculations we have explicitly taken into account the strong energy dependence of the scattering cross section recently reported by Robinson. The results suggest a much less efficient energy loss rate than previously envisaged using the classical thermal cross sections. Such thermal cross sections have been used in previous calculations to explain the high sputtering pressure required for preparing high critical transition temperature superconductors Nb3Ge and Nb3Sn.
A new effusion cell arrangement for fast and accurate control of material evaporation under vacuum conditions
Authors: Beck A. , Jungen H. , Bullemer B. , Eisele I.
Published: July 2002

A new type of effusion cell has been developed for thermal evaporation of materials up to 1300 °C under ultrahigh vacuum conditions. The evaporation rate, measured by a quadrupole mass spectrometer, is controlled by moving a mechanical shutter connected to the cell and not by varying the temperature. An electronic feedback circuit positions the shutter and allows computer programming of arbitrary profiles. Compared to common thermal control, any desired evaporation rate can be stabilized faster, for example, in less than 2 s.
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o studies of He–Ni and He–Cu interaction potentials
Authors: Beckmann H. O. , Whitten J. L. , Batra Inder P.
Published: July 2002

Helium diffraction data from the nickel (110) surface has indicated a very small corrugation which decreases with increasing incident energy of He atoms while for copper a larger corrugation effect is observed. None of the theoretical calculations based on surface electronic charge density reported to date have been successful in reproducing the value or the trend for Ni(110). It is suggested that the differences between Ni and Cu are due to the unfilled d shell of Ni. Configuration interaction calculations on He–Ni14 and He–Cu14, using an embedding theory, have been performed for low lying electronic states to determine interaction potentials and softness parameters. For Ni the interaction potentials are found to be similar for atop atom and midbond He trajectories, while for Cu, the atop atom site is much more repulsive in accord with the He diffraction data.
On the surface diffusion of tin on gold in air at room temperature
Authors: Tompkins Harland G.
Published: July 2002

A tin-plated knife edge held against a gold surface has been aged at room temperature in air for about 2×108 s (6-1/2 years). Auger electron spectroscopy is used to detect the presence or absence of Sn on the Au surface at various locations near the knife edge. With a practical horizontal resolution limit of a few microns, very little surface diffusion was detected. The values (or upper bounds) of diffusion coefficients are calculated, and these values are compared and contrasted to the values predicted from classical surface diffusion measurements. In air, at room temperature, Sn in contact with an Au surface appears to diffuse slower than projected from extrapolation from higher temperature.
Surface chemistry of wear scars
Authors: Thomas M. T. , Glaeser W. A.
Published: July 2002

The surface chemistry of the wear scars formed on Cu-3% Al alloy worn by a carburized steel ring have been studied by high-resolution scanning Auger electron spectroscopy. A FALEX-1 tester was used to perform the wear experiments. A number of conditions were studied including wear scars produced in an unlubricated air environment and wear scars produced using a 1% stearic acid dodecane lubricant. Iron was detected on the surface and in the near surface region of the lubricated and unlubricated specimens. Carbon and oxygen deposits a few tens of nanometers thick produced a mottled appearance on the lubricated wear scar. The iron transfer on the lubricated specimens was associated with the deposits, which were most likely a metallic soap. In addition to the iron, a larger concentration of aluminum was measured in the soap deposits. Iron was also detected on the dry wear scar. In this case, iron was not associated with any hydrocarbon deposits, but was randomly distributed throughout the wear scar. The iron concentration varied by more than an order of magnitude from one location to another and the iron Auger signal increased as the surface was removed by ion sputtering. The iron was probably in the form of very small particles incorporated into a Cu–Al ‘‘transfer layer.’’
A Zr–Al composite-cathode sputter-ion pump
Authors: Okano T. , Ohsaki A. , Tuzi Y.
Published: July 2002

