bluuebunny/crossref_metadata_2025 huggingface dataset:
Brillouin light scattering on Fe/Cr/Fe thin-film sandwiches
Authors: Kabos P. , Patton C. E. , Dima M. O. , Church D. B. , Stamps R. L. , Camley R. E.
Published: July 2002

Brillouin light scattering (BLS) in the backscattering configuration has been used to study the magnetic excitations in epitaxial Fe(38 Å)/Cr(13 Å)/Fe(38 Å) thin-film sandwiches. Spin-wave frequency was measured versus in-plane wave vector k and static in-plane magnetic field H for both [100] and [110] direction fields and with k perpendicular to H. The range of applied fields was 50–1500 Oe. The wave-number range was 0.45×105–2.3×105 rad/cm. The BLS spectra correlate with magnetization versus field profiles and confirm the antiferromagnetic coupling between the Fe layers. Under low-field conditions and near-antiparallel alignment of the Fe layer magnetization vectors, the spin-wave frequencies from the Stokes and anti-Stokes sides of the BLS spectra are different. These frequencies merge at high field. The low-field splitting feature is very sensitive to small differences in thickness for the magnetic layers and indicates a thickness difference of 9%. Matchups between features of the BLS data and magnetization curves were obtained for the following parameters: magnetic layer saturation induction 4πMs=18.6 kG; cubic anisotropy field HA=550 Oe; in-plane [110] uniaxial anisotropy field HU=76 Oe; antiferromagnetic interlayer exchange coupling field HJ=120 Oe. Spin-wave frequency calculations based on these parameters show quantitative agreement with the measurements. The quantitative fits require inclusion in the theory of an iron layer surface anisotropy with an effective surface anisotropy field of 2 kOe.
Effect of cadmium to sulfur ratio on the photoluminescence of CdS-doped glasses
Authors: Okamoto Hideki , Matsuoka Jun , Nasu Hiroyuki , Kamiya Kanichi , Tanaka Hiroshi
Published: July 2002

In order to determine the origin of the long-wavelength photoluminescence spectra of CdS-doped glasses, luminescence spectra from glasses doped with CdSx having various Cd to S ratios were examined. The intensity of the luminescence peak decreased with increasing sulfur content, which indicates that the luminescence could be associated with sulfur-deficient trap centers. With the shift of the band gap of CdSx to lower energy by crystal growth, the peak position of the trap-center-related luminescence also shifted to lower energy. The ratio of these two energy shifts indicates that the trap center is donorlike, not acceptorlike. The shape of this luminescence band was dependent on the excitation wavelength, which indicates that more than two types of trap centers exist in the glass.
The evaluation of surface recombination velocity from normal-collector geometry electron-beam-induced current line scans
Authors: Luke Keung L.
Published: July 2002

There are two well-known point source-based methods for the evaluation of the surface recombination velocity s from normal-collector geometry electron-beam-induced current (EBIC) line scans. The first was proposed by Jastrzebski, Lagowski, and Gatos [Appl. Phys. Lett. 27, 537 (1975)], the second was by Watanabe, Actor, and Gatos (WAG) [IEEE Trans. Electron Dev. ED-24, 1172 (1977)]. Scheer, Wilhelm, and Lewerenz [J. Appl. Phys. 66, 5412 (1989)] were unsuccessful in using the first method to extract s from their EBIC data. Hakimzadeh, Möller, and Bailey [J. Appl. Phys. 72, 2919 (1992)] applied the second method to evaluate s from their EBIC data without accounting for the mismatch between the theoretical requirement and the experimental condition relating to source size and electron penetration depth at which the WAG expression is to be evaluated. In this article these two methods are evaluated and their applicability to both point and extended-source data is examined quantitatively. Their limitations and shortcomings led us to suggest a way to extend the applicability of the WAG expression to include extended sources and to formulate two new Gaussian source-based methods to evaluate the surface recombination velocity. A number of computed curves are provided to facilitate the application of these proposed new methods to GaAs and other semiconductors with diffusion lengths in the range of 0.5–3.0 μm and (surface recombination velocity/diffusion coefficient) values in the range of 103–106 cm−1.
Effects of the substrate bias on the formation of cubic boron nitride by inductively coupled plasma enhanced chemical vapor deposition
Authors: Ichiki Takanori , Momose Toshihiro , Yoshida Toyonobu
Published: July 2002

Cubic boron nitride (cBN) films were prepared on 2×2 cm2 Si(100) substrates from the B2H6+N2+He+Ar system at 900 °C by low pressure inductively coupled plasma (ICP) enhanced chemical vapor deposition. ICP was generated by 13.56-MHz 7-kW input at 1×10−3 Torr. The effects of the sheath potential on the formation of boron nitride polymorphism have been mainly investigated. Films were deposited at various self-bias potentials by varying an auxiliary 13.56-MHz radio-frequency power to the substrate. The plasma potential measured by an emissive probe method at 11 mm above the substrate was constant irrespective of the rf input power to the substrate. The deposition rates derived from the thickness observation are in good agreement with those estimated from the infrared absorption spectroscopy by evaluating the absorption coefficients of cubic BN (at 1060 cm−1) and hexagonal BN (at 1370 cm−1) to be 23 000 cm−1 and 30 000 cm−1, respectively. Using these values, growth rates of cubic and hexagonal BN have been estimated as the functions of the sheath potential. The optimum sheath voltage for cBN growth in this study was 80–86 V, at which the cBN content of the film reached about 75%.
Effect of multiple reflection propagation on photon recycling in GaAs/AlGaAs double heterostructures
Authors: Miller K. L. , Fardi H. Z. , Hayes R. E.
Published: July 2002

