bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-assisted deposition of mixed TiO2-SiO2 films
Authors: Netterfield R. P. , Martin P. J. , Pacey C. G. , Sainty W. G. , McKenzie D. R. , Auchterlonie G.
Published: July 2002

Mixed thin films of TiO2 and SiO2 were produced by coevaporation from separate electron-beam sources and simultaneous bombardment of the growing film with oxygen ions. The optical properties of the films were determined during growth by in situ ellipsometry and the surface composition of the deposited films studied by in situ ion scattering spectroscopy, ex situ x-ray photoelectron spectroscopy, and energy filtered electron diffraction. The correlation between the optical and surface characterization is presented. There is evidence of local variations in the relative concentrations of TiO2 and SiO2. The position of the Si 2p binding energy depends on the TiO2 content in the film, indicating the possible formation of an intimate mixture.
Overlapping electron traps in n-type silicon studied by capacitance transient spectroscopy
Authors: Svensson B. G. , Rydén K.-H. , Lewerentz B. M. S.
Published: July 2002

In n-type Czochralski-grown silicon samples, a broad unidentified level is observed ∼0.32 eV below the conduction band after high-energy electron irradiation. This level has been investigated in detail using deep-level transient spectroscopy and capacitance-versus-time measurements. The broad level consists of two overlapping but independent peaks which are clearly resolved. The generation rate of these peaks, as a function of bombardment dose and as a function of sample depth, as well as their annealing kinetics has been investigated. The identities of the overlapping peaks are discussed, and our findings are compared with optical and electron paramagnetic resonance (EPR) measurements performed by other authors. In particular, the importance of performing depth profiling when identifying unknown peaks is emphasized. One level is tentatively assigned to a gold-related complex, while the other shows several similarities with the EPR G15 center.
Magnetic anisotropy by ferromagnetic particles alignment in a magnetic field
Authors: Yamaguchi K. , Matsumoto K. , Fujii T.
Published: July 2002

Magnetic and optical properties of films composed of ferromagnetic fine particles aligned in a magnetic field were investigated. The spin-coated films were prepared by using a solution of magnetite fine particles dissolved in water-diluted polyvinyl alcohol (PVA) on glass substrates, and followed by drying at 80 °C and solidifying at 200 °C in a magnetic field. Linear-chain clusters of magnetite particles were formed in a considerably weak field below 1 kOe, which give rise to magnetic and optical uniaxial anisotropies. Both properties vary depending on preparation conditions such as the particle concentration, the viscosity of the solution, and the field strength during drying.
Unsteady adiabatic isentropic expansion of gas into vacuum from a toroidal puff valve
Authors: Pedrow Patrick D. , Nasiruddin Abutaher M. , Mahalingam R.
Published: July 2002

Observations were made on the expansion of polyatomic (CF4) and diatomic (O2) gases into vacuum from a toroidal puff valve. Fast ionization gauge measurements have been compared with an unsteady adiabatic isentropic model. Observed temporal and spatial gas density profiles closely followed model predictions until the arrival of gas reflected from the upstream wall of the vacuum vessel.
Second harmonic generation in corona poled, doped polymer films as a function of corona processing
Authors: Hampsch Hilary L. , Torkelson John M. , Bethke Shelly J. , Grubb Stephen G.
Published: July 2002

A novel technique for examining corona processing variables in thin-film organic second-order nonlinear optical materials is discussed. Positive and negative polarity dc-coronas were used to pole doped glassy polymer films in situ at room temperature in air, helium, and nitrogen environments to create materials capable of second harmonic generation (SHG). Films are poled in the beam path and are continuously sampled. For a given atmosphere and poling time, films poled in a positive corona show greater SHG intensities than those poled with negative coronas. The temporal stability of the SHG intensity for films poled with a positive corona increases from air to nitrogen to helium, and for a negative corona is similar in nitrogen and helium atmospheres, and less stable in air. Possible mechanisms are discussed.
Energy absorption by metal-vapor-dominated plasma during carbon dioxide laser welding of steels
Authors: Miller R. , DebRoy T.
Published: July 2002

During laser welding, the plasma plume affects the amount of energy reaching the weld surface and the composition and properties of the welds. Light emissions during welding were recorded by emission spectroscopy to understand the energy absorption and the nature of the plasma formed during welding of various grades of steels. The flow of gases and the concentrations of the various metal vapors were computed by solving the Navier Stokes equation and the equations of conservation of various species. The variables studied were shielding gas composition and flow rate and the base metal composition. Until now, self-absorption of emissions arising from species present at high concentrations within the plasma has kept researchers limited to either analyzing ideal situations that are unrelated to the welding process or not accounting for the attenuation of the emissions. It is demonstrated that during welding, the peaks in the emission spectra that are affected by the self-absorption process can be eliminated on the basis of the initial and the terminal energy levels for electronic transitions. By selectively eliminating the affected transitions and by using the numerically computed local concentrations of metal vapors, the absorption of the laser beam energy by the plasma can be accurately determined.
A thermionic energy converter with a molybdenum-alumina cermet emitter
Authors: Gubbels G. H. M. , Wolff L. R. , Metselaar R.
Published: July 2002

