bluuebunny/crossref_metadata_2025 huggingface dataset:
Photodissociation of propargyl bromide and photoionization of the propargyl radical
Authors: Fan H. , Pratt S. T.
Published: April 2006

Velocity map imaging was used to study the 193nm photodissociation of propargyl bromide C3H3Br as well as the photoionization dynamics of the resulting propargyl radical C3H3. Images were recorded by using single-photon vacuum ultraviolet ionization of the propargyl radical and by using two-photon resonant, three-photon ionization of the ground state Br(P3∕22) and spin-orbit excited Br*(P1∕22) atoms. Analysis of these data allowed the determination of the branching ratio Br:Br* as well as the photofragment angular distributions. Images of C3H3 produced by the photodissociation of both C3H3Br and C3H3Cl were recorded at several energies between 8.97 and 9.12eV, as well as at 9.86eV, and showed no obvious internal energy dependence of the relative photoionization cross sections.
The state-to-state-to-state model for direct chemical reactions: Application to D+H2→HD+H
Authors: Gustafsson Magnus , Skodje Rex T.
Published: April 2006

A simple theoretical model is developed to predict the state-to-state dynamics of direct chemical reactions. Motivated by traditional ideas from transition state theory, expressions are derived for the reactive S matrix that may be computed using the local transition state dynamics. The key approximation involves the use of quantum bottleneck states to represent the near separable dynamics taking place near the transition state. Explicit expressions for the S matrix are obtained using a Franck-Condon treatment for the inelastic coupling between internal states of the collision complex. It is demonstrated that the energetic thresholds for various initial reagent states of the D+H2 reaction can be understood in terms of our theory. Specifically, the helicity of the reagent states are found to correlate directly to the symmetry of the quantum bottleneck states, which thus possess very different thresholds. Furthermore, the rotational product state distributions for D+H2 are found to be associated with interfering pathways through the quantum bottleneck states.
A Morse-theoretical analysis of gravitational lensing by a Kerr-Newman black hole
Authors: Hasse Wolfgang , Perlick Volker
Published: April 2006

Consider, in the domain of outer communication M+ of a Kerr-Newman black hole, a point p (observation event) and a timelike curve γ (worldline of light source). Assume that γ (i) has no past endpoint, (ii) does not intersect the caustic of the past light cone of p, and (iii) goes neither to the horizon nor to infinity in the past. We prove that then for infinitely many positive integers k there is a past-pointing lightlike geodesic λk of (Morse) index k from p to γ, hence an observer at p sees infinitely many images of γ. Moreover, we demonstrate that all lightlike geodesics from an event to a timelike curve in M+ are confined to a certain spherical shell. Our characterization of this spherical shell shows that in the Kerr-Newman space-time the occurrence of infinitely many images is intimately related to the occurrence of centrifugal-plus-Coriolis force reversal.
Boron nitride microfibers grown by plasma-assisted laser chemical vapor deposition without a metal catalyst
Authors: Komatsu Shojiro , Kazami Daisuke , Tanaka Hironori , Shimizu Yoshiki , Moriyoshi Yusuke , Shiratani Masaharu , Okada Katsuyuki
Published: April 2006

Boron nitride fibers were found to grow on polycrystalline nickel and Si(100) substrates by plasma-assisted laser chemical vapor deposition from B2H6+NH3 using an excimer laser at 193nm. Their diameter was typically a few hundreds of nanometers, while the length was a few tens of micrometers. They were stoichiometric or boron-rich BN in chemical composition. When the substrate was rotated during deposition, spiral fibers were found to grow. We conclude that they grew with the help of laser light by other than the vapor - liquid - solid mechanism.
Dielectric properties of glycerol/water mixtures at temperatures between 10 and 50°C
Authors: Behrends R. , Fuchs K. , Kaatze U. , Hayashi Y. , Feldman Y.
Published: April 2006

At six temperatures T between 10 and 50°C and at mole fractions xg of glycerol (0<xg⩽0.9) the complex (electric) permittivity ϵ(ν) of glycerol/water mixtures has been measured as a function of frequency ν between 1MHz and 40GHz. The spectra of the glycerol/water mixtures can be well represented by a Davidson-Cole [J. Chem. Phys. 18, 1417 (1950)] relaxation function that reveals an unsymmetric relaxation time distribution. The effective dipole orientation correlation factor derived from the static permittivity displays an unspectacular behavior upon mixture composition. The dielectric relaxation time reveals a simple relation to the shear viscosity of the mixtures, but both quantities are not proportional to one another. The relaxation times at high temperatures nicely complement previously determined low temperature data, following a Vogel-Fulcher-Tammann-Hesse [Z. Phys. 22, 645 (1925); J. Am. Chem. Ceram. Soc. 8, 339 (1923); Z. Anorg. Allg. Chem. 156, 245 (1926)] (VFTH) temperature dependence. When the Eyring behavior is assumed a limiting high temperature form of the VFTH relation, enthalpy, and entropy of activation values are found which adopt significantly higher values in the glycerol rich mixtures than in the water rich liquids. The relaxation time distribution parameter at high water content indicates a dynamically heterogeneous structure of the liquids. Likely there exist glycerol rich and water rich microphases.
Critical behavior of 2,6-dimethylpyridine-water: Measurements of specific heat, dynamic light scattering, and shear viscosity
Authors: Mirzaev S. Z. , Behrends R. , Heimburg T. , Haller J. , Kaatze U.
Published: April 2006

