bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoluminescence spectroscopy and decay time measurements of polycrystalline thin film CdTe/CdS solar cells
Authors: Bridge C. J. , Dawson P. , Buckle P. D. , Özsan M. E.
Published: July 2002

The results of room temperature photoluminescence spectroscopy and decay time measurements carried out on CdTe/CdS solar cells are reported. The as-grown structures were annealed in air at temperatures in the range 350–550 °C. For excitation via the CdTe/CdS interface, longer photoluminescence decay times were observed as the anneal temperature was increased, this is attributed to localized passivation of nonradiative states possibly due to the effect of S interdiffusion. When the photoluminescence is excited via the CdTe free surface, the decay curves consist of a fast and slow component. The fast component (<130 ps) of the photoluminescence is attributed to nonradiative recombination at grain boundaries or the CdTe free surface. The slow component is attributed to the effects of carrier drift and diffusion and subsequent recombination at the CdTe/CdS interface. Modeling of the transport process has led to the extraction of a value of 0.20±0.03 cm2 s−1 for the minority carrier diffusion coefficient of the CdTe for the sample annealed at 450 °C. These results are correlated with improvements in device efficiency determined from illuminated current density–voltage measurements.
Equivalent pyroelectric coefficient of a pyroelectric bimorph structure
Authors: Pintilie L. , Pintilie I. , Matei I.
Published: July 2002

A detailed formula for the equivalent pyroelectric coefficient of a bimorph structure acting as a pyroelectric detector was deduced. It is shown that electric fields occur in the structure when it is subjected to a temperature variation, due to the unequal charges generated by the two components. The field dependence of the ferroelectric polarization has to be considered in this case and the (∂P/∂E) derivative appears explicitly in the deduced formula. The effect is that the equivalent pyroelectric coefficient has different values for heating and cooling. This could lead to a redressing effect on the pyroelectric signal if the temperature difference varies periodically. The equivalent pyroelectric coefficient is, also, thickness dependent. This fact offers the possibility of designing structures with high values of pyroelectric coefficient compared with the values of the component phases.
Dephasing of individual rotational states in liquids
Authors: Jang Joonkyung , Stratt Richard M.
Published: July 2002

We continue our previous examination of the fate of individual rotational quantum states in liquids by an analysis of the rotational Raman spectrum of solutions of H2 and D2 in Ar(l). Rewriting the conventional Kubo treatment allows us to show how the character of the spectrum is an immediate consequence of the rotational friction felt by the solutes. On evaluating that friction via classical molecular dynamics we find that the spectra should consist of well-resolved, homogeneously broadened lines, reflecting the picosecond-long dephasing times. We find, in particular, that the rotational states in H2 should relax predominantly by pure dephasing, whereas D2, with its smaller rotational quanta, should exhibit significant energy relaxation as well. The linewidths predicted for H2 are nicely in accord with those computed by more involved nonadiabatic, mixed quantum-classical simulations.
Theoretical prediction of the rate constant for I+O2(a 1Δg) electronic energy transfer: A surface-hopping trajectory study
Authors: Kaledin Alexey L. , Heaven Michael C. , Morokuma Keiji
Published: July 2002

The temperature dependence of the rate constant for the electronic energy transfer process I(2P3/2)+O2(a 1Δg)→I(2P1/2)+O2(X 3Σg−) has been studied theoretically. Seven ab initio diabatic potential energy surfaces, four for the entrance channel and three for the exit channel, and the coupling elements between them, were adopted. Energy transfer dynamics was simulated with the semiclassical surface-hopping trajectory calculation, using Tully’s “fewest switches” model for electronic transition. Approximately 5×105 trajectories were statistically averaged over a range of impact parameters and collision energies to calculate thermal rate constants for the temperature range 10–300 K. It was found that collisions resulting in energy transfer were dominated by single hop trajectories. The calculated energy transfer rate constant was found to decrease smoothly with increasing temperature over the range 100–300 K. The predicted value was in excellent agreement with the experimental result for 150 K, but the calculations underestimate room temperature data by a factor of 1.6. The rate constant increases with decreasing energy because (i) long-range attractive forces draw slow moving collision partners together and (ii) longer lifetime of slow collisions increases the probability of surface hopping. It is also found that there is a competition between rotational relaxation of O2(a) and electronic energy transfer.
Mixture model description of the T-, P dependence of the refractive index of water
Authors: Cho C. H. , Urquidi J. , Gellene Gregory I. , Robinson G. Wilse
Published: July 2002

In this paper the temperature/pressure dependence of the refractive index of liquid water is analyzed using the two-state outer-neighbor mixed bonding structural model. So far, this theoretical model has been successful in reproducing, usually within the experimental uncertainty, the temperature/pressure dependence of the density, the viscosity, and the oxygen–oxygen pair correlation functions, in addition to the isothermal compressibility and isotope effects of this important substance. The philosophy of the present paper is to use the high accuracy of refractive index measurements to further test this model. It is shown that a very simple linear dependence with respect to temperature and pressure of the specific refractions LI and LII of the two contributing structural components in this two-state model is sufficient to give better than 5-decimal-point agreement with the experimental refractive index data at low pressures and temperatures between about −10 °C and +70 °C. The maximum in the refractive index between −5 °C and +5 °C is reproduced to an even better precision. Generally better than 4-decimal-point accuracy is achieved for higher pressures, where the experimental data are less accurately known. The pressure dependence considered here also allows the calculation of the isothermal piezo-optic coefficient as a function of temperature, which exhibits a minimum near 50 °C.
Electrostatic waves in streaming magnetized plasma: Linearly independent polarized modes
Authors: Naik Antaryami , Mohanty J. N.
Published: July 2002

