bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum dynamics of the N(4S)+O2 reaction on the X 2A′ and a 4A′ surfaces: Reaction probabilities, cross sections, rate constants, and product distributions
Authors: Defazio Paolo , Petrongolo Carlo , Oliva Carolina , González Miguel , Sayós Ramón
Published: September 2002

We report real wave packet (WP) calculations of reaction probabilities, cross sections, rate constants, and product distributions of the reaction N(4S)+O2(X 3∑g−)→NO(X 2∏)+O(3P). We propagate initial WPs corresponding to several O2 levels, and employ reactant coordinates and a flux method for calculating initial-state-resolved observables, or product coordinates and an asymptotic analysis for calculating state-to-state quantities. Exact or J-shifting calculations are carried out at total angular momentum J=0 or J>0, respectively. We employ the recent X 2A′ S3 potential energy surface (PES) by Sayós et al. and the earlier a 4A′ PES by Duff et al. In comparing S3 results with the WP ones of a previous X 2A′ S2 PES, we find lower S3 energy thresholds and larger S3 probabilities, despite the higher S3 barrier. This finding is due to the different features of the doublet PESs in the reactant and product channels, at the transition state, and in the NO2 equilibrium region. We analyze the effects of the O2 initial level and show that tunneling through the S3 barrier enhance the room-temperature rate constant by ∼3.7 times with respect to the previous S2 WP rate. The agreement with the room-temperature experimental result is thus notably improved. The NO vibrational distribution is inverted and the rotational ones are strongly oscillating. We explain these nonstatistical results showing that the reaction partners approach each other with a large impact parameter. The WP vibrational distribution is however different from that observed, which is oscillating. WP calculations show that the new S3 PES describes accurately several features of the X 2A′ state, although a lowering of its barrier height by ∼0.56 kcal/mol should bring calculated and observed rate constants in full agreement.
Ferroelectric properties of vanadium-doped Bi4Ti3O12 thin films deposited by a sol–gel method
Authors: Kim S. S. , Song T. K. , Kim J. K. , Kim Jinheung
Published: September 2002

We report the enhancement of ferroelectric properties in vanadium-doped Bi4Ti3O12 (BIT) thin films deposited by a sol–gel method. Compared to the undoped BIT, V-doped BIT (BTV) showed higher polarizations and a better fatigue resistance as reported in ceramic systems recently [Noguchi et al., Appl. Phys. Lett. 78, 1903 (2001)]. BTV showed a remanent polarization (2Pr) of 15.9 μC/cm2, higher than the value for BIT, 12.5 μC/cm2. The polarization of the BTV thin film capacitor decreased by 19%, while that of the BIT decreased by 23% after the fatigue test with 4×1010 switching cycles.
Resonant optical microcavity based on crystalline silicon active layer
Authors: Sotta D. , Hadji E. , Magnea N. , Delamadeleine E. , Besson P. , Renard P. , Moriceau H.
Published: September 2002

Crystalline silicon microcavities resonant at 1.1 μm were fabricated by using submicron thick Si membranes from a silicon on insulator substrate. These membranes were composed of a single crystalline Si film layered above and below two thin silicon dioxide layers. The low temperature photoluminescence (PL) of the membranes originated from the electron–hole condensed phase, which is characteristic of ultrapure crystalline silicon. The microcavities are then formed by depositing dielectric mirrors on both sides of the membranes. Optical properties of microcavities are studied by optical transmission and PL spectroscopy. The Si PL spectrum is strongly modified by the cavity: at the resonance the PL linewidth is reduced by a factor 3 and the emission is highly angle dependent.
Electron emission from N-doped homoepitaxially grown diamond
Authors: Okano Ken , Kamio Takaaki , Yamada Takatoshi , Sawabe Atsuhito , Koizumi Satoshi
Published: September 2002

The electron emission properties of N-doped homoepitaxially grown diamond have been measured and discussed in order to clarify the electron emission mechanism by excluding the effects of polycrystallinity. As a result, N-doped homoepitaxially grown diamond exhibits extremely low threshold electron emission even from extremely flat smooth surfaces without grain boundaries. This result strongly implies that the low threshold electron emission from N-doped diamond should be caused by the resistance of the film rather than by high β whatever the underlying mechanism is.
SiO
2
–
TiO
2
interfaces studied by ellipsometry and x-ray photoemission spectroscopy
Authors: Gallas B. , Brunet-Bruneau A. , Fisson S. , Vuye G. , Rivory J.
Published: September 2002

We present an in situ study of the formation of the interfaces between TiO2 and SiO2 evaporated thin films using spectroscopic ellipsometry and x-ray photoemission spectroscopy (XPS). The growth of TiO2 on SiO2 was studied previously, but the reverse case has not received much attention up to now. In this article, we show that a common description is valid for both interfaces, which are formed by crosslinking Ti–O–Si bonds. We show also that the growth of TiO2 on SiO2 begins with an amorphous interface layer even when growth occurs at 400 °C. The interface is sharp, a few angstroms, as determined by angular XPS; when SiO2 grows on TiO2, the interface is thicker, about 10 Å. Roughness and interdiffusion play roles in interface formation and their role will be discussed.
Electrical conductivity of Wesgo AL995 alumina under fast electron irradiation in a high voltage electron microscope
Authors: Howlader M. M. R. , Kinoshita C. , Shiiyama K. , Kutsuwada M.
Published: September 2002

