bluuebunny/crossref_metadata_2025 huggingface dataset:
Equivalency principle for magnetoelectroelastic multiferroics with arbitrary microstructure: The phase field approach
Authors: Ni Yong , He Linghui , Khachaturyan Armen G.
Published: July 2010

A phase field method is proposed to determine the equilibrium fields of a magnetoelectroelastic multiferroic with arbitrarily distributed constitutive constants under applied loadings. This method is based on a developed generalized Eshelby’s equivalency principle, in which the elastic strain, electrostatic, and magnetostatic fields at the equilibrium in the original heterogeneous system are exactly the same as those in an equivalent homogeneous magnetoelectroelastic coupled or uncoupled system with properly chosen distributed effective eigenstrain, polarization, and magnetization fields. Finding these effective fields fully solves the equilibrium elasticity, electrostatics, and magnetostatics in the original heterogeneous multiferroic. The paper formulates a variational principle proving that the effective fields are minimizers of appropriate close-form energy functional. The proposed phase field approach produces the energy minimizing effective fields (and thus solving the general multiferroic problem) as a result of artificial relaxation process described by the Ginzburg–Landau–Khalatnikov kinetic equations.
Pyrimidine and halogenated pyrimidines near edge x-ray absorption fine structure spectra at C and N K-edges: experiment and theory
Authors: Bolognesi P. , O’Keeffe P. , Ovcharenko Y. , Coreno M. , Avaldi L. , Feyer V. , Plekan O. , Prince K. C. , Zhang W. , Carravetta V.
Published: July 2010

The inner shell excitation of pyrimidine and some halogenated pyrimidines near the C and N K-edges has been investigated experimentally by near edge x-ray absorption fine structure spectroscopy and theoretically by density functional theory calculations. The selected targets, 5-Br-pyrimidine, 2-Br-pyrimidine, 2-Cl-pyrimidine, and 5-Br-2-Cl-pyrimidine, allow the effects of the functionalization of the pyrimidine ring to be studied either as a function of different halogen atoms bound to the same molecular site or as a function of the same halogen atom bound to different molecular sites. The results show that the individual characteristics of the different spectra of the substituted pyrimidines can be rationalized in terms of variations in electronic and geometrical structures of the molecule depending on the localization and the electronegativity of the substituent.
Growth and electric-elastic properties of KTiOAsO4 single crystal
Authors: Gao Z. L. , Sun Y. X. , Yin X. , Wang S. P. , Jiang M. H. , Tao X. T.
Published: July 2010

We report the successful growth of high quality potassium titanyl arsenate, KTiOAsO4 (KTA) crystals with size of 34×67×72 mm3 through a K6As4O13 based flux method. The dielectric, piezoelectric, and elastic constants of KTA crystal were determined by the resonance technique and impedance analysis, respectively. The thermal dependence of the elastic constants were also determined by the transmission method over −50–110 °C. The first, second, and third order temperature coefficients of the elastic constants were calculated (T0=25 °C).
A mixed large eddy simulation model based on the residual-based variational multiscale formulation
Authors: Wang Z. , Oberai A. A.
Published: July 2010

A mixed model based on the residual-based variational multiscale (RBVM) formulation is proposed for the large eddy simulation of turbulent flows. In this model the cross stresses are modeled by the RBVM term and the Reynolds stresses are represented by a Smagorinsky eddy viscosity. The mixed model is motivated by an a priori analysis of a turbulent flow field that indicates that the RBVM term correctly models the dissipation induced by the cross-stress term but underpredicts the contribution from the Reynolds stress term. The dynamic version of the mixed model is implemented in a Fourier-spectral code in order to predict the decay of incompressible, three-dimensional homogeneous isotropic turbulence. It is found that the mixed model yields better agreement with direct numerical simulation solution than the dynamic Smagorinsky and the RBVM models, which are its building blocks.
Charge carrier self-organization in ferroelectromagnetic semiconductors Eu0.8Ce0.2Mn2O5
Authors: Golovenchits E. I. , Sanina V. A. , Zalesskii V. G. , Scheglov M. P.
Published: July 2010

Giant permittivity (ε′∼104) and ferromagnetism have been observed above 185K (including room temperature) in single crystals of the dilute semiconductor manganite-ferroelectromagnetic Eu0.8Ce0.2Mn2O5 in the investigations of x-ray diffraction, dielectric and magnetic properties, and conductivity. X-ray diffraction study has revealed a layered superstructure along the c axis at room temperature. A model of the state with giant ε′ including as-grown 2D layers with doping impurities, charge carriers, and double-exchange coupled Mn3+–Mn4+ ion pairs is suggested. At low temperatures these layers form isolated electrically neutral small-size 1D superlattices, in which de Haas van Alphen oscillations were observed. As temperature and hopping conductivity increase, charge-carrier self-organization in the crystal cause the formation of a layered superstructure consisting of charged layers (with an excess Mn3+) alternating with dielectric layers of the initial crystal—the ferroelectricity state due to charge ordering. Ferromagnetism results from double exchange between Mn3+ and Mn4+ ions through charge carriers in the charged layers.
Electronic spectroscopy and electronic structure of diatomic CrC
Authors: Brugh Dale J. , Morse Michael D. , Kalemos Apostolos , Mavridis Aristides
Published: July 2010

