bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of electronic transport in noncrystalline junctions
Authors: Nardone M. , Karpov V. G. , Shvydka D. , Attygalle M. L. C.
Published: October 2009

A theory of electronic transport in noncrystalline junctions is developed and compared to the experimental data. Junction transport is represented as hopping in both real space and energy space, which is dominated by rare yet exponentially effective optimum channels representing favorable configurations of localized states. Our work correlates the current-voltage characteristics of noncrystalline, thin-film devices with material parameters and predicts large ideality factors that increase under light and depend on applied bias. Also, the frequently observed variations in efficiency and degradation between nominally identical devices are a natural consequence of the theory. The theory is shown to be in good qualitative agreement with our measurements extracted from a large set of experimental data on thin-film cadmium telluride/cadmium sulfide solar cells.
Intermolecular shielding contributions studied by modeling the C13 chemical-shift tensors of organic single crystals with plane waves
Authors: Johnston Jessica C. , Iuliucci Robbie J. , Facelli Julio C. , Fitzgerald George , Mueller Karl T.
Published: October 2009

In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all C13 nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm.
Plasmon-induced terahertz radiation generation due to symmetry breaking in a nonlinear metallic nanodimer
Authors: Zharov A. A. , Noskov R. E. , Tsarev M. V.
Published: October 2009

We suggest an alternative way of terahertz radiation generation utilizing the effect of spontaneous symmetry breaking in a nonlinear metallic nanodimer illuminated by light. We show that the symmetry breaking is caused by instability of plasmon eigenmodes of the system and can lead either to spontaneous magnetization of the dimer or to a periodic self-modulation regime of light scattering. We find that the modulation frequency lies in the terahertz band and may be tuned within a wide range.
Accurate control of ion bombardment in remote plasmas using pulse-shaped biasing
Authors: Kudlacek P. , Rumphorst R. F. , van de Sanden M. C. M.
Published: October 2009

This paper deals with a pulsed biasing technique employed to a downstream expanding thermal plasma. Two pulsed biasing approaches are presented: asymmetric rectangular pulses and modulated pulses with a linear voltage slope during the pulse, and their applicability is discussed on the basis of the intrinsic capacitance of the processed substrate-layer system. The substrate voltage and current waveforms are measured, and the relation to the obtained ion energy distributions is discussed. Accurate control of the ion bombardment is demonstrated for both aforementioned cases, and the cause of broadening of the peaks in the ion energy spectra is determined as well. Moreover, several methods to determine the modulated pulse duration, such that the sloping voltage exactly compensates for the drop of the substrate sheath potential due to charging, are presented and their accuracy is discussed.
Comprehensive study on the deep depletion capacitance-voltage behavior for metal-oxide-semiconductor capacitor with ultrathin oxides
Authors: Cheng Jen-Yuan , Huang Chiao-Ti , Hwu Jenn–Gwo
Published: October 2009

The deep depletion behaviors at the structure of Si/SiO2 with various equivalent oxide thicknesses (EOTs) are comprehensively studied by magnified capacitance versus gate voltage (C-V) curves of metal-oxide-semiconductor (P-substrate) capacitors in this work. According to the correlation between inversion tunneling current and deep depletion, it was found that the initiation voltage of deep depletion phenomenon increases with EOT (2.8–3.1 nm). After the constant voltage stress, the early occurrence of initiation voltage of deep depletion is observed after oxide breakdown. In addition, the uniform area ratio concept is proposed for the electrical characterization of deep depletion via local depletion capacitance model. It was novel for the evaluation of interfacial property between dielectric and Si substrate.
Large birefringence and polarization holographic gratings formed in photocross-linkable polymer liquid crystals comprising bistolane mesogenic side groups
Authors: Emoto Akira , Matsumoto Taro , Yamashita Ayumi , Shioda Tatsutoshi , Ono Hiroshi , Kawatsuki Nobuhiro
Published: October 2009

Polarization gratings with large birefringence are formed in photoreactive polymer liquid crystals with bistolane moiety and terminal cinnamic acid moiety by the use of polarized ultraviolet interference light and subsequent annealing. The polarized ultraviolet light causes the axis-selective photoreaction between the cinnamic acid groups and subsequent annealing induce the reorientation of peripheral molecules without cross-linking along the cross-linked groups. Long bistolane mesogenic moiety exhibits large birefringence in comparison with a biphenyl mesogenic moiety, the value of the induced birefringence in the bistolane mesogenic liquid crystalline (LC) polymer is strongly dependent on both the grating constant and the wavelength of the reconstruction light.
A study of preferential growth of carbon nanotubes with semiconducting behavior grown by plasma-enhanced chemical vapor deposition
Authors: Mizutani Takashi , Ohnaka Hirofumi , Okigawa Yuki , Kishimoto Shigeru , Ohno Yutaka
Published: October 2009

