bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of transparent conductive thin films of indium oxide
Authors: Molzen Walter W.
Published: July 2002

A metal alloy target of indium doped with about 5% by weight tin was rf sputtered in 100% oxygen onto quartz substrates. These films of indium−tin oxide were then annealed at temperatures up to 600°C in an argon−flow system. Their optical and electrical properties were examined as a function of annealing temperature. Optimum film properties include a sheet resistance of 2−3 Ω/⧠ with a transparency of 95% over the entire visible region. Optical extinction coefficients, percent transmission, and refractive indices were determined as a function of annealing temperature and sheet resistance. Results show that the infrared reflection loss of films of indium−tin oxide can be attributed to the amount of oxygen vacancies which are incorporated into the film.
Morphological and electrical properties of rf sputtered Y2O3-doped ZrO2 thin films
Authors: Greene J. E. , Wickersham C. E. , Zilko J. L. , Welsh L. B. , Szofran F. R.
Published: July 2002

The structural, compositional, and electrical properties of rf sputter-deposited Y2O3-doped ZrO2 films have been investigated as a function of sputtering conditions. The results show that the application of an rf substrate bias during deposition has a large effect on both the morphological and electrical properties of the films. Auger electron spectroscopy, electron diffraction, and scanning-electron-fractography results show that films deposited at P=20 mTorr (2.67 Pa), VT=−500 V, and VS=−40 V are nearly stoichiometric, have a cubic crystal structure, and a relatively equiaxed microstructure. The results of electrical measurements indicate that films grown under these sputtering conditions have an ionic transference number which is nearly zero below 100 °C and rises to approximately 0.4 at 200 °C.
Growth and characterization of doped ZrO2 and CeO2 films deposited by bias sputtering
Authors: Greene J. E. , Klinger R. E. , Welsh L. B. , Szofran F. R.
Published: July 2002

The deposition rate, chemistry, microstructure, and optical and electrical characteristics of rf sputter deposited Y2O3-doped ZrO2 films have been investigated as a function of applied substrate bias VS. Some preliminary results on Y2O3-doped CeO2 are included. All films were deposited in Ar at a pressure of 20 mTorr (2.67 Pa). The deposition rate of both materials initially increased with VS and then decreased as VS/VT exceeded ∠0.08, where VT is the target voltage. In the doped ZrO2 films, the O/Zr ratio, microstructure, and ionic conductivity activation energy were dependent upon VS. For VT=−500 V, deposited films were approximately stoichiometric at VS?−70 V, while films grown at −VS<60 or ≳80 V were oxygen deficient. Films grown at −VS?40 V had a very columnar microstructure, while films deposited with −VS≳60 V appeared quite dense with little structure visible in fracture cross-section electron micrographs. Electrical measurements indicated ionic-transference numbers within 1% of unity at temperatures T?180°C. Linear Arrhenius plots of measured film resistance versus T in the range 150–550°C yielded activation energies in the range 0.9–1.15 eV and indicated a single-conduction mechanism. All doped ZrO2 and CeO2 films exhibited high optical transmission over most of the visible and near-infrared spectrum. The refractive index decreased with increasing oxygen content and agreed reasonably well with published values for pure ZrO2 films.
Materials processing in space
Authors: Patten J. W.
Published: July 2002

Fluid flow phenomena in high-melting-point-materials systems are promising areas for future space processing experiments. The influence of the absence of gravity on the structure of these materials during a liquid-phase or partially liquid-phase processing history includes the most significant processing phenomena. Specifically, density differences due to nucleation of solids on freezing, thermal gradients, composition gradients, and other effects produce fluid flow in liquid systems subjected to a gravitational field. The absence of gravity should result in much less flow with attendant structural differences on solidification. However, zero-gravity segregation in two-phase structures (l+l, l+s, or l+g) does not proceed in the manner usually predicted. In addition, more fluid flow than expected often influences other phenomena of interest, such as dendrite growth and solidification-front behavior. Considerable attention should be devoted to improving understanding of fluid flow behavior in solidifying materials systems that are not influenced by gravitational field.
Elastic and inelastic contributions to secondary electron yield structure
Authors: den Boer M. L. , Cohen P. I. , Park Robert L.
Published: July 2002

The secondary electron yield of solid surfaces contains weak but complicated structure, which is greatly enhanced by differentiation with respect to primary electron energy. Auger electron appearance potential features, corresponding to yield changes due to core level excitations, and diffraction features are the major contributions to this structure. The magnitude of the diffraction features decreases with primary energy and depends strongly on temperature and surface order. Surprisingly, even for polycrystalline materials the diffraction features extend out to about 400 eV and completely obscure appearance potential features in this region. We have measured the energy distribution of electrons contributing to each of these kinds of features. The diffraction structure is due almost entirely to elastic electrons while the appearance potential peaks result primarily from electrons with energy less than 30 eV. This difference can be exploited using a double modulation scheme with four-grid LEED optics to separate the two kinds of features. This extends the useful range of Auger electron appearance potential spectroscopy down to energies below 200 eV.
Surface analysis by electron spectroscopy at high pressures
Authors: Powell C. J.
Published: July 2002