The evolution of two linearly independent polarized modes due to transverse propagation of electrostatic waves in a two-component streaming magnetic plasma is analytically studied. The modified frequency spectra reveal that the refractive index and amplification factor markedly increase with the rise in thermal energy, especially in strong magnetic-field lines (B0∼103 kG). However, with the increase in streaming velocity, the refractive index sharply diminishes. In weak magnetic-field lines (B0∼10−2 kG), the refractive index decays with the increase in thermal energy, whereas the amplification shows an increasing trend.
Second-order quasi-degenerate perturbation theory with quasi-complete active space self-consistent field reference functions
Authors: Nakano Haruyuki , Nakatani Junji , Hirao Kimihiko
Published: July 2002

A quasi-degenerate perturbation theory (QDPT) is presented that is based on quasi-complete active space self-consistent field (QCAS-SCF) reference functions. The perturbation method shown here is an extension of a previously proposed QDPT with CAS-SCF reference functions (CAS-QDPT) but is a more compact perturbation method that can employ a much smaller reference configuration space with the same number of active electrons and orbitals as the CAS case. A computational scheme to second-order using a diagrammatic approach is described. The second-order effective Hamiltonian consists of the contribution from external excitations, which involve core or/and virtual orbitals, and internal excitations, which involve only active orbitals. The importance of the internal excitation contribution is emphasized. The method is tested on the potential energy curves of the LiF molecule, the Rydberg excitation energies of furan, and the transition state barrier height of the reaction, H2CO→H2+CO. The results are in very good agreement with the corresponding CAS-SCF reference QDPT results and available experimental data. The deviations from the CAS-QDPT values in the energy are less than 0.1 eV on the average for the excitation energies of furan and less than 1 kcal for the barrier height of the reaction, H2CO→H2+CO. The deviation from the experimental values is 0.11 eV at most for the excitation energies, and 1.2 kcal/mol, which is within the twice the experimental uncertainty, for the barrier height.
Scale dependence, correlations, and fluctuations of stresses in rapid granular flows
Authors: Glasser B. J. , Goldhirsch I.
Published: July 2002

It is shown that, unlike in simple molecular fluids, the stress field in granular fluids may be strongly scale, or resolution, dependent. This is a result of the intrinsic lack of scale separation in these fluids. Another consequence of the lack of scale separation in granular fluids is that microscopic stress fluctuations, whose origin (like in molecular fluids) is the underlying discreteness of the system, may appear as observables in macroscopic measurements; the correlation (or decay) time of the stress fluctuations is of the order of the mean-free time, which is also a macroscopic time. All of these properties are intrinsic to granular fluids and not (for example) results of the practical lack of scale separation that is dictated by the fact that grains are of macroscopic dimensions or the limited statistics in simulations. Numerical evidence, based on molecular-dynamic simulations of shear flows of smooth disks in a two-dimensional enclosure, serves to demonstrate the above phenomena.
Low stacking-fault density in ZnSe epilayers directly grown on epi-ready GaAs substrates without GaAs buffer layers
Authors: Hong Soon-Ku , Kurtz Elisabeth , Chang Ji-Ho , Hanada Takashi , Oku Masaoki , Yao Takafumi
Published: July 2002

We report a remarkably low stacking-fault density in ZnSe epilayers directly grown on commercial epi-ready GaAs (001) substrates without GaAs buffer layer growth. It is found that proper pregrowth treatments on epi-ready GaAs (001) substrates to obtain clean surfaces are crucial for two-dimensional layer-by-layer growth and suppression of stacking fault generation. Chemical etching using a NH4OH-based solution is found to reduce not only the thickness of the oxide layers but also the ratio of Ga2O3 to As2O3 to about half of that before etching. A clean GaAs (001) surface characterized by a (4×1) reconstruction in the present case is obtained after thermal cleaning followed by Zn pre-exposure. Reflection high-energy electron diffraction intensity oscillations with more than 50 periods are observed even from the very beginning of ZnSe growth on GaAs substrates cleaned as such. The stacking fault density in such a ZnSe layer is in the low-105 cm−2 range.
Spectral line shapes in dissipative systems: Molecules adsorbed on metal surfaces
Authors: Miret-Artés S. , Micha D. A. , Beksic D.
Published: July 2002

The temporal evolution of rates and probabilities of transitions, induced by light between states of a molecule interacting with a dissipative medium, are derived for a Hamiltonian containing an anti-Hermitian term which describes dissipation. Our theoretical treatment introduces a biorthonormal basis set of decaying eigenstates to obtain the rates and probabilities from perturbation theory. The formalism is developed for excitation by continuous and pulsed light. As an example, it is applied to the excitation of molecules adsorbed on solid surfaces, taking into account the dissipation of energy into the solid as the molecule relaxes or is desorbed.
A bifurcation analysis of two coupled calcium oscillators
Authors: Bindschadler Michael , Sneyd James
Published: July 2002

