bluuebunny/crossref_metadata_2025 huggingface dataset:
Gibbs ensemble simulation of water in spherical cavities
Authors: Brovchenko Ivan , Paschek Dietmar , Geiger Alfons
Published: July 2002

Chemical equilibration with a bulk reservoir is the crucial problem in computer simulations of liquids in confined geometries. The Gibbs ensemble simulation method is used in the present paper to solve this problem for water in pores. MC simulations of TIP4P water in spherical cavities with smooth surfaces and radii from 6 to 15 Å were done in equilibrium with bulk water at T=300 and 350 K. Chemical equilibration between confined and bulk water was obtained by an essential number of molecular transfers. To our knowledge this is the first application of the Gibbs ensemble simulation method for the equilibration of two dense liquid water systems. As most important result we find that liquid water exists in a cavity only if the water–substrate interaction exceeds some critical value. An increase of the average water density by about 20% with the strengthening of the interaction is observed. For all systems there are two prominent water layers near the cavity surface which exhibit strong orientational ordering. The pair correlation functions evidence a strong distortion of the tetrahedral water structure in the first, outer layer towards a square lattice arrangement. The diffusivity of the water in the cavity always decreases with respect to the bulk.
Comparative ab initio study of the structures, energetics and spectra of X−⋅(H2O)n=1–4 [X=F, Cl, Br, I] clusters
Authors: Kim Jongseob , Lee Han Myoung , Suh Seung Bum , Majumdar D. , Kim Kwang S.
Published: July 2002

X − ⋅(H 2 O) n=1–4  [X=F, Cl, Br, I] have been studied using high level ab initio calculations. This extensive work compares the structures of the different halide water clusters and has found that the predicted minimum energy geometries for different cluster are accompanied by several other structures close to these global minima. Hence the most highly populated structures can change depending on temperature due to the entropy effect. As the potential surfaces are flat, the wide-ranging zero point vibrational effects are important at 0 K, and not only a number of low-lying energy conformers but also large amplitude motions can be important in determining structures, energies, and spectra at finite temperatures. The binding energies, ionization potentials, charge-transfer-to-solvent (CTTS) energies, and the O–H stretching frequencies are reported, and compared with the experimental data available. A distinctive difference between F−⋅(H2O)n and X−⋅(H2O)n (X=Cl, Br, I) is noted, as the former tends to favor internal structures with negligible hydrogen bonding between water molecules, while the latter favors surface structures with significant hydrogen bonding between water molecules. These characteristics are well featured in their O–H spectra of the clusters. However, the spectra are forced to be very sensitive to the temperature, which explains some differences between different spectra. In case of F−⋅(H2O)n, a significant charge transfer is noted in the S0 ground state, which results in much less significant charge transfer in the S1 excited state compared with other hydrated halide clusters which show near full charge transfers in the S1 excited states. Finally, the nature of the stabilization interactions operative in these clusters has been explained in terms of many-body interaction energies.
Large strain electrostrictive actuation in barium titanate
Authors: Burcsu E. , Ravichandran G. , Bhattacharya K.
Published: July 2002

Large strain electrostriction in single-crystal ferroelectric materials is investigated. The mode of electrostriction is based on a combined electromechanical loading used to induce cyclic, 90° domain switching. Experiments have been performed on crystals of barium titanate with constant compressive stress and oscillating electric-field input. Induced strains of more than 0.8% have been measured. Strains as large as 5% are predicted for other materials of the same class. The results demonstrate a possible avenue for obtaining large actuation strains in electromechanical devices.
Energy disposal in collisions of nitric oxide with molecular adlayers on transition metal single crystal surfaces: Rotational energy disposal
Authors: Ainsworth M. K. , McCombie J. , McCoustra M. R. S. , Chesters M. A.
Published: July 2002

The dynamics of the scattering of nitric oxide (NO) from well-characterized and ordered layers of carbon monoxide (CO) and ethylidyne (CCH3) adsorbed on a Pt(111) substrate have been investigated through resonance-enhanced multiphoton ionization (REMPI) measurements of the rotational quantum state distributions of the scattered NO molecules for a range of incident NO translational energies between 10 and 50 kJ mol−1 from scattering substrates at 108 and 300 K. The measurements reveal that, where in principle the interaction potential resembles that of the NO–Ag(111) system more so than that of the NO–Pt(111) system, the scattering differs remarkably from that expected from a weakly bound system in that it occurs both into a trapping-desorption channel and a direct inelastic channel. Experimental data are presented that indicate both an incident translational energy dependence and substrate surface temperature dependence of the scattering, which is interpreted in terms of a hard-cube model.
Ion velocities in vacuum arc plasmas
Authors: Yushkov George Yu. , Anders André , Oks Efim M. , Brown Ian G.
Published: July 2002

Ion velocities in vacuum arc plasmas have been measured for most conducting elements of the Periodic Table. The method is based on drift time measurements via the delay time between arc current modulation and ion flux modulation. A correlation has been found between the element-specific ion velocity and average ion charge state; however, differently charged ions of the same element have approximately the same velocity. These findings contradict the potential hump model but are in agreement with a gasdynamic model that describes ion acceleration as driven by pressure gradients and electron-ion friction. The differences between elements can be explained by the element-specific power density of the cathode spot plasma which in turn determines the temperature, average charge state, and ion velocity of the expanding vacuum arc plasma.
Two-dimensional direct numerical simulation of parametrically excited surface waves in viscous fluid
Authors: Murakami Youichi , Chikano Masatsugu
Published: July 2002

