bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation energy and dispersion interaction in the ab initio potential energy curve of the neon dimer
Authors: Bytautas Laimutis , Ruedenberg Klaus
Published: June 2008

A close approximation to the empirical potential energy curve of the neon dimer is obtained by coupled-cluster singles plus doubles plus noniterative triples calculations by using nonaugmented correlation-consistent basis sets without counterpoise corrections and complementing them by three-term extrapolations to the complete basis set limit. The potential energy is resolved into a self-consistent-field Hartree–Fock contribution and a correlation contribution. The latter is shown to decay in the long-range region in accordance with the empirical dispersion expansion.
Electronically excited states of water clusters of 7-azaindole: Structures, relative energies, and electronic nature of the excited states
Authors: Svartsov Yuriy N. , Schmitt Michael
Published: June 2008

The geometries of 1H-7-azaindole and the 1H-7-azaindole(H2O)1–2 complexes and the respective 7H tautomers in their ground and two lowest electronically excited π−π* singlet states have been optimized by using the second-order approximated coupled cluster model within the resolution-of-the-identity approximation. Based on these optimized structures, adiabatic excitation spectra were computed by using the combined density functional theory/multireference configuration interaction method. Special attention was paid to comparison of the orientation of transition dipole moments and excited state permanent dipole moments, which can be determined accurately with rotationally resolved electronic Stark spectroscopy. The electronic nature of the lowest excited state is shown to change from Lb to La upon water complexation.
Rotationally resolved electronic spectroscopy of water clusters of 7-azaindole
Authors: Vu Thi Bao Chau , Kalkman Ivo , Leo Meerts W. , Svartsov Yuriy N. , Jacoby Christoph , Schmitt Michael
Published: June 2008

The rotationally resolved electronic spectra of the electronic origin of the 7-azaindole-(H2O)1 and of the 7-azaindole-(H2O)2 clusters have been measured in a molecular beam. From the rotational constants the structures in the S0 and S1 electronic states were determined as cyclic with the pyrrolo NH and the pyridino N atoms being bridged by one and two water molecules, respectively. Excited state lifetimes of about 10ns for both clusters have been found. In the spectrum of the 7-azaindole-(H2O)2 cluster a splitting of the rovibronic band is observed, which can be traced back to a large amplitude motion, involving the out-of-plane hydrogen atoms of the water chain. Both the changes of the rotational constants upon electronic excitation and the orientation of the transition dipole point to a solvent induced state reversal between the La and the Lb states upon microsolvation.
Accuracy of recent potential energy surfaces for the He–N2 interaction. II. Molecular beam scattering and bulk gas relaxation phenomena
Authors: Sanchez-Fortún Stoker Jamie , Dham Ashok K. , McCourt Frederick R. W. , Dickinson Alan S.
Published: June 2008

A new semiempirical exchange-Coulomb model potential energy surface for the N2–He interaction was reported recently [A. K. Dham et al., J. Chem. Phys. 127, 054302 (2007)] and, using it, the temperature dependence of bulk gas properties of N2–He mixtures, such as the second virial coefficient and traditional transport phenomena, most of which depend primarily on the isotropic component of the interaction potential energy surface, was determined. Values of these properties, along with values calculated using two high-quality ab initio potential energy surfaces [C.-H. Hu and A. J. Thakkar, J. Chem. Phys. 104, 2541 (1996); K. Patel et al., ibid 119, 909 (2003)] were compared critically to available experimental data. The present paper reports on the ability of the same three potential energy surfaces to predict state-to-state and total differential cross sections, total integral cross sections, and the temperature dependence of bulk gas relaxation phenomena (including magnetic field effects on transport coefficients). While all three potential energy surfaces give total differential and higher speed integral scattering results that fall within the experimental uncertainties, integral scattering results and state-to-state differential cross section measurements consistently exceed the calculated values. All three surfaces give similar agreement with the relaxation properties of N2–He binary mixtures, with the semiempirical exchange-Coulomb model potential energy surface giving slightly better overall agreement with experiment than the two ab initio potential energy surfaces.
Nucleation in the presence of slow microscopic dynamics
Authors: Sear Richard P.
Published: June 2008

Nucleation of a new thermodynamic phase is often a slow process due to the need to overcome a high free-energy barrier. However, there are other sources of slow dynamics; for example, at high densities/low temperatures, the movement of individual molecules or spins may be slow. Here, we study nucleation in a simple phenomenological model that has this type of slow microscopic dynamics. We do this to better understand how the two sources of slow dynamics interact. We find that as nucleation is intrinsically slow, only very slow microscopic dynamics strongly affect how nucleation occurs. The composition of the nucleus at the top of the nucleation barrier is much less sensitive to slow microscopic dynamics than is the composition of the nucleus once it is postcritical. However, slow dynamics affects not only the rate but also the pathway, which no longer goes over the saddle point in the free energy. We also find that the slow microscopic dynamics can cause sampling problems in an algorithm developed to calculate nucleation rates, and so cause it to predict the rate incorrectly.
Performance and transport characteristics of α,ω-dihexylsexithiophene- based transistors with a high room-temperature mobility of 0.16cm2∕Vs
Authors: Seo Hoon-Seok , Zhang Ying , Jang Young-Se , Choi Jong-Ho
Published: June 2008

