Far infrared optical properties of amorphous semiconductors As?S systems

Far infrared reflection, Raman, and Brillouin spectra of amorphous semiconductor As–S systems are measured. From the reflection spectra, the optical constants are calculatured by the Kramers Kronig analysis. The existence of some intermediate range interaction among molecular units AsS₃ is suggested. From the analysis of the Boson peak at low frequency region in Raman scattering, the correlation length is obtained to be ca. 6 Å. From the absorption coefficient in the low frequency region about 3% fluctuation of charge is suggested for As₂S₃ by schlömann theory.     

Differential approximations for transient radiative transfer through a participating medium exposed to collimated irradiation

First, we apply the modified differential approximation (MDA) suggested by Chandrasekhar to transient radiative transfer in a scattering planar medium exposed to collimated pulse irradiation. Next, a hybrid method of the P_1/3 approximation suggested by Olson and the MDA is developed. The hybrid method may be referred to as the modified P_1/3 approximation (MP_1/3A) and is also applied to the same example. Comparisons of the results obtained by solving the MDA, the MP_1/3A and the exact integral equation are made. The comparisons show that the temporal distribution of the transmissivity obtained by the MDA contains a small protuberance or an abrupt slope change, which decreases with the decrease of the scattering albedo. The results obtained by the MP_1/3A are more accurate than those obtained by the MDA for most of the cases considered, because the MP_1/3A corrects the propagation speed of the transmitted radiation.     

Cation inter-diffusion between LaMnO3 and LaCoO3 materials

Cation inter-diffusion between polycrystalline LaMnO₃ and LaCoO₃ pellets has been studied at 1373-1673 K in air by electron microprobe analysis. Inter-diffusion coefficients were evaluated by the Boltzman-Matano method from Mn³⁺ to Co³⁺ concentration profiles. The cation inter-diffusion is thermally activated and follows Arrhenius behaviour. The activation energies have been calculated and the mechanism for the B-site cation diffusion in La(Mn,Co)O₃ solid solution suggested. Cation diffusion coefficients in the end members LaMnO₃ and LaCoO₃ were estimated. Cation mobility in LaMnO₃ is higher than in LaCoO₃. It is suggested that higher cation diffusion in LaMnO₃ is due to the specific defect chemistry of this material, caused by the relative stability of manganese in a higher oxidation state (Mn⁴⁺). The results are compared to previous reports on cation diffusion in perovskite oxides.     

Electron spin resonance study of a CuIr2S4 single crystal

A spinel sulphide CuIr₂S₄ single crystal, which exhibits an orbitally induced Peierls phase transition at ～230?K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir⁴⁺ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir⁴⁺ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir⁴⁺ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE _JT is much smaller than the spin-dimerization gap.     

Decreased n-type behavior of monolayer MoS2 crystals annealed in sulfur atmosphere

Herein, we report decreased n-type behavior of mechanically exfoliated monolayer MoS₂ crystals via annealing in sulfur atmosphere. The Raman, photoluminescence, and X-ray photoelectron spectroscopy (XPS) measurements consistently suggested decreased n-type behavior of the monolayer MoS₂ crystals after an hour of thermal annealing at 200 °C in sulfur atmosphere. Such decreased n-type behavior could be attributed to the reduced concentration of sulfur vacancies after the annealing, suggested by the analysis of XPS spectra. Furthermore, after the annealing in sulfur atmosphere, the monolayer MoS₂ transistors exhibited positively shifted threshold voltages and reduced on-currents, confirming decreased n-type conduction. These results demonstrate that the reduction of the concentration of sulfur vacancies decreases n-type behavior in monolayer MoS₂, providing valuable information on understanding the effect of sulfur vacancies on the performance of monolayer MoS₂ devices.     

Effects of surface-modification with Bi2O3 on the thermal stability and photoinduced charge property of nanocrystalline anatase TiO2 and its enhanced photocatalytic activity

Bi₂O₃ surface-modified TiO₂ nanoparticle has been synthesized by sol-hydrothermal processes, followed by post-treatment with an appropriate amount of bismuth nitrate solution, and also characterized by XRD, Raman, BET, TEM, FT-IR, XPS, UV-vis DRS and SPS techniques. The effects of the surface-modification with Bi₂O₃ on the thermal stability, photoinduced charge separation and photocatalytic activity for degrading rhodamine B (or phenol) under ultraviolet (or visible) irradiation are investigated in detail, along with their relationships and the activity enhancement mechanisms are also suggested. The results show that the modification with Bi₂O₃ can improve the thermal stability of the as-prepared anatase crystallites, consequently enhancing the anatase crystallinity so as to promote the photoinduced charge separation. And the modification with Bi₂O₃ also extends the optical response range. It can be concluded that the activity enhancement of surface-modified TiO₂ is mainly attributed to the increase in the photoinduced charge separation rate and to the extent of the optical response range, compared with un-modified ones. Moreover, the inhibition phase transformation mechanism related to Bi₂O₃ is suggested.     

