bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorption of oxygen on the Si(110)5×1 surface via interaction with O2
Authors: Keim Enrico G. , van Silfhout Arend , Wolterbeek Lambert
Published: July 2002

Auger electron spectroscopy, low-energy electron diffraction, and differential reflectometry in the photon energy range 1.5–4.5 eV have been used to study the room-temperature adsorption of O2 on the Si(110) surface with an initial 5×1 superstructure. The reaction kinetics are complicated. Five adsorption stages can be discerned, the first stage (0–2 L) being remarkably fast with an initial sticking probability near unity. Our results suggest that the surface sites which constitute the higher-order reconstructions and possibly also defects, are highly reactive. In the second stage (2–200 L) the O2 adsorption can be described by a dissociative process on the first-layer Si atoms, the sticking probability being about 2×10−3. Incorporation of oxygen into the subsurface Si lattice and possibly also adsorption of a molecular oxygen species are the main processes of the third stage (200–1000 L). In the fourth stage (103–4×104 L) O2 adsorption completely removes the dangling bonds. This occurs at 0.79±0.15 monolayer oxygen coverage. The number of dangling bonds per 5×1 unit cell (ten atoms) is thus eight or less. The fifth stage (>4×104 L) comprises a slow further oxygen adsorption with a sticking probability of ∼10−6: oxygen mainly goes into a bridging position between two first-layer Si atoms in the uppermost chains of the ideal (110) surface. The optical spectrum indicates that the clean Si(110) surface probably has several types of (dangling bond) surface states.
Vacuum annealing studies of thin TiC layers on steels
Authors: Wendler B. , Jakubowski K.
Published: July 2002

Single-phase δ-TiC and two-phase (α-Ti and δ-TiC) layers deposited by activated reactive evaporation and biased activated reactive evaporation methods have been exposed to 1-h vacuum annealing in the temperature range 700–1400 K. The effects of that annealing on the chemical composition, morphology, microstructure, lattice parameter of the δ-TiC phase, and mechanical characteristics (microhardness and adhesion) have been investigated. Three ranges of the annealing temperatures have been ascertained in which particular changes of the above characteristics are occurring, viz., 700–900, 900–1100, and 1100–1400 K. Apart from these results, which could have been expected on the basis of the recovery, recrystallization, and grain-coarsening processes, the crucial effects of the diffusion of C atoms from the steel substrate to the deposit have also been ascertained.
The decomposition of alkyl silanes (SiMenH4−n, 0≤n≤4) on Ni(100)
Authors: Dubois L. H. , Zegarski B. R.
Published: July 2002

While the adsorption of hydrocarbons on a wide variety of transition metals is a well-studied area of surface science, very little is known about the reactions of alkyl silanes on these same surfaces. In the present study we use primarily temperature programmed desorption and Auger electron spectroscopy to follow the low-temperature adsorption and subsequent decomposition of a complete series of alkyl substituted silanes of the formula SiMenH4−n (0≤n≤4) as well as Si2Me6. The effects of increasing methyl substitution are dramatic: for n≤3 substantial decomposition is observed while for both tetramethylsilane and hexamethyldisilane desorption is predominantly molecular. The extent of decomposition and the maximum desorption temperature of the resulting fragments are strongly determined by the concentration of steps and/or other defects on the surface as well as the presence of carbon and silicon impurities.
Alkali adsorption and its effect on hydrogen saturated Si(111) surface
Authors: Avci R. , Dabbousi O. B. , Al-Harthi A. S.
Published: July 2002

The coverage-dependent effects of alkali additives on hydrogenated Si(111)-7×7 surface are monitored using high-resolution electron energy-loss spectroscopy. A ∼0.2-monolayer (ML) coverage of alkali causes a large broadening in the quasielastically scattered 4.8-eV electrons from the surface. No appreciable broadening is observed either at high alkali coverages (∼1 ML) or when the deposition of ∼0.2 ML of alkali is followed by hydrogen saturation. Quasielastic broadening is explained in terms of single-particle excitations of low-density conduction electrons. Within the first ML of alkali coverage the H–Si stretch loss energy decreases almost linearly with coverage by ∼20 meV. The increase in the width of the stretch loss peak is correlated with the inhomogeneous distribution of H–Si dipoles with respect to the surface layer, and the increase in the intensity of the stretch loss excitation is correlated with the formation of the image dipoles.
High-resolution electron energy-loss spectroscopy studies of hydrogen adsorption on the GaP(110) surface
Authors: Chen Yu , Frankel D. J. , Anderson J. R. , Lapeyre G. J.
Published: July 2002

High-resolution electron energy-loss spectroscopy studies of H chemisorption on cleaved GaP(110) are reported. The stretch modes for both the cation (Ga–H at 233 meV) and anion (P–H at 285 meV) are observed. Adsorption on the cleaved surface after light sputtering shows an enhancement of the anion stretch intensity. The GaP results are contrasted to those obtained earlier for GaAs and InP. In the InP case the cation–H stretch at 215 meV is observed but the anion–H line at 287 meV is weak. Sputtering produces a strong anion–H line. For the GaAs case, on the other hand, an anion line at 262 meV of about one-third the intensity of the 232-meV cation line is observed for both cleaved and sputtered surfaces. Such chemical trends for these III–V surfaces allow one to assess the differences in the dangling bond properties of their surfaces.
Surface oxidation of a Pt–20% CO alloy: An x-ray photoelectron spectroscopy and low-energy electron diffraction study on the [100] and [111] oriented single-crystal surfaces
Authors: Bardi Ugo , Beard B. C. , Ross P. N.
Published: July 2002

