bluuebunny/crossref_metadata_2025 huggingface dataset:
TMX plasma edge parameters: Passive solid-state probe measurements
Authors: Pontau A. E. , Bastasz R. , Wilson K. L. , Bauer W. , Wampler W. R. , Drake R. P. , Allen S. L.
Published: July 2002

Passive solid-state probes have been exposed at selected orientations and positions in the tandem mirror experiment (TMX). The energy of deuterium in the center cell incident on a grounded probe at a fixed radial position, r=30 cm, varied markedly with probe orientation. The deuterium energy measured on samples facing radially inward was kT=50±15 eV while along the axial direction it was ≊150 eV. The deuterium flux also varied with radial position of the probe in the center cell. The measured flux to a sample facing radially inward was 4×1017D/cm2 s at r=30 cm and decreased to 1.5×1017 D/cm2 s at r=40 cm. Oxygen, titanium, iron, and sometimes copper impurities were observed on the probes. Analysis of probes placed on the end wall indicated that, under certain operating conditions, a significant portion of the trapped neutral beam current was lost axially rather than radially. These measurements in TMX have added to the understanding of confinement properties of tandem mirrors.
Threshold electron excitation of Auger-electron and x-ray emissions in La
Authors: Chamberlain M. B. , Burr A. F. , Liefeld R. J.
Published: July 2002

The intensities of the M5O3 and M5N3 characteristic x-ray lines and the M5N4,5N4,5 Auger-electron line from La were measured as functions of the electron excitation energy near the M5 ionization energy. The excitation curve of each of these emissions contains a linelike structure a few eV above the threshold. The full width at half maximum (3.0±0.2 eV) and relative height (4×) of this structure are the same in these three excitation curves; however, they are different than the respective values (2.3±0.2 eV and 200×) we previously measured for a resonant bremsstrahlung emission observed when the electron excitation energy was near the M5 ionization energy. These results support our earlier proposal that two distinct states are excited for near threshold, electron excitation of the La M5 level: the 3d94f 0 state which decays via the M5 series characteristic x-ray and Auger-electron emissions, and the 3d 94f 2 intermediate bound state which appears to decay by only a single channel—the emission of a resonant x ray with a photon energy of 832±1 eV. These results may be evidence of a closed channel resonance in the electron scattering cross section in solid La, similar to resonances found in Ne gas.
Differences between positrons and electrons in elastic and inelastic processes at surfaces
Authors: Canter K. F. , Lynn K. G.
Published: July 2002

The elastic scattering of 30–300 eV positrons differs significantly from electrons, i.e., a lack of an exchange interaction and ion core repulsion, instead of attraction. Inelastic scattering also differs because there are no final scattering states for the positron which are excluded by the Pauli principle, thus resulting in a shorter positron elastic mean free path. The resulting advantages of LEPD over LEED will be discussed. When a positron is implanted and thermalizes in a solid, many possible fates occur which differs from electrons. The dominant processes for positrons occurring as a metallic surface are (i) localization in a surface state, (ii) direct reemission from the metal into the vacuum in those systems which exhibit a negative positron work function; during this reemission process the positrons can loose energy by exciting molecular vibrations, and (iii) reemission into the vacuum with an electron, thus forming positronium.
Hydrogen mixing effects on reactive ion etching of GaAs in chlorine containing gases
Authors: Semura Shigeru , Saitoh Hiroshi
Published: July 2002

Etching profile, surface morphology, and radiation damage are studied for GaAs reactive ion etching. The etching characteristics are greatly improved by H2 mixing with CCl4, Cl3F, and CCl2F2. Anisotropic profile and residue-free surfaces are obtained when H2 is mixed with these gases. Rutherford backscattering and x-ray photoelectron spectroscopies show that the surface etched in CCl4/H2 has damage extending several atomic layers from the surface and contains the etching species as the contaminant.
LEED and AES study of structural and chemisorptive properties of Zr overlayers on the Pt(100) crystal face
Authors: Bardi U. , Ross P. N. , Somorjai G. A.
Published: July 2002

Zirconium overlayers were deposited onto a Pt(100) surface by electron beam evaporation in UHV, and the composition and structure of the surface was determined by AES and LEED. The overlayers were highly reactive towards oxygen, carbon monoxide, and hydrocarbons, forming oxide or carbide overlayers. Several metastable ordered structures were observed by LEED when oxidized overlayers were thermally annealed in UHV. Protracted annealing at >900 K results in reduction and dissolution of the oxidized overlayer with complete disappearance of zirconium from the surface. Oxygen dosing of annealed surfaces at 25 °C caused resegregation of zirconium to the surface, and the formation of an ordered PtZrxOy surface phase which may be a zirconia analog to the yttria ternary oxide PtYO3.5. This phase was stable in oxygen at 25–300 °C, but oxygen dosing at above 300 °C resulted in precipitation of ZrO2 islands on top of the Pt(100)-(1×1) substrate.
A cascade diffusion pump system for an electron microscope
Authors: Yoshimura Nagamitsu , Hirano Haruo , Norioka Setsuo , Etoh Terukazu
Published: July 2002