Organic thin-film transistors (OTFTs) based upon α,ω-dihexylsexithiophene (DH6T) have been fabricated and characterized. The DH6T thin films were prepared using neutral cluster beam deposition (NCBD) methods on room-temperature SiO2 substrates. The effects of surface modification were examined. The geometric effects of the gate dielectric thickness, channel length, and width on the device characteristics were also systematically studied. A combination of the NCBD technique and octadecyltrichlorosilane (OTS) pretreatment was most efficient for producing high-quality crystalline DH6T films. The temperature dependence of the field-effect mobility (μeff) indicated that the transistor performance was strongly correlated with the structural and morphological properties of the DH6T active layers and that the surfactant pretreatment significantly enhanced the μeff. A room-temperature μeff of 0.16cm2∕Vs for the OTS-pretreated transistors was found to be best so far reported for DH6T-based OTFTs using a SiO2 gate dielectric layer.
Interaction of narrow carbon nanotubes with nitronium tetrafluoroborate salts
Authors: Cabria I. , López M. J. , Alonso J. A.
Published: June 2008

Density functional calculations have been performed to investigate the destruction of narrow carbon nanotubes (CNTs) under the attack of nitronium tetrafluoroborate salts. The dissociation of these salts in a solvent produces nitronium and tetrafluoroborate ions which coadsorb on the external surface of the tubes. It is shown that the ions bind strongly to both metallic and semiconducting narrow nanotubes, although stronger to the metallic ones. The nitronium cations bind to the CNTs through a charge transfer mechanism, whereas the tetrafluoroborate anions remain negatively charged upon adsorption on the nanotubes. The surface of the nanotubes gets substantially deformed around the adsorption site of the nitronium ion, but it is hardly changed around the adsorption site of the tetrafluoroborate ion. These results are the theoretical basis to explain the destruction of the narrow CNTs found in the experiments and also to unravel, in agreement with the experimental interpretation, the distinct role played by the nitronium and the tetrafluoroborate ions. The tetrafluoroborate ions contribute to separate the CNTs from the bundles into individual tubes, without affecting the tubes. The nitronium ions, in contrast, modify the electronic and geometrical structures of the narrow tubes leading eventually to their destruction. The implications for the selective removal of intermediate diameter metallic CNTs found in the experiments are also discussed. The adsorption of the neutral nitrogen dioxide molecule is also studied, and the results show that the weak interactions of this molecule with both metallic and semiconducting tubes cannot be used as a model for the strong attack of the nitronium ions to the narrow tubes. The sensor effect of the nanotubes toward adsorption of nitrogen dioxide is also discussed.
Solvation phenomena in dilute multicomponent solutions I. Formal results and molecular outlook
Authors: Chialvo Ariel A. , Chialvo Sebastian , Simonson J. Michael , Kalyuzhnyi Yu. V.
Published: June 2008

We derive second-order thermodynamically consistent truncated composition expansions for the species residual partial molar properties—including volume, enthalpy, entropy, and Gibbs free energy—of dilute ternary systems aimed at the molecular account of solvation phenomena in compressible media. Then, we provide explicit microscopic interpretation of the expansion coefficients in terms of direct and total correlation function integrals over the microstructure of the corresponding infinite dilution reference system, as well as their pressure and temperature derivatives, allowing for the direct prediction of the species partial molar properties from the knowledge of the effective intermolecular interactions. Finally, we apply these formal results (a) to derive consistent expressions for the corresponding properties of the binary system counterparts, (b) to illustrate how the formal expressions converge, at the zero density limit, to those for multicomponent mixtures of imperfect gases obeying the virial equation of state Z=1+BP∕kT, and (c) to discuss, and highlight with examples from the literature, the thermodynamic inconsistencies encountered in the currently available first-order truncated expansions, by pinpointing the mathematical origin and physical meaning of the inconsistencies that render the first-order truncated expansions invalid.
On mesh-based Ewald methods: Optimal parameters for two differentiation schemes
Authors: Stern Harry A. , Calkins Keith G.
Published: June 2008

The particle-particle particle-mesh Ewald method for the treatment of long-range electrostatics under periodic boundary conditions is reviewed. The optimal Green’s function for exact (real-space differentiation), which differs from that for reciprocal-space differentiation, is given. Simple analytic formulas are given to determine the optimal Ewald screening parameter given a differentiation scheme, a real-space cutoff, a mesh spacing, and an assignment order. Simulations of liquid water are performed to examine the effect of the accuracy of the electrostatic forces on calculation of the static dielectric constant. A target dimensionless root-mean-square error of 10−4 is sufficient to obtain a well-converged estimate of the dielectric constant.
Correlation between magnetic spin structure and the three-dimensional geometry in chemically synthesized nanoscale magnetite rings
Authors: Eltschka M. , Kläui M. , Rüdiger U. , Kasama T. , Cervera-Gontard L. , Dunin-Borkowski R. E. , Luo F. , Heyderman L. J. , Jia C.-J. , Sun L.-D. , Yan C.-H.
Published: June 2008