The interaction of oxygen with the surface of a Pt alloy containing ∼20 at. % of cobalt was studied by low-energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS). At this composition, cobalt was found to be randomly substituted in the Pt fcc lattice both in the bulk and at the surface. [111] and 100] oriented single-crystal surfaces as well as polycrystalline surfaces were studied. Dosing these surfaces with oxygen at room temperature at pressures lower than ∼1×10−5 Torr resulted in the formation of a chemisorbed oxygen layer. At temperatures over ∼700 K dosing with oxygen in the same range of pressures led to the formation of a sequence of ordered oxide overlayers. XPS and LEED data showed that the first layer to form was an epitaxial monolayer structurally equivalent to either the (111) or (100) plane of cobalt monoxide (CoO). Under conditions of controlled oxygen dosing, CoO islands of monatomic thickness nucleated and randomly decorated a nearly pure Pt surface. This surface-decoration structure was metastable over a narrow range of oxygen partial pressures and surface temperature. At higher temperatures and pressures, the oxide islands first coalesced, forming a compact monolayer that completely blocked the surface for chemisorption, then changed in stoichiometry and structure to form a structural precursor to Co3 O4.
Helium-ion-induced release of hydrogen from graphite
Authors: Langley R. A.
Published: July 2002

The ion-induced release of hydrogen from AXF-5Q graphite was studied for 350-eV helium ions. The hydrogen was implanted into the graphite with a low energy (∼200 eV) and to a high fluence. This achieved a thin (∼10-nm), saturated near-surface region. The release of hydrogen was measured as a function of helium fluence. A model that includes ion-induced detrapping, retrapping, and surface recombination was used to analyze the experimental data. A value of (1.65 ±0.2)×10−16 cm2 was obtained for the detrapping cross section, and a value of (0.5–4)×10−14 cm4 /s was obtained for the recombination coefficient.
Analysis of self-regenerating coatings for pulsed-mode fusion plasma operation
Authors: DeWald A. B. , Krauss A. R. , Lam N. Q.
Published: July 2002

One promising approach to the fusion plasma impurity and material erosion associated with surfaces subject to high heat/particle fluxes has been the development of strongly segregating alloy systems capable of producing self-sustaining low-Z coatings. Previous plasma-material analyses of self-regenerating alkali-metal-bearing alloys such as Cu–Li and Al–Li and proposed ternary refractory composites have focused on the steady-state regime of advanced engineering tokamak designs without addressing adequately the pulsed-mode operation of present and planned near-term magnetic confinement devices. The survivability of ‘‘regenerative’’ coatings is coupled directly to thermal and radiation diffusion/segregation defect fluxes induced in the material by the plasma pulse. The lithium solute transport in Al–Li and Cu–Li alloys has been modeled as a function of the operational cycle, plasma-edge temperature, lithium secondary-ion fraction, and alloy composition. The pulse duration has been varied in order to investigate related transient effects upon the buildup and decay of the alkali-metal segregation and diffusion. Pulse widths ranging from 25 ms to 2.5 s have been chosen to simulate magnetic confinement fusion devices.
The role of strain in Si(111)7×7 and related reconstructed surfaces
Authors: Robinson I. K.
Published: July 2002

X-ray diffraction measurements of the sputter-annealed Si(111) 7×7 surface have been made at the National Synchrotron Light Source, Brookhaven. Technical advances have improved the reliability of such data significantly. The 120 structure factor intensities agree with the widely accepted structural model of Takayanagi at the 4σ level, but can be made to show complete agreement if the atomic coordinates of this model are allowed to relax. In this way, 15 of the 17 possible two-dimensional positional coordinates in three layers have been determined to an accuracy of ∼0.02 Å. The displacement pattern can be simply interpreted as a superposition of strain fields around the adatoms, in the dimers, and within the triangular island regions. These new observations of strain are discussed in the light of theoretical calculations of the local strain fields around adatoms, observations of reconstructed states of surfaces prepared under external strain, and theoretical attempts to understand the origin of strain.
The ‘‘other side’’ of the Schottky barrier formation process: Si 3×3 overlayers on Al(111)
Authors: Chang Y. , Colavita E. , Tache N. , Margaritondo G.
Published: July 2002

We present a photoemission and electron diffraction study of Si overlayers on Al(111). The overlayers exhibit 3×3 electron diffraction patterns at submonolayer coverages, and become disordered at higher coverages. The core-level photoemission spectra indicate that the interface is sharp, like those obtained by depositing Al on Si. The interface position of the Fermi level, however, is different with respect to the case of Al on Si.
A quantitative characterization of tellurium suboxide thin films by x-ray photoelectron spectroscopy
Authors: Raychaudhuri Pranab K. , Reznik S.
Published: July 2002

An analytical technique for the quantitative analysis of oxygen and tellurium in tellurium suboxide optical recording media is proposed. This involves the use of x-ray photoelectron spectroscopy but avoids the customary semiquantitative approach. The bulk concentration of oxygen is determined from the relative abundance of various tellurium species beneath the surface, taking into account the reduction rate of oxide due to ion beam sputtering.
Heat transport in doubly contained uranium storage beds
Authors: Heics A. G. , Shmayda W. T. , Kherani N. P.
Published: July 2002

