bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of domain refined grain-oriented silicon steel by grooving
Authors: Sato K. , Honda A. , Nakano K. , Ishida M. , Fukuda B. , Kan T.
Published: July 2002

Recently a heat-proof magnetic domain refining technique has been developed which is characterized by the introduction of grooves on a surface of steel sheet after final cold rolling. In this paper, magnetic properties and the domain refining effect of grooving are investigated. A grooving process is constituted by resist printing on the surface of steel sheets after final cold rolling and succeeding electrolytic etching. The grooves were introduced almost perpendicular to the rolling direction of steel sheets. The width and depth of each grove are about 200 and 20 μm, respectively. With this newly developed method, about 10% reduction in iron loss was achieved and less than 0.34 W/lb at 1.5 T, 60 Hz was obtained. Using this new material, the iron loss of wound core transformers can be reduced by about 10% as compared with nongrooved material. Domain width was dramatically reduced by grooving, which caused the reduction of eddy current loss. This reduction is considered to be caused by the demagnetizing field effect due to free poles in the vicinity of grooves. It was clarified that in grooved sheets the magnetization on the ungrooved surfaces proceeded faster than on the grooved surfaces and therefore, hysteresis loss and magnetizing characteristics did not deteriorate by grooving.
High-temperature behavior of impurities and dimensionality of the charge transport in unintentionally and tin-doped indium selenide
Authors: Martinez-Pastor J. , Segura A. , Chevy A.
Published: July 2002

A systematic study of the electron transport and shallow impurity distribution in indium selenide above room temperature or after an annealing process is reported by means of far-infrared-absorption and Hall-effect measurements. Evidences are found for the existence of a large concentration of deep levels (1012–1013 cm−2), related to impurities adsorbed to stacking faults in this material. Above room temperature impurities can migrate from those defect zones and then become shallow in the bulk. The subsequent large increase of 3D electrons can change the dimensionality of the electron transport, which in most cases was 2D. The temperature dependence of the resistivity parallel to the c axis can be explained by the observed increase of the 3D electron concentration, whose motion across the layers is limited by stacking-fault-related potential barriers. The observed macroscopic resistivity is thus determined by tunneling through those barriers.
An empirical rule for band offsets between III-V alloy compounds
Authors: Ichii A. , Tsou Y. , Garmire E.
Published: July 2002

We present a method to empirically predict relative valence band positions of III-V semiconductor alloys. The method has been successfully applied to all the experimental data measured to date by the capacitance-voltage profiling technique.
Mirror temperature of a semiconductor diode laser studied with a photothermal deflection method
Authors: Bertolotti M. , Liakhou G. , Li Voti R. , Peng Wang Ruo , Sibilia C. , Yakovlev V. P.
Published: July 2002

The mirror temperature response of a diode laser to injection current is studied through the photodeflection method. A theoretical model is presented together with some experimental measurements. Theoretical results are compared with experimental measurements for an AlGaAs quantum well laser diode.
Formation, structure, and crystallization of Al-rich metallic glasses
Authors: Sabet-Sharghi R. , Altounian Z. , Muir W. B.
Published: July 2002

The formation, structure, and the crystallization of Al85YxNi15−x are studied using x-ray diffraction and differential scanning calorimetry. The results show two distinct glasses depending on composition. Y-rich glasses (x≥8) are homogeneous with a well-defined glass transition. The x-ray diffraction patterns have a single main peak. These glasses crystallize through a nucleation and growth process. Y-poor glasses (x<8) do not show a glass transition and have a shoulder on the high-angle side of the main peak in their x-ray diffraction patterns. We show that the shoulder peak is due to quenched-in Al nuclei. These glasses are shown to crystallize through the growth of these nuclei. Y-rich glasses (x≥8) are more stable as demonstrated by the presence of the glass transition and their higher crystallization temperature, enthalpy, and activation energy. The occurrence of a prepeak for all compositions is attributed to Y-Y pairs.
Absorption coefficient of silicon: An assessment of measurements and the simulation of temperature variation
Authors: Bücher K. , Bruns J. , Wagemann H. G.
Published: July 2002

The absorption coefficient of crystalline silicon is an important input for designing solar cells and extracting recombination parameters from device measurements. Since many contradicting measurements have been published, an assessment of data is given based on device measurements and on the discussion of experiments in the literature. An absorption coefficient for the ultraviolet to infrared spectral range is proposed, based on the results of three groups. These data can be described semiempirically by the theory of direct and indirect band transitions. This formulation enables the determination of the optical absorption in crystalline silicon at an arbitrary temperature. The interpretation and design of solar cells for operation at temperatures above room temperature is now possible.
Hyperbolic temperature profiles for laser surface interactions
Authors: Vedavarz Ali , Mitra Kunal , Kumar Sunil
Published: July 2002

