bluuebunny/crossref_metadata_2025 huggingface dataset:
Wavelength-dependent resonant homodyne and heterodyne transient grating spectroscopy with a diffractive optics method: Solvent effect on the third-order signal
Authors: Xu Qing-Hua , Ma Ying-Zhong , Stiopkin Igor V. , Fleming Graham R.
Published: July 2002

We carried out a wavelength-dependent homodyne and heterodyne transient grating (TG) studies on a resonant system, rhodamine 640 in dimethylsulfoxide, with a simplified diffractive optics method. The real and imaginary components of the third-order molecular polarization at different excitation wavelengths have a similar longtime decay (>200 fs), while the amplitude of the real component is strongly wavelength dependent. The nonresonant solvent and the resonant solute contributions to the third-order polarization are found to have a similar magnitude in a dilute solution. The interference of the wavelength-dependent resonant solute contributions with the nonresonant solvent contribution is found to be crucial to properly understand the wavelength dependence of the initial dynamics in homodyne TG and other four-wave mixing techniques. Such an interference effect is further confirmed by concentration-dependent homodyne TG measurements.
Wetting-induced interaction between rigid nanoparticle and plate: A Monte Carlo study
Authors: Shinto Hiroyuki , Uranishi Katsushige , Miyahara Minoru , Higashitani Ko
Published: July 2002

The interaction forces between a nanosphere and a flat plate in undersaturated vapors are examined. We perform grand canonical Monte Carlo simulations, where the surfaces of the sphere and the plate are treated as rigid smooth and the vapors are modeled as a Lennard-Jones fluid of nonpolar spherical molecules. The following results are obtained: (i) The force between the sphere and plate becomes attractive at the surface distances where capillary condensation takes place in the gap between the surfaces; (ii) the onset of the attractive force becomes farther as the relative vapor pressure increases; (iii) the curve of the pull-off force (or the adhesion force) as a function of the relative vapor pressure has a peak, where the peak position shifts to a higher relative pressure and the peak height becomes smaller with decreasing the attractive interaction of the surfaces with a fluid molecule; (iv) at the relative vapor pressure where the pull-off force becomes maximum, the coverage of the surface by fluid molecules is about 0.45 regardless of the strength of the surface–fluid attraction; in addition, the gap between the sphere and plate exhibits the same feature of wetting, that is, a circular string of fluid molecules plus an adsorbed layer on each surface. The results of our simulations will be compared in details with those of force measurements by the atomic force microscope and the surface force apparatus.
A self-consistent weighted-density-functional approach to the structure of simple fluids
Authors: Patra Chandra N. , Ghosh Swapan K.
Published: July 2002

A self-consistent procedure for studying the structure of simple fluids is developed, where a modified density expression of Denton–Ashcroft version of weighted density approximation is used as a closure in the integral equation theory for the uniform fluids. The density equation uses the more accurate Carnahan–Starling equation of state and is made to satisfy the sum rule at contact. This new self-consistent approach is employed to predict the structure of nonuniform hard-sphere fluids near a hard wall. The calculated results on the radial distribution function and the density profiles are shown to compare well with the available simulation data.
A quantum chemical study of the self-directed growth mechanism of styrene and propylene molecular nanowires on the silicon (100) 2×1 surface
Authors: Kang Jeung Ku , Musgrave Charles B.
Published: July 2002

We use density functional theory to investigate the self-directed growth mechanism of molecular nanowires on the Si (100)-2×1 monohydride surface from the molecular precursors styrene (H2C=CH–C6H5) and propylene (H2C=CH–CH3). The reaction is initiated using a scanning tunneling microscope tip to create a Si dangling bond on the surface. This dangling bond then attacks the C=C π bond to form a Si–C bond and a C radical. Next, the C radical abstracts a H atom from a neighboring surface site, which results in a new Si dangling bond to propagate the chain reaction. For the case of H2C=CH–C6H5 the predicted hydrogen abstraction barrier of 18.0 kcal/mol from a neighboring dimer along the dimer row for C–H bond formation is smaller than H2C=CH–C6H5 desorption energy of 22.6 kcal/mol. On the other hand, for the case of H2C=CH–CH3 the predicted hydrogen abstraction barrier of 10.8 kcal/mol for C–H bond formation from a neighboring dimer is significantly larger than H2C=CH–CH3 desorption barrier of 2.7 kcal/mol. Consequently, the predicted barriers indicate that the self-directed growth of nanowires on (100) silicon using styrene occurs while a self-directed chain reaction using propylene should not occur, in agreement with experimental observations.
Imperfect gluing bifurcation in a temporal glide-reflection symmetric Taylor–Couette flow
Authors: Marques F. , Lopez J. M. , Iranzo V.
Published: July 2002

The unfolding due to imperfections of a gluing bifurcation occurring in a periodically forced Taylor–Couette system is numerically analyzed. In the absence of imperfections, a temporal glide-reflection Z2 symmetry exists, and two global bifurcations occur within a small parameter region: a heteroclinic bifurcation between two saddle two-tori and a gluing bifurcation of three-tori. Due to the presence of imperfections, these two global bifurcations collide, strongly reducing the range of validity of the generic unfolding of the gluing bifurcation.
High levels of alkali-metal storage in thin films of hexa-peri- hexabenzocoronene
Authors: Keil M. , Samorı́ P. , dos Santos D. A. , Birgerson J. , Friedlein R. , Dkhissi A. , Watson M. , Müllen K. , Brédas J. L. , Rabe J. P. , Salaneck W. R.
Published: July 2002

