bluuebunny/crossref_metadata_2025 huggingface dataset:
Second harmonic generation of p-polarized laser radiation in an inhomogeneous laser-produced plasma
Authors: Salimullah Md. , Amin Md. Ruhul
Published: July 2002

In this paper, we have made a theoretical investigation of second harmonic generation from intense p-polarized laser radiation in an inhomogeneous plasma. The fluid equations have been employed to obtain the nonlinear response of the plasma electrons. The power conversion efficiency of the generated second harmonic wave depends drastically on the scale length of the plasma inhomogeneity and the angle of incidence of the laser radiation with the density gradient of the plasma.
Clustering of oxygen atoms around carbon in silicon
Authors: Fraundorf P. , Fraundorf G. K. , Shimura F.
Published: July 2002

Transmission electron microscope studies of carbon-doped Czochralski silicon, when combined with previous infrared data on the same specimens, reveal a double peak in the carbon-sited oxygen-cluster size distribution after 64 h at 750 °C. The first peak, which represents most of the carbon and oxygen in the specimen, is comprised of clusters with an average of two oxygens per carbon atom. These clusters can survive 64 h at 1000 °C although they are not created by such an anneal, suggesting that carbon atoms have difficulty trapping a first oxygen atom at 1000 °C. The second peak in the distribution near 104 oxygen atoms in size is populated with regular {111}-octahedral precipitates having large dilatational strain fields. The two peaks in the size distribution, and their dependences on heat treatment, indicate roles for both seeding (creation of metastable clusters below critical size) and nucleation (achievement of energetic stability) in the formation of carbon-sited precipitates. The observations confirm a trend toward octahedral precipitate morphologies in carbon-doped specimens. However, the trend may result not from site differences but from effects of carbon or point defects on strain energy during precritical cluster growth. Finally, differences between secondary defects associated with precipitation in low- and high-carbon specimens suggest that substitutional carbon atoms at 1000 °C act as sites for silicon self-interstitial condensation near precipitates.
Study of surface photovoltage in hydrogenated amorphous silicon
Authors: Kumar Shailendra , Agarwal S. C.
Published: July 2002

Surface photovoltage (SPV) in hydrogenated amorphous silicon (a-Si:H) has been measured as a function of temperature and wavelength, intensity and chopping frequency of light. Effects of surface treatments on SPV, including etching and exposure to moisture, are also studied. It is concluded that SPV cannot be directly related to the band bending at the surface of a-Si:H. By solving Poisson’s equation in dark and light, it is shown that in a material such as a-Si:H, the observation of a finite SPV necessarily implies a transfer of charge between the surface states and the space-charge region. This explains our experimental observations since it means that SPV measurement may not be relied upon to give the surface potential of a-Si:H. Notwithstanding this handicap, it is shown that by measuring SPV and conductance on an a-Si:H sample subjected to cycles of moisture and light soaking, we can conclude that light soaking affects the surface as well as the bulk of a-Si:H.
Two calculations of the influence of electrostriction on the detectivity limit in liquid-filled photoacoustic cells
Authors: Burt J. A.
Published: July 2002

A finite difference and a Ritz–Galerkin analysis has been made of the differential equations describing a photoacoustic cell where a pulsed laser beam traversing a liquid causes pressure due to electrostriction and optical absorption. Electrostriction does not appear to limit photoacoustic absorption measurements for a soft-cell boundary model. In particular, for water and benzene, the electrostrictive pressure is 8 orders of magnitude less than the photoabsorptive pressure.
Band offsets and the optical properties of HgTe-CdTe superlattices
Authors: Wu G. Y. , McGill T. C.
Published: July 2002

The effect of variation in the band offset on the band gap and optical properties of the HgTe-CdTe superlattice is examined. If we define the valence-band offset ΔEν to be the energy of the valence-band edge of the HgTe with respect to the valence-band edge of the CdTe, both the band gap and optical properties are smooth functions about ΔEν≊0.
Electrical conductivity of layered GeSe related to extended faults
Authors: Kyriakos D. S. , Anagnostopoulos A. N.
Published: July 2002

The electrical conductivity measured parallel and perpendicular to the layer planes of p-type GeSe single crystals was found to be anisotropic at low temperatures. Additionally, an irreversible increase of the conductivity parallel to the layer planes was observed at high voltages. This anisotropy is correlated to the stacking disorder of the crystal layers and to dislocation sets lying on the layers. Extended planar faults parallel to the crystallographic c axis are attributed to the conductivity switching observed perpendicular to this axis. The ratio σ∥/σ⊥ obeys an exponential law, with an activation energy ΔE of about 25 meV. This effect seems to be the predominant one while the switching effect is of minor importance even in the low-temperature range.
Monte Carlo study of ionization zone electron kinetics in negative pin-plane coronas in atmospheric air
Authors: Kline L. E.
Published: July 2002

Monte Carlo simulation techniques are used to study the electron transport properties in the high electric field region near the pin in negative pin-plane corona discharges in atmospheric air. The results of the calculations show that the discharge electrons are nearly in equilibrium with the high local electric field near the pin tip. Consequently, a simpler computational model can be used to predict the voltage-current characteristics of these discharges. The results also show that ionization growth is very rapid for the pin-tip radii, gap lengths, and applied voltages which have been studied experimentally.
Changes in Curie temperature due to irradiation and thermal annealing in amorphous Fe20Ni60P14B6
Authors: Fisher D. G. , Murray R. B. , Swann C. P.
Published: July 2002