Several DP systems have been discussed and evaluated with respect to dynamic evacuation under actual operating conditions of an electron microscope. As a result, a cascade DP system has been found to be the most reasonable for an electron microscope where the column is evacuated by the first DP backed by the second DP, and for the camera chamber by the second DP with a large volume foreline backed by a mechanical pump. A spectrum of the residual gases in an electron microscope with a cascade DP system indicates a very clean vacuum with hydrocarbon partial pressures of less than 3×10−7 Pa.
A design analysis of intelligent, articulated vacuum processing systems
Authors: Bonge N. J.
Published: July 2002

The current trend toward the use of computers and robotics in vacuum system design is providing practical solutions to increasingly difficult process applications. These systems require a great degree of flexibility for process development and often require high throughput capability. Economical development and reliable performance depends largely upon the proper integration of mechanisms and control devices. This paper focuses upon successfully proven design and programming techniques drawn from the development of fully automated batch and in-line sputtering systems. In the design analysis, complex processes are divided into a series of basic functions. Each requires a mechanism, sensing device, and hardware/software interface. Functions acting together to perform a specific portion of the process form a module. The module is designed as an independent unit and is controlled by a dedicated program subroutine. The main program accepts operator input and receives data from each module; it then performs necessary calculations, displays information, and controls overall system operation. This approach allows diverse processes to be created, varied, and expanded, resulting in a new generation of highly versatile vacuum systems.
An underground remotely controlled cryopump vacuum system utilizing 460-m long helium gas lines
Authors: Karpenko Victor P. , Beat Tom , Wong Ken , Sullenburger James , Kountainis Bill , Price Stephen
Published: July 2002

A 1600 l vacuum chamber buried 300 m underground required a continuous operational vacuum of <1×10−6 Torr. Due to physics criteria, high gas load (2×10−2 Torr l/s), space limitations, harsh operating environment and reliability requirements, a cryopump vacuum system was designed to meet all design and operational requirements. The vacuum system consisted of downhole and uphole subsystems linked by 460 m long pressurized copper helium gas lines and control cables. The uphole subsystem consisted of the helium compressors, automatic control, and monitoring system. The downhole system consisted of the vacuum pumps and all related supported hardware necessary for long unattended remote operation. The design, installation, and operational requirements are reviewed and summarized for this initial and unusual application of remotely operated cryopumps.
Laser target fabrication activities in the United Kingdom
Authors: Reichelt J. M. A.
Published: July 2002

Two main laser fabrication facilities exist in the United Kingdom (UK), one at AWRE and the other at the Central Laser Facility, Rutherford–Appleton Laboratory, which operates in support of a University research program. An overview of target microfabrication, characterization, and materials technology at these Laboratories are presented. Emulsion technology processes have been used to manufacture hollow polymer microspheres in a range of sizes. Large diameter spheres are used for individual targets and the smallest sizes are bulk packed to form a low density foam material. Polymeric foam materials are also made using the phase inversion method, plasma polymerization technique, and by a surface catalyst on compacted powder which is subsequently leached. Metal and polymer layer coatings for targets are carried out by thermal evaporation, sputtering, electroplating, plasma polymerization, and vapor phase pyrolysis techniques. Improved adhesion in multilayer foil targets is achieved by dynamic recoil mixing during the coating process. Ion beam milling and UV laser etching methods have been used to micromachine and structure targets. A range of optical, radiographic, and charged particle techniques are used to characterize targets. The use of laser generated x-ray backlighting for target material inspection is described.
Thickness uniformity measurements of plastic-coated glass shells by image analysis of x-ray radiographs
Authors: Alexander-True Susan M. , True Michael A.
Published: July 2002

Digitized x-ray radiographs of plastic-coated glass shells were analyzed for thickness uniformity. The glass shells were 2 μ thick with a radius of 100 μ and the plastic coating was 20 μ thick. Nearly circular contours of image intensity for the inner edge of the glass shell and the outer edge of the plastic coating were constructed. The difference between the contour radii (the thickness of the glass and plastic) was interpolated on an evenly spaced angular grid along the circumference. The thickness was Fourier analyzed with respect to the angle variable. Low angular frequency perturbations which characterize large scale thickness nonuniformity were observed.
Glass shell preparation
Authors: Belanger Raymond P. , Miller Wayne J.
Published: July 2002

Glass shells for inertial confinement fusion (ICF) targets are required over a large range of diameters and wall thicknesses. In order to efficiently fabricate these targets we have developed an empirical model based on the effects of 14 parameters on the properties of the resulting shells. With this model we can predict the optimum set of processing parameters to produce specific shell properties and characteristics.
MARS—Mirror Advanced Reactor Study
Authors: Logan B. G.
Published: July 2002

A recently completed 2-year study of a commercial tandem mirror reactor design [Mirror Advanced Reactor Study (MARS)] is briefly reviewed. The end plugs are designed for trapped particle stability, stability against MHD ballooning modes, balanced geodesic curvature, and small radial electric fields in the central cell. New technologies such as lithium-lead blankets, 24T hybrid coils, gridless direct converters, and plasma halo vacuum pumps are highlighted.
Time-resolved impurity fluxes in the TEXTOR plasma edge
Authors: Zuhr R. A. , Wampler W. R.
Published: July 2002