An analysis is presented to accurately calculate the effects of photon recycling on the minority-carrier lifetime in the active region of GaAs/Al0.3Ga0.7As double heterostructures. It is shown that the minority-carrier lifetime multiplication factor and resulting minority-carrier lifetime are dominated by multiple reflection propagation for samples with thicknesses of approximately less than 1.0 μm. The calculated results are in good agreement with previously published experimental data on the variation of the minority-carrier lifetime multiplication factor with active region thickness, indicating the usefulness of the analysis to accurately model the effects of photon recycling in transient photoluminescence measurement of thin devices. This may lead to accurate determination of the minority-carrier lifetime, diffusion coefficient, and surface recombination velocities at the levels of interest for device applications.
Magnetic properties of materials in the CaO-P2O5-Fe2O3 system
Authors: Kumar Binod , Chen Christina H.
Published: July 2002

The magnetic properties of numerous compositions in the ternary CaO-P2O5-Fe2O3 system have been studied. A relatively wide glass formation region is located around the P2O5 corner of the system. The Fe2O3-containing glasses exhibit paramagnetic behavior. The specimens inside the composition range Fe2O3≥30% consist of both paramagnetic and ferrimagnetic phases.
Impurity levels in layer semiconductor p-GaSe doped with Mn
Authors: Shigetomi S. , Ikari T. , Nakashima H.
Published: July 2002

The impurity levels in Mn-doped GaSe have been investigated by using photoluminescence (PL), Hall effect (HE), and deep-level transient spectroscopy (DLTS) measurements. The emission band at 1.82 eV is observed on the PL spectra of the samples doped with Mn of wide range from 0.01 to 1.0 at. %. We find, from the temperature dependences of PL intensity and peak energy, that the 1.82 eV emission band is due to the transition between the conduction band and the acceptor level at 0.32 eV above the valence band. The acceptor level located at about 0.34 eV above the valence band is detected by using HE and DLTS measurements. The dominant acceptor level in the carrier transport shows almost the same position as that of the radiative recombination center. This acceptor level is probably associated with the defects formed by Mn atoms in the interlayer or interstices.
Local structural investigation of buried InAsxP1−x/InP interfaces
Authors: Lamberti C. , Bordiga S. , Boscherini F. , Pascarelli S. , Schiavini G. M. , Ferrari C. , Lazzarini L. , Salviati G.
Published: July 2002

A local structural investigation has been carried out on the 10 Å InAsxP1−x layer in ad hoc grown InAsxP1−x/InP epitaxial multistructures deposited by low pressure metallorganic chemical vapor deposition by means of extended x-ray absorption fine structure spectroscopy, high resolution transmission electron microscopy, and high resolution x-ray diffraction analyses. The goal was to characterize the local structure of the unwanted, strained, interface layers of InAsxP1−x produced by the exposure of the InP surface to AsH3 as occurs during the growth of InP/In0.53Ga0.47As heterostructures optimized for photonics. High resolution x-ray diffraction and high resolution transmission electron microscopy confirm the high crystalline perfection of the investigated interfaces. As K-edge extended x-ray absorption fine structure analysis shows, the first shell environment of As at these interfaces is similar to that found in bulk InAsxP1−x alloys of similar composition, as determined experimentally and by comparison with recent theories of bond lengths in semiconductor alloys. In particular we measure an As—In bond length which varies at most 0.02 Å with As concentration at the interface; this implies that epitaxy with InP is accompanied by local structural distortions, such as bond angle variations, which accommodate the nearly constant As—In bond length.
A study of Cu50Fe50 produced by mechanical alloying and its thermal treatment
Authors: Macrí P. P. , Rose P. , Frattini R. , Enzo S. , Principi G. , Hu W. X. , Cowlam N.
Published: July 2002

A specimen of Cu50Fe50 equiatomic composition was mechanically alloyed (MA) by ball milling starting from the pure elements, which are immiscible according to the equilibrium phase diagram. Structural analysis by x-ray and neutron diffraction has shown that the mechanical process initially reduces the crystallite size of both elements as a function of the milling time. The diffraction data show that the bcc iron phase is subsequently consumed, due to progressive incorporation of the iron atoms into the fcc copper matrix. The Mössbauer spectra of a specimen MA for 16 h has a broad magnetic profile typical of a Fe-Cu extended solid solution, with some evidence of two local environments of the iron atoms and a small admixture of the γ-Fe. The annealing of these MA treated specimens effects a decomposition of the extended solid solution into FCC copper and both α- and γ-iron allotropes. This decomposition process is discussed in relation to spinodal decomposition and to nucleation-and-growth mechanisms.
dc electric field effect on the microwave properties of YBa2Cu3O7/SrTiO3 layered structures
Authors: Findikoglu A. T. , Doughty C. , Anlage S. M. , Li Qi , Xi X. X. , Venkatesan T.
Published: July 2002

