bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of dust in the sheath of weakly electronegative plasmas
Authors: Wang Zheng-Xiong , Wang Xiaogang , Liu Jin-Yuan , Liu Yue
Published: January 2005

The dynamics of dust in the sheath of weakly electronegative plasmas are investigated with the single dust model as well as the self-consistently variable dust charge. It is shown that when the dust particles enter the sheath region from the sheath edge with different initial velocities they may display different motion states: levitation in the sheath, returning from the sheath edge, and traversing the sheath region, under action of electrostatic, gravitational, ion-drag, and neutral collision forces. Furthermore, the electronegativity also plays an important role in the dust particle motion states in the sheath besides affecting the distributions of the spatial potential and the charging of the dust particles.
Excited electronic states of small water clusters
Authors: Chipman Daniel M.
Published: January 2005

The lowest electronic states that are initially formed upon excitation of small water clusters having a central water molecule with one stretched OH bond are studied with electronic structure methods. It is found that in water dimer, trimer, and pentamer the lowest excited singlet and triplet states are each nondissociative for stretching of an OH bond that is hydrogen bonded in an icelike configuration to a neighboring water molecule. This is in marked contrast to the behavior of an isolated gas phase water monomer, where it is well known that the lowest excited state is strongly dissociative upon OH stretching. The conclusions of this study may serve as a basis to interpret recent experimental evidence that suggests a significant lifetime for excited water in irradiated thin ice films, and may also have important implications for the behavior of excitation of liquid water.
Excimer emission in electroluminescence and photoluminescence of polyfluorene derivatives: Effects of local heating and exciton density
Authors: Vacha Martin , Ha Jaekook , Ito Yuichi , Shimada Takahiro , Mo Son Jhun , Sato Hisaya
Published: January 2005

We report a study of excimer emission from copolymers of dibutylfluorene and butylphenylphenoxazine. Temperature dependence of photoluminescence (PL) spectra measured from room temperature to above glass transition temperature, and excitation power dependence of PL spectra reveal that the observed differences in excimer intensity between PL and electroluminescence spectra are neither solely due to local heating by electric current nor to differences in exciton density. Instead, different nature of the excitations upon photoexcitation and excitation by passing current has to be considered to explain the different behavior.
Organic magnetic-field-effect transistors and ultrasensitive magnetometers
Authors: Yu Z. G. , Berding M. A. , Krishnamurthy S.
Published: January 2005

We propose organic magetic-field-effect transistors and ultrasensitive magnetometers that exploit spin transport in organics and its sensitive dependence on a transverse magnetic field due to spin precession. The device design is based on experimentally observed magnetoresistance in magnet/polymer/magnet structures and on the theory of spin transport in these structures. It is shown that at room temperature the magnetometers are capable of detecting sub nT magnetic fields, and the I–V characteristics of the transistors can be strongly modified by magnetic fields of a few G with response times of a few ns.
Internal laser probing: A theoretical study of wave propagation effects and the physical limits of measurement accuracy
Authors: Thalhammer Robert
Published: January 2005

The transient distribution of charge carriers and temperature in semiconductors has become accessible to experiments by internal laser probing techniques that exploit the electro-optical and the thermo-optical effect. In this article, two representative methods, namely free carrier absorption and laser deflection measurements, are theoretically investigated. The study makes use of analytical calculations and the recently introduced concept of virtual experiments, which is based on a physically rigorous simulation of the entire measurement process. Wave propagation phenomena and parasitic effects introduced by preparing the sample or performing the actual measurement are thoroughly analyzed to identify major sources of error and to reveal the theoretical limits of measurement accuracy and resolution. We derive a consistent evaluation rule for extracting carrier and temperature gradients from the detector signals of deflection measurements. It is quantitatively demonstrated how to optimize the setup with respect to a desired purpose, e.g., a large measurement range or a large sensitivity.
Calorimetric studies of the A1 to L1 transformation in binary FePt thin films with compositions in the range of 47.5–54.4at.% Fe
Authors: Barmak K. , Kim J. , Berry D. C. , Hanani W. N. , Wierman K. , Svedberg E. B. , Howard J. K.
Published: January 2005

Differential scanning calorimetry, in conjunction with x-ray and electron diffraction, is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 47.5–54.4at.% Fe. The kinetic ordering temperature, taken as the calorimetric peak temperature at a heating rate of 40°C∕min, decreases from 447to357°C in this composition range. In contrast with the kinetic ordering temperature, the Curie temperature of the L10 ordered phase increases from 384to455°C as the Fe content is increased. The activation energies of ordering lie between 1.4 and 2.0eV, and the transformation enthalpies are in the range of −8.2to−13.6kJ∕g-at. The Avrami exponent for the transformation is lower than expected and lies in the range of 1.1–1.8. The lattice parameter of the A1 phase and the c∕a ratio of the L10 phase decrease with increasing Fe content.
Perpendicular magnetic properties of CoCr films on GaAs
Authors: Manago T. , Kuramochi H. , Akinaga H.
Published: January 2005

