High performance phase change optical recording disk has been developed by using an oxygen-doped Ge–Sb–Te recording layer. The 5×105 overwrite cycles were achieved with this 6 at. % oxygen-doped phase change optical recording disk. The transmission electron microscope observation shows that the crystal grain size was enlarged and the “self-sharpening effect” disappeared with increasing of oxygen concentration. It is thought that the oxygen doping made it easy to grow the uniform large grain size without the self-sharpening effect around the amorphous mark and therefore, the overwrite cyclability of the phase change optical recording disk was improved.

The structural phase transition of ?-Fe precipitates in a Cu matrix is studied using the x-ray diffraction technique. At low temperature, the FCC lattice uniformly contracts along the c axis by 0.17%. In the c plane the mean value of the lattice spacing expands by 0.19%, but the atomic positions are modulated by a sinusoidal wave propagating along the [ l 1 01 direction with the (1 i 0) polarisation vector. Various properties of the periodic lattice wave (PLW) are studied. The wavelength and amplitude of the PLW depend on the size of the precipitates. The origins of the PLW and the size effects are discussed.

A high-performance phase change optical recording disk, which has a five-layered structure, was proposed. This disk has a ZnS adhesion layer between a GeSbTe recording layer and a ZnS-SiO 2 second dielectric layer. A 2 × 10 5 overwrite cyclability was achieved with the original five-layered phase change optical recording disk. The cross-sectional transmission electron microscope observation and the in-plane X-ray diffraction measurement indicate that both the five-layered disk and the fourlayered disk have almost the same crystalline structure. The contact angle measurements, however, indicate that the ZnS adhesion layer improves the adhesive force between the GeSbTe recording layer and the ZnS-SiO 2 second dielectric layer. It is considered that the high overwrite cyclability results from this improvement of the adhesive force. Moreover, the electron probe microanalysis results indicate that the ZnS layer acts as a protective layer against the Ge diffusion from the GeSbTe recording layer.

A phase-change optical disc was observed using a reflection-mode scattering-type scanning near-field optical microscope (RS-SNOM). In an a.c.-mode SNOM image, the 1.2 microm x 0.6 microm recording marks were successfully observed although the data were recorded on the groove. In contrast, no recording marks could be resolved in a d.c.-mode SNOM image. These results are in good agreement with those from a numerical simulation using the finite difference time domain method. The resolution was better than 100 nm with a.c.-mode SNOM operation and the results indicate that recording marks in phase-change optical media can be directly observed with the RS-SNOM.

The ammonio group of 2-phenylethylammonium cation links tetracyanonickelate(1i) anions at the N atoms of square-planar Ni(CN)4 moieties through hydrogen bonds to form a layer of dou bly-CN-bridged one dimensional extensions of [(PhCH2CH2NH3)2Ni(CN)4]n with protrusion of the 2-phenylethyl groups into the interlayer space; these groups act as the spacers to produce the cavities for the guest N,N-dimethylaniline molecules.