bluuebunny/crossref_metadata_2025 huggingface dataset:
A deep level transient spectroscopy study of beryllium implanted n-type 6H-SiC
Authors: Chen X. D. , Fung S. , Beling C. D. , Gong M. , Henkel T. , Tanoue H. , Kobayashi N.
Published: July 2002

Beryllium implantation induced defects in 6H-SiC pn junctions have been investigated by deep level transient spectroscopy. Five defect centers labeled BE1, BE2, BE3, BE4, and BE5 have been detected in the temperature range 100–450 K. A comparative study has also been performed in low beryllium doped n-type 6H-SiC, which proved that the BE1, BE2, and BE3 centers are electron traps located at 0.34, 0.44, and 0.53 eV, respectively, below the conduction band edge. On the other hand, the BE4 and BE5 centers have been found to be hole traps which are situated at 0.64 and 0.73 eV, respectively, above the valence band edge. Possible defect configurations associated with these deep levels are discussed.
Validity of linear analysis in early-stage spinodal decomposition of a polymer mixture
Authors: Hayashi Masaki , Jinnai Hiroshi , Hashimoto Takeji
Published: July 2002

A two-step phase separation was imposed to a binary mixture of deuterated polybutadiene and protonated polyisoprene with nearly critical composition in the following way: the system was first subjected to phase separation via spinodal decomposition (SD) so that the system developed coexisting two phases characteristics of the late stage of SD (the first-step phase separation). It was then brought into a deeper quench so that both two phases again fell into spinodal region and hence further SD took place within each phase (the second-step phase separation at T2). In the very early stage after this second-step phase separation, the two-phase structure developed in the first-step phase separation was almost unchanged with time, but the composition fluctuation was newly developed within each phase, giving rise to an excess light scattering (LS) at large scattering vectors. The very early stage in this second-step phase separation process was studied by time-resolved LS. We found that the early-stage SD after the second-step phase separation at T2 can be well described by the linearized theory of SD. However the characteristic parameters, especially the collective diffusivity, obtained from the linear analysis, were different from those obtained by the single-step SD at T2 for the corresponding single-phase mixtures. The results unveil an intriguing effect of initial structure or space confinement on early stage SD, reflecting an intrinsically nonlinear phenomenon.
Dielectric tensor for interfaces and individual layers in magnetic multilayer structures
Authors: Gao Xiang , DeVries Michael J. , Thompson Daniel W. , Woollam John A.
Published: July 2002

The magneto-optical Kerr response of metallic magnetic multilayers has been studied by determining the dielectric tensors (dielectric functions) for individual layers, including the magnetic and nonmagnetic interfacial layers. The diagonal components of these tensors were determined using in situ ellipsometric analysis, where the ellipsometric data were taken in real time during multilayer deposition. The off-diagonal components were determined by regression fitting magneto-optic polar Kerr rotation and ellipticity data to models supported by electromagnetic theory. The Voigt parameters (ratio between off-diagonal and diagonal components of dielectric tensors) were determined from these model fits. Higher magnitudes for the Voigt parameters were found at interfaces, corresponding with stronger Kerr responses observed in those materials. Five different magnetic multilayer systems were studied, including Pt/Co, Pd/Co, Au/Co, Cu/Co, and Pt/Fe multilayer structures. The Voigt parameters for the magnetic layers and magnetic–nonmagnetic interfaces in all five structures were determined, and in turn the dielectric tensors for the respective layers were also determined.
Polarization and spectroscopy analysis of the scattering by nanoscopic objects in the near-field optics
Authors: Richard Nicolas
Published: July 2002

We show, in this article, the polarization effects around nanoscopic objects in the near-field optics. This analysis accounts of the variation of the total electric field intensity scattered by the objects with the incident wavelength. These are illuminated through a transparent glass substrate under the condition of total internal reflection. The use of different materials is discussed in the optical images according to the incident wavelength at constant height. Using numerical simulations based on the Green’s dyadic technique, we compute the total transmitted intensity of the scattered light in the attenuated total reflection configuration at constant height by varying the incident wavelength. The role of localized plasmon resonance is brought to the fore in the optical images for nanoscopic and metallic objects.
Magneto-optical spectroscopy study of the solid-state reaction in Ti/Ni multilayered films
Authors: Kudryavtsev Y. V. , Nemoshkalenko V. V. , Lee Y. P. , Kim K. W. , Kim C. G. , Szymanski B.
Published: July 2002

A comparative study of the solid-state reaction (SSR) in a series of Ti/Ni multilayered films (MLF) with a bilayer period of 0.65–22.2 nm and constant Ti to Ni sublayer thickness ratio has been performed by magneto-optical (MO) spectroscopy as well as x-ray diffraction (XRD). The spectral and sublayer-thickness dependences of the MO properties of the Ti/Ni MLF were explained on the basis of the electromagnetic theory. A threshold nominal Ni-sublayer thickness of about 3 nm in the as-deposited Ti/Ni MLF is necessary for observing the equatorial Kerr effect. Such a fact is explained by the formation, by solid-state reaction, of nonmagnetic alloyed regions between pure components. The SSR in the Ti/Ni MLF caused by the low temperature annealing leads to a formation of an amorphous Ti/Ni alloy and takes place mainly in Ti/Ni MLF with “thick” sublayers. In the case of Ti/Ni MLF, MO turns out to be more sensitive in determining the thickness of the reacted zone, while XRD is more useful for the structural analysis. It was also suggested that the very thin nonreacted Ni sublayers have MO properties different from the bulk.
Sample morphology and porosity in electron stimulated desorption: N2* from N2 adsorbed onto nanoscale ice films
Authors: Vichnevetski E. , Bass A. D. , Sanche L.
Published: July 2002