The effects of proton (H+), deuteron (D+), and helium (He+) irradiations at 2.0 MeV on the Curie temperature of amorphous Fe20Ni60P14B6 are reported and compared to thermal annealing effects. Changes in Curie temperature are reported following isochronal anneals (5-h duration) at temperatures up to 325 °C and following room-temperature irradiations. The Curie temperature increase for samples irradiated with H+ is greater than that observed with D+, which is greater than that observed with He+. Reversibility of Curie temperature has been reported by other workers for thermal annealing of various amorphous magnetic alloys. In this paper, reversibility of Curie temperature is reported for samples successively irradiated with H+, He+, and then D+. A qualitative interpretation of irradiation effects is given in terms of transient heating about the track of a projectile ion.
Amorphous phase separation in polypropylene block copolymers as revealed by thermostimulated depolarization measurements. I. Complex spectra study
Authors: Ronarc’h D. , Audren P. , Moura J. L.
Published: July 2002

The thermally stimulated depolarization (TSD) technique was used to observe the amorphous phase separation in polypropylene block copolymers and to attribute its various dielectric relaxations to precise mobile entities. The complex thermostimulated spectra of polypropylene block copolymers were compared to complex spectra of polymers of the same nature as those of its main components, i.e., isotactic polypropylene, high-density polyethylene, and propylene-ethylene rubber. With TSD we then studied a binary blend of polypropylene and high-density polyethylene and another blend of polypropylene and propylene-ethylene rubber and also the various parts of polypropylene block copolymer which were separated by a selective solvent extraction. From peak-position and intensity considerations we suggested the origin of the three relaxations appearing from 90 to 290 K in the TSD complex spectra of polypropylene block copolymer.
Maximum stress produced by bubble growth in a condensed phase
Authors: Ward C. A. , Yee D. , Tikuisis P.
Published: July 2002

It has been recently predicted that after bubble nucleation in an isothermal liquid-gas solution of constant volume and mass, the bubble would grow to a final, stable equilibrium size, and a method was given for predicting the final stress that the bubble would produce within the system. An experimental examination has been made of these conclusions using a water-nitrogen solution contained in a stainless steel vessel of constant volume. The evolution of a bubble to the final, stable equilibrium size was observed, and the predicted final stress was found to lie within the experimental uncertainty.
Solid-state reaction of iron on β-SiC
Authors: Kaplan R. , Klein P. H. , Addamiano A.
Published: July 2002

The solid-state reaction between Fe and β-SiC has been studied using Auger-electron and electron-energy-loss spectroscopies and ion sputter profiling. Fe films from submonolayer coverage to 1000 Å thickness were grown in ultrahigh vacuum, and annealed at temperatures up to 550 °C. Auger line-shape changes occurred even for initial Fe coverage at 190 °C, indicating substantial bond alteration in the SiC substrate. A 1000-Å film was largely consumed by reaction with Si and C diffused from the substrate during a 500 °C anneal, and exhibited both Fe silicide and carbide throughout most of its original volume and free C present as graphite primarily at the surface. As an aid in identifying the reaction products studied in this work, Auger line shapes were first determined for the SiLVV peak in Fe silicide and for the CKLL transition in Fe carbide.
Electron traps with similar concentrations in n-type Al0.1Ga0.9As grown by metalorganic chemical vapor deposition
Authors: Sakamoto Masamichi , Okada Tsunekazu , Mori Yoshifumi
Published: July 2002

Electron traps in n-type Al0.1Ga0.9As grown by metalorganic chemical vapor deposition were studied by deep level transient spectroscopy. The concentrations of the 0.27- and 0.41-eV trap levels were found to be nearly equal over two orders of magnitude, suggesting that the levels originate from the same center. The increase of the concentrations of these traps with increasing arsine flow rate when using the arsine source possibly contaminated with water vapor implied that these traps are related to water vapor. The photoluminescence intensity of the epilayers was found to have a strong correlation to the total concentration of these traps.
Effect of surface chemistry on the morphology, resistance, and colloidal behavior of small silver particles
Authors: Schwab Scott D. , McCreery Richard L. , Cummings Kevin D.
Published: July 2002

Raman spectrometry, transmission electron microscopy, and elemental analysis were used to characterize small silver particles prepared by evaporation of silver from a molybdenum or tungsten boat into a reduced-pressure atmosphere of argon and oxygen. Particles prepared with both molybdenum and oxygen present were 50–400-Å-diam spheres, but much larger aspherical particles resulted if either molybdenum or oxygen was absent. The spherical particles were coated with approximately one monolayer of polymeric molybdenum oxide formed during fabrication from volatile MoO3. The polymolybdate-coated particles form a stable suspension in water and have high electrical resistance, while those prepared in the absence of molybdenum have low resistance and do not suspend in water. No evidence of silver oxide formation was obtained, even for particles prepared by silver evaporation in oxygen in the absence of molybdenum, We conclude that the polymolybdate coating prevents the formation of very large (>1000 Å) particles during fabrication. Furthermore, the coating becomes negatively charged in polar solvents, leading to formation of a stable colloidal suspension. Thus the molybdenum boat is essential for the fabrication of small spherical particles, and has a large effect on the properties of the final material. While silver oxide formation cannot be rigorously ruled out, it is clear that molybdenum, not silver, oxides determine the morphology and resistance of the particles.
Evidence for complex acceptors related to Cu and Li in GaAs
Authors: Gislason H. P. , Wang Z. G. , Monemar B.
Published: July 2002