A study is made of the properties of cermets as electrode materials for thermionic energy converters. For thermodynamic reasons it is expected that all cermets composed of pure Mo and refractory oxides have the same bare work function. From data on the work function of Mo in an oxygen atmosphere this bare work function is estimated to be Φ=4.9 eV (at T=1400 °C). Experimentally, the bare work function of Al2O3-Mo cermets was found to be Φ=4.5 eV, independent of the relative amounts of Al2O3 and Mo. The cesiated work function of the Al2O3-Mo cermets was found to be 0.15 eV lower than the cesiated work function of pure Mo. The bare work function of Mo3Al was found to be Φ=4.0 eV. The cesiated work function of Mo3Al at collector temperature conditions was 0.3 eV lower than the cesiated work function of pure Mo. The electrical power density of a diode with an Al2O3-Mo cermet emitter was 0.4 W/cm2 at 1300 °C. The barrier index at this temperature was 2.36 V. The high barrier index is attributed to a high plasma voltage drop Vd=0.91 V.
Deposition of diamondlike films by electron cyclotron resonance microwave plasmas
Authors: Pool F. S. , Shing Y. H.
Published: July 2002

Hard a-C:H films have been deposited through electron cyclotron resonance (ECR) microwave plasma decomposition of CH4 diluted with H2 gas. It has been found that hard diamondlike films could only be produced under a rf-induced negative self-bias of the substrate stage. Raman spectra indicate the deposition of two distinct film types: one film type exhibiting well-defined bands at 1360 and 1580 cm−1 (the graphitic D and G bands) and another displaying a broad Raman peak centered at approximately 1500 cm−1. The optical gaps of these films are from 1.0 to 1.6 eV, respectively, with resistivities >1012 Ω cm. Variation of the mirror magnetic-field profile of the ECR system was examined, demonstrating the manipulation of film morphology through the extraction of different ion energies.
Study of back reflectors for amorphous silicon alloy solar cell application
Authors: Banerjee A. , Guha S.
Published: July 2002

The role of back reflectors in enhancing the absorption of weakly absorbing, long-wavelength light has been investigated as applied to amorphous silicon alloy solar cells. The reflectance and scattering properties of various types of back reflectors have been studied. The performance of p-i-n amorphous silicon alloy solar cells deposited on different back reflectors has been analyzed. The studies elucidate the role of back reflectors in improving the short-circuit current density and thereby the efficiency of the cell.
The influence of deposition temperature and annealing temperature on the optoelectronic properties of hydrogenated amorphous silicon films
Authors: Kunst M. , Neitzert H.-C.
Published: July 2002

The relaxation of pulse-induced mobile charge carriers in a-Si:H films is followed by transient photoconductivity measurements in the microwave frequency range (time resolved microwave conductivity measurements). It is shown that a-Si:H films deposited at substrate temperatures lower than 150 °C are characterized by a lower electron drift mobility and a higher deep trap concentration for electrons than a-Si:H films deposited at 250 °C, where films deposited at 150 °C have only a lower drift mobility. Annealing of a film deposited at 30 °C leads to a higher drift mobility and a lower deep trap concentration with increasing annealing temperature. However, the (opto)electronic properties of the annealed films are still inferior to those of films deposited at the annealing temperature.
Raman study of stress-relieved silicon-on-sapphire films prepared by cw-laser annealing
Authors: Mavi H. S. , Shukla A. K. , Jain K. P. , Abbi S. C. , Beserman R.
Published: July 2002

Continuous-wave laser annealing experiments for producing stress-relieved crystalline silicon-on-sapphire (c-SOS) films are reported. A comparative study of laser annealing has been made on c-SOS and phosphorous-implanted c-SOS films. Raman scattering was used to monitor stresses during the laser annealing process and for characterizing the processed films. The best stress-relieved c-SOS films were obtained by laser annealing the phosphorous-implanted chemical-vapor-deposition-grown SOS films.
Thin films of CuInSe2 produced by rf sputtering with intentional oxygen doping
Authors: Yamaguchi Toshiyuki , Matsufusa Jiro , Kabasawa Hideki , Yoshida Akira
Published: July 2002

Structural, electrical, and optical properties of CuInSe2 thin films produced by rf sputtering from a stoichiometric target in an Ar/O2 atmosphere are presented. The growth rate decreases rapidly with increasing constituent gas ratio [O2]/([Ar]+[O2]). From x-ray diffraction, Auger electron spectroscopy, and x-ray photoelectron spectroscopy, it can be seen that CuInSe2 and In2O3 are mixed in the thin films for [O2]/([Ar]+[O2])≳3%. SeO2, CuO, and In2O3 coexist together at the surface of these thin films. Hot probe analyses indicate that these thin films show n-type conduction. The Van der Pauw measurements and the optical transmittance measurements show that the resistivity decreases and the band gap increases with an increase in the [O2]/([Ar]+[O2]) ratio.
Reactions at the interfaces of thin films of Y-Ba-Cu- and Zr-oxides with Si substrates
Authors: Fenner D. B. , Viano A. M. , Fork D. K. , Connell G. A. N. , Boyce J. B. , Ponce F. A. , Tramontana J. C.
Published: July 2002

