bluuebunny/crossref_metadata_2025 huggingface dataset:
Excimer laser ablation of ferrites
Authors: Tam A. C. , Leung W. P. , Krajnovich D.
Published: July 2002

Laser etching of ferrites was previously done by scanning a focused continuous-wave laser beam on a ferrite sample in a chemical environment. We study the phenomenon of photo-ablation of Ni-Zn or Mn-Zn ferrites by pulsed 248-nm KrF excimer laser irradiation. A transfer lens system is used to project a grating pattern of a mask irradiated by the pulsed KrF laser onto the ferrite sample. The threshold fluence for ablation at the ferrite surface is about 0.3 J/cm2. A typical fluence of 1 J/cm2 is used. The etched grooves produced are typically 20–50 μm wide, with depths achieved as deep as 70 μm . Groove straightness is good as long as a sharp image is projected onto the sample surface. The wall angle is steeper than 60 degrees. Scanning electron microscopy of the etched area shows a ‘‘glassy’’ skin with extensive microcracks and solidified droplets being ejected that is frozen in action. We found that this skin can be entirely removed by ultrasonic cleaning. A fairly efficient etching rate of about 10 nm/pulse for a patterned area of about 2 mm×2 mm is obtained at a fluence of 1 J/cm2. This study shows that projection excimer laser ablation is useful for micromachining of ferrite ceramics, and indicates that a hydrodynamic sputtering mechanism involving droplet emission is a cause of material removal.
A parametric study of extrinsic bistability in the current-voltage curves of resonant-tunneling diodes
Authors: Jogai B. , Koenig E. T.
Published: July 2002

We report numerical simulations of typical experimental conditions under which current-voltage (I-V) measurements of resonant-tunneling diodes are conducted. We find that curve tracer measurements can cause bistability and hysteresis in the negative differential resistance (NDR) region. We also find that dc measurements can produce oscillations which distort the shape of the I-V curve. When the series resistance is large, there are three states for a given bias in the NDR region because of the folding of the I-V curve. We believe this phenomenon, extrinsic tristability, to be the source of extrinsic bistability.  
Low-frequency self-field effect on the critical temperature of bulk high-temperature superconductor
Authors: Crisan O. , Liu M. , Ayub M. N. , Yu Q.
Published: July 2002

The critical temperature (Tc) of sintered and melt-textured YBa2Cu3O7+x samples carrying current with different rms values and frequencies were measured. The low-frequency self-field effect on the Tc value is reported here. For the sintered samples, Tc shifts with both the rms value and the frequency of applied transport current. A similar effect is not observed in the melt-textured samples.
Coupling effects in triple quantum wells
Authors: Juang C. , Hwang R. Y. , Pan H. C. , Chang C. M. , Lee B. J.
Published: July 2002

A theoretical and experimental investigation of coupling effects in triple quantum wells is presented. Photoluminescence spectra of various triple coupled well structures prepared by metalorganic chemical vapor deposition show the effects of the well width on the electron to heavy hole transition energy and on the full width of half maximum. Also, the experimental results are compared to the time-independent solutions of the Schrödinger equation obtained by the inverse power method.
Optically controlled characteristics of Schottky gated poly(3-alkylthiophene) field effect transistor
Authors: Yoshino Katsumi , Takahashi Hiroyuki , Muro Keiro , Ohmori Yutaka , Sugimoto Ryuichi
Published: July 2002

A Schottky gated field effect transistor (FET) has been prepared utilizing poly(3-alkylthiophene) containing photodissociative diphenyliodonium hexafluoroarsenate (Ph2IAsF6). Upon irradiation of light on the FET, the FET characteristic has changed drastically which can be explained in terms of enhanced carrier density and carrier mobility due to the photodissociation of Ph2IAsF6. The relation between enhancement of carrier density and that of carrier mobility has been discussed. Monolithic field effect transistors composed of poly(3-alkylthiophene) containing Ph2IAsF6 have been also proposed.
Oxidation of Si1−xGex alloys at atmospheric and elevated pressure
Authors: Paine D. C. , Caragianis C. , Schwartzman A. F.
Published: July 2002

The oxidation of alloys of Si1−xGex differs significantly from that of pure Si in both the thermodynamics of the process and in the kinetics of the oxidation reaction. In this paper these fundamental differences are explored and are used to explain experimental observations of Si1−xGex oxidation that are presented herein and elsewhere in the literature. Alloys of Si1−xGex (with x=5.4, 11.6, and 17 at. %) approximately 200 nm thick were oxidized using the following two processes: (i) dry oxygen at 680 atm at a temperature of 550 °C and (ii) conventional, 1-atm steam at 800 °C. The wet oxidation conditions were chosen to produce an oxide thickness comparable (≊100 nm for xGe=11.6 at. %) to that obtained during high-pressure oxidation at 550 °C. Auger sputter depth profiling, x-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy were used to characterize the as-grown oxides. XPS studies reveal that high-pressure oxides formed from alloys of Si1−xGex chemically incorporate Ge directly into the oxide. In contrast, atmospheric oxidation of the same alloy composition produces oxides with no Ge incorporation that is detectable using XPS. It is shown that the selective removal of Si from alloys of Si1−xGex is predicted from Si-Ge-O ternary-phase equilibrium considerations. High-pressure oxidation conditions, however, allow the growth of oxides at much lower temperatures which minimizes Si-Ge interdiffusion and, as a consequence, prevents the selective oxidation of Si from the alloy. These results have direct significance to future device fabrication in Si1−xGex and to the issues of oxidation of multicomponent systems in general.
The oxide nitride oxide film deposition on the tunnel-structured polycrystalline silicon (polysilicon) electrodes for high-density dRAMs
Authors: Matsuo Naoto , Nakata Yoshirou , Okada Shouzou
Published: July 2002

The uniform deposition of the oxide nitride oxide (ONO) film on the tunnel-structured polysilicon electrodes was examined by measuring the electrical characteristics of the capacitor and by using transmission electron microscopy. The conventional low pressure chemical vapor deposition method was adopted for the deposition of the nitride film of the ONO. The tunnel length is varied from 1.6 to 15.6 μm. The ONO film deposited over the entire tunnel of 15.6 μm showed good electrical characteristics, and the thickness uniformity as well. In addition to the maximum tunnel length which can accommodate the uniform ONO deposition, the growth mechanism of the ONO film inside of the tunnel is discussed.
Stripe width dependence of oxidation-enhanced diffusion in submicron local oxidation of silicon structures
Authors: Shibata Yoshiaki , Taniguchi Kenji , Hamaguchi Chihiro
Published: July 2002

Oxidation enhanced diffusion (OED) of phosphorus under very narrow oxidized region is investigated. The OED effect is found to depend on the oxidized region width for below 4–5 μm, i.e., the enhancement of phosphorus diffusivity decreases with decreasing the oxidized region width. In order to clarify the mechanism, two dimensional numerical simulations are carried out using various models for silicon self-interstitial generation at the Si/SiO2 interface during thermal oxidation. A series of OED observations is well simulated by using the new model in which the self-interstitial concentration at the oxidized interface is determined by the balance of (a) the interstitial generation due to oxidation reaction at the interface, (b) the kinetics of surface regrowth, and (c) the flux of interstitials into previously formed oxide. Effective surface regrowth rate constants for self-interstitials at the nonoxidized interface are then extracted. It is found that the surface regrowth rate constants in local oxidation of silicon structures are considerably large compared with those extracted from back side oxidation experiments.
Influence of B concentration on recrystallization of polycrystalline Si
Authors: Carlsson J. R. A. , Gong S. F. , Li X.-H. , Hentzell H. T. G.
Published: July 2002

B-doped polycrystalline Si films were prepared by electron beam evaporation and heat treatment in order to study the influence of B concentration and annealing temperature on recrystallization of polycrystalline Si. By using cross-sectional transmission electron microscopy and Auger electron spectroscopy it is shown that: (1) at a B concentration between 1 and 10 at. %, post-annealing at 1100 °C results in an enhanced solid phase epitaxial growth; (2) at a B concentration higher than 10 at. %, post-annealing results in a retarded recrystallization of polycrystalline Si; (3) a relatively stable amorphous alloy can form at a B concentration of ∼35 at. % up to 1100 °C. The mechanisms of the enhancement and the retardation are discussed.
A Monte Carlo study of many-valley effects on the temporal electron transient transport in silicon
Authors: Chen Roger Y. , Pan Dee-Son
Published: July 2002

Six-valley effects on electron transient transport in silicon (Si) are investigated by temporal Monte Carlo simulations. The effects on velocity overshoot, carrier repopulation, and average electron energy are studied using two well-known models of Si. Substantial differences in transient carrier repopulation and average energy are found using the two models. For transient carrier velocity, the two models give essentially the same response. A simple one-valley model for Si with optimized parameters is presented for saving computer time when accuracy is not strictly demanded. The significance of these results is discussed.
Polymeric electro-optic phase modulators formed by self-alignment over channels etched into indium phosphide
Authors: Hill J. R. , Pantelis P.
Published: July 2002

Waveguides which are single mode at a wavelength of 1.32 μm, and which have linear electro-optic properties, have been fabricated by spin coating polymers onto etched indium phosphide. The side-chain polymer, which comprises the core of the waveguide, develops linear electro-optic properties following an electric field alignment process. A phase modulator has been fabricated by this method and was found to have a switching voltage of 30 V, for a π phase change. The total insertion loss of the device was measured between single-mode lensed fibers to be 9.4 dB. The electro-optic coefficient of the core polymer was calculated from the switching voltage using the geometry of the device and found to range from 6 to 11×10−12 m/V.
Surface-emitting, distributed feedback InGaAs/AlGaAs lasers by organometallic vapor phase epitaxy
Authors: Bour D. P. , Carlson N. W. , Evans G. A. , Liew S. K. , Kirk J. B. , Reichert W. F.
Published: July 2002

The growth, fabrication, and operation of InGaAs/AlGaAs distributed feedback (DFB) grating surface emitting (GSE) lasers are described. These devices contain a continuous, buried second-order diffraction grating, for which two organometallic vapor phase epitaxial growths are required. Compared to more conventional distributed Bragg reflector surface emitting lasers, the grating and its coupling coefficient are much more uniform, since it is patterned onto a planar surface. Operation of ten-element linear arrays, and a 10×10 array of DFB-GSEs is also demonstrated, and the threshold dependence on both the layer and array structure is discussed.
Lasing of ArF with a microsecond electron beam
Authors: Glessner J. W. , McAuliffe M. J. , Smith B. D. , Floyd K. B.
Published: July 2002