Optical spectra of jet-cooled diatomic CrC have been recorded in the near infrared region using resonant two-photon ionization spectroscopy combined with mass-selective detection of the resulting ions. Several weak transitions have been observed, along with one relatively strong band near 842 nm. Rotational resolution and analysis of this band confirms that the ground state is of Σ3− symmetry. Ab initio calculations have been performed that demonstrate that the ground state is highly multiconfigurational in nature, with a leading configuration of 1σ22σ21π41δ2 for the ten valence electrons. From the rotational analysis of the 842 nm Σ3−←X Σ3− band, the derived spectroscopic constants of the ground and excited states for C52rC12 are B0″=0.659 97(49), λ0″=6.74(24), γ0″=−0.066(20), T0=11 870.7660(65), B′=0.608 29(39), λ′=7.11(24), and γ′=0.144(17) cm−1. Here and throughout this article, 1σ error limits are reported in parentheses. These rotational constants may be inverted to provide the bond lengths in the ground and excited states, r0″=1.6188(6) Å and r′=1.6861(5) Å, respectively. Ab initio calculations show that the upper state is the third state of Σ3− symmetry.
Strain-effect for controlled growth mode and well-ordered structure of quaterrylene thin films
Authors: Hayakawa Ryoma , Turak Ayse , Zhang XueNa , Hiroshiba Nobuya , Dosch Helmut , Chikyow Toyohiro , Wakayama Yutaka
Published: July 2010

We investigated the evolution of quaterrylene thin films on SiO2 and on an octadecyltrichlorosilane self-assembled monolayer (OTS-SAM) to examine the impact of film strains on the growth processes and evolving structure. Surface modification by SAMs allowed tailoring of the growth process from a Stranski–Krastanov (SK) mode (layer-plus-island) on the SiO2 surface to a Frank–van der Merwe mode (layer-by-layer) on the OTS surface. Detailed structural analysis by x-ray diffraction techniques confirmed that the SK mode was driven by lattice strain in the initial wetting layers on the SiO2 surface. On the other hand, strain-free wetting layers were already formed at the beginning of growth on the OTS surface, thereby suppressing three-dimensional island formation. Moreover, the films on the SiO2 surface were found to incorporate high microstrain induced by crystal defects such as dislocations and a mosaic structure. In contrast, few crystal defects were present in the films on OTS surface, demonstrating that OTS treatment enables marked improvement of the molecular alignment. These results clearly indicate that the lattice strain induced by the molecular-substrate interaction is essential for controlling the overall growth process.
Magnetoelectric effect in magnetostriction-piezoelectric multiferroics
Authors: Bichurin M. I. , Petrov V. M.
Published: July 2010

The present stage in the study of magnetoelectric (ME) composite multiferroics is analyzed. The ME effect in materials of this kind is due to the magnetostriction and piezoelectric properties of the components. The elastic mechanical interaction between the magnetostriction and piezoelectric phases engenders a giant magnetoelectric response in magnetoelectric composite materials. The ME effect is more than 100 times stronger near an electromechanical resonance. The recently obtained nanostructural composites made from ferroelectric and magnetic oxides with dimensions of the order of nanometers made in the form of films on a substrate engender interest in the possibility of constructing integrated devices. The ME interaction between ferroelectrics and magnetic oxides with nanometer dimensions is the same as in ordinary composite materials. Just as for bulk ME composites, sensors, transducers and diverse reading/writing devices are some of the possible applications of the ME effect in nanocomposites
Basis set effects on the hyperpolarizability of CHCl3: Gaussian-type orbitals, numerical basis sets and real-space grids
Authors: Vila Fernando D. , Strubbe David A. , Takimoto Yoshinari , Andrade Xavier , Rubio Angel , Louie Steven G. , Rehr John J.
Published: July 2010

Calculations of the hyperpolarizability are typically much more difficult to converge with basis set size than the linear polarizability. In order to understand these convergence issues and hence obtain accurate ab initio values, we compare calculations of the static hyperpolarizability of the gas-phase chloroform molecule (CHCl3) using three different kinds of basis sets: Gaussian-type orbitals, numerical basis sets, and real-space grids. Although all of these methods can yield similar results, surprisingly large, diffuse basis sets are needed to achieve convergence to comparable values. These results are interpreted in terms of local polarizability and hyperpolarizability densities. We find that the hyperpolarizability is very sensitive to the molecular structure, and we also assess the significance of vibrational contributions and frequency dispersion.
Magnetoelectric and magnetoelastic properties of rare-earth ferroborates
Authors: Kadomtseva A. M. , Popov Yu. F. , Vorob’ev G. P. , Pyatakov A. P. , Krotov S. S. , Kamilov K. I. , Ivanov V. Yu. , Mukhin A. A. , Zvezdin A. K. , Kuz’menko A. M. , Bezmaternykh L. N. , Gudim I. A. , Temerov V. L.
Published: July 2010

The magnetic, electric, magnetoelectric, and magnetoelastic properties of rare-earth ferroborates RFe3(BO3)4 (R=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) as well as yttrium ferroborate YFe3(BO3)4 have been studied comprehensively. A strong dependence not only of the magnetic but also magnetoelectric properties on the type of rare-earth ion, specifically, on its anisotropy, which determines the magnetic structure and the large contribution to the electric polarization, has been found. This is manifested in the strong temperature dependence of the polarization below the Néel point TN and its specific field dependence, which is determined by the competition between the external and exchange f-d fields. A close correlation has been found between the magnetoelastic properties of ferroborates and the magnetoelastic and magnetic anomalies at magnetic-field induced phase transitions. It is found that in easy-plane ferroborates, together with magnetic-field induced electric polarization spontaneous polarization also arises below the Néel point. The ferroelectric ordering in ferroborates is of extrinsic character, giving rise to strong magnetoelectric coupling below TN. Aside from the antiferromagnetic phase transition, the particulars of the structural phase transition accompanied by anomalies of the dielectric and magnetoelectric properties are examined for the first time. The character of the dielectric anomalies at a structural transition is analyzed for the first time on the basis of Landau’s approach.
Monte Carlo study of oligopyrroles in condensed phases
Authors: Dai Yafei , Blaisten-Barojas Estela
Published: July 2010

