bluuebunny/crossref_metadata_2025 huggingface dataset:
Heavy-ion versus electron-beam excitation of an excimer laser
Authors: Moratz Thomas J. , Saunders Todd D. , Kushner Mark J.
Published: July 2002

A model is described for the heavy-ion pumping of an XeF(B) laser by uranium fission fragments (FF).The model is a self-consistent accounting of the generation and transport of the FF’s through the fission foils, slowing of the fragments in the gas, evolution of the secondary-electron-source function and distribution, and the XeF laser plasma kinetics. By simulating the same quantities for an e-beam-pumped plasma, direct comparisons can be made for laser performance. We found that the secondary-electron source generated by the e-beam is more energetic than that for direct ionization by FF’s due to a more favorable mass ratio for momentum transfer collisions with orbital electrons. This difference in the electron-source functions significantly affects W values and excitation fractions. The impact on laser performance, though, is not large due to the high efficiency of channeling deposited energy to the upper laser level in XeF lasers. For conditions typical of FF excitation (power deposition 1–3 kW cm−3, pulse length ≊200 μs), e-beam excitation results in 10%–15% higher gain than heavy-ion excitation.
Polarization-dependent gain-current relationship in (111)-oriented GaAs/AlGaAs quantum-well lasers
Authors: Hayakawa T. , Suyama T. , Takahashi K. , Kondo M. , Yamaoto S. , Hijikata T.
Published: July 2002

Detailed measurements of polarization-dependent gain-current characteristics have been carried out on (111)- and (100)-oriented GaAs/AlGaAs single-quantum-well lasers by using Hakki and Paoli’s method. Polarization-dependent gain-current characteristics have been found to strongly depend on the well width and the quantization direction. The saturation of gain with the injection current and the width of the gain spectrum depends on the well width, and they are also affected by the transition between the higher-order subbands. Experimental results of polarization-dependent spontaneous emission are also presented. The simple selection rule and the effective-mass theories do not quantitatively account for the experimental results.
Lattice theory of fracture of solids with layered structure
Authors: Tian Decheng , Xu Yin-Hua , Li Guo-Ming , Guan Wei-Ho
Published: July 2002

The lattice trapping effect of a crack in solids with layered structure has been studied with a double-chain model. It is shown that the difference in physicomechanical properties between different atomic planes has significant influence upon this effect, and the stress range for stability of a crack can be enhanced by increasing the difference. This perhaps, provides a way for the lattice trapping effect to be made observable by appropriately synthesizing solids with superlattices of special design.
Interfacial solid-state reaction at thermally oxidized In1−xGaxAsyP1−y alloys
Authors: Kubo Minoru , Sasai Yoichi , Ogura Mototsugu , Kohiki Shigemi
Published: July 2002

The interfacial reaction between thermally oxidized In1−xGaxAsyP1−y and an In1−xGaxAsyP1−y epilayer was studied using Raman and x-ray photoelectron spectroscopy (XPS) analyses. In Raman spectra, it was found that the appearance of the phonon modes, i.e., the first-order longitudinal (LO) and transverse-optical (TO) modes for crystalline arsenic, was due to the In1−xGaxAsyP1−y -oxide interfacial reaction. The XPS analyses showed that this reaction corresponded to the GaAs-oxide interfacial reaction, i.e., As2O3+2GaAs→Ga2O3+4As. Furthermore, the reaction depends on the composition y of In1−xGaxAsyP1−y, which may be due to the enhancement in the initial transient reaction by thermal damage of In1−xGaxAsyP1−y occurring at the interface.
Hydrogen-deuterium reactions on palladium-iron bilayers: A permeation investigation
Authors: Kuhn David K. , Johnson Herbert H.
Published: July 2002

The permeation of hydrogen, deuterium, and hydrogen-deuterium through iron coated with thin surface films of palladium has been measured. The experimental steady-state fluxes show the expected isotope diffusivity dependence in iron. A new observation is that hydrogen and deuterium react on the palladium surface to form HD, and this affects the permeation fluxes. The results are in good agreement with a model incorporating second-order surface kinetics which allow for competition between hydrogen and deuterium for surface sites. The theory predicts that the hydrogen/deuterium surface coverage ratio on palladium is ∼4 at room temperature for equal H2 and D2 pressures.
Graphoepitaxial growth of ZnS on a textured natural crystalline surface relief foreign substrate
Authors: Kanata T. , Takakura H. , Mizuhara H. , Hamakawa Y. , Kariya T.
Published: July 2002

A new type of graphoepitaxial growth of zinc sulfide (ZnS) crystalline thin films has been investigated. The substrate is polyimide coated with various thin films. It has an inverted pyramidal replica pattern taken from textured (100) single-crystalline silicon. Crystallinity and growth orientation of films were examined by scanning electron microscopy and x-ray pole figures. It has been confirmed that the crystal was grown from the bottom of the inverted pyramids. The results show that the graphoepitaxial effects are strongly sensitive to the ability of the semiconductor to wet the substrate coating materials at the nucleation temperature. The controllability of the crystallographic orientation normal to the substrate by the synthetic pattern is more than 85% in the present technology status.
Temperature dependence of photoluminescence spectra of the pentanary alloy semiconductor (AlxGa1−x)1−zInzPyAs1−y
Authors: Emura Shuichi , Sumida Hitoshi , Gonda Shun-ichi , Mukai Seiji
Published: July 2002

Photoluminescence spectra of the pentanary alloy semiconductor (AlxGa1−x)1−zInzPyAs1−y (x<0.33, y<0.18, z<0.09) are observed at various temperatures between 300 and 13 K. The spectrum at higher temperatures is of a single peak, in which the line shape is well reproduced by an expression of C(E−Eg)1/2 exp[−(E−Eg)/kBT], where E is the photon energy, Eg the band gap, kB Boltzmann constant, and T temperature. At lower temperatures, a band on the lower energy side grows up rapidly. The plot of integrated luminescence intensity of a high-energy peak as a function of reciprocal temperature shows a single exponential slope. The temperature dependence of the peak energy of the high-energy band is of a hyperbolic cotangent form. These experimental results suggest that the peak on the higher-energy side is attributed to a band-to-band transition.
A correlation between crystalline qualities and growth parameters in GaAs on Si grown by molecular-beam epitaxy
Authors: Ohbu I. , Ishino M. , Nakatani M. , Shimada T.
Published: July 2002

The effects of the As4/Ga flux ratio and the growth temperature on the crystalline qualities are demonstrated in the heteroepitaxy of GaAs on Si grown by molecular-beam epitaxy. To improve surface morphology, either the As4/Ga flux ratio must be optimized to 8 when grown at 560 °C or the growth temperature must be increased. In electron-beam-induced current images, a lot of complicated dark regions have been observed. The dark regions decreased and photoluminescence intensity became strong with the increase in the growth temperature.
Selectively δ-doped quantum well transistor grown by gas-source molecular-beam epitaxy
Authors: Kuo T. Y. , Cunningham J. E. , Schubert E. F. , Tsang W. T. , Chiu T. H. , Ren F. , Fonstad C. G.
Published: July 2002

We report electrical measurements on structures generated by δ doping the AlGaAs barriers of a GaAs quantum well. These structures are made unique by quantum size effects that occur both in the δ-doped barrier and in the GaAs well. Both the Hall-effect and capacitance-voltage measurements reveal that high-density, 4×1012 cm−2, two-dimensional electron gas forms in the well along with good mobility. We fabricate field-effect transistors with this structure to obtain transconductances of 300 mS/mm.
Single-pixel bistability with nonlinear interference filters
Authors: Abraham E. , Kar A. K. , Suttie M. R. , Harris R. M. , Walker A. C. , Smith S. D.
Published: July 2002

We present a theoretical model describing a pixellated, optically bistable, interference filter illuminated by a Gaussian beam. Preliminary experiments using ZnSe devices and 514-nm wavelength radiation show good agreement with this model for pixels of area 80×100 μm2 and a depth of 60 μm. Critical powers and cooling rates are presented for different combinations of materials and pixel dimensions.
Monte Carlo algorithms for collisional broadening and intracollisional field effect in semiconductor high-field transport
Authors: Reggiani Lino , Lugli Paolo , Jauho Antti-Pekka
Published: July 2002

We present a computational scheme which can be readily included in a standard Monte Carlo code to give quantitative estimates of the intracollisional field effect (ICFE) or of collisional broadening (CB). The central quantity in our theory is the joint spectral density K(εi, εf ) which connects the initial and final kinetic energy of a carrier in a scattering event. Crucial approximations, connected with the algorithms which model the joint spectral densities obtained from the appropriate Dyson equation, are clearly stated and discussed. Numerical results for a simple model semiconductor are provided for illustrative purposes. These show that both ICFE and CB lead to a significant increase of carriers in the high-energy tail of the distribution function.
Performance characteristics of a chemical oxygen-iodine laser without a water vapor trap
Authors: Kikuchi Toshio , Tsuruyama Toru , Uchiyama Taro
Published: July 2002

The effect of water vapor on the operation of a chemical oxygen-iodine laser without a water vapor trap is described. The maximum cw laser power of 87 W was obtained without the water vapor trap at a Cl2 flow rate of 740 mmol/min. An alkaline H2 O2 solution (90 wt. % H2 O2 , 50 wt. % KOH) was cooled down to about −30 °C in order to control the saturated H2 O2 -H2 O vapor pressure less than 100 mTorr. Two porous pipes made of carbon were utilized as a singlet oxygen generator.
Ultraviolet-light irradiation of a radio-frequency plasma applied to fluoropolymer sputtering deposition
Authors: Sugimoto Iwao , Miyake Shojiro
Published: July 2002

The excited states of molecular species in plasma play an important role in the organic film deposition process. The film structure and its characteristics are very dependent on this film preparation process. Although plasma species are in an excited transition state to spontaneously decompose and react easily with relatively stable molecules, they are not excited to the electronic transition state sufficiently to dissociate into multivalenced carbon species and polymerized into a polyolefinic film. In this research, ultraviolet-light irradiation is used during radio-frequency fluoropolymer sputtering as an excitation source to enhance the dissociation of molecular species in plasma. The film obtained has an olefin and cross-linking rich structure. The effects of this process on the film structure and its lubricating characteristics are examined. The plasma-emission analysis and mass spectroscopy showed that the bond dissociation of the sputtered segments has been stimulated by this photoassisted process. Consequently, the number of C■C bonds in the film obtained from photoassisted sputtering has increased in comparison with a film obtained from conventional sputtering, as observed by IR and XPS analyses. The resistance of the film to Ar ion bombardment was enhanced by the photoassisted sputtering. The film obtained from polychlorotrifluoroethylene (PCTFE) sputtered in CF4 had an extremely long lubrication life due to an increase in the rigid olefinic structure.
The dynamics of titanium ethoxide-doped dodecane droplet microencapsulation
Authors: Rubel Glenn O.
Published: July 2002

Single-droplet electrodynamic trapping is used to monitor the microencapsulation of titanium ethoxide-doped dodecane droplets immersed in water vapor. During the evaporation of volatile dodecane, titanium ethoxide reacts with water vapor to form a titanium dioxide film at the droplet surface. The onset of film formation is determined from changes in the droplet light transmission. It is shown that the time for film formation is dependent on the droplet size, water partial pressure, and initial concentration of titanium ethoxide. The reaction dynamics is liquid phase controlled and is first order in the ethoxide concentration. The porosity of the film is determined from the effect of the film formation process on droplet evaporation, as well as from scanning electron microscopy. For initial ethoxide concentrations less than 50% by weight, microencapsulation is characterized by porous films that have no observable effect on the evaporation rate. For ethoxide concentrations exceeding 50% by weight, impermeable films are formed that exhibit minimal porosity.
Lifetimes of cold cathodes for helium-neon gas lasers
Authors: Hall Lawrence H.
Published: July 2002

The energy distribution of ions, which are incident on the cathode of a glow discharge, is used to derive an expression for the rate of sputtering of a cold cathode as a function of the discharge parameters. The calculated rate of sputtering is compared with measured helium-neon cathode longevity as a function of discharge current density and fillgas pressure, and a model for helium-neon cathode mortality is developed. This theory is used to estimate the expected longevity of laser cathodes made from different materials.
Schottky diode: Comments concerning the diode parameters determination from the forward I-V plot
Authors: Manifacier J.-C. , Brortryb N. , Ardebili R. , Charles J.-P.
Published: July 2002

Some methods, which have recently been proposed, allow the determination of the diode parameters even in the presence of a high series resistance. A similar but much simpler treatment is presented here. Using the I-V plot, a straightforward determination of the series resistance R and the ideality factor n is obtained. These methods should be used cautiously anyway as in certain circumstances they can lead to erroneous results.
Mean-field analysis of the new type of noncollinear ferrimagnetic mixed systems for thermomagnetic recording
Authors: Kaneyoshi T.
Published: July 2002

A mean-field analysis is developed for a mixed Ising ferrimagnetic system consisting of spin- 1/2 and spin-1 with different transverse fields, which may have potential applications in thermomagnetic recording and magneto-optical readout systems. The phase diagram and the thermal behaviors of magnetizations are studied. We find that a compensation point induced by the different transverse fields is obtained, as well as the typical temperature dependencies of magnetization usually found in crystalline (or amorphous) ferrimagnetic alloys, although the system never exhibits any compensation point for the zero transverse fields.
Pulsed laser heating of silicon-nitride capped GaAs: Optical properties at high temperature
Authors: Bhat A. , Yao H. D. , Compaan A. , Horak A. , Rys A.
Published: July 2002

The optical properties of silicon nitride and gallium arsenide were studied at temperatures up to and beyond the melting point of GaAs by means of laser heating. XeCl excimer and pulsed dye laser pulses, ∼10 ns in duration, were used to heat the semiconductor under nitride capping layers of varying thickness. The transient reflectivity response at 514.5 nm was used together with a multilayer interference analysis to obtain the optical constants of solid and molten GaAs and of solid Si3N4 near the 1513-K melting point of GaAs. In addition, we report the melt duration as a function of laser pulse energy for GaAs with and without capping layers.
New determination method of electro-optic constants and relevant nonlinear susceptibilities and its application to doped polymer
Authors: Uchiki Hisao , Kobayashi Takayoshi
Published: July 2002

A new method is proposed for the determination of the electro-optic constants and relevant nonlinear susceptibilities. It was applied to polycarbonate films doped with 4-diethylamino-4′-nitrostilbene. The real and imaginary parts of the third-order nonlinear susceptibility X(3) (−ω;ω, 0,0) of the film were determined by the method between 600 and 800 nm at room temperature. X(3) (−ω;ω, 0,0) is (6+4i)×10−12 esu or quadratic electro-optic constant R is (−1−0.7i)×10−20 m2/V2 at 597 nm.
Secondary grain growth and formation of antiphase domains in ordered Cu3Au thin films
Authors: Chou T. C. , Tu K. N.
Published: July 2002

Anomalously large grains due to secondary grain growth in the ordered Cu3 Au thin film were observed by annealing the disordered thin film at 250 °C. No secondary grain growth was observed in the films annealed at 300 and 350 °C. The secondary grains have a preferred orientation of 〈111〉. Formation of antiphase domains with sizes larger than the normal grain size was found to accompany the growth of the secondary grains. Transmission electron microscopy showed that the coalescence of ordered grains contributed appreciably to the enlargement of secondary grains and antiphase domains. The driving forces of secondary grain growth and enhanced ordered domain growth are discussed on the basis of surface energy anisotropy and grain boundary migration.
Deep radiative levels in as-grown and implanted rapid thermal annealed InP
Authors: Rao Mulpuri V. , Aina Olaleye A. , Fathimulla Ayub , Thompson Phillip E.
Published: July 2002

Deep radiative levels in as-grown and Si-, Be-, and Hg-implanted InP:Fe activated by rapid thermal annealing are studied by photoluminescence measurements. A broadband centered at 1.07 eV is observed in unimplanted InP:Fe. The 1.17- and 0.775-eV peaks in the spectra of Si-implanted InP:Fe, and the 0.861-eV peak in the spectra of Be-implanted InP:Fe are believed to be due to the dopant-defect complexes. In Hg-implanted samples HgIn acceptor related peak is observed at 1.329 eV with longitudinal optical phonon peaks at 1.286 (1-LO) and 1.244 eV (2-LO). A peak at 0.919 eV is observed as an intrinsic peak in all InP samples. A single peak or several peaks with shoulders are also observed in the range 0.65–0.725 eV in many InP samples.
Variable focusing due to refractive-index gradients in a diode-array traveling-wave amplifier
Authors: Andrews John R.
Published: July 2002

Focusing of beams injected into a diode-array traveling-wave amplifier has been observed. The gradient in the complex index of refraction responsible for this lensing is well described by a quadratic profile centered over the array. Measurements both resonant and nonresonant with the gain spectrum indicate that the real part of the refractive index associated with a thermal gradient is the dominant source of the index gradient. The strength of the quadratic refractive-index coefficient varies from 0 to 0.19 mm−2 for amplifier currents between 0 and 550 mA. Adjustment of the focusing of the injected signal by translating a single cylindrical lens in an anamorphic telescope allows for near-diffraction-limited performance at any current. A far-field lateral beam divergence of 0.37° was observed for a 110-μm aperture (the calculated diffraction limit is 0.36°).
Effect of space charge on polarization reversal in a copolymer of vinylidene fluoride and trifluoroethylene
Authors: Ikeda Susumu , Fukada Tomohiro , Wada Yasaku
Published: July 2002

Polarization-reversal phenomena in ferroelectric copolymers of vinylidene fluoride and trifluoroethylene are affected by the time interval elapsed after poling of samples. Measurements of switching current demonstrated that this waiting effect is enhanced with the increase of space charges and switching curves with different waiting intervals satisfy the scaling rule when each switching curve is scaled by the switching time. These facts suggest that the electric field that reverses the spontaneous polarization decreases due to the electric field coming from space charges in the amorphous phase. A model with a prolate ellipsoid crystal and space charges in the amorphous phase explains such experimental facts. The difference of the waiting effect among samples crystallized under different conditions is also explained through the difference in the depolarization field coefficient of crystals.
Influence of atomic hydrogen on the growth reactions of amorphous boron films in a low-pressure B2H6+He+H2 plasma
Authors: Komatsu Shojiro , Moriyoshi Yusuke
Published: July 2002

The activation energy (E) of the growth reactions of boron films in plasma-assisted chemical vapor deposition from B2H6+He+H2 at a pressure of 300 Pa was measured at a range of substrate temperature from 750 to 1200 K. It was found that the E decreases continuously from 1.83 to 0.54 kcal/mol and then increases up to 4.97 kcal/mol with the increase of partial pressure of atomic hydrogen ([H]). The continuous change of E is supposed to be due to the transition of the dominant rate determining growth reaction, which is accompanied with the change of the composition of adsorbed layer on a film surface. The variation of E as a function of [H] can be explained with a kinetic model proposed here, in which the E of the growth reaction through BH3 is assigned to 1.83 kcal/mol, that through BH2 to 0.54 kcal/mol, and E of migration of BH2 on the film surface covered with hydrogen is related to be 4.97 kcal/mol.
A detailed analysis on donors in Te-doped Ga1−xAlxAs alloys near energy-band crossover points
Authors: Lee Hyung Jae , Choi Choon Tae
Published: July 2002

Based on the resultant analysis of the electron transport properties measured as a function of temperature, the donor levels in Te-doped Ga1−xAlxAs alloys near the band crossover points are investigated. The activation energy values of the deep donors vary with both temperature and composition, and the temperature coefficients of the activation energy variations are similar in magnitude to those of the band-gap variations and show decreasing trend with increasing Al concentration. The maximum activation energy ∼130 meV is observed at x=∼0.405, the Γ-X crossover point, at room temperature. The concentration ratio of shallow to deep donors decreases with increasing Al concentration in the compositions considered here.
Nonlinear optical waveguide directional coupler employing multiple quantum well structure
Authors: Hsieh H. C. , Robson P. N.
Published: July 2002

The nonlinear, lossy optical waveguide coupler employing GaAs/GaAlAs multiple quantum well structure has been analyzed. Using properly defined distributed circuit parameters, we model a system of coupled waveguides with a system of coupled transmission lines. The equivalent transmission line system parameters are derived in terms of the rectangular coupled waveguide system parameters. The coupled-mode theory, developed for the study of the nonlinear lossy transmission line system, is then applied to the equivalent transmission line system. The coupled-mode equations are solved numerically with the aid of the Runge–Kutta method, and the mode powers are calculated. It is shown that the variation of output power of the coupler and the division of powers between the two guides of the coupler depend strongly on the input power. The minimum input power required for the coupler to switch from the cross-over state to the straight-through state depends upon the losses of the guide as well as on the separation between the two guides of the coupler.
Stimulated Raman scattering in lead vapor pumped by a long-pulse 1-J XeCl excimer laser
Authors: Lou Qihong , Huo Yunsheng
Published: July 2002

The parametric dependence of the output energies and efficiencies for the Raman conversion of the radiation from a long-pulse 1-J XeCl excimer laser in Pb vapor was investigated. The effects of atom depletion and buffer gas on the stimulated Raman scattering output were discussed in detail. Multipeak structures of the waves of the Raman-shifted pulses were observed which could be attributed to the coherent effects in Raman scattering. A computer model was introduced to explain the multipeak structures of the stimulated Raman scattering waveforms.
Computer simulation of reflection of P ions from Si(100) crystalline targets in grazing incidence ion implantation
Authors: Oura Kenjiro , Ugawa Hiroaki , Hanawa Teruo
Published: July 2002

Reflection of 50-keV P ions from Si(100) crystalline targets has been studied using the binary collision cascade program marlowe. Implantation profiles, damage profiles, reflection coefficients, energy, and angular distributions of reflected particles have been calculated as a function of incident angles. The calculated data reveal a strong dependence of the implantation and reflection feature on the incident angle, particularly at grazing incidence conditions. An enhanced reflection is also found to occur at a critical angle which can be described by the surface channeling theory.
Surface polygonization on GaAs wafers
Authors: Gray M. L. , Abemathy C. R. , Caruso R. , Jordan A. S. , Parsey J. M.
Published: July 2002

Polygonized surface structure produced by furnace annealing GaAs wafers was studied by optical and scanning electron microscopy. The surface structure was revealed by chemically etching wafers which had been implanted with silicon and subjected to a furnace annealing cycle. Cathodoluminescence micrographs demonstrate an absence of impurity segregation to the polygon boundaries. No correlation was found between growth-induced dislocations and the polygonal networks. It is proposed that the surface structure results from a vacancy-condensation process. Related surface effects were observed for rapidly annealed wafers. A correlation between the furnace annealed and rapidly annealed GaAs is presented.
Influence of test signal frequency on the determination of band discontinuity of GaAs/AlGaAs heterojunctions from capacitance-voltage measurements
Authors: Subramanian S. , Vengurlekar A. S.
Published: July 2002

We have simulated the effects of deep donors in AlGaAs (DX centers) in the determination of band discontinuity (ΔEc) of GaAs/AlGaAs heterojunctions using the capacitance-voltage measurements. In addition to the partial ionization of the deep donors, the ability of the traps (deep donors) to respond to the test signal used for capacitance measurement has also been included in the analysis. We find that the deep-level effects lead to an underestimation or overestimation of ΔEc, depending upon whether the frequency of the test signal is low or high, respectively, as compared to the emission rate of the traps.
Photoemission and inverse photoemission studies of La adatom interactions with YBa2Cu3O6.9
Authors: Gao Y. , Wagener T. J. , Aldao C. M. , Vitomirov I. M. , Weaver J. H. , Capone D. W.
Published: July 2002

The surface reactions that occur when adatoms of La are deposited onto the high-temperature superconductor YBa2Cu3O6.9 have been studied using high-resolution synchrotron radiation photoelectron spectroscopy and inverse photoelectron spectroscopy. These adatoms lead to the depletion of oxygen from the substrate as La-O forms at low coverage. The process of oxygen withdrawal quickly becomes kinetically limited as the thickening overlayer impedes mass transfer. At the same time, Cu atoms released from the disrupted, no-longer- superconducting substrate outdiffuse into, and segregate to the top of, the growing La overlayer. The complex reacted interface, therefore, exhibits phases which are likely to be superconducting, insulating, and metallic.
A bulk optically controlled semiconductor switch
Authors: Germer Rudolf K. F. , Schoenbach Karl H. , Pronko Steven G. E.
Published: July 2002

Turn-on and turn-off of bulk semiconductor switches, based on excitation and quenching of photoconductivity, respectively, have been demonstrated with copper-doped II-VI semiconductor crystals. The increase of the conductivity (turn-on) was realized with a xenon flash-lamp pulse of 15-μs duration. A reduction of the conductivity (turn-off) was obtained by irradiating the samples with IR light using an 8-ns Nd:YAG laser pulse (YAG denotes yttrium aluminum garnet). For turn-on in CdS:Cu the conductivity follows the xenon flash excitation. The turn-off time constant was 250 ns. ZnS and ZnSe crystals showed a slower response. A memory effect for the IR light was observed.
Annealing effects for implanted Y-Ba-Cu-O superconductors
Authors: Matsui S. , Ochiai Y. , Matsutera H. , Fujita J. , Yoshitake T. , Kubo Y.
Published: July 2002

Annealing effects of Y-Ba-Cu-O superconductor thin films implanted by 200-keV Ne+ have been investigated. Transition temperature (Tc) end points for 0, 1×1014, 1×1015, and 1×1016 ions/cm2 doses are 75, 71, 62, and 16 K, respectively. The film implanted at 1×1017 ions/cm2 dose indicates nonsuperconductors. The c-lattice constant increases were observed for the implanted films. It is confirmed that the superconducting characteristics for film, which is implanted at 1×1016 ions/cm2 dose, are recovered by annealing in O2 atmosphere at 940 °C for 4 h. Moreover, microcrystal growth caused by annealing the implanted film was observed on the surface.
X-ray efficiency of phosphor screens in the 20–60 kV range
Authors: Giakoumakis G. E.
Published: July 2002

