bluuebunny/crossref_metadata_2025 huggingface dataset:
Gain and saturation of the atomic fluorine laser
Authors: Sadighi-Bonabi R. , Lee F. W. , Collins C. B.
Published: February 2003

In this work a dilute fluorine plasma pumped by the ion-ion recombination of H+2 and F− has been operated as a pulsed amplifier. Two synchronously excited plasmas were produced by preionized discharges in an atmospheric electrical avalanche device switched by hydrogen thyratrons. Two principal outputs having wavelengths of 745 and 635 nm were obtained from the tube serving as an oscillator. These were dispersed so that they could be individually threaded through the second discharge. Calibrated attenuation of the beam from the oscillator subsequently injected into the amplifier provided data on the overall amplification ratio. From these data effective saturation intensities of 1.2 and 4.5 kW/cm2 were found for the transitions at 745 and 635 nm, originating on the 3p4P05/2 and 3p4S03/2 states of F*, respectively. Corresponding small signal gains were found to be extremely high, reaching 0.44 and 0.31 cm−1, for the two transitions, respectively.
Recording mechanisms in antireflection trilayer structures
Authors: Bell Alan E.
Published: February 2003

Any recording mechanism which produces a high-reflectivity spot by disrupting the interference condition which results in the initially low reflectivity of the trilayer structure is a potential mode of recording and data storage. Experimental results are presented for deep pit and bubble modes of recording. In the deep pit mode both the absorber and dielectric layers are melted so that the pit penetrates to the reflector layer. In the bubble mode, outgassing of the dielectric layer results in a micron-sized raised blister or bubble in the absorber layer. The bubble mode, in particular, offers the potential for high sensitivity and high SNR recording characteristics without the use of low melting point absorber layer materials.
Extended variational solution for scattering from flaws in plates
Authors: King R. B. , Fortunko C. M.
Published: February 2003

A variational solution is obtained for scattering of horizontally polarized shear (SH) waves from cracks in plates. The solution permits a trial function for the displacement jump across the crack in the form of a series with arbitrary coefficients to be inserted in the variational expression for the scattering coefficients. This multiple term variational solution is preferable to one-term solutions when increased accuracy is desired or when the form of the displacement jump across the crack is not apparent. Numerical results are presented for scattering from edge cracks in plates.
Dilatation wave/soliton dynamics in variable density flows
Authors: Hokenson Gustave
Published: February 2003

The dynamics of dilatation has been investigated for variable density flows which exhibit a temporal evolutionary character. In lieu of decomposing the conservation of mass equation (appropriate for strictly nondiffusive/incompressible flows) and utilizing div u = 0 to generate a Poisson pressure equation, the closure relation ’’small div u’’ was used. This suggests an approximate decomposition of the div u governing equation into a steady elliptic pressure equation and a time-dependent equation for nonacoustic waves which governs div u (herein denoted by Ω̃): (∂Ω̃/∂τ)−[1+∫Ω̃dx̃−(1/4 Re)(∂ lnρ̃/∂x̃)](∂Ω̃/∂x)=Ω̃2+(1/Re)(∂2Ω̃/∂Ω̃2), utilizing the exact equations of continuity and momentum. The solution of this (’’vorticity-like’’) equation provides information on how an initially small div u field evolves, frequently into a solitary wave. Should the dilatation remain ’’small,’’ rather than be (nonphysically) forced equal to zero, the full conservation relations may be utilized. However, if div u grows large, the elliptic pressure equation is inconsistent with the untampered governing equations. The motivation for this approach is to provide a structure within which: (1) small diffusive/compressibility effects may be studied, (2) the significance of div u physics, in flows which are traditionally treated as approximately dilatation free, may be analyzed, and (3) evolutionary pressure transport formalisms may be developed and evaluated for computational efficiency/accuracy and the inclusion of nonlinear acoustic waves.
Investigations on the fundamental longitudinal acoustic resonance of high pressure discharge lamps
Authors: Schäfer R. , Stormberg H.-P.
Published: February 2003

Cylindrical high pressure mercury discharge lamps were operated on a sinusoidal supply voltage at frequencies in the vicinity of their fundamental longitudinal acoustic resonance band. The sound spectrum emitted from the lamp allows the detection of pressure waves in the lamp gas volume. With this method it is shown that there are acoustic resonances which are not combined with visual arc instabilities. In this case the influence of the acoustic resonance on arc and wall temperature profiles was measured. The experimental results can be explained by an additional axial heat flow caused by the acoustic pressure waves.
Brillouin backscattering from a double-pulse CO2 laser incident on planar targets
Authors: Decoste R. , Lavigne P. , Pépin H. , Mitchel G. R. , Kieffer J.-C.
Published: February 2003

The Brillouin backscattering instability is studied for a range of preformed plasma conditions and using a CO2 laser in the 1012–1013 W/cm2 regime. A short prepulse is incident on a planar target ahead of the main-pulse to produce the preformed plasma. The instability appears in a short burst of back-reflected light. Saturation of the backscatter level is observed for an individual increase of the prepulse energy, main-pulse intensity, and prepulse-to-main-pulse delay. Ion Landau damping is strong and average back-reflected intensities are limited to less than 30% of incident. Backscattered light spectra suggest that the critical surface is involved in the backscatter process when the laser beam is at best focus onto the target surface. Otherwise, the spectral signature is similar to those obtained from underdense plasmas.
Cataphoresis and dissociation of dye vapors in a positive column of direct-current glow discharge
Authors: Sakurai Takeki , Watanabe Shinji
Published: February 2003