We have measured the electron-stimulated desorption of metastable molecular nitrogen (N2*) from N2 condensed onto solid thin films of water of varying preparation. Structures seen in the N2* yield function permit the quantity of N2 at the film–vacuum interface to be monitored and hence allow one to study changes in the effective surface area of the water film. This latter quantity is itself related to the porosity of the film. When deposited onto porous water, N2 molecules penetrate into the film and throughout its pores covering their large surface area. Under these conditions, the signal of desorbing N2* particles is inversely proportional to the surface area of the pores. We present a simple model for N2 film growth on a porous film. Its mathematical formulation allows the pore area and pore volume of amorphous water films to be measured. The surface region of crystalline water films is also found to be rough. Moreover, the porosity of solid water films is found to be dependent on the substrate on which the film is grown.
An initial boundary value problem of Camassa–Holm equation
Authors: Kwek Keng-Huat , Gao Hongjun , Zhang Weinian , Qu Chaochun
Published: July 2002

In this paper, the local existence and blow-up for an initial boundary value problem of the Camassa–Holm equation are obtained.
Aeroacoustics of a stagnation flow near a rigid wall
Authors: Povitsky Alex
Published: July 2002

Propagation of disturbances in a nonuniform mean flow is investigated by high-order numerical simulation for various initial conditions. Monopole and dipole acoustic, vortical and entropy pulses are embedded in an incompressible stagnation flow, which is taken as a prototype of a nonuniform low Mach number mean flow near a rigid wall at high angle of attack. Numerical results are discussed in terms of baroclinic generation of disturbance vorticity that appear to be a key process in energy transfer between a nonuniform mean flow and a propagating disturbance. These phenomena lead to amplification of sound waves originated from an acoustic pulse. Vorticity generation governs wave radiation of a near-wall entropy pulse and makes the radiated waves similar to those from a vortical dipole. Interaction of initial pulse vorticity with generated vorticity leads to various radiated wave patterns discussed here.
The state-to-state predissociation dynamics of OC–HF upon HF stretch excitation
Authors: Oudejans L. , Miller R. E.
Published: July 2002

Photofragment angular and state distributions have been measured following the vibrational predissociation of the OC–HF complex. An F-center laser is used to pump the fundamental H–F stretching vibration of the complex and a second F-center laser is used to probe the rotational states of the HF fragment as a function of recoil angle. The complex dissociates via two different sets of channels, one that produces vCO=1, JHF=6,5,4 (intermolecular V–V transfer) and the other vCO=0, JHF=11 (V–R transfer). Analysis of the data gives correlated final state distributions, as well as an accurate value for the dissociation energy (D0) of the complex, namely 732±2 cm−1.
Fast simulation of dynamic two-dimensional nuclear magnetic resonance spectra for systems with many spins or exchange sites
Authors: Dumont Randall S. , Assalone Rosa
Published: July 2002

An efficient sparse-matrix-based numerical method is constructed to simulate two-dimensional nuclear magnetic resonance spectra of many-spin systems including the effects of chemical exchange and/or relaxation. The method employs efficient numerical time propagation requiring O(22n) operations in the case of an n spin 1/2 system. Pulses are treated with a fast implementation algorithm achieving O(n22n) scaling (case of n spins 1/2). The method is tested in simulations of double-quantum-filter correlation spectroscopy and exchange spectroscopy experiments on five- and seven-spin systems with two sites. Observed scaling is consistent with the analytic predictions. © 2000 American Institute of Physics.
Spectacular decrease of the melting magnetic field in the charge-ordered state of Pr0.5Ca0.5MnO3 films under tensile strain
Authors: Prellier W. , Haghiri-Gosnet A. M. , Mercey B. , Lecoeur Ph. , Hervieu M. , Simon Ch. , Raveau B.
Published: July 2002

An insulator-to-metal transition below 240 K is induced by applying a 7 T magnetic field in Pr0.5Ca0.5MnO3 thin films grown by the pulsed laser deposition technique on [100]-SrTiO3 substrates. This value of the melting magnetic field, much lower that the one required in bulk (∼20 T), is assumed to be an effect of the tensile stress. These results confirm the importance of the bandwidth in the control of the physical properties of this compound and open the route to get colossal magnetoresistive properties by using strain effects.
Association behavior of binary polymer mixtures under elongational flow
Authors: Dormidontova Elena E. , ten Brinke Gerrit
Published: July 2002

The influence of elongational flow on the association behavior of binary mixtures of functionalized polymers capable of forming single reversible orientationally dependent bonds, such as hydrogen bonds, is studied analytically. Applying a mean-field approach with an external potential representing the effect of the elongational flow, the orientation distribution functions for the dumbbell model and the freely jointed model of a polymer chain were obtained. Two opposite factors determine the association of “linear” diblock copolymerlike chains: the unfavorable extra stretching under flow of associated polymer chains and the favorable orientation of the chains (segments) along the flow direction. The former dominates and the fraction of associated “linear” chains decreases with increasing flow rate. For mixtures of polymers which are capable of forming associated T-chains, the association also decreases, however, more slowly, and this time due to unfavorable orientational effects. If the formation of associated linear and T-polymers as well as complex linear/T-polymers is possible, a strong preference for the formation of associated T-chains is found. At high flow rates any type of association becomes unfavorable.
Electronic states of the copper, silver, and gold silicides and their ions
Authors: Turski Przemysław , Barysz Maria
Published: July 2002