In many cell types, asynchronous or synchronous oscillations in the concentration of intracellular free calcium occur in adjacent cells that are coupled by gap junctions. Such oscillations are believed to underlie oscillatory intercellular calcium waves in some cell types, and thus it is important to understand how they occur and are modified by intercellular coupling. Using a previous model of intracellular calcium oscillations in pancreatic acinar cells, this article explores the effects of coupling two cells with a simple linear diffusion term. Depending on the concentration of a signal molecule, inositol (1,4,5)-trisphosphate, coupling two identical cells by diffusion can give rise to synchronized in-phase oscillations, as well as different-amplitude in-phase oscillations and same-amplitude antiphase oscillations. Coupling two nonidentical cells leads to more complex behaviors such as cascades of period doubling and multiply periodic solutions. This study is a first step towards understanding the role and significance of the diffusion of calcium through gap junctions in the coordination of oscillatory calcium waves in a variety of cell types.
BeCdSe as a ternary alloy for blue-green optoelectronic applications
Authors: Ivanov S. V. , Nekrutkina O. V. , Sorokin S. V. , Kaygorodov V. A. , Shubina T. V. , Toropov A. A. , Kop’ev P. S. , Reuscher G. , Wagner V. , Geurts J. , Waag A. , Landwehr G.
Published: July 2002

Bulk BeCdSe layer lattice-matched to a GaAs substrate, as well as a BeCdSe/ZnSe quantum well (QW) structure have been grown using the submonolayer digital alloying mode of molecular beam epitaxy. The structures have demonstrated bright photoluminescence up to room temperature and good structural quality. Stimulated emission under optical pumping has been obtained for a 2 nm BeCdSe/ZnSe multiple QW structure at 80 K. The bowing parameter of the energy gap of this ternary alloy has been estimated as about 4.5 eV.
Introduction to wave heating and current drive in magnetized plasmas
Authors: Pinsker R. I.
Published: July 2002

The development of high-power wave heating and current drive in magnetized plasmas in the last 40 years is a major ongoing success story in plasma science. A hallmark of this area of research has been the detailed quantitative comparison of theory and experiment; the good agreement consistently found is indicative of the robustness and the predictive power of the underlying theory. This tutorial paper is a brief overview of the fundamental concepts and applications of this branch of plasma science. Most of the high-power applications have been in three frequency regimes: the ion cyclotron range of frequencies (ICRF), the lower hybrid range of frequencies (LHRF), and the electron cyclotron range of frequencies (ECRF). The basic physics of wave propagation and damping in these regimes is briefly discussed. Some of the coupling structures (antennas) used to excite the waves at the plasma boundary are described, and the high-power systems used to generate the wave energy are touched on. Representative examples of the remarkably wide range of applications of high-power wave heating and current drive in high-temperature fusion plasmas will be discussed.
High-power high-frequency-induced Langmuir turbulence in the smooth ionosphere at Arecibo. II. Low duty cycle, altitude-resolved, observations
Authors: Cheung P. Y. , Sulzer M. P. , DuBois D. F. , Russell D. A.
Published: July 2002

This is the second of two papers comprising a theoretical and observational study of new, altitude-resolved, observations at Arecibo of Langmuir turbulence induced in the ionosphere by a new, more powerful, high frequency heater operated at very low duty cycles. Altitude resolution of 150 m in incoherent scatter radar spectra is made possible by the coded-long-pulse method. Here we present the first observation at Arecibo of the well-developed parametric decay instability and the Langmuir decay instability cascade features in the Thomson scatter radar power spectrum, of the plasma line, at the unmodified matching altitudes under near-cold start conditions. The dependence of the plasma line spectra on altitude, pump power, and density scale length have been studied. The temporal growth and saturation of the spectra during heating and the decay of the spectra in the afterglow of heating has also been studied in detail. Comparisons are made here with the theoretical predictions of the companion paper I [DuBois et al., Phys. Plasmas 8, 791 (2001)]. From these comparisons and a comparison with recent observations at both Arecibo and Tromso/, we conclude that all the predictions of modern Langmuir turbulence theory for the radar spectral signatures of the turbulence in a smooth ionosphere have now been verified.
Kinetic simulation of nonlinear phenomena of an ion acoustic wave in gas discharge plasma with convective scheme
Authors: Matsunaga Yasushi , Hatori Tadatsugu , Kato Tomokazu
Published: July 2002

Nonlinear phenomena of the ion acoustic wave in a negatively charged plasma–sheath system are observed in the simulation with a convective scheme described by a two-dimensional phase space, and are theoretically analyzed. Subharmonics of a fundamental mode are excited and show the bifurcation phenomena when the intensity of the ion source relating to the ionization is increased. A reversed electric field from the cathode to anode reveals that the ponderomotive force due to a high frequency mode pushes the ions toward the cathode. A nonlinear coupling of two modes through the ponderomotive force is a key idea to construct the model. Nonlinear dynamical model equations involving the coupling of the two modes and an interaction of the sheath with the two modes, i.e., two nonlinear effects, are proposed. The period-doubling bifurcations of the fundamental mode are examined by using the same growth rates with the flow velocity as in our previously published linear theory.
Striation phenomenon in the plasma display panel
Authors: Shon Chae Hwa , Lee Jae Koo
Published: July 2002