Standing surface waves on a viscous fluid driven parametrically by a vertical harmonic oscillation are investigated, based on direct numerical simulations of the two-dimensional Navier–Stokes equation, together with appropriate boundary conditions. The condition for the onset of the waves in the experiments by Lioubashevski et al. [Phys. Rev. Lett. 76, 3959 (1996)] is reproduced by our numerical simulation. The time evolution and the flow structures are investigated in detail. The form of the surface elevation is analyzed and the dependence of the saturated amplitude on the forcing strength shows a normal bifurcation. Instead of a localized state, spatially uniform standing waves are formed in an extended system. Using initial perturbations of the uniform state, numerical simulations show that the uniform standing waves are stable to two-dimensional disturbances, which suggests that three-dimensionality is essential for the spatially localized state to occur.
Addition-insertion-elimination reactions of O(3P) with halogenated iodoalkanes producing HF(v) and HCl(v)
Authors: Marcy Timothy P. , Reid Jonathan P. , Qian Charles X. W. , Leone Stephen R.
Published: July 2002

The reaction of CH2ICF3 and other fluorinated or chlorinated iodoalkanes with O(3P), generated by microwave discharge of O2 or 193 nm photolysis of SO2, produces vibrationally excited HF(v) or HCl(v), as observed by steady state or time-resolved Fourier transform infrared (FTIR) emission spectroscopy. This process occurs even in competition with possible pathways to form HOI or IO products. The proposed mechanism is an addition–insertion–elimination process. The nascent vibrational distribution of the HF(v) produced from O+CH2ICF3 is determined to be 0.58±0.10, 0.29±0.08, and 0.12±0.03 for v=1, 2, and 3, respectively, with an upper bound of 0.04 from a few observed lines of v=4. The monotonically decreasing vibrational distribution suggests a reaction involving HF(v) elimination from an intermediate complex. There are a number of possible single or multistep kinetic pathways that could produce HF(v) under these conditions. To determine the predominant pathway that produces the observed HF(v), the dependence of the time-resolved HF(v) emission signal on reactant concentrations is measured and compared with kinetics simulations. The results suggest a single step mechanism involving initial O(3P) attack on the iodine of the CH2ICF3, in a manner similar to the start of the reaction of O(3P) with C2H5I that produces HOI. This is followed by insertion of the oxygen atom into the carbon–iodine bond of the CH2ICF3, producing an activated complex with sufficient energy to eliminate HF(v).
Ultrafast relaxation dynamics of neutral soliton pairs in a quasi-one-dimensional halogen-bridged mixed-valence platinum complex [Pt(en)2][Pt(en)2Br2](ClO4)4
Authors: Sugita Atsushi , Yamashita Masahiro , Kobayashi Takayoshi
Published: July 2002

Ultrafast optical response of photoexcited states is studied by femtosecond pump and probe spectroscopy in a quasi-one-dimensional halogen-bridged mixed-valence platinum complex, [Pt(en)2][Pt(en)2Br2](ClO4)4 (en=ethylenediamine). We observed two kinds of photo-induced absorption (PA) signals, and both of the PA signal intensities follow non-exponential decay profiles. The signals are ascribed to two kinds of neutral soliton pairs with different configurations, that is, a spatially confined soliton and antisoliton pair and a noncorrelated soliton and antisoliton pair. Their formations are found to be closely related with both the excitation energy and the excitation density.
Low-frequency, high-density, inductively coupled plasma sources: Operation and applications
Authors: Xu S. , Ostrikov K. N. , Li Y. , Tsakadze E. L. , Jones I. R.
Published: July 2002

Operation regimes, plasma parameters, and applications of the low-frequency (∼500 kHz) inductively coupled plasma (ICP) sources with a planar external coil are investigated. It is shown that highly uniform, high-density (ne∼9×1012 cm−3) plasmas can be produced in low-pressure argon discharges with moderate rf powers. The low-frequency ICP sources operate in either electrostatic (E) or electromagnetic (H) regimes in a wide pressure range without any Faraday shield or an external multipolar magnetic confinement, and exhibit high power transfer efficiency, and low circuit loss. In the H mode, the ICP features high level of uniformity over large processing areas and volumes, low electron temperatures, and plasma potentials. The low-density, highly uniform over the cross-section, plasmas with high electron temperatures and plasma and sheath potentials are characteristic to the electrostatic regime. Both operation regimes offer great potential for various plasma processing applications. As examples, the efficiency of the low-frequency ICP for steel nitriding and plasma-enhanced chemical vapor deposition of hydrogenated diamond-like carbon (DLC) films, is demonstrated. It appears possible to achieve very high nitriding rates and dramatically increase micro-hardness and wear resistance of the AISI 304 stainless steel. It is also shown that the deposition rates and mechanical properties of the DLC films can be efficiently controlled by selecting the discharge operating regime.
Accurate effective pair potentials for polymer solutions
Authors: Bolhuis P. G. , Louis A. A. , Hansen J. P. , Meijer E. J.
Published: July 2002