We present a summary of our work on the dc electric field effect on the microwave properties of YBa2Cu3O7/SrTiO3 (YBCO/STO) layered structures. We briefly describe the fabrication of these layered structures, their structural and electrical properties related to the microwave response, and experimental methods to investigate dc electric field effects at microwave frequencies. Analysis of microwave measurements shows that dc electric field modulated changes in both the complex conductivity of YBCO layers and the dielectric properties of the STO layers contribute to the overall device response. At low temperatures (<50 K) and large electric fields, good samples show linear gate-voltage modulation of microwave surface resistance and surface reactance attributable to field induced superconducting hole filling and depletion in the dominant YBCO layer.
Photorefractive damage in LiNbO3 thin-film optical waveguides grown by liquid phase epitaxy
Authors: Yamada Atsuo , Tamada Hitoshi , Saitoh Masaki
Published: July 2002

Photorefractive damage in LiNbO3 thin film optical waveguides grown by liquid phase epitaxy (LPE) was evaluated by the in-plane scattering method at the irradiation wavelength of 514 nm. We were particularly interested in comparing films grown from a Li2O–B2O3 flux and a Li2O–V2O5 flux, and investigating the effect of Mg and Fe doping. Two powerful tools were used for data analysis: the Glass model and the ray model, which estimates the refractive index change. The LPE film grown from the Li2O–B2O3 flux showed a much higher resistance to photorefractive damage than the LPE film grown from the Li2O–V2O5 flux. The photorefractive effect was suppressed by Mg doping and enhanced by Fe doping as in the bulk crystal. The refractive index change in the 0.7 mol % Mg-doped LPE film grown from the Li2O–B2O3 flux was small enough (10−5 at most) to induce no beam fanning. Conventional Ti-indiffused, H+-exchanged, and annealed H+-exchanged waveguides were used as reference samples.
Radiation-induced shallow donors in Czochralski-grown silicon crystals saturated with hydrogen
Authors: Markevich V. P. , Suezawa M. , Sumino K. , Murin L. I.
Published: July 2002

Far-infrared absorption has been investigated in n-type Czochralski-grown silicon saturated with hydrogen and then irradiated with fast electrons. Two series of absorption bands in the range 200–330 cm−1 are observed upon postirradiation annealing of the crystals at 300–550 °C. These bands are associated with ground–to–excited-state electronic transitions in two kinds of shallow donors with ionization energies of 37.0 and 42.6 meV, which are described well with the effective-mass approximation. These donors are related to defects observed earlier in electrical measurements.
Investigation of lattice distortions in InP crystals implanted with Fe+ ions by means of high-resolution x-ray diffraction and x-ray standing-wave methods
Authors: Bocchi C. , Franzosi P. , Imamov R. M. , Lomov A. A. , Maslov A. V. , Mukhamedzhanov E. Kh. , Yakovchick Yu. V.
Published: July 2002

Lattice distortions due the implantation of Fe+ ions in InP semi-insulating crystals have been investigated by means of high-resolution x-ray-diffraction and x-ray standing-wave methods. The effects of both the implantation dose and the annealing time were studied. It is shown that the x-ray standing-wave method provides valuable complementary information on strain and damage in the subsurface layer and permits one to distinguish between different distortion profiles that give practically the same kinematical diffraction curve.
Analysis and interpretation of time dependent magnetic phenomena (invited)
Authors: Folks L. , Street R.
Published: July 2002

Time dependence of intensity of magnetization is the result of thermal activation of metastable domain processes. The simple (M,H) representation of magnetic behavior may be extended to include time dependent effects using a constitutive equation. Magnetic processes may be described by the movement of a point over a three-dimensional surface with coordinates M, H, and Ṁ. The parameters required to define the surface, Λ (or fluctuation field Hf) and χ, may be derived from measurements of the time dependence of magnetization. A review of the utilization of the constitutive equation is given and simple methods for obtaining the material parameters from conventional magnetic viscosity measurements (under constant applied field conditions) are described. Measurements of Λ in particular provide additional quantitative information on magnetization processes which may be compared with predictions of proposed models of magnetization. The results of measurements of Λ and susceptibility χ for CrO2 powders and sintered and melt-quenched rare earth-transition metal borides are presented. Conclusions about the magnetization mechanisms of these materials are discussed.
Photoluminescence and excitation spectroscopy of Er-doped As2S3 glass: Novel broad band excitation mechanism
Authors: Gu S. Q. , Ramachandran S. , Reuter E. E. , Turnbull D. A. , Verdeyen J. T. , Bishop S. G.
Published: July 2002

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy carried out on bulk samples of Er:As2S3 glasses demonstrate that Er3+ is incorporated in optically active sites in the glass and gives rise to a broad ∼1500–1600 nm, 4I13/2→4I15/2 emission spectrum similar to those observed in Er-doped oxide glasses. In addition to the expected 980 nm (4I15/2→4I11/2) Er3+ PLE band, the 1500–1600 nm Er3+ PL band in the glass exhibits a remarkably broad PLE spectrum which extends from the As2S3 Urbach absorption edge at ∼550 nm to beyond 1000 nm. This broad PLE band corresponds closely to an exponential PLE band observed in the ‘‘band tail’’ spectral range for Er-doped Ge33As12Se55 glasses. These unusual PLE spectra indicate that in Er-doped chalcogenide glasses there is an additional broad-band, below gap, extrinsic absorption mechanism which efficiently excites the characteristic 1550 nm, 4I13/2→4I15/2 Er3+ emission band. It is not possible to determine at present whether the Er dopants themselves are responsible for the broad band absorption which excites the Er3+ PL bands, or if photoexcited carriers attributable to absorption by other impurities transfer their energy to the excited states of the Er3+ 4f shells. Microscopic characterization techniques reveal that the Er2S3-doped glasses also contain residual Er2S3 crystallites which give rise to sharp, narrow line 1550, 980, and 810 nm Er3+ optical spectra characteristic of polycrystalline Er2S3. The temperature dependence of the Er2S3 PL and PLE spectra enables the energy levels of the 4I13/2 excited state and 4I15/2 ground state manifolds to be determined.
Ion-beam induced oxidation of GaAs and AlGaAs
Authors: Alay J. L. , Vandervorst W. , Bender H.
Published: July 2002