The electrical properties of carbon nanotubes (CNTs) grown by plasma-enhanced chemical vapor deposition (PECVD) have been studied by measuring the I-V characteristics of many CNT-field effect transistors. The ratio of modulation current to total current was as high as 97%, with a small nondepletable OFF current component. This suggests that CNTs with semiconducting behavior were preferentially grown in the PECVD process. Raman scattering spectroscopy of the PECVD-grown CNTs, however, revealed several peaks of the radial breezing mode, which correspond to the presence of metallic CNTs. Scanning gate microscopy measurement of the CNT-FET with an ON/OFF ratio of 100 revealed the existence of a potential barrier in the metallic CNTs. These results suggest that observation of the preferential growth of CNTs with semiconducting behavior in the CNT-FETs fabricated via the present PECVD process results from the opening of the band gap due to defects caused by irradiation damage during the PECVD growth.
Thermomechanical model for the plastic deformation in high power laser diodes during operation
Authors: Martín-Martín A. , Avella M. , Iñiguez M. P. , Jiménez J. , Oudart M. , Nagle J.
Published: October 2009

A thermomechanical model for the mechanism of rapid degradation of AlGaAs based high power laser bars (808 nm) is presented. Thermal stresses induced in the device by local heating around a facet defect by nonradiative recombination and self-absorption of photons are calculated, as well as the conditions for the beginning of plastic deformation, when these thermal stresses overcome the yield strength. The values of the power density and of the local temperature at which the yield limit is surmounted are in agreement with the threshold values for the degradation of Al based lasers given in the literature. The present model can also elucidate the role played by the packaging stress, being able to explain how this stress reduces the optical power density threshold for failure of these lasers.
Influence of gas pressure and applied voltage on Xe excimer radiation from a micro dielectric barrier discharge for plasma display panel
Authors: Uchida Giichiro , Uchida Satoshi , Kajiyama Hiroshi , Shinoda Tsutae
Published: October 2009

We present the influence of gas pressure and applied voltage on Xe excimer radiation from a microdielectric barrier discharge (micro-DBD) in Ne/Xe gas mixture for plasma display panel. Measurements show that the excimer radiation with the 172 nm band lines is strongly observed in the afterglow, and drastically increases with an increase in gas pressure and applied voltage. It is also found that for high gas pressure and low voltage, excimer molecule (Xe2∗) is efficiently produced because of less infrared emission from Xe excited atom. The reaction processes of Xe metastable atom (Xe1s5∗), which is a precursor for Xe2∗, are theoretically analyzed using a one-dimensional fluid model. Increasing gas pressure results in large excimer radiation due to the enhancement of the following three processes, i.e., the conversion process from Xe1s5∗ to Xe2∗, the direct electron impact excitation from ground state to Xe1s5∗, and the collisional de-excitation process from upper level (Xe∗∗) to Xe1s5∗. The simulation analytical result shows that for lower voltage, Xe1s5∗ is efficiently produced due to the increase in the ratio of direct excitation to Xe1s5∗ from ground state and the suppression of the stepwise ionization from Xe1s5∗ by electron collisions. While for high voltage operation of micro-DBD, the recombination process with Xe molecular ion (Xe2+) and electron contributes to the total excimer radiation, which can be responsible for the large excimer radiation observed in experiment.
The effect of pinhole formation/growth on the tunnel magnetoresistance of MgO-based magnetic tunnel junctions
Authors: Teixeira J. M. , Ventura J. , Carpinteiro F. , Araujo J. P. , Sousa J. B. , Wisniowski P. , Freitas P. P.
Published: October 2009

In this study, we focus on how the formation and enlargement of metallic pinholes in MgO barriers (induced by large electrical currents) affect the tunnel magnetoresistance (TMR) of low and high resistance (R) magnetic tunnel junctions. The junctions were deposited by physical vapor deposition with barrier thicknesses of either 0.75 or 1.35 nm. For the parallel state, temperature-dependent R(T) measurements readily revealed a metallic conductance in the low-R sample, indicating that pinholes are already present in its thin barrier; a slight R(T) decrease with increasing temperature is observed for the high-R junction. After applying large current pulses to the low-R sample, we observe that the initially small R-decrease (∼6%) is accompanied by a significant TMR increase (∼20% at 20 K). Higher applied electrical currents continue to decrease R, leading to a gradual but steady TMR decrease. In contrast, the high-R sample exhibits a sharp and immediate decrease in TMR as soon as the first pinhole is formed. The origin of these effects will be discussed in terms of a thermally induced improvement of the barrier/electrode interfaces and the possibility of a magnetoresistance mechanism occurring through the metallic pinholes.
Evidence of disorder induced magnetic spin glass phase in Sr2FeMoO6 double perovskite
Authors: Poddar Asok , Bhowmik R. N. , Muthuselvam I. Panneer , Das Nilanjan
Published: October 2009

The present work described the disorder induced magnetic properties of Sr2FeMoO6 (SFMO) samples. The crystal structure and magnetic order of SFMO samples with nanosized grains were studied using x-ray diffraction spectrum, scanning electron microscope morphology, and magnetic measurements. Thermal annealing of as prepared chemical routed materials showed an increase in grain size and in the magnetic moment per formula unit. A small decrease in magnetic moment was noted at higher annealing temperature. At the same time, the ac susceptibility measurement indicated the presence of a magnetic spin glass phase in the material, coexisting with the ferromagnetic matrix. The observation of the magnetic glassy phase confirmed the presence of intrinsic disorder in the lattice structure of SFMO. The signature of intrinsic disorder in the samples, irrespective of annealing temperatures, is also realized from the splitting of temperature dependent field cooled and zero field cooled magnetization curves. Such magnetic splitting in the temperature dependence of magnetization curves is suppressed at a higher magnetic field. A careful analysis of the temperature and field dependent magnetization data provided more insight on the grain size dependent disorder in the double perovskite structure.
Environmental stability of candidate dielectrics for GaN-based device applications
Authors: Herrero A. M. , Gila B. P. , Gerger A. , Scheuermann A. , Davies R. , Abernathy C. R. , Pearton S. J. , Ren F.
Published: October 2009