The internal configuration of the TEXTOR tokamak at Kernforschungsanlage (KFA) Jülich, Federal Republic of Germany, has been modified recently to include antennas for Ion Cyclotron Resonance Heating (ICRH) of the plasma. Passive deposition probe measurements of edge impurity fluxes were made for typical Ohmic discharges with this new liner configuration. The time-resolved behavior of impurities in the edge was determined as a function of radius and limiter position using rotating probe techniques. The dominant metallic impurities were found to be iron and the other components of stainless steel. Average deposited iron fluxes circulating along the field lines were found to be ∼1015/cm2 s at 5 cm behind the limiter radius. Radial profiles of the principal metallic impurities demonstrate a characteristic decrease with increasing radius outside the limiters and show an e-folding length of ∼1.9 cm. The limiting effects of the rf antenna are also evident in the radial profiles. Present results are compared with previous measurements of edge fluxes made prior to the modifications to the plasma-side liner of TEXTOR.
Plasma-edge studies using carbon resistance probes
Authors: Wampler W. R.
Published: July 2002

Characterization of erosion and hydrogen-recycling processes occurring at the edge of magnetically confined plasmas requires knowledge of the energy and flux of hydrogen isotopes incident on the materials. A new plasma-edge probe technique, the carbon resistance probe, has been developed to obtain this information. This technique utilizes the increase in electrical resistance caused in thin carbon films by energetic particle bombardment to characterize the flux and energy of the incident ions and neutrals. The method is relatively easy to implement and gives data in real time. Energy resolution of low dose exposures has been achieved using thin insulating films over the carbon. Calibrations using ion implantation show that the particle energies and fluxes which can be measured with resistance probes are well matched to those typically encountered near the wall in plasma devices. This paper describes the experimental technique and the model used to relate the measured resistance changes to the energy and flux of particles. Experiments are then described in which resistance probes were used to study energetic particles in the PLT and TEXTOR tokamaks and the TMX-U tandem mirror.
Thermal desorption spectroscopy of Xe at the Si(111) as a local probe for surface structures
Authors: Bartha J. W. , Barjenbruch U. , Henzler M.
Published: July 2002

The binding energy of noble gases depends on the arrangement of atoms close to the adatom. Due to the weak forces of physisorption a rearrangement of the substrate during adsorption is unlikely. Therefore, the desorption of noble gases reveals the local arrangement of surface atoms. It is demonstrated that the structures of the Si(111) surface produced by adsorption of gases or metal overlayers have besides the well-known long range order quite different desorption spectra which point to specific short range order or local atom arrangements.
High-resolution electron energy loss spectroscopy as a probe of surface morphology and electronic states at metal/semiconductor interfaces
Authors: Chambers S. A. , del Giudice M. , Ruckman M. W. , Anderson S. B. , Weaver J. H. , Lapeyre G. J.
Published: July 2002

The covering and consumption of sp3 hybridized Si atoms in reactions between a metal and Si(111) are monitored by the use of a chemical probe—atomic hydrogen. The surface vibrational spectrum of H on Cu/Si(111) has been measured at various stages of interface growth. The presence of Si atoms with dangling bonds results in covalent bonding with free H atoms, as seen in the Si–H stretching and bending modes in the HREELS spectrum. As Cu is deposited, the morphology of the surface layer can be deduced by observing the disappearance of Si–H vibrational excitations and correlating with Si 2p photoelectron line shape and attenuation behavior. The picture which emerges from this analysis is that Cu atoms form clusters from 0 to 3 Å and that at 3 Å the clusters disrupt the surface and trigger outdiffusion of Si. Atomic hydrogen also constitutes a powerful probe of surface electronic states. Previous Auger electron diffraction measurements on the annealed 1 ML Cu/Si(111) interface showed that the surface reconstructs to a planar arrangement with Cu atoms in the hollow sites, and suggested that strong overlap occurs between Cu 4s and Si 2p orbitals normal to the surface. This result is confirmed by the inertness of the interface to atomic hydrogen.
A theoretical and chemical view of surface chemistry: Chemisorption and reactions of acetylene
Authors: Silvestre Jérôme , Hoffmann Roald
Published: July 2002

The cluster–surface analogy suggests a similarity between discrete organometallic molecules and surfaces. But the detailed working out of the electronic changes that guide chemisorption and reactivity, here illustrated by acetylene on Pt(111), remains. The translation from delocalized band calculations to a localized chemical picture is made possible by decompositions of the densities of states of an extended surface—adsorbate slab and by the analysis of crystal orbital overlap population curves—scaled bond orders in the solid. The preference of the hydrocarbon for a specific surface site, the strength of its bonding, and its reactivity are determined by a balance of surface—acetylene bonding versus the loss of such bonding within the surface and/or within the organic adsorbate. Surface reconstruction and dissociative chemisorption are merely extremes of this delicate balance.
Cleanup and gettering during the Beryllium Limiter Experiment in Impurity Study Experiment-B
Authors: Clausing R. E. , Heatherly L. , von Seggern J. , Tschersich K. G. , Isler R. C. , Mioduszewski P. K. , Simpkins J. E. , Zuhr R. A.
Published: July 2002

