bluuebunny/crossref_metadata_2025 huggingface dataset:
Switching of self-organized patterns in mutually modulating liquid crystal devices for beam control
Authors: Iino Yoshiki , Davis Peter
Published: July 2002

An optical circuit for beam pointing using self-organized roll patterns is proposed and demonstrated. The circuit contains two mutually coupled spatial light modulators (SLMs). It is shown that abrupt beam switching can be realized by changing a bias voltage applied to the liquid crystal layer of one of the SLM. The pattern forming and beam switching mechanism is explained using a theoretical model which includes the effects of diffraction, feedback displacement, and nonlinearity of the SLM.
Optimized subamorphizing silicon implants to modify diffusion and activation of arsenic, boron, and phosphorus implants for shallow junction creation
Authors: Aronowitz S. , Puchner H. , Kimball J.
Published: July 2002

Subamorphizing silicon preimplants were combined with relatively high dose drain (1014atoms/cm2) arsenic, boron, and phosphorus implants. The studies included as-implanted distributions. Extensive secondary ion mass spectrometry and spreading resistance profiling (SRP) analyses were carried out. It was found that the SRP analyses could be used to optimize the silicon implant energy. The resulting dopant profiles showed that not only was channeling suppressed and dopant diffusion reduced but activation also could be controlled. Equivalent medium doped drain regions of 150 nm were created using conventional furnace anneals. It was concluded that subamorphizing silicon preimplants could be used to create very shallow junctions in the medium dose drain regions of silicon-based devices.
Redshift of the longitudinal optical phonon in neutron irradiated GaP
Authors: Kuriyama K. , Miyamoto Y. , Okada M.
Published: July 2002

Redshift of the longitudinal optical (LO) phonon relating to the defect structure in neutron-irradiated GaP has been studied using Raman scattering, electron paramagnetic resonance, x-ray diffraction, and Fourier-transform infrared absorption methods. The defect structure is discussed for the two cases of vacancy-interstitials and antisites using a simple model of the LO–transverse optical phonon frequency splitting (Δω). It is suggested that the slight reduction of Δω originates from the vacancy-interstitial clusters rather than the antisite defects, considering the annealing behavior of the antisite defect concentrations, the volume expansion, and infrared absorption in neutron-irradiated samples. The clusters are associated with a volume expansion of about 0.13% observed in the neutron-irradiated samples.
The importance of high-index surfaces for the morphology of GaAs quantum dots
Authors: Platen J. , Kley A. , Setzer C. , Jacobi K. , Ruggerone P. , Scheffler M.
Published: July 2002

Results of a combined experimental and theoretical study are presented. GaAs{113} and {112} surfaces have been prepared by molecular beam epitaxy and analyzed in situ by low-energy electron diffraction and ex situ by atomic-force microscopy. The experimentally found structures are in full agreement with surface energies calculated by density-functional theory. The {112} surfaces are unstable under faceting into low-index planes, whereas the {113} surfaces appear as singular surfaces. Particularly, for GaAs(113) the surface energy is comparable with the values for the low-index surfaces. The impacts of these results on the interface between InAs quantum dots and the embedding GaAs matrix are discussed.
Stress relaxation in CuNi thin films
Authors: Brückner W. , Weihnacht V.
Published: July 2002

Stress relaxation in sputtered and annealed Cu0.57Ni0.42Mn0.01 thin films has been studied at various temperatures. The microstructure of the films stabilized by a thermal cycle to 550 °C showed twinned grains of the dimension of the film thickness. Below 200 °C, a small low-temperature high-stress plasticity was observed, probably due to obstacle-controlled dislocation glide. Between 300 and 550 °C distinct plasticity was detected. This can be described by two relaxation processes with exponentially decreasing stress towards a final value. The activation energies for the two processes agree (0.4 eV/atom), the deformation rates differ by a factor of 10. We suppose that (i) the slower process is flow by grain-boundary diffusion limited as a result of the attachment of the film onto the substrate and (ii) the faster process is mechanical twinning with diffusional accommodation at the grain boundaries.
Electrical properties of K-doped superfulleride thin films
Authors: Swami Nathan , Thompson Mark E. , Koel Bruce E.
Published: July 2002

K-doped superfulleride films (KxC60, x>6) of an average homogeneous composition of K11±0.3C60 and a strong [111] texture were prepared by depositing C60 on K multilayers at 200 K, in a proportion such that K:C60>12:1, and then annealing these layers to 300 K. This K11C60 superfulleride film was doped with C60 to form another superfulleride phase of average composition K8C60 and then doped further with C60 to form homogeneous K6C60 and K3C60 fulleride phases. The electrical properties of these superfulleride films are compared to those of alkali metal fulleride and alkaline earth metal fulleride films. The doping-resistivity profile showed a resistivity minimum, ρmin1=4.0×10−3 Ω cm due to the half filled t1u band in K3C60 and another dip in resistivity to 9.5×10−3 Ω cm at higher K-doping levels of K11C60, presumably due to the unfilled t1g band, as in the alkaline earth metal fullerides. The resistivity of the K3C60 and K11C60 films showed only minimal variations with film thickness, probably because the films prepared in this study had large grain sizes, and hence, resistivity was invariant with film thickness. The temperature dependence of the resistivity for 300 Å films of K3C60, K8C60, and K11C60 was also studied in the 200–350 K temperature range. K11C60 films showed a metallic behavior like K3C60 films, while conduction in K8C60 films exhibited an activated behavior that could be described by a granular metal model for resistivity in the dielectric region.
Transport of alternating current and direct current by hard superconductors. Critical and resistive state
Authors: Ulyanov Alexander N.
Published: July 2002

