Orientation Dