bluuebunny/crossref_metadata_2025 huggingface dataset:
Electromagnetic modes of a ferromagnetic slab
Authors: Ruppin R.
Published: July 2002

The dispersion relations of the long-wavelength retarded magnetic modes of a ferromagnetic slab magnetized in its plane are derived for a general direction of propagation. A comparison with the magnetostatic Damon–Eshbach modes is presented, and the parameters affecting the deviations of the magnetostatic modes from the exact ones are discussed. The theory is applied to a calculation of the ferromagnetic resonance lines of a yttrium iron garnet film, and the dependence of the propagation shift of the lines on the dimensions of the sample is demonstrated.
Modeling of pulsed-laser-induced gas detrapping, chemical reactions, diffusion, and desorption
Authors: Terreault B.
Published: July 2002

Short, intense laser pulses can thermally desorb hydrogen and other gases from the near surface (∼1 μm) of solids. This can be used, with some advantages, to study the trapping mechanisms, whether physical or chemical, the diffusion, and the surface recombination of these gases. By assuming a laser pulse with a Gaussian time profile, these successive steps are modeled with a finite difference code by using realistic temperature- and concentration-dependent material parameters. We show explicit results for the magnitude of the desorption puff as a function of the laser energy and for the depth profiles of the remaining gas under various assumptions for the detrapping mechanism, the diffusion coefficient, and the surface recombination coefficient. The results demonstrate that in spite of the poorer control on temperature, compared to isochronal or ramp anneals, the rate-limiting process can be identified and the activation energies determined.
A theoretical study of the critical radius of precipitates and its application to silicon oxide in silicon
Authors: Vanhellemont J. , Claeys C.
Published: July 2002

A theoretical expression is derived describing the influence of the extrinsic and intrinsic point-defect concentration and of the strain energy on the critical radius of precipitates. It is shown that an exponential distribution of the precipitate radii leads to analytical expressions for the content of precipitating species present under the form of sub- and supercritical precipitate nuclei. The application of the obtained theoretical results is illustrated by a few case studies on silicon-oxide precipitates in silicon. Excellent agreement between the calculated and observed subcritical oxygen content in as-grown Czochralski silicon is obtained.
The spin-dependent resonance signal from silicon
Authors: Kachwalla Z. , Miller D. J.
Published: July 2002

The inhomogeneous spin-dependent resonance signal from the depletion region of a p-n junction in silicon is investigated by modulating the external magnetic field as well as the microwave power. The signal is detected at the microwave power modulation frequency using lock-in detection. It is shown that the details of the component lines of the inhomogeneous signal can be obtained from measurements of the dependence of the overall signal on the external magnetic field modulation amplitude and frequency.
Preparation and aging of sputtered tungstic oxide films
Authors: Akram Hossain , Tatsuoka Hirokazu , Kitao Michihiko , Yamada Shoji
Published: July 2002

Conditions for the preparation of electrochromic tungstic oxide films with high efficiency for coloration have been investigated. Tungstic oxide films were deposited on glass substrates by rf sputtering in Ar-O2 mixture from a compressed powder WO3 target. As-deposited films require an ‘‘aging process,’’ in which the density of charges extracted in bleaching is smaller than that injected in coloring. It is considered that a part of the protons introduced during the aging combine with bonds of unstable oxygen contained in the as-deposited films. After the aging period, sputtered films have reversible coloration and bleaching cycles. Maximum electrochromic coloration efficiencies are 0.09 and 0.04 cm2/mC at wavelengths of 800 and 500 nm, respectively. They are obtained when the sputtering atmosphere is 0.04–0.05-Torr total pressure and 5% oxygen content. At any rate, substrate temperature should be kept at 100 °C or less.
Parametric investigation of the sheath potential in a low-frequency rf discharge
Authors: Chan Chung , Jin Zhong-Jun , Whitaker Christopher
Published: July 2002

The interdependence of the sheath potential, sheath thickness, electron density, and electron temperature as a function of the gas pressure and rf voltage is examined experimentally in a parallel-plate discharge. It is found that the key to the understanding of the complex behavior of the discharge lies in the understanding of the collective responses of these plasma parameters. We have also presented a simple Langmuir probe method for determining the sheath thickness
Polycrystalline Si thin-film transistors fabricated at ≤800 °C: Effects of grain size and {110} fiber texture
Authors: Kung K. T.-Y. , Reif R.
Published: July 2002

The grain size and {110} fiber texture of low-pressure chemical-vapor-deposited polycrystalline Si films were first modified using the ‘‘seed selection through ion channeling’’ process. These films were self-implanted at 200 keV, at normal incidence, to various doses (5–20×1014 cm−2), and were subsequently recrystallized at 600 °C. The as-deposited film was characterized by the smallest grain size, 0.08 μm, among all films and a weak {110} texture. The film processed with a dose of 11×1014 cm−2 had an intermediate average grain size of 1.0 μm but was characterized by the strongest {110} texture among all films. The film processed with a dose of 20×1014 cm−2, on the other hand, was characterized by the largest average grain size of 2.0 μm among all films but had no crystallographic texture. Metal-oxide-semiconductor thin-film transistors were then fabricated on these three films to examine the effects of grain size and fiber texture on device performance. Both n- and p-channel transistors were fabricated, using a self-aligned process with a maximum processing temperature of 800 °C. For both types of transistors, the as-deposited film offered the worst device performance, exhibiting the highest threshold voltages (4 and −4 V, respectively) and the lowest channel mobilities (0.4 and 0.5 cm2/V s, respectively). The 11×1014 cm−2 film offered the best device performance, exhibiting the lowest threshold voltages (1.2 and −3.0 V, respectively) and the highest channel mobilities (42 and 34 cm2/V s, respectively). The 20×1014 cm−2 film, on the other hand, exhibited equal or slightly worse threshold voltages (1.6 and −3.0 V, respectively) and channel mobilities (35 and 24 cm2/V s, respectively, than the 11×1014 cm−2 film. These results demonstrate that both the grain size and grain orientation can be important factors in determining polycrystalline transistor performance. For grain sizes in the order of 1–2 μm, a stronger {110} texture can, in fact, lead to a better transistor material than a larger average grain size.
Variable collision frequency effects on hose and sausage instabilities in relativistic electron beams
Authors: Slinker Steven P. , Hubbard Richard F. , Lampe Martin
Published: July 2002

A relativistic electron beam propagating in a dense gas typically ionizes the gas weakly, and the resulting plasma conductivity evolution strongly influences beam stability properties. We note in this paper that the electric field E and the plasma electron temperature Te usually decrease with distance ζ behind the beam head; as a result, the plasma electron neutral collision frequency νm decreases with ζ, which depresses the conductivity σ in the front of the beam and increases σ further back in the beam. We find that this variation of νm, which has generally been ignored in previous models, substantially modifies beam instability evolution. Hose instability growth tends to increase very rapidly in the beam head and taper off to an asymptotic value for large ζ, in contrast to the pure power law growth seen when νm and dσ/dζ are assumed to be constant. A second effect arises from local decreases in the perturbed conductivity σ, produced by perturbed electric field driven increases in the local collision frequency. This destabilizing effect causes the beam to behave as if the monopole conductivity σ0 were replaced by σ*=σ0 [1−(E/νm)(∂νm/∂E)]≡σ0(1−q̄). Analytical models for the case of constant q̄ illustrate the pattern of rapid hose instability growth in the beam head followed by a ‘‘plateau’’ in hose amplitudes that is also observed in hose simulations with the VIPER model. The destabilizing effect of variable νm on the perturbed conductivity also occurs for the resistive sausage instability. However, the model calculation presented here shows that the threshold for sausage instability is not likely to be reached for reasonable beam and plasma parameters.
Analysis of the effect of thermal nitridation of silicon dioxide on silicon interstitial concentration
Authors: Dunham Scott T.
Published: July 2002

The thermal nitridation of SiO2 has been analyzed in order to understand how the process results in large interstitial supersaturations in the silicon substrate as manifested by the greatly enhanced diffusivity of substitutional impurities such as phosphorus and boron and the growth of stacking faults. It is postulated that the interstitial injection is due to the growth of a thin oxygen-rich layer at the dielectric/silicon interface and is magnified by the presence of a nitrogen-rich layer near the interface which constrains the interstitials to the interface region. Because of the slow rate of growth of the oxide-rich layer, an initial transient period exists during which many of the interstitials created at the interface are injected into the substrate, raising the concentration in the silicon. For long times, a steady-state analysis shows that almost all of the interstitials generated at the interface diffuse back into the oxide. By extending a previous analysis for standard oxidation of silicon, a quantitative model was developed for interstitial supersaturation in the silicon which incorporates the transient regime and successfully predicts the diffusion enhancement of phosphorus with time. In addition, nitrogen incorporation in the bulk of the oxynitride and oxidation at the dielectric/silicon interface were modeled by an exponential decay to an equilibrium structure with a common time constant.
Continuous transition from multiple quantum-well regime to superlattice regime in GaAlAs/GaAs system as observed by spectroscopic ellipsometry with high lateral resolution
Authors: Erman M. , Alibert C. , Theeten J. B. , Frijlink P. , Catte B.
Published: July 2002

A multiple quantum-well structure grown by organometallic chemical vapor deposition and exhibiting a thickness gradient over the sample surface has been analyzed by spectroscopic and spatially resolved ellipsometry. The sample has been scanned in energy from 1.4 to 4.0 eV, with 5–10-meV resolution, and in position over a 46-mm line, with a 100-μm optical resolution. Using multilayer modeling we have first determined the structural parameters and particularly the aluminum concentration in the barrier, and the barrier and the quantum-well thicknesses. These two thicknesses vary from 95 to 10 Å along the 46-mm scanned line, while their ratio as well as the aluminum concentration (64%) remain constant. The ellipsometric spectra, namely, the effective dielectric function which can be deduced from the tan Ψ and cos Δ curves, allow for the determination of the multiple quantum-well optical transitions around Γ. In the thicker part of the wafer the optical spectra exhibit the well-known feature of a multiple quantum well associated to N=1, 2, and 3 heavy holes → electron transitions. As the thicknesses decrease, the coupling between quantum well increases, and the structure becomes a superlattice. For a barrier thickness of 30 Å, we observe the splitting of the fundamental level into two components: the first attributed to the symmetrical wave function and the second to the antisymmetrical wave function. The splitting is observed for both the heavy- and light-hole transitions. As the coupling between wells still increases, the dielectric function of the superlattice tends towards the one of the GaAlAs alloy with an average aluminum concentration of 32%. The evolution of the optical transitions versus barrier and quantum-well thickness has also been investigated theoretically by solving the Schrödinger equation for a periodic structure. The calculations have been done for two values of two conduction-band offsets: 60% and 85%. The overall agreement between theory and experiment is very good for the 60% conduction-band offset.
Numerical simulation of recorded domain shapes on a rotating magneto-optical disk
Authors: Takahashi Masahiko , Sukeda Hirofumi , Ojima Masahiro , Ohta Norio
Published: July 2002