Changes in plasma impurities and radiated power due to cleanup and gettering during the Beryllium Limiter Experiment are related to changes of the surface composition of the torus walls and residual gases in the torus. Pulse discharge cleaning was very effective in cleaning the ISX-B vacuum vessel after installation of the beryllium limiter. As a result of discharge cleaning, areas near the limiter were soon covered with a beryllium rich deposit containing some iron, nickel, chromium, and titanium as well as oxygen, carbon, sulfur, and nitrogen. Oxygen levels on the wall were reduced to below 10 at. %. Materials transport during discharge cleaning was apparently due to sputtered neutrals. Evaporation of beryllium from the limiter and subsequent deposition on the torus walls caused by high power tokamak shots produced gettering of the machine equal or better than that previously obtained with titanium or chromium. This gettering by beryllium eliminated the need for further discharge cleaning or other gettering. Beryllium transport in this case appears to be mostly as ions in the plasma edge.
Application of focused ion beam technology to maskless ion implantation in a molecular beam epitaxy grown GaAs or AlGaAs epitaxial layer for three-dimensional pattern doping crystal growth
Authors: Miyauchi Eizo , Hashimoto Hisao
Published: July 2002

We report on a new microfabrication process in UHV, implemented with a focused ion beam implanter (FIBI)–molecular beam epitaxy (MBE) crystal growth system with a computer controlled ion beam writing system. By using this combination process technology, GaAs/AlGaAs multilayer pattern doping structures are fabricated by iteration of growing a molecular beam epitaxy (MBE) GaAs or AlGaAs layer followed by implanting focused ion beams, arbitrarily choosing such impurity ions as Be ( p-type) or Si (n-type). This process technology is considered as a basis for integrating optical or electrical devices three dimensionally. An application of this technology to a new structure for an AlGaAs/GaAs DH laser is also described.
Thin film transducers and sensors
Authors: Anderson J. C.
Published: July 2002

The transducers discussed are those which make use of the unique features of thin films. These include metal and semiconductor film strain gauges and manganin high pressure gauges for use in lubricated bearings. Optical transducers include photoresistors, vidicon screens, solar cells, and IR detectors with special reference to the use of hydrogenated amorphous silicon. Chemical sensors are discussed in terms of surface states arising from chemisorption of a gas on the film surface. Examples of oxide film sensors for various gases are given. Magnetic transducers include semiconductor and amorphous metal Hall effect devices and magnetoresistive devices. References are given for each of the transducers discussed.
Extended energy-loss fine-structure study of carbon and oxygen on cobalt
Authors: Atrei A. , Bardi U. , Rovida G. , Torrini M. , Zanazzi E. , Maglietta M.
Published: July 2002

The structure of the monolayer phases which form upon carbon and oxygen chemisorption on the (112̄0) face of cobalt was studied using the extended energy-loss fine-structure technique for the K edges of the two adsorbates. The preliminary results obtained for the Co(112̄0)-1×1-O structure did not permit us to derive a reliable radial distribution function. In the case of the Co(112̄0)-2×5-C phase, a single strong maximum in the radial distribution curve attributable to the C–Co distance was obtained. The C–Co bond distance, calculated applying different methods based on the theoretical phase shifts, was found to be 1.75+0.05 Å. This result permitted us to reduce the number of the possible structural models for this surface which are in agreement with the low-energy electron diffraction data.
Reduction of oxidized Fe(110) by hydrogen
Authors: Vink T. J. , Sas S. J. M. , Gijzeman O. L. J. , Geus J. W.
Published: July 2002

The reduction of oxidized Fe (110) by hydrogen has been studied by ellipsometry, combined with Auger electron spectroscopy and low-energy electron diffraction (LEED). Oxide island formation occurs after partial reduction of oxidized Fe(110) by hydrogen, as was observed with LEED. At this stage the reaction rate becomes first order in the hydrogen pressure. When compared with the results obtained on Fe(100), it appeared that the reaction probability and the apparent activation energy of the reduction processes are of the same order of magnitude for both surfaces. However, a striking example of plane specific reaction behavior was observed, since the reduction on Fe(100) is incomplete, approximately one monolayer of oxygen remaining on the surface, whereas on Fe(110) the reaction proceeds quantitatively under similar reaction conditions.
Bond relaxation in Hg1−xCdxTe and related alloys
Authors: Hass K. C. , Vanderbilt David
Published: July 2002

The local structural properties of Hg1−xCdxTe, Hg1−xZnxTe, and Cd1−xZnxTe are examined using a self-consistent pseudopotential approach. An accurate description of the limiting crystals is obtained by adding empirical corrections to ab initio total energies calculated with the group-II d states included in the cores. Similar calculations for x=0.5 ordered alloys confirm the presence of nearest-neighbor bond-length differences in these systems without violation of Vegard’s law. An anomalously large ‘‘relaxation’’ is predicted here for Hg1−xCdxTe (∼2% bond-length difference in the alloy compared to only 0.3% between limiting crystals) due to the dominance of chemical effects neglected from simple valence force models. The implications of the present results for alloy mixing energies and possible deviations from randomness are discussed.
The effect of gas scattering on the deposition profile of optical thin films
Authors: Hansen G. L. , Ahonen R. G.
Published: July 2002

A Monte Carlo simulation is presented which represents the effects of gas scattering and mask design on the deposition profile of optical thin films. The results verify that gas scattering can be a primary cause of the convex profile seen on multilayer dielectric coatings. The model also predicts shifts in wavelength centering which can be seen in real optics. The fit of the theory to data is qualitatively good, but the model tends to underestimate the amount of real curvature. This difference may be attributed to the simplicity of the assumptions used in the calculations.
Analysis of forces on inertial confinement fusion targets during ablation layer coating
Authors: Gracewski S. M. , Gram R. Q.
Published: July 2002