The results of theoretical calculations for the ground state and low-lying excited states of SiCu, SiAg, and SiAu, and their ions SiCu+, SiAg+, SiAu+ and SiCu−, SiAg−, SiAu− are presented. Calculations were carried out with high-level correlated methods including relativistic corrections at the level of the Douglas–Kroll approximation. The ground state data are compared with the recent experimental findings and they differ in the assignment of the ground-state symmetry. All neutral silicides are predicted to have the electronic ground state of Π2 symmetry, in agreement with earlier theoretical data. The neutral species and both negative and positive ions of silicides are found to be quite stable in the ground electronic state and in several low-lying excited states. The relativistic effects bring significant contribution to the stabilization of the gold silicide and its ions in all electronic states investigated in this paper. © 2000 American Institute of Physics.
The best structural data of liquid ammonia based on the pair approximation: First-principles Monte Carlo simulation
Authors: Hannongbua Supot
Published: July 2002

Monte Carlo simulations have been performed for liquid ammonia at 277 K and 1 atm based on the pair approximation with and without adjusted analytical pair potentials. The NH3–NH3 potential function used in the first simulation has been developed on the basis of ab initio dimer calculations at the Hartree–Fock level with triple zeta plus polarization function basis sets. For the second run without the pair potential, the pair interactions have been calculated directly during the simulation using the first-principles ab initio method with the same basis sets. The nitrogen–nitrogen radial distribution function (RDF) obtained from the latter case, which is considered the best structural data based on the pair approximation, shows a first peak at 3.4 Å followed by a broad shoulder ranging from 4.2 to 4.8 Å. This shoulder has been observed for the first time, theoretically, in addition to that reported experimentally at 3.7 Å. Furthermore, energetic error due to three-body effects has been examined. Its effects on the N–N RDF at short distances has been clearly detected. Sensitivity of the structural properties of the solution on the intermolecular (both pair and three-body) interactions has been extensively discussed.
Photoconductance measurements on thin InGaN layers
Authors: Reverchon Jean-Luc , Huet Frédéric , Poisson Marie-Antoinette , Duboz Jean-Yves
Published: July 2002

We report photoluminescence (PL), transmission and photoconductance (PC) studies of InxGa1−xN and GaN alloys grown by metalorganic chemical vapor deposition. We demonstrate that PC measurements can provide reliable gap estimates for a large range of film thicknesses in contrast to transmission or photoreflectance experiments. We show that PC measurements give the expected classical value for thick GaN layers by using an elementary model for absorption. They also give the same value as transmission experiments in the case of thin InGaN layers. We have performed PL and PC measurements in InGaN layers. The comparison between the PL peak and PC measurements gives a direct access to the Stokes shift. We study the Stokes shift as a function of temperature. Depending on the particular film, the Stokes shift can be explained in terms of localization or the Burstein–Moss effect. Indeed, Hall measurements show a high electron concentration in some of the films. Thus, our measurements show that very homogeneous InGaN layers with high indium content (22%) can be obtained with a very small Stokes shift and with a very narrow PL peak. In addition, we give the temperature dependence of the InGaN band-gap.
Infrared spectra of the C2H2–HCl complexes: An experimental and ab initio study
Authors: Çarçabal P. , Broquier M. , Chevalier M. , Picard-Bersellini A. , Brenner V. , Millié P.
Published: July 2002

By means of a pulsed slit jet and an infrared tunable diode laser spectrometer, the vibration–rotation absorption spectra of the complexes C2H2–H35Cl and C2H2–H37Cl have been observed for the first time in the 3.6 μm region of the ν1 band correlated with the HCl stretch. All the lines of the spectrum have been assigned for J=0 to 18 and Ka=0, 1, 2, 3. To determine the band origin and the rotational and centrifugal constants, the observed line frequencies have been fitted to those determined by the Watson Hamiltonian in the A reduction. A force constant model has been used to derive the binding energy De of the complex and the intermolecular stretching harmonic frequency from the experimental spectroscopic constants. The available experimental results concerning these complexes and other isotopic forms D35Cl and D37Cl were compared with ab initio calculations performed at the coupled-cluster single double triple [CCSD(T)] level of theory. The comparison turned out to be very good for all the properties considered (geometries, frequencies, energies).
Radiotracer identification of a Ta-related deep level in 4H–SiC
Authors: Grillenberger J. , Achtziger N. , Sielemann R. , Witthuhn W.
Published: July 2002

