bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal changes of optical properties observed in some suboxide thin films
Authors: Ohta Takeo , Takenaga Mutsuo , Akahira Nobuo , Yamashita Tadaoki
Published: February 2003

Suboxide thin films of SbOx, TeOx, MoOx, and GeOx (x is smaller than the stoichiometric value for each component) were found to have the property of showing a critical change in their absorption coefficients and refractive indices at elevated temperatures. The thin-film samples were prepared by evaporating a mixture of the stoichiometric oxide powder and a deoxidization metal powder such as tungsten. The critical temperatures of these thin films are 150, 120, 150, and 280 °C, respectively. The absorption coefficients before and after the heat treatment are 2.5×104 (before) and 6.1×104 (after), 8×104 and 1.0×105, 5.6×103 and 1.1×104, and 4.9×104 and 1.8×105 cm−1, respectively. Their refractive indices are 1.8 (before) and 1.9 (after), 3.1 and 3.5, 1.8 and 2.1, and 2.5 and 2.8, respectively. As determined by x-ray diffraction analysis, these thin films are composed of very small metal grains and stoichiometric oxide grains. The thermal changes accompanied by the optical constant changes are mainly due to structural changes in the metal grains. These thin films are concluded to have the feasibility of application to optical disk memories of the laser heat-mode type.
Theory of rotating mirror Q-switching in a helical transversely excited CO2 laser
Authors: Nundy U. , Chatterjee U. K.
Published: February 2003

In a rotating mirror Q-switching scheme under suitable experimental conditions an effect termed ‘‘mode sweeping’’ can play an important role in the buildup of the laser pulse. A theoretical model has been developed which takes into account this effect and also considers the nonuniform gain distribution resulting from the helical arrangement of the discharge pins. A number of approximations simplify the computation. The agreement between theory and experiment is excellent. The basic limitation of the theory is discussed. The discrepancies between theory and experiment can be attributed to the neglect of the ‘‘thermal lensing’’ in the gas medium, that normally occur in such discharges.
Second-harmonic diffraction field in nonlinear propagation of transversely limited surface acoustic wave beams
Authors: Alippi A. , Palma A. , Palmieri A. , Socino G. , Verona E.
Published: February 2003

The study of the Fresnel field of the second harmonic of a finite width surface acoustic wave, parametrically generated through the nonlinear interaction on a LiNbO3 substrate, is performed both theoretically and experimentally. Theoretically, a model has been developed which computes the acoustic field at each point as given by the sum of all the second-harmonic plane wave fronts nonlinearly generated by the interaction of any two plane wave fronts present in the fundamental wave angular spectrum. Experimentally, a phase contrast optical probing technique has been used, which permits separating the contributions of the second-harmonic field from that of the fundamental wave. Theoretical and experimental transversal amplitude profiles of the surface acoustic wave second-harmonic field are presented, relative to the case of an acoustic beam launched from a 24-wavelength-wide transducer on the free surface of a LiNbO2 sample, at the fundamental frequency of 34.5 MHz.
Investigation of gaseous heat transfer between surfaces by photoacoustic effect
Authors: Monchalin J.-P. , Parpal J.-L. , Bertrand L. , Gagné J.-M.
Published: February 2003

The heat transfer, by the interstitial gas, between two metallic surfaces in contact has been investigated by photoacoustic effect. The thermal conductance is determined by interpreting the phase data obtained by varying the laser source modulation frequency. Our experimental results confirm the hypothesis, implicit in most theoretical formulations of the photoacoustic effect, that the surface thermal resistance is generally negligible.
Target design of an archival electron beam memory
Authors: Wolfe J. C.
Published: February 2003

A new concept for archival electron beam accessed memory has recently been proposed. In the write mode, a high intensity electron beam selectively melts columnar bits in a two-dimensional lattice which is supported by a thin membrane. The force of surface tension transforms the melted columns into droplets. In the read mode, a low intensity beam interrogates the bits. Transmission contrast is generated by the difference in cross-sectional area of the columnar and spherical bits. We study the relationship between physical target parameters and system performance of such a memory. Monte-Carlo simulation of the electron beam-target interaction has been used to design a target consistent with the following system performance goals: (a) 107 bit/sec data rate, (b) 1010 bit/cm2 data density, and (c) 10−9 error rate.
Properties of the electromagnetic wave propagation in a helix-loaded waveguide
Authors: Uhm Han S. , Choe Joon Y.
Published: February 2003

Properties of the electromagnetic waves propagating through a helix-loaded waveguide are investigated, including the important influence of the outer conducting wall on the dispersion properties. A closed algebraic dispersion relation for the eigenfrequency ω and the axial wave number k is obtained for arbitrary azimuthal harmonic number. It is shown that in the limiting case, where the outer conducting wall approaches close to the helix, this dispersion relation is reduced to three distinctive modes. These are the transverse electric mode, the transverse magnetic mode, and the helix mode, which can be further simplified to straight lines in the (ω, k) parameter space. Numerical investigation of the dispersion relation is also presented.
A technique for inferring outward displacement of magnetic flux surfaces in toroidal plasmas, using multichord interferometry
Authors: Jacobson Abram R.
Published: February 2003

