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Intrinsic defects in Bi2Te3 were analyzed using first-principles density functional theory calculations. The results demonstrated that antisite defects were dominant in both p- and n-type Bi2Te3. To investigate the characteristics of these defects, n-type Bi2(Te,Se)3 compounds were fabricated using powder prepared by high-energy ball milling and their electrical properties were examined. Electrical resistivity and the Seebeck coefficient increased with ball milling time. These changes in both properties were attributed to a reduction in the carrier concentration, which was supported by the Hall coefficient measurement. The antisite defects were found to be responsible for the changes in carrier concentration. Lattice parameter analysis supported the postulate that variations in the concentration of antisite defects were responsible for the changes in carrier concentration. These findings suggest that optimization of carrier concentration should be considered in the high-energy ball milling process, in which reductions in grain size are expected to improve thermoelectric properties.VC [ABSTRACT FROM AUTHOR]

In this study, the effect of Ag or Sb addition on the thermoelectric properties of PbTe including the Seebeck coefficient, the electrical resistivity, and the thermal conductivity, was studied in the temperature range from 323 to 723 K. The major carriers in the Ag-doped and the Sb-doped PbTe are holes and electrons, respectively. A degenerate semiconductor behavior in the electrical transport properties was observed in the Ag-doped, whereas the semi-metallic in the Sb-doped. It was suggested from the results of the Hall effect measurement and the Seebeck coefficient that the effective mass was significantly altered by the Sb-doping. The maximum dimensionless figure of merit, ZT, of Pb1-xAgxTe and Pb1-xSbxTe (x=0.1) alloys showed 0.27 and 0.62 at 723 K, respectively. Based on the analysis of the Seebeck coefficient of the Ag or the Sb-doped PbTe, the interaction between Ag and Sb in PbTe, as expected in the AgPbmSbTem+2 (LAST-m), may be supposed. [ABSTRACT FROM AUTHOR]

We report on the enhanced light output of GaN-based flip-chip light-emitting diodes (LEDs) fabricated with SiO2/TiO2 distributed Bragg reflector (DBR) on mesa sidewall. At the wavelength of 400 nm, five pairs of SiO2/TiO2 DBR coats on the GaN layer showed a normal-incidence reflectivity as high as 99.1%, along with an excellent angle-dependent reflectivity. As compared to the reference LED, the LED fabricated with the DBR-coated mesa sidewall showed an increased output power by a factor of 1.32 and 1.12 before and after lamp packaging, respectively. This could be attributed to an efficient reflection of the laterally guided mode at the highly reflective mesa sidewall, enhancing the subsequent extraction of light through the sapphire substrate. [ABSTRACT FROM AUTHOR]

In this study, the thermoelectric properties of AgPbmSbTem+2 (LAST-m, m=12, 16, 18, 20, 22, and 26), including the Seebeck coefficient, the electrical resistivity, and the thermal conductivity, were studied in the temperature range from 323 to 773 K. The Seebeck coefficient and the electrical resistivity exhibited the behavior of a degenerate semiconductor. The measured results of the carrier concentration supported the conclusions of the electrical transport properties. The lowest electrical resistivity and the thermal conductivity were observed, which leads to the best thermoelectric performance in LAST-18 and the dimensionless figure of merit ZT value of 0.8 at 773 K. [ABSTRACT FROM AUTHOR]

We present evidence for the formation of transient hydroxyls from the reaction of water with atomic oxygen on Au(111) and investigate the effect of adsorbed oxygen on the hydrogen bonding of water. Water is evolved in peaks at 175 and 195 K in temperature programed reaction experiments following adsorption of water on oxygen-covered Au(111). The peak at 175 K is ascribed to sublimation of multilayers of water, whereas the peak at 195 K is associated with oxygen-stabilized water or a water-hydroxyl surface complex. Infrared reflection absorption spectra are consistent with the presence of molecular water over the entire range of coverages studied, indicating that isolated stable hydroxyls are not formed. Isotopic exchange of adsorbed 16O with H218O following adsorption and subsequent temperature programed reaction, however, indicates that transient OH species are formed. The extent of oxygen exchange was considerable—up to 70%. The degree of oxygen exchange depends on the initial coverage of oxygen, the surface temperature when preparing oxygen adatoms, and the H218O coverage. The hydroxyls are short-lived, forming and disproportionating multiple times before water desorption during temperature programed reaction. It was also found that chemisorbed oxygen is critical in the formation of hydroxyls and stabilizing water, whereas gold oxide does not contribute to these effects. These results identify transient hydroxyls as species that could play a critical role in oxidative chemical reactions on gold, especially in ambient water vapor. The crystallinity of adsorbed water also depended on the degree of surface ordering and chemical modification based on scanning tunneling microscopy and infrared spectra. These results demonstrate that oxidation of interfaces has a major impact on their interaction with water. [ABSTRACT FROM AUTHOR]

The structure, magnetic properties, and magnetostriction of Sm[sub 0.5]R[sub 0.5](Fe[sub 1-x]Co[sub x])[sub 2] compounds (R = Nd, Pr) have been investigated by using x-ray diffraction analysis, ac initial susceptibility, vibrating sample magnetometer, and standard strain techniques. It was found that the (Sm[sub 0.5]Nd[sub 0.5])Fe[sub 2] compound with MgCu[sub 2]-type cubic structure possesses low magnetocrystalline anisotropy and high ratio of magnetostriction to magnetocrystalline anisotropy. When Co is substituted for Fe, the Curie temperature of (Sm[sub 0.5]Nd[sub 0.5])(Fe[sub 1-x]Co[sub x])[sub 2] alloys exhibit a peak at x = 0.25 and the saturation magnetization increases with increasing Co content when x<0.25 and decreases when x≥0.5. The microstructure of (Sm[sub 0.5]Pr[sub 0.5])(Fe[sub 1-x]Co[sub x])[sub 2] alloys is nearly a single phase in the range of 0.75≤x≤1. The saturation magnetization and magnetostrictiom of the alloys exhibit a peak at x = 0.25 and x = 0.5, respectively. [ABSTRACT FROM AUTHOR]

The goal of the present paper is to investigate the phase stability and soft magnetic properties of amorphous CoNbZr films when Pd is added. The CoNbZrPd films deposited on Si wafers exhibited amorphous structures independent of the amount of Pd. On the addition of 4.34% Pd, excellent soft magnetic characteristics of the films were observed with a coercive force of 0.54 Oe and an anisotropy field of 11 Oe, whereas a coercive force of 1 Oe and an anisotropy field of 3.5 Oe were shown in the film without the addition of Pd. The increased anisotropy field and low coercive force of the films may be attributed to the occupancy of Pd in preferred sites parallel to an external magnetic field applied during the deposition process. A permeability of about 1100 was constant at operation frequencies ranging up to 100 MHz, which can be explained by the Landau-Lifshitz formula. [ABSTRACT FROM AUTHOR]