Ablation layer coating of inertial confinement fusion targets is accomplished while the targets are bounced on the surface of a mechanical resonator. Under certain conditions the targets stick to the resonator at low amplitudes and bounce too high and escape or break at high amplitudes. An analytical model of a bouncing target is considered to determine important parameters in the bouncing process. The resonant frequency of the target is found to be two orders of magnitude higher than the mechanical resonator frequency and therefore not an important factor in unsticking targets. Experiments have been carried out to determine the adhesive force between the mechanical resonator and the targets and the effect of a plasma on this adhesive force.
Dynamic pumping and pulsed outgassing in waveguides and vacuum systems for plasma physics experiments
Authors: Melin G.
Published: July 2002

Some aspects of the vacuum problems raised by present plasma physics experiments, i.e., lower hybrid heating and current drive in tokamak discharges, are considered. Short time scale transient phenomena, such as a few milliseconds long outgassing pulses in waveguides used as antennas for plasma heating, may be observed. In these conditions the pressure distribution effects in long pipes cannot by neglected. Then the use of a one-dimensional model for the pressure is required. In the molecular flow regime the pressure is found to be the solution of a heat-conduction-type equation. Most usual vacuum problems may be solved by including appropriate boundary conditions. A few examples are developed by using the Laplace transform technique. The particular case of a pumping step at one end of a tube is presented as it applies to a tokamak discharge. While pumping at a pipe inlet, the pulsed localized and distributed outgassings in the pipe are examined. An application to the specific case of waveguide conditioning by short radio frequency power pulses is presented. The gas flow rate being released and its location are deduced from pressure measurements.
Image potential at metal surfaces
Authors: Ossicini Stefano , Bertoni C. M.
Published: July 2002

The density-functional theory is applied to calculate the self-consistent electron density distribution and the surface potential at metal surfaces with different electron densities. The surface potential yields the correct long-range image potential, since a nonlocal exchange-correlation energy functional is used. It is shown that within this scheme it is possible to calculate the position of the image plane as a function of the bulk density, the influence of the image potential on the binding energy of the image potential states, and the correct behavior of the interface barrier height for metal–metal tunneling electrons.
The reconstruction and relaxation of Ir(110) and Au(110) surfaces
Authors: Copel M. , Fenter P. , Gustafsson T.
Published: July 2002

We have applied medium-energy ion scattering using channeling and blocking to study the Au(110) and Ir(110) surfaces. Both surfaces are composed of rows of close-packed atoms which, when atomically clean, exhibit (1×2) reconstructions, i.e., a doubling of the unit cell in the direction perpendicular to the rows. We find that the Au(110) reconstruction corresponds to a missing row structure with a large contraction of the first interplanar spacing. We directly show that the contraction is accompanied by deep, multilayer distortions of the surface. The clean Ir(110) surface is similar to Au(110), characterized by a missing row reconstruction but with a smaller contraction of the first interplanar spacing. We have also examined the phase transition on Ir(110) from a (1×2) structure to an oxygen stabilized (1×1) structure. For the two phases, the yield of backscattered ions shows drastic differences only observable in the blocking directions, differences that could not have been observed in a conventional ion channeling experiment.
Electron beam effects in the analysis of compound semiconductors and devices
Authors: Kazmerski L. L. , Burnham N. A. , Swartzlander A. B. , Nelson A. J. , Asher S. E.
Published: July 2002

The effects of electron beams on the analysis of CuInSe2 surfaces are examined in this paper. Potential changes in the surface chemistry—including oxidation and desorption—under a range of incident probe conditions, are investigated for possible artifactual information generation. Emphasis is placed on the relationships between beam conditions and oxygen chemisorption and physisorption, since oxygen treatments of devices utilizing this semiconductor are critical to performance. Single crystals and polycrystalline thin films are analyzed and compared to establish the beam-induced phenomena.
Mass spectrometric determination of trace oxygen
Authors: Lieszkovszky L. , Borossay J.
Published: July 2002

The calibration factor of the oxygen/argon ion current ratio has been found to depend on the background of the mass spectrometer in the 1–1000 ppm oxygen (in argon) range. Adsorption on the surface seems to be responsible for the phenomenon. Coverage-dependent pumping speed of the surface is assumed in the interpretation of the results. By applying the background-dependent calibration curve instead of a simple factor, accuracy greater than 10% can be achieved with substantially fewer calibration measurements.
Surface conditioning of fusion devices by carbonization: Hydrogen recycling and wall pumping
Authors: Winter J.
Published: July 2002

