Michihide Kitamura

X‐ray absorption near‐edge structure of complex compounds (NH4)3RhCl6, K3RuCl6, and Ru(NH3)6Cl3

X‐ray absorption spectra of chlorine K edge, ruthenium LIII edge, and rhodium LIII edge from (NH4)3[RhCl6], K3[RuCl6], and [Ru(NH3)6]Cl3 have been measured with a Johann‐type 50 cm bent crystal vacuum spectrograph. The white lines due to the transitions to the incompletely filled antibonding molecular orbital (MO) 2t2g(π*) or nonbonding orbital t2g and the empty antibonding MO 3eg(σ*) for the octahedral complexes have been observed in the Cl K edge, Ru LIII edge, and Rh LIII edge regions. It is found that the two absorption peaks at the Ru LIII edge reflect the ligand‐field effect. An interpretation for experimental results of the Cl K edge and the Ru LIII edge absorption spectra in K3RuCl6 on the basis of the MO scheme leads us to the conclusion that the white lines at the Cl K edge suffer from the effect of core hole.

Sulfur-K X-Ray Spectra and Electronic Structure of a Semiconductor Ag2S

The Kβ emission and K-absorption spectra of sulfur in Ag2S are carefully measured and compared with the sulfur Kβ emission and K-absorption spectra of Cu1.8S reported previously. The spectra of Ag2S clearly show the existence of the energy gap in semiconducting Ag2S in contrast to the metallic phase Cu1.8S where the Kβ band edge overlaps with the K absorption edge. The sulfur-Kβ emission spectrum of Ag2S consists of two prominent peaks. The intensity of the high-energy peak is much greater than that of the low-energy peak, contrary to the sulfur-Kβ emission spectrum of Cu1.8S. It is suggested that the bottom of the conduction band of Ag2S arises mainly from the sulfur 4p states.

Electronic structure calculations of perovskite-type oxides using the self-consistent-charge extended Hückel tight-binding method

Abstract Electronic structures of nine cubic perovskite-type oxides ABO3s including SrTiO3, SrZrO3, SrHfO3, BaTiO3, BaZrO3, BaHfO3, PbTiO3, PbZrO3 and PbHfO3 were calculated using a band theory based on the self-consistent-charge extended Huckel tight-binding (SCC-XHTB) method incorporating the relativistic effects except for the spin-orbit interaction in order to examine how the electronic structure changes due to the substitution of the A or B site atom. Moreover, calculations were also made for the tetragonal PbTiO3 to study the electronic structural changes due to the structural change from the cubic phase to the tetragonal one. It is shown that the upper valence band of all the ABO3s considered in the present paper consists of the 2p orbital of oxygen mixed with the d valence electrons of the B atom. The shape remains nearly the same in spite of the A or B site substitution. For the conduction band, it is shown that the bottom of which is made up from the ndt 2g band of the B atom for SrTiO3, SrZrO...

A study of hydrogen doped semiconductors using the INDO method

Stability of monoatomic hydrogen in Si and GaAs crystals is studied by using quantum chemical Intermediate Neglect of Differential Overlap (INDO) method. Some interstitial positions are considered for a H-impurity and their energetical preferences are studied for an intrinsic, n-type and p-type semiconductors. The charge transfer and the positions of defect levels due to the inserted hydrogen are discussed.

An Integrated Acoustooptic Frequency Shifter Driven by Surface Acoustic Wave for 1.55 µm Optical Wavelength

An integrated acoustooptic frequency shifter in a crossed-channel waveguide is demonstrated at an optical wavelength of 1.55 ?m. A novel tapered device was designed to make the acoustooptic interaction region longer and thus the driving surface acoustic wave (SAW) power lower, and the device was fabricated by the proton-exchange method and post-annealing in a 128? rotated Y-cut LiNbO3 substrate. At SAW power of 1.4 W, a 40% diffraction efficiency and a bandwidth of 5 MHz centered at 196 MHz were obtained. The frequency shift of Bragg diffracted light was confirmed in an optical heterodyne experiment.

Simple expressions for elastic constants c11, c12, and c44 and internal displacements of semiconductors

Simple expressions are given for elastic stiffness constants c 11, c 12, and c 44 and Kleinman’s internal displacement parameter ζ. They all are represented by the bulk modulus and covalency alone, and predict fairly well the experimental results. These expressions are useful for getting a simple estimate of ζ as well as c 11, c 12, and c 44.

Influence of ligands on the x‐ray absorption near‐edge structure of palladium(II) complex compounds

The palladium LIII absorption and chlorine K absorption spectra from [Pd(NH3)4]Cl2 ⋅ H2O and Pd(OCOCH3)2 have been reported for the first time and discussed in connection with the Pd LIII absorption and Cl K absorption spectra of K2PdCl4, reported previously. The influence of the ligands Cl−, OCOCH−3, and NH3 has been observed in the pallaldium LIII absorption spectra of these compounds. The observed chemical shift of a strong ‘‘white line’’ at the Pd LIII absorption threshold can be explained in terms of the spectrochemical series of the ligands. An intense white line disappears at the Cl K absorption threshold of [Pd(NH3)4]Cl2 ⋅ H2O in contrast to the Cl K absorption spectrum of K2PdCl4.

Multiple-scattering calculation of sulfur K x-ray absorption spectra for FeS, CoS and NiS

Abstract Sulfur K X-ray-absorption near-edge-structures (XANES) are calculated for the first time for NiAs-type FeS, CoS and NiS crystals having a hexagonal structure from a multiple-scattering approach within a muffin-tin approximation. Comparison between the calculated and experimental results indicates that a core hole created in the absorbing S atom does not so strongly affect the S K XANES of the metallic phase FeS, CoS and NiS.

Hydrogens in semiconductors

A periodic supercell model based on the large unit cell (LUC) method within the Hartree-Fock molecular orbital (MO) theory is used to explore the stability of hydrogen dimers placed on a number of sites in common semiconductors: Si, GaAs and CdTe. Within the rigid band model approximation the different types of crystals, intrinsic, n-type and p-type, are considered by converting the total number of valence electrons in the supercell. The results show that the most energetically favourable configuration is to form a H2 molecule. The net charges of atoms and the electron populations on a bond are presented, and the values of the charge transfer and energies of defect levels due to the inserted hydrogens are given. The results are compared with the available theoretical and experimental data, and the origin of disagreement of results already reported elsewhere is clarified.

X-ray-absorption near-edge-structure study of diamond: A multiple-scattering approach

Abstract The X-ray absorption near-edge structure (XANES) on diamond has been studied for the first time from a multiple-scattering (MS) approach in the framework of muffin-tin approximation. The general feature of an experimental K -XANES spectrum except for the first peak is accounted for by the MS approach containing a self-consistent-field (SCF) calculation to take into account the effect of core holes. The origin of the missing of the first peak is discussed.