The specific heat Cp at constant pressure, the shear viscosity ηs, and the mutual diffusion coefficient D of the 2,6-dimethylpyridine-water mixture of critical composition have been measured in the homogeneous phase at various temperatures near the lower critical demixing temperature Tc. The amplitude of the fluctuation correlation length ξ0=(0.198±0.004)nm has been derived from a combined evaluation of the ηs and D data. This value is in reasonable agreement with the one obtained from the amplitude A+=(0.26±0.01)J∕(gK) of the critical term in the specific heat, using the two-scale-factor universality relation. Within the limits of error the relaxation rate Γ of order parameter fluctuations follows power law with the theoretical universal exponent and with the amplitude Γ=(25±1)×109s−1. No indications of interferences of the critical fluctuations with other elementary chemical reactions have been found. A noteworthy result is the agreement of the background viscosity ηb, resulting from the treatment of ηs and D data, with the viscosity ηs(ν=0) extrapolated from high-frequency viscosity data. The latter have been measured in the frequency range of 5–130MHz using a novel shear impedance spectrometer.
Divergence-ratio axi-vision camera (Divcam): A distance mapping camera
Authors: Iizuka Keigo
Published: April 2006

A novel distance mapping camera the divergence-ratio axi-vision camera (Divcam) is proposed. The decay rate of the illuminating light with distance due to the divergence of the light is used as means of mapping the distance. Resolutions of 10mm over a range of meters and 0.5mm over a range of decimeters were achieved. The special features of this camera are its high resolution real-time operation, simplicity, compactness, light weight, portability, and yet low fabrication cost. The feasibility of various potential applications is also included.
Free energy surfaces from nonequilibrium processes without work measurement
Authors: Adib Artur B.
Published: April 2006

Recent developments in statistical mechanics have allowed the estimation of equilibrium free energies from the statistics of work measurements during processes that drive the system out of equilibrium. Here a different class of processes is considered, wherein the system is prepared and released from a nonequilibrium state, and no external work is involved during its observation. For such “clamp-and-release” processes, a simple strategy for the estimation of equilibrium free energies is offered. The method is illustrated with numerical simulations and analyzed in the context of tethered single-molecule experiments.
A three-dimensional ab initio potential energy surface and predicted infrared spectra for the He–N2O complex
Authors: Zhou Yanzi , Xie Daiqian , Zhang Dong Hui
Published: April 2006

We report a three-dimensional ab initio potential energy surface for He–N2O using a supermolecular method at the coupled-cluster singles and doubles with noniterative inclusion of connected triple level. Besides the intermolecular stretching and bending modes, we included the Q3 normal mode for the ν3 antisymmetric stretching vibration of N2O molecule in order to simulate the observed infrared spectra in the ν3 region of N2O, especially to explain the frequency shift of the band origin in the infrared spectra. The harmonic oscillator approximation is used for the potential curve of the Q3 mode of the isolate N2O molecule. The intermolecular potential energy surfaces are calculated for five potential-optimized discrete variable representation grid points of the Q3 mode. The three-dimensional discrete variable representation method was employed to calculate the rovibrational states without separating the inter- and intramolecular nuclear motions. The calculated transition frequencies and line intensities of the rotational transitions in the ν3 region of N2O for the van der Waals ground vibrational state are in good agreement with the observed infrared spectra. The calculated band shifts are found to be 0.1704 and 0.1551cm−1 for He4–N2O and He3–N2O, respectively, which agree well with the observed values of 0.2532 and 0.2170cm−1.
Origin of threefold symmetric torsional potential of methyl group in 4-methylstyrene
Authors: Sinha Rajeev K. , Pradhan B. , Singh Bhanu P. , Kundu T. , Biswas Partha , Chakraborty T.
Published: April 2006

To understand the effect of the para position vinyl group substitution in toluene on methyl torsion, we investigated 4-methylstyrene, a benchmark molecule with an extended π conjugation. The assignment for a 33cm−1 band in the excitation spectrum to the 3a2 torsional transition, in addition to the assignments suggested previously for the other bands in the excitation spectrum, leads to the model potentials for the ground as well as excited states with V3″=19.6cm−1, V6″=−16.4cm−1 and V3′=25.6cm−1, V6′=−30.1cm−1, respectively. These potentials reveal that both in ground and excited states, the methyl group conformations are staggered with a 60° phase shift between them. MP2 ab initio calculations support the ground state conformations determined from experiments, whereas Hartree-Fock calculations fail to do so. The origin of the modified ground state potential has been investigated by partitioning the barrier energy using the natural bond orbital (NBO) theoretical framework. The NBO analysis shows that the local delocalization (bond-antibond hyperconjugation) interactions of the methyl group with the parent molecule is sixfold symmetric. The threefold symmetric potential, on the other hand, stems from the interaction of the vinyl group and the adjacent ring π bond. The threefold symmetric structural energy arising predominantly from the π electron contribution is the barrier forming term that overwhelms the antibarrier contribution of the delocalization energy. The observed 60° phase shift of the excited state potential is attributed to the π*-σ* hyperconjugation between out of plane hydrogens of the methyl group and the benzene ring.
Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)
Authors: Ma Yunsheng , Matsushima Tatsuo , Shobatake Kosuke , Kokalj Anton
Published: April 2006