Cocktail effect of Fe2O3 and TiO2 semiconductors for a high performance dye-sensitized solar cell

The bi-semiconductors of TiO₂ and Fe₂O₃ were used as a photoelectrode material in a high performance dye-sensitized solar cell due to cocktail effects from the two conduction bands. The size of the semiconductors was reduced by using a paint shaker to enlarge the contact area of the semiconductor with the dye or electrolyte. The fill factor and the efficiency of the prepared dye-sensitized solar cell were improved by over 16% and 300%, respectively; these parameters were measured from a current-voltage curve that was based on the effects of the Fe₂O₃ co-semiconductor and the size reduction. A mechanism is suggested wherein the conduction band of Fe₂O₃ works to prohibit the trapping effects of electrons in the conduction band of TiO₂. This result is attributed to the prevention of electron recombination between electrons in the TiO₂ conduction band with dye or electrolytes. The mechanism is suggested based on impedance results, which indicate improved electron transport at the interface of the TiO₂/dye/electrolyte.     

Multipulse sequences for explosives detection by NQR under conditions of magnetoacoustic and piezoelectric ringing

A number of methods for cancelling magnetoacoustic and piezoelectric ringing signals in the spectroscopy of the nuclear quadrupole resonance are presented. The suggested methods include using the sequence (?₀)_?-(τ-?_x-2τ-? _y -2τ-?_?x -2τ-?_?y -τ) _n and a multipulse analog of the two-pulse Hahn sequence with the first pulse replaced by a short steady-state sequence. Another method presented is the method of orthogonal effective fields for a fast saturation of the quadrupole spin system which can be used for subtracting the magnetoacoustic and piezoelectric components from the signal. The suggested methods can be used for the practical purposes of detecting explosive substances and narcotics.     

Spontaneous current and DC bias induced current in nickel–metal hydride secondary battery

The responses to biasing a nickel–metal hydride secondary battery with a dc pulse train, as well as to spontaneous discharging, are studied. A comparison is made between the current during biasing, i _e, and the current during off-biasing, i _g. It is suggested that both currents arise from the motion of the same charge carriers in the electrolyte, possibly the OH⁻ ions. The only difference is that the motive force for i _e is a bias voltage, while the motive force for i _g is an open-circuit voltage of the battery. It is suggested that battery action proceeds by a single electrochemical reaction. In the course of discharging, the current drops abruptly by the formation of a resistive layer, possibly by depletion of the OH⁻ ions in the vicinity of the positive electrode.     

Local structures and electronic structures of Hf?O?N thin films: x‐ray absorption fine structure study and first‐principles calculations

The local structures of Hf? O? N thin films were analyzed using an extended x‐ray absorption fine structure (EXAFS) study of the Hf L₃‐edge and first‐principles calculations. Depending on their composition and atomic configurations, Hf₄O₅N₂ [coordination number (CN): 6.25], Hf₄O₂N₄ (CN: 5.5) and Hf₄O₂N₄ (CN: 5.0) were suggested as the local structures of Hf? O? N thin films. Using the suggested local structures, the electronic structures of Hf? O? N thin films were calculated. The variations of the valence band were analyzed with the film composition and compared with the experimental valence band. The optical band gaps of Hf? O? N thin films were compared with the calculated values. The transition rate for the optical absorption was suggested as another reason for the band gap difference. Copyright © 2006 John Wiley & Sons, Ltd.     

Green and red photoluminescence from ZnAl2O4:Mn phosphors prepared by sol–gel method

Luminescence investigations of Mn-activated ZnAl₂O₄ phosphors prepared by using sol–gel method were described. The phosphor was characterized by X-ray diffraction (XRD) and electronic paramagnetic resonance (EPR). The EPR spectra of the samples suggested that Mn ions possessed homogeneous distribution in ZnAl₂O₄ phosphors. Photoluminescence studies of the prepared phosphors showed green and red emissions. The red emission became weaker, and vanished at last with sintering temperature increasing from 600 to 900 °C in reducing atmosphere, while the intensity of green emission peak increased. Furthermore, when the phosphor was sintered at 900 °C in air, the intensity of red and green emissions decreased, but the value of intensity ratio increased. It suggested that the green emission resulted from Mn²⁺ and the red emission resulted from Mn⁴⁺.     

Semi-empirical calculations and the assignment of valence photoelectron spectra of large molecules : Phenalen-9-amino-1-imine.

The He(I) photoelectron spectrum of phenalen-9-amino-1-imine (C₁₃H₁₀N₂) has been assigned using the SPINDO and HAM/3 semi-empirical methods. The molecular orbital patterns and properties suggested by the calculations are compared for the low energy region (7–12 ev).     

Homogeneity range of high temperature Ni3±x S2

The activity of sulphur inside and at the boundaries of the homogeneity range of “Ni_3±x S₂” was accurately determined by stepwise reduction with hydrogen at temperatures between 815 and 1044 K. It is suggested that a second order phase transition inside the homogeneity range takes place.     

