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The crystallographic and magnetic structures of the HfFe6Ge6-type compound Ho0.5Y0.5Mn6Sn6 have been studied by powder neutron diffraction and in-situ Lorentz transmission electron microscopy. Besides the nonlinear thermal expansion of lattice parameters, an incommensurate conical spiral magnetic structure was determined in the temperature interval of 2–340 K. A spin reorientation transition has been observed from 50 to 300 K, where the alignment of the c-axis component of magnetic moments of the Ho sublattice and the Mn sublattice transfers from ferrimagnetic to ferromagnetic. [ABSTRACT FROM AUTHOR]

Research describing temperature dependent photoluminescence characteristics of zinc-selenium epilayers is presented. Excitation dependent parameters of chlorine doped ZnSe layers are also investigated.

CdZnTe compound semiconductor was investigated to observe microphotoluminescence mapping.

Electrical properties for Au- and Ag-InGaAs Schottky diodes containing metal electrodes deposited both at low temperature and room temperature were systematically investigated. Values of the parameters of the diodes were derived by superimposing the current-voltage-temperature curves over the temperature range 100-300 K and the deep defect defect centers in InGaAs material were characterized using deep level transient spectroscopy. The results revealed a deep defect level at 0.321 eV under the bottom of the conduction band in the InGaAs sample.

Research was conducted on (100) Hg1-xCdxTe epilayers grown via molecular beam epitaxy based on various Hg and Te flux ratios. The Hg and Te flux ratios were found to significantly influence hillockdensity, electron concentration and electron mobility. Results also showed thatoptimal Hg ad Te ratios reduced structural defects caused by nonstoichiometry.

Recently, nanoglass (NG) was found to exhibit a surprising homogeneous superplastic deformation behavior. However, how the presence of notch affects its mechanical properties remains unexplored. Here, we perform molecular dynamics simulations on a superplastic Cu50Zr50 NG containing a pre-existing notch under tensile loading, with focus on the notch sensitivity. Our results show that when the notch size is smaller than or comparable to the average grain size (d), the NG still exhibits a superplastic deformation and shows notch-insensitivity. When the notch size is larger than d, however, the NG fails by localized shear banding emanating from the notch root and shows notch-sensitivity. The origin of this transition arises from the competition between the shear band nucleation induced by the stress concentration at the notch root and the growth of shear transformation zones distributed in the glass-glass interfaces. Our results provide useful guidelines for the design and engineering of NG with notch for structural applications. [ABSTRACT FROM AUTHOR]

A master equation for describing the polar nanoregions (PNRs) dynamics with adaptive-volume-dependent activation energy barrier has been established based on mean field approximation to investigate the anomalous temperature- and frequency-dependent dielectric properties of relaxor ferroelectrics. In the proposed model, the activation energy was correlated with the applied electric field and mean volume of PNRs. By expressing the PNRs mean volume as a function of temperature and pressure, and then fitting it to some existing experimental data, the results obtained reproduced the experimentally observed dielectric response including the broad temperature- and frequency-dependent peaks, frequency shift and dispersion of susceptibility. Finally, it has been found that the pressure and applied electric field led to the decrease of the PNRs relaxation time, and thus the peak of the real part of the dielectric constant was shifted to a lower temperature, which is consistent with the existing experimental data. The present study shows that polar cluster dynamics provides a better understanding of the macroscopic dielectric properties of relaxor ferroelectrics. [ABSTRACT FROM AUTHOR]

The time invariant behaviors of topological insulators are expected to be changed with magnetic doping, which motivate the present study. Here, we show that for Bi2-xCrxSe3 (0.01 ≤ x ≤ 0.3) thin films grown on Si, the non-trivial topological surface state is weakened by the Cr dopants. The band gap of surface is opened and monotonically increased with Cr concentration up to ∼100 meV at 10 K. Meanwhile, the semiconducting behavior is well-maintained in the bulk owing to the reduction of background doping by means of a modified growth strategy and an in situ passivation method. Besides, we also observe the existence of unconventional ferromagnetic ordering below 35 K, for which the Curie-Weiss Law and conventional/modified Arrott equations do not apply. These observations may further help us investigate extraordinary magneto-electric effect in topological insulators, and the result will also pave the way for realizing the quantized anomalous Hall effect. [ABSTRACT FROM AUTHOR]