ArF(B-X) laser emission has been observed under long pulse electron-beam excitation at relatively low pump rate. ArF lasing only occurred with Ne buffered gas mixtures. Optimum performance of 1.93 J/ℓ at an intrinsic efficiency of 1.35% occurred with an Ar/F2 mixture of 1/0.075% using a Ne buffer to 4.0 amagats. Total energy of 290 mJ in a 2-cm2 beam with a 1.0-μs full width at half maximum pulse width was recorded.
On the in-plane acceleration sensitivity of contoured quartz resonators supported along rectangular edges
Authors: Tiersten H. F. , Zhou Y. S.
Published: July 2002

It is shown that the resultant in-plane acceleration sensitivity of contoured quartz resonators symmetrically supported along rectangular edges always vanishes. This result is a consequence of symmetry and applies to any shape for which the support system is symmetric with respect to the center of the mode shape. When the active plate is supported on one side only, a state of flexure is induced in the resonator which degrades the in-plane sensitivity. This emphasizes the importance of a symmetric support system to achieve low acceleration sensitivities. The extensional and induced in-plane flexural biasing deformations are determined by means of our variational approximation procedure using the variational principles in which all conditions appear as natural conditions. The resulting biasing states are employed in an existing perturbation equation along with the mode shapes of the contoured resonators to calculate the nonvanishing acceleration sensitivities when the resonator is supported on one side only.
A simple new laser diode array model for thermal interaction analysis
Authors: Murata Setsuko , Nishimura Kazutoshi
Published: July 2002

A simple new laser diode array model using the boundary element method is presented. This model−which needs few boundary elements and little calculation time−represents a multilayer chip as a single-layer chip and distributed heat sources as a line heat source in the center of an active region, and neglects the grooves between array elements. For three types of laser diode array chips with element spacing greater than 50 μm, the simple model estimates thermal interactions to within 2%. The interactive thermal influence of laser diode array packing density and the number of elements is discussed in terms of this simple model: Submounts and stems with high thermal conductivity are shown to be effective for increasing the number of elements packed within an array chip. With a type-IIa diamond submount, for example, the number of elements packed within a 400-μm width on an array chip can be increased from five elements 100 μm apart to nine elements 50 μm apart without increasing thermal interaction.
Trapping of atomic hydrogen in silicon by disordered regions
Authors: Srikanth K. , Ashok S.
Published: July 2002

This paper addresses issues related to migration and acceptor neutralization of hydrogen (H) in crystalline Si. From spreading resistance measurements, it is shown that disordered regions, both surface and subsurface, directly inhibit the penetration of H. Further, these effects are shown to be independent of the kind of disorder and the method of hydrogenation. Secondary-ion mass spectrometry profiles of deuterated samples confirm the suppression of deuterium movement through the disordered regions. We observe that annealing of these hydrogenated damage regions results in generation of an acceptor deactivation profile which is persistent for temperatures up to 800 °C and durations up to 1 min. This sustained deactivation phenomenon results in up to four decade change in free-carrier concentration. Our results unequivocally suggests that H-soaked damage region acts as a source of atomic hydrogen under rapid thermal annealing.
Synchrotron x-ray diffraction studies of the lattice and magnetic structure of epitaxial Dy films in LaF3/Dy/LaF3 sandwiches
Authors: Farrow R. F. C. , Toney M. F. , Hermsmeier B. D. , Parkin S. S. P. , Wiesler D. G.
Published: July 2002

Lattice and magnetic x-ray diffraction from a 2000 Å thick film of Dy, sandwiched by LaF3 films on a GaAs(111) substrate, are reported. The structure was grown by molecular beam epitaxy with the c axis of the Dy parallel to the LaF3 c axis and GaAs [111] axis. We find that the c-axis lattice constant of the Dy has a similar temperature dependence to bulk Dy from room temperature to about 110 K, but below this, the film is different from bulk. The transition to ferromagnetic ordering at ∼86 K exhibits temperature hysteresis which is also evident in the magnetic x-ray scattering and SQUID magnetometry data. This hysteresis may arise from a combination of the strain-energy barrier accompanying the transition and magnetic inhomogeneities in the film. The temperature dependence of the magnetic wave vector is qualitatively similar to bulk, although a weaker dependence is observed below ∼110 K, which is possibly caused by magnetoelastic effects. The magnetic coherence length (310 Å) is significantly shorter than the structural coherence length (730 Å).
A numerical simulation of hole and electron trapping due to radiation in silicon dioxide
Authors: Vasudevan V. , Vasi J.
Published: July 2002

The one-dimensional Poisson, continuity, and the trap rate equations are solved numerically to study the buildup of charge in silicon dioxide due to radiation. The flat-band voltage shift (ΔVfb) is obtained as a function of total dose, the oxide thickness, the applied gate voltage, and the centroid of the trap distribution. The effect of including electron traps is studied. The results of the simulation are found to compare well with experimental data.
Long-term stability of hydrogenated amorphous germanium measured by infrared absorption
Authors: Ghazala M. Abo , Beyer W. , Wagner H.
Published: July 2002

The long-term compositional stability of hydrogenated and deuterated amorphous germanium was studied by infrared absorption measurements. The results reveal for substrate temperatures below about 200 °C the growth of a void-rich material which is oxidized rapidly by ambient oxygen and water.
Magnetostriction and magnetomechanical coupling in Ho0.85Tb0.15Fe2−xCox system
Authors: Dhilsha K. R. , Markandeyulu G. , Rama Rao K. V. S.
Published: July 2002