The affects of alkali-metal atoms on the electronic structure of disordered and highly ordered thin films of the medium-size aromatic hydrocarbon hexa-peri-hexabenzocoronene (HBC) have been investigated by valence and core level photoelectron spectroscopies—ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS)—and accompanying quantum-chemical calculations. Deposition of Li or Na atoms in situ leads to new spectral features in the UPS spectra, which are related to formerly unoccupied molecular states. The binding energies and intensities of these features depend on the nature of the counterion. The smaller Li ion exhibits a stronger influence on the electronic structure than its sodium counterpart. In the intercalation of sodium into ordered films, a high degree of molecular order is preserved, and, at high deposition levels, a surface dipole is formed that is associated with the layered structure of the compound. Remarkably, high levels of alkali-metal storage of at least one alkali-metal atom for each four carbon atoms have been observed, indicating clearly the potential use of these graphene materials in lithium-ion batteries with a high charge-storage capacity.
Degradation of MgB2 under ambient environment
Authors: Serquis A. , Zhu Y. T. , Peterson D. E. , Mueller F. M. , Schulze R. K. , Nesterenko V. F. , Indrakanti S. S.
Published: July 2002

The superconductivities of samples prepared by several procedures were found to degrade under ambient environment. The degradation mechanism was studied by measuring the change of surface chemical composition of dense MgB2 pellets (prepared by hot-isostatic pressure, HIPed) under atmospheric exposure using x-ray photoelectron spectroscopy (XPS). Results showed that samples with poor connectivity between grains and with smaller grain sizes degrade with time when exposed to ambient conditions. In these samples, the TC did not change with time, but the superconducting transition became broader and the Meissner fraction decreased. In contrast, our well-sintered and the HIPed samples remained stable for several months under ambient condition. The degradation was found to be related to surface decomposition as observed by XPS. We observed the formation of oxidized Mg, primarily in the form of a Mg hydroxide, the increase of C and O contents, and the reduction of B concentration in the surface layer of MgB2 samples.
Magnetic moment and anisotropy in FenCom clusters
Authors: Kortus J. , Baruah T. , Pederson M. R. , Ashman C. , Khanna S. N.
Published: July 2002

Electronic structure calculations of FenCom (n+m=5 and 13) are used to examine the effects of alloying on the magnetic moment and magnetic anisotropies. Our density-functional studies show that many mixed clusters have moments comparable to or higher than the pure clusters. The mixed clusters, however, have very low anisotropies and could be ideal as soft magnetic materials. It is shown that shape, composition, and compositional ordering must be considered for optimization of anisotropy energies.
Universal estimates for critical circle mappings
Authors: Khanin K. M.
Published: July 2002

A thermodynamic formalism is constructed for critical circle mappings. It is used to prove universal estimates for the asymptotic behavior of renormalized mappings. Certain applications of statistical mechanics to research on the ergodic properties of critical homeomorphisms of a circle are also discussed.
Dynamo theory, vorticity generation, and exponential stretching
Authors: Friedlander Susan , Vishik Misha M.
Published: July 2002

A discussion is given of the analogy between the dynamo equation for the generation of a magnetic field by the motion of an electrically conducting fluid and the equation for the evolution of vorticity of a viscous fluid. In both cases exponential stretching is an important feature of the underlying instability problem. For the ‘‘fast’’ dynamo problem, the existence of exponential stretching (i.e., the positivity of the Lyapunov exponent) somewhere in the flow is a necessary condition when the flow is smooth. An example is presented of a flow with exponential stretching (an Anosov flow) that supports fast dynamo action. A parallel treatment is described for the linearized Navier–Stokes equations for the motion of a viscous fluid. In this problem the analogous necessary condition for ‘‘fast vorticity generation’’ is the existence of some instability in the corresponding Euler (i.e., inviscid) equation. Dynamo theory methods give a second related result, namely a universal geometric estimate from below on the growth rate of a small perturbation in an inviscid fluid. This bound gives an effective sufficient condition for local instability for Eulers equations. In particular, it is proved that a steady flow with a hyperbolic stagnation point is unstable. The growth rate of an infinitesimal perturbation in a metric with derivatives depends on this metric. This dependence is completely described.
Photoluminescence in transmutation doped liquid-phase-epitaxial gallium arsenide
Authors: Garrido J. , Castaño J. L. , Piqueras J. , Alcober V.
Published: July 2002

Photoluminescence and Hall-effect measurements on neutron transmutation doped liquid-phase-epitaxial GaAs layers were performed. The obtained results clearly point out that at least a part of the Ge atoms introduced by transmutation of Ga leave their original lattice site behaving as acceptors. The probable cause of these displacements are the recoils during γ and β emissions from the unstable Ga isotopes.
Optically enhanced oxidation of III-V compound semiconductors
Authors: Fukuda Mitsuo , Takahei Kenichiro
Published: July 2002

Oxidation of III-V compound semiconductor (110) cleaved surfaces under light irradiation is studied. The light irradiation enhanced the reaction rate of oxidation but the relationship between oxide growth and oxidation time under logarithmic law scarcely changed within this experimental range. The oxidation trend observed under light irradiation is similar to that of thermal oxidation for GaP, GaAs, InP, InAs, InGaAs, and InGaAsP. Semiconductors having As as the V element tend to be easily oxidized, while those of the above mentioned six kinds of materials having Ga as the III element are quickly oxidized in their initial stage. Ternary and quaternary compound semiconductors have less tendency to be oxidized compared to their constituent binary materials. off
Model for a Josephson sampling gate
Authors: Van Zeghbroeck B. J.
Published: July 2002