A detailed analysis, based on kinetic and fluid simulations, of striation phenomenon in the plasma display panel cell has been presented. Numerical studies indicate that the phenomenon of striation occurs primarily due to the accumulation of space charge near the anode electrode. These space charges locally create multiple-layer potential distribution near the anode region. The ion density in the vicinity of this region groups up due to ionization processes, which are caused by electron species. However, the electrons are further attracted by the anode. Well-like deformations occur in the anode potential distribution, which confine electrons and produce density humps. On the contrary, cathode plasma density depends on the secondary-electron emission by ions that are attracted to the anode dielectric surface.
Toward quantum information processing by nuclear magnetic resonance: Pseudopure states and logical operations using selective pulses on an oriented spin 3/2 nucleus
Authors: Sinha Neeraj , Mahesh T. S. , Ramanathan K. V. , Kumar Anil
Published: July 2002

Nuclear magnetic resonance spectroscopy has demonstrated significant experimental progress toward the development of quantum computations. The developments so far have taken place mainly through the use of spin 12 nuclei. In this paper we describe the use of a spin 32 nucleus, oriented in a liquid crystal matrix for the creation of pseudopure states and the implementation of a complete set of two-qubit reversible logic gates using single-quantum transition-selective pulses, extending the range of practice of NMR toward quantum computation.
Solute–solute spatial distribution in hydrogen bonding liquids probed with time-dependent intermolecular electron transfer
Authors: Tavernier H. L. , Fayer M. D.
Published: July 2002

Solute–solute spatial distribution in strongly hydrogen bonding solvents is investigated using photoinduced electron transfer dynamics between rhodamine 3B (R3B) and N,N-dimethylaniline (DMA) in a series of monoalcohols, polyalcohols, and alcohol mixtures. Fluorescence up-conversion data are presented on electron transfer in ethylene glycol and are compared to data characterizing electron transfer in seven other solvents. The data are analyzed with a detailed statistical mechanical theory that includes a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solute–solute radial distribution functions. When the standard assumption is made that for low concentration solutes the solute–solute spatial distribution follows that of the solvent’s radial distribution function, a single parameter fit to the electronic coupling matrix element results in the same value, independent of solvent, for data from five solvents. However, it is impossible to fit the data from the solvent ethylene glycol using the model based on the solvent radial distribution function. When the assumption that the solute–solute spatial distribution tracks the single molecule solvent radial distribution function is relaxed by using a large “effective” solvent diameter to establish the donor–acceptor distance distribution and hydrodynamic effect, excellent fits to the electron transfer data are obtained. The fits give the same parameters for ethylene glycol and two other solvents with high OH/C ratios as the five “normal” solvents. The results suggest that the solute–solute (donor–acceptor) spatial distributions in the high OH/C ratio solvents are determined by multiple hydrogen bond solvent “aggregates” that inhibit solute molecules from distributing freely among solvent molecules.
Dynamics of axisymmetric core-annular flow in a straight tube. I. The more viscous fluid in the core, bamboo waves
Authors: Kouris Charalampos , Tsamopoulos John
Published: July 2002

Nonlinear dynamics of the concentric, two-phase flow of two immiscible fluids in a circular tube is studied. The viscosity of the fluid around the axis of symmetry of the tube is larger than the viscosity of the fluid that surrounds it and gravity acts against the applied pressure gradient. A pseudo-spectral numerical method is coupled with an implicit second order time-integration scheme to solve the complete mass and momentum conservation equations as an initial value problem. The simulations originate with the analytical solution for the pressure driven, steady, core-annular flow (CAF) in a tube. In order to replicate as closely as possible the experimental conditions reported by Bai, Chen and Joseph (1992), the volume fraction of each fluid in the tube and the total flow rate of both fluids are imposed. Furthermore, the length of the tube is taken to be as long as computationally possible in order to allow for multiple waves of different lengths to develop and interact as reported in the experiments and in earlier weakly nonlinear analyses. Having performed simulations of CAF for conditions under which the reported flow charts indicate that both phases retain their integrity but the original steady flow is unstable, it was found that indeed traveling waves develop with slightly sharper crests (pointing towards the annular fluid) than troughs, the so-called “bamboo waves.” Despite the uneven interface, the flow in the core fluid closely resembles Poiseuille flow, but in the annular fluid small recirculation zones develop at the level of each crest. As the Reynolds number or the flow rate of the core fluid increase, the average wavelength and the amplitude of these waves decrease, whereas the holdup ratio of the core to the annular fluid approaches two. Their specific values for each examined case are in closer agreement with the experiments than in earlier theoretical reports. For large values of interfacial tension, waves with even different wavelength move with the same velocity, whereas for small values, they attain variable velocities and approach or repel each other but no wave merging or splitting is observed.
Large-scale local-density-approximation band gap-corrected GaAsN calculations
Authors: Wang Lin-Wang
Published: July 2002

The electronic structure of a GaAsN alloy is calculated using a 4096 atom supercell, with a 70 Ry plane wave basis cutoff and Ga atom 3d electrons as valence electrons. The charge density of this supercell is generated by patching the charge density of a small unit cell with the charge density of bulk GaAs. The local-density-approximation band gap error is corrected by modifying the nonlocal pseudopotentials. A localized nitrogen state [a1(N)] is obtained,and it plays an important role in the band gap reduction of GaAsN.
Spin-reorientation transition in magnetic alloy films CoxNi1−x/Cu(100)
Authors: Lin W. C. , Kuo C. C. , Chiu C. L. , Lin Minn-Tsong
Published: July 2002