Magnetostriction and magnetomechanical coupling coefficient have been measured on Ho0.85Tb0.15Fe2−xCox (x=0, 0.5, and 1.2) alloys. The alloys were prepared by arc melting as well as by arc melting followed by zoning using induction furnace. Saturation magnetostriction (λs) and magnetomechanical coupling coefficient are found to decrease with the increase of cobalt concentration. The λs values of the zoned samples of x=0 and 0.5 are seen to be more than those of arc melted samples whereas, it is otherwise in the case of x=1.2. Magnetomechanical coupling coefficient values for all the samples are seen to increase with zoning. Change in the easy direction of magnetization in the case of x=1.2 is reflected in the magnetostriction of zoned samples.
Defect structures in YBa2Cu3O7−δ with enhanced pinning at low fields
Authors: Kulik J.
Published: July 2002

The defects present in a sample of YBa2Cu3O7−δ, which has been prepared by the chemical decomposition of YBa2Cu4O8, are examined in detail in an attempt to ascertain with a high degree of probability which of them is primarily responsible for the enhanced flux pinning at low fields. The CuO precipitates are not significant in this regard as they are not numerous enough and produce little if any strain in the surrounding matrix. Imperfections in the twin boundaries are also found to have little if any contribution to pinning in this material. It appears that the partial dislocations bounding stacking faults in the material are the major contributor to the flux pinning as has been suggested previously in the literature.
Initial permeability of (111) oriented Fe-Si polycrystalline thin films
Authors: Hosono Akihiko , Shimada Yutaka
Published: July 2002

Initial permeability (μi) of polycrystalline Fe-based alloy films with (111) orientation is investigated both theoretically and experimentally. It is expected from the calculation that (111) oriented films have higher μi than those of films with other orientations and good frequency characteristics. Fe-7-wt%-Si films with (111) orientation are expected from the calculation to have μi higher than 2000. Experimentally, (111) oriented Fe-6.9-wt%-Si films exhibit μi of about 1700 and are independent of frequencies up to 60 MHz. The results are in fairly good agreement with the calculation. The differences between the results of experiment and calculation can be explained by imperfect orientation of (111) planes and surface roughness in the actual films.
Spatial profiles of trapped hydrogen or centers excited by hydrogen diffusion
Authors: Richards Peter M.
Published: July 2002

Nearly step-function-like profiles of trapped hydrogen or of properties, such as donor concentration, related to hydrogen diffusion are often observed in semiconductors. Expressions are derived for the depth of such profiles and their finite width as a function of time for arbitrary ratios of hydrogen concentration to trap concentration and for nonzero detrapping rates. The depth scales as t1/2 for normal trapping, but as (t ln t)1/2 if the observed quantity is excited by hydrogen passing in the vicinity without being trapped. The width of the profile is time-independent if hydrogen traps irreversibly. For reversible trapping or excitation without trapping the width is proportional to t1/2 or (t ln t)1/2, respectively.
Influence of viscosity variation on salt-finger instability in a fluid layer, a porous layer, and their superposition
Authors: Chen Falin , Lu Jay W.
Published: July 2002

We consider the effect of temperature-dependent viscosity on the onset of buoyancy-driven salt-finger convection (stratifications of salt and temperature being destabilizing and stabilizing, respectively) in a horizontal fluid layer, a horizontal layer of a stratified porous medium, and in a horizontal fluid layer overlying a saturated porous medium. It is found that the viscosity variation affects the stability characteristics through two mechanisms. One is the formation of a relatively viscous sublayer which leads to multicellular convection and stabilizing; the other is the decrease of viscosity which favors the onset of convection. In a horizontal porous layer, the destabilizing mechanism prevails so that the motionless state becomes less stable as γ=ln(νmax/νmin), where ν is kinematic viscosity of the fluid, increases, and a general relation between critical solute (Rcsm) and thermal (Rm) Rayleigh numbers is found as Rcsm = Rm + 4π2H(γ), where H(γ) is determined by curve fitting on the basis of calculated results.

In a horizontal fluid layer, the first mechanism predominates the convection when γ<6.86 and the second mechanism prevails when γ≳6.86; the motionless state is most stable at approximately γ=6.86. Another general relation between critical solute (Rcs) and thermal (R) Rayleigh numbers is also determined based on the calculated results as Rcs = R + 1070.76 G(γ). For superposed fluid and porous configuration, the stability characteristics become more complex and depend on the variations of γ,ζ (ratio of fluid layer depth to porous layer depth), and Rm, and so on. In general, the unicellular convection occurs for ζ=0.1 and the multicellular convection is observed for ζ≥ (R18)0.2; for Rm = 1, the stabilizing mechanism and destabilizing mechanism compete with each other; for Rm = 50, nevertheless, the stabilizing mechanism prevails so that increasing γ leads to stabilization; the fluid layer dominates the superposed system by convection at large γ for all ζ considered. The current results would provide valuable information for understanding the double-diffusive convection during the directional solidification of binary alloys.
Regrowth of In0.53Ga0.47As/InP p-n heterojunctions by organometallic chemical vapor deposition
Authors: Frei M. R. , Hayes J. R. , Shirokmann H. F. , Caneau C.
Published: July 2002