When flow can be neglected and when heat conduction parallel to the magnetic field is sufficiently strong, a confined plasma’s surfaces of constant magnetic flux are also surfaces of constant plasma density. Thus, in principle, measurements of the internal density asymmetries can also determine the internal profile of flux-surface displacement along major radius caused by toroidal effects. This paper develops a simple algorithm for doing this with multichord interferometer data in toroidal plasmas having circular minor cross section and illustrates the technique with data from the ZT-40M reversed-field pinch.
Imperfections in the crystal structure of Cd1−xMnxTe
Authors: Wu A. Y. , Sladek R. J.
Published: February 2003

We have made x-ray diffraction and etching studies of Cd1−xMnxTe samples with x≥0.05, and optical transmission studies when x≥0.45. We found that samples with x=0.05 and x=0.57 were zinc-blende-structured monocrystals, but that those with x=0.20 and 0.35 lacked four-fold symmetry and were heavily twinned. Those with 0.45 and 0.65 showed 6-mm symmetry which is most likely due to multiple twinning, but could be due to the presence of hexagonal crystallites with a c/a ratio of (6)1/2.
Buckling instabilities in cholesterics
Authors: Scaramuzza N. , Bartolino R. , Barbero G.
Published: February 2003

Quantitative measurements on the threshold of mechanically induced buckling instabilities are presented. We report the data obtained by light scattering experiments, and by optical spectroscopy measurements. We verify de Gennes’ model for this instability qunatitatively, in analogy with the smectic A case, obtaining an equivalent penetration length of the order of the cholesteric pitch length. The distribution of the deformation versus the position of the light spot on the sample is reported.
Switching characteristics of a bistable cholesteric twist cell
Authors: Heffner W. R. , Berreman D. W.
Published: February 2003

We recently described the structure of a liquid-crystal twist cell possessing bistable states while a holding field is applied. We now present detailed measurements of operating parameters and switching characteristics. The voltage range for bistable operation and the switching times were determined as functions of temperature and of cell thickness to pitch ratio. We have shown that the holding voltage cell can be matrix addressed using either 2:1 or 3VH matrix addressing, although the cell is best suited for 3VH addressing. Using E-7 liquid-crystal mixture doped with cholesterol nonanoate, a 15 μ cell can be written with a 20-msec pulse of three times the holding voltage or about 5 V.
Gap-states measurement of chemically vapor-deposited amorphous silicon: High-frequency capacitance-voltage method
Authors: Sasaki Goro , Fujita Shizuo , Sasaki Akio
Published: February 2003

A high-frequency (1 MHz) capacitance-voltage method is proposed to measure the gap-state density in a chemically vapor-deposited (CVD) amorphous (a-)Si. The density is derived from the analysis of high-frequency capacitance-voltage characteristics of a CVD a-Si and n-type crystalline (c-)Si junction. The density near the Fermi level in the CVD a-Si deposited at 550 °C is obtained of the order of 1017∼1018 cm−3 eV−1. Further, the energy band diagram of CVD a-Si and c-Si junction is described, and the electron affinity of CVD a-Si is derived to be less than 3.75 eV.
Electron traps in ZnSe grown by liquid-phase epitaxy
Authors: Kosai K.
Published: February 2003

Deep electron levels in n-type liquid phase epitaxial ZnSe have been studied using thermally stimulated capacitance, photocapacitance, and deep level transient spectroscopy (DLTS). Electron traps have been observed with activation energies of 0.17, ∼0.3, 0.64, and 1.4 eV below the conduction band. The electron emission-rate dependence on temperature as measured by DLTS has been found to vary among samples for the 0.3 eV level.
The work function of sputter-formed Re-1% Pt. II. Recrystallized surface
Authors: Gordon R. L.
Published: February 2003

The work function and surface composition changes occurring on a recrystallized surface of a sputter-formed Re-1% Pt alloy have been measured as a function of temperature. The work function was found to decrease with heat-induced segregation of Pt to the surface of the alloy. This behavior is the same as reported previously for a surface of the same material showing minimal recrystallization and can be explained by the Topping model of dipole formation. The dipole moment and polarizability of the surface Pt obtained from the combined data for both surfaces are (8.1±1.5)×10−30 C-m and (28.1±6.3) Å3, respectively. In cases where the surface Pt concentration was highly nonuniform, the derivative curve of the diode characteristic exhibited structure due to the patch effect. This structure in the data has been satisfactorily modeled by the superposition of two patches, each having a Gaussian work function distribution. Negative portions of the derivative curve were attributed to electron channeling and reflection.
Pd–thin-SiO2–Si diode. I. Isothermal variation of H2-induced interfacial trapping states
Authors: Keramati Bahman , Zemel Jay N.
Published: February 2003

The current-voltage characteristic and the small-signal frequency-dependent admittance response of Pd–thin-SiO2–Si diodes are measured. It is found that the characteristics undergo reversible changes by switching the ambient gas between hydrogen diluted in nitrogen and pure oxygen. Dispersive peaks and structures are observed in the C-V and G-V plots obtained under hydrogen which are absent under oxygen. It is concluded that hydrogen-generated interfacial trapping states are responsible for the induced electrical changes in the Pd–thin-SiO2–Si diodes.
Pd–thin-SiO2–Si diode. II. Theoretical modeling and the H2 response
Authors: Keramati Bahman , Zemel Jay N.
Published: February 2003