Small amounts of dye vapors are mixed with helium in a positive column of a direct-current discharge. The distributions of dye vapor from a central reservoir towards the anode and towards the cathode are asymmetrical due to cataphoresis. In addition to this, the concentration of dye vapor along the tube axis sharply decreases with distance form the reservoir due to dissociation by electronic collision. From the comparison between experimental and calculated results the degree of ionization α is estimated to be 10−3∼10−4 for 1,4-Di-[2-(5-phenyloxazolyl)]-benzene (POPOP) and 3×10−3 for perylene, and the cross section for dissociation by electronic collision σd is estimated to be 2×10−16 cm2 for both POPOP and perylene. The upper limit of pulse rise time, required to produce a dye vapor discharge with positive gain, is discussed in relation to the value of σd.
Threshold current for fireball generation
Authors: Dijkhuis Geert C.
Published: February 2003

Fireball generation from a high-intensity circuit breaker arc is interpreted here as a quantum-mechanical phenomenon caused by severe cooling of electrode material evaporating from contact surfaces. According to the proposed mechanism, quantum effects appear in the arc plasma when the radius of one magnetic flux quantum inside solid electrode material has shrunk to one London penetration length. A formula derived for the threshold discharge current preceding fireball generation is found compatible with data reported by Silberg. This formula predicts linear scaling of the threshold current with the circuit breaker’s electrode radius and concentration of conduction electrons.
Particle acceleration in the drift orbit cyclotron
Authors: Hong Ruey-Maw , Burke John M.
Published: February 2003

The drift orbit cyclotron was investigated both theoretically and experimentally. A drift orbit cyclotron was designed and constructed, and acceleration experiments using electrons in high vacuum were performed. Theoretical calculations using the guiding center approximation match the experimental results. Improvement of the acceleration efficiency was observed by using the stochastic acceleration technique.
Slow metastable atomic hydrogen beam by optical pumping
Authors: Harvey K. C.
Published: February 2003

A beam source of atomic hydrogen is described which produces metastable atoms in the 2S1/2 state by optical pumping. A beam flux of 1016 atoms/s is generated in the ground state. The atoms in the beam pass in front of a lamp producing Lyman-β (1026 Å) radiation, where some of them are excited to the 3P level and cascade with a branching ratio of 12% to the 2S1/2 state. The number of metastable atoms produced is measured by quenching them with an electric field and detecting the emitted Lyman-α (1216 Å) radiation. Beams of 106 metastable atoms/s were obtained. Using the Bethe-Lamb theory for the quenching process, a metastable beam effective temperature of 100 K was measured.
Ion beam transport in laser-initiated discharge channels
Authors: Olsen J. N. , Leeper R. J.
Published: February 2003

Inertial-confinement fusion reactors with light ion-beam drivers will require that several intense ion beams propagate a few meters from separate diodes to a single target. Each beam would be confined and guided by a laser-initiated z discharge in a background gas. In this experiment we have studied the transport of a proton beam in such a laser channel. A pulsed, line-tuned, CO2 laser triggers the discharge in 4–20 Torr of ammonia gas. When the discharge current reaches peak value, an ion beam is injected from a pinch-reflex ion diode on the Hydra accelerator. The transported proton beam is detected by nuclear activation of carbon targets. Total current transport efficiencies of up to 50% were achieved in 13–45 kA, one-meter-long discharges. The most reproducible results were found for discharge currents of less than 30 kA; framing photography shows that the channel is unstable for kink modes at higher currents. Conditions in the discharge which led to this kink instability are examined, and the implications for reactor studies are considered. Operational data for the pinch-reflex diode operating in a high-impedance mode are also presented.
Method for locating and characterizing neutron sources
Authors: Fleischer Robert L. , Paretzke Herwig G.
Published: February 2003

Counting neutron-induced tracks in plastics as a function of the orientation relative to the arrival direction of incident neutrons makes possible a rugged method of measuring the direction, fluence, and average energy of a directional flux of fast neutrons and the distance and strength of the source.
Microwave method for determining the electron density in a high-density plasma
Authors: Ghorai S. , Basu J. , Das S. K.
Published: February 2003

A microwave method for determining the electron density in a high-density plasma with or without a static magnetic field is presented. The method utilizes the cutoff frequency characteristic of a dielectric-rod waveguide embedded in the plasma, the mode of propagation along the waveguide being such that it corresponds to the TMom mode at cutoff. In certain cases the density can be calculated from simple formulae if the cutoff frequency is measured. The higher limit of the density that can be measured by usual microwave techniques can be increased considerably by using this method.
Observation of compressibility-related effects in shaped charge jet penetration
Authors: White III J. J. , Wahll M. J. , Backofen J. E.
Published: February 2003

