bluuebunny/crossref_metadata_2025 huggingface dataset:
Inertial fusion energy target output and chamber response: Calculations and experiments
Authors: Peterson Robert R. , Haynes Donald A. , Golovkin Igor E. , Moses Gregory A.
Published: July 2002

The emission of photons and energetic ions by the burn and subsequent explosion of inertial fusion energy (IFE) targets poses a threat to the survival of the target chambers in future IFE power plants. Immediately after the deposition of target output, the chamber can experience sufficient heating to cause vaporization, melting, and shock loading on chamber walls. Until high-yield targets can be ignited in laboratory experiments, predictions of the nature of the target output and the response of the target chamber must be made with radiation-hydrodynamics computer codes that need to be validated with relevant smaller scale experiments. Physical models of equation of state, opacity, and radiation transport are in special need of validation. Issues of target output and chamber response requiring experiments and computer modeling are discussed and initial results from experiments are presented. Calculations of x ray and debris output from direct-drive IFE targets are shown and sensitivity of the output spectra and chamber response to details of the physics models are discussed.
Color centers in LiCaAlF6 single crystals and their suppression by doping
Authors: Sato Hiroki , Machida Hiroshi , Shimamura Kiyoshi , Bensalah Amina , Satonaga Tomohiko , Fukuda Tsuguo , Mihokova Eva , Dusek Michal , Nikl Martin , Vedda Anna
Published: July 2002

LiCaAlF 6 (LiCAF) single crystals pure and doped with MgF2 and BaF2 were successfully grown by the Czochralski technique. Optical absorption measurements in the UV/Visible spectral regions following x-ray irradiation (radiation induced absorption) were performed in order to investigate the radiation damage of the crystals. The F-center absorption band at 262 nm is the dominating induced absorption feature. The amplitude of the F-absorption band is suppressed by more than a factor of 3 in Mg-doped LiCAF compared to undoped, while for Ba-doped LiCAF, almost no variation is obtained. In Mg-doped crystals the optimum doping concentration is of about 0.2 mol % of MgF2 in the melt.
Statistical analysis of mean-flow effects on the pressure–velocity correlation
Authors: Yoshizawa Akira
Published: July 2002

Mean-flow effects on the pressure–velocity correlation in the turbulent-energy equation are investigated with the aid of a two-scale direct-interaction approximation. Those effects are composed of strain, vorticity, and momentum-diffusion effects, which correspond to the modeling of the rapid term in the pressure–strain correlation of the Reynolds-stress equation. They are missing in the current turbulence modeling in striking contrast to the latter, and become important in turbulent flows accompanying large mean-velocity gradients and curvatures.
Nanosize effects on the microstructure of BaFe10.3Co0.85Ti0.85O19 hexaferrite
Authors: Somogyvári Z. , Sváb E. , Mészáros Gy. , Krezhov K. , Konstantinov P. , Nedkov I. , Bourée F.
Published: July 2002

Nanosized and microcrystalline BaFe10.3Co0.85Ti0.85O19 samples were investigated by neutron diffraction. A strong anisotropy of the thermal expansion coefficient and its dependence on the grain size was established. The cation distributions and the magnetic moments were determined. The refined magnetic moments proved to be much lower than the theoretical spin only moments, especially for the 4e and 12k sites, indicating a local noncollinearity with short-range ordering.
Laser-assisted (1+1′)-photon ionization-detected absorption spectrum of the 3pπ 2Π state of HCO and DCO
Authors: Robinson J. D. , Foltynowicz R. J. , Prentice K. , Bell P. , Grant E. R.
Published: July 2002

We re-examine the ionization-detected ultraviolet absorption spectrum of the 3pπ 2Π←X 2A′ transition in HCO and DCO using a high-power visible laser to enhance the observation of first-photon resonant features. This technique, which we term here, assisted REMPI, significantly improves the signal-to-noise ratio of the spectrum, making many weak vibronic sub-bands visible for the first time. A comprehensive fit to the structure evident in a progression of bending levels from (000) to (040) refines the assignment of Song and Cool [X. M. Song and T. A. Cool, J. Chem. Phys. 96, 8664 (1992)] to yield a set of rotational constants that vary with K in relation to v2, together with a higher-order contribution to the Renner–Teller splitting in HCO, which is mirrored in DCO for all levels but (040). The (040) band falls at a frequency that is commensurate with that of CD stretch, and Fermi resonance between 3pπ 2Π(1000)Π and the higher-energy (040) K=1(Π) component gives rise to an added splitting that increases the energy of this (040) component and causes an apparent increase in the Renner parameter.
Magnetotransport properties of La2/3Sr1/3MnO3 thin film
Authors: Mandal P. , Choudhury P. , Bärner K. , von Helmolt R. , Jansen A. G. M.
Published: July 2002

We report the temperature and magnetic field dependence of the resistivity of La2/3Sr1/3MnO3 thin film over a wide temperature range and in high magnetic fields up to 20 T. Both above and below the ferromagnetic (FM) transition, the field dependence of the magnetoresistance (MR) can be described well using the extended Mott hopping conduction model. The large MR is proportional to the Brillouin function BJ in the FM phase and to BJ2 in the paramagnetic state which is consistent with this model. The value of spin moment J deduced from the temperature and magnetic field dependence of the MR is large (∼60) in the vicinity of the FM transition. This large value of J has been attributed to the presence of magnetic clusters due to the short-range FM ordering.
The effect of Lagrangian chaos on locking bifurcations in shear flows
Authors: Finn John M.
Published: July 2002

