bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical and electrochromic properties of the amorphous and crystalline tungsten oxide thick films prepared under reducing atmosphere
Authors: Miyake K. , Kaneko H. , Sano M. , Suedomi N.
Published: February 2003

The physical and electrochemichromic properties of the amorphous and crystalline tungsten oxide films prepared by thermal evaporation of WO3 powder under a reducing atmosphere have been investigated. The oxide films with 850–24 500 Å thick were deposited on the substrates maintained at a temperature ranging from 50 to 500 °C under a vacuum below 1×10−5 Torr. Properties of the oxide films formed depend considerably on the deposition temperature. The as-prepared oxide films formed at a temperature higher than 400 °C have a resistivity of 10−3−10 Ω cm, and are blue colored, and mainly composed of crystalline WO3. The oxide films formed at a temperature lower than 350 °C have a resistivity of 105–109 Ω cm, and are transparent and amorphous. Both of the amorphous and crystalline oxide films have good electrochemichromic properties. From x-ray analysis, the crystalline WO3 thick films were found to change to hydrogen tungsten bronze films with a chemical composition of H0.33WO3 during electrochemical coloration, and the H0.33WO3 films were found to be reversed to the WO3 films during bleaching. In the electrochemical coloration using the cells composed of a crystalline or amorphous oxide film, the transmittance (λ=0.5 μm) and current were found to reach simultaneously an electrochromic steady state when a sufficient charge was injected. The density of the tungsten oxide films with 5000–24 500-Å thickness was also measured, and found to be 5.3–6.6 g/cm3 depending on the deposition temperature. The optical properties and the results of observations by scanning electron microscopy are also described.
Damping factor measurement of the Riedel singularity in niobium point contact Josephson junctions
Authors: Vernet G. , Hénaux J-C. , Adde R.
Published: February 2003

A new experimental method is presented to investigate directly the far-infrared frequency dependence of the Josephson ac current amplitude near the superconducting gap. The lowest value of the damping factor δ of the Riedel singularity in niobium contacts at 4 K is found to be δ=(2+2−1)×10−3 and is attributed to quasiparticle damping.
Compositional short-range order and kinetics of ordering in amorphous zero magnetostrictive CoNiFe-SiB alloy
Authors: Yokota R. , Takeuchi M. , Komatsu T. , Matusita K.
Published: February 2003

Isotropic compositional short-range order (CSRO) and the kinetics of ordering were studied in the amorphous zero magnetostrictive alloy of composition (Co0.525  Fe0.075  Ni0.4)73 (Si0.4  B0.6)27, which has a sufficiently low Curie temperature (TC) and high crystallization temperature. Resistivity and/or TC measurements after quenching from preannealing temperature show that the reversible equilibrium CSRO is formed at a temperature greater than TC and this CSRO can be separated from the nonreversible topological short-range order (TSRO). The reasons why CSRO can be separated from TSRO in this alloy are considered. The kinetics of ordering of CSRO were determined by resistivity measurements in well-annealed samples; the activation energy and the frequency factor for ordering of CSRO were determined to be 1.82 eV and 1.83×1013 sec−1, respectively. The kinetic data reveal the existence of a distribution of relaxation times of width β, where β was calculated to be 2.5 assuming a log-normal distribution. The approximate theory of CSRO was given by the formulation of which CSRO representing the mean square of the concentration fluctuation contributes to resistivity.
Effects of optically excited carriers on Raman spectra from InP
Authors: Nakamura T. , Katoda T.
Published: February 2003

Raman spectra from InP were measured at various power densities of the exciting laser. Concentration of the optically excited excess carriers Δn calculated from the frequency of the coupled longitudinal optical phonon-plasmon mode was about 0.5–1.7×1017 cm−3 at the laser power density of 5×102 W/cm2 for InP with equilibrium carrier concentration 0.9–5×1017 cm−3. Surface recombination velocity estimated from Δn assuming that the bulk lifetime was larger than 10−7 s was 1–8×103 cm/s. Such dependence of Raman spectra on laser power density could not be observed for GaAs.
Electronically active defects in cw beam-annealed Si. II. Deep-level transient spectroscopy
Authors: Sheng N. H. , Merz J. L.
Published: February 2003

Deep-level transient spectroscopy, a powerful capacitance method for the study of deep defect levels in semiconductors, is used to study cw beam-annealing processes (scanned Ar+ laser and scanned electron beam) for ion-implanted Si. A dominant hole trap (Ev +0.45 eV), whose concentration increases by more than one order of magnitude with increasing laser power, was observed in cw laser-annealed samples immediately after sample preparation. In contrast, only a low concentration of hole traps appears in electron-beam-annealed Si. This laser-induced defect is not stable at room temperature; instead it decays as a function of time and transmutes to a shallow level at Ev +0.10 eV. The recovery of the Ev +0.45 eV level can be stimulated by low-temperature annealing or by minority carrier injection. For the furnance-annealed control samples, rapid quenching from sufficiently high temperature into water produces the same defect energy level and annealing characteristics as the laser-induced defects. By correlating these results with those in the published literature, the laser-induced, quenched-in defects are identified as interstitial Fe and Fe-B pair reactions in Si. Possible sources of Fe in Si will be discussed.
A new method for determining electron beam proximity correction parameters in a double layer siloxane-diazo resist system
Authors: Jones Fletcher , Paraszczak Jurij , Speth Albert
Published: February 2003