With better than 1% control of alloy composition, binary alloy films CoxNi1−x/Cu(100) with x⩽10% were prepared for the study of the spin-reorientation transition at variations of composition, thickness, and temperature. Only the films with a Co concentration less than 10% reveal the spin-reorientation with the film thickness. The critical thickness for the spin-reorientation transition was shifted drastically from 7.5 to 17.5 monolayers for a Co concentration variation from 0% to 8%. These findings indicate a strong influence of the composition on the magnetoelastic anisotropy. A kind of temperature-driven spin-reorientation from in-plane to perpendicular with increasing temperature was also found.
Magnetization reversal of a multilayered FeGd dot array imaged by transmission x-ray microscopy
Authors: Eimüller T. , Fischer P. , Schütz G. , Scholz M. , Bayreuther G. , Guttmann P. , Schmahl G. , Köhler M.
Published: July 2002

The magnetization reversal of an array of 1 μm squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4 Å Fe/4Å Gd)×75 multilayered FeGd system has been prepared on a 30 nm thin Si3N4 membrane by sputtering and structured by optical lithography and ion beam etching techniques. Both the domain structure within each single dot and the collective switching behavior could be observed with MTXM. A large variation in the nucleation field of the dots was found and can be attributed to the shape of the dots. A correlation between the nucleation field and the perimeter of each dot could be deduced. Hysteresis loops of individual dots are derived, taking into account the proportionality of the dichroic contrast to the magnetization of the sample. The stepped profile of the magnetization loop of a single dot is found to be clearly distinct from a continuous film. The high lateral resolution and the possibility to record the images in varying external magnetic fields proves that MTXM is a highly adapted tool to investigate nanostructured magnetic systems.
Tailoring anisotropic magnetoresistance and giant magnetoresistance hysteresis loops with spin-polarized current injection
Authors: Wegrowe J.-E. , Kelly D. , Hoffer X. , Guittienne Ph. , Ansermet J.-Ph.
Published: July 2002

Current pulses were injected into magnetic nanowires. Their effect on the magnetoresistance hysteresis loops was studied for three morphologies: homogeneous Ni wires, copper wires containing five cobalt/copper bilayers, and hybrid structures composed of a homogeneous Ni half wire and a multilayered Co/Cu half wire. The characteristic features of the action of the current on the magnetization are shown and discussed.
Properties of dc magnetron sputtered indium tin oxide films on polymeric substrates at room temperature
Authors: Shin J. H. , Shin S. H. , Park J. I. , Kim H. H.
Published: July 2002

Indium tin oxide (ITO) thin films were deposited on polymeric substrates at room temperature by dc reactive magnetron sputtering from an In–Sn (90–10 wt%) alloy target. The electrical, optical, and mechanical properties of ITO films on various substrates such as polycarbonate, acrylic, polyethylene terephthalate, and glass are influenced sensitively by sputtering parameters. Therefore, the dependence of these properties on dc power, working pressure, and partial oxygen content has been systematically investigated. Low dc power was applied to avoid the deformation of polymeric substrates. The electrical resistivity of as-deposited ITO films decreases initially and then increases as oxygen partial pressure (PO2) increases. The optical transmittance at visible wavelength of 550 nm was as much as 85%. The friction force of as-deposited ITO films on various substrates is increased with an increase of dc power, and behaves similarly to the optimum curve of resistivity with increasing PO2.
Dimensionality of photoluminescence spectrum of GaAs/AlGaAs system
Authors: Fu Y. , Willander M. , Li Z. F. , Lu W.
Published: July 2002

We have theoretically studied the radiative recombination process between a conduction-band electron and a valence-band hole to analyze the photoluminescence (PL) spectrum. It is shown that due to the characteristics of the energy density of states, the line shape of the PL peak depends strongly on the dimensionality of the system under investigation, thus indicating the importance of the PL line shape in the identification of the corresponding optical transition process. Increasing the quantum confinement of a system from three-dimensional (3D bulk material) to two-dimensional (quantum well), one-dimensional (quantum wire) and zero-dimensional (quantum dot) results in a transition from a highly nonsymmetric PL peak to a symmetric Lorentzian one centered at the optical transition energy.
High-resolution electron microscopy study of tunnelling junctions with AlN and AlON barriers
Authors: Shang Ping , Petford-Long Amanda K. , Nickel Janice H. , Sharma Manish , Anthony Thomas C.
Published: July 2002

Spin-dependent tunnel junctions with AlON and AlN barriers have been investigated using high-resolution electron microscopy. Plasma gas composition, nitridation time, and deposited Al thickness were studied independently. Plasma-nitrided Al produces thinner tunnel barriers than those obtained with an oxygen or oxygen+nitrogen plasma, for the same plasma exposure time. Experiments to study an increase in plasma nitridation time for a constant Al deposition thickness showed that overexposure to the plasma resulted in a thinner barrier—possibly due to the competing processes of nitride formation and slight etching of the barrier. The AlN barrier thickness increases monotonically with deposited Al thickness for a constant nitridation time. Electron energy loss spectroscopy compositional mapping has confirmed that nitrogen is present in the barrier layer. The roughness between the barrier layer and the two ferromagnetic layers has also been estimated.
Visible-light induced persistent photoconductivity in trilayered films of perovskite manganites
Authors: Dai J. M. , Song W. H. , Wang S. G. , Wang K. Y. , Ye S. L. , Du J. J. , Sun Y. P.
Published: July 2002