Thin films were deposited by pulsed uv-laser (ablation) deposition of Y1Ba2Cu3O7−x (YBCO), and composite zirconia and yttria targets onto silicon wafers. These films were analyzed to ascertain the chemical and physical structure of the film interfaces and further the development of Si substrates for superconducting YBCO films. Substrates were Si(100) with either a high-quality, thermal oxide (SiO2) film, or a spin-etch processed, oxide-free, hydrogen-terminated surface (Si:H). X-ray photoelectron spectroscopy (XPS) of Y, Ba, Cu, and Si core levels revealed adverse reactions for thin (nominally 2 nm) YBCO films deposited directly onto either substrate surface. The surfaces of thicker YBCO films (50–100 nm) and various oxide powders were compared with XPS results from these thin films. The thicker-film surfaces are similar to those of fractured bulk YBCO, while the thin YBCO films decomposed, as evidenced by changes in the Ba and Cu XPS. The Si XPS on these films showed the formation of metal-silicate compounds, even at deposition substrate temperatures of 550 °C, and silica (SiO2), especially for 670 °C deposition. A direct consequence of these reactions is that growth of high-quality epitaxial YBCO on Si will require the use of a buffer film. Yttria-stabilized zirconia (YSZ) shows considerable promise for use as a buffer, and XPS of thin films (4 and 8 nm thick) of ZrO2 on SiO2/Si and YSZ on Si:H substrates did not show any indication of decomposition, even at deposition temperatures near 800 °C. Transmission electron microscopy of cross-sectioned samples of YBCO/YSZ/Si showed that the lower YSZ interface is rough on the preoxidized (SiO2/Si) substrates but atomically sharp on the spin-etched Si wafers (Si:H). These sharp YSZ interfaces showed the presence of 3–5 nm of regrown oxide (SiOx ) next to the crystalline Si substrate. This regrown oxide was observed in samples deposited under a variety of conditions.
Measurement of bulk lifetime and surface recombination velocity by infrared absorption due to pulsed optical excitation
Authors: Ling Z. G. , Ajmera P. K.
Published: July 2002

Knowledge of both carrier bulk lifetime τb and surface recombination velocity S are necessary to analyze and model electron devices. In this paper, the analytical results of Luke and Cheng [J. Appl. Phys. 61, 2282 (1987)] are applied to examine excess carrier decay due to pulsed Gaussian optical excitation to extract values of τb and S under low level injection. The nondestructive, contactless measurement technique utilizes a visible pulsed laser pump beam and a CW infrared laser probe beam. Values for τb and S are obtained for a number of different Si samples. The effect of varying the pump beam frequency is examined. The technique is simple to use in the laboratory and the parameter extraction from the measured data is straightforward.
Coherent stress relaxation in a half space: Modulated layers, inclusions, steps, and a general solution
Authors: Glas Frank
Published: July 2002

We first calculate analytically the elastic displacement and strain fields and the elastic energy of the system composed of a misfitting layer of finite thickness coherently deposited on a bulk semi-infinite substrate and covered by a capping layer, when the intrinsic stress-free strain in the intermediate layer is a sinusoidal modulation of dilatation along a direction parallel to the substrate surface. This is achieved by the direct application of Eshelby’s method and the determination of the appropriate stress function. We show that, combined with Fourier analysis, this basic calculation provides a new general analytical solution to the problem of the coherent relaxation of any misfitting dilatational inhomogeneity in a half space. More specifically, this method is here applied to the full analytical solution of the cases of a coherent misfitting parallelepipedic inclusion buried under a planar free surface, and of a coherent step at the interface between a substrate and a misfitting overlayer. Applications are briefly discussed.
Differential photoreflectance from a high-mobility and highly luminescent two-dimensional electron gas
Authors: Sydor Michael , Badakhshan Ali
Published: July 2002

We present a differential modulation technique which is effective in extracting the photoreflectance from GaAs/AlxGa1−xAs samples exhibiting excessive room-temperature photoluminescence. Using the technique, we obtain the photoreflectance from the triangular potential-well region of a high-electron-mobility transistor. Surprisingly, the signal from the potential well can be extracted from underneath two layers of heavily doped material, making differential photoreflectance useful in detection of two-dimensional electron gas in high-electron-mobility transistors cladded with doped protective GaAs caps which usually obliterate the PR from the buried interfaces. We isolate absorptionlike photoreflectance peaks at 1.447 and 1.472 eV and show that their energies and the ratio of their amplitudes agree with the 2DEG theory for asymmetric triangular potential well.
Impurity effects on both the creation and the migration of Ga vacancies in GaAs
Authors: Lee Jong-Lam , Wei Long , Tanigawa Shoichiro , Kawabe Mitsuo
Published: July 2002

The effects of impurities, such as Si and Be, on both the creation and the migration of Ga vacancies in annealing of GaAs were investigated by a slow positron beam technique. The results show that vacancies diffuse from the surface during the annealing and one of the dominant types is a monovacancy of Ga, VGa, in Be-doped GaAs and/or Si-doped GaAs, while the other is a divacancy of VGa-VAs in undoped GaAs. In annealing the bilayer structures composed of the Si-doped layer grown on the Be-doped layer, it was found that VGa is a major type of defect rather than VGa-VAs if the Si concentration is higher or lower than the Be one in GaAs, but VGa-VAs is dominant if the concentrations of the impurities are similar. This proposes that the interaction between Si and Be is stronger than that of VAs-BeGa and/or VGa-SiGa. The Ga interstitial IGa is created in the Be-doped layer where IGa interacts with VGa created from the surface and suppresses the migration of VGa. This supports the validity of the kick-out mechanism involving a column-III interstitial rather than the Longini mechanism for Be diffusion in GaAs. In Si-doped GaAs, VGa is created from the surface and the diffusion constant of VGa decreases with the increase of Si doping concentration. This implies that VGa forms a complex of SiGa-VGa and the interaction time of VGa at the Si donor by making a complex of SiGa-VGa is a rate-limiting step in the diffusion of VGa in GaAs. The present results propose the creation of IGa and VGa in the Be-diffused GaAs and in Si-diffused GaAs, respectively. This is consistent with the Fermi-level effect of the impurities on the creation of those defects.
Thermal stability of anisotropy in TbFe films prepared by dc-magnetron sputtering
Authors: Cheng S-C. N. , Kryder M. H.
Published: July 2002