Double layer resist systems have recently become very popular in electron beam lithography because of the ease of defining a high quality, high density very large scale integrated circuit (VLSI) pattern in the thin top layer of resist. However, in order to delineate high density VLSI patterns of high quality using electron beams, the electron scattering processes or proximity effects must be accurately characterized and appropriate steps taken to compensate for them. In this paper, theoretical considerations are combined with experimental observations in order to show how proximity correction parameters can be measured in a double layer system where the top layer is a thin (1200 Å) electron beam sensitive, negative resist.
Study of boron nitride gate insulators onto InP grown by low-temperature chemical vapor deposition
Authors: Yamaguchi Eiichi , Minakata Makoto
Published: February 2003

Thin films of phosphorus-doped boron nitride have been grown onto InP, as a new gate insulator, by low-temperature chemical vapor deposition using the reaction of NH3, B2H6, and PH3. Characteristics of the pyrolytic boron nitride obtained have been investigated by ellipsometry, x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and conductivity measurement. The results of XPS and AES have shown that a stable and comparatively stoichiometric boron nitride film was successfully obtained, even at low temperatures (300–600 °C), by using the two-temperature zone technique. The density of interface states for the BN/InP system has been found to be about 1010 cm−2 eV−1 or less around the midgap.
High mobility n-channel metal-oxide-semiconductor field-effect transistors based on SiO2-InP interface
Authors: Pande K. P. , Nair V. K. R.
Published: February 2003

Low temperature (250–300 °C) deposition of SiO2 gate oxide using a novel plasma-enhanced chemical vapor deposition technique is described. In this technique, the substrate was not directly exposed to the plasma, thereby minimizing radiation damage to both the substrate and the film. A dc potential was used to generate the plasma and the deposition of the film was achieved at low pressures (0.8–1.0 Torr) and extremely low plasma power (0.3 W/cm2) using silane (SiH4) and nitrous oxide (N2O) reactant sources. The dielectric films deposited using this process, typically had resistivities ≥1015 Ω cm, a dielectric constant of 3.95, refractive index of 1.462, and breakdown fields ≥5×106 V/cm. Metal-oxide-semiconductor (MOS) capacitors showed sharp interfaces with densities of states in the range of 5×1011 cm−2 eV−1. 4-μm gate length enhancement mode metal-oxide-semiconductor field-effect transistors were processed on p-InP substrates using a 1000-Å SiO2 gate oxide. No hysteresis loops were observed in the dc characteristics of the transistors nor was any significant channel current typical at zero gate bias. An effective electron channel mobility of 2600 cm2 V−2 s−1 was obtained for the transistors which exhibited a threshold voltage of +0.22 V and transconductance in the range of 40 mS/mm.
Theoretical and experimental study of the operation of ovonic switches in the relaxation oscillation mode. I. The charging characteristic during the off state
Authors: Schmidt Pierre E. , Callarotti Roberto C.
Published: February 2003

A simple theory of the charging cycle is presented for ovonic switches operating in the relaxation oscillation mode. The theory takes into account the variation of the OFF-state resistance with bias voltage. An analytical expression for the period of oscillation as a function of circuit components and device parameters is obtained showing that a nonlinear increase of the period of oscillation exists with increasing series resistance. The presented theory is in good agreement with experimental results.
Texture effects on megahertz dielectric properties of calcite rock samples
Authors: Kenyon W. E.
Published: February 2003

Dielectric measurements have been made from 0.5 to 1300 MHz on Whitestone, a quarried calcite rock, saturated with salty water. Whitestone shows a large increase in dielectric permittivity (dispersion) at the low end of this frequency range. When the conductivity of the water is varied, the dielectric permittivity of Whitestone is found to scale as water conductivity/frequency, i.e., as the complex dielectric constant of water. This is believed to be unique in measurements on insulator-conductor mixtures, and establishes that the dispersion is primarily caused by the geometry of the sample. Two other calcite samples show much lower dielectric dispersion. Micrographs indicate that the variation in dispersion among the three samples is in rough proportion to grain platiness. This is consistent with the platey grain mechanism, one of three mechanisms proposed by Sen to explain dielectric dispersion in water-saturated rocks. A model consisting of water containing insulating spheroids of identical aspect ratio, isotropically distributed in orientation, predicts that increased grain platiness reduces both low-frequency conductivity and high-frequency dielectric permittivity in a closely related way; this is observed experimentally. However, this model does not fit simultaneously all electrical properties of Whitestone; evidently a more complex geometrical model is needed. Dielectric dispersion caused by texture is of practical importance in estimating water content of subsurface rocks from borehole measurements of dielectric permittivity, particularly at high water salinities.
Boron segregation at Si-SiO2 interface during neutral anneals
Authors: Charitat G. , Martinez A.
Published: February 2003

In this article the boron segregation at Si-SiO2 interface is investigated from 850 to 1200 °C in neutral ambient (nitrogen) for Si-SiO2 and Si-SiO2-Si3N4 structures. The segragation coefficient m, directly measured by means of an ionic probe, increases from 850 to 1000 °C and then decreases from 1000 to 1200 °C for both types of structures. For nitride coated oxides, the values of m obtained range from one and a half to two times greater than those obtained for free oxides. A thermodynamic study of the segregation phenomenon led to a formulation of the coefficient m involving the pressure in the oxide. The variations of the latter, according to time and temperature are due to the viscoelastic relaxation of silica. This model enables us to describe the qualitative behavior of m as observed experimentally.
Transition metal diffusion in InP: Photoluminescence investigation
Authors: Skolnick M. S. , Foulkes E. J. , Tuck B.
Published: February 2003