A method is developed to calculate the dc response and the small signal admittance of a metal-insulator-semiconductor (MIS) diode under a given applied voltage. The method is based on the quasiequilibrium approximation of Garrett and Brattain. It starts with basic equations and solves for the diode response in a self-consistent manner. The position of different quasi-Fermi levels at the Si-SiO2 interface is plotted as a function of the applied voltage. It furnishes a useful scheme for the interpretation of the theoretical calculations and provides new insight into the behavior or real MIS diodes. Direct comparison of the admittance response of the Pd–thin-SiO2–Si diodes and the corresponding theoretical characteristics reveal that hydrogen is actively involved in the development of at least two interfacial traps at the Si-SiO2 interface with approximate energies of 0.65 and 0.4 eV below the Si conduction band with saturated densities of about 2×1012 cm−2.
Superconducting transition temperatures of thin V3Si layers formed by the interaction of V films with thinly oxidized Si wafers
Authors: Oya Gin-ichiro , Inabe Hiroto , Onodera Yutaka , Sawada Yasuji
Published: February 2003

Superconducting thin V3Si layers with overlying VOx layers have been formed by the interaction of thin evaporated V films (300–3500 Å thick) with thinly (∼100 Å thick) oxidized Si wafers between ∼650 and ∼1000 °C. V3Si layers having thicknesses up to ∼800 Å have been obtained. The growth of the V3Si layers has been observed to depend on the annealing temperature and time, and to be affected by the oxygen concentration in VOx layers formed on the V3Si layers, and by the disappearance of SiOx layers on the Si wafers. The transition temperatures of the V films annealed on the oxidized Si wafers can be interpreted with regard to proximity effects between the V3Si layers formed and overlying VOx layers simultaneously formed, and between the V3Si layers and underlying Si-richer VSix layers additionally formed in the films.
Effect of additives on the properties of zinc-manganese ferrite
Authors: Rao K. H. , Gaur N. K. , Aggarwal K. , Mendiratta R. G.
Published: February 2003

The dielectric properties and the variation in lattice constant, Curie temperature, saturation magnetization, and initial permeability have been investigated for various dopant concentrations of Cr, Al, and In in zinc-manganese ferrite. Possible mechanisms contributing to conduction process and dielectric properties are discussed. From the temperature dependence of dielectric relaxation, activation energies for various samples have been obtained and compared with those obtained from the observed temperature dependence of dc resistivity.
The kinetics of pressure-induced α→ω transformation in Ti
Authors: Singh A. K. , Mohan Murali , Divakar C.
Published: February 2003

The kinetics of the pressure-induced α→ω transformation in titanium is reported in the pressure range 5–9 G Pa. The occurrence of this transformation under shock loading has been discussed using the observed pressure dependence of the kinetics.
Molecular beam epitaxial growth of lattice-mismatched In0.77Ga0.23As on InP
Authors: Chai Young G. , Chow Robert
Published: February 2003

It is demonstrated that lattice-mismatched InxGa1−xAs (x = 0.77) can be grown by molecular beam epitaxy on InP substrates with mobilities and photoluminescence (PL) intensities comparable to those of the lattice-matched InxGa1−xAs (x = 0.53). This was accomplished using a graded buffer layer and superlattice dislocation barrier between the substrate and the In0.77Ga0.23As layer. The lattice-mismatched layers have Hall mobilities of 7000–8000 cm2/V sec at room temperature and photoluminescence intensities at liquid nitrogen temperature of 1/2–1/3 of that from the lattice-matched InxGa1−xAs. We also found that the conventional AB etch is not a reliable guide to the electrical and optical qualities of InGaAs layers.
Hole injection into silicon from ions in solution
Authors: Morrison S. Roy
Published: February 2003

It is shown that ions in solution with an ’’energy level’’ below the valence band edge of n-silicon can inject holes, whereas weaker oxidizing agents in solution cannot inject holes. The injection is detected by the collection of the holes at the far side of the thin silicon wafer using a reverse biased silicon/electrolyte Schottky barrier diode.
Photoconductivity effects in extremely high mobility modulation-doped (Al,Ga)As/GaAs heterostructures
Authors: Drummond T. J. , Kopp W. , Fischer R. , Morkoç H. , Thorne R. E. , Cho A. Y.
Published: February 2003

Single period modulation doped Al0.35Ga0.65 As/GaAs heterostructures were grown by molecular beam epitaxy. The mobilities and sheet carrier concentrations were measured as a function of lattice temperature in the dark and in room light. Mobilities as high as 8490, 105 000, and 221 000 cm2/Vs at 300, 78, and 10 K, respectively, were obtained for samples measured in the dark. When measured in light, these mobilities increased to 9090, 136 000, and 286 000 cm2/Vs at the same respective temperatures. In all cases the sheet carrier concentrations were between 4.5×1011 and 9.5×1011 cm−2. These values represent one of the best dark values reported to date and are significant with respect to field effect transistor applications. The 300 K mobility of 9090 is equivalent to the best mobilities obtained in ultrapure GaAs (n⩽1013 cm−3). The change in the mobility and sheet carrier concentration is the result of a persistent photoconductivity effect which is attributed to the ionization of electrons from traps in the (Al,Ga)As layer. Electron hole pair generation, though smaller, also affects the electron mobility because of increased screening.
Impact ionization at very low voltages in silicon
Authors: Eitan B. , Frohman-Bentchkowsky D. , Shappir J.
Published: February 2003