With the oblique-incidence reflectivity difference (OIRD) technique, we successfully label-free detected the interaction of swine IgG with different concentrations of 0.125, 0.25, 0.5, 1 mg/ml, and 5 μg/ml goat anti-swine IgG, and real-time detected the reaction dynamic processes of 0.5 mg/ml swine IgG and goat anti-swine IgG with different concentration of 5, 10, and 20 μg/ml, respectively. The interaction times are about 2043, 1828, and 1347 s for the reactions of 0.5 mg/ml swine IgG and goat anti-swine IgG of 5, 10, and 20 μg/ml, respectively. By fitting the reaction dynamic curves, we obtained that the association constant of swine IgG and goat anti-swine IgG is 1620.77 M-1·S-1 at temperature about 22 °C. The experimental results demonstrate that the OIRD is a promising and competing method for label-free and real time detecting the biomolecular interactions and achieving the quantitative information of reaction kinetics. [ABSTRACT FROM AUTHOR]

Mn1.85Co0.3Ni0.85O4 (MCN) thin films with pure spinel phase and different grain size were prepared on Al2O3 substrates by chemical deposition method. Temperature dependent ac impedance spectroscopy was employed to analyze the grain size influence on the electrical conduction of intrinsic grain and grain boundary (GB) in MCN thin films. The conduction mechanisms of grain and GB both followed the small-polaron hopping model. It was found that the hopping types of GB (nearest-neighbor-hopping (NNH)) and grain (a transition from variable-range-hopping (VRH) to NNH) were not affected by the grain size, while the resistance, characteristic temperature, and activation energy of grain and GB were affected by the grain size in varying degrees. Additionally, the mechanisms concerning the dependence of electrical conduction of grain and GB on the grain size of MCN thin films were discussed in detail. These studies will also provide a comprehensive understanding of the conduction behaviors of a system with mixed NNH and VRH. [ABSTRACT FROM AUTHOR]

Recently, unusual magnetic properties were found experimentally in otherwise diamagnetic nanoparticles. Our experiments and analysis revealed that a universal expression can describe the size-dependent magnetic moments in ultrafine diamagnetic systems, including Au, Pd, and HfO2 nanoparticles. A model was presented to explain the observed phenomenon. It suggested that the up and down spins in ultrafine diamagnetic systems are spatially separated and form asymmetric spin-singlet pairs. The correlation lengths of the spin-singlet pairs in Au, Pd, and HfO2 nanoparticles were estimated to be about 1.65, 13, and 4.4 nm, respectively. On the basis of this model, we explain (a) the origin and the size dependence of magnetic moments in diamagnetic nanoparticles, and (b) the origin of the extremely large anisotropy in diamagnetic nanoparticles. [ABSTRACT FROM AUTHOR]

A particle-in-cell/Monte Carlo collision simulation study of femtosecond laser stimulation of electrical discharges in submicron gaps between platinum scanning tunneling microscope cathode tips and gold film anodes in atmospheric pressure argon gas is described. The breakdown potential of gaps containing either preloaded electrons or preloaded neutral and ionized platinum atoms and electrons at various densities were compared to the breakdown potential of gaps with background argon gas alone. It was found that gaps preloaded with sufficient densities of either electrons or partially ionized electrode materials broke down at cathode potential of -80 V while gaps with background argon gas alone required applied cathode potentials between -200 to -250 V to cause a breakdown. Also, partially ionized material was much more effective at stimulating breakdown than electrons alone. The density of preloaded partially ionized platinum required to lower breakdown cathode potential to -80 V was approximately 12.5 times smaller than that required for the preloaded electrons alone in the same size gap. Analysis of the mechanism by which the preloaded partially ionized material promoted breakdown showed that laser ablated ions located near the cathode tip increased the local field at the cathode surface and the field-emitted electron flux from the cathode. This higher electron flux ionized background argon gas and preloaded platinum which resulted in gap breakdown. The threshold density of partially ionized platinum for gap breakdown varied approximately linearly with applied cathode potential. [ABSTRACT FROM AUTHOR]