CoCr films were deposited on three types of GaAs substrates, GaAs(001), GaAs(111), and Al oxide∕GaAs(001). The perpendicular magnetic properties were investigated by magneto-optical Kerr-effect measurements. The direct deposition of the CoCr film on the GaAs substrate did not show any perpendicular magnetic properties. This fact indicates that the lattice distortion influenced by the GaAs lattice suppresses the perpendicular magnetism. The CoCr film on the Al oxide layer showed a tilted squarelike hysteresis loop. The thickness dependence of the hysteresis loop and the magnetic force microscopy showed that the onset thickness of ferromagnetism was 6.5nm. The domain size of the CoCr films monotonously decreases with the increasing thickness (6.5–75nm).
Josephson tunnel junction controlled by quasiparticle injection
Authors: Giazotto Francesco , Pekola Jukka P.
Published: January 2005

A Josephson tunnel junction transistor based on quasiparticle injection is proposed. Its operation relies on the manipulation of the electron distribution in one of the junction electrodes. This is accomplished by injecting quasiparticle current through the junction electrode by two additional tunnel-coupled superconductors. Both large supercurrent enhancement and fast quenching can be achieved with respect to equilibrium by varying quasiparticle injection for proper temperature regimes and suitable superconductor combinations. Combined with large power gain, this makes the device attractive for applications where reduced noise and low-power dissipation are required.
Minority-carrier lifetime enhancement in edge-defined film-fed grown Si through rapid thermal processing-assisted reduction of hydrogen-defect dissociation
Authors: Nakayashiki Kenta , Rohatgi Ajeet , Ostapenko Sergei , Tarasov Igor
Published: January 2005

This paper demonstrates that a very short, 1-s, simultaneous firing of screen-printed Al at the back and SiNx antireflection (AR) coating at the front can significantly enhance the minority-carrier lifetime in edge-defined film-fed grown (EFG) ribbon Si via SiNx-induced hydrogen passivation of defects. It was found that 1-s firing in a rapid thermal processing system at an optimum temperature improved the average minority-carrier lifetime from 3to>80μs, resulting in ∼16% efficient 4-cm2 screen-printed EFG Si cells. It is proposed that rapid thermal firing enhances the retention of hydrogen at defect sites by minimizing the hydrogen-defect dissociation. A combination of simulations and experiments reveals that the dissociation of hydrogen is extremely rapid at conventional firing temperatures of ∼700°C. An activation energy of 2.4–2.6eV was determined for the hydrogen-defect dissociation in EFG Si. This activation energy, in conjunction with the room-temperature photoluminescence data, suggests that the impurity-decorated dislocations are the dominant hydrogenation and dehydrogenation sites in the EFG Si. Based on the above understanding, a manufacturable process, involving rapid co-firing of SiNx AR coating, screen-printed Al-doped back surface field (Al-BSF), and screen-printed Ag front grid, was developed in a conventional belt furnace to minimize the degree of dehydrogenation while producing good Al-BSF and ohmic contacts. This process produced 4-cm2 screen-printed EFG Si cells with an efficiency of 15.9%.
In situ surface-enhanced Raman spectroscopy of monodisperse silver nanowire arrays
Authors: Sauer G. , Brehm G. , Schneider S. , Graener H. , Seifert G. , Nielsch K. , Choi J. , Göring P. , Gösele U. , Miclea P. , Wehrspohn R. B.
Published: January 2005

Highly ordered two-dimensional arrays of monodisperse coinage metal nanowires embedded in an alumina matrix have been prepared. When light is propagating in the direction of the long axis of the nanowire, plasmon-enhanced absorption and light guidance of the nanowire were observed by optical microspectroscopy and scanning near-field optical spectroscopy and compared to Mie scattering theory. By selectively dissolving the matrix at a constant etching rate, we detected in situ and ex situ the surface-enhanced Raman scattering (SERS) of organic dyes. In contrast to earlier publications, we find that the SERS signal is linearly proportional to the free-surface area of the nanowires that are in contact with the dye. We cannot detect any change in the enhancement factor due to the releasing of the nanowires from the host structure.
Investigation of dislocation loops associated with As–Sb nanoclusters in GaAs
Authors: Chaldyshev V. V. , Kolesnikova A. L. , Bert N. A. , Romanov A. E.
Published: January 2005

A model is developed for the elastic stress relaxation via formation of prismatic dislocation loops in a vicinity of the As–Sb nanoclusters built in GaAs matrix. The model is based on the experimental investigation of the microstructure of the As–Sb nanoclusters, which can be produced in Sb-doped GaAs films by the molecular-beam epitaxy at low temperature and subsequent anneal. A strong anisotropic mismatch between the As–Sb nanoclusters and GaAs matrix has been revealed by transmission electron microscopy. This mismatch was proven to be a reason for the formation of nanoscale dislocation loops near the nanoclusters. Our theoretical model explores the elastic properties of an inclusion with uniaxial dilatation. For such inclusions, the elastic stresses and stored energy are determined in a closed analytical form. The theoretical analysis predicts a specific nonlinear dependence of the dislocation loop diameter on the cluster diameter, which fits well the experimentally observed one. It is demonstrated that both the change in the inclusion self-energy due to diminishing dilatation and the interaction between the dislocation loop and inclusion are important in the relaxation phenomena in precipitated semiconductors.
Brownian dynamics simulation study of self-assembly of amphiphiles with large hydrophilic heads
Authors: Bourov Geuorgui K. , Bhattacharya Aniket
Published: January 2005