The correlation between magnetic spin structure and geometry in nanoscale chemically synthesized Fe3O4 rings has been investigated by transmission electron microscopy. We find primarily the flux closure vortex states but in rings with thickness variations, an effective stray field occurs. Using tomography, we determine the complete three-dimensional geometries of thicker rings. A direct correlation between the geometry and the magnetization which points out of plane in the thickest parts of the ring yielding an intermediate magnetic state between the vortex state and the tube state is found. The interaction between exchange coupled rings leads to antiparallel vortex states and extended onion states.
Tailoring the magnetoresistance of MnAs∕GaAs:Mn granular hybrid nanostructures
Authors: Michel C. , Elm M. T. , Goldlücke B. , Baranovskii S. D. , Thomas P. , Heimbrodt W. , Klar P. J.
Published: June 2008

The magnetoresistance properties of GaAs:Mn∕MnAs granular hybrid structures consisting of ferromagnetic MnAs clusters within a paramagnetic GaAs:Mn host differ considerably from those of paramagnetic and ferromagnetic (Ga,Mn)As alloys. We analyze the magnetoresistance effects on the basis of a resistor network model. Typical experimental findings are reproduced and their dependence on cluster density and random spatial arrangement of the clusters are revealed. Controlled spatial positioning of the MnAs clusters within the GaAs:Mn host offers interesting opportunities for optimizing the magnetoresistance properties for applications and for overcoming problems of miniaturization arising from cluster statistics.
Electron-pair density relaxation holes
Authors: Piris Mario , Lopez Xabier , Ugalde Jesus M.
Published: June 2008

The electron-pair density relaxation hole has been defined as the electron-pair density of the real molecule minus the electron-pair density of a reference system consisting of overlapping, spherically averaged, undeformed atoms, positioned at the molecular nuclear coordinates. We have shown how it can be calculated from one- and two-electron reduced density matrices expanded in a Gaussian type basis set. Analysis of the calculated radial electron-pair density holes, from full configuration interaction one- and two-electron reduce density matrices, for the ground states of the hydrogen molecule, the helium dimer and the lithium and beryllium hydrides reveal that the different types of bonding interactions yield distinctively visually recognizable different topological patterns of the electron-pair density relaxation hole.
Power efficiency improvement in a tandem organic light-emitting diode
Authors: Liao L. S. , Klubek K. P.
Published: June 2008

When a tandem light-emitting diode (OLED) utilizes unoptimized electroluminescent (EL) units, it is fairly easy to improve the power efficiency of such a device. However, when a tandem OLED utilizes optimized EL units, improved power efficiency can only be achieved if each intermediate connector has excellent carrier injection capabilities along with a negligible voltage drop across it. Four organic intermediate connectors were studied in this work, one of which consisting of a Li-doped 4,7-diphenyl-1,10-phenanthroline layer and a 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile layer, exhibits the best power efficiency improvement for tandem OLEDs.
Piezoresponse and ferroelectric properties of lead-free [Bi0.5(Na0.7K0.2Li0.1)0.5]TiO3 thin films by pulsed laser deposition
Authors: Wang D. Y. , Lin D. M. , Wong K. S. , Kwok K. W. , Dai J. Y. , Chan H. L. W.
Published: June 2008

Polycrystalline lead-free piezoelectric [Bi0.5(Na0.7K0.2Li0.1)0.5]TiO3 (BNKLT) thin films were grown on Pt∕Ti∕SiO2∕Si substrates using pulsed laser deposition (PLD). In this letter, we report the ferroelectric properties and piezoresponse of the PLD-produced BNKLT thin films. X-ray diffraction characterization revealed a good crystallinity and a pure perovskite structure in the films. The films exhibited a well-defined polarization hysteresis loop with a remnant polarization Pr of 13.9μC∕cm2 and a coercive field Ec of 10.2MV∕m. The domain structure and its thermal-driven evolution from the ferroelectric to nonferroelectric phase were observed by piezoresponse force microscopy. The results were consistent with the phase transition profile of BNKLT bulk ceramics. Typical butterfly-shaped piezoresponse loop was obtained and the effective piezoelectric coefficient d33,f of the BNKLT thin films was about 64pm∕V.
Templated growth of an ordered array of organic bidimensional mesopores
Authors: Écija David , Trelka Marta , Urban Christian , de Mendoza Paula , Echavarren Antonio , Otero Roberto , Gallego José María , Miranda Rodolfo
Published: June 2008

We report on a method to fabricate a porous two dimensional (2D) array of porphyrins on c(2×2)N∕Cu(001) with pore sizes larger than 5nm, larger than the reported sizes for hydrogen-bonded or coordination porous organic networks. When deposited on the square nanopattern created by partial nitridation of the Cu(001) surface, the porphyrin molecules prefer to adsorb on clean copper instead of adsorbing on the CuN islands, forming a porous 2D array. This nanopatterning technique can be straightforwardly extended to other molecular species to form the pore walls since its working principle only depends marginally on the nature of the intermolecular interactions.
Fluorescence decay of quasimonolayered porphyrins near a metal surface separated by short-chain alkanethiols
Authors: Zhang X.-L. , Chen L.-G. , Lv P. , Gao H.-Y. , Wei S.-J. , Dong Z.-C. , Hou J. G.
Published: June 2008