New photoluminescence (PL) bands are reported in GaAs doped with Cu and Li as well as with Li only. A study of a PL band at 1.41 eV appearing after both subsequent and simultaneous diffusions of Cu and Li into a range of different GaAs samples under varying doping conditions shows an unequivocal correlation between this band and the presence of both Cu and Li in the samples. Also, an observed decrease of the 1.36-eV Cu PL band as the 1.41-eV Cu-Li band increases suggests a common component of the corresponding two centers, presumably CuGa. A model is proposed, assigning the 1.41-eV PL band to recombination involving a 0.11-eV CuGa-Lii acceptor level. It is suggested that a PL peak at 1.34 eV appearing after Li doping of bulk material involves transitions to the doubly ionized LiGa acceptor. Other new PL bands appear after Li diffusion as well. The absence of bound exciton (BE) states associated with these acceptors is also discussed.
Comments on ‘‘Equivalence of the Lorentz and Ampere force laws in magnetostatics [ J. Appl. Phys. 5
7, 1743 (1985)]’’
Authors: Graneau Peter
Published: July 2002

This communication disputes the claim made by Ternan [J. Appl. Phys. 57, 1743 (1985)] that the Ampere and Lorentz force laws are equivalent. Two examples are quoted in which the two laws make different predictions. Particle beams in vacuum obey Lorentz’s law but in metallic circuits Ampere’s law prevails.
Interdiffusion in the Ta-W system
Authors: Romig A. D. , Cieslak M. J.
Published: July 2002

Interdiffusion in the Ta-W system, a continuous body-centered-cubic solid solution, has been investigated in the temperature range 1300–2100 °C with single-phase diffusion couples prepared by chemical vapor deposition. Fine inclusions, presumably oxides or carbides, decorated the couple interfaces and served as Kirkendall markers. The diffusion annealing times ranged from 16 h to 220 days. The resulting concentration profiles were measured with the electron microprobe and analytical electron microscope. The chemical diffusion coefficient was determined by the classical Boltzmann–Matano technique. The intrinsic diffusivities were determined by the technique of Darken. In the composition range 20–80 at. % W, the activation energy Q for chemical diffusion was constant at 130.5±1.5 kcal/mole. The activation energies for the intrinsic diffusion coefficients at the composition of the Kirkendall marker plane, approximately 70 at. % W, were Q(Ta)=132.3±0.5 kcal/mole and Q(W)=122.0±0.5 kcal/mole.
Open-circuit voltage-decay behavior in p-n junction diode at high injection
Authors: Gopal R. , Dwivedi R. , Srivastava S. K.
Published: July 2002

The open-circuit voltage-decay of a highly forward biased p-n junction diode switched off abruptly after reaching steady state is studied theoretically for high-level injection. The present theory takes into account the terminal voltage instead of junction voltage as the open-circuit voltage, and is based on ambipolar diffusion phenomenon. The results are in qualitative agreement with the available experimental results for the entire range of decay characteristics.
Simulation for static and dynamic performance of a superconducting analog-to-digital converter
Authors: Kim N. S. , Jack M. D.
Published: July 2002

The simulation of a superconducting flux counting analog-to-digital (A/D) converter for advanced high-speed signal processing systems is performed to investigate its performance and sensitivity. This report describes the algorithms and the results associated with simulating the whole sequence (count-store-readout-reset-count). Parameter sensitivities are also checked and optimized.
PtSi contact metallurgy: Effect of silicide formation process
Authors: Chang Chin-An
Published: July 2002

PtSi films have been formed by different formation processes using sputtered Pt. Two annealing sequences are compared: a single-temperature annealing at 550 °C and a three-temperature annealing at 200–300–550 °C; and three annealing gases are compared: forming gas, nitrogen, and oxygen. Silicide films formed using the single-temperature process all show incomplete reaction between Pt and Si, leaving a protective surface oxide layer of poor quality, which extends rather deeply into the PtSi film and is completely etched off by aqua regia. The silicide films formed by the three-temperature process in forming gas, however, show a complete reaction between Pt and Si, and a thin surface oxide layer with excellent protection of the PtSi layer from the subsequent aqua regia etching often needed for device fabrication.
Theory of microwave pulse propagation during gas breakdown: Linear approximation
Authors: Robiscoe R. T.
Published: July 2002

We develop a theory describing the propagation of a pulse of electromagnetic energy through a gas in which breakdown is occurring (by means of the pulse-induced electron cascade). The theory is based on solutions to a model wave equation for the pulse electric field, which incorporates the electron cascade in an approximate fashion, and which is derived from the appropriate Maxwell equations coupling the pulse fields to the cascading electron current. Nonlinear effects are ignored, but solutions to the model wave equation appear useful in identifying major trends in the pulse propagation, such as the pulse attenuation and its dependence on the input pulse nominal frequency, spectral breadth, width, rise time, and overall shape. Our results are of relatively simple analytical form, they semiquantitatively confirm available data, and they imply that the pulse energy transport through the electron cascade can be enhanced by choice of certain combinations of the input pulse parameters.
Quantum model of the free-electron laser in a uniform magnetic field
Authors: Šoln Josip
Published: July 2002