A simple model for the Josephson sampling gate is presented. The sampler response was calculated analytically for a step-function signal. Two tradeoffs were found: one between time resolution and overshoot and another between time resolution and sensitivity. The model also explains a prepulse in the sampling gate response.
Parametric studies of pulsed-laser cutting of thin metal plates
Authors: Lee C. S. , Goel A. , Osada H.
Published: July 2002

In this paper, we report a parametric study of pulsed-laser cutting of thin metal plates. The physical processes of laser-material interaction involving material removal are explored through a systematic study of pulsed-laser cutting of various metal plates of different physical properties. The roles of assist gas in the cutting process was also investigated.
Microstructure of ion-bombarded Fe–Ti and Fe–Ti–C multilayered films
Authors: Hirvonen J-P. , Nastasi M. , Mayer J. W.
Published: July 2002

Ion-beam-induced microstructure of the iron-rich end of the Fe–Ti and Fe–Ti–C systems was studied by using multilayered thin-film samples with a linearly varying composition of the metallic constituents. The ion bombardment was carried out using Xe++ ions at 600 keV. A mixing of iron and titanium in binary samples was complete after a bombardment with 8×1015 ions/cm2 whereas Fe–Ti–C samples were only partially mixed after the fluence of 1.8×1016 ions/cm2. Transmission electron microscope studies revealed that the microstructure of Fe–Ti samples was amorphous or amorphous and crystalline iron over a wide range of the compositions investigated. In the case of Fe–Ti–C, the microstructure consisted of crystalline iron and titanium together with a very little amorphous phase.
Charge-state changes of substitutional nitrogen impurities in silicon induced by additional impurities and defects
Authors: Itoh Hisayoshi , Murakami Kouichi , Takita Kôki , Masuda Kohzoh
Published: July 2002

Charge states of substitutional N impurities (Ns) in Si are found to be controllable by doping with P, B, and O impurities in N-ion implanted and subsequently pulsed-laser annealed Si (Si:N system). Electron-spin resonance measurements of the Si:N system doped with P, B, or O impurities show that the spin density of neutral Ns (N0s) decreases because of doping with these impurities. Compensation by multiple doping with equal amounts of P and B impurities leaves the density of N0s essentially unchanged. These results yield evidence for charge-state changes of Ns due to the Fermi level shift. Oxygen doping is found to introduce donors. Three charge states, i.e., positive (N+s) , neutral (N0s) , and negative (N−s) are assigned to off-center substitutional N in Si.
A Mössbauer effect study of the magnetic properties of Nd2(Fe1−xCox)14B and Y2(Fe1−xCox)14B
Authors: Tharp Dwayne E. , Yang Ying-chang , Pringle O. A. , Long Gary J. , James W. J.
Published: July 2002

The atomic and magnetic structures of Nd2(Fe1−xCox)14B, with x equal to 0.0, 0.1, 0.2, and 0.3, and Y2(Fe1−xCox)14B, with x equal to 0.0, 0.1, 0.2, 0.3, and 0.4, have been investigated by Mössbauer spectroscopy at room temperature and 85 K. A Mössbauer effect spectral component analysis, based on neutron diffraction site populations in Nd2(Fe1−xCox)14B, has revealed a stronger compositional dependence for the hyperfine field and magnetic moment on the j2 site than is observed for the other five iron sites. A similar analysis for the Y2(Fe1−xCox)14B compounds shows lower hyperfine fields and hence moments on the c and e sites, as well as a significant decrease in the hyperfine field at the j1 site as the cobalt concentration is increased. The iron site hyperfine fields, and their dependence on cobalt content, are consistent with the local site coordination environments in both series of compounds.
Guiding of an electron beam from a rf accelerator by a laser-ionized channel
Authors: Carlson R. L. , Downey S. W. , Moir D. C.
Published: July 2002

The first guiding of multiple pulses from a rf accelerator by an ultraviolet-laser-ionized channel in low-pressure benzene has been demonstrated. In particular, two 5-ns, 750-A, 30-MeV pulses separated by 20 ns were transported a maximum distance of 13.5 m. Detailed measurements of the temporal behavior of the beam as it propagated versus distance, laser-channel parameters, and accelerator conditions were made.
Multilevel cooperative amplified spontaneous emission from the I2(B→X) system
Authors: Glessner J. W. , Davis S. J.
Published: July 2002

Amplified spontaneous emission (ASE) on the I2(B→X) system has been studied as a function of excitation wavelength by using a narrow-band pulsed dye-laser pump source. ASE output in the range 1.1–1.3 μm has been observed for dye-laser excitation wavelengths between 515 and 600 nm. Cooperative emission from several adjacent rotational levels has been observed and provides an explanation for anomalous spectral features. The conversion efficiency of dye-laser photons to ASE output was as high as a few percent. Pump energy thresholds as low as 5.0 μJ were observed.
Generation and annealing of defects in silicon dioxide
Authors: Reisman A. , Williams C. K. , Maldonado J. R.
Published: July 2002

