Explosive crystallization mechanism of ultradisperse amorphous films

TL;DR

This paper investigates the explosive crystallization process in ultradisperse amorphous germanium films, revealing mechanisms, patterns, and modeling approaches that connect self-heating and criticality phenomena.

Contribution

It introduces a new model of explosive crystallization based on self-organized criticality and ultrametric diffusion, with experimental validation and analytical expressions.

Findings

Crystallization initiates at small thickness via local heating.

Fractal patterns characteristic of diffusion limited aggregation are observed.

A Lorenz system models the transition between crystallization modes.

Abstract

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.