The thermal and chemical stability of potential dielectrics for GaN-based devices in a GaN metal organic chemical vapor deposition (MOCVD) environment is investigated, and their suitability for use as a gate dielectric and as a regrowth mask for the selective area growth of GaN is discussed. Thin films of MgO, Sc2O3, and Sc2O3/MgO were grown by molecular beam epitaxy on GaN/sapphire substrates and then annealed in a MOCVD reactor under GaN growth conditions except for the lack of trimethylgallium. All films were processed into metal-oxide-semiconductor diodes and were characterized before and after being annealed using atomic force microscopy, x-ray reflectivity, x-ray photoelectron spectroscopy, current-voltage (I-V), and capacitance-voltage (C-V) measurements. The Gibbs free energy of all possible reactions was calculated, and their probability and possible influence on the characterization results is examined. After being annealed, the atomic force microscopy of the oxide films showed some degree of roughening for all of them. Despite the surface roughening, all the oxide films examined showed potential for use as a regrowth mask. The MOCVD anneal caused the electrical properties of the MgO film to degrade considerably, and the Sc2O3 films were unable to be electrically characterized after annealing due to shorting, which is believed to be caused by the formation of a ScN layer on the surface. The effect of the thickness of the Sc2O3 cap for MgO films was investigated. The characterization results indicate that the Sc2O3 film dissolved into MgO during annealing and that a ScN film did not form on the surface. Of all the oxide films examined in this study, the Sc2O3/MgO stack with the thinner Sc2O3 cap exhibited the greatest stability with respect to its electrical properties.
Hybrid vertical architecture transistor with magnetic-field-dependent current amplification as organic magnetocurrent investigation tool
Authors: Yusoff Abd R. B. M. , Hümmelgen Ivo A.
Published: October 2009

We prepare hybrid vertical architecture transistors that show magnetic-field-dependent electrical characteristics using tris-(8-hydroxyquinoline) aluminum (Alq3), sulfonated polyaniline (SPAN), and n-type silicon. These transistors have n-type silicon as collector, a 200 nm thick SPAN layer as the base, and an emitter composed by Al/Ca/Alq3(60 nm) layers, showing permeable-base transistor characteristics. The emitter shows very high magnetocurrent when the Al/Ca is negatively polarized with respect to the SPAN, which is the condition of forward active operation mode. The rate of electrons that cross emitter and base layers and reach the collector is affected by the magnetic field, leading to magnetic-field-dependent common-emitter current gain larger than 1. We also demonstrate that the magnetocurrent is due to the contribution of electrons.
Atom probe microscopy of three-dimensional distribution of silicon isotopes in Si28∕Si30 isotope superlattices with sub-nanometer spatial resolution
Authors: Shimizu Yasuo , Kawamura Yoko , Uematsu Masashi , Itoh Kohei M. , Tomita Mitsuhiro , Sasaki Mikio , Uchida Hiroshi , Takahashi Mamoru
Published: October 2009

Laser-assisted atom probe microscopy of 2 nm period Si28∕Si30 isotope superlattices (SLs) is reported. Three-dimensional distributions of Si28 and Si30 stable isotopes are obtained with sub-nanometer spatial resolution. The depth resolution of the present atom probe analysis is much higher than that of secondary ion mass spectrometry (SIMS) even when SIMS is performed with a great care to reduce the artifact due to atomic mixing. Outlook of Si isotope SLs as ideal depth scales for SIMS and three-dimensional position standards for atom probe microscopy is discussed.
Phase transitions in Ge–Te phase change materials studied by time-resolved x-ray diffraction
Authors: Raoux Simone , Muñoz Becky , Cheng Huai-Yu , Jordan-Sweet Jean L.
Published: October 2009

Resistivity versus temperature measurements and time-resolved x-ray diffraction were used to study Ge–Te phase change materials. Resistivity versus temperature measurements showed one sharp drop in resistivity for films with 30, 50, and 70 at. % Ge, two steps for films with 40 at. % Ge, and a gradual transition for films with 60 at. % Ge. Films with 30, 50, and 70 at. % Ge crystallized in a single-step process with GeTe and Te, only GeTe, and GeTe and Ge diffraction peaks, respectively. Films with 40 and 60 at. % Ge crystallized in a two-step process with GeTe peaks appearing first and additional Te or Ge peaks, respectively, appearing at higher temperature.
Linear and nonlinear optical properties of a series of Ni-dithiolene derivatives
Authors: Serrano-Andrés Luis , Avramopoulos Aggelos , Li Jiabo , Labéguerie Pierre , Bégué Didier , Kellö Vladimir , Papadopoulos Manthos G.
Published: October 2009