We have found that stresses induced during magnetron sputter deposition of amorphous TbFe films are very important in determining the thermal stability of the perpendicular anisotropy, Ku. To determine the stress-induced contribution to the anisotropy, the anisotropy was measured with a torque magnetometer before and after peeling films from their substrates. Data clearly show that the fractional change in anisotropy which occurs when the film is peeled from its substrate, ΔKu/Ku, decreases with increasing Ar pressures. Furthermore, annealing studies reveal that the thermal stability of Ku improves with increasing Ar sputtering pressure−a trend which is in conflict with the tendency for films sputtered under low Ar pressure to be more oxidation resistant. This trend is attributed to the large stress-induced anisotropy component which exists at low argon pressures and its tendency to decrease as a result of long-term annealing. Measurements of the anisotropy of films which had been annealed at 200 °C for 815 h showed that the residual Ku after annealing increased with argon pressure. Measurements of the width of the peak in coercivity around Tcomp in these films shows that Hc increases monotonically with argon pressure. This monotonic increase in Hc is attributed to larger local variations in anisotropy caused by the less dense microstructure and the more random local anisotropy produced by the larger angle of incidence of adatoms which results from the increased scattering in the higher pressure sputtering gas.
Surface passivation of GaAs with P2S5-containing solutions
Authors: Wang Yun , Darici Yesim , Holloway Paul H.
Published: July 2002

The surface chemistry of GaAs passivated with P2S5 solutions modified with sulfur and other sulfides has been studied with x-ray photoelectron spectroscopy, room-temperature photoluminescence, scanning Auger electron spectroscopy, and scanning electron microscopy. The degree of passivity achieved was measured by determining the intensity of room-temperature photoluminescence before and after passivation. An increase in luminescence intensity of up to 23 times was observed after a treatment by solutions containing P2S5 and (NH4)2S buffered with sulfur due to reduced surface nonradiative carrier recombination. Phosphorus oxides and sulfur bound to the Ga and As species were present on the passivated surface. In addition, all the surfaces treated with sulfide solutions were covered to a variable extent with crystallized residues, and a treatment was devised to eliminate these residues while still retaining a passivated surface. Exposure of passivated surfaces to room-temperature air increased the amount of gallium bound to oxygen, while simultaneously reducing the concentration of As on the surface. Arsenic oxide was absent from solution passivated surfaces, even after three weeks in air, but was detected on surfaces passivated in ultrahigh vacuum (UHV) by either evaporation of solid sulfur or adsorption of hydrogen sulfide. Upon exposure to air, the luminescence intensity decreased from all sample whether passivated in UHV or in aqueous solutions; however, the rate and degree of degradation was dependent upon whether passivation was done in vacuum (severe) or by solution (better) and depended upon the exact solution composition. However, the barrier height of Au/GaAs Schottky contacts with passivated interfaces was not changed by exposure to air for times up to one week.
Adhesion and mechanical properties of amorphic diamond films prepared by a laser plasma discharge source
Authors: Davanloo F. , Lee T. J. , Jander D. R. , Park H. , You J. H. , Collins C. B.
Published: July 2002

Amorphic diamond films can be grown in an ultrahigh vacuum environment free from hydrogen with a laser plasma discharge source. This technique produces films that adhere more readily to materials for which there are important applications as protective coatings. In this work adhesion and mechanical properties of amorphic diamond films have been examined. A beam bending method has been used to measure the internal stress and a relatively low value of compressive stress was found. The dependence of stress on the laser intensities at the graphite ablation target has been studied. Analyses of these films on silicon, SiO2, ZnS, and TiAl6V4 by Rutherford backscattering spectrometry show significant interfacial layers with compositions of SiC, C0.5SiO2, C2.5ZnS, and C0.62Ti0.35Al0.05V0.02, respectively. Adhesion properties on ZnS and other substrates have also been examined for harsh environments. The mechanical properties of hardness, Young’s modulus, and stiffness have been obtained with a nanoindentation technique. These results together with the minimal amount of hydrogen in our process, make amorphic diamond an excellent candidate for direct deposition on several substrates including ZnS.
Slit morphology of electromigration induced open circuit failures in fine line conductors
Authors: Sanchez John E. , McKnelly L. T. , Morris J. W.
Published: July 2002

Detailed transmission and scanning electron microscopic images of electromigration-induced open circuit failures are presented for fine line aluminum alloy thin film interconnects. A characteristic slit open circuit, similar to stress migration open circuits in narrow interconnects, is shown for various film compositions, processing, and deposition conditions. It is suggested that slit failure morphology is more generally observed for low (≊1) ratios of conductor line width to film grain size. The slit failures observed often occur near copper rich precipitates. The morphology of several slit voids suggests that they are transgranular across the linewidth, consistent with other recent reports of electromigration induced damage in single crystal interconnects.
Effect of near-contact regions on the interpretation of ohmic behavior in trap-dominated relaxation semiconductors
Authors: Derhacobian N. , Madok J. H. , Haegel N. M.
Published: July 2002