Impact ionization in germanium and silicon has been the subject of extensive theoretical and experimental work. The general agreement in the literature for the value of the threshold energy for impact ionization is 1.5 times the energy gap (EG) at room temperature which corresponds to 1.65 eV in the case of silicon. In this work, using a metal semiconductor field effect transistor (MOS device), as a sensitive tool for detecting small multiplication currents, impact ionization is investigated in a region where the total potential drop over which carriers are accelerated is less than the threshold energy for impact ionization. Impact ionization currents are detected for potential drop as low as 1.1 V. The positive temperature coefficient in this region suggests that the initial thermal distribution of the electrons dominates impact ionization for very low accelerating voltages.
Interface morphology of epitaxial growth of Ge on GaAs and GaAs on Ge by molecular beam epitaxy
Authors: Chang Chin-An
Published: February 2003

Interface morphology of the molecular beam epitaxial growth of Ge on (100) GaAs and of GaAs on (100) Ge at 400 °C has been studied by reflection high energy electron diffraction. The (100) Ge surface shows a (2×2) reconstruction pattern. A smooth and planar growth of Ge on GaAs is observed; growth of GaAs on Ge, however, shows a rougher surface with a roughness estimated to be several angstroms which is in agreement with our studies on the Ge-GaAs superlattices using other techniques.
Comment on the complex-dielectric constant of sea ice at frequencies in the range 0.1–40 GHz
Authors: Farrelly B. A.
Published: February 2003

A modification is suggested to the model of Vant, Ramseier, and Makios [J. Appl. Phys. 49, 1264 (1978)] for the dielectric constant of sea ice.
Photoacoustic phase signatures of closed cracks
Authors: Kuo P. K. , Favro L. D. , Inglehart L. J. , Thomas R. L. , Srinivasan M.
Published: February 2003

The photoacoustic phase signatures of closed cracks are calculated and compared with experimental observations. The differential signals from near subsurface lateral cracks are advanced in phase by 45° with respect to the background signal, in contrast to the 45° lag in phase observed for a near lower surface step.
Hall effect and mobility in heterojunction layers
Authors: Keever M. , Drummond T. J. , Morkoç H. , Hess K. , Streetman B. G. , Ludowise M.
Published: February 2003

A method for uniquely determining the mobilities and carrier concentrations of layers in a multilayer heterostructure is shown. Calculations are presented which use hot electron measurements in addition to Hall effect data to evaluate these quantities for a superlattice with two characteristic carrier concentrations and mobilities which cannot be determined from the Hall effect results alone.
Diffraction of ion-acoustic waves
Authors: Okutsu E. , Nakamura Y. , Lonngren K. E.
Published: February 2003

The diffraction of an ion-acoustic wave from an obstacle is experimentally examined. The measured diffraction pattern is compared with the measured radiation pattern from an equivalent source.
Techniques for producing uniform linear filamentary laser sparks
Authors: Schmieder Robert W.
Published: February 2003

Experimental techniques are discussed for producing uniform linear filamentary laser sparks suitable for use as an imaging probe of nonuniform gases and other applications. A new technique is described which is based on controlling the laser flux as the breakdown front propagates through a focus. Several methods of initiating the filaments are described.
One-dimensional static sheath characteristics
Authors: Nightingale J. L. , Ault E. R. , Mondelli A. A.
Published: February 2003

The boundary layer between an electrode biased to a large negative potential (relative to the electron temperature eφ≫kTe ) and a collisionless argon plasma (n∼1×109 cm−3, kTe ∼2.5 eV) was studied using Langmuir probes. A simple model based on Child’s law, including finite electron temperature effects, was fit to data obtained from both cold and emitting probes. A convenient method was developed to locate the sheath edge using cold probes. The emitting probe experiments demonstrated what we believe is a new technique for measuring the potential within the non-neutral sheath region.
Simple approximate treatment of unipolar space-charge-dominated coronas: The Warburg law and the saturation current
Authors: Sigmond R. S.
Published: February 2003

Unipolar space-charge distribution ρ(t) drifting with constant ion mobility μ in gas under time and space dependent electric fields will evolve according to the unipolar charge drift formula [1/ρ(t)]−[1/ρ(t0)] = (μ/ε0)(t−t0), neglecting diffusion effects. This general formula is especially useful as a starting point for approximate treatment of space-charge effects, both in ion drift and diffusion experiments, and in electrical coronas. A first simple derivation of an equivalent of the Warburg cos5ϑ current-density distribution for point-to-plane coronas is given, together with a formula for the maximum possible unipolar ion current (the unipolar saturation current) Is ≊2με0 V2/d, for a given corona voltage V and point-to-plane distance d. It is demonstrated that corona currents in excess of this limit always involve free electron or bipolar conduction phenomena, like streamers.
Alignment signals from silicon tapered steps for electron beam lithography
Authors: Lin Yi-Ching , Neureuther Andrew R. , Adesida Ilesanmi
Published: February 2003