A quantum model of the single particle free-electron laser in a uniform magnetic field is given. Here the classical electron current due to electrons in helical orbits (caused by a uniform magnetic field) interacts with a quantized radiation in the interaction volume of finite extent. The description of this free-electron laser is through the S matrix which incorporates the quantum recoil completely and yields directly the full ‘‘quantum mechanical’’ gain. Taking the relativistic electron factor γ to be approximately equal to 2.4 and the magnitude of the magnetic field in the range of 0.6–1.6 T, this free-electron laser should be capable of generating radiation in the far infrared-microwave spectral region. From the analysis of the asymptotic (classical limit) gain (a gain due to the ‘‘infinite’’ number of photons in the interaction volume V), we conclude that it is generally easier to generate radiation in the forward, rather than backward, direction. We also discuss the dependence of the gain on the electron velocity in the z direction, the strength of the uniform magnetic field, and the fact that our (asymptotic) gain scales as L3, which is similar to the gain of the usual (wiggler) free-electron laser.
Theory of transverse multimode generation in a laser with a loss guiding structure
Authors: Takeshima Masumi
Published: July 2002

A theoretical consideration is given of the transverse multimode generation in a laser which is equipped with a lossy layer below an active layer for mode control, e.g., the buried twin-ridge substrate laser, the channeled substrate planar laser, and the V-shape inner stripe laser. The multimode generation occurs as a result of the reduction of the first-order mode threshold to the fundamental mode threshold. It is shown that even a small asymmetry of the lossy layer causes large reduction of the first-order mode threshold.
Mixing of Al in Si by Ne+ ions
Authors: Whitlow H. J. , Keinonen J. , Hautala M.
Published: July 2002

Ion-beam mixing has been studied for the case where all components are collisionally similar. In this study a thin Al marker was mixed by implanting 40-keV 22Ne+ into electron-beam-evaporated Si. The mixing was studied with the nuclear resonance broadening technique. It is characterized by a broadening that is proportional to the square root of ion fluence. The data obtained at room temperature, where the negligible solubilities and thermal diffusivities do not contribute to the intermixing of Al and Si, indicate that even in the absence of the long-range transport there is a diffusion mechanism which enhances the mixing with a magnitude some 3–6 times that expected for ballistic mixing. The data is applicable for preparing Al/Si contacts by Al implantation.
Acceptorlike electron traps and thermally reversible barrier heights for Al on UHV-cleaved (110) InP
Authors: Slowik John H. , Richter H. W. , Brillson L. J.
Published: July 2002

Temperature-dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements reveal that a low but nonzero barrier is present at the interface of Al deposited on ultrahigh-vacuum-cleaved n-InP (110), and that the true barrier height lies between 0.21–0.26 eV. An analysis which allows for the presence of trapped charge near the interface provides the most accurate and consistent determination of the effective barrier. The effective barrier is strongly and reversibly temperature dependent, corresponding to movement of the Fermi level with temperature. The trapped interfacial charge resides in acceptorlike electron traps 0.10 eV below the conduction-band edge. The traps are distributed 100–200 Å into the space-charge region. These results are discussed in terms of models of defect electrical activity at metal-semiconductor interfaces, and are related to results of annealing studies.
Magneto-optical properties of 100-keV Ne+-implanted epitaxial Y3Fe5O12 thin films
Authors: Martens J. W. D. , Godlieb W. F.
Published: July 2002

Magneto-optical spectroscopy and hysteresis loops have been used to study nondestructively the effect of 100-keV Ne+ implantation in epitaxial Y3Fe5O12 thin films. The results show the formation of a damaged layer of 0.13 μm thickness. The stress-induced anisotropy field reaches maximum values of 3.2×104 A/m for an ion dose of 2×1014 cm−2. A decrease in both magnetization and magnetostriction down to 3.6×104 A/m and −1.2×10−6, respectively, was observed for an ion dose of 4×1014 cm−2. The magneto-optical spectra were found to reduce in magnitude but not in shape with increasing implantation dose.
rf-plasma oxidation process of Pb alloy performed using oxygen isotope observed by secondary ion mass spectroscopic analysis
Authors: Wada Masato , Nakano Jun’ichi , Oshima Masaharu
Published: July 2002

Observation is made on the rf-plasma oxidation process of a Pb alloy across the priorly existing thermal oxide. This is carried out through the analyses of the ultrathin (several nanometers) oxide formed by the oxygen isotope with the secondary ion mass spectroscopy. It shows that a good deal of oxygen arriving at the oxygen–oxide interface remains and forms oxides in the outer portion of the oxide. Hence the interstitial or substitutional transport of metal ions or substitutional transport of oxygen ions through the thermal oxide is more important than the oxygen-ion interstitial transport that has been considered responsible for rf-plasma oxidation. Furthermore, it is elucidated that the thermal oxide remains even after rf-plasma oxidation except for a probable slight decrease due to sputtering in the early stages of rf-plasma oxidation. This explains the importance of the thermal oxide in determining the properties of the oxide as a whole.
Surface passivation and oxidation of cadmium telluride and properties of metal-oxide-CdTe structures
Authors: Chu T. L. , Chu Shirley S. , Ang S. T.
Published: July 2002

