bluuebunny/crossref_metadata_2025 huggingface dataset:
Halide formation and etching of Cu thin films with Cl2 and Br2
Authors: Park Seongju , Rhodin T. N. , Rathbun L. C.
Published: July 2002

Etching mechanisms of Cu thin films under the exposure of an argon ion beam and halogen molecules (Cl2, Br2) were examined in a UHV system using a quartz crystal oscillator and x-ray photoelectron spectrometer. Chlorine exposure at room temperature produced a very stable chlorine overlayer on the Cu surface. The passivation of Cu by chemisorbed Cl reduced the etch rate of Cu film under argon ion bombardment for pressure up to 10−3 Torr of chlorine. Cuprous chloride was formed at 210 K, where multilayers of Cl2 are adsorbed on the Cu surface. Br2, however, diffused into the Cu substrate at 10−6 Torr at room temperature. A linear growth rate of the halide film was observed. The etch rates of copper were not enhanced by ion bombardment in the presence of either halogen. Large amounts of free halogens were incorporated in the halide films. These results suggest that the halogenation of a copper surface is dominated by the unactivated place exchange mechanism with constant sticking coefficient. The relative flux ratios of neutral and ion species as well as surface temperature were found to play important roles in halide formation and in the etching of copper.
Sputter deposition of Tl2SeAs2Te3 chalcogenide glass
Authors: van der Jagt A. , Chen Wenpeng
Published: July 2002

The composition of films produced by ion beam sputtering of an amorphous chalcogenide glass (Tl2SeAs2Te3) target was investigated. Changes in the target surface temperature during the sputter process by means of changes in the ion energy or the total number of ions colliding with the target revealed that the target surface temperature is an important parameter in determining the film composition. When target temperature is kept low, the arsenic content of the film is less than the target (preferential sputtering). Raising the target temperature has, initially, only a small effect on the composition, but when it becomes so high that the target material begins to soften, its influence increases exponentially. This effect may possibly be explained by assuming the presence of thermal spikes, created by the ions. It was also noted that the compositions of multiple, thick, sputter-deposited films are very constant provided the process parameters have not changed. Examination of the target surfaces show that they become very pitted, causing a greater number of available atoms, which could explain this composition uniformity. The configuration of the ion beam setup may play an important role in keeping the target temperature uniform. In summary, it is possible to sputter deposit films having the same composition as the target material provided the proper parameters are selected.
Room temperature postimplantation He release measurements as a technique for the study of the properties of He implanted materials
Authors: Lifshitz Y. , Cheifetz E.
Published: July 2002

Room temperature postimplantation He release from implanted titanium hydride films was investigated. The release decreased with time obeying the equation log(dN/dt)=−m log t+A, where 0.5<m<1. The value of m was practically flux independent for a given sample. Therefore, the He release rate taken at an arbitrary time of 10 days after implantation could serve as a measure of the integral He release as well as any instantaneous release rate, from a sample during the period 1–100 days after the implantation. The flux dependence of this release rate 10 days after implantation showed a sharp increase at a ‘‘critical flux,’’ behavior similar to that found in the reemission of He during implantation measurements. This postimplantation release was interpreted as originating from atomic diffusion processes. The measurement of postimplantation He release rates was therefore found to be a useful technique for the investigation of the properties of He implanted samples.
Direct observations of surface chemical and structural changes resulting from the CO oxidation reaction on rhodium
Authors: Kellogg G. L.
Published: July 2002

Surface modifications resulting from the CO oxidation reaction on Rh have been investigated by imaging atom-probe mass spectroscopy and field ion microscopy. Rhodium field emitter samples were heated to 500–600 K in 1–15 Torr of the reactant gases and transferred under UHV to the analysis chamber. Imaging atom-probe analysis was used to detect changes in surface composition, and field-ion microscope analysis was used to detect changes in surface morphology. For reaction temperatures of 500 K and total pressures between 1 and 2 Torr, the surface composition was found to change from primarily CO and surface carbon to Rh2O3 as the O2/CO ratio was increased beyond 30/1. This ratio correlates with previous observations of the deactivation of the CO oxidation reaction providing direct evidence that the deactivation is oxide-induced. Field ion microscope images of Rh surfaces following the CO oxidation reaction in stoichiometric mixtures of CO and O2 at total pressures from 1.5–15 Torr indicate morphological changes which differ from changes due to thermal annealing alone. The nature of the changes are in qualitative agreement with previous studies of ammonia oxidation and decomposition on macroscopic Pt spheres.
Fermi level pinning during oxidation of atomically clean n-InP(110)
Authors: Bertness K. A. , Kendelewicz T. , List R. S. , Williams M. D. , Lindau I. , Spicer W. E.
Published: July 2002

Previously a donor defect level at about −0.1 eV below the conduction band minimum has been associated with InP, in part to explain the nonmonotonic movement of the Fermi level within the band gap during the oxidation of n-InP. We present here new soft x-ray photoemission spectroscopy results which associate this behavior with a level in the oxide on the surface of the InP rather than with a native defect such as a P vacancy. Specifically, we have observed that the reversal in Fermi level movement occurs at exactly the same oxygen exposure as the appearance of structure in the In 4d core line indicative of the formation of In oxide (s). Phosphorus oxide is also indicated, as expected, along with elemental P, but the In oxide is particularly relevant because In2O3 has a sufficient density of shallow donor states to make it an n-type semiconductor. These oxide donor states, rather than native defect states, can compensate native acceptor defect states and cause the observed Fermi level movement. The Fermi level changes which are seen during the reduction of the surface In oxide to In metal are also consistent with the removal of the donor states. This interpretation changes strongly the overall picture of extrinsic states near InP–adatom interfaces, as there is no need to postulate the existence of native shallow donor defects to explain the InP–oxide interface.
Time and angle resolved ultraviolet photoemission spectroscopy studies of single crystal surface and interfaces
Authors: Haight R. , Bokor J. , Freeman R. R. , Bucksbaum P. H.
Published: July 2002