Monte Carlo simulations based on a continuous slowing-down approximation (CSDA) model have been used along with experiment to study the alignment signals formed by electrons that are backscattered from anisotropically etched bare-silicon tapered step marks. The CSDA model is demonstrated to be useful for the study of electron backscattering, particularly for materials with low atomic number. It is shown that a step angle of 54.7° gives a backscattered electron signal close to the maximum and that universal curves for the effects of step height and beam voltage on contrast and average signal slope can be obtained by normalizing to the Bethe range. Alignment signals in ternary takeoff angles and quadrantal azimuthal angles are studied. The tradeoff in expanded signal-to-noise ratios for various detector angular configurations and for processed signals is examined. The detector scheme using low takeoff angles in the azimuthal quadrant facing the step is found to be the best. Experimental results from an ETEC Autoscan Scanning Electron Microscope (SEM) confirm may theoretically predicted aspects of alignment signals. The crystallographic effect of electron channeling which is not considered in the Monte Carlo simulation is evaluated experimentally.
Electric-field-induced texture and phase transformation of liquid-crystal films
Authors: Lin-Hendel Catherine G.
Published: February 2003

The electric-field-induced liquid-crystal (LC) cholesteric-to-nematic (C-N) phase transformation and its relaxation (N-C) are examined using the anisotropic color absorption properties of a dichroic dye dopant. A tristability is observed. The stable memory associated with the tristability has potential application to display devices. The N-C relaxation characteristics are found to be related to the ratio of LC-film thickness to pitch length (d/p).
Thermally stimulated processes involving defects in γ- and x-irradiated spinel (MgAl2O4)
Authors: Lorincz A. , Puma M. , James F. J. , Crawford J. H.
Published: February 2003

Thermally stimulated conductivity (TSC) and thermally stimulated luminescence (TSL) of spinel single crystals exposed to ionizing radiation have been studied. TSC exhibits peaks at 70, 125, and 340 °C whereas TSL peaks occur at 70 and 260 °C. The 70 °C peak has an activation energy of 0.95 eV and is due to electron release; it has two main spectral components at 260 nm (4.8 eV) and 310 nm (4.0 eV) due to electron capture at trapped holes. The 260 °C TSL peak is broad but singly activated (1.5 eV activation) and is dominated by 710 nm (1.75 eV) and 520 nm (2.39 eV) emission due to hole capture at Cr2+ and V2+, respectively. The broad 340° TSC peak appears to contain a substantial contribution due to electron release in the 240–310 °C range which makes only a small contribution (260 and 310-nm light) to the TSL peak in this region. Dose dependence and room-temperature decay indicate that initially a substantial portion of the 260-nm afterglow is due to tunneling recombination.
Microstrain behavior of nickel single crystals in stage II deformation
Authors: Pinatti D. G. , Roberts J. M.
Published: February 2003

The microstrain damping loops in Ni single crystals prestrained between 10 to 24% in stage II have been studied as a function of stress amplitude (in the range 9.8–78.4 MPa) and temperature in the range 77–300 K. The isothermal modulus defect in this prestrain range decreases from about 20–10% and appears to be associated with bowing of the primary dislocations. Experiments performed with and without a magnetic field suggest that the total microstrain decrement can be decomposed into magneto-elastic, hysteretic, and relaxational components. The magneto-elastic contribution is ≃0.10 of the observed decrement and is independent of temperature. The relaxational contribution appears to be negligible at room temperature. The predominant hysteretic contribution to the observed decrement is analyzed according to the theory proposed by Roberts which deals with the hysteresis associated with primary dislocation breakaway from attractive dislocation junctions. Good agreement between theory and experiment is found for the hysteresis.
Production and annealing of ion-bombardment damage in silicides of Pt, Pd, and Ni
Authors: Tsaur B-Y. , Anderson C. H.
Published: February 2003

Sheet resistance measurements on polycrystalline films of seven transition-metal silicides have been used to study the production of damage by Ar+-ion bombardment. The sensitivity of the compounds to bombardment, as measured by the relative increase in resistance for a given ion dose, increases in the following order: Pd2Si, Pt2Si, PdSi, Ni2Si, PtSi, NiSi, NiSi2. The heat of formation per metal atom, which is believed to be correlated with the degree of covalent bonding, increases in the same order. In experiments on films of Pd2Si, PtSi, and NiSi2, the difficulty in removing bombardment damage by thermal annealing was found to increase in the same order as the sensitivity to bombardment.
Temperature rise induced in Si by continuous xenon arc lamp radiation
Authors: Lietoila A. , Gold R. B. , Gibbons J. F.
Published: February 2003

It is shown that practical beam annealing of silicon can be accomplished with a high intensity arc lamp. The use of a one-dimensional, steady-state solution for temperature is justified. The Kirchhoff transform is utilized to include the temperature dependence of the thermal conductivity. Surface temperatures produced by a xenon arc lamp are calculated for 300- and 375-μm thick silicon samples, using substrate temperatures of 350 and 500 °C. It is shown that substantial reduction of the radiation intensity required for a given surface temperature can be obtained by placing a quartz wafer between the silicon sample and the heat sink.
Laser processing for high-efficiency Si solar cells
Authors: Young R. T. , Wood R. F. , Christie W. H.
Published: February 2003

High-efficiency silicon solar cells can be fabricated by ion implantation followed by pulsed laser annealing. The proper choice of implantation parameters (energy and dose), laser energy density, substrate temperature, etc., and the improvement of the minority carrier diffusion length of the starting material are important factors in obtaining high efficiency cells. In this paper, we report on experiments which show that substrate heating during pulsed laser annealing can improve the electrical properties of the emitter regions of solar cells. We have also found that the open circuit voltage and the fill factor of ion-implanted, laser-annealed cells can be improved by increasing the emitter dopant concentration, whereas the short circuit current remains fairly constant; these results are in only qualitative agreement with theoretical predictions. By using ion implantation followed by laser annealing to form p-n junctions, laser damage gettering to enhance the minority carrier diffusion length, and laser-induced diffusion for incorporating back surface fields, Si solar cells with efficiencies of over 16% AM1 have been obtained.
Heterojunction phototransistors for long-wavelength optical receivers
Authors: Campbell J. C. , Ogawa K.
Published: February 2003