The persistent photoconductivity (PPC) effect has been observed in trilayered films made of perovskite manganites La2/3Ca1/3MnO3/(La0.3Nd0.7)2.3Ca1/3MnO3La2/3Ca1/3MnO3(LNL) induced by He–Ne laser with wavelength of 632.8 nm. According to the result obtained in the thin film of (La0.3Nd0.7)2/3Ca1/3MnO3(LNCMO), which the PPC effect is also observed below ∼50 K, the PPC effect observed in trilayered film LNL should originate from the middle layer LNCMO. Compared with the thin film of LNCMO, the PPC effect of the trilayered film LNL appears at ∼86 K, which is higher than that of LNCMO at ∼50 K. The PPC effect of LNL can be quenched on thermal cycling in the vicinity of 98 K, which is also higher than that of LNCMO at ∼77 K. The difference of PPC behavior between the thin films of LNCMO and LNL can be attributed to the variation of cluster-glass state in the trilayered films of LNL caused by the strong coupling of interlayer between the middle layer LNCMO and the top/bottom layers LCMO.
Ising dipoles on the triangular lattice
Authors: Rößler U. K.
Published: July 2002

A cluster Monte–Carlo (MC) method for systems of classical spins with purely dipolar couplings is presented. It is tested and applied for finite arrays of perpendicular Ising dipoles on the triangular lattice. This model is a modification with long-range interactions of the geometrically frustrated Ising antiferromagnet. From measurements of integrated autocorrelation times for energy, magnetization, and staggered magnetizations, a high efficiency of the cluster MC algorithm compared to a single-spin-flip algorithm is found. For the investigated model, a finite temperature transition is found which is characterized by a peak in the specific heat and in the staggered susceptibilities.
Studies of the three-dimensional frustrated antiferromagnetic ZnCr2O4
Authors: Martinho H. , Moreno N. O. , Sanjurjo J. A. , Rettori C. , Garcı́a-Adeva A. J. , Huber D. L. , Oseroff S. B. , Ratcliff W. , Cheong S.-W. , Pagliuso P. G. , Sarrao J. L. , Martins G. B.
Published: July 2002

Results of studies of the susceptibility, magnetic specific heat, and electron paramagnetic resonance spectrum of the geometrically frustrated antiferromagnetic ZnCr2O4 are presented. The temperature dependence of the susceptibility and the specific heat are in good agreement with the predictions of the quantum tetrahedral mean field model for exchange-coupled spin-3/2 ions on a pyrochlore lattice. The origin of the anomalous behavior of the resonance intensity below 90 K is discussed.
Erratum: “Heat Capacity of Liquids. Critical Review and Recommended Values. Volumes I and II.” [J. Phys. Chem. Ref. Data, Monograph No. 6 (1996)]
Authors: Zábranský Milan , Růžička Vlastimil , Majer V. , Domalski Eugene S.
Published: July 2002

The errata are arranged in the format shown below and are listed as found according to successive pages in the 1996 Monograph No.6. After the page number for specific erratum, there is information provided which indicates the location on the specific erratum on a given page, such as: number and name of table, reference squib, compound name or other pertinent information. If a given error occurs on more than one page, the page numbers are listed for occurrence of each error in a block of consecutive lines. Next, the erratum appears as it is found in the publication; thereafter one finds the correction. The last line offers a comment or explanation about the erratum.
Dominant role of the size effect for saturation resistivity and giant magnetoresistance in Co/Cu multilayers
Authors: Elefant D. , Tietjen D. , van Loyen L. , Moench I. , Schneider C. M.
Published: July 2002

Co/Cu multilayers were prepared by dc magnetron sputtering, varying the individual layer thicknesses tCu≅tCo in the range of t=0.6–50 nm. Additionally, the ratio tCo/tCu was varied as tCo/tCu=0.4–4. Giant magnetoresistance (GMR) and saturation ferromagnetic (FM) resistivity for the first three antiferromagnetic (AFM) coupling maxima were measured as a function of temperature in the range of T=4.2–300 K, with the GMR values ranging up to 115%. For equidistant Co and Cu layers the saturation resistivity at T=4.2 K matches the size effect dependence in single thin films. Even when changing the single layer thickness or the Co/Cu thickness ratio by an order of magnitude a uniform normalized temperature dependence ρ(T,t)/ρ(T0,t) is found and no shunting effects are observed for tCo,tCu<10 nm. The results favor the following GMR model: The resistivity in the FM (aligned) state is dominated by (hybridized) majority spin electrons, the states of which at similar s like regions of the Fermi surfaces of face-centered-cubic majority Co and Cu allow them to transmit the Co/Cu interfaces with a large mean free path λ. The temperature dependence of λ is governed by the transmittance and it is therefore uniform. Diffuse scattering at crystalline defects at the interfaces reduces λ in accordance with the size effect in single layers. The transition to the AFM state reduces the large λ to the dimensions of Cu–Co↑, ↓–Cu trilayers, that can be understood in terms of a temperature independent size effect, too.
Fast switching and coercivity in thin-film recording media
Authors: Middleton B. K. , Miles J. J.
Published: July 2002