The new technique of time and angle resolved ultraviolet photoemission spectroscopy (UPS) is used to study electron dynamics at single crystal surfaces and interfaces in the picosecond time domain. A single laser source is used to photoexcite electrons into normally unoccupied states at a surface or interface and provides the UV radiation for photoemission studies of the excited system. In this paper we briefly review studies of the unoccupied surface state on the clean InP(110) surface and present new results for three related interfaces. We have studied the transiently excited Al/InP, O/GaAs, and Au/GaAs interfaces, and have for the first time directly observed with photoemission normally unoccupied interface states above the Fermi level in these systems.
Kinetic study of Schottky barrier formation of In on GaAs(110) surface
Authors: Chin K. K. , Kendelewicz T. , McCants C. , Cao R. , Miyano K. , Lindau I. , Spicer W. E.
Published: July 2002

The kinetics of the Schottky barrier formation of In on GaAs(110) surfaces has been studied by photoemission. A temperature dependence of the profile of the n-GaAs(110) surface band bending versus In coverage has been observed. At liquid nitrogen temperature (LNT), the band bending attenuation is observed compared with a room and higher temperature band bending profile. Temperature dependence of the In growth mode is also observed. Spectroscopic evidence indicates that the GaAs band bending is correlated with the In metallic cluster growth. The experimental results are discussed in terms of the unified defect model. A possible transition from Bardeen limit (with pinning centers) to Schottky picture (without pinning centers) of the Schottky barrier formation of In on GaAs(110) is also discussed.
Bucket-type ion source for ion milling
Authors: Ono Y. , Kurosawa T. , Sato T. , Oka Y. , Hashimoto I.
Published: July 2002

A bucket-type ion source for ion milling applications has been investigated. Experiments showed that uniformity of the ion beam profile is subject to the cusp field. In order to extract uniform and well-collimated ion beams, operating conditions were optimized for 500 eV argon beam extraction. Current density (0.55 mA/cm) was constant within ±5% over the center of an 8 cm diam in a 10 cm acceleration system. Uniformity of milling rate for Cr–Cu–Cr film (520 Å/min) was constant within ±6% over a 7.6 cm wafer without substrate rotation. Micrographs of the etched patterns were studied. It was concluded that a bucket-type ion source is suitable for ion milling applications, especially large-area ion milling systems.
Silicon nitride and silicon diimide grown by remote plasma enhanced chemical vapor deposition
Authors: Tsu D. V. , Lucovsky G.
Published: July 2002

We discuss the deposition of silicon nitride (Si3N4) and silicon diimide [Si(NH)2] thin films by remote plasma enhanced chemical vapor deposition (RPECVD). We show that the use of two different nitrogen source gases N2 and NH3 leads to qualitatively different local bonding in the deposited films. We present studies of the local chemical bonding as a function of the substrate temperature (Ts) and the dilution of the nitrogen containing species with the rare gases Ar and He. We show that diluting the N2 with He by a factor of about 10 to 1 increases the growth rate for thin film formation by a factor of more than 3. Dilution of NH3 with He, reduces the deposition rate and also the amount of bonded hydrogen.
X-ray photoemission spectroscopy study of the activated oxidation of GaAs(1̄1̄1̄)
Authors: López de Ceballos I. , Muñoz M. C. , Goñi J. M. , Sacedón J. L.
Published: July 2002

The onset of characteristic As2O3, As2O5, and Ga2O3 chemical shifts (Ch.Sh.) is detected by the line analysis of Ga 3d, As 3d, and O 1s spectra. Exposure of GaAs(1̄1̄1̄) surfaces to excited O2 produces Ga2O3, As2O5, and a small quantity of As2O3, preceded by the appearance of As and Ga suboxides (Ch.Sh.=2.6 and 1.34 eV). Subsequent electron bombardment in the absence of O2 transforms the As2O5 and As suboxide into As2O3 and metallic As. These experiments have allowed for the first time the isolation of the contribution of the As■O bond in the O 1s spectrum, which has been decomposed in α, β1, and a new β2 state, in addition to O(As■O). The β1 grows during pre- and oxidation stages and the β2 during the oxidation. The unitary dependence between As5+ and O■ allows the calibration of the O 1s components, and consequently the determination of the compositions for the oxide net and suboxides.
Electron beam induced Hg desorption and the electronic structure of the Hg depleted surface of Hg1−xCdxTe
Authors: Shih C. K. , Friedman D. J. , Bertness K. A. , Lindau I. , Spicer W. E. , Wilson J. A.
Published: July 2002

