Sticky steps inhibit step motions near equilibrium

TL;DR

This paper demonstrates that short-range step-step attraction causes faceted macro-steps to inhibit their motion near equilibrium, leading to self-pinning of steps and surface roughening effects, analyzed through Monte Carlo simulations and theoretical modeling.

Contribution

It introduces a lattice model with short-range attraction showing self-pinning of macro-steps and derives an analytic surface stiffness tensor for vicinal surfaces.

Findings

Faceted macro-steps inhibit step motion near equilibrium.

Short-range attraction causes step-droplets and surface roughening.

Step-droplets slow down step velocity by smoothing merged steps.

Abstract

Using a Monte Carlo method on a lattice model of a vicinal surface with short-range step-step attraction, we show that, at low temperature and near equilibrium, there is an inhibition of the motion of macro-steps. This inhibition leads to a pinning of steps without defects, adsorbates, or impurities (self-pinning of steps). We show that this inhibition of the macro-step motion is caused by faceted steps, which are macro-steps that have a smooth side surface. The faceted steps result from discontinuities in the anisotropic surface tension (the surface free energy per area). The discontinuities are brought into the surface tension by the short-range step-step attraction. The short-range step-step attraction also originates `step-droplets', which are locally merged steps, at higher temperatures. We derive an analytic equation of the surface stiffness tensor for the vicinal surface around the (001) surface. Using the surface stiffness tensor, we show that step-droplets roughen the vicinal surface. Contrary to what we expected, the step-droplets slow down the step velocity due to the diminishment of kinks in the merged steps (smoothing of the merged steps).