For realizing a very high density magneto-optical recording such as a domain-edge recording, the way to control domain shapes and sizes precisely was studied by comparing a numerical simulation with an optical observation of recorded domains on a high-speed rotating disk. The numerical simulation based on a heat flow analysis was applied to a multilayer structure disk. A teardroplike domain shape was analyzed by this simulation, which causes a timing error of edge detection. This shape could be corrected to a symmetrical shape by using a modulated laser pulse. Moreover, it was found that a distance between two domains was affected by a thermal correlation of two laser pulses. This effect is remarkable when the time interval between two pulses is short.
Misch-metal-iron based magnets
Authors: Gong W. , Hadjipanayis G. C.
Published: July 2002

The hard magnetic properties of Fe-Mm-B alloys have been studied in melt-spun ribbons and sintered magnets. The as-spun ribbons were magnetically soft and high coercive fields (Hc∼7 kOe) were obtained after a heat treatment at about 700 °C. This caused crystallization of the sample into the Mm2Fe14B phase. The magnetization and Curie temperature of the crystallized samples were found to be 70 emu/g and 250 °C, respectively. The coercive fields of Mm-Fe-B sintered magnets is lower. Small additions of Al and Dy2O3 are found to increase the coercive field in the range of 6–10 kOe.
Activated dynamic scaling and magnetic ordering in Cd1−xMnxTe : Spin glass or random antiferromagnet? (invited)
Authors: Geschwind S. , Ogielski A. T. , Devlin G. , Hegarty J. , Bridenbaugh P.
Published: July 2002

The dynamics of magnetic fluctuations have been investigated in the random frustrated antiferromagnet Cd1−xMnxTe. The frequency-dependent susceptibility, χ′(ω,T) has been measured by Faraday rotation for x=0.4 and 0.65. The departure of the susceptibility from equilibrium Δχ′=[χeq(T)−χ′(ω,T)]/χeq(T) is found to obey activated dynamic scaling similar to that seen in random field systems. These results in conjunction with neutron measurements by others which revealed the abrupt saturation of the antiferromagnetic correlation length for x=0.65 at the onset of slow dynamics near Tc suggest a dynamically inhibited transition to a type-III AF state rather than a spin-glass transition.
Analysis of second level resonant tunneling diodes and transistors
Authors: Schulman J. N. , Waldner M.
Published: July 2002

Calculations of the current-voltage characteristics in double-barrier resonant tunneling diodes and transistors in which the tunneling occurs through the second or higher level in the well are presented. The alloy compositions outside of the barriers and in the well can be adjusted so that the lowest level in the well is truly confined. The resonant tunneling current is then found to be a sensitive function of the charge in the well. This suggests a new type of tunneling transistor in which the voltage on the base modulates the amount of charge in the first level, thus modulating the collector current. The base resistance can be made small by providing sufficient carriers in the well.
Quantized energy levels in Si inversion layers: A simplified self-consistent approach
Authors: Magnus W. , Sala C. , De Meyer K.
Published: July 2002

A quasi-analytical approximation scheme has been derived to calculate energies, wave functions and populations for the quantum states of electrons in p-Si inversion layers. The analytical character of the wave functions is preserved throughout the computation, and the usual constraint of satisfying Poisson’s and Schrödinger’s equations self-consistently everywhere in space is bypassed by putting forward physically justified guesses for the functional form of the wave function and the inversion layer potential, and imposing the equality of the first few electrical and quantum-mechanical moments. The values obtained compare favorably with earlier results extracted from purely numerical methods.
Stability of magnets levitated above superconductors
Authors: Davis L. C. , Logothetis E. M. , Soltis R. E.
Published: July 2002

The stability of a permanent magnet levitated above a slab of hard superconductor is considered. The force on a dipole magnet over a perfectly diamagnetic disk is calculated. It is found that the radial component of the force is directed outward and is 10%–20% of the image (vertical) force near the edge. Estimates of the magnetic friction force due to flux motion in a hard superconductor are made using Bean’s model. The magnitude of the magnetic friction is large enough to stabilize the magnet over most of the disk for typical values of the critical current in ceramic superconductors (∼103 A/cm2), but too small for the highest values reported (>106 A/cm2). It is conjectured that flux trapping due to inhomogeneities gives rise to transient restoring forces.
Far-infrared absorption of silicon crystals
Authors: Ohba Tetsuhiko , Ikawa Shun-ichi
Published: July 2002

Far-infrared absorption coefficients of silicon crystals grown by the Czochralski method (CZ) and by the floating-zone method (FZ) in the range of 20–200 cm−1 were obtained from transmission measurements at two different thicknesses, allowing for the effect of the multiple internal reflection. The CZ and FZ specimens used were not intentionally doped and had dc resistivities of 9.4±0.3 Ω cm and (5±2)×104 Ω cm, respectively. The impurity-induced absorption of the CZ crystal is well explained by the Drude model, while the FZ crystal showed only a weak absorption which is attributed to a wing of the intrinsic lattice band of silicon.
A generalized plasma etching model
Authors: Zawaideh Emad , Kim N. S.
Published: July 2002