The generation and annealing of fixed positive and fixed negative charges are discussed in the context of neutral hole and neutral electron traps. The analyses are based on the results of experimental studies involving hydrogen ambient atmosphere annealing and/or electron injection of gate insulators in insulated gate field-effect transistors which have been damaged by 1.5-keV x rays. It is found, for example, that annihilation of fixed positive charge either by hydrogen annealing, or by electron injection results in indistinguishable ‘‘repair’’ of this defect, indicating that such repair probably involves loss of an electron by the hydrogen to an E′γ center. It is postulated that a new electron spin resonance (ESR) center representing fixed negative charge, Nn, which is derived from a large cross-section neutral electron trap might be detected under the proper conditions. Since large cross-section neutral traps (10−15 cm2) are known to exist in significant concentrations in insulators damaged with ionizing radiation, but have not been correlated to any structural defect detected using ESR, it would appear that they are not paramagnetic.
Microwave response of thin-film superconductors
Authors: Sridhar S.
Published: July 2002

The interaction of microwaves with superconductors was explored via extensive measurements of the surface resistance Rs and reactance Xs at 10 GHz of superconducting Sn. The measurements were carried out as functions of thickness d and temperature T for Sn films ranging in thickness from 190 Å to bulk. By varying the thickness with accompanied variation of mean free path, we were able to examine the wave-vector dependence of the microwave-superconductor interaction. An analysis, based on the Bardeen–Cooper–Schrieffer electrodynamical kernel, was developed for calculating Rs and Xs as functions of d, T, and frequency. Details of the measurement techniques and analysis are presented. Experiment and theory agree excellently, with no adjustable parameters. For films with d<800 Å we find that the electrodynamics is local because of impurity scattering, while for thicker films nonlocal effects are important. The results imply that superconducting films with microwave response that agrees with theoretical expectations can be fabricated for potential applications in a variety of superconducting structures.
Brillouin scattering from collective spin waves in magnetic superlattices (invited)
Authors: Hillebrands B. , Boufelfel A. , Falco C. M. , Baumgart P. , Güntherodt G. , Zirngiebl E. , Thompson J. D.
Published: July 2002

We report on the observation and the analysis of collective magnetostatic spin-wave excitations in magnetic superlattices. The influence of interface anisotropies, which can become dominant for small modulation wavelengths, is discussed. For the system Fe/Pd we show that Brillouin spectroscopy experiments in combination with the measurement of the saturation magnetization by a SQUID magnetometer give evidence for a magnetic polarization of the Pd spacer layers, as well as for a small negative out-of-plane interface anisotropy constant of Ks =−0.15 erg/cm2.
Neutral radical deposition from silane discharges
Authors: Gallagher Alan
Published: July 2002

The fractional contributions of the various SiHn radicals (n=0–3) to deposition are calculated for low-power, pure-silane rf and dc discharges. This is done using a radical diffusion plus reaction equation, combined with current knowledge of SiH4 dissociation fractionation, of SiHn+SiH4 reactions, and of the distributed source of radicals. The conclusion reached is that more than 98% of neutral radical deposition is by SiH3 for typical deposition pressures (>100 mT at 240 °C). The effect of SiH3+SiH3 reactions at higher power is also evaluated using an estimated reaction rate coefficient (k3). The resulting loss in deposition rate is given as a function of film growth rate and of k3.
Investigation of collisional effects in the plasma erosion opening switch
Authors: Grossmann J. M. , Kulsrud R. , Neri J. M. , Ottinger P. F.
Published: July 2002

During the conduction phase of the plasma erosion opening switch (PEOS), magnetic field has been observed experimentally to penetrate completely through plasmas up to 30 cm long. Current channels in the main body of the plasma have been observed that are more than 10 cm (or more than about 60 collisionless skin depths) wide. In addition, the maximum current carried by the switch before opening (the conduction current) seems to scale roughly linearly with plasma density n and switch length l. Collisionless pic code simulations of the plasma switch show current conducted in skin-depth-like channels, with the conduction current scaling close to l 2/5 and n1/4. In this paper, the effect of collisions on the behavior of the PEOS is investigated and is shown to bring the pic simulations and experimental results in closer agreement. In collisional simulations, current channels as wide as those in experiments are observed, and the conduction current scales linearly with l and as n1/2 in the anode-dominated case. In the cathode-dominated case, linear scaling with both length and density can be inferred from the cathode penetration distance versus time.
Trap creation in silicon dioxide produced by hot electrons
Authors: DiMaria D. J. , Stasiak J. W.
Published: July 2002

Trap creation in both the bulk of silicon dioxide films and at its interfaces with silicon and metallic contacting electrodes is shown to depend on the presence of hot electrons in the oxide. For thick oxides (≥100 Å), little trap creation is observed in the near-thermal transport regime at electric field magnitudes less than 1.5 MV/cm. At these low fields, electrons travel in a streaming fashion close to the bottom of the oxide conduction band at energies less than that of the dominant optical phonon mode at 0.153 eV. At higher electric fields, the rate of bulk trap creation is proportional to the average energy of the hot electrons, which move in a dispersive manner and can reach energies as large as 4 eV. For thin oxides (<100 Å) where electrons can travel ballistically (i.e., without scattering), traps are not produced unless injected electrons acquire more than 2 eV of kinetic energy from the applied electric field, regardless of the magnitude of this field. All data on both thin and thick oxides are shown to give a threshold for trap creation of about 2.3 eV by the hot electrons in the oxide conduction band. Also, trap creation is shown to be suppressed by lowering the lattice temperature below ≊150 K. Our results are discussed in terms of a model involving hydrogen-related-species release from defect sites near the anode by the hot electrons and the subsequent motion of these molecules to regions near the cathode where they can interact with the lattice and form the trapping sites which are measured.
Equation of state for extrapolation of high-pressure shock Hugoniot data
Authors: Oh Ki-Hwan , Persson Per-Anders
Published: July 2002