Voltage, voltage waveform, and losses in hard superconductors carrying alternating current (ac) and direct current (dc) transport current have been calculated in the framework of the critical and resistive state models for an arbitrary relation between the value of transport and critical current. The calculated results are in good agreement with the experimental ones. Voltage rectification by a superconductor carrying transport current, I(t)=Idc+Iac cos ωt, is explained. It is due to the shifting of the “working point” of the current–voltage (I–V) characteristic [point with coordinates current, jw=Idc, voltage, uw=f(Idc)] if the transport current contains a dc as well as an ac component. The peculiarities of the voltage across the superconductor with high value of the ac transport current versus time are predicted.
Crystallinity evaluation of phosphorus-doped n-type diamond thin film
Authors: Shimomura M. , Nishimori T. , Aukawa T. , Takakuwa Y. , Sakamoto H. , Kono S.
Published: July 2002

The crystallinity of a phosphorus-doped n-type diamond thin film as grown on a C(001) substrate by gas source molecular beam epitaxy has been examined by x-ray photoelectron diffraction (XPD) and atomic force microscopy (AFM). AFM showed that the growth mode of the n-type film is not an island-growth type that hinders the application of XPD. C 1s XPD patterns for the n-type film and the substrate showed almost perfect similarity. This proves that, like the substrate, the phosphorus-doped n-type thin film is in a good diamond structure.
Growth and characterization of nanoscale 3C–SiC islands on Si substrates
Authors: Miyasato Tatsuro , Sun Yong , Wigmore J. Keith
Published: July 2002

Three-dimensional nanoscale SiC islands were grown directly on to (111) crystalline Si substrates by reaction with hydrogen-plasma-containing Si and C radicals at temperatures between 650 and 900 °C. X-ray diffraction and transmission electron microscopy observations show that the islands are composed of (111)-oriented cubic SiC (3C–SiC) grains. Nucleation of the islands took place at conical projections on the Si substrate surface produced by hydrogen plasma etching. At the highest substrate temperatures the diameter and density of the islands were smallest, while their height was greatest and their structure most disordered.
First principles modeling of magnetic random access memory devices (invited)
Authors: Butler W. H. , Zhang X.-G. , Schulthess T. C. , Nicholson D. M. C. , Oparin A. B. , MacLaren J. M.
Published: July 2002

Giant magnetoresistance (GMR) and spin-dependent tunneling may be used to make magnetic random access memory devices. We have applied first-principles based electronic structure techniques to understand these effects and in the case of GMR to model the transport properties of the devices.
Dependence of magnetic properties on magnetic layer thickness in SmCo/Cr films
Authors: Takei Shigeto , Otagiri Yoshihiro , Morisako Akimitsu , Matsumoto Mitsunori
Published: July 2002

SmCo/Cr films were prepared with the thickness of SmCo layer varying from 1 to 400 nm, and the dependence of the magnetic properties on SmCo layer thickness was studied. Atomic force microscopy (AFM) measurement revealed that both the Cr underlayer and SmCo/Cr films were very similar in surface morphology with the surface roughness (Ra) of about 6 nm for the SmCo layer thinner than 100 nm. The Cr underlayer contributes to generate small grain size and smooth surface for SmCo layer as well as to improve its magnetic properties. The maximum coercivity was about 3.3 kOe, and the squareness and the coercive squareness in the plane direction were about 0.91 and 0.97, respectively, when the SmCo layer thickness was 40 nm. The diameter of switching unit estimated by the magnetic switching volume was smaller than 30 nm, while AFM observations show a grain size of 50 nm or more. The magnetic properties and the microstructure of SmCo/Cr bilayer films promise to be suitable for high density recording media applications.
Photon emission and related hot-carrier effects in polycrystalline silicon thin-film transistors
Authors: Farmakis F. V. , Dimitriadis C. A. , Brini J. , Kamarinos G. , Gueorguiev V. K. , Ivanov Tz. E.
Published: July 2002

The photon emission induced by the drain avalanche in polycrystalline silicon thin-film transistors (polysilicon TFTs) has been studied in wide drain and gate voltage ranges. As the photon emission phenomenon is closely related to hot-carrier effects, the gate and drain bias conditions for maximum device degradation have been determined from measurements of the emitted light intensity. In n-channel polysilicon TFTs, the effects of bias stressing at the maximum light emission are related to hot-hole trapping into the gate oxide near the drain and to formation of acceptor-like interface states consisted of midgap states and band tails.
The effect of magnetic field configuration on plasma beam profiles in curved magnetic filters
Authors: Bilek M. M. M.
Published: July 2002

Curved magnetic filters are commonly used with cathodic vacuum arcs to remove macroparticles from the plasma stream, making it suitable for the preparation of smooth, dense, and defect free films. Although a variety of filters have been investigated experimentally, the influence of the magnetic field configuration on the shape and position of the plasma beam at the filter exit has not been recognized. In this work the magnetic field configurations for a wide range of filter designs have been calculated and compared with measured beam profiles. The results show that the field configurations can be used to predict the dimensions of the plasma beam and in-plane off-axis shifts at the filter exit, as well as identifying regions of high loss. Magnetic field configuration calculations are shown to be a valuable design and optimization tool for curved magnetic field filters of various designs.
Does plastic deformation proceed near thermodynamic equilibrium? The case made for shear-strained lamellar diblock copolymers
Authors: Kuhlmann-Wilsdorf Doris , Winey Karen I.
Published: July 2002