The effects of finite-switching rates of media on measured coercivities are studied using two methods. The first starts from expressions for the switching times of magnetic media and goes on to derive simple expressions for the coercivities of media subjected to various applied field wave forms. The second uses a well-developed numerical micromagnetic model to investigate both the switching times and coercivities. The variations of coercivity with frequency derived using the two methods show similar results.
Temperature dependence of domain-wall bias and coercivity
Authors: Wee L. , Stamps R. L. , Camley R. E.
Published: July 2002

Some models for exchange bias at the interface of a ferromagnet and antiferromagnet involve the formation of partial domain walls in the antiferromagnet layer. Numerical calculations of mean-field temperature dependence are used to examine thermally induced instabilities in the partial domain wall at ideal compensated and uncompensated antiferromagnet interfaces. At compensated interfaces, depinning of the partial wall results in a total loss of bias. At uncompensated interfaces, thermal effects at the interface cause the wall to move into the antiferromagnet. The critical fields for this partial depinning are different for the forward and reverse magnetization directions. This mechanism on uncompensated interfaces allows for simultaneous loop shift and coercivity, which is not found in the compensated case.
Theory and simulations of two-dimensional vortex motion driven by a background vorticity gradient
Authors: Schecter David A. , Dubin Daniel H. E.
Published: July 2002

This paper examines two-dimensional vortex motion in a shear-flow with nonuniform vorticity. Typically, a vortex travels to an extremum in the background vorticity distribution. In general, the rate of this migration increases with the magnitude of the background vorticity gradient; however, a retrograde vortex, which rotates against the local shear, moves orders of magnitude faster than a prograde vortex of equal strength. Retrograde and prograde vortices travel at different speeds because they perturb the background vorticity differently. Linearized equations accurately describe the background vorticity perturbation that is created by a weak retrograde vortex, whereas nonlinear effects dominate for a prograde vortex of any strength. An analytic theory is developed for the velocity of a retrograde vortex, based on the linearized equations. The velocity of a prograde vortex is obtained by a simple “mix-and-move” estimate, which takes into account the nonlinear trapping of fluid around the vortex. Both velocity predictions are verified by vortex-in-cell simulations. If the ratio of background shear to background vorticity gradient exceeds a critical level, there is no vortex motion up or down the background vorticity gradient. Estimates of the critical shear are obtained for both prograde and retrograde vortices. These estimates compare favorably to vortex-in-cell simulations.
Micromagnetic simulation of domain structures in patterned magnetic tunnel junctions
Authors: Schrefl T. , Fidler J. , Chapman J. N. , Kirk K. J.
Published: July 2002

The magnetization reversal process of patterned magnetic tunnel junctions was investigated using finite element micromagnetics, taking into account the magnetostatic interactions between the pinned and the free layer. Two different reversal modes were observed in the simulations depending on the domain structure for zero applied field. In order to reduce the magnetostatic energy, end domains form in the free layer either in the S state or the C state. If the system is in the S state, the end domains grow under the influence of a reversed field. The end domains touch each other, leading to the reversal of the center. Finally, the residual domains along the edges parallel to the field direction reverse. If the system is in the C state, the growth of the end domains leads to a four domain flux closure structure. The domain with the magnetization in favor of the field direction expands until the free layer becomes reversed at a field. The S state and the C state were found to differ in energy by less than 0.2%.
Fabrication of GaN suspended microstructures
Authors: Strittmatter R. P. , Beach R. A. , McGill T. C.
Published: July 2002

We report on a versatile processing technology for the fabrication of micro-electromechanical systems in gallium nitride (GaN). This technology, which is an extension of photo-electrochemical etching, allows for the controlled and rapid undercutting of p-GaN epilayers. The control is achieved through the use of opaque metal masks to prevent etching in designated areas, while the high lateral etch rates are achieved by biasing the sample relative to the solution. For GaN microchannel structures processed in this way, undercutting rates in excess of 30 μm/min have been attained. We propose two mechanisms to account for these high etch rates.
A 10 kW high-voltage pulse generator for corona plasma generation
Authors: Yan K. , van Heesch E. J. M. , Pemen A. J. M. , Huijbrechts P. A. H. J. , van der Laan Piet C. T.
Published: July 2002

In this article we discuss a 10 kW high-voltage pulse generator for producing corona-induced plasma. The generator mainly consists of a three-step resonant charging circuit switched by thyristors, a transmission line transformer, and a triggered spark-gap switch. Voltage pulses of 30–100 kV with a rise time of about 20 ns, a pulse duration of 50–250 ns, pulse repetition rate of 1–900 pulses per second, energy of up to 12 J/pulse, and an average power of up to 10 kW have been achieved with a total energy transfer efficiency of about 80%–90%. At each frequency, the deviation of the energy per pulse is around 1.0%. Moreover, the generator has been tested for more than 100 h for both industrial demonstrations and laboratory investigations at an average output power of 1–10 kW.
Strain-tunable photonic band gap crystals
Authors: Kim Sungwon , Gopalan Venkatraman
Published: July 2002