The 3d transition metals (TM’s) from Cr to Cu introduced into InP by diffusion are studied using low temperature photoluminescence (PL). Luminescence bands from Mn, Co, and Cu are observed whereas for the remaining TM’s, Cr, Fe, and Ni, no optical effects related to the diffused species are detected. This behavior is found to correlate with electrically active, compensating deep acceptor levels found for Mn, Co, and Cu in C-V measurements, but not for the other TM’s. For Mn diffusions at 800 °C deep level PL peaking at 1.15 eV ascribed to substitutional Mn2+In is observed. For the case of Cu three different PL bands are found peaking at 1.2, 1.17, and 0.99 eV, respectively. It is speculated that the 1.0-eV band may arise from CuIn centers. The higher energy bands arise from Cu-related complexes. Reasons for the electrical and PL activity of Mn and Co, but not for the adjacent fast diffusing TM’s Cr and Fe which are electrically active in growth doped material, are discussed in terms of the particularly deep acceptor levels formed by Mn and Co.
Intensity dependence of the minority-carrier diffusion length in amorphous silicon based alloys
Authors: Hack M. , Shur M.
Published: February 2003

In this paper we present results showing the intensity dependence of the minority-carrier diffusion length in an amorphous silicon-based alloy. A theoretical analysis shows that this dependence can be related to the energy dependence of the density of states near the valence band, which assumed to be exponential, has a characteristic energy of approximately 240 mV around 1.2 eV below the conduction band edge.
Frequency dependence of flat-band capacitance of metal/insulator/glow-discharge deposited hydrogenated amorphous silicon diodes
Authors: Sasaki Goro , Fujita Shizuo , Sasaki Akio
Published: February 2003

The frequency dependence of the flat-band capacitance of a metal/insulator/semiconductor diode where the semiconductor film is glow-discharge deposited amorphous Si:H (a-Si:H) was measured at various temperatures. The response time and trap density at the insulator/a-Si:H interface or a-Si:H space-charge region could be evaluated by a simple model.
Optical-absorption coefficient near the fundamental absorption edge of GaAs1–xPx
Authors: Hasegawa S. , Tanaka A. , Sukegawa T.
Published: February 2003

The absorption coefficients of GaAs1–xPx with compositions 0.0, 0.23, and 0.38 have been measured by the differential photocurrent method. The results were analyzed with the theory of optical absorption due to the exciton formation. Theoretical absorption curves for GaAs1–xPx alloy (x≤0.38) were provided in the photon energy range higher than the band gap.
Activation energy associated with the annealing of buried implanted oxides in silicon
Authors: Das K. , Censlive M. , Franks E. , Butcher J. B.
Published: February 2003

The activation energy associated with the annealing of buried implanted oxides in silicon is observed to be 0.15 eV. This value is much lower than those involved in the oxidation of silicon using other processes.
Thin film Nb3Ge dc-SQUID with high operating temperature
Authors: Rogalla H. , David B. , Rühl J.
Published: February 2003

Small area planar Nb3Ge dc-SQUIDs with wide operating temperature range were obtained using thin (40 nm) Nb3Ge films with high transition temperature Tc and small critical current per unit length. The SQUIDS were fabricated using electron beam lithography and reactive ion etching. SQUID operation was observed in the temperature range from 10 to 18.4 K with a best modulation depth of 11%.
Electron swarm parameters in rare gases and mixtures
Authors: Lagushenko R. , Maya J.
Published: February 2003

Calculations of the steady-state electron swarm parameters in rare gases and mixtures are reported. The Townsend ionization coefficient α, electron drift velocity W, and diffusion coefficient D for He, Ne, Ar, and (10% Ar+90% Ne) are calculated as a function of E/N over an extended range (up to 5650 Td) by solving the Boltzmann equation. Total excitation cross sections qx for He, Ne, and Ar have been determined by fitting calculated values of α to experimental literature values over E/N=28–280 Td. Our treatment of the Boltzmann equation takes into account effects of electron density gradient, generation of new electrons and electron-electron interaction. Calculated values of α and W are in good agreement with available experimental data up to highest values of E/N. Comparison of the other parameters has not been made due to insufficient experimental data, especially for high E/N.
Stress relaxation in electron bombarded silicate glasses
Authors: Primak W.
Published: February 2003

In contrast to the behavior of vitreous silica which has developed internal stresses consequent upon nonuniform irradiation with ions (e.g., protons, deuterons, helium ions), the electron-bombarded vitreous silica does not show a post-irradiation stress relaxation. The complex silicate glasses which have been irradiated nonuniformly with electrons display large post-irradiation internal stress changes, which may be increases or decreases. It is evident that in them both positive and negative dilatation centers were formed and that they possess different annealing properties. It is not clear to what extent the internal stress changes found in these irradiated glasses are caused by annealing or by stress relaxation. Since plates which had been irradiated until they fractured did not appear to behave differently from unfractured samples, it is concluded that the stress changes are a microscopic rather than a macroscopic phenomenon. The reduced power dependence of the ionization compaction of vitreous silica on dose is discussed.
Phase formation in Au-Al and Cu-Al thin-film systems under ion beam bombardment
Authors: Chang Chu Te , Campisano S. U. , Cannavó S. , Rimini E.
Published: February 2003