A generalized plasma etching model has been developed. The new model is a generalization of our previous model presented in a recent paper [E. Zawaideh and N. S. Kim, J. Appl. Phys. 62, 2498 (1987)]. The new model includes the effects of multi-ion and multineutral gas species. New generalized plasma transport equations are also introduced. These equations are derived for multi-ion species. No restrictions on the anisotropy of the ion distribution functions are imposed. The new generalized plasma transport equations are valid for collisional to weakly collisional plasma [λ/L≤0(1)], where λ is the ion mean free path and L is the smallest of the scale lengths of the gradient in the electric field or in the macroscopic plasma parameters. A new particle balance model has also been introduced which incorporates the effects of gas composition, gas flowrate, pumping rate, ion and neutral gas chemistry, and atomic reactions on the neutral gas and plasma parameters (e.g., densities and pressures of the various neutral gas and plasma species). As an example, silicon dioxide (SiO2) plasma etching using carbon tetrafluoride (CF4) gas is used to illustrate this new generalized model. The model has shown good agreement with the experimental etch rates of SiO2 for various plasma and reactor parameters (e.g., neutral gas pressure, CF4 flowrate, and rf power).
Hydrogenation kinetics in oxidized boron-doped silicon irradiated by keV electrons
Authors: Lin Wallace Wan-Li , Sah Chih-Tang
Published: July 2002

Hydrogenation kinetics of boron acceptors in oxidized silicon during and after repeated 8-keV electron irradiation (225–2700-μC/cm2 stresses and 10–168-h interirradiation anneals) at room temperature are reported. Hydrogenation proceeds rapidly during irradiation but continues for many hours after the 8-keV electron beam is removed. Postoxidation process dependencies show that postoxidation and postmetallization annealing processes reduce the hydrogenation effect during the 8-keV electron irradiation, while exposure of the oxide to water prior to aluminum electrode deposition enhances it. The data can be interpreted by our two-reaction model consisting of the hydrogen capture reaction by the boron acceptor and the hydrogen recombination reaction to form hydrogen molecule.
Magnetic properties of BiFeO3-BaTiO3 and BiFeO3-PbTi(Zr)O3 glassy sputtered films
Authors: Fujii T. , Jinzenji S. , Asahara Y. , Kajima A. , Shinjo T.
Published: July 2002

Magnetic properties of glassy oxide films which exhibit ferromagnetism and ferroelectricity simultaneously above room temperature prepared by reactive rf sputtering are presented. Nominal film composition is the solid solution compound system expressed by (1−x)BiFeO3-x ABO3, x=0–1 where ABO3 denotes ferro- (antiferro-) electric perovskites, such as BaTiO3, PbTiO3, and PbZrO3. Spontaneous magnetization 4πMs for as-deposited films is small behaving paramagnetically and does not show the compositional dependence. After annealing at temperatures of 600–700 °C in either air or PbO atmosphere, considerably large 4πMs exceeding 1 kG appears at the solid solution composition. All samples with large 4πMs are x-ray amorphous and a rapid decrease in 4πMs takes place after annealing at higher temperatures (≳800 °C), where still unidentified crystallites are precipitated. Mössbauer absorption spectra were done to understand the origin of ferromagnetism. Besides pronounced magnetic (and/or dielectric) properties, these films have a high transmittance from visible through near-infrared regions, so that they are expected to be useful as optoelectronic device materials.
Amplified spontaneous emission in high power KrF lasers
Authors: Sasaki Akira , Ueda Ken-ichi , Takuma Hiroshi , Kasuya Koichi
Published: July 2002

A three-dimensional computer code of amplified spontaneous emission for a high power krypton fluoride (KrF) laser amplifier having a cylindrical symmetry and small aspect ratio is developed. The analysis using the present code indicates that the transverse and the longitudinal gain-length product should be smaller than 3 and 10, respectively, if high extraction efficiency is required. Together with a recent experimental result obtained in our 500-J laser, the present code guarantees high efficiency extraction of 500 kJ in a single beam having a 2×3 m2 cross section and a pulse duration of 1 μs.
Domain structure and microstructure of CoNi oblique incidence thin films
Authors: Ho Huei-Min , Gau George J.-S. , Thomas Gareth
Published: July 2002

The magnetic properties of thin films produced by vacuum evaporation depend on the deposition conditions, such as incident angle(α) and substrate temperature. These effects have been investigated in CoNi oblique incidence thin films by transmission electron microscopy. Both incident angle and substrate temperature are observed to have significant effects on the magnetization easy direction in the films. Low-angle films (α≤60°) are magnetically continuous with in-plane easy axes and reverse their magnetization by domain wall motion. On the contrary, high-angle films are magnetically isolated with an out-of-plane easy axis and reverse their magnetization by an incoherent rotation process. Microstructural results show that a c-axis texture increases with increasing incident angle. In high-angle films, the columns are single crystals and have a high defect density. The c axis of the columns does not coincide with the column axis. Thus, it is concluded that the origin of the magnetic anisotropy in low-angle films is mainly due to shape anisotropy. On the other hand, in high-angle films, crystalline anisotropy and stress anisotropy should be taken into account in addition to the shape anisotropy.
A segmented electrostatic undulator design for generating arbitrarily polarized soft x rays at the Stanford Positron Electron Project
Authors: Tatchyn Roman
Published: July 2002

