bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of interfacial interactions on the initial growth of Cu on clean SiO2 and 3-mercaptopropyltrimethoxysilane-modified SiO2 substrates
Authors: Hu Minghui , Noda Suguru , Tsuji Yoshiko , Okubo Tatsuya , Yamaguchi Yukio , Komiyama Hiroshi
Published: July 2002

The effect of interfacial interactions on the initial growth of Cu on clean SiO2 and 3-mercaptopropyltrimethoxysilane (MPTMS)-modified SiO2 substrates by sputter deposition was studied using transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. Plasma damage during sputter deposition makes surfaces of MPTMS-modified SiO2 substrates consist of small MPTMS islands several tens of nanometers in diameter and bare SiO2 areas. These MPTMS islands are composed of disordered multilayer MPTMS aggregates. The initial growth behavior of Cu on MPTMS-modified SiO2 substrates differs from that on clean SiO2 substrates, although Cu grows in three-dimensional-island mode on both of them. After a 2.5-monolayer Cu deposition on clean SiO2 substrates, spherical Cu particles were formed at a low number density of 1.3×1016 /m2 and at a long interparticle distance of 5 nm. In contrast, after the same amount of deposition on MPTMS-modified SiO2 substrates, Cu particles preferentially grow on MPTMS islands at a high number density of 3.9×1016 /m2 and at a short interparticle distance of 3 nm, but do not grow on bare SiO2 areas. The increased number density and the decreased interparticle distance indicate that Cu has a lower mobility on MPTMS islands on MPTMS-modified SiO2 substrates than on clean SiO2 substrates. This difference in Cu mobility is attributed to the enhanced interfacial interactions between Cu and S on MPTMS islands on MPTMS-modified SiO2 substrates via the formation of Cu–S bonds, compared with the relatively weak interfacial interactions between Cu and Si or O on clean SiO2 substrates.
Characterization of thin ZrO2 films deposited using (ZrOi–Pr)2(thd)2 and O2 on Si(100)
Authors: Chen H.-W. , Landheer D. , Wu X. , Moisa S. , Sproule G. I. , Chao T.-S. , Huang T.-Y.
Published: July 2002

The properties of ZrO2 films deposited using molecular oxygen and a recently developed precursor, zirconium Zr(Oi–Pr)2(thd)2 have been investigated. The organometallic was dissolved as a 0.15 molar solution in octane and introduced into the deposition chamber using a liquid injection system. The deposition rate was insensitive to molecular oxygen flow but changed with liquid injection rate and was thermally activated in the range 390 °C–550 °C. Carbon concentrations, <0.1 at. %, the detection limit of the x-ray photoelectron spectroscopy depth profiling measurements, were obtained at the lowest deposition temperatures and deposition rates. High-resolution transmission electron microscopy showed the films to be polycrystalline as deposited, with a zirconium silicate interfacial layer. After proper annealing treatments, an equivalent oxide thickness (EOT) of around 2.3 nm has been achieved for a 5.2 nm thick film, with a leakage current two orders of magnitude lower than that of SiO2 with the same EOT. Promising capacitance–voltage characteristics were also achieved, but some improvements are required if these films are to be used as a gate insulator.
Source Contamination Effects on the Epitaxy of Ge Films on Ge
Authors: Davey John E.
Published: July 2002

The effect of source contamination on the structure of Ge films deposited simultaneously onto single-crystal Ge substrates and amorphous quartz Hall substrates has been investigated. Deposition from the refractory metals, from quartz crucibles, and from extensively outgassed and vacuum-loaded graphite crucibles, produce single-crystal films when deposited at a substrate temperature of 350 °C; the electrical properties of the films deposited simultaneously onto the Hall substrates are typical of Ge films with good structural properties. Deposition from un-outgassed graphite crucibles (either resistive or radiative heating) and Al2O3 in either crucible or cataphoretic forms, produce films ranging from amorphous to polycrystalline when deposited on single-crystal Ge at 350 °C. Evaporations from these latter materials will produce single-crystal films on Ge single crystals only for extensive vacuum outgassing and vacuum loading of the Ge charge and for substrate temperatures in excess of 500 °C.
Observation of Adsorption and Crystal Nucleation by Mass-Spectrometric Techniques
Authors: Hudson J. B. , Sandejas J. S.
Published: July 2002

An experimental technique is described in which both the kinetics of nucleation of vapor deposits and certain of the related physical processes, such as the thermal accommodation of vapor at the substrate surface and the adsorptive properties of the nucleant species, can be measured simultaneously. The technique described is based on the use of a small mass spectrometer to monitor the flux of vapor molecules leaving the substrate while adsorption or nucleation processes are taking place. Results obtained for cadmium vapor impinging on an atomically clean tungsten surface indicate the formation of two distinct adsorbed phases. A primary phase, obeying the relation τa=0.94×10−10exp(41100/RT), forms on initial exposure of the clean substrate to the vapor. At lower temperatures a secondary phase, which obeys the relation τa=1.42×10−10exp(21200/RT), forms on top of the primary phase. Measurements of the critical supersaturation required for crystal nucleation indicate. that adsorbed layers, several monolayers thick, are present on the surface prior to crystal nucleation. Thus the nucleation process in this case cannot be described in terms of current theories.
New imaging and deflection concept for probe-forming microfabrication systems
Authors: Pfeiffer H. C.
Published: July 2002