We investigated the spectral feature and fluorescence lifetime of quasimonolayered porphyrins at very short distance to metal substrates (1–2.5nm) through fine-tuning the length of alkanethiols. The ordered self-assembled monolayers of alkanethiols on Au(111) act as a uniform electronic decoupling layer and suppress the interface quenching via charge transfer. However, the fluorescence quenching via nonradiative energy transfer to the metal still prevails in the porphyrin-alkanethiol-metal sandwich structures. The decay rates are found to follow a 1∕d3 dependency on spacer thickness, which suggests that the classical electromagnetic theory appears still valid at distance down to 1nm through volume damping.
Reduction in helium thermal conductivity by 1mg∕cc silica aerogel foam
Authors: Kugland N. L. , Moody J. D. , Kozioziemski B. J. , Rubenchik A. M. , Niemann C.
Published: June 2008

Ultralow density 1mg∕cc aerogel foam reduces the thermal conductivity of pure helium gas by about a factor of 3 at 1Torr and 20K, with smaller reductions at higher temperatures and pressures. The measurements were made using the dc hot wire method over temperatures ranging between 15 and 300K and pressures ranging from 0.05to100Torr. The results are generally consistent with a simple model that accounts for a reduction in the He mean free path due to the foam.
Inherent inhomogeneity in the crystals of low-doped lanthanum manganites
Authors: Rozenberg E. , Auslender M. , Shames A. I. , Gorodetsky G. , Mukovskii Ya. M.
Published: June 2008

The X-band electron paramagnetic resonance (EPR) technique and the model analysis of the EPR susceptibility versus temperature were employed to characterize the dopant distribution in a number of La-manganite crystals, low doped with Ca, Sr, and Ba in a La site. Such distribution appears to be inhomogeneous as a result of technological-driven effect. It is emphasized that the above chemical disorder influences strongly both magnetic state and transport of the low-doped manganite crystals.
Measurement of electron temperature and density in an argon microdischarge by laser Thomson scattering
Authors: Belostotskiy Sergey G. , Khandelwal Rahul , Wang Qiang , Donnelly Vincent M. , Economou Demetre J. , Sadeghi Nader
Published: June 2008

Laser Thomson scattering in a novel, backscattered configuration was employed to measure the electron temperature (Te) and electron density (ne) in argon dc microdischarges, with an interelectrode gap of 600μm. Measurements were performed at the center of the gap that corresponds to the positive column. For 50mA microdischarge current and over the pressure range of 300–700Torr, the plasma parameters were found to be Te=0.9±0.3eV and ne=(6±3)×1013cm−3, in reasonable agreement with the predictions of a mathematical model.
Optimization of the thermoelectric properties of Ba8Ga16Ge30
Authors: Martin J. , Wang H. , Nolas G. S.
Published: June 2008

Polycrystalline Ba8Ga16Ge30 clathrates with a systematic variation in the Ga:Ge stoichiometry were prepared to investigate the thermoelectric properties as a function of carrier concentration. Their corresponding transport properties were evaluated to identify the optimal carrier concentration for high temperature thermoelectric performance. These polycrystalline specimens demonstrate thermoelectric properties comparable to those obtained in single-crystal Ba8Ga16Ge30, confirming that polycrystalline clathrates can be optimized for high temperature thermoelectric applications.
Microwave Hall mobility studies on polymer-single walled carbon nanotube composite fibers
Authors: Murthy D. V. B. , Subramanian V. , Sundaray Bibekananda , Natarajan T. S.
Published: June 2008

Composite fibers of single walled carbon nanotubes dispersed in poly(methyl methacrylate) and polystyrene are prepared using electrospinning. The single fiber electrical conductivity is measured as a function of the composition of carbon nanotubes. A noncontact method of measuring the carrier mobility at microwave frequency (14GHz) using bimodal cavity is employed. The mobility measurements indicate lower percolation threshold for mobility compared to electrical conduction. For higher concentrations of carbon nanotubes, the mobility is found to decrease indicating possible carrier-lattice scattering.
Subwavelength patterning of alkylsiloxane monolayers via nonlinear processing with single femtosecond laser pulses
Authors: Hartmann N. , Franzka S. , Koch J. , Ostendorf A. , Chichkov B. N.
Published: June 2008

Femtosecond laser patterning of octadecylsiloxane monolayers on quartz glass at λ=800nm, τ<30fs, and ambient conditions has been investigated. Selective decomposition of the coating with single laser pulses at subwavelength resolution can be carried out over a wide range of fluences from 4.2 down to 3.1J∕cm2. In particular, at a 1∕e laser spot diameter of 1.8μm, structures with a width down to 250nm and below were fabricated. This opens up a facile route towards laser fabrication of transparent templates with chemical structures down into the sub-100-nm-regime.
Influence of photon reabsorption on temperature dependent quasi-steady-state photoluminescence lifetime measurements on crystalline silicon
Authors: Rüdiger Marc , Trupke Thorsten , Würfel Peter , Roth Thomas , Glunz Stefan W.
Published: June 2008

Due to their robustness against various experimental artifacts and the high sensitivity at low minority carrier concentrations, quasi-steady-state photoluminescence lifetime measurements are well suited to provide the experimental data required for advanced defect spectroscopy methods. However, for a correct evaluation, photon reabsorption has to be considered. In this work it is evaluated quantitatively, to what extent and in which temperature range photon reabsorption in silicon wafers is significant. A method to correct the effect of photon reabsorption within silicon wafers on temperature dependent quasi-steady-state photoluminescence lifetime measurements is presented.
Low threshold two-dimensional organic photonic crystal distributed feedback laser with hexagonal symmetry based on SiN
Authors: Dong Ying , Zhao Han , Song Junfeng , Gao Fubin , Cheng Chuanhui , Chang Yuchun , Du Guotong , Yu M. B. , Lo G. Q.
Published: June 2008