Electrical conductivity of a 295-μm-thick Wesgo AL995 alumina has been measured before and during 1 MeV electron irradiation in a dc electric field of 300 kV/m at temperatures up to 723 K. The difference between the activation energies before (0.49±0.02 eV) and during (0.19±0.06 eV) irradiation indicates a substantial impact of irradiation on the conductivity of Wesgo AL995 alumina. The electrical conductivity of Wesgo AL995 alumina is lower by approximately 2 orders of magnitude than its requirement for the magnetic coils in the international thermonuclear experimental reactor (ITER). Thermal disruption may not impact on Wesgo AL995 alumina insulating material in ITER because of the absence of thermally stimulated conductivity peaks in it. Although no substantial bulk degradation is observed under irradiation up to a fluence of 7.0×1022 e/m2 (7.97×10−5 dpa) at 723 K, surface degradation is detected that could limit the application of Wesgo AL995 in ITER as a potential insulator.
Charge injection and transport in electrochemical films of poly(3-hexylthiophene)
Authors: Valaski R. , Moreira L. M. , Micaroni L. , Hümmelgen I. A.
Published: September 2002

We have produced and characterized poly(3-hexylthiophene) (PHT) thin films by electrochemical deposition onto tin–oxide (TO) or gold covered glass substrates. PHT film thickness and roughness depend on deposition charge density and are also dependent on substrate material. From electrical measurements we determine an electrical conductivity of 9×10−5 S cm−1 when Ni and Au electrodes are used. An energy barrier of 0.8 eV for positive charge carrier injection into PHT at Al/PHT and TO/PHT interfaces was determined. We estimate the mobility of positive charge carriers in electrochemically deposited PHT as being 1×10−4 cm2 V−1 s−1. An energy diagram of PHT is proposed.
Automatically reigniting dc vacuum arc plasma source
Authors: Li Liuhe , Zhang Tao , Chu Paul K. , Brown Ian G.
Published: September 2002

A spark reignition system designed and produced to enhance vacuum arc deposition is presented. The system, in which the metal arc can be automatically reignited so as to minimize film contamination, not only initially ignites the arc by means of a spark component, but also reignites the spark automatically when the arc is near extinguishing. This automatic reignition system can effectively curb the pressure fluctuations induced by arc extinction and thus enhance the deposition procedure.
A novel algorithm for characterization of order in materials
Authors: Shetty Ritesh , Escobedo Fernando A. , Choudhary Devashish , Clancy Paulette
Published: September 2002

In this work, we present a simple approach for devising order parameters (OPs) for atomic systems based on pattern recognition techniques. It exploits the fact that all crystalline substances are characterized by a unique “signature” cell (SC) which is constructed using a central atom and its nearest NSC neighbors in a given crystal. The algorithm measures the local degree of similarity between a SC and the system to be analyzed. The best fit of a SC to NSC atoms surrounding a given atom in the system is determined by maximizing a fictitious energy of binding among those atoms and the SC atoms. The fictitious potential energy is designed to give maximum attractive energy for maximum overlap. The maximum binding energy of interaction attained in this process is used as a measure of similarity between the crystal structure and the system (i.e., as an OP). The proposed method provides a unified and intuitive approach for constructing relevant OPs for a given system. We used these OPs to characterize the order of different phases in the Lennard-Jones system and in a model silicon system. It is shown that these novel OPs give a more complete description and a better understanding of the structural order in amorphous silicon than conventional OPs.
Mutual diffusion coefficient of charged particles in the solvent-fixed frame of reference from Brownian dynamics simulation
Authors: Dufrêche J.-F. , Jardat M. , Olynyk T. , Bernard O. , Turq P.
Published: September 2002

An expression for the mutual diffusion coefficient of electrolyte solutions on the Smoluchowski level is proposed and is used in Brownian dynamics simulations. In particular, the divergence of this diffusion coefficient due to the long range of hydrodynamic interactions is solved by introducing explicitly the solvent-fixed frame of reference. The result is used to compute the mutual diffusion coefficient of KCl and LiCl aqueous solutions in the framework of the primitive model at room temperature. Simulations with and without hydrodynamic interactions were performed. Results are in excellent agreement with those obtained by an analytical transport theory which was recently proposed [J.-F. Dufrêche et al., J. Chem. Phys. 116, 2085 (2001)] and which yields reliable estimates for transport coefficients. Moreover, it is shown that electrostatic relaxation effects which cancel exactly in the analytical theory have indeed little influence on the mutual diffusion.
Anisotropic random resistor networks: A model for piezoresistive response of thick-film resistors
Authors: Grimaldi C. , Ryser P. , Strässler S.
Published: September 2002

Considerable evidence suggests that thick-film resistors are close to a metal–insulator transition and that tunneling processes between metallic grains are the main source of resistance. We consider as a minimal model for description of transport properties in thick-film resistors a percolative resistor network, with conducting elements governed by tunneling. For both oriented and randomly oriented networks, we show that the piezoresistive response to an applied strain is model dependent when the system is far away from the percolation thresold, while in the critical region it acquires universal properties. In particular close to the metal–insulator transition, the piezoresistive anisotropy shows a power law behavior. Within this region, there exists a simple and universal relation between the conductance and the piezoresistive anisotropy, which could be experimentally tested by common cantilever bar measurements of thick-film resistors.
Scanning capacitance microscopy with ZrO2 as dielectric material
Authors: Brezna W. , Harasek S. , Bertagnolli E. , Gornik E. , Smoliner J. , Enichlmair H.
Published: September 2002

