Explosive crystallization mechanism of ultradisperse amorphous films

Abstract

The explosive crystallization of germanium ultradisperse amorphous films has been studied experimentally. We show that crystallization may be initiated by local heating at the small film thickness but is realized spontaneously at large thickness. The fractal pattern of the crystallization phase is discovered to be inherent in the phenomena of diffusion-limited aggregation. It is shown that in contrast to the ordinary crystallization mode, the explosive one is connected with the instability which is caused by self-heating. A transition from the first mechanism to the second one is modelled by the Lorenz system. The process of explosive crystallization is represented on the basis of the self-organized criticality conception. The front movement is described as the effective diffusion in the ultrametric space of hierarchically subordinated avalanches, corresponding to the explosive crystallization of elementary volumes of ultradisperse powder. The expressions for the stationary crystallization heat distribution and the steady-state heat current are obtained. The heat needed for initiation of the explosive crystallization is obtained as a function of the thermometric conductivity. The time dependence of the spontaneous crystallization probability in a thin film is examined.