The effect of an externally imposed perturbation on an unstable or weakly stable shear flow is investigated, with a focus on the role of Lagrangian chaos in the bifurcations that occur. The external perturbation is at rest in the laboratory frame and can form a chain of resonances or cat’s eyes where the initial velocity vx0(y) vanishes. If in addition the shear profile is unstable or weakly stable to a Kelvin–Helmholtz instability, for a certain amplitude of the external perturbation there can be an unlocking bifurcation to a nonlinear wave resonant around a different value of y, with nonzero phase velocity. The interaction of the propagating nonlinear wave with the external perturbation leads to Lagrangian chaos. We discuss results based on numerical simulations for different amplitudes of the external perturbation. The response to the external perturbation is strong, apparently because of non-normality of the linear operator, and the unlocking bifurcation is hysteretic. The results indicate that the observed Lagrangian chaos is responsible for a second bifurcation occurring at larger external perturbation, locking the wave to the wall. This bifurcation is nonhysteretic. The mechanism by which the chaos leads to locking in this second bifurcation is by means of chaotic advective transport of momentum from one chain of resonances to the other (Reynolds stress) and momentum transport to the vicinity of the wall via chaotic scattering. These results suggest that locking of waves in rotating tank experiments in the presence of two unstable modes is due to a similar process.
Microstructure and electrical transport property of Fe/Cu nanoscale multilayered materials
Authors: Jin Xuesong , Zhou Y. , Kim C. O. , Lee Y. P. , Xu Huibin , Gong S. K.
Published: July 2002

The microstructures and electrical conductivity (σ) at room temperature of Fe/Cu multilayered material, which was prepared by the electron-beam physical-vapor-deposition technique, were investigated to understand the dependence of σ on the bilayer thickness (Λ=dFe+dCu) and the sublayer thickness ratio (χ=dFe/Λ), where d is the sublayer thickness. Satellite peaks in the x-ray diffraction spectra were observed, indicating a layered structure in the multilayered material. The specimen was polycrystalline, and the in-plane grain size is independent of the sublayer thickness. σ at a fixed χ increases with increasing Λ, and keeps nearly constant when Λ is larger than 30 nm. σ at a fixed Λ decreases linearly with increasing χ. The size dependence of σ is explained using a model that takes into account scattering by the sublayer interfaces and the grain boundaries. The scattering at interfaces and grain boundaries is thought to be the dominant mechanism for the size dependence of σ on Λ when dFe is smaller and larger, respectively, than the estimated electron mean free path in the Cu sublayer.
Temperature dependence of electrical properties of N2O/O2/N2O-grown oxides on strained SiGe
Authors: Samanta S. K. , Chatterjee S. , Bera L. K. , Banerjee H. D. , Maiti C. K.
Published: July 2002

Temperature dependence of electrical properties of split-N2O grown oxides on strained SiGe layers by rapid thermal oxidation is reported. The reliability and thermal stability of ultrathin oxides have been examined by high frequency capacitance–voltage and current density versus electric field measurements. It is observed that at a low (<6 MV/cm) electric field, the shallow trap-assisted conduction mechanism is responsible for the leakage current below 100 °C and the Frenkel–Poole conduction dominates above 100 °C. At a high (>11 MV/cm) electric field, however, the leakage current is mainly governed by the Fowler–Nordheim tunneling. Charge-to-breakdown measurements at a constant current stressing show a higher reliability for the split-N2O grown oxides.
A compact general-purpose fast high-power pulser for inductive load
Authors: Flaxer Eli
Published: July 2002

We present the design principles of a compact general-purpose fast high-power (and low-cost) pulser for inductive load, using an isolate gate bipolar transistor, a dedicated smart driver unit and digital control designed in very high speed integrated circuit hardware description language. We demonstrate the performance of this pulser as a driver for a high-pressure supersonic pulsed valve.
Development of a light source with an injection-locked Nd:YAG laser and a ring-mode cleaner for the TAMA 300 gravitational-wave detector
Authors: Nagano Shigeo , Barton Mark A. , Ishizuka Hideki , Kuroda Kazuaki , Matsumura Sumihiro , Miyakawa Osamu , Miyoki Shinji , Tatsumi Daisuke , Tomaru Takayuki , Uchiyama Takashi , Ando Masaki , Arai Koji , Kawabe Keita , Ohishi Naoko , Takamori Akiteru , Taniguchi Shinsuke , Tochikubo Kuniharu , Tsubono Kimio , Yamamoto Kazuhiro , Fujimoto Masa-Katsu , Fukushima Mitsuhiro , Kawamura Seiji , Kozai Yoshihide , Miyama Shoken , Ohashi Masatake , Sato Shuichi , Takahashi Ryutaro , Telada Souichi , Yamazaki Toshitaka , Mio Norikatsu , Moriwaki Shigenori , Horikoshi Gen’ichi , Kamikubota Norihiko , Ogawa Yujiro , Saito Yoshio , Suzuki Toshikazu , Musha Mitsuru , Nakagawa Ken’ichi , Ueda Akitoshi , Ueda Ken-ichi , Araya Akito , Kanda Nobuyuki , Nakamura Takashi , Tanaka Takahiro , Sasaki Misao , Tagoshi Hideyuki , Futamase Toshifumi , Kawashima Nobuki , Mizuno Eiichi , Kojima Yasufumi , Matsuda Namio , Oohara Ken-ichi , Tsuda Nobuhiro
Published: July 2002