The recent introduction of high-energy storage rings with very long straight sections for dedicated synchrotron radiation research has significantly expanded the parameter space accessible to insertion devices as well. In particular, when the generation of soft x rays on a storage ring such as the Stanford Positron Electron Project (PEP) is considered, its straight sections, which exceed 100 m, may be shown to be naturally amenable to low-to-medium K undulators with a large number of relatively long periods. This in turn allows for the establishment of relatively weak on-axis fields in such devices. In this paper it is shown that these conditions permit the use of electrostatic fields, as well as the concomitant development of fixed-gap, variable-period undulators. Such devices are shown to be superior in many respects to the variable-gap magnetostatic undulators currently in vogue. Two novel variable-period undulator designs, one for a transverse electrostatic undulator and the other for a helical device (HEU) are described. The performances of both devices are calculated, and the numerous advantages of the HEU configuration in producing either soft or hard x rays of arbitrary polarization on high-energy rings such as PEP are pointed out.
Simple and approximate expressions of demagnetizing factors of uniformly magnetized rectangular rod and cylinder
Authors: Sato M. , Ishii Y.
Published: July 2002

Demagnetizing factors of the rectangular rod and cylinder magnetized uniformly along the long axis are found to be expressed by the simple and approximate expressions 1/(2n+1) and 1/[2(2n/(π)1/2) +1], respectively, where n is the dimensional ratio. The error which is the difference of the value evaluated by 1/(2n+1) from the value evaluated by the exact expression of the demagnetizing factor is less than 5.48% for the rectangular rod with n<70. The error of the value evaluated by the expression 1/[2(2n/(π)1/2) +1] for the cylinder is also found to be less than 4.25% for n<100.
Optical properties of α-Sn
Authors: Adachi Sadao
Published: July 2002

A method is described for calculation of the real (ε1) and imaginary (ε2) parts of the dielectric function of α-Sn at temperatures of 296 and 100 K in the entire range of photon energies (0–6.0 eV), in which the model is based on the Kramers–Kronig transformation and strongly connected with the electronic energy-band structure of the medium. This model reveals distinct structures at energies of the E1, E1+Δ1 [three-dimensional (3D) M1 critical point (CP), or two-dimensional (2D) M0 CP], E′0, E0+Δ′0 (3D M0 CP), E2 [a mixture of damped harmonic oscillator (DHO) and 2D M2 CP], E1, and E′1+Δ1 CPs (DHO). Results are in satisfactory agreement with the experimental information over the entire range of photon energies. Dielectric-connected optical data of α-Sn, the normal-incidence reflectivity, the refractive index, and the extinction coefficient are also presented as an example of the ability of our model.
Frequency locking and quasiperiodicity in a modulated external cavity injection laser
Authors: O’Gorman J. , Hawdon B. J. , Hegarty J. , Heffernan D. M.
Published: July 2002

We report the observation of frequency locking and quasiperiodicity in a modulated external cavity injection laser. The order of appearance of the frequency-locked regions follows a Farey sequence as the modulation frequency is scanned at a fixed value of the modulation depth. Quasiperiodic behavior is observed when the modulation frequency is incommensurate with the external cavity round-trip frequency. The observed behavior is found to be in good agreement with a rate equation model.
Thin-film transistors based on nickel phthalocyanine
Authors: Guillaud G. , Madru R. , Sadoun M. Al , Maitrot M.
Published: July 2002

Thin-film transistors have been made using nickel phthalocyanine (PcNi) as active component. The characteristics of these transistors are studied with positive and negative gate-source and drain-source polarizations. The channel conductivity was p type. Very different thicknesses of PcNi layer are used, showing that in the two polarizations the effects are interfacial.
Deep levels in Ga-doped ZnSe grown by molecular-beam epitaxy
Authors: Venkatesan S. , Pierret R. F. , Qiu J. , Kobayashi M. , Gunshor R. L. , Kolodziejski L. A.
Published: July 2002

Results of a deep-level transient spectroscopy study of Ga-doped ZnSe thin films grown by molecular-beam epitaxy are presented. Two prominent deep levels were observed in all the samples investigated. The concentration of the trap detected at 0.34 eV below the conduction-band edge was essentially independent of the doping concentration and is attributed to native defects arising from Se vacancies in the ZnSe films. The second level with an activation energy of 0.26 eV shows a very strong doping dependence and is tentatively identified as arising from dopant-site (gallium-on-zinc-site) defects complexed with selenium vacancies. Preliminary results also indicate that planar doping of ZnSe significantly reduces the concentration of the Ga-vacancy complex.
Modeling of plasma-induced self-healing in organic dielectrics
Authors: Kammermaier J. , Rittmayer G. , Birkle S.
Published: July 2002

Plasma-induced self-healing in organic dielectrics, which is of extremely great importance for capacitor technology, is dependent, in a complicated manner, upon electrical and physicochemical processes, which cannot be determined by metrology. Accordingly, a theoretical model was developed which describes the spatiotemporal distribution of potential and current in the plasma of a self-healing breakdown, the formation of gas as a consequence of decomposition of material, and the consequent graphite deposition in the insulating areas. In this way it is also possible to compute the insulating areas as well as the entire gas formation as a function of voltage, capacitance, and thickness of the metal electrodes, and the limits for reliable self-healing.
Controlled coercivity in barium ferrite rigid disk coatings
Authors: Chagnon M. , Keirstead R.
Published: July 2002