Penetration results are reported for four low strength materials attacked by a non-precision, copper-shaped charge jet. The materials are methanol, Plexiglas, glycerol, and mild steel. The results are not entirely consistent with the recent compressibility-based predictions by B. S. Haugstad and O. S. Dullum [J. Appl. Phys. 52, 5066 (1981)] and by N. A. Zlatin and A. A. Kozhushko [Combust. Explos. Shock Waves USSR 16, 559 (1980)]. Methanol and Plexiglas have extraordinary penetration resistance due to a combination of shock wave formation, plastic flow resistance, vaporization, and decomposition. The more chemically stable glycerol has simpler behavior that is similar to mild steel.
Oxygen stabilization of molecular beam epitaxial Al-GaAs Schottky barrier heights
Authors: Okamoto K. , Wood C. E. C. , Rathbun L. , Eastman L. F.
Published: February 2003

Aluminum Schottky barrier heights (φn) to GaAs depend heavily upon the deposition conditions and the gallium arsenide surface stoichiometry. After annealing to approximately 320 °C diodes show φb approximately 0.69 eV in association with oxygen at the Al/GaAs interface. We infer that these ’’stabilized’’ barrier heights are associated with oxygen-induced surface-state pinning of the GaAs Fermi level. Al deposition on arsenic stabilized surfaces show variable barrier heights and no oxygen peak indicating variable Al induced states in intermediate AlGaAs layers between the Al and GaAs.
Molecular-beam epitaxial group III arsenide alloys: Effect of substrate temperature on composition
Authors: Wood Colin E. C. , Morgan David V. , Rathbun Lynn
Published: February 2003

Ion dechanneling and sputter-auger spectroscopy have shown the composition of molecular-beam epitaxial ternary group III arsenide alloys to depend upon the growth temperature in a manner consistent with preferential congruent desorption of the more volatile group III element.
Effect of energy-band structures on the propagation of ultrasound in degenerate semiconductors
Authors: Wu Chhi-Chong , Tsai Jensan
Published: February 2003

The effect of parabolic and nonparabolic band structures on the propagation of ultrasound at an angle ϑ relative to the direction of a dc magnetic field B in a degenerate semiconductor such as n-type InSb is investigated by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. Numerical results show that the absorption coefficient and change in sound velocity depend strongly on the direction of the propagation of ultrasound relative to the magnetic field for both parabolic and nonparabolic band structures. However, the absorption coefficient and change in sound velocity for the nonparabolic band structure will diminish and become small in the intermediate-magnetic-field region when the angle ϑ is larger than 30°.
Spectral response of Schottky diodes on hydrogenated amorphous silicon: Effects of gap states
Authors: Arene E. , Baixeras J. , Longeaud Ch.
Published: February 2003

The spectral response of Schottky diodes on hydrogenated amorphous silicon has been determined between 1 and 3.5 eV. An anomalous absorption peak clearly appears at low energy from these experiments. We have demonstrated that this peak is due to optical transitions from localized states near the valence band to the conduction band, and is connected with hole trapping during the transport.
Electron paramagnetic resonance of extended defects in semi-insulating GaAs
Authors: Goltzene A. , Meyer B. , Schwab C.
Published: February 2003

The temperature dependence, over the 4.2–100 K range, of the narrow EPR line, labeled X, with an isotropic value of g = 2.002 has been investigated in a semi-insulating GaAs:Cr sample. From its Curie-Weiss behavior, leading to a (T+13.1)−1 law, it is concluded that it may result from antiferromagnetic exchange coupled spins, originating from dangling bonds located on extended defects present in the crystal.
Modification of open-circuit voltage of metal-insulator-semiconductor solar cells due to a nonuniform insulating layer
Authors: Chau H. L. , Cheng Y. C.
Published: February 2003

The effect of nonuniformity of the insulating layer on metal-insulator-semiconductor, open-circuit voltage is examined. It is based on a simplified model in which insulator limits the dark current via different effects. The enhancement in Voc could be greatly degraded by surface roughness.
Concept for energy-storage rings at 10–100 MJ
Authors: Felber F. S. , Hunter R. O.
Published: February 2003

A concept is considered for storing 10–100 MJ of electrical energy in a relatively lightweight and compact device. Energy is stored as electron kinetic energy confined in the vertical betatron field of a toroidal ring. Electrons are injected into a ring at full voltage but low current and low power. The stored electron energy is released on a fast time scale. Synchrotron radiation, wall fields, and instabilities constrain the energy that can be stored in each ring.
Normal modes of magnetic domain wall motion in a confined stripe domain lattice
Authors: Spreen J. H. , Argyle B. E.
Published: February 2003

We report the observation of standing wave modes in an array of stripe domains confined by a pair of parallel cracks in a Gd, Ga:YIG film. These modes appear in the response spectrum of the confined lattice as shallow minima or maxima at frequencies lower than that of the usual domain wall resonance peak. A simple model, analogous to the forced response of a membrane clamped at the edges, fits the spatial patterns of wall motion observed at the frequencies of the maxima and minima. Experimental frequency-wave vector values, interpreted with guidance from this analogy, provide the first experimental dispersion curve for a stripe domain lattice. We compare this result with recent theoretical calculations. The experimental value of the uniform mode frequency is 41.5 ± 0.2 MHz, with a long wavelength group velocity of 330±50 m/sec. A surprising conclusion from the observed extrema of the spatial patterns is that the damping of the waves is an order of magnitude less than expected from the damping of the uniform mode. The estimated decay length for a propagating wave is 400 μ.
Electron beam method for detecting charge distributions in thin P
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Authors: Sessler G. M. , West J. E. , Seggern H. von
Published: February 2003