We have studied the effect of shape of an amphiphilic molecule on micellization properties by carrying out stochastic molecular dynamics simulation on a bead-spring model of amphiphiles for several sizes of hydrophilic head group with a fixed hydrophobic tail length. Our studies show that the effect of geometry of an amphiphile on shape and cluster distribution of micelles is significant. We find the critical micelle concentration increases with the increasing size of the hydrophilic head. We demonstrate that the onset of micellization is accompanied by (i) a peak in the specific heat as found earlier in the simulation studies of lattice models, and (ii) a peak in the characteristic relaxation time of the cluster autocorrelation function. Amphiphiles with larger hydrophilic head form smaller micelles with sharper cluster distribution. Our studies are relevant to the controlled synthesis of nanostructures of desired shapes and sizes using self-assembling properties of amphiphiles.
Influence of Te impurity on morphology of GaSb epilayer grown on GaSb (001) patterned substrate by liquid phase epitaxy
Authors: Zhang G. , Jayavel P. , Koyama T. , Kumagawa M. , Hayakawa Y.
Published: January 2005

We have studied the effect of Tellurium (Te) impurity on morphology of GaSb epilayer grown on GaSb (001) circular patterned substrates by liquid phase epitaxy. The results of the Te doped GaSb epilayers have been compared with the undoped GaSb epilayer under identical growth conditions. After the addition of Te impurity up to 0.12mol% in the starting solution, it is observed that a (311)B facet is formed instead of a (111)B facet while there is no such transition in the (111)A facet. The reason for the transition of the (111)B facet to the (311)B is discussed and an atomic model is proposed to explain the transition of the facet. The cross-sectional (110) plane of the Te doped GaSb epilayer after stain etching in a permanganate etchant reveals that two boundaries are separating differently doped upper and lateral regions of the epilayer. Furthermore, a few Te impurity striations are observed in the lateral region of the epilayer but none are found in the upper region. The growth time dependence of the morphology of Te doped GaSb epilayer shows that the (311)B facet is initially formed and becomes dominant after three hours growth.
Phase transition and chemical order in the ferroelectric perovskite (1−x)Bi(Mg3∕4W1∕4)O3–xPbTiO3 solid solution system
Authors: Stringer C. J. , Eitel R. E. , Shrout T. R. , Randall C. A. , Reaney I. M.
Published: January 2005

Building on the ferroelectric family based on the Bi(Me+3)O3–PbTiO3 solid solutions, the complex solid solution (1−x)Bi(Mg3∕4W1∕4)O3–xPbTiO3 [(1−x)BMW–xPT] was investigated. This system was found to exhibit a broad morphotropic phase boundary at x∼0.48mol% PbTiO3 with a corresponding Curie temperature of 205°C separating pseudocubic and tetragonal ferroelectric phases. Based on dielectric, x-ray diffraction (XRD), and calorimetric data, a simple dielectric phase field diagram was established. On further structural analysis with diffraction contrast transmission electron microscopy along with XRD, evidence of B-site chemical ordering was found for the (1−x)Bi(Me′Me″)O3–xPbTiO3 perovskite family.
Ultraviolet Raman scattering of GaN nanocrystallites: Intrinsic versus collective phenomena
Authors: Chen Xiang-Bai , Morrison John L. , Huso Jesse , Bergman Leah , Purdy Andrew P.
Published: January 2005

Resonant Raman scattering in wurtzite structured GaN nanocrystallites of various morphologies were studied. The polar mode A1(LO) exhibited Fröhlich-type resonant Raman scattering whose characteristics were found to depend weakly on the morphology of the crystallites. In contrast, the UV-laser heating and heat retention in the porous media of a crystallite ensemble were discovered to drastically modify the Raman properties: A Raman thermal redshift was observed that might mask any redshift due to the confinement effect. The thermal redshift was found to depend on the laser power and on the ensemble size. An ensemble temperature on the order of 550K was inferred from the electron–phonon interaction model, a result that was verified via Raman scattering experiments at the elevated temperature regime. For a small ensemble that contains ∼10–20 crystallites and with nominal laser-heating effect, the Raman line shape was found to have mainly a Lorentzian component indicative of phonon-lifetime broadening mechanism. The line shape had no pronounced Gaussian component and had similar characteristics to the line shape of GaN film, implying that a collective of a few crystallites still reflects the Raman properties of an individual crystallite. Complementary photoluminescence investigations concur with the Raman findings.
Six-dimensional quantum dynamics of dissociative chemisorption of H2 on Ru(0001)
Authors: Vincent Jonathan K. , Olsen Roar A. , Kroes Geert-Jan , Luppi Marcello , Baerends Evert-Jan
Published: January 2005

Six-dimensional quantum dynamics calculations on dissociative chemisorption of H2 on Ru(0001) are performed. The six-dimensional potential energy surface is generated using density functional theory. Two different generalized gradient approximations are used, i.e., RPBE and PW91, to allow the results to be compared. The dissociation probability for normally incident H2 on a clean Ru(0001) surface is calculated. Large differences between the reaction probabilities calculated using the RPBE and PW91 are seen, with the PW91 results showing a much narrower reaction probability curve and a much higher reactivity. Using the reaction probabilities and assuming normal energy scaling reaction rates are generated for temperatures between 300 and 800 K. The rate generated using the PW91 results is higher by about a factor 5 than the rate based on the RPBE results in the range of temperatures relevant to ammonia production.
Underwater electrical explosion of a Cu wire
Authors: Grinenko A. , Sayapin A. , Gurovich V. Tz. , Efimov S. , Felsteiner J. , Krasik Ya. E.
Published: January 2005

