Self-epitaxial nucleation origin of fractal aggregation

The self-epitaxial nucleation and growth origin of the formation and transformation of crystalline fractal pattern is identified for the first time. Two universal parameters, so-called relative elemental branching period <(l) over tilde > and the anisotropy or structural match parameter m, are introduced to describe the pattern transformation. These two parameters can be predicted according to our model. Fractal patterns arise when <(l) over tilde >less than or equal to 1. Fractal patterns have a strong anisotropy (m --> 1) at relatively low surface supersaturations, and a very weak anisotropy (m -->-1) at high surface supersaturations. The theoretic results are in excellent agreement with experiments. (C) 2000 American Institute of Physics. [S0021-9606(00)72133-7].