Imaging C60 fullerite at 4.5 K by scanning tunneling microscopy

Intramolecular contrast of C₆₀ molecules has been observed by scanning tunneling microscopy at 4.5 K on a C₆₀ fullerite thin film sample. This result provides strong evidence for the freezing of the rotational motion of C₆₀ molecules at low temperature as recently proposed by refinement analysis of neutron diffraction data. Different intramolecular patterns are observed. Interpretation of these patterns is suggested by assigning them to carbon ring structures of the C₆₀ molecules in various orientations.     

Adsorption and decomposition of symdimethylhydrazine and hydrogen cyanide on Pt (111)

Adsorption and decomposition of sym-dimethylhydrazine on Pt (111) has been studied at ～ 290 K. Decomposition occurs by two pathways. One yields CH₄ and N₂ at room temperature; the second, analogous to decomposition of ethylene diamine, yields mainly dehydrogenation products. These include HCN, which it is suggested is initially adsorbed molecularly on this surface and β₂-C₂N₂.     

Nonequilibrium acoustic phonons in Y3Al5O12-based nanocrystalline ceramics

The phonon transport processes in high-transparency nanocrystalline laser ceramics based on cubic Y₃Al₅O₁₂ garnet oxide were investigated by the heat-pulse technique. The propagation kinetics of nonequilibrium acoustic phonons was studied in the range of helium temperatures (1.7–3.8 K). The structural model is suggested for the intergrain layers, and their thickness is estimated.     

Study of ferromagnetism in Bi2S3 and ZnS nanocrystalline powders

Results of magnetic measurements suggested that Bi₂S₃ and ZnS nanocrystalline powders prepared by hydrothermal method could possibly exhibit room temperature ferromagnetism. The measured saturation magnetization of the powders increases with an increase of annealing temperature from 300 to 500 °C. Ab initio calculations suggested that the cation vacancies on the surface of Bi₂S₃ and ZnS nanograins could be responsible for the observed magnetic moments. Heat-treatment of Bi₂S₃ or ZnS nanocrystalline powders in Bi or Zn vapor could bring about an enhancement of ferromagnetism. The calculation results indicated that the interstitial Bi or Zn atoms in Bi₂S₃ (0 0 1) or ZnS (0 0 1) surface could induce magnetic moments.     

高温超导材料YBa2Cu3O7-δ在可见光区的电场调制光反射光谱

本文报道了用调制光谱手段对YBa₂Cu₃O_7-δ化合物所进行的光学测量和研究。从对可见光区调制光谱结构的分析和讨论表明调制光谱可以用于研究超导体化合物的电子态结构。从而提出了又一种研究高温超导材料光学特性的新的测试手段。 关键词：     

Sulphur conductive solid electrolytes in MeS–Ln2S3 systems

The principal possibility of sulphide transfer in phases based on BaZrS₃ and MLn₂S₄ has been considered. The regions of solid solutions based on tertiary compounds have been defined. The systematic study of these phases by methods of conductometry, EMF in chemical concentration chains with and without transfer, potentiostatic chronoamperometry has been performed. A possible defect forming mechanism at consecutive alloying of the tertiary sulphides by the binary ones has been suggested.     

线形天线阵的单位圆上零点分布的一个普遍函数

在本文中,作者提出了与线形天线阵辐射图形中零点相对应的复量多项式的根在复数面中单位圆上的一个分布函数,它比作者在前一篇论文中所提出的分布函数有更普遍的意义。这个普遍函数是:ψ_K=ψ₀{1+ξK^{((ln(ψ_m/ψ₀-1)-lnξ)/(ln m))}}.当ψ₀和ξ被适当地选择时,这个普遍函数所代表的天线阵将包括以下各式天线阵作为特例:(1)均匀横射式天线阵;(2)均匀端射式天线阵;(3)谢昆诺夫天线阵;(4)道尔夫-捷比谢夫天线阵当阵中单元数不超过7时。但是,应用所提出的分布函数并当合理地选择ψ₀和ξ时,却可以改善以上各式天线阵,尤其在压小主瓣附近的旁瓣方面。这一情况是具有重大实用意义的。此外,因为天线阵中各单元的场强或其方向图中的旁瓣一般都随着离开主瓣的角距的增加而下降的,所以为了使天线阵的总方向图有均等或接近均等的小的旁瓣(这是具有实用意义的),就必须设计一个由均匀辐射器所组成的天线阵,它有随着离开主瓣的角距的增加而上升的小的旁瓣。利用谢昆诺夫的分布或道尔夫-捷比谢夫的分布都不能达到此目的,但是应用所提出的分布函数却可以办到。计算结果证实了上述各点。在本文中,作者还将代表各式天线阵的多项式的乘积形式加以展开,从而将其中的系数化为显式以便于阵中各单元上相对电流的计算。