A classical model potential to simulate pyrrole oligomers in condensed phases is developed in this work. The new potential contains ten parameters that are optimized on a database of energy points calculated within the density functional theory approach. Based on this potential the condensed phase of systems composed of pyrrole oligomers with 4 and 12 monomers is studied as a function of system density. The binding energy, end-to-end distance, radius of gyration, vector and orientational order parameters, and pair correlation functions are reported at T=300 K. The mechanical equilibrium density is determined for both systems. The bulk modulus is reported at these densities, showing that systems composed of short oligomers are softer than systems containing longer oligomers. Analysis of pair correlation functions and order parameters indicates that at equilibrium the system of short oligomers has characteristics of a liquid while the system of longer oligomers shows a chain stacking trend.
Analysis of electron traps at the 4H–SiC/SiO2 interface; influence by nitrogen implantation prior to wet oxidation
Authors: Pintilie I. , Teodorescu C. M. , Moscatelli F. , Nipoti R. , Poggi A. , Solmi S. , Løvlie L. S. , Svensson B. G.
Published: July 2010

Electron states at the SiO2/4H–SiC interface have been investigated using capacitor structures and especially, the influence of excess nitrogen, introduced by ion implantation, at the interface is studied in detail. Implanted and nonimplanted n-type samples with an interfacial concentration of nitrogen of ∼1019 cm−3 and 1016 cm−3, respectively, were analyzed by capacitance-voltage (C-V) measurements, performed at different temperatures and probe frequencies, and thermal dielectric relaxation current (TDRC) measurements performed in the temperature range of 35–295 K. Three main categories of electron states are disclosed, true interface states (Dit), fast near interface states (NIToxfast) and slow near interface states (NIToxslow). The density versus energy distributions of Dit and NIToxfast have been deduced from the TDRC data and they are shown to give a close quantitative agreement with the shape and frequency dependence of the C-V curves. Further, the amount of NIToxslow extracted from TDRC is demonstrated to be responsible for the parallel shifts and hysterezis effects occurring in the C-V characteristics. All three categories of electron states are reduced in concentration in the implanted samples. This holds particularly for NIToxfast with a peak at ∼0.1 eV below the conduction band edge of 4H–SiC that is suppressed by at least two orders of magnitude relative to the nonimplanted samples. The decrease for Dit is also substantial (a factor of ∼10) while the loss for NIToxslow is considerably smaller (only ∼30%). The results provide firm evidence that NIToxfast and NIToxslow do not originate from the same kind of defect center.
Quantum corrected Langevin dynamics for adsorbates on metal surfaces interacting with hot electrons
Authors: Olsen Thomas , Schiøtz Jakob
Published: July 2010

We investigate the importance of including quantized initial conditions in Langevin dynamics for adsorbates interacting with a thermal reservoir of electrons. For quadratic potentials the time evolution is exactly described by a classical Langevin equation and it is shown how to rigorously obtain quantum mechanical probabilities from the classical phase space distributions resulting from the dynamics. At short time scales, classical and quasiclassical initial conditions lead to wrong results and only correctly quantized initial conditions give a close agreement with an inherently quantum mechanical master equation approach. With CO on Cu(100) as an example, we demonstrate the effect for a system with ab initio frictional tensor and potential energy surfaces and show that quantizing the initial conditions can have a large impact on both the desorption probability and the distribution of molecular vibrational states.
A new tandem mass spectrometer for photofragment spectroscopy of cold, gas-phase molecular ions
Authors: Svendsen Annette , Lorenz Ulrich J. , Boyarkin Oleg V. , Rizzo Thomas R.
Published: July 2010

We present here the design of a new tandem mass spectrometer that combines an electrospray ion source with a cryogenically cooled ion trap for spectroscopic studies of cold, gas-phase ions. The ability to generate large ions in the gas phase without fragmentation, cool them to ∼10 K in an ion trap, and perform photofragment spectroscopy opens up new possibilities for spectroscopic characterization of large biomolecular ions. The incorporation of an ion funnel, together with a number of small enhancements, significantly improves the sensitivity, signal stability, and ease of use compared with the previous instrument built in our laboratory.
DNA separation on surfaces
Authors: Braiman Avital , Thundat Thomas , Rudakov Fedor
Published: July 2010

Recent experimental work on DNA separation on surfaces reveals a power law behavior of the mobility with size. We employed a simple model that elucidates the observed power law trend. When the external electric field is barely larger than the critical value required for initiating translational motion, the mobility is approximately inversely proportional to the DNA size. At larger fields, mobility scales as N−α with 0<α<1, while showing oscillatory structure. Finally, at very large fields, mobility becomes size independent. Our model provides insight into separation mechanisms and presents numerical results that explain power law scaling.
Optical excitation energies, Stokes shift, and spin-splitting of C24H72Si14
Authors: Zope Rajendra R. , Baruah Tunna , Richardson Steven L. , Pederson Mark R. , Dunlap Brett I.
Published: July 2010