This study theoretically analyzes the transient temperature distributions in laser irradiated materials by considering a hyperbolic heat conduction model. Exact and limiting mathematical solutions for the temperature distributions are developed and important parameters are identified. Traditional Fourier transient heat conduction models are parabolic in nature, which imply an infinite speed of propagation of the thermal signal in the material. Hyperbolic non-Fourier models have been introduced to account for the finite speed of the thermal wave. The effects of finite speed are significant in short-pulse applications where the time period of the laser input is comparable to the thermal characteristic time of the material, and the resultant temperature variations are significantly different from that of traditional infinite-speed Fourier predictions. Two different types of materials, biological materials and inorganic solids, are considered for laser-surface interactions in the study. The parameter of greatest significance is found to be the ratio of thermal characteristic length to the laser beam width. Values of this parameter in the range between 0.1 and 3, corresponding to different applications, are examined and local temperature maximas, or hot spots, are found to occur at initial time periods for values greater than ∼0.2.
Si(001)2×1 gas-source molecular-beam epitaxy from Si2H6: Growth kinetics and boron doping
Authors: Bramblett T. R. , Lu Q. , Karasawa T. , Hasan M.-A. , Jo S. K. , Greene J. E.
Published: July 2002

The growth rates RSi of Si films deposited on Si(001)2×1 from Si2H6 by gas-source molecular-beam epitaxy were determined as a function of temperature Ts (500–950 °C) and impingement flux JSi2H6 (0.3–7.7×1016 cm−2 s−1). RSi (Ts,JSi2H6) curves were well described using a model, with no fitting parameters, based upon dissociative Si2H6 chemisorption followed by a series of surface decomposition reactions with the rate-limiting step being first-order hydrogen desorption from Si monohydride. The zero-coverage Si2H6 reactive sticking probability in the impingement-flux-limited growth regime was found to be 0.036, more than two orders of magnitude higher than that for SiH4. B doping concentrations (CB=5×1016–3×1019 cm−3) from B2H6 increased linearly with increasing flux ratio JB2H6/JSi2H6 at constant Ts and decreased exponentially with 1/Ts at constant JB2H6/JSi2H6. Secondary ion mass spectrometry analyses of modulation-doped samples revealed sharp profiles with no detectable B segregation. Hole mobilities in uniformly doped samples were equal to bulk values.
Magnetic anisotropy and magnetization processes in 3:29 and 1:12 Nd(FeTi)-based compounds
Authors: Pareti L. , Paoluzi A. , Albertini F. , Ibarra M. R. , Morellon L. , Algarabel P. A.
Published: July 2002

The temperature behavior of the magnetic anisotropy and magnetization processes in the tetragonal Nd(FeTi)12 and monoclinic Nd3(FeTi)29 have been studied and compared. Both compounds are characterized by the occurrence of temperature-induced spin reorientation transitions, as well as field-induced magnetization processes of different types, which have been interpreted as first-order magnetization process. In both systems the resultant anisotropy of Nd favors the occurrence of an easy magnetization direction out of the principal axes at low temperature. On the contrary the overall Fe sublattice anisotropy favors the tetragonal c-axis in the 1:12 and seems to prefer the monoclinic a-axis in the 3:29 compound.
New bounds on the elastic moduli of suspensions of spheres
Authors: Quintanilla J. , Torquato S.
Published: July 2002

We derive rigorous three-point upper and lower bounds on the effective bulk and shear moduli of a two-phase material composed of equisized spheres randomly distributed throughout a matrix. Our approach is analogous to previously derived three-point cluster bounds on the effective conductivity of suspensions of spheres. Our bounds on the effective elastic moduli are then compared to other known three-point bounds for statistically homogeneous and isotropic random materials. For the case of totally impenetrable spheres, the bulk modulus bounds are shown to be equivalent to the Beran–Molyneux bounds, and the shear modulus bounds are compared to the McCoy and Milton–Phan-Thien bounds. For the case of fully penetrable spheres, our bounds are shown to be simple analytical expressions, in contrast to the numerical quadratures required to evaluate the other three-point bounds.
Photoacoustic frequency heat-transmission technique: Thermal and carrier transport parameters measurements in silicon
Authors: Todorović D. M. , Nikolić P. M. , Dramićanin M. D. , Vasiljević D. G. , Ristovski Z. D.
Published: July 2002

Photoacoustic frequency heat-transmission technique is used to study thermal and carrier transport properties in low-doped silicon wafers. Amplitude and phase photoacoustic signals as a function of modulation frequency of incident optical beam are measured using different experimental conditions. The thermal diffusivity, coefficient of excess carrier diffusion, carrier lifetime, and the surface recombination velocity were determined by comparing experimental results and calculated theoretical photoacoustic signals. The suitability of the photoacoustic frequency heat-transmission technique as a contactless diagnostic method is assessed in comparison with the more conventional photothermal deflection and photothermal modulated reflection techniques.
A generalized Ramo–Shockley theorem for classical to quantum transport at arbitrary frequencies
Authors: Yoder P. D. , Gärtner K. , Fichtner W.
Published: July 2002

We present a generalized Ramo–Shockley theorem to evaluate particle currents and energy currents at device contacts, in classical drift-diffusion or hydrodynamic simulation techniques as well as for semiclassical Monte Carlo and quantum mechanical transport simulation. In contrast to the Ramo–Shockley theorem, our technique (1) is derived for conditions of extreme time dependence in the charge carriers and forces (including particle-induced radiation), (2) explicitly accounts for particle generation and recombination processes such as photoexcitation, forward and inverse Auger processes, or Shockley–Read–Hall recombination, and (3) distinguishes clearly between the contributions of electrons, holes, and the displacement current. The resulting simple new formalism reduces to the standard Ramo–Shockley theorem as a special case.
Background Si-doping effects on Zn diffusion-induced disordering in GaAs/AlGaAs multiple-quantum-well structures
Authors: Ky Nguyen Hong , Ganière J. D. , Reinhart F. K. , Blanchard B.
Published: July 2002