The quality of interfaces regrown by organometallic chemical vapor deposition is evaluated from the electrical characteristics of In0.53Ga0.47As/InP p-n heterojunction diodes. The I-V curves are undistinguishable from those of junctions obtained by continuous growth, with ideality factors η≊1.1 and no observable contribution from interface recombination in the measured current range. An upper limit of 200 cm/s is obtained for the interface recombination velocity. The results show that high-quality interfaces can be obtained in spite of prior air exposure. The technique can be used for the realization of regrown heterojunction bipolar transistors.
Electron mobility in a SixGe1−x quantum well limited by alloy-disorder scattering
Authors: Paul Sajal K. , Basu P. K.
Published: July 2002

A calculation has been made of the mobility of a two-dimensional electron gas in a quantum well composed of Si and SixGe1−x. Both the type-I and type-II band alignments are assumed and the strain-induced splitting of the six-fold degenerate conduction-band minima is considered. For a type-I alignment, the electrons are confined in the alloy layer and the mobility is severely limited by alloy-disorder scattering. In the case of type-II alignment, the electrons confined in the Si layer are scattered by alloy disorder in the barrier and the mobility becomes higher.
Propagation and nonlinear interaction of acoustic boundary waves on interface between magnetostrictive polycrystalline ferrites and LiNbO3
Authors: Ermolov V. , Luukkala M.
Published: July 2002

Results on boundary acoustic waves propagated along the plane boundary between magnetostrictive polycrystalline ferrites and LiNbO3 are presented. The propagation velocity can be varied by changing the applied magnetic field. Convolution of oppositely traveling boundary waves has been produced. Possible applications of boundary acoustic waves are suggested.
Free-carrier plasma and optical amplification in undoped and modulation-doped Ga0.47In0.53As/Al0.48In0.52As multiple-quantum-well structures
Authors: Moro C. , Ferrara M. , Cingolani R. , Zhang Y. H. , Ploog K.
Published: July 2002

We report the results of a systematic investigation of radiative recombination processes of the free-carrier plasma confined in Ga0.47In0.53As/Al0.48In0.52As multiple-quantum-well structures on InP substrate, either undoped or modulation doped. Photoluminescence under low- and high-excitation intensity, luminescence excitation, and optical gain measurements have been used to study the electronic transitions and the optical amplification in the temperature range 10–300 K. Space-resolved luminescence has also been adopted to distinguish between the spontaneous and the stimulated spectral contributions to the observed luminescence collected along different directions with respect to the [001] growth axis of the heterostructures. Optical gain up to 300 K has been observed in the undoped samples under photoexcitation quasiresonant with the confined states in the quantum wells. The theoretical analysis of the optical gain spectra furnishes quantitative data on the electron-hole plasma ground level. In the n-type modulation-doped samples the application of intense optical pumping allows us to observe the transition from the one-component electron plasma to a two-component electron-hole plasma through the rising of a sharp stimulated emission in the optical spectra. Also in this case we observe optical gain up to room temperature.
Optoelectronic device mapping using differential imaging techniques
Authors: Sizer II Theodore , Woodward T. K. , Chiu T-H , Sivco D. L. , Cho A. Y.
Published: July 2002

A mapping technique has been developed that uses differential imaging to characterize semiconductor optoelectronic devices. Although the technique was developed for examination of optical modulators, it has been extended to provide information on the uniformity and bandgap of any material through which one can transmit light. The sharpness of the bandedge, maximum absorption strength, and the film thickness determine the sensitivity of the technique for any particular application. For example, the bandedge sensitivity in 100 periods of InGaAs/GaAs multiple quantum wells was ±20 μeV and can be detected at each location in the field of view in under three minutes. This technique has been applied to modulators designed using strained layer materials for use at a 1-μm operating wavelength.
Preparation of copper thin films at ambient temperature by microwave plasma-enhanced chemical vapor deposition from the copper (II) acetylacetonate-argon-hydrogen system
Authors: Pelletier J. , Pantel R. , Oberlin J. C. , Pauleau Y. , Gouy-Pailler P.
Published: July 2002

Copper-containing films were prepared at room temperature by microwave plasma-enhanced chemical vapor deposition from the Cu(C5H7O2)2-Ar-H2 system. The structure and composition of films as well as the concentration depth profiles of Cu, Si, C, and O atoms in the Cu/Si and Cu/Cr/Si contact structures were determined by x-ray-diffraction techniques, Auger electron spectroscopy, Rutherford backscattering spectroscopy, and nuclear reaction analyses. Carbon atoms were found as major impurities in the deposited material. The carbon content and resistivity of films were strongly dependent on the direct bias voltage of substrates and gas-phase composition. Pure copper films with a resistivity of 2–3 μΩ cm were deposited on Si substrates with a direct bias voltage of −50 V and a hydrogen-rich Cu(C5H7O2)2-Ar-H2 gas phase.
Temperature and composition dependence of the energy gap in Cd1−xFexSe
Authors: Stankiewicz Jolanta
Published: July 2002

Wavelength modulated reflectivity spectra near the fundamental absorption edge of Cd1−xFexSe (0.01≤x≤0.07) solid solutions have been measured in the temperature range 8–300 K. A line-shape analysis of the structures observed allows us to determine the temperature and composition dependence of interband transition energies. The energy gap varies linearly with composition in the range studied. The temperature variation of the energy gap can be well fitted by the empirical Varshni relation.
Optical absorption in silver overcoated with a granular tungsten oxide film
Authors: Ashrit P. V. , Bader G. , Girouard F. E. , Richard T. , Truong Vo-Van
Published: July 2002