Auger electron spectroscopy (AES), x-ray photoemission spectroscopy (XPS), low energy electron diffraction (LEED), and angle-resolved ultraviolet photoemission spectroscopy (ARPES) were used to study the electron beam induced Hg desorption from a cleaved (110)Hg1−xCdxTe surface and the electronic structure of the Hg depleted surface. Solid state recrystallized Hg1−xCdxTe single crystals were used. It was found that the electron beam heating dominated the electron beam induced Hg desorption on Hg1−xCdxTe. At the electron beam energy used, the electron beam heating extended several thousand angstroms deep. However, the Hg depletion saturated after a few monolayers were depleted of Hg atoms. At the initial stage of Hg loss (only 3%), the surface band bends upward (more p type). The ARPES spectrum showed the loss of some E vs k dispersion after 22% Hg atoms were removed from the surface region, and no dispersion was observed after 43% Hg atoms were removed. These results have important implications on the electronic structure of the surfaces and interfaces of which the stoichiometry is altered.
Growth of microprojections arising from sputter etching of Cu–Ag sandwich
Authors: Tanemura M. , Okuyama F.
Published: July 2002

It is demonstrated that the sputter etching of a Cu–Ag sandwich using a focused Ar+-ion beam creates a crater covered with densely distributed microprojections, offering a crater-edge profile poor in resolution. The projections grew in a variety of shapes, ranging from a rod to a wide-angle cone, and their number density reached ∼109/cm2. The dimensions of the projections were also not uniform, increasing discernibly with depth. It is believed that an enhanced surface mobility of Cu and Ag atoms during the sputtering played a role in growing the projections.
Recent developments in the production of thin-film magnetic media by electron beam evaporation
Authors: Wright Michael
Published: July 2002

The design and operation of an electron beam roll coating machine, utilizing oblique angle incidence of the evaporant, for the production of magnetic tape is outlined. The use of a magnetic bending system and backscattered electron confinement is discussed with respect to the particular problems associated with the coating of thin polymer films. Preliminary results are reported for magnetic tape produced on such a machine with respect to magnetic and structural properties which indicate that the product exhibits characteristics suitable for video recording.
Quantized Hall effect and weak localization effects in two-dimensional HgTe–CdTe superlattices
Authors: Ong N. P. , Moyle John K. , Bajaj J. , Cheung J. T.
Published: July 2002

Electronic transport in the two-dimensional gas formed in superlattices of HgTe–CdTe has been investigated in both the weak-field (B<4 mT) and the intense-field regime (up to 29 T). We find that in high-mobility samples (53 000 cm2/V s) coherent backscattering effects (weak localization) are easily observable in the first regime while in the second regime quantized Hall steps are obtained in the same sample. The weak localization results have been exploited to obtain the temperature dependence of the electron dephasing rate and the spin–orbit scattering rate. Unlike AlGaAs–GaAs and Si–metal–oxide semiconductor field-effect transistor systems the spin–orbit scattering rate is very large (0.6 times the elastic scattering rate.) The quantized Hall-effect data are complicated by three factors which we discuss. These complications prevent an unambiguous interpretation at present, although differences from the AlGaAs–GaAs superlattice results are observed.
Spatial distribution of sputtered atoms from magnetron source
Authors: Swann S.
Published: July 2002

The macroscopic distribution of atomic material leaving a magnetically enhanced sputtering source is described for dissimilar materials and for different target grain structures. This information is useful to the thin-film process engineer and the magnetron designer. Results obtained give data on the flux of material sputtered from different areas of the target. A 110-mm-diam planar magnetron is used, powered by a 5-kW dc supply in an Edwards ESM100 coating system. Al and Cu electrodes, 6.35 mm thick, are sputtered at 5×10−3 mbar in argon. Profilometric data are obtained from pinhole camera deposited images of the magnetron surface. Direct images of the sputtered atoms leaving the cathode surface are obtained by collecting them on glass substrates after passing through a small aperture in a manner analogous to a pinhole camera. Thickness distribution is measured by a Rank Taylor Hobson Talystep. By collecting data from such images the atomic emissions from points on the magnetron surface are quantified. Improvements in thickness distribution are made by calculating mask dimensions from these data.
Interference structure in optical scattering from oxide/metal interfaces
Authors: Bergkvist M. , Roos A. , Ribbing C.-G.
Published: July 2002

Interference in the optical reflectance from oxide coated metals has been studied. The variation of the diffuse component exhibits a variation which is oppositely phased to the interference structure in the specular reflectance. The scattering originates from roughness which is created by the growth of the oxide. The behavior has been observed for the bilayers Al2O3/Al, Cu2O/Cu, TiO2/Ti, and SiO2/Si. The variation inside the oxide layer of the time average of the squared electric field of the light wave has been calculated. It was found that the diffuse reflectance scales closely with the intensity at the oxide/metal interface, both as a function of wavelength and oxide thickness.
Resistive synaptic interconnects for electronic neural networks
Authors: Lamb J. L. , Thakoor A. P. , Moopenn A. , Khanna S. K.
Published: July 2002

High-density, nonvolatile, associative electronic memories, based on neural network models, require large arrays of highly uniform, small-area, resistive (106–107 Ω) synaptic-feedback connections. Such passive, two-terminal resistors (very weak connections) are uncommon in the current very large scale integrated (VLSI) world. We report on the use of resistivity-tailored amorphous Ge1−xMx alloy (M=Al, Cu; 2≤x≤25 at. %) and Pt/Al2O3 cermet thin films as the resistive interconnects for the associative memories. Resistivity of the films is primarily controlled by their metal contents and deposition conditions. Arrays of highly uniform (±5%) interconnects, typically 10–20 μm long, 10 μm wide, and 0.1 μm thick, have been fabricated employing conventional photolithography. Suitability of the α-Ge:M and Pt/Al2O3 connections in the fault-tolerant, neural network memories is discussed.
Desorption of the catalyst agent after catalytic oxidation of semiconductors
Authors: Bakshi M. H. , Soukiassian P. , Gentle T. M. , Hurych Z.
Published: July 2002

