Toshihiro Arai

Vibrational properties and network topology of amorphous AsS systems

Abstract We have measured the Raman scattering and the infrared absorption and reflection spectra of a-As x S 1− x (0.1≤ x ≤0.4) systems and have calculated the vibrational frequencies at the center of Brillouin zone and the intensity of the oscillator strengths of the stretching modes of crystalline As 2 S 3 . These results indicate that the IR and Raman modes in a-AsS systems are originated in the AsS network rather than in a pyramidal unit. The calculations of the vibrational frequencies in the S 8 ring molecule and the rigid-layer modes of crystalline As 2 S 3 show that the long range interactions between the non-bonded atoms are weak but important.

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.

Vibrational Spectra and Effective Charges in Some Spinels

The infrared reflectivity spectra have been observed for sintered MCr2S4(M=Zn, Cd, Hg) near normal incidence in the range from 30 to 900cm-1. The effective charges of Cr and S ions are determined from the frequencies of transverse and longitudinal modes within small error. The Szigetieffective charges es* per effective valency Zeff for anions show the correlation with the low frequency electronic dielectric constant e∞ which has been established for selenide and oxide spinels and expressed as e∞-1=2.0/((es*/Zeffe)+(es*/Zeffe)2). By using this empirical relationship, the magnitude of effective charge of cation M is determined within the error in the charge of Cr ion. By the comparison among the obtained effective charges, dielectric constants e∞ and the lattice parameters, the increase of ionicity with the decrease of anion radius and a weak influence of chromium ion in comparison with that of cation M to the dielectric constant are shown. From these results, the similarity and the difference of dielectric properties between binary and ternary compounds are discussed.

Photo-polymerization of vacuum evaporated amorphous (As2S3)1−x(As2Se3)xsystems

Abstract Photo-induced changes of the infrared absorption spectra in vacuum evaporated amorphous As2S3As2Se3 systems are studied in the wave number region 100–500 cm−1 at room and liquid nitrogen temperatures, and conversion of the species of the molecular units and local structures of these systems are studied. After mercury light irradiation the spectrum becomes similar to that of a thermally annealed sample, accordingly, similar to that of a bulk material. Just after evaporation, such molecular units as As4, As4S3, As4S4, S8, As4Se4, etc. may be bonded by Van der Waals forces, and the observed photo-induced changes in the infrared absorption spectra are interpreted by rearrangement (polymerization) of bonding configurations.

ZnO Thin Films Prepared by Ion-Assisted Deposition Methods

Transparent conducting ZnO films were prepared by an ion-assisted deposition method. The glass substrate was irradiated with Ar ions during deposition of amorphous films and the c-axis-oriented ZnO film with the lowest resistivity is obtained when the growing film is irradiated with Ar plasma. Optical emission lines due to Ar, Zn2, Zn and O of neutral species were detected. In particular, the ratio of emission line intensity O(777 nm)/Zn(635 nm) is closely related with film properties. The control of plasma conditions by the check of the emission line intensity provides a method of obtaining a high-quality transparent conducting ZnO film.

Effect of magnetic ordering on phonon parameters for infrared active modes in ferromagnetic spinel CdCr2S4

Infrared reflectivity spectra of sintered crystal CdCr2S4 have been measured in the temperature range of 15–300 K. The frequencies of transverse and longitudinal phonon modes were determined from the spectra with the Kramers–Kronig relation. The temperature dependencies of those showed anomalously large shifts near the Curie temperature. The shifts for two modes on the higher‐energy side increase and those for other two modes decrease with temperature. These shifts are described well by the terms of spin‐correlation function and concluded to be originated from the spin‐dependent force constant. The mode dependence of shifts is explained qualitatively from the relation between the linkage of super‐exchange interaction and the direction of vibration of the ion. The effects of magnetic ordering were also observed on Szigeti effective charge, optical and static dielectric constants, and phonon damping constants. These are discussed from the viewpoint of the red shift of the absorption edge.

Raman scattering in 3RNbS2

Abstract Raman scattering spectra on a layer type compound 3RNbS2 were measured at 300 and 77 K, and three peaks were observed at 382, 325 and 281 cm−1 at 300 K. The vibration modes were analyzed in terms of Bromleys nearest neighbour model, and a good agreement with the experiment was obtained.

Intermediate range correlation in a-Se1−x Tex and a-(As2S3)1−x Agx systems

Abstract The composition dependence of the physical which are expected to be more sensitive to molecularity has been investigated for a-Se 1−x Te x and a-(As 2 S 3 ) 1tx Ag x systems. The physical properties exhibit critical composition dependence near x = 0.15 for a-Se 1−x Te x system and near X = 0.02 for a-(As 2 S 3 ) 1−x Ag x system. These results are interpreted in terms of intermediate range topological aspects. It is suggested that the weak, but important, intermediate range non-bonding forces affect strongly the structural order and the character of the glassy state.

Infrared reflection spectra of tetragonal and orthorhombic ErBa2Cu3Ox and HoBa2Cu3Ox

Abstract The infrared reflection spectra of the tetragonal and orthorhombic ErBa 2 Cu 3 O x and HoBa 2 Cu 3 O x are measured at room temperature. The infrared reflection spectra of tetragonal Ln Ba 2 Cu 3 O x (Ln= Y, Er, Ho) exhibit Reststrahlen vibration, and the spectra of the orthorhombic Ln Ba 2 Cu 3 O x ( Ln = Y, Er, Ho) exhibit the characteristics of free carriers. The reflection spectra of the tetragonal YBa 2 Cu 3 O x , ErBa 2 Cu 3 O x and HoBa 2 Cu 3 O x are shown to be quite similar to each other in the wave number range 210–700 cm −1 , and those of the orthorhombic YBa 2 Cu 3 O x , ErBa 2 Cu 3 O x and HoBa 2 Cu 3 O x are also shown to have quite similar vibration structures to each other.

Ag photodoping in chalcogenide glass As2S3

Abstract Change of the thickness of the photodoped layer on the variation of the irradiated photon energy and time was measured and two stages behaviours of the photodoping process were studied. The process of the 2nd stage is put under the control mainly by the photon with the energy higher than Eg. The process of the 1st stage is, however, still influenced by the photon having the energy lower than the energy gap Eg. Processes of Ag-photodoping were also studied by means of Rutherford backscattering of oxygen ions. The composition ratio of the Ag and As in the direction perpendicular to the surface was observed to be constant in the all Ag doped region.