We have developed a light source suitable for laser interferometric gravitational-wave detectors. The developed light source has high power, TEM00 mode, linear polarization, high frequency stability, and low intensity noise. The light source with the quality is essential for attaining the goal sensitivity in the TAMA 300 and was found to be available for a observation run of a gravitational-wave detector.
Residual images in charged-coupled device detectors
Authors: Rest Armin , Mündermann Lars , Widenhorn Ralf , Bodegom Erik , McGlinn T. C.
Published: July 2002

We present results of a systematic study of persistent, or residual, images that occur in charged-coupled device (CCD) detectors. A phenomenological model for these residual images, also known as “ghosting,” is introduced. This model relates the excess dark current in a CCD after exposure to the number of filled impurity sites which is tested for various temperatures and exposure times. We experimentally derive values for the cross section, density, and characteristic energy of the impurity sites responsible for the residual images.
Beam measurements on the H− source and low energy beam transport system for the Spallation Neutron Source
Authors: Thomae R. , Gough R. , Keller R. , Leung K. N. , Schenkel T. , Aleksandrov A. , Stockli M. , Welton R.
Published: July 2002

The ion source and low energy beam transport (LEBT) section of the front-end systems presently being built at Lawrence Berkeley National Laboratory are required to provide 50 mA of H− beam current at a 6% duty factor (1 ms pulses at 60 Hz) with a normalized root mean square emittance of less than 0.20 π mm mrad. Experimental results, including emittance, chopping, and steering measurements, on the performance of the ion source and LEBT system operated at the beam parameters demanded will be discussed.
New quenching scheme for the generation of a nearly transform-limited picosecond pulse in a distributed feedback dye laser
Authors: Deguchi T. , Takeyasu N. , Imasaka T.
Published: July 2002

We report on the generation of a background-free nearly transform-limited picosecond pulse using a simple quenching scheme in a distributed feedback dye laser. The pulsewidth and spectral linewidth were 65 ps and 10 pm, respectively. The product of these values is 0.650, which is close to the transform limit of 0.441 for a Gaussian pulse.
In situ x-ray absorption fuel cell
Authors: Viswanathan Rameshkrishnan , Liu Renxuan , Smotkin Eugene S.
Published: July 2002

An in situ x-ray absorption spectroscopy cell was designed to study the structural and electronic properties of high performance polymer electrolyte fuel cell electrocatalysts. The cell was operated as a standard fuel cell and x-ray absorption data were collected simultaneously as the fuel cell operating conditions were varied. The cell was used to examine platinum–ruthenium alloy electrocatalysts incorporated in the anode of a fuel cell membrane and electrode assembly. In situ Pt LIII and Ru K edge x-ray absorption near-edge structure (XANES) data were collected at five selected current densities of the operating fuel cell. The XANES data show that under normal fuel cell operating conditions, the metallic nature of the Pt–Ru catalyst is retained. The cell design enabled an in situ fuel cell study at a synchrotron source in which no additional electrolytes were required.
Tuning surface morphologies of ion-assisted diamondlike carbon film on the nanometer scale
Authors: Zhu X. D. , Naramoto H. , Xu Y. , Narumi K. , Miyashita K.
Published: July 2002

We report the unstable surface feature in nanometer-scale of diamondlike carbon (DLC) films deposited through C60 evaporation with simultaneous bombardment of 1.5 keV Ne+ ions. The periodical ripples, commonly appearing in postprocessing of the deposited films, form directly at 550 °C and 700 °C, which is qualitatively consistent with the theoretical model based on sputtering yield variation with surface curvature. A dramatic transition from ripple surface to mounding roughening occurs at 400 °C. The graphitization with increasing temperature induces the different dominant smoothening mechanisms, which is responsible for the morphological change observed. Further, the calculations of height–height correlation function show that the roughness exponents are around 0.8 at 200 °C and 400 °C, implying self-affinity of roughened surfaces. This study exhibits a potential of ion beam assisted deposition to tune DLC morphologies by controlling the deposition parameters to drive the competition between ion erosion and film deposition.
Experimental investigation and modeling of diffusion in the InP/(In,Ga)As heterostructures
Authors: Bursik Jiri , Malakhov Dmitri V. , Wang Yaoji , Weatherly George C. , Purdy Gary R.
Published: July 2002

The interdiffusion of lattice-matched InP/(In,Ga)As superlattice structures (nominally undoped, p-doped and n-doped) has been studied by analytical electron microscopy (x-ray analysis) using a field emission gun, scanning transmission electron microscope. The point-spread function of the electron beam was used to correct the experimental data (obtained as x-ray maps, 50×50 nm in area) in order to derive diffusion profiles of the group V elements (As, P) after annealing. The results, showing a marked asymmetry in the As profiles after annealing, are interpreted using a model based on the coherent diffusion of the group III and V elements on their own sublattices, each of which is treated as a regular solution. A mathematical procedure, based on the minimization of the difference between the measured and predicted concentration profiles, is employed to compute the two lattice-specific composition-dependent velocities from the experimental diffusion profiles. A good agreement is found between the experimental measurements and the predictions of the model. The role of coherency strains in the interdiffusion process is discussed.
Sensitivity in extracting static dielectric constants from multiple film stacks
Authors: Mueller A. H. , Suvorova N. A. , Irene E. A.
Published: July 2002