Results and analysis of a microsecond time scale underwater electrical wire explosion are presented. Experiments were carried out with a Cu wire exploded by a current pulse ⩽100kA with microsecond time duration. The analysis is based on shadow and spectrally resolved streak photography which were used to monitor the evolution of the discharge channel and the shock wave. The obtained data were used for hydrodynamic calculation of the generated water flow parameters, such as pressure and flow velocity distribution between the discharge channel and the shock wave. In particular, the pressure at the discharge channel boundary and the energy transferred to the water were estimated. The results of the calculation have been verified by comparing the measured and calculated trajectories of the shock wave. Based on the results of the calculation the energy transferred to the water was estimated. In addition, the analysis shows that the energy initially deposited in the discharge channel continues to produce mechanical work after the deposition of the electrical energy has ended.
Pressure effect on radial breathing modes of multiwall carbon nanotubes
Authors: Wang C. Y. , Ru C. Q. , Mioduchowski A.
Published: January 2005

This paper studies the pressure effect on radial breathing modes (RBMs) of multiwall carbon nanotubes (MWNTs). The analysis is based on a multiple-elastic shell model which assumes that each of the concentric tubes of a MWNT is an individual elastic shell and coupled with adjacent tubes through van der Waals interaction. The pressure effect on RBMs of MWNTs is mainly attributed to the pressure-induced reduction of interlayer spacing and the increase of the interlayer vdW interaction coefficient defined by the second derivative of the energy-interlayer spacing relation of MWNTs. In the absence of external pressure, the RBM frequencies and vibration modes predicted by the present shell model are found to agree very well with the available experimental and molecular-dynamics simulation results. In the presence of an external pressure, our results show that high external pressure considerably raises the vdW interaction coefficients especially between the outermost few layers of MWNTs. As a result, some of the RBM frequencies of MWNTs increase significantly with increasing external pressure. The most significant pressure effect occurs for the highest-frequency mode of large-diameter MWNTs (with the innermost diameter greater than 2nm) or an intermediate-frequency mode of small-diameter MWNTs (with the innermost diameter less than 2nm), and is always associated with those RBMs in which adjacent outermost layers vibrate in opposite directions with significant change in interlayer spacing.
Characterization of Si1−xGex∕Si layers and depth profile of their heterobipolar transistor structures by high-resolution x-ray diffractometry and computer simulations
Authors: Bhagavannarayana G. , Halder S. K.
Published: January 2005

Using high-resolution x-ray diffractometry (HRXRD) and computer simulations, germanium content x, thickness T of pseudomorphic Si1−xGex layers, and Ge depth profile in their advanced heterobipolar transistor (HBT) structures grown on (001)Si substrates have been determined. High-resolution rocking curves (RCs) with well-resolved intensity oscillations have been recorded by using a double-crystal x-ray diffractometer in (+,−) geometry with CuKα1 radiation from a 12-kW rotating anode x-ray generator. The experimental RCs were simulated with the in-house developed computer program based on the semikinematical theory. In addition to the Ge depth profile, the thickness of SiGe layer, Si cap layer, and SiGe plateau layers of the HBT structures have been determined for the best fit of the experimental RCs with the theoretically simulated RCs. Due to the decay of intensity oscillations, in the case of partially relaxed layers, the values of germanium content x and relaxation R were calculated from the perpendicular and parallel (in-plane) lattice constants a⊥ and a‖ obtained by recording a pair of RCs from symmetric and asymmetric lattice planes. The simulation method using HRXRD has been described with the help of typical results obtained from samples of different structures. In this method the maximum error values of x and T are, respectively, ±0.5% and 1%. The error in the value of R is ±2% for partially relaxed samples. In the case of HBT structures, the maximum error in the value of thickness of SiGe and cap layers is ±1% and that of plateau layer is ±5%. The method is very convenient, faster, accurate, and nondestructive in comparison with other methods such as transmission electron microscopy and Secondary-ion-mass spectroscopy.
Symmetry, delocalization, and molecular conductance
Authors: Delaney P. , Nolan M. , Greer J. C.
Published: January 2005

Molecules bonded between two metal contacts form the simplest possible molecular devices. Coupled by the molecule, the left and right contact-based states form symmetric and antisymmetric pairs near the Fermi level. We relate the size of the resulting energy splitting ΔE to the symmetry and degree of delocalization of the coupling molecular orbital. Qualitative trends in molecular conductances are then estimated from the variations in ΔE. We examine benzenedithiol and other molecules of interest in transport.
Density-functional study of oxygen adsorption on Mo(112)
Authors: Kiejna Adam , Nieminen R. M.
Published: January 2005

Atomic oxygen adsorption on the Mo(112) surface has been investigated by means of first-principles total energy calculations. Among the variety of possible adsorption sites it was found that the bridge sites between two Mo atoms of the topmost row are favored for O adsorption at low and medium coverages. At about one monolayer coverage oxygen atoms prefer to adsorb in a quasithreefold hollow sites coordinated by two first-layer Mo atoms and one second layer atom. The stability of a structural model for an oxygen-induced p(2×3) reconstruction of the missing-row type is examined.
Ferromagnetic resonance and ac conductivity of a polymer composite of Fe3O4 and Fe3C nanoparticles dispersed in a graphite matrix
Authors: Guskos N. , Anagnostakis E. A. , Likodimos V. , Bodziony T. , Typek J. , Maryniak M. , Narkiewicz U. , Kucharewicz I. , Waplak S.
Published: January 2005

