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

TL;DR

This study reveals superdiffusive intermixing in Pt/Ti multilayers caused by ion sputtering, characterized by nonlinear atomic displacement growth, and contrasts it with normal diffusion in Ta/Ti, providing insights into anomalous interdiffusion mechanisms.

Contribution

The paper demonstrates superdiffusive behavior in Pt/Ti due to ion sputtering and explains the underlying nonlinear forces, a novel insight into interdiffusion phenomena.

Findings

Superdiffusive intermixing observed in Pt/Ti with $<R^2> \\sim t^2$ scaling.

Normal diffusion behavior with linear $<R^2> \\sim t$ in Ta/Ti multilayers.

Explanation based on anharmonic lattice forces causing accelerative effects.

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.