The influence of near-contact electrical field nonuniformities on the injection of minority carriers into semi-insulating GaAs has been investigated experimentally. Variable length p+-v-n+ (200–10 μm) diodes are used to show that near-contact regions do affect the electrical measurements in high-resistivity trap-dominated semiconductors even though linear I-V characteristics are observed. As the diode length is decreased from 200 to 10 μm, the current density through the device, at a constant average field, decreases by a factor of 10. The experimental results are compared, with good agreement, to a previously proposed theoretical model in which semi-insulating GaAs is treated as a trap-dominated relaxation semiconductor.
High transfer-efficiency microsurface acoustic wave directional couplers
Authors: Haruvi-Busnach I. , Zilberstein M. , Golan G. , Seidman A. , Croitoru N.
Published: July 2002

Surface acoustic waves (SAWS) directional couplers have long been known in both microwave and integrated acoustic applications. Such couplers, when both channels are of different widths and different dispersion characteristics, may also be used as electronic filters. SAW directional couplers are ideal for inclusion in acoustical signal processing devices, as modulators or switches. This article represents formulation and physical properties of advanced high transfer efficiency SAW directional couplers, using the coupled mode theory. One kind of directional coupler is especially considered and discussed in detail. The obtained coupling parameters are applicable to any guided modes in parallel waveguides of the same cross section, similar to 1/v index of refractive and identical shapes. Coupling constants and physical parameters for the coupled acoustic modes, computed according to this theory, are shown and seem to agree very well with experimental data.
Magnetic properties of epitaxial single crystal ultrathin Fe3Si films on GaAs (001)
Authors: Liou S. H. , Malhotra S. S. , Shen J. X. , Hong M. , Kwo J. , Chen H. S. , Mannaerts J. P.
Published: July 2002

Magnetic properties of Fe3Si films with thickness from 2 to 210 monolayers (ML) epitaxially grown on GaAs (001) were studied using a superconducting quantum interference device and alternating gradient force magnetometers. Growth of these single-crystal intermetallic compound films were carried out in a multichamber molecular beam epitaxy (MBE) system. The samples were covered in situ with Au 50 Å thick to prevent oxidation when the samples were removed from the MBE chamber. All the films are ferromagnetic even for samples as thin as 2 ML. The easy magnetization direction of the films is parallel to the film surface. The magnetic coercivity forces (Hc) of the samples increase as the film thickness decreases to 10 ML, and then decrease when the film thickness decreases further to 2 ML.
Nonthermal viscosity in magnets: Quantum tunneling of the magnetization (invited)
Authors: Tejada J. , Zhang X. X. , Balcells Ll.
Published: July 2002

In this article we present experimental results on the magnetic relaxation in different systems (single domain particles, magnetic grains, and random magnets). The existence of two relaxation regimes is demonstrated. At high temperatures, the magnetic viscosity S≡1/M0∂M/∂ ln(t) is proportional to temperature in accordance with theoretical expectation for thermally activated processes. At low temperatures, the viscosity is independent of temperature, providing evidence to quantum tunneling of magnetization. Qualitative agreement between theory and experiment is found.
Charge freezing and surface anisotropy on magnetite (100)
Authors: Coey J. M. D. , Shvets I. V. , Wiesendanger R. , Güntherodt H-J.
Published: July 2002

Scanning tunneling microscope images of the (100) surface of slightly nonstoichiometric magnetite taken at room temperature show static arrays of pairs of Fe2+ ions with short-range order, and a charge fluctuation time greater than 103 s. The surface appears to be a Wigner glass with electron pairs localized on adjacent ions as the basic unit. The explanation of Wigner localization at room temperature on the surface only is that the spin-polarized minority-spin band derived from dyz orbitals is stabilized and narrowed by the absence of an apicial oxygen from the B-site octahedron. This leads to surface anisotropy where the Fe2+ spins are pinned normal to the {100} surfaces. Surface anisotropy is expected to outweigh bulk anisotropy in submicron particles.
Reptation effects in particulate systems. I. Theoretical predictions
Authors: El-Hilo M. , O’Grady K. , Chantrell R. W.
Published: July 2002

In this paper we derive a theory which describes the effects of field cycles on the magnetization in particulate systems, i.e., the reptation effects. This theory predicts that the difference between reptation and time-dependence measurements arises from time dependence which occurs during the cycling of the magnetic field, i.e., during the field sweep. These predictions are found to be in good agreement with experimental data published in the following article [Lewis et al. (these proceedings)].
Diffusion-induced stresses in a long bar of square cross section
Authors: Chu J.-L. , Lee Sanboh
Published: July 2002

The diffusion-induced stresses in a long bar of square cross section have been investigated. Two mass transfers consisting of constant average concentration and constant surface concentration were considered. The concentration distribution was obtained in an analytic form. The displacement and stress fields were obtained numerically using a Jacobi iterative method. The maximum stress is located at the corner for constant average concentration and at the midedge for constant surface concentration. A comparison of stresses built up in the bar of a square cross section and in a thin slab was made.
Determination of magnetic anisotropy by transverse susceptibility measurement—an application to NdFeB
Authors: Zimmermann G.
Published: July 2002