Ferromagnetic resonance (FMR) and ac conductivity have been applied to study a polymer composite containing as filler a binary mixture of magnetite (Fe3O4) and cementite (Fe3C) nanoparticles (30–50nm) dispersed in a diamagnetic carbon matrix, which was synthesized by the carburization of nanocrystalline iron. Ac conductivity measurements showed thermally activated behavior involving a range of activation energies and power law frequency dependence at high frequencies similar to conducting polymer composites randomly filled with metal particles. Ferromagnetic resonance measurements revealed a relatively narrow FMR line at high temperatures indicating the presence of ferromagnetic nanoparticles, where thermal fluctuations and interparticle interactions determine the FMR temperature variation. An abrupt change of the FMR spectra was observed at T<81K (ΔT⩽1K) coinciding with a sharp anomaly resolved in the temperature derivative of the ac conductivity. This behavior is attributed to the Verwey transition of Fe3O4 nanoparticles, where the concurrent skin depth variation unveils the FMR of large magnetite conglomerates and thus allows discriminating their contribution from relatively isolated nanoparticles.
Compression studies of TiB2 using synchrotron x-ray diffraction and ultrasonic techniques
Authors: Amulele George M. , Manghnani Murli H.
Published: January 2005

The compressibility of TiB2 has been determined separately by synchrotron x-ray diffraction and ultrasonic measurements on samples loaded in diamond-anvil cells and in multianvil high-pressure apparatus up to pressures of 65.9GPa and 13.9GPa, respectively, at ambient temperature. The high-pressure x-ray diffraction measurements, carried out on a pure polycrystalline sample, show a monotonic decrease of the lattice parameters with pressure, with the c∕a ratio variation suggesting an increase in the structural rigidity along the c direction. No structural transition is observed even after laser heating of the sample up to 2200K at 40GPa, indicating a phase stability of TiB2 in this pressure range. The ultrasonic measurements of compressional Vp and shear Vs velocities on a cylindrical specimen show linear pressure dependencies. Using the third-order Eulerian finite strain equation to fit the pressure-volume x-ray data, we obtain an isothermal bulk modulus of KTo=232.9±4.2GPa and its pressure derivative KTo′=3.86±0.23. Similarly, the parameters derived from fitting the finite strain equation to the ultrasonic data give an adiabatic bulk modulus of KSo=232.9±1.6GPa and KSo′=3.02±0.24, in good agreement with the x-ray diffraction measurements. The shear modulus and its pressure derivative derived from the ultrasonic measurements are GSo=259.8±0.4 and GSo′=2.52±0.01, respectively.
Classical description of current-induced spin-transfer torque in multilayer structures
Authors: Dugaev V. K. , Barnaś J.
Published: January 2005

We develop a classical description of the current-induced torque due to spin transfer in a layered system consisting of two ferromagnetic films separated by a nonmagnetic layer. The description is based on the classical equations for time-space evolution of the macroscopic magnetization. It is assumed that the perpendicular component of the nonequilibrium magnetization relaxes very fast in ferromagnetic films. Such a fast relaxation is due to a strong exchange field. Accordingly, the perpendicular component is totally absorbed at the interfaces giving rise to the torque. The longitudinal component, on the other hand, decays on a much longer distance defined by the spin diffusion length.
Effect of uniaxial stress on the electromechanical response of ⟨001⟩-oriented Pb(Mg1∕3Nb2∕3)O3–PbTiO3 crystals
Authors: Feng Zuyong , Lin Di , Luo Haosu , Li Shang , Fang Daining
Published: January 2005

The ⟨001⟩-oriented 0.7PMN–0.3PT and 0.67PMN–0.33PT crystals are characterized under uniaxial stress and electric field loading above the coercive field. Strain-electric-field and electric-displacement-electric-field hysteresis loops are measured at various compressive stresses showing a notable effect of stress on the electromechanical coupling. A moderate uniaxial stress can advance their electromechanical properties. Stress-strain curves are run at zero electric field, showing that depolarization for ⟨001⟩-oriented 0.7PMN–0.3PT crystal begins at 7MPa, while as little as 3MPa for 0.67PMN–0.33PT crystal, placing a severe limitation in actuator applications.
Origin of pinning enhancement in a ferromagnet-superconductor bilayer
Authors: Cieplak Marta Z. , Cheng X. M. , Chien C. L. , Sang Hai
Published: January 2005

Vortex pinning has been studied for the superconducting Nb film covering ferromagnetic Co∕Pt multilayer with perpendicular magnetic anisotropy, in which the magnetization reversal proceeds via domain-wall motion. Large enhancement of pinning in the Nb film has been observed in the final stages of the reversal process, and we demonstrate that it is caused by residual uninverted dendrite-shaped magnetic domains.
Ultrahigh field multiple Gunn domains as the physical reason for superfast (picosecond range) switching of a bipolar GaAs transistor
Authors: Vainshtein S. N. , Yuferev V. S. , Kostamovaara J. T.
Published: January 2005