The oxidation of GaAs and AlxGa1−xAs targets by oxygen irradiation has been studied in detail. It was found that the oxidation process is characterized by the strong preferential oxidation of Al as compared to Ga, and of Ga as compared to As. This experimental observation, which has been accurately quantified by using x-ray photoelectron spectroscopy, is connected to the different heats of formation of the corresponding oxides. The oxide grown by ion-beam oxidation shows a strong depletion in As and relatively low oxidation of As as well. The depletion can be associated with the preferential sputtering of the As oxide in respect to other compounds whereas the low oxidation is due to the low heat of formation. In contrast Al is rapidly and fully oxidized, turning the outermost layer of the altered layer to a single Al2O3 overlayer, as observed by transmission electron microscopy. The radiation enhanced diffusion of oxygen and aluminum in the altered layer explains the large thickness of these altered layers and the formation of Al oxides on top of the layers. For the case of ion-beam oxidation of GaAs a simulation program has been developed which describes adequately the various growth mechanisms experimentally observed.
Growth and thermal decomposition of ultrathin ion-beam deposited C:H films
Authors: Schenk A. , Winter B. , Biener J. , Lutterloh C. , Schubert U. A. , Küppers J.
Published: July 2002

Several monolayers thick hydrogenated carbon films, C:H, were prepared by ion beam deposition from hydrocarbon process gases onto Pt and monolayer C covered Pt single crystal surfaces and investigated with Auger electron and thermal desorption spectroscopies in an UHV environment. Efficient deposition was achieved at ion energies in the 160–300 eV range. The deposited thickness and H/C ratio of the films depend on both, target temperature and H/C ratio of the process gas. It is shown that the C monolayer is crucial for efficient on-top deposition. Irrespective of the process gas used for deposition, the films grow as a C network and assume a constant H/C ratio at thicknesses greater than ∼ 3 monolayers. The H/C ratio of the films scale with the H content of the hydrocarbon process gas, a H/C ratio of 0.4 was obtained for ethane at 350 K substrate temperature. Upon thermally activated decomposition the films release molecular hydrogen as the major gaseous species and various hydrocarbons as minority species. The latter products signal chemical erosion of the film. It is shown that the rate determining step towards erosion via methane is a C–C bond breaking event which releases methyl radicals from the C network in the film. The activation energies for this step are determined as a 10 kcal/mol wide Gaussian distribution centered at 56 kcal/mol. Transport through the film is found to be so fast that it does not contribute to the observed gas release rates.
Angular-selective optical transmittance of anisotropic inhomogeneous Cr-based films made by sputtering
Authors: Le Bellac D. , Niklasson G. A. , Granqvist C. G.
Published: July 2002

Thin Cr-based films were made by sputtering with oblique incidence of the deposition flux onto a substrate. The films had an inclined columnar microstructure, as verified by atomic force microscopy and scanning electron microscopy. The optical transmittance showed pronounced angular selectivity as well as spectral selectivity. Scaling relations were found for the thickness-dependent transmittance. The optical data could be reconciled with a model based on the Bruggeman effective medium theory.
Torsional mode magnetoelastic resonance in ferromagnetic amorphous wire
Authors: Velázquez J. , Navarro E. , Vázquez M. , Hernando A. , Rivero G. , Barandiarán J. M.
Published: July 2002

A torsional pendulum has been built using a stress relieved FeSiB amorphous wire. Torsional motion is magnetoelastically induced by means of the simultaneous application of longitudinal Hz and circular Hφ magnetic fields. The experimental setup allows one to determine both the torsional deformation and the changes in the longitudinal magnetization Mz of the wire. Free and forced oscillations are observed depending on the parameters of the applied fields. In both forced and free oscillation modes two resonant peaks are observed. Their frequency and amplitude dependences on the axial Hz and circular fields Hφ have been studied. Changes in shear modulus ΔG valued 60% in excess have been measured. To interpret the experimental results a theoretical model is developed taking into account the existence of two different magnetic regions in the wire, core, and shell having a different distribution of axial, radial, and shear stresses. The calculations explain the more remarkable aspects of the observed behavior.
Spectroscopic characteristics of Nd3+-doped strontium fluorovanadate and their relationship to laser performance
Authors: Hong P. , Zhang X. X. , Peale R. E. , Weidner H. , Bass M. , Chai B. H. T.
Published: July 2002

High slope efficiency and low threshold laser performance have been achieved for both long pulsed and cw operation at 1.065 μm in Nd3+-doped strontium fluorovanadate crystal, Nd3+:Sr5(VO4)3F, when pumped by narrow band pulsed Cr:LiSAF and cw Ti:sapphire lasers. However, there are inequivalent Nd3+ sites in the crystal. The absorption of Nd3+ ions in secondary sites, sites other than the site which contributes to lasing, may reduce the pumping efficiency and, consequently, the lasing efficiency. Strong concentration quenching of the Nd3+ 4F3/2 state was also observed reducing the quantum efficiency of the laser transition from this state.
Raman investigation of undoped, niobium-doped, and lanthanum-doped lead zirconate-titanate ceramics
Authors: El-Harrad I. , Becker P. , Carabatos-Nédelec C. , Handerek J. , Ujma Z. , Dmytrow D.
Published: July 2002