Surface analyses are now made by techniques such as Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and appearance potential spectroscopy (APS). These techniques utilize low-energy electrons and have high surface sensitivity but cannot be used at high pressures [≳10−4 Torr(≳10−2 Pa)]. Optical techinques can be used at high pressures but their surface sensitivity is poor. It is proposed to combine these approaches by using the high-pressure gas as a converter. Two situations are considered. First, variable-energy x-rays are used to produce variable-energy photoelectrons from the gas which impinge on the sample; these electrons constitute a suitable source for APs. Second, the variable-energy x-rays produce photoelectrons from the sample (XPS) of variable energy; these electrons can be detected using the gas for APS. In both cases, the derivative of the x-ray yield from the gas-sample cell is measured as a function of incident x-ray energy; features in the derivative spectrum can be correlated with the core levels of surface atoms of the sample. Design calculations based on x-ray intensities from available sources indicate that the proposed method could only be useful for specialized applications.
High resolution Auger sputter profiling study of the effect of phosphorus pileup on the Si–SiO2 interface morphology
Authors: Schwarz S. A. , Helms C. R. , Spicer W. E. , Taylor N. J.
Published: July 2002

We have used Auger electron spectroscopy in conjunction with sputter etching and crater-edge profiling to study the distribution of phosphorus near the Si–SiO2 interface and the effect of the phosphorus distribution on the width of the interface transition region. The samples studied consisted of thermal oxides approximately 1000-Å-thick grown on Si (111) substrates with initial phosphorus concentrations up to 6×1020 cm−3. Phosphorus pileup at the Si–SiO2 interface was observed with the phosphorus peak (after correcting for electron escape depth effects) on the Si side within 5 Å of the interface. The 10%–90% width of the Si–SiO2 transition region as measured by the SiLVV transition varies from 25 (low doping limit) to 38 Å (bulk doping level of 6×1020 cm−3). Results are interpreted in terms of a recently proposed model for the Si–SiO2 interface.
Reduction of contamination in triode sputtering systems
Authors: Ryden W. D. , Bindell J. B. , Holschwandner L. H. , Labuda E. F.
Published: July 2002

The fabrication of silicon integrated circuits with a beam lead metallization system consisting of Ti, Pt, and Au requires an effective technique for depositing thin films (500–2000 Å) of Ti and Pt. Altough sputtering is a particularly advantageous technique, it does have one particular disadvantage: Films deposited by sputtering are prone to contamination, since the ions causing the sputtering cannot be completely restricted to the desired target material. The contamination problem can be more serious in a supported plasma apparatus (triode), as opposed to the usual diode configuration, because of the additional fixturing which can act as sources of contamination. The contamination in a triode system has been examined and the major source was found to be the plasma confinement tube. A model has been developed that explains the origin of the contamination; the contamination results obtained by Auger analysis are in full agreement with the model. Furthermore, based on the model, the confinement tube was split into electrically isolated segments. With this split tube configuration the contamination from the tube was reduced by over an order of magnitude.
Purposeful modification by gas adsorption of atomically clean iron surfaces at room temperature and characterization by 21.2-eV photoemission
Authors: Russo Carl , Kaplow Roy
Published: July 2002

We have previously explored purposeful exposure of an atomically clean surface to controlled environments as a technique for obtaining surfaces with desired properties. The incorporation of nitrogen into atomically clear iron is an example of beneficial clean surface modification and results in enhancement of resistance to corrosion at room temperature in dry and moist air, relative to initially air exposed samples. The in situ 21.2-eV photoelectron spectroscopy, using a windowed discharge lamp and residual gas analysis were performed on clear iron and iron in the course of N2 and H2O exposures as well as N2–O2 and N2–H2O sequential exposures. These room-temperature UPS adsorption studies, which covered pressures from 5×10−8 to 0.5 Torr indicate the following: dissociative adsorption of N2 and H2O; molecular H2O adsorption at pressures greater than 0.05 Torr; the dissociative adsorption of oxygen on nitrogen-treated surfaces (as on untreated surfaces); and a complex reaction between preadsorbed nitrogen and water vapor. The in situ adsorption results are consistent with spin orbital electronegativity concepts together with electronic structure calculations in the self-consistent field-Xα approximation. The Fe–N2–H2O study is consistent with a proposed model in which the inhibition of molecular water vapor adsorption on nitrogen-treated iron is responsible for the resistance to corrosion noted.
Surface reflectance spectroscopy on low-index planes of tungsten
Authors: Passler M. A. , Stiles P. J.
Published: July 2002

The fractional changes in optical reflectance for s and p polarization, ΔRs/Rs and ΔRp/Rp, have been determined for the adsorption of H2, O2, and CO on the low-index planes of W. Structure in the spectra of ΔRs/Rs and ΔRp/Rp are very similar, implying that the microscopic corrections to the classical equations for ΔRp/Rp are small for photon energies 0.5–4.5 eV. Similarities in the spectra for the chemisorption of the different adsorbates on W(111) imply that the main effect is due to the mere presence of the adsorbate, rather than the identity of the adsorbate. It is possible that this lack of specificity can be explained by a surface relaxation upon chemisorption.
Ni(100) with chalcogen overlayers: Theory for structures, force constants, binding energies, photoemission spectra; importance of final-state multiplet splittings
Authors: Anderson Alfred B.
Published: July 2002