Uranium storage beds form part of tritium handling systems and as such are placed in gloveboxes. During typical operating scenarios, these beds can impose significant heat loads on components in their vicinity and on the box in general. Doubly contained beds are an effective method to reduce the delivered heat load. During operations which require intimate contact with ambient box conditions, the annulus can be backfilled with helium. In the designs described, the net heat transport can be increased fivefold from the primary vessel to the box atmosphere.
Lateral interactions in binary monolayer alloys
Authors: Markert K. , Dolle P. , Niemantsverdriet J. W. , Wandelt K.
Published: July 2002

Thermal desorption spectroscopy of Ag and Au has been employed to study the lateral interactions in monolayer and bilayer AgAu-alloy films on Ru(001). The variations of the Ag-peak shape and peak maximum temperature as a function of Au concentration are in agreement with the exothermicity of the Ag–Au bond and provide detailed insight in the distribution of both metals within the films (at desorption temperature).
Japanese programs and facilities for synchrotron radiation lithography and problems related to resists
Authors: Okada K.
Published: July 2002

According to the recent Japanese status of technology, this paper reviews the programs aimed at developing small synchrotron radiation (SR) rings applied for SR lithography as well as the facilities now in operation for studying SR lithography. Also, concerning problems related to resists, the effects of exposure atmosphere on negative resist crosslinking and the x-ray resist sensitivity deterioration in an atmospheric environment are reviewed. A compact test ring ‘‘NIJI-1,’’ 4 m in mean diameter, has been developed for studying low-energy injection subjects. A compact SR ring, based on a newly designed half-integer resonance injection method, is now being constructed. The machine, 3-m o.d., comprises a superconducting weak-focusing, single-body magnet. A SR facility design has been offered which consists of a superconducting linac and storage rings. Each storage ring, employing superconducting magnets and a superconducting cavity, has three superperiods in its lattice. The TELL-TERAS and the Photon Factory (PF) are now in operation for studying SR lithography. The vertical undulating beam orbits around the whole horizontal ring orbit have been observed in TERAS. Private companies, such as NTT, Hitachi, NEC, and Fujitsu, are investigating SR lithography under competitive conditions, in the PF. Recently, NEC has constructed a highly reliable SR lithography beam line.
On the pressure distribution of a ring accelerator: A Green’s function approach
Authors: Kanazawa K.
Published: July 2002

A method of calculating a pressure distribution in a one-dimensional cyclic vacuum system is presented using Green’s function. The method is similar to one used in accelerator physics to investigate the motion of a particle in the guide field of a ring accelerator. The quantity which corresponds to the betatron function of an accelerator appears and it contains full information on the pumping characteristics of the system.
Automated x-ray photoelectron spectroscopy x-ray source motor drive for ion sputtering applications
Authors: Streber R. J. , Pian T. R. , Smullen D. A.
Published: July 2002

The x-ray source on a commercial x-ray photoelectron spectroscopy system has been retrofitted with an automated stepper motor drive. This device increases the x-ray flux to the sample during sputter depth profiling and reduces the data collection time by as much as a factor of  4. In this note we discuss the mechanical, electrical, and computer modifications necessary to implement the device.
Magnetic anisotropy of direct-current magnetron sputtered CoCr films
Authors: Li Z.-M. , Parsons R. R.
Published: July 2002

The magnetic anisotropy constant of dc magnetron sputtered CoCr films are investigated as a function of the sputtering power and the target-to-substrate distance. The results can be interpreted in terms of the dependence of adatom diffusion on the supttering parameters. The orientation of the easy (hard) axis of the uniaxial magnetic anisotropy is found to be tilted away from the film normal and varies with the orientation of the substrate with respect to the target.
Quantification of surface Li in 16.4% CuLi alloys by direct recoil and Auger analysis of element specific chemisorption complexes
Authors: Schmidt H. K. , Anderson L. R. , Schultz J. A. , Krauss A. , Biwer B. , Gruen D. M. , Shamir N. , Mintz M.
Published: July 2002

Methoxyl carbon and oxygen are shown to specifically add to the lithium fraction of a CuLi surface exposed to methanol. The lithium surface fraction is determined by direct recoil spectroscopic (DRS) measurement of the H, C, and O added to the surface by methanol exposure and by subsequent comparison to the amounts of C, O, and metal determined by Auger electron spectroscopy (AES) or x-ray photoelectron spectroscopy (XPS). Direct determination of surface Li by AES or XPS is complicated by relatively large sampling depths (5 or 20 Å). The indirect determination of surface Li by methanol chemisorption/AES has been used to calibrate the sensitivity of 5-keV K+ DRS for lithium.
Modeling of impurity release rates during wall conditioning of a vacuum vessel by electric discharge
Authors: Dimoff K. , Boucher C. , Parbhakar K. J. , Vijh A. K.
Published: July 2002

An analytic expression is derived for the time behavior of impurity levels measured by residual gas analyzer during the conditioning of a vacuum vessel wall by an electric discharge in molecular hydrogen at low pressure. Physical pumping and diffusive outgassing of impurity-related molecules from within the vessel wall suffice to give a time dependence which follows the measurement process more precisely than the phenomenologically deduced t−δ law, where 0.7≤δ≤2.
Correlation of interface chemistry and growth mode of Ce on polyimide (pyromellitic dianhydride–oxydianiline)
Authors: Clabes J. G.
Published: July 2002

