Yoshikiyo Sakaguchi

Optical absorption spectra of liquid As2S3 and As2Se3 over a wide temperature range

The authors have measured the optical absorption coefficient of liquid As2S3 and As2Se3 up to 900 degrees C in a wide absorption range up to about 3*105 cm-1. They have developed an optical cell of their own design with a sample thickness of about 2000 AA. The optical gap obtained from the spectra decreases rapidly with increasing temperature, eventually becoming zero at about 950 degrees C for liquid As2Se3, where the semiconductor-to-metal transition starts to occur.

Photoinduced polymerization and relaxation in liquid sulphur

In order to study the dynamics of the polymerization in liquid sulphur we have measured the transient absorption spectra after illuminating with a pulsed laser below and above the polymerization temperature, Tp. We have found that photoinduced polymerization occurs below Tp and there exist two kinds of relaxation process, that is, the fast and slow ones. The slow one can be observed after illumination with a very weak pulsed laser and the relaxation time is of the order of ten minutes. The fast one is observed just after stopping the illumination of a rather stronger pulsed laser and the relaxation time is about 30 seconds. The fast one is always followed by the slow one. On the basis of these findings we conclude that the fast relaxation process corresponds to the relaxation from a polymeric chain to a charge transfer complex and the slow one the relaxation from the charge transfer complex to the most stable ring molecule. With further increase of the intensity of the pulsed laser we have found that giant molecules with colloidal form are generated and they lie on parallel lines. The relaxation time is about one minute.

Photo-induced structural changes in liquid sulfur

Abstract The pattern which appears in liquid sulfur when a pulsed laser with an intensity more than 20 mJ/pulse illuminates the sample below the polymerization temperature was investigated. For the investigation, specially designed quartz cells with sample thicknesses from 0.3 μm to 2.0 mm were developed. When the sample is very thin, there appears a colored pattern like a rainbow. Observation using a microscope revealed an inhomogeneous region, which seems to consist of macromolecules with an ordered structure. In contrast, when the sample is very thick, another new pattern, which seems to be a thin film with wrinkles, was found. On the basis of these findings, the origin of these patterns is discussed.