A theory combining Hellmann–Feynman electrostatic forces and one-electron molecular orbital energies is used to determine spectroscopic properties for diatomic and surface nickel chalcogenides. The small cluster model for the surface is found adequate for all properties considered. The absorbate p photoemission bands are interpreted in terms of final-state chalcogen atom multiplet splittings, opposed to previous studies which attributed the complicated spectra to unusual bonding interactions between the absorbate and substrate.
Effect of primary ion energy and surface chemistry on the secondary ion yields in low-energy SIMS experiments
Authors: Yu Ming L.
Published: July 2002

The chemisorption of oxygen on W(100) and Mo(100) single-crystal surfaces was studied using a static mode SIMS technique at primary ion energies ranging from 150 eV to 2 keV. The following secondary ion yields O−, WO−2, and MoO−2 were found to be sensitive to the changes in the chemisorbed oxygen layer at different stages of chemisorption. Significant enhancement in the sensitivity of the O− yield to the chemisorption process was observed when the energy of the Ne+ primary ion energy was below 500 eV.
Auger study of surface carbon and oxygen on thorium following ion bombardment
Authors: Bastasz R. , Colmenares C.
Published: July 2002

The composition of a thorium metal surface has been monitored using Auger electron spectroscopy following Ar+ bombardment at different temperatures. After extended Ar+, bombardment, enough contaminated overlayers were removed to expose a surface region containing only thorium, bulk impurities, and imbedded argon. The main impurities, carbon and oxygen, differed in their behavior when the sample was annealed following bombardment. The amount of surface carbon either increased or remained constant during annealing depending upon the temperature of the sample during bombardment. The amount of surface oxygen decreased rapidly when the sample was heated above 500°C regardless of the sample temperature during bombardment. These experiments indicate that preparation of clean, annealed thorium surfaces requires ion bombardment at temperatures ?400°C.
Surface segregation of boron in nitrogen-strengthened stainless steel
Authors: Stulen R. H. , Bastasz R.
Published: July 2002

The characteristic surface segregation of both impurities as well as major alloy constituents in 21Cr–6Ni–9Mn (21–6–9), a nitrogen strengthened austenitic stainless steel, has been studied using scanning Auger microscopy (SAM), x-ray photoelectron spectroscopy (XPS), and sputter Auger techniques. Segregation effects were examined for polycrystalline material heated to temperatures ranging up to 800° C. The SAM results show both a nonuniform spatial distribution of the various segregating species, as well as a strong cosegregation of boron with nitrogen at temperatures above approximately 700° C. Based on a bulk concentration of less than 10 ppm, the resulting surface-to-bulk concentration ratio for boron is greater than approximately 5×104. Both the boron and nitrogen Auger and XPS spectra associated with commercially available boron nitride material are identical to those obtained from the segregated layer on 21–6–9 and indicate that the boron and nitrogen cosegregate to form a boron nitride surface layer. This segregated BN layer, which initially is formed at high temperatures and uniformly covers the surface after one hour of heating, is found to be stable down to room temperature. The observed Auger peak positions are compared with semiempirically calculated values based on the XPS results.
Optical and electrical properties of ZnO films prepared by spray pyrolysis for solar cell applications
Authors: Aranovich Julio , Ortiz Armando , Bube Richard H.
Published: July 2002

Zinc oxide films were produced by spray pyrolysis starting with aqueous solutions of ZnCl2, ZnCl2 plus H2O2, and Zn acetate, and structural, optical, electrical, and thermoelectrical properties of the deposited films were investigated. Highly transparent films with resistivity as low as 10−3 Ω cm can be produced by suitable control of deposition procedures and by postdeposition annealing in hydrogen.
Performance limits in 1:1 UV projection lithography
Authors: Bruning J. H.
Published: July 2002

A modified optical design of the 1:1 Perkin–Elmer printer was evaluated at 3100 Å and 4000 Å for fine-line photolithography. Special optical coatings were applied to the reflecting surfaces to optimize overall transmission at a 3100 Å exposure wavelength while allowing selection of the exposing wavelength by optical filters. A test mask was designed for this evaluation which consists of an array of meander patterns for imaging onto metallized silicon wafers which can be electrically probed for integrity after etching. The array of 300 sites contains meander patterns with widths and spaces varying from 0.5 μm in 0.25 μm steps to 2.5 μm. A plot of the electrical probe yield of the meander patterns with respect to feature dimension indicates performance of the lithography.
Ion beam deposition of special film structures
Authors: Weissmantel C.
Published: July 2002

