bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of oxygen implantation upon secondary ion yields
Authors: Morgan A. E. , de Grefte H. A. M. , Tolle H. J.
Published: July 2002

The useful degree of ionization β+η of boron, present as a dopant in various substrates, has been measured using O+2 primary ions. The measurements also yielded β+η for the matrix elements and the steady-state sputtering yield S of the substrate. Two SIMS instruments were employed in order to vary the bombardment parameters. Auger electron spectroscopy was used to measure the surface concentration of implanted oxygen. Neither this quantity nor (β+η)B are simply related to the inverse of S as has been proposed in the literature. Further, β+η of a matrix element, when referenced to the corresponding (β+η)B, does not exhibit an exponential variation with the ionization potential.
GaAs–oxide interface states: Gigantic photoionization via Auger-like process
Authors: Lagowski J. , Kazior T. E. , Walukiewicz W. , Gatos H. C. , Siejka J.
Published: July 2002

Spectral and transient responses of photostimulated current in MOS structures were employed for the study of GaAs–anodic oxide interface states. Discrete deep traps at 0.7 and 0.85 eV below the conduction band were found with concentrations of 5×1012 cm−2 and 7×1011 cm−2, respectively. These traps coincide with interface states induced on clean GaAs surfaces by oxygen and/or metal adatoms (submonolayer coverage). In contrast to surfaces with low oxygen coverage, the GaAs-thick oxide interfaces exhibited a high density (about 1014 cm−2) of shallow donors and acceptors. Photoexcitation of these donor–acceptor pairs led to a gigantic photoionization of deep interface states with rates 103 times greater than direct transitions into the conduction band. The gigantic photoionization is explained on the basis of energy transfer from excited donor–acceptor pairs to deep states.
Fermi level pinning on (110) GaAs surfaces studied by CPD and SPV topographies
Authors: Palau J. M. , Testemale E. , Lassabatere L.
Published: July 2002

Contact potential difference (CPD) and surface photovoltage (SPV) has been associated in topographic (110) GaAs surfaces studied in n and p type samples. Measurements are performed in situ on cleaved and submonolayer silver covered surfaces. Acceptor and donor surface states have been found on all these surfaces. For cleaved surfaces, cleavage defects are clearly correlated to states. For silver covered surfaces, Fermi level pinning is effective and results can agree with the unified model for III–V semiconductors proposed by Spicer et al.
A numerical and experimental study of the electric field distribution within field emission systems
Authors: Eaton H. C.
Published: July 2002

The design of field electron and field ion sources which are useful in device fabrication systems, electron or ion microscopes requires an accurate and complete knowledge of the electric field distribution both within the gun and near the field emitter itself. Analysis has not been possible by conventional analytical methods due to the intractable nature of the equations. An analysis is presented in the present work which is obtained using the method of finite elements. The numerical approach allows the consideration of the geometric detail common to field ion and field electron microscopes. In these microscopes the ion or electron source serves as the actual specimen to be observed. It is shown that instrument features as far away as 105 tip diameters can substantially affect the electric field at the emitter. The dependence of the electric field at the apex is found to vary as k1 exp(−k2ϑ) where ϑ is the emitter shank angle. The constant k2 describes the strength of the shank angle dependence. These constants may be experimentally determined. Experiments are discussed, and ion images are shown, which demonstrate the marked effect of system geometry on ion trajectories. The ion images illustrate the large amount of trajectory bending which results from a change in the position of a microchannel plate detector. One case is shown in which a crystallographic analysis of the image confirmed that certain trajectories originate from regions on a bulb-shaped emitter which were not within the line of sight of the detector.
An improved method for numerical analysis of point electron and ion source optics
Authors: Kang N. K. , Orloff J. , Swanson L. W. , Tuggle D.
Published: July 2002

Numerical calculation of the potential for point source geometries such as a field emitter diode, has long proved to be a difficult problem due to the extreme difference in the magnitude of the sizes of the cathode and anode. The difference can be as large as 106 in extreme cases, and is normally in excess of 103. A number of approaches have been attempted including numerical calculations, analytical calculations, and a combination of the two. Unfortunately, no approach has had sufficient speed and accuracy to be truly versatile. The present approach makes use of a spherical coordinate system in which the radial mesh size increases with radius according to a geometrical series with a term ratio (1−hϑ)−1, where hϑ is the angular mesh size, in radians. With this method the truncation error in the finite difference formulas is small, the accuracy of the calculated potential is everywhere uniform and the form of the difference formulas is quite simple. As a result, one can achieve high accuracy with a comparatively small number of mesh points. Computations performed on several electrode structures which had a geometrical range of 10 to 103 and which could be solved analytically, showed that errors as small as 10−5 in the potential could be attained when hϑ≊0.05. The error is even smaller if hϑ is reduced. Space charge effects are easily incorporated into the analysis. Computation formulas are presented, along with results for a pointed LaB6 cathode structure and for a thermal-field emission source.
Plasma pretreatment to improve resist properties by reduction of resist flow during postbake
Authors: Moran J. M. , Taylor G. N.
Published: July 2002