The superfast (picosecond range) high-current switching observed recently in a GaAs junction bipolar transistor is explained by practically homogeneous carrier generation in the volume of the switching channels by a moving train of avalanching Gunn domains of large amplitude. The very fast (∼200ps) reduction in the collector voltage is determined by shrinkage of each domain, provided the negative electron mobility in ultrahigh electric fields is taken into account and current filamentation takes place. The results of one-dimensional simulations show good quantitative agreement with experimental voltage and current wave forms when the simulated switching area is equal to the summed areas of the filaments observed in the experiment.
Electron spin resonance study of Zn-codoping effect on the local structure of the Er-related centers in GaAs:Er,O
Authors: Yoshida Makoto , Hiraka Kensaku , Ohta Hitoshi , Fujiwara Yasufumi , Koizumi Atsushi , Takeda Yoshikazu
Published: January 2005

Electron spin resonance (ESR) measurements of Zn-codoped GaAs:Er,O grown by organometallic vapor phase epitaxy have been performed at 9.49GHz. Several anisotropic ESR signals (named as A, B, and C) are observed. The angular and temperature dependences of the A, B, and C signals are quite consistent with those observed in GaAs:Er,O. We found that the intensity of the C center decreases together with the decrease of the photoluminescence (PL) intensity by changing the doping amount of Zn, while the change of the ESR intensity of the B center is relatively small. This indicates that the Zn codoping selectively disturbed the formation of C center. Furthermore, the PL intensity seems to be scaled to the intensity of the signal C. This finding indicates that the C center plays an important role in the host excited PL of GaAs:Er,O.
Photoelectron spectroscopy of nickel-benzene cluster anions
Authors: Zheng Weijun , Nilles John M. , Thomas Owen C. , Bowen Kit H.
Published: January 2005

( Nickel ) n ( benzene ) m − cluster anions were studied by both mass spectrometry and anion photoelectron spectroscopy. Only Nin(Bz)m− species for which n⩾m were observed in the mass spectra. No single-nickel Ni1(Bz)m− species were seen. Adiabatic electron affinities, vertical detachment energies, and second transition energies were determined for (n,m)=(2,1), (2,2), (3,1), and (3,2). For the most part, calculations on Nin(Bz)m− species by B. K. Rao and P. Jena [J. Chem. Phys. 117, 5234 (2002)] were found to be consistent with our results. The synergy between their calculations and our experiment provided enhanced confidence in the theoretically implied magnetic moments of several nickel-benzene complexes. The magnetic moments of small nickel clusters were seen to be extremely sensitive to immediate molecular environmental effects.
Organic thin-film transistors with improved characteristics using lutetium bisphthalocyanine as a buffer layer
Authors: Wang Jun , Wang Haibo , Zhang Jian , Yan Xuanjun , Yan Donghang
Published: January 2005

Organic thin-film transistors (OTFTs) with a buffer layer sandwiched between source/drain electrodes and organic semiconductor are demonstrated. An intrinsic molecular semiconductor, Lutetium bisphthalocyanine (LuPc2), is used as the buffer layer due to its high carrier density (1016cm3). Compared with conventional OTFTs, the introduction of the buffer layer leads to on-state current increases from 700nA to 2.5μA, field-effect mobility increases from 0.7×10−2 to 1.58×10−2cm2∕Vs, and threshold voltage downshifts from −21 to −11V for the linear region. The on/off current ratio is improved to a level of 104. Mechanisms of performance improvement are attributed to include the difference of the Fermi level and interface dipolar between LuPc2 and Au. Our results demonstrate that it is an effective method to improve linear region characteristics by using a molecular semiconductor as the buffer layer.
Electrostatic correlations and fluctuations for ion binding to a finite length polyelectrolyte
Authors: Tan Zhi-Jie , Chen Shi-Jie
Published: January 2005

A statistical mechanical model is presented which explicitly accounts for the fluctuations, the electrostatic, and the excluded volume correlations for ions bound to a polyelectrolyte such as DNA. The method can be employed to treat a wide range of ionic conditions including multivalent ions. The microscopic framework of the theory permits the use of realistic finite length and grooved structural model for the polyelectrolyte and modeling of the finite size of the bound ions. Test against Monte Carlo simulations suggests that the theory can give accurate predictions for the ion distribution and the thermodynamic properties. For multivalent ions, the theory makes improved predictions as compared with the mean-field approach. Moreover, for long polyelectrolyte and dilute salt concentration, the theory predicts ion binding properties that agree with the counterion condensation theory.
Surface enhanced Raman scattering arising from multipolar plasmon excitation
Authors: Laurent G. , Félidj N. , Aubard J. , Lévi G. , Krenn J. R. , Hohenau A. , Schider G. , Leitner A. , Aussenegg F. R.
Published: January 2005

Visible and near infrared extinction spectra of gold nanorod regular arrays exhibit several bands assigned to high multipolar order plasmon resonances. These up to ninth order multipolar resonances generate surface enhanced Raman scattering spectra with typically 5×104 enhancement which is of similar magnitude as those obtained for dipolar excitations.
Influence of In incorporation on the electronic structure of ZnO nanowires
Authors: Bae Seung Yong , Choi Hyun Chul , Na Chan Woong , Park Jeunghee
Published: January 2005