Measurements made in the tokamak Torus Experiment for Technology Oriented Research (TEXTOR) with carbonized graphite limiters and carbonized Inconel liner (‘‘all carbon machine’’) and from a carbonized simulation vessel are presented and discussed with particular emphasis on hydrogen recycling phenomena. The hydrogen recycling during tokamak discharges is strongly affected by the wall temperature. Slow loading or deloading of the wall with hydrogen occurs at low (150 °C) wall temperatures, whereas stationary conditions are reached rapidly at 350 °C. At 350 °C, recycling coefficients smaller than 1 can be achieved. Active density control during tokamak discharges is demonstrated by using the wall pumping effect in combination with shifts of the plasma position. No tendency for saturation of the wall pumping as a function of the discharge number is found when the wall temperature is 350 °C. A model is presented for the explanation of the observed effects. It involves particle induced desorption, thermal outgassing, and implantation of hydrogen. Particle induced desorption dominates at low temperatures and high hydrogen concentrations in the carbon films, thermal outgassing becomes increasingly important at higher temperatures. Hydrocarbon formation and release at wall areas exposed to high hydrogen fluxes and the codeposition of C:H at areas of low fluxes is a possible additional hydrogen sink, which could be effective during the wall pumping phenomenon.
Experiment on first-wall carbon coating: Focusing hydrogen concentration
Authors: Sakamoto Y. , Amemiya H. , Ishibe Y. , Kato S. , Okazaki K. , Oyama H. , Yano K. , Akaishi K. , Noda N. , Masuda T. , Tsurita Y. , Amemiya S. , Minagawa H. , Hino T. , Yamashina T. , Matsumoto S.
Published: July 2002

As a back-up experiment for investigations on first-wall carbon coatings of toroidal machines, we constructed the RIKEN ECR-2 device and carried out simulation experiments. By electron cyclotron resonance discharges we obtain an amorphous, hard, and dense carbon film. It is possible to decrease the atomic H/C ratio of carbon films by high-energy ion bombardment. Harmful carbon films deposited on observation windows can be cleaned up by a local pure hydrogen plasma.
Recent progress in wall material development and of surface technology for fusion devices at the Japan Atomic Energy Research Institute
Authors: Murakami Y. , Abe T.
Published: July 2002

The research and development of materials and material processes associated with the plasma–wall interaction in magnetically confined fusion devices includes current and near-term problems which must be solved to advance plasma confinement research. The major elements to be considered for the materials and processes are (a) impurity release and surface modification; (b) hydrogen isotope recycling, retention, and permeation; (c) high heat flux removal and thermomechanical response; and (d) the effects of plasma disruptions. The development of wall materials and processes and the associated plasma–wall interaction study at the Japan Atomic Energy Research Institute have been carried out primarily from the device-oriented standpoint. The weight is laid on the development and performance tests of new materials and processes for plasma-interactive components. In the JT-60 tokamak, TiC-coated molybdenum and TiC-coated Inconel tiles are currently used as most plasma-interactive components. The JAERI coating program also includes the development of in situ coating techniques for TiC and C. For the near-term devices, actively cooled components will be developed. The major technical issues are to improve ceramic materials and to develop ceramic–metal bondings which satisfy the requirements specific to fusion devices.
Vacuum gauge calibration by a combination of expansion and pumpdown methods
Authors: Huang Zhen-Bang , Zhou Xiao-Ou , Fan Jia-Wen
Published: July 2002

A combined approach to the calibration of vacuum gauges is described. It is based on the principle of expansion and pumpdown methods. Two chambers V1 and V2 are connected by conductance Ck. Gas is first expanded into V1 (expansion method), admitted into V2 via Ck, and then pumped away through an orifice of conductance C2. The pressure P2 in V2 decreases exponentially (pumpdown method). A formula for computing P2 is given. Calibration of a Bayard–Alpert type ionization gauge has been carried out in the range 10−4–5×10−7 Torr (1.3×10−2–6.7×10−5 Pa). Possible experimental errors are discussed. A total uncertainty of about 5.2% has been estimated.
Curious zig–zag in modulation characteristic curves of a Bayard–Alpert gauge in the extrahigh-vacuum region and its analysis by computer simulation
Authors: Kanaji T. , Urano T. , Ueki N. , Grosse G. , Messer G.
Published: July 2002

The modulation characteristic curves of a three-grid modulation Bayard–Alpert gauge were studied. This modulation gauge had operated satisfactorily in rather high-pressure regions. But, in very low-pressure regions, curious zig–zags appeared in the modulation characteristic curves, and it was difficult to determine optimum working conditions of this gauge. By experimental studies and computer simulation, it was clarified that these zig–zags were caused by the change of x-ray flux irradiating on the ion collector and that the flux change was induced by the change in trajectories of electrons emitted from the filament depending on a special geometrical construction of the gauge.
Angular distributions of photon stimulated desorption in a vacuum duct observed by using a unidirectional detector
Authors: Kobayashi Masanori , Matumoto Manabu , Ueda Shinjiro
Published: July 2002

Pressures in the vacuum duct of the electron storage rings depend on photodesorption. A multicapillary-type mass spectrometer was applied to observe local outgassing rates in the duct, in which the duct surfaces were irradiated by directly incident photons and/or by scattered photons. Local outgassing rates were nonuniform along the periphery of the duct. The desorption rates at the directly incident point were higher than at the other surfaces when photon dose was less than 200 mA h. At over 9000 mA h the rates at that point decreased more, while the desorption rates at the other surfaces decreased less. Angular distributions of photocurrent were also measured. The distributions were almost uniform except near the directly incident point.
An oxide-impregnated nickel-matrix cathode for 35-MeV proton linear accelerator
Authors: Ji Yaer , Luo Heying , Xia Degong , Wu Riguang , Liu Dionkui
Published: July 2002