Observations on kink bands in lamellar diblock copolymers (SEP 40–70), caused by unidirectional or oscillatory shear strain, are interpreted in terms of the low-energy structure (LES) hypothesis, to wit: “In a material subject to mechanical stresses, that structure will be approached which has the lowest free energy among all structures which are in equilibrium with the tractions and are accessible to the system.” This is the generalization of the low-energy dislocation structure (LEDS) hypothesis applicable to dislocation structures in crystalline materials. In agreement with the LES hypothesis, moderate fatigue cycling of initially disordered material establishes an order such that the plane of the lamellae is parallel to the plane of shear stress application, being the orientation of lowest shear modulus and, hence, for fixed fatigue amplitude, of lowest strain energy. At fatigue strain amplitudes above about 40% the material develops kink bands on account of the compressive stress along the body diagonal of the samples. The geometry of these kink bands shows that the plane parallel to the lamellae serves as preferred slip plane with the lowest resistance against sliding among all possible directions. Also the kink band morphology conforms with the LES hypothesis. Specifically, on average the ratio of kink band length (L) to the square of kink band width (W), i.e., L/W2, is nearly constant as expected from the minimization of kink band boundary energy and the elastic strain energy on account of the strain discontinuity at the ends of the bands. Subsequent experiments on a different copolymer in a range of temperatures additionally verify the LES hypothesis through establishing that, throughout, large-amplitude cycling causes the lamella orientation of lowest shear modulus.
Feasibility of stimulated emission to measure R-line shifts in shock compressed ruby
Authors: Knudson M. D. , Gupta Y. M.
Published: July 2002

In previous studies, ruby R-line shifts under shock compression and tension have been measured using the spontaneous luminescence from optically pumped samples. The signal intensities obtained are limited by the short time duration of the experiments in comparison to the long lifetime of the luminescence. We have investigated the use of stimulated emission for measuring R-line shifts in shocked ruby crystals. Experiments were performed both at ambient conditions and under shock compression to 6 GPa using an experimental configuration similar to that used for time resolved ruby luminescence measurements in previous shock wave studies. Signal gain due to stimulated emission was observed, with gains ranging from 1.1 to 3.4, in agreement with calculations performed for the particular experimental configuration used. The present results make a good case for incorporating this technique into the measurement of shock induced R-line shifts in ruby.
Anisotropic effective mass and scattering of electrons in mismatched heteroepitaxial films
Authors: Schneider D. , Himstedt B. , Schlachetzki A. , Tang G.-P.
Published: July 2002

InP layers grown epitaxially on silicon substrates show a pronounced anisotropy of the transverse magnetoresistance. We use this effect to study the ensuing anisotropy of the effective mass and scattering mechanisms of electrons. We investigated samples with an electron concentration from 7×1016 to 9.6×1017 cm−3 at temperatures ranging from 4.2 to 30 K in magnetic fields of up to 15 T. The sample with the lowest electron concentration showed an anisotropic negative magnetoresistance which we attribute to weak localization. This allows the characteristic times for inelastic scattering (coherence time) and for spin–orbit interaction to be determined. For the InP layers on Si of higher electron concentration we measured for the first time Shubnikov-de Haas oscillations, showing again anisotropy of the effective mass and of the Dingle temperature. We quantitatively ascribe differences from the bulk values to biaxial mechanical strain, distorting the Fermi sphere of bulk material to an ellipsoid. We assume that the observed anisotropies are due to a preferential orientation of crystal defects as a result of differences in the thermal expansion coefficient of the InP film and the Si substrate.
Flux reversal time in thin film write heads: A nonlinear system theoretic approach
Authors: Prabhakar A. , Filips S.
Published: July 2002

Large amplitude write currents elicit a nonlinear frequency response from thin film write heads. Saturation of the yoke structure causes the measured inductance to be a simultaneous function of both frequency and amplitude. Density plots are used to study the change in inductance over a two dimensional input parameter space comprising ac write current frequency (1<f<150 MHz) and dc write current amplitude (0<I<60 mA). A simple lumped element reluctance model representing such coupled behavior is proposed. The model extends quasistatic measurements that indicate a quadratic relation between the input magneto-motive force and the magnetic flux in the yoke structure. The circuit consists of a nonlinear reluctance element, described by a Volterra series, connected in series to a linear inductive element. The superposition theorem allows an analytic estimation of the flux reversal time for increasing write current amplitudes. A typical thin film write head that exhibits a quadratic dependence of flux on write current amplitude is analyzed. The model predicts a 30% decrease in flux reversal time over that predicted by a linear model as the amplitude of a stepped input write current is increased by a factor of 10.
Proton irradiation-induced intermixing in InGaAs/(Al)GaAs quantum wells and quantum-well lasers
Authors: Fu L. , Tan H. H. , Johnston M. B. , Gal M. , Jagadish C.
Published: July 2002