The oxidation of single-crystal p-type CdTe of {111} orientation by thermal, wet chemical, and plasma techniques has been investigated. The C-V measurements of metal-oxide-semiconductor (MOS) structures prepared from various oxides indicate that device quality thermal oxide can be prepared by hydrogen annealing of CdTe prior to oxidation. The thermal oxide consists mainly of TeO2. MOS structures prepared from oxidation of the Cd(111) or Te(1̄1̄1̄) face of CdTe show low oxide fixed charge density (1011/cm2) and low interface state density (1010/cm2 eV). MOS structures prepared from wet chemical oxide and plasma oxide have less desirable properties.
Spontaneous emission in a free-electron laser with a discrete taper
Authors: Becker W. , McIver J. K.
Published: July 2002

Spontaneous emission in a tapered free-electron laser is considered for the case where the magnetic field of the undulator is described by an expression that varies discretely from one half-period to the next. This geometry permits the utilization of the knowledge of the electron trajectories in untapered undulators. The method can be applied for any conceivable configuration of tapered undulators with electrons propagating either on or off axis and yields the spectrum of radiation at arbitrary angles including harmonics. The approach is developed for linear polarization; however, circular polarization may be treated as well.
Analysis of ion-implanted surface and interface structures by computer-simulated backscattering spectra
Authors: Kido Y. , Kakeno M. , Yamada K. , Kawamoto J. , Ohsawa H. , Kawakami T.
Published: July 2002

Computer codes for synthesizing random and channeling backscattering spectra have been elaborated to characterize the surface and interface structures formed or modified by ion implantation. Both effects of isotopes and energy fluctuation are taken into account in the spectrum simulation. This backscattering measurement combined with the simulation method is applied to characterization of the N+-implanted Al films and to quantitative analysis of chemical reaction and interdiffusion induced by ion-beam mixing. An ion-beam-induced damage profile and its epitaxial recovery of crystallinity are analyzed by the simulation of channeling spectra from ion-implanted Al2O3 substrates.
Comment on ‘‘Transmit versus receive gains for microwave dish antennas [J. Appl. Phys. 5
4, 3528 (1983)]’’
Authors: Love A. W.
Published: July 2002

A theoretical paper published in this journal some months ago purported to analyze the performance characteristics of microwave dish antennas. The paper, however, contains three serious errors which totally negate the results described therein. In this communication the nature of these errors is explained and the proper corrections are indicated.
Reply to ‘‘Comment on ‘Transmit versus receive gains for microwave dish antennas’  [J. Appl. Phys. 5
4, 3528 (1983)] ’’
Authors: Richter John L.
Published: July 2002

A. W. Love points out three alleged errors in our paper [J. Appl. Phys. 54, 3528 (1983)]. We agree that he is correct with regard to the second and third issues, but the first and perhaps most important point is correct. This regards the inequality of transmit and receive patterns of microwave antennas. The standard proof of equality of the patterns, cited by A. W. Love, is shown to be incorrect.
Inhomogeneities of shock-wave deformation in Fe-32 wt. % Ni-0.035 wt. % C alloy
Authors: Thadhani N. N. , Meyers M. A. , Erlich D. C.
Published: July 2002

Low-pressure plane impact experiments performed on Fe-32 wt. % Ni-0.035 wt. % C alloy revealed, after recovery, markings which are attributed to shock-induced inhomogeneities. Shear of the material does not occur homogeneously, but in preferential planar regions. These regions are made visible by a martensitic transformation [fcc (austenite)→bcc (martensite)] produced by the tensile pulses generated by the reflection of the compressive shock wave at a free surface. The bands with higher plastic deformation served as preferential nucleation sites for martensitic transformation. The formation of these bands is attributed to inhomogeneous yielding due to work softening of the material during tensile loading.
Approximation for the Fermi–Dirac integral with applications to the modeling of charge transport in heavily doped semiconductors
Authors: Sobhan M. Abdus , NoorMohammad S.
Published: July 2002

Analytical formulas for evaluating Fermi–Dirac integral of order (1)/(2) has been proposed. The formulas exhibit a degeneracy factor C which controls essentially the applicability of the integrals both to the nondegenerate as well as highly degenerate semiconductors. The accuracies with which the derivative can be evaluated by differentiation and integration of the proposed formulas are acceptable. The formulas have been successfully used in the calculation of effective carrier concentration and current density.
Potential fluctuations of well-defined magnitude superimposed to a Gaussian distribution: Effect of annealing in semi-insulating GaAs
Authors: Abdalla S. , Pistoulet B.
Published: July 2002

Complex conductivity measurements of unannealed and annealed semi-insulating GaAs crystals are reported. A model of fluctuations of well-defined magnitude superimposed to a Gaussian distribution accounts for the σac ∝ ω2 dependence observed above 106 Hz in some unannealed samples. The effect of annealing on the magnitude of long-range potential fluctuations and on the average carrier density is analyzed.
Domain wall pinning at planar defects
Authors: Aharoni Amikam
Published: July 2002