Core level photoemission spectroscopy using synchrotron radiation is performed to study the catalytic action of cesium and sodium on the oxidation of semiconductors. On InP(110) the presence of a cesium monolayer provoked, at room temperature, a very large enhancement of the oxidation rate (by 1013) leading to the formation of phosphates as InPO4. On Si(100)2×1 cesium and sodium promoted the oxidation rate by 104 to 106. Furthermore, by annealing at moderate temperatures, the alkali metals were removed and a clean SiO2–Si interface was formed.
Contrast enhancement techniques for submicron optical lithography
Authors: Mack Chris A.
Published: July 2002

Contrast enhancement lithography (CEL), in which a bleachable film is deposited on a conventional photoresist, is studied theoretically and described mathematically. The resulting CEL model is used to understand the behavior of contrast enhancement lithography as well as the materials used. Effects such as resist sidewall angle improvement, exposure latitude, CEL thickness latitude, and CEL parameter optimization are studied. Other methods of ‘‘contrast enhancement’’ are explored.
Correlations between the chemical and electronic structure of thermally treated anodized InSb
Authors: Bregman J. , Shapira Yoram , Calahorra Z.
Published: July 2002

We investigated the effects of heat treatments on the interfacial chemical and electronic properties of InSb metal–oxide–semiconductor structures prepared by plasma and wet anodization. Using line–shape depth profiling by Auger electron spectroscopy, we note that annealing at increasingly elevated temperatures monotonically enhances the extent of O indiffusion, increases the width of the In–In oxide and Sb–Sb oxide interfaces, and changes their overlap and relative positions. The effect of the heat treatments on the capacitance–voltage (C–V) characteristics was noted by a marked decrease in the oxide trap and fast interface state densities for both oxidation methods. However, the fixed oxide charge density increased for wet anodic oxides and decreased for plasma-grown samples. The asymmetric effect of the bias voltage on the C–V curves was also analyzed. We present a model which correlates the electrically active species with different spatial positions and oxidation states of In and Sb at the oxide layers and at their interfaces. The model successfully explains the experimental observations.
Surface vibrational studies with electron energy-loss spectroscopy
Authors: Ibach H.
Published: July 2002

The development of electron energy-loss spectroscopy in studies of collective surface excitation, the physics and chemistry of adsorbates, and phonon dispersion measurements is briefly reviewed. Technical features of a spectrometer adapted to momentum resolving energy-loss spectroscopy in a wide range of impact energies are described.
X-ray photoelectron and infrared spectroscopy of microwave plasma etched polyimide surfaces
Authors: Chou N. J. , Paraszczak J. , Babich E. , Heidenreich J. , Chaug Y. S. , Goldblatt R. D.
Published: July 2002

I n situ x-ray photoelectron spectroscopy (XPS) and thermal desorption measurements indicate that etching of polyimide (PI) in a microwave oxygen plasma results in increased carbonyl (C–O) bonds on the etched surfaces, which can be removed by heating. Addition of CF4 to oxygen plasma enhances the etch rate, but also gives rise to fluorine coverages which appear to scale with the atomic F concentration in the gas mixture. XPS study of selected fluorinated model compounds shows that changes in the C 1s spectra of PI surfaces, etched in plasmas with different CF4 concentrations can be interpreted either as formation of Teflon-like passivation layers or as simply fluorinated benzenes. Exposure to x-ray irradiation at a constant flux or isothermal heating in vacuum caused the fluorine coverage to desorb in two stages, suggestive of two different fluorine-containing desorbing species. Experimental evidence obtained by multiple internal reflectance and transmission Fourier transform infrared spectroscopy indicates that for up to 50% CF4 additions, etching is accompanied by an increasing degree of fluorination of aromatic carbon. This is in contrast to the general belief that formation of a Teflon-like layer is responsible for inhibition of etch rate at higher CF4 concentrations in the gas mixture. A self-consistent model is proposed to explain these observations.
A simple mirror electron microscope–low-energy electron diffraction apparatus for surface studies
Authors: Shern C. S. , Unertl W. N.
Published: July 2002

A new mirror electron microscope–low-energy diffraction (MEM–LEED) apparatus based on previous designs has been constructed. In addition to its simplicity of fabrication, advantages of MEM–LEED over conventional LEED include: (1) A variable magnification, real-space image of the surface is obtained. In our system, the magnification is 10–40. (2) The diffraction pattern is imaged on a flat screen and the spot spacings do not change with incident energy. Our instrument has a transfer width greater than 40 nm. (3) Only one vacuum port is required. (4) Changes in the surface potential are easily measured. (5) Large magnetic fields near the sample do not degrade the performance; for example, operation at 7-eV incident energy in 10-G fields is routine for our instrument. (6) Fabrication costs are low. In our MEM–LEED an 8-keV primary beam is decelerated by a Johansson lens of which the sample forms the mirror element. The focal length is 25 cm. A major practical advantage in our MEM–LEED, unlike previous designs, is that the sample is near ground potential. The system is mounted through a 10-cm-diam port and is retractable. Examples of applications are given and the performance is demonstrated to surpass that of conventional display LEED systems.
Investigation of the mechanism of the activation of GaAs negative electron affinity photocathodes
Authors: Gao Huai-rong
Published: July 2002