Proton irradiation with subsequent rapid thermal annealing was used to investigate intermixing of InGaAs/GaAs and InGaAs/AlGaAs quantum wells. Large photoluminescence (PL) energy shifts were observed in both materials. Comparatively, InGaAs/AlGaAs samples showed larger PL energy shifts than InGaAs/GaAs samples because of the presence of Al in the barriers and also better recovery of PL intensities, which is mainly due to dynamic annealing effects in AlGaAs during irradiation. Based on this, InGaAs/AlGaAs quantum-well lasers were fabricated and up to 49.3-nm-emission wavelength shift was observed in the proton-irradiated laser with no significant degradation in device characteristics.
Relation between the substitutional fraction and electrical activation of carbon in heavily C-ion implanted GaAs
Authors: Kuriyama K. , Koyama T. , Kushida K. , Hayashi N. , Kobayashi N. , Hasegawa M.
Published: July 2002

Nuclear reaction analysis (NRA), using the C12(d,p)13C reaction, in conjunction with Rutherford backscattering spectrometry (RBS) in the channeling geometry was used to evaluate the substitutional fraction of C in (100)-oriented semi-insulating GaAs implanted with C12 ions to a dose of 5×1016 cm−2. The substitutional fraction of the implanted C12 evaluated by NRA was 19% in the samples annealed at 600 °C, whereas the electrical activation rate of the same sample was 2.1%, as measured by the van der Pauw method. It is suggested that a possible origin of this discrepancy is the compensating centers such as As vacancy (VAs) and/or VAs-CAs complex introduced in the annealing processes. This was supported by both the surface precipitation of As observed by Raman scattering and the enhancement of the surface peak in RBS-channeling yield which was measured by using a 1.5 MeV He+4-ion beam.
On the migration behavior of metal impurities in Si during secondary ion mass spectrometry profiling using low-energy oxygen ions
Authors: Deenapanray Prakash N. K. , Petravic Mladen
Published: July 2002

Secondary ion mass spectrometry (SIMS) was used to investigate the segregation of several metal impurities in Si under low-energy oxygen ion bombardment. Our results suggested that both the segregation of Ca, Cr, and Ta at the SiO2/Si interface, and the antisegregation of Ti, Hf, and Zr into the oxide were thermodynamically driven. The migration behavior of Ca indicates that CaO, having a higher heat of formation than Si, was most probably formed under oxygen bombardment. Sharper in-depth profiles were obtained for Ti, Zr, and Hf (metals with lower heat of oxide formation than Si) by bombarding at angles of incidence for which a stoichiometric surface oxide is formed. The effect of impurity diffusivity is demonstrated through SIMS measurements at elevated temperatures (∼350–380 °C) for Cr, Zr, Ta, and Ti.
Investigation of optical properties of interfaces between heavily doped Al0.48In0.52As:Si and InP (Fe) substrates by photoreflectance analysis
Authors: Laureto E. , Dias I. F. L. , Duarte J. L. , Di Mauro E. , Iwamoto H. , Freitas M. T. P. , Lourenço S. A. , Filho D. O. Toginho , Harmand J. C.
Published: July 2002

A set of heavily doped Al0.48In0.52As samples grown by molecular beam epitaxy on InP (Fe) substrates was investigated using the photoreflectance (PR) technique. The spectra at 300 K are characterized by a transition in the vicinity of the InP energy gap, followed by strongly damped Franz–Keldysh oscillations (FKOs) which do not appear when the spectra are obtained at 77 K. The builtin electric field estimated from FKOs shows a small doping dependence but is substantially affected by the inclusion of a thin layer of AlxGayIn1−x−yAs (x≡0.22) at the interface between InP (Fe) and AlInAs:Si. In order to explain these results, a model based on the discontinuity of the energy bands in the InP/AlInAs and InP/AlGaInAs/AlInAs systems and also on the matching of the Fermi levels between the different materials is suggested.
Current density and ac field effects on 1/f noise in spin valve sensors
Authors: Stokes Scott W. , Wilson William L. , Lairson Bruce M.
Published: July 2002

Low frequency noise in patterned NiFe/Co/Cu/Co/FeMn (ΔR/R>9%) spin valves was investigated. The spin valves were sputter deposited and patterned by lift-off to form 75 μm×1000 μm lines. Noise power spectra were measured in the frequency range from 1 Hz to 10 kHz for ac and dc fields applied both parallel and perpendicular to the easy axis. An increase in the low frequency noise power spectrum was observed for an ac field applied along the easy axis. Increasing the ac drive frequency from 500 Hz to 5 kHz reduced the low frequency noise power to near the zero field background level.
Boron segregation to extended defects induced by self-ion implantation into silicon
Authors: Xia Jianxin , Saito Tomoya , Kim Ryangsu , Aoki Takenori , Kamakura Yoshinari , Taniguchi Kenji
Published: July 2002

The evolution of boron segregation to extended defects during thermal annealing was studied with secondary ion mass spectrometry and cross-sectional transmission electron microscopy. Czochralski Si wafers with a boron concentration of 3×1017 cm−3 were implanted with 50 keV Si ion for doses from 5×1013 to 2×1015 cm−2 and then annealed at 720, 820, or 870 °C in nitrogen ambient for various annealing times. The evolution of boron segregation peaks to three types of dislocation loops, end-of-range (EOR) dislocation loops, clamshell defects, and Rp (the projected range) defects, is closely related to the evolution of dislocation loops. As annealing temperature and time increase, the boron segregation peaks grow, remain stable, and then disappear together with the dislocation loops. For lower temperature annealing, the boron segregation peaks grow more slowly and reach higher peak concentrations. In addition to the boron segregation to dislocation loops, boron segregation to {311} defects was also found. The boron segregation peak to {311} defects is unstable and dissolves completely after annealing at 820 °C for 10 min. An analytic model for the boron segregation to EOR dislocation loops was developed under equilibrium condition by taking account of the average radius and area density of the EOR dislocation loops. The boron segregation energy to the EOR dislocation loops was found to be 0.75 eV. The evolution of the boron segregation peak was explained with the analytic model. The experimental boron segregation profiles can be well reproduced with the analytic model.
Microfabrication and characteristics of magnetic thin-film inductors in the ultrahigh frequency region
Authors: Yamaguchi M. , Suezawa K. , Arai K. I. , Takahashi Y. , Kikuchi S. , Shimada Y. , Li W. D. , Tanabe S. , Ito K.
Published: July 2002