An empirical equation of state is proposed for accurate extrapolation of high-pressure shock Hugoniot states to other thermodynamic states. The proposed equation of state complements the Mie–Grüneisen equation of state and allows extrapolating a reference state to much different energy states where knowledge of the Grüneisen function is still uncertain. Examples are given of extrapolations of porous Hugoniots from corresponding solid Hugoniot data.
Time-resolved x-ray-induced conductivity in polyethyleneterephthalate
Authors: Filho R. Gregório , Gross Bernhard
Published: July 2002

Time-resolved measurements of the conductivity induced in foils of polyethyleneterephthalate by irradiation with x rays at exposure rates between 280 and 420 R/s and fields between 104 and 4.8×105 V/cm show the occurrence of a maximum of the induced current. This maximum is attributed to the combined effects of trap filling and recombination. The influence of polarization and space-charge effects was proved to be negligible. Current-time curves measured at different exposure rates and field strengths were explained satisfactorily by the rate theory of induced conduction.
Simulation of reactive ion etching pattern transfer
Authors: Shaqfeh Eric S. G. , Jurgensen Charles W.
Published: July 2002

This paper describes a model that simulates etching profiles and process latitudes in glow-discharge bombardment-induced reactive-etching processes. Numerical results are presented for the pattern-transfer step in trilayer lithography, but this analysis is applicable to many other pattern-transfer processes. The inputs to the interface-evolution model described here are a kinetic model for the yield per incident energetic particle and a statistical mechanical model that relates the incident-yield-weighted angular distribution to the pressure, sheath thickness, and sheath voltage drop. The kinetic model is based on experimental evidence and assumes that the yield per bombarding particle is proportional to its energy. The resulting interface-evolution equation is mathematically analogous to a free-surface evolution equation in hydrodynamics. This convective partial differential equation is reduced to a coupled set of ordinary differential equations via the method of characteristics and solved numerically. More general energy-dependent yields are easily incorporated in the present formulation, but angle-dependent yields are more difficult and are not treated here. This model describes how shadowing of the surface being etched results in proximity effects in line etching and aspect-ratio-dependent etching rates in trench etching. Simulated profiles are compared to experimental trilayer etching profiles and qualitatively describe their shape and the trends that are observed as pressure or other processing parameters are varied. Simulations showing the effect of angular distributions, line proximity, and trench aspect ratio on process latitudes in trilayer lithography are presented and discussed.
Measurement of electron energy deposition necessary to form an anode plasma in Ta, Ti, and C for coaxial bremsstrahlung diodes
Authors: Sanford T. W. L. , Halbleib J. A. , Poukey J. W. , Pregenzer A. L. , Pate R. C. , Heath C. E. , Mock R. , Mastin G. A. , Ghiglia D. C. , Roemer T. J. , Spence P. W. , Proulx G. A.
Published: July 2002

Measurements are made of surface doses necessary to initiate an anode plasma by electron bombardment of Ta, Ti, and C anodes for coaxial geometries characteristic of high-power electron-beam diodes. Measured lower and upper bounds of doses necessary to form an anode plasma are 54±7–139±16 J/g in Ta, 214±23–294±71 J/g in Ti, and 316±33–494±52 J/g in C. Within these bounds, probable values for the threshold are given under specific assumptions. The measurements are consistent with a thermal desorption model for plasma formation.
Micromagnetics below saturation
Authors: Bryant Paul , Suhl Harry
Published: July 2002

In the limit of negligible exchange and anisotropy (except uniaxial), certain shapes of magnetic samples in certain subsaturating field configurations can be analyzed analytically to obtain magnetization and domain wall patterns. Here we consider two cases: (1) generalized cylindrical objects of arbitrary cross section (with several specific examples given) and (2) a general ellipsoid. We also discuss a ‘‘tipping instability’’ which might occur in an ellipsoid with uniaxial anisotropy, resulting in a sudden transition from a ‘‘curling’’ state to a ‘‘transverse vortex’’ state.
Generation of several kinds of oxygen-related thermal donors around 520 °C in Czochralski silicon
Authors: Kamiura Yoichi , Hashimoto Fumio , Yoneta Minoru
Published: July 2002

We have found that at least four kinds of oxygen-related thermal donors are distinguishable by their deep-level transient spectroscopy peaks and generation kinetics around 520 °C for 10–106 min in phosphorus-doped Czochralski silicon. Each kind of thermal donors successively appeared with its preceding kind decaying. The first appearing kind is identified as a family of thermal donors that have been most studied by many investigators. It is suggested that several kinds of thermal donors arise from various oxygen clusters with different sizes and thermal stabilities.
Electrical and chemical characterization of a-C:H prepared by rf glow discharge
Authors: Varhue W. J. , Pandelisev K. A. , Shinseki B. S.
Published: July 2002