Au-Al and Cu-Al thin film bilayers were bombarded at 80 K with Kr+ ions of 60–240 keV energy. The Au2Al+AuAl2 and Al4Cu9 phases formed during bombardment and they were investigated by backscattering and x-ray diffraction techniques. In all the cases the growth kinetics is linear with the parameter (fluence × interfacial deposited energy density)1/2 suggesting a correlation with a diffusion-like process. Comparison with calculations of diffusion enhanced within the collision cascade gives good agreement with the experimental results.
Thermal properties of thin insulating layers using pulse transient hot strip measurements
Authors: Gustafsson Silas E. , Chohan Mohammad Aslam , Ahmed Kamaluddin , Maqsood Asghari
Published: February 2003

A transient method for measuring thermal conductivity and thermal diffusivity has been developed for studies of insulating solid surface layers with thicknesses down to a few micrometers. The method is based on a procedure by which a string of square pulses, via an ac-coupled circuit, is applied to the hot strip (deposited thin film), which is acting both as a heat source and a sensor of the temperature increase of the substrate. By performing transient experiments over short times (selecting a short pulse duration), it is possible to limit the depth under the hot strip beyond which the thermal properties of the substrate does not influence the recorded thermal properties. A series of experiment with probing depths ranging from 4 to 10 μm has shown that the thermal properties measured with this technique agree very well with independently measured values provided the pulse duration is small compared to the pulse period. Because of the small probing depth and the size of the thermal probe this novel technique should open up possibilities for studying thermal properties of evaporated and sputtered layers of insulators, a kind of solids which up to now has not been accessable for direct measurements of thermal properties.
Extracting physical structure information from thin organic films with reflection absorption infrared spectroscopy
Authors: Debe M. K.
Published: February 2003

A RATIO method has been developed to extract physical structure information from anisotropic thin organic films on metal substrates using reflection absorption infrared spectroscopy (RAIR). The physical structure information referred to are the Euler angles, θ and ψ, specifying the molecular orientation relative to the surface normal and f, the fraction of material oriented in that manner. Such films are viewed as consisting of polycrystalline domains which have a natural tendency to orient preferentially with respect to the substrate normal direction. Two equations are developed involving these three physical structure parameters and two measured quantities obtained from the thin-film RAIR spectra. These measured quantities are derived from the ratios of band absorbances, the transition moments of which belong to different symmetry groups. The method is tested by applying it to vacuum-deposited metal-free phthalocyanine (H2Pc) films on air-oxidized aluminum. The molecular orientation derived in the α-H2Pc crystallites is in very good agreement with the stacking configurations published in the literature for the isomeric phthalocyanine derivatives, predicting a ‘‘standing b-axis’’ orientation with the normal to the molecular planes inclined 26.5° with respect to the b-axis. In addition, spectroscopic evidence is presented for the first time of the existence of more than one metastable α polymorph of H2Pc. The less stable α polymorph is thermally converted by vacuum annealing to the more stable α polymorph and the first order rate kinetics measured. The resulting activation enthalpy and entropy are very close to those reported by Sharp and Miller for the higher temperature α to β-H2Pc transition.
Operation of an electrostatic ion trap in a uniform magnetic field
Authors: Johnson C. E.
Published: February 2003

The electrostatic ion trap consisting of an outer cylinder with end caps plus a concentric central wire is relatively easy to construct compared to rf and Penning ion traps. Its use in a uniform magnetic field of several Gauss has been studied so that, for example, optical pumping of the trapped ions would be possible for an appropriate ionic species. Initial investigations using either He or Ar ions trapped in the approximately logarithmic potential between the outer cylinder and the central wire indicate that the trapping time is slightly reduced when a 25–50 G magnetic field is applied parallel to the trap axis. However, the use of the magnetic field allows the trap to be filled initially with substantially more ions. Computer plots of numerous nonperiodic ion orbits for several revolutions both with and without a magnetic field serve as a guide to understanding the operation of the trap in a uniform magnetic field. These plots show that the major features of the trajectories remain unchanged for magnetic fields up to 100 G, although ions with almost zero initial angular momentum about the central wire can be trapped when a magnetic field is present.
Improved theory of laser-enhanced ionization in flames: Comparison with experiment
Authors: Axner O. , Berglind T. , Heully J. L. , Lindgren I. , Rubinsztein-Dunlop H.
Published: February 2003

An improved theory for laser enhanced ionization in flames has been developed for one- and two-step laser excitations. The model gives an analytical expression for the sensitivity of the method for a given transition of any element. The theoretical expression is compared with experimentally measured signals for a number of elements and the agreement is found to be generally good.
Nonlinear Rayleigh waves: Harmonic generation, parametric amplification, and thermoviscous damping
Authors: Lardner R. W.
Published: February 2003

The propagation of surface acoustic waves in a nonlinear isotropic elastic material is investigated. The effects of heat conduction and viscous internal damping, both assumed small, are included. The method of multiple scales is used to investigate the slow modulation of a wave of arbitrary initial profile and a coupled system of integrodifferential equations is obtained for the variation of the different harmonic constituents. Explicit numerical solutions are obtained for the generation of higher harmonics by an initially sinusoidal wave and for the parametric amplification of a weak signal by a pump wave of twice the frequency.
Acoustic microscopy of materials and surface layers
Authors: Wilson R. G. , Weglein R. D.
Published: February 2003