This article presents the results of combined experimental and theoretical studies of elastic and thermal properties of Zr2Al3C4 carbide. The full set of second order elastic constants, bulk modulus, shear modulus, and Young’s modulus of Zr2Al3C4 were calculated and compared with those of Zr3Al3C5 and ZrC. The experimentally measured Young’s modulus and shear modulus are in good agreement with theoretical ones. The calculated Debye temperature from elastic constants of Zr2Al3C4 is 830 K, which is slightly higher than that of Zr3Al3C5, and exhibits pronounced enhancement in comparison with that of ZrC. The highest Debye temperature of Zr2Al3C4 is related with its highest specific stiffness, i.e., the stiffness-to-weight ratio. The heat capacity and thermal conductivity of Zr2Al3C4 were measured by means of the flash method. The thermal conductivity of Zr2Al3C4 decreases with increasing temperature, for instance the values at room temperature and 1600 K are 15.5 and 10.1 W/m K, respectively. The investigations provide information on elastic and thermal properties of Zr2Al3C4 with promising high temperature applications. [ABSTRACT FROM AUTHOR]

A combination of molecular dynamics simulations and experiments has been used to investigate the use of various low energy ion assisted vapor deposition approaches for controlling the interfacial structures of a model copper/tantalum multilayer system. Films were grown using argon ion beam assistance with either a fixed or modulated ion energy during metal deposition. The effect of sequential ion assistance (after layer’s deposition) was also investigated. The argon ion energy was varied between 0 and 50 eV and the effect on the atomic scale structure of Ta/Cu film interfaces and the film electrical resistivity were studied. The use of simultaneous argon ion assistance with an ion energy of ∼10 eV and an ion/metal atom flux ratio of ∼6 resulted in atomically sharp interfaces with little intermixing, consistent with simulation predictions. Ion impacts in this range activated surface atom jumping and promoted a step flow film growth mode. Higher energies were also successful at interface flattening, but they caused significant intermixing between the layers and increased film’s resistivity. This could be reduced using modulated ion energy and sequential ion beam assistance. This was again consistent with atomic scale simulations, which indicated that metal layers deposited over an interface before ion assistance was initiated impeded atom exchange across interfaces and therefore intermixing. [ABSTRACT FROM AUTHOR]

A series of sharp intense peaks was observed in the low-temperature photoluminescence spectrum of unintentionally doped GaN in the photon energy range between 3.0 and 3.46 eV. We attributed the majority of these peaks to excitons bound to unidentified structural and surface defects. Most of the structural- and surface-related peaks (at 3.21, 3.32, 3.34, 3.35, 3.38, and 3.42 eV) were observed in Ga polar films. In N polar GaN, we often observed the 3.45 eV peak attributed to excitons bound to the inversion domain interfaces. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Viscosity and reptation studies on five different magnetic tapes indicate the dependency of remanence percentage reduction P on number of field pulses n and their width tou. Changes in the linear regime of the tapes are consistent with the quasistatic experimental errors of viscosity measurements.

A combination of molecular dynamics simulations and experiments is used to investigate the use of various low energy ion assisted vapor deposition approaches for controlling the interfacial structures of a model copper/tantalum multilayer system. The results have confirmed that the very low energy ion assisted growth hypotheses identified by simulations are realizable by using the biased target ion beam deposition approach.