Thin-film inductors for 1 GHz-drive mobile communication handset application has been demonstrated. This is the possible practical application of soft magnetic films in 1 GHz range. Fe61Al13O26 with Ms=1.2 T, ρ=500 μΩ cm, fr=2 GHz were used for the inductors. L=7.6 nH, R=6.5 Ω, and Q=7.4 were obtained at 1 GHz in a 370 μm×370 μm square four turn spiral of line/space=11 μm/11 μm covered with 0.1-μm-thick slitted Fe61Al13O26 film with Cr underlayer. The L was increased over the flux saturated inductor by 8.6% without any degrade of quality factor.
Young-modulus determination of an orthotropic thin plate in the through-thickness direction
Authors: Kim Sudook , Ledbetter Hassel
Published: July 2002

We give a new approach to obtain the Young modulus of a thin orthotropic plate in the through-thickness-direction. This new approach minimizes errors because eight of nine measurements are made along principal directions. To compare the results, we used a macroscopically orthotropic textured copper plate, which we also measured by acoustic-resonance spectroscopy. The proposed method also yields all off-diagonal elastic coefficients simultaneously and self-consistently.
Electron inelastic interactions with overlayer systems
Authors: Kwei C. M. , Chiou S. Y. , Li Y. C.
Published: July 2002

An overlayer system composed of a thin film on the top of a semi-infinite substrate was studied in this work for electron inelastic interactions. Analytical expressions for the depth-dependent inelastic differential and integral inverse mean free paths were derived for both incident and escaping electrons. The interface (film-substrate) effect and the surface (vacuum-film) effect were analyzed by comparing the results of an overlayer system and a semi-infinite system. It was found that the interface effect extended to several angstroms on both sides of the interface for a 500 eV electron incident into or escaping from the vacuum–SiO2–Si and the vacuum–Au–Ni systems. An application of the spatial-varying inelastic differential inverse mean free paths was made by Monte Carlo simulations of the electron elastic backscattering from an overlayer system. Good agreement was found between results calculated presently and data measured experimentally on the elastic reflection coefficient.
SiC/SiO
2
interface-state generation by electron injection
Authors: Afanas’ev V. V. , Stesmans A. , Bassler M. , Pensl G. , Schulz M. J. , Harris C. I.
Published: July 2002

Generation of interface states caused by electron injection in n- and p-type (3C, 4H, 6H)–SiC/SiO2/metal structures was studied using photoinjection methods. The charge trapping in the oxides on SiC was found to be similar to the charging of thermal oxides on Si. However, the generation of interface states in SiC/SiO2 was larger than in Si/SiO2. The interface-state production was found to be enhanced on the C face of SiC as compared to the Si face, and was also found to be enhanced after carbonization of the SiC surface prior to oxidation, which refers to carbon involvement in the SiC/SiO2 interface-state creation. The observed significant influence of the particular SiC polytype on the interface degradation also suggests an involvement of SiC crystal surface imperfections in the interface-state generation.
Photoluminescence studies on gray tracked KTiOPO4 single crystals
Authors: Deepthy A. , Satyanarayan M. N. , Rao K. S. R. K. , Bhat H. L.
Published: July 2002

The photochromic, electrochromic and x-ray irradiation damages (commonly called the gray tracks) produced in KTiOPO4 single crystals have been studied using photoluminescence (PL) spectroscopy. Gray tracks were produced in this material by exposure to high laser powers (∼MW/cm2), application of electric fields (∼kV), and exposure to x rays (30 kV). The PL spectra recorded for such gray tracked samples at 4.2 K, exhibited a luminescence band in the 1–1.8 eV range with a peak at 1.41 eV. Temperature and excitation intensity dependence of PL peaks were carried out to probe the exact nature of the broad emission band in the gray tracked samples. The observed photoluminescence is attributed to transitions in the Ti3+ levels, created on irradiation. The microscopic effects produced in the crystal by electric field, optical field, and x rays are similar, as can be concluded from the similarity of PL spectra as well as their intensity and temperature dependences.
Assessment of the normalization procedure used for interlaboratory comparisons of positron beam measurements
Authors: Goldberg R. D. , Knights A. P. , Simpson P. J. , Coleman P. G.
Published: July 2002

Variable-energy positron annihilation data from ion implanted and unirradiated Si and SiO2 were obtained at five separate laboratories. Line-shape analysis of the 511 keV annihilation γ rays yielded normalized S parameter signatures for radiation defect distributions in both types of samples. Laboratory-to-laboratory variations are found which, although small, lie outside the expected range of reproducibility. Large variations found in the extracted values for positron diffusion lengths L+ in silicon are identified and thought to arise from differences in sample surface conditions. Possible sources of the observed discrepancies are discussed, together with methods for reducing them.
Acoustic properties of lead-vanadate glasses
Authors: Paul A. , Maiti A. , Basu C.
Published: July 2002

