Structural characteristics of fractal clusters grown during vapor-solid transformation

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Abstract
Fractal growth of molybdena, iodine, and carbon during vapor-solid transformation was studied experimentally. Three types of self-similar fractal clusters were observed, respectively. These clusters included two different crystalline structures, that is, single crystal and amorphous solid. The microstructure of single crystals included whiskers, ribbonlike crystals, and dendrites. The whiskers or ribbonlike crystals stacked together easily, and formed a bifurcation aggregate such as a molybdena fractal cluster. Under certain conditions, some dendrites were distorted and became branches of a network cluster, such as an iodine quasifractal cluster. The branching amorphous clusters of carbon aggregated at the edge of a glass sample after being irradiated by an electron beam. It is revealed phenomenologically from the experimental results that microstructures of these fractal clusters depended strongly on their growth conditions.