Softening and subsequent flowing of resist during postexposure baking, used to promote resist adhesion, often results in reduced resolution and linewidth control. This is unacceptable for the fabrication of very fine feature VLSI devices since linewidth variations of 0.5–1.5 μm can be observed under certain baking conditions. Treatment of positive and negative resists with a nitrogen plasma prior to postbaking reduces resist flow significantly and enables linewidth integrity to be maintained. Minimal resist erosion occurs upon plasma treatment. In one example a series of 1.4-μm-diam windows were exposed and developed in 0.8-μm-thick HPR-204 positive photoresist. Samples treated with a 400 W unshielded nitrogen plasma for 10 min exhibited no change in feature width whereas the untreated control, baked as above, exhibited completely closed windows due to excessive resist flow. A model is proposed to account for the improved flow characteristics.
UV hardening of photo- and electron beam resist patterns
Authors: Hiraoka H. , Pacansky J.
Published: July 2002

A simple UV-hardening process is described that renders micron sized images in AZ resists resistant to flow when heated to temperatures above 210 °C. The UV treatment prevents the image flow problems usually encountered in reactive ion etching processes. Mechanistic studies with infrared spectroscopy and ESCA indicate that the indene carboxylic acid generated from diazo-oxide photoactive compounds or its salt may be responsible for rendering the films resistant to flow, while the ester linkages between the photoactive compound and the host resin do not provide flow resistance.
Computation of the elliptic functions used in calculating electron emission from surfaces
Authors: Sidhu S. S.
Published: July 2002

Four functions involving elliptic integrals—v( y), t( y), s( y), and ϑ( y) [or fmg ( y)]—are used in calculating electron emission from surfaces under the influence of temperature and external electric fields. Published tables and various types of approximations for their calculation exist in the literature. Limitations to their use are discussed. A method is described whereby they can be computed directly by evaluating the complete elliptic integrals through an iterative algorithm that can be programmed even on pocket calculators.
Ni/Cr interface width dependence on sputtered depth
Authors: Davarya F. , Roush M. L. , Fine J. , Andreadis T. D. , Goktepe O. F.
Published: July 2002

The composition depth distribution of an interface as determined by Auger sputter depth profiling is dependent, to a large extent, on both the ion-bombardment-induced cascade mixing and on the surface topography generated as a result of ion erosion. We assess the relative influence of these two processes on the depth resolution by comparing interface widths obtained by Auger sputter depth profiling (resulting from both the cascade mixing and the topography) to interface widths obtained by computer simulation (due to cascade mixing alone). Depth profiles were measured at eight successive interfaces of a multilayered Ni/Cr/Ni/Cr ⋅⋅⋅ thin-film structure using both 1- and 3-keV argon ion beams for sputter profiling. These interface widths increase with sputter depth, the increase being more rapid for the 3-keV bombardment. The calculations with the computer code evolve contain modeling of all contributions to interface broadening, except that of surface topography, thus resulting in constant values of interface widths. The difference in width obtained from the measured and calculated data is used to estimate the extent of the topography produced as a function of sputtered depth.
A new sputter ion-pump element
Authors: Pierini M. , Dolcino L.
Published: July 2002

A new ion-pump element is described which has high pumping speeds for noble gases, excellent hydrogen pumping, low leakage current, and long life. The long term pumping of argon is very stable with this element. Performance is superior in comparison to diode pumps with differential cathodes and in comparison to conventional triode pumps. The experimental results suggest that the geometrical structure of the cathode enhances the production of high energy neutral atoms, the mechanism by which noble gases are pumped. The low leakage current allows accurate pressure measurement to the 10−8 Pa range, which is not possible with conventional triode designs. The geometrical structure of the cathode also ensures uniform erosion. Therefore, cathode life will be longer than that of conventional elements. Resistance to deformation caused by pumping of large quantities of hydrogen is high.
Characterization of the first wall of TEXTOR with respect to hydrogen recycling
Authors: Winter J. , Waelbroeck F. G. , Wienhold P. , Rota E. , Banno T.
Published: July 2002

The recycling constant Rc=D/2σkr of the wall (D=diffusivity, 2σkr=surface release rate constant of hydrogen) is an essential parameter for the understanding of the hydrogen recycling phenomena in fusion devices. It has been measured in situ in TEXTOR, using the wall pump and release effect. The method is described and data are presented in the temperature range of 150–300 °C for surfaces prepared by different conditioning techniques. The values are compared to available literature data from other tokamaks and from laboratory experiments.
Gas release from first wall coatings under electron impact
Authors: Auciello O. , Haasz A. A. , Stangeby P. C.
Published: July 2002

Wall coatings produced for JET (TiC, SiC, TiO2, MgAl2O4, Al2O3, and Si on Inconel 600) and coatings produced by General Atomic for Doublet III, PDX, and TFTR (TiC and C–SiC on POCO graphite) were subjected to low energy (300 eV) electron bombardment and the release of various gas species were monitored. Virgin samples, samples baked for various periods at various temperatures, and samples exposed to air after baking are compared. Release rates for hydrogen and methane span the ranges 10−1 to 10−3 H2/e− and 10−2 to <10−4 CH4/e−, respectively. X-ray diffraction analysis was performed on coatings of TiC and SiC on Inconel (JET) and TiC and C–SiC on POCO graphite (GA) samples. This analysis indicates that the stoichiometry of the coating material may depend on the coating process.
Low energy electron channeling observed by current image diffraction (CID)
Authors: Jette A. N. , Nall B. H. , Bargeron C. B.
Published: July 2002