The angular and velocity distributions of desorbing product N2 were examined over the crystal azimuth in steady-state NO+CO and N2O+CO reactions on Pd(110) by cross-correlation time-of-flight techniques. At surface temperatures below 600K, N2 desorption in both reactions splits into two directional lobes collimated along 41°–45° from the surface normal toward the [001] and [001¯] directions. Above 600K, the normally directed N2 desorption is enhanced in the NO reduction. Each product desorption component, as well as CO2, shows a fairly asymmetric distribution about its collimation axis. Two factors, i.e., the anisotropic site structures and the reactant orientation and movements, are operative to induce such asymmetry, depending on the product emission mechanism.
Time-dependent perturbation theory for vibrational energy relaxation and dephasing in peptides and proteins
Authors: Fujisaki Hiroshi , Zhang Yong , Straub John E.
Published: April 2006

Without invoking the Markov approximation, we derive formulas for vibrational energy relaxation (VER) and dephasing for an anharmonic system oscillator using a time-dependent perturbation theory. The system-bath Hamiltonian contains more than the third order coupling terms since we take a normal mode picture as a zeroth order approximation. When we invoke the Markov approximation, our theory reduces to the Maradudin-Fein formula which is used to describe the VER properties of glass and proteins. When the system anharmonicity and the renormalization effect due to the environment vanishes, our formulas reduce to those derived by and Mikami and Okazaki [J. Chem. Phys. 121, 10052 (2004)] invoking the path-integral influence functional method with the second order cumulant expansion. We apply our formulas to VER of the amide I mode of a small amino-acid like molecule, N-methylacetamide, in heavy water.
The potential energy curve of the ground state of the potassium dimer, XΣg+1 K2
Authors: Zavitsas Andreas A.
Published: April 2006

The most recently published listings of vibrational term values and corresponding turning points of the potential energy curve of XΣg+1 K2 consist of two sets of data: energy levels v″=0–73 and v″=74–81. The two sets of data are found to exhibit a discontinuity. This is due to different Dunham coefficients used to produce a listing of turning points for levels v″=0–73 and for levels v″=74–81. This work provides an explicit, self-consistent listing of turning points for the entire domain of observed vibrational term values. New values are reported for levels v″=53–81. This potential yields eigenvalues in excellent agreement with experimental vibrational term values and predicts two more bound levels. A “universal” function proposed in 1991 for predicting potential energy curves yields eigenvalues for levels v″=0–81 (99.96% of dissociation) that have an average absolute deviation from the experiment of 0.95cm−1.
Accurate measurement of C13–N15 distances with solid-state NMR
Authors: Lee Jae-Seung , Khitrin A. K.
Published: April 2006

Solid-state NMR technique for measuring distances between heteronuclei in static powder samples is described. It is based on a two-dimensional single-echo scheme enhanced with adiabatic cross polarization. As an example, the results for intramolecular distances in α-crystalline form of glycine are presented. The measured NMR distances Cα13–N15 and C′13–N15 are 1.496±0.002 and 2.50±0.02Å, respectively.
Semiflexible amphiphilic polymers: Cylindrical-shaped, collagenlike, and toroidal structures
Authors: Vasilevskaya Valentina V. , Markov Vladimir A. , Khalatur Pavel G. , Khokhlov Alexei R.
Published: April 2006

A coarse-grained model is used to study the conformational properties of semiflexible polymers with amphiphilic monomer units containing both hydrophilic and hydrophobic interaction sites. The hydrophobically driven conformational transitions are studied using molecular dynamics simulations for the chains of varying stiffness, as characterized by intrinsic Kuhn segment lengths that vary over a decade. It is shown that the energy of hydrophobic attraction required for the realization of the coil-to-globule transition increases with increasing chain stiffness. For rather stiff backbone, the coil-to-globule transition corresponds to a first order phase transition. We find that depending on the chain stiffness, a variety of thermodynamically stable anisometric chain morphologies are possible in a solvent selectively poor for hydrophobic sites of amphiphilic monomer units. For flexible chains, the amphiphilic polymer forms a cylindrical globule having blob structure with nearly spherical blobs. With increasing stiffness, the number of blobs composing the globule decreases and the shape of blobs transforms into elongated cylinder. Further increase in stiffness leads to compaction of macromolecules into a collagenlike structure when the chain folds itself several times and different strands wind round each other. In this state, the collagenlike structures coexist with toroidal globules, both conformations having approximately equal energies.
An apparent critical point in binary mixtures: Experimental and simulation study
Authors: Śliwińska-Bartkowiak Małgorzata , Ratajczak Błażej , Golibrocki Leszek , Banaszak Michał
Published: April 2006

We report the experimental and simulation studies for the system of nitrobenzene-cyclododecane, showing an apparent critical point, which lies in their metastable, experimentally inaccessible state, below their melting point, affecting physical and chemical properties of this system in the stable liquid phase. The nonlinear dielectric effect (NDE) was measured in the mixture of nitrobenzene with cyclododecane. The mixture has been found to show an apparent critical point which lies below the melting point, manifested as anomalous NDE behavior in the vicinity of the critical concentrations in the stable liquid phase. The melting temperature of this system was estimated using the differential scanning calorimetry method. For such a system, we also performed Monte Carlo (MC) simulations that aimed to analyze the kinds of phase transitions observed and the conditions of their occurrence in Lennard-Jones mixture. The enthalpy, configurational energy, and radial distribution function have been estimated by the MC simulation method in the N-P-T system. Immiscibility conditions according to the approach by Schoen and Hoheisel [Mol. Phys. 57, 65 (1986)] are also discussed.
Negative linear compressibility in confined dilatating systems
Authors: Vakarin E. V. , Duda Yurko , Badiali J. P.
Published: April 2006