Identical GaAs/Al0.2Ga0.8As multiple-quantum-well (MQW) structures uniformly doped with Si at various concentrations ranging from 1×1017 to 1×1019 cm−3 are grown by molecular-beam epitaxy to study the effects of the background Si-doping level on the Zn diffusion-induced disordering process. After Zn diffusions at 575 °C for 4 and 16 h, the structures are investigated by secondary-ion-mass spectrometry, and by transmission electron microscopy on cleaved wedges of the sample. The results show that the totally and partially disordered regions are always behind the Zn diffusion front. A dependence of the effective Zn diffusivity and of the disordering rate of the structures on the background Si-doping level is observed. The effective Zn diffusivity and the disordering rate are significantly reduced with increasing background Si concentration. Before Zn diffusion, photoluminescence spectra of the Si-doped MQW structures exhibit an increase in intensity of the Si donor–column-III vacancy complex emission band with increasing Si-doping level. This indicates that the concentration of column-III vacancies in the MQW structures increases as the background Si concentration increases. After Zn diffusion, an important decrease in intensity of the column-III vacancy related emission band is observed on the photoluminescence spectra taken in the Zn-diffused regions.

The systematical analysis of the photoluminescence spectra of the Zn-diffused MQW structures as a function of diffusion time and as a function of etching depth below the sample surface makes it possible to describe the physical processes occurring during Zn diffusion. A model based on the ‘‘kick-out’’ mechanism of Zn diffusion is proposed to explain the effect of the background Si-doping level on the effective Zn diffusivity. The model shows that the effective Zn diffusivity is controlled by the concentration of column-III interstitials behind the Zn diffusion front and by the donor concentration in the sample. During the incorporation of Zn into the crystal lattice, column-III interstitials are generated. The supersaturation of these interstitials behind the Zn diffusion front is responsible for the enhancement of Al–Ga interdiffusion. Since column-III interstitials and column-III vacancies can mutually annihilate, the concentration of column-III interstitial and column-III vacancy in the Zn-diffused region is reduced with increasing Si-doping level, leading to a retardation of Zn diffusion into the MQW structure. On the other hand, a decrease of the effective Zn diffusivity caused by an increase in donor concentration in the samples is also demonstrated.

Our results give evidence for the Fermi-level effect and the interactions between different point defects during Zn diffusion-induced disordering of GaAs/AlGaAs multilayered structures.
Evolution of the texture of TiN films prepared by filtered arc deposition
Authors: Zhao J. P. , Wang X. , Shi T. S. , Liu X. H.
Published: July 2002

Three kinds of textures, i.e., (200), (111), and (220) of TiN films prepared by filtered arc deposition have been continuously observed with varying film thickness and bombarding energy of the deposited particles. The evolution of the texture from (200) to (111), then to (220) is discussed on the basis of the so-called overall energy which consists of the surface energy, the strain energy, and the stopping energy of the films.
Deformation-enhanced thermal stability of an amorphous Fe80B20 alloy
Authors: Fan G. J. , Quan M. X. , Hu Z. Q.
Published: July 2002

By means of differential scanning calorimeter (DSC) measurements, the thermal stability of an amorphous Fe80B20 alloy after various periods of low-energy ball milling has been studied. The results indicate that the thermal stability of the amorphous Fe80B20 ribbons can be enhanced upon mechanical deformation with a low milling intensity. The crystallization temperature Tp, the crystallization enthalpy ΔH, and the crystallization activation energy Ex increase with milling time. The above observations will be compared with our previous findings that extensive mechanical deformation with a high milling intensity can otherwise induce a structural relaxation in an amorphous Fe80B20 alloy. Based on conventional thermodynamic and kinetic arguments, a reasonable interpretation will be made to explain the enhanced thermal stability of the amorphous Fe80B20 alloy after mechanical deformation.
Characteristics of hard x-ray emission from subpicosecond laser-produced plasmas
Authors: Schnürer M. , Nickles P. V. , Kalachnikov M. P. , Sandner W. , Nolte R. , Ambrosi P. , Miquel J. L. , Dulieu A. , Jolas A.
Published: July 2002

Calibrated thermoluminescence dosimeters have been used to measure the angular and spectral dependence of hard x-ray emission produced from intense subpicosecond laser irradiation of solid targets. A dosimeter detector set with nine filter channels (13.5–400 keV) has been tested successfully. Total bremsstrahlung conversion up to 0.23% and conversion of 8×10−5 from laser energy to Ta Kα line emission (photon energy ≊57 keV) was determined. The scaling of the hard x-ray yield with laser intensities ranging from 3×1016 to 3×1018 W/cm2 was investigated.
Photoluminescence properties of ZnS epilayers
Authors: Tran T. K. , Park W. , Tong W. , Kyi M. M. , Wagner B. K. , Summers C. J.
Published: July 2002