Dilute or semidilute solutions of nonintersecting self-avoiding walk (SAW) polymer chains are mapped onto a fluid of “soft” particles interacting via an effective pair potential between their centers of mass. This mapping is achieved by inverting the pair distribution function of the centers of mass of the original polymer chains, using integral equation techniques from the theory of simple fluids. The resulting effective pair potential is finite at all distances, has a range of the order of the radius of gyration, and turns out to be only moderately concentration-dependent. The dependence of the effective potential on polymer length is analyzed in an effort to extract the scaling limit. The effective potential is used to derive the osmotic equation of state, which is compared to simulation data for the full SAW segment model, and to the predictions of renormalization group calculations. A similar inversion procedure is used to derive an effective wall–polymer potential from the center of mass density profiles near the wall, obtained from simulations of the full polymer segment model. The resulting wall–polymer potential turns out to depend strongly on bulk polymer concentration when polymer–polymer correlations are taken into account, leading to a considerable enhancement of the effective repulsion with increasing concentration. The effective polymer–polymer and wall–polymer potentials are combined to calculate the depletion interaction induced by SAW polymers between two walls. The calculated depletion interaction agrees well with the “exact” results from much more computer-intensive direct simulation of the full polymer-segment model, and clearly illustrates the inadequacy—in the semidilute regime—of the standard Asakura–Oosawa approximation based on the assumption of noninteracting polymer coils.
Quantitative noninterferometric Lorentz microscopy
Authors: De Graef Marc , Zhu Yimei
Published: July 2002

Noninterferometric phase reconstruction based on the transport of intensity equation (TIE) is applied to experimental images for a Permalloy thin film and to a computational magnetization pattern for a high density magnetic recording medium. An alternative derivation of the TIE is given, based on linear image formation theory. A compact formal solution, suitable for numerical computation, is given.
Gauge invariant coupled cluster response theory using optimized nonorthogonal orbitals
Authors: Pedersen Thomas Bondo , Fernández Berta , Koch Henrik
Published: July 2002

Using the time-dependent Lagrangian response approach, the recently revived orbital optimized coupled cluster (OCC) model is reformulated using nonorthogonal orbital rotations in a manner that conserves the commutativity of the cluster excitation operators. The gauge invariance and the simple pole structure of the OCC linear response function are retained, while the dimension of the eigenvalue problem is reduced by a factor of 2. Restricting the cluster operator to double excitations, we have carried out the first implementation of gauge invariant coupled cluster response theory. Test calculations of the excitation energy, and length and velocity gauge oscillator strengths are presented for the lowest electric dipole allowed transitions of the CH+ molecular ion and the Ne atom. Additionally, the excitation energies to the four lowest-lying states of water are calculated.
High resolution absorption spectrum of N2O between 75 000 and 104 000 cm−1
Authors: Cossart-Magos Claudina , Jungen Martin , Launay Françoise
Published: July 2002

The absorption spectrum of N2O was photographed at a resolution limit of 0.0008 nm, from 134 nm to the ionization potential, at 96 nm. Ab initio calculations of the electronic energies and transition moments were carried out including spin–orbit interaction in the frozen core approximation. Rydberg states considered are those corresponding to l=0–5 and principal effective quantum number n* up to 5.5 (6s and 6p, 5d, 5f, and 5g terms), and three ionic cores X̃ 2Π, Ã 2Σ+, and B̃ 2Π. It is shown that in N2O, like in CO2 or CS2, npπ terms are at lower energy than npσ. The strongest band of the low-resolution absorption spectrum, at about 77 900 cm−1 is too broad and diffuse to be observed here. It is assigned to the origin of the …2π33pπ1Σ+–X̃ 1Σ+ transition. The most prominent bands in the 84 000–104 000 cm−1 interval are the electronic origins of the …2π3npσ transitions, observed from n=3 to n=19. Previous low-resolution absorption and resonance enhanced multiphoton ionization spectra are reviewed in the light of the present results.
A dual length scale method for plane-wave-based, simulation studies of chemical systems modeled using mixed ab initio/empirical force field descriptions
Authors: Yarne Dawn A. , Tuckerman Mark E. , Martyna Glenn J.
Published: July 2002

Mixed ab initio/empirical force-field simulation studies, calculations in which one part of the system is treated using a fully ab initio description and another part is treated using an empirical description, are becoming increasingly popular. Here, the ability of the commonly used, plane wave-based generalized gradient approximation to density functional theory is extended to model systems in which the electrons are assumed to be localized in a single small region of space, that is, itself, embedded within a large chemically inert bath. This is accomplished by introducing two length scales, so that the rapidly varying, short range, electron–electron and electron–atom interactions, arising from the region where the electrons are localized, can be treated using an appropriately large plane wave basis, while the corresponding, slowly varying, long range interactions of the electrons with the full system or bath, can be treated using a small basis. Briefly, a novel Cardinal B-spline based formalism is employed to derive a smooth, differentiable, and rapidly convergent (with respect to the small basis) expression for the total electronic energy, which explicitly contains the two length scales. The method allows reciprocal space based techniques designed to treat clusters, wires, surfaces and solids/liquids (open, and 1-D and 2-D periodic boundary conditions, respectively) to be utilized. Other plane wave-based “mixed” methods are restricted to clusters. The new methodology, which scales as N log N at fixed size of the chemically active region, has been implemented for parallel computing platforms and tested through applications to both model and realistic problems including an enzyme, human carbonic anhydrase II solvated in an explicit bath of water molecules.
Interlayer coupling in Tb/Fe bilayers and Tb/Au/Fe trilayers with sharp or rough interface
Authors: Shypil E. V. , Pogorily A. M. , Podyalovski D. I. , Pogoryelov Y. A.
Published: July 2002

