Kiyoto Matsuishi

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.

Raman scattering under pressure in ZnGa2Se4

Abstract The Raman scattering spectra of ZnGa 2 Se 4 under pressure were investigated at 300 K up to 18.9 GPa. Two stages were observed in the pressure dependences of Raman bands. Such behavior in accordance with the experimental findings existing in literature and was attributed as arising due to the order–disorder phase transition in the cation sublattice. Using the Harrison–Keatings model of the lattice dynamics modified for the crystals with the tetragonal structure, the bulk modulus B and the mode-Gruneisen parameters Γ i were determined for the first time. It is shown that a better agreement between the experimental and calculated values of Γ i is observed, if one takes into consideration different frequency-pressure behavior for the bond-bending and the bond-stretching parameters, which determine the low- (lower than 140 cm −1 ) and high- (higher than 140 cm −1 ) frequency phonons, respectively.

Photoluminescence of CdS nanoparticles suspended in vacuum and its temperature increase by laser irradiation

We report here photoluminescence of CdS nanoparticles suspended in vacuum. The CdS nanoparticles, whose size distribution was bimodal having peaks at 11.3 and 43.1 nm, were produced by the gas-evaporation method and the nanoparticle beams were formed within the rarefied inert-gas flow. The band-edge emission and surface luminescence of the CdS nanoparticles, whose surfaces were completely free from adsorption, reaction or contamination with their surroundings, were observed. As the excitation intensity increased, the band-edge emission shifted to lower energy and the surface state luminescence shifted to higher energy. These energy shifts in the photoluminescence spectra as functions of excitation intensity were interpreted as an internal temperature rise of the CdS nanoparticles suspended in vacuum, and the internal temperature of the CdS nanoparticles was evaluated by means of photoluminescence. It was found that the nanoparticles suspended in vacuum were heated by much weaker laser irradiation than the bulk surface due to the large surface-to-volume ratio.

Multi-stimuli-triggered release of charged dye from smart PEGylated nanogels containing gold nanoparticles to regulate fluorescence signals

Polyion complex nanoparticles based on 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PSA) and stimuli-responsive PEGylated nanogels composed of PEG tethered chains and a cross-linked poly[2-(N,N-diethylamino)ethyl methacrylate] gel core containing gold nanoparticles showed a remarkable regulation of the fluorescence signal synchronizing with the multi-stimuli-triggered release of the PSA in response to pH, temperature and light.

Structural relaxation in the glass transition region of chalcogenide amorphous semiconductors (GeS2)1−Y(Sb2S3)Y

The structural relaxation in the glass transition of the amorphous (GeS2)1−Y(Sb2S3)Y (0.1⩽Y⩽0.9) system has been investigated with heat capacity data obtained from differential scanning calorimetry experiments. The heat capacity curves were analyzed by the Moynihan formulation with a Kohlrausch–Williams–Watts relaxation function φ(t)=exp[−(t/τ0)β] (0<β⩽1) and we used the Narayanaswamy expression for τ0. The values of model parameters, the non-exponentiality, β, the activation energy, Δh, and non-linearity, x, were obtained from the best model-fitting to experimental data. The dimension in the structural relaxation decreased with increasing Y. This tendency is consistent with decreasing network dimensionality with increasing Y. The values of the non-exponentiality, β, were in the range of 0.6 to 0.8 and changed with the composition Y. The change in the network dimensionality with composition Y is responsible for the change in β for the GeS2 rich composition range (Y⩽0.3).

Raman spectroscopic studies on Sb nanoparticles in SiO2 matrix prepared by rf-cosputtering technique

Abstract Antimony nanoparticles in SiO2 matrix were prepared by rf-cosputtering method. We report the effect of substrate temperature, sputtering power, sputtering pressure, weight of antimony during sputtering and sputtering time on average size of the particle as studied by Raman spectroscopic technique. The first-order Raman lineshape has been analyzed by confined optical modes and the average size of the particle has been estimated from this analysis. We found that the average size of the particle increases with increase in substrate temperature and sputtering power, while it decreases with increase in sputtering pressure and weight of antimony during sputtering. The average size of the particle does not change with sputtering time. The Raman lineshape of antimony particles embedded in SiO2 matrix also does not change with annealing till 250 °C for 48 h. We have discussed the growth process of the particles in this system.

Equation of state and intermolecular interactions in fluid hydrogen from Brillouin scattering at high pressures and temperatures

Brillouin scattering spectra of fluid hydrogen were measured at high pressures (1 to 13 GPa) and temperatures (293 to 526 K). From these sound velocity data together with previously reported volume and ultrasonic velocity data at low pressures and temperatures, we determined a Benedict-type P-V-T equation of state valid for fluid hydrogen up to the maximum pressures and temperatures of this study with an average deviation of 1.0% from the new and previously published experimental data. Using the equation of state, the pressure and temperature dependences of thermodynamic properties were calculated. We examined three types of intermolecular potentials for fluid hydrogen, and found that the Hemley–Silvera–Goldman potential gives superior fits to the experimentally derived equation of state over a wide temperature range above 6 GPa. Discrepancies found in the high temperature range at low pressures provide additional constraints on determination of the intermolecular potential.

Raman scattering and photodarkening of amorphous Ge1-xSx (0 ≤ X ≤ 0.62) films

Abstract Amorphous Ge1−XSX films with Ge-rich composition of 0⩽X⩽0.62 were prepared by the laser ablation method to investigate the effect of sulfur on optical properties. From Raman spectra, it is found that the structure changes gradually with composition X. The change of properties from tetrahedral to chalcogenide semiconductors was examined in terms of photodarkening phenomena. As X increased, the photodarkening effect began to be observed at X=0.2 and enhanced significantly at X=0.5.

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.

Photo-induced transformation of C60 films and single crystals by laser irradiation

Abstract The effects of crystallinity and diffused oxygen molecules on the photo-induced transformation of C60 films and single crystals have been studied by Raman scattering and optical absorption measurements. With laser irradiation onto C60 films, the Raman intensities of the original C60 molecular vibrational modes decreased exponentially with nearly the same time constants, and simultaneously some new modes appeared. The time constants of newly appearing modes were classified into, at least, three groups, suggesting that the photo-induced transformation occurs with multi-steps. We have found that the photo-induced phenomena in single crystals depend strongly on the laser irradiance and the presence of oxygen molecules in the C60 lattice. An oxygen-diffused C60 single crystal was easily transformed to a glassy graphitic phase by laser irradiation. The phototransformation from solid C60 to the graphitic phase is also discussed.