An electron beam method is used to determine the spatial distribution of real and polarization charges in electroded 24-μm Polyethyleneterphthalate iephthalate films. The method consists of irradiating the samples with a monoenergetic electron beam whose energy is increased in steps. Evaluation of the currents from the nonirradiated electrode yields the charge distribution with a resolution of about 25% of the respective depth. Results for samples charged by electron beam in open circuit show relatively narrow distributions with a width corresponding to about half the maximum penetration depth.
Piezoelectricity of a high-content lead zirconate titanate/polymer composite
Authors: Yamada Takeshi , Ueda Toshinobu , Kitayama Toyoki
Published: February 2003

A binary system consisting of polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT) powder was investigated to determine its dielectric constant, piezoelectric constant, and Young’s modulus. An expression was obtained for the piezoelectric constant, and expressions for the dielectric constant and Young’s modulus were also mentioned. The calculated values had good agreement with the observed values for the composite with a large PZT volume fraction. The dielectric constant and the piezoelectric constant were 152 and 48.3×10−12 C/N, respectively, for the composite with the PZT volume fraction of 0.67. Changing the mixing ratio of PVDF and the fluorine elastomer, Young’s modulus was varied without changing the piezoelectric constant.
Index of refraction of n-type InP at 0.633- and 1.15-μm wavelengths as a function of carrier concentration
Authors: Whalen M. S. , Stone J.
Published: February 2003

Accurate values of the refractive index of n-type InP samples have been measured at two wavelengths, n = 0.633 μm and 1.15 μm, using a near-Brewster-angle reflectivity technique. For highly doped samples (carrier concentration ≳1018 cm−3) a relationship between carrier density and refractive index has been observed which can be explained in terms of conduction band filling.
Laser writing on silicon-metal bilayers for optical storage. II. Microscopic study
Authors: Herd S. R. , Tu K. N. , Ahn K. Y. , Di Stefano T. H. , Mazzeo N. J.
Published: February 2003

The nature of structural changes caused by laser writing on metal-silicon thin-film bilayers has been investigated by transmission electron microscopy and electron diffraction. Bilayers of amorphous Si and metals such as Au, Co, Pd, Pt, V, and Rh were reacted by laser writing for periods as long as 0.1 sec and as short as 5 nsec with varying powers by use of neutral density filters. Silicides formed by short laser pulses in bilayers on solid substrates are generally amorphous, while silicides formed on thin membrane substrates require less power for threshold writing and can be crystalline due to lower quench rates. Metallurgical reactions such as grain growth, interdiffusion, and compound formation, which normally require thermal anneals of up to 900 °C, have been observed to take place under laser writing with pulses as short as 5 nsec. Writing with excess power results in melting and hole formation as well as a sharp decrease in reflectivity. The maximum change of reflectivity can be obtained at proper (amorphous or crystalline) silicide formation. Effects of film composition and layer thickness on writing power and reflectivity change were investigated in Au-Si and Pd-Si. From all the systems investigated Rh-Si appears to be most promising due to its relatively low writing power and excellent archival properties.
Threshold energy density for pulsed-laser annealing of ion-implanted silicon
Authors: Hoonhout D. , Saris F. W.
Published: February 2003

The threshold energy density for recrystallization of ion-implanted silicon by Q-switched laser irradiation has been measured as function of type and dose of implanted impurity, thickness of the disordered layer, temperature during implantation, and substrate orientation, using 2-MeV He+-backscattering plus channeling. Many of the observed effects can be ascribed to the dependence of photon absorption on degree of amorphization, layer thickness, doping level, and laser wavelength. The extent to which our findings can be explained by a strictly thermal model based on transient melting and freezing of a surface layer, is discussed. Qualitatively, our results do not disagree with this model.
Optical spectroscopy during reactive ion beam etching of Si and Al targets
Authors: Dzioba Steven , Naguib H. M.
Published: February 2003

This paper presents results on the use of an optical spectroscopic system in the study of reactive ion beam etching (RIBE) of Si wafers and Al thin films deposited on glass substrates. Ion beams derived from Ar, CF4, and CCl4 gases have been used at energies in the range of 0.3–1.7 keV. The emission of ultraviolet and visible photons from sputtered excited substrate particles has been observed. Of particular interest was the detection of SiF and AlCl excited molecules during RIBE of Si and Al substrates, respectively. The effects of ion energy to ion current, and the presence of residual O2 in the etching chamber have been investigated. The results, analyzed on the basis of existing sputtering theories, indicate that at energies below ?500 eV, RIBE is mainly characterized by the sputtering of molecules adsorbed on the bombarded surface. At higher energies, the etching is dominated by the sputtering of elemental atomic species. The addition of small amounts of O2 to the etch chamber was found to enhance the etch rate of both Si and Al substrates. This has been attributed to the removal of a carbonaceous layer formed on the substrate surface as a result of ion-impact dissociation of the bombarding species.
Epitaxial regrowth of intrinsic, 31P-doped and compensated (31P+11B-doped) amorphous Si
Authors: Lietoila A. , Wakita A. , Sigmon T. W. , Gibbons J. F.
Published: February 2003

