Temperature dependent formation of surface undulations in explosively crystallized films

Abstract

Van Saarloos and Weeks have recently proposed an instability theory which predicts that self-sustained explosive crystallization can result in a thermal instability which leads to the formation of periodic surface undulations in the transformed film. We have obtained experimental results which verify the essential features of this model. That is, large scale undulations with amplitudes of the order of micrometers are observed when amorphous In1−xGaxSb alloys are explosively crystallized at temperatures Tt near the critical minimum transformation temperature T*. The thermal instability vanishes at higher values of ΔT=(Tt−T*) and the films exhibit only a uniform small scale roughness. For intermediate ΔT values, the amplitude of the undulations decreases with increasing ΔT. Transmission electron microscopy results indicate that the surface undulations are due to density differences in alternating regions of polycrystalline material with an average grain size of the order of 100 nm and regions of amorphous or very fine grained polycrystalline material. The uniform small scale surface roughness obtained at large ΔT was produced by complete surface melting followed by rapid quenching.