The absolute efficiency of phosphor screens under x-ray excitation is studied for tube voltages ranging from 20 to 60 kV. The screens were prepared of ZnS:Cu, ZnCdS:Ag, Y2O2S:Tb, Gd2O2S:Tb, and CaWO4, which are the phosphors most commonly used in the x-ray applications. This efficiency appears to be about 100 times lower than the efficiency of the same screens under fluoroscopy conditions.
The effect of heat treatment on redistribution of fast diffusing impurities in polycrystalline silicon
Authors: Kumar Rajesh , Kotnala R. K. , Arora N. K. , Das B. K.
Published: July 2002

The effect of heat treatment on minority carrier surface recombination velocity in polycrystalline silicon samples has been examined in the temperature range (600–900 °C) using the electron-beam induced-current mode of a scanning electron microscope. Minority carrier trap center density, calculated from minority carrier surface recombination velocity data, varying from 8.9×1011 to 6.37×1013 cm−2 have been measured. A finite variation in the minority carrier trap center density indicates that metallic impurities diffuse to the surface from the bulk of the sample. The activation energy of impurity atom diffusion is found to be 1.1±0.1 eV.
Inversion and gain in hydrogenic ion levels induced by photoionization pumping
Authors: Goodwin D. G. , Fill E. E.
Published: July 2002

If a low-Z plasma is subjected to ionizing radiation, stationary inversions on hydrogenic ion level populations occur. The plasma conditions and pumping requirements to achieve gain on the Lyman-α and Balmer-α lines are investigated by means of a collisional-radiative model. The calculations are carried out for two cases: first, for the case in which the electron temperature is determined solely by radiative cooling, and second, for the case in which additional electron cooling is provided. In the first case, measurable gain on the Balmer-α line is found, although the Lyman-α transition remains uninverted. In the second case, the Balmer-α gain is dramatically enhanced, and sizable Lyman-α gain is predicted.
Mass transport during photochemical oxidation of Hg1−xCdxTe
Authors: Kao T.-M. , Sigmon T. W.
Published: July 2002

We report determination of the mechanism of photochemical oxide growth (after initial film formation) when transport through the film dominates. Photochemical oxides grown in different ambients, i.e., O2 or N2O, are found to have different stoichiometry, especially at the ambient/oxide interface. Oxides grown in O2 with ultraviolet light exhibit Hg-rich surface layers, however growth in N2O often results in Hg-depleted surfaces. By sequentially oxidizing Hg1−xCdxTe epilayers in these ambients and analyzing the in-depth atomic profiles with Rutherford backscattering spectrometry and secondary ion mass spectrometry, the dominant diffusion mechanism is determined. Investigation of the migration of oxygen during the oxidation is carried out by oxidation in an 18O enriched ambient. We conclude that growth of these photochemical oxides involves both the diffusion of the substrate elements and oxygen, with the oxidation occurring primarily at the oxygen-oxide interface.
Mechanical properties of LaNi5 thin films prepared by sputtering and vapor deposition methods and determination of the hydrogen content in these films
Authors: Sakaguchi H. , Taniguchi N. , Seri H. , Shiokawa J. , Adachi G.
Published: July 2002

Amorphous LaNi5 films were prepared using a sputtering method. Mechanical properties and hydrogenation characteristics of the films were investigated and the results were compared with those of the deposited films. The density of the sputtered LaNi5 film was about 6 g/cm3, which was larger than that of the evaporation deposited film but smaller than that of crystalline LaNi5. Thermal conductivities of amorphous films were larger than those of bulk samples. Mechanical strength of the sputtered films deposited on various substrates was measured after 100 cycles of hyrogen absorption–desorption process. The result was in the following order for the substrates used: Ni foil>Ni>Al foil>Cu foil>Cu>Al>glass. The hydrogen content in a sputtered film with a thickness of 1.3 μm was found to be 2.4 H/LaNi5. The hydrogen concentration in the film increased monotonically with increasing the hydrogen pressure in both cases between 333 and 363 K.
Study of epitaxial growth of ZnTe on GaAs (001) by channeling
Authors: Chami A. C. , Ligeon E. , Fontenille J. , Feuillet G. , Danielou R.
Published: July 2002

Channeling is used to describe defects associated with molecular-beam epitaxy growth of (001) ZnTe on (001) GaAs. A high dislocation density (2×1011/cm2) is found in the immediate vicinity of the interface, in addition to misfit dislocations at the interface. Channeling is found to be a strain sensitive method useful for misfit dislocation analysis. Direct scattering on misfit dislocations together with elastic theory calculations reveals that the extent of the misfit dislocation elastic field increases with the interface roughness.
Ion-beam mixing at Fe:metallic-glass (Fe67Co18B14Si1) interface: A conversion-electron Mössbauer spectroscopic study
Authors: Bhandarkar Y. V. , Ghaisas S. V. , Ogale S. B.
Published: July 2002

