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A study was conducted to analyze magnetic hysteresis and giant magnetoimpedance in amorphous glass-covered Co-Si-B and Co-Mn-Si-B wires. The influence of the moment rotation and domain wall motion were examined. The dependencies of the modulus of impedance at several frequencies were then analyzed. Experimental results indicated the importance of the rotational component that increases with the field in small fields.

Heterostructure composed of electron-doped high-Tc superconductor La1.89Ce0.11CuO4 (LCCO), ferroelectric Ba0.5 Sr0.5 TiO3 (BST) and colossal magnetoresistance (CMR) La0.67 Sr0.33 MnO3 (LSMO) thin films were deposited on the (001) SrTiO3 (STO) substrate by pulsed laser deposition method. The current-voltage measurement shows that the LCCO/BST/LSMO structure has strong rectification comparing to the LCCO/LSMO, LCCO/BST and BST/LSMO bilayer structures. The experiment indicates that both the BST and LCCO layers play important roles in the rectifying effect in the oxide heterostructures. We discuss the mechanism of their rectification based on the energy band bending as well as the depletion and the diffusion of the charge carriers at the interfaces. The growth conditions and the multilayer features as well as the properties of individual material in the heterostructures were also investigated. [ABSTRACT FROM AUTHOR]

The influences of biaxial and uniaxial strain on the ultraviolet emission efficiencies of both c- and m-plane AlxGa1-xN films with different Al concentrations are investigated under the framework of k·p perturbation theory. The optimal high efficiency windows, for ultraviolet light emissions are quantitatively estimated. c-plane AlxGa1-xN modified by uniaxial strain, shows more advantages over biaxial-strained AlxGa1-xN. This is due to the relatively more flexible tuning range and the advantage of obtaining pure linear polarization, which can be utilized to design polarized emission devices. For m-plane AlxGa1-xN, there are always in-plane polarized emissions under both biaxial and uniaxial strain conditions, thus, it is more likely to obtain high surface emission efficiency. [ABSTRACT FROM AUTHOR]

Composites containing pure, uniform, and well-dispersed ferroelectric barium titanate (BaTiO3) nanocrystallites with various particle sizes as active phase and polyvinylidene fluoride (PVDF) polymer as matrix are fabricated using a two-step mixing and hot-pressing technique. The dependences of the dielectric and ferroelectric properties of the as-prepared composites on the nanoparticle sizes are investigated systematically. The polarization-electric field hysteresis loops are displayed, indicating the ferroelectricity for the BaTiO3/PVDF nanocomposites. The remanent polarization is found to increase as the size of BaTiO3 particles increases from 25 to 500 nm. The dielectric constant of the composites exhibits a complex variation as a function of the BaTiO3 nanoparticle sizes: it reaches a maximum value in the composites with BaTiO3 nanoparticle sizes of 80–100 nm and decreases again when the particle size is further reduced under 50 nm. [ABSTRACT FROM AUTHOR]

As-doped ZnO films were grown by the radio frequency magnetron sputtering method. As the substrate temperature during growth was raised above ∼400 °C, the films changed from n type to p type. Hole concentration and mobility of ∼6×1017 cm-3 and ∼6 cm2 V-1 s-1 were achieved. The ZnO films were studied by secondary ion mass spectroscopy, x-ray photoelectron spectroscopy (XPS), low temperature photoluminescence (PL), and positron annihilation spectroscopy (PAS). The results were consistent with the AsZn–2VZn shallow acceptor model proposed by Limpijumnong et al. [Phys. Rev. Lett. 92, 155504 (2004)]. The results of the XPS, PL, PAS, and thermal studies lead us to suggest a comprehensive picture of the As-related shallow acceptor formation. [ABSTRACT FROM AUTHOR]

Wavelength-matched vibrational excitations of ethylene (C2H4) molecules using a tunable carbon dioxide (CO2) laser were employed to significantly enhance the chemical vapor deposition (CVD) of diamond in open air using a precursor gas mixture of C2H4, acetylene (C2H2), and oxygen (O2). The CH2-wag vibration mode (ν7) of the C2H4 molecules was selected to achieve the resonant excitation in the CVD process. Both laser wavelengths of 10.591 and 10.532 μm were applied to the CVD processes to compare the C2H4 excitations and diamond depositions. Compared with 10.591 μm produced by common CO2 lasers, the laser wavelength of 10.532 μm is much more effective to excite the C2H4 molecules through the CH2-wag mode. Under the laser irradiation with a power of 800 W and a wavelength of 10.532 μm, the grain size in the deposited diamond films was increased by 400% and the film thickness was increased by 300%. The quality of the diamond crystals was also significantly enhanced. [ABSTRACT FROM AUTHOR]

Large-area Au/Pt/n-In0.2Ga0.8N Schottky contacts have been fabricated for photovoltaic devices. The current transport mechanisms of the Schottky contacts to n-In0.2Ga0.8N with different background carrier concentrations are investigated. The thermionic emission is a dominating current transport mechanism at the Pt/n-InGaN interface in a low background carrier concentration sample, while the defect-assisted tunneling current and trap-related recombination current play important roles in high background carrier concentration samples. The Schottky diode fabricated using the low background carrier concentration sample gives much better Schottky barrier characteristics and exhibits a three to four order of magnitude higher spectral responsivity and a larger rejection ratio in comparison with those fabricated using the high background carrier concentration samples. [ABSTRACT FROM AUTHOR]