In this article, we explore the properties of ZrO2 as dielectric material for scanning capacitance microscopy (SCM). The ZrO2 layers were grown by chemical vapor deposition (CVD) at T=450 °C. The low growth temperature together with the good reproducibility of the CVD process and the high dielectric constant make ZrO2 a very promising material for SCM applications. Compared with SiO2 as dielectric material, much thicker ZrO2 layers can be used resulting in reduced leakage currents and improved signal quality. For SiO2 and ZrO2 layers having the same thickness, the latter yields higher signals and therefore an enhanced sensitivity. Furthermore, ZrO2 was found to be quite insensitive to parasitic charging effects, which often disturb SCM measurements on samples with SiO2 layers.
Double-junction effect in proton-irradiated silicon diodes
Authors: Castaldini A. , Cavallini A. , Polenta L. , Canali C. , Nava F.
Published: September 2002

This article concerns the existence of a double-junction effect in proton-irradiated silicon p+-ν-n+ (pin) diodes demonstrated by surface potential and optical-beam-induced current (OBIC) investigations. By increasing the diode biasing, the junctions existing at both ends in the irradiated devices move towards each other up to join, hence, causing a full depletion of the diodes. Due to the inhomogeneity of the electric field, however, the charge-carrier collection is strongly dependent on the position. The extent of the diode depletion layers at both ends and the shape of the electric field within the p+-ν-n+ diodes are determined as a function of the bias applied. Three-dimensional photocurrent maps obtained by OBIC profiles allow for imaging the double junction. The deep level analysis evidences the presence of irradiation-induced defects, which are responsible for the double-junction effect.
Electronic states in the conduction band of V-groove quantum wires
Authors: Gvozdić Dejan M. , Schlachetzki Andreas
Published: September 2002

The article proposes a method to calculate eigenstates and eigenfunctions of the conduction band in V-groove quantum wires, which is based on conformal mapping and Fourier expansion. Consequently, the method relies essentially on an analytical calculation with input data as measured with V-groove quantum wires. The method allows one to take into account the hermiticity of the Schrödinger equation as well as the nonparabolicity of the effective mass. We analyze the influence of both effects on the calculated results, showing that an error of up to 30% is incurred if both effects are neglected.
The structure of liquid fluorosulfuric acid investigated by neutron diffraction
Authors: McLain S. E. , Benmore C. J. , Turner J. F. C.
Published: September 2002

The results of an investigation into the liquid structure of fluorosulfuric acid measured using neutron diffraction with isotopic substitution are reported. The first-order neutron difference function is extracted from data recorded at 300 and 193 K from isotopically labeled FSO3H and FSO3D. Analysis of the derived radial distribution functions shows that unique, multisite hydrogen bonding is present in the liquid. These results suggest hydrogen bonding between the hydrogen and fluorine as well as oxygen occurs in the liquid. The fraction of molecules that is hydrogen bound in each way varies with temperature, with the 193 K data showing a more tightly bound system.
Computational study of high-speed liquid droplet impact
Authors: Haller K. K. , Ventikos Y. , Poulikakos D. , Monkewitz P.
Published: September 2002

We are investigating the fluid dynamics of high-speed (500 m/s) small size (200 μm in diameter) droplet impact on a rigid substrate. Utilizing a high-resolution axisymmetric solver for the Euler equations, we show that the compressibility of the liquid medium plays a dominant role in the evolution of the phenomenon. Compression of the liquid in a zone defined by a shock wave envelope, very high velocity lateral jetting, and expansion waves in the bulk of the medium are the most important mechanisms identified, simulated, and discussed. Comparisons of computationally obtained jetting inception times with analytic results show that agreement improves significantly if the radial motion of liquid in the compressed area is taken into account.
Raman scattering in doped transition metal pentatellurides
Authors: McGuire K. , Lowhorn Nathan D. , Tritt Terry M. , Rao A. M.
Published: September 2002

We have measured the Raman spectra of Sb doped (ZrTe5−xSbx; 0<x<0.25) and Hf doped (ZryHf1−yTe5; 0<y<1) pentatellurides in the 90–300 cm−1 range, and compared them to the corresponding spectrum for the parent material ZrTe5. X-ray diffraction data revealed that the pentatelluride structure prevails at all doping concentrations. With increasing Sb concentration, the linewidths for three of the four Raman peaks observed at 115, 120, and 147 cm−1 in the parent material broadened with insignificant change in the linewidth for the fourth peak at 180 cm−1. Interestingly, the peak intensity for the mode at 180 cm−1 gradually diminishes in ZrTe5−xSbx up to x=0.15, and completely vanishes in the x=0.20 compound. On the other hand, the electrical and Raman properties of ZryHf1−yTe5 exhibit a systematic shift from the corresponding properties of ZrTe5 to that of HfTe5 for increasing Hf concentration in the sample. Implications of the disappearance of the resistivity anomaly with concomitant vanishing of 180 cm−1 Raman mode in the Sb doped samples for x=0.20 composition are presented.
Stresses in inhomogeneous suspensions
Authors: Dhont Jan K. G. , Briels W. J.
Published: September 2002