Ion-beam mixing at an Fe:metallic glass (Fe67Co18B14Si1) interface is studied by employing the technique of conversion electron Mössbauer spectroscopy (CEMS). A 230-Å-thick overlayer of iron (enriched to 33% in the concentration of 57Fe Mössbauer isotope) was deposited on the shiny surface of metallic glass and such composites were bombarded with 100-keV Kr+ ions at dose values in the range between 1×1015 and 2×1016 ions/cm2. The transformations in the local atomic arrangements across the interface were investigated by monitoring the changes in the hyperfine-interaction parameters. It is shown that mixing leads to significant changes in the composition, in the vicinity of the interface as a function of the ion dose. At low dose (1×1015 ions/cm2) the local atomic coordination is found to be rich in the transition-metal concentration, while at a higher dose (2×1016 ions/cm2) it is observed to be rich in the boron concentration. Interestingly, at an intermediate dose 1×1016 ions/cm2 the composite near the interface region partially crystallizes and this structural state is found to revert back to the amorphous state upon thermal annealing at 300 °C. The observations made on the basis of CEMS are well supported by x-ray diffraction measurements.
Growth of αRh2As on GaAs (001) in a molecular-beam epitaxy system
Authors: Guivarcrsquo;h A. , Secoué M. , Guenais B. , Ballini Y. , Badoz P. A. , Rosencher E.
Published: July 2002

Thin films of αRh2As were grown on top of GaAs (001) in a molecular-beam epitaxy system by codeposition of rhodium and arsenic from separate sources. αRh2As is a good metal with a resistivity equal to 20 μΩ cm, suitable for electronic applications. The holes, the only type of carriers, have a concentration equal to 2.5×1022 cm−3, i.e., a value of the same order of magnitude as that of the best silicides. However, in spite of several features common to αRh2As and GaAs (symmetry, almost equivalent unit-cell constant, and fcc As sublattices), the epitaxial arrangement [100](011)αRh2As//[110](001)GaAs mainly prevails instead of the expected simple unrotated relationship [100](001)αRh2As//[100](001)GaAs. This points out that the achievement of the minimum lattice mismatch is not always the driving force for the epitaxy. In agreement with the ternary phase diagram Rh-Ga-As, the (polycrystalline αRh2As)/GaAs system interacts above 400 °C and leads to the formation of the binary compounds RhGa and RhAs2.
Recent progress in studies of a-CSiSn:H alloys
Authors: Demichelis F. , Kaniadakis G. , Tagliaferro A. , Tresso E. , Rava P. , Della Mea G.
Published: July 2002

The a-CSiSn alloy produced by rf magnetron sputtering in SiH4, CH4, and Ar atmosphere was studied as a function of the substrate temperature. The composition of the films was determined by elastic recoil detection analysis and by Rutherford backscattering measurements, and the density was then deduced. Results of a study of optical and electrical properties and of the bonding and structure of the films indicate that with the increase of the substrate temperature, the density and the imaginary part of the dielectric constant increases, the optical gap decreases, and the dark conductivity presents a different conduction mechanism depending on the substrate temperature. A correlation between the results obtained from nuclear measurements and IR spectroscopy is presented.
Chirp in pulsed, rf-excited CO2 waveguide lasers
Authors: Sharp Richard C.
Published: July 2002

An experimental investigation has been conducted to determine the frequency stability of a pulsed, rf-excited waveguide CO2 laser. Unlike transversely excited atmospheric CO2 lasers, for which the optical extraction of energy (laser-induced medium perturbation) is typically the dominant source of frequency instability, the driver in the long pulse (>30 μs) waveguide laser is the thermal heating of the gain medium due to the rf input energy. Modeling of the chirp in the pulsed waveguide laser is performed. Included are both finite V-T effects in the short term and heat conduction and particle migration out of the laser bore by the gaseous gain medium in the long term.
Laser power absorbed outside the beam spot on a rippled metallic surface as determined by a matrix calorimetric method
Authors: Ursu I. , Mihailescu I. N. , Campan Calina-Diana , Prokhorov A. M. , Konov V. I. , Tokarev V. N.
Published: July 2002

A new modified matrix calorimetric method is presented that allows one to determine, with the use of only one thermocouple, the distribution of power dissipation across an extended heat source. This method allows experimental determination of the fraction of the incident laser power (energy) absorbed on a metallic surface outside an irradiation spot located on a rippled area. It is shown that this fraction can amount to a significant part of the total incident laser power (energy). The effect is important in high-intensity laser irradiation of metals when periodic surface structures are induced within the irradiation spot by action of the laser radiation.
Temporal contraction of solitons in a nonuniform transmission line
Authors: Ikezi H. , Wojtowicz S. S. , Waltz R. E. , Baker D. R.
Published: July 2002

We present experimental and numerical evidence of temporal contraction of electromagnetic pulses propagating in nonuniform, nonlinear dispersive transmission lines. The pulses are both contracted and amplified by orders of magnitude.
Effects of deposition angle on perpendicular anisotropy and internal stress in evaporated TbFeCo films
Authors: Lee Yong Ho , Lee Sang Soo
Published: July 2002

The effects of deposition angle on perpendicular magnetic anisotropy and internal stress in thermally evaporated amorphous TbFeCo thin films are investigated. We have found that the perpendicular anisotropy and the internal stress depend strongly on the deposition angle, and above a threshold value (30°), the perpendicular anisotropy disappears and the in-plane anisotropy appears. The measurement of internal stress, which is due to the substrate constraint, reveals that the compressive stress is the major contribution to the perpendicular anisotropy. The measurements of Kerr hysteresis loops in the polar and longitudinal directions show that, as the deposition angle increases, the polar Kerr hysteresis loop deteriorates, while the longitudinal Kerr hysteresis loop becomes prominent.
The etching of doped polycrystalline silicon by molecular chlorine
Authors: Ogryzlo Elmer A. , Flamm Daniel L. , Ibbotson Dale E. , Mucha John A.
Published: July 2002