The structure and properties of thin solid films deposited in vacuum can be influenced substantially if additional energy and momentum is provided to the growing layers by energetic, inert or film-forming species. Various ion beam configurations for investigating these effects are discussed. Recent results are presented in conjunction with the following special film structures: (1) epitaxial, graphoepitaxial, and hydrogenated amorphous silicon deposits; (2) hard and unusual films of carbon and of boron nitride. Though the basic structure of the latter films is quasi-amorphous, microcrystals of high-pressure phases could be detected. Further trends are outlined.
Droplet emission in liquid metal ion sources
Authors: Wagner A. , Venkatesan T. , Petroff P. M. , Barr D.
Published: July 2002

Liquid indium ions sources were operated in a transmission electron microscope. The formation of a Taylor cone was directly observed during source operation. In addition, dynamic instabilities were observed on the needle shank behind the Taylor cone with the formation of liquid droplets which grew in size and left the shank. Droplets on the shank were also found in SEM observations of rapidly frozen liquid gold ion sources. The surface of silicon targets on which the ion current from a gallium ion source was allowed to impinge was studied by Rutherford backscattering spectrometry. The amount of material emitted from the ion source was measured as a function of the angle of emission and the ion current. A comparison of these emitted mass distributions with the corresponding current distributions indicated that the average mass to charge ratio of the beam decreased with angle of emission. In addition, the ratio of the amount of material to the total charge leaving the source was found to increase monotonically with the ion current with a sharp increase occurring for ion currents greater than approximately 10 μA.
Measurement of semiconductor–insulator interface states by constant-capacitance deep-level transient spectroscopy
Authors: Johnson N. M.
Published: July 2002

Localized electronic states at the semiconductor–insulator interface adversely affect the operation of insulated-gate, field-effect devices. Characterization of interface states provides essential information for minimizing their effect through process optimization, for predicting device performance, and ultimately for microscopic identification of interface defects. This paper reviews the application of deep-level transient spectroscopy (DLTS) for characterizing interface states on metal–insulator–semiconductor capacitors, with emphasis on the constant-capacitance (CC) mode of measurement. The DLTS measurement yields both the energy distribution of interface states and their cross section for capturing free carriers. In addition, it has the versatility of being applicable to both interface and bulk defect characterization. The CC-DLTS technique offers the combined features of high sensitivity (<1×109 eV−1 cm−2), minimum signal distortion at high defect densities, high energy resolution, and the determination of dynamic properties. After a description of the measurement system and experimental procedures, the theoretical basis is developed for data reduction of majority-carrier-dominated transients for the following cases: (1) under saturating-pulse conditions and (2) with Fermi-level controlled trap occupancy. Under the first topic is included a summary of transient-current spectroscopy, and the second is illustrated with the energy-resolved DLTS technique. The presentation includes an analysis of the effect of surface generation on the DLTS measurement of interface states near the semiconductor midgap and an analysis of the limits of applicability of the transient-capaci tance mode for DLTS measurement of interface states. The techniques are illustrated with measurements of electronic defect levels at the Si–SiO2 interface.
A technique using a Wheatstone bridge to study the minute differences in nucleation and growth of two metallic films
Authors: Chaturvedi U. K. , Agrawal S. K. , Nigam A. K.
Published: July 2002

A technique has been developed to study the differences in the nucleation and growth of metallic films during their vacuum thermal deposition. The ‘‘P’’ and ‘‘Q’’ resistance arms of a Wheatstone bridge are made equal and arms ‘‘R’’ and ‘‘S’’ are replaced by two substrates having proper contacts, facing the vapor source in the vacuum chamber. During deposition, if nucleation and growth conditions of the films on these substrates are exactly identical, no voltage difference is developed across the junctions ‘‘P Q’’ and ‘‘R S’’ of the bridge throughout the growth of the films. If, however, there is even a minute difference in the nucleation and growth sequence of these films, the critical time at which the films become conductive may be different for both the films which ultimately gives a rectangular pulse-type signal which is recorded by the X–Y recorder. As the critical thickness at which the metal film becomes suddenly conductive is dependent on a large number of factors, e.g., flux and species of vapor, structure and temperature of the substrate, residual gas pressure and its nature, fields present on or nearby the substrate etc., this technique has potential applications in metallic thin film technology.
Emission characteristics of single-crystal LaB6 cathodes with large tip radius
Authors: Furukawa Y. , Yamabe M. , Inagaki T.
Published: July 2002

Emission characteristics of single-crystal LaB6 cathodes of 〈100〉, 〈110〉, 〈111〉, 〈210〉, 〈310〉, and 〈321〉 orientations, with large tip radius (100 μm), were investigated. In cathodes of small tip radius (less than 10 μm) emission from the conical face is dominant, as it has the small area of the top surface. Cathodes of large tip radius have a large emission area at the top surface, which includes various crystal faces, according to the orientation and the cone angle. It has become clear that it is important to use as the tip axis the orientation having rotational symmetry and a crystal face of low work function at the cathode top to get good beam uniformity. In this respect the 〈100〉 cathode was found to be superior to cathodes of other orientations. Emission characteristics of the 〈100〉 cathode during long-term operation were investigated. A flat (100) face was formed at the top due to LaB6 material consumption, and emission characteristics reflecting this tip shape were measured.
Magnetically confined low-pressure gas discharge generated in a vacuum switch
Authors: Kageyama Katsuhiro
Published: July 2002