Interface properties such as chemical bonding and structure play an important role in adhesion of metals in polymers. Ce, a highly reactive metal, was chosen for these experiments in order to promote enhanced chemistry at the interface to polyimide [pyromellitic dianhydride–oxydianiline (PMDA–ODA)] and to distinguish anticipated reaction products on the basis of their valency. We have studied the progression of interface formation upon metal deposition over a wide coverage range, in situ, by high-resolution x-ray photoelectron spectroscopy, monitoring the polyimide- and Ce-related core levels and changes in the valence-band regime. The interaction is completely dominated by compound formation which differentiates this metal–polymer (MP) system from others studied thus far. The results suggest less selectivity towards the PMDA moiety, indicative of parallel reaction pathways. One can therefore conclude that charge transfer is not a necessary prerequisite of subsequent compound formation for this MP interface. The termination of this spontaneous reaction process at room temperature is evidenced by the peculiar nucleation of unreacted metal at surface defects and the growth of huge planar islands. No other MP system has exhibited such distinct behavior.
Wavelength-dependent studies of optical second-harmonic generation from Fe–18Cr–3Mo(110) in ultrahigh vacuum
Authors: Hamilton J. C. , Anderson R. J.
Published: July 2002

This paper describes second harmonic generation which is a promising surface diagnostic that will alloys surface studies under ambient pressure and studies of liquid−solid and solid−solid interfaces. The structure and composition of the interface can be determined by this method. This metho d is demonstrated for Fe−18Cr−3Mo (100) in ultrahigh vacuum. (AIP)
Hydrogen detection in hydrogenated amorphous silicon by ion-induced Auger spectroscopy
Authors: Hirata G. A. , Farías M. H. , Cota-Araiza L. , Galván D. H. , Asomoza R. , Vidal M. A. , Quintero R.
Published: July 2002

We present experimental results using ion-induced Auger spectroscopy on samples of hydrogenated amorphous silicon (a-Si:H) films. They show that there is a linear relationship between the amplitude ratio of the main characteristic peaks in the L2,3VV Auger transition of silicon and the hydrogen concentration in the a-Si:H film.
Differential optical reflection spectroscopy of thin TiSi2 films on Si(111)
Authors: Tanaka M. , Schmid P. E. , Piaggi A. , Lévy F.
Published: July 2002

The microstructures of thin TiSi2 films with nominal thicknesses of 2.4 to 10.8 nm on Si(111) substrates have been estimated in situ. The change of normal incidence optical reflectance was measured in the course of film formation. Surface roughness was monitored by diffuse light scattering. It is an important factor in the analysis of the optical properties. The reflectivity is calculated on the basis of a three-parameter model which accounts for both structural and compositional fluctuations. The values of the parameters agree with the results of electron microscopy studies on TiSi2 films of ∼100 nm. The method presented gives quantitative estimates of coverage, in contrast with Auger electron spectroscopy which suffers from an excessive surface sensitivity.
Highly porous and electrically insulating films deposited by reactive physical vapor deposition
Authors: Lang Walter
Published: July 2002

Highly porous metallic films can be deposited by a modified physical vapor deposition process. The deposition of those films is investigated for several metals. For application in infrared optics and sensors it is often necessary to deposit a highly porous and electrically insulating film. This type of film can be produced by reactive physical vapor deposition of aluminum in a low-pressure O2/Ar atmosphere.
A new design for the disk-type molecular pump
Authors: Tu J. Y. , Zhu Y. , Wang X. Z.
Published: July 2002

This new design of the disk-type molecular pump, in which the direction of momentum transferring to gas molecules by a rotating disk is identified with the pumping direction of the pump, is described in this paper. When a pump is constructed in a series of two stages, the pumping speed and maximum compression ratio of the present pump for dry air increases by 50% and 53%, respectively, as compared with the previous type.
Vacuum pumping for inertial-confinement-fusion reactors
Authors: Pitts John H. , Patton Howard G.
Published: July 2002

We describe a vacuum system for the HYLIFE and Cascade inertial-confinement-fusion reactor concepts that consists of an axial-flow compressor followed by mechanical booster pumps in series having a combined total of four stages. Vacuum components are placed outside the reactors and operate at a temperature of 300 K. Pumping speeds necessary to remove hydrogen isotopes and helium from the reactors were conservatively calculated to be a maximum of 24 to 36 m3/s at 1.3 Pa (10−2 Torr) when laser drivers are used and 310–620 m3/s at 0.13 Pa (10−3 Torr) when heavy-ion-beam drivers are used. Openings in the reactors, required for illumination of the fuel pellets and for establishing the flowing blankets inside the reactors, have large enough conductances for removal of the gases from inside the reactors. A fuel recovery system separates deuterium and tritium from hydrogen and helium. The former are recycled for use in manufacturing fuel pellets.
Vacuum vessel system design for the compact ignition tokamak
Authors: Reddan W.
Published: July 2002