A Ritz model of a one-dimensional wall is used to study this wall passing the barrier created by planar imperfections, in an infinite slab of a hard ferromagnetic material, with a finite thickness.
Thermal strain-induced degradation mechanism in the visible AlGaAs/GaAs laser
Authors: Ikeda M. , Ueda O. , Komiya S. , Umebu I.
Published: July 2002

We fabricated and life-tested visible AlGaAs/GaAs channeled-substrate-planar-type lasers and found that some are degraded within 100 h of operation. We investigated these using photoluminescence and transmission electron microscopic images. The characteristic features in photoluminescence images are dark defects that run parallel to the channeled stripe. Using transmission electron microscopy, we found that these dark defects are composed of precipitates, dislocation loops, and dislocation dipoles. In order to know the relation between these degradation phenomena and the thermal strain induced by lattice mismatch, we calculated the stress distribution in the semiconductor laser using the finite element method. According to this simulation, a stress concentration in the active layer arises near the edges of the channeled stripe where the volume dilatation is maximal. Combining the results of experiments and simulation, we concluded that interstitial atoms created by nonradiative recombination migrate to the edges of the stripe, and that ultimately dark defects appear near the edges of the stripe.
Time-dependent quantum-well and finite-superlattice tunneling
Authors: Coon D. D. , Liu H. C.
Published: July 2002

Theoretical considerations which pertain to electric currents through quantum-well structures or finite superlattices in the presence of periodic time-dependent applied potentials are presented. The paper includes (1) a time-dependent generalization of the time-independent, noninteracting electron, one-dimensional potential model of Tsu and Esaki, (2) a derivation of generalized unitarity identities which relate all of the elastic and inelastic transitions which a particle can undergo when it interacts with a periodic time-dependent, one-dimensional, arbitrarily shaped potential barrier, and (3) an analysis of many-body effects which reveals additional non-Tsu-Esaki current terms which disappear when the time-dependent part of the applied potential is turned off. All of the results are expressed in terms of one-particle scattering matrices which can be computed from the ordinary single-particle, time-dependent Schrödinger equation. This work may have high-frequency device applications.
Langevin noise sources for the Boltzmann transport equations with the relaxation-time approximation in nondegenerate semiconductors
Authors: Min H. S. , Ahn Doyeol
Published: July 2002

An analytic and useful form of the noise sources due to intraband scattering for the Boltzmann transport equations in the relaxation-time approximation is obtained for nondegenerate semiconductors. It is shown that the derived noise source gives the Nyquist’s theorem.
Electroreflectance, photoreflectance, and photoabsorption properties of polycrystalline CdTe thin films prepared by the gradient recrystallization and growth technique
Authors: Vázquez-López C. , Navarro H. , Aceves Raúl , Vargas M. C. , Menezes Cornelius A.
Published: July 2002

In this work we report electroreflectance, photoreflectance, and photoabsorption measurements on CdTe polycrystalline thin films. These thin films were prepared by the gradient recrystallization and growth technique. The measurements were performed around the fundamental energy gap of the semiconductor at room temperature. The energy gap of this polycrystalline material coincides with that corresponding to the single-crystal material, and the phenomenological energy broadening parameter is larger than that corresponding to the single-crystal semiconductor by a factor of three, approximately. The photoabsorption signal is obtained by studying the origin of a low-energy peak which appears in the photoreflectance spectrum.
Order and disorder behavior of superparamagnetic particles of ferric hydroxysulfate seen through Mössbauer spectroscopy
Authors: Morais P. C. , Neto K. Skeff
Published: July 2002

A connection between the temperature behavior of the internal magnetic field and Mössbauer linewidth broadening for a system which exhibits superparamagnetism is proposed.
Determination of the rotational viscosity from the director pattern relaxation in twisted nematic cells
Authors: Leenhouts F.
Published: July 2002

The rotational viscosity γ1 is an essential physical quantity directly related to the response times of liquid crystals. We have developed a new method to determine γ1 which utilizes the capacitive detection of the director pattern relaxation in a twisted nematic cell upon switching off the applied voltage of the twisted nematic liquid-crystal display. Measurements have been performed on two liquid-crystal mixtures. The agreement between the results obtained with the new method and those obtained from a magnetic field-induced nematic deformation method is quite satisfactory.
Integral representation of the diffracted intensity from one-dimensional stepped surfaces and epitaxial layers
Authors: Pimbley J. M. , Lu T.-M.
Published: July 2002

An integral representation of the diffracted intensity from one-dimensional stepped surfaces and overlayers is obtained based on the single-scattering (kinematic) theory. We find exact solutions for an arbitrary terrace or island size distribution on stepped surfaces or epitaxial layers in an extremely simple manner. This theory greatly expands the utility of the kinematic analysis of electron, atom, or grazing x-ray diffraction data. A particularly useful area of application is the quantitative study of the nucleation kinetics during the epitaxial growth of thin films. Several surface ordering models are discussed in terms of this simplified approach.
Propagation of nonlocal elastic waves in a cylindrical hole containing a fluid
Authors: Nowinski J. L.
Published: July 2002