High-density Zn0.85In0.15O and Zn0.75In0.25O nanowires were synthesized by thermal evaporation method. They consist of single-crystalline wurtzite ZnO structure with uniform [010] growth direction. X-ray diffraction (XRD) reveals the structural defects caused by the In incorporation. X-ray photoelectron spectrum (XPS) analysis suggests that In withdraw the electrons from Zn and increase the dangling-bond O2p states. The lower energy shift and green-band enhancement of photoluminescence are well correlated with the results of XRD and XPS.
In situ detection method for obtaining permeability of Fe-based amorphous alloys: ac resistance measurement for Fe84Nb7B9
Authors: Ichitsubo Tetsu , Matsubara Eiichiro , Tanaka Satoshi , Nishiyama Nobuyuki , Amiya Kenji
Published: January 2005

In this letter, we propose an in situ detection method for obtaining permeability of soft magnetic Fe-based amorphous alloys. The temperature dependence of ac resistance was measured at different frequencies during heat treatment of Fe84Nb7B9 amorphous alloys. A significant increase in the ac (∼1000kHz) resistance appears at around 920 K during the heating process, which arises from the skin effect caused by a marked increase in sample permeability. This skin effect diminishes when the sample is heated to approximately 1100 K, which corresponds to the decrease in its permeability. Consequently, we note that the ac resistance measurement is useful for quick in situ assessment to achieve the soft magnetic property of an Fe-based amorphous alloy.
True-molecular resolution imaging by frequency modulation atomic force microscopy in various environments
Authors: Fukuma Takeshi , Ichii Takashi , Kobayashi Kei , Yamada Hirofumi , Matsushige Kazumi
Published: January 2005

In this study, we discuss the relationship between Q factor of the cantilever in various environments and frequency noise in frequency modulation atomic force microscopy (FM-AFM). We first present true-molecular resolution FM-AFM images of alkanethiol self-assembled monolayers taken in a moderate vacuum environment (vacuum pressure: 6 Pa) and in air (cantilever Q factor: 390) using FM-AFM with a low noise cantilever deflection sensor. The results reveal that the minimum Q factor to obtain true-molecular resolution in FM-AFM can be less than a few hundred.
Anomalous behaviors of E1∕E2 deep level defects in 6H silicon carbide
Authors: Chen X. D. , Ling C. C. , Gong M. , Fung S. , Beling C. D. , Brauer G. , Anwand W. , Skorupa W.
Published: January 2005

Deep level defects E1∕E2 were observed in He-implanted, 0.3 and 1.7MeV electron-irradiated n-type 6H–SiC. Similar to others’ results, the behaviors of E1 and E2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E1∕E2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E1∕E2. The activation energy and the capture cross section of this defect are EC−0.31eV and σ∼8×10−14cm2, respectively.
Relationship between DNA fragmentation and nuclear status of in vitro-matured porcine oocytes: role of cumulus cells
Authors: Wongsrikeao Pimprapar , Otoi Takeshige , Murakami Masako , Karja Ni Wayan Kurniani , Budiyanto Agung , Murakami Masao , Nii Masaru , Suzuki Tatsuyuki
Published: January 2005

The present study was conducted to investigate the effects of the attachment of cumulus cells to oocytes and coculture with cumulus cells during maturation culture on the nuclear status and DNA fragmentation of porcine denuded oocytes (DOs). In the first experiment, cumulus cells were removed from cumulus–oocyte complexes (COCs) at 0, 8, 16, 24 or 32 h after the onset of maturation culture and the DOs were then cultured in their original droplets until 42 h of culture was reached. In the second experiment, all COCs were denuded before the onset of culture and the DOs were cocultured with their removed cumulus cells. The DOs were transferred into fresh medium at 0, 8, 16, 24 or 32 h after the onset of coculture with cumulus cells and then cultured until 42 h of culture was reached. After culture, DNA fragmentation and the nuclear status of oocytes were examined using the terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling (TUNEL) method. When the DOs were returned to the same droplets after removal of the cumulus cells, the removal of the cumulus cells after 16 h of culture significantly decreased the proportion of oocytes remaining at the germinal vesicle (GV) stage. However, coculture treatment of DOs in the presence of their removed cumulus cells had no significant effects on the GV breakdown (GVBD) of oocytes. There were no significant differences in the proportion maturing to MII oocytes among the groups following removal of cumulus cells after the onset of maturation culture; however, DOs cocultured with cumulus cells until the end of maturation culture exhibited an increased maturation rate compared with DOs cocultured for 8 and 16 h. The total proportion of TUNEL-positive oocytes of oocytes remaining at the GV stage was higher than that of oocytes reaching other stages, irrespective of the removal of cumulus cells and coculture treatments. However, coculture for more than 16 h decreased the total proportion of TUNEL-positive oocytes. Our results indicate that the attachment of cumulus cells to oocytes may have a critical role for oocytes undergoing GVBD and that coculture with cumulus cells promotes the ability of oocytes to complete maturation. Moreover, coculture with cumulus cells may assist the oocyte to avoid undergoing DNA fragmentation.
Reproductive performance in female ClockΔ19 mutant mice
Authors: Kennaway David J. , Boden Michael J. , Voultsios Athena
Published: January 2005