To identify tantalum-related deep levels, deep level transient spectroscopy (DLTS) measurements were performed on Ta-implanted n-type 4H–silicon carbide. The DLTS spectra of samples implanted with stable Ta181 exhibit one dominating peak representing a trap energy of about ET=EC−0.67 eV. Due to superimposed signals of intrinsic defects, the exact value depends on the annealing conditions. To achieve a definite assignment of this peak to tantalum, the radioactive isotope Ta177 was recoil implanted into n-type 4H–SiC. DLTS spectra measured subsequently during the nuclear decay of Ta177 to Hf177 reveal a trap with decreasing concentration according to the elemental transmutation. This effect definitely proofs the identification of a Ta-related level at 0.68 eV below the conduction band edge. There is no further DLTS peak of time-dependent height, indicating that there is no deep level of Hf in the part of the band gap investigated.
Density-functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (II): Examination of functional dependence
Authors: Mitani Masaki , Yamaki Daisuke , Takano Yu , Kitagawa Yasutaka , Yoshioka Yasunori , Yamaguchi Kizashi
Published: July 2002

As a first step toward examination of ferromagnetic polymers and dendrimers by ab initio crystal orbital methods, we elucidated candidates for monomer units with the high-spin ground states in the previous study of Part I [J. Chem. Phys. 113, 4035 (2000)] by employing density-functional (DFT) methods using Becke’s and Becke’s three parameter exchanges with Lee–Yang–Parr correlation or Hartree–Fock (HF) molecular orbital and post HF approximations. However, it was found that further computations applying other DFT functionals should be carried out to clarify the level of approximations which appropriately describe the electronic structures of magnetic molecules. In this part II, we present details of numerical results concerning magnetic properties and electronic structures for m-phenylene molecules with three neutral and one cation radicals by spin-polarized density functional methods using variety of local and nonlocal functionals and unrestricted molecular orbital methods including Mo/ller–Plesset and coupled-cluster (CC) correlation corrections. The dependence of total, exchange and correlation energies, and spin densities on various approximated functionals is investigated thoroughly. The effective exchange integrals in the Heisenberg model are calculated by local and nonlocal DFT methods, and they are compared with those of complete active space (CAS) CI, CASSCF, and CASPT2. It is concluded that nonlocal DFT with density-gradient corrections can be used as a practical alternative to UCCSD(T) and CASPT2. The broken-symmetry Unrestricted Hartree–Fock (UHF) and DFT calculations of m-phenylene polyradicals with polar substituents are carried out to elucidate roles of superexchange interactions arising from the significant mixing of charge-transfer (CT) configurations. The resonance of covalent structures with CT or zwitterionic structures entails antiferromagnetic exchange interactions even in polyradicals with m-phenylene bridges; for example, substituted nitroxide polyradicals. Stable ferromagnetic polymers and dendrimers are designed on the basis of the theoretical grounds.
The dynamics of the O(1D)+HD reaction: A quasiclassical trajectory multisurface study
Authors: Aoiz F. J. , Bañares L. , Brouard M. , Castillo J. F. , Herrero V. J.
Published: July 2002

Integral and differential cross sections for the O(1D)+HD reaction have been obtained from adiabatic and nonadiabatic quasiclassical trajectory calculations performed on new ab initio versions of the 1A′, 1A″ and 2A′ potential energy surfaces at the collision energies of 0.089 and 0.196 eV (2.05 and 4.53 kcal/mol, respectively). Results are reported for both the OH+D and OD+H exit channels of reaction. The new data are compared with those from previous theoretical studies employing other potential energy surfaces, and are also used to simulate experimental differential cross sections obtained from recent molecular beam measurements, which are partially resolved in the internal states of the products. The comparison provides evidence that excited electronic states do participate in the title reaction at 0.196 eV, but that their contribution, particularly that of the A″ state, is overestimated by the quasiclassical trajectory (QCT) calculations employing the latest, and most accurate, potential energy surfaces.
Correlation between switching and fatigue in PbZr0.3Ti0.7O3 thin films
Authors: Grossmann M. , Bolten D. , Lohse O. , Boettger U. , Waser R. , Tiedke S.
Published: July 2002

Fast pulse switching experiments with variable width and amplitude of the write pulse were performed on PbZr0.3Ti0.7O3 thin films and the results were correlated to fatigue measurements with varying frequency and amplitude of the fatigue signal. It was found that small amplitudes in combination with a small pulse width of the write pulse does not provide sufficient switching of the ferroelectric film. Furthermore, for the fatigue measurements, it is shown that the degree of switching caused by the fatigue excitation signal strongly influences the fatigue results. In the case of complete switching, the fatigue behavior is found to be independent of the fatigue frequency and only the number of switching cycles is decisive for the polarization decrease.
Observation of magnetic domain structure in a ferromagnetic semiconductor (Ga, Mn)As with a scanning Hall probe microscope
Authors: Shono T. , Hasegawa T. , Fukumura T. , Matsukura F. , Ohno H.
Published: July 2002

We have performed low-temperature scanning Hall probe microscopy on a ferromagnetic semiconductor (Ga0.957Mn0.043)As. The observed magnetic domain structure is a stripe-shaped pattern as has been observed in conventional nonsemiconductor ferromagnetic materials, and the measured magnetic field from the sample surface was small, reflecting the weak magnetization of (Ga, Mn)As. The domain width increased and the measured magnetic field decreased with raising temperature, which are consistent with calculated results, in which the exchange interaction between Mn spins deduced from the Curie temperature is assumed.
Effect of radiation-induced defects on silicon solar cells
Authors: Karazhanov S. Zh.
Published: July 2002