We report on the characterization of low threshold second-order organic photonic crystal distributed feedback laser based on SiN with hexagonal lattice. SiN can increase the index contrast in the photonic crystal distributed feedback as well as the confinement in the waveguide which results in a decrease in the threshold. Low threshold energy of 0.65kW∕cm2 and full width at half maximum of 0.9nm were achieved in lasers. As a result, we observe surface-emitting lasing action and hexagonal emission pattern of side beams whose direction slightly deviates from the normal. We explain the feedback mechanisms by using semiclassical laser theory.
Hybrid nanocrystals-organic-semiconductor light sensor
Authors: Aqua T. , Naaman R. , Aharoni A. , Banin U. , Paltiel Y.
Published: June 2008

We present a light sensing device based on nearly spherical, defect free colloidal nanocrystals (NCs) of InAs acting as a light activated gate for a GaAs∕AlGaAs field effect semiconductor transistor. We use self-assembled organic monolayer as linkers that attach the InAs NCs to the surface of the semiconductor device, instead of the gate that exists in common transistors. When the NCs absorb light, at a frequency corresponding to their resonance, a change in the current through the transistor takes place while no current flows through the NCs themselves.
Enhancement in microwave modulation efficiency of vertical cavity surface-emitting laser by optical feedback
Authors: Gavra Nemi , Ruseva Valentina , Rosenbluh Michael
Published: June 2008

We investigate a versatile vertical cavity surface-emitting laser (VCSEL) with a slight optical feedback from a simple wedge positioned at a well determined distance from the VCSEL. We use such a laser in conjunction with a miniature Rb atomic cell to detect coherent population trapping (CPT) when the external cavity mode spacing frequency corresponds to half the hyperfine frequency of Rb. The feedback greatly enhances the rf modulation efficiency of the VCSEL and as a result we obtain high contrast CPT signals at an input of −16dBm of rf modulation power compared to +1.25dBm needed in the absence of the external cavity.
Parametrically coupled multiharmonic force imaging
Authors: Abak M. Kurtuluş , Aktas Ozan , Mammadov Rashad , Gürsel İhsan , Dâna Aykutlu
Published: June 2008

We report use of nonlinear tip-sample interactions to parametrically convert the frequency components of periodic tip-sample interaction forces to frequencies where they can be resonantly detected. One flexural mode of a cantilever is used for tapping-mode imaging and another flexural mode is used for detection of forces converted in presence of an externally injected mechanical oscillation at the difference frequency of the detecting mode and a harmonic of the tapping mode. Material contrast in attractive and repulsive regimes are demonstrated on samples with polymethyl methacrylate patterns and with deoxyribonucleic acid strands on silicon.
Low-frequency noise in top-gated ambipolar carbon nanotube field effect transistors
Authors: Xu Guangyu , Liu Fei , Han Song , Ryu Koungmin , Badmaev Alexander , Lei Bo , Zhou Chongwu , Wang Kang L.
Published: June 2008

Low-frequency noise of top-gated ambipolar carbon nanotube field effect transistors (CNT-FETs) with aligned CNT growth onto the quartz substrate is presented. The noise of top-gated CNT-FETs in air is lower than that of back-gated devices, and is comparable to that of back-gated devices in vacuum. It shows that molecules in air act as additional scattering sources, which contribute to the noise. Different noise amplitudes in the electron-conduction and the hole-conduction regions are due to different Schottky barriers with respect to the conduction and valance bands as well as the scattering in the channel.
Preparation and characterization of highly L21-ordered full-Heusler alloy Co2FeAl0.5Si0.5 thin films for spintronics device applications
Authors: Wang Wenhong , Sukegawa Hiroaki , Shan Rong , Furubayashi Takao , Inomata Koichiro
Published: June 2008

We report the investigation of structure and magnetic properties of full-Heusler alloy Co2FeAl0.5Si0.5 (CFAS) thin films grown on MgO-buffered MgO (001) substrates through magnetron sputtering. It was found that single-crystal CFAS thin films with high degree of L21 ordering and sufficiently flat surface could be obtained after postdeposition annealing. All the films show a distinct uniaxial magnetic anisotropy with the easy axis of magnetization along the in-plane [110] direction. These results indicate that the use of the MgO buffer for CFAS is a promising approach for achieving a higher tunnel magnetoresistance ratio, and thus for spintronics device applications.
Tuning the Schottky barrier height of nickel silicide on p-silicon by aluminum segregation
Authors: Sinha Mantavya , Chor Eng Fong , Yeo Yee-Chia
Published: June 2008

We report the Schottky barrier height (SBH) tuning at the nickel silicide (NiSi)∕p-Si junction by the introduction of aluminum (Al) using ion implantation and its segregation after silicidation. The SBH for holes has been found to decrease with increasing concentration of Al at the NiSi∕p-Si interface. We demonstrate the achievement of one of the lowest reported SBH for holes of 0.12eV, with less than 0.1at.% Al in NiSi, which is promising for application in p-channel Schottky source/drain transistors.
Effect of epitaxy and lattice mismatch on saturation magnetization of γ′-Fe4N thin films
Authors: Atiq Shahid , Ko Hyun-Seok , Siddiqi Saadat Anwar , Shin Sung-Chul
Published: June 2008