A comprehensive study is reported of the photoluminescence properties of ZnS thin films between 1.6 and 320 K grown by metalorganic molecular beam epitaxy and chemical beam epitaxy on GaAs substrates. Both heavy- and light-hole free excitons were observed at low temperatures with linewidths of 7.0 and 5.3 meV, respectively, as well as donor- and acceptor-bound excitons and free-to-bound recombination along with their longitudinal optical (LO) phonon replicas. The free exciton emission was observed up to 320 K, and enabled the room temperature band gap of ZnS to be unambiguously determined as 3.723 eV. The temperature dependence of the peak position, intensity, and linewidth was well described by the conventional empirical relations and by Toyozawa’s exciton line shape theory. The bound exciton peak positions were found to follow the temperature dependence of the band gap whereas the free-to-bound recombination feature was displaced by (1/2)kT above the band gap energy. Thermal quenching of the donor-bound exciton was described by a one-step quenching process with an activation energy of 14.4 meV. The self-activation (SA) center was also observed at 2.846 eV with a linewidth of 410 meV. The temperature dependence of the SA emission was well described by the configuration coordinate model. From the thermal broadening of the SA emission, an average phonon energy of 47.5 meV was determined, in good agreement with the LO phonon energy.
Some unusual features in the Raman spectrum of amorphous carbon films obtained by pyrolysis of maleic anhydride
Authors: Subramanyam S. V. , Sayeed Ahmed , Meenakshi V. , Bhattacharya Somnath , Cholli Ashoke , Tripathi Sukant
Published: July 2002

Laser micro-Raman spectroscopic measurements were done on the amorphous conducting carbon films obtained from maleic anhydride by pyrolysis process. We have found a predominant broad peak around 1140 cm−1, in addition to the normally observed peaks in amorphous carbons around 1350 and 1600 cm−1, and peak of medium intensity around 800 cm−1. Here we discuss the possibility of conjugated polymer like bond alternating structure which can give rise to these unusual Raman features.
Angular dispersion of optical phonon frequencies in strained cubic crystals
Authors: Anastassakis E.
Published: July 2002

The use of Raman spectroscopy for strain characterization of materials often requires scattering configurations in which the optical phonon wavevector does not coincide with any of the strain-modified phonon eigenvectors. It is shown that the optical phonon frequencies in strained zincblende crystals exhibit angular dispersion similar to that of optical phonons in unstrained biaxial and uniaxial crystals. The entire formalism is developed on the basis of the relative magnitude of the longitudinal-transverse frequency splittings and the strain-induced frequency splittings. The shifts produced at grazing incidence are above the usual spectroscopic limits of accuracy and can influence the interpretation of data in terms of strain relaxation or defects. The model is applied to diamond- as well as zincblende-type structures. Specific examples are worked out in detail for scattering geometries under grazing incidence in [001] and [111] strained heterojunctions.
Distribution of anisotropy field in recording media deduced from the hysteresis curve
Authors: Bottoni G. , Candolfo D. , Cecchetti A.
Published: July 2002

The distribution of anisotropy fields in magnetic recording media is carried out by performing the second derivative of the magnetization curve detected in perpendicular direction with respect to the easy axis of the system, following a procedure similar to that used for the soft magnetic materials. The method is applied to the CoCr films with the anisotropy direction perpendicular to the film plane. It was found that the field at the peak of the distribution function agrees with the anisotropy field measured by the torque method. For particulate media, the shape of the anisotropy distribution function depends both on the particle orientation ratio and on the interparticle interactions; as a consequence, the anisotropy distribution function determined on these materials does not represent the intrinsic anisotropy field distribution of the particles but the anisotropy distribution as it appears in that particular specimen. In any case, this function is useful for understanding the magnetic behavior of the system.
Texture study in hot deformed magnequench NdFeB magnets
Authors: Wang Y. R. , Guruswamy S. , Panchanathan V.
Published: July 2002

Plastic deformation plays an important role in enhancing the texture and magnetic anisotropies of Nd–Fe–B magnets made from melt-spun ribbons. The effects of hot deformation on texture in Nd–Fe–B magnets was examined using inverse pole figures and pole figures for magnets with different % die-upsets. It is shown that W50, the average of widths of the 50% intensity contour in pole figure, can be used as a good quantitative index of texture. With increase in % die-upset from 50% to 70%, W50 systematically decreases from 32.3° to 18.4°. The energy product, (BH)max, increased from 17 MGOe for a 0% die-upset magnet to 46 MGOe for a 70% die-upset magnet.
Modeling the dielectric response of incipient ferroelectrics
Authors: Vendik Orest G. , Zubko Svetlana P.
Published: July 2002

Interest in incipient ferroelectrics has been renewed due to their promise for applications at cryogenic temperatures. The dependence of the dielectric constant of an incipient ferroelectric on temperature and the applied biasing field can be modeled correctly by solution of the Ginsburg–Devonshire equation. A set of simple and correct formulas is derived to provide simulation of the dielectric constant of an incipient ferroelectric as a function of temperature and the biasing field. As a typical representative of this, SrTiO3 is used. The inhomogeniety of the composition or/and structure of the material is quantitatively described by a specially introduced coefficient. The correlation effect is used to describe the size effect for a thin film capacitor. The boundary conditions for a ferroelectric polarization on the surface of electrodes are considered. The boundary conditions are specified for the interface between the ferroelectric and the metal or the high temperature superconductor. Comparison of the simulated and experimental data for both the bulk sample and for the thin film capacitor shows good numerical agreement. The model is intended to be used for developing the computer aided design of microwave components and devices based on ferroelectric films.
Magnetic force microscopy study of domain walls on a thin cobalt film
Authors: Lin H.-N. , Chiou Y. H. , Chen B.-M. , Shieh H.-P. D. , Chang Ching-Ray
Published: July 2002