This study points out that there is a hyperbolic relationship between the static dielectric constants (Ks) in a dielectric film stack. It is shown using experimental data that this relationship renders K values that are extracted from capacitance–voltage measurements very sensitive to the other input values such as dielectric constants and film thicknesses. Errors as large as 100% and larger can be made in K from small changes in the input parameters. Thus there is a requirement for accurate film thicknesses and a specific knowledge of the nature of interface film(s) and dielectric properties are necessary for accurate K determinations.
Elastic properties of the rotator phases of pentacosane C25H52
Authors: Mukherjee Prabir K.
Published: July 2002

Pentacosane C25H52 exhibits two different rotator to rotator phase transitions. A phenomenological theory of the elastic properties of the rotator phases is developed on the basis of a free energy expansion. The temperature dependence of the elastic constants is calculated for the various rotator phases. We discuss the temperature variation of the heat capacity in the rotator phases in terms of the elastic constants. The theoretical predictions are found to be in good qualitative agreement with available experimental results.
Instantaneous normal mode analysis of Morse liquids
Authors: Shah Pooja , Chakravarty Charusita
Published: July 2002

Instantaneous normal mode (INM) analysis of a set of bulk Morse systems is performed to monitor the changes in the curvature distribution that occur as a result of changing the range and curvature of the Morse potential. The liquids are bound by Morse pair potentials, Vα(r)=ε[e−α(1−(r/re))−1]2−ε, and share a common well-depth, ε, and equilibrium pair distance, re, but possess different values of range parameter, α, which is inversely correlated with the range and softness of the potential. INM analysis is used to index the changes in the curvature distribution of the potential energy surface that take place as the range parameter of the pair potential is varied and is shown to provide considerable insights into the accompanying dynamical changes. For example, the fraction of imaginary frequency modes, and therefore the diffusivity, is expected to rise with increasing temperature and decreasing range. In contrast, the Einstein frequency, which is a measure of the curvature of the effective potential well that traps a tagged particle in the liquid state, shows a nonmonotonic behavior with range. We also consider the behavior of INM spectra of liquids in relation to that of solids and gases. It is shown that INM analysis can be used to monitor the transition of a fluid from a liquidlike regime, dominated by collective rearrangements, to a gaslike regime, dominated by binary collisions. The transition to a collision-dominated regime is promoted by decreasing the range of the pair potential. Key INM spectral features are shown to undergo a discontinuous change on melting. Minimization of instantaneous configurations to the nearest saddle removes the imaginary frequencies in the solid phase but not in the liquid phase.
Theoretical study of predissociation dynamics of HCN/DCN in their first absorption bands
Authors: Xu Dingguo , Xie Daiqian , Guo Hua
Published: July 2002

Predissociation dynamics of HCN and DCN in the α absorption band is studied using a newly calculated ab initio potential energy surface of the first excited singlet (1 1A″) state and the corresponding transition dipole surface. The recently proposed complex-symmetric single Lanczos propagation method is applied to generate absorption spectra and fragment internal state distributions for the photodissociation of both HCN and DCN. The absorption spectra of both molecules are dominated by bending progressions, thanks to the linear-to-bent transition. For most low-lying resonances, the CN fragment is found predominantly in its ground vibrational state even when significant energy is available. The absence of fragment vibrational excitation is attributed to the coincidence of the C–N distance at the exit barrier and the dissociation asymptote, and to the lack of final-state interaction outside the barrier. On the other hand, the CN rotational distribution is found to be highly oscillatory and depend on the vibrational quanta of the resonance. The exit barrier plays a role in restricting rotational excitation in the CN fragment. The calculated results provide detailed information about the dissociation dynamics.
Lagrangian turbulence in nonstationary 2-D flows
Authors: Chernikov A. A. , Neishtadt A. I. , Rogal’sky A. V. , Yakhnin V. Z.
Published: July 2002

Lagrangian particle transport in nonstationary 2-D flows is studied both analytically and numerically. Analytic expressions for the diffusion coefficients are obtained for the adiabatic regime. Numerical estimates of the diffusion coefficients are found to agree with the theoretical results.
Homoclinic connections and period doublings of a ship advancing in quartering waves
Authors: Spyrou K. J.
Published: July 2002

The large-amplitude motions of a ship running in waves are analyzed with a mathematical model reduced to a system of eight coupled nonlinear ordinary differential equations. Bifurcation analysis in relation to the surf-riding condition, with control parameter the angle of the rudder, shows the existence of a region of oscillatory behavior, containing also a chaotic domain. This region ends with a homoclinic connection and a dangerous jump toward the overtaking-wave mode, which can incur ship capsize. Addition of linear control removes the chaotic domain while giving rise to new regions of oscillation.
On a general concept of multifractality: Multifractal spectra for dimensions, entropies, and Lyapunov exponents. Multifractal rigidity
Authors: Barreira Luis , Pesin Yakov , Schmeling Jörg
Published: July 2002

We introduce the mathematical concept of multifractality and describe various multifractal spectra for dynamical systems, including spectra for dimensions and spectra for entropies. We support the study by providing some physical motivation and describing several nontrivial examples. Among them are subshifts of finite type and one-dimensional Markov maps. An essential part of the article is devoted to the concept of multifractal rigidity. In particular, we use the multifractal spectra to obtain a “physical’’ classification of dynamical systems. For a class of Markov maps, we show that, if the multifractal spectra for dimensions of two maps coincide, then the maps are differentiably equivalent.
Autonomous gel/enzyme oscillator fueled by glucose: Preliminary evidence for oscillations
Authors: Leroux Jean-Christophe , Siegel Ronald A.
Published: July 2002