The rate of solid-phase epitaxial regrowth of implantation amorphized 〈100〉 Si was studied in intrinsic, phosphorus-doped and compensated (boron- and phosphorus-doped) materials. The anneals were performed in flowing Ar gas in the temperature range from 477 to 576 °C, and the regrowth was analyzed by 2.2-MeV 4He+ channeling techniques. The intrinsic and compensated samples exhibited nearly equal growth rates with thermal-activation energies of 2.85 eV (intrinsic) and 2.8 eV (compensated). The growth rate in the 31P-doped (constant concentration of 1.7×1020 cm−3) was enhanced by a factor of 6 to 8, while little change in the activation energy was observed.
Auger electron spectroscopy study on interfacial reactions in multilayer thin film systems
Authors: Pandelišev Kiril A. , Wang Edward Y.
Published: February 2003

Interfacial reactions at room temperature in multilayer thin film systems have been investigated by the Auger Electron Spectroscopy method. The multilayer thin film structure consists of metal, native oxide, and/or deposited interfacial layers on metal and semiconductor substrates. Various combinations of metals and interfacial layers on different substrates have been investigated. For the multilayer systems Au, Ag, Cu, and Cr were used as metals, GeO2, Bi2O3, SnO2, Sb2O3, Ga2O3, and As2O3 were used as interfacial layers, and GaAs, Si, and Fe were used as substrates. Only ’metal’ atoms from the interfacial oxide layers (Ge from GeO2, Sb from Sb2O3, Bi from Bi2O3, Sn from SnO2, and Ga and As from the native oxide mixture of Ga2O3 and As2O3) were detected on the metal surface of Metal-Interfacial layer-Semiconductor and Metal-Interfacial layer-Metal-Semiconductor structures. This indicates that the interfacial reaction takes place only at the metal-interfacial layer interface. ’Drive-out’ diffusion is present at all interfacial reactions. The interfacial reactions and the drive-out diffusion processes are thought to play an important role in the degradation of thin film multilayer structures.
Grain boundary recombination analysis of GaAs Schottky barrier solar cells
Authors: Soukup R. J. , Bartunek G. P.
Published: February 2003

A cylindrical grain is used to model the short circuit current density of a thin film polycrystalline GaAs Schottky barrier solar cell. Both backwall and frontwall solar cells are considered and it is found that the optimum thickness for either cell is less than 2.5 μm if reflection of solar energy from the back metallic contact is considered. The grain size and grain boundary recombination velocity affects each cell in the same way. However, the ohmic contact recombination velcocity has a greater influence on the backwall solar cell. The conclusion of this study is that although the backwall cell is potentially more efficient, the frontwall cell is less influenced by semiconductor and contact parameter variation and thus, for production quantities, the frontwall cell will yield more consistent results.
The relationship among electromigration, passivation thickness, and common-emitter current gain degradation within shallow junction NPN bipolar transistors
Authors: Hemmert R. S. , Prokop G. S. , Lloyd J. R. , Smith P. M. , Calabrese G. M.
Published: February 2003

In very large-scale integration, the trend towards smaller horizontal dimensions and shallower doping profiles within NPN bipolar devices aggravates degradation mechanisms affecting common-emitter current gain (beta). It is experimentally shown for shallow junction NPN bipolar transistors operating in the conduction mode that the degradation of beta is electromigration related. Increasing the passivation thickness simultaneously improves metal conductor lifetime and aggravates beta degradation. Both increases are attributed to the electromigration-induced compressive stress. The complete recovery of beta after a 400 °C anneal indicates that the electromigration-induced compressive stress is relieved by creep in an aluminum-based metallization. The experimental results for beta degradation are consistent with an existing theory that takes into account the effects of stress on the effective mass of light and heavy holes.
Optical properties of a new bistable twisted nematic liquid crystal boundary layer display
Authors: Thurston R. N. , Cheng Julian , Boyd G. D.
Published: February 2003

In a new display cell, a holding voltage compresses the regions where the director is not essentially vertical into thin boundary layers adjacent to the surfaces. With opposite surfaces tilt biased in opposite senses, and with suitable isolation regions, the director field contains a horizontal director line. Above a certain threshold voltage the stable states are asymmetric, with the horizontal director line nearer one surface than the other. In a twist cell, these bistable states can be discriminated optically with either a dichroic dye and a single polarizer or with two polarizers using birefringence effects. A dye gives poor results because the horizontal absorbing layers are thin. However, the birefringence effects enable good contrast to be obtained. We examine the brightness and contrast by studying the transmission of monochromatic light passing normally through the cell in the two states. We include an analysis of polarized light propagating through two birefringent layers of arbitrary phase difference, and whose principal planes are at arbitrary angles to each other and to the polarizers. A separate analysis relates the phase difference of the layers to the voltage and cell boundary conditions. In order to determine suitable operating conditions with two polarizers, we carry out several different calculations. These include: (1) calculating, with one state totally extinguished, the transmission of the other state when the cell twist is 45° and when the cell twist is adjusted to maximize that transmission; (2) calculating the transmission and contrast ratio under conditions that maximize the transmission difference of the two states; and (3) calculating the contrast ratio when the polarizer and cell twist are set to make the brighter state give circular polarization (in order to minimize chromatic effects). A qualitative experimental confirmation is included.
Microstructure and light emission of ac thin-film electroluminescent devices
Authors: Venghaus H. , Theis D. , Oppolzer H. , Schild S.
Published: February 2003