The role of a matrix response to a fluid insertion is analyzed in terms of a perturbation theory and Monte Carlo simulations applied to a hard sphere fluid in a slit of fluctuating density-dependent width. It is demonstrated that a coupling of the fluid-slit repulsion, spatial confinement, and the matrix dilatation acts as an effective fluid-fluid attraction, inducing a pseudocritical state with divergent linear compressibility and noncritical density fluctuations. An appropriate combination of the dilatation rate, fluid density, and the slit size leads to the fluid states with negative linear compressibility. It is shown that the switching from positive to negative compressibility is accompanied by an abrupt change in the packing mechanism.
Molecular reorientation in hydrogen-bonding liquids: Through algebraic ∼t−3∕2 relaxation toward exponential decay
Authors: Gelin M. F. , Kosov D. S.
Published: April 2006

We present a model for the description of orientational relaxation in hydrogen-bonding liquids. The model contains two relaxation parameters which regulate the intensity and efficiency of dissipation, as well as the memory function which is responsible for the short-time relaxation effects. It is shown that the librational portion of the orientational relaxation is described by an algebraic ∼t−3∕2 contribution, on top of which more rapid and nonmonotonous decays caused by the memory effects are superimposed. The long-time behavior of the orientational relaxation is exponential, although nondiffusional. It is governed by the rotational energy relaxation. We apply the model to interpret recent molecular dynamic simulations and polarization pump-probe experiments on HOD in liquid D2O [C. J. Fecko et al., J. Chem. Phys. 122, 054506 (2005)].
Measurement of temperature rises in the femtosecond laser pulsed three-dimensional atom probe
Authors: Cerezo A. , Smith G. D. W. , Clifton P. H.
Published: April 2006

A previous Letter [B. Gault et al., Appl. Phys. Lett. 86, 094101 (2005)] interpreted measurements of the field evaporation enhancement under femtosecond pulsed laser irradiation of a field emitter in terms of a direct electric field enhancement by the intrinsic field of the laser light. We show that, on the contrary, the field evaporation enhancement is predominantly a thermal heating effect. Indirect measurements of the peak specimen temperature under irradiation by femtosecond laser pulses are consistent with temperature rises obtained using longer laser pulses in a range of earlier work.
Prediction of phase behavior of nanoconfined Lennard-Jones fluids with density functional theory based on the first-order mean spherical approximation
Authors: Mi Jianguo , Tang Yiping , Zhong Chongli , Li Yi-Gui
Published: April 2006

The recently proposed first-order mean spherical approximation (FMSA) [Y. Tang, J. Chem. Phys. 121, 10605 (2004)] for inhomogeneous fluids is extended to study the phase behavior of nanoconfined Lennard-Jones fluids, which is consistent with the phase equilibria calculation of the corresponding bulk fluid. With a combination of fundamental measure theory, FMSA provides Helmholtz free energy and direct correlation function to formulate density functional theory, which implementation is as easy as the mean-field theory. Following previous success in predicting density profiles inside slit pores, this work is focused specially on the vapor-liquid equilibrium of the Lennard-Jones fluids inside these pores. It is found that outside the critical region FMSA predicts well the equilibrium diagram of slit pores with the sizes of 5.0, 7.5, and 10 molecular diameters by comparing with available computer simulation data. As a quantitative method, FMSA can be treated as an extension from its bulk calculation, while the mean-field theory is only qualitative, as its bulk version.
Spin distribution and hydrogen-bond effect in ferromagnetic α-phase crystal of 2-(2′,5′-dihydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide
Authors: Zhang Y. S. , Yao K. L. , Liu Z. L. , Yu L. H. , Wang X. L.
Published: April 2006

The ferromagnetic phenyl nitronyl nitroxide derivate α-phase 2-(2′,5′-dihydroxyphenyl)- 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide has been studied by the electronic structure calculation based on the density functional theory. The result shows that the spin delocalization due to hyperconjugation effect plays an important role in the spin distribution and ferromagnetic coupling of the crystal.
Multireference Brillouin-Wigner coupled clusters method with noniterative perturbative connected triples
Authors: Demel Ondřej , Pittner Jiří
Published: April 2006

We developed and implemented the state-specific Brillouin-Wigner coupled cluster method with singles, doubles, and noniterative perturbative triples, called MR BWCCSD(T), for a general number of closed- and open-shell reference configurations. To assess the accuracy of the method, we performed calculations of the three lowest electronic states of the oxygen molecule and of the automerization barrier of cyclobutadiene. For the oxygen molecule, the results were in a good agreement in comparison with those of the iterative MR BWCCSDTα method. For cyclobutadiene, the effect of connected triples was found to be minor, which is in agreement with the previous study by and Balková and Bartlett [J. Chem. Phys. 101, 8972 (1994)].
Systematic analysis of silicon oxynitride interfacial layer and its effects on electrical characteristics of high-k HfO2 transistor
Authors: Rhee Se Jong , Zhu Feng , Kim Hyoung-Sub , Kang Chang Yong , Choi Chang Hwan , Zhang Manhong , Lee Tackhwi , Ok Injo , Krishnan Siddarth A. , Lee Jack C.
Published: April 2006