The application of pulsed reflection acoustic microscopy to the characterization of bulk materials and thin layers of various materials on surfaces is illustrated. The factors that contribute to sharp image contrast, edge definition, and image reversal are delineated and illustrated. Acoustic material signatures of a variety of bulk materials and thin layers of materials on surfaces of a different material are shown. The origin and nature of acoustic material signatures is discussed.
Optical properties and solar selectivity of coevaporated Co-Al2O3 composite films
Authors: Niklasson G. A. , Granqvist C. G.
Published: February 2003

Co-Al2O3 composite films were produced by electron-beam coevaporation in a system with elaborate process control. The deposits were analyzed by transmission electron microscopy, electron diffraction, Auger electron spectroscopy, secondary ion mass spectroscopy, Rutherford backscattering, field ion microscopy, mechanical stylus measurements, and electrical dc and ac measurements. A uniform separated-grain structure with regular hcp Co particles embedded in Al2O3 was found for Co contents (fCos’) up to ∼30 vol %. The complex dielectric permeability ε̄ was evaluated in the 0.3≲λ≲40-μm wavelength range for samples with 0.11≲ fCo ≲0.60 by carefully selected combinations of spectrophotometric transmittance and reflectance data. Numerical accuracy and internal consistency were investigated. Effective medium theories for ε̄ were derived by applying classical scattering theory to spherical random unit cells defined so as to properly represent a number of typical microgeometries. The formulations due to Maxwell Garnett, Bruggeman, and others were thus rederived in a unified way. Large-size limits of validity and extensions to nonspherical particles were treated. It was found that the Maxwell Garnett theory could reproduce the experimental ε̄’s in detail at low fCo provided that some Co was taken to be dispersed in the insulating matrix. At larger fCo’s we found discrepancies which are likely to be due mainly to dipole-dipole coupling among adjacent particles. A comparison of the experimental ε̄’s and the rigorous Bergman–Milton bounds, which hold irrespective of detailed microgeometry, gave several interesting results: the ε̄’s varied monotonically along one of the bounds for isotropic materials as fCo was increased, at large fCo we found evidence for anisotropy, and at λ≊12.5 μm we noted certain cases of disagreement with even the most generous bounds. The empirical ε̄’s were used to construct surfaces which combine a high solar absorptance as with a low hemispherical thermal emittance eH. From a computer optimization study we found that as =0.95 and eH =0.07 could be obtained with 0.07 μm of Co-Al2O3 ( fCo≊0.6) antireflected with 0.07 μm of Al2O3 and laid on Ni. These results were verified by measurements on samples which approximate the ideal design.
Impurity doping in chemically vapor-deposited amorphous hydrogenated silicon from disilane
Authors: Ashida Y. , Mishima Y. , Hirose M. , Osaka Y.
Published: February 2003

Physical properties of amorphous hydrogenated silicon produced by the chemical vapor deposition (CVD) of disilane have been investigated as a function of doping ratio of phosphine or diborane. The growth rate is decreased by phosphine doping and increased by boron doping. It is found that the electrical conductivity can be controlled over a wide range by phosphorus or boron doping. The optical band gap is lowered by doping as a result of decrease in hydrogen content. Also, a wide band gap of a-SixN1−x:H has been prepared by CVD of a Si2H6+NH3 gas mixture.
Quantum efficiency of internal photoeffects in narrow-gap semiconductors. II. Calculation results in comparison with experimental data
Authors: Scharoch Pawel , Pawlikowski Janusz M.
Published: February 2003

The spectral characteristics of quantum efficiency of internal photoeffects η* are calculated for narow-gap InSb and mixed CdxHg1−xTe crystals (with different molar compositions) using the model presented in the first part of the work. Computation results of η* are shown for several different band structure parameters. A comparison of the results is done with the experimental data for photovoltaic detectors made of CdHgTe crystals and reasonable qualitative accordance is found between them. A strong dependence of quantum efficiency on the carrier concentration in the generation volume (via screening effect) is observed in both the model and the experimental results.
Photoacoustic spectroscopy of semiconductor heterostructures by piezoelectric transducers
Authors: Kubota K. , Murai H. , Nakatsu H.
Published: February 2003

Photoacoustic spectroscopy was applied to characterize a semiconductor heterostructure layer on a substrate. Some III-V semiconductor samples were measured, including GaAs-AlAs superstructures. Observation of the indirect-transition edge on the higher-energy side above the direct-transition edge is reported, and the mechanism discussed.
Cathodoluminescence efficiency of binary compound phosphors
Authors: Inoue M.
Published: February 2003

A theoretical treatment is given of binary compound cathodoluminescence efficiency on the basis of the statistical model treating the branching process of ionization scattering and phonon emission. Energy loss mechanisms of hot electrons in semiconductors are quantitatively examined using Penn’s model assuming an optical phonon deformation potential and polar-mode electron-phonon interactions. The quantum yield of e-h pairs is calculated with three parameters, the band-gap energy Eg, and two loss parameter constants Sd and Sp which are determined completely in terms of material parameters including Eg, the mass density, the lattice constant, the covalency, the optical phonon frequency, and dielectric constants. The material characterization of efficient phosphors is discussed in terms of empirical correlations between cathodoluminescence efficiency and the physical constants. Dependence of efficiency on the crystal structure of the phosphor host is particularly noticeable. Comparisons are made with previous work.
Influence of the tank circuit on the low frequency impedance of an rf-biased R-SQUID
Authors: Seppä Heikki
Published: February 2003

