Time resolved dynamics of rapid melting and resolidification of Sb thin films under ns and ps laser pulse irradiation

Abstract

Real time reflectivity measurements with ps time resolution at the wavelength λ=514.5 nm have been used to analyze the rapid melting and solidification dynamics of Sb thin films on glass substrates irradiated with a visible laser pulse (λ=583 nm) of duration either 30 ps or 2 ns. Significant differences in the solidification dynamics have been obtained for the three different film thickness investigated (25, 50, and 200 nm) as well as between ps and ns laser pulse excitation. Bulk solidification is the dominant mechanism observed at high laser fluence in the thinner films, no matter the pulse duration used, while interfacial solidification is the only mechanism observed in the thicker film for both pulse durations. These results have been interpreted in terms of the differences of the effective thermal conductivity of the films. The comparison of the behavior of these films with the case of Sb-rich GeSb ones makes it clear that relatively minor changes in the film composition can lead to big changes in the solidification dynamics under similar heat flow conditions that are beneficial for the application of such films in phase change optical recording with ultrashort pulses. The optical properties of molten phase of Sb and of the solid material at the melting temperature have been also been determined at 514.5 nm.