In a previous article, we proved and characterized a phase transition of an order-disorder type, below room temperature, in the Pb1−3X/2LaX⧠X/2(Zr0.95Ti0.05)O3 (X=0.5–4 wt % La) ceramics. In the present article, the analysis of this order-disorder transition is continued on the basis of the comparative study of Raman scattering, as a function of the Nb or La dopant. The parallel analysis and the interpretation of the Raman spectra of the nondoped, Nb-doped, and La-doped Pb(Zr0.95Ti0.05)O3 ceramics lead to new information concerning the identification of the vibrational modes involved. In addition, the correlation between the phase transitions and the nature of the dopants is established. New information concerning the cell doubling, during the ferroelectric low temperature to ferroelectric high temperature phase transition, is obtained as well. The Raman study of the lead-lanthanum zirconate-titanate ceramics allowed us to identify for the first time the so-called ‘‘antiferroelectric mode’’ and ‘‘ferroelectric mode’’ which had been theoretically predicted.
Experimental results of photothermal microstructural depth profiling
Authors: Lan T. T. N. , Seidel U. , Walther H. G. , Goch G. , Schmitz B.
Published: July 2002

Experimental results of thermal conductivity depth profiling of case-hardened steel and mechanically loaded ceramics are presented, based on an inversion algorithm for a sample with piecewise linearly inhomogeneous depth profile of the thermal conductivity. The photothermally obtained profiles are interpreted or compared with results from conventional or destructive measuring techniques.
Blue electroluminescent devices based on soluble poly(p-pyridine)
Authors: Gebler D. D. , Wang Y. Z. , Blatchford J. W. , Jessen S. W. , Lin L.-B. , Gustafson T. L. , Wang H. L. , Swager T. M. , MacDiarmid A. G. , Epstein A. J.
Published: July 2002

We have fabricated unilayer electroluminescent devices from soluble poly(p-pyridine) (PPy). The solubility of PPy in weak acids allows direct spin casting of the polymer films. The electroluminescence spectrum peaks at 2.5 eV (497 nm) corresponding to white light weighted towards the blue end of the spectrum. The photoluminescence spectrum peaks at 2.35 eV (530 nm). The operating voltages of the devices ranged from 4 to 12 V with current densities of 6 to 8 mA/mm2. We compare our devices with similar blue emitting devices based on poly(p-phenylene).
Light-emitting diodes using n-type conducting polymer: Poly(p-pyridyl vinylene)
Authors: Onoda Mitsuyoshi
Published: July 2002

A yellow-orange electroluminescent (EL) diode using an n-type conducting polymer, poly(p-pyridyl vinylene) (PPyV), as an emitting layer has been demonstrated and its EL properties are discussed. The EL emission of this device can be interpreted in terms of radiative recombination of the singlet polaron exciton formed by the injection of electrons and holes. Although the EL intensity of the PPyV light-emitting diode is weak, yellowish-orange EL emissions were clearly observed under normal room light. Changing from the PPyV EL device to the PPV‖PPyV EL device using poly(p-phenylene vinylene) (PPV) as a hole-transporting layer increased the maximum quantum efficiency from 0.0065% to 0.08% photons per electron. Detailed electrical and optical properties for these diodes with aluminum as the electron-injecting contacts are presented and an improved quantum efficiency for light emission has been achieved.
Heat capacity of ternary compounds RNiGe(R=Gd, Dy, Er, and Y)
Authors: Long Y. , Fu H. , Hashimoto T. , Matsumoto K. , Onishi A. , Satoh T.
Published: July 2002

The heat capacity of the ternary compounds RNiGe(R=Er, Dy, Gd, and Y) was studied in the temperature range between 2 and 40 K. From the heat capacity curves, Néel temperatures are found to be 3.3, 7.4, and 10.7 K for ErNiGe, DyNiGe, and GdNiGe, respectively. The heat capacity of YNiGe was well fitted with an average Debye temperature of 272 K in the temperature range between 2 and 40 K. The changes of magnetic entropy indicate a strong influence of the crystal field on the Er+3 and Dy+3 ion in ErNiGe and DyNiGe compounds. These results suggest the possibility of using these compounds as magnetic regenerator materials near the temperature of 4.2 K.
The EL2 trap in highly doped GaAs:Te
Authors: Castaldini A. , Cavallini A. , Fraboni B. , Piqueras J.
Published: July 2002

We have investigated highly doped GaAs:Te at different doping concentrations (≳1017 cm−3) to assess the presence of the EL2 trap. We have utilized both capacitance and current transient spectroscopy techniques. The crucial parameter for the detection of EL2 is the relative position of the electron quasi-Fermi level in the depletion region. The observed shift of the EL2 apparent activation energy with increasing doping concentration is also discussed.
Semiconductor device simulation with the Lei–Ting balance equations
Authors: Cai J. , Cui H. L.
Published: July 2002