Some linear and nonlinear optical (NLO) properties of Ni(SCH)4 and several of its derivatives have been computed by employing a series of basis sets and a hierarchy of methods (e.g., HF, DFT, coupled cluster, and multiconfigurational techniques). The electronic structure of Ni(SCH)4 has been also analyzed by using CASSCF/CASPT2, ab initio valence bond, and DFT methods. In particular we discuss how the diradicaloid character (DC) of Ni(SCH)4 significantly affects its NLO properties. The quasidegeneracy of the two lowest-energy singlet states 1 A1g and 1 B11u, the clear DC nature of the former, and the very large number of low-lying states enhance the NLO properties values. These particular features are used to interpret the NLO properties of Ni(SCH)4. The DC of the considered derivatives has been estimated and correlated with the NLO properties. CASVB computations have shown that the structures with Ni(II) are the dominant ones, while those with Ni(0) and Ni(IV) have negligible weight. The weights of the four diradical structures were discussed in connection with the weight of the structures, where all the electrons are paired. Comparative discussion of the properties of Ni(SCH)4 with those of tetrathia fulvalene demonstrates the very large effect of Ni on the properties of the Ni-dithiolene derivatives. A similar remarkable effect on the NLO properties is produced by one or two methyl or C3S groups. The considered Ni-dithiolene derivatives have exceptionally large NLO properties. This feature in connection with their other physical properties makes them ideal candidates for photonic applications.
Comparison of electrical properties and deep traps in p-AlxGa1−xN grown by molecular beam epitaxy and metal organic chemical vapor deposition
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Kozhukhova E. A. , Dabiran A. M. , Chow P. P. , Wowchak A. M. , Lee In-Hwan , Ju Jin-Woo , Pearton S. J.
Published: October 2009

The electrical properties, admittance spectra, microcathodoluminescence, and deep trap spectra of p-AlGaN films with an Al mole fraction up to 45% grown by both metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were compared. The ionization energy of Mg increases from 0.15 to 0.17 eV in p-GaN to 0.3 eV in 45% Al p-AlGaN. In p-GaN films grown by MBE and MOCVD and in MOCVD grown p-AlGaN, we observed additional acceptors with a concentration an order lower than that of Mg acceptors, with a higher hole capture cross section and an ionization energy close to that of Mg. For some of the MBE grown p-AlGaN, we also detected the presence of additional acceptor centers, but in that case the centers were located near the p-AlGaN layer interface with the semi-insulating AlGaN buffer and showed activation energies considerably lower than those of Mg.
Faraday rotation in magnetite-polymethylmethacrylate core-shell nanocomposites with high optical quality
Authors: Lopez-Santiago A. , Gangopadhyay P. , Thomas J. , Norwood R. A. , Persoons A. , Peyghambarian N.
Published: October 2009

Wavelength dependent Faraday rotation measured at room temperature in a polymer containing varying concentrations of crosslinked magnetite core poly(3-methyl)methacrylate (PMMA) shell nanocomposite particles is reported. The magnitude of the FR in these composites appears to be strongly dependent on the concentration of the particles, the wavelength of measurement, and the size and shape of the nanoparticles. Comparison of the figure of merit of 2.1° in these core-shell nanocomposites to that of 4.2° for yttrium iron garnet at 980 nm indicates that these nanocomposites may find applications in various magnetic and magneto-optic sensors and devices.
Tradeoff regimes of lifetime in amorphous silicon thin-film transistors and a universal lifetime comparison framework
Authors: Hekmatshoar Bahman , Wagner Sigurd , Sturm James C.
Published: October 2009

We report that the dependence of the lifetime of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) versus channel sheet resistance (Rsheet) exhibits two distinctly different regimes. At low Rsheet (high gate electric field) the lifetime is strongly dependent on Rsheet, decreasing as Rsheet is decreased. At high Rsheet (low gate electric field), the lifetime becomes independent of Rsheet. These two regimes of lifetime are dominated by different degradation mechanisms. By including hydrogen dilution in the deposition process, the extrapolated time for the 10% and 50% decay of the TFT current under dc operation in the low gate field regime can be raised to over 2 and 1000 yr, respectively.
Microviscoelasticity of adhesive hard sphere dispersions: Tracer particle microrheology of aqueous Pluronic L64 solutions
Authors: Kloxin Christopher J. , van Zanten John H.
Published: October 2009

DWS-based tracer particle microrheology is demonstrated to be a useful way to study the dynamics of aqueous Pluronic L64 solutions, which is viewed as a model adhesive hard sphere (AHS) system. The short-time dynamics of aqueous Pluronic L64 solutions indicate a purely hydrodynamic high frequency microviscosity as predicted by Batchelor for colloidal dispersions. The evolution of the micellar dynamics reveals a zero shear microviscosity in good agreement with steady shear viscosity measurements. As the temperature is increased, the dynamics become dominated by an apparent attractive intermicellar potential observed in microscopic creep measurements. While Pluronic L64 solutions have been reported to form a percolated micellar network, DWS-based microviscoelasticity measurements do not detect the previously observed G′∼G″∼ωΔ scaling expected for a static percolated network at low frequencies. This most likely owes to the fact that tracer particle microrheology is dominated by local Pluronic L64 micelle dynamics in the near sphere region and not the bulk mechanical properties as measured by traditional rheometry. The sensitivity of tracer particle microrheological measurements to the true dynamic nature of the percolated network in weak physical gels highlights the distinct differences between these micro- and macrorheology measurement techniques. Such discrepancies should be most evident in systems that are dominated by association processes such as those occurring in AHS solutions or polymer solutions approaching a phase boundary. Despite this, the AHS potential is qualitatively consistent with the results found here.
Optimization of the first order gradiometer for small sample magnetization measurements using pulse integrating magnetometer
Authors: Trojanowski S. , Ciszek M.
Published: October 2009