The high applied magnetic field required to produce good orientation in particulate rigid disk coatings can induce a problem with dispersions of hexagonal barium ferrite particles. The hexagonal platelets form stacked assemblies, which produce a media coercivity (Hc ) 75%–100% higher than the powder Hc , despite the use of a functional surfactant. (Oriented Co-modified Fe2 O3 particles exhibit only 15% higher Hc .) The unusually high observed Hc is due to orthogonal shape and magnetic anisotropies and can be described by the model Hc =c(2K/Ms −NMs ). A surface modification has been developed to limit the stacking of barium ferrite particles and the associated high Hc without sacrificing orientation. The surface treatment uses an organometallic compound applied to the particles during the dispersion process in addition to a conventional surfactant. All other aspects of the dispersion process are unchanged. The coatings produced in this manner exhibit longitudinal coercivity 15%–20% higher than the powder Hc . Longitudinal squareness is greater than 0.75 and the in-plane orientation ratio is 2.5–3.0 to 1. The surface-treatment does not produce a simple stearic effect. The surface treated particles require a different surfactant functionality than the untreated particles, suggesting that the organometallic compound provides new sites for surfactant adsorption.
Magnetization reversal in spherical particles (abstract)
Authors: Chen W. , Fredkin D. R.
Published: July 2002

Bifurcation analysis has been applied to nucleation of magnetization reversal by curling1 in spherical particles. Nucleation is a pitchfork bifurcation, with the external magnetic field as control parameter. Curling occurs as a local minimum of the energy when it exists as a solution of Brown’s nonlinear equation2 for external field in excess of the critical value for curling. The existence of such a solution can be determined from second-order perturbation theory. When it exists, the magnetization varies continuously as the external field exceeds the critical value; otherwise, it must suffer a discontinuity. We have computed the solutions to Brown’s equation to second order near nucleation. The transition is always a continuous one when the anisotropy constant K is not sufficiently large.
Excimer laser induced doping of phosphorus into silicon
Authors: Slaoui A. , Foulon F. , Siffert P.
Published: July 2002

Doping of single-crystal silicon in PF5 atmosphere by means of an ArF (193 nm) excimer laser has been investigated as a function of laser fluence, number of pulses, and PF5 gas pressure. We find that phosphorus atoms are only produced by pyrolysis of the PF5 molecules but not by photolysis. The doping experiments were performed in PF5 ambients or using an adsorbed PF5 layer. The results indicate that the incorporation process is external rate limited for doping in PF5 ambients and mainly diffusion limited when using the adsorbed layer. Moreover, the evolution of the incorporated dose with the PF5 pressure shows that at low pressures (<0.5 Torr), the phosphorus atoms are supplied by a chemisorbed PF5 layer formed at the silicon surface, whereas at high pressures the main dopant source appears to be a layer of loosely bound PF5 molecules which has been physisorbed at the surface. It is also found that the surface quality is affected neither by the successive irradiation or by the heavy doping.
Study of a WSi2/polycrystalline silicon/monocrystalline silicon structure for a complementary metal-oxide-semiconductor for a compatible self-aligned bipolar transistor emitter
Authors: Giroult G. , Nouailhat A. , Gauneau M.
Published: July 2002

A WSi2 /polycrystalline silicon/Si bulk system has been studied in the framework of a complementary metal-oxide-semiconductor compatible self-aligned bipolar transistor technology. The WSi2 silicide is implanted with As and used as a dopant source for the formation of the polycrystalline silicon-bulk emitter. The effect of the polycrystalline silicon/monocrystalline silicon interface has been investigated, as well as the reproducibility of the process for the emitter formation. The role of boron on the arsenic diffusion process has been analyzed, with boron being implanted (a) in the silicon bulk for the intrinsic base formation, and (b) in the WSi2 silicide at the extrinsic base implantation step in the self-aligned process. Experimental results give dopant diffusion and segregation coefficients and are used to adjust the parameters of our process simulation program on the technological process.
Excitation of long-range surface polaritons in silver films by a finite-width light beam
Authors: Li Guifang , Seshadri S. R.
Published: July 2002

The evanescent wave excitation of a long-range surface polariton in a silver film is treated including the effects of the finite width of the incident laser beam and the slow spatial variation of the amplitude of the surface polariton. The theoretical results of the antiresonance characteristics in the angular response of the reflectivity are compared with the available experimental observations.
Nitrogen ion dynamics in low-pressure nitrogen plasma and plasma sheath
Authors: Gerassimou D. E. , Cavadias S. , Mataras D. , Rapakoulias D. E.
Published: July 2002

Laser-induced fluorescence (LIF) excitation and time-resolved LIF spectroscopy have been used to explore the interaction of a nitrogen plasma with a metal surface. The rotational temperature, the concentration of N+2, and the lifetime of N+2(B2Σ+u)υ=0 were measured as a function of distance from the metal surface. It was observed that the lifetime of the excited ion decreases sharply in the plasma sheath which is created in front of the metal surface. The concentration of N+2(X 2Σ+g), which was measured simultaneously with the lifetime of excited N+2, indicates a quasilinear decrease from the cathode to the grounded surface. Trot undergoes a gradual reduction from the bulk plasma up to the surface where its value is a good approximation of the surface temperature. An interpretation of these phenomena including a numerical simulation of the lifetime decrease is proposed here. The calculated values are in good agreement with experimental results. The dependence of lifetime decrease on the sheath potential as well as on other important parameters (cross section, profile of the electric field) is further discussed.
Effective medium approximation of 3-D Voronoi networks
Authors: Vrettos Nikolas A. , Imakoma Hironobu , Okazaki Morio
Published: July 2002

