Bunch width versus macrostep height: A quantitative study of the effects of step-step repulsion

TL;DR

This study investigates how varying the strength of short-range step-step repulsion affects the dynamics and morphology of step bunching during crystal growth, revealing a competition between bunch width and macrostep height.

Contribution

It introduces a parameterized step-step repulsion into an atomistic model, showing its differential impact on bunching depending on the driving force direction.

Findings

Step-step repulsion alters bunch profiles and stability.

A new time scale emerges from the interplay of macrosteps and bunches.

Bunch height remains relatively unaffected by repulsion.

Abstract

Bunching of steps at the surface of growing crystals can be induced by both directions of the driving force: step up and step down. The processes happen in different adatom concentrations and differ in character. In this study we show how the overall picture of the bunching process depends on the strength of short range step-step repulsion. The repulsive interaction between steps, controlled by an additional parameter, is introduced into the recently studied atomistic scale model of vicinal crystal growth, based on cellular automata. It is shown that the repulsion modifies bunching process in a different way, depending on the direction of the destabilizing force. In particular, bunch profiles, stability diagrams and time-scaling dependences of various bunch properties are affected when the step-step repulsion increases. The repulsion between steps creates a competition between two characteristic sizes - bunch width and macrostep height, playing the role of the second length scale that describes the step bunching phenomenon. A new characteristic time scale dependent on the step-step repulsion parameter emerges as an effect of interplay between (01) faceted macrosteps and (11) faceted bunches. The bunch height being the major characteristic size of the bunches is not influenced dramatically by the repulsion.