The first order anisotropy field strength of sintered orientated NdFeB samples is determined by transverse susceptibility measurement. It is shown that this method yields reliable data, even if the applied field is much smaller than the anisotropy field to be detected. Systematic and technical error sources are discussed on the basis of calculation results.
Fabrication of high mobility two-dimensional electron and hole gases in GeSi/Si
Authors: Xie Y. H. , Fitzgerald E. A. , Monroe D. , Silverman P. J. , Watson G. P.
Published: July 2002

A procedure for the fabrication of two-dimensional carrier (electron and hole) gases in modulation doped GeSi/Si heterostructures is presented. The best 4.2 K mobilities measured for the two-dimensional electron and hole gases are 180 000 cm2/V s and 18 000 cm2/V s, respectively. Recently, two-dimensional hole gases with mobilities as high as 55 000 cm2/V s have been obtained. The carrier gases are fabricated on top of relaxed, compositionally graded GexSi1−x buffer layers with low threading dislocation densities (≊106 cm−2). Experimental evidence indicates that the function of the graded buffer is to promote dislocation propagation while suppressing nucleation. A comparative analysis is carried out for two dimensional electron gases in GeSi/Si/GeSi and in AlGaAs/GaAs structures. Although molecular beam epitaxy is used to grow the samples, the principle discussed here is independent of growth technique.
On the hot-carrier effects in 1.3 μm InGaAsP diodes
Authors: Honc T. , Zavadil J.
Published: July 2002

Hot-carrier effects induced by injected carriers are reported for In1−xGaxAsyP1−y 1.3 μm laser diodes. These effects are manifested by changes of electroluminescent spectra produced by the variation of injected current and heat-sink temperature. By analyzing the positions of the peaks of envelope spectral curves and of the individual Fabry–Perot peaks we come to the conclusion that carrier heating and not that of the lattice is responsible for the observed effects.
Kinetic limits for sensing tip morphology in near-field scanning optical microscopes
Authors: Yakobson B. I. , Moyer P. J. , Paesler M. A.
Published: July 2002

The lateral spatial resolution provided by near-field scanning optical microscopes depends critically on the shape and size of the sharpened tip of the optical fiber used as a source of light or sensing element. The fabrication of a tip by the commonly used heating and pulling method is examined. It consists of an initially pulling and rupture followed by a cooling and relaxation. The presented analysis leads to a deeper physical understanding of these processes and suggests avenues for technical improvements.
Cleaning of Si (100) surface by As ionized cluster beam prior to epitaxial growth of GaAs
Authors: Shinohara M. , Saraie J. , Ohtani F. , Ishiyama O. , Ogawa K. , Asari M.
Published: July 2002

It has been found that the exposure of a Si (100) surface to an As ionized cluster beam (ICB) is effective in the preparation of the surface prior to epitaxial growth of GaAs under conventional high vacuum conditions of 2×10−5 Pa. This process is achieved at a temperature as low as 600 °C. A clear 1×2 or 2×2 reflection high energy electron diffraction pattern observed after the procedure indicates good ordering of the sample surface. The cleaning process is attributed to chemical and physical sputtering by As ICB in the first stage and to the subsequent As termination of Si dangling bonds. It has been found that the optimum preparation conditions are an accelerating voltage of the As ionized cluster beam of 1.3 kV and a substrate temperature of 600 °C. GaAs films deposited on As ICB treated Si (100) substrates show good crystal quality with single domain structure.
Effect of disk topography on the flying height of a slider
Authors: Ma F. , Kim S.
Published: July 2002

This article addresses the topographic effect of surface roughness of a rotating magnetic disk on the flying height of a slider. Equations describing the dynamics of a slider are solved by numerical techniques to obtain the flying height. Variations in the flying height of the slider are given for topographic structures involving both deterministic and random surface asperities of the disk. It is found that surface roughness of a rotating disk plays a significant role in inducing flying-height fluctuations, and different topographic structures of the surface roughness lead to different statistical variations in the flying height. The influence of topographic parameters such as the amplitude, shape, and wavelength of surface asperities on the flying-height fluctuations is also investigated.
X-ray diffraction of nonuniform GexSi1−x/Si strained-layer superlattices
Authors: Li J. H. , Mai Z. H. , Cui S. F.
Published: July 2002

GexSi1−x/Si strained-layer superlattices have been studied by means of double-crystal x-ray rocking curves. Double peaks in the same order superlattice reflections or strong oscillation fringes near the superlattice peaks were observed in the rocking curves for two different samples. Good agreement between theoretical simulations and their experimental counterparts were obtained. Our results demonstrate that these phenomena are attributed to serious local variation in layer thickness and composition.
Characterization and depth profiling of E′ defects in buried SiO2
Authors: Vanheusden K. , Stesmans A.
Published: July 2002

Oxygen-vacancy defects (E′) generated at the surface of buried SiO2 (BOX) layers formed by O+ implantation during the separation by implantation of oxygen process have been studied by electron spin resonance at 4.3 K. The E′ generation tool used was exposure to a dc Ar glow discharge that produces E′ defects predominantly in a surface layer of ≊100-Å thick, reaching local volume densities at the surface up to 8×1019 cm−3. This glow discharge exposure, alternated with step-by-step etch back, allowed mapping of the defect generation sensitivity depth profile for the entire buried layer, revealing a fairly uniform sensitivity with a strong decline towards the BOX/substrate interface. Besides the usual E′γ signal, the E′δ center—a delocalized variant of the E′ center—has been newly observed in the BOX. Reoxidation (950 °C; 1.1 atm O2) of the BOX was observed to reduce the E′ sensitivity close to that of regular dry thermal oxide (≥29 times lower), while the E′δ signal could no longer be generated—again similar to conventional thermal oxide. These data suggest an adapted model for the E′δ defect, based on the existence of small Si clusters (≳5 atoms) in the BOX serving as defect precursors. Generally, the results imply that the buried oxide contains excess Si, exceedingly so near the BOX/substrate interface.
Laser-induced temperature distribution in substrates with periodic multilayer structures
Authors: Lu Yong-Feng
Published: July 2002