This paper deals with the propagation of elastic longitudinal waves in a cylindrical hole in an infinite space, the hole being filled with an ideal fluid. The Biot’s problem is treated within the context of the nonlocal elasticity allowing one to extend the Biot solution to the domain of ultrashort waves. A numerical example is solved and illustrated by a graph.
Current densities and closure rates in diodes containing laser-driven, cesium-coated thermionic cathodes
Authors: Lee Chunghsin , Oettinger Peter E.
Published: July 2002

Cathodes emitting electron current pulses of 102–103 A/cm2 for durations of longer than 1 μs, with very low emittance, are desirable for free electron laser and high-power microwave tube applications. Not all of these criteria can be satisfied by either dispenser thermionic cathodes or plasma forming field emitters. However, pulse-laser heated smooth cesiated refractory metal surfaces have the potential to achieve these conditions. In this paper, test results from low-voltage (2–20 kV) diodes containing cesiated tungsten cathodes are discussed. Space-charge-limited current densities of up to 30 A/cm2 were obtained in fields with maximum strengths of 40 kV/cm. Plasma closure rates at these currents were measured to be 0.17–0.4 cm/μs. Such slow velocity fronts are postualted to be due to the domination of the plasma by massive cesium ions generated from species desorbed from the cathode, rather than to light hydrogen ions (as in the case of field-emission-type cathodes).
Self-consistent T-matrix solution for the effective elastic properties of perfectly disordered multiphase solids
Authors: Middya T. R. , Basu A. N. , Sengupta S.
Published: July 2002

A self-consistent solution for the effective elastic properties of polycrystalline and perfectly disordered multiphase composites has been discussed by using the T-matrix method under certain suitable approximations. Compared to the existing formulas these new relations for the disordered composites are very useful in practical situations for a quick and more accurate estimate of the effective elastic properties, in particular for a case where the composite has components with widely different values of the elastic constants. For comparison we have discussed the results based on Kröner’s theory which also purports to solve the same problem. It is found that the two solutions do not agree. To resolve the difference we take help of Hill’s exact solution of the composite problem when the components have equal rigidities. It is found that while Kröner’s theory is inconsistent with the exact result the present self-consistent solution analytically reproduces it. Another interesting finding of the present investigation is that the approximations made in obtaining the self-consistent solution are exact in the limit of composites with equal-shear moduli. Finally it is indicated that although the results for composites have been derived for isotropic and cubic components it can be easily adapted for a composite with noncubic components.
Surface recombination velocity and barrier width from surface photovoltage measurements
Authors: Storr G. J. , Haneman D.
Published: July 2002

Data from surface photovoltage measurements on CdSe films are analyzed using two theoretical treatments. Only the more accurate theory is found to be satisfactory and yields values, not only of minority carrier-diffusion lengths, but also surface barrier widths and surface recombination velocities. The latter, for CdSe films in contact with alkaline sulfur redox systems, are in the range (4.5–12) ×105 cm s−1, leading to charge transfer velocities in the region of 4×105 cm s−1.
Dominant recombination process in amorphous silicon alloys
Authors: Guha S. , Hack M.
Published: July 2002

We have critically examined experimental results on photoconductivity in hydrogenated amorphous silicon alloys to ascertain whether recombination at a single defect site (namely, the dangling bonds) or a continuous distribution of centers (dangling bonds together with other defects) provides a realistic model to explain the available experimental data. We find from both these results and from additional experimental data that, for good quality, low defect density material, room temperature recombination is controlled by a continuous distribution of states located between the trap-quasi-Fermi levels.
Dual field effect on liquid-crystal molecular relaxation
Authors: Wu Shin-Tson
Published: July 2002

The dual field effect on the relaxation time of the liquid-crystal BDH-E7 has been analyzed and demonstrated experimentally by using static magnetic and pulsed optical fields. The novelty of this effect is in the use of a strong external field to accelerate the molecular relaxation process. An improvement factor on decay time up to 10 or higher depending on the field strength can be achieved. At high fields, this relaxation time is inversely proportional to the external field intensity and is independent of the liquid-crystal thickness. Since this effect does not rely on the specific properties of liquid crystals, potential applications exist among many nematic liquid-crystal materials.
Phase modulation technique for eliminating phase noise in picosecond T2 measurements based on stimulated Raman gain
Authors: De Mazière Martine , Schoemaker Dirk
Published: July 2002

The pump and probe variant of the stimulated Raman gain technique permits the measurement of picosecond dephasing times with low-power, continuous-wave mode-locked lasers, but it suffers by its susceptibility to inevitable randomly induced fluctuations in the relative phases of the interacting laser fields. The resulting severe requirements on optical stability can be circumvented through application of a double-modulation–detection scheme that we have developed. It is based on rms detection of the T2 signal as generated through application of a low-frequency phase modulation of precise amplitude, additional to the commonly applied rf modulation with corresponding lock-in detection. A detailed description of the method and its experimental realization is presented. T2 measurements on the 656 cm−1 vibration of liquid CS2 illustrate its performance. In comparison with previous techniques, precision is improved by about a factor of 4. But more important is the fact that the technique permits to make a continuous recording of the T2 signal, while achieving at the same time a reduction in measurement time by an order of magnitude. Furthermore, optimization of the optical setup is possible, through direct monitoring of the dephasing signal at any delay. Automating the data taking and processing should be straightforward.
Reduction of enhanced arcing by some electronegative gases
Authors: Gray Eoin W. , Schubert Rudolf
Published: July 2002