Mode and current paths for a discharge in a vacuum switch placed in a magnetic field were investigated experimentally and analytically to find a possible method for measuring the pressure in the switch. A low-pressure gas discharge is generated in the switch, and discharge properties show evidence that the arc shield, which is electrically floating, is an essential element. Simulators of the vacuum switch were assembled to determine the effects of the shield on the discharge. Pressure dependence and current distributions in various electric-field configurations in the simulators were measured and analyzed. The discharge in the vacuum switch is identified as a series discharge of an inverted magnetron and of a magnetron through the shield as a common electrode. The mode for each elemental discharge is the same as that employed by cold-cathode vacuum gauges. In the inverted magnetron, the current flows from the switch-contact periphery at positive high voltage radially to the shield. In the magnetron, it flows from the shield end radially to the rod of a switch electrode, which is electrically grounded.
Properties of a series crossed-field discharge in a vacuum switch
Authors: Kageyama Katsuhiro
Published: July 2002

Properties of low pressure gas discharges generated in a vacuum switch placed in a magnetic field were investigated for an approach to a method of measuring pressure. The discharge was identified in a previous paper as a series crossed-field discharge of an inverted magnetron and of a magnetron. The present experiments reveal discharge–current dependences on pressures, discharge voltages and magnetic-field strengths. These dependences agree well with those deduced from properties of the two elemental discharges that are applicable to pressure measurement. Discharges were generated in various gas species, and discharge–current dependence on gas species was obtained. The series crossed-field discharge was proved to be self-sustaining, and an estimate supports the discharge stability.
Compensation densities in n-type Hg1−xCdxTe from transport properties of optically generated free carriers
Authors: Bartoli F. J. , Hoffman C. A. , Meyer J. R.
Published: July 2002

Improvements to a photoneutralization technique for accurately determining compensation densities in narrow-gap Hg1−xCdxTe are discussed. A more comprehensive theoretical understanding of the electron mobility as a function of optically excited carrier density has been established, incorporating a theory for dynamic dielectric screening in the treatment of electron-hole scattering. In addition, uniform carrier generation has been demonstrated using two-photon absorption of CO2 laser radiation for compositions in the range 0.24<x<0.27. This eliminates the need for nonuniformity corrections to the photo-Hall data for appropriate compositions of Hg1−xCdxTe. Good agreement between theory and experiment verifies the accuracy of the technique.
Resonance of 4f partial photoionization cross section of Yb and Eu near the 5p threshold
Authors: Yeh J. J. , Nogami J. , Rossi G. , Lindau I.
Published: July 2002

The 4f partial photoionization cross section of the divalent metals Yb and Eu are measured by photoelectron spectroscopy in the 15 to 30 eV range. Both metals show the same resonance effect above the threshold of the first peak of the 5p multiplets in spite of different configurations of valence electrons: the appearance of a replica of the valence band region at fixed kinetic energy arising from a 5p core hole induced Auger-like decay process. An apparently dissimilar resonance effect is observed above the second peak of the Eu 5p multiplets: no clear feature except a weak enhancement of 4f peak intensity similar to the 4d→4f resonance in oxidized Yb. It is possible that similar process effects exist in all the lanthanides.
Derivation of the density of unoccupied states in polycrystalline ferromagnetic Fe, Co, and Ni from highly resolved appearance potential spectra
Authors: Schulz S. W. , Schleicher K.-Th. , Rück D. M. , Chun H.-U.
Published: July 2002

By means of a deconvolution technique, which preserves energy resolution and provides stable results, the densities of unoccupied states in polycrystalline ferromagnetic Fe, Co, and Ni have been derived from highly resolved soft x-ray appearance potential spectra of the respective 2p3/2 core levels. The maximum of the empty d states is found at 0.23 eV for Ni, 0.55 eV for Co, and 0.92 eV for Fe with energies relative to the Fermi level and errors within ±0.1 eV. Although APS essentially probes a localized DOS, there is good agreement with single-particle band structure calculations for Ni and probably for Co, too. The higher lying 4s states exhibit a bandlike character in the APS derived DOS. Their energetic position can be reconciled with results from photoemission within the equal core approximation. Deviations from theory in the APS derived DOS for the empty d states in Fe can be explained by invoking either a surface effect or an orbital symmetry dependent final state effect. The exchange splitting between unoccupied states in Fe is determined as 1.9±0.2 eV at H25.
Evolution of the mirror machine
Authors: Damm C. C.
Published: July 2002

The history of the magnetic-mirror approach to a fusion reactor is primarily the history of our understanding and control of several crucial physics issues, coupled with progress in the technology of heating and confining a reacting plasma. The basic requirement of an MHD-stable plasma equilibrium was achieved following the early introduction of minimum B multipolar magnetic fields. In refined form, the same magnetic-well principle carries over to our present experiments and to reactor designs. The higher frequency microinstabilities, arising from the non-Maxwellian particle distributions inherent in mirror machines, have gradually come under control as theoretical prescriptions for distribution functions have been applied in the experiments. Even with stability, the classical plasma leakage through the mirror posed a serious question for reactor viability until the principle of electrostatic axial stoppering was applied in the tandem mirror configuration. Experiments to test this principle successfully demonstrated the substantial improvement in confinement predicted. Concurrent with advances in mirror plasma physics, development of both high-power neutral beam injectors and high-speed vacuum pumping techniques has played a crucial role in ongoing experiments. Together with superconducting magnets, cryogenic pumping, and high-power radio frequency heating, these technologies have evolved to a level that extrapolates readily to meet the requirements of a tandem mirror fusion reactor.
Electrolytic gettering of tritium from air
Authors: Souers P. C. , Tsugawa R. T. , Stevens C. G.
Published: July 2002

