  The explosive crystallization of germanium ultradisperse amorphous films is
studied experimentally. We show that crystallization may be initiated by local
heating at the small film thickness but it realizes spontaneously at the large
ones. The fractal pattern of the crystallized phase is discovered that is
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 the self-heating. A transition from the
first mechanism to the second one is modelled by 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 films is examined.