Recent experiments indicated an anomalous degradation of n+–p–p+ silicon space solar cells irradiated with high-energy protons or electrons. Several models have been proposed, which assumes that radiation-induced defects are responsible for the degradation. The effect of the radiation-induced deep defects with energy levels Ec−0.17, Ec−0.1, Ec−0.43, and Ev+0.36 eV on solar cells is studied in this article. It is shown that among these defects only the defect with energy level Ec−0.1 eV causes the anomalous degradation, when the base thickness W is approximately 250 μm.
Damage profiles in high-energy As implanted Si
Authors: Lulli G. , Bianconi M. , Parisini A. , Sama S. , Servidori M.
Published: July 2002

Deep distributions of lattice disorder induced in Si by room temperature, high-energy (3 MeV), nonamorphizing As ion implants have been characterized by Rutherford backscattering spectrometry channeling (RBS-C), double crystal x-ray diffractometry (DCXD), and cross-sectional transmission electron microscopy (XTEM). After accurate calibration of the measurement conditions, the depth positions of the profiles of displaced atoms, lattice strain, and XTEM weak-beam dark-field contrast in a sample implanted at a dose of 1014 As cm−2 agree within 3%. This confirms that the quantities measured by the three techniques have a similar qualitative correlation with the depth profile of as-implanted damage. The shape of the disorder profiles indicates different rates of damage accumulation as a function of depth, which have been characterized by a series of DCXD measurements at doses in the range 1012–1014 As cm−2. The problem of a quantitative determination of the number of defects is also addressed. In particular, the result of RBS-C, which gives as output the concentration of displaced atoms, is sensitive to the configuration of damage assumed when fitting experimental spectra. As a consequence, to give a reliable estimate of defect number a more refined microstructural model of damage (including, for instance, the deformation induced in the background lattice by heavily displaced atoms) should be used within the simulation of the measurement process.
Ab initio studies of anionic clusters of water pentamer
Authors: Kulkarni Sudhir A. , Bartolotti Libero J. , Pathak Rajeev K.
Published: July 2002

Conformers of water anionic pentamer cluster (H2O)5− have been reported here in using ab initio as well as density functional methods. Relative stabilities of these conformers obtained from inclusion of electron correlation at various levels indicate that they are very close in energies. The plots of singly occupied molecular orbital (SOMO) reveal that the excess electron exhibits stabilization selectively as either a surface state or an internal state. Vibrational frequencies of some of the conformers have also been reported at the MP2 level.
Reflection surface x-ray diffraction patterns: k-space images
Authors: Hong Hawoong , Wu Z. , Chiang T.-C. , Zschack P. , Jemian P. , Chen Haydn , Aburano R. D.
Published: July 2002

For the past two decades, x-ray diffraction has been utilized for surface structural determination. Unlike reflection high-energy electron diffraction (RHEED) which is a complicated dynamical scattering process, x-ray surface analysis is simple and straightforward due to the kinematic nature of x rays. Using high brilliance x rays from an undulator beamline and a highly sensitive charge coupled device detector, we successfully observed RHEED-like x-ray diffraction patterns. The patterns were recorded during the preparation of Si(111)-(7×7), transformation to Ge/Si(111)-(5×5) and Ge growth. Also, simultaneous measurements of x-ray reflectivity and crystal truncation rods are shown feasible with this technique.
An innovative approach to multiparticle three-dimensional imaging
Authors: Strasser D. , Urbain X. , Pedersen H. B. , Altstein N. , Heber O. , Wester R. , Bhushan K. G. , Zajfman D.
Published: July 2002

An innovative technique for three-dimensional imaging is presented, which uses the ratio of intensities of a pair of two-dimensional images to extract timing information. The principal advantage of this method is the ability to measure position and time for an almost unlimited number of particles hitting the detector simultaneously. The detector is capable of subnanosecond time resolution and position resolution of about 50 μm. The photodissociation of H2+ is used to demonstrate the capability of the detector.
Hydration free energy of hydrophobic solutes studied by a reference interaction site model with a repulsive bridge correction and a thermodynamic perturbation method
Authors: Kovalenko Andriy , Hirata Fumio
Published: July 2002

We modify the site–site as well as three-dimensional (3D) versions of the reference interaction site model (RISM) integral equations with the hypernetted chain (HNC) closures by adding a repulsive bridge correction (RBC). The RBC treats the overestimation of water ordering around a hydrophobic solute in the RISM/HNC approximation, and thus refines the entropic component in the hydration free energy. We build up the bridge functions on r−12 repulsive core potentials, and propose RBC expressions for both the site–site and 3D-RISM approaches. To provide fast calculation, we obtain the excess chemical potential of hydration by using the thermodynamic perturbation theory (TPT). The site–site RISM/HNC+RBC as well as 3D-RISM/HNC+RBC approaches are applied to calculate the structure and thermodynamics of hydration of rare gases and alkanes in ambient water. For both approaches, the RBC drastically improves the agreement of the hydration chemical potential with simulation data and provides its correct dependence on the solute size. For solutes of a nonspherical form, the 3D treatment yields the hydration structure in detail and better fits simulation results, whereas the site–site approach is essentially faster. The TPT approximation gives the hydration thermodynamics in good qualitative agreement with the exact results of the thermodynamic integration, and substantially reduces computational burden. The RBC–TPT approximation can improve the predictive capability of the hybrid algorithm of a generalized-ensemble Monte Carlo simulation combined with the site–site RISM theory, used to describe protein folding with due account for the water effect at the microscopic level. The RBC can be optimized for better fit to reference simulation data, and can be generalized for solute molecules with charged groups.
Direct observations of electric field-induced domain boundary cracking in 〈001〉 oriented piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal
Authors: Tan X. , Xu Z. , Shang J. K. , Han P.
Published: July 2002