High-k hafnium oxide dielectric metal-oxide-semiconductor field-effect transistors with several physical thicknesses of silicon oxynitride interfacial layers were investigated to understand the relationship of their effects to electrical properties. Both flatband voltage and threshold voltage were negatively shifted with reduction of leakage current density as the thickness of silicon oxynitride interfacial layer increased. Charge pumping measurement revealed that the density of interface states were proportional to the physical thickness of the interfacial layer. The large amount of positive charge and interface state density for the thick interfacial layer affected the effective channel electron mobility, resulting in 20% of low-field peak mobility degradation. In addition, less stress immunity under stress was observed when silicon oxynitride interfacial layer increased.
Time evolution of a single spin inhomogeneously coupled to an interacting spin environment
Authors: Huang Zhen , Sadiek Gehad , Kais Sabre
Published: April 2006

We study the time evolution of a single spin coupled by exchange interaction to an environment of interacting spin bath modeled by the XY Hamiltonian. By evaluating the spin correlator of the single spin, we observed that the decay rate of the spin oscillations strongly depends on the relative magnitude of the exchange coupling between the single spin and its nearest neighbor J′ and coupling among the spins in the environment J. The decoherence time varies significantly based on the relative coupling magnitudes of J and J′. The decay rate law has a Gaussian profile when the two exchange couplings are of the same order J′∼J but converts to exponential and then a power law as we move to the regimes of J′>J and J′<J. We also show that the spin oscillations propagate from the single spin to the environmental spins with a certain speed. The effect of varying the anisotropic parameter, external magnetic field, and temperature on the decaying rate of the spin state is also discussed.
Zn and ZnO nanoparticles fabricated by ion implantation combined with thermal oxidation, and the defect-free luminescence
Authors: Amekura H. , Umeda N. , Sakuma Y. , Plaksin O. A. , Takeda Y. , Kishimoto N. , Buchal Ch.
Published: April 2006

Silica glass implanted with Zn ions of 60keV to 1.0×1017ions∕cm2 was annealed in oxygen gas to form ZnO nanoparticles (NPs). In as-implanted state, the implanted Zn atoms form Zn metallic NPs inside of the silica. After annealing at 600°C, ZnO NPs form on the surface, while Zn metallic NPs still remain in the deep region. At 700°C, most of Zn atoms move to the surface to form the droplet-shaped ZnO NPs which show two photoluminescence bands, i.e., an exciton band at 375nm and a defect band at ∼500nm. The defect band almost disappears in the samples annealed at 600°C, which include both ZnO NPs and Zn NPs.
Sliding friction between polymer surfaces: A molecular interpretation
Authors: Allegra Giuseppe , Raos Guido
Published: April 2006

For two contacting rigid bodies, the friction force F is proportional to the normal load and independent of the macroscopic contact area and relative velocity V (Amonton’s law). With two mutually sliding polymer samples, the surface irregularities transmit deformation to the underlying material. Energy loss along the deformation cycles is responsible for the friction force, which now appears to depend strongly on V [see, e.g., N. Maeda et al., Science 297, 379 (2002)]. We base our theoretical interpretation on the assumption that polymer chains are mainly subjected to oscillatory “reptation” along their “tubes.” At high deformation frequencies—i.e., with a large sliding velocity V—the internal viscosity due to the rotational energy barriers around chain bonds hinders intramolecular mobility. As a result, energy dissipation and the correlated friction force strongly diminish at large V. Derived from a linear differential equation for chain dynamics, our results are basically consistent with the experimental data by Maeda et al. [Science 297, 379 (2002)] on modified polystyrene. Although the bulk polymer is below Tg, we regard the first few chain layers below the surface to be in the liquid state. In particular, the observed maximum of F vs V is consistent with physically reasonable values of the molecular parameters. As a general result, the ratio F∕V is a steadily decreasing function of V, tending to V−2 for large velocities. We evaluate a much smaller friction for a cross-linked polymer under the assumption that the junctions are effectively immobile, also in agreement with the experimental results of Maeda et al. [Science 297, 379 (2002)].
Femtosecond-laser-induced delamination and blister formation in thermal oxide films on silicon (100)
Authors: McDonald Joel P. , Mistry Vanita R. , Ray Katherine E. , Yalisove Steven M. , Nees John A. , Moody Neville R.
Published: April 2006

Silicon (100) substrates with thermal oxide films of varying thickness were irradiated with single and multiple 150fs laser pulses at normal and non-normal incidences. A range of laser fluence was found in which a blister or domelike feature was produced where the oxide film was delaminated from the substrate. At normal and non-normal incidences blister features were observed for samples with 54, 147, and 1200nm of thermal oxide. The blister features were analyzed with optical and atomic force microscopy. In addition, the time frame for blister growth was obtained using pump-probe imaging techniques.
Scaling of the saturation energy in microcavity saturable absorber devices
Authors: Massoubre David , Oudar Jean-Louis , Dion Julie , Harmand Jean-Christophe , Shen Alexandre , Landreau Jean , Decobert Jean
Published: April 2006

Several all-optical switching devices based on quantum well microcavity structures have been studied in view of their possible use for all-optical regeneration of telecommunication signals. Experiments and modeling show that the saturation energy is inversely proportional to a scaling factor describing the enhancement of the intracavity intensity at the Fabry-Perot resonance. As a result the saturation energy is approximately proportional to the number of quantum wells in the device and can be kept small by a proper cavity design.
Lattice strain in epitaxial BaTiO3 thin films
Authors: He Feizhou , Wells B. O.
Published: April 2006