The compact ignition tokamak (CIT) is envisioned to be the test bed for the study of self- sustained, or ignited, fusion plasmas. The design basis for CIT is a 11-T toroidal field, 12-MA plasma current and peak fusion power of 500 MW. A major portion of this project is the vacuum vessel system, which includes the vacuum chamber, the divertor, first wall, and the robotics systems necessary to maintain the in-vessel components. The vacuum chamber is 2.1 m major radius torus with a D-shaped cross section. For hydrogenic species the base pressure is 10−7 Torr, with a total pumping speed of 5000 ℓ/s. It is designed to withstand the forces resulting from plasma disruptions and be bakeable to approximately 350 °C. A swept divertor and fixed limiters are provided. Both are carbon based structures designed to accommodate heat fluxes as large as 40 MW/m2 during the 5 s pulse. Articulated booms and manipulators will be deployed for in-vessel maintenance tasks, such as first wall removal/replacement and leak checking. This paper summarizes the engineering considerations and design status. In addition, the unique organization of the project’s national design team, led by the Princeton Plasma Physics Laboratory, and the integration into this organization of the industrial consortium responsible for the design and fabrication of the vacuum vessel system is described.
Cryosorption of helium on argon frost in Tokamak Fusion Test Reactor neutral beamlines
Authors: Kamperschroer J. H. , Cropper M. B. , Dylla H. F. , Garzotto V. , Dudek L. E. , Grisham L. R. , Martin G. D. , O’Connor T. E. , Stevenson T. N. , von Halle A. , Williams M. D. , Kim J.
Published: July 2002

Helium pumping on argon frost has been investigated on Tokamak Fusion Test Reactor (TFTR) neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are ∼25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, >20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a twofold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 Torr ℓ of helium, the beamline base pressure rose to 2×10−5 Torr from an initial value of 10−8 Torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 Torr ℓ of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity.
An Auger electron spectroscopy study of the oxidation and mechanical degradation of Ta thin film protective overlayers at microelectronic solid/liquid interfaces
Authors: Goho S. Matts
Published: July 2002

Auger electron spectroscopy (AES), a laser deflection technique and scanning electron microscopy (SEM) have been utilized to characterize cavitation damage in Ta thin films. The damage is incurred during vapor bubble collapse adjacent to these film surfaces when submerged in heated inks during microelectronic printer operation. Sample surfaces subjected to continued bubble collapse are monitored with an in situ laser deflection technique and examined with small-spot AES and SEM to monitor sample wear. The use of Ta2O5/Ta as a reference standard in AES analysis is widespread and has enabled the determination of sensitivity factors for the Ta peaks occurring in the 170–185 eV region and the oxygen triplet centered near 500 eV for either Ta or Ta2O5 matrices. This was achieved by noting the relative ratio of the Ta N5N6,7N6,7 and N4N6,7N6,7 transition intensities. Surface roughness was considered for its effect on altering Auger electron emission from the embrittled regions. Two distinct regimes of surface attack are observed; first, an embrittlement of the Ta surface exposed to the maximum bubble collapse pressure, followed by localized pitting. These embrittled regions contain higher levels of oxygen than nonfatigued areas along the same sample surface, with grain boundaries acting as nucleation sites for the observed oxidation and subsequent failure. It is clear that an understanding of such unique thin film behavior offers insights into the chemical, electrical and mechanical character of solid/liquid interfaces.
Surface composition of dilute Cu–Ag alloys: A comparison between experiment and Monte Carlo modeling
Authors: Hoffmann M. A. , Wynblatt P.
Published: July 2002

The equilibrium surface compositions of Cu-0.83 atomic percent (a/o) Ag and Cu-0.61 a/o Ag have been determined by Auger electron spectroscopy over the temperature range 450–600 °C. These alloys show strong segregation of silver to the surface. Surface compositions have also been obtained by Monte Carlo simulations, performed in conjunction with an embedded atom method description of interatomic interactions. The results of the simulations have been interpolated by means of an analytical expression based on the regular solution approximation. Comparisons of the simulated surface compositions with experiment indicate reasonable quantitative agreement between calculated and measured surface compositions, but the temperature dependence of the computed surface composition is weaker than that observed experimentally. Possible reasons for the discrepancies are discussed.
Outgassing characteristics and composition analysis of aluminum alloy extrudate under electron beam irradiation
Authors: Konno Osamu , Ohi Tsutomu
Published: July 2002

Outgassing characteristics and a combined surface analysis of two kinds of aluminum alloy extrudate produced in both a dry nitrogen shrouding and in air have been examined to investigate their suitability for a beam duct of an electron linear accelerator. Under conditions closely simulating the environment in the accelerator, the outgassing rate and partial pressure have been measured. Auger electron spectroscopy and secondary ion mass spectroscopy have been used to examine the surface composition and depth profile. The maximum outgassing rates per current during 55 μA irradiation were 9.1×10−8 and 1×10−8 (Torr ℓ/s cm2)/μA for the aluminum alloy extrudates produced in air and nitrogen shrouding processes, respectively. There were significant differences in partial pressure of H2, H2O, CO, and CO2 for the two extrudates, which were found to depend on the thickness of the oxide layer on the surface and the surface composition. The Auger and secondary-ion depth profile analysis revealed that after irradiation, the oxide layers on the surfaces were thicker than before irradiation by 15.5 and 40 Å for samples extruded in nitrogen and air, respectively. It seems that the observed changes in surface composition result not only from heating effects but also directly from interactions of the electrons in the alloy.
Effect of sputtered Co–Mo–Zr amorphous underlayer on the c-axis dispersion of sputtered Co–Cr films
Authors: Suzuki Hiroyuki , Tsumita Norikazu , Uesaka Yasutaro
Published: July 2002

