High resolution electron microscopic observation on a pentagonal nucleus formed in amorphous germanium films

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Abstract
A structure analysis has been carried out on the nucleus formed in amorphous Ge films at the initial stage of crystallization by means of high resolution electron microscopy. Small crystallites displaying fivefold symmetries were formed in the amorphous matrix with sizes down to about 10 nm. A columnar structure model for the nuclei which consists of five-membered rings, stacking with a common axis, has been proposed and the computer-simulated electron microscope image produced, based on this model, is in good agreement with the observed images. The results suggest the existence of pentagonal structural units in amorphous germanium which play a salient role as preferential nucleation sites at the stage of incipient crystallization.