In situ transmission electron microscopy study of electric field-induced cracking has been conducted on 〈001〉 oriented 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 crystal. Fracture of the 90° domain boundary was directly observed in the tetragonal area under both static and alternating electric fields. The field strength required to induce domain boundary cracking was lower for alternating electric field than for static field.
Giant capacitance effect and physical model of nano crystalline CuO–BaTiO3 semiconductor as a CO2 gas sensor
Authors: Wei Q. , Luo W. D. , Liao B. , Liu Y. , Wang G.
Published: July 2002

A CO2 sensor made of nano crystalline CuO–BaTiO3 semiconductor, which has a giant capacitance effect, is designed based on the principle of the physical effect in the nano cluster. After an experimental investigation of its microstructure, the correlation between the quantum size effect and the giant capacitance effect is suggested. The characteristic physical quantities relating to the giant capacitance effect of the sensor are studied systematically with the aid of a gas detector. The quantum size effect is introduced as an interpretation for the mechanism of the giant capacitance effect and a model is proposed for describing the giant capacitance effect of the sensor.
Light-induced conductance resonance in ultrasmall Si nanoparticles
Authors: Therrien Joel , Belomoin Gennadiy , Nayfeh Munir
Published: July 2002

Ultrasmall, uniform-size (∼1 nm) Si nanoparticles, dispersed from p-type boron-doped silicon, are reconstituted on a Si substrate. Electronic transport processes are studied by current–voltage spectroscopy at room temperature, using scanning tunneling microscopy, in a two-terminal configuration, under both dark conditions and light illumination. Unlike the dark conditions, we observe, under light irradiation, for negative tip biasing, a regular structure at ∼1.0 eV period. The series is discussed in terms of light-induced hole states that otherwise are highly infrequent in ultrasmall Si particles, under standard low doping.
Doping of n-type 6H–SiC and 4H–SiC with defects created with a proton beam
Authors: Lebedev A. A. , Veinger A. I. , Davydov D. V. , Kozlovski V. V. , Savkina N. S. , Strel’chuk A. M.
Published: July 2002

Deep centers in n-type 4H–SiC and 6H–SiC irradiated with 8 MeV protons have been investigated by capacitance spectroscopy and electron paramagnetic resonance (EPR). Samples were fabricated by sublimation epitaxy or commercially produced by CREE Inc. Research Triangle Park, NC. It is showed that irradiation of wide-band gap semiconductors may lead to an increase in the concentration of uncompensated donors in an n-type material. The spectrum of deep centers in both SiC polytypes is independent of the technology of material growth or type of charged particles. However, the parameters and behavior of the radiation defects in 6H– and 4H–SiC are different. A conclusion about the possible nature of the irradiation induced centers is made on the basis of annealing behavior and EPR data. The obtained results show that proton irradiation can be used in SiC device fabrication technology for producing local high-resistance regions in the semiconductor.
Adsorption dynamics of CO on the polar surfaces of ZnO
Authors: Becker Th. , Kunat M. , Boas Ch. , Burghaus U. , Wöll Ch.
Published: July 2002

Measurements of initial adsorption probabilities, S0, as well as the coverage dependence of the adsorption probability, S(ΘCO), of CO on Zn–ZnO [ZnO(0001)] and O–ZnO [ZnO(0001̄)] are presented. The samples have been characterized by He atom scattering, He atom reflectivity measurements, LEED, and XPS. Samples with different densities of defects were examined, either by investigating different samples with identical surface termination (for O–ZnO) or by inducing defects by ion sputtering at low temperatures (for Zn–ZnO). The influence of kinetic energy and impact angle (for Zn–ZnO) as well as adsorption temperature on the adsorption dynamics have been studied. For both polar surfaces the shape of the coverage dependent adsorption probability curves are consistent with a precursor mediated adsorption mechanism. Adsorbate assisted adsorption dominates the adsorption dynamics for high impact energies and low adsorption temperatures, especially for Zn–ZnO. The He atom reflectivity measurements point to the influence of an intrinsic precursor state. In contrast to the Zn–ZnO surface, for O–ZnO a weak thermal activation of the CO adsorption was observed. Total energy scaling is obeyed for Zn–ZnO. The heat of adsorption for CO on both polar faces varies between 7 kcal/mol (low coverage) and 5 kcal/mol (high coverage). A comparison of He atom reflectivity with S(ΘCO) curves demonstrates that CO initially populates defect sites on both surfaces. For O–ZnO an increase in S0 with decreasing density of defects was observed, whereas for the Zn-terminated surface S0 was independent of the defect density within the range of parameters studied.
Ab initio energetics of boron-interstitial clusters in crystalline Si
Authors: Lenosky Thomas J. , Sadigh Babak , Theiss Silva K. , Caturla Maria-Jose , de la Rubia Tomas Diaz
Published: July 2002