A general model and analytical results have been derived to obtain laser-induced temperature rise in substrates with periodic multilayer structures. The substrate can be equivalent to a homogeneous substrate with anisotropic thermal conductivity, if the dimension of the periodic structure is much smaller than the laser spot size. The laser-induced temperature rise can be then obtained by solving the three-dimensional heat equation with the different thermal conductivities in directions parallel and perpendicular to the layer structure. This model has been applied to calculate the laser-induced temperature rise in Si and Mn–Zn ferrite composite materials. A different temperature rise can be obtained when a laser beam irradiates the substrate surface, which is oriented in parallel or perpendicular to the layer structure.
On optimizing maximum efficiency of finite-time engines
Authors: Romm Fredy
Published: July 2002

The literature data about finite-time engines have been reviewed. We have shown that the modern technical thermodynamics largely use the finite-time engines concept. We use the apparatus of finite-time thermodynamics to describe a stationary engine—assemblage of multiple thermodynamically identical nonstationary engines working at a fixed phase difference. The author proposes a new model which considers an assemblage of thermodynamically identical engines functioning at different phases. The assemblage is itself a stationary engine. The model allows one to evaluate the internal energy dissipation caused by interaction of the elementary engines that is equivalent to the influence of the environment. We obtained the equations describing the system considered and found the conditions for maximum efficiency.
Time resolved photoluminescence studies of perpendicular transport in CdTe/Cd1−xMnxTe short-period superlattices
Authors: Hellmann R. , Pohlmann A. , Göbel E. O. , Yakovlev D. R. , Waag A. , Bicknell-Tassius R. N. , Landwehr G.
Published: July 2002

We present time-resolved photoluminescence studies of perpendicular transport and the subsequent capture of photoexcited carriers in II–VI semiconductor superlattices with an enlarged quantum well. The trapping dynamics are investigated as a function of the superlattice period in the range of 30–80 Å. We observed an efficient collection of electrons and holes in an enlarged CdTe quantum well confined by a short-period CdTe/Cd1−xMnxTe superlattice. Both the characteristic time and the efficiency of carrier collection are found to be strongly dependent on the superlattice period. A time constant less of than 25 ps is determined for the carrier collection in a 30-Å-period superlattice. Our experimental findings give evidence of Bloch type perpendicular transport in electron and heavy-hole minibands.
Micropatterned diamond substrates
Authors: Glesener J. W. , Tonucci R. J.
Published: July 2002

The patterning and characterization of a single crystal diamond substrate with a regular array of 8 micron features is described. Patterned arrays in diamond have been formed by a process consisting of the evaporation of ferrous metals through a glass channel mask onto the (100) surface of diamond. The evaporation was followed by a high temperature heat treatment to form a metal carbide. The carbide was then removed by acid etching, leaving behind a positive two-dimensional pattern on the diamond surface. Further pattern transfers were reproducibly accomplished by pressing the etched diamond surface into gold and aluminum foils.
Rubidium beam flux dependence of film properties of Ba1−xRbxBiO3 deposited by molecular-beam epitaxy using distilled ozone
Authors: Ogihara M. , Toda F. , Makita T. , Abe H.
Published: July 2002

We have focused our attention on the dependence of Ba1−xRbxBiO3 (BRBO) film composition ratio and film properties on rubidium-beam-flux intensity. BRBO films were deposited on MgO(100) substrates by molecular-beam epitaxy (MBE) using distilled ozone. Systematic measurements showed that the rubidium content was nearly independent of rubidium-beam-flux intensity in a wide beam-flux range. Therefore, it can be concluded that some degree of self-control of rubidium stoichiometry is actually possible in BRBO film growth by MBE. This study also revealed that the BRBO film properties had strong dependences on rubidium-beam-flux intensity even in the range for self-control of rubudium stoichiometry. Our study also clarified that rubidium-beam flux affects the barium content in the BRBO film.
Statistical theory of x-ray diffraction by one-dimensional randomly disordered TlBa2Ca2Cu3O9/Tl2Ba2Ca2Cu3O10 superconducting thin films
Authors: Holstein W. L.
Published: July 2002