Bilayer films Fe/Tb (Tb on Fe) having a sharp interface and Tb/Fe (Fe on Tb) having a rough interface are prepared by molecular beam epitaxy to study the interlayer magnetic coupling. The magnetic properties of these bilayers are characterized ex situ using ferromagnetic resonance (FMR). The polar magnetooptical Kerr effect, and a SQUID magnetometer. The resulting perpendicular magnetic anisotropy (PMA) is discussed as an effect of the interlayer magnetic coupling. PMA is observed at rough as well as at sharp interfaces, and the anisotropy energies are estimated. When a monolayer of Au is interposed at either kind of interface, the PMA is observed to disappear and the overall magnetic moment increases. It is also shown that in ultrathin films the demagnetizing factor depends on the substrate roughness and should be taken into account in the FMR data.
Ion beam deposition of fluorinated amorphous carbon
Authors: Ronning C. , Büttner M. , Vetter U. , Feldermann H. , Wondratschek O. , Hofsäss H. , Brunner W. , Au Frederick C. K. , Li Quan , Lee S. T.
Published: July 2002

We have studied the growth and the properties of (t)a-C:F films prepared by the deposition of mass separated 12C+ and 19F+ ions as a function of the F concentration. The films are always strongly F deficient due to the formation of volatile F2 and CFx molecules during the deposition process. A maximum F content of about 25 at. % is obtained for an ion charge ratio of C+:F+=1:1. The observed mechanical, optical, electrical, and structural properties as well as the thermal stability of the films are strongly influenced by the F content. A three step progression of the film structure is evident for increasing F concentration: the amorphous three-dimensional network of tetrahedrally bonded carbon atoms of pure carbon films (ta-C) with diamondlike properties is doped for very low F concentrations (ta-C:F). A further increase of the F content results first in transformation to a graphitelike amorphous structure (a-C:F) before the deposited films become porous and to a polymerlike one for the highest F content.
Ohmic contact formation mechanism of Ni on n-type 4H–SiC
Authors: Han Sang Youn , Kim Ki Hong , Kim Jong Kyu , Jang Ho Won , Lee Kwang Ho , Kim Nam-Kyun , Kim Eun Dong , Lee Jong-Lam
Published: July 2002

Ohmic contact formation mechanism of Ni on n-type 4H–SiC is proposed by comparing the electrical properties with microstructural change. The ohmic behavior was observed at temperatures higher than 900 °C, but Ni2Si phase, as formerly reported to be responsible for ohmic contact, was formed after annealing at 600 °C. The higher work function of Ni2Si than Ni and the observation of graphite phase on the surface of Ni silicide after annealing at 950 °C support that a number of carbon vacancies were produced below the contact, playing a key role in forming an ohmic contact through the reduction of effective Schottky barrier height for the transport of electrons.
Interaction of two laser shocks inside iron samples
Authors: de Rességuier T. , Hallouin M.
Published: July 2002

The interaction of two plane symmetric shocks in a solid sample induces a significant increase of both the pressure and the temperature in the central zone where the incident compressive pulses cross each other. In iron samples, such loading conditions may produce typical structural defects (twins, dislocations) and phase transitions that can be revealed by posttest examination of the recovered targets. We have used two high-power laser beams to irradiate simultaneously both surfaces of thin iron foils. The recovered samples have been sectioned and observed in optical microscopy. A very dense twin distribution in the central zone has confirmed the pressure amplification due to the interaction of the incident shocks. The occurrence of a phase transition has been inferred from the presence of short characteristic twins. Spall fraction has been observed near both irradiated surfaces, and additional damage has been evidenced at the center of the samples. Numerical tools have been adapted to simulate the experiments. Computations have provided estimates of the stress histories inside the samples, and the ability of simple twin, phase change, and spall models has been tested to predict the observed results.
The direct calculation of diabatic states based on configurational uniformity
Authors: Nakamura Hisao , Truhlar Donald G.
Published: July 2002

In order to provide a practical framework for the calculation of diabatic (technically quasidiabatic) states, we generalize the diabatization procedures of Atchity and Ruedenberg to include more general types of crossings and avoided crossings of potential energy surfaces. The resulting diabatization procedure involves two steps: (i) the construction of diabatic orbitals and (ii) the construction of many-electron diabatic state functions in terms of the diabatic orbitals. The procedure for step (i) is more general than the previously proposed occupation number and natural orbital method, and the procedure for step (ii) remains valid even for chemical reactions that require multiple diabatic prototypes. The method is illustrated by applications to LiH, ozone, H2 dimer, and the reaction Li(2S,2P)+HF→LiF+H.
Generation of coherent acoustic phonons in strained GaN thin films
Authors: Huang Yue-Kai , Chern Gia-Wei , Sun Chi-Kuang , Smorchkova Yulia , Keller Stacia , Mishra Umesh , DenBaars Steven P.
Published: July 2002