As an initial step toward the synthesis and characterization of sila-diamondoids, such as sila-adamantane (Si10H16,Td), the synthesis of a fourfold silylated sila-adamantane molecule (C24H72Si14,Td) has been reported in literature [Fischer et al., Science 310, 825 (2005)]. We present the electronic structure, ionization energies, quasiparticle gap, and the excitation energies for the Si14(CH3)24 and the exact silicon analog of adamantane Si10H16 obtained at the all-electron level using the delta-self-consistent-field and transitional state methods within two different density functional models: (i) Perdew–Burke–Ernzerhof generalized gradient approximation and (ii) fully analytic density functional (ADFT) implementation with atom dependent potential. The ADFT is designed so that molecules separate into atoms having exact atomic energies. The calculations within the two models agree well, to within 0.25 eV for optical excitations. The effect of structural relaxation in the presence of electron-hole-pair excitations is examined to obtain its contribution to the luminescence Stokes shift. The spin-influence on exciton energies is also determined. Our calculations indicate overall decrease in the absorption, emission, quasiparticle, and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, ionization energies, Stokes shift, and exciton binding energy when passivating hydrogens in the Si10H16 are replaced with electron donating groups such as methyl (Me) and trimehylsilyl (–Si(Me)3).
From golden spirals to constant slope surfaces
Authors: Munteanu Marian Ioan
Published: July 2010

In this paper, we find all constant slope surfaces in the Euclidean 3-space, namely, those surfaces for which the position vector of a point of the surface makes constant angle with the normal at the surface in that point. These surfaces could be thought as the bidimensional analog of the generalized helices. Some pictures are drawn by using the parametric equations we found.
Tunable ultrafast extreme ultraviolet source for time- and angle-resolved photoemission spectroscopy
Authors: Dakovski G. L. , Li Y. , Durakiewicz T. , Rodriguez G.
Published: July 2010

We present a laser-based apparatus suitable for visible pump/extreme UV (XUV) probe time-, energy-, and angle-resolved photoemission spectroscopy utilizing high-harmonic generation from a noble gas. Tunability in a wide range of energies (currently 20–36 eV) is achieved by using a time-delay compensated monochromator, which also preserves the ultrashort duration of the XUV pulses. Using an amplified laser system at 10 kHz repetition rate, approximately 109–1010 photons/s per harmonic are made available for photoelectron spectroscopy. Parallel energy and momentum detection is carried out in a hemispherical electron analyzer coupled with an imaging detector. First applications demonstrate the capabilities of the instrument to easily select the probe wavelength of choice, to obtain angle-resolved photoemission maps (GaAs and URu2Si2), and to trace ultrafast electron dynamics in an optically excited semiconductor (Ge).
A novel flat-response x-ray detector in the photon energy range of 0.1–4 keV
Authors: Li Zhichao , Jiang Xiaohua , Liu Shenye , Huang Tianxuan , Zheng Jian , Yang Jiamin , Li Sanwei , Guo Liang , Zhao Xuefeng , Du Huabin , Song Tianming , Yi Rongqing , Liu Yonggang , Jiang Shaoen , Ding Yongkun
Published: July 2010

A novel flat-response x-ray detector has been developed for the measurement of radiation flux from a hohlraum. In order to obtain a flat response in the photon energy range of 0.1–4 keV, it is found that both the cathode and the filter of the detector can be made of gold. A further improvement on the compound filter can then largely relax the requirement of the calibration x-ray beam. The calibration of the detector, which is carried out on Beijing Synchrotron Radiation Facility at Institute of High Energy Physics, shows that the detector has a desired flat response in the photon energy range of 0.1–4 keV, with a response flatness smaller than 13%. The detector has been successfully applied in the hohlraum experiment on Shenguang-III prototype laser facility. The radiation temperatures inferred from the detector agree well with those from the diagnostic instrument Dante installed at the same azimuth angle from the hohlraum axis, demonstrating the feasibility of the detector.
Giant Stark effect in the emission of single semiconductor quantum dots
Authors: Bennett Anthony J. , Patel Raj B. , Skiba-Szymanska Joanna , Nicoll Christine A. , Farrer Ian , Ritchie David A. , Shields Andrew J.
Published: July 2010

We study the quantum-confined Stark effect in single InAs/GaAs quantum dots embedded within a AlGaAs/GaAs/AlGaAs quantum well. By significantly increasing the barrier height we can observe emission from a dot at electric fields of 500 kV cm−1, leading to Stark shifts of up to 25 meV. Our results suggest this technique may enable future applications that require self-assembled dots with transitions at the same energy.
First-principles calculations on anharmonic vibrational frequencies of polyethylene and polyacetylene in the Γ approximation
Authors: Keçeli Murat , Hirata So , Yagi Kiyoshi
Published: July 2010

The frequencies of the infrared- and/or Raman-active (k=0) vibrations of polyethylene and polyacetylene are computed by taking account of the anharmonicity in the potential energy surfaces (PESs) and the resulting phonon-phonon couplings explicitly. The electronic part of the calculations is based on Gaussian-basis-set crystalline orbital theory at the Hartree–Fock and second-order Møller–Plesset (MP2) perturbation levels, providing one-, two-, and/or three-dimensional slices of the PES (namely, using the so-called n-mode coupling approximation with n=3), which are in turn expanded in the fourth-order Taylor series with respect to the normal coordinates. The vibrational part uses the vibrational self-consistent field, vibrational MP2, and vibrational truncated configuration-interaction (VCI) methods within the Γ approximation, which amounts to including only k=0 phonons. It is shown that accounting for both electron correlation and anharmonicity is essential in achieving good agreement (the mean and maximum absolute deviations less than 50 and 90 cm−1, respectively, for polyethylene and polyacetylene) between computed and observed frequencies. The corresponding values for the calculations including only one of such effects are in excess of 120 and 300 cm−1, respectively. The VCI calculations also reproduce semiquantitatively the frequency separation and intensity ratio of the Fermi doublet involving the ν2(0) fundamental and ν8(π) first overtone in polyethylene.
Excited state geometry of photoactive yellow protein chromophore: A combined conductorlike polarizable continuum model and time-dependent density functional study
Authors: Wang Yali , Li Hui
Published: July 2010