A novel prototype gel oscillator that functions by dissipating the chemical energy of glucose by an enzyme-mediated reaction is proposed. The product of the reaction modulates the degree of swelling and hence the permeability of a poly(N-isopropylacrylamide-co-methacrylic acid) gel membrane which in turn regulates the flow of substrate to the enzyme. No external energy is required aside from the chemical energy of glucose present externally at constant concentration. A negative chemomechanical feedback loop is established which, coupled with hysteresis in the membrane permeability characteristics, produces pulsing oscillations. In this study, we introduce a simple model which provides guidelines for experimental design, and report preliminary experimental evidence for oscillation. Application of this prototype system to the episodic delivery of drugs and hormones is envisaged.
Self-consistent chaotic transport in fluids and plasmas
Authors: del-Castillo-Negrete Diego
Published: July 2002

Self-consistent chaotic transport is the transport of a field F by a velocity field v according to an advection-diffusion equation in which there is a dynamical constrain between the two fields, i.e., O(F,v)=0 where O is an integral or differential operator, and the Lagrangian trajectories of fluid particles exhibit sensitive dependence on initial conditions. In this paper we study self-consistent chaotic transport in two-dimensional incompressible shear flows. In this problem F is the vorticity ζ, the corresponding advection-diffusion equation is the vorticity equation, and the self-consistent constrain is the vorticity–velocity coupling ẑ⋅∇×v=ζ. To study this problem we consider three self-consistent models of intermediate complexity between the simple but limited kinematic chaotic advection models and the approach based on the direct numerical simulation of the Navier–Stokes equation. The first two models, the vorticity defect model and the single wave model, are constructed by successive simplifications of the vorticity–velocity coupling. The third model is an area preserving self-consistent map obtained from a space-time discretization of the single wave model. From the dynamical systems perspective these models are useful because they provide relatively simple self-consistent Hamiltonians (streamfunctions) for the Lagrangian advection problem. Numerical simulations show that the models capture the basic phenomenology of shear flow instability, vortex formation and relaxation typically observed in direct numerical simulations of the Navier–Stokes equation. Self-consistent chaotic transport in electron plasmas in the context of kinetic theory is also discussed. In this case F is the electron distribution function in phase space, the corresponding advection equation is the Vlasov equation and the self-consistent constrain is the Poisson equation. This problem is closely related to the vorticity problem. In particular, the vorticity defect model is analogous to the Vlasov–Poisson model and the single wave model and the self-consistent map apply equally to both plasmas and fluids. Also, the single wave model is analogous to models used in the study of globally coupled oscillator systems.
Intermetallic compound formations in titanium-copper thin-film couples
Authors: Liotard J. L. , Gupta D. , Psaras P. A. , Ho P. S.
Published: July 2002

Formation of intermetallic compounds in Ti-Cu thin film bilayer samples has been studied between 300–475 °C by Rutherford backscattering and glancing-angle x-ray diffraction techniques. The first intermetallic compound to be formed was TiCu and was followed by TiCu3, the latter showed detectable deviations from the stoichiometry. The thickening of both compounds obeyed a parabolic relationship with time. The interdiffusion coefficient derived from compound formation can be described by the following expressions: TiCu:D=4.85×10−4 exp(—1.48eV/kT) cm2/sec, TiCu3:D=7.73×10−2 exp(—1.82eV/kT) cm2/sec.
Magnetic and structural studies in rapidly quenched iron-rare-earth-metalloid alloys
Authors: Tao Y. F. , Hadjipanayis G. C.
Published: July 2002

The crystallization of the amorphous phase into the tetragonal Fe14R2B phase and the observed magnetic hysteresis have been examined in melt-spun Fe-R-M alloys. The results show that the Fe14R2B phase is stable in melt-spun alloys with R≡Ce to Tm and with M≡B but not in Fe-La-B. The estimated Curie temperatures for the Fe14R2B phases are in the range of 300–380 °C and are found to be strongly correlated with the deGennes factor. A phase with an ordering temperature not very much different from that of Fe14R2B is also observed when boron is replaced by other metalloids. However, it is not clear yet whether this is the Fe14R2M phase. The crystallized samples show large hysteresis with coercivities up to 6 kOe.
Effect of Auger recombination on laser operation in Ga1−xAlxAs
Authors: Takeshima Masumi
Published: July 2002

The effect of band-to-band Auger recombination on laser operation in Ga1−xAlxAs is discussed. Theoretical calculation of the Auger recombination rate is carried out and tested by comparison with experiments. On this basis laser-threshold current is calculated on a buried twin-ridge substrate laser. It is shown that the Auger recombination gives an important contribution to the threshold current in a laser, especially with a thin active layer at temperatures over 300 K.
Inhomogeneity model for anomalous Hall effects in n-type Hg0.8Cd0.2Te liquid-phase-epitaxy films
Authors: Chen M. C. , Parker S. G. , Weirauch D. F.
Published: July 2002

Anomalous Hall effects, i.e., peaks in the temperature dependence of the Hall coefficient and Hall mobility, have been observed in liquid-phase-epitaxy (LPE) Hg0.8 Cd0.2Te films. After establishing that surface effects are not the cause of the anomalies and that our LPE films are indeed n type, we propose an inhomogeneity model with a network of extended p-type inclusions in an n-type matrix. Good fits to the experimental data have been obtained by computer simulation based on this model.
Dislocation patterning in fatigued metals as a result of dynamical instabilities
Authors: Walgraef Daniel , Aifantis Elias C.
Published: July 2002

