Sb-Te alloy films are developed as rewritable optical recording materials based on amorphous crystalline phase transformations. The crystallization process of Sb-Te sputtered films is systematically studied through measurement of recording characteristics to solve the trade-off problem between data (amorphous) stability and erasing sensitivity. Sb2Te3 is shown to be the best practical phase change medium, having room-temperature stability in amorphous states, short erasing times, and potentially good reversibility. The carrier-to-noise ratio of 50 dB in writing and a decrease in the carrier level of over 30 dB in erasing are achieved in dynamic measurement with a single beam optical head. These favorable properties are attributable to the wide composition margin for a single phase formation in the Sb-Te alloy system.

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synopsisThe molecular orientation distribution of injection-molded polycarbonate discs is studied using birefringence and heat-shrinkage measurements and laser-Raman spectroscopy. Bire-'fringence and heat shrinkage, which result from the molecular orientation, increase as the distance from the inflow gate decreases and as cylinder temperature decreases. Molecular orientation is reduced following annealing. Laser-Raman spectroscopy is used to measure the molecular orientation distribution along the disc cross-section perpendicular to the radial direction of disc. The relative intensity. ratio for the 635 cm-l and 703 cm-l peaks in the Raman spectra correlate well with the degree of molecular orientation. The disk crossgection is found to consist of three different molecular orientation zones; a skin zone which is in contact with the mold, a core zone located at the center, and a shear zone between the skin and the core zones. Molecules in the skin zone are nonoriented while the orientation of molecules in the core zone is considerably relaxed. The shear zone consists of highly oriented molecules. The formation process of the molecular orientation distribution is discussed in relation to birefringence and heat shrinkage.