We report the effect of epitaxial growth and lattice mismatch on the enhancement of saturation magnetization (Ms) of ferromagnetic γ′-Fe4N thin films deposited on different single crystal substrates having lattice mismatches from 0% to 11%. It was found that Ms in the γ′-Fe4N film increased with increasing degree of epitaxy and minimizing lattice mismatch between the film and the substrate. Maximum saturation magnetization of 1980±20emu∕cm3 (about 24% higher than previous result) was obtained with LaAlO3(100) substrate having zero lattice mismatch after postannealing of 30min, which is believed to originate from magnetovolume effect in well-ordered epitaxially grown films.
Fabrication and properties of epitaxial growth BiScO3–PbTiO3 thin film via a hydrothermal method
Authors: Zhong C. F. , Wang X. H. , Wen H. , Li L. T. , Nan C. W. , Lin Y. H.
Published: June 2008

Bi Sc O 3 – Pb Ti O 3 thin film was hydrothermally deposited on Nb-doped SrTiO3 [100] single crystal substrate at 180°C with a large thickness of 3.1μm. The x-ray diffraction and high resolution transmission electron microscopy confirmed the epitaxial growth relationship between the BSPT thin film and Nb-STO substrate. Single-crystal-like polarization hysteresis loops were observed, with the remanent polarization of 30μC∕cm2. Piezoelectric force microscopy revealed a single +c domain structure of the film, while exceptional linear piezoelectric response was observed with the effective piezoelectric constant d33* of 65pm∕V. The temperature dependence of the effective d33* indicated that this film exhibited a high temperature stability.
Integration of single carbon nanofibers in standard via interconnects
Authors: Coiffic J. C. , Mariolle D. , Chevalier N. , Olivier S. , Lafond D. , Fayolle M. , Maitrejean S. , Le Poche H.
Published: June 2008

We present an innovative integration process to obtain via interconnects made of one single carbon nanofiber structurally close to multiwall nanotubes. The nanofiber’s growth is obtained thanks to a self-aligned Co based layer which plays the role of catalyst and diffusion barrier at the same time. scanning spreading resistance microscopy has been used to determine locally the electrical properties of such interconnects. We have measured resistances down to 10kΩ for 40nm wide integrated wires.
Synchrotron microbeam x-ray radiation damage in semiconductor layers
Authors: Polvino Sean M. , Murray Conal E. , Kalenci Özgür , Noyan I. C. , Lai Barry , Cai Zhoghou
Published: June 2008

Radiation induced structural damage is observed in silicon-on-insulator (SOI) and SiGe on SOI samples illuminated with monochromatic (11.2keV) x-ray microbeams approximately 250nm in diameter. The x-ray diffraction peaks from the irradiated layers irreversibly degrade with time, indicating permanent structural damage to the crystal lattice. The size of the damaged regions is almost an order of magnitude larger than the beam size. The magnitude of damage decreases as one moves away from the center of the illuminated volume. We discuss the threshold dosage required for damage initiation and possible mechanisms for the observed damage.
Epitaxial BiAlO3 thin film as a lead-free ferroelectric material
Authors: Son J. Y. , Park C. S. , Shin Y.-H.
Published: June 2008

We fabricated high quality epitaxial BiAlO3 thin films that exhibited a relatively high c∕a ratio of about 1.05 with a pseudotetragonal structure. On the atomic force microscope morphology of the BiAlO3 thin film, we observed large terraces with a width of about 1000Å and terrace heights of nearly the same to one lattice constant. This indicates that the BiAlO3 thin film has an ideal layer-by-layer growth mode. The BiAlO3 thin film also showed a good ferroelectric property with a high remanent polarization of about 29μC∕cm2.
Ion exclusion by sub-2-nm carbon nanotube pores
Authors: Fornasiero Francesco , Park Hyung Gyu , Holt Jason K. , Stadermann Michael , Grigoropoulos Costas P. , Noy Aleksandr , Bakajin Olgica
Published: June 2008

Biological pores regulate the cellular traffic of a large variety of solutes, often with high selectivity and fast flow rates. These pores share several common structural features: the inner surface of the pore is frequently lined with hydrophobic residues, and the selectivity filter regions often contain charged functional groups. Hydrophobic, narrow-diameter carbon nanotubes can provide a simplified model of membrane channels by reproducing these critical features in a simpler and more robust platform. Previous studies demonstrated that carbon nanotube pores can support a water flux comparable to natural aquaporin channels. Here, we investigate ion transport through these pores using a sub-2-nm, aligned carbon nanotube membrane nanofluidic platform. To mimic the charged groups at the selectivity region, we introduce negatively charged groups at the opening of the carbon nanotubes by plasma treatment. Pressure-driven filtration experiments, coupled with capillary electrophoresis analysis of the permeate and feed, are used to quantify ion exclusion in these membranes as a function of solution ionic strength, pH, and ion valence. We show that carbon nanotube membranes exhibit significant ion exclusion that can be as high as 98% under certain conditions. Our results strongly support a Donnan-type rejection mechanism, dominated by electrostatic interactions between fixed membrane charges and mobile ions, whereas steric and hydrodynamic effects appear to be less important.
Endosome fusion induced by diphtheria toxin translocation domain
Authors: Antignani Antonella , Youle Richard J.
Published: June 2008

