Phase-Change Kinetics of Bi-Fe-(N) Layer for High-Speed Write-Once Optical Recording

Abstract

In this work, we present the phase-change kinetics of Bi-Fe-(N) layers for write-once optical recording. In situ reflectivity measurement indicated that the phase-change temperature (T(x)) of the Bi-Fe-(N) layers is strongly related to the heating rate. The T(x)'s were about 170 degrees C at low heating rates and approached the melting point of the Bi phase (i.e., 271.4 degrees C) at high rate of heating provided by laser heating. For a 100-nm-thick Bi-Fe-(N) layer, Kissinger's analysis showed that the activation energy of phase transition (E(a)) = 1.24 eV, while the analysis of isothermal phase transition in terms of the Johnson-Mehl-Avrami (JMA) theory showed that the average Avrami exponent (m) = 2.2 and the appropriate activation energy (Delta H) = 5.15 eV. With the aid of X-ray diffraction (XRD) analysis, a two-dimensional phase transition behavior in the Bi-Fe-(N) layers initiated by the melting of the Bi-rich phase was confirmed. For optical disk samples with optimized disk structure and write strategy, the signal properties far exceeding the write-once disk test specifications were achieved. Satisfactory signal properties indicated that the Bi-Fe-(N) system is a promising alternative for high-speed write-once recording in the Blu-ray era. (C) 2011 The Japan Society of Applied Physics