A strong resonant absorption near 400 nm is found when minute quantities of WO3 are deposited on Ag surfaces. In order to explain this behavior, a granular structure is assumed for the WO3 overcoat on the metallic substrate. This phenomenon could arise from the coupling of light with surface plasma waves via the mirror-image effect. The WO3 material by itself shows nonabsorptive behavior in the spectral region considered. Experimental evidence is provided by differential reflectance measurements from 350 to 1000 nm for WO3 overcoats with a mass thickness varying from 1.5 to 15 nm. A well-defined peak in the magnitude of the differential reflectance is found, shifting from 390 to 410 nm with increasing overcoat thickness. The observed behavior is consistent with predictions by an effective-medium theory for the granular WO3 deposit, which takes into account the dipole–dipole interactions between particles and the mirror-image effect in the metallic substrate.
Evidence for the buffer zone in a plasma accelerator
Authors: Thomas Keith A. , Clothiaux Eugène J.
Published: July 2002

The existence of an absorbing layer, or buffer zone, of weakly ionized gas between the rear of the projectile and the front of the plasma arc armature in a plasma accelerator has been postulated. In the studies reported here a technique for finding the position of the projectile as a function of time is given and compared to the plasma armature position as determined by inductive probes. Analyses of these signals provide the basis for a description of the in-bore motion of the projectile with respect to the plasma arc armature. The experimental evidence appears to support the existence of a buffer zone.
Highly oriented thin films of hepta-(tetrathiafulvalene) pentaiodide formed by double-source evaporation of tetrathiafulvalene and iodine
Authors: Yudasaka M. , Hironaga K. , Yamochi H. , Saito G.
Published: July 2002

Highly conductive thin films of a charge-transfer complex, hepta-(tetrathiafulvalene) pentaiodide (TTF7I5), were prepared by double-source evaporation of TTF and iodine in vacuum. Crystalline films of TTF7I5 were obtained when substrate temperatures were kept between 0 and 25 ° C. Orientation of the crystallites were affected by supply rate of iodine. By controlling it, we could make the c axes of the crystallites parallel with a mica substrate, which made angles of +30° or −30° with the b axes of mica.
Theoretical study of thin and thick emitter silicon solar cells
Authors: Morales-Acevedo Arturo
Published: July 2002

We describe a complete theoretical model to calculate the open circuit voltage, the light generated current density, and the conversion efficiency of thin and thick emitter silicon solar cells. We show the importance of the Fermi carrier degeneracy, in addition to the heavy doping effects such as band-gap narrowing and Auger recombination. For example, in contradiction to recent calculations, the conversion efficiency of thin passivated emitter solar cells is shown to be independent of the surface dopant concentration. Also, in agreement with experimental results, but contrary to old conventional cell designs, it is shown that the conversion efficiencies of thick emitter solar cells can be as high as those of thin emitter cells. The last result will occur whenever the emitter is well passivated and the surface impurity concentration is relatively low (Ns=1×1019 cm−3). For non-passivated solar cells it is better to have thin emitters and high surface dopant concentrations (Ns≳2×1020 cm−3) as usual in conventional solar cells.
Reactive etching of polycrystalline CdS and ZnS films by electron cyclotron resonance hydrogen plasma
Authors: Tonouchi Masayoshi , Miyasato Tatsuro
Published: July 2002

The reactive etching effect of polycrystalline CdS and ZnS films in electron cyclotron resonance (ECR) hydrogen discharge has been studied. The etch rates were strongly dependent on the material itself, the substrate temperature, and the microwave power. The activation energy for the CdS and ZnS etching was estimated to be 1.0 and 1.3 eV, respectively, and high-rate etching at the rates of 18 μm/min for the CdS and 7 μm/min for the ZnS was demonstrated. The optical emission spectral observation emitted from ECR hydrogen plasma revealed that the etch rates closely correlated with the emission intensity from the hydrogen radical and suggested that the removal process of the one molecule required three hydrogen radicals at the same time.
Charge distributions and energy spectra of heavy fragments from cosmic-ray 12C- and 16O-induced nuclear fragmentation of large-scale integration devices materials
Authors: Barghouty A. F.
Published: July 2002

A statistical nuclear fragmentation model is used to calculate the charge distributions and energy spectra of heavy (z≳4) fragments produced in 1 GeV per nucleon collisions of cosmic-ray 12C and 16O with the large-scale integration devices materials: 16O, 28Si, 70Ga, 75As, and 197Au. Results for 56Fe+12C at 980 MeV per nucleon are also presented and compared with available data. Calculated charge distributions show a clustering pattern into three z-number groups while kinetic-energy spectra reveal soft shapes over a 100-MeV range. Charge-distribution and energy-spectrum absolute cross sections from 16O-induced fragmentation of 28Si are 1–2 orders of magnitude larger than those from 12C-induced fragmentation.
Direct comparison of quantum and classical descriptions of high-field carrier transport in semiconductors
Authors: Sano Nobuyuki , Yoshii Akira
Published: July 2002