This paper has discussed the mechanism of the formation of negative electron affinity (NEA) GaAs photocathodes which are treated with cesium and oxygen. The formation is mainly due to the drop of the electron affinity when the GaAs surface is covered with cesium atoms. This drop is not due to the formation of surface dipoles as usually supposed. The essence is that in cesium processing the surface potential barrier of GaAs is caused by the considerably weak nuclear force field of the surface cesium layer rather than by that of GaAs. The further decrease of the electron affinity by oxygen is due to the formation of O−2 ions below the cesium layer. These O−2 ions would let the excited photoelectrons in the conduction band pass easily into the weak nuclear force field of the cesium layer and get into the vacuum. A surface structure model and the energy diagram are suggested.
(100) versus (111)B crystallographic orientation of Hg1−xCdxTe grown by molecular-beam epitaxy
Authors: Arias J. M. , Shin S. H. , Cheung J. T. , Chen J. S. , Sivananthan S. , Reno J. , Faurie J. P.
Published: July 2002

Here, we report a study of the molecular-beam epitaxial (MBE) growth of HgCdTe on (100) and (111)B CdTe substrates. We show that the growth on the (100) orientation is easier to control than on the (111)B orientation, mainly because twinning, caused by excess Hg, is not observed. The structural quality, as probed by double-crystal x-ray rocking curve, is consistently of better quality for the (100) orientation. As-grown n- and p-type HgCdTe epilayers grown on both orientations exhibit high Hall mobilities. For the first time, p-type HgCdTe grown by MBE on the (100) orientation is demonstrated in this work. The HgCdTe layers grown on the (100) orientation have normal n- and p-type annealing behavior, but those grown on the (111)B behave abnormally, probably because of the presence of twins and stacking faults like defects created during growth. Improving MBE growth conditions could lead to a reduction in density of these defects on the (111)B plane.
The structure and electroluminescent characteristics of ZnS:Mn thin films
Authors: Nakanishi Yoichiro , Shimaoka Goro
Published: July 2002

The dependence of structure and the electroluminescent properties of ZnS:Mn thin films on the substrate temperature has been investigated. The samples were electron-beam deposited on polycrystalline Y2O3 film and quartz glass substrates. Reflection high-energy electron diffraction experiments showed that the films had a zinc-blende structure and were composed of a double-fiber structure with the two [111] axes inclined at an angle to the substrate at substrate temperatures between 25 and 180 °C. At 200 °C substrate temperature the films consisted of a single-fiber structure with the [111] axis nearly perpendicular to the substrate surface. Electron-spin resonance measurements indicated that Mn2+ content in the films was nearly constant at substrate temperatures above 140 °C but steeply decreased below this temperature. Maximum electroluminescent intensity was obtained when the films were produced at 200 °C substrate temperature.
Reactive and nonreactive ion mixing of Ni films on carbon substrates
Authors: Galuska A. A. , Uht J. C. , Adams P. M.
Published: July 2002

The effects of nonreactive and reactive ion mixing on the interfacial chemistry, morphology, and adhesion of Ni films on carbon substrates (glassy carbon, a-face pyrolytic graphite, and c-face pyrolytic graphite) were examined and compared to the effects of thermal processing. Nonreactive ion mixing was performed with 180-keV 84Kr+ at doses of 1 and 5×1016 Kr/cm2. Reactive ion mixing was performed with 150-keV 28Si+ at doses of 1 and 5×1017 Si/cm2. The as-deposited specimens were also vacuum annealed at 1000 °C for 3600 s. The chemistry and morphology induced by the 1000 °C anneal varied substantially with substrate structure. Adhesion enhancements resulting from the anneal were small (1–40×) and varied greatly with substrate structure. Krypton implantation induced collisional mixing at each of the different Ni/C interfaces, but did not influence specimen chemistry. Large adhesion increases (1–3 orders of magnitude) were observed in all of the 84Kr+ implanted specimens, regardless of substrate structure. Silicon implantation induced extensive Ni diffusion into the glassy carbon, a-face pyrolytic graphite, and c-face pyrolytic graphite substrates. Nickel segregation to the 28Si+ implant profiles resulted in the formation of buried Ni2Si layers. Substantial adhesion increases (1–3 orders of magnitude) were observed in all of the 28Si+ implanted specimens. These adhesion increases were attributed to the mechanical interlocking of films and substrates. The Ni2Si produced by 28Si+ implantation was formed too deep in the carbon substrates to influence interfacial bonding. Topographical changes induced by ion implantation included void and bubble formation, pitting, erosion, and carbon aggregation. These topographical changes varied with substrate structure, ion species, ion dose, and substrate temperature. Film characterization was performed using secondary ion mass spectrometry, Auger electron spectroscopy, scanning electron microscopy with energy dispersive x-ray analysis, and x-ray diffraction. Adhesion was examined using a scratch test.
Compatibility of spinning rotor gauge with tritium handling systems
Authors: Miyake Hitoshi , Matsuyama Masao , Watanabe Kuniaki , Kaneko Kumetaro , Kobayashi Yoichi
Published: July 2002

The uses of spinning rotor pressure gages for tritium handling systems dicsussed. The calibration of these gages and their compatibility with tritium handling systems and fusion experiments is also discussed. (AIP)
Use of successive expansion technique to determine volume ratios of ≊5000 for vacuum gauge calibration
Authors: Sharma J. K. N. , Mohan Pardeep
Published: July 2002

