Instability and decomposition on the surface of strained alloy films

TL;DR

This paper develops a continuum dynamical model to analyze the morphological and compositional instabilities on strained alloy film surfaces, considering elastic effects and their complex interplay, with implications for surface stability and experimental observations.

Contribution

It introduces a coupled elastic model accounting for composition-dependent elastic moduli and surface-bulk interactions, advancing understanding of alloy film surface stability.

Findings

Elastic effects cause complex stability behavior.

Tensile and compressive layers show asymmetry.

Surface decomposition can be suppressed below critical temperature.

Abstract

A continuum dynamical model is developed to determine the morphological and compositional instabilities on the free surface of heteroepitaxial alloy films in the absence of growth. We use linear stability analysis to study the early nonequilibrium processes of surface evolution, and calculate the stability conditions and diagrams for different cases of material parameters. There are two key considerations in our treatment: the coupling between top free surface of the film and the bulk phase underneath, and the dependence of both Young's and shear elastic moduli on local composition. The combination and interplay of different elastic effects caused by lattice misfit between film and substrate (misfit strain), composition dependence of film lattice parameter (compositional strain) and of film elastic constants lead to complicated and rich stability results, in particular the joint stability or instability for morphological and compositional profiles, the asymmetry between tensile and compressive layers, as well as the possible stabilization and suppression of surface decomposition even below the effective critical temperature. We also compare our results with the observations of some postdeposition annealing experiments.