Activation or enhanced arc durations due to the presence of minute quantities of organic contaminants in low-current arcing atmospheres is becoming a problem in the reliability of the new generation of miniature relays sealed in plastic or metal containers. This article describes arc duration reduction by the addition of the electronegative gases, SF6 and C2Cl3F3 to the arcing atmosphere when part-per-million hydrocarbon impurities were present. The effects of hydrogen on the arc durations is also examined.
Trapping parameters in GaSxSe1−x solid solutions
Authors: Micocci G. , Rizzo A. , Tepore A.
Published: July 2002

Systematic investigations of trapping centers parameters have been carried out on the complete series of GaSxSe1−x solid solutions by using space-charge-limited-current and thermally stimulated current measurements. Crystals have been grown from the vapor by means of the iodine-assisted transport method by varying the sulphur percentage x in steps of 0.1. Electron mobility, resistivity, and electron concentration have been carried out at room temperature by means of the Van der Pauw method, with the current flowing along the layers. Three well-defined electron traps have been found, the energy depth of which varies continuously from GaSe to GaS.
Powder layer photoelectrochemical structure
Authors: Hetrick Robert E.
Published: July 2002

This paper describes a planar photoelectrochemical structure consisting of a thin porous layer of nonmetallized semiconducting powder above a metallic film. Suited to the photocatalysis of redox reactions in an aqueous gas-phase environment, the properties of the structure are illustrated using the TiO2 sensitized photodecomposition of formic acid which was observed to occur at quantum efficiencies as high as 30%. A photoelectrochemical mechanism is proposed which is the powder-layer analogue of that describing the catalytic activity of dispersed metallized powders. The approach holds potential for fabricating more complex photochemical structures as well as providing new ways of studying powder-sensitized reactions.
A method of rapidly obtaining concentration-depth profiles from x-ray diffraction
Authors: Wiedemann K. E. , Unnam J.
Published: July 2002

The construction of composition profiles from x-ray diffraction peaks is an important and reliable technique, but it has not been widely adopted because it required hours of computer time and/or complicated optimization routines. The method proposed here utilizes an easily evaluated analysis of the diffraction peak. It is applicable to thin films and thick specimens for which the variation with composition of lattice parameters, linear absorption coefficient, and reflectivity are known. A deconvolution scheme is outlined that includes corrections for the instrumental broadening and singlet or doublet radiation.
Determination of the external magnetic field of systems containing two-dimensional semi-infinite plates and one finite cross-sectional plate
Authors: Owen D. , Parris A. J.
Published: July 2002

Certain two-dimensional symmetrical systems of magnetic conductors, consisting of semi-infinite and finite plates are examined using a mapping method. Four examples are studied.
Influence of the dynamic Stark effect on the small-signal gain of optically pumped 4.3-μm CO2 lasers
Authors: Brimacombe R.K. , Reid J.
Published: July 2002

Experimental results are presented which show that the dynamic Stark effect significantly reduces the small-signal gain (in discharge-excited CO2) and absorption (in unexcited CO2) at the line center of 4.3-μm laser lines directly coupled to 10.4-μm sequence-band pump transitions. In unexcited CO2, population transfer by the pump radiation is negligible and the influence of coherent effects can be observed unambiguously. The results of comparing experiment and theory in this simple case are used to modify a rate-equation model of the 4.3-μm gain dynamics, and the modified calculations are shown to be in good agreement with measured 4.3-μm gain coefficients.
Formation of pyrene crystalline thin films assisted by helium ion bombardment
Authors: Migita Masahito , Taniguchi Yoshio , Ishihara Heigo , Akagi Motoo , Ishiba Tsutomu , Tamura Hifumi
Published: July 2002

This paper reports on the effect of low energy He+ ion-beam bombardment upon the structure of pyrene thin films formed on quartz substrates. Films are prepared by vacuum evaporation during ion bombardment at room temperature. The structure of the film is controlled by the kinetic energy and current density of the ions. The colorless and transparent crystalline films preferentially oriented with their {001} plane parallel to the substrates are obtained by bombardment of 350 to 500 eV, 60 nA/cm2 He+ ions. Ion-beam irradiation of the higher ion current density enhances intermolecular chemical reactions and, as a result, a crystalline polymer with its {001} plane parallel to the substrate is produced.
Computation of fragment mass distributions for HF-1 steel explosive-filled cylinders
Authors: Mock Willis , Holt William H.
Published: July 2002

Computations using a one-dimensional computer program have been performed to determine fragment mass distributions for exploding cylinders of HF-1 steel. Experiments were performed to guide the computations. Nucleation and growth models were used to simulate the brittle fracture and shear band damage that occurred in the metal cylinders prior to complete fragmentation. Material input parameters for these models have been previously determined. Computations were performed for two heat treatments of HF-1 steel. The calculated brittle crack and shear band distributions were converted to fragment mass distributions using one of the experimental fragment shapes. Based upon the experimental results, suggestions are made for future refinements in the area of fragmentation modeling.