The performance of a diode sputter-ion pump which has a pair of cathode plates made of Zr and Al has been studied. The main purpose of the study was to reduce the memory effect of prepumped gases, especially hydrogen. Sputtered Zr and Al atoms from each cathode plate form deposits of Zr–Al alloy which have gettering properties superior to those of pure Zr or Al. Results showed that trapping on the sputtered deposits reduced the re-emission of trapped gases from the sputtered region by ion bombardment. The composition of the deposited layers was determined by Auger electron spectroscopy. The pumping characteristics of the Zr–Al cathode were compared to a Ti cathode of the same configuration. Ratios of the pumping speeds (SZr–Al/STi), at 10−5 Pa are 1.8 and 3.3 for N2 and Ar, respectively. Re-emission of D2 by subsequent pumping of Ar was measured after 1.3×10−2 Pa m3 of D2 were pumped by each cathode. At an Ar pressure of 1×10−5 Pa, re-emission of D2 for the Zr–Al cathode is less than 40% of that for the Ti cathode.
Investigation of the plasma impact on liner samples in TEXTOR
Authors: Besocke K. , Flentje G. , Tschersich K. G.
Published: July 2002

Various liner samples were placed on two poloidally different positions inside the TEXTOR torus using the ‘‘Swiss manipulator’’ for the first time. After 16 well-reproduced plasma discharges, the samples were removed and investigated with SIMS and AES. The influence of plasma impact became clearly apparent in respect to surface and depth distribution of H, D, and O by applying a simple but effective test method of direct comparison between exposed and shaded parts of the specimen. Pronounced deviations of the poloidal plasma symmetry as well as a memory effect due to the preceding TEXTOR operation were detected.
Safety hazard from gas discharge interactions with the Bayard–Alpert ionization gauge
Authors: Morrison Charles F.
Published: July 2002

Human contact between ground and the vacuum chamber could be lethal under conditions of open chamber ground and high pressure during ion gauge operation. At pressures of 0.1 Pa and greater, the Bayard–Alpert (BA) gauge typically generates sufficient plasma that significant coupling can occur between the grid of the BA gauge and the metal parts of the vacuum chamber. This coupling is especially severe during electron bombardment degassing, involving both glow discharge and vacuum arc mechanisms. This coupling causes significant currents to flow through the ground between the vacuum chamber and controller chassis. At high pressures, loss of the vacuum chamber ground connection floats the chamber at a voltage near that of the BA gauge grid. Contact between ground and these voltages can cause fibrillation or cardiac arrest.
New ideas for computer-aided photoemission data acquisition
Authors: Mahowald P. H.
Published: July 2002

A new data acquisition program used for photoemission and related experiments which scans one or two variables and records up to ten variables is described with respect to the new advantages for the experimenter. The system runs on the Digital Equipment Corporation (DEC) RSX multitasking operating system and uses the CAMAC interface standard for interface with the experiment.
Microcomputer-multichannel analyzer data system for foreground-background data collection and analysis
Authors: Beard Bruce C. , Dahlgren David , Ross Philip N.
Published: July 2002

A microcomputer-multichannel analyzer (MCA) system was assembled to obtain foreground-background performance in data collection and analysis for x-ray photoelectron spectroscopy. The MCA performs pulse counting analysis, while the microcomputer is free to evaluate previously down-loaded data or perform other computing functions. No special interfacing hardware is required beyond single digital to analog (D/A), and analog to digital (A/D) converters. Analysis and computing time is optimized with a minimum interfacing expense.
A sputtering wind
Authors: Hoffman D. W.
Published: July 2002

A directional pressure probe extending from a capacitance manometer and rotatable over 360 deg of orientation was inserted at midlength near a high-rate magnetron sputtering source. Actuating the cathode at currents up to 12 A gave rise to a pressure difference between probe orientations facing toward and away from the source. The greater pressure was observed when facing away. The difference was as large as 10% of the base pressure and varied systematically with the base pressure and the cathode current. It appears that energetic particles emanating from the source collide with the ambient gas, pumping it preferentially toward the ends of the cylindrical magnetron and driving opposed toroidal circulation cells that return the gas to the cathode at midlength. A freewheeling fanblade was installed and observed to rotate when the sputtering source was on. Blocking the direct incidence of condensible particles with a shutter caused the direction of rotation to reverse. This counter-rotation was in accord with the gas circulation model and confirmed the existence of a brisk ‘‘sputtering wind.’’
Technical aspects of the joint JET-ISX-B beryllium limiter experiment
Authors: Edmonds P. H. , Dietz K. J. , Mioduszewski P. K. , Watson R. D. , Emerson L. C. , Gabbard W. A. , Goodall D. , Simpkins J. E. , Yarber J. L.
Published: July 2002