The method of successive expansion first used by Elliott and Clapham [National Physical Laboratory (U.K.) Report No. MOM28, 1978] for measuring volume ratios of ∼100 has been shown to be feasible for measuring volume ratios of ∼2830 with uncertainties of ±0.15 % while using a capacitance manometer with a lower pressure range for measuring the final pressures. The volume ratios thus determined have enabled the authors to reduce the systematic errors associated with the pressures generated by the series expansion system in their laboratory. Further, an attempt has been made to quantify the error in the measurement of volumes of chambers consisting of one or more metal diaphragm valves. In order to completely eliminate errors on this account an alternative calibration procedure has been outlined. The possibility of extending the measurement to ratios of ≊5000 has also been discussed.
Epitaxial growth and x-ray structural characterization of Zn1−xFexSe films on GaAs(001)
Authors: Jonker B. T. , Qadri S. B. , Krebs J. J. , Prinz G. A.
Published: July 2002

We have grown single-crystal (001) epilayers of the diluted magnetic semiconductor Zn1−xFexSe on GaAs(001) substrates by molecular beam epitaxy. The films were characterized with Auger electron spectroscopy (AES) and reflection high-energy electron diffraction, followed by x-ray θ–2θ, rocking curve, and topography measurements. AES data show that the surface stoichiometry does not change significantly under electron beam exposure, indicating that (Zn,Fe)Se is a more stably bonded compound than (Zn,Mn)Se, where large variations are observed. The variation of the lattice parameters both parallel and perpendicular to the surface is obtained as a function of Fe concentration. The Zn1−xFexSe epilayers are cubic in structure for x≤0.22 and thicknesses up to at least 2 μm, although films with x>0.05 exhibit a slight tetragonal distortion (1≤c/a<1.002). The onset of this distortion is reflected in a broadening of the x-ray double-crystal rocking curve. Dislocation densities obtained from the rocking curve linewidth range from 1 to 7.5×108 cm−2. X-ray topographs reveal a degree of mosaic structure which increases with Fe content.
Particle balance in the Tokamak Fusion Test Reactor
Authors: Ulrickson M. , Dylla H. F. , LaMarche P. H. , Buchenauer D.
Published: July 2002

Plasma particle pumping effects with carbon limiters have been seen in Tokamak Fusion Test Reactor (TFTR), Joint European Torus (JET), and Torus Experiment for Technology Oriented Research (TEXTOR). The pumping effects in TFTR were induced by conditioning the large-area axisymmetric bumper limiter with low-density, helium initiated discharges. As a result of the conditioning ∼150 Torr l of gas are removed from the carbon limiter tiles. The conditioning has reduced the particle recycling coefficient from near unity to values as low as 0.5. The low recycling conditions are not permanent. A pumping capacity of ∼100 Torr l has been determined from wall loading experiments. The total particle input has been compared to the total outgassing after a discharge for Ohmic plasmas in both helium and deuterium, and for deuterium neutral beam heated discharges. Ohmic deuterium plasmas have less outgassing than input. Ohmic helium plasmas have equal or greater outgassing compared to gas input. Neutral beam heated discharges have a slight deficit in outgassing, but it is much less than that for Ohmic shots. The low recycling conditions last much longer with neutral beams than in Ohmic discharges. The limiter pumping effect and the reduction in recycling is a prerequisite for the enhanced confinement neutral beam heated discharges observed on TFTR.
Magnetron plasma diagnostics and processing implications
Authors: Rossnagel S. M.
Published: July 2002

Numerous diagnostics have been used to help characterize and understand conventional magnetron plasmas. These include Langmuir probe studies, magnetic measurements of the drift currents, optical measurements of the sheath, along with emission spectroscopy of the sputtered species. The plasma conductivity is described by Bohm diffusion, and the sheaths by Child’s law. Local gas density measurements in the near-cathode region show significant reductions in the gas density as a function of discharge current. The plasma in a magnetron is strongly perturbed by the energetic sputtered species. The plasma impedance as a function of current is significantly altered by the magnitude and energy of the sputtered species, as well as the gas cross section and velocity. This effect has been modeled in terms of the energetic sputtered atom flux into the plasma region and the thermal conductivity of the gas. Deposition measurements on the cathode itself document the effects of gas scattering and the density modification due to the heating by the sputtered flux. The gas rarefaction effect modifies the energetic particle bombardment of the film in a nonlinear way with rate. It modifies the effective energy transferred to a film with each depositing atom, and alters the transition of elemental targets to the compound form when sputtering in a reactive atmosphere.
Resistivity changes and phase evolution in W–N films sputter deposited in Ne–N2 and Ar–N2 discharges
Authors: Huber Karl John , Aita Carolyn Rubin
Published: July 2002

The effect of discharge N2 content and rare carrier gas type on the crystal structure and electrical resistivity of sputter deposited W–nitride films is reported here. A diode apparatus was used to sputter a W target in rf-excited Ne–N2 and Ar–N2 discharges spanning composition range from pure rare gas to pure N2. Postdeposition analysis included x-ray diffraction and four-point probe resistivity measurements. The results show that in Ar–N2 discharges, phase evolution proceeds with increasing discharge N2 content as follows: αW+βW→low-resistivity microcrystalline phase, a-W(N)→W2N1+x→high-resistivity phase, X.W–nitride. Ths use of Ne–N2 discharge accelerated the formation of the higher N content phases and suppressed the formation of a-W(N).
Scanning tunneling microscopy of Langmuir–Blodgett films on graphite
Authors: Lang C. A. , Hörber J. K. H. , Hänsch T. W. , Heckl W. M. , Möhwald H.
Published: July 2002

