Crystal symmetry, step-edge diffusion and unstable growth

TL;DR

This paper investigates how crystal symmetry and step-edge diffusion influence surface currents, revealing two main contributions that destabilize flat surfaces and depend on surface orientation and symmetry.

Contribution

It introduces a detailed analysis of anisotropic surface currents, distinguishing between terrace and step contributions, and explores their effects on surface stability and morphology.

Findings

Two types of destabilizing surface currents identified: terrace and step currents.

Surface symmetry affects the singularity and stability analysis of surface currents.

Step current influences step bunching and meandering depending on orientation.

Abstract

We study the effect of crystal symmetry and step-edge diffusion on the surface current governing the evolution of a growing crystal surface. We find there are two possible contributions to anisotropic currents, which both lead to the destabilization of the flat surface: terrace current (j_t), which is parallel to the surface slope, and step current (j_s), which has components parallel (j_pa) and perpendicular (j_pe) to the slope. On a high-symmetry surface, terrace and step currents are generically singular at zero slope, and this does not allow to perform the standard linear stability analysis. As far as a one-dimensional profile is considered, (j_pe) is irrelevant and (j_pa) suggests that mound sides align along [110] and [1-10] axes. On a vicinal surface, (j_s) destabilizes against step bunching; its effect against step meandering depends on the step orientation, in agreement with the recent findings by O.Pierre-Louis et al. [Phys. Rev. Lett. 82, 3661 (1999)].