A projection lens with an integrated deflection yoke has been developed as part of a probe-forming system for microfabrication. A single yoke is located at the center of the polepiece gap for the purpose of minimizing deflection aberrations through compensation. The concept of a linked imaging trace generates a shaped beam at the target plane. The following performance parameters have been experimentally verified: a resolution of 20 000 lines per field, forming a square spot of 1.25×1.25 μm with an edge slope of 0.25 μm, over a field of 5×5 mm, and a spot current of 0.75 μA, which corresponds to a current density of 50 A/cm2.
Properties of superconducting weak links produced by ion implantation
Authors: Harris E. P.
Published: July 2002

A new technique has been developed for making superconducting weak links, making use of the fact that the superconducting transition temperature (Tc) of certain metals (e.g., W, Mo) can be greatly increased by ion implantation. By implanting controlled patterns of N+ and S+ ions into Mo films, structures have been produced in which two heavily doped Mo regions with high Tc are joined by a short (≲1 μm) lightly doped Mo region with lower Tc which acts as a weak link. These rugged and stable structures display the ac and dc Josephson effects. These techniques lend themselves to the production of superconducting integrated circuits containing weak links.
Design of a reflection–absorption experiment for studying the ir spectrum of molecules adsorbed on a metal surface
Authors: Greenler Robert G.
Published: July 2002

This paper discusses the experimental requirements for maximizing the infrared reflection–absorption bands from a thin layer on a metal surface. Calculated curves are shown for 19 different metals for two spectral regions (2100 and 500 cm−1). From these curves, one can determine the performance of a particular experimental system (e.g., using only one reflection or using two reflections) relative to the theoretical best performance of the optimum system. In many cases, one reflection may yield a band intensity acceptably close to the maximum theoretical intensity.
Surface photovoltage and Auger spectroscopy studies of (112̄0) CdS surface
Authors: Brillson L. J.
Published: July 2002

Modifications of the electronic structure of (112̄0) CdS surfaces as determined by Kelvin photovoltage spectroscopy have been related to changes in their atomic compositions as measured by Auger electron spectroscopy. Effects of chemical contamination, nonstoichiometry, and lattice disorder on the surface electronic properties could be separated by AES and low−energy electron diffraction for air−exposed, ion−bombarded, annealed, cleaved, and adsorbate−covered surfaces. Carbon contamination of CdS surfaces in ultrahigh vacuum is found to decrease photovoltage sensitivity. Argon ion bombardment and oxygen chmisorption produce nonstoichiometric surfaces. Ion−bombarded CdS exhibits a new pair of surface state levels which dominate the spectra of these surfaces. All of the photovoltage features attributed to surface state levels on (112̄0) CdS can be correlated with the chemical condition of the surface.
Velocity distributions of As2 and As4 scattered from GaAs
Authors: Arthur J. R. , Brown T. R.
Published: July 2002

The velocity distribution of particles scattered from surfaces can provide information about the dynamics and energetics of the interaction process. In a series of preliminary measurements on clean, well−characterized GaAs (111) we have measured the velocity distributions of both scattered and evaporated As2 and As4, with substrate temperatures ranging from 25° to 700°C. The results indicate that the molecular species As2 and As4 both scatter and evaporate from the surface with velocity distributions ’’cooler’’ than that characteristic of the substrate temperature. On the other hand, the Ga velocity distributions are well described by a Maxwell−Boltzmann distribution at the substrate temperature. In addition, the experiments provide an unambiguous identification of species leaving a surface, establishing in this case that As2 is the only detectable arsenic species evaporating from GaAs at 500°C.
Influence of a thin oxide layer between metal and semiconductor on Schottky diode behavior
Authors: Nicollian E. H. , Schwartz B. , Coleman D. J. , Ryder R. M. , Brews J. R.
Published: July 2002

Two frequently observed problems with Schottky diodes are soft current–voltage characteristics and low avalanche breakdown voltages. These problems are sometimes found immediately upon fabrication, or they may develop during use. It is proposed that these phenomena can be explained by the existence of a thin layer (25–250 Å thick) between the metal and semiconductor which (i) has a high charge density, (ii) has a high trap density, and (iii) is conducting. Observed barrier height changes are explained by the trapping of charge carriers flowing through the layer and the lowered avalanche breakdown voltage by heating of carriers in the high field in the intervening layer. These explanations have been confirmed by measurements on GaP and GaAs diodes having a deliberately grown thin interfacial oxide ∠100 Å thick. Such an interfacial layer can be detected using a pulsed current–voltage technique described in the paper.
Broad-frequency chopper with adjustable duty cycle
Authors: Sawin Herbert H. , Wilkinson Donald D. , Chan Wai Ming , Smiriga Steve , Merrill Robert P.
Published: July 2002