The microstructure of ac-thin film electroluminescent devices was studied by transmission electron microscopy (TEM) of cross-sectional specimens, and was correlated to electro-optical characteristics of the devices. The cross sections reveal the microstructure of the BaTiO3/ZnS:Mn/BaTiO3 layer structure as a function of film depth. The rf-sputtered BaTiO3 films are amorphous; the electron-beam evaporated ZnS films are polycrystalline. The first-to-grow region of the ZnS layers always exhibits a very small grain size. With increasing film thickness the growth of larger columnar grains is observed. At higher substrate temperatures the grains have a more conical shape. The Mn-concentration, measured by x-ray microanalysis on the cross-sectional specimens in a scanning TEM, shows an overall increase with growing ZnS film thickness, because the ZnS was evaporated from a single ZnS:Mn source. Annealing at 550 °C improves the electro-optic characteristics of the samples considerably, without changes in microstructure being observable. Annealing at 850 °C induces strong recrystallization. The initial fine-grained region disappears and the grains extend from the bottom to the top of the ZnS film.
Quantitative methods for microgeometric modeling
Authors: Lin C. , Cohen M. H.
Published: February 2003

The microgeometry or texture of a porous medium determines its physical properties, e.g., the electromagnetic, acoustical, and fluid dynamic properties of sedimentary rock. Unified functional models of texture are clearly needed to test and provide insight for texture-dependent theories relating different properties or explaining empirical observations. A class topological models of sedimentary rock is introduced, together with the necessary topological concepts. Each sample is modeled by two 3-D networks, pore and grain, together with a set of measured parameters such as integranular contact areas or pore/throat ratios (of which any given application may use only a subset). An intuitive example of thin modeling process is provided. A description is given of data acquisition and image analysis procedures used for measurements from reconstructed serial rock sections. Preliminary observations of grain and pore statistics are presented, with comparisons to other related data. The ’’connectivity’’ of the pore (or grain) system of Berea is lower than the connectivities of regular monosized sphere packs with similar porosities and the same mean grain ’’diameters’’. A wide distribution of sizes, aspect ratios, and coordination number were also found for Berea. Illustrative applications of this kind of modeling to nuclear-magnetic resonance, fluid flow, and frame modulus are given.
Changes in capacitance of amorphous Se:As alloy films during structural relaxation below the glass transition temperature
Authors: Abkowitz M. , Pochan D. F. , Pochan J. M.
Published: February 2003

Reversible hysteresis behavior of capacitance and ac conductance of amorphous Se:As alloy films (alloy range 0–4% As) below the glass transition temperature (Tg) is observed when measurements are carried out at fixed frequency in the temperature scan mode over an experimental range encompassing Tg. In this measurement mode, annealing effects which follow either cycling or film formation by evaporation can be continuously monitored, via film capacitance, as the film undergoes kinetically arrested isothermal relaxation toward a quasistable state. Arsenic addition to amorphous Se alters many of its physical properties. For example, in a previous study of the same series of films, it was found that both the dielectric increment measured just above their respective Tg ’s and the widths of the associated relaxation distribution function varied significantly with composition. In the present study, dielectric and thermodynamic measurements indicate that arsenic addition to amorphous Se significantly slows the rate of structural relaxation near room temperature (?15 K below respective Tg ’s). However, it is found that the shape of the capacitance relaxation function, associated in this case with structural relaxation below Tg, is relatively insensitive to alloy composition. The changes in room temperature relaxation, reflected in capacitance measurements, can in fact be adequately accounted for, phenomenologically, solely in terms of the shift in Tg induced by arsenic alloying. It is suggested (1) that dielectric relaxation in the melt above Tg and structural relaxation during annealing below Tg are controlled by a different set of dynamic processes or (2) progressive arsenic alloying skews the relaxation distribution function so that the very low frequency-spectral components which dominate relaxation below Tg remain unaffected.
Field evaporation events as Markov chains: A time-of-flight atom-probe study of iridium, Pt-Rh alloys, and metallic glasses
Authors: Tsong T. T. , McLane S. B. , Ahmad M. , Wu C. S.
Published: February 2003

