Fingerprint of super-interdiffusion: anomalous intermixing in Pt/Ti

Abstract

The ion-sputtering induced transient enhanced intermixing has been studied by molecular dynamics (MD) simulations in Pt/Ti and its anomalous nature has been explained as a superdiffusive transient enhanced interdiffusion. We find ballistic mixing and a robust mass effect in Pt/Ti. The sum of the square of atomic displacements ($<R^2>$) asymptotically grows nonlinearily and scales as $N^2$ and $\sim t^2$, where $N$ and $t$ are the ion-number fluence and the time of ion-sputtering, respectively. This anomalous behavior explains the high diffusity tail in the concentration profile obtained by Auger electron spectroscopy depth profiling (AES-DP) analysis in Pt/Ti/Si substrate (Pt/Ti) multilayer. In Ta/Ti/Pt/Si multilayer we find a linear time scaling of $<R^2>\propto t$ at the Ti/Pt interface indicating the suppression of superdiffusive features. We propose a qualitative explanation based on the accelerative effect of nonlinear forces provbided by the anharmonic host lattice.

8 pages, 4 figures, RevTex format