Two types of 180° domain walls on a 115 nm cobalt film are observed by magnetic force microscopy. The surface Néel wall on top of an asymmetric Bloch wall is found inhomogeneous with the width estimated to be around 200 nm. The width of the rhomb-structured cross-tie wall, on the other hand, is approximately 400 nm. The coexistence of these two types of domain walls indicates that their wall energies are comparable at the film thickness.
Effects of GaAs substrate misorientation on strain relaxation in InxGa1−xAs films and multilayers
Authors: Goldman R. S. , Kavanagh K. L. , Wieder H. H. , Ehrlich S. N. , Feenstra R. M.
Published: July 2002

We have investigated the effects of GaAs substrate misorientation on strain relaxation in InxGa1−xAs films and multilayers. Our calculations of shear stresses due to misfit strain, resolved on the glide plane in the glide direction, reveal that the α and β 60° slip systems are influenced in a nearly identical fashion, for all substrate misorientation directions. Thus, classical models for nucleation and glide of 60° dislocations predict that a substrate misorientation will not influence the degree of 〈110〉 asymmetry in strain relaxation in lattice-mismatched zincblende semiconductor films. Contrary to these predictions, our experimental results reveal asymmetries in strain relaxation (for partially relaxed single layers) which favor those dislocations aligned with the offcut axis. These asymmetries depend on the substrate misorientation and growth temperature, and are not easily explained by differences in the intrinsic core properties of α and β dislocations. Furthermore, in fully relaxed multilayers (grown at lower temperatures), and single layers (grown at higher temperatures), epilayer tilt which increases the (111)B substrate miscut is observed. In the multilayers, this behavior is found to be correlated with the presence of micron-scale surface facets. We consider possible explanations for these results, including nucleation of partial dislocations, interaction of gliding threading dislocations, and strain relaxation predominated by forward and backward gliding α threading dislocation segments. Together, these results support the conclusion that local surface or interface step morphologies are more important than bulk stress effects in determining misfit dislocation formation in the InGaAs/GaAs system.
Optical properties of stepped InxGa1−xAs/GaAs quantum wells
Authors: D’Andrea A. , Tomassini N. , Ferrari L. , Righini M. , Selci S. , Bruni M. R. , Schiumarini D. , Simeone M. G.
Published: July 2002

The presence of a ternary alloy as well material in InxGa1−xAs/GaAs(001) strained quantum wells introduces a disorder mechanism by which the optical selection rules for symmetric wells may be relaxed and forbidden transitions usually appear in optical spectra. Strain and alloy disorder are studied as a function of well thickness and indium concentration in noninteracting double quantum wells of InxGa1−xAs/GaAs(001). Optical spectra are compared with an accurate Wannier exciton model. The agreement between theory and experiments points out that the optical selection rule for symmetric wells is restored in “high quality” and rather thin quantum wells. Finally, the presence of forbidden transitions in optical spectra is used as a fingerprint of nonhomogeneous indium concentration in thick quantum wells. This property is promising in order to study indium composition for well thicknesses in the range of quasi-two-dimensional behavior of the Wannier exciton.
Capture cross sections of electron irradiation induced defects in 6H–SiC
Authors: Hemmingsson C. , Son N. T. , Kordina O. , Janzén E. , Lindström J. L.
Published: July 2002

An investigation of electron irradiation induced deep levels in 6H–SiC p+n diodes grown by chemical vapor deposition has been performed. Deep level transient spectroscopy (DLTS) reveals several overlapping peaks in the temperature range 140–650 K. The electron capture cross sections have been measured by directly observing the variation of the DLTS peak height with the duration of the filling pulse and fitting the capacitance transient using multiple linear regression. Temperature dependence studies of the electron capture cross section were performed on three of the observed levels.
Precise determination of deep trap signatures and their relative and absolute concentrations in semi-insulating GaAs
Authors: Pavlović M. , Desnica U. V.
Published: July 2002

The new analytical method, simultaneous multiple peak analysis (SIMPA) which comprises simultaneous fitting of whole measured thermally stimulated current (TSC) spectra is presented. The procedure clearly resolves contributions from various overlapping TSC peaks, which results in precise determination of trap parameters (signature) for each trap. In combination with photocurrent temperature dependent measurements, IPC(T), which reflects free carrier lifetime temperature dependence, the estimates of relative and absolute trap concentrations were made as well. The advantage of the SIMPA method in comparison with the single peak approach was demonstrated and analyzed. The SIMPA method was applied to different semi-insulating (SI) GaAs samples, particularly to samples having very high and others having very low deep trap concentrations; and for both extremes excellent fits were achieved. The method also seems very promising for characterization of deep levels and other similar SI materials, like SI InP or SI CdTe.
Absorption measurements of liquid crystals in the ultraviolet, visible, and infrared
Authors: Wu Shin-Tson
Published: July 2002