Electron channeling patterns observed at LEED energies contain surface structural information. Calculations indicate that surface layer relaxations contribute to the width of the channeling lines and large relaxations can result in line splitting. Possible evidence of this has been observed on aluminum. CID images containing lines due to elastic scattering from different sets of planes can be used to determine the inner potential and planar separation simultaneously at a specified primary electron beam energy. Generally, these channeling patterns observed experimentally are in good agreement with computations based on the simple Bragg theory.
Direct determination of surface structures from photoelectron diffraction
Authors: Barton J. J. , Bahr C. C. , Hussain Z. , Robey S. W. , Klebanoff L. E. , Shirley D. A.
Published: July 2002

Angle-resolved photoemission extended fine structure (ARPEFS) is induced by interference between primary and elastically scattered photoelectron waves originating from an adsorbate core level on an ordered surface. Analysis by procedures analogous to those used in surface EXAFS yields absolute surface structures directly. ARPEFS appears capable of yielding bond distances with the same accuracy as EXAFS, and accurate bond angles. The coordination number is unambiguous with ARPEFS. Experiments have been performed with c(2×2)S/Ni(001), along [001] and [011], and p(2×2)S/Cu(001), along [011]. The differential photoelectron cross section in the [011] direction, for example, is modulated by ±50% in ARPEFS, in contrast to the ±2–3% effects observed in surface EXAFS. Single-scattering theory yields a simple dependence of χ(k)=[I(k)−I0(k)]/I0(k) on the angles αj=cos−1(p,pj), βj=cos−1(ε,pj), and γ=cos−1 (ε,p) relating the primary wave propagation direction p, the direction pj of scattering off atom j, and the photon polarization direction ε.
X-ray gauge measures areal density variations as small as 0.1%
Authors: Stupin David M.
Published: July 2002

A gauge measures areal density variations as small as 0.1% in low density plastic foams and other materials. It has a spatial resolution of 0.5 mm. This system is safe, portable, easy to use, and is readily automated. The 6-keV x-ray flux from a 55Fe source is collimated to a 0.5-mm-diameter beam and attenuated by the sample. Transmitted x rays are detected with a proportional gas detector and counted with a scaler-timer. After measuring the x-ray attenuation in two areas of the sample, the areal density variation is calculated using an expression derived from I/I0=exp(−upx), where I is the transmitted flux, I0 is the incident flux, u is the mass attenuation coefficient of the sample, p is the foam density, x is the thickness of the sample, and the product px=D is the areal density. Measurements sensitive to 1% and 0.1% areal density variations take 3 min and 4 h per point, respectively, in 0.05-g/cm3 plastics, 1 cm thick. Absolute areal density is also measured to ±3% using existing x-ray attenuation tables. However, better accuracy may be obtained by calibrating the system with known samples.
Fabrication of polymeric microballoons for ablative inertial fusion targets
Authors: Guglielmi F.
Published: July 2002

Low-Z polymer microballoons required for ablative inertial fusion (IF) targets, reduce radiative preheat of the fuel upon irradiation by a 351 nm laser. Furthermore, the plastic shells are relatively transparent to x rays from the imploded core, thus enabling diagnosis of the implosion. Since the targets are required to hold DT gas they must exhibit good barrier qualities along with the usual requirements for concentricity and wall uniformity stipulated for IF targets. Using a microencapsulation technique we have been able to fabricate plastic microballoons which meet these requirements. By altering experimental procedures and conditions, shells made from polyacryconitrile, polyvinyl acetate, and polystyrene have been manufactured.
Status of TFTR with Ohmic heating and neutral beam injection
Authors: Grove D. J.
Published: July 2002

The main body of the paper addresses the current status of the Tokamak Fusion Test Reactor (TFTR) as of December 1984, with emphasis on the vacuum and surface physics aspects of its operation. A brief review is given of the first paper on the vacuum aspects of controlled fusion research to be presented to a Symposium of the American Vacuum Society. This was given at the Fifth Symposium in October 1958 by the author of this paper. A comparison is made of the devices of that time with TFTR. The vacuum vessel diameter has gone from 2 in. to 7 ft., the plasma durations from 2 ms to many seconds, and the energy confinement time has increased by a factor of 1000 to 0.4 s. TFTR plasmas have reached densities of 4×1013 cm−3 with electron and ion temperatures of 3 keV. Very preliminary results, with the injection of only 2 MW of 50–70 keV neutral hydrogen into deuterium plasma, show the expected ion heating and increase in neutron flux. These experiments also show roughly a 30% reduction in the energy confinement time from that of plasmas with only Ohmic heating, as has been noted in other tokamaks. Attention is called to the continuing importance of impurity control in fusion devices.
Construction, operation, and enhancement of JET
Authors: Duesing G. , Dietz K. J.
Published: July 2002