A hydrodynamical simulation model of carrier transport in semiconductor devices based on the Lei–Ting balance equations is presented. Unlike conventional hydrodynamical models derived from moments of the Boltzmann transport equation, where collisions with impurities and phonons are represented by momentum and energy relaxation times, we represent the scattering interaction in terms of frictional forces acting on the carriers and energy-loss rate of the carriers. As such, these quantities are calculated within the model itself, as functions of the carrier drift velocity and carrier temperature, along with the carrier density, which are themselves solved for self-consistently within our hydrodynamical model. In addition to the usual advantages of hydrodynamical approach, such as its capability to deal with high-field, nonlinear, nonstationary, and hot-electron effects, along with its modest computational cost, the new model incorporates electron–electron interactional effects (e.g., nonlocal, dynamical screening).
The composition of octahedron structures that act as an origin of defects in thermal SiO2 on Czochralski silicon
Authors: Itsumi Manabu , Akiya Hideo , Ueki Takemi , Tomita Masato , Yamawaki Masataka
Published: July 2002

Recently, octahedron structures have been found in the Czochralski-silicon substrate surface layer just under the oxide defects. An attempt is made to characterize these structures by analysis with transmission electron microscopy and energy-dispersive x-ray spectroscopy. Several results indicate that the structure is full of vacancies. This is contrary to previously reported results suggesting that the octahedron structures found in Si bulk are filled with amorphous SiO2. A model for the formation of an octahedron structure with many vacancies is proposed.
Two carrier analysis of persistent photoconductivity in modulation-doped structures
Authors: Schacham S. E. , Mena R. A. , Haugland E. J. , Alterovitz S. A.
Published: July 2002

A simultaneous fit of Hall and conductivity data gives quantitative results on the carrier concentration and mobility in both the quantum well and the parallel conduction channel. In this study this method was applied to reveal several new findings on the effect of persistent photoconductivity (PPC) on free-carrier concentrations and mobilities. The increase in the two-dimensional electron-gas (2DEG) concentration is significantly smaller than the apparent one derived from single carrier analysis of the Hall coefficient. In the two types of structures investigated, delta doped and continuously doped barrier, the apparent concentration almost doubles following illumination, while analysis reveals an increase of about 20% in the 2DEG. The effect of PPC on mobility depends on the structure. For the sample with a continuously doped barrier the mobility in the quantum well more than doubles. This increase is attributed to the effective screening of the ionized donors by the large electron concentration in the barrier. In the delta doped barrier sample the mobility is reduced by almost a factor of 2. This decrease is probably caused by strong coupling between the two wells, as is demonstrated by self-consistent analysis.
Amorphous and microcrystalline silicon by hot wire chemical vapor deposition
Authors: Heintze M. , Zedlitz R. , Wanka H. N. , Schubert M. B.
Published: July 2002

Amorphous hydrogenated silicon (a-Si:H) was deposited by SiH4 decomposition on a hot tungsten filament. The substrate temperature was held at 400 °C for all samples, maintaining conditions where material combining a low defect density and a low hydrogen content is obtained. A systematic study of the effects of gas pressure, substrate-to-filament distance, and filament temperature on film properties is presented, allowing insight into the growth condition required for this material as well as the significance of secondary gas phase reactions. Material of good optoelectronic quality is obtained at high growth rates. The stability with respect to light degradation was compared to typical plasma deposited films. Conditions for the transition from amorphous to microcrystalline films, observed under gas phase dilution with hydrogen, were investigated. By in situ ellipsometry and atomic force microscopy the nucleation and film morphology were shown to be significantly different from those for plasma-chemical vapor deposition material.
Spectral analysis and homogeneity characterization of quantum wells by differential reflectance modulation technique
Authors: Bellotti U. , Campagnoli G. , Nosenzo L. , Reguzzoni E.
Published: July 2002

Differential reflectance modulation measurements in InGaAs/GaAs and GaAs/AlGaAs multiple quantum wells at room temperature are presented and discussed. In the energy range of the excitonic transitions the spectra obtained are strongly related to the first derivative of the reflectance curves. An exhaustive analysis of the line shape is carried out. It is shown how the modulation signal is related to the fluctuations of the alloy composition and of the well width. An estimate of the degree of inhomogeneity is obtained. The potential of the technique in spectral analysis and for homogeneity characterization is discussed.
The formation of stable Co/Co2MnSn two phase magnets
Authors: Kim T. W. , Gambino R. J.
Published: July 2002

The phase equilibria in the system Co–Mn–Sn have been studied with compositions along the join Co–CoMnSn. This is part of an effort to form a macroscopic ferrimagnet with two metallic ferromagnetic phases, Co and Co2MnSn. As-cast arc melted alloys have been made with Co compositions from 33 to 78 at. %. Three different phase and magnetization regions are observed with increasing Co composition. Cobalt becomes the primary phase at more than 71 at. % Co and crystallizes out of a Co2MnSn rich matrix. It is shown from x-ray diffraction analysis and the Tc change with Co compositions that the Co phase in Co2MnSn matrix is probably a Co–Mn solid solution. From the break in the magnetization vs temperature curves of two phase magnets with two different compositions, Curie temperatures are determined as approximately 160 °C and 175 °C for the Co–Mn solid solution phase. The exchange coupling at phase boundary is proposed by the analysis of coercivity vs temperature data.
Magnetic recording measurements of high coercivity longitudinal media using magnetic force microscopy (MFM)
Authors: Giljer P. , Sivertsen J. M. , Judy J. H. , Bhatia C. S. , Doerner M. F. , Suzuki T.
Published: July 2002