A fully quantum-mechanical description of high-field carrier transport in real space representation in semiconductors is developed. The present approach treats a high electric field unperturbatively, while a realistic electron-phonon interaction is included through the perturbation scheme. Direct comparisons of transport properties at very short time in real space with the corresponding semiclassical (Monte Carlo) descriptions are presented. The results explicitly show the quantum effects on the spreading of electron wave packets due to the electron-phonon interaction and help to clarify the limitation of semiclassical descriptions based on the Boltzmann transport equation.
Material selectivity in synchrotron radiation-stimulated etching of SiO2 and Si
Authors: Takahashi Jun-ichi , Utsumi Yuichi , Urisu Tsuneo
Published: July 2002

Rate differences in synchrotron radiation-stimulated etching among several kinds of SiO2 and Si materials have been studied. The SiO2 etching rate is almost independent of the crystallinity. On the other hand, the Si etching rate decreases with improved crystallinity and increased activated dopant density. Impurity doping into polycrystalline (poly-) Si leads to etching rate reduction irrespective of the conduction type. These material selectivities are explained by a reaction model that is described in terms of reaction centers produced by electronic excitation of the material surface.
Damage formation and substitutionality in 75As++-implanted diamond
Authors: Gorbatkin S. M. , Zuhr R. A. , Roth J. , Naramoto H.
Published: July 2002

Rutherford backscattering spectrometry (RBS) has been used to study damage formation and substitutionality in synthetic diamonds implanted with 250-keV 75As++ at either 600 °C or room temperature. Lattice damage following implantation at 600 °C was substantially less than damage following room-temperature implantation and appears to be composed of a higher fraction of extended defects. A significant portion of the As implanted at 600 °C was found to be in substitutional lattice sites with substitutional fractions as high as 50%. Changing the ion flux by three orders of magnitude during high-temperature implantation had no effect on either residual damage or substitutionality as indicated by the RBS analysis.
Modifications in α-Si:H during thermal annealing: In situ spectroscopic ellipsometry
Authors: Logothetidis S. , Kiriakidis G. , Paloura E. C.
Published: July 2002

Device-quality a-Si:H thin films, grown by rf magnetron sputtering, were annealed in the temperature range up to 850 °C and studied by in situ ellipsometry, spectroscopic ellipsometry, and thermal evolution measurements. Annealing causes a volume reduction which can be as high as 5%, and after annealing at T≳800 °C the material becomes microcrystalline with an average crystallite size that depends on the annealing temperature. A detailed analysis of the peak height of the imaginary part of the pseudodielectric function 〈ε(ω)〉, combined with the examination of the fundamental gap, the average gap (Penn gap), and the refractive index of a-Si:H, provides new insight on the role of hydrogen and the structural modifications induced by thermal annealing. Based on the presented experimental findings we propose the following: (a) annealing below Ts causes reduction of the isolated microvoids; (b) the weakly bound hydrogen is correlated with regions with a high density of microvoids; and (c) the evolution of weakly bound hydrogen does not drastically influence the optical properties of the film while evolution of isolated hydrogen does. The rate of change of the optical properties as a function of T is (a) nearly constant for TT< Ts, (b) increases for T ≳ Ts, and (c) decreases dramatically for T≳600 °C, therefore indicating irreversible structural changes at T ≳ Ts mainly due to isolated hydrogen loss.
Oxidation and protection in copper and copper alloy thin films
Authors: Li Jian , Mayer J. W. , Colgan E. G.
Published: July 2002

The oxidation kinetics of copper thin films have been studied at temperatures below 200 °C in air. The protection of copper from oxidation can be achieved by alloying copper film with Ti, Pd, Cr, or Al. The influence of the composition and microstructure to the oxidation rate has been studied. The compounds Cu3Ti, Cu3Pd, and CuAl2 are stable in the oxidation ambient. The formation of Cr-oxide, which is a passive oxide, explains the inhibition of oxidation on Cu-Cr films. Compared with the crystalline phase, the amorphous Cu65Ti35 alloy film is more oxidation resistant. A TiN layer with oxygen incorporated is more effective in preventing copper oxidation than a TiN layer without oxygen incorporated. A passivating Si3N4 layer on copper thin films can prevent copper oxidation effectively at 350 °C in oxygen ambient.
Hybrid multiple diffraction in Renninger scan for heteroepitaxial layers
Authors: Morelhão S. L. , Cardoso L. P. , Sasaki J. M. , de Carvalho M. M. G.
Published: July 2002

In this paper, we report the successful observation of the hybrid multiple diffraction (hybrid MD) in Renninger scans (RS) [M. Renninger, Z. Kristallogr. 106, 141 (1937)]. These diffractions occur when the beam first diffracted by an inclined layer (or substrate) plane with respect to the sample surface crosses the interface layer/substrate to be rescattered by another substrate (or layer) plane towards the detector. The construction of an incidence diagram allows to establish the occurrence of the hybrid MD for heteroepitaxial layers. The layer imperfection (mosaic spread) is used to explain these extra features in RS together along the normal MD features. The case of a GaAs layer grown on a Si substrate is investigated.
The explanation of the so-called Auger-like thermal recovery of the EL2 defect in n-type GaAs
Authors: Dreszer Piotr , Baj Michal/
Published: July 2002