The paper highlights features of the construction of JET with an emphasis on the vacuum system. It reports on the operation of the vacuum system. The experimental results of JET operation up to August 1984 are summarized. Three areas of enhancement of the device are dealt with—limiters and walls, heating systems, and tritium handling.
Polyvinyl alcohol coating of polystyrene inertial confinement fusion targets
Authors: Annamalai P. , Lee Mark C. , Crawley Richard L. , Downs Raymond L.
Published: July 2002

An inertial confinement fusion (ICF) target made of polystyrene is first levitated in an acoustic field. The surface of the target is then etched using an appropriate solution (e.g., cyclohexane) to enhance the wetting characteristics. A specially prepared polyvinyl alcohol solution is atomized using an acoustic atomizer and deposited on the surface of the target. The solution is air dried to form a thin coating (2 μm) on the target (outside diameter ∼350–850 μm). Thicker coatings are obtained by repeated applications of the coating solution. Preliminary results indicate that uniform coatings may be achievable on the targets with a background surface smoothness in the order of 1000 Å.
Infrared thermography of first wall components on the Tandem Mirror Experiment Upgrade
Authors: Watkins J. G. , Dykhuizen R. C. , Hsu W. L. , Hill D. N. , Allen S. L.
Published: July 2002

Infrared thermography in the 8–12 μ wavelength range was used to measure surface heating on the low energy neutral source (LENS) plates in the Tandem Mirror Experiment Upgrade (TMX-U). A surface temperature rise of 3.5 °C was observed at the plasma edge during discharges lasting 70 ms with edge densities of approximately 1012 cm−3. However, surface heating appeared to be nonuniform azimuthally in that the bottom plates showed a greater temperature rise. A few seconds after the termination of the discharge an axial view of the TMX-U revealed an additional form of surface heating. This is consistent with observations from the x-ray diagnostic which showed that a significant concentration of energetic electrons remained after the bulk thermal plasma had disappeared; these electrons disappeared only after the magnets were turned off. Details of the experiment and our experiences with this diagnostic tool will be presented.
Weight change measurements of erosion/deposition at beryllium limiter tiles in the Impurity Study Experiment-B
Authors: Roberto J. B. , Edmonds P. H. , England A. C. , Gabbard A. , Zuhr R. A.
Published: July 2002

The weight changes of Be tiles which functioned as a rail limiter in ISX-B for more than 3500 beam-heated discharges have been determined. The net weight loss for the limiter was 2.0 g, with the central tiles losing a total of 3.2 g, and the inboard tiles gaining 1.2 g. The weight loss is attributed primarily to the release of Be droplets as a result of limiter surface melting. The weight gains resulted from an inward flow of molten material along the limiter surface. The results indicate high erosion (melt loss) with incomplete and nonuniform redeposition (melt flow) of limiter material during periods of limiter melting.
Auger and electron energy loss study of the electronic structure of U–M(M=Fe,Co,Ni) metallic glasses
Authors: Bevolo Albert J. , Drehman Alvin J.
Published: July 2002

Auger intensity measurements from a series of U100−xMx(M=Fe,Co,Ni) metallic glasses confirms a predicted change in local order about the uranium atoms for alloy compositions near U72M28. As x increases, independent of M, more electrons are charge transferred out of the uranium local density of valence states (LDOVS). At the highest x value measured, U42Co58, more than half of the valence electrons in the uranium LDOVS have been lost. The 5d core level electron energy loss spectra suggest that for x≤28,6d valence states are involved in the charge transfer, while for x≥28, it is mostly the 5f states that are involved.
Energy loss spectroscopy study of Si(111)–alkali metal interfaces at low temperatures
Authors: Avci Recep
Published: July 2002

Studies are made at ∼150 K under ultrahigh vacuum conditions on a wide range of alkali metal coverages on Si(111)-7×7. Negative second-derivative backscattered electron energy loss spectroscopy is used with 100 eV primary electrons. The interaction of the alkali metals with the silicon substrate goes through two stages as a function of alkali coverage: In the initial coverages, for less than ∼0.3 monolayer of alkali atoms, the basic reaction is that of charge transfer from the alkali atoms to the Si surface with a loss peak at ∼3.3 eV associated with the charge transfer states. The second stage of reaction—starting after the depletion of all the Si surface states—falls in a coverage range between ∼0.3 and ∼1 monolayer, in which the formation of a metallic layer with a coverage-dependent loss feature at about 2 eV is observed. At still higher coverages, multiple surface and bulk plasmon excitations and their combinations are dominant. In the overall scattering processes most of the parallel momentum (∼3 Å−1) is transferred to the sample during the elastic backscattering from the surface, and all the losses are essentially attributed to the forward inelastic scattering before and/or after the elastic process takes place near the metal/Si interface.
Field emission energy distribution study of laser-induced thermal effects
Authors: Gao Y. , Reifenberger R.
Published: July 2002