In the paper we present an analytical calculation method for determination of the sensitivity of a pulse field magnetometer working with a first order gradiometer. Our considerations here are especially focused on a case of magnetic moment measurements of very small samples. Derived in the work analytical equations allow for a quick estimation of the magnetometer’s sensitivity and give also the way to its calibration using the sample simulation coil method. On the base of the given in the paper calculations we designed and constructed a simple homemade magnetometer and performed its sensitivity calibration.
Strain-relief pattern as guide for the formation of surface-supported bimolecular nanoribbons
Authors: Aït-Mansour K. , Cañas-Ventura M. E. , Ruffieux P. , Jaafar R. , Bieri M. , Rieger R. , Müllen K. , Fasel R. , Gröning O.
Published: October 2009

We demonstrate the suitability of the Ag/Pt(111) strain-relief pattern as efficient template for controlling the formation of well defined heteromolecular nanostructures. Two different species of molecular building blocks with complementary end-group functionalities are combined on this surface, which results in the formation of robust bimolecular nanoribbons driven by the interplay of the site specific adsorption on the strain-relief pattern with the highly directional intermolecular hydrogen-bonding intrinsic to the free bimolecular system.
Kelvin force gradient microscopy of pBTTT transistors in both the linear and saturation electrical regimes
Authors: Bain S. , Smith D. C. , Wilson N. R. , Carrasco-Orozco M.
Published: October 2009

Kelvin force gradient microscopy of pBTTT transistors biased in both the linear and saturation electrical regimes is presented. The linear regime potential profiles are dominated by the contacts and the true material mobility, 0.11±0.01cm2V−1s−1, is ten times higher than that derived from device electrical characteristics. In the saturation regime the potential profiles are well fitted by a simple model assuming a very weakly gate potential dependent mobility in the range 0.021–0.028cm2V−1s−1. These measurements indicate that contrary to the conclusion drawn from the device electrical characteristics, the linear mobility is larger than the saturation mobility.
Electrical and optical characteristics of silicon nanocrystal solar cells
Authors: Kim Sang-Kyun , Cho Chang-Hee , Kim Baek-Hyun , Park Seong-Ju , Won Lee Jae
Published: October 2009

We investigated the relationship between the absorption in silicon nanocrystals (Si NCs) and the photocurrent of Si NC solar cells. Here, the absorption of Si NCs in the blue and green light regions was enhanced by up to 14 times compared to bulk Si. In addition, the photocurrent in Si NC solar cells was found to originate from absorption in the Si NCs. The photocurrent of the Si NC solar cells, however, was smaller than the predicted value due to the slow carrier transport in the silicon nitride film containing the Si NCs.
First principles calculation of the thermal conductance of GaN/Si and GaN/SiC interfaces as functions of the interface conditions
Authors: Kazan M.
Published: October 2009

First principles calculation and a statistical model are employed to calculate the thermal conductance (TC) of the interfaces GaN/Si and GaN/SiC. For an interface with zero tangential correlation length (L), TC of both GaN/Si and GaN/SiC increases with increasing the interface roughness. For an infinite L, TC of GaN/Si is almost insensitive to the roughness, while TC of GaN/SiC decreases rapidly with increasing the interface roughness. Generally speaking, for L=0, TC increases with increasing the interface roughness, whereas, for L=∞ the effect of the interface roughness on the interface TC depends on the phonon characteristics of the materials in contact.
Alignment of electrospun nanofibers using dielectric materials
Authors: Yan Hao , Liu Luqi , Zhang Zhong
Published: October 2009

Morphology control of electrospun nanofibers is one of the major tasks in order to facilitate their wide potential applications. In the present work, various dielectric materials were employed as parallel collectors for obtaining electrospun nanofiber meshes with improved nanofiber alignment. Experimental results presented the relationship between nanofiber alignment and the collectors’ relative permittivity. Theoretical simulations revealed that the electric field can be tuned manually by choosing different dielectric materials as collectors. The horizontal electric field strength Ex is a key factor to stretch electrospun jet across gap, and to eventually achieve aligned nanofiber meshes. This work is believed to be able to lead to a deeper understanding to the mechanisms of nanofiber alignment, and should be of help to the design of practical collecting structures for promoting the applications of electrospinning technique.
Ionic-to-electronic conductivity transition in an oxide glass doped with gold
Authors: Jain Himanshu , Issa Ahmed , Anavekar Rajan V. , Böhmer Roland , Kanert Otmar , Küchler Reiner
Published: October 2009