The dc -impedance of an rf-biased R-SQUID is studied analytically for the nonhysteretic regime. A mathematical analysis of the intrinsic behavior of an R-SQUID, including the mutual interaction between the tank circuit and the SQUID loop, is presented. The results obtained give good agreement with some experimentally observed features. Although the main aim of the present paper was to find an analytic solution for the dc -impedance of an R-SQUID, the results given here can also be used to estimate the R-SQUID parameters and to optimize the performance of a R-SQUID noise thermometer. The theory presented here also provides a good basis for modelling the noise properties of a Josephson junction noise thermometer.
Noise properties in an rf-biased Josephson junction noise thermometer
Authors: Seppä Heikki
Published: February 2003

Frequency fluctuation in an rf-biased R-SQUID noise thermometer operating in an nonhysteretic mode is examined. The noise sources caused by the shunt resistor and by the dissipative elements in the tank circuit are included in the model. The results demonstrate that the noise in the tank circuit has a significant influence on the accuracy of the Josephson junction noise thermometer.
Characterization of process-induced defects and device properties of ion beam sputter-deposited Mo contacts on Si
Authors: Auret F. D. , Paz O. , Bojarczuk N. A.
Published: February 2003

The effects of ion beam sputter deposition conditions and post deposition isochronal annealing on the characteristics of molybdenum devices on n- and p-type Si were investigated by I-V and C-V measurements. The sputter-induced damage below the contact was characterized by deep level transient spectroscopy and electron-beam induced current techniques. It was observed that the barrier height, diffusion length, and the concentration of the process-induced defects depend on the sputtering voltage and annealing temperature. Further, we found that the observed defects were introduced during the initial stages of deposition. Defects were still present after annealing at 500 °C.
Laser recrystallization of Si over SiO2 with a heat-sink structure
Authors: Kawamura S. , Sasaki N. , Nakano M. , Takagi M.
Published: February 2003

Complete single crystalline silicon films over SiO2 have been produced with a heat-sink structure designed for best utilization of temperature gradients during resolidification process induced by an incident cw Ar laser beam. The structure includes device regions with thin SiO2 layers which act as a heat sink to the substrate and the peripheral regions with thick SiO2 layers. By using this technique, residual grain boundaries in the laser recrystallized silicon over insulator can be eliminated. N-channel metal-oxide-semiconductor field-effect transistors fabricated in the recrystallized silicon films with a heat-sink structure exhibit good device characteristics, having a surface electron mobility of 500 cm2/V s which is comparable to that of bulk devices.
Spin correlations near the ferromagnetic-to-spin-glass crossover (invited)
Authors: Aeppli G. , Shapiro S. M. , Maletta H. , Birgeneau R. J. , Chen H. S.
Published: February 2003

We have performed neutron scattering studies on two very different alloys which undergo transitions from ferromagnetic (FM) to spin-glass (SG) states as the temperature is reduced. The alloys are EuxSr1−xS, a crystalline insulator, and (FexMn1−x)75P16B6Al3, an amorphous metal, and their FM-SG multicritical points are at x≂0.50, T=4 K and x≂0.65, T=42 K respectively. In spite of the substantial differences between these materials, the neutron scattering data show that their spin correlations are remarkably similar. In particular, for the samples near the multicritical points, a single Lorentzian describes the magnetic scattering very well. Its width κ corresponds to a ferromagnetic correlation length ξ which, as T is reduced, first increases to a value indistinguishable from infinity, and then decreases to a finite value, as expected for a ferromagnet which evolves into a reentrant spin glass. As the Fe or Eu content is raised, the scattering function at low temperatures deviates increasingly from the Lorentzian form, and is better described by a power law Q−α with 2<α<3. We find no evidence for coexistence of ferromagnetic order with freezing of the transverse spin components, as proposed by Gabay and Toulouse. We argue on general grounds that the zero-field Gabay-Toulouse state cannot exist in real magnets. However, our results can be explained in terms of the random field effects which arise when ferromagnetic and spin-glass order parameters are coupled together.
Triad anisotropy of spin glasses and torque experiments (invited)
Authors: Fert A. , Arvanitis D. , Hippert F.
Published: February 2003

We present torque experiments on CuMn alloys which illustrate the triad anisotropy of spin glasses. We also discuss the mechanisms giving rise to the triad anisotropy and we show how the anisotropy can be ‘‘shaped’’ at will.
Chaotic spin glasses: An upper critical dimension (invited)
Authors: McKay Susan R. , Berker A. Nihat
Published: February 2003