We have investigated the out-of-plane lattice strain related to the ferroelectric transitions in epitaxial BaTiO3 (BTO) films using synchrotron x-ray diffraction. Under either compressive strain or tensile strain, there is evidence for two structural phase transitions as a function of temperature. The transition temperature TC is a strong function of strain, which can be as much as 100K above the corresponding TC in bulk. Under compressive strain, the tetragonality of BTO unit cell implies that the polarization of the first ferroelectric phase is out of plane, while under tensile strain, the polarization is in plane. The transitions at lower temperature may correspond to the aa→r or c→r transitions, following the notations by Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)]. The orientations of the domains are consistent with theoretical predictions.
Self-controlled growth and two-dimensional ordering of metallic nanoparticles
Authors: Vigolo B. , Mafouana R. , Goyhenex C. , Faerber J. , Arabski J. , Hirlimann C. , Rehspringer J.-L.
Published: April 2006

The control of synthesis, stabilization, and organization of metallic nanoparticles is one of the most active subjects in condensed matter science because of possible applications in high performance technology. A route to prepare a collection of ordered nanoparticles in large quantities consists of using the original combination of soft chemistry and surface science. A metal thin film deposited onto a self-assembled two-dimensional silica bead array can restructure through annealing. Pure metallic nanoparticles do form in an ordered array offering the opportunity of studying properties of an individual nanoparticle, thanks to a natural amplifier effect.
Photon-counting microscopy of terahertz radiation
Authors: Ikushima Kenji , Yoshimura Yasuhiro , Hasegawa Takuma , Komiyama Susumu , Ueda Takeji , Hirakawa Kazuhiko
Published: April 2006

Photon-counting imaging of terahertz radiation is demonstrated with a spatial resolution of 50μm for a free-space wavelength of 132μm by incorporating a quantum-dot single photon detector into a scanning confocal optical system. Terahertz radiation of 10−19–10−16W or 102–105photons∕s is imaged. Applying the microscope to the study of semiconductor quantum Hall devices, a threshold behavior of the cyclotron emission is found and the mechanism is discussed.
Novel time-of-flight electron spectrometer optimized for time-resolved soft-x-ray photoelectron spectroscopy
Authors: Paulus A. , Winterfeldt C. , Pfeifer T. , Walter D. , Gerber G. , Spielmann C.
Published: April 2006

We developed a time-of-flight electron spectrometer optimized for the detection of photoelectrons generated with femtosecond laser-generated extreme ultraviolet pulses. The low number of electrons requires an electrostatic lens design with a very high transmission over a broad energy range. We show that with an asymmetric lens geometry the chromatic aberration can be reduced and the overall transmission be increased. The setup can be further optimized employing a closed-loop optimization with an evolutionary algorithm to increase the throughput by varying the voltages applied to the lens plates.
All-diamond cantilever probes for scanning probe microscopy applications realized by a proximity lithography process
Authors: Malavé A. , Oesterschulze E.
Published: April 2006

All-diamond probes with an integrated tip were fabricated by means of a proximity lithography process and hot-filament chemical vapor deposition of polycrystalline diamond. Fabrication relies on the separate definition of the vertical and lateral cantilever probe geometries in two successive process steps. This process scheme offers the capability to adapt the mechanical properties of cantilever probes, e.g., the momentum of inertia of the cantilever beam, i.e., its compliance and resonance frequency, and the inclination angle of the tip with respect to the sample surface. Atomic force microscopy investigations of a SrTiO3 calibration sample demonstrate the application potential of these probes.
Fast and accurate determination of the Wigner rotation matrices in the fast multipole method
Authors: Dachsel Holger
Published: April 2006

In the rotation based fast multipole method the accurate determination of the Wigner rotation matrices is essential. The combination of two recurrence relations and the control of the error accumulations allow a very precise determination of the Wigner rotation matrices. The recurrence formulas are simple, efficient, and numerically stable. The advantages over other recursions are documented.
Si emission from the SiO2∕Si interface during the growth of SiO2 in the HfO2∕SiO2∕Si structure
Authors: Ming Zhao , Nakajima Kaoru , Suzuki Motofumi , Kimura Kenji , Uematsu Masashi , Torii Kazuyoshi , Kamiyama Satoshi , Nara Yasuo , Yamada Keisaku
Published: April 2006

Hf O 2 ∕ Si O 2 ∕ Si ( 001 ) structures were annealed in dry oxygen, and compositional depth profiles were measured by high-resolution Rutherford backscattering spectroscopy. Growth of the interfacial SiO2 layer and simultaneous surface accumulation of Si were observed. The observed result indicates that silicon species are emitted from the SiO2∕Si interface to release the stress induced by oxidation as was predicted by recent theoretical studies.
Significant improvement of field emission by depositing zinc oxide nanostructures on screen-printed carbon nanotube films
Authors: Yu Ke , Zhang Y. S. , Xu F. , Li Q. , Zhu Z. Q. , Wan Q.
Published: April 2006

In order to improve the field emission properties of screen-printed carbon nanotube films, ZnO nanostructures were deposited on multiwall carbon nanotubes (MWNTs) using vapor phase transport method. Based on the combined effect of geometrical structure of MWNT/ZnO, a low turn-on field of ∼0.7V∕μm at current density of 0.1μA∕cm2, a low threshold field of ∼2.3V∕μm at current density of 1mA∕cm2, a high field enhancement factor of 8.2×103, and a homogeneous emission image with emission spot density of ∼105cm−2 were obtained from ZnO nanomultipods grown on MNWT film.
Active microfluidic mixer chip
Authors: Niu Xize , Liu Liyu , Wen Weijia , Sheng Ping
Published: April 2006