A chopping system with in situ adjustable frequency and duty cycle has been designed and constructed for use in modulating molecular beams. Two choppers in series driven by three-phase synchronous motors are phase shifted to adjust the duty cycle. The three-phase power signal and phase lag control are synthesized with digital logic which provides for stable control of both frequency and phase lag over a broad range of frequencies (1–1000 Hz). The stability of the system is limited by the ’’hunting’’ of the hysteresis motors which is less than ±3 μsec between 100 and 1000 Hz. With the chopper blades used here the duty cycle is adjustable from 0%–50%. The gating function of this chopping system is displayed at 100 and 1000 Hz for duty cycles of <1% and 50%. Time-of-flight distributions for a Mach 9 helium beam is also shown for 1000 Hz and both duty cycles.
Effect of reconstruction during epitaxial growth
Authors: Van Vechten J. A.
Published: July 2002

Surface reconstructions are first-order phase transitions observed at the solid–vacuum interface for low index surfaces of many covalently bonded materials. It is generally held that they result in the removal of bonds dangling into vacuum from the ideal surface and in a strengthening of back bonds in the crystal. Consequently, they are also expected to occur when the crystal is growing from its own melt or some other phase into which it cannot satisfy its dangling bonds. This consideration leads to prediction of rate-of-growth and orientation-of-growth substrate effects upon the perfection of the resultant crystal. Such effects are observed in good agreement with theory in several instances.
Automatic rf sputtering system
Authors: Halperin Arnold , Silano Paul , West Len
Published: July 2002

Radio frequency rf-sputtered films of closely controlled compositions and properties can now be reproducibly made by independently and simultaneously controlling the target and substrate voltages to better than 0.2%. Two independent feedback loops are used, each containing a controlled rf generator and an automatic matching network. A common exciter and delay line set the phase difference between the target and substrate voltages. Automatic controls makes this system simple to operate and ideal for both laboratory and production use.
Electron–solid interactions: Their nature and consequences
Authors: Duke C. B.
Published: July 2002

During the past two decades electron scattering and emission spectroscopies have become utilized almost universally to characterize the properties of solid surfaces. Two major trends have created this situation: The increasing availability of suitable, convenient experimental apparatus, and the recognition and exploitation of those features of electron–solid interactions which render these measurements sensitive to surface properties. Whereas prior Welch Award lectures have dealt with the former trend, the latter is examined herein. Three concepts are central to an understanding of the interaction of ’’low-energy’’, 10≲E≲103-eV electrons with the constituents of solids. First, their strong Coulombic interaction with the valence electrons of the solid renders their mean free paths for inelastic collisions of atomic dimensions, i.e., 2≲λ≲20 Å. Thus, elastically scattered or emitted electrons in this energy range must have emanated from the uppermost few atomic layers of the solid. Second, the interactions of these electrons with the core electrons are comparable to those with the valence electrons. Therefore, multiple elastic scattering as well as rapid energy loss characterizes their scattering and emission. Third, resonant processes associated with electronic states localized at a surface can be as important as inelastic processes in establishing surface sensitivity. Examples of this phenomenon are found in resonant field emission through adsorbates and resonant photoemission associated with the excitation of transitions characteristic of adsorbed complexes. The major portion of this article is devoted to an indication of how exploitations of these three concepts have led to quantitative surface analysis methodologies for metals and covalent solids. In the case of polymers and molecular solids, however, one further concept is required: the localization of electronic states caused by fluctuations in relaxation energy. These fluctuations lead to localized molecular ion (or exciton) states rather than extended band states. The final portion of this article is devoted to exploring the consequences of this additional concept and how it led to the invention of yet another electron spectroscopy, contact charge exchange spectroscopy, for the examination of molecular ion states in polymers.
Surface photovoltage spectroscopy of defects and impurities in trigonal selenium
Authors: Brillson L. J. , Griffiths C. H.
Published: July 2002

The bulk electronic structure associated with defects and impurities in trigonal selenium has been determined by surface photovoltage spectroscopy. Surface and bulk photovoltage contributions were separated by varying the UHV surface conditions as monitored by Auger electron spectroscopy. Lattice defects formed during crystal growth exhibited deep and shallow bulk traps, identical to mechanical damage features. Ar+ bombardment produced surface defect levels in the band gap at the same bulk defect energies. No intrinsic surface states were measured on the clean (101̄0) face. Bulk Cl and As dopants in trigonal selenium produced additional discrete levels in the band gap at energies consistent with known transport properties. Since the trigonal selenium surface is not strongly reactive, bulk lattice defects rather surface states dominate the surface electronic structure.
Optical properties of selectively absorbing metal insulator composite films
Authors: Craighead H. G. , Buhrman R. A.
Published: July 2002

The optical properties of Ni/Al2O3, V/Al2O3, V/SiO2, V/MgO, Fe/Al2O3 and Fe/MgO composite films have been studied with consideration given to their applicability as selective solar energy absorbers. Thin films were produced by coevaporation and the microstructure examined by electron microscopy. The optical properties of Ni/Al2O3 composites, measured over the range of the solar spectrum, are in good accord with the predictions of Maxwell–Garnett theory provided the Ni volume fraction is ≲0.2. The Ni/Al2O3 films have excellent spectral selectivity for the absorption of solar radiation with a solar absorptivity of 0.94 obtained for a film produced with a graded composition. Low-temperature emissivities of ∠0.1 have been obtained for Ni/Al2O3 on a highly reflecting metal backing. The composite Ni/Al2O3 is stable at high temperatures in air. The V and Fe composite studies have optical properties different in character from the predictions of Maxwell–Garnett theory and are not as suitable for solar energy applications as Ni composites.
Profile control by reactive sputter etching
Authors: Lehmann H. W. , Widmer R.
Published: July 2002