Coherent acoustic phonon oscillations were generated and studied in strained GaN thin films. Inside the bulk GaN film, the longitudinal interference of an ultraviolet femtosecond pump pulse created periodic carrier distribution that screened out the strain-induced piezoelectric field and initiated the coherent longitudinal acoustic phonon oscillations corresponding to the carrier periods. The created coherent phonon oscillation modulated the piezoelectric field thus modified the absorption property of the GaN thin film through Franz–Keldysh effect. This time-dependent absorption modulation was reflected in the transmission variation of the followed probe pulses, resulting a long decay time ∼300 ps for the initiated coherent phonon oscillations.
Radial contraction of microwave-sustained plasma columns at atmospheric pressure
Authors: Kabouzi Y. , Calzada M. D. , Moisan M. , Tran K. C. , Trassy C.
Published: July 2002

Plasma columns sustained at high enough gas pressures undergo radial contraction as manifested by their glow not entirely filling the radial cross-section of the discharge tube. This phenomenon has been reported with direct current, radio frequency, and microwave discharges. However, its modeling is still incomplete, in particular for rf and microwave discharges, a situation attributed to a lack of experimental data. To fill this gap, we took advantage of the extreme flexibility in terms of field frequency, tube diameter and gas nature of surface-wave sustained discharges to achieve a parametric study of this phenomenon. Special attention was paid to filamentation, specific to rf and microwave discharges, which is the breaking of a single channel of plasma into two or more smaller filaments as a result of the skin effect. We used emission spectroscopy as the main diagnostic means. Electron density was obtained from Stark broadening of the Hβ line, while molecular-band spectra emitted by the OH radical and the N2+ molecule were employed to determine the discharge gas temperature, leading to its radial distribution upon performing Abel inversion. For a given tube radius, contraction is shown to increase with decreasing thermal conductivity of the discharge. As a result, He and N2 discharges are the least contracted, while contraction increases with increasing atomic mass of noble gases. Of all these discharges, the N2 discharge appears to be the closest to local thermodynamic equilibrium.
Nucleation of threading dislocations in sublimation grown silicon carbide
Authors: Sanchez E. K. , Liu J. Q. , De Graef M. , Skowronski M. , Vetter W. M. , Dudley M.
Published: July 2002

The structural defects in sublimation-grown silicon carbide layers have been investigated by transmission electron microscopy, atomic force microscopy, x-ray topography, and KOH etching. Nucleation of two-dimensional islands on damage free surfaces of high quality Lely seeds led to formation of stacking faults at the initial stages of growth. The location and number of stacking faults correlates with threading dislocation density. Also, the growth rate is shown to have a pronounced effect on the threading dislocation densities. Elementary screw dislocation density has been observed to increase from 20 cm−2 to 4×103 cm−2 for growth rates increasing from 0.02 to 1.5 mm/h. Growth on seeds miscut 5° off the c axis resulted in screw dislocation densities almost two orders of magnitude lower than on axis growth. The results are interpreted as due to SiC stacking disorder at the initial stages of growth.
A bi-Hamiltonian formulation for triangular systems by perturbations
Authors: Ma Wen-Xiu
Published: July 2002

A bi-Hamiltonian formulation is proposed for triangular systems resulting from perturbations around solutions, from which infinitely many symmetries and conserved functionals of triangular systems can be explicitly constructed, provided that one operator of the Hamiltonian pair is invertible. Through our formulation, four examples of triangular systems are exhibited, which also show that bi-Hamiltonian systems in both lower dimensions and higher dimensions are many and varied. Two of four examples give local 2+1 dimensional bi-Hamiltonian systems and illustrate that multiscale perturbations can lead to higher-dimensional bi-Hamiltonian systems.
Filamented transport of laser-generated relativistic electrons penetrating a solid target
Authors: Gremillet Laurent , Bonnaud Guy , Amiranoff François
Published: July 2002

The paraxial propagation of a relativistic electron beam in a solid target is examined, within a three-dimensional model of particles interacting with the target electron return current via a diffusive electromagnetic field. Simulations of a modulated beam show amplification of the modulation seed, with growth rates comparing reasonably well with the linear analysis of the model. Scenarios of beam fragmentation are observed and discussed in more realistic conditions, when beam collisions on both target ions and electrons and the resulting solid heating and ionization are taken into account.
Analysis of leakage current conduction phenomenon in thin SrBi2Ta2O9 films grown by excimer laser ablation
Authors: Bhattacharyya S. , Laha Apurba , Krupanidhi S. B.
Published: July 2002