A microscopic expression for the divergence of the stress tensor is derived for inhomogeneous suspensions of rigid colloidal particles of arbitrary shape. This expression is valid for arbitrary large gradients in the shear rate, concentration, and orientational order parameters. The corresponding Navier–Stokes equation is a necessary ingredient to describe phenomena like shear-banding, phase separation kinetics, and phase coexistence under shear flow conditions.
Revealing the physicochemical mechanism for ultrasonic separation of alcohol–water mixtures
Authors: Kirpalani D. M. , Toll F.
Published: September 2002

The selective separation of ethanol from ethanol–water mixtures by ultrasonic atomization has been reported recently by Sato, Matsuura, and Fujii [J. Chem. Phys. 114, 2382 (2001)]. In that work, experimental data were reported that confirmed the generation of an ethanol-rich droplet mist and attempted to explain the selective separation in terms of parametric decay instability of the capillary wave formed during sonication. In the present work, an alternate mechanism based on the conjunction theory has been postulated for the process of ultrasonic atomization. This mechanism involves the formation of cavitating bubbles in the liquid during sonication and their eventual collapse at the liquid surface into a cloud of microbubbles that moves upwards in a capillary fountain jet. The selective separation of alcohols has been explained as a corollary effect of the physical mechanism resulting in a surface excess of alcohol molecules formed at the surface of the microbubbles. The alcohol molecules vaporize into the microbubbles and release an alcohol-rich mist on their collapse in regions of high accumulation of acoustic energy.
Electron diffusion in the annular Penning trap
Authors: Quraishi Qudsia , Robertson Scott , Walch Bob
Published: September 2002

Transport by cross-field diffusion has been studied in the annular Penning trap in which a nonneutral plasma of electrons is contained between concentric cylinders. At densities sufficiently low (<105 cm−3) to suppress mobility transport arising from the space charge electric field, the dominant sources of transport are diffusion from collisions of electrons with added helium gas and asymmetry transport from stray fields. The collisional diffusivity is shown to scale linearly with collision frequency and inversely with the square of the axial magnetic field. The measured mean energy is initially 0.3 eV and the least energetic electrons are lost more slowly as a consequence of the energy dependence of the diffusivity. Decay constants are about a factor of four higher than calculated from the electron–helium momentum transfer collision frequency. Both the asymmetry transport and the collisional transport are shown to depend upon the cleanliness of the trap surfaces.
On the possible correlation between dark conductivity, photoconductivity, and photorefractivity in dye-doped nematic liquid crystals
Authors: Klysubun Prapong , Indebetouw Guy
Published: September 2002

The dc conductivity of dye-doped nematic liquid crystal cells exhibits a characteristic transition from a cubic current–voltage relationship at applied voltages smaller than about 1 V to a linear one at voltages larger than about 1.5 V. The photoconductivity, and the related photorefractive response of these cells exhibit an apparent threshold at about the same characteristic voltage: An applied voltage larger than about 1.5 V is needed to measure sizeable photocurrents and photorefractive responses. We propose a model that is consistent with all these observations. At low applied voltages, a residual space charge limits the dc current, and prevents the participation of photoexcited charge carriers to photoconductivity and photorefractivity, while at higher applied voltages, the disappearance of the residual space charge allows the manifestation of these photoinduced responses. Experimental results seem to confirm the validity of the model.
Polarity dependence in pulsed scanning tunneling microscopy fabrication and modification of metal nanodots on silicon
Authors: Park Jeong Young , Phaneuf R. J.
Published: September 2002

We have investigated the fabrication and modification of gold and aluminum nanodots on Si (100) with scanning tunneling microscopy (STM). Dots of ∼10 nm diameter were deposited on a Si (100) substrate by the application of a voltage pulse between a coated STM tip and the sample. The pulse duration required for dot formation is several orders or magnitude longer than on metal substrates, and depends both on dopant type and concentration. Modification of existing nanodots was carried out by the application of additional, larger voltage pulses. For Au, negative tip pulses increase the size of a Au dot, while positive pulses allow “erasure” of Au dots. In contrast, negative tip pulses result in erasing Al dots while positive pulses lead to enlarging Al dots. The sense of the polarity dependence for the fabrication and modification of dots is consistent with the calculated difference in threshold for field evaporation between Au and Al negative and positive ions.
Effect of textured Pb(Zr1−xTix)O3 seed layer on fatigue properties of ferroelectric Pb0.99[(Zr0.6Sn0.4)0.85Ti0.15]0.98Nb0.02O3 thin films
Authors: Yoon Ki Hyun , Shin Hyun Cheol , Park Jihoon , Kang Dong Heon
Published: September 2002

Ferroelectric Pb0.99[(Zr0.6Sn0.4)0.85Ti0.15]0.98Nb0.02O3 (PZSTN) thin films with different preferred orientations were fabricated by modifying with 20 mol % excess lead that contained a Pb(ZrxTix−1)O3 seed layer (x=0,0.3,0.52,0.65). Ferroelectric properties were investigated in terms of the texturing character of the PZSTN thin film. With an increase in Zr content in the seed layer, the (100) texturing of the PZSTN film was enhanced. The highly (100) texture (∼97%) was developed by inserting a seed layer with x=1 between the Pt-coated substrate and the PZSTN thin film, whereas in the case of annealing in a reduced condition, the orientation of the film became nearly (111). The (111)-oriented PZSTN film showed relatively higher remanent polarization compared to that of the (100)-oriented film, while the (100)-oriented PZSTN film showed more fatigue behavior than the (111)-oriented film after 109 switching cycles. The (111)-oriented PZSTN film with rhombohedral structure is believed to be suspected to significant stress along applied field direction, resulting in the production of many defects, causing degradation of the polarization during switching cycles.
Thermalization range distributions for photoelectrons injected into dielectric liquids
Authors: Guelfucci J. P. , Terrissol M. , Baird J. K.
Published: September 2002

