The Avrami-Johnson-Mehl model, heterogeneous nucleation and ion-irradiation-induced phase changes

It is shown that the Avrami-Johnson-Mehl (AJM) model of phase transformations described by Shewmon (1969, Transformations in Metals (New York: McGraw Hill)) requires slight modification to include the finite initial volume in a transformation event. It is then demonstrated that AJM approaches cannot satisfactorily explain experimental measurements of ion-irradiation-induced amorphization processes in semiconductors, and a model, based upon the thermal and radiation-induced annealing of the instantaneous amorphous fraction, is developed. Although more complex, the results are shown to compare qualitatively with the limited experimental data available on ion flux density and temperature dependences of amorphization rates and to predict the trends correctly. Irradiation-induced crystallization is amenable to a modified AJM approach but inclusion of a time-varying finite amorphized volume is necessary.