The results of investigation on the acoustic velocity and acoustic attenuation by ultrasonic technique in the temperature range from 80 to 300 K in lead-vanadate glasses with different compositions have been presented. The temperature variation of these ultrasonic properties has been explained most successfully. The temperature dependence of attenuation can be interpreted in terms of a thermally activated relaxation process while the variation of velocity with temperature is explained by the combined effect of relaxation, anharmonicity, and frozen-in fluctuations causing microscopic inhomogeneity of elasticity in glasses.
Thermodynamic and kinetic study of solid state reactions in the Cu–Si system
Authors: Chromik R. R. , Neils W. K. , Cotts E. J.
Published: July 2002

It has been shown that significant changes in the course of solid state reactions can be realized by decreasing length scale, temperature, or by varying parent microstructures. In the case of the formation of Cu3Si by interdiffusion of Cu and Si, previous research has shown that over a large temperature range reaction rates are determined by the rate of grain boundary diffusion of Cu through the growing Cu3Si phase. We have examined the effect of replacing crystalline Si with amorphous Si (a-Si) on these solid state reactions, as well as the effect of decreasing the temperatures and length scales of the reactions. Multilayered thin film diffusion couples of Cu and a-Si were prepared by sputter deposition, with most average composite stoichiometries close to that of the equilibrium phase Cu3Si. Layer thicknesses of the two materials were changed such that the modulation (sum of the thickness of one layer of Cu and a-Si), λ, varied between 5 and 160 nm. X-ray diffraction analysis and transmission electron microscopy analysis were used to identify phases present in as prepared and reacted diffusion couples. Complete reactions to form a single phase or mixtures of the three low temperature equilibrium silicides (Cu3Si, Cu15Si4, and Cu5Si) were observed. Upon initial heating of samples from room temperature, heat flow signals were observed with differential scanning calorimetry corresponding to the growth of Cu3Si. At higher temperatures (>525 K) and in the presence of excess Cu, the more Cu-rich silicides, Cu15Si, and Cu5Si formed. Based on differential scanning calorimetry results for samples with average stoichiometry of the phases Cu3Si and Cu5Si, enthalpies of formation of these compounds were measured. Considering the reaction of these phases forming from Cu and a-Si, the enthalpies were found to be −13.6±0.3 kJ/mol for Cu3Si and −10.5±0.6 kJ/mol for Cu5Si. The growth of Cu3Si was found to obey a parabolic growth law: x2=k2t, where x is the thickness of the growing silicide, k2 is the temperature dependent reaction constant, and t is the reaction time. Also, the form of the reaction constant, k2, was Arrhenius: k2=k0 exp(−Ea/kbT) with kb being Boltzmann’s constant and the prefactor, k0=1.5×10−3 cm2/s, and activation energy, Ea=0.98 eV. These results indicate a much slower reaction to form Cu3Si in thin film Cu/a-Si diffusion couples than indicated by previous researchers using mostly bulk samples of Cu and crystalline Si (x-Si).
Effect of excimer laser annealing on the structural and electrical properties of polycrystalline silicon thin-film transistors
Authors: Angelis C. T. , Dimitriadis C. A. , Miyasaka M. , Farmakis F. V. , Kamarinos G. , Brini J. , Stoemenos J.
Published: July 2002

The structural and electrical properties of excimer laser annealed polycrystalline silicon thin-film transistors (polysilicon TFTs) are investigated in relation to the laser energy density. The devices were fabricated on 50 nm thick polysilicon films prepared by excimer laser crystallization (ELA) of amorphous silicon or by a combined solid phase crystallization (SPC) and ELA process. The structural properties of the polysilicon films have been investigated by transmission electron microscopy analysis. The effective density of states distributions in the polysilicon films and in the oxide traps near the oxide/polysilicon interface have been determined from low frequency noise measurements. The TFT performance parameters are compared with respect to their correlation with the structural properties of the polysilicon films and their electrically active defects, the basic variables being the starting material (amorphous silicon or SPC polysilicon) and the laser energy density.
Room-temperature vacancy migration in crystalline Si from an ion-implanted surface layer
Authors: Larsen Arne Nylandsted , Christensen Carsten , Petersen Jon Wulff
Published: July 2002

Migration of vacancies in crystalline, n-type silicon at room temperature from Ge+-implanted (150 keV, 5×109–1×1011 cm−2) surface layers was studied by tracing the presence of P–V pairs (E centers) in the underlying layer using deep level transient spectroscopy (DLTS). Under the conditions we have examined, the vacancies migrate to a maximum depth of about 1 μm and at least one vacancy per implanted Ge ion migrates into the silicon crystal. The annealing of the E centers is accompanied, in an almost one-to-one fashion, by the appearance of a new DLTS line corresponding to a level at EC−Et≈0.15 eV that has donor character. It is argued that the center associated with this line is most probably the P2–V complex; it anneals at about 550 K. A lower limit of the RT-diffusion coefficient of the doubly charged, negative vacancy is estimated to be 4×10−11 cm2/s.
Double-barrier THz source based on electrical excitation of electrons and holes
Authors: Buot F. A. , Krowne C. M.
Published: July 2002