Laser-induced thermal effects on various surfaces of tungsten and molybdenum have been studied using field emitted electrons. Energy distributions measured by a dispersive electron energy analyzer allow the temperature increase of a laser-illuminated surface to be determined to within ±10 K. In addition to estimating the temperature rise, an analysis of the data also shows a sensitivity to small temperature-induced variations in the work function Φ. Fits to experimental data indicate that changes in Φ of a laser-illuminated surface can be estimated to within ±2 meV. The technique has been used to study W(100) surface reconstruction.
Secondary ion mass spectrometry and Auger study of lithium niobate processing for integrated optics
Authors: Landheer D. , Mitchell D. F. , Sproule G. I.
Published: July 2002

The impurities introduced into lithium niobate crystals by diffusion furnaces typically used for Ti:LiNbO3 integrated optical devices are probed using semiquantitative surface Auger analysis and secondary ion mass spectrometer (SIMS) depth profiling. It is shown that reactions in silica furnaces that accompany aging or contamination by lithium niobate result in the transfer of large amounts of silica to the crystal surfaces. High purity alumina furnaces can result in surface layers of 0.2–0.6 at. % sodium. Many common crystal cleaning methods should be adequate for the processing of lithium niobate optical waveguides.
Relation between flow, power, and presence of carrier gas during plasma deposition of thin films
Authors: Kaganowicz G. , Robinson J. W.
Published: July 2002

Plasma deposition processes have become an integral part of the manufacturing of microelectronic devices. Control of proper deposition parameters and understanding their relation to the composition of the plasma, and therefore to the film properties, is essential for depositing films in a repeatable and a predictable way. Using mass spectrometry, we have studied the influence of input rf power, reactant gas flow, and the presence and concentration of carrier gas on the degree of decomposition of a wide range of starting materials used during plasma deposition. It is shown that all three parameters influence the decomposition of the starting material and therefore the composition and properties of the deposit. It is also shown that different degrees of decomposition for different materials cannot always be predicted from the bonding energy between species being dissociated by a plasma. Using silicon nitride as an example, it is shown that the N/Si atomic ratio in films deposited at various conditions corresponds to the relative degree of decomposition of the reactant gases NH3 and SiH4.
Predicting negative ion resputtering in thin films
Authors: Kester Daniel J. , Messier Russell
Published: July 2002

Negative-ion bombardment of a growing thin film can lead to changes in growth rate, surface morphology, and composition of the film through resputtering of the deposited material. A model was examined which predicts the probability of negative-ion formation based on ion potential and electron affinity values (I–EA) of the elements in the material being sputtered. It was found that I–EA values are but one of many factors influencing the amount and distribution of resputtering effects occurring. The model was found to be most useful in comparing isostructural materials resputtered under identical conditions. Since the resputtering is not uniform, and in some cases can lead to conical etch pits extending part way, or even completely, through the film to the substrate, their elimination will be a prime requirement for devices with bulk properties.
A comparison of outgassing rate of 304 stainless steel and A6063-EX aluminum alloy vacuum chamber after filling with water
Authors: Chen June-Rong , Liu Yuen-Chung
Published: July 2002

Outgassing rates of A6063-EX aluminum alloy and SUS 304 stainless steel, in the form of a vacuum chamber, before and after filling the chambers with water were compared. The results showed that the outgassing rate of the aluminum alloy was greater than that of the stainless steel before baking. However, after in situ vacuum bakeout, the outgassing rate of the aluminum alloy became lower than that of the stainless steel, even for the chamber which had been filled with water. The Auger depth profile analysis reveals that the surface of the aluminum alloy, before bakeout, may have a porous aluminum oxide layer which increases the amount of the adsorbed gas molecules resulting in a large outgassing rate.
A short, flexible ultrahigh vacuum thermal and electrical conductor
Authors: Fowler G. L.
Published: July 2002

A procedure is described for fabrication of a short, flexible ultrahigh vacuum thermal and electrical conductor for cryogenic applications.
A constant flow electropolishing wand
Authors: Fowler G. L.
Published: July 2002

This note describes an inexpensive, lightweight wand that simplifies local electropolishing inside, outside, and around newly welded appendages or sidearms of a vacuum vessel. The wand is easy to manipulate, and allows electropolishing solution to be continuously pumped into the working region at a constant rate without the necessity of submerging the entire workpiece in electropolishing solution. An insulating guard that acts as a reservoir for the electropolishing solution prevents shorting to the workpiece.
Angle resolved photoemission study of the alloy scattering effect in Hg1−xCdxTe
Authors: Shih C. K. , Silberman J. A. , Wahi A. K. , Carey G. P. , Lindau I. , Spicer W. E. , Berding M. A. , Sher A.
Published: July 2002