We have achieved the first direct gettering of tritium gas from moist air using the dc electrical action of the solid proton electrolyte, hydrogen uranyl phosphate (HUP). The HUP action is imperfect as 90% of the original 1 ppm is gettered by the HUP while the remaining 10% forms tritiated water. Modifications to the HUP unit may be possible to reduce this HTO background.
Properties of interfaces in (CdZn)S/CuInSe2 heterojunctions
Authors: Kazmerski L. L. , Ahrenkiel R. K. , Matson R. J. , Massopust T. P. , Dick J. R. , Osterwald C. R. , Ireland P. J. , Jones K. M.
Published: July 2002

The efficiency and operational characteristics of the (CdZn)S/CuInSe2 heterojunction solar cell are significantly improved as a result of a postfabrication heat treatment in an oxygen containing environment. The effects of this critical annealing process on the microchemical and microelectrical properties of the various cell layers and interfaces are investigated. Time-resolved EBIC and laser scanning techniques are correlated with cell performance data to identify two separate mechanisms that affect cell response. High resolution SIMS is used to evaluate compositional changes and interdiffusion effects, showing that penetration of the Cu-ternary layer by the oxygen is minimal. Light and dark current–voltage characteristics and diagnostic spectral response data are used to explain changes in cell operation.
Schottky barrier formation on amorphous semiconductors: Au on Ge(111), a-Ge, and hydrogenated a-Ge
Authors: Quaresima C. , Perfetti P. , Daniels R. R. , Margaritondo G.
Published: July 2002

The formation of Ge–Au interfaces was studied by synchrotron-radiation photoemission measurements of evaporated Au on both crystalline and amorphous Ge substrates. The results show surprising similarities among the two kinds of interface. In particular, we found evidence for the formation of the same interface compound, which was identified as Au3Ge in a previous study.
The effects of ICRF heating on plasma edge conditions in PLT
Authors: Colestock P. L. , Cohen S. A. , Hosea J. C. , Hwang D. Q. , Greene G. J. , Wilson J. R. , Ono M. , Manos D. , Budny R. , Hammett G. , Kaita R.
Published: July 2002

The interaction of ICRF heating with the plasma edge in Princeton large torus (PLT) is reviewed and possible mechanisms responsible for the observations are discussed. Ion and neutral sputtering are found to be the most significant producers of impurities, which are observed to increase in moderate amounts during ICRF heating. Collisional edge heating by the rf is evaluated as a possible explanation of measured electron density increases and particle fluxes. Antenna conditioning is also discussed, relating to the processing necessary to achieve the highest power handling capability per antenna in PLT.
Neutral-fueling pressure measurements and modeling near the plasma edge in TMX-U
Authors: Pickles W. L.
Published: July 2002

Large variations in pressure from external gas-fueling sources and from plasma-induced wall reflux along the TMX-U plasma have been observed. These pressure variations can produce locally high neutral density in the plasma, which strongly affects the plasma parameters. These local pressure measurements include data from a newly installed neutral-pressure diagnostic system of fast magnetron gauges. The plasma-induced warm-wall reflux has been observed to be primarily HD and H2 as opposed to D2. This observation supports the model that all of the neutral D2 gas enters the plasma region, strikes the plasma first, and is dissociated. The part of the D2 gas, which is not absorbed as ions, strikes a wall, where it is converted to HD. Electron induced wall desorption measured by a mass spectroscopy and actual analysis of the Ti indicates predominately H2 instead of D2 wall loading in TMX-U.
Species-specific densities of states of Ga and As in the chemisorption of CO and C on GaAs(110)
Authors: Childs K. D. , Lagally M. G.
Published: July 2002

Changes in the local charge distributions around the Ga and As atoms are measured as a function of coverage for CO, C, and sequential C and O adsorption on cleaved GaAs(110), using Auger line shape analysis. The charge distribution at the Ga sites is affected by CO adsorption in a manner similar to that for O adsorption, but is unaffected by C adsorption. The charge distribution at the As sites is affected differently by O and CO adsorption. Sequential adsorption of C and O demonstrates that this difference is due to a combination of C and O. It is concluded that CO adsorbs dissociatively at Ga sites, with only the O forming a chemical bond, but that some combination of C and O forms a chemical bond at the As sites.
Kinetic modeling of plasma-limiter interaction in the TEXTOR edge region
Authors: Harris J. A. , McGrath R. T.
Published: July 2002