The nucleation of persistent slip bands in stressed materials is described as a cooperative phenomenon for dislocation populations. It is the competition between their mobility and their nonlinear interactions (creation, annihilation, and pinning) which causes the instability of uniform dislocation distributions versus inhomogeneous ones and leads to the formation and persistence of dislocation patterns.
Reaction of atomic and molecular chlorine with aluminum
Authors: Danner D. A. , Hess D. W.
Published: July 2002

In order to quantify the contributions of atomic and molecular chlorine during the plasma etching of aluminum, a discharge-flow system was used to generate chlorine atoms upstream of a parallel-plate reactor in which aluminum samples were etched with the afterglow. Molecular dissociation in excess of 70% was achieved. Dissociation was measured in the parallel-plate reactor by gas-phase titration of the chlorine atoms with NOC1 using the chemiluminescent emission resulting from atom recombination as an end point indicator. Molecules etched aluminum at least four times faster than atoms and displayed an activation energy near zero (0.02–0.04 eV/molecule) between 35 and 150 °C. Below 25 °C etching was quenched due to the inability of products and/or contaminants to desorb. The higher molecular etch rate is believed to be the result of an enhanced sticking coefficient on the chlorinated surface. Calculation of molecular sticking coefficients based on the assumption of adsorption-limited etching are in good agreement with reported values. Temperature-dependent atom recombination on the in situ electrodes prevented accurate determination of the molecule/atom etch rate ratio and masked the activation energy for atom etching.
Kinetics of Pd2Si layer growth measured by an x-ray diffraction technique
Authors: Coulman Betty , Chen Haydn
Published: July 2002

An x-ray diffraction approach has been developed for determination of the kinetics of growth of Pd2Si layers. Epitaxial Pd2Si films were grown on Si(111) substrates over a temperature range of 160–222 °C by a solid-state reaction between the substrates and the Pd overlayers. The parabolic rate equation was verified and rate constants showed Arrhenius behavior with an activation energy Ea=1.06 eV and prefactor k0=7×10−4 cm2/s. The low value of Ea suggests a short-circuit diffusion mechanism. It is reasonable to expect that impurities and microstructure may play important roles in the growth process. Impurity levels in the specimens were evaluated by analytic techniques suited to thin-film study: Rutherford backscattering spectrometry, secondary ion mass spectrometry, and Auger electron spectrometry. No impurities were present at concentrations approaching 1 at. %. Some O, C, and F were detected at the Pd2Si/Si interfaces. The annealing ambient was the major source of further contamination. Upon emergence of the growth interface through the sample surface (some Pd2Si on surface), impurity pickup was detected. Interfacial roughness was indicated by all the techniques to be on the order of 20 nm.
Molecular-beam epitaxy of Si on a CaF2/Si (100) structure
Authors: Sasaki Masayoshi , Onoda Hiroshi
Published: July 2002

Heteroepitaxial growth of Si on a CaF2/Si (100) structure by molecular-beam epitaxy has been investigated. High-quality Si layers have been grown at low temperatures (650–760 °C) by amorphous Si predeposition and careful heat treatment prior to the Si molecular-beam epitaxy. It has been found that the predeposited Si layer is crystallized by solid-phase epitaxy, and the behavior of the predeposited Si has been discussed. Ca segregation at the Si surface has been found and related to the superstructures of the Si surface. The Ca segregation has been reduced by the solid-phase epitaxy of Si performed on top of the molecular-beam-epitaxial Si layer.
Radiation-induced conductivity of as-grown and electrodiffused quartz
Authors: Martini M. , Spinolo G. , Vedda A.
Published: July 2002

Thermoluminescence, phosphorescence, and ac conductivity measurements have been performed at room temperature on as-grown or Li-, Na-, and Cu- electrodiffused synthetic quartz, beta or x ray irradiated, to confirm the ionic nature of the charge carriers in the radiation-induced conductivity (RIC). Comparison between RIC and phosphorescence time dependence has allowed us to propose a mechanism for the annealing process of the RIC.
Hole diffusion length investigation by photon and electron excitation of GaAs Schottky barriers
Authors: Tarricone Luciano , Frigeri Cesare , Gombia Enos , Zanotti Lucio
Published: July 2002

A hole diffusion length in liquid-encapsulated-czochralski (LEC) GaAs monocrystals (Si-doped, n≂1015–1016 cm−3) in the range (0.4–3.0) 10−4 cm, has been determined by photon and electron bombardment through semitransparent Au or Cr Schottky electrodes. A minority-carrier lieftime in the range (0.3–9.7) 10−9 s was estimated. Schottky barrier diodes with abrupt junctions giving optimum electrical characteristics were prepared. The absorption length of the examined samples was evaluated by optical transmission measurements. The diffusion length investigation, which was carried out by the steady-state surface photovoltage (SPV) and the scanning electron microscope electron-beam-induced current (SEM-EBIC) techniques, has been related to the spectral quantum efficiency of Schottky diodes. SPV and EBIC techniques are emphasized as complementary methods for the investigation of bulk photoelectronic properties.
The computation of transmission electron microscope image profiles for dislocation loops in GaAs
Authors: Ardren S. P. , Ball C. A. B. , Neethling J. H. , Snyman H. C.
Published: July 2002