Crystallographic orientations of Co–Cr films on Co–Mo–Zr amorphous underlayers, the morphology and the surface state of the Co–Mo–Zr film were investigated. The morphology of Co–Mo–Zr film depends on the substrate temperature and sputtering modes for deposition. When the effective substrate temperature is higher than a critical temperature (225 °C), the surface is smooth and columnar structure disappears, and the c-axis dispersion (Δθ50) of Co–Cr film on this underlayer becomes small. Flat surface of Co–Mo–Zr film is one of the essential conditions for small c-axis dispersion of Co–Cr film. Effects of surface contamination are also examined. Carbon is effective to lower the surface energy and to improve the c-axis orientation of Co–Cr film.
Cooling reservoir for horizontal manipulator
Authors: Fowler G. L.
Published: July 2002

A new reservoir design makes it possible to retain liquid nitrogen in a horizontal manipulator without sacrificing any movements of an x–y–z, rotational manipulator. The entanglement of leads and nitrogen tubes encountered in conventional cooling designs is eliminated. A fixture was also developed to insure proper axial alignment when installing the reservoir.
High fidelity in Auger spectroscopy: Dependence on experimental parameters
Authors: Saijo Hiroshi , Konda Yuji , Shiojiri Makoto
Published: July 2002

Experimental conditions for high fidelity electron spectroscopy are discussed when digitized sweep generator is used to drive spectrometer with lock-in signal detection and computerized data acquisition/processing. Spectral quality were evaluated in terms of signal to noise ratio (S/N ratio) and full width at the half-maximum (FWHM) in N(E) mode or energy separation of peak maxima in differential mode. Optimums of following terms were discussed from points of noise reduction ability and due time for measurement: (1) nature of noise signal; (2) sweep mode and repeat times of measurement; (3) parameters of the lock-in amplifier and scanning speed; (4) numerical treatment on spectral data.
Nuclear relaxation of deuterium–tritium adsorbed onto silica aerogel
Authors: Souers P. C. , Fearon E. M. , Sater J. D. , Mapoles E. R. , Gaines J. R. , Fedders P. A.
Published: July 2002

The longitudinal nuclear relaxation times of tritons in equilibrium deuterium–tritium (eD–T, actually D2–DT–T2 ) adsorbed onto amorphous silica aerogel has been measured from 4.2 to 23 K from 0.5 to 6.2 monolayers of coverage. Below 7 K, the relaxation time dramatically increases with decreasing temperature, especially for low coverages. A value of 16 s for 0.5 monolayer at 4.2 K may be compared with the usual electric quadrupole–quadrupole (EQQ) determined relaxation time of 0.1 s. It is shown that absorption of 10% of the tritium beta particle energy occurs in aerogel fully loaded with D–T. This decreases the concentration of J=1 T2 and increases the nuclear relaxation time. Similar energy absorption calculations in the thin layers shows that long relaxation times are expected, and that the measured values must be caused by spin–lattice relaxation with the aerogel surface. Both (temperature)−7 and exponential mechanisms are considered with no final decision being possible. Electric field gradients from the aerogel walls are considered the likely relaxation mechanism. These findings suggest that a long triton relaxation time may be achievable in ultrapure DT in the silica aerogel. Such a result would be of considerable importance to nuclear polarized inertial confinement fusion targets.
Determination of the carrier concentration of doped ZnSe from infrared measurements
Authors: Deneuville A. , Tanner D. B. , Park R. M. , Holloway P. H.
Published: July 2002

Determination of the carrier concentration of n-type ZnSe/GaAs heteroepitaxial films from absorption measurements is reported over the wave number range 30<W<600 cm−1. Transmission and reflection curves are very sensitive to the doping level, n above 3×1016 and 3×1017 cm−3 levels, respectively. Absorption coefficients, αf are derived from the transmitted intensities and vary between 500 and 14400 cm−1 in this wave number range. Around W=100 cm−1, αf varies as n1/2. This allows the determination of n from αf. The αf variations versus wave number and doping are compared to available models for various absorption processes.
Au interfaces with epitaxially grown CdTe(111): Chemistry and barrier heights
Authors: Vitomirov I. M. , Chang S. , Brillson L. J. , Rioux D. F. , Sivananthan S. , Faurie J. P.
Published: July 2002

We have used high-resolution soft x-ray photoemission spectroscopy (SXPS) to study chemistry, atomic distributions, and Fermi level (EF) movement caused by Au deposition on molecular beam epitaxy (MBE) -grown CdTe(111)-B surfaces. Using etch-and-anneal cycles, we produce clean surfaces with characteristic valence-band and core-level photoemission spectra. Au atoms disrupt substrate bonds releasing both Cd and Te atoms into the overlayer. Anions segregate preferentially to the free surface, while cations are more interspersed in the Au matrix. These first SXPS studies of CdTe(111) surfaces indicate that the atom-induced disruption is comparable or less than that for cleaved (110) substrates. After correcting for photovoltaic effects, we obtain an equilibrium Fermi-level position 0.55 eV above the valence-band maximum (Ev), intermediate between stabilization positions for Au on (i) cleaved, bulk-grown CdTe(110) (Ev+0.8 to 1.1 eV), and (ii) cleaved, bulk-grown CdTe(110) with a Yb interlayer (Ev+0.45 eV). Despite clear evidence for interfacial diffusion, EF for MBE-grown CdTe(111) lies closer to the position expected on the basis of work function difference than does EF for bulk-grown CdTe(110). These results indicate that the structural and electronic quality of the CdTe crystal plays a major role in the Schottky barrier formation.
Surface modification of steel sheets using dry process
Authors: Hyodo T. , Kagechika H. , Kibe H. , Yasue Y. , Okude N.
Published: July 2002

