Transition from anomalous kinetics toward Fickian diffusion for Si dissolution into amorphous Ge

Over the last years, several experimental and theoretical studies of diffusion kinetics on the nanoscale have shown that the time evolution (x proportional to t(c)(k)) differs from the classical Fickian law (k(c)=0.5). However, all work was based on crystalline samples or models, so far. In this letter, we report on the diffusion kinetics of a thin amorphous Si layer into amorphous Ge to account for the rising importance of amorphous materials in nanodevices. Employing surface sensitive techniques, the initial k(c) was found at 0.7 +/- 0.1. Moreover, after some monolayers of Si dissolved into the Ge, k(c) changes to the generally expected classical Fickian law with k(c)=0.5. (C) 2008 American Institute of Physics.