Reactive sputter etching in fluorocarbon gases (i.e. CF4, CHF3) not only results in a large increase of the etch rates, but it can also be used for a high fidelity pattern transfer from patterns delineated in positive photoresist into underlaying substrates (i.e. Si, SiO2, Si3N4). Square wave gratings with micron and submicron periodicities and etch depths of up to 3 μm have been etched. A relatively large etch selectivity of SiO2 over Si has been observed (etch rate ratio=15:1). Reactive sputter etching is primarily a chemical process due to highly reactive species produced on the substrate surface by an ion–molecule reaction between ions from the plasma and neutral gas molecules impinging onto the substrate surface.
Solute segregation in iron-based alloys
Authors: McMahon C. J. , Marchut L.
Published: July 2002

Segregation of metalloid impurities to grain boundaries of iron and its alloys can produce brittle intergranular cracking under a variety of external conditions. This set of phenomena is reviewed in terms of: segregation in dilute iron–metalloid binary alloys, interactions of metalloid elements with other solutes to enhance or retard segregation, the thermodynamics of segregation in binary and ternary alloys, the use of Auger electron spectroscopy for analysis of fracture surfaces and for studies of segregation to free surfaces, and the effects of segregation on mechanical behavior. The derivation of the general equations of segregation in a ternary regular solution from the Guttmann analysis is given in the Appendix.
Optical studies of the anodic oxide on GaAs
Authors: Palik E. D. , Ginsburg N. , Holm R. T. , Gibson J. W.
Published: July 2002

Reflection and transmission measurements of an anodic-oxide film grown on GaAs have been carried out from 0.01 to 6 eV (100 to 48 000 cm−1). The dispersion in the index of refraction has been determined in the high-frequency range from an analysis of reflection interference fringes. The ir reflection and transmission spectra of crystalline arsenolite, amorphous As2O3, polycrystalline β-Ga2O3, and amorphous Ga2O3 have been measured and compared with the anodic-oxide spectrum. In the anodic oxide, three vibration bands at 305, 600, and 800 cm−1 have been found and two bands at 350 and 550 cm−1 have been inferred, all of which can be assigned to the arsenic-oxide and gallium-oxide constituents of the film. Lines assigned to arsenic oxide in the anodic oxide have much broader widths than the corresponding lines in amorphous arsenic oxide. The anodic-oxide bands are analyzed to determine their contribution to the dc dielectric constant.
Ge–GaAs(110) interface formation
Authors: Bauer R. S. , McMenamin J. C.
Published: July 2002

The heterojunction chemistry for Ge grown by molecular beam epitaxy (MBE) on in situ cleaved GaAs exhibits significant interdiffusion in short times at growth temperatures TG of 430°C (significantly lower critical TG than that reported for moderate-vacuum physical vapor deposition). This results in profound changes in the electronic properties of the interface as probed by synchrotron-radiation-excited 3d core electron photoemission. Even when there is significant alloying of the two lattice-matched semiconductors, there is nearly equal probability for Ge to bond to either a Ga or an As atom at the initial stage. As Ge becomes the dominant species, we find As preferentially diffusing toward the Ge side of the junction. This As is distributed throughout the overlayer in contrast to metal–semiconductor interface formation where the diffusing constituent resides only on the free, growing surface. We show that these behaviors are consistent with the kinetic and thermodynamic properties of the atomic species. The valence band discontinuity is negligible over atomic dimensions, while for an abrupt interface (TG=350°C) we measure ΔEV=0.7±0.050.3 eV. The photoemission changes character rapidly with temperature, indicating an activation barrier for the diffusion below which simple expressions for attenuation of the photoelectrons by electron–electron scattering are applicable. In that case we deduce an escape depth of 7.0±0.5 Å, indicating uniform growth of Ge, with composition changing abruptly from GaAs over ∠1 bond length in the (110) direction. A negligible (<0.2 eV) localized interface dipole layer is formed in the process.
Cadmium selenide thin-film transistors
Authors: Erskine J. C. , Cserhati A.
Published: July 2002

Vacuum-deposited CdSe thin-film transistors (TFT’s) with reproducible good stability, performance, uniformity, and yield were made using sputtered SiO2 gate insulator, Cr source–drain (s–d) electrodes, and postdeposition annealing in N2. These materials and procedures permit the use of multiple pumpdown fabrication methods with no loss in ac characteristics and little sacrifice in dc stability. Promising results were obtained using photolithography (PL) to delineate s–d electrodes, further simplifying fabrication. The dc instability is electron-trapping type and the drain current decay exhibits a logarithmic time dependence. The slope of this decay curve is used as a parameter to describe device stability and its dependence on the fabrication methods studied: M=0.03–0.06 for one-pumpdown devices, 0.05–0.08 for multiple pumpdown TFT’s, and 0.1–0.2 for TFT’s with PL-delineated s–d electrodes. Preliminary reliability studies show that suitably encapsulated TFT’s have long time stability comparable to the good short time stability observed for fresh devices, indicating the absence of built-in failure mechanisms and the capability for a satisfactory operating life.
Response of a quartz crystal microbalance to a liquid deposit
Authors: Glassford A. P. M.
Published: July 2002