The plasma flow properties along a field line intercepting a limiter or other neutralizing surface are significantly altered through charge exchange and reionization of neutrals produced at the surface. This problem is investigated using a one-dimensional, steady state kinetic model. The collisional Boltzmann equation is solved for the ion, electron, and neutral particle distribution functions in one velocity variable as a function of distance from the neutralizing surface. The collisional operator in the Boltzmann equation includes the effects of charged particle collisions and calculates charge exchange and electron impact ionization rates through direct integration of the distribution functions. Results have been obtained for plasma conditions simulating those observed for ALT-I operation on TEXTOR. Spatial profiles of particle density, temperature, and presheath electric field strength on flux surfaces at various distances into the scrape-off are calculated. We find that neutral recycle reduces ion temperatures by as much as 30% as the plasma flows toward the neutralizing surface while electron temperatures remain unchanged. Collisional sources generate small presheath electric fields directed away from the limiter surface that have integrated potentials of only a few volts.
Arcing from coated surfaces: Test facility development and coating deposition using ion plating techniques
Authors: Cain B. L. , Miley G. H.
Published: July 2002

Electrical arcing from surfaces is recognized as a potentially deleterious source of plasma impurities for next generation fusion devices. Surface coatings and/or surface conditioning techniques can be applied to reduce the amount of such arc generated impurity atoms. In order to investigate the arcing phenomenon and to assess the arcing performance of various coatings and coating techniques, a unique experimental facility is being developed. This dual purpose facility, developed around an existing ion plating system, allows for the convenient joint studies of arcing phenomenon and coating deposition processes. Completed work includes the construction of an arcing test fixture for study of coating performance in a ‘‘glow discharge to biased surface’’ configuration, and the deposition of selected coating materials using ion plating techniques. Work is continuing toward the development of arc testing and diagnostic instrumentation.
Experimental measurements of melting and vaporization due to simulated plasma disruptions
Authors: Easoz J. R. , Bajaj R.
Published: July 2002

The first wall and limiter surfaces of magnetic confinement fusion devices will be subjected to intense pulsed thermal loads due to plasma disruptions which can result in vaporization and melting limiting the lifetime of these components. This paper presents experimental data on the vaporization and melting of AXF-5Q graphite, Type 316 stainless steel, OFHC copper and tantalum due to thermal loads varying up to 2400 J/cm2 applied for times between 1 and 50 ms. The surface thermal loads were simulated with a 120-keV electron beam in the electron beam surface heating (ESURF) facility. The analysis procedure consisted of determining vaporization losses through weight-loss measurements and evaluation of the melt zone thickness through a metallographic sectioning procedure. Comparisons with some of the more recent theoretical predictions are made. The data trends (i.e., increasing melt and vaporization with energy density, existence of threshold energy densities, and melt thickness limits at high energy density due to increased vaporization) are generally found to agree with the analytical predictions. However, the magnitude of the melt zone thicknesses and vaporization losses show differences significant enough to warrant investigation of both modeling assumptions and the experimental techniques and conditions.
Surface and bulk structural defects in Hg1−xCdxTe
Authors: Cole S. , Carey G. P. , Silberman J. A. , Spicer W. E. , Wilson J. A.
Published: July 2002

The techniques of optical microscopy and transmission electron microscopy (TEM) have been used to study the structural characteristics of a surface of a solid state recrystallized Hg1−xCdxTe crystal (x=0.35) cleaved at room temperature. Such surfaces are of special interest because of their wide use in photoemission spectroscopy studies. HgCdTe cleaved surfaces were found to be much rougher than similar surfaces of GaAs crystals, containing numerous steps and regions where fracture was clearly ductile rather than brittle. TEM observations indicate that a step is associated with numerous dislocations where the crack presumably arrested prior to changing direction, implying that the room temperature cleaved surface has a high defect density compared to the bulk crystal. TEM has also been used to characterize the defects associated with etch pits developed using ‘‘Polisar etch 2’’ on the (111)A face of a Hg1−xCdxTe crystal grown by the solid state recrystallization process. While in some cases dislocations were found, a much higher proportion of etch pits were observed to be associated with precipitates, believed to be Te. In general, these precipitates were isolated, although occasionally they were associated with a dislocation line. The form of the precipitates, along with the distribution of the etch pits, suggests that the final defect structure is strongly influenced by the casting stage.
Extension of the Heitler–London approach to adsorption problems: ESD of CO–W(100)
Authors: Refolio M. C. , López-Sancho J. M. , Rubio J.
Published: July 2002

A configuration interaction is set in terms of atomic (molecular) orbitals of an adsorbed atom (molecule) and representative orbitals of a metal surface. The electrons are then allowed to propagate through the metal band by means of a Green function which is the Hilbert transform of a joint density of states. The method is applied to adsorption–desorption of CO on W(100).
Hydrogen isotope exchange and conditioning in graphite limiters used in the Tokamak Fusion Test Reactor
Authors: LaMarche P. H. , Dylla H. F. , McCarthy P. J. , Ulrickson M.
Published: July 2002