This article deals with the determination of the effective (apparent) diffusivity from the topological characteristics of microscopically inhomogeneous materials. The porous medium is modeled as a three-dimensional network of interconnected pores by means of the Voronoi–Delaunay tesselation. The calculation procedure is based on an improved version of the effective medium theory and the smooth field approximation. We investigate the case where the pores in the effective network are transformed to pores of a uniform cross-sectional area, and the case where the pore conductances are all replaced by an effective one. The results are compared with the numerical network solution. It is shown that the effective cross-section area approach reproduces the ‘‘exact’’ calculated transport coefficient with an error of less than 9%, whereas the effective uniform conductance approach fails considerably, displaying an error of 62%.
Observation of {111} ordering and [110] modulation in molecular beam epitaxial GaAs1−ySby layers: Possible relationship to surface reconstruction occurring during layer growth
Authors: Murgatroyd I. J. , Norman A. G. , Booker G. R.
Published: July 2002

Transmission electron diffraction (TED) was used to observe extra diffraction spots in the TED patterns of molecular beam epitaxial GaAs1−y Sby layers with y=0.25, 0.50, and 0.71 grown at 520 °C on (001) GaAs substrates. Half-order diffraction spots in the TED patterns indicated ordering on the (1̄11) and (11̄1) planes of the Group V sublattice, and streaks with subsidiary spots indicated a modulation in the [110] direction with a periodicity of ∼4d110 . Streaks in the [001] direction indicated monolayer disruptions of the {111} ordering and the [110] modulation in the [001] direction. As the composition parameter y varied, there were progressive changes in the {111} ordering, the [110] modulation, and the [001] disruptions, and these correlated with corresponding changes in the reconstruction of the dangling bonds at the growing layer surface, as determined by reflection high-energy electron diffraction. A model is proposed to explain the observed effects in terms of ordered atomic arrangements of the Group V atoms resulting from the surface reconstruction being incorporated into the bulk epitaxial layers.
Structure and chemical composition of water-grown oxides of GaAs
Authors: Liliental-Weber Z. , Wilmsen C. W. , Geib K. M. , Kirchner P. D. , Baker J. M. , Woodall J. M.
Published: July 2002

Previously it has been shown that the electronic surface properties of GaAs can be improved by photochemical treatment in water. If this photowashing technique is carried out with intense white light, oxides several hundred angstroms thick can be grown. This paper reports the structure and composition of this photowashed oxide and one grown by soaking in stagnant water in low light. The oxide was determined by TEM cross sections to be highly porous, but with thin continuous oxide layers both at the surface and at the oxide/GaAs interface. The oxide is composed of Ga2O3 with a low concentration of As2O3. The layer is primarily a fine grain Ga oxide crystal with a structure which appears different from the common forms of Ga2O3.
Subdomain zinc ferrite particles: Synthesis and characterization
Authors: Pannaparayil T. , Komarneni S. , Marande R. , Zadarko M.
Published: July 2002

Ultrafine and nearly spherical particles of zinc ferrite were synthesized under mild hydrothermal conditions by precipitating from metal nitrates. These particles exhibited antiferromagnetic ordering below 13 K. Mössbauer spectroscopic measurements revealed the subdomain superparamagnetic nature of the particles having a narrow particle size distribution. The hydrothermal ferrite powders were found to sinter to almost theoretical density with little or no intragranular porosity.
The structure and properties of phthalocyanine films grown by the molecular beam epitaxy technique. I. Preparation and characterization
Authors: Dann Anthony J. , Hoshi Hajime , Maruyama Yusei
Published: July 2002

Ultrathin films of the cofacially stacked F-bridged Al-phthalocyanine polymer, (AlPcF)n , have been grown using the highly controlled technique of molecular beam epitaxy. A parallel orientation of the polymer backbone to the substrate surface occurs in films on silicon and quartz, but epitaxy is not apparent. On single-crystal alkali halide substrates, the backbone is perpendicular to the substrate surface, and an epitaxial relationship exists that is influenced by the interaction between the substrate and phthalocyanine molecule. The transmission electron microscopy studies indicate that the most highly ordered films are produced on KBr(100) and have good continuity and unidirectional crystallite orientation.
Electrically induced light scattering from anisotropic gels
Authors: Hikmet R. A. M.
Published: July 2002

Anisotropic gels were produced by photopolymerization of an oriented liquid-crystalline (LC) mixture containing LC diacrylates and conventional LC molecules. Gels produced in this way were clear and did not give rise to excess scattering of light. Upon application of an electric field across the gel, the system turned translucent. Light scattered by the gel was found to be highly dependent on the direction of polarization and wavelength of the incident light.
Microstructure and contact resistance temperature dependence of Pt/Ti ohmic contact to Zn-doped GaAs
Authors: Katz A. , Nakahara S. , Savin W. , Weir B. E.
Published: July 2002