Analytic gradient of the combined conductorlike polarizable continuum model (CPCM) and time-dependent density functional theory method is derived and implemented. Due to the use of the fixed points with variable areas tessellation scheme, the excited state potential energy surfaces (PESs) are rigorously continuous and smooth. The CPCM/TD-B3LYP method is used to study an analog of the photoactive yellow protein chromophore, anionic thiomethyl p-coumaric acid (TMpCA−). Although CPCM/TD-B3LYP method may not be accurate in predicting solvent effect on vertical excitation of TMpCA−, it may be used to predict redshiftings of emission maxima relative to absorption maxima with an accuracy of ∼0.1 eV. We also found that the excited trans-TMpCA− tends to form a single bond twisted structure in the gas phase but a double bond twisted structure in aqueous solution. The TD-B3LYP minimum energy isomerization pathway shows a barrier of 3.6 kcal/mol in aqueous solution and 5.2 kcal/mol in the gas phase. The gas phase double bond twisted structure is trapped in a well of the excited state PES, with a depth of ∼20 kcal/mol (0.88 eV), in good agreement with an experimental value of ∼1 eV.
Note: Microelectromechanical systems Coulter counter for cell monitoring and counting
Authors: Wu Yifan , Benson James D. , Critser John K. , Almasri Mahmoud
Published: July 2010

This note describes the design, fabrication, and testing of a novel microelectromechanical systems Coulter counter. The Coulter counter will be used to detect and monitor impedance changes of cells as a function of time in response to different experimental extracellular environments. The device consists of SU-8 (negative photoresist) microchannels, vertical electroplated electrodes, polydimethylsiloxane cover, and is divided into a passive mixing region, a focusing region using negative dielectrophoretic forces, and a measuring region defined by multiple electroplated electrode pairs. The devices were tested using both microbeads in saline water and fibroblast cells in phosphate buffered saline solution. The results show that the proposed microsystem is capable of monitoring impedance of cells at different positions along the Coulter microchannel.
Enhanced electron-mediated ferromagnetism in Co-doped ZnO nanowires
Authors: Choi Eun-Ae , Lee Woo-Jin , Chang K. J.
Published: July 2010

We perform density functional calculations to investigate the magnetic coupling properties of Co-doped ZnO nanowires (NWs). The ferromagnetism of NWs is strongly affected by the position of the minority Co ta levels and their population that is controlled by additional electron doping. While the antiferromagnetic state is energetically more favorable than the ferromagnetic state in carrier-free NWs, electron doping greatly enhances the stability of ferromagnetism. Compared with bulk ZnO, the minority ta levels relative to the conduction band edge have a tendency to decrease with decreasing of the wire diameter, indicating that electron concentrations to achieve the ferromagnetism are much reduced. The short-range nature of the magnetic coupling between two Co ions suggests that sufficiently high doping levels of the Co ions are needed to yield ferromagnetic NWs.
Effect of mobile ions on ultrathin silicon-on-insulator-based sensors
Authors: Fernandes P. G. , Seitz O. , Chapman R. A. , Stiegler H. J. , Wen H. -C. , Chabal Y. J. , Vogel E. M.
Published: July 2010

The presence of mobile Na+ and K+ ions in biological solutions often lead to instabilities in metal-oxide-semiconductor devices and is therefore an important consideration in developing sensor technologies. Permanent hysteresis is observed on silicon-on-insulator field-effect-transistors based sensors after exposure to Na+-based buffer solutions but not after exposure to K+-based solutions. This behavior is attributed to the difference in mobilities of the ions in silicon dioxide. Mobile charge measurements confirm that ions can be transferred from the solution into the oxide. Self-assembled monolayers are shown to provide protection against ion diffusion, preventing permanent hysteresis of the sensors after exposure to solutions.
Reduced thermal resistance of the silicon-synthetic diamond composite substrates at elevated temperatures
Authors: Goyal V. , Subrina S. , Nika D. L. , Balandin A. A.
Published: July 2010

The authors report results of experimental investigation of thermal conductivity of synthetic diamond-silicon composite substrates. Although composite substrates are more thermally resistive than silicon at room temperature they outperform conventional wafers at elevated temperatures owing to different thermal conductivity dependence on temperature. The crossover point is reached near ∼360 K and can be made even lower by tuning the polycrystalline-grain size, film thickness, and interface quality. The reduction of thermal resistance of composite wafers at temperatures, typical for operation of electronic chips, may lead to better thermal management and new phonon-engineered methods for the electron mobility enhancement.
High voltage-derived enhancement of electric conduction in nanogap devices for detection of prostate-specific antigen
Authors: Park Hyung Ju , Chi Young Shik , Choi Insung S. , Yun Wan Soo
Published: July 2010

