Reversible structural change has been studied in a thin film system of parylene/Ga
xSe
1-x/parylene structure in order to find a range of conditions for the crystallization, a crytical initialization for as-deposited film to become erasable optical memories. The influence of the illumination by a xenon lamp (photocrystallization) and the heat treatment (thermal crystallization) were analyzed mainly for the composition x = 0.05, using X-ray diffraction and XMA. Finely crystallized area with retaining an adequate surface smoothness, assigned as A-region, developed radially to form a circular crystals when treated at 210°C for 3 min. under the simultaneous illumination of 100 mW/cm
2. Lower temperatures and more intense illumination levels were not suitable because of the formation of coarse grains with sharp grain boundaries, B-region. Repeated write/erase was possible for the sandwich structure, using a focused (2μφ) He-Ne laser with power levels of 3.75 mW for 2 ms for vitrification (transparent) and of 2.1 mW for 8000 ms for crystallization (absorbing), respectively. The A-region was found to be connected by scratching Ga
xSe
1-x film with a sharp needle followed by a treatment for the A-type crystallization, which possibly enables us to provide a recording track on the surface, with better S/N ratios. The local stress caused by the scratch may be responsible for the nucleation of connected A-type crystals. It was also found that the film composition changed to become Se-rich on the scratch and deficient on both sides of the scratch.
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