The dc conduction behavior of thin films of SrBi2Ta2O9 (SBT) has been investigated on the basis of space-charge limited current theory. The theory was generalized to account for the traps, which were inevitably present in this case. The relative percentage of trapped injected charge and the free injected charge was seen to follow a dynamical equilibrium instead of the true thermal equilibrium as the temperature of the sample was raised during the measurement. The onset voltage of the trap filled region (VTFL) showed a decreasing trend with the increase of temperature. This reduction of VTFL was ascribed to the appearance of some excess charge in the conduction band. It was seen that the thermodynamically stable distribution of charges among the energy levels could not be taken to explain such a situation. A dynamic model was proposed to explain this kind of a nonequilibrium distribution of trapped and free charges.
Microsecond carrier lifetimes in InGaAsP quantum wells emitting at λ=1.5 μm
Authors: Smith J. M. , Buller G. S. , Marshall D. , Miller A. , Button C. C.
Published: July 2002

Time-resolved photoluminescence measurements of an undoped InGaAsP multiple-quantum-well heterostructure at excess carrier densities between 1014 and 1016 cm−3 reveal unexpectedly long carrier lifetimes, in excess of 2 μs. By fitting the appropriate rate equation parameters to our results, we establish that radiative recombination is the dominant relaxation process, and show that nonradiative recombination is much less pronounced than in similar quantum-well structures measured previously.
Quasi-two-dimensional dynamics of plasmas and fluids
Authors: Horton Wendell , Hasegawa Akira
Published: July 2002

In the lowest order of approximation quasi-two-dimensional dynamics of planetary atmospheres and of plasmas in a magnetic field can be described by a common convective vortex equation, the Charney and Hasegawa–Mima (CHM) equation. In contrast to the two-dimensional Navier–Stokes equation, the CHM equation admits ‘‘shielded vortex solutions’’ in a homogeneous limit and linear waves (‘‘Rossby waves’’ in the planetary atmosphere and ‘‘drift waves’’ in plasmas) in the presence of inhomogeneity. Because of these properties, the nonlinear dynamics described by the CHM equation provide rich solutions which involve turbulent, coherent and wave behaviors. Bringing in nonideal effects such as resistivity makes the plasma equation significantly different from the atmospheric equation with such new effects as instability of the drift wave driven by the resistivity and density gradient. The model equation deviates from the CHM equation and becomes coupled with Maxwell equations. This article reviews the linear and nonlinear dynamics of the quasi-two-dimensional aspect of plasmas and planetary atmosphere starting from the introduction of the ideal model equation (CHM equation) and extending into the most recent progress in plasma turbulence.
Light trapping properties of pyramidally textured surfaces
Authors: Campbell Patrick , Green Martin A.
Published: July 2002

The light trapping properties of textured optical sheets have become of recent interest in photovoltaic energy conversion since light trapping allows a significant reduction in the thickness of active solar cell material. Previous analyses have concentrated on sheets with randomly textured (Lambertian) surfaces. The texturing of crystalline silicon substrates with anisotropic etches to give surfaces covered by square based pyramids defined by intersecting (111) crystallographic planes is a widely used technique for reflection control in silicon solar cells. This paper analyzes the light trapping properties of substrates with such pyramidally textured surfaces. Important differences are found from the case of Lambertian surfaces with practical consequences for the design of high efficiency silicon solar cells.
Hot-electron transport in In0.53Ga0.47As
Authors: Long A. P. , Beton P. H. , Kelly M. J.
Published: July 2002

A Monte Carlo routine has been used to simulate hot-electron transport across narrow regions of heavily doped In0.53Ga0.47As. The doping level/widths considered correspond to those proposed for the base of hot-electron transistors. For doping levels of order 1018 cm−3, the injected hot electrons suffer inelastic scattering by the coupled plasmon-optic phonon mode. The performance of hot-electron transistors is characterized by the base transfer factor which relates a change in collector current with a change in emitter current. The base transfer factor is determined from the simulations for a range of base widths and operating conditions. Results for InGaAs are compared with those for GaAs. Under comparable operating conditions, the InGaAs hot-electron transistor offers a higher transport efficiency and hence, higher current gain compared with that of GaAs. We have used the Monte Carlo routine to simulate the performance of experimental results from InGaAs hot-electron transistors. The simulations are in good agreement with the experimental results.
Generalized expressions for the calculation of elastic constants by computer simulation
Authors: Lutsko J. F.
Published: July 2002

The general expressions, valid for any potential, for the calculation of elastic constants through computer simulation are given. At zero temperature, the elastic constants are found to be the sum of a generalization of the Born term and a term accounting for internal relaxations that arise when a system with more than one atom in the primitive unit cell is strained. The fluctuation formulae used in finite temperature simulations are found to be straightforward generalizations of those used for pair potentials. The connection between the finite-temperature and zero-temperature methods is also made.
Analysis of low pressure rf glow discharges using a continuum model
Authors: Park Sang-Kyu , Economou Demetre J.
Published: July 2002

A continuum model was used to analyze charged particle transport and potential distribution in low-pressure radio frequency (rf) glow discharges. The method of lines with orthogonal collocation on finite elements for the spatial discretization was found to be an effective numerical technique for solving the model equations. An argonlike (electropositive) discharge was compared to a pure chlorine (electronegative) discharge. The electronegative discharge was found to have much thinner sheaths, much greater potential drop and electric field strength in the bulk plasma, and severe modulation by the applied rf (10 MHz frequency) of the electron temperature, ionization, and excitation rate, even in the bulk. The effect of varying excitation frequency was also examined. The results showed that continuum models can capture the essential features of both kinds of discharges. Integration of these models with neutral species transport and reaction can result in powerful tools for the modeling and design of plasma reactors.
The optical properties of tellurite glasses
Authors: El-Mallawany Raouf
Published: July 2002