A low-power-consumption oxide-impregnated nickel-matrix cathode used in the duoplasmatron ion source of the 35-MeV proton linear accelerator is described. The activation process of the cathode made under enough hydrogen pressure is discussed. The arc discharge current is about 24 A at 100-μs pulse width. After operating for 234 h the cathode was put in rough vacuum for 360 h and was exposed to atmosphere for 24 h, then repeated depressurization for 514 h and was put in rough vacuum for 7200 h again. After that the cathode still worked for 130 h. As a result, using this type of cathode, the preinjector gives 200-mA ion beam current, and 70-mA ion beam current is obtained at the output of the linear accelerator. This cathode has been operated for 522 h, repeatedly depressurized, and exposed to atmosphere 50 times; it still works in the accelerator normally.
Structural order in Si–N and Si–N–O films prepared by plasma assisted chemical vapor deposition process
Authors: Budhani R. C. , Prakash S. , Doerr H. J. , Bunshah R. F.
Published: July 2002

Local bonding modes and the nearest-neighbor environment of the constituent atoms in glow discharge silicon nitride and oxynitride films have been probed with Fourier-transform infrared spectroscopy. The silicon nitride films prepared under a wide range of (NH3+N2)/SiH4 ratio and rf power levels all show characteristic absorption bands of N–H, Si–H, and Si–N bonds. The Si–H stretch mode absorption peak shifts to higher wave numbers with the increasing number of N–H bonds in the material. This behavior is observed for all power levels and gas flow combinations. The observed universal dependence of the Si–H stretch frequency on the concentration of the N–H bonds, and the sign of the shift indicate that the change in the frequency is caused by the increasing number of nitrogen atoms at the Si site. Arguments advanced on the basis of the electronegativity of the constituents suggest that the formation of N–H and Si–H bonds at the Si–N site leads to opposite shifts in the Si–N frequency. Thermal annealing studies show that the N–H and Si–H bonds dissociate at and above 600 °C. The Si–N stretch mode absorption in the oxynitride films shifts towards the higher wave numbers with the increasing number of Si–O bonds in the material. The refractive index correspondingly approaches to that of a-SiO2. The observed one-to-one correspondence between the Si–N peak position and the refractive index decisively indicates that the oxynitride films are comprised of a complete network of bonds between the Si, N, and O without any phase separation.
Correlation of microstructure and composition of sputtered titanium nitride films with electrical and optical properties
Authors: Thorpe T. P. , Elam W. T. , Morrish A.
Published: July 2002

A set of TiNx films grown on quartz substrates at temperatures between 140 and 850 °C have been characterized by x-ray absorption fine structure and x-ray photoelectron spectroscopy measurements. Ti coordination number, crystal structure, and relative proportions of film constituents in particular valence states have been determined as a function of deposition temperature, and are related to measured optical and electrical properties. Measurements show that polycrystalline material with the B1-NaCl structure is formed at all temperatures, but that substantial levels of carbon and oxygen are present. The measured Ti coordination number decreases and the fraction of Ti atoms bound to impurities increases with decreasing deposition temperature. This trend, coupled with decreased electrical resistivity and increased infrared reflectivity, indicates a reduction in material defects at higher temperatures.
Optical characterization of SiO1.1 silicon oxide layers on InSb
Authors: Remond G. , Caye R. , Holloway P. H. , Ruzakowski P.
Published: July 2002

Layers of known thicknesses of SiO1.1 and SiO2 deposited onto InSb substrates have been studied by optical microreflectometry, electron microprobe analysis, and x-ray photoelectron spectroscopy. A model was used to calculate the resulting reflectance coefficient for an absorbing substrate covered with multiple homogeneous superimposed layers or with a single heterogeneous surface film. Comparisons of experimental and calculated reflectance curves are used to determine the composition of the SiOx layers of known thicknesses. The same samples were analyzed with the electron microprobe and Si Kβ emission showed that Si was present both as elemental silicon and silicon bonded as SiO2 within the SiO1.1 surface films. A surface layer ionization model was used to reduce the measured x-ray intensities in terms of weight concentrations and the SiOx was shown to have a composition of SiO1.1. Finally, XPS data agree well with the SiO1.1 stoichiometry, but the Si 2p peak could split into three separate peaks tentatively assigned to SiO2, SiO, and Si–Si bonding. The complementary nature of the various data sets are discussed.
Paramagnetic point defects in boron-implanted Hg0.7Cd0.3Te and CdTe
Authors: Bowman R. C. , Venturini E. L. , Witt S. N.
Published: July 2002

This paper describes the initial observations of electron paramagnetic resonance (EPR) spectra from Hg0.7Cd0.3Te and CdTe after implantation with boron ions. Sharp and nearly isotropic EPR signals with the free-electron g values were easily detected at low temperatures (i.e., ≤ 78 K) when the boron ion implant dose was 1×1016 ions/cm2 or larger. For identical implant conditions, more intense signals and narrower peaks were obtained from Hg0.7Cd0.3Te samples when compared to the spectra for CdTe. However, the g factors for all implanted Hg1−xCdxTe samples appear to be equivalent and are very similar to the values reported for the dangling-bond defects in other ion-implanted semiconductors. The EPR spectra produced by the boron implants do not seem to correspond to either the degenerate conduction electron bands that form in ion-implanted Hg1−xCdxTe or the shallow donor states previously found in chemically doped CdTe. When implanted crystals are cooled below 4 K, partially resolved two-component line shapes are observed at some orientations. Increasing temperature causes these two-component lines to collapse into nearly Lorentzian line shapes with temperature-dependent widths. This behavior is consistent with a thermally activated process by which the paramagnetic spins hop between inequivalent locations.
Low-temperature epitaxy of Si and Ge by direct ion beam deposition
Authors: Zuhr R. A. , Appleton B. R. , Herbots N. , Larson B. C. , Noggle T. S. , Pennycook S. J.
Published: July 2002