The response of a quartz crystal microbalance (QCM) to a liquid deposit is less than to a solid deposit of the same mass per unit area because of viscous effects in the deposit. In this paper the relationship between the loss of QCM response and the deposit parameters is derived analytically, using the Navier–Stokes equation to determine the velocity distribution in the deposit, and a Rayleigh perturbation analysis to determine the response. The theoretical model considers droplet type as well as uniform film deposit morphology, and includes the influence of droplet size and distribution parameters. To examine the validity of the theory two series of experiments have been conducted using DC 704 silicone oil deposited on a Celesco Model 700A QCM of 10 MHz frequency. In one series the deposit mass was held constant and the QCM temperature was varied, while in the other series these conditions were reversed. Satisfactory agreement between the measured data and the theoretical predictions for QCM response loss was obtained. By making a more detailed interpretation of the data, with the help of the theory, the droplet deposit area coverage and number density were estimated.
EXAFS and surface-EXAFS studies in the soft x-ray region using electron yield spectroscopy
Authors: Stöhr Joachim
Published: July 2002

This paper discusses extended x-ray absorption fine-structure (EXAFS) measurements using monochromatized synchrotron radiation in the 300–1000-eV range. EXAFS spectra were obtained by detecting the secondary electron yield from the sample. The electron yield technique is shown to exhibit several unique advantages over conventional absorption measurements. In particular, no thin-film samples are needed and, more important, measurements of surface phemonema become feasible. Results are presented for the N K-edge EXAFS in Si3N4 and for the O K-edge surface EXAFS of an oxygen monolayer on Ni (100).
Reactions of vacuum-deposited thin Schottky barrier metallizations on gallium arsenide
Authors: Mukherjee S. D. , Morgan D V. , Howes M. J. , Smith J. G. , Brook P.
Published: July 2002

A series of metals (namely Pt, Ni, Al, Cr, Ti, Ta, Mo, and W) were considered and investigated metallurgically as possible candidates for Schottky barrier metals for high-power GaAs IMPATT diode and FET applications. Interdiffusion, compound formation, lack of adhesion, and stability against humid and oxidizing atmospheres were studied in the temperature range of 250°–550°C using Rutherford backscattering of 2.0–2.25-MeV helium ions, secondary ion mass spectrometry (CAMECA IMS 300), and scanning electron microscopy with energy-dispersive x-ray analysis facility. In this paper we discuss the results and attempt to classify the metals qualitatively into four groups according to the main degradation mechanisms which are likely to limit their use as a Schottky barrier at high operating temperatures.
Substrate effect on the lattice constants of the MBE-grown In1−xGaxAs and GaSb1−yAsy
Authors: Chang Chin-An , Segmüller Armin
Published: July 2002

We have analyzed the lattice constants of InAs and GaSb grown on GaAs using molecular beam expitaxy (MBE). The observed deviations between the MBE and bulk samples, especially for GaSb, can be largely accounted for by the thermal stress induced in the films. Our analysis indicates that a similar thermal stress could cause ≲ 20% variation in alloy compositions of In1−xGaxAs required to match the lattices of two GaSb1−yAsy films which have the same y but are separately grown on GaAs and GaSb substrates.
Morphology and electronic structure of Si–SiO2 interfaces and Si surfaces
Authors: Helms C. R.
Published: July 2002

This paper will concern itself primarily with effects related to the Si–SiO2 interface for thermal oxides used as the gate dielectric in MOS structures. Studies of the morphology, chemistry, and electronic structure of the Si–SiO2 interface have been performed using two approaches. First, oxides are grown on Si substrates at aroung 1000 °C to thicknesses of around 1000 Å. Of interest here are oxidation kinetics, interface morphology and composition, interface electronic state density, and oxide impurity content. A microscopic understanding of these properties has been the goal of the second type of study performed, using the tools of surface science to investigate single-crystal surfaces. In this paper, we will review some of the important aspects of each of these two approaches. Finally, the relationship between them will be discussed and further studies to tie them together suggested.
Surface states at clean, cleaved GaAs(110) surfaces
Authors: Mönch W. , Clemens H. J.
Published: July 2002

The work function of cleaved GaAs(110) surfaces was measured in dependence of temperature between room temperature and 400 °C. Surfaces cleaved from p-type and tellurium-doped n-type crystals exhibit a reversible behavior, while silicon-doped n-type samples showed an irreversible decrease of the work function after the first heating cycles. In the presence of cleavage steps the work function and its temperature dependence are determined by step-induced surface states via band bending and by step-induced changes of the surface dipole.
The Xα-scattered wave cluster approach to modeling interfaces
Authors: Messmer Richard P.
Published: July 2002

The basic ideas of the Xα-scattered wave cluster method are discussed. Special attention is given to discussing both the weaknesses (such as the present lack of a convenient, accurate method for calculating total energies) and strengths (such as easy, reliable approach to calculating valence and core level excitations) of the method. Two applications to metal–adsorbate systems, Al (100)+O and Cu (100)+CO, are briefly described. Finally some comments on future developments of the method are presented and the potential for treating compound semiconductor interfaces is considered
Reconstruction and oxidation of the GaAs(110) surface
Authors: Barton John J. , Goddard III William A. , McGill T. C.
Published: July 2002