An experiment has been performed on the Impurity Study Experiment (ISX-B) tokamak to test beryllium as a limiter material. Beryllium is an attractive candidate for a limiter and has been proposed for use in the Joint European Torus (JET) experiment. A temperature-controlled, segmented, beryllium top-rail limiter was located inside the plasma radius described by the existing titanium limiters. An extended set of diagnostics was added for measurement of scrapeoff and limiter parameters. These included visible and infrared monitoring systems, probes, and surface analysis experiments. Tokamak experiments included parameter surveys of both Ohmically heated and neutral-beam-heated plasmas and an extended fluence test of the limiter. The most significant effect of operation with a beryllium limiter was the reduction in low-Z impurities caused by gettering action of beryllium deposited on the liner walls. The experiment required the design and implementation of contamination control apparatus and work procedures to prevent the accidental dispersion of beryllium dust.
Angle-resolved photoemission spectroscopy of Hg1−xCdxTe
Authors: Silberman J. A. , Laser D. , Shih C. K. , Friedman D. J. , Lindau I. , Spicer W. E. , Wilson J. A.
Published: July 2002

Angle-resolved photoemission spectroscopy, a technique which provides direct information on the quantum numbers k and E which characterize the electron states in a periodic solid, has been used to study the electronic structure of the alloy Hg1−xCdxTe for x=1.0, 0.31, 0.23, and 0.0. Data were collected mainly for emission along the normal to the cleaved (110) face of these crystals as a function of photon energy with various directions of polarization. The structure observed in the spectra of the alloy are similar in dispersion and polarization dependence to that obtained for CdTe. Preliminary analysis of the observed features using a free electron final state reveals the bulk origin of the measured transitions by comparison to calculated valence bands and elucidates aspects of the composition dependence of the valence band states involved in the optical excitation.
Field emission from band gap states
Authors: Kolář M. , Davison S. G.
Published: July 2002

The field-emission tunneling current from the region of the energy gaps is calculated in a way analogous to the 1-electron treatment of the band states. The method adopted does not require that a surface state exists before the external electric field is applied to obtain a nonzero tunneling current from the gap. Nevertheless, the numerical results obtained for the Kronig–Penney crystal suggest that, in the case of weak fields, the tunneling current is significant only in the vicinity of the region where such a surface state exists.
Microscopic control of semiconductor surface oxidation
Authors: Franciosi A. , Chang Shu , Philip P. , Caprile C. , Joyce J.
Published: July 2002

We examined the effect of ultrathin (0.1–10 Å) chromium overlayers on the reactivity with oxygen of Si(111) and GaAs(110) cleavage surfaces. Synchrotron radiation photoemission shows that for Cr coverages below a critical threshold coverage the overlayer does not affect substantially the oxygen adsorption rate. For chromium coverage above threshold the overlayer sharply enhances the oxygen adsorption kinetics so that most semiconductor atoms in the surface and near surface region appear oxidized at activated oxygen exposures as low as 100 L. The critical threshold coverage corresponds to the onset of reactive interdiffusion at the Si(111)–Cr and GaAs(110)–Cr interfaces. Therefore we suggest that ultrathin Si–Cr and As–Cr reacted phases created at the surface act as activation layers for semiconductor oxidation.
An ultrahigh vacuum reaction chamber/transfer mechanism attached to an Auger electron spectrometer for the study of the reactions of clean lithium surfaces
Authors: Nebesny Kenneth W. , Armstrong N. R.
Published: July 2002

An ultrahigh vacuum reaction chamber/transfer system is described which is used for the production of clean lithium and other soft group I metals. The system is used to study the reactions of clean lithium surfaces with small molecules of interest in electrochemical applications. Auger electron spectroscopy, in a spectrometer coupled to this chamber, shows that the product of the reaction of SO2 with the clean Li surface is a combination of Li2S and Li2O in a 1 : 2 ratio. The transfer system/reaction chamber also allows for the study of the rates of reaction of small molecules with the clean surface. Mechanical scraping of the metal transforms the passive surface into the active, clean state. Study of the SO2/Li reactions at a variety of temperatures (made possible by the special temperature control in the reaction chamber) shows a low activation energy for the dissociation reaction (2–5 kcal/mol).
Broad-beam electron source
Authors: Kaufman Harold R. , Robinson Raymond S.
Published: July 2002