Endosomal cargo travels through a dynamic vesicle network en route to degradation by lysosomes or recycling through the Golgi apparatus back to the cell surface. Rab5 is a key determinant of the early endosomes by organizing effector proteins in specific subdomains and mediating early endosome fusion. We find that early endosome morphogenesis and maturation is disrupted by diphtheria toxin (DT). Rab5 bound endosomes increase in size and in Rab5 content due to luminal toxin exposure, whereas Rab7 positive endosomes are not detectably altered. These changes appear to be caused by an activity of the toxin entry domain (T domain) as mutations inactivating either the receptor binding (CRM107) or ADP-ribosyl transferase (CRM197) activities do not inhibit the effect of DT on endosome morphogenesis. In contrast, mutations in the T domain or diminishing the endosomal pH gradient, which prevents T domain membrane insertion, inhibit these endosome changes. The change in size appears to be due to changing the early endosome fission-fusion equilibrium. The Rab5 membrane exchange rate, assessed with photoactivatable GFP-Rab5, decreases in the presence of DT. These changes to endosomes may reflect activities of the T domain that mediate toxin entry to the cytosol. The nontoxic mutant DT, CRM197, yields a new tool to manipulate endosome dynamics in living cells.
Peripheral circadian clock for the cuticle deposition rhythm in
Drosophila melanogaster
Authors: Ito Chihiro , Goto Shin G. , Shiga Sakiko , Tomioka Kenji , Numata Hideharu
Published: June 2008

Insect endocuticle thickens after adult emergence by daily alternating deposition of two chitin layers with different orientation. Although the cuticle deposition rhythm is known to be controlled by a circadian clock in many insects, the site of the driving clock, the photoreceptor for entrainment, and the oscillatory mechanism remain elusive. Here, we show that the cuticle deposition rhythm is regulated by a peripheral oscillator in the epidermis in
Drosophila melanogaster
. Free-running and entrainment experiments
in vitro
reveal that the oscillator for the cuticle deposition rhythm is independent of the central clock in the brain driving the locomotor rhythms. The cuticle deposition rhythm is absent in null and dominant-negative mutants of clock genes (i.e.,
period
,
timeless
,
cycle
, and
Clock
), indicating that this oscillator is composed of the same clock genes as the central clock. Entrainment experiments with monochromatic light–dark cycles and

cry
b

flies reveal that a blue light-absorbing photoreceptor, cryptochrome (CRY), acts as a photoreceptor pigment for the entrainment of the cuticle deposition rhythm. Unlike other peripheral rhythms in
D. melanogaster
, the cuticle deposition rhythm persisted in

cry
b

and

cry
OUT

mutant flies, indicating that CRY does not play a core role in the rhythm generation in the epidermal oscillator.
TRPM7 facilitates cholinergic vesicle fusion with the plasma membrane
Authors: Brauchi Sebastian , Krapivinsky Grigory , Krapivinsky Luba , Clapham David E.
Published: June 2008

TRPM7, of the transient receptor potential (TRP) family, is both an ion channel and a kinase. Previously, we showed that TRPM7 is located in the membranes of acetylcholine (ACh)-secreting synaptic vesicles of sympathetic neurons, forms a molecular complex with proteins of the vesicular fusion machinery, and is critical for stimulated neurotransmitter release. Here, we targeted pHluorin to small synaptic-like vesicles (SSLV) in PC12 cells and demonstrate that it can serve as a single-vesicle plasma membrane fusion reporter. In PC12 cells, as in sympathetic neurons, TRPM7 is located in ACh-secreting SSLVs. TRPM7 knockdown by siRNA, or abolishing channel activity by expression of a dominant negative TRPM7 pore mutant, decreased the frequency of spontaneous and voltage-stimulated SSLV fusion events without affecting large dense core vesicle secretion. We conclude that the conductance of TRPM7 across the vesicle membrane is important in SSLV fusion.
3
He: cosmological and atomic physics experiments
Authors: Bunkov Yuriy M
Published: June 2008

Because the superfluid
3
He order parameter exhibits many similarities with that of our Universe, the superfluid condensate may be considered as a quantum vacuum that carries various types of quasiparticles and topological defects. The condensate thus provides a test system for the experimental investigation of many general physics problems in cosmology, atomic or nuclear physics that are otherwise difficult or even impossible to investigate experimentally.
Do superconductors change as fast as possible when quenched?
Authors: Rivers Ray , Monaco Roberto , Mygind Jesper , Aaroe Morten , Koshelets Valery
Published: June 2008

If superconductors change as fast as possible as they pass through a phase transition, then the initial domain structure is constrained by causality. We shall see that Josephson junctions do indeed display such behaviour. However, we shall argue that causal bounds arise through the Gaussian nature of the order parameter, which can be thought of as a consequence of instabilities growing as fast as possible.
Involvement of the MADS-Box GeneZMM4in Floral Induction and Inflorescence Development in Maize
Authors: Danilevskaya Olga N. , Meng Xin , Selinger David A. , Deschamps Stéphane , Hermon Pedro , Vansant Gordon , Gupta Rajeev , Ananiev Evgueni V. , Muszynski Michael G.
Published: June 2008