Gold doped ruby glasses are classical examples of metal-glass nanocomposites that have been investigated for their striking optical properties. For the example of weakly Au doped lithium-borate glasses these materials are shown to exhibit a transition from ionic to electronic conduction within the same sample. It is achieved via appropriate heat treatment, presumably by introducing polarons formed from the trapping of electrons at partially ionized gold atoms. This unique electrical response is expected to introduce new functionality to this class of nanocomposites.
Two-particle microrheology at oil-water interfaces
Authors: Wu Chih-yuan , Song Yanmei , Dai Lenore L.
Published: October 2009

We have explored and validated two-particle (2P) microrheology at polydimethylsiloxane (oil)-water interfaces using confocal laser scanning microscopy. The loss and storage moduli of the oil-water interfaces as a function of frequency are quantified using different tracer particles. In contrast to one-particle interfacial microrheology in which the measured rheological results depend largely on the surface chemistry of tracer particles, the work here suggests that 2P tracking significantly minimizes the tracer particle effect. The viscous response dominates the oil-water interfaces and varies linearly with frequency, over the experimental range of the oil viscosity and frequency.
Lattice model for strained nanoscale ferroelectric capacitors: Investigation on fundamental size limits in ferroelectricity
Authors: Wang Xing-Yuan , Wang Ying-Long , Yang Rong-Jia
Published: October 2009

To study the size effect for ferroelectricity of epitaxial SrRuO3/BaTiO3/SrRuO3 capacitors, we modify the mean-field Landau-type theory by incorporating the dipole-dipole interaction energy density, realistic lattice structure, epitaxial stress, and metal electrodes. The calculated depolarization field is consistent well with the experimental data. The critical thickness tc is predicted to be six unit cells, according to the result calculated by first-principle calculations. We demonstrate that tc can be reduced to four unit cells by selecting the Pt electrode. The compressive strain can reduce the tc. We discover the decrease of the lateral dimensions of the film can enhances the spontaneous polarization.
UV-activated room-temperature gas sensing mechanism of polycrystalline ZnO
Authors: Fan Shan-Wei , Srivastava Arvind K. , Dravid Vinayak P.
Published: October 2009

The effects of UV illumination on the electronic properties and gas sensing performance of ZnO are reported. It is found that UV light improves the sensitivity and the sensor response and recovery rate. By investigating the photoresponse behavior of ZnO, we observe that the electrons generated by UV light promote the adsorption of oxygen and form the photoinduced oxygen ions [O2−(hv)]. These ions [O2−(hv)] are responsible for the room-temperature gas sensing phenomena and promise enhanced sensor performance through further optimization.
Gyrokinetic δf particle simulations of toroidicity-induced Alfvén eigenmode
Authors: Lang Jianying , Chen Yang , Parker Scott E. , Fu Guo-Yong
Published: October 2009

Gyrokinetic δf particle simulation is used to investigate toroidicity-induced Alfvén eigenmodes (TAEs). Both thermal ions and energetic particles are fully kinetic, but a reduced fluid model is used for the electrons. Simulation of a single n=2 global TAE is carefully analyzed and benchmarked with an eigenmode analysis, and a very good agreement is achieved in both mode structure and mode frequency. The instability of the mode in the presence of energetic particles is demonstrated. In particular, gyrokinetic simulations demonstrate the kinetic damping effect of thermal ions, where the finite radial structure of kinetic Alfvén waves is well resolved and the damping rate is compared to and found to agree well with analytical theory.
Dynamical disorder in 2-methyl-4-nitroaniline and its deuterated analogue crystals studied by Fourier transform infrared and nuclear magnetic resonance
Authors: Okwieka Urszula , Hołderna-Natkaniec Krystyna , Misiaszek Tomasz , Medycki Wojciech , Baran Jan , Magdalena Szostak M.
Published: October 2009

The Fourier transform infrared spectra of the thin layers of 2-methyl-4-nitroaniline (MNA) and its deuterated analog were recorded in the 500–4000 cm−1 region in the 10–300 K temperature range. Activation energies of the –CH3, –NH2, and –NO2 groups reorientations were estimated. The H1-NMR spin-lattice relaxation time, T1, and the second moment of H1-NMR resonance line, M2, measured in the 80–298 K temperature range, were used to determine the parameters of the –CH3 group motion. The experimental potential barriers for the amine, nitro, and methyl group reorientations are considered in the context of strengths of the N–H…O, C–H…O intermolecular hydrogen bonds, and other short contacts, recognized recently [U. Okwieka et al., J. Raman Spectrosc. 39, 849 (2008)], and they agree with the barriers calculated by quantum chemical methods. The dynamical disorder found in the MNA crystal in the large temperature range seems to be important from the point of view of its nonlinear optical and other properties.
Absolute and convective instability of cylindrical Couette flow with axial and radial flows
Authors: Martinand Denis , Serre Eric , Lueptow Richard M.
Published: October 2009

