Explosive crystallization mechanism of ultradisperse amorphous films

The explosive crystallization of germanium ultradisperse amorphous films ha s been studied experimentally. We show that crystallization may be initiate d by local heating at the small film thickness but is realized spontaneousl y at large thickness. The fractal pattern of the crystallization phase is d iscovered to be inherent in the phenomena of diffusion-limited aggregation. It is shown that in contrast to the ordinary crystallization mode, the exp losive one is connected with the instability which is caused by self-heatin g. A transition from the first mechanism to the second one is modelled by t he Lorenz system. The process of explosive crystallization is represented o n the basis of the self-organized criticality conception. The front movemen t is described as the effective diffusion in the ultrametric space of hiera rchically subordinated avalanches, corresponding to the explosive crystalli zation of elementary volumes of ultradisperse powder. The expressions for t he stationary crystallization heat distribution and the steady-state heat c urrent are obtained. The heat needed for initiation of the explosive crysta llization is obtained as a function of the thermometric conductivity. The t ime dependence of the spontaneous crystallization probability in a thin fil m is examined. (C) 2000 Elsevier Science B.V. All rights reserved.