Amorphous, polycrystalline, and epitaxial thin films of Si and Ge have been grown by ion beam deposition (IBD) under ultrahigh-vacuum conditions. IBD involves the direct deposition of ions onto single-crystal substrates from mass- and energy-analyzed beams with energies of 10 to 200 eV. The IBD films were characterized by Rutherford backscattering, ion channeling, cross-section transmission electron microscopy, and x-ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning were studied. Differences in the formation of epitaxial thin films on p- and n-type Si substrates were observed with n− Si showing better epitaxy at low temperatures. Epitaxial overlayers which showed good minimum yields by ion channeling (3%–4%) have been produced at temperatures as low as 375 °C for Ge on Ge(100) and Si on Si(100).
Quantitative analysis and depth profiling of rare gases in solids by secondary-ion mass spectrometry: Detection of (CsR)+ molecular ions (R=rare gas)
Authors: Ray M. A. , Baker J. E. , Loxton C. M. , Greene J. E.
Published: July 2002

A new secondary-ion mass spectrometry technique is described for the quantitative analysis and depth profiling of rare gases incorporated in thin films and bulk solids. A Cs+ primary-ion beam incident on the sample surface was used to produce sputtered (CsR)+ (R=rare gas) molecular ions whose yield was proportional to the rare-gas concentration in the analyzed region of the sample. Depth profiles have been measured for Ar and Kr implants in single-crystal Si, Ge, and GaAs wafers and a Kr implant in polycrystalline Ni. Detection limits ranged from ∼4×1017 cm−3 for Ar in Ge to ∼1019 cm−3 for Kr in GaAs where the sensitivity was decreased due to interference with (Ga2As)+ ions at mass 217. The Cs+ primary-ion current density used in these experiments was 6 mA cm−2. It was not possible to obtain sufficiently high Cs+ current densities in our system to observe R+ secondary ions, although they were detectable using an O+2 primary ion beam incident at 35–40 mA cm−2. The high current densities required in the O+2 experiments, however, resulted in a correspondingly high sputter etching rate and hence a decrease in the depth resolution. Measurements of secondary-ion intensities as a function of primary-ion current density and secondary-ion energy distributions showed that (CsR)+ molecular ions were formed by surface-ionization processes, while R+ secondary ions were formed primarily by inelastic gas-phase collisions involving rare-gas atoms released from the samples with thermal velocities.
Secondary ion mass spectrometry depth profiling of Mo/SiO2/Si structural samples
Authors: Fujinaga Kiyohisa , Kawashima Izumi
Published: July 2002

This report describes the influence of surface roughness resulting from the Mo film sputter process on oxygen profiles of the thin SiO2 interlayer in an Mo/SiO2/Si structural sample. The sputter-induced surface roughness causes expansion of oxygen profiles. The expansion increases as the Mo grain size increases. This is why the original surface roughness of an Mo film deposited on an SiO2 surface is almost all proportional to Mo grain size (20–300 nm) and why the sputter-induced surface roughness is developed by the original Mo surface roughness. The relation between sputter-induced inexactness resulting from the Mo film sputter process and an expanded oxygen profile of the thin SiO2 interlayer is obtained. The Mo grain size is controlled by postdeposition heat treatment (800–1100 °C).
Characteristics of radiated power for various Tokamak Fusion Test Reactor regimes
Authors: Bush C. E. , Schivell J. , McNeill D. H. , Medley S. S. , Hendel H. W. , Hulse R. A. , Ramsey A. T. , Stratton B. C. , Dylla H. F. , Grek B. , Johnson D. W. , Taylor G. , Ulrickson M. , Wieland R. M.
Published: July 2002

Power loss studies were carried out to determine the impurity radiation and energy transport characteristics of various Tokamak Fusion Test Reactor (TFTR) operation and confinement regimes including low mode, detached plasma, co-only neutral beam injection (energetic ion regime), and the enhanced confinement (‘‘supershot’’) regime. Combined bolometric, spectroscopic, and infrared photometry measurements provide a picture of impurity behavior and power accounting in TFTR. The purpose of this paper is to make a survey of the various regimes with the aim of determining the radiated power signatures of each.
Applications of surface analytical techniques to the characterization of catalytic reactions
Authors: Campbell Charles T.
Published: July 2002

Instrumentation which combines ultrahigh vacuum surface analytical methods with an attached high-pressure microcatalytic reactor has received increasing use in the study of structure/function relationships in heterogeneous catalysis. In particular, the activities and selectivities of model catalysts which are very homogeneous and well characterized in terms of atomic-level surface structure and composition have been compared for a number of simple reactions of industrial interest. The results are helping to elucidate the nature of active sites on catalyst surfaces; the roles of poisons, promoters, and supports; and electronic factors in catalysis. This article briefly discusses some design considerations for instrumentation used in this approach, and extensively reviews its applications by many laboratories to study simple catalytic reactions.