We have performed an extensive first-principles study of the energetics of boron clustering in silicon in the presence of excess self-interstitial atoms (SIAs). We consider complexes with up to four B atoms and two SIAs. We have conducted an extensive search for the ground-state configurations and charge states of these clusters. We find the cluster containing three B atoms and one SIA(B3I) to be remarkably stable, while all our clusters with more than 80% boron content are unstable. Hence, we propose B3I to be a stable nucleus that can grow to larger clusters. The energetics presented here can be used as input to large-scale predictive models for B diffusion and activation during ion implantation and thermal annealing.
Sound propagation in liquid He in impurity–helium solids
Authors: Kiselev S. I. , Khmelenko V. V. , Lee D. M.
Published: July 2002

The observed features of the attenuation of ultrasound in Im–He samples created after the introduction of impurity particles (D2,N2, Ne, Kr) in a volume of helium II show that a porous substance consisting of a loosely interconnected continuous network is created. It is formed by impurity particles encapsulated in solidified helium. The propagation of ordinary sound in these porous samples is similar to the fast sound mode in light aerogels. The temperature dependence of the attenuation for different Im–He samples is investigated. It is established that the character of the attenuation in D2–He samples is considerably different from that in heavier Im–He solids (Im=N2, Ne, Kr). Analysis of the attenuation leads to the conclusion that Im–He samples have a wide distribution of pores, from 8 nm to 800 nm. The study of ultrasound in helium in Im–He samples near the λ point shows the presence of broadening in the attenuation peak as compared with bulk liquid helium. The suppression of Tc is very small, ⩽ 0.2 mK.
Optimum charge-carrier mobility for a polymer light-emitting diode
Authors: Blom P. W. M. , Vissenberg M. C. J. M. , Huiberts J. N. , Martens H. C. F. , Schoo H. F. M.
Published: July 2002

The performance of polymer light-emitting diodes (PLEDs) consisting of various poly-p(phenylene vinylene) (PPV)-based derivatives has been investigated. It is demonstrated that an increased charge carrier mobility gives rise to an enhancement of the quenching of the electroluminescence at the metallic cathode. As a result the power efficiency of PPV-based LEDs under operating conditions exhibits a distinct optimum at a mobility of about 10−11 m2/V s.
The effect of shear flow on morphology and rheology of phase separating binary mixtures
Authors: Zhang Zhenli , Zhang Hongdong , Yang Yuliang
Published: July 2002

The morphology and the corresponding rheological properties of phase separating binary mixtures under shear flow are studied by computer simulation based on the modified time-dependent Ginzburg–Landau (TDGL) model. In order to investigate the hydrodynamic effect, model H in three dimensions has been used to simulate the phase separation of binary fluids under shear flow. For the sake of comparison, the simulation has also been performed based on simple binary solid model (model B). It is found that, for deep and critical quench, the domain grows faster and the domain anisotropy is lower in binary fluids due to the internal flow field induced by hydrodynamic interaction. For deep and off-critical quench, the internal flow field makes the elongated domain quickly relax to their original spherical shape before they are mutually contacted each other. Thus, it reduces the domain merging probability. It is also found that, for deep and critical quench, there are two peaks appeared in the shear viscosity as a function of shear strain at low shear rate, which agrees with the experimentally observations quite well. For shallow quenching, the broader interfaces suppress the internal flow caused by hydrodynamic interaction and thus the difference between binary solids and binary fluids is small. All these observed unique characters have been explained according to the hydrodynamic interaction and the relaxation rate of the deformed interface.
Rigorous algorithm for the electron repulsion integral over the generally contracted solid harmonic Gaussian-type orbitals
Authors: Ishida Kazuhiro
Published: July 2002

A rigorous general formula can be derived for the electron repulsion integral (ERI) over the generally contracted (GC) solid harmonic (SH) Gaussian-type orbitals by the use of the “reducing triply mixed solid harmonics” defined in this article. A general algorithm is obtained inductively from the general formula by the use of the “triply mixed solid harmonics” defined in this article. This algorithm is named as ACEb3k3-SH-GC. This ACEb3k3-SH-GC is rigorous and capable of computing the above SH-ERI very fast. Numerical assessment can be performed for (LL|LL) class of SH-ERIs (L=2–5). It is found that the present ACEb3k3-SH-GC is severalfold to a thousandfold faster than the ACEb3k3 algorithm for the usual segment contraction (which is named as ACEb3k3-SH-SC and is the fastest algorithm of all methods in the literature) for the generally contracted (LL|LL) class of SH-ERIs.
Degradation of ferroelectric Pb(Zr, Ti)O3 under reducing conditions
Authors: Shimakawa Y. , Kubo Y.
Published: July 2002

The degradation mechanisms of Pb(Zr, Ti)O3 (PZT) under reducing conditions were investigated. Although no apparent changes were seen from the results of thermogravimetric and x-ray diffraction measurements after H2 annealing at typical process temperatures, the PZT material had changed: The sample appearance changed from white to black. A small amount of PZT (less than 0.3% even after 4% H2 annealing at 550 °C) decomposed into Pb in the reducing atmosphere. This, however, was too little to cause all of the change in the sample appearance. Systematic changes in the lattice constants and the black color of the sample strongly suggest that oxygen defects were introduced into the PZT during H2 annealing. Oxygen defects would produce a donor level within the PZT band gap, which would account for the change in color, and would increase leakage current in capacitors. We have also found that PbZrO3 decomposed through oxygen dissociation more easily than PbTiO3. Oxygen atoms in PbZrO3 are weakly bonded to Zr compared to Ti–O bonds in PbTiO3 due to a significant antibonding component in the hybridized orbitals.
The ground state of harmonium
Authors: Cioslowski Jerzy , Pernal Katarzyna
Published: July 2002