We report the design and fabrication of a chaotic mixer based on the electrorheological (ER) fluid-controlled valves. The flow in the main channel is perturbed by liquid flow in orthogonal side channels, driven by hydrodynamic pulsating pumps. Each pulsating pump consists of a chamber with diaphragm plus two out-of-phase ER valves operating in a push-pull mode. All the valves, pumps, and mixing channels are integrated in one polydimethylsioxane chip. Mixing characteristics in the main channel are controlled by the strength and frequency of external electric fields applied on the ER fluid.
Misfit relaxation of InN quantum dots: Effect of the GaN capping layer
Authors: Lozano J. G. , Sánchez A. M. , García R. , Gonzalez D. , Briot O. , Ruffenach S.
Published: April 2006

The strain state on InN quantum dots (QDs) over GaN/sapphire substrates was analyzed by transmission electron microscopy. Changes in the in-plane lattice parameter of uncapped and capped InN QD heterostructures have been measured using moiré fringe analysis. The uncapped QDs are almost completely relaxed, due to a misfit dislocation network present at the InN∕GaN interface without generating any threading dislocations inside the QDs. In addition, a low-temperature-GaN capping process on InN QDs heterostructures was evaluated. Although this deposition avoids the InN decomposition, it modifies the QDs’ morphology, decreases both the aspect ratio and, consequently, the plastic relaxation of the heterostructure.
Visible range whispering-gallery mode in microdisk array based on size-controlled Si nanocrystals
Authors: Zhang Rong-Jun , Seo Se-Young , Milenin Alexey P. , Zacharias Margit , Gösele Ulrich
Published: April 2006

Microdisks based on in-plane embedded size-controlled Si nanocrystal∕SiO2 superlattices (Si-NCs∕SiO2 SLs) were mass-fabricated arranged in well-ordered arrays. The microdisks were fabricated with size irregularity of below 0.2% over large-scale areas. Overlapping whispering-gallery modes (WGM) of the visible nanocrystalline-silicon luminescence were observed. A comparison between analytical calculation and experimental results is reported. We found that only one axial and one radial WGM exist due to their thin disk thickness and birefringence characteristic of Si-NCs∕SiO2 SLs, and that the mode spacing is 15nm and 6nm for microdisks with a diameter of 8.8μm and 23.7μm, respectively. The advantages of such size-controlled Si-NCs∕SiO2 embedded in microdisk arrays for Si-based photonic application will be discussed.
Deep energy levels in RuO2∕4H–SiC Schottky barrier structures
Authors: Stuchlikova L. , Buc D. , Harmatha L. , Helmersson U. , Chang W. H. , Bello I.
Published: April 2006

RuO 2 ∕ 4 H – SiC Schottky diode structures based on n-type 4H–SiC (7×1017cm−3) with stoichiometric RuO2 Schottky contacts were characterized by electrical capacitance-voltage and current voltage methods and deep-level transient spectroscopy in order to determine their unique semiconducting and electronic properties. The RuO2 films exhibited electrical conductivity of 60μΩcm for Schottky barrier heights of approximately 0.88eV. These Schottky structures revealed two deep energy levels with thermal activation energies of 0.56 and 0.85eV with reference to the conduction band.
Fabrication of an As2S8 stripe waveguide with an optical stopping effect by exposure to ultraviolet irradiation
Authors: Zou L. E. , Chen B. X. , Chen L. , Yuan Y. F. , Hamanaka M. , Iso M.
Published: April 2006

Amorphous As2S8 chalcogenide glass is shown to undergo changes in the refractive index upon exposure to ultraviolet light. This phenomenon is employed to fabricate an As2S8 stripe waveguide, which is shown to be an effective guided mode device with a useful switching functionality based on the photo-optical effect.
Spatial distributions of trapping centers in HfO2∕SiO2 gate stacks
Authors: Heh Dawei , Young Chadwin D. , Brown George A. , Hung P. Y. , Diebold Alain , Bersuker Gennadi , Vogel Eric M. , Bernstein Joseph B.
Published: April 2006

A methodology to analyze charge pumping (CP) data, which allows positions of probing traps in the dielectric to be identified, was applied to extract the spatial profile of traps in SiO2∕HfO2 gate stacks. The results suggest that traps accessible by CP measurements in a wide frequency range, down to few kilohertz, are located within or near the interfacial SiO2 layer rather than in the bulk of the high-k film.
Low-band gap poly(di-2-thienylthienopyrazine):fullerene solar cells
Authors: Wienk Martijn M. , Turbiez Mathieu G. R. , Struijk Martin P. , Fonrodona Marta , Janssen René A. J.
Published: April 2006

Two side-chain substituted poly(di-2-thienylthienopyrazine)s (PBEHTT and PTBEHT) are used as electron donor together with phenyl-C61 butyric acid methyl ester (PCBM) as an electron acceptor in low-band gap bulk heterojunction polymer solar cells. These low-band gap polymers absorb light up to ∼1μm. Under simulated AM1.5 conditions PTBEHT:PCBM devices provide a short circuit current of Jsc=3.5mA∕cm2, an open circuit voltage of Voc=0.56V, and a power conversion efficiency of η=1.1%. Photoresponse up to 1μm has been observed with external quantum efficiencies exceeding 15% in the 700–900nm region.
High-current and low-voltage operation of metal-base organic transistors with LiF∕Al emitter
Authors: Nakayama Ken-ichi , Fujimoto Shin-ya , Yokoyama Masaaki
Published: April 2006