Complete absorption spectra of three liquid crystals with different conjugation length were measured in the 0.185–20 μm spectral range. In the ultraviolet region, the absorption is dependent on whether σ or π electrons are involved. In the mid and long infrared regions, several localized molecular vibration bands exist. The saddle absorption minimum occurs at around λ∼0.8 μm that is far from the electronic resonance and is right before the overtone molecular vibration begins.
Density of CH3 radicals and the ionic composition in a low pressure methane plasma beam
Authors: Okada Katsuyuki , Komatsu Shojiro
Published: July 2002

A low pressure methane plasma beam (LPMPB) was generated by a 13.56 MHz inductively coupled radio frequency (rf) plasma with a magnetic field (∼300 G) at a pressure of 2.5×10−2 Pa. The threshold ionization technique by using a quadruple mass spectrometer has been applied to measure the absolute density of CH3 radicals (n) in the LPMPB. At the rf power of 200 W, n was 1.4×1010 cm−3. The ions in the LPMPB were composed of C1, C2, C3, and H2 fragment ions and the ionic composition was found to be different from that of previous results at high pressures up to 4×102 Pa. The n and the relative intensities of C2, C3, and H2 fragment ions increased with the multiplication of rf power.
Correlation between optical properties and barrier composition in InxGa1−xP/GaAs quantum wells
Authors: Martínez-Pastor J. , González L. , Aragón G. , Guenaud Ch. , Deleporte E.
Published: July 2002

In this work high structural and optical quality InxGa1−xP/GaAs quantum wells in a wide range of thicknesses have been successfully grown on GaAs substrates by low temperature atomic layer molecular beam epitaxy. We demonstrate that compositional fluctuations in the barrier alloy are responsible for the inhomogeneous broadening and spatial localization effects observed in the excitonic recombination, the influence of quantum well width fluctuations being negligible in comparison. An important change of the optical transition energies in these quantum wells is observed when tuning a 10% In–Ga ratio in the alloy around the lattice match composition (x=0.48). This change is related to the barrier band gap variation and the intrinsic characteristics of the InGaP/GaAs heterostructure: different exciton binding energy from tensile to compressive strain in the barrier, and a possible dependence of the conduction band offset on the In composition.
Dependence of the electron irradiation induced decomposition of cadmium chloride thin films on the beam energy dissipation profile
Authors: Aidinis C. J.
Published: July 2002

The influence of primary beam energy and film thickness on decomposition by uniform electron irradiation of vacuum deposited thin films of cadmium chloride on silicon substrates has been studied for primary beam energies from 1 to 5 keV. Remaining film thickness versus dose measurements, obtained by ellipsometry, are compared to a theoretically derived model. This model is based on a steady state solution of the continuity equation for beam generated excess carriers within the thin film with a carrier generating function proportional to the Gaussian approximation for the rate of energy dissipation versus depth function. The proportionality constant is equal to the energy of formation of an electron–hole pair. The variation of the rate of energy dissipation with depth is derived from Monte Carlo calculations. The principle of scaling is shown to apply when energy loss is normalized with respect to the primary beam energy and depth with respect to the Bethe range. An energy-independent, universal thickness-versus-dose curve is proposed in view of the application of this material as an electron beam resist.
Analysis of structure change of Si solar cells irradiated with high fluence electrons
Authors: Imaizumi Mitsuru , Taylor Stephen J. , Yamaguchi Masafumi , Ito Tadashi , Hisamatsu Tadashi , Matsuda Sumio
Published: July 2002

An anomalous increase in short-circuit current of Si space solar cells, followed by an abrupt decrease and cell failure has been induced by fluences greater than 1016 cm−2 of 1 MeV electrons. This can be explained by a reduction in carrier concentration of the base region, in addition to a decrease of minority-carrier diffusion length. A change in the spectral response has been observed along the change in the short-circuit current. The spectral response has been modeled to account for radiation-induced changes in the cell structure. The results show that the junction depth increases when the degradation occurs. Also, spectral response after cell failure has been explained by conduction-type conversion of the base layer. This conversion is confirmed by a cross-sectional electron-beam-induced current signal. A mechanism for these phenomena has been proposed, which consists of the generation of vacancies and the vacancy-mediated diffusion of phosphorous.
Strain amplitude-dependent anelasticity in Cu–Ni solid solution due to thermally activated and athermal dislocation–point obstacle interactions
Authors: Kustov S. , Gremaud G. , Benoit W. , Golyandin S. , Sapozhnikov K. , Nishino Y. , Asano S.
Published: July 2002