Presented are the results of a systematic study of the effects of reactor pressure and rf power level on the electrical and chemical characteristics of a-C:H films prepared by glow discharge. Electrical resistivity has been found to increase rapidly with decreasing reactor pressure. This increase in electrical resistivity corresponded to an increase in the sp3 bonding content of the film. This composition change has been attributed to increased ion bombardment energy and greater time for adatom surface migration. Electrical resistivity decreased with rf power level. The sp2 bonding content of the film decreased while the sp3 bonding content increased with rf power level. The resistivity change and corresponding composition change could not be explained with the present model.
Facet oxidation of InGaAs/GaAs strained quantum-well lasers
Authors: Okayasu Masanobu , Fukuda Mitsuo , Takeshita Tatsuya , Uehara Shingo , Kurumada Katsuhiko
Published: July 2002

Aging tests were carried out on as-cleaved InGaAs/GaAs strained quantum-well ridge waveguide lasers. Although the lasers have immunity to sudden failure and have degradation rate as low as 2×10−5 h−1, after over 6000 h of operation, they readily suffered facet oxidation. The measured oxidation rate was comparable to that of GaAs quantum-well lasers and one order of magnitude higher than that of lattice-matched InGaAs/InP lasers. This high oxidation rate is considered to be caused by light absorption in the vicinity of the facet where the band gap is reduced because of the stress variation from biaxial to uniaxial.
Influence of ionic migration on the Faraday rotation of GdIG:Al single crystals
Authors: Ostorero J. , Soulette F.
Published: July 2002

The influence of diamagnetic cation migration on magneto-optical (MO) properties has been studied on single crystals of garnets Gd3Fe5−zAlzO12 (0.3<z<1.3) quenched at two different temperatures Tq = 1297 and 1473 K. Faraday rotations (FR) were performed at 1150 nm from 5 K to the Curie temperature in an applied magnetic field up to 20 kOe. The influence of Tq on the Faraday rotation is important in the narrow region of the magnetic compensation temperature Tcomp which is shifted towards lower temperatures when Tq increases. In contrast, quenching experiments have little noticeable effect on the MO compensation temperature and the absolute FR values. These FR results are interpreted on the basis of the model of Crossley et al. [Phys. Rev. 181, 896 (1969)] where the sublattice magnetizations and the magneto-optical coefficients take into account the cationic distribution in a and d sites of the garnet due to heat treatments. At low temperatures, the contribution of Gd3+ to FR is predominantly due to magnetic dipole transitions.
A magnetic evaluation of interaction and noise characteristics of CoNiCr thin films
Authors: Mayo P. I. , O’Grady K. , Kelly P. E. , Cambridge J. , Sanders I. L. , Yogi T. , Chantrell R. W.
Published: July 2002

The nature of media recording noise in metallic, quasiparticulate thin films is principally related to the grain size, crystallographic orientation, and intergranular exchange and magnetostatic coupling in the films. In this study the results of a magnetic evaluation of magnetostatic interactions in CoNiCr thin films of varying Cr underlayer thickness are reported. The evaluation is undertaken through the measurement and comparison of remanence curves. The results presented here indicate enhanced cooperative switching as Cr underlayer thickness is reduced from 2000 to 100 Å, with a strong correlation between signal-to-noise measurements. In addition, the transition from principally exchange-coupled to quasiparticulate thin films, as Cr underlayer thickness increases, has been established.     
Magneto-optical Kerr effect and perpendicular magnetic anisotropy of evaporated and sputtered Co/Pt multilayer structures
Authors: He Ping , McGahan William A. , Woollam John A. , Sequeda F. , McDaniel T. , Do H.
Published: July 2002

Thin and ultrathin Co/Pt multilayered structures have been prepared on glass substrates by electron-beam evaporation at room temperature and by sputtering at various substrate temperatures and sputtering pressures. Perpendicular magnetic anisotropy was found in samples with Co/Pt bilayer thicknesses near 3 Å/10 Å and total thicknesses of the layer stack of no greater than 300 Å. X-ray diffraction was performed on the samples to determine layer spacing and integrity, and possible crystallinity of films. Crystalline structures in the interface between the Co and Pt layers were found and identified. The effects of sputtering parameters, such as pressure and substrate temperature, on the magneto-optical Kerr effect were studied. The two deposition methods, electron-beam evaporation and sputtering, resulted in different magneto-optical properties in samples with the same nominal layer structures. We have also investigated optical properties (reflectance, index of refraction, and extinction coefficient) of these materials using ellipsometry.
Relationship of the gold related donor and acceptor levels in silicon
Authors: Koteswara Rao K. S. R. , Kumar V. , Premachandran S. K. , Raghunath K. P.
Published: July 2002

The relation between gold related levels in silicon is studied with deep level transient spectroscopy (DLTS) using linearly graded junctions. Since the depletion layer extends equally on both sides in the linearly graded junction, both the acceptor level in the upper half and the donor level in the lower half of the band gap are simultaneously monitored as majority-carrier traps. It is observed that the concentration of the acceptor level is about four times more than the donor level. The defect concentrations have been calculated using modified DLTS theory for linearly graded junctions where the influence of free-carrier tail has been properly considered for both the traps. The difference in concentrations indicates that the two deep levels originate from different configurations of the gold impurity in silicon.
Temperature dependence of the Landau–Lifshitz damping parameter for iron
Authors: Cochran J. F. , Rudd J. M. , Muir W. B. , Trayling G. , Heinrich B.
Published: July 2002

