Parabolic vs linear interface shift on the nanoscale

Abstract

It was shown very recently that diffusion nonlinearity, caused by the strong composition dependence of diffusion coefficients, can lead to surprising effects on the nanoscale: a nonparabolic shift of interfaces (both in ideal and phase separating systems) and sharpening of an initially diffuse interface in ideal systems. Some of these can not be interpreted even qualitatively from Fick’s classic equations. For instance, the nonparabolic shift of an interface at the very beginning is a consequence of the violation of Fick’s first equation on the nanoscale, and the transition from this to the classic parabolic behavior depends on the strength of the nonlinearity and the value of the solid solution parameter V (proportional to the heat of mixing). Experimental and theoretical efforts to explore the above phenomena are summarized in this paper.