The chaotic renormalization-group trajectories exhibited by frustrated hierarchical Ising models have been interpreted as signaling a spin-glass phase, since, as the system is probed at successive length scales, strong and weak correlations are encountered in a chaotic sequence. Cluster-hierarchical models have been introduced, with susceptibilities behaving as in Bravais lattices. Frustrated cluster-hierarchical models again show an ordered phase characterized by chaotic rescaling and a smooth specific heat at the transition (α<−5). Scans in dimensionality reveal an upper critical dimension for the chaotic spin-glass phase, via a boundary crisis mechanism. Beyond this dimension, the system has no long-range order at any temperature. Nevertheless, a low-temperature regime can be distinctly identified, exhibiting intermediate-range chaotic spin-glass order.
Evidence for a breakdown of analyticity deduced from dynamical measurements of an insulating spin glass
Authors: Rajchenbach J. , Bontemps N.
Published: February 2003

We have performed dynamical measurements on the insulating spin-glass Eu0.4 Sr0.6S by means of Faraday rotation experiments. We have measured the out-of-phase component χ″(H, T, ν) of the magnetic susceptibility as a function of the field H, the temperature T and the frequency ν (0 Oe<H<50 Oe, 102 Hz<ν<105 Hz, 1.3 K<T<2.0 K). The set of lines Tg (H, ν) which characterize the onset of irreversible properties for a given frequency ν, as derived from these χ″(H, T, ν) data, exhibit a gradual breakdown of analyticity for small fields as the frequency, or the temperature, is lowered. We suggest a general scaling of these lines according to the form Tg(H,ν)−Tg(0,ν)=HC  f{[Tg(0,ν)−Tg(0,0)]/HC} which leads to Tg (0, 0)=1.55±0.03 K and G=0.5±0.2. Consistently, χ″(H) does not exhibit any longer an analytic expansion (versus even power of H) in the vicinity of a characteristic temperature TM(ν). When the frequency, or the temperature is lowered, we observe a sharp increase of the initial slope of χ″(H, TM) as TM (ν) approaches Tg(0,0). These results suggest a breakdown of analyticity in the expansion of a ‘‘characteristic relaxation time’’ versus H.
On the field dependence of the spin glass susceptibility peak
Authors: Barbara B. , Malozemoff A. P. , Barnes S. E.
Published: February 2003

In amorphous GdAl spin glass, as in a number of other spin glasses, the susceptibility cusp first increases, then decreases in temperature with increasing field. An explanation for this behavior is found in terms of a competition between the noncritical linear susceptibility and the critical nonlinear susceptibility.
Irreversibility of infinite range spin glasses
Authors: Soukoulis C. M. , Grest Gary S.
Published: February 2003

By employing the ‘‘slow-cooling’’ iterative solution of the mean field equations, we study the free energy surface of the isotropic, infinite range Ising and Heisenberg spin glasses with up to 800 spins. Ising model results for the field cooled and zero field cooled magnetizations as well as the magnetic hysteresis loops are similar to those found for the short ranged model. However, the results for the Heisenberg model depend strongly on the range of the interaction. The infinite range model shows macroscopic irreversiblity, in contrast to the short range isotropic Heisenberg case which has no irreversibility.
Spin flip Raman scattering in Eu0.54Sr0.46S
Authors: Carlson N. W. , Geschwind S. , Devlin G. E. , Batlogg B. , Dillon J. F. , Rupp L. W. , Maletta H.
Published: February 2003

Spin flip Raman scattering (SFRS) from the Eu2+ in a single crystal of Eu0.54Sr0.46S has been used to study the spin dynamcis from 1.6 to 20 K in magnetic fields from 4 to 10 kG. At low temperatures, an anomalous intensity in the Stokes/anti-Stokes ratio is observed connected with an interference between spin flip terms linear and quadratic in M.
ESR measurements on amorphous FeNiSi thin films in the ferromagnetic-spin glass transition regime
Authors: Suran G. , Gerard P.
Published: February 2003

The magnetic properties of amorphous Fe16Ni64Si20 thin films determined by electron spin resonance measurements are reported. These films were prepared by ion mixing, and samples irradiated at 77 °K by Xe ions at a dose of 3×1015 Xe+/cm2 with an energy of 400 keV are amorphous. At room temperature the films possess soft ferromagnetic properties. One observes a well defined standing spin wave (SSW) spectrum from which the temperature dependence of exchange stiffness D, the spin wave linewidth ΔHn(T) and Ms=f(T) could be deduced. At low temperature the results are characteristic of reentrant behavior. For T<75 °K Ms deviates from T3/2, D decreases, and ΔHn increases with decreasing temperature.
Low field magnetization studies on (FexNi1−x)75P16B6Al3 ribbons
Authors: Mazumdar P. , Bhagat S. M. , Manheimer M. A. , Chen H. S.
Published: February 2003

We report dc magnetization measurements on (FexNi1−x)75P16B6Al3 alloys, prepared both with ordinary B and pure B11, for x=0.25 and 0.30. For each alloy we identify two temperatures where ferromagnetism collapses. The transition temperatures are strongly influenced by the B isotope. The samples exhibit permanent moments at 4 K, even when cooled in zero field from 77 K, provided that they have been exposed to a finite field at 77 K.
Critical scattering in dilute ferromagnets
Authors: Salamon M. B. , Murani A. P.
Published: February 2003