A detailed dynamical analysis of an all solid-state THz source is given. This is based on the polarization-induced autonomous oscillation in resonant tunneling heterostructure with staggered band-gap alignment. The physical model consists of the following processes: (a) Generation by Zener tunneling of holes trapped in the barrier and electrons drifting in the depletion layer of the drain, whose rate decreases with the polarization between the barrier and quantum well. (b) Stimulated generation of barrier-well polarization. (c) Nonradiative decay of barrier-well polarization through barrier-hole recombination and quantum-well electron discharge. It is shown that a limit cycle oscillation of the barrier-well polarization and trapped-hole charge in the barrier can occur which induce THz oscillations in the resonant tunneling current across the device. The time-averaged results agree with the measured current–voltage characteristic of AlGaSb/InAs/AlGaSb staggered band-gap double-barrier structure. In particular, the measured smaller current offset at forward bias compared to that of reverse bias in the current–voltage hysteresis loop is predicted by our physical model and limit cycle analysis. Thus, we have experimental evidence indicating the correctness of our approach and the promising potential of this device as a novel all solid-state THz source.
Room temperature spectral hole burning and electron transfer in Sm-doped aluminosilicate glasses
Authors: Song Hongwei , Hayakawa Tomokatsu , Nogami Masayuki
Published: July 2002

Persistent spectral hole burning (PSHB) and light-induced absorption spectra with the pump of burning light were measured and studied in the Sm2+-doped xAl2O3⋅(100−x)SiO2 glasses to reveal the electron transfer and the formation of PSHB at room temperature. It was observed that the density of Sm2+ at the burnt sites decreased, while that of Sm3+ increased after the burning. The hole depth increased with the increase of Al2O3 concentration. The formation of PSHB is attributed to a one-step electron transfer by tunneling through the excited state, D05. The traps that capture the electrons produced by the ionization of Sm2+ may be related to the oxygen vacancies. In addition, the thermal activated barrier height between the burnt and unburnt configuration was estimated as ∼1.0 eV by thermal hole filling.
Random telegraph signal of a multiple quantum well infrared photodetector
Authors: Kore L. , Bosman G.
Published: July 2002

A model is proposed that is useful for extraction of transport parameters from the random telegraph signal in a multiple quantum well infrared photodetector, at low current bias and low temperature. Data were obtained using a three well, multiperiod device. Electron mobility was found to be from 2×105 to 4×105 cm2/V s. The number of carriers contributed for transport by each well-barrier-well region was found to be less than five. Two distinct activation energies were obtained that corresponded with the two distinct pulse heights in the random telegraph signal.
Shubnikov–de Haas effect and persistent photoconductivity in In0.52Al0.48As
Authors: Skuras E. , Stanley C. R. , Long A. R. , Johnson E. A. , MacKinnon A. , Yaguchi H. , van der Burgt M. , Singleton J.
Published: July 2002

The Shubnikov–de Haas effect in InAlAs measured using pulsed magnetic fields up to 50 T is reported. The InAlAs samples were grown by molecular beam epitaxy (MBE) and were either δ or slab doped with silicon at densities up to 7×1012 cm−2. Comparison of experimental subband densities with those calculated self-consistently shows that spreading of Si occurs by surface segregation at growth temperatures of ∼520 °C, similar to its behavior in MBE-grown InGaAs. In contrast to InGaAs, the InAlAs exhibits persistent photoconductivity which appears to be caused by a bulk defect rather than DX(Si) states.
Dynamic parameter space method to represent the operation modes of liquid crystal displays
Authors: Cheng Hongfei , Gao Hongjin , Zhou Fushan
Published: July 2002

We have developed a dynamic parameter space method to represent the operation modes of general twisted nematic liquid crystal displays. This method was based on the efficient calculation programs for director distributions by variation technique and optical properties by Berreman’s 4×4 matrix technique. Transmission or reflectance of liquid crystal display devices could be calculated in {φ,dΔn,β} space with varying voltage applied. The dynamic parameter space method is a useful tool to optimize the operation modes of liquid crystal displays.
Analysis of the scanning electron microscope mirror method for studying space charge in insulators
Authors: Wintle H. J.
Published: July 2002

We give a detailed analysis of the scanning electron microscope mirror method for studying a cloud of charge stored near the surface of an insulator, paying particular attention to the approximations that are often made. We discuss the effect of the finite size of the experimental chamber, of the thickness of the sample, and of relativistic corrections, and we demonstrate that interpretation of the observations cannot be unique. By making a detailed computation of the electron orbits in the presence of extended sources, we then test the commonly made assumption that the method measures the radius of curvature of the equipotentials, and we show that this is only partially true. Finally, we show that the sensitivity could be improved by increasing the scattering angle.
Compensation centers in ZnSeTe
Authors: Maruyama T. , Hasegawa T. , Komuro N. , Yamada H. , Ohtsuka W. , Akimoto K. , Kitajima Y. , Maeda K. , Yagi E.
Published: July 2002

Extended x-ray absorption fine structure (EXAFS), Rutherford-backscattering ion channeling, and particle induced x-ray emission channeling (PIXE/C) measurements have been performed in order to investigate compensation centers in Cl doped ZnSeTe. The EXAFS results from Cl doped ZnSeTe suggest that almost all Cl atoms are incorporated into substitutional Se lattice sites, which seems to indicate that Cl atoms themselves are not responsible for the compensation centers. The PIXE/C angular profiles were measured across the 〈100〉, 〈110〉, and 〈111〉 axes for undoped ZnSeTe. Comparing the angular profiles for Zn Kα, Se Kα, and Te Lα x-ray yields, it was found that some portion of the Te atoms (∼1020 cm−3) are located at tetrahedral interstitial sites. From these results, the difficulty of realizing n-type ZnSeTe is considered to be due to the existence of the interstitial Te atoms which act as acceptors.
Thermal diffusivity measurement of polymeric thin films using the photothermal displacement technique. I. Free-standing film case
Authors: Ogawa Ennis T. , Hu Chuan , Ho Paul S.
Published: July 2002