We report the repeated observation at molecular resolution of lipid and fatty acid mono- and bimolecular layers on graphite in air. The films of di-myristoyl-phosphatidic acid and cadmium–arachidate were deposited by the Langmuir–Blodgett technique. This confirms the possibility of gaining scanning-tunneling microscopy (STM) images by electron transfer through layers more than 50 Å thick. Sample preparation, STM technique, and results are discussed.
The Au/Si(111)7×7 interface: Correlation between electronic and morphological properties by high-resolution electron energy-loss spectroscopy, ultraviolet photoemission spectroscopy, and transmission electron microscopy
Authors: Mathieu G. , Contini R. , Layet J. M. , Mathiez P. , Giorgio S.
Published: July 2002

We have studied the diffusive Au/Si(111)-7×7 interface by surface sensitive techniques (high-resolution electron energy-loss and ultraviolet photoemission spectroscopies) and by transmission electron microscopy (TEM). The combination of the spectroscopic methods with TEM allows us to propose a new morphological description of the layer growing at room temperature, namely, that there are crystallites of pure Au embedded in an amorphous AuxSi1−x alloy matrix.
Thermal desorption of deuterium and helium implanted in oxide overlayers on molybdenum
Authors: Baba Y. , Sasaki T. A.
Published: July 2002

The thermal desorption behaviors of deuterium and helium implanted in oxidized molybdenum have been investigated. Both ions are hardly trapped in metallic molybdenum, whereas the trapping efficiency grows with increasing oxidation temperature of molybdenum. There exist two different trapping sites in molybdenum trioxide: interstitial sites and oxygen vacancies. The ions trapped at interstitial sites desorb without surface chemical changes, whereas desorption of ions trapped in oxygen vacancies accompanies the recovery of the surface chemical state, i.e., Mo(IV)→Mo(VI). The activation energies for the detrapping processes of deuterium trapped at interstitial sites and in oxygen vacancies are determined to be 0.45 and 1.0 eV, respectively.
Geometrical and surface effects in the sputtering process
Authors: Schwarz S. A.
Published: July 2002

A semiempirical model of the sputtering process [S. A. Schwarz and C. R. Helms, J. Appl. Phys. 50, 5492 (1979)] is reexamined in light of subsequent developments. In this model, the energy dependence of the sputtering yield results from a geometrical effect, in contrast to the common approximation in which this dependence is determined by the stopping power of the incident atom. A direct comparison may now be made with recent stopping-power formulas, Monte Carlo simulations, and experimental data. Monte Carlo results in the literature suggest a material dependence of the sputtering yield which is inherent in the geometrical model and absent in the stopping-power approximation. The surface escape probabilities derived from this model also show a material dependence, and an inverse correlation with positive ion yields, which cannot be solely attributed to surface binding energies or oxygen contamination.
Electron spin resonance of inherent and process induced defects near the Si/SiO2 interface of oxidized silicon wafers
Authors: Poindexter Edward H. , Caplan Philip J.
Published: July 2002

Major point defects, inherent and process induced, near the Si/SiO2 interface of metal–oxide–silicon structures have now been identified by electron spin resonance. The most pervasive defect is the Pb center, a trivalent silicon atom bonded to the Si at the interface, with dangling orbital aimed into the SiO2 (e.g., .Si≡Si3). The Pb orbital is the source of about one-half of the electrical interface traps (density Dit) in as-oxidized or radiation- or injection-damaged Si. Concentration of Pb is dependent on oxidation and other thermal treatments, and is a sensitive gauge of interface physicochemical disposition. Radiationlike processing methods—ion implantation, rapid thermal annealing, plasma etching, and electron-beam lithography—generate additional point defects, including charged E′ centers (O3≡Si. . . . +Si≡O3), nonbridging oxygen hole centers (O3≡Si–O. . . . H–O–Si≡O3), peroxy radicals (O3≡Si–O–O. . . . Si≡O3) in the oxide, and D centers (.Si≡Si3)n in the silicon. Subsequent thermochemical treatments yield results similar to those observed for bulk fused SiO2 defects, but with some unresolved differences. The stability or hardness of Si/SiO2 devices appears to be related to initial defects, despite apparent anneal by thermal processing stages. A number of studies to define the detailed physicochemical behavior of these potentially troublesome defects are now in progress.
Ultraviolet laser-induced ion emission from silicon
Authors: Chen Lee , Liberman Vladimir , O’Neill James A. , Wu Zhen , Osgood Richard M.
Published: July 2002

Si and Ge ion ejection is observed to occur from clean silicon and germanium surfaces upon excimer laser irradiation at fluences (0–150 mJ/cm2) well below that necessary to cause thermionic emission or melting of the substrate. Quadrupole mass spectrometric techniques were employed to for the detection of emitted positive ions. Laser intensity dependent measurements were performed at 193, 248, and 351 nm to elucidate the laser fluence and photon energy threshold behavior of each of the charged species.
Studies of Co/Ga1−xAlxAs interfaces fabricated in ultrahigh vacuum
Authors: Palmstro/m C. J. , Chase E. W. , Hwang D. M. , Harbison J. P. , Chang C. C. , Kaplan A. S. , Nazar L.
Published: July 2002