The refractive index for a family of optical glasses (tellurite containing halide) has been analyzed. From the dielectric theory, the relationship between the refractive index and number of ions/unit volume (N/V) with polarizability α has been discussed. Halogen substitution resulted in a lower dielectric constant, along with lower density and lower refractive index. The reduced number of polarizable ions per unit volume was primarily responsible for the reduction in the dielectric constant, although reductions in electronic polarization also affected the dielectric properties.
Mössbauer and magnetization studies of nickel ferrites
Authors: De Marco M. , Wang X. W. , Snyder R. L. , Simmins J. , Bayya S. , White M. , Naughton M. J.
Published: July 2002

Nickel ferrites have been produced by the rf plasma deposition technique for the first time. This technique has promise for large scale fine particle production of ferrites. Powder x-ray diffraction linewidth measurements show an average particle size of about 55 nm. Mossbauer measurements show the presence of both the nickel ferrite and the nickel zinc ferrite with Fe3O4 created in each ferrite production process as an impurity. Magnetization and Mössbauer measurements show evidence that the aerosol prepared samples have small particle characteristics as compared to solid state reacted bulk materials.
Electromagnetic theory on a lattice
Authors: Chew W. C.
Published: July 2002

A self-contained electromagnetic theory is derived on a regular lattice. The discretized form of integral and differential calculus, which is called discrete calculus, is used to describe this theory. It is shown that discrete forms of Gauss’ theorem, Stokes’ theorem, Green’s theorem, and Huygens’ principle can be derived. Moreover, many electromagnetic theorems can also be derived in this discretized world, for example, reciprocity theorem, uniqueness theorem, and Poynting’s theorem. The preservation of these theorems and the conservation of charge imply that the use of this discretized form of Maxwell’s equations for numerical simulation will not give rise to spurious solutions due to spurious charges.
Ion-assisted pulsed laser deposition of cubic boron nitride films
Authors: Friedmann T. A. , Mirkarimi P. B. , Medlin D. L. , McCarty K. F. , Klaus E. J. , Boehme D. R. , Johnsen H. A. , Mills M. J. , Ottesen D. K. , Barbour J. C.
Published: July 2002

Ion-assisted pulsed laser deposition has been used to produce films containing ≳85% sp3-bonded cubic boron nitride (c-BN). By ablating from a target of hexagonal boron nitride (h-BN), BN films have been deposited on heated (50–800 °C) Si(100) surfaces. The growing films are irradiated with ions from a broad beam ion source operated with Ar and N2 source gasses. Successful c-BN synthesis has been confirmed by Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (TEM), selected-area electron diffraction, electron energy-loss spectroscopy, and x-ray diffraction. The films are polycrystalline and show grain sizes up to 300 Å. In addition, Rutherford backscattering, elastic recoil detection, and Auger electron spectroscopies have been used to further characterize the samples. The effects of varying ion current density, substrate growth temperature, growth time, and ion energy have been investigated. It is found that stoichiometric films with a high c-BN percentage can be grown between 150 and 500 °C. Below ∼150 °C, the c-BN percentage drops dramatically, and the deposited film is completely resputtered at the current densities and ablation deposition rates used. As the deposition temperature rises above ∼500 °C the c-BN percentage also drops, but less dramatically than at low temperatures.

In addition, the IR-active c-BN mode narrows considerably as the deposition temperature increases, suggesting that the c-BN material has fewer defects or larger grain size. It is found that films with a high c-BN percentage are deposited only in a narrow window of ion/atom arrival values that are near unity at beam energies between 800 and 1200 eV. Below this window the deposited films have a low c-BN percentage, and above this window the deposited film is completely resputtered. Using FTIR analysis, it is found that the c-BN percentage in these samples is dependent upon growth time. The initial deposit is essentially all sp2-bonded material and sp3-bonded material forms above this layer. Consistently, cross-section TEM samples reveal this layer to consist of an amorphous BN layer (∼30 Å thick) directly on the Si substrate followed by highly oriented turbostratic BN (∼300 Å thick) and finally the c-BN layer. The h-BN/t-BN interfacial layer is oriented with the 002 basal planes perpendicular to the plane of the substrate. Importantly, the position of the c-BN IR phonon changes with growth time. Initially this mode appears near 1130 cm−1 and decreases with growth time to a constant value of 1085 cm−1. Since in bulk c-BN the IR mode appears at 1065 cm−1, a large compressive stress induced by the ion bombardment is suggested. Possible mechanisms are commented on for the conversion process to c-BN based upon the results.
Possible performance of capacitively coupled single-electron transistors in digital circuits
Authors: Korotkov Alexander N. , Chen Ruby H. , Likharev Konstantin K.
Published: July 2002