A photocurrent can be produced by direct illumination of a dielectric liquid with photons having energies in the vacuum ultraviolet (VUV). The kinetic energy initially imparted to an electron by absorption of a photon is subsequently dissipated through random collisions with molecules in the liquid. With the parent cation at the origin, the distance, r, traveled by the electron in coming into thermodynamic equilibrium with the liquid is called the thermalization range. Electron energy thermalization range distribution functions were determined for electrons created by photoionization of cyclohexane, 2,2-dimethylbutane, tetramethylsilane, and two polydimethylsiloxane oils. Except for cyclohexane, the function [r2/2(B3)3]exp(−r/B3), where B3 is an energy-dependent range parameter, gave the best agreement between the calculated and experimental photocurrents at all photon energies considered. Using a Monte Carlo simulation (Goulet type) to represent the slowing down of the electrons after their injection into the liquid, it was found that four to ten collisions along the thermalization path were sufficient to generate this range distribution function. Electrons can also be injected into these liquids by UV illumination of a photocathode. By taking into account electron scattering back to the image charge in the photocathode, it was possible to use the Monte Carlo simulation to demonstrate the consistency between the range distribution function for electron injection by UV exposure of the photocathode and the range distribution function for electron injection by direct VUV illumination of the bulk liquid.
Thickness dependence of superconducting transition temperature in Co/SC/Co trilayers and SC/Co bilayers with SC=NbTi, Nb
Authors: Liang Jun-Jih , Lee S. F. , Shih W. T. , Chang W. L. , Yu C. , Yao Y. D.
Published: September 2002

Superconducting transition temperatures Tc of sputtered Co/SC/Co trilayers and SC/Co bilayers with SC=Nb and NbTi were studied by the electrical resistivity and magnetic susceptibility. For a fixed Co layer thickness, Tc decreases with decreasing SC layer thickness. By applying a published model for the effects of pair breaking, the critical SC layer thickness dSC was deduced. The effect of interface roughness on Tc(dSC) is discussed from the viewpoint of the superconducting coherence length.
Three-dimensional simulations of reversible bimolecular reactions. II. The excited-state target problem with different lifetimes
Authors: Popov Alexander V. , Agmon Noam
Published: September 2002

We report a first microscopic simulation for the diffusional kinetics of a reversible excited-state reaction, A+B↔ AB, where A and AB have different lifetimes and the B-particles are in excess. When the excited species equilibrate fast compared with the excited-state lifetimes, one obtains the pre-equilibrium approximation. The full time-dependence in this case is approximated by a shifted infinite-lifetime expression, and this allows us to derive an analytic expression for the asymptotic exponent. Multiplying this exponential is a t−3/2 term. When the excited-state decay of AB is fast, we obtain the quasistationary approximation. Quantitative comparison between various theories and simulation is presented.
Classical trajectory and statistical adiabatic channel study of the dynamics of capture and unimolecular bond fission. VI. Properties of transitional modes and specific rate constants k(E,J)
Authors: Maergoiz A. I. , Nikitin E. E. , Troe J. , Ushakov V. G.
Published: September 2002

Transitional modes in simple unimolecular bond fission and in the reverse recombination reactions are characterized quantitatively by statistical adiabatic channel (SACM) and classical trajectory (CT) calculations. Energy E- and angular momentum J-specific numbers of open channels (or activated complex states) W(E,J) and capture probabilities w(E,J) are determined for a series of potentials such as ion—dipole, dipole–dipole, and various model valence potentials. SACM and CT treatments are shown to coincide under classical conditions. Adiabatic as well as nonadiabatic dynamics are considered. The dominant importance of angular momentum couplings is elaborated. A sequence of successive approximations, from phase space theory neglecting centrifugal barriers E0(J), via phase space theory accounting for centrifugal barriers E0(J), toward the final result, expressing the effects of the anisotropy of the potentials by specific rigidity factors frigid(E,J), is described. This approach emphasizes the importance to characterize the employed potentials by their centrifugal barriers E0(J). The derived specific rigidity factors frigid(E,J) are consistent with previously calculated thermal rigidity factors frigid(T). The present approach properly accounts for angular momentum conservation and, at the same time, facilitates the calculation of specific rate constants k(E,J) and falloff curves for unimolecular bond fission and the reverse radical recombination reactions.
Competing dissociation channels in the photolysis of S2Cl2 at 235 nm
Authors: Einfeld Tina S. , Maul Christof , Gericke Karl-Heinz , Chichinin Alexei
Published: September 2002