Longitudinal magnetic recordings written on high coercivity medium (Hc=2500 Oe) were investigated using magnetic force microscopy (MFM). Recorded tracks with bit density up to 6000 fr/mm were investigated. A variety of qualitative information about the recorded tracks and domain structure in the medium was obtained. It was determined that the recorded bits strongly interacted with domains in the medium at the track edges, causing severe jitter. Also bit bending due to the head field was observed. A new method for the quantitative analysis of recorded tracks was used. Using this method, recording signal and medium signal-to-noise ratio were calculated from MFM data. Parameters obtained in this way showed excellent agreement with signal and signal-to-noise ratio obtained from the recording measurement using a MR head.
Transient response of photodetectors
Authors: Dunn G. M. , Walker Alison B. , Vickers A. J. , Wicks V. R.
Published: July 2002

Calculations by drift diffusion and Monte Carlo methods and experimental data on the transient response of metal–semiconductor–metal photodetectors are reported. We have shown how the interplay of carrier and displacement currents, inhomogeneities in field and charge distributions, and hot electron effects determines observed structure in the transient response. In particular, we have demonstrated the role played by the regions under the contacts that are not illuminated in forming peaks in the transient response. We have also demonstrated that the peaks in the transient response need not be attributed to velocity overshoot and the scaling of detector response with contact separation has been studied.
Morphological stability of a heterophase interface under electromigration conditions
Authors: Klinger L. , Levin L. , Srolovitz D.
Published: July 2002

The evolution of the interface between two mutually insoluble metallic phases, under the influence of a strong electric field is examined. A slight perturbation of the interface away from a plane y=h(x) leads to a component of the electric field along the interface. This creates a diffusion flux of the individual atoms along the interface which, in turn, leads to an increase in the amplitude of the initial perturbation and thus to an interfacial profile instability. The processes is expected to be controlled by interface diffusion in response to three distinct driving forces: the electric field, internal stresses (which arise due to the accumulation or depletion of matter at the interface), and the interfacial curvature. The stress distribution along the interface was found from a self-consistent solution of the elastic problem. For the instability to occur, differences in effective atomic charges, elastic moduli and/or atomic mobilities of the two constituent metals are required. Small sinusoidal corrugations are shown to grow with time for a range of wavelengths. The corrugations can grow monotonically or vary in oscillatory manner, depending on their wavelength.
Plasma distribution of cathodic arc deposition systems
Authors: Anders Simone , Raoux Sébastien , Krishnan Kannan , MacGill Robert A. , Brown Ian G.
Published: July 2002

The plasma distribution using a cathodic arc plasma source with and without magnetic macroparticle filter has been determined by depositing on a transparent plastic substrate and measuring the film absorption. It was found that the width of the distribution depends on the arc current, and it also depends on the cathode material which leads to a spatial separation of the elements when an alloy cathode is used. By applying a magnetic multicusp field near the exit of the magnetic filter, it was possible to modify the plasma distribution and obtain a flat plasma profile with a constant and homogeneous elemental distribution which was demonstrated by depositing FeNd thin films.
Possible nearly loss-free ferrimagnetic resonance in small samples
Authors: Sokoloff J. B.
Published: July 2002

Relaxation occurs in ferrimagnetic resonance by processes which transfer energy from the uniform precession magnon mode, which is excited in the resonance process, to other magnons and to phonons. The relaxation due to these processes is usually calculated using Fermi Golden Rule time dependent perturbation theory, whose application depends on the modes involved in the relaxation processes forming a continuum. Since for a finite isolated solid this is not generally true, the possibility exists that such relaxation processes might not occur for sufficiently small samples. Because it is reasonable to consider the phonons as belonging to both the sample and sample holder, it is reasonable to assume that they form a continuum. The intrinsic linewidth (i.e., inverse lifetime for a defect-free single crystal), which is due to phonons excited by the Kasuya–Le Craw mechanism, is already comparable to the magnon mode spacing for samples of linear dimensions of the order of 10 μm, indicating that finite sample effects could potentially become important for samples of fairly large size. Previous work by the present author on the one-dimensional Heisenberg model has shown that nonlinearity in the magnons can lead to a transition from lossy to loss-free behavior as the sample size decreases, if the temperature is sufficiently low. Here, model calculations of this effect in a two-dimensional Heisenberg model magnet are presented in order to show that loss-free behavior can occur for sufficiently low temperature and sufficiently small sample size. These results open up the interesting possibility of producing high anisotropy magnetic materials as a collection of very small crystals with extremely small linewidths.
Growth of epitaxial films of iron oxide, nickel oxide, cobalt oxide, strontium hexagonal ferrite, and yttrium iron garnet by laser ablation (abstract)
Authors: Kennedy Robin J.
Published: July 2002

Thin films of iron oxide, nickel oxide, cobalt oxide, strontium hexagonal ferrite, and yttrium iron garnet have been grown by laser ablation. With the exception of Co3O4 deposited on LaAlO3, the first three materials deposited on [100] LaAlO3, SrTiO3, and MgO result in high quality c axis [100] growth. Co3O4 deposited on LaAlO3 produces highly oriented but random in-plane growth. Similar highly oriented but random in-plane growth occurs for all three materials deposited on glass. The same three materials deposited on cubic zirconia grow [111] oriented and twinned. Strontium hexagonal ferrite and yttrium iron garnet have been deposited on [111] large lattice constant garnet. Epitaxial [0001] films are obtained for the former while the latter gives [111]-oriented films. For yttrium iron garnet the closeness of lattice match to the substrate necessitates that the mosaicity (rocking curves) obtained from area maps be compared to the growth temperatures and pressures to determine the optimum growth conditions for epitaxiality.
Two-dimensional sheath evolution in a negative ion plasma
Authors: El-Zein Yasser , Amin Ali , Shen Chonghui , Yi Seungjun , Lonngren Karl E. , Sheridan Terrence E.
Published: July 2002