Vibrational resonant excitation of ethylene (C2H4) molecules using a carbon dioxide laser was employed to promote reactions in precursors of ethylene, acetylene (C2H2), and oxygen to enhance diamond deposition. One of the vibrational modes (CH2 wag mode, v7) of the C2H4 molecules was selected to achieve the resonant excitation in the reactions. Optical emission spectroscopy was used to study the effects of laser resonant excitation on the reactions for diamond deposition. The optical emissions of CH and C2 species were enhanced with the laser excitation, indicating that there are more active species generated in the reactions. Thicknesses and grain sizes of the deposited films were increased correspondingly. Temperature calculations from the line set in the R-branch of CH emission spectra indicated that a nonthermal process is involved in the enhanced diamond deposition. [ABSTRACT FROM AUTHOR]

This article reports on the study of microstructure and dislocation of InN films using high resolution x-ray diffraction grown on sapphire (0001) both by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). The mosaic tilt, twist, and correlation lengths of InN films are determined by using symmetrical and asymmetrical reflections as well as reciprocal space mapping. Deducing from these results, MBE-grown InN film exhibits the edge-type dislocations of 4.0×109 cm-2, which is about ten times higher than the density of screw-type dislocations. In MOCVD-grown InN sample, the edge-type dislocations density is as high as 2.1×1010 cm-2, and the screw-type dislocations density is 1.3×109 cm-2. They indicate that edge type is the predominant dislocation type in the InN films. By comparing the reported transmission electron microscopy results, the accuracy of evaluation for the dislocation density using the mosaic model is proved. [ABSTRACT FROM AUTHOR]

In this article, domain wall motion and the extrinsic contributions to the dielectric and piezoelectric responses in sol-gel derived lead zirconate titanate (PZT) films with compositions near the morphotropic phase boundary were investigated. It was found that although the films had different thicknesses, grain sizes, and preferred orientations, similar intrinsic dielectric constants were obtained for all films between 0.5 and 3.4 μm thick. It was estimated that about 25%-50% of the dielectric response at room temperature was from extrinsic sources. The extrinsic contribution to the dielectric constant of PZT films was mainly attributed to 180° domain wall motion, which increased with both film thickness and grain size. In studies on the direct and converse longitudinal piezoelectric coefficients of PZT films as a function of either stress or electric driving field, it was found that the ferroelastic non-180° domain wall motion was limited. Thus extrinsic contributions to the piezoelectric response were small in fine grain PZT films (especially those under 1.5 μm in thickness). However, as the films became thicker (>5μm), nonlinear behavior between the converse piezoelectric coefficient and the electric driving field was observed. This indicated that there was significant ferroelectric non-180° domain wall motion under high external excitation in thicker films. The activity of the non-180° domain walls was studied through non-180° domain switching. For fine grain films with film thicknesses less than 2 μm, non-180° switching was negligible. Transmission electron microscopy plan-view micrographs evidenced non-180° domain fringes in these films, where the vast majority of grains were 50-100 nm in diameter and showed a single set of domain fringes. Taken together, these measurements suggest that the pinning of non-180° domain walls is very strong in films with thickness less than 2 μm. In thicker films, non-180... [ABSTRACT FROM AUTHOR]

Discusses a study which experimented a bistable twisted nematic (BTN) liquid crystal (LC) cell, electrically switched between two quasistable twisted states in the development of LC display. Optical properties for a transmissive BTN; Details on the experiment; Results and discussion; Conclusions.

Presents information on a study which examined the optics of reflective bistable twisted nematic (BTN) liquid crystal display for general values of twist angle and polarizer angle. Parameter space for reflective BTN; Brightness and efficiency of reflective BTN modes; Reflectance spectra; Conclusions.

Synchrotron radiation photoemission study showed that the energy level alignment at the interface between N, N'-bis(naphthalene-1-y1)-N, N'-bis(phenyl) benzidine (NPB), a typical hole transport material, and Al could be adjusted by precovering a thin C60 layer on Al. The interface dipoles so formed could shift both the highest occupied molecular orbital level of NPB and the secondary electron cutoff measured at the early stage of the NPB deposition. The barrier height for hole injection from Al to NPB could thus be lowered by as much as 0.98 eV, and the optimal thickness of the inserted C60 layer was found to be 8-12 Å. [ABSTRACT FROM AUTHOR]

The effects of a long-duration high-temperature annealing in an air ambient on the strain of the AlGaN barrier layer and high-temperature transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures were investigated. The results show that the annealing induces a nonreversible lattice relaxation in the AlGaN layer and increases remarkably the 2DEG density due to the incorporation of oxygen atoms into the AlGaN surface and decreases the 2DEG mobility in the AlGaN/GaN heterostructure. However, the conductivity of the 2DEG has no obvious change in our samples within the measured temperature range before and after the annealing, indicating that AlGaN/GaN heterostructures are possibly promising for electron devices operated at high temperatures based on atmospheric exposure. [ABSTRACT FROM AUTHOR]

In this letter we report the experimental result on the study of light scattering in a one-dimensional quasiperiodically poled LiTaO3 crystal. The infrared scattering signal in the crystal was upconverted into visible band by sum frequency with incident light, forming a set of coaxial conical second harmonic beam with a quasiperiodic ratio at the radius. The quasi-phase-matching significantly enhanced such a nonlinear interaction. The angular distribution of scattering light in crystal was extracted from the experimental result. This reveals a possible application of quasiperiodic structure on the study of light scattering. [ABSTRACT FROM AUTHOR]