Field evaporation events in time-of-flight atom-probe analyses were treated as Markov chains. Both the random chain and the chain with a given distribution of cluster sizes were considered. The validity of the analysis was checked with a set of atom-probe data of iridium. The data agree with a random distribution of the two isotopes. Two sets of atom-probe data were collected from Pt-Rh alloys, and were analyzed and compared with these models. It is found that the experimental distributions fit best with the distributions including slight degrees of clustering in the field evaporation events. Thus, microclustering of Rh and Pt atoms occurs in Pt-Rh alloys, which are generally believed to be complete random solid solutions over the entire composition range. From the atom-probe data, however, we are not yet able to estimate the cluster size distribution of Rh and Pt atoms in the alloys. Our atom-probe data of a metallic glass agree well within the statistical uncertainty of the data with a random distribution of the constituents. If microclustering occurs, it is still beyond the sensitivity of the method as constrained by the amount of data available.
A comparison of initial damage rates due to electron and neutron irradiations measured by internal friction techniques. III. Neutron energy dependence (67 keV to 1 MeV)
Authors: Goldstone J. A. , Parkin D. M. , Simpson H. M.
Published: February 2003

Neutron energy dependence of the initial dislocation pinning rate was studied from 67 keV to 1 MeV on a copper sample. By comparing the initial pinning rates of 0.5-MeV electron irradiations and the neutron irradiations and using the defect production rate for electron bombardments, an estimate of the free interstitial production cross sections for neutrons was made. Comparison with the Norgett-Robinson-Torrens production cross section for the total number of defects was made to estimate the fraction of defects surviving as free interstitials. Previous data covering the neutron energy range of 2–24 MeV showed this fraction to be a constant. However, the present lower energy data show that the survival fraction increases at low energies, from 0.7% at 1 MeV to 2% at 67 keV. The entire data set is compared with two additional models, one which considers experimental data and computer models supporting a recoil energy dependent displacement efficiency and one which yields the number of free vacancies after short-term annealing. Our results are best described by the latter. It is concluded that the surviving fraction of defects in displacement cascades is a function of primary knock-on energy in the few keV range and that this behavior must be considered in modeling radiation effects.
A molecular dynamics simulation study of the influence of the lattice atom potential function upon atom ejection processes
Authors: Harrison Don E. , Webb Roger P.
Published: February 2003

A molecular dynamics simulation has been used to investigate the sensitivity of atom ejection processes from a single-crystal target to changes in the atom-atom potential function. Four functions, three constructed from the Gibson potentials with Anderman’s attractive well, and a fourth specifically developed for this investigation, were investigated in the Cu/Ar+ system over a range of ion energies from 1.0 to 10.0 kev with the KSE-B ion-atom potential. Well depths and widths also were varied. The calculations were done at normal incidence on the fcc (111) crystal orientation. Computed values were compared with experimental data where they exist. Sputtering yields, multimer yield ratios, layer yield ratios, and the ejected atom energy distribution vary systematically with the parameters of the atom-atom potential function. Calculations also were done with the modified Moliere function. Yields and other properties fall exactly into the positions predicted from the Born-Mayer function analysis. Simultaneous analysis of the ejected atom energy distribution and the ion energy dependence of the sputtering yield curve provides information about the parameters of both the wall and well portions of the atom-atom potential function.
Nonequilibrium water permeation in SiO2 thin films
Authors: Pfeffer Robert , Lux Robert , Berkowitz Harry , Lanford W. A. , Burman C.
Published: February 2003

Nuclear resonance profiling was used to measure the distributions of hydrogen incorporated into dry SiO2 films by thermal treatments in steam. Thermal oxides were grown on silicon to a thickness of 260 nm in dry O2 and were subsequently treated in steam at temperatures of 320 and 500 C for periods lasting between 390 and 6×105 s. The concentrations of hydrogen carried in by permeating water were then profiled with 6.4 MeV 15N ions using the resonant nuclear reaction 1H(15N, αγ)12C. Water was seen to penetrate the films rapidly and to slowly react with the SiO2 uniformly throughout the films. Two distinct stages were observed in the buildup of H, indicating that the water/SiO2 reaction involves at least two concurrent processes rather than a single-stage process.
Selective-area molecular beam epitaxy of ZnSe thin films
Authors: Yao Takafumi , Minato Tetsuo , Maekawa Shigeru
Published: February 2003

Monolithic electroluminescence devices require planar growth of isolated devices on a substrate. Planar growth has been realized by selective-area molecular beam epitaxy (MBE). Selective-area growth of ZnSe thin films by MBE has been successfully achieved over a GaAs substrate partially coated with SiO2 film, where active device positions are defined by windows in SiO2 layers. Extensive characterization has been carried out for both monocrystalline and polycrystalline materials. It is found that the device-quality single-crystal layer is isolated by the insulating polycrystalline layer. The difference in the etch rate of polycrystalline layers from that of monocrystalline layers enables the fabrication of three-dimensional structures. Schottky barrier electroluminescence diodes have been fabricated by an in situ process. The diodes show white emission for applied voltages as low as 6 V.
Thermal-wave depth profiling: Theory
Authors: Opsal Jon , Rosencwaig Allan
Published: February 2003

We have developed a one-dimensional model for thermal-wave depth profiling that provides expressions for the temperature at the surface of the sample and for the thermoelastic response beneath the surface. The model shows that elastic wave interference effects produce significant differences between samples with mechanically free and constrained surfaces, and that thermal- wave images of thermal conductivity variations are obtainable from the thermoelastic signal only if the front surface is mechanically free. We have also considered the case of subsurface heating and found that for heating occurring at depths of more than a few thermal diffusion lengths, the thermoelastic signal becomes independent of thermal conductivity variations. This has important implications for thermal-wave image range and resolution.
Temperature dependence of electron field effect mobility of laser recrystallized silicon film metal-oxide-semiconductor transistors
Authors: Lee Han-Sheng
Published: February 2003