A troubling aspect of dilute magnetism is the failure of the spin-spin correlation length, measured in neutron scattering, to diverge at TC. New data for (FepNi1−p)80P20 show an increase in critical scattering at small Q (≲0.02 Å−1) near TC. We propose, using scaling arguments, that a change occurs in effective correlation length from a finite 1D length at Q≫ξ−1p to a divergent 3D length for Q≪ξ−1p, where ξp is the geometrical connectedness length.
Ferro- and antiferromagnetism of Pd77.5−xCu6Si16.5(Fe,Mn)x glasses
Authors: Herlach D. M. , Kästner J. , Heller A. , Wassermann E. F.
Published: February 2003

ac susceptibility and static magnetization measurements are reported on amorphous alloys Pd67.5Cu6Si16.5TM10, TM=Fe or Mn. The lower concentrated alloys (x≲5 at.% Fe or Mn) show only PM-SG type transitions. A 10 at.% Fe alloy shows long range ferromagnetic order prior to a transition into a spin glass like state at low temperatures. A 10 at.% Mn alloy, however, undergoes a transition from PM to a mixed magnetic state with predominantly antiferromagnetic order. With further decreasing temperature the AFM becomes unstable causing a rapid upturn of the susceptibility. Finally, a sharp peak of the zero field ac susceptibility marks a transition into a spin frozen state.
Cooling rate effect upon the field-cooled magnetization of an insulating spin-glass
Authors: Wenger L. E. , Mydosh J. A.
Published: February 2003

The field-cooled magnetization (FCM) of two cobalt aluminosilicate spin-glasses have been measured as a function of applied magnetic field and the rate of cooling through the spin-glass freezing temperature, Tf. For the lowest fields, a difference of ∼5% in the magnitude of the FCM for T<Tf was observed between the fastest cooling rate of ≳200 mK/s and the slowest rate of 1 mK/s. The magnitude of the FCM at a constant T<Tf did not change over a period of 8×104 s; and as long as the warming rate was the same as the cooling rate, the FCM was essentially ‘‘reversible.’’ These cooling rate effects show striking similarity to a real liquid-glass transition and suggest the FCM ‘‘plateau’’ may arise from the cooling rate being faster than the time necessary for the magnetic spins to relax to their true thermodynamic equilibrium.
Light-induced magnetic effects in an insulating spin glass
Authors: Ferré J. , Ayadi M.
Published: February 2003

We report on the photoinduced magnetic phenomena in an insulating spin glass, the cobalt alumino silicate glass (13.3 at. % Co) below its freezing temperature Tf =5 K. In particular the illumination of the sample by near infrared radiation speeds up the relaxation of the thermoremanent magnetization, and enhances significantly the magnetic susceptibility near and below Tf. We proposed a simple phenomenological model which explains why the magnetic metastability is strongly affected by light illumination. The temperature and magnetic field dependence of the photomagnetic effects are also discussed.
ESR study of Fe-Ni spin glass alloys
Authors: Hou M. K. , Salamon M. B. , Ziman T. A. L.
Published: February 2003

Amorphous Fe8Ni72P20 and Fe10Ni70P20 spin-glass alloys show progressive changes of ESR lineshape in going from the paramagnetic to spin-glass phase. We use the Kubo-Toyabe model to explain such changes in line shape and demonstrate that there is a tendency for the relaxation rate to vanish as Tf is approached. The data also suggest that there is a static anisotropy field which develops in the spin-glass phase.
Ferromagnetic resonance and magnetic ordering in amorphous (FeMn)CP alloys
Authors: Sarkissian B. V. B.
Published: February 2003

The magnetic properties of a series of amorphous (FexMn1−x)80P16C4 metallic glasses have been studied via ferromagnetic resonance and zero field ac susceptibility measurements. We find that the Fe ferromagnetism is rapidly destroyed by the competition with the antiferromagnetic coupling of the Mn moment, leading to a cluster glass or spin glass phase in the concentration range x≲70%. Alloys with x greater than 70% show a transition to ferromagnetism with well defined critical behavior. In addition, both the susceptibility and the magnetic resonance reveal a marked anomaly at lower temperatures which can be attributed to the coexistence of ferromagnetism and spin glass order. These anomalies become weaker as the alloys become more strongly ferromagnetic. No resonance signals were detected in alloys with x≲20%.
Crystallization and ferromagnetic resonance behavior of evaporated Gd-Fe alloy films
Authors: Lee S. R. , Miller A. E. , Blackstead H. A.
Published: February 2003

The composition and temperature dependence of the ferromagnetic resonance, as-deposited structures, and in situ crystallization behavior were investigated for evaporated Gd-Fe alloy films. The origin of multiple ferromagnetic resonance peaks in the amorphous alloy film was speculated to be due to compositionally different short-range ordered structures. The composition dependence of the structural variations in the as-deposited alloy films were consistent with the two sphere size hard sphere model. The in situ crystallization reactions of Gd-Fe alloy films were characterized by three separate reaction stages.
Effect of the heating rate used during stress relief annealing on the magnetic properties of amorphous alloys
Authors: Taub A. I.
Published: February 2003

The effect of the heating rate used during stress relief annealing of amorphous alloy toroids on the final soft magnetic properties has been investigated by comparing three different annealing techniques. Batch furnace annealing of a completely formed toroid provides the slowest heating rate and the poorest properties. The hot block method tested in this study, provides a faster heating rate but only a small improvement in properties. This technique involves annealing the ribbon layer by layer as it is wound, the heat being applied by passing the ribbon over a hot block whose radius of curvature is the same as that of the final toroid. A similar annealing technique in which the hot block is replaced by a quartz line heater, provides the fastest heating rate and a significant improvement in properties. The latter method is however considerably slower than the hot block technique.