The relationship between circadian rhythmicity and rodent reproductive cyclicity is well established, but the impact of disrupted clock gene function on reproduction has not been well established. The present study evaluated the reproductive performance of mice carrying the ClockΔ19 mutation that were either melatonin deficient (ClockΔ19/Δ19) or had the capacity to synthesise melatonin reinstated (ClockΔ19/Δ19+MEL). The ClockΔ19/Δ19 mice took 2–3 days longer to mate, and to subsequently deliver pups, than their control line. The melatonin-competent mutants had a smaller, but still significant (P < 0.05), delay. The ClockΔ19 mutation resulted in smaller median litter sizes compared with control lines (seven v. eight pups; P < 0.05), whereas melatonin proficiency reversed this difference. Survival to weaning was 84% and 80% for the ClockΔ19/Δ19 and ClockΔ19/Δ19+MEL lines, respectively, compared with 94–96% for the two control lines. The ClockΔ19/Δ19 mutants became behaviourally arrhythmic in constant darkness but, despite this, seven of seven became pregnant when paired with males after at least 14 days of constant darkness (five of seven within 4 days of pairing). In the ClockΔ19/Δ19+MEL mice, seven of 15 became arrhythmic in constant darkness but still became pregnant. The seven mice that free ran for at least 14 days in constant darkness with a period of 27.1 h also became pregnant. The present study has demonstrated that the ClockΔ19 mutation has significant, but subtle, effects on reproductive performance. The reintroduction of melatonin competency and/or other genes as a result of crosses with CBA mice reduced the impact of the mutation further. It would appear that redundancy in genes in the circadian system allows the reproductive cyclicity to persist in mice, albeit at a suboptimal level.
Embryonic disc development and subsequent viability of cattle embryos following culture in two media under two oxygen concentrations
Authors: Fischer-Brown A. E. , Lindsey B. R. , Ireland F. A. , Northey D. L. , Monson R. L. , Clark S. G. , Wheeler M. B. , Kesler D. J. , Lane S. J. , Weigel K. A. , Rutledge J. J.
Published: January 2005

Bovine embryos were produced in vitro using a 2 × 2 design of modified medium (KSOM or SOF) and oxygen concentration (5% or 20%). Day 7 blastocysts were transferred in bulk (n = 11, on average) to recipient heifers and recovered non-surgically at Day 14. In two replications of a Latin square, eight heifers received embryos from each combination of factors. Recovered embryos were evaluated for trophoblast length and width, as well as the presence and diameter of an embryonic disc (ED). An ED was detected in a higher percentage of embryos that had been cultured in KSOM than SOF (72% v. 46%, respectively; P < 0.05). The aim of a second series of experiments was to associate Day 14 morphology with subsequent developmental capacity. In vitro-produced blastocysts were transferred (n = 17–20) on Day 7 to each of eight heifers and recovered at Day 14. Thirty-eight blastocysts were retransferred to heifers following morphological evaluation. Embryos in which an ED with no signs of degeneration had been detected maintained more pregnancies than other embryos in which an ED had either shown signs of degeneration or had not been detected (5/8 v. 2/30, respectively; P < 0.01). Further investigation into ED integrity at the elongating stage may contribute to our understanding of pregnancy establishment and maintenance.
Gene expression analysis of the pro-oestrous-stage rat uterus reveals neuroligin 2 as a novel steroid-regulated gene
Authors: Kang Han-Seung , Lee Chae-Kwan , Kim Ju-Ran , Yu Seong-Jin , Kang Sung-Goo , Moon Deog-Hwan , Lee Chang-Hee , Kim Dong-Kyoo
Published: January 2005

In the present study, differential gene expression in the uteri of ovariectomised (OVX) and pro-oestrous rats (OVX v. pro-oestrus pair) was investigated using cDNA expression array analysis. Differential uterine gene expression in OVX rats and progesterone (P4)-injected OVX rats (OVX v. OVX + P4 pair) was also examined. The uterine gene expression profiles of these two sets of animals were also compared for the effects of P4 treatment. RNA samples were extracted from uterine tissues and reverse transcribed in the presence of [α32P]-dATP. Membrane sets of rat arrays were hybridised with cDNA probe sets. Northern blot analysis was used to validate the relative gene expression patterns obtained from the cDNA array. Of the 1176 cDNAs examined, 23 genes showed significant (>two-fold) changes in expression in the OVX v. pro-oestrus pair. Twenty of these genes were upregulated during pro-oestrus compared with their expression in the OVX rat uterus. In the OVX v. OVX + P4 pair, 22 genes showed significant (>two-fold) changes in gene expression. Twenty of these genes were upregulated in the OVX + P4 animals. The genes for nuclear factor I–XI, afadin, neuroligin 2, semaphorin Z, calpain 4, cyclase-associated protein homologue, thymosin β-4X and p8 were significantly upregulated in the uteri of the pro-oestrus and OVX + P4 rats of both experimental pairs compared with the OVX rat uteri. These genes appear to be under the control of P4. One of the most interesting findings of the present study is the unexpected and marked expression of the neuroligin 2 gene in the rat uterus. This gene is expressed at high levels in the central nervous system and acts as a nerve cell adhesion factor. According to Northern blot analysis, neuroligin 2 gene expression was higher during the pro-oestrus and metoestrus stages than during the oestrus and dioestrus stages of the oestrous cycle. In addition, neuroligin 2 mRNA levels were increased by both 17β-oestradiol (E2) and P4, although P4 administration upregulated gene expression to a greater extent than injection of E2. These results indicate that neuroligin 2 gene expression in the rat uterus is under the control of both E2 and P4, which are secreted periodically during the oestrous cycle.