Experimental investigations of the internal friction and the Young’s modulus defect in single crystals of Cu-(1.3–7.6) at. % Ni have been performed for 7–300 K over a wide range of oscillatory strain amplitudes. Extensive data have been obtained at a frequency of vibrations around 100 kHz and compared with the results obtained for the same crystals at a frequency of ∼1 kHz. The strain amplitude dependence of the anelastic strain amplitude and the average friction stress acting on a dislocation due to solute atoms are also analyzed. Several stages in the strain amplitude dependence of the internal friction and the Young’s modulus defect are revealed for all of the alloy compositions, at different temperatures and in different frequency ranges. For the 100 kHz frequency, low temperatures and low strain amplitudes (∼10−7–10−5), the amplitude-dependent internal friction and the Young’s modulus defect are essentially temperature independent, and are ascribed to a purely hysteretic internal friction component. At higher strain amplitudes, a transition stage and a steep strain amplitude dependence of the internal friction and the Young’s modulus defect are observed, followed by saturation at the highest strain amplitudes employed. These stages are temperature and frequency dependent and are assumed to be due to thermally activated motion of dislocations. We suggest that the observed regularities in the entire strain amplitude, temperature and frequency ranges correspond to a motion of dislocations in a two-component system of obstacles: weak but long-range ones, due to the elastic interaction of dislocations with solute atoms distributed in the bulk of the crystal; and strong short-range ones, due to the interaction of dislocations with solute atoms distributed close to dislocation glide planes. Based on these assumptions, a qualitative explanation is given for the variety of experimental observations.
Investigations of morphotropic phase transformations in the solid solution of Bi4Ti3O12 and Bi2Ti4O11 accompanied by defect dipole orientation and oxygen vacancy migration
Authors: Jiang A. Q. , Hu Z. X. , Zhang L. D.
Published: July 2002

Nanopowders of Bi2Ti2O7 with various Na+ modifications were synthesized by chemical coprecipitation, and their phase structures transform into a solid solution of Bi4Ti3O12 and Bi2Ti4O11 after sintering at high temperature. The dielectric peak at around 517 °C in Bi4Ti3O12 is related to the domain transformation at 445 °C in Bi2Ti2O7 and at 468 °C in Bi2Ti4O11 and moves to a higher temperature with increasing Bi2Ti4O11 concentration in the solid solution. Consequently, a dramatic drop of dielectric value in the solid solution was observed under a direct current bias due to the loss of relaxation mechanisms originated from the defect dipole orientation as well as oxygen vacancy migration. Furthermore, E-field dependent resistive measurements in Bi2Ti4O11 ceramics at various temperatures assert the defect dipole rotation and oxygen vacancy migration in combination with macrodomain alignment inside grains. Especially around phase transition, the field-induced phase switching leads to the abnormal jump of resistivity. Finally, the P–E hysteresis loop measurements show a good ferroelectricity in the solid solution.
On the initial stages of AlN thin-film growth onto (0001) oriented Al2O3 substrates by molecular beam epitaxy
Authors: Heffelfinger J. R. , Medlin D. L. , McCarty K. F.
Published: July 2002

Conventional and high-resolution transmission electron microscopy are used to characterize the initial stages of AlN thin-film growth. AlN films are deposited by molecular beam epitaxy onto annealed (0001) oriented α-Al2O3 (sapphire) substrates. During the initial stages of film growth (film thickness ∼25 nm) AlN forms islands of varying alignment with the Al2O3 substrate. Some of the AlN islands are well aligned with the [112̄0]AlN∥[101̄0] Al2O3 and (0001)AlN∥(0001)Al2O3, which matches closed-packed planes and directions. Other islands exhibit either an alignment of one set of planes, i.e., grains are aligned with the (11̄01)AlN∥(112̄0) Al2O3, or are misaligned with respect to the Al2O3 substrate. As the AlN film grows in thickness (film thickness ∼100 nm), the film becomes continuous, and the closed-packed planes and directions of the film and substrate are aligned for the majority of the film. Islands of AlN with an alignment other than this predominant orientation disturb the growth near the AlN/Al2O3 interface and create displacements along the [0001] AlN direction in overlying AlN grains. These misaligned AlN grains provide one source for the formation of planar defects in the epitaxial AlN films. The evolution of the AlN film microstructure and the reasons for the observed orientation relationships are discussed.
Magnetoresistance and Hall effect of chromium dioxide epitaxial thin films
Authors: Li X. W. , Gupta A. , McGuire T. R. , Duncombe P. R. , Xiao Gang
Published: July 2002

Epitaxial CrO2 thin films have been grown on TiO2(100) and Al2O3(0001) substrates by atmospheric pressure chemical vapor deposition. The films have a Curie temperature (Tc) of around 393 K with the ones grown on TiO2 exhibiting in-plane uniaxial magnetic anisotropy. They also display metallic characteristics, with room temperature resistivity of about 285 μΩ cm, dropping by about two orders of magnitude upon cooling down to 5 K. Magnetoresistance (MR) properties of the films have been measured with the magnetic field in the plane. For a field of 40 kOe, a positive transverse MR of about 25% at 5 K and a negative MR of about 7% at near Tc have been observed. In addition, Hall resistivity has been measured with magnetic field up to 40 kOe. A positive ordinary Hall effect is found at low temperatures, indicating the conduction carriers are holes.
Exchange-spring systems: Coupling of hard and soft ferromagnets as measured by magnetization and Brillouin light scattering (invited)
Authors: Grimsditch M. , Camley R. , Fullerton E. E. , Jiang S. , Bader S. D. , Sowers C. H.
Published: July 2002