A scanned cw Ar ion laser was used to recrystallize polycrystalline and amorphous silicon films. N-channel metal-oxide-semiconductor transistors were fabricated on these recrystallized films and used for electron field effect mobility measurements. The electron conduction in the samples which had polycrystalline silicon substrates and were annealed at higher power (⩾12 W) was dominated by the lattice scattering mechanism. Other relatively minor factors, such as the scattering by surface imperfections, impurities, and very small intercrystalline potential barriers, altered the magnitude and the temperature dependence of the measured mobilities. For the unannealed and lower power (⩽11 W) annealed polycrystalline samples, scattering at the intercrystalline potential barrier dominated the electron conduction. The role of additional phosphorus doping in the substrate is also discussed. In the higher power annealed polycrystalline devices, the scattering caused by the ionized phosphorus atoms not only lowered the magnitude but also reduced the negative temperature coefficient of the mobility. For the lower power annealed devices, the segregation of the phosphorus atoms to the grain boundary regions may be responsible for the lack of increase of the positive temperature coefficient in the mobility measurements. The unannealed and annealed (10–15 W) amorphous silicon samples also showed that the electron conduction was dominated by scattering at the intercrystalline potential barrier.
Depth dependence of trapped holes in thin-film CdS/Cu2S solar cells determined from photoinduced transient capacitance
Authors: Manthey W. J.
Published: February 2003

Trapping of light-generated holes in copper-doped CdS is important to the operation of the thin-film CdS/Cu2S solar cell. Consequently, there is interest in determining the distribution of the hole traps both in energy and in x, the depth from the junction. Capacitance transients are a useful probe of the depth dependence of trapped hole density, pT (x), since capacitance can be related by electrostatic theory to depletion layer width and charge density. It is shown from variation of capacitance in 1-cm2 thin-film CdS/Cu2S solar cells, prepared at the Institute of Energy Conversion with temperature, heat-treatment time, infrared quenching, and illumination intensity, that the observed photocapacitance is characteristic of copper impurity centers in CdS. Measurements of photocapacitance decay in these cells following abrupt shutoff of intense blue light show a time dependence different from that predicted by the usual theoretical treatment of p–n junctions. This starts from the assumption of a uniform fixed-charge density and leads to a prediction that C2−C2∞ decays exponentially with time, where C∞ is the dark capacitance. The theoretical relations have been rederived using a pT varying as exp(−x/d), where d is a distance characteristic of the depth dependence. The resulting expressions predict that pT should vary as C−2∞ −C−2. It is shown that this relation is closely satisfied by the measured photocapacitance transient data for temperatures from 77.5 K to ∼190 K, for times up to several tens of seconds, and for shorter times at higher temperatures. It is pointed out that some other dependence which confines the trapped hole density near the junction could equally well be used to fit the data. Possibilities for the physical origin of this depth dependence are discussed. It is shown that the relation of electric field at the junction to the measured capacitance derived from this model gives better agreement with measurements of the variation of collection efficiency with illumination intensity.
Line spread function, crosstalk, and modulation transfer function for silicon IR detector arrays
Authors: Nelson R. D. , Schechter D.
Published: February 2003

The line spread function, crosstalk, and modulation transfer function (MTF) are computed for stripe geometries, assuming the absorption length is greater than the detector resolution element size. It is assumed that the radiation incident surface is antireflection coated and that the reflectivity of the exit face is a parameter. Numerical computations are carried out to find the optimal focal-plane depth (least crosstalk), and the crosstalk is calculated at this optimal focal-plane depth as a function of both absorption coefficient and detector width. The MTF is then calculated for various detector widths.
Characteristics and behavior of electrodeposited surfactant phthalocyanine photovoltaic cells
Authors: Dodelet J.-P. , Pommier H.-P. , Ringuet M.
Published: February 2003

The photovoltaic characteristics of Al/surfactant aluminum phthalocyanine (SlAlPc)/Ag cells are reported. The electrodeposition technique is used to plate  S1AlPc. This technique could easily produce large size depositions of pigment. Maximum values of 0.7% for power conversion efficiency and 18% for quantum yield for charge production have been obtained at 638 nm and 4 μW cm−2 with a light exponent of 0.58 for the photocurrent. Photovoltaic properties decrease with time in the dark and under constant illumination. This behavior seems to be related to the presence of a hydrated aluminum oxide layer at the interface Al/S1AlPc and could be rationalized in terms of deeply trapped electrons in the oxide and on its surface. The decrease of the photovoltage and the photocurrent are calculated on the basis of the trapped electron hypothesis.
Schottky barrier of nonuniform contacts to n-type and p-type silicon
Authors: Thompson R. D. , Tu K. N.
Published: February 2003

A current-voltage measurement and thermionic emission theory have been applied to discrete parallel diodes (nonuniform diodes) with the unusual result that the sum of the apparent Schottky barriers to n Si and p Si is not equal to the band gap of Si.