Ohmic contacts to p-GaAs, Zn doped at 5×1018 and 1×1019 cm−3, with the best specific contact resistance of 1.2×10−5 and 2.4×10−6 Ω cm2, respectively, have been formed with deposited layers of Ti and Pt. These layers, which were sequentially evaporated and then rapid thermally processed at 450 °C for 30 s, contained an interfacial layer constituted mainly of the TiAs phase adjacent to the substrate and the TixGa1−x solid solution in between it and the Ti layer. In addition, a significant amount of the Pt3Ti intermetallic was found at the Ti/Pt interface. The same metallization scheme, applied to 1×1018 cm−3 Zn-doped GaAs, produced a Schottky contact for the as-deposited and heat-treated samples. The temperature dependence characteristic of the specific contact resistance of the as-deposited Pt/Ti contacts to 5×1018 and 1×1019 cm−3 Zn-doped GaAs revealed a thermionic emission dominated carrier transport mechanism with an apparent barrier height of about 0.118 and 0.115 eV, respectively. This mechanism remained as the dominated one for the heat-treated contacts to the lower doped substrate. The contact resistance of the heat-treated contacts to the more heavily doped substrate, however, revealed a weaker temperature dependence. This indicates a conversion to a mixture of thermionic and field-emission carrier transport mechanisms across the interfacial barrier, and a reduced barrier height to a minimum value of 0.068 eV measured after sintering at 450 °C.
Assessment of Fe-doped semi-insulating InP crystals by scanning photoluminescence measurements
Authors: Longère J. Y. , Schohe K. , Krawczyk S. K. , Coquille R. , L’Haridon H. , Favennec P. N.
Published: July 2002

Room-temperature scanning photoluminescence (SPL) measurements were performed on Fe-doped semi-insulating InP wafers obtained from various suppliers. It was found that defects and inhomogeneities such as short- and long-range doping striations, dislocations, and subsurface extended defects are associated with specific ‘‘signatures’’ in SPL images, regardless of the origin of the samples. Because SPL measurements are fast and nondestructive, they appear to be useful for the evaluation of this material.
Observation of gold evaporated on graphite (00.1) cleaved surfaces
Authors: Kuwabara M. , Smith D. A. , Clarke D. R.
Published: July 2002

Gold evaporated on air-cleaved (00.1) graphite was observed by scanning tunneling microscopy. Most individual gold islands were not stable during scanning; some islands even appeared to translate. These observations suggest that the interaction between the gold islands and the scanning tunneling microscope tip is stronger than that between the gold and the air-cleaved graphite substrate. Some gold islands were observed to be stable. It was deduced that stable islands at steps were located on the upper layer rather than on the lower layer. It is also deduced that the alignment of the elongated gold grains in the continuous film may be related to cleavage steps.
Nonspiking ohmic contact to p-GaAs by solid-phase regrowth
Authors: Han C. C. , Wang X. Z. , Wang L. C. , Marshall E. D. , Lau S. S. , Schwarz S. A. , Palmstro/m C. J. , Harbison J. P. , Florez L. T. , Potemski R. M. , Tischler M. A. , Kuech T. F.
Published: July 2002

A low-resistance and nonspiking contact consisting of a layered structure of Si/Ni(Mg) on p-GaAs is formed by solid-phase regrowth. Backside secondary-ion mass spectrometry and cross-sectional transmission electron microscopy show an initial reaction between Ni and GaAs to form NixGaAs which is later decomposed to form NiSi by reacting with the Si overlayer. This reaction leads to the solid-phase epitaxial regrowth of a p+ -GaAs layer doped with Mg. The total consumption of substrate is limited to a few hundred angstroms. The as-formed ohmic contact structure is uniform and planar with an average specific contact resistivity of ∼7×10−7 Ω cm2 on substrates doped to 8×1018 cm−3. The thermal stability of this contact scheme is also reported.
Numerical modeling of effects of power imbalance on irradiation nonuniformities
Authors: McKenty P. W. , Verdon C. P. , Skupsky S. , McCrory R. L. , Bradley D. K. , Seka W. , Jaanimagi P. A.
Published: July 2002

We report on the importance of various sources of power imbalance of the 24 beam OMEGA laser system in contributing to laser irradiation nonuniformity. Long spatial wavelength irradiation nonuniformities on target are investigated numerically by adapting existing uniformity codes to incorporate time-dependent density and temperature profiles. The analysis shows that power imbalance due to slightly detuned (≤100 μrad) frequency conversion crystals and small differences in the ultraviolet (UV)-transport losses (ΔE/E≤5%) makes only a modest contribution to the overall nonuniformity. However, power imbalance from pulse shape distortion was found to create substantial irradiation nonuniformity on the target early in the implosion. The predictions of the present analysis were verified by an experiment in which a well controlled power imbalance was applied. Good agreement was found between the experimentally observed core positions and those predicted by the simulation.
Optical properties of dilute hydrogen tungsten bronze thin films
Authors: Green Mino , Hussain Z.
Published: July 2002

Transmission and reflection spectra in the range of 0.5–4.1 eV have been obtained for HxWO3 polycrystalline thin films of 5-nm mean grain size. The composition range x=0–0.16 has been investigated. The measurements were refined to give the absorption coefficient and other optical parameters versus photon energy. The data have been interpreted in terms of the interband transition model due to Green and Travlos [Philos. Mag. B 51, 501 (1985)]. It is noted that main gap changes because of changes in crystal structure, and there is a sensitivity of the main gap value to grain size which may have its origins in quantum confinement effects.