The photothermal displacement technique has been used to measure the out-of-plane thermal diffusivity in free-standing polymer thin films. The technique can be applied to a single sample as well as a collection of samples of different film thickness. Polymers are well suited for this method because they usually possess a large vertical coefficient of thermal expansion and readily absorb UV laser radiation. In particular, this method yields a value of the thermal diffusivity for polymer films with thickness ranging from 125 to about 10 μm. Different polymers have been studied with particular attention paid to UPILEX-S (biphenyl tetracarboxylic dianhydride-p-phenyl diamine) polyimide whose thermal diffusivity has been determined to be 0.0025±0.0005 cm2/s. Our study shows that the measurements are not strongly affected by uncertainties in the optical absorption coefficient of the polymer as well as photothermal displacement contributions from the backside of the free-standing film. Furthermore, neither the effect of heat dissipation into the surrounding media of the polymer film nor miraging of the probe beam should significantly affect the results. Finally, analysis shows that the value of the thermal diffusivity determined is that of the out-of-plane value as long as the in-plane value is not orders of magnitude larger. This article is the first part of a two-part examination of the thermal properties of polymers using this nondestructive method.
Structural and optical properties of distyrylbenzene derivative thin films
Authors: Ni J. P. , Ueda Y. , Hanada T. , Takada N. , Ichino Y. , Yoshida Y. , Tanigaki N. , Yase K. , Wang D. K. , Wang F. S.
Published: July 2002

In order to understand the relationship between the molecular orientation and optical properties of oligophenylenevinylene film, oriented thin films of 1,4-di(p-methoxystyryl)benzene (DSB-1) and 1,4-di(p-methoxystyryl)-2,5-dimethoxybenzene (DSB-2) were fabricated on a potassium bromide (KBr) (001) surface by the vacuum-evaporation method. The structures and optical properties of DSB films have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and polarized photoluminescence (PL) spectroscopy, respectively. DSB-1 molecules orient obliquely and/or parallel to the substrate surface depending on the substrate temperature. On the other hand, DSB-2 molecules tend to grow epitaxially with the molecular plane parallel to the substrate surface. The anisotropic molecular orientations represent the polarized PL. The epitaxial growth and molecular orientations observed by TEM and AFM at the local and microscopic scale are confirmed by polarized PL measurement on a macroscopic scale.
External electro-optic measurement utilizing poled polymer-based asymmetric Fabry–Perot reflection film
Authors: Zhang D. M. , Yi M. B. , Tian X. J. , Sun W. , Hou A. L. , Sun J. Z. , Ma Y. G. , Tian W. J. , Shen J. C.
Published: July 2002

An external linear electro-optic measuring system based on a poled polymer asymmetric Fabry–Perot multiple reflection film has been built, and the electric signals propagating on an indium tin oxide coplanar strip transmission line have been successfully measured. The nonlinear polymer spin coated on the high-reflectivity glass substrate was corona poled, thus an asymmetric Fabry–Perot film was fabricated based on polymer reflectivity and high reflectivity glass. The film standing-free technique and reflective configuration were adopted in this system. The principle of the system was analyzed by multiple reflection and index ellipsoid methods. The voltage sensitivity about 5 mv/Hz was obtained as 1 kHz sine input electric signals propagating on coplanar electrodes.
Magnetoresistance in low-temperature grown molecular-beam epitaxial GaAs
Authors: Betko J. , Morvic M. , Novák J. , Förster A. , Kordoš P.
Published: July 2002

Conductivity, Hall effect as well as “physical” and “geometrical” magnetoresistances were measured at 290–440 K in molecular-beam epitaxial GaAs layers grown at 200–400 °C. The experimental data were analyzed taking into account the combined band and hopping conductance regime. Positive hopping magnetoresistance parameters (Δρ/ρ0B2)h≈10−4 T−2 and hopping Hall mobilities lower than 1×10−4 m2 V−1 s−1 were determined in the as-grown layers. A transverse-to-longitudinal hopping magnetoresistance ratio of about 2, consistent with hopping transport theories, was obtained. In the annealed layer grown at 200 °C (J200a) the band mobility determined from the geometrical magnetoresitance (GMR) mobility was found to be significantly higher than the band Hall mobility. It is related to a mixed band conductivity regime with the hole concentration p exceeding the electron one n. The difference between GMR and Hall mobilities decreases with increasing growth temperature as far as a typical single-carrier band conductivity regime (n>p) is present in the layer grown at 400 °C. In contradiction to the layers grown at higher temperatures, the J200a layer showed the opposite (positive) sign of the hopping Hall coefficient as well as the largest hopping magnetoresistance parameter (≈3×10−2 T−2).
Field-dependence of quantum tunneling in small antiferromagnetic particles
Authors: Kim Gwang-Hee
Published: July 2002

The quantum tunneling of small antiferromagnetic particle is studied in the presence of an external magnetic field at an arbitrary angle. It is found that for antiferromagnetic particle with noncompensated sublattices the Wentzel-Kramers-Brillouin exponent and the crossover temperature from the thermal to the quantum regime depend on the direction and strength of the applied field. This features can be tested with the use of existing experimental techniques.