The photodissociation of disulfur dichloride (S2Cl2) at 235 nm has been studied by three-dimensional (3D) imaging of the chlorine product recoil in its ground state P3/22[Cl] and excited spin–orbit state P1/22[Cl*] employing the resonance enhanced multiphoton ionization and time-of-flight techniques. The photodissociation proceeds mainly along the three channels forming S2+2Cl (1), S2Cl+Cl (2), and 2 SCl (3) photoproducts where slow and fast Cl fragments are released in (1) and (2), respectively. The relative yield of channel (1) with respect to channel (2) was determined to be 1.2:1.0. The yield of Cl*, φ(Cl*)=P(Cl*)/[P(Cl)+P(Cl*)], was found to be 0.35. The obtained state-specific velocity distributions of Cl and Cl* are mainly different in the high energy range: For Cl* the two dissociation channels are almost equally present, whereas in the case of ground state Cl the contribution of dissociation channel (2) is of minor importance. The dependence of the anisotropy parameter β on the fragment recoil velocity was directly determined due to the novel technique where the 3D momentum vector of a single reaction product is observed. For both spin–orbit states the anisotropy parameters differ for slow, intermediate, and fast chlorine atoms. The observed β values change from zero to slightly negative values up to positive values with increasing kinetic energy. These observations can be explained by two overlapping dissociation channels, where the two-body channel (2) releases the chlorine atom with high kinetic energy and a positive β parameter via an excited A1 state, whereas the three-body channel (1) proceeds mainly sequentially, where the first Cl atom is released with intermediate speed and a slightly negative β value via an excited B1 state, while the second Cl product atom in the decay of S2Cl is released isotropically with slow recoil velocities.
Analyzing intramolecular vibrational energy redistribution via the overlap intensity-level velocity correlator
Authors: Keshavamurthy Srihari , Cerruti Nicholas R. , Tomsovic Steven
Published: September 2002

Numerous experimental and theoretical studies have established that intramolecular vibrational energy redistribution in isolated molecules has a hierarchical tier structure. The tier structure implies strong correlations between the energy level motions of a quantum system and its intensity-weighted spectrum. A measure, which explicitly accounts for this correlation, was first introduced by one of us as a sensitive probe of phase space localization. It correlates eigenlevel velocities with the overlap intensities between the eigenstates and some localized state of interest. In this work we investigate the usefulness of the correlator in understanding the classical-quantum correspondence of effective spectroscopic Hamiltonians. Application to a model two dimensional effective spectroscopic Hamiltonian shows that the correlation measure can provide information about the terms in the molecular Hamiltonian which play an important role in an energy range of interest and the character of the dynamics. Moreover, the correlation function is capable of highlighting relevant phase space structures including the local resonance features associated with a specific bright state. In addition to being ideally suited for multidimensional systems with a large density of states, the measure can also be used to gain insights into phase space transport and localization. It is argued that the overlap intensity-level velocity correlation function provides a novel way of studying vibrational energy redistribution in isolated molecules. The correlation function is ideally suited to analyzing the parametric spectra of molecules in external fields.
Experimental and ab initio investigation of the O–H overtone vibration in ethanol
Authors: Weibel Jason D. , Jackels Charles F. , Swofford Robert L.
Published: September 2002

The intracavity dye laser photoacoustic absorption spectra of ethanol, ethanol (1,1-d2), and ethanol (2,2,2-d3) are reported for the region 16 550–16 700 cm−1, which contains the O–H fourth overtone (ΔνOH=5) vibration. The distinct absorption bands have been assigned to the trans and gauche conformational isomers. Comparison of the spectra reveals a coupling between the OH and methylene CH vibrations in only the gauche conformer of ethanol, an effect that had not been observed in the fundamental spectrum. Ab initio electronic structure and vibrational frequency calculations are used to clarify and support the analysis of the ethanol OH vibrational spectrum and to evaluate the relative energies of the conformers.
Metastable dissociation of the zirconium Met-Car, Zr8C12, and connections to the production of the delayed atomic ion
Authors: Stairs J. R. , Davis K. M. , Castleman A. W.
Published: September 2002

An investigation of the metastable unimolecular dissociation channels and decay fractions of ZrxCy+ is made using a reflectron time-of-flight mass spectrometer coupled with a laser vaporization source. Useful information pertaining to the decay channels is elucidated. Evidence pertaining to the source of the delayed atomic ion (a phenomenon only observed in the Met-Car system) as a fragmentation event in the acceleration region is also uncovered.
Photonic band structure and emission characteristics of a metal-backed polymeric distributed feedback laser
Authors: Andrew Piers , Turnbull Graham A. , Samuel Ifor D. W. , Barnes William L.
Published: September 2002

Optical losses associated with the metallic contacts necessary for charge injection are an obstacle to the development of an electrically pumped polymer laser. We show that it may be possible to overcome these losses by demonstrating the operation of a distributed-feedback polymer laser fabricated upon a silver substrate. The device lasing threshold was ∼150 times greater than that of an otherwise similar metal-free device, though similar to early polymer lasers. The device emission characteristics correlated well with the measured photonic band structure, allowing an explanation of the effect of the microstructure on device operation.
Dependence of boron cluster dissolution on the annealing ambient
Authors: Radic Ljubo , Lilak Aaron D. , Law Mark E.
Published: September 2002