The reactions of in situ UHV fabricated and annealed Co/Ga1−xAlx As structures for x=0–1 have been studied using a number of elemental and structural techniques. Cobalt starts to react with Ga1−xAlx As at 370 °C and forms a quaternary phase of approximate composition Co2Ga1−xAlx As. The variation in Schottky barrier heights for reacted Co/Ga1−xAlx As is not consistent with the Fermi-level pinning position predicted from Tersoff’s model for metal induced gap states. However, it is consistent with the effective work function model after consideration of the interface composition and Fermi-level pinning by defects at the reacted layer/Ga1−xAlx As interface.
Kinetic and structural aspects of trapping and recycling of hydrogen on metallic surfaces exposed to low-pressure hydrogen plasma
Authors: Veprek S. , Mattenberger F. , Heintze M. , Wiggins M. , Kitajima M. , Yamashita K. , Gotthardt R.
Published: July 2002

Studies of hydrogen trapping and recycling were performed on cleaned and on contaminated metallic surfaces exposed to a hydrogen discharge with parameters typical of the scrape-off layer in devices for controlled nuclear fusion research. Detailed analysis of the time- and temperature- dependent trapping and release of hydrogen upon start and termination of the discharge, respectively, allows one to draw conclusions regarding the nature of the trapping sites. These data were complemented by transmission electron microscopic investigation of the structural damage in the near-surface region and by the measurement of the amount of hydrogen trapped in the damaged area. Formation of dislocation loops at small doses and their agglomeration into an extended dislocation network at a fluence of ≤1017 cm−2 were found. The data indicate that the defects are located within a depth significantly larger than the projected range of the impinging ions. The concentration of hydrogen within this area reaches up to several tens of at . %, and its stability with respect to thermal release suggests that hydrogen is strongly trapped at the defect sites. Only a small fraction (10%–30%) of the implanted hydrogen takes part in the recycling during a 10–30 s long discharge pulse at a wall temperature of ≤300 °C. Implications of these results for the current models of hydrogen recycling are discussed.
Process for large-scale production of magneto-optical disks
Authors: Asari S. , Miyamoto K. , Ota Y. , Nakamura K. , Itoh A.
Published: July 2002

The so-called pass-by coating with an in-line sputtering system is considered to be most suitable for large-scale production of magneto-optical (MO) disks. In this experiment, we confirm the feasibility of in-line, continuous coating of magneto-optical media. Applying such processes as preheating for substrates, rf reactive sputtering for dielectric layers, and dc sputtering with an alloy target for magnetic layers, it is possible to prepare MO disks having excellent characteristics at a high production rate even without substrate rotation.
The preparation of amorphous Si:H thin films for optoelectronic applications by glow discharge dissociation of SiH4 using a direct-current saddle-field plasma chamber
Authors: Kruzelecky R. V. , Zukotynski S. , Ukah C. I. , Gaspari F. , Perz J. M.
Published: July 2002

Hydrogenated amorphous silicon films (a-Si:H) have been prepared by glow discharge decomposition of silane (SiH4) in a dc saddle-field cavity. In the saddle-field electrode configuration, electrons can oscillate along the axis of the plasma chamber, increasing the effective path length for ionizing collisions. This allows discharge formation over a wide range of pressures, avoiding the tuning problems that are encountered with rf techniques while providing better control of the ion energy, direction of ion motion, and ion density. The high discharge current density that is obtainable at moderate pressures facilitates relatively high growth rates exceeding 5 Å/s. The fraction of hydrogen incorporated can be directly controlled by coevaporating Si during the discharge deposition. a-Si:H films exhibiting high photoconductive gains that exceed 103 under AM1 illumination have been obtained over a wide range in bonded hydrogen content, from about 5 to 25 at. %. The dependence of the optical gap on hydrogen content allows considerable flexibility to tailor the photoresponse of the resulting photoreceptors.
Temperature-dependent interface morphology and Schottky barrier evolution for Au/InP(110)
Authors: Waddill G. D. , Aldao C. M. , Vitomirov I. M. , Gao Y. , Weaver J. H.
Published: July 2002

Results of extensive high-resolution synchrotron radiation photoemission studies reveal significant differences between Au/InP(110) interfaces formed at 300 and at 60 K. At 300 K, Au atom deposition results in substantial substrate disruption and, for coverages ≥2 Å, a thickening Au overlayer containing intermixed In and P atoms. For atom deposition at 60 K, the amount of substrate disruption is not significantly changed, but surface segregation of the released In and P atoms is largely, though not entirely, inhibited. These reults show that the distinctly different temperature-dependent Schottky barrier evolution on n- and p-type InP(110) cannot be attributed to thermally controlled reaction since there is little such control. Low-temperature changes in Fermi-level pinning for Au coverages at 2–4 Å appear related to the development of metallic character in the overlayer.
Minority-carrier lifetime in AlxGa1−xAs
Authors: Ahrenkiel R. K. , Dunlavy D. J.
Published: July 2002

The minority-carrier lifetime of AlxGa1−xAs has been measured in epitaxial materials grown by liquid phase epitaxy (LPE) and metalorganic chemical vapor deposition (MOCVD). A general trend shows that the lifetime decreases with aluminum concentration x as reported previously. The lifetime at x∼0.4 is appreciably larger in LPE material than in MOCVD material. At all x values, the lifetime of MOCVD material increased with the growth temperature. The results indicate that bulk Shockley–Read–Hall recombination dominates the lifetime. The latter are very dependent upon the growth conditions.