We have designed a two-dimensional strain-tunable photonic band gap crystal by distorting the symmetry of the crystal from a regular hexagonal to a quasihexagonal lattice by means of field driven strain using a piezoelectric material. Calculations predict that the original high symmetry energy bands split up into several strained energy bands depending on the magnitude and direction of the strain. In the proposed structures, we show that 2% (3%) shear strain can be used to tune ∼52% (73%) of the original undistorted absolute band gap of a two-dimensional photonic band gap crystal. These device structures can be used for optical switching and modulation.
Fermi-level effect on the interdiffusion of InAs and InGaAs quantum dots
Authors: Shchekin O. B. , Deppe D. G. , Lu D.
Published: July 2002

Data are presented on the Fermi level influence on interdiffusion in self-organized quantum dots. Modulation doping is used to place either electrons or holes in the quantum dots’ zero-dimensional levels. The ground state emission energy and discrete level energy separations show that p-type modulation doping enhances the interdiffusion of the quantum dot material with its surrounding barriers, while n-type doping inhibits the interdiffusion. The results are consistent with the interdiffusion proceeding through interstitial crystal defects.
Photoluminescence and photoreflectance of GaInNAs single quantum wells
Authors: Shirakata Sho , Kondow Masahiko , Kitatani Takeshi
Published: July 2002

The temperature dependence of photoluminescence (PL) and photoreflectance (PR) was studied on a 10 nm GaInNAs/GaAs single quantum well prepared by molecular-beam epitaxy using a solid As source. PL was dominated by the near-band edge PL peak with a full width at half maximum (FWHM) value of 16–28 meV for 50–280 K. This indicates that the GaInNAs epilayer was of good quality. The temperature dependence of the band gap energy was studied by the PR measurements, and the dependence was comparable to that of the GaInAs. The near-band edge PL at low temperature exhibited a blueshift with an increase in excitation intensity and temperature (8–50 K). It had a large FWHM value of 24–26 meV at 8 K. These results are discussed in terms of carrier localization.
Copper complex with a magnetic ordering temperature above 400 K
Authors: Yang X. D. , Si Lun , Ding Jun , Ranford John D. , Vittal Jagadese J.
Published: July 2002

A monohydrated CuII dimer [Cu2(Sala)2(H2O)]n [H2Sala=N-(2-hydroxybenzyl)-L-alanine] exists as a coordination-helical polymer in the solid state. Thermal dehydration at 340–373 K converts this helical polymer to three-dimensional chiral network polymer, [Cu2(Sala)2]n. Both the hydrated and the anhydrous samples exhibit canted antiferromagnetism at room temperature. A compensation temperature was observed at around 20 K. The hydrated sample has a magnetic ordering temperature of 300 K, while the anhydrous structure possessed a magnetic ordering temperature as high as 435 K.
Photodissociation–ionization dynamics of molecular chlorine Rydberg states using velocity map imaging
Authors: Parker D. H. , Bakker B. L. G. , Samartzis P. C. , Kitsopoulos T. N.
Published: July 2002

Velocity map images are reported for photoelectrons and atomic chlorine ions produced during one-color REMPI (resonance enhanced multiphoton ionization) of molecular chlorine via the v=0–15 vibrational levels of the 2 1Πg(4s) Rydberg state. Previous magnetic bottle photoelectron studies by Koenders et al. of the same process have shown that REMPI proceeds by two-photon resonant excitation, followed by core-excitation to a super-excited Rydberg state at the three-photon level. This state undergoes (auto)-ionization, resulting in the formation of ground-state molecular chlorine ions, and/or dissociation to neutral products, resulting in the production of electronically excited neutral chlorine atoms. Photoelectrons arise from ionization of Cl2 and electronically excited Cl atoms, while Cl+ ions arise from the dissociation of Cl2+ and from ionization of the excited Cl atoms. The chlorine ion velocity map images reveal new information on the dissociation–ionization dynamics of superexcited Cl2 and the dissociation dynamics of the subsequently formed Cl2+ ions. In the latter case an unexpected low-energy Σ←Π (perpendicular) dissociation pathway to Cl+(1D)+Cl(3P) product atoms is observed. Results from the photoelectron images are compared with those from the magnetic bottle studies. While the imaging kinetic-energy resolution is less than that of the magnetic bottle spectrometer, the angular distribution information and lack of velocity bias of imaging is advantageous. Most of the trends observed in the electron and Cl+ images can be rationalized in terms of single-electron excitation processes and the known molecular orbital structure of the electronic states involved.
Comparison of near-threshold reactivity of ground-state and spin-orbit excited chlorine atoms with methane
Authors: Kim Zee Hwan , Alexander Andrew J. , Bechtel Hans A. , Zare Richard N.
Published: July 2002

A 4:1 mixture of CH4 and BrCl diluted in He are coexpanded into a vacuum chamber and the reaction of methane with atomic chlorine is initiated by photolysis of BrCl. Near 420 nm, the resulting mixture of ground- and excited-state chlorine atoms have spatial anisotropies of βphot=−0.7 for the Cl(2P3/2)+Br channel and βphot=+1.8 for the Cl*(2P1/2)+Br channel. The speed-dependent spatial anisotropy βrxn(ν) of the CH3(ν=0) reaction product is detected by 2+1 resonance-enhanced multiphoton ionization. Our results indicate that the Cl*+CH4 reaction is unimportant in the near-threshold collision energy range of 0.13–0.16 eV, whereas the reaction with ground-state Cl atoms with CH4 excited with one quantum in the ν2 (torsion) or ν4 (bending) mode is dominant.