Using an arc-discharge ion plating, effects of pretreatments and plating conditions on performances of deposited films are investigated. Both preheating and argon ion bombardment were essential pretreatments before ion plating in order to improve adhesion and formability of ion-plated chromium films, because these pretreatments attribute to the sputter cleaning effect on the surface of the steels and the formation of the mixing zone of the deposited film and the substrate. Epitaxially grown platelike grains, which appeared in the ion-plated films pretreated by preheating and argon ion bombardment, were effective in improving the formability by coarsening their grains. Much greater formability of the chromium films and the titanium films was achieved compared to vacuum deposition. This is because ion-plated films initially grew uniformly on the substrates and the grain sizes were coarsened with the minus bias voltage increased. This resulted in the reduction of the grain boundaries, which could be the initiation sites and the propagation paths of the cracks. In addition, the low hardness of the ion-plated films resulted in the easy deformation and hence excellent formability.
Comparison of ion-bombardment removal rates of sputter-deposited niobium during deposition and after deposition
Authors: Merz M. D. , McClanahan E. D.
Published: July 2002

Studies of 50–200 eV Kr+ ion removal rates of niobium with a triode discharge system were conducted. A comparison was made of the removal rates of sputter-deposited material removed during high-rate sputter deposition and during ion bombardment after deposition. The removal rate of wrought niobium was also measured under similar plasma conditions for comparison. The results indicated that the removal rates were not affected by conditions of deposition and depended only on the energy of bombarding Kr+ ions, and were nearly the same for sputter deposited and wrought niobium. The results are discussed in terms of the neutral Kr atoms reflected from the target, Kr+ ions incident on the niobium substrates, and crystallographic texture of the niobium being bombarded.
Structural investigation of Rb adsorption on Al(111) using normal incidence standing x-ray wavefield absorption triangulation
Authors: Kerkar M. , Fisher D. , Woodruff D. P. , Jones Robert G. , Diehl R. D. , McConville C. F. , Cowie B.
Published: July 2002

The adsorption site, and adsorbate-substrate bondlength, has been investigated for the adsorption system Al(111)/Rb, using normal incidence standing x-ray wavefield absorption (NISXW), over a range of coverages from 0.12 to 0.33 ML including the ordered (2×2) and (√3×√3)R30° phases. By measuring both (111) and (1̄11) Bragg reflections in NISXW we obtain Rb–Al layer spacings in two real space directions and can therefore fully determine the adsorption structure by triangulation. For all phases we find adsorption in the atop sites, with a coverage-independent bondlength corresponding to an effective radius for the adsorbed Rb of 1.70±0.10 Å, significantly closer to the ionic (1.48 Å) than the metallic (2.43 Å) value. The NISXW results also show that the adsorbed Rb atoms have large vibrational amplitudes parallel to the surface which may be associated with the atop site adsorption.
Carbon–carbon bond forming reactions on Cu(110) surfaces
Authors: Chiang C.-M. , Wentzlaff T. H. , Jenks C. J. , Bent B. E.
Published: July 2002

The coupling of one-carbon (C1) fragments to form carbon–carbon bonds has been studied on a Cu(110) surface. In these studies, methyl (CH3) and methylene (CH2) groups have been generated on Cu(110) by the dissociative adsorption of CH3I and CH2I2, respectively. Formation of CH3(a) below 200 K on this surface is inferred from the lack of molecular desorption as well as the lack of recombinative hydrogen desorption in temperature-programmed reaction (TPR) experiments. Similar low temperature C–I bond dissociation in CH2I2 to form CH2(a) is implicated based on the evolution of ethylene at 300 K in TPR studies. By studying the reactions of CD3(a) and CH2(a) coadsorbed and adsorbed separately on Cu(110), three C–C bond forming reactions have been identified: methyl coupling above 400 K to form ethane, methylene coupling at ∼300 K to form ethylene, and methyl/methylene coupling (methylene insertion) at 300–350 K to produce ethyl groups. To our knowledge, this is the first time that methylene insertion, a potentially important chain growth step in hydrocarbon syntheses, has been definitively established on metal surfaces.
Method for recoating phosphor on commercial low-energy electron diffraction optics
Authors: Flynn-Sanders D. K. , Chang S.-L. , Thiel P. A. , Imbihl R.
Published: July 2002

We describe a method for applying a new coat of phosphor to a commercial low-energy electron diffraction screen. The method is based on sedimentation of a phosphor suspension onto the screen.
High pressure magnetron sputter gun
Authors: Ling S. H. , Wong H. K.
Published: July 2002

A commercial planar magnetron sputter gun was modified for operation in argon or oxygen at pressure up to 2 Torr. This high pressure gun may be useful for uniform deposition of high Tc superconductor thin films and synthesis of nanocrystalline materials.
Diamond synthesis by sputtering
Authors: Matsuoka Morito , Hoshino Koichi , Ono Ken’ichi
Published: July 2002

Almost single-phase diamond films with sp3 bonds are synthesized on Si at temperatures as low as 600 °C by a triode-assisted sputtering system with an electric mirror. The growth rate varies between 1 and 10 nm/min. The rate depends on the deposition parameters, including substrate temperature, gas pressure, He gas fraction. The diamond is found to nucleate on a double-layered interlayer formed on the Si surface, consisting of a 3–7 nm thick granular W layer condensed on a 3–15 nm amorphous SiC layer. The structure of this interlayer arises from the preferential diffusion of C atoms into the Si substrate. The density of diamond nucleation reaches 109–1010 cm−2. This density does not depend on the pretreatment of the substrate surface. The preferential crystallite orientation occurs along the 〈111〉 or 〈110〉 directions, and is well controlled by the He fraction during sputtering.
Particle contamination in low pressure organometallic chemical vapor deposition reactors: Methods of particle detection and causes of particle formation using a liquid alane (AlH3) precursor
Authors: Simmonds Michael G. , Gladfelter Wayne L. , Li Haojiang , McMurry Peter H.
Published: July 2002