We have carried out a theoretical analysis of the possible performance of single-electron transistors with capacitive coupling in simple logic and memory circuits. Both resistively loaded and complementary transistors have been analyzed, with a detailed account of parasitic factors including thermal fluctuations and background charge variations. The analysis shows that at optimal values of the parameters including the background charge, the maximum operation temperature is close to 0.025e2/CkB, where C is the capacitance of the smallest tunnel junction. At T∼0.01e2/CkB the parameter margins are relatively wide; for the structures with 2-nm minimum feature size, the latter temperature is close to 77 K. A typical margin for background charge fluctuations is on the order of 0.1e; these fluctuations may be a major obstacle for practical ultradense single-electron circuits.
Optical properties of wurtzite CdS
Authors: Ninomiya Susumu , Adachi Sadao
Published: July 2002

The complex dielectric functions ε(E)=ε1(E)+iε2(E) of wurtzite CdS have been measured by spectroscopic ellipsometry in the photon-energy range between 1.2 and 5.7 eV at room temperature. The measurements are made on the surface parallel to the optic axis c to extract ε(E) spectra for both the ordinary (E⊥c) and extraordinary (E∥c) rays. The measured data reveal distinct structures at energies of the E0 and E1 critical points. These data are analyzed on the basis of a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental data over the entire range of photon energies. Dielectric-function-related optical constants of wurtzite CdS, such as the complex refractive index n*=n+ik, absorption coefficient α, and normal-incidence reflectivity R, are also presented. To facilitate design of various optoelectronic devices, the refractive-index data in the transparent region have been fitted to the first-order Sellmeier equation. As a byproduct, the high-frequency and static dielectric constants of wurtzite CdS are obtained as ε∞=5.23 and εs=8.28 for E⊥c and ε∞=5.29 and εs=8.73 for E∥c.
Influence of spring stiffness and anisotropy on stick-slip atomic force microscopy imaging
Authors: Kerssemakers J. , De Hosson J. Th. M.
Published: July 2002

This paper presents a detailed analysis of high-load friction atomic force microscopy (AFM) images of layered structures in terms of a discrete stick-slip model. It turned out that based on a geometric approach, the characteristics of slip behavior can be linked to the cantilever/sample spring anisotropy. In particular, the use of polar scans is emphasized to analyze and to quantify these characteristics. The measured stiffness as derived from the slip behavior is in correspondence with the stiffness inferred from static friction. It is concluded that the combined stiffness of substrate and cantilever is constant during an AFM scan in a given direction, which supports the simple stick-slip model.
Infrared dielectric constant of gallium arsenide
Authors: Moore W. J. , Holm R. T.
Published: July 2002

The real dielectric constant of gallium arsenide has been determined at 300 and at 5 K from fits to observed interference in transmission of thin samples with parallel surfaces. Measurement was carried out over all or part of the range 30–4000 cm−1. An accuracy of ±0.5% is estimated based on the quality of the analytic fits and the sample thickness measurement technique. We find at 300 K, ε0=12.90 and ε∞=10.86. At 5 K, ε0=12.46 and ε∞=10.58. An analytic expression for the dielectric function is given which allows accurate values of the real dielectric constant to be determined throughout most of the 0–4000 cm−1 spectral range. The observed ratio ε0/ε∞ agrees with the Lyddane–Sachs–Teller relation calculated with Raman values of transverse and longitudinal optical phonon frequencies to better than 0.1% at 300 and at 5 K.
Ion beams in silicon processing and characterization
Authors: Chason E. , Picraux S. T. , Poate J. M. , Borland J. O. , Current M. I. , Diaz de la Rubia T. , Eaglesham D. J. , Holland O. W. , Law M. E. , Magee C. W. , Mayer J. W. , Melngailis J. , Tasch A. F.
Published: July 2002

General trends in integrated circuit technology toward smaller device dimensions, lower thermal budgets, and simplified processing steps present severe physical and engineering challenges to ion implantation. These challenges, together with the need for physically based models at exceedingly small dimensions, are leading to a new level of understanding of fundamental defect science in Si. In this article, we review the current status and future trends in ion implantation of Si at low and high energies with particular emphasis on areas where recent advances have been made and where further understanding is needed. Particularly interesting are the emerging approaches to defect and dopant distribution modeling, transient enhanced diffusion, high energy implantation and defect accumulation, and metal impurity gettering. Developments in the use of ion beams for analysis indicate much progress has been made in one-dimensional analysis, but that severe challenges for two-dimensional characterization remain. The breadth of ion beams in the semiconductor industry is illustrated by the successful use of focused beams for machining and repair, and the development of ion-based lithographic systems. This suite of ion beam processing, modeling, and analysis techniques will be explored both from the perspective of the emerging science issues and from the technological challenges.
Plasma characteristics at off-axis high pressure magnetron YBa2Cu3O7−δ sputtering
Authors: Marchenko V. A. , Znamenskii A. G. , Helmersson U.
Published: July 2002

Plasma characteristics at high pressure YBa2Cu3O7−δ reactive magnetron sputtering were investigated with a probe technique and in situ film resistance measurements. The experimental features of probe measurements in oxygen plasma are discussed. Electron energy distribution is the sum of two Maxwell distributions with kTe≈1.5 eV and kTe≈0.3 eV. N2O addition to a gas mixture results in the generation of negative ions with a density virtually equal to the density of positive ions. The energies of ions, impinging the film surface under film biasing, are discussed in collisionless and drift approximations. Low energy ion bombardment of the film surface at temperatures ≈400 °C results in a reduction of film oxygen content.