A new type of broad-beam electron source has been developed. The use of a plasma as the source of electrons permits balanced operation of multiple-aperture electron optics. As a result, far higher total beam currents are obtainable with this source than are possible using single-aperture electron extraction. At the same time, the required working gas flow is low enough to permit operation in a high-vacuum environment. The electron beam energy is controllable over a range from below 100 eV to at least 1000 eV. This unique combination of performance characteristics for a broad-beam electron source should result in its use in a wide variety of applications.
Reactive sputtering of copper and silicon near the sputtering threshold
Authors: Mayer T. M. , Harper J. M. E. , Cuomo J. J.
Published: July 2002

We have investigated reactive sputtering of copper and silicon by oxygen in the ion energy regime near the sputtering threshold, using low-energy ion-beam and quartz-crystal microbalance techniques. Surface oxidation is observed to increase the ion energy threshold for copper sputtering, and oxide film growth by low-energy ion bombardment of copper and silicon is characterized. It is demonstrated that oxidation of copper is primarily by oxygen ion bombardment, while silicon exhibits greater reactivity to neutral oxygen molecules. Copper oxide layers as much as 150 Å thick can be formed at ion energy below the copper sputter threshold at room temperature. No evidence for selective formation of CuO or Cu2O was observed over the range of conditions investigated.
Cone formation as a result of whisker growth on ion bombarded metal surfaces
Authors: Wehner G. K.
Published: July 2002

We were able to show experimentally that the seed metals which can cause cone development on ion bombarded metal targets need not to have a lower sputtering yield as widely believed but rather a higher melting point. By lowering the bombarding ion energy to near sputtering threshold values (<100 eV) one observes the growth of genuine single crystal whiskers which point in all directions not related to the direction of ion incidence. We are now convinced that (intentional or unintentional) seed cones are the result of an interplay among whisker growth, surface movement of atoms, and the effects of sputtering.
Highly selective argon–oxygen ion beam etching process for Pb alloys
Authors: Moore D. F. , Dietrich H. P. , Kleinsasser A. W. , Harper J. M. E.
Published: July 2002

We report an ion-beam subtractive etch process for patterning the Pb-alloy counter electrode of superconducting Josephson tunnel junction devices. There is no resist on the wafer during the critical steps of cleaning and oxidizing the Nb base electrode to form the tunnel barrier, in contrast to the usual case of lift-off patterning. To remove the undesired PbAuIn, we use a 500-eV argon beam with 5%–10% oxygen, which etches Pb alloy about ten times faster than the underlying SiO and Nb. In contrast, a pure argon beam gives a selectivity of only ∼2 against SiO. The added oxygen enhances the selectivity for etching PbAuIn by decreasing the etch rate of materials which are more readily oxidized.
Physics and chemistry of beryllium
Authors: Stonehouse A. James
Published: July 2002

The combination of properties of beryllium which results in this very low Z element being a candidate for use in fusion reactors is reviewed. The occurrence, availability, and processing of beryllium from both bertrandite (domestic) and beryl (imported) ores are described. The available beryllium grades are characterized. The purity level of these grades, which are all unalloyed in the usual sense, is presented in detail. The crystallographic factors which establish the physical and mechanical characteristics are reviewed. Powder metallurgy techniques are used almost exclusively to provide beryllium with modest ductility at room temperature (e.g., 3% tensile elongation) and excellent strain capacity at elevated temperature (>40% tensile elongation at 400 °C). The metallurgical behavior of the powder metallurgy product is summarized. The physical properties of this low density metal (1.85 g/cm3) are reviewed with emphasis on the favorable thermal properties. Mechanical properties at room and elevated temperature are presented. The solubility and reactivity of hydrogen with beryllium are both nil while it is an extremely good ‘‘getter’’ for small amounts of oxygen. The combination of beryllium characteristics which has led to the proposed use of beryllium in tokamak reactors as limiter surfaces and in fusion breeders as a neutron multiplying shield are reviewed.