The etching reaction of molecular chlorine with phosphorus-doped polycrystalline silicon was measured as a function of dopant concentration between 300 and 500 °C. The effective activation energy of the gasification reaction is 13.4±1 kcal/molec and does not change with doping level within experimental uncertainty. However, the isothermal reaction rate at constant reactant flux increases sharply with doping level, and the preexponential factor rises from 4×10−12 to 1×10−10 (Å cm3/molec min K1/2) as the phosphorus content is increased from 3.3×1018 to 1.6×1020 atoms/cm3. This rise in the preexponential factor is consistent with the charge-transfer model, in which doping makes Si-Cl bonding more ionic and increases the number of effective adsorption sites.
Steady-state Nyquist theorem for nondegenerate semiconductors
Authors: Min H. S.
Published: July 2002

The steady-state Nyquist theorem (or the steady-state fluctuation-dissipation theorem), which reduces to the Nyquist theorem in thermal equilibrium, is obtained for nondegenerate semiconductors by solving the Langevin-type Boltzmann transport equations with the relaxation-time approximation. This theorem is an extension of the Nyquist theorem to nonequilibrium systems for nondegenerate semiconductors. The derived theorem holds for any nondegenerate semiconductor device with one-dimensional geometry when the quasi-Fermi levels of electrons and holes can be defined for the steady-state electron and hole distributions at any position inside the device, i.e., when at any position inside the device the steady-state electron and hole distributions are not driven far away from the Maxwellian distributions. The derived theorem resembles almost exactly the functional form of the Nyquist theorem. As an application of this theorem the thermal noise in double-injection space-charge-limited solid-state diodes is calculated using this theorem.
Determination of the degree of alignment and intrinsic magnetic properties of barium ferrite in bonded magnets (abstract)
Authors: Hopstock David M.
Published: July 2002

Departures from ideal demagnetization characteristics of bonded barium ferrite magnets may result from incomplete alignment of the ferrite platelets or from physical damage to the crystals induced by stresses during the production process. It is desirable to separate these two effects. Vibrating sample magnetometer measurements were made in three orthogonal directions on cubes cut from bonded magnet specimens. From these results parameters characterizing the platelet orientation distribution function were obtained. It was then possible to estimate the magnetic properties of ideally aligned crystals. Some of the factors influencing the degree of alignment are discussed.
Determination of angular dependence of the critical field of barium ferrite from remanence and microwave measurements (abstract)
Authors: Schumacher F. , Hempel K. A. , von Staa F.
Published: July 2002

The distribution of the critical field of nontextured polycrystalline ferrite is determined. Barium ferrite samples are saturated in one direction and measured with a field H applied at an angle θ to the saturation field. The measured quantities are the remanent magnetization and the microwave hysteresis including minor loops. Especially the microwave absorption curves allow direct analysis of the critical field as a function of the orientation angle ϑ0 between H and the easy axis. Starting with these data a fit of the calculated to the measured remanence curves yield the distribution. The figure shows the critical field distribution of a ferrite sample with large coercivity. Additionally the calculated and measured resonance fields ares are given. All field strengths are normalized to the anisotropy field, which can also be determined from the microwave measurement.1
A new magnetic shield using C-shaped magnetic materials
Authors: Haga A. , Nasuno H. , Kikuchi S.
Published: July 2002

This paper describes the structure and the characteristics of a new magnetic shielding device. This magnetic shielding device utilizes a certain magnetic circuit in which the C-shaped magnetic materials are combined in a cagelike shape. This shield is a nonenclosing structure, like a spherical shell. It is effective in reducing the leakage flux from a Helmholtz coil. This device has a number of excellent features, i.e., the shield is free from heat generated by the coil because of the open structure, there is a decrease in fabrication costs because of the simple structure, and it is easy to build a practical shield of this type.
Pipe locator for imaging underground pipelines (abstract)
Authors: Miyamoto Y. , Wasa Y. , Mori K. , Kondo Y.
Published: July 2002

Recently, it becomes more important to locate the complex piping patterns such as tee, bend, riser, and the others with high accuracy for maintenance and protection of city gas pipelines. Hence, we have developed a new pipe locator system for imaging the complex underground pipelines using magnetic remote sensing techniques. The main framework of this development is the application of the pattern recognition of the magnetic field distribution to the location of buried pipelines in urban areas. The first step for imaging the complex pipelines is to measure the three-dimensional magnetic field distribution with high accuracy which is generated by the passage of the alternating signal current through buried pipeline. For this purpose a portable trolley unit which is capable of scanning the ground to collect data, the 10 three-axes coil sensors with a sensitivity of 1 μG which are aligned in the unit, and a filter system using a FFT signal processor which eliminates urban magnetic noise as high as 10 mG in some cases, were developed. The second step is to process the magnetic field distribution data, to extract the feature of the underground pipeline using the contour diagram and the three-dimensional drawing of the magnetic field, and to identify the complex piping patterns. Further, we recognized that a nonlinear least-square method algorithm for calculation of the pipeline’s position was useful to improve the location accuracy.