Presents information on a study which investigated the molecular beam epitaxially grown short period (001) Hg[sub1-x]Cd[subx]Te-HgTe superlattices. Advantage of the superlattices in infrared applications compared to the alloy; Experimental and theoretical details; Results and discussion; Conclusions.

Details a study which measured low-frequency noise on small p-i-n indium gallium arsenide/indium phosphide photodiodes designed to be used in optical communication systems. Methods; Results and discussion; Conclusion.

Presents information on the measurements of 1/f noise in vacuum photodiodes. Theoretical expression for the Hooge parameter; Discussion on the classical 1/f noise due to fluctuations in the electron affinity of the cathode; Explanation of the poisoning effects observed in the noise of aged tubes.

Magnetic properties of Sm0.5Sr0.5MnO3 nanoparticles with different particle sizes are investigated. It is found that all the nanoparticles show a first-order ferromagnetic transition under low magnetic fields, but a second-order one above a critical field HCR. As the particle size decreases, the ferromagnetic transition temperature, the thermal hysteresis width in the magnetizations, and HCR exhibit a significant decrease, which indicates that the ferromagnetism is weakened and the first-order transition is softened. A detailed analysis on the magnetic susceptibilities of these nanoparticles reveals that this weakening and softening are attributed to the weakened double-exchange interactions and the strongly suppressed charge-ordered antiferromagnetic state by the size reduction, respectively. [ABSTRACT FROM AUTHOR]

Polycrystalline Cd0.7Fe0.3Cr2S4 has been prepared by a solid state reaction. A crystalline structure study shows that the x-ray diffraction pattern can be indexed successfully in a cubic spinel phase. Its magnetic and dielectric properties have been investigated. A ferrimagnetic phase transition of the material was identified at 123 K. Larger permittivity and loss tangent are observed than those of CdCr2S4 in the frequency range 300 Hz–1 MHz. An anomaly cusp induced by the internal magnetic field on [variant_greek_epsilon]-T and tan δ-T curves is observed near its magnetic transition point, implying an existence of magnetodielectric effect. At low temperature TN, the permittivity variation Δ[variant_greek_epsilon] depends on magnetization M and shows clearly a linear relationship between Δ[variant_greek_epsilon] and M2, indicating an interplay of permittivity and magnetism. Furthermore, compared to CdCr2S4, Cd0.7Fe0.3Cr2S4 exhibits smaller values of dielectric relaxation time and activated energy above TC due to Fe2+ doping. [ABSTRACT FROM AUTHOR]

Intersubband transitions in Si-doped molecular beam epitaxy grown GaN/AlGaN multiple quantum wells on c-plane sapphire were investigated using the Fourier-transform infrared optical absorption technique. Several GaN quantum well samples were grown with either AlGaN bulk or GaN/AlGaN short period superlattice barriers. The measurements were made in a waveguide configuration utilizing a facet polished at 45° to the c plane. The integrated area of the intersubband transitions in several waveguides cut from different location of the wafer was measured, from which we estimated the two-dimensional electron gas density (σ). The measured values of σ are about two orders of magnitude larger than the Si doping level of ∼8 × 10[SUP17]cm[SUP-3], which is consistent with the polarization effects, particularly considering the large number of GaN/AlGaN interfaces. The internal quantum efficiency of the intersubband transitions was estimated to be on the order of 40% for samples with superlattice barriers. [ABSTRACT FROM AUTHOR]

Polycrystalline Cd0.7Fe0.3Cr2S4 has been prepared by a solid state reaction. A crystalline structure study shows that the x-ray diffraction pattern can be indexed successfully in a cubic spinel phase. Its magnetic and dielectric properties have been investigated. A ferrimagnetic phase transition of the material was identified at 123 K. Larger permittivity and loss tangent are observed than those of CdCr2S4 in the frequency range 300 Hz–1 MHz. An anomaly cusp induced by the internal magnetic field on [variant_greek_epsilon]-T and tan δ-T curves is observed near its magnetic transition point, implying an existence of magnetodielectric effect. At low temperature T