Textured TlBaCaCuO superconducting thin films identified by electron microscopy as consisting of a mixture of TlBa2Ca2Cu3O9 and Tl2Ba2Ca2Cu3O10 layers with no long range crystalline order normal to the basal planes have been prepared. The Tl1+xBa2Ca2Cu3O9+x thin films yield complex x-ray diffraction patterns with a nonrational series of basal reflections. In order to further understand the structure of this material, a statistical model for x-ray diffraction by partially disordered layered structures was formulated for a material consisting of a random mixture of two types of layers in which both the layer thickness and scattering power of the layers differ. The scattering equation was solved computationally for x-ray scattering from the basal planes of layered materials consisting of random mixtures of TlBa2Ca2Cu3O9 and Tl2Ba2Ca2Cu3O10 layers. The results were applied to the modeling of the x-ray diffraction scattering intensity for 1.0-μm-thick textured thin films of TlBa2Ca2Cu3O9, Tl2Ba2Ca2Cu3O10, and Tl1+xBa2Ca2Cu3O9+x. The computational results support the identification of one such Tl1+xBa2Ca2Cu3O 9+x thin film as consisting predominantly of a nearly random mixture of 50% TlBa2Ca2Cu3O9 and 50% Tl2Ba2Ca2Cu3O10 layers (x≂0.5). The model was also used to examine the effect of intergrowth layers in TlBaCaCuO compounds on the intensity, location, and width of the basal plane reflections.
Saturation of intersubband absorption and optical rectification in asymmetric quantum wells
Authors: Zal/użny M.
Published: July 2002

The problem of saturation of intersubband absorption and optical rectification in asymmetric quantum wells is discussed theoretically using the density matrix formalism. The effects of the electron-electron interaction are taken into account. It is shown that near the resonance the spectral shapes of the nonlinear optical absorption coefficient and the nonlinear optical rectification coefficient are very similar. In the absence of the electron-electron interaction the spectral responses are nearly Lorentzian. The electron-electron interaction plays an important role in heavy doped systems. In structures with large spatial separation of the ground and the excited states wave functions, the depolarization effect is small and the absorption spectrum is affected mainly by the electrostatic Coulomb interaction. This interaction shifts the absorption peak to higher energy by an amount depending on the intensity of the incident light and leads to the significant distortion (asymmetry) of the line.
Effects of aluminum doping upon color formation in zinc oxide powders
Authors: Rafla-Yuan H. , Cordaro J. F.
Published: July 2002

The effects on the reflectance spectra of zinc oxide powders, of heat treatment, and of mechanical grinding were investigated for both undoped and aluminum-doped ZnO. A broad absorptance band at 390–400 nm was induced in the undoped powders both by heating in air and by grinding. From a comparison with electron paramagnetic resonance data from the literature, the band could be related to oxygen vacancies. It was found that aluminum doping suppresses the band formation induced by grinding; however, the doping does not suppress the band formation induced by heat treatment.
Superconducting Ba1−xKxBiO3 thin films and junctions
Authors: Amano Jun , Ko H. , Narbutovskih M. , Sheats J. , Tibbs K.
Published: July 2002

Superconducting Ba1−xKxBiO3 (BKBO) thin films and heteroepitaxial multilayers were deposited by in situ off-axis sputtering on various substrate at 400 °C. A typical superconducting BKBO thin film on the SrTiO3 and MgO substrates had a very sharp zero resistance transition at a temperature of 22–24 K as measured by transport four point and mutual inductance probes. The normal state resistivity exhibited metallic to semiconductive characteristics depending on film composition with the lowest room temperature resistivity of about 0.25 mΩ cm. The film orientation was highly epitaxial to both SrTiO3 and MgO substrates. Normal metal-insulator-superconductor (NIS) type tunnel functions with native insulator layer and deposited MgO layer were reproducibly fabricated. The superconducting energy gap of about 3.6 meV was obtained from those NIS junctions. Heteroepitaxial superconductor- insulator-superconductor (SIS) trilayer junctions were also fabricated using MgO insulator layers. For a 5 nm thick insulator layer, quasiparticle SIS tunnel junctions with nonhysteric I-V characteristics were obtained. By reducing MgO insulator layer thickness down to 3 nm, SIS tunnel junctions with Josephson supercurrent were obtained with hysteric I-V characteristics.
Thin-film growth and compositional effects in YBa2Cu3O7−x layers prepared by metalorganic chemical vapor deposition
Authors: Hudner J. , Thomas O. , Mossang E. , Chaudouet P. , Weiss F. , Boursier D. , Senateur J. P. , Östling M. , Gaskov A.
Published: July 2002

Thin-film growth and compositional effects of c-axis oriented YBa2Cu3O7−x (YBCO) thin films synthesized by metalorganic chemical vapor deposition have been investigated. The formation of single cation films using tetramethylheptanedionate precursors was shown to be mass controlled, exhibiting a ratio of deposited to evaporated species in the increasing order Ba, Y, and Cu. The physical properties of off-stoichiometric YBCO films deposited on MgO substrates were measured in the compositional range 1.1≤Ba/Y≤2.3 and 1.5≤Cu/Ba≤4.6. While structural properties such as c-axis values and rocking curves appeared unaffected to variations in cation stoichiometry, morphology was observed to be extremely sensitive even to slight changes in composition. Off-stoichiometric layers with Cu/Ba≳1.5 were observed to exhibit Cu-rich precipitates embedded in a 1:2:3 YBCO film matrix. The zero-resistivity temperatures were above 77 K for all cation film compositions measured. However, sharp ac-susceptibility transitions were restricted to a more narrow compositional range (1.9<Cu/Ba<3.6). The best superconducting properties [Tc=85 K, Jc (77 K)≳106 A/cm2] were observed for films with relatively rough surface morphologies (Ba/Y=1.6 and Cu/Ba=3.5). An optimum trade-off between smooth surfaces and superconducting properties was found for Ba/Y=1.5 and Cu/Ba=1.9, yielding Tc=81 K and Jc (77 K)=3×105 A/cm2.