Boron is introduced into silicon via implantation to form p-type layers. This process creates damage in the crystal that upon annealing causes enhanced diffusion and clustering of the boron layer. Reactivation of the boron is not a well-understood process. In this letter we experimentally investigate the effect of the annealing ambient on boron reactivation kinetics. An oxidizing ambient which injects silicon interstitials is compared to an inert ambient. Contrary to published theory, an excess of interstitials does not accelerate the reactivation process.
Efficient isotropic magnetic resonators
Authors: Gay-Balmaz Philippe , Martin Olivier J. F.
Published: September 2002

We study experimentally and numerically a novel three-dimensional magnetic resonator structure with high isotropy. It is formed by crossed split-ring resonators and has a response independent of the illumination direction in a specific plane. The utilization of such elements to build a finite left-handed medium is discussed.
Electronic Raman scattering through a stripe ordering transition in La2−xSrxNiO4
Authors: Gnezdilov V. P. , Yeremenko A. V. , Pashkevich Yu. G. , Lemmens P. , Güntherodt G. , Tranquada J. M. , Buttrey D. J. , Nakajima K.
Published: September 2002

We describe the results of electronic Raman scattering experiments in two differently doped single crystals of La2−xSrxNiO4 (x=0.225 and 1/3). In B1g symmetry a crossover from weakly interacting to pseudogap-like behavior is observed at a charge-ordering temperature Tco. In B2g symmetry a redistribution of electronic continua with decreasing temperature is accompanied by a loss of spectral weight below Tco in the low-frequency region due to opening of a pseudogap. The slope of the Raman response at vanishing frequencies is investigated, too. Its temperature behavior in B2g symmetry, which predominantly selects charge carriers with momenta along the diagonals of the NiO2 bonds, provides clear evidence for one-dimensional charge transport in the charge-ordered phase.
Exchange interaction and magnetoresistance in La2/3Ca1/3MnO3: experiment and models
Authors: Beznosov A. B. , Belevtsev B. I. , Fertman E. L. , Desnenko V. A. , Naugle D. G. , Rathnayaka K. D. D. , Parasiris A.
Published: September 2002

The magnetization M(T) and electrical resistivity ρ(T) of a La2/3Ca1/3MnO3 film have been studied in the temperature range 5 K⩽T⩽320 K in the magnetic field intervals 10 Oe⩽H⩽400 Oe and 0⩽H⩽50 kOe, respectively. It is found that the M(T)/M(0) value is larger than that predicted by the conventional molecular field model below the Curie point T=267 K, and that the ln ρ(T) dependence is close to linear in the temperature range 80 K<T<200 K (accordingly, ∂ ln ρ/∂T is constant in this region). A model of the electrical conductivity and magnetoresistivity of the system describing qualitatively the experimental results is proposed (the Δmτ model). The model includes a thermally activated (with characteristic energy Δ) mechanism of conductivity, dependence of the concentration and the effective mass (m) of the itinerant charge carriers on the magnetization, as well as scattering (with characteristic time τ) of the charge carriers by static breakings of the translational symmetry, thermal fluctuations of the magnetic order, and phonons.
Magnetohydrodynamics measurements in the von Kármán sodium experiment
Authors: Bourgoin Mickaël , Marié Louis , Pétrélis François , Gasquet Cécile , Guigon Alain , Luciani Jean-Baptiste , Moulin Marc , Namer Frédéric , Burguete Javier , Chiffaudel Arnaud , Daviaud François , Fauve Stephan , Odier Philippe , Pinton Jean-François
Published: September 2002

We study the magnetic induction in a confined swirling flow of liquid sodium, at integral magnetic Reynolds numbers up to 50. More precisely, we measure in situ the magnetic field induced by the flow motion in the presence of a weak external field. Because of the very small value of the magnetic Prandtl number of all liquid metals, flows with even modest Rm are strongly turbulent. Large mean induction effects are observed over a fluctuating background. As expected from the von Kármán flow geometry, the induction is strongly anisotropic. The main contributions are the generation of an azimuthal induced field when the applied field is in the axial direction (an Ω effect) and the generation of axial induced field when the applied field is the transverse direction (as in a large scale α effect). Strong fluctuations of the induced field, due to the flow nonstationarity, occur over time scales slower than the flow forcing frequency. In the spectral domain, they display a f−1 spectral slope. At smaller scales (and larger frequencies) the turbulent fluctuations are in agreement with a Kolmogorov modeling of passive vector dynamics.
Electron charging and discharging in amorphous silicon quantum dots embedded in silicon nitride
Authors: Park Nae-Man , Choi Suk-Ho , Park Seong-Ju
Published: September 2002

Electron charging and discharging were produced in metal-insulator-semiconductor structures containing amorphous silicon quantum dots (a-Si QDs) by increasing the applied voltage in a stepwise fashion without changing its sign. The metal-insulator-semiconductor structure was fabricated using an insulating silicon nitride film containing a-Si QDs by plasma-enhanced chemical vapor deposition. This charging behavior suggests that a-Si QDs in the silicon nitride are positively charged due to nitrogen dangling bonds. The surface state of the a-Si QDs is considered to play a dominant role in the charging properties such as electron storage and charge-loss rate in the a-Si QDs.
Electromagnetic resonances in individual and coupled split-ring resonators
Authors: Gay-Balmaz Philippe , Martin Olivier J. F.
Published: September 2002