We report a simple method of enhancing electric conductance in nanogap devices without any additional treatments, such as silver-enhancing process. The low electric conductance after selective immobilization of biofunctionalized gold nanoparticles in the gap region was greatly enhanced by repeated I-V scans at relatively high voltage ranges of −5 to 5 V, which was attributed to the formation of a new conduction pathway across the gap. The higher conduction state of the nanogap device showed a very stable I-V curve, which was used as an excellent measure of the existence of prostate-specific antigen.
Organic tandem solar cells with complementary absorbing layers and a high open-circuit voltage
Authors: Cheyns D. , Rand B. P. , Heremans P.
Published: July 2010

Tandem organic solar cells with peak conversion efficiencies (η) of 5.15% are demonstrated. This is achieved by stacking two different planar heterojunction devices, each with a high open-circuit voltage (Voc). The phthalocyanine based donor materials in the employed subcells possess complementary absorption, a quality of critical importance to optimize photocurrent in a series connected tandem cell. The tandem structure produces Voc values of nearly 2 V, while fill factor remains above 60%. The measured η corresponds to a 40% increase compared to η of the optimal single cells.
Polycrystals under applied loads: Second-order grain statistics
Authors: Turner Joseph A. , Ghoshal Goutam
Published: July 2010

The authors report results for the second-order statistics of the effective elastic moduli of polycrystals as a function of applied stress. These results are indicative of scattering behavior that occurs in such materials at ultrasonic frequencies. Numerical examples are given for materials of general interest with cubic symmetry subject to an applied uniaxial stress. The results suggest that the second-order statistics (scattering) may be more significantly affected than the first-order statistics (wave speed) with application of load for some materials. This work may be useful for development of techniques for monitoring changes in stress of loaded structures.
High peak power λ∼3.3 and 3.5 μm InGaAs/AlAs(Sb) quantum cascade lasers operating up to 400 K
Authors: Commin J. P. , Revin D. G. , Zhang S. Y. , Krysa A. B. , Kennedy K. , Cockburn J. W.
Published: July 2010

We demonstrate λ∼3.5 μm and λ∼3.3 μm strain compensated In0.7Ga0.3As/AlAs(Sb)/InP quantum cascade lasers operating in pulse regime at temperatures up to at least 400 K. Peak optical power exceeding 3.5 W at 300 K has been achieved at both wavelengths for 10 μm wide 4 mm long lasers with high reflectivity coated back facets. Threshold current densities of 2.5 kA/cm2 and 3.5 kA/cm2 have been observed at 300 K for the devices emitting at λ∼3.5 μm and λ∼3.3 μm, respectively.
The hydrogen bond network structure within the hydration shell around simple osmolytes: Urea, tetramethylurea, and trimethylamine-N-oxide, investigated using both a fixed charge and a polarizable water model
Authors: Kuffel Anna , Zielkiewicz Jan
Published: July 2010

Despite numerous experimental and computer simulation studies, a controversy still exists regarding the effect of osmolytes on the structure of surrounding water. There is a question, to what extent some of the contradictory results may arise from differences in potential models used to simulate the system or parameters employed to describe physical properties of the mixture and interpretation of the results. Bearing this in mind, we determine two main aims of this work as follows: description of the water-water hydrogen bond network structure within the solvation layer around solute molecules (urea, trimethylamine-N-oxide, and tetramethylurea), and also comparison of rigid simple point charges (SPC) and polarizable (POL3) models of water. The following quantities have been examined: radial distribution functions of water molecules around the investigated solutes, both local and overall characteristics of the hydrogen bond network structure (using recently elaborated method), along with estimation of the mean energy of a single hydrogen bond, and also the probability distributions which describe the orientation of a single water particle plane relatively to the center of mass of the solute molecule. As an independent method for the evaluation of the degree of changes in local structural ordering, a harmonic approximation has been adopted to estimate the absolute entropy of water. It was found that within the solvation shell of the investigated solutes, the structure of hydrogen bond network changes only slightly comparing to bulk water. Therefore, we conclude that the investigated osmolyte molecules do not disturb significantly the structure of surrounding water. This conclusion was also confirmed by calculations of the absolute entropy of water using a harmonic approximation. In the immediate vicinity of the solutes, we observe that the water-water hydrogen bonds are slightly more stable; they are slightly less distorted and a little shorter than in bulk water. Nevertheless, although this local water structure is more stable and stiffer, our results do not indicate that it is more ordered compared to bulk. Finally, the comparison of both used models of water, the fixed charge and the polarizable, leads to unambiguous conclusion that rigid (SPC) water model may be successfully used in simulations instead of polarizable (POL3), as no significant differences between these two models have been observed.
Resonant slow modes in phononic crystal plates with periodic membranes
Authors: Sun Che-Yuan , Hsu Jin-Chen , Wu Tsung-Tsong
Published: July 2010

We propose a distinct phononic-crystal plate structure that comprises periodic circular membranes and present the theoretical and experimental investigation of elastic-wave propagation in the structure. Owing to the weak rigidity of the membranes, there are slow propagating resonant modes appended to the band structure. These resonant modes can also be engineered to locate inside the complete band gap. The frequencies and group velocities can be tuned by changing the membrane thickness and radius. By utilizing the laser-ultrasonic technique, the resonance and slow group velocity are observed. The measured results are in good agreement with the theoretical predictions.
Transparent organic photodiodes with high quantum efficiency in the near infrared
Authors: Campbell I. H.
Published: July 2010