We demonstrate by measurement and analysis that previously reported InP/InGaAs heterojunction phototransistors are promising photodetectors for long-wavelength optical receivers. The gain characteristics of these devices are shown to reflect the benefit of a wide band-gap emitter as well as the effects of recombination centers near the base-emitter heterojunction. In order to analyze the noise characteristics we derive a model which accounts for the three principal noise sources: the shot noise of the base current, the shot noise of the collector current, and the thermal noise of the load resistor. Using this model and experimental device parameters, we calculate the sensitivity of an optical receiver which utilizes a heterojunction phototransistor. This calculation indicates that the performance of this monolithic device can be as good as or exceed that of a hybrid p–i–n photodiode/field effect transistor-preamplifier combination.
Thermal focusing of a doughnut-shaped laser mode
Authors: Soni V. S. , Nayyar V. P.
Published: February 2003

In this communication thermal focusing of a doughnut-shaped mode around the points of irradiance maxima has been studied. Relative variation of axial and extraparaxial irradiance with the depth of penetration inside the medium has been assessed. The effect of initial ellipticity in the beam shape on the nonlinear behavior of the axial irradiance has also been studied.
Determination of mean and deviatoric stresses in shock loaded solids
Authors: Chartagnac P. F.
Published: February 2003

Models for the behavior of solids submitted to shock waves include an equation of state and a plastic yield surface, which represents the plastic potential. The general purpose of this work concerns various methods used to obtain these equations by means of the determination of the mean and deviatoric shock streeses. Emphasis is placed on the method of ’’piezoresistive deviatoric gauges’’ that we have been using since 1973. This method does not include any theoretical hypothesis, and is suitable for all materials that can be gauged. Examples of applications on polymethyl metacrylate, limestone, and steel are reported and show that the precision of the piezoresistive deviatoric gauges method depends upon the material, namely the deviator magnitude, and upon the stress range explored.
On the dynamical response of particulate-loaded materials. II. A theory with application to alumina particles in an epoxy matrix
Authors: Drumheller D. S.
Published: February 2003

If stiff solid particles are tightly packed into a soft matrix material, the response of the composite material cannot be modeled by simple mixing rules. The loads resulting from interparticle contact give rise to a complex response which includes dilatancy of the mixture during shearing. A three-dimensional theory which includes the interparticle contact stresses is derived and applied to a mixture of alumina particles in epoxy. The stress wave response of this mixture is studied. These studies include a detailed comparison to the pressure-shear experiments of Chhabildas and Swegle contained in Part I of this work. [J. Appl. Phys. 53, xxx (1982)].
A technique for investigating the properties of surfaces, thin films, and interfaces by means of a mechanical marginal oscillator
Authors: Miller G. L. , Soni M. , Fenstermacher R. L.
Published: February 2003

Surface modification techniques such as ion implantation, laser alloying, and ion beam mixing are currently of interest in a variety of areas. Such procedures typically alter the physical and compositional structure of materials to a depth of less than ∼1 μm, thereby requiring surface-sensitive techniques to reveal the properties of the resulting systems. To this end a method has been devised in which a small mechanical marginal oscillator acts as a substrate for the material(s) of interest, allowing investigation of changes in specifically mechanical properties to be monitored in situ during ion implantation or other material modifying procedures.
The regrowth and impurity diffusion processes in the arc annealing of ion-implanted silicon
Authors: Lue Juh-Tzeng , Chao Chen-Chung
Published: February 2003

The strong diffusion model has been used to solve the one-dimensional heat conduction equation in the light-flash annealing of ion-implanted silicon. The threshold energy for surface melting, the depth of melting, the recrystallization velocity, and the dopant redistribution at different irradiation energy densities for a pulse duration of 100 μs have been computed. Liquid-phase impurity diffusion has been used for the calculation of dopant distributions after arc annealing.
Waveguiding in oxide-isolated stripe-geometry diode lasers
Authors: Manning Joanne S. , Olshansky Robert
Published: February 2003

The stimulated emission profiles of oxide-isolated double-heterostructure diode lasers with 8-μm stripes are predicted using a dielectric profile completely determined by measurement. The profiles inferred from the spontaneous emission vary as 1 − (‖x‖/w)α with α≅4. The current-induced changes in gain and index are determined from the Fabry-Perot mode spectrum. A simple model with no adjustable parameters is used to predict near- and far-field widths to within 6%.
Conductivity behavior in polycrystalline semiconductor thin film transistors
Authors: Levinson J. , Shepherd F. R. , Scanlon P. J. , Westwood W. D. , Este G. , Rider M.
Published: February 2003