Two methods of analyzing particles were interfaced to a low pressure chemical vapor deposition reactor used to deposit Al films from the liquid precursor dimethylethylamine alane. A laser light scattering particle counter was used to monitor particles (≳200 nm) in real time and established that the appearance of particles corresponded to the flow of precursor into the reactor. A particle impaction system was used to collect particles (≳20 nm) for analysis using analytical transmission electron microscopy and electron diffraction. Typical sizes of the Al particles were in the range 20–1000 nm. Purposely introducing trace amounts of H2O, CO, and O2 into the reactor during the flow of the precursor caused an increase in the number of particles. Our results suggested that Al particle formation was induced by impurities in the gas phase (particularly H2O) although competing mechanisms could not be ruled out.
Repair of a liquid metal ion emitter by a liquid metal ion emitter
Authors: Rüdenauer F. G. , Fehringer H. M. , Steiger W. , Sieber A.
Published: July 2002

Liquid metal ion source (LMIS) indium emitters which have been poisoned by contamination with backsputtered material were successfully repaired by sputtering off the contamination layer, using a focused indium ion beam from an indium LMIS. It is essential that the repair beam consists of In ions to prevent the emitters from getting poisoned by the repair process itself. Poisoned emitters have excessively high firing voltages, but usually normal operating voltages. Following repair, firing voltage and operating voltage differed by not more than 150 V. Repairs worked equally well if the indium film on the emitter to be repaired was cold or hot (molten). Repairs were performed on fully assembled emitter modules where the emitter tip was recessed behind a stack of beam forming electrodes. Repair times are of the order of 10–15 min.
Anisotropic effects in glass substrates heated in vacuum
Authors: Wu Qi hong , Hodgkinson Ian J.
Published: July 2002

In situ normal incidence transmission anisotropy is used to monitor changes in the polarization parameters Ψ and Δ induced by temperature gradients as substrates are heated and cooled in vacuum. Strategies for managing the polarization effects, so that they do not mask anisotropic effects in thin films, are discussed.
In situ deposition of YBa2Cu3O7−x superconducting thin film without high pressure oxygen during film cooling*
Authors: Song Wendong , Liu Daming , Jiao Shuliang , Lu Dongshen , An Chenwu , Lu Ling , Yang Huiqing , Li Zaiguang
Published: July 2002

YBa2Cu3O7−x thin films were deposited by excimer laser ablation with three different kinds of film-cooling processes. The films cooled under 300 Torr of oxygen pressure and 200 mTorr of oxygen pressure with dc discharge assistance were superconductive. The zero-resistance temperatures were 86.5 K and critical current densities in zero field at 77 K were more than 106 A/cm2, while the films cooled under 200 mTorr of oxygen pressure were semiconductive.
Corrosion behavior of sputtered amorphous magnetic thin films, with and without protective overlayers
Authors: Wallace John L.
Published: July 2002

Thin films of Fe78B13Si9, (similar in chemical composition to Metglas(R) 2605S2) and Fe81B13.5Si3.5C2 (similar to Metglas(R) 2605-SC) with a thickness of approximately 1 μm were deposited by dc magnetron sputtering onto substrates of Si, SiO2, and GaAs. Some of the films were overcoated with approximately 500 Å of Si3N4; others were overcoated with 300 Å of Cr; and others were left uncoated. The samples were exposed to various environments ranging from an air-conditioned laboratory to an outdoor, tropical marine ambient. The morphology, low-frequency magnetic properties, and chemical composition of the films were measured before and after exposure.
Outgassing characteristics and surface analysis of pure aluminum plates under electron beam irradiation
Authors: Ohi Tsutomu , Konno Osamu
Published: July 2002

In order to develop aluminum with suitable surface properties for use in beam lines and scattering chambers, where ultrahigh vacuum is required; tests were carried out on aluminum samples with two different surface preparations. For one sample (specimen N) the surface was milled with a diamond cutter while in an atmosphere of dry nitrogen; for the other (specimen EP), the surface was electropolished. The surface properties and the outgassing of each sample were studied, after the samples had been irradiated with a flux of 60 MeV electrons. The outgassing from specimen N was found to be the lower. The surface composition was studied using x-ray photoelectron spectroscopy, and indicated that the surface hydration of specimen N was lower than for specimen EP; this was true both before and after irradiation. It is shown that, before irradiation, both specimens had surface layers of a mixture of Al2O3(H2O) and Al2O33(H2O); after irradiation the surface of specimen N contained only Al2O3(H2O) while the surface of specimen EP contained a mixture of Al2O3(H2O) and Al2O33(H2O). Not only does the proportion of Al2O33(H2O) on the surface change after irradiation, but so does the thickness of the hydroxide layer. The dissociation of water from the hydroxide layer by the electron beam irradiation would appear to be a significant source of gas desorption. Thus the indications are that surface preparation as with specimen N (machining in dry nitrogen) is preferable if the aluminum is to be used in a high-vacuum situation.