The two-beam dynamical theory of electron diffraction has been used to calculate transmission electron microscope image profiles for small dislocation loops in GaAs. It is shown that the method of matching computed and experimental image profiles of loops is useful in the determination of their Burgers vectors. The results also indicate that the isotropic elasticity theory may be used to a good approximation for GaAs.
Observation of strain effects and evidence of gallium autodoping in molecular-beam-epitaxial ZnSe on (100)GaAs
Authors: Mar H. A. , Park R. M.
Published: July 2002

An analysis of the two-electron satellites of the dominant donor-bound exciton line in photoluminescence of ZnSe layers grown on (100)GaAs by molecular-beam epitaxy indicates that the donor impurity is likely gallium. Strain in the ZnSe epitaxial layers as evidenced by a shift in the positions of the excitonic lines is shown to depend on the growth temperature and is a minimum at about 365 °C. At growth temperatures different from 365 °C the IGa20 line is observed shifted by as much as 3 meV. The relatively small shift of ∼0.4 meV in our layers grown at 365 °C may be due to a strain-relief inelastic process; it is suggested that one possibility might be the formation of a misfit dislocation network at the interface.
Directional dependence of the demagnetizing energy in imperfect thin magnetic films
Authors: Yafet Y. , Gyorgy E. M. , Walker L. R.
Published: July 2002

The magnetostatic energy of imperfect films having a two-dimensional square-lattice structure with voids between square islands of magnetic material is calculated for arbitrary ratios of thickness and island size to the period of the lattice. These calculations are relevant to the understanding of the uniaxial anisotropy observed in many thin films used as magnetic-storage media.
Photoluminescence spectra and line-shape synthesis of a conduction-band-to-deep-acceptor transition in GaAs:Sn
Authors: Zemon S. , Vassell M. O. , Lambert G. , Bartram R. H.
Published: July 2002

A systematic photoluminescence (PL) study of a deep level in liquid-phase-epitaxy-grown GaAs:Sn is presented. Experimental details and results are reported on PL spectra and decay-time measurements in the temperature range T=4.2–300 K for selected carrier concentrations between n=6×1016 and 2×1018 cm−3. Qualitative interpretation of the measured data is shown to be consistent with a conduction-band-to-deep-acceptor transition. This interpretation was further supported by synthesis of the high-temperature line shapes, using general techniques developed for analyzing free-to-bound transitions. The effects of electron-lattice interaction in the narrow-coupling limit of the initial electronic state continuum, and of inhomogeneous broadening by the random distribution of impurities, are taken into account. Values predicted for the parameters of a three-state configuration-coordinate diagram for the transition correlate well with measured T and decay-time results, as well as with estimates obtained from a moment analysis of the line shapes.
Effects of transition-metal elements on tellurium alloys for reversible optical-data storage
Authors: Young R. T. , Strand D. , Gonzalez-Hernandez J. , Ovshinsky S. R.
Published: July 2002

Tellurium-based alloys are being applied to phase-change, reversible optical-data storage. In order to improve the disk performances, research efforts have been concentrated on increasing the erase speed (crystallization rate) while maintaining good film stability. We report, for the first time, that certain transition-metal elements added to Te-alloy films can substantially improve the rate of crystallization without any reduction of the amorphous-phase stability.
Behavior of dopant diffusion in a silicon-on-insulator structure formed by high-dose oxygen implantation
Authors: Fahey P. , Solmi S.
Published: July 2002

Diffusion of Sb and P in a silicon-on-insulator (SOI) structure formed by heavy-dose oxygen implantation has been studied and compared to diffusion in normal bulk wafers. It is found that the nonequilibrium effects on diffusion during direct nitridation or nitridation of an SiO2 layer are mitigated in the SOI structures, while under oxidizing conditions there are no large differences in diffusion behavior between bulk and SOI samples. We also demonstrate that the spatial extent of the low-concentration tail region of a P diffusion from POCl3 is reduced in the SOI structure.
New ultrafast switching mechanism in semiconductor heterostructures
Authors: Hess K. , Higman T. K. , Emanuel M. A. , Coleman J. J.
Published: July 2002

A new switching mechanism in a two-terminal semiconductor heterolayer structure is proposed which capitalizes on nonlinear electron temperature effects in adjacent heterolayers. The estimated switching speed of an optimized heterostructure hot electron diode should be extremely fast, perhaps as fast as 200 fs. Data are presented on prototype devices which show the expected negative differential resistance and indicate that the basic physical model is correct.
Photoresponse of asymmetrically doped GaAs-AlAs heterostructures under external bias
Authors: Woodward T. K. , McGill T. C. , Burnham R. D.
Published: July 2002

We present new experimental results in the photoresponse behavior of GaAs-AlAs-GaAs heterostructures. Structures consisted of a layer of AlAs several thousand angstroms thick, sandwiched between layers of GaAs which were several microns thick. The layer of GaAs nearest the surface was doped degenerately n type, whereas, the layer beneath the AlAs was doped nondegenerately n type. The asymmetric doping and the AlAs layer are shown to play an important role in determining the photoresponse. We present photocurrent per incident photo data, as a function of incident light energy, at a variety of external biases. We also present current-voltage curves taken while samples were illuminated by an incandescent lamp. Zero bias photocurrent consistent with electron transport from the nondegenerate region beneath the AlAs to the degenerate region forming the surface is observed. As negative voltage is applied to the top of the sample, this photocurrent changes sign. These results are explained by introducing the concept of a ‘‘collecting interface’’ to account for fields and scattering in the AlAs. Further, we explain why the shape of the photocurrent spectrum depends upon the sign of the photocurrent.
Hashin–Shtrikman bounds on the effective elastic moduli of polycrystals with trigonal (3,3̄) and tetragonal (4,4̄,4m) symmetry
Authors: Watt J. Peter
Published: July 2002