We present an experimental study of the EL2-defect thermal recovery in n-type GaAs under hydrostatic pressure up to 1.2 GPa. The most characteristic experimental result is the nonmonotonous pressure dependence of the temperature at which the EL2 defect thermally recovers. We solve numerically the equations describing the recovery process, and we prove that in order to explain our experimental data it is absolutely necessary to take into account the existence of the recently discovered acceptorlike level of the metastable EL2. Moreover, we show that the most straightforward explanation of all our experimental results should assume that in n-type GaAs the recovery process always proceeds via the negative-charge state of the metastable EL2. Since our explanation of the recovery process does not require the recovery rate to be directly proportional to the free-electron concentration, the problem of the so-called Auger-like thermal recovery of the EL2 defect in n-type GaAs seems to be finally gone.
Experimental studies of stability and amplification in four overmoded, two-cavity gyroklystrons operating at 9.87 GHz
Authors: Calame J. P. , Lawson W. , Granatstein V. L. , Latham P. E. , Hogan B. , Striffler C. D. , Read M. E. , Reiser M. , Main W.
Published: July 2002

The performance of four overmoded (TE011 circular), two-cavity gyroklystron amplifier tubes operating in X band is reported. A summary of the theoretical design procedure is presented, followed by a description of the experimental setup. The stability and amplification properties of the four gyroklystron tubes are subsequently described, each being modified in sequence to improve performance. The fourth tube produced 2.0–2.7 MW pulses at 9.87 GHz for 0.5–1.0 μs, and exhibited gains of 17–19 dB and efficiencies of 5%. The results were obtained using electron beams with voltages, currents, and computed beam alphas (v⊥/vz) of 407–425 kV, 115–135 A, and 0.8–1.0, respectively. The presence of instabilities in the gun downtaper and drift tube prevented operation at the design point (500 kV, 160 A, and alpha 1.5). The effects of varying input frequency, input power, and beam parameters (voltage, current, magnetic compression) on the amplifier operation are reported. Detailed descriptions of the instabilities observed in the gyroklystrons are presented, and the use of lossy dielectrics to suppress the instabilities is discussed. The amplifier experimental performance is compared with simulations. Improvement schemes are summarized and follow-up experiments are outlined.
High-quality Y1Ba2Cu3O6.5+x films on large area by chemical vapor deposition
Authors: Busch H. , Fink A. , Müller A.
Published: July 2002

The β-diketonate process for chemical vapor deposition Y1Ba2Cu3O6.5+x is extended to deposition on enlarged areas up to 20 cm2. The films are prepared on monocrystalline SrTiO3 and reveal a surface topography comparable to films by laser ablation. The inductively measured transition temperature Tc is up to 93 K and the transition width is smaller than 1 K; Tc is well reproduced from run to run. The critical current density jc at 77 K attains values as high as 6×106 A/cm2 in zero magnetic field; the current carrying capacity in magnetic fields up to 8 T is presented.
Resonant steps in the characteristics of a Josephson junction coupled to a transmission line
Authors: Blackburn James A. , Smith H. J. T. , Gro/nbech-Jensen N.
Published: July 2002

A novel circuit is described which functions as an electronic analog of lumped element transmission line. The circuit requires only operational amplifiers, resistors, and capacitors. This module was coupled to a Josephson junction simulator and current voltage characteristics of the combined system were recorded. Steps were observed at voltages determined by the appropriate line resonances. When the transmission line was terminated with loads less than the characteristic impedance, chaos was seen in the lower steps. Similar results were obtained by numerical integration of the corresponding system of differential equations.
180° wall movement in a magnetic thin-film closure domain structure in a high-frequency field
Authors: Ishikawa Chiaki , Sasaki Shinobu , Moriwaki Eijin , Hamakawa Yoshihiro , Shiiki Kazuo , Shinagawa Kiminari
Published: July 2002

The dynamic behavior of a 180° wall was observed in a Co-based amorphous alloy film using a Kerr microscope. As a function of an anisotropy direction the amplitude of the 180° wall movement was measured with the drive field applied transverse to the 180° wall of the closure domain structure. The anisotropy direction was varied by magnetic heat treatment. It was found that the 180° wall moved independently of the anisotropy direction, that is, the 180° wall movement is related only to the applied high-frequency field. To clarify the cause of the 180° wall movement, the magnetic energy of the domain structure and the eddy current loss caused by the high-frequency field were calculated. However, the movement could not be understood completely in terms of energy balance since the magnetostatic energy increases faster than the decrease of the eddy current loss, when the 180° wall moves.
Time-of-flight measurements of pulsed neutrons and 2d detectors for texture analysis of deformed polycrystals
Authors: Wenk Hans-Rudolf , Larson Allen C. , Vergamini Phillip J. , Schultz Arthur J.
Published: July 2002

A method is described to measure deformation textures in polycrystals by time-of-flight of thermal neutrons with a 2d position sensitive detector. The procedure is illustrated for a standard sample of deformed calcite limestone and results from the Los Alamos Neutron Scattering Center and the Intense Pulsed Neutron Source at Argonne National Laboratory are compared with those from more conventional neutron diffraction experiments.
Laser heating of a sintered oxide superconductor
Authors: Shi Y. H. , Lee M. J. G. , Moskovits M. , Hsu A. , Carpick R.
Published: July 2002

Raman spectroscopy, in which a laser beam serves the dual role of exciting the Raman spectrum and annealing the sample, shows promise as a means of investigating oxygen effects in the oxide superconductors. A technique is described, based on measurements of the ratios of the areas of corresponding peaks in the anti-Stokes and Stokes spectra, whereby the temperature of the illuminated region of the sample can be determined as a function of the power in the incident laser beam. It is found that, for sintered samples of bismuth 2122, a small correction must be made for the departure from thermodynamic equilibrium induced by the pumping effect of the laser beam.