CdSe thin film transistor (TFT) structures which have been ion implanted with 50 keV 52Cr, 50 keV 27Al, or 15 keV 11B have a very steeply rising conductivity above some threshold dose and exhibit modulated transistor characteristics over certain ranges of implant dose, even though there is no thermal annealing during or after ion implantation. These results are interpreted using a model based on grain boundary trapping theory. The dependence of leakage current on implant dose, and of drain current (at a fixed dose) on gate voltage are described very well by this model, when the drain voltage is very small. Using this simple model, the important parameters of the polycrystalline CdSe film, namely the trap density per unit area in the grain boundary, the donor density, grain size, and electron mobility can be deduced. The effect of thermal annealing on implanted and unimplanted CdSe TFT’s has also been studied and the model appears to give a general description of the conductivity behavior in polycrystalline semiconductor TFT’s. This is illustrated by applying the model to devices fabricated by other groups from polycrystalline CdSe, poly-Si and laser-annealed poly-Si semiconductor layers.
Formulation of normalized nonlinear free electron laser equations
Authors: Tang Cha-Mei , Sprangle P.
Published: February 2003

The general nonlinear self-consistent equations describing the FEL in the steady-state amplifying configuration is derived with the space-charge effects and all the efficiency enhancement schemes: (i) a spatially varying wiggler amplitude and/or period and (ii) a dc electric field Edc (z) = [−∂φdc /∂z]êz. All the efficiency enhancement schemes are shown to be somewhat equivalent. For a variable period magnetic wiggler, the FEL equations can be appropriately normalized to a three-parameter set of coupled equations. All operating regimes are covered by these normalized equations. The condition for space charge to be unimportant is given. In the absence of the space-charge effects, the three-parameter set of equations reduces to a two-parameter set. The inclusion of additional efficiency enhancement schemes increases the number of parameters to describe the FEL. Curves showing the efficiency, radiation amplitude, and growth rate will be presented.
Experimental investigation of electrical breakdown in nitrogen and oxygen induced by focused laser radiation at 1.064 μ
Authors: Stricker J. , Parker J. G.
Published: February 2003

The characteristics of laser-induced breakdown in N2 and O2 at a wavelength of 1.064 μ were investigated using 10-nsec pulses for pressures ranging from 1 to 50 atm. The pressure dependence of the experimentally determined threshold field intensities for these two gases is essentially the same except at the lowest pressures where the O2 values are slightly lower than those for N2. Comparison of this data with existing microwave data can be accomplished most directly by means of a ’’universal plot’’ of the type used effectively in the latter case. The general trends of the microwave and optical data are essentially the same; however, actual numerical values for the optical data tend to be lower than the corresponding microwave values by a constant factor of roughly 0.5. The fact that the two sets of data correspond so closely in spite of the large difference in frequencies has to be regarded as providing substantial evidence supporting the validity at optical frequencies of the cascade theory of breakdown used to interpret microwave breakdown measurements. Time-resolved and time-integrated emission spectra were analyzed, from which the electron density and temperature were obtained for the initial stage of spark development. The spectral characteristics, the electron densities, and temperatures are similar to those determined previously by other investigators for air.
Ion energy-dependent electrical properties of sulfur implants in GaAs
Authors: Yeo Y. K. , Kwor R. , Park Y. S.
Published: February 2003

The dependence upon ion energy of the electrical properties of sulfur-implanted GaAs was investigated. For low doses, electrical activation was found to increase with energy up to 300 keV and then decrease with increasing energy. A correlation was found between the activation dependence upon energy and upon dose. An activation efficiency of 80% was obtained for a dose of 4×1013/cm2 at 300 keV. The carrier-profile dependence upon the energy was also determined, showing a maximum carrier concentration of 1×1018/cm3.
On the measurement of barrier height in metal-insulator-semiconductor (GaAs) structures by internal photoemission technique
Authors: Arora B. M. , Srivastava A. K. , Guha S.
Published: February 2003

It is shown that photoexcitation of interface states which causes nonlinearity in the Fowler plot for Au-thin oxide-(n)GaAs structures can be reduced by the use of a thicker (∼500 Å) Au electrode. The linearity in the Fowler plot extends over a wider range of photon energy using this scheme and this allows accurate determination of barrier height.
Electrochromism of WO3/LiAlF4/LiIn thin-film overlayers
Authors: Oi Tetsu , Miyauchi Katsuki , Uehara Keiichi
Published: February 2003

A thin, amorphous LiAlF4 film, with lithium ion conductivity of 1×10−4 S/m at 25 °C, has been prepared by vacuum evaporation. Utilizing this thin film as a solid electrolyte, an ITO/WO3/LiAlF4/LiIn overlayer has been constructed (ITO: indium-tin-oxide). For it, the electrochromism of WO3 due to lithium ion injection was observed.
Reply to ’’Comments on ’Thermal oxidation of InP and properties of oxide film’ ’’
Authors: Yamaguchi Masafumi
Published: February 2003

Comments made for the infrared absorption data in our previous paper have pointed out that the assignments of thermally grown oxide products are in error. From comparing the infrared absorption spectra for the thermal oxide with those for In2O3, P2O5, and InP, and analyzing the electron diffraction data for the thermal oxide, it is concluded that conclusions reached in our previous paper have been conservative, and unknown infrared absorption band for the thermal oxide may originate from InPO4 as described in the comments.
Spin density waves in organic metals (invited)
Authors: Scott J. C.
Published: February 2003