In order to improve the performance and clarify the operation mechanism of the vertical-type metal-base organic transistor with a simple organic/metal/organic layered structure, the influence of the electron injection at the emitter electrode interface on modulation current has been investigated using the several emitter metal electrodes. The low injection barrier resulted in large modulation current. When a LiF∕Al emitter electrode was used for C60 organic semiconductor, this device achieved a high current modulation—exceeding 250mA∕cm2 for a low collector voltage of 3.0V and a base voltage of 1.25V.
Giant and composition-dependent optical band gap bowing in dilute GaSb1−xNx alloys
Authors: Belabbes A. , Ferhat M. , Zaoui A.
Published: April 2006

Ab initio pseudopotential plane wave calculations and large 64-atom relaxed supercells are used to investigate the structural and electronic properties of GaNxSb1−x dilute alloys. While the band gaps of conventional III-V semiconductors have a simple and weak dependence on composition, this work illustrate a violation of this expected behavior. We show that the band gap decreases rapidly with increasing compositions of N and that GaNxSb1−x show an abnormal giant gap reduction. As a consequence, the optical band gap bowing is found to be giant and composition dependent as found for other mixed anion III-V–N systems.
Efficient light extraction and beam shaping from flexible, optically integrated organic light-emitting diodes
Authors: Melpignano P. , Biondo V. , Sinesi S. , Gale Michael T. , Westenhöfer Susanne , Murgia M. , Caria S. , Zamboni R.
Published: April 2006

Efficient out-coupling light extraction and optical beam shaping have been combined to form an integrated, flexible illuminator that is based on organic light-emitting diodes (OLEDs). Spherical refractive microlenses were replicated by a cost-effective UV-casting technique onto a plastic foil to achieve the customized Gaussian distribution of the electroluminescence of an OLED pixel (50μm) matrix. The fabricated optical device, namely a ceiling light illuminator, shows an improvement of 70% in the out-coupled emission measured in the far field. The result corresponds to the theoretical prediction for isotropic emitting sources.
The effect of low-frequency microvibrations on nanoparticle networks embedded in liquid crystals
Authors: Nersisyan Sarik R. , Tabiryan Nelson V.
Published: April 2006

We describe an opportunity of orienting liquid crystals in nanoparticle networks (LCNNs) which considerably enhances the transmission of the material and makes feasible switching between the transparent and opaque states of the material in an all-mechanical process that can be performed without invoking electrical fields. The technique employs a process in which one of the substrates of the LCNN cell is fixed while the other substrate is brought into low-frequency shearing microvibrations. The optical transmission of the material proves to be highly sensitive to the vibration frequency, as well as to its amplitude.
Aging and stability of cerium-based bulk metallic glass
Authors: Luo Q. , Zhang B. , Zhao D. Q. , Wang R. J. , Pan M. X. , Wang W. H.
Published: April 2006

The aging behavior and the stability of a Ce68Al10Cu20Fe2 bulk metallic glass (BMG) with low glass transition temperature Tg have been investigated upon isothermal annealing near Tg. The annealing time-dependent acoustic velocities, density, elastic constants, and thermodynamic parameters are determined to monitor the structural and properties changes upon aging, and the structural relaxation progress is monitored by the change of enthalpy recovery after annealing. It is found that BMG with Tg near room temperature has high thermal and property stabilities. Stable BMG provides an ideal system to investigate relaxation and supercooled liquid state in alloys.
Positive edge effects for arboreal marsupials: an assessment of potential mechanisms
Authors: Harding Elaine K. , Gomez Shirin
Published: April 2006

In this study we examined the potential for positive edge effects on folivorous arboreal marsupials inhabiting upland rainforest in the Wet Tropics region of far north Queensland, Australia. We predicted that the folivores should have increased densities at edges relative to interior forest 90 m from the edge owing to the following causal factors, either separately or in combination: (a) increased foliar biomass, measured as vertical foliage density; and/or (b) increased abundance of preferred food trees. To test these hypotheses, we conducted surveys of the lemuroid ringtail possum (Hemibelideus lemuroides), the green ringtail possum (Pseudochirops archeri), the Herbert River ringtail possum (Pseudochirulus herbertensis) and the coppery brushtail possum (Trichosurus vulpecula johnstonii) at two remnant rainforest sites with ‘hard’ edges such as roads or pasture. Because arboreal species are often difficult to survey accurately within forests, we utilised pellet counts as an index of the population and compared this to the common survey technique of night spotlighting. Our results indicated that pellet counts, combined over all species, were positively and strongly correlated with spotlighting results. Using pellet counts as a relative index of arboreal folivore populations, we found that edge transects contained a higher abundance of all species combined than did interior transects. Further, total foliage density in the 10–30-m vertical transect was found to be significantly correlated with total pellet counts at edge transects. Total preferred tree species was not significantly different between edge and interior transects. From these results we propose that foliage density, as a surrogate for biomass, is a possible mechanism explaining the higher abundance of arboreal marsupials at the edges of these two highland rainforest sites in north Queensland.