The switch from vegetative to reproductive growth is marked by the termination of vegetative development and the adoption of floral identity by the shoot apical meristem (SAM). This process is called the floral transition. To elucidate the molecular determinants involved in this process, we performed genome-wide RNA expression profiling on maize (Zea mays) shoot apices at vegetative and early reproductive stages using massively parallel signature sequencing technology. Profiling revealed significant up-regulation of two maize MADS-box (ZMM) genes, ZMM4 and ZMM15, after the floral transition. ZMM4 and ZMM15 map to duplicated regions on chromosomes 1 and 5 and are linked to neighboring MADS-box genes ZMM24 and ZMM31, respectively. This gene order is syntenic with the vernalization1 locus responsible for floral induction in winter wheat (Triticum monococcum) and similar loci in other cereals. Analyses of temporal and spatial expression patterns indicated that the duplicated pairs ZMM4-ZMM24 and ZMM15-ZMM31 are coordinately activated after the floral transition in early developing inflorescences. More detailed analyses revealed ZMM4 expression initiates in leaf primordia of vegetative shoot apices and later increases within elongating meristems acquiring inflorescence identity. Expression analysis in late flowering mutants positioned all four genes downstream of the floral activators indeterminate1 (id1) and delayed flowering1 (dlf1). Overexpression of ZMM4 leads to early flowering in transgenic maize and suppresses the late flowering phenotype of both the id1 and dlf1 mutations. Our results suggest ZMM4 may play roles in both floral induction and inflorescence development.
The Transcription Factor VvMYB5b Contributes to the Regulation of Anthocyanin and Proanthocyanidin Biosynthesis in Developing Grape Berries
Authors: Deluc Laurent , Bogs Jochen , Walker Amanda R. , Ferrier Thilia , Decendit Alain , Merillon Jean-Michel , Robinson Simon P. , Barrieu François
Published: June 2008

Among the dramatic changes occurring during grape berry (Vitis vinifera) development, those affecting the flavonoid pathway have provoked a number of investigations in the last 10 years. In addition to producing several compounds involved in the protection of the berry and the dissemination of the seeds, final products of this pathway also play a critical role in berry and wine quality. In this article, we describe the cloning and functional characterization of VvMYB5b, a cDNA isolated from a grape berry (V. vinifera ‘Cabernet Sauvignon’) library. VvMYB5b encodes a protein belonging to the R2R3-MYB family of transcription factors and displays significant similarity with VvMYB5a, another MYB factor recently shown to regulate flavonoid synthesis in grapevine. The ability of VvMYB5a and VvMYB5b to activate the grapevine promoters of several structural genes of the flavonoid pathway was confirmed by transient expression of the corresponding cDNAs in grape cells. Overexpression of VvMYB5b in tobacco (Nicotiana tabacum) leads to an up-regulation of genes encoding enzymes of the flavonoid pathway and results in the accumulation of anthocyanin- and proanthocyanidin-derived compounds. The ability of VvMYB5b to regulate particularly the anthocyanin and the proanthocyanidin pathways is discussed in relation to other recently characterized MYB transcription factors in grapevine. Taken together, data presented in this article give insight into the transcriptional mechanisms associated with the regulation of the flavonoid pathway throughout grape berry development.
A Class I ADP-Ribosylation Factor GTPase-Activating Protein Is Critical for Maintaining Directional Root Hair Growth in Arabidopsis
Authors: Yoo Cheol-Min , Wen Jiangqi , Motes Christy M. , Sparks J. Alan , Blancaflor Elison B.
Published: June 2008

Membrane trafficking and cytoskeletal dynamics are important cellular processes that drive tip growth in root hairs. These processes interact with a multitude of signaling pathways that allow for the efficient transfer of information to specify the direction in which tip growth occurs. Here, we show that AGD1, a class I ADP ribosylation factor GTPase-activating protein, is important for maintaining straight growth in Arabidopsis (Arabidopsis thaliana) root hairs, since mutations in the AGD1 gene resulted in wavy root hair growth. Live cell imaging of growing agd1 root hairs revealed bundles of endoplasmic microtubules and actin filaments extending into the extreme tip. The wavy phenotype and pattern of cytoskeletal distribution in root hairs of agd1 partially resembled that of mutants in an armadillo repeat-containing kinesin (ARK1). Root hairs of double agd1 ark1 mutants were more severely deformed compared with single mutants. Organelle trafficking as revealed by a fluorescent Golgi marker was slightly inhibited, and Golgi stacks frequently protruded into the extreme root hair apex of agd1 mutants. Transient expression of green fluorescent protein-AGD1 in tobacco (Nicotiana tabacum) epidermal cells labeled punctate bodies that partially colocalized with the endocytic marker FM4-64, while ARK1-yellow fluorescent protein associated with microtubules. Brefeldin A rescued the phenotype of agd1, indicating that the altered activity of an AGD1-dependent ADP ribosylation factor contributes to the defective growth, organelle trafficking, and cytoskeletal organization of agd1 root hairs. We propose that AGD1, a regulator of membrane trafficking, and ARK1, a microtubule motor, are components of converging signaling pathways that affect cytoskeletal organization to specify growth orientation in Arabidopsis root hairs.