Using ab initio methods (generalized valence bond with small clusters to represent the surface), we have studied reconstruction of the GaAs (110) surface and the initial steps of oxidation. The relaxation of the surface atoms (26° twist angle) is found to be in good agreement with the results of recent LEED experiments (27°±2° twist angle). The results indicate that the reconstruction is dominated by hybridization effects of orbitals localized at the surface. The calculations of chemisorbed O2 and O support the following picture: (i) Molecular O2 can bond only weakly (physisorb) to the perfect GaAs(110) surface. Chemisorption of the O2 requires a defect site which may then catalyze decomposition of the O2. (ii) There is an intermediate oxidized state at low coverages (before O is inserted in the GaAs bonds) in which O atom is chemisorbed to a surface As (donor–acceptor bond). For this intermediate oxide we calculate chemical shifts of 2.6 eV (deeper) in the 3d levels of the surface As and 0.8 eV (deeper) in the 3d levels of the surface Ga, which are in agreement with recent experiments. We propose several experiments to test various aspects of the initial stages in the oxidation process.
Hot-electron attenuation length in Ag/InP Schottky barriers
Authors: Escher J. S. , Gregory P. E. , Maloney T. J.
Published: July 2002

The attenuation length for ∠1.0 eV hot electrons in thin evaporated silver films on atomically clean p-InP(100) surfaces is deduced from the ratio of external to internal photoemission yield from carriers generated in the bulk InP. Unusually short attenuation lengths of 40–60 Å are measured for films 35–120 Å thick. Ag–InP interdiffusion or possible epitaxial strain effects may account for the reduced attenuation lengths.
Measurements of interface recombination velocity by capacitance/collection efficiency variation in Cu2S/CdS heterojunctions
Authors: Convers Wyeth N. , Rothwarf A.
Published: July 2002

The interface recombination velocity SI in the Cu2S/CdS heterojunction has been measured by a new technique using junction capacitance and collection efficiency. The method capitalizes on changes in the junction field strength due to the photocharging of traps in the depletion region, as measured by junction capacitance. The variation in junction collection efficiency is related to the field strength changes to obtain SI values of order ∠3×105 cm/s. These compare well with estimates from other experiments and simple theoretical predictions. This measurement technique could be applied to other systems, so long as photosensitive trapping states exist that alter the depletion layer width upon external illumination.
Graphoepitaxy of silicon on fused silica using surface micropatterns and laser crystallization
Authors: Geis M. W. , Flanders D. C. , Smith Henry I. , Antoniadis D. A.
Published: July 2002

Uniform crystallographic orientation of silicon films, 500 nm thick, has been achieved on amorphous fused silica substrates by laser crystallization of amorphous silicon deposited over surface-relief gratings etched into the substrates by reactive ion etching. The gratings had a square-wave cross section with a 3.8 μm spatial period, a 100–nm depth and corner radii of about 5 nm. The 〈100〉 directions in the silicon were parallel to the grating to within ±18°, and perpendicular to the substrate plane to within ±2.5°. A simple model for the graphoepitaxy process is presented. Sheet resistivity of phosphorous doped graphoepitaxial silicon was 2.5 times larger than that of bulk silicon of the same doping. Graphoepitaxy is a new application of microstructure fabrication that may lead to new combinations of substrates and overlayer films, and perhaps to three-dimensionally integrated electronic devices and other novel configurations.
Ion projection system for IC production
Authors: Stengl G. , Kaitna R. , Löschner H. , Wolf P. , Sacher R.
Published: July 2002

An ion projection system suitable for production of IC’s is described. Self-supporting metal masks are imaged with a demagnification of 10 : 1 onto a wafer. The resolution of the system is below 1 μm. Direct structuring of oxide and metal layers without any resist, pattern transposition with thin inorganic resists (40 nm) into semiconductor layers and pattern generation in organic resists is described. Exposure times per chip in the order of magnitude of seconds for all these materials are achieved.
Optical step and repeat camera with dark field automatic alignment
Authors: Wilczynski Janusz S.
Published: July 2002

A laboratory step and repeat wafer exposure camera is described. It includes a simple automatic alignment system on every chip based on bright field illumination and dark field intensity detection. Maximum intensity of the dark field light flux corresponds to mask and wafer alignment. The masks are prealigned on a jig borer. The focusing and leveling are accomplished by reading three air gauges and correcting the wafer height accordingly.
Effects of hydrogen incorporation in some deposited metallic thin films
Authors: Meyer Donald E.
Published: July 2002

Incorporation of gases in thin films, either added purposely or inherently present due to deposition system or process, can have significant effects on thin film stress and electromigration. Aluminum thin films which effects on thin film stress and electromigration. Aluminum thin films which were deposited in high partial pressures of hydrogen mostly in the atomic state were observed to have unusually long mean times to failure for current densities above 1×106 A/cm2. The role of hydrogen in increasing film conductivity and decreasing grain boundary diffusion is discussed.
Bonding, shake-up energies and shake-up intensities in Cr(NO)4
Authors: Loubriel G.
Published: July 2002