We study experimentally and numerically the electromagnetic resonances in split ring resonators (SRRs), around 1 GHz. For an individual SRR, we show that both electric and magnetic fields can induce resonances, the magnetic one being the strongest. The utilization of such resonant structures as efficient microwave filter is also demonstrated. The coupling between two or more SRRs can be quite complex and strongly depends on their geometrical arrangement. For small separation distances, very strong coupling, leading to sharp resonances with high quality factors are observed. In that case a magnetic field circulation which connects neighboring elements is established. The practical implications of these results for the fabrication of a left-handed metamaterial are discussed.
Thermodynamic and kinetic studies of laser thermal processing of heavily boron-doped amorphous silicon using molecular dynamics
Authors: Wang Liguo , Clancy Paulette , Thompson Michael O. , Murthy Cheruvu S.
Published: September 2002

Laser thermal processing (LTP) has been proposed as a means to avoid unwanted transient enhanced diffusion and deactivation of dopants, especially boron and arsenic, during the formation of ultrashallow junctions. Although experimental studies have been carried out to determine the efficacy of LTP for pure Si and lightly B-doped junctions, the effects of high concentrations of dopants (above 2% B) on the thermodynamic and kinetic properties of the regrown film are unknown. In this study, a classical interatomic potential model [Stillinger–Weber (SW)] is used with a nonequilibrium molecular dynamics computer simulation technique to study the laser thermal processing of heavily B-doped Si in the range 2–10 at. % B. We observe only a small effect of boron concentration on the congruent melting temperature of the B:Si alloy, and thus the narrowing of the “process window” for LTP is predicted to be small. No significant tendency for boron to segregate was observed at either the regrowth front or the buried c-Si interface during fast regrowth. The B-doped region regrew as defect-free crystal with full activation of the boron atoms at low boron concentrations (2%), in good agreement with experiments. As the concentration of boron increased, the number of intrinsic Si defects and boron interstitials in the regrown materials increased, with a minor amount of boron atoms in clusters (<2%). An instability limit for crystal regrowth was observed at around 8%–10% boron atoms during fast regrowth; systems with 10% B showed partial amorphization during regrowth. Comparison with tight-binding quantum mechanical calculations showed that the SW model gives similar diffusivities in the liquid and tendency to cluster, but the lifetimes of the SW clusters are considerably too long (>150 ps, compared to 5 ps in tight binding). The importance of adequate system size is discussed.
Vibrational relaxation at water surfaces
Authors: Vieceli John , Chorny Ilya , Benjamin Ilan
Published: September 2002

The vibrational relaxation of several diatomic molecules at the surface of liquid water is studied using classical molecular-dynamics computer simulations and compared with the same process in the bulk liquids. Both nonequilibrium classical trajectory calculations and equilibrium force autocorrleation functions are used to elucidate the factors that influence vibrational energy relaxation at the liquid surface region. We find that in general vibrational relaxation rates at interfaces are slower than in the bulk due to reduced friction. However, the degree of the slowing-down effect depends on the contribution of electrostatic forces and is correlated with the structure of the first solvation shell.
Molecular terms, magnetic moments, and optical transitions of molecular ions C60m±
Authors: Nikolaev A. V. , Michel K. H.
Published: September 2002

Starting from a multipole expansion of intramolecular Coulomb interactions, we present configuration interaction calculations of the molecular energy terms of the hole configurations (hu+)m, m=2–5, of C60m+ cations, of the electron configurations t1un, n=2–4, of the C60n− anions, and of the exciton configurations (hu+t1u−), (hu+t1g−) of the neutral C60 molecule. The ground state of C602− is either T1g3 or Ag1, depending on the energy separation between t1g and t1u levels. There are three close (∼0.03 eV) low lying spin triplets T1g3, Gg3, T2g3 for C602+, and three spin quartets T1u4, Gu4, T2u4 for C603+, which can be subjected to the Jahn–Teller effect. The number of low lying nearly degenerate states is largest for m=3 holes. We have calculated the magnetic moments of the hole and electron configurations and found that they are independent of molecular orientation with respect to an external magnetic field. The coupling of spin and orbital momenta differs from the atomic case. We analyze the electronic dipolar transitions (t1u)2→t1ut1g and (t1u)3→(t1u)2t1g for C602− and C603−. Three optical absorption lines (3T1g→3Hu, 3T1u, 3Au) are found for the ground level of C602− and only one line (4Au→4T1g) for the ground state of C603−. We compare our results with the experimental data for C60n− in solutions and with earlier theoretical studies.
A revised MRCI-algorithm. I. Efficient combination of spin adaptation with individual configuration selection coupled to an effective valence-shell Hamiltonian
Authors: Strodel Paul , Tavan Paul
Published: September 2002

We present a revised multi-reference configuration interaction (MRCI) algorithm for balanced and efficient calculation of electronic excitations in molecules. The revision takes up an earlier method, which had been designed for flexible, state-specific, and individual selection (IS) of MRCI expansions, included perturbational corrections (PERT), and used the spin-coupled hole–particle formalism of Tavan and Schulten (1980) for matrix-element evaluation. It removes the deficiencies of this method by introducing tree structures, which code the CI bases and allow us to efficiently exploit the sparseness of the Hamiltonian matrices. The algorithmic complexity is shown to be optimal for IS/MRCI applications. The revised IS/MRCI/PERT module is combined with the effective valence shell Hamiltonian OM2 suggested by Weber and Thiel (2000). This coupling serves the purpose of making excited state surfaces of organic dye molecules accessible to relatively cheap and sufficiently precise descriptions.