Shin-ichi Kondo

Amorphous to Crystalline Transformation of Cold Condensed TlBr Films

High quality amorphous films of TlBr which are completely transparent below the absorption edge were obtained by the deposition of the substance onto cold substrates kept at 77 K. The films shows a sharp crystallization behavior upon heating in a small temperature range, less than 1.5 K near 95 K for a film about 1700 A thick. The as-crystallized films just above the crystallization temperatures have microcrystalline nature characterized by the absence of the first exciton band; the exciton band grows at higher temperatures.

Optical Characterization of Amorphous PbI2 Films and Their Crystallization

High-quality amorphous PbI2 films were obtained by quench deposition. They were completely transparent below the absorption edge. The absorption spectra of the films were shown to change reversibly with temperature below 195 K, confirming the stability of the amorphous state. Upon heating at a rate of 0.5 K/min, the films showed a sharp crystallization behavior in a narrow temperature range of about 1.5 K near 198 K.

Dispersion Studies of CdI2, CdBr2 and CdCl2

The ordinary and the extraordinary refractive indices of CdI 2 , CdBr 2 and CdCl 2 single crystals have been measured at room and liquid nitrosen temperatures in the region from 7000 A to the shorter wavelength up to the absorption edge. The measurements have been carried out by an interference method in which both indices can be determined together with the thickness of the sample crystal. The results show birefringent optical characteristics or the negative crystal. The characteristics are interpreted in terms of dichroic absorption. The dispersion behavior of the indices in the energy region well below the absorption edge is analyzed using a single-effective-oscillator model.

Amorphous CdI2 Films and Their Crystallization Studied by Simultaneous Measurements of Optical Absorption and Reflection

Amorphous CdI2 films with excellent transmittance below the absorption edge were obtained by quench-deposition onto 77 K substrates. By annealing at 300-340 K, they crystallized in a previously unknown crystal structure which exhibited a very sharp exciton peak at 3.934 eV. It was suggested that the films, amorphous or crystalline, were due to covalent bonds between Cd and I atoms. The covalent bonds brought about small values of the real part of refractive index. Further annealing at higher temperatures transformed the crystal structure of the films to the ordinary, CdI2 structure. The resultant films showed anomalous spectral behavior leading to a new understanding of crystallinity in the films.

Core Absorption Spectra of Crystalline and Amorphous GeTe Thin Films

Core absorption spectra of crystalline ( c -) and amorphous ( a -) GeTe thin films have been measured in the 26-70 eV region. Photoemission spectra have also been measured to determine the binding energies of Ge 3 d and Te 4 d core levels. In the c -phase Ge 3 d absorption shows excitonic peaks which can be explained in atomic picture, while Te 4 d absorption shows broad structures which reflect DOS of the conduction band. A small peak was found below the broad structures of Te 4 d absorption, the origin of which is the excitonic transition or the transition to the hole states generated by Ge vacancies located near the top of the valence band. In the a -phase Ge 3 d absorption shows a broad structure while Te 4 d absorption somewhat sharp doublet. The difference in the spectral features in both phases suggests that the bonding character is more covalent in a -GeTe than in c -GeTe.

Optical Constants and Polarization-Dependent Reflection Spectra of CdCl2 and CdBr2 Single Crystals

Optical constants of CdCl 2 and CdBr 2 at room and liquid helium temperatures have been determined in the region 4–11 eV for ordinary ray from reflection spectra of the cleaved surfaces. The structures near the optical gap in the optical conductivity spectra are interpreted in terms of the optical transitions occuring at the \(\varGamma\) point in the Brillouin zone. The interpretation has been confirmed by the measurements of the polarization-dependent reflection spectra of the polished surfaces parallel to the c axis. The structures in the deep interband energy region are related to the transitions at the Z point on the basis of their polarization dependence.

Quench Deposited Amorphous TlI Films and Their Crystallization Studied by Optical Absorption Measurements

High quality amorphous TlI films were obtained which are stable below 111 K and completely transparent below the absorption edge. Upon heating, they show a sharp crystallization behavior in a small temperature range less than 2 K near 121 K. The as-crystallized films just above the crystallization temperature have a microcrystalline nature characterized by the blue shift of the 1st exciton band. The blue shift is attributed to the quantum size effect on excitons confined in a microcrystlline grain with a mean size of a few times the exciton Bohr radius.

Reflection Spectra of CdCl2-CdBr2 Mixed Crystals in the Region of Band Gap Excitons

Reflection spectra have been measured on CdCl 2 -CdBr 2 mixed crystals in the region of band gap excitons using the cleaved surfaces. It is found that both the persistence and the amalgamation types of the spectral behavior upon making mixture can occur in this system. The behavior is interpreted in terms of the exciton transitions at the \( \varGamma \) point from halogen p -like valence bands to a cadmium s -like conduction band: The amalgamation-type behavior comes from an admixture of the p z -state wave function to the \( \varGamma_{4}^{-}\) valence states, and the persistence-type behavior is ascribed to the p x - and p y -like character of the \( \varGamma_{5}^{-}\) and \( \varGamma_{6}^{-}\) valence states.

Annealing behavior of cold condensed amorphous TlCl films studied by UV absorption measurements

TlCl, thin film, cold condensed film, microcrystal, optical absorption, exciton, size effect

Chevron layer structure and focal conics in chiral smectic C liquid-crystal cells aligned by SiO oblique evaporation technique

Chevron layer structures and focal conics in chiral smectic C liquid crystals were investigated by means of polarizing microscope observation and X-ray analysis for two kinds of cells (parallel cells and antiparallel cells) aligned on obliquely evaporated SiO film. For parallel cells, symmetric chevron layer structures and symmetric focal conics were formed. For antiparallel cells, asymmetric chevron layer structures and asymmetric focal conics were formed.