Isotopic exchange experiments performed in the Tokamak Fusion Test Reactor (TFTR) are used to examine the outgassing and diffusive properties of graphite used as the plasma limiter. Changeover from hydrogen to deuterium for different periods ranges from ∼600 to 60 plasma discharges, which appears to be correlated in the limiter temperature. We present a simple analytical model that predicts a fast transient (∼10 plasma discharges) changeover, where the deuterium fueling dilutes the adsorbed and near surface hydrogen, and a slowly changing term where bulk hydrogen diffuses to the surface. Using this model we can extract an activation energy for diffusion of 0.15±0.02 eV. We hypothesize that interpore diffusion for this porous (∼15%) material is consistent with our observations.
Ion cyclotron resonance heating in the divertor tokamak ASDEX
Authors: Steinmetz K. , Wesner F. , Niedermeyer H. , Becker G. , Braun F. , Eberhagen A. , Fussmann G. , Gehre O. , Gernhardt J. , v. Gierke G. , Gruber O. , Haas G. , Hofmeister F. , Janeschitz G. , Karger F. , Keilhacker M. , Klüber O. , Kornherr M. , Lackner K. , Lisitano G. , Mayer H.-M. , McCormick K. , Meisel D. , Mertens V. , Müller E. R. , Murmann H. , Noterdaeme J.-M. , Poschenrieder W. , Rapp H. , Roth J. , Schmitter K. H. , Schneider F. , Siller G. , Smeulders P. , Söldner F. , Söll M. , Speth E. , Steuer K. , Vollmer O. , Wagner F. , Wedler H. , Bartiromo R. , Giuliana A. , Kislyakov A. , Kotzé P. B. , Ryter F.
Published: July 2002

The main topics of ICRF investigations in ASDEX are the influence of the divertor on impurity production and transport in ICRH heated discharges, and the heating efficiency and plasma confinement in various scenarios (minority and harmonics regimes). The first experiments were conducted in November 1984 at 67 MHz, corresponding to second harmonic heating of a hydrogen plasma at B0=2.2 T. A transmitted power of 2.5 MW has been reached so far, the total capability being 3 MW. A linear increase of the central electron and ion temperature with the rf power is observed in Ohmically preheated plasmas (ΔTe∼280 eV, ΔTi∼500 eV, ΔWp∼17 kJ at a power of 1.2 MW coupled to the plasma and n̄e=3.5×1013 cm−3). The total radiation increases linearly with the power, too, and the ratio Prad/Ptot∼0.35 stays approximately constant. However, first investigations indicate that with a divertor, ICRF operation is also accompanied by a significant increase in impurity production. The presence of neutral beam injection in addition to ICRH clearly enhances the absorption of the wave energy from about 50% to up to 90% with respect to the coupled power. With neutral beam injection (PNI≤3.5 MW) the increment of the plasma energy content due to ICRH (Prf≤2 MW) is found to be almost twice as large as in case OH+ICRH. Global heating efficiencies of up to 3×1013 eV/kW cm3 compare quite well with other ICRH experiments. First observations indicate a degradation of plasma confinement with ICRH to values in between L-type and OH confinement.
A review of recent developments in thin gate dielectrics for very large scale integration
Authors: Baglee David A.
Published: July 2002

Some of the recent advances in thin dielectrics for use in very large scale integration (VLSI) circuits are discussed. Included are the properties and characteristics of thin layers of silicon dioxide as well as the newer areas of trench technology. The effects of VLSI processing on thin dielectrics are also considered.
Synchrotron x-ray scattering studies of semiconductor (111) surface reconstruction
Authors: Robinson I. K.
Published: July 2002

Some unifying principles of the mechanisms governing reconstruction at semiconductor surfaces will be discussed. Sources of synchrotron x-radiation are then shown to be an important asset in the problem of surface structure determination. Three recent examples of the application of x-ray diffraction techniques to semiconductor (111) surfaces will then be presented to illustrate the general remarks. (i) A structure determination of the InSb(111) surfaces shows very clear evidence of charge transfer leading to valence change in the top two layers of the structure. (ii) Structural analysis of the famous Si(111) 7×7 reconstructed is discussed in the light of certain models. (iii) A 7×7 state of Ge(111) seen in epitaxial films of Ge on Si(111) is attributed to compressive strain.
Particle and impurity control in toroidal fusion devices
Authors: Wootton A. J.
Published: July 2002

A review of working particle and impurity control techniques used in and proposed for magnetic fusion devices is presented. The requirements of both present-day machines and envisaged fusion reactors are considered. The various techniques which have been proposed are characterized by whether they affect sources, sinks, or fluxes; in many cases a particular method or device can appear in more than one category. Examples are drawn from published results. The solutions proposed for the large devices which will be operating during the next 5 years are discussed.
Surface topography development on Teflon under keV Xe atom bombardment
Authors: Michael R. , Stulik D.
Published: July 2002

Topography development on the surface of Teflon■ (polytetrafluoroethylene) subjected to different doses of 6 keV xenon atoms were studied. It is shown that the surface-impurity model can only describe some unusual topographical features and is not adequate to explain in whole our current observations. A new model based on microcrack development, surface splitting, filament formation, and subsequent filament-to-cone transformation is discussed and some experimental evidence for its validity is presented.