Temperature dependence of fractal formation in ion-implanted<i>a</i>-Ge/Au bilayer thin films

Abstract

Fractal regions appearing in ion-implanted (amorphous Ge)/(polycrystalline Au) bilayer thin films after annealing have been investigated. The fractal dimensions and fractal density (number of fractals per unit area) are temperature dependent. At lower temperature both the morphologies and fractal dimensions closely resemble those arising in two-dimensional diffusion-limited-aggregation (DLA) simulations. But our transmission electron micrographs show that after annealing at 100 \ifmmode^\circ\else\textdegree\fi{}C there are many Ge crystallites located randomly in the amorphous Ge matrix, which means that the growth mechanism is very different from that of traditional DLA's, so that a random successive nucleation model has been proposed to explain the results.