An experimental and theoretical study is presented of the normal magnetic modes in spiral ferromagnetic structures. The bilayer system studied consists of Fe layers (25, 50, 100, and 200 Å thick) that are exchange coupled to 200 Å thick SmCo films that have ≈200 kOe anisotropies. The Fe spiral—induced by an external magnetic field that is applied opposite to the direction of the magnetized film—results in a structure similar to that encountered in a Bloch domain wall. The magnetization and the field dependence of the magnons in various Fe films are explained by the theoretical model.
Observation of orbital moment in NiO using magnetic x-ray scattering
Authors: Neubeck W. , Vettier C. , Fernandez V. , de Bergevin F. , Giles C.
Published: July 2002

The spin and orbital contribution to the total magnetization have been measured in NiO by exploiting the polarization dependence of nonresonant x-ray magnetic scattering. Although the orbital moment is usually neglected, we observed that the orbital moment actually plays an important role with a contribution of 17% to the total magnetization density. By performing azimuthal scans, it was found that spin and orbital moments are collinear.
Low-frequency noise in n-GaN with high electron mobility
Authors: Levinshtein M. E. , Rumyantsev S. L. , Look D. C. , Molnar R. J. , Khan M. Asif , Simin G. , Adivarahan V. , Shur M. S.
Published: July 2002

We report on the results of measurements of low frequency noise in n-type gallium nitride (GaN) grown on sapphire with 300 K electron mobility of 790 cm2/V s. The noise spectra have the form of 1/f noise with a Hooge parameter α of approximately 5×10−2. This value of α is two orders of magnitude smaller than that observed before in n-GaN. The obtained results show that the level of flicker noise in GaN, just like that in GaAs and Si, strongly depends on the structural perfection of the material (the amplitude of the 1/f noise is much smaller in material with high mobility). The effects of band-to-band illumination on the low-frequency noise show that 1/f noise in GaN might be caused by the occupancy fluctuations of the tail states near the band edges. This mechanism of the 1/f noise is similar to that in GaAs and Si.
Secondary electron emission coefficient of a MgO single crystal
Authors: Choi Eun-Ha , Lim Jae-Yong , Kim Young-Guon , Ko Jae-Jun , Kim Dae-Il , Lee Choon-Woo , Cho Guang-Sup
Published: July 2002

The secondary electron emission coefficient γ of different MgO single crystal has been measured by γ-focused ion beam system. It is found that the MgO single crystal with (111) orientation has the highest γ from 0.08 up to 0.21, while from 0.06 to 0.19 for (200) and from 0.05 to 0.15 for (220) orientation for operating Ne+ ions ranging from 50 to 300 eV throughout this experiment. It is also found that these observations can be explained by work functions, which are dependent on the crystal orientations of MgO.
Enhancement of critical Pr ion concentration (xcr) in (La1−xPrx)Ba2Cu3Oz
Authors: Murugesan M. , Ishigaki T. , Kuwano H. , Chen M. , Liu R. S. , Nachimuthu P.
Published: July 2002

The substitutional effect of Pr ion for La in (La1−xPrx)Ba2Cu3Oz bulk samples prepared under modified synthesis condition has been studied. Low field magnetization studies showed that superconductivity is retained up to the critical Pr ion concentration, xcr=0.40. The effective magnetic moment of Pr3+ free ion is very low in the present series of compounds. Results of X-ray absorption near-edge structure spectra for the series of (La1−xPrx)Ba2Cu3Oz compounds with 0.00<x<0.60 reveal that the doped Pr ion reduces hole concentration within the CuO2 planes, leading to a destruction of superconductivity.
Photocurrent multiplication at organic/metal interface and surface morphology of organic films
Authors: Nakayama Ken-ichi , Hiramoto Masahiro , Yokoyama Masaaki
Published: July 2002

Photocurrent multiplication occurring at an organic pigment/metal interface was revealed to be strongly dependent on the surface morphology of the organic film. The polycrystalline pigment film having a microscopically rough surface showed large photocurrent multiplication reaching the gain of more than 104-fold, while amorphous pigment film having a smooth surface and Au film showed little multiplication. Because of imperfect contact with an Au electrode deposited on a bumpy film surface, there exists a large number of blind alleys (structural trap) which can hold off photogenerated holes. The accumulation of hole carriers builds up high electric field at organic/metal interface and triggers the tunneling injection of electrons from the Au electrode. Emergence of the photocurrent multiplication phenomenon was successfully demonstrated to be controllable through changing the organic film morphology. The present results also pointed out the existence of a large number of blind alleys acting as structural traps at organic/metal interface.
High attenuation tunable microwave notch filters utilizing ferromagnetic resonance
Authors: Cramer N. , Lucic D. , Camley R. E. , Celinski Z.
Published: July 2002

We have constructed a series of microstrips for transmission of microwaves. These microstrips incorporate ferromagnetic and dielectric layers and therefore absorb microwave energy at the ferromagnetic resonance (FMR) frequency. The absorption notch in transmission can be tuned to various frequencies by varying an external applied magnetic field. For our devices, which incorporate Fe as the ferromagnetic material, the resultant FMR frequencies range from 10–20 GHz for applied fields up to only 1000 Oe. This frequency range is substantially higher than those found in devices utilizing a dielectric ferrimagnet such as YIG. We constructed devices using monocrystalline Fe films grown in a molecular beam epitaxy system. Our devices are of different construction than other Fe dielectric microstrips and show much improvement in terms of notch width and depth. We observed maximum attenuation on the order of 100 dB/cm, much larger than previously reported values of 4 dB/cm.