Angle resolved photoemission spectroscopy (ARPES), a technique which provides information on the k-resolved density of states, has been used to study the alloy disorder effect in Hg1−xCdxTe alloys in order to make comparison with theory. Using off-normal emission with photon energies from 15 to 30 eV and assuming free-electron final states, the band dispersions along the [111] and [100] directions were determined for CdTe and HgTe as well as for Hg0.7Cd0.3Te. Within the framework of the coherent potential approximation (CPA), the alloy disorder effect is characterized by a self-energy term which is complex and energy dependent. The real and imaginary parts of the self-energy term characterize the shifted energy and the damping of a particular virtual crystal eigenstate ‖n,k〉. Because of the k-resolving power of ARPES, the alloy scattering effect can be studied by comparing the spectra of the alloy Hg1−xCdxTe, and the binaries CdTe and HgTe. The deviation of the peak position from the virtual-crystal approximation (VCA) value and the extra broadening of the line shape reflect the energy shift and the damping of the VCA Bloch states due to the alloy disorder. Our studies show that for the lower valence-band states (binding energy from 2 to 6 eV) the alloy disorder effect agrees with the CPA calculation using the empirical tight-binding method by Hass et al. However, the uppermost bands show anomalous behavior: the binding energies of the upper bands of Hg0.7Cd0.3Te lie outside the CdTe and HgTe limits, indicating that there are effects not included in the original theoretical approach. A possible explanation in terms of anion disorder due to different Te renormalization, depending on whether a Te is bonded to Cd or Hg atoms, is discussed.
Formation of (M+Me)± ions from ultrahigh-vacuum-prepared amino acid layers on metals
Authors: Holtkamp D. , Kempken M. , Klüsener P. , Benninghoven A.
Published: July 2002

The secondary ion emission from amino acids evaporated onto clean metal surfaces under UHV conditions was investigated. Besides the well-known quasimolecular ions (M±H)± and (M+Me)+, where Me stands for the substrate metal, a considerable (M+Me)− signal was detected additionally. For an alanine monolayer on Au the yields of (M+Au)+ and (M+Au)− were comparable while the Au−/Au+ intensity was greater than 103. Regarding Ni, the coadsorption with deuterium demonstrated that the amino acids are adsorbed intact. During glycine adsorption/desorption cycles a similar behavior of (M–H)− and (M+Ni)−, on one hand, and of (M+H)+ and (M+Ni)+, on the other, was observed. Both the (M+H)+ and the (M+Ni)+ formation required multilayer structures. In contrast to that, (M±H)± and (M+Au)± showed the same increase during glycine layer growth on Au. As many of these results cannot be explained by the models of organic ejection which are currently being discussed, it is believed that cluster dissociation processes are important in organic secondary ion formation, at least for the quasimolecular ions (M+Me)±.
Investigation of trapped ions with a clearing electrode
Authors: Miyahara Yoshikazu
Published: July 2002

The properties of trapped ions in the circulating electron beam in an electron storage ring were investigated with a clearing electrode. The drift velocity, production rate, and neutralization factor of the trapped ions are discussed and compared with experimental data.
Electron energy-loss spectroscopy investigation of core levels and valence excitations of Pd2Si
Authors: Nannarone S. , Fiorello A. M. , del Pennino U. , Mariani C. , Betti M. G. , De Crescenzi M.
Published: July 2002

An electron energy-loss spectroscopy investigation of Pd2Si valence band and core edges is presented. The interpretation of the different observed structures allows us to understand the changes which occur in full (d bonding) and empty (s,p antibonding) electronic states on passing from pure Pd to the Pd2Si compound. The local structure around the Pd atom is derived through the analysis of the extended loss features above the N2,3 levels.
Surface analysis of palladium boride liquid metal ion beam deposition on silicon single-crystal solid surface
Authors: Higuchi-Rusli R. H. , Corelli J. C. , Steckl A. J. , Jin H.-S.
Published: July 2002

Surface analysis of a palladium boride liquid metal ion beam deposition on a silicon single-crystal (100) solid surface was analyzed by optical microscopy, Auger electron spectroscopy, and Rutherford backscattering spectroscopy. The beam composition prior to the deposition on silicon was analyzed with a quadrupole mass spectrometer. Droplet formation was observed experimentally from a 10-μm emitter tip radius which can be estimated from calculation to be due to higher mass flow rate associated with a larger emitting tip radius. Auger electron spectroscopy results show that the main element contaminants (Fe, Ni, Cr, and Re) come mostly from extractor material (Fe, Ni, and Cr) sputtering, and emitter tip erosion. Rutherford backscattering analysis of beam deposit from a 10-μm emitter tip radius on silicon surface shows no change in stoichiometry between the deposit and alloy source despite droplet formation on silicon surface.
Electron energy-loss microscopy of oxide films
Authors: Mitchell D. F. , Graham M. J.
Published: July 2002

A transmission electron microscope (Zeiss model 902) with a Castaing/Ottensmeyer prism–mirror–prism energy dispersive unit, located before the final projector lens, has been used to obtain images of the elemental distribution within thin films. The advantages of the electron energy-loss imaging technique are (1) speed (1-s images of 512×480 pixels are typical); (2) lateral resolution, ≤3 nm; and (3) detectability limit as low as a hundred atoms of a given element. The speed of the technique allows multiple images to be taken at energies below the excitation edge which can be used to correct diffraction effects, and uneven illumination or screen sensitivity. Examples of application of the technique will center on observations of segregation within oxide films.
Summary Abstract: A quantum chemical study of BaO/W cathode surfaces
Authors: Müller Wolfgang
Published: July 2002