We report the results of SCF-xα-multiple scattering calculations of the electronic structure of Cr(NO)4 in its neutral ground state and in several positive-ion states. This allows a description of the bonding of NO to the Cr atom, explains how the screening of core holes (created in a XPS measurement) is effected and yields the N1S shake-up spectrum. There is good agreement with the experimental valence region photoemission spectra peak positions and with the shake-up peak positions and intensities.
Thermal diffusion of chromium in polycrystalline CdSe films
Authors: Ingrey S. J. , Shepherd F. R. , Westwood W. D.
Published: July 2002

The effect of thermal annealing of CdSe and multilayer Cr/CdSe thin films has been studied by Auger spectroscopy and nuclear reaction analysis. Films with thicknesses from 0.05 to 0.3 μm were deposited by evaporation onto glass and platinum substrates and annealed for up to 120 min at temperatures between 240° and 400°C in flowing nitrogen. Auger spectra were obtained as the films were sputtered by 3 keV Ar+ in a scanning Auger microprobe. There was no significant change in the composition of the CdSe films except when CdSe and Cr films were in contact. For example, Cr diffused through a 0.3-μm overlayer in a few minutes at 300°C. There was an associated increase in the oxygen content of the film. This was confirmed by nuclear reaction analysis using16O (d,p)17O reaction. In the absence of Cr, there was no significant oxygen uptake. Diffusion profiles were obtained by Auger depth studies and an activation energy of 1.2±0.2 eV determined from the temperature dependence. Since Cr is an n-type dopant in CdSe, the diffusion probably affects the electrical properties and, thus, may have an important effect on CdSe thin film transistors which use Cr as a source-drain metallization.
Comparison of low-temperature oxides on polycrystalline InP by AES, SIMS, and XPS
Authors: Kazmerski L. L. , Ireland P. J. , Sheldon P. , Chu T. L. , Chu S. S. , Lin C. L.
Published: July 2002

Oxides and their interfaces with polycrystalline InP are examined using complementary high-resolution AES, SIMS, and XPS. The oxides, grown by low-temperature dry and wet processes, are compared for composition and phase content. SIMS and AES depth-composition data are used to compare the uniformity of the oxide layers and the composition of the interfacial region. Confirmation of impurity accumulation at the oxide–InP interfaces is presented, including buildup of elemental P and InP dopant, S. Other impurities assocaited with the growth of the wet oxide are found to be localized at the interface. Some evidence of impurity accumulation at grain boundaries at the wet-oxide–polycrystalline-InP interface is provided by SIMS and EBIC.
Combined LEED, AES, and work function studies during the formation of Ge : GaAs(110) heterostructures
Authors: Mönch W. , Gant H.
Published: July 2002

On clean, cleaved GaAs(110) surfaces Ge was deposited by MBE up to a thickness of 100 monolayers at different growth temperatures. At the interface Ge reacts with the GaAs. As measured by AES (0.65±0.25) monolayers of arsenic are dissolved and mainly segregated at the surface of the growing film. At a growth temperature of 295 °C the interface is abrupt, but broadened by diffusion for growth at 395 °C. With Ge films thicker than 5 monolayers a well developed 3×1 LEED pattern is observed which converts to a 2×1 pattern during an anneal above 400 °C. The LEED patterns are interpreted by surface segregation of GeAs2 and GeAs layers, respectively, one to two monolayers thick. The observed increase of the work function in the submonolayer coverage range is explained by band bending due to chemisorption induced surface states at Ess−Ev=0.89 eV and with a charge transfer of −(0.2±0.1) e0 per Ge atom. Therefore it is concluded that the Ge atoms bond to As atoms in the initial growth stage. The band scheme of the heterostructure is discussed, and the conduction band discontinuity of the Ge:GaAs(110) heterstructure is estimated as ΔEc?0.12) eV.
Laser surface treatment studies in ultrahigh vacuum
Authors: Cowan P. L. , Golovchenko J. A.
Published: July 2002

Q-switched lasers are potentially a useful tool for the preparation of surfaces in UHV for surface analysis. The (111), (110), and (100) faces of Si were studied following various surface preparations including exposure to ruby laser pulses. Surface preparations involving laser irradiation were shown to have several advantages over other methods.
Theory of deep substitutional s
p3-bonded impurity levels and core excitons at semiconductor interfaces
Authors: Hjalmarson H. P. , Allen R. E. , Büttner H. , Dow J. D.
Published: July 2002

A theory of the major chemical trends in the binding energies of deep substitutional sp3-bonded impurity levels and Frenkel core excitons at interfaces is presented and applied to a GaAs/AlAs (110) interface.
The role of polymers in optical recording media
Authors: Smith T. W.
Published: July 2002

In this review, the utility of polymers as disk substrates, surfacing/subbing layers, protective overcoatings, and ablative imaging layers in optical recording media is exemplified. Each of these applications may require specific different polymers. Amorphous polymers such as poly(methylmethacrylate) and poly(4-methylpentene-1) may be particularly advantageous as disk substrates. Specialty polymers may find application in surfacing/subbing layers which are used to perfect the disk surface and to provide an appropriate surface for the deposition of the imaging layer. Crosslinked siloxane elastomers have been widely used as protective overcoatings for ablative imaging layers. Depolymerizable polymers, polymers which solublize dyes, and polymers which are effective in the formation of homogeneous colloidal pigment or metal dispersions are essential in a promising new class of optical recording media, polymer/absorber composites.
Overview of requirements for optical storage media
Authors: Jamberdino A. A.
Published: July 2002