The spatial and temporal evolution of the components of a plasma surrounding a 90° convex and a 90° concave electrode whose potential is suddenly decreased in a three-component plasma is numerically investigated. The quasineutral plasma consists of positive ions and various proportions of negative ions and electrons. The results are compared and contrasted with those that are obtained in a normal two-component plasma. The transient or ion matrix sheath is identified and its subsequent evolution is investigated. Effects of perturbations in the electrode are investigated.
Scaling of the thermoremanent relaxation in FeNiCr
Authors: Li D. , Roshko R. M.
Published: July 2002

We present measurements of the relaxation of the low field thermoremanent magnetization of Fe0.65Ni0.24Cr0.11 over four decades of observation time 1 s<t≤104 s, as a function of temperature T and system age tw. The system orders ferromagnetically at Tc≂110 K and then, near TR≂50 K collapses into a much less responsive low-temperature phase, with glassy, age-dependent dynamics appearing below Tg≂22 K. We have analyzed the data using a model of random traps developed by Bouchaud, according to which the relaxation curves for different tw at a given temperature T will scale onto a universal curve when plotted as a function of t/tw, provided that proper account is taken of the distribution of ergodic times terg possessed by a real system. With the assumption of a log-normal distribution P(terg), we have calculated the nonuniversal correction-to-scaling factor explicitly, and we have shown that the data do indeed collapse remarkably well onto a universal curve, with a suitable choice of values for the two distribution parameters, and for the two relaxation function parameters.
Stress and magnetic properties in high moment FeN thin films
Authors: Sin Kyusik , Wang Shan X.
Published: July 2002

Single layer FeN films with low coercivity and low residual stress were prepared on Corning 0211 glass and Si substrates using rf diode sputtering without postannealing. Substrates and a small amount of nitrogen in the film had a significant effect on the magnetic properties and residual stress of FeN films. The residual stress in the pure Fe films showed tensile characteristics due to thermal stress. The stress decreased with increasing N2/Ar flow ratio and passed a zero point at a flow rate ratio of ∼3.5%, accompanied with a low coercivity. The stress changed to compressive with further increasing nitrogen in the lattice. The tensile-to-compressive transition in residual stress can be explained by the increase in lattice constant in FeN films. The lattice constant increased with increasing nitrogen flow during deposition, which was probably due to more nitrogen incorporation in the bcc Fe lattice.
Modulation of magnetostatic surface wave in garnet film by optical pulses
Authors: Fetisov Y. K. , Makovkin A. V.
Published: July 2002

Microwave power modulation in a magnetostatic surface wave (MSSW) transmission line containing an yttrium-iron-garnet film of thickness 20 μm in the 3–4 GHz frequency band with optical pulses of duration 2 ms and energy of 20 μJ has been investigated. At microwave powers less than 1 mW a slow thermal modulation with magnitude up to 4% and characteristic time of 0.5 ms took place. At power levels 1–100 mW a fast modulation of the transmitted signal with magnitude up to 10% and characteristic time of about 1 μs caused by nonlinear properties of MSSW was observed.
Impedance studies on Li insertion electrodes of Sn oxide and oxyfluoride
Authors: Stro/mme M. , Isidorsson J. , Niklasson G. A. , Granqvist C. G.
Published: July 2002

Films of Sn oxide and oxyfluoride were made by reactive rf magnetron sputtering onto ITO-coated glass. We analyzed the composition by Rutherford backscattering spectrometry, the structure by x-ray diffraction, and the surface topography by atomic force microscopy. Li intercalation from a liquid electrolyte was more facile in the oxide than in the oxyfluoride, as found from cyclic voltammetry. Impedance spectra were taken for a wide range of frequencies and polarizing voltages. Nyqvist diagrams were interpreted from a circuit model with elements representing Li insertion at the electrolyte/film interface and electron insertion at the film/ITO interface. The data were consistent with a fractal surface of the Sn oxide film, with a dimension in excellent agreement with measures obtained through several independent techniques. The chemical diffusion coefficient was ∼10−13 cm2/s and slightly decreasing with increasing potential for all films.
Unified two-dimensional model for grating dynamics in photorefractive materials
Authors: Solymar L. , Aguilar María , Agulló-López F.
Published: July 2002

A two-dimensional treatment suitable both for perpendicular (Pockels readout optical modulators, etc.) and for parallel (image amplifiers, etc.) photorefractive devices is presented. A partial differential equation of the third order, valid for both families of devices, is set up and solved analytically for the relevant initial and boundary conditions in the full time domain. The results are illustrated in a few examples showing the relative significance of bulk and surface charges, and some new features of the solution for the perpendicular configuration.
A simple method for calculating strain distributions in quantum-wire structures
Authors: Faux David A. , Downes James R. , O’Reilly Eoin P.
Published: July 2002

We present a simple method for calculating the stress and strain distributions due to an initially uniformly strained quantum wire with a cross section of arbitrary shape buried in an infinite medium. The method involves the evaluation of a path integral around the boundary of the quantum wire and is therefore considerably more straightforward to implement than alternative stress evaluation techniques. Published results for the strain distribution due to a rectangular quantum wire are confirmed and results for a quantum wire of triangular cross section are presented.