The magnetic properties of the (TMTSF)2X family of organic conductors are reviewed. Susceptibility, ESR, and NMR measurements have led to the conclusion that the metal-insulator transition for X = PF−6, AsF−6, and SbF−6 is driven by the onset of a spin density wave. Near the transition temperature (TSDW), the ESR line shifts, broadens, and rapidly loses intensity. In the semiconducting phase of (TMTSF)2PF6 the static susceptibility is anisotropic and reveals a spin-flop transition at 6 kG. The increase in the proton NMR linewidth yields a value for the SDW amplitude of μ/μB∼ 10−1, in rough agreement with the prediction of mean field theory. Fluctuations near TSDW contribute to proton spin-lattice relaxation.
Solitons in an easy-plane ferromagnetic chain
Authors: Kumar P. , Samalam V. K.
Published: February 2003

We report here the results from an analysis of the mapping of an easy-plane ferromagnet on the sine-Gordon theory. The mapping is found to be inadequate except for very small velocities and magnetic field. The real system contains many rich and interesting features, including soft modes and instabilities that can be analyzed.
Correlation theory applied to the static and dynamic properties of EuO and EuS
Authors: Lindgård Per-Anker
Published: February 2003

The paramagnetic scattering was recently measured for EuO.1) It was found that spin-wave-like excitations develop for wave vectors approaching the zone boundary. The spectrum was found to be well described by damped harmonic oscillators (also called the two-pole approximation). This approximation was used previously in the correlation theory2) primarily to calculate static properties. Self-consistent dynamic and static calculations have here been performed for EuO, which is an ideal Heisenberg magnet with significant second-nearest-neighbor interaction (J2 = J1/5). The two-pole approximation describes accurately the correlation range, the static susceptibility, and the qualitative behavior of the dynamic properties (i.e., the wave vector at which peaks appear in the spectrum as a function of temperature). However, in order to also obtain the correct frequency scale it is necessary to use a cutoff of the spectrum at high frequencies, which cannot be seen experimentally, but which significantly influences the frequency moments. It was found that the finite J2 has significant importance for a comparison between theory and experiment. It is concluded that the calculation for a simple cubic n.n. magnet by Hubbard3) does not describe the EuO data accurately, neither with respect to line shape nor frequency scale. Significant differences are to be expected between EuO and EuS having opposite sign for J2.
Hysteresis losses and magnetic phenomena in oscillating disks of type II superconductors
Authors: Cave J. R. , LeBlanc M. A. R.
Published: February 2003

Hysteresis losses and the behavior of the magnetic flux threading superconducting disks of Nb oscillating slowly over various angular displacements in static magnetic fields H0 directed perpendicular to the axis of rotation have been investigated by continuously monitoring 〈Bz〉 and 〈By〉, the average components of the magnetic induction, in the plane of the disk, parallel and perpendicular to H0. A simple model proposed previously satisfactorily accounts for the initial changes, starting from various initial flux configurations, the subsequent cyclical behavior, and the hysteresis losses. Expulsion of flux from the disk occurs during part of the first oscillation, then the amount of flux threading the disk remains constant during the subsequent oscillations, although the orientation distribution of the flux profile undergoes spectacular periodic variations. The analysis shows that dψ/dx = ±k dB/dx describes the orientation of the sheets of flux lines with respect to H0 with distance from the flat surfaces. dB/dx is the critical gradient of flux density and k(T) is the shearing parameter of the flux lattice for the sample. The surface step, ignored in the previous work, is introduced in the model using simple approximations.
General theory of the coercive force due to domain wall pinning
Authors: Paul D. I.
Published: February 2003

Due to the nonlinear nature of the relevant mathematical equations, previous solutions to the geometrically simple problem of pinning of a 180° ferromagnetic domain wall by a single planar defect in an infinite medium contain the approximation of small deviations in the nature of the defect material relative to the host matrix. We have enlarged the theory of such domain wall pinning to include all magnitudes of deviation of the magnetic anisotropy Ki , magnetization Mi , and/or magnetic exchange energy Ai , characterizing the defect for all defect widths. In particular, we have obtained graphs for the resultant reduced coercive force hc = HcM1/K1 , due to such domain wall pinning, as a function of the dimensionless constants F = A2M2/A1M1 and E = A2K2/A1K1 and of the defect width, as well as graphs for the maximum obtainable coercive force as a function of F and E. (Here i = 1 represents the host material and i = 2 the defect.) As an example, we discuss these results in terms of applications to the Sm2(Co,Cu,Zr,Fe)17 hard magnetic materials.
Strained-layer superlattices from lattice mismatched materials
Authors: Osbourn G. C.
Published: February 2003

Results are presented from the first theoretical study of the electronic properties of strained-layer semiconductor superlattices made from lattice mismatched materials. The energy gaps and electronic states of GaAs-GaAs0.2P0.8 (100) superlattices are studied as a function of layer thicknesses using a tight binding model. The superlattice band gaps are found to depend on the layer thicknesses through quantum mechanical effects and through the strains in the layers.
Charge profile in thin layers of Al2O3
Authors: Kliem H. , Schmidt R. , Arlt G.
Published: February 2003

The distribution of trapped electrons with respect to space and energy in thin layers of aluminum oxide of MAOS (metal-aluminumoxide-siliconoxide-silicon) capacitors was studied by photoionization. The oxide layers were charged from the n-type silicon by high field injection in the dark. Afterwards it was possible to release more than 85% of the trapped carriers using photons with energies up to 4.2 eV. The measurements of both the flatband voltages and the discharge currents of several bands of photon energies yielded two parameters for the determination of the spatial distribution for the trapped electrons in each energy interval.