The temperature dependence of the Landau–Lifshitz damping parameter for pure iron has been obtained over the temperature range 290–800 K from the observed amplitude of 73-GHz microwave radiation transmitted through thin single-crystalline slabs, approximately 45 μm thick, at an applied magnetic field corresponding to ferromagnetic antiresonance (FMAR). FMAR occurs when the internal flux density B satisfies the condition B=ω/γ, where ω is the circular frequency of the microwave radiation and γ is the gyromagnetic ratio. An applied magnetic field parallel with the specimen plane was used. The Landau–Lifshitz damping parameter was found to increase slowly and monotonically with temperature from the room-temperature value (0.70 ± 0.06) × 108 Hz to (0.86 ± 0.06)× 108 Hz at 800 K.
Optimum operating conditions for an optically pumped CF4 laser amplifier
Authors: Sinha Sucharita
Published: July 2002

We report the results of a theoretical study of the performance characteristics of an optically pumped CF4 laser amplifier in terms of a rate equation model. In order to achieve the best output from such an amplifier it is necessary to optimize its operating parameters. Our calculations indicate that, for a given pump rate, there exists an optimum gain length for the amplifier at which the output energy is a maximum. This optimum gain length is a function of the amplifier pump rate as well as its operating pressure and temperature. Our results also show that proper synchronization of the CO2 pump pulse and the CF4 laser pulse leads to the highest amplified output energy.
The possibility of formation of large ferroelectric domains in a copolymer of vinylidene fluoride and trifluoroethylene
Authors: Li Guo-Rong , Kagami Nobuyuki , Ohigashi Hiroji
Published: July 2002

Two Curie temperature Tc peaks in differential scanning calorimetry (DSC) are observed in a well-crystallized, nonpoled film of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene [P(VDF-TrFE)] when it is reannealed at temperatures near Tc. The DSC peak at higher Tc shifts to higher temperature with increasing reannealing temperature, the phenomenon being very similar to that observed in thermally depolarized P(VDF-TrFE) film. This result can be explained by the formation of large 60° or 180° domains during reannealing. The free energy of the simple 180° domain model is used to discuss the temperature dependence of Tc on the domain width and thickness. It is concluded that large domains are generally formed in a P(VDF-TrFE) film by reannealing at temperatures near Tc irrespective of its macroscopic polarization.
Origin of inhomogeneous linewidth of Eu3+ fluorescence in several oxide glasses
Authors: Todoroki S. , Hirao K. , Soga N.
Published: July 2002

The local structure around Eu3+ ions in several oxide glasses (silicate, borate, germanate, and aluminosilicate) was investigated using both Mössbauer spectroscopy and fluorescence measurement including the fluorescence line narrowing technique. The origin of inhomogeneous broadening of fluorescence spectra is discussed. Except for silicate glasses, the isomer shift of 151Eu varied with the population of oxygen species with different microscopic optical basicity. For silicate glasses, it was found that the isomer shift and Stark splitting of 7F1 level showed no compositional dependence. It was assumed that regardless of alkali content, Eu3+ ions in silicate glasses attract a certain number of nonbridging oxygens (NBOs), which is the only species with a negative charge, when incorporated stably into a glass matrix. Further, it was generally found that larger amounts of alkali ions or smaller amounts of macroanions, such as BO4■, AlO4■, and GeO62■, bring about smaller values of inhomogeneous linewidth, ΔνIH. It was concluded that the compositional dependence of ΔνIH in oxide glasses is successfully explained from the viewpoint of the NBO-donating ability of the glass matrix, which is related to the NBO concentration and the flexibility of the glass matrix.
Growth of Si on Si(100) via H/Cl exchange and the effect of interfacial boron
Authors: Koleske D. D. , Gates S. M. , Beach D. B.
Published: July 2002

Using alternating exposures of Si2H6 and Si2Cl6, very thin Si layers have been grown on the Si(100) surface at temperatures (T) as low as 475 °C. Although this growth method is not truly self-limiting, some of the desired features for Si atomic layer epitaxy (ALE) are retained, as discussed here. The growth rate of new Si on Si(100) using this method is limited by the thermal desorption of H2 and HCl. Doping the surface with boron atoms can lower the growth temperature, due to a weakening of the Si—H and Si—Cl bonds on the surface as observed in the temperature programmed desorption results from H2, HCl, and SiCl2 desorption from the clean and the boron-doped Si(100) surfaces.
The microstructure of hot formed neodymium–iron–boron magnets with energy product 48 MG Oe
Authors: Mishra Raja K. , Panchanathan V. , Croat John J.
Published: July 2002

Melt-spun Nd–Fe–B ribbons containing small amounts of Co, Ga, and C were die upset to 60% and 70% reduction in height in an argon atmosphere between 750 and 800 °C. The magnet, which was die upset 70%, has a remanence of 14.2 kG, Hci of 14.8 kOe, and (BH)max of 48 MG Oe. The interior of the magnet consists of well-aligned Nd2Fe14B grains separated by a Nd-rich intergranular phase. Intermixed with such aligned grains, we observed zones of unaligned fine-grained material without any intergranular phase. Since the intergranular phase is a key factor for deformation and alignment and it is uniformly distributed in the hot pressed precursor, it will be possible to enhance the alignment further by controlling the redistribution of the intergranular phase during die upsetting.
Time-resolved reflection and transmission studies of amorphous Ge-Te thin-film crystallization
Authors: Libera M. , Chen M.
Published: July 2002