We demonstrate organic photodiodes with a transparency of ∼80% throughout the visible spectrum and with up to ∼80% external quantum efficiency (EQE) in the near infrared under reverse bias. The diodes use thin films of soluble naphthalocyanine (Nc) molecules prepared by spin casting, with or without thermal annealing. Annealing of the naphthalocyanine layer preferentially orients the planar Nc molecules parallel to the substrate surface. Annealed diodes have improved EQE at zero bias and photoconductive gain at small reverse bias.
Pressure-temperature-La concentration three-dimensional phase diagram of La-modified PbTiO3 determined by Raman scattering
Authors: Joya M. R. , Pizani P. S.
Published: July 2010

A detailed Raman scattering study was performed on lanthanum-modified lead titanate (PLT) with compositions varying from pure PbTiO3 to La 20.0 at. %, for temperatures ranging from 8 K to temperatures above the Curie temperature and hydrostatic pressures up to 7.5 GPa. A complete La concentration-pressure-temperature three dimensional phase diagram was determined, by using the E(TO1) soft mode frequency as the main probe.
Size-dependent strain effects on electronic and optical properties of ZnO nanowires
Authors: Yang Yurong , Yan X. H. , Xiao Yang , Lu Di
Published: July 2010

The electronic and optical properties of ZnO nanowires under uniaxial strain are investigated using first-principles calculations. The results show that the electronic band gap for the ultrathin ZnO nanowires displays a nonmonotonic relationship with the strain, while the gap is inversely proportional to strain and shows a linear relationship for the nanowires with diameter larger than 2.4 nm. Optical properties calculations show that the dielectric function peaks for ultrathin nanowires display a redshift with decreasing uniaxial strain, this energy shift decreases with increasing diameter and vanishes as the diameter increases to 2.4 nm.
Ambipolar behavior of 2,5-diphenyl-1,4-distyrylbenzene based field effect transistors: An experimental and theoretical study
Authors: Wang Yan , Liu Dandan , Ikeda Susumu , Kumashiro Ryotaro , Nouch Ryo , Xu Yuanxiang , Shang Hui , Ma Yuguang , Tanigaki Katsumi
Published: July 2010

New organic semiconductor molecule 2,5-diphenyl-1,4-distyrylbenzene (trans-DPDSB) was synthesized and its single crystal was grown for light-emitting field effect transistors (FETs). This molecule forms J-aggregate crystals which show high luminescent efficiency compared with the corresponding H-aggregates. Although J-aggregates have a weak point of lower mobility, the FETs using trans-DPDSB single crystals and Au–Ca asymmetrical electrodes showed light emission from the channel. This study shows that the design and modification of organic molecular stacking modes are useful in realization of highly efficient light-emitting FETs.
High conductance bottom-contact pentacene thin-film transistors with gold-nickel adhesion layers
Authors: Kitamura Masatoshi , Kuzumoto Yasutaka , Kang Woogun , Aomori Shigeru , Arakawa Yasuhiko
Published: July 2010

Bottom-contact pentacene thin-film transistors (TFTs) with different electrode types have been fabricated to investigate influence of the adhesion layers and surface modification on the transistor characteristics. Gold-nickel alloy or Ti was used for the adhesion layer; the drain/source electrodes were modified with pentafluorobenzenethiol (PFBT) or nonmodified. The TFTs with AuNi layers and PFBT-modified electrodes exhibit channel-length independent saturation mobility. The electrode-type TFT with a channel length of 2.2 μm has a saturation mobility of 0.73 cm2/V s and a transconductance of 229 μS/mm. The high performance is attributed to the low contact resistance of 408 Ω cm.
Limiting efficiency of intermediate band solar cells with spectrally selective reflectors
Authors: Strandberg Rune , Reenaas Turid Worren
Published: July 2010

So far, theoretical efficiency limits for the intermediate band solar cell have been calculated under the assumption that the absorptivity of the solar cell is 1 for all photon energies larger than the smallest subband gap. In the present work, efficiency limits have been calculated under the assumption that the cell is covered by spectrally selective reflectors. The efficiency limit for the 1 sun 6000 K black body spectrum is found to increase from 46.8% to 48.5% and the limit for the AM1.5G spectrum (as defined by ASTM G173–03) is found to increase from 49.4% to 52.0%.
Elastic, dielectric, and piezoelectric constants of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal poled along [011]c
Authors: Sun Enwei , Zhang Shujun , Luo Jun , Shrout Thomas R. , Cao Wenwu
Published: July 2010

Ternary single crystals xPb(In1/2Nb1/2)O3–(1−x−y)Pb(Mg1/3Nb2/3)O3–yPbTiO3 (PIN-PMN-PT) poled along [011]c showed remarkable electromechanical properties. We report complete sets of elastic, dielectric, and piezoelectric constants of PIN-PMN-28%PT and PIN-PMN-32%PT, measured by using combined resonance and ultrasonic methods. The electromechanical coupling coefficients k15, k32, and k33 can reach 0.95, 0.90, and 0.92, and the piezoelectric strain coefficients d15, d32, and d33 are as high as 3354 pC/N, −1781 pC/N, and 1363 pC/N, respectively. These full matrix data sets provide the base for fundamental studies on domain engineering phenomena as well as urgently needed input data for the design of electromechanical devices using [011]c poled PIN-PMN-PT single crystals.
Management of tar spot disease caused by Phyllachora grevilleae subsp. grevilleae on Hakea myrtoides (Proteaceae)
Authors: Davison E. M. , Tay F. C. S.
Published: July 2010