Imposing axial flow in the annulus and/or radial flow through the cylindrical walls in a Taylor–Couette system alters the stability of the flow. Theoretical methods and numerical simulations were used to determine the impact of imposed axial and radial flows, homogeneous in the axial direction, on the first transition of Taylor–Couette flow in the framework of convective and absolute instabilities. At low axial Reynolds numbers the convective instability is axisymmetric, but convective helical modes with an increasing number of helices having a helicity opposite that of the base flow dominate as the axial flow increases. The number of helices and the critical Taylor number are affected only slightly by the radial flow. The flow becomes absolutely unstable at higher Taylor numbers. Absolutely unstable axisymmetric modes occur for inward radial flows, while helical absolute instability modes having a helicity identical to that of the base flow occur at high enough axial Reynolds numbers for outward radial flow.
Spin relaxation of fullerene C70 photoexcited triplet in molecular glasses: Evidence for onset of fast orientational motions of molecules in the matrix near 100 K
Authors: Uvarov Mikhail N. , Kulik Leonid V. , Dzuba Sergei A.
Published: October 2009

Electron spin echo (ESE) was applied to study transversal spin relaxation of photoexcited triplet state of fullerene C70 molecules in glassy o-terphenyl and cis-/trans-decalin matrices (glass transition temperatures of 243 and 137 K, respectively). The relaxation rate T2−1 was found to increase sharply above 110 K in o-terphenyl and above 100 K in decalin. It is suggested that this increase arises from interaction of C370 pseudorotation with fast molecular librations in the matrix. Both these types of motion involve atomic vibrations and are uniaxial in their nature, the known literature data on Raman light scattering and others indicate that molecular librations may be thermally activated in glasses just near 100 K. The increase in T2−1 near 100 K is not observed for photoexcited triplet state of fullerene C60, for which pseudorotation is not uniaxial. As the fullerene molecule has a size much larger than that for glass solvent molecules, it is likely that molecular librations in the matrix are of collective nature.
Controlled growth of carbon nanotubes on electrodes under different bias polarity
Authors: Gao Y. , Zhou Y. S. , Xiong W. , Mahjouri-Samani M. , Mitchell M. , Lu Y. F.
Published: October 2009

Carbon nanotubes (CNTs) of different alignments, such as surface-bounded and vertically aligned arrays, enable applications in different fields. In this study, controlled growth of CNTs with different alignments was achieved by electrically biasing catalyzed electrodes with different polarities in a laser-assisted chemical vapor deposition process. CNT growth was suggested to be guided by the movement of electrically charged catalyst-nanoparticles under the influence of an external electric field. This discovery provides a convenient approach to control the alignment of CNT arrays for different applications.
Magnetoresistance of CdSe/CdS quantum dot films
Authors: Pourret Alexandre , Ramirez Adan , Guyot-Sionnest Philippe
Published: October 2009

Films of n-type CdSe/CdS colloidal quantum dots show positive and negative magnetoresistance (MR) with magnetic field lower than 0.4 T. The MR sign and magnitude vary with the occupancy of the lowest state, the temperature, and the electrical field. Low occupancy leads to +20% MR at 10 K, while high occupancy leads to ∼−5% MR. The MR reaches +35% in mixed samples of large and small dots. Intrinsic films are photoconductive and display positive MR.
Disease Painting or Painting Disease: How Does Illness and Hospitalisation Affect Children's Artistry?
Authors: Bayrakci Benan , Forouz Aria , Şahin Ahmet B , Abali Mustafa , Aliyeva Gyulten Z
Published: October 2009

There are numerous speculations about famous artists and how their perception was affected by their medical conditions. In this study, we examined how illness and hospitalisation affect children's art. A total of 157 paintings by 122 hospitalised children were interpreted by three reputed artists. Works of ill children were compared with those of a control group from an international art exhibition. We also comment on how diseases influenced the technique of famous artists to further examine the possible impact of illness on the artistry of hospitalised children. Developmental delay in painting was evident in the study group. Use of ready-made schemas was a common practice (55%). 56% of the work from patients older than eight years failed in perspective and site perception. The theme in 89% of the drawings had no human figures. Projection of self sufferings, prominent elementary lines, and reflection of distorted perception could be clearly recognised in various study materials; anxiety about assigned surgery was exhibited by scribbling. There exists a close relationship between medicine and humanities. The interpretation of fine art from a medical perspective may help to increase our appreciation of the suffering of an individual. It is obvious that diseases change the artistic style and inner perspective. The question is how do healthcare specialists view this?
Voluntary Action Affects Perception of Bistable Motion Display
Authors: Mitsumatsu Hidemichi
Published: October 2009

Hand action can bias the perceived direction of ambiguously moving objects (Wohlschlager, 2000 Vision Research40 925–930). A common coding framework has been proposed to account for action–perception interaction, assuming goal-based feature matching between action and perception [Prinz, 2003, in Agency and Self-Awareness (New York: Oxford University Press)]. I investigated whether and how movement representation and a distal action goal are implicated in biased motion perception using a stream–bounce display as stimulus. By moving a mouse, participants controlled the progression of disks, which were initially separated and then moved toward each other. Mouse movement was found to bias perception toward the stream when the directional motion of the mouse and disk were consistent; however, this biased perception was not observed when the directions were orthogonal. Subsequent experiments revealed that this induced stream percept could not be attributed to the processes of attention, and the action goal of disk control was critical to the occurrence of biased motion perception. These results suggest that feature matching occurs at the level of movement representation, and the action goal is important in linking movement representation to perceptual representation.
Duration Discrimination in Crossmodal Sequences
Authors: Grondin Simon , McAuley J Devin
Published: October 2009

