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Bo Bian, Tadakatsu Ohkubo, Yoshihiko Hirotsu, Crystallization and Fractal Formation in Annealed a-Ge/Au Bilayer Films, Journal of Electron Microscopy, Volume 44, Issue 4, August 1995, Pages 182–190, https://doi.org/10.1093/oxfordjournals.jmicro.a051168
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Abstract
The crystallization and fractal formation in a-Ge/Au have been studied by in situ TEM and HREM. It was demonstrated that both the crystallization and the fractal formation depend on the continuity of the Au underlayer and the thickness of the a-Ge layer. As the Au film changed from semicontinuous to discontinuous, the crystallization temperature increased and the morphology of the Ge crystallites changed from fractal to non-fractal. Both the dimension and the growth rate of Ge fractal increased with an increase in the thickness of a-Ge layer. The Au grain boundaries at the interface between the Au and a-Ge layers were suggested to be the nucleation sites for Ge grains, which caused a great reduction in the crystallization temperature. It was observed that the growth of Ge was closely related to the receding of Au grains. Kinetic study showed that the crystallization process was two-dimensional diffusion-controlled growth with nucleation. HREM study showed that the nucleation and growth of new Ge grains could change the direction of the branch and cause splitting of the tip of the fractals. The formation of fractal was explained by random successive nucleation and growth process, where growth is predominant over nucleation. The <110> or <211> direction was found to be the preferred growth direction of Ge grains and the Au [110]//Ge [110], Au (001)//Ge (110) orientation relationship was suggested to be preferred between Au and Ge grains.