Continuing advances in the technologies supporting wideband communications and information handling are leading to extremely large volume, wide bandwidth digital data systems. Until recently conventional storage techniques, through evolutionary product improvements, have been able to keep pace with the growth. However, a point has been reached where moderate technical improvements are becoming economically impractical. Recognizing these and other problems inherent to this specialized application of wideband, high density recording, RADC has undertaken through its exploratory and advanced development programs to satisfy two specific areas: First, to improve and expand upon the technology base that exists in conventional and nonconventional magnetic recording to overcome several of its deficiencies; second, in those instances where magnetic recording is not feasible due to bandwidth or packing density limitations, RADC has exploited alternative approaches. Techniques ranging from laser and electron beam on film to laser holography and optical digital disk are under investigation or in various stages of development.
DREXONTM optical memory media for laser recording and archival data storage
Authors: Drexler J.
Published: July 2002

The objective of this paper is to present the concept, description, and characteristics of a new class of direct-read-after-write (DRAW) reflective laser recording material which has been given the tradename DREXONTM. Information is recorded by thermal melting of the media surface. The material consists of an organic film containing dispersed metal particles which have such a high volume concentration that the surface has a mirrorlike appearance. However, the particles do not touch one another; and, therefore, the surface is electrically nonconductive. When recording, the laser-beam energy is absorbed by the metal particles, which rise in temperature and cause melting of the organic film at temperatures in the range of 200°C. This melting creates spots of low reflectivity in a field of high reflectivity. The metal particles do not melt since their melting temperature is much highter than that of the underlying organic film. It is possible that one version of the media could achieve archival life of a hundred years. This version comprises three ingredients, all of which have rated archival lives of hundreds of years: (1) cross-linked, photographic-quality gelatin, (2) filamentary silver crystals, and (3) spheroidal silver crystals. This archival version of the media is produced from special, fine-grained silver-halide emulsions.
Solvent-coated organic materials for high-density optical recording
Authors: Howe D. G. , Wrobel J. J.
Published: July 2002

Bilayer structures consisting of organic dye/polymer binder systems solvent-coated on reflective substrates are useful for real-time high-density optical recording. Information is recorded by using focused actinic light that is highly absorbed in the vicinity of the surface of the dye/binder layer. Recorded marks consist of steep-walled flat-bottomed depressions or ’’pits’’ that have depth designed to impart a phase shift of ∠r/2 to a focused readout light beam having a wavelength at which the dye/binder layer is essentially transparent. The optical and physical characteristics of these structures that lead to good recording sensitivity and high levels of playback performance are discussed.
Emission of electrons and positive ions upon fracture of oxide films
Authors: Dickinson J. T. , Donaldson E. E. , Snyder D. B.
Published: July 2002

During tensile deformation of oxide-coated aluminum, small cracks a few hundredths of a mm in length occur in the oxide film. During and following the appearance or elongation of these cracks, electron emission (EE) and positive ion emission (PIE) are detected in the surrounding vacuum. Crack propagation in the oxide coating can be detected with an acoustic emission (AE) transducer. Correlations between charged particle emission and film fracture can then be determined. A comparison of rates of EE, PIE, and AE, the distribution of the number of electrons or ions per burst, and the time distributions relative to crack propagation of both EE and PIE are presented. The time distributions indicate distinct differences in the rate limiting steps governing EE and PIE.
Atom probe analysis of rf-sputtered a-Si:H films
Authors: Krishnaswamy S. V. , Messier R. , Wu C. S. , McLane S. B. , Tsong T. T.
Published: July 2002

Using a computerized energy compensated time of flight atom probe (APFIM), we have obtained the average composition (Si,H,O) of two widely differing hydrogenated amorphous silicon rf-sputtered films which were deposited onto W field emitter tips. Analysis of the evaporated ion species shows that the films prepared at the lower total gas pressure (5 mTorr) contain predominantly SiH and Si units while at the higher pressure (20 mTorr) the additional units of SiH2 and SiH3 are also present. These results are compared to films prepared and characterized on planar substrates and found to be in agreement.
Bonding and photoemission of chemisorbed molecules: Molecular orbital cluster model theory
Authors: Bagus P. S. , Hermann K. , Steel M.
Published: July 2002

This paper will review the use of ab initio Hartree–Fock wave functions for small metal/ligand clusters as a basis for the interpretation of processes related to molecular chemisorption. The primary concern will be with absorbate derived photoemission spectra (PES). It will be shown that quite small clusters can, indeed, give considerable insight into the structure, shifts, and character of this spectra. Ab initio molecular orbital theory is a particularly valuable approach since it permits one to relate these features of the PES to the nature of the adsorbate bonding in a direct way. The satellite structure originating from screening of the absorbate hole by metal electrons will be analysed for both core and valence levels. The decomposition of adsorbate shifts into initial and final state contributions will be considered (in order to understand the relationship of these shifts to the binding).