Four duration-discrimination experiments were carried out to compare crossmodal and unimodal timing conditions. For all experiments, participants were presented with two sequences, each consisting of 1 or 4 time intervals (marked by 2 or 5 signals), and asked to indicate whether the interval(s) of the second sequence was (were) shorter or longer than the interval(s) of the first. Markers in the first and second sequences were, respectively, tones and flashes (experiment 1), flashes and tones (experiment 2), both flashes (experiment 3), and both tones (experiment 4). In all modality conditions, except when using only tones (experiment 4), increasing the number of repetitions of the variable interval reduced duration-discrimination thresholds, independently of whether the fixed interval was presented first or second within the sequence pair. Moreover, judgments about sequence timing were best for tones–tones sequence pairs, worst for flashes–flashes sequence pairs, and intermediate for crossmodal (flashes–tones or tones–flashes) sequences. Finally, presenting a fixed interval in the first sequence resulted in better discrimination than presenting a variable interval in the first sequence. Implications for theories of timing are discussed.
Macroevolution and the biological diversity of plants and herbivores
Authors: Futuyma Douglas J. , Agrawal Anurag A.
Published: October 2009

Terrestrial biodiversity is dominated by plants and the herbivores that consume them, and they are one of the major conduits of energy flow up to higher trophic levels. Here, we address the processes that have generated the spectacular diversity of flowering plants (>300,000 species) and insect herbivores (likely >1 million species). Long-standing macroevolutionary hypotheses have postulated that reciprocal evolution of adaptations and subsequent bursts of speciation have given rise to much of this biodiversity. We critically evaluate various predictions based on this coevolutionary theory. Phylogenetic reconstruction of ancestral states has revealed evidence for escalation in the potency or variety of plant lineages' chemical defenses; however, escalation of defense has been moderated by tradeoffs and alternative strategies (e.g., tolerance or defense by biotic agents). There is still surprisingly scant evidence that novel defense traits reduce herbivory and that such evolutionary novelty spurs diversification. Consistent with the coevolutionary hypothesis, there is some evidence that diversification of herbivores has lagged behind, but has nevertheless been temporally correlated with that of their host-plant clades, indicating colonization and radiation of insects on diversifying plants. However, there is still limited support for the role of host-plant shifts in insect diversification. Finally, a frontier area of research, and a general conclusion of our review, is that community ecology and the long-term evolutionary history of plant and insect diversification are inexorably intertwined.
Rapid DNA loss as a counterbalance to genome expansion through retrotransposon proliferation in plants
Authors: Hawkins Jennifer S. , Proulx Stephen R. , Rapp Ryan A. , Wendel Jonathan F.
Published: October 2009

Transposable elements, particularly LTR-retrotransposons, comprise the primary vehicle for genome size expansion in plants, while DNA removal through illegitimate recombination and intrastrand homologous recombination serve as the most important counteracting forces to plant genomic obesity. Despite extensive research, the relative impact of these opposing forces and hence the directionality of genome size change remains unknown. In
Gossypium
(cotton), the 3-fold genome size variation among diploids is due largely to copy number variation of the
gypsy
-like retrotransposon
Gorge3
. Here we combine comparative sequence analysis with a modeling approach to study the directionality of genome size change in
Gossypium
. We demonstrate that the rate of DNA removal in the smaller genomes is sufficient to reverse genome expansion through
Gorge3
proliferation. These data indicate that rates of DNA loss can be highly variable even within a single plant genus, and that the known mechanisms of DNA loss can indeed reverse the march toward genomic obesity.
Mechanisms of gold biomineralization in the bacterium
Cupriavidus metallidurans
Authors: Reith Frank , Etschmann Barbara , Grosse Cornelia , Moors Hugo , Benotmane Mohammed A. , Monsieurs Pieter , Grass Gregor , Doonan Christian , Vogt Stefan , Lai Barry , Martinez-Criado Gema , George Graham N. , Nies Dietrich H. , Mergeay Max , Pring Allan , Southam Gordon , Brugger Joël
Published: October 2009

While the role of microorganisms as main drivers of metal mobility and mineral formation under Earth surface conditions is now widely accepted, the formation of secondary gold (Au) is commonly attributed to abiotic processes. Here we report that the biomineralization of Au nanoparticles in the metallophillic bacterium
Cupriavidus metallidurans
CH34 is the result of Au-regulated gene expression leading to the energy-dependent reductive precipitation of toxic Au(III)-complexes.
C. metallidurans
, which forms biofilms on Au grains, rapidly accumulates Au(III)-complexes from solution. Bulk and microbeam synchrotron X-ray analyses revealed that cellular Au accumulation is coupled to the formation of Au(I)-S complexes. This process promotes Au toxicity and
C. metallidurans
reacts by inducing oxidative stress and metal resistances gene clusters (including a Au-specific operon) to promote cellular defense. As a result, Au detoxification is mediated by a combination of efflux, reduction, and possibly methylation of Au-complexes, leading to the formation of Au(I)-C-compounds and nanoparticulate Au
0
. Similar particles were observed in bacterial biofilms on Au grains, suggesting that bacteria actively contribute to the formation of Au grains in surface environments. The recognition of specific genetic responses to Au opens the way for the development of bioexploration and bioprocessing tools.