Hashin–Shtrikman bounds are given for the effective bulk and shear moduli of randomly oriented aggregates of materials with trigonal (crystal classes 3, 3̄) and tetragonal (classes 4, 4̄, 4m) symmetry. The Hashin–Shtrikman bounds are narrower than the widely used Voigt and Reuss bounds by factors of 2–13. This study completes the development of explicit Hashin–Shtrikman bounds for polycrystals of all crystal symmetries and classes, except triclinic.
Lattice mismatch and band offsets in strained layers
Authors: Coon D. D. , Liu H. C.
Published: July 2002

Lattice mismatch effects are obscured by the standard envelope wave-function approach to electronic states because the lattice potential does not appear. A theoretical analysis of the first-order effect of lattice mismatch is presented using the deformable ion approximation. It is found that a potential barrier of height Δ, normally associated with a band offset, acquires an additional energy (E) dependent term becoming Δ+η(Δ−E) where η is the fractional lattice mismatch in the growth direction. For strained layers, Δ includes the effect of deformation in the strained layer. Quantitatively, the lattice mismatch effect can be comparable to or larger than the deformation potential effect on the band offset. A scattering approach is employed.
High-resolution electron microscopy study of (Ca,Sr)F2/GaAs grown by molecular-beam epitaxy
Authors: Héral Hélène , Bernard Louis , Rocher André , Fontaine Chantal , Munoz-Yague Antonio
Published: July 2002

GaAs/(Ca,Sr)F2/GaAs structures have been studied by means of high-resolution electron microscopy; two substrate orientations, (100) and (111)As, were considered. The (Ca,Sr)F2 layers were observed to be monocrystalline, while their crystalline orientation was found to be the same as that of the substrate (A type). The surface morphology of the (Ca,Sr)F2 layers appeared to be highly sensitive to the orientation: it was observed to be atomically flat for the (111) case and to consist of facets, {111} oriented for the (100) orientation. For both orientations, the transmission electron microscopy observations show that the interface seems to be composed of coherent and incoherent structures. These results are discussed and compared to those obtained on similar heteroepitaxial systems.
Biased charge collector analysis for intense ion beam measurements
Authors: Kraft R. , Kusse B. R.
Published: July 2002

An analysis of a biased charge collector for measuring intense ion beam parameters is presented. The propagating ion beam is assumed to be current and space charge neutralized by a thermalized, background electron population. Space-charge effects inside the charge collector are included and it is shown that in addition to the ion current density, information on the electron temperature can also be obtained from the I-V characteristics of the collector. Finally, the design requirements for the construction of a biased charge collector are summarized.
Doping superlattices in GaP
Authors: Kitamura M. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

Atmospheric pressure organometallic vapor-phase epitaxy was used to grow GaP doping superlattices. Measurements are reported for the first doping superlattice with a band gap which is indirect in both real space and k space. The first observations of phonon replicas in a n-i-p-i photoluminescence (PL) spectrum and a n-i-p-i-like PL peak coming from donor–acceptor transitions are also reported. Large energy shifts of 60 meV per decade of excitation intensity have been observed. The n-i-p-i peak intensities increased linearly with excitation intensity, and the bound exciton peak intensities increased superlinearly, at low illumination intensity, as expected for a periodically modulated space-charge potential. The distribution coefficients for Te and Zn in GaP were found, at 630 °C, to be 34 and 3.0×10−3, respectively.
Effects of vanadium and chromium on aluminum electromigration
Authors: Towner Janet M. , Coulman Betty
Published: July 2002

A systematic study was made of electromigration in homogeneous Al-V and Al-Cr thin films. V and Cr concentrations were varied in the range of 0–2 wt. %, and films were prepared both with and without 1% Si. The addition of as little as 0.1% V caused significant improvements in lifetime relative to pure Al. In the most concentrated alloy studied, the activation energy of mass transport had increased from 0.54 eV for pure Al to 0.92 eV for Al-1.1% V. For the Al-Cr alloys, a maximum in lifetime was found at 0.4% Cr. Higher concentrations of Cr resulted in a gradual degradation of the enhanced lifetime. Lifetimes were reduced when 1% Si was added to either alloy system. Alloy microstructure was examined using transmission electron microscopy. Contrary to results for other Al alloys, lifetimes were reduced in films with extensive precipitation.
High-frequency domain wall motion and energy dissipation in soft ferromagnetic metallic glasses
Authors: Allia P. , Vinai F. , Beatrice C. , Mazzetti P.
Published: July 2002

High-frequency domain wall motion has been studied on two soft ferromagnetic metallic glasses, suitably stressed to deal with simple static domain patterns. Magnetization measurements were supported by direct observation of the magnetic domain configurations. Domain wall motion is dominated by energy dissipation effects. For small wall displacements, the measured coefficient of domain wall damping is very close to the eddy-current value. The power dissipated in the magnetization process decreases with increasing applied field, mainly owing to domain wall multiplication. A possible mechanism for such a multiplication is outlined.