Measurements of the temperature and time dependence of visible diode laser transmission and reflection are combined with transmission electron microscopy (TEM) to study the crystallization of two 75 nm Ge-Te thin films. Near-stoichiometric Ge48Te52 transforms by the rapid growth of crystals through the film thickness followed by 2D growth in the film plane. Changes in film reflection and transmission are directly related to the volume fraction transformed. The optical measurements are interpreted in terms of classical Johnson–Mehl–Avrami kinetics. A Kissinger analysis gives an activation energy for crystallization of 1.7 eV. Isothermal measurements lead to an Avrami exponent of 4.5. The data are modeled using a numerical temperature-dependent expression developed by Greer [Acta Metall. 30, 171 (1982)]. Off-stoichiometric Ge54Te46 films show markedly different crystallization behavior. Transmission and reflection measurements indicate that the transformation proceeds by rapid growth of a crystalline layer at the free surface of the film followed by 1D growth of this layer through the film. The observation is confirmed by TEM imaging and diffraction. This work shows that reflection and transmission measurements can be an effective method for the study of crystallization kinetics of amorphous thin films, particularly when more traditional calorimetric methods cannot be employed.
High-remanence rapidly solidified Nd-Fe-B: Die-upset magnets (invited)
Authors: Fuerst C. D. , Brewer E. G.
Published: July 2002

The best starting materials for die-upset magnets are moderately overquenched melt-spun ribbons of Nd-Fe-B alloys with ∼20 at. % more rare earth than stoichiometric Nd2Fe14B. Remanence increases with increasing die-upset (DU) level, reaching a maximum of 13.5 kG at 70% DU for ternary Nd-Fe-B magnets, beyond which cracking limits performance. Remanence is also limited by nonuniform deformation, particularly for moderately die-upset magnets. Heat treatments, dysprosium substitutions, or low-level additives can be used to compensate for the decreases in coercivity which accompany increases in die-upset level. By die upsetting in stages and removing misaligned surfaces, a large Nd-Fe-Co-B-Ga magnet (∼30 g) has been produced with both a high remanence (14.2 kG) and a high-energy product (48.5 MG Oe).
dc magnetization measurements in Eu2CuO4:Gd3+
Authors: Zysler R. D. , Butera A. , Fainstein A. , Tovar M. , Fisk Z.
Published: July 2002

dc magnetization measurements in a Gd doped Eu2CuO4 single crystal indicate the appearance below TN=243 K, of a weak ferromagnetic component Ms(T), in addition to the Van Vleck paramagnetism of the Eu3+ ions. Ms(T) is oriented parallel to the (001) plane and its magnitude and in-plane angular dependence are strongly dependent on the cooling conditions. For samples cooled in zero magnetic field the magnetization is isotropic in the (001) plane with Ms(0)=2.2(4)×10−3 μB/formula unit. For samples cooled in a field (FC), Ms(T) increases as a function of the field applied for cooling, HFC, reaching Ms(0)=5.0(5)×10−3 μB/formula unit for HFC=10 kG. A uniaxial magnetic anisotropy develops in this case with an easy axis along the [110] crystallographic direction lying closer to the orientation of HFC. A magnetic free energy including second and fourth order in-plane anisotropy terms provides a good description of the experimental results, with H(2)=−85(5) G and H(4)=10(3) G.
Complex ac susceptibility studies of the disordered molecular based magnets V(TCNE)x: Role of spinless solvent
Authors: Morin B. G. , Zhou P. , Hahm C. , Epstein A. J. , Miller Joel S.
Published: July 2002

The effect of different spinless solvents on the magnetism of V(TCNE)x⋅y(solvent) (TCNE=tetracyanoethylene) is studied by temperature (T) dependent ac susceptibility above 2.3 K. Though V(TCNE)x⋅y(CH2Cl2) has a critical temperature Tc ∼400 K, for V(TCNE)x⋅y(C4H8O), Tc ∼205 K and the coercive field is reduced, while for V(TCNE)x⋅y(CH3CN), Tc ∼140 K or below and a spin glass phase exists below a spin freezing temperature of Tf∼7–15 K. The variations with solvent are suggested to be due to spin dilution and random anisotropy introduced by the spinless solvents.
Bragg reflector of GaAlAs/AlAs layers with wide bandwidth applicable to light emitting diodes
Authors: Saka T. , Hirotani M. , Kato T. , Susawa H. , Yamauchi N.
Published: July 2002

Reflective spectra of the Bragg reflectors applied to GaAs infrared light emitting diodes were simulated. Bragg reflectors are composed of alternating Al0.2Ga0.8As/AlAs layers where the ratio of high- and low-refractive indices is as small as 1.16. The reflectance bandwidth can be broadened by employing chirped structures where the optical thicknesses of the respective layers are changed arithmetically. On the other hand, for chirped Bragg reflectors, resonant reflection drops appeared at some wavelengths. These drops can be corrected by inserting periodic alternating layers. The reflectance band of 80% reflectivity is 2.7 times as wide as that of the conventional reflector of the periodic sequence in the case of 66 layer stack.
Microwave/millimeter-wave generation in a counterstreaming-beam-plasma system
Authors: Schumacher R. W. , Santoru J. , Rosenberg M. , Krall N. A.
Published: July 2002

Radiation from 8 to 60 GHz is generated by injecting counterstreaming, high-power (up to 50 keV and 4 A) electron beams into an unmagnetized, plasma-loaded waveguide. The radiation is emitted at twice the plasma frequency and is amplitude modulated on the ion plasma frequency time scale. The beam-to-millimeter-wave power conversion efficiency at 31 GHz is ≳0.04%. A turbulence theory model is consistent with the radiation characteristics and power scalings.