A detailed analysis that benefits from a slate of new approximate numerical and exact asymptotic results produces highly accurate properties of the ground state of the harmonium atom as functions of the confinement strength ω and quantifies the domains of the weakly and strongly correlated regimes in this system. The former regime, which encompasses the values of ω greater than ωcrit≈4.011 624×10−2, is characterized by the one-electron density ρ(ω;r1) with a global maximum at r1=0. In contrast, the harmonium atom within the latter regime, which corresponds to ω<ωcrit, differs fundamentally from both its weakly correlated counterpart and Coulombic systems. Resembling a Wigner crystal of a homogeneous electron gas, it possesses a radially localized pair of angularly correlated electrons that gives rise to ρ(ω;r1) with a “fat attractor” composed of a cage critical point and a (1, −1) critical sphere. Allowing for a continuous variation in ω, the new compact representation of the ground-state wave function and accurate approximants for the corresponding electronic properties are designed to facilitate the use of harmonium in research on electron correlation and density functionals.
Luminescence enhancement from hydrogen-passivated self-assembled quantum dots
Authors: Le Ru E. C. , Siverns P. D. , Murray R.
Published: July 2002

We have measured a large increase (by a factor of up to 50) in the room-temperature emission of InAs/GaAs self-assembled quantum dots subjected to a hydrogen-passivation treatment. Smaller enhancements were measured at low temperatures. We tentatively attribute the improved optical signal to passivation of defects within the GaAs matrix and wetting layer adjacent to the dots. Annealing studies show that these benefits are lost following annealing at temperatures above 600 °C for 5 min.
Diffusions in (In,Se)–Cu(In,Ga)Se2/SnO2 thin film structures
Authors: Djessas K. , Abatchou A. , Massé G.
Published: July 2002

In this article we study (In,Se)–Cu(In,Ga)Se2/SnO2 thin film heterostructures for solar cells, the light coming through SnO2. The Cu(In,Ga)Se2 layers were grown by close-spaced vapor transport and the (In,Se) layers by close-spaced sublimation. We first clear up the main results obtained in the fabrication and characterization of the samples. Then, the diffusion mechanisms appearing in these structures are studied, from secondary ion mass spectroscopy studies. Copper diffusion is probably the key of the creation of a p–n junction lying near SnO2 and responsible for the photovoltaic effect that is observed.
Magnetoimpedance measurements of ferromagnetic resonance and antiresonance
Authors: Britel M. R. , Ménard D. , Melo L. G. , Ciureanu P. , Yelon A. , Cochrane R. W. , Rouabhi M. , Cornut B.
Published: July 2002

We report the observation of both ferromagnetic resonance and antiresonance in a magnetic metal using a magnetoimpedance technique. In this experiment, the magnetoimpedance was measured as the frequency was swept from 30 MHz to 11 GHz at constant magnetic fields ranging up to 1.1 kOe (88 kA/m). The sample was an amorphous NiCo-rich soft-magnetic wire with a saturation magnetization sufficiently small to meet both the resonance and antiresonance conditions at frequencies below 10 GHz. A saturation magnetization, very close to that obtained through magnetometry, was deduced using a simultaneous fit to the field dependence of the resonance and antiresonance frequencies. This experiment clearly demonstrates that magnetoimpedance provides a powerful tool for characterizing the intrinsic properties of magnetic metals, with several advantages compared to standard ferromagnetic resonance techniques.
Nitrogen-induced enhancement of the free electron concentration in sulfur implanted GaNxAs1−x
Authors: Yu K. M. , Walukiewicz W. , Shan W. , Wu J. , Ager J. W. , Haller E. E. , Geisz J. F. , Ridgway M. C.
Published: July 2002

We have achieved a large increase of the activation efficiency of sulfur atoms implanted into GaNxAs1−x thin films. For thin films with only 0.8% N content, we find a maximum free electron concentration of >6×1018 cm−3 for implanted S concentration higher than 1019 cm−3, about 20 times larger than that in semi-insulating GaAs implanted and annealed under the same conditions. This large increase of the free electron concentration can be quantitatively explained with the recently developed band anticrossing model.
Improved analysis of the time domain response of scanning force microscope cantilevers
Authors: Todd Brian A. , Eppell Steven J. , Zypman Fredy R.
Published: July 2002

The snap-to-contact instability encountered in scanning force microscopy-force spectroscopy (SFMFS) limits the range of forces measurable in SFM force–distance experiments. We have generalized the flexural beam theory for SFM cantilevers to include tip interactions that are present in the snap-to-contact region. We compare solutions for the beam theory with the simple harmonic oscillator (SHO) that is often used to approximate SFM cantilevers. The limitations of the SHO model are encountered when large force gradients are present. This causes the beam shape to change leading to error when the SHO is used to reconstruct force curves collected in the snap-to-contact region. We quantify the error introduced into a force–separation curve reconstructed using the SHO approximation by numerical simulation. The force–separation curve reconstructed by the SHO was significantly inaccurate and had distorted separation dependence. This makes physical interpretation of force curves reconstructed using the SHO approximation tenuous when force microscope data from the snap-to-contact region is used.