Hakea myrtoides Meisn. is an attractive shrub that has a restricted distribution in the south-west of Western Australia. It is not killed by fire but re-sprouts from basal lignotubers. Its leaves are often severely affected by tar spot disease, caused by the biotrophic, stromatic ascomycete Phyllachora grevilleae (Lév.) Sacc. subsp. grevilleae (Lév) Sacc. This disease is spread by ascospores that are produced during the wettest months of the year: late autumn, winter and spring. Badly infected populations of H. myrtoides were burnt, either in a controlled burn in November 2007, or in a wildfire in January 2008. The incidence of tar spot disease on leaves of burnt plants in 2008 and 2009 was 4.4%, while its incidence on unburnt plants was significantly higher (25.1%). The incidence of flowering in 2009 was similar in both burnt and unburnt populations. Tar spot disease is common on H. myrtoides; it is present on 77% of collections of this host in the Western Australian Herbarium (PERTH).
Molecular origins of fluorocarbon hydrophobicity
Authors: Dalvi Vishwanath H. , Rossky Peter J.
Published: July 2010

We have undertaken atomistic molecular simulations to systematically determine the structural contributions to the hydrophobicity of fluorinated solutes and surfaces compared to the corresponding hydrocarbon, yielding a unified explanation for these phenomena. We have transformed a short chain alkane, n-octane, to n-perfluorooctane in stages. The free-energy changes and the entropic components calculated for each transformation stage yield considerable insight into the relevant physics. To evaluate the effect of a surface, we have also conducted contact-angle simulations of water on self-assembled monolayers of hydrocarbon and fluorocarbon thiols. Our results, which are consistent with experimental observations, indicate that the hydrophobicity of the fluorocarbon, whether the interaction with water is as solute or as surface, is due to its “fatness.” In solution, the extra work of cavity formation to accommodate a fluorocarbon, compared to a hydrocarbon, is not offset by enhanced energetic interactions with water. The enhanced hydrophobicity of fluorinated surfaces arises because fluorocarbons pack less densely on surfaces leading to poorer van der Waals interactions with water. We find that interaction of water with a hydrophobic solute/surface is primarily a function of van der Waals interactions and is substantially independent of electrostatic interactions. This independence is primarily due to the strong tendency of water at room temperature to maintain its hydrogen bonding network structure at an interface lacking hydrophilic sites.
NMDA receptor-dependent GABA
B
receptor internalization via CaMKII phosphorylation of serine 867 in GABA
B1
Authors: Guetg Nicole , Aziz Said Abdel , Holbro Niklaus , Turecek Rostislav , Rose Tobias , Seddik Riad , Gassmann Martin , Moes Suzette , Jenoe Paul , Oertner Thomas G. , Casanova Emilio , Bettler Bernhard
Published: July 2010

GABA
B
receptors are the G-protein–coupled receptors for GABA, the main inhibitory neurotransmitter in the brain. GABA
B
receptors are abundant on dendritic spines, where they dampen postsynaptic excitability and inhibit Ca
2+
influx through NMDA receptors when activated by spillover of GABA from neighboring GABAergic terminals. Here, we show that an excitatory signaling cascade enables spines to counteract this GABA
B
-mediated inhibition. We found that NMDA application to cultured hippocampal neurons promotes dynamin-dependent endocytosis of GABA
B
receptors. NMDA-dependent internalization of GABA
B
receptors requires activation of Ca
2+
/Calmodulin-dependent protein kinase II (CaMKII), which associates with GABA
B
receptors in vivo and phosphorylates serine 867 (S867) in the intracellular C terminus of the GABA
B1
subunit. Blockade of either CaMKII or phosphorylation of S867 renders GABA
B
receptors refractory to NMDA-mediated internalization. Time-lapse two-photon imaging of organotypic hippocampal slices reveals that activation of NMDA receptors removes GABA
B
receptors within minutes from the surface of dendritic spines and shafts. NMDA-dependent S867 phosphorylation and internalization is predominantly detectable with the GABA
B1b
subunit isoform, which is the isoform that clusters with inhibitory effector K
+
channels in the spines. Consistent with this, NMDA receptor activation in neurons impairs the ability of GABA
B
receptors to activate K
+
channels. Thus, our data support that NMDA receptor activity endocytoses postsynaptic GABA
B
receptors through CaMKII-mediated phosphorylation of S867. This provides a means to spare NMDA receptors at individual glutamatergic synapses from reciprocal inhibition through GABA
B
receptors.
22-nucleotide RNAs trigger secondary siRNA biogenesis in plants
Authors: Chen Ho-Ming , Chen Li-Teh , Patel Kanu , Li Yi-Hang , Baulcombe David C. , Wu Shu-Hsing
Published: July 2010

The effect of RNA silencing in plants can be amplified if the production of secondary small interfering RNAs (siRNAs) is triggered by the interaction of microRNAs (miRNAs) or siRNAs with a long target RNA. miRNA and siRNA interactions are not all equivalent, however; most of them do not trigger secondary siRNA production. Here we use bioinformatics to show that the secondary siRNA triggers are miRNAs and transacting siRNAs of 22 nt, rather than the more typical 21-nt length.
Agrobacterium
-mediated transient expression in
Nicotiana benthamiana
confirms that the siRNA-initiating miRNAs, miR173 and miR828, are effective as triggers only if expressed in a 22-nt form and, conversely, that increasing the length of miR319 from 21 to 22 nt converts it to an siRNA trigger. We also predicted and validated that the 22-nt miR771 is a secondary siRNA trigger. Our data demonstrate that the function of small RNAs is influenced by size, and that a length of 22 nt facilitates the triggering of secondary siRNA production.