(Received 18 September 1987; accepted 11 January 1988)
99.99% Al/6063 alloy coextruded cryogenic beam tube
Authors: Ishimaru H. , Narushima K. , Kanazawa K. , Suetsugu Y. , Bintinger D. , Jöstlein H. , Trobojevic D.
Published: July 2002

A beam tube composed of 6063 alloy aluminum with a coextruded inner surface of 99.99% pure aluminum is proposed for the Superconducting Super Collider (SSC). It has higher electric conductivity than oxygen-free pure copper at liquid-helium temperature. Thermal desorption rate is ∼10−12 Pa l/s cm2 after 150 °C 24-h baking. Dynamic gas desorption by synchrotron radiation from the inner surface at liquid-helium temperature was measured with and without magnetic field. Magnetic field reduces the pressure rise by synchrotron radiation by one order of magnitude at liquid-helium temperature. If a pure Al clad beam tube is accepted for SSC vacuum system, vacuum components of aluminum alloy which can be operated at liquid-helium temperature are needed. Dynamic bellows, nonmagnetic feedthroughs, an all metal gate valve, a compact turbomolecular pump, an automatic welding machine, and a new type of pressure monitor along the ring have been developed.
The effects of p+ implant species and dose on black gold formation
Authors: Arac Sabri , Packwood Donald , Juanitas Mark
Published: July 2002

Au:31 at. % Si, commonly known as black gold, has been a serious problem since gold has been used as interconnects. Black gold has usually been observed in the p+ contact regions. 11B+, BF+2, and F+ were implanted into test structures. Then the wafers were annealed and metallized with W:15 wt. % Ti (reactively sputtered in N2) followed immediately with gold sputtered in Ar. After annealing the metal in N2 at 400 °C, only the wafers implanted with high-dose BF+2 and F+ showed severe black gold. Thermodynamic calculations indicate that a possible cause is related to a super saturation of F in the Si lattice with the high-dose implants. Scanning electron micrographs taken of these regions showed pits as deep as 1/2  μm, apparently due to SiF4 formation. Transmission electron microscopy cross sections of the p+/metal contacts indicate heavy Si damage at the metal/Si.
The role of sandwich holography in inertial confinement fusion
Authors: Pattinson Theodore R. , Musinski Donald L. , Felmlee William J.
Published: July 2002

At KMS Fusion we have adapted the technique of Sandwich Holography to characterize cryogenic targets used in inertial confinement fusion (ICF). The procedure allows us to expose a holographic film at a given moment and later (minutes, hours, days) expose a second plate. On reconstruction of the two images, we have a holographic interferogram of any change of state of the fuel. This means that on large ICF target chambers, in spite of vibration and thermal induced motions, it is possible to characterize cryogenic targets. The technique also holds great promise for observing the fuel layers produced in beta heating experiments now in progress. In these experiments it can be minutes to days between the required exposures. A micropositioner is necessary for interferometric reconstruction, since indexing of the order of a wavelength of light is required to interpret the resulting fringe pattern. The procedure and some practical applications are discussed in the paper.
Circuit modeling of GaAs: a-SiC interfaces
Authors: Soukup R. J. , Sullivan J. R.
Published: July 2002

Using a previously developed modeling system, the electrical properties of the GaAs-amorphous SiC interface have been studied. The metal–insulator–semiconductor structures were fabricated by sputter deposition of SiC onto GaAs substrates. These devices were analyzed by the measurement of complex impedance versus frequency from 5 Hz to 13 MHz. The frequency dependence of the various parameters derived from the measured complex impedance were compared with the same parameters calculated from the RC electrical circuit model. Using a least-squares fit technique, sets of initial element values were obtained. Determining the correct set of values from the six possible that result from this technique was accomplished using known physical parameters. Once a set was selected, the element values could be fine tuned interactively to obtain the best match possible between the circuit model and the physical data. These element values were then used to characterize the properties of the interface, such as interface state concentration, depletion or accumulation mode, and trap levels. The preliminary results indicate that the SiC–GaAs interface has a reasonably low density of active interface states, but the SiC is not as highly insulating as desirable.
Material contrast using the scanning tunneling microscope in ambient conditions
Authors: Strecker H. , Stahl C. , Starke H.
Published: July 2002

Using a scanning tunneling microscope, material contrast could be achieved with two different measuring methods during tunneling in air. First, the tunneling voltage was modulated and the cutoff frequency of the feedback loop was adjusted below the modulation frequency. The response of the tunnel current was picked up by a lock-in amplifier and stored simultaneously to the topographical signal in a second channel. In a second experiment, the tunneling tip was vibrated with a frequency above the cutoff frequency of the feedback loop. The corresponding tunneling current was also picked up by the lock-in amplifier. Two different samples were examined, a carbon substrate partly covered with gold and a high temperature alloy containing carbides. The voltage modulation method was successfully applied for both samples. The modulation of the tunneling current changed with the material resulting in ‘‘material contrast’’ images. The tip vibration method also works for the carbon–gold sample, but with a poor signal-to-noise ratio. The method was not tested for the other sample type.
Auger crater-edge profiling of multilayer thin films by scanning Auger spectroscopy
Authors: Wang Y. X. , Cui Y. D. , Chen Z. G. , Lambers Eric , Holloway Paul H.
Published: July 2002

Multilayer Tb/Si thin films and AlAs/GaAs semiconductor superlattice thin films have been examined using an Auger crater-edge profiling technique. The data show that the true thickness of layers (in length rather than sputtering times) and differential sputtering ratios for different materials can be rapidly determined from the crater-edge profiles.
Characterization of interfacial failure in SiC reinforced Si3N4 matrix composite material by both fiber push-out testing and Auger electron spectroscopy
Authors: Eldridge J. I. , Honecy F. S.
Published: July 2002

An investigation into the mechanical/chemical properties of the fiber/matrix interface in an SCS-6 SiC reinforced reaction bonded Si3N4 composite is made using a fiber push-out test for determining interfacial shear strength and Auger electron spectroscopy (AES) depth profiling for elemental composition in the interface region. Special emphasis is placed on locating the weak point where interfacial failure occurs. Fiber push-out tests determined the interfacial frictional shear stress to have an average value of 8 MPa and was found to depend only on frictional stresses. AES depth profiles were obtained for composite fracture surfaces as well as pushed-out fibers. For both composite fracture and fiber push-outs, the interfacial failure was determined to occur either between the two C-rich coatings that are present on the double-coated SCS-6 SiC fibers or between the inner C-rich coating and the SiC fiber. Failure was not observed between the outer C-rich coating and the matrix. AES depth profiles indicated that interface failure occurs at points of very abrupt concentration changes. Evidence is presented for substantial mass transport within the fiber coating during composite fabrication.
Scanning tunneling microscopy of deoxyribonucleic acid during replication
Authors: De Stasio Gelsomina , Rioux D. , Margaritondo G. , Mercanti Delio , Trasatti L. , Moore C.
Published: July 2002

Scanning tunneling microscopy was used to produce topographic images of uncoated and unlabeled deoxyribonucleic acid (DNA) in air, on a graphite substrate. The images show for the first time a DNA molecule that had been isolated while it was replicating.
Electronic interactions in bimetallic systems: Core-level binding energy shifts
Authors: Rodriguez José A. , Campbell Robert A. , Goodman D. Wayne
Published: July 2002

The electronic properties of Cu, Ni, and Pd films supported on single-crystal metal surfaces have been examined by means of x-ray photoelectron spectroscopy (XPS). The shifts in core-level binding energies indicate that adatoms in a monolayer of Ni, Cu, or Pd are electronically perturbed with respect to surface atoms of Ni(100), Cu(100), or Pd(100). The present results show a correlation between the shifts in XPS surface core-level binding energies and variations in the desorption temperature of CO from metal adlayers. The shifts in XPS binding energies and CO desorption temperatures can be explained in terms of (1) variations that occur in the admetal–admetal interactions when the admetal adopts the lattice parameters of the substrate and (2) effects of the admetal–substrate interaction. Chemisorption of CO induces a large decrease in the electron density of the metal adlayers. This is a consequence of (1) charge transfer from the metal adlayer to the substrate (induced by a repulsive interaction between the admetal σ charge and electrons in the 5σ orbital of CO) and (2) transfer of electrons from the admetal into the 2π orbitals of CO (π backbonding).
X-ray photoelectron spectroscopy characterization of the oxidation and reduction of polycrystalline ZrPt3 and HfIr3 from 300 to 1700 K
Authors: Fisher R. F. , Alvey M. D. , George P. M.
Published: July 2002

Samples of the Engel–Brewer intermetallic compounds ZrPt3 and HfIr3 are characterized by x-ray photoelectron spectroscopy (XPS) after in vacuo exposure to oxygen, water vapor, and hydrogen at temperatures ranging from 300 to 1700 K. Results from these experiments indicate that both ZrPt3 and HfIr3 only partially react with oxygen and water vapor up to 1700 K, forming a surface oxide layer no thicker than approximately 35 Å. The surface nature of the oxide layer is confirmed by angle-resolved XPS studies on HfIr3. Vacuum annealing and hydrogen dosing prior to oxidation passivate the surface, inhibiting oxidation, while hydrogen exposure after oxidation reduces the surface oxide. Consequently, as a result of their stability in a high-temperature oxidizing environment, these materials show promise for use as oxidation-resistant coatings for high-temperature carbon–carbon composite applications.
Reaction mechanism between BN-sprayed graphite and molten Al in vacuum, and its application to the evaporation source for reactive metals including Al
Authors: Jeong J. I. , Lim B. M. , Moon J. H. , Hong J. H. , Kang J. S. , Lee Y. P.
Published: July 2002

We investigated the reaction mechanism between BN-sprayed graphite and molten Al in vacuum using the various analytical tools. The interfacial compound layer was well-defined, and made mainly of AlN with underlying thin mixed layer of Al4C3 and Al8B4C7. The analysis results were interpreted in terms of the free energy of formation. We prepared the BN-sprayed and annealed graphite boat, and evaluated the performance characteristics for the evaporation of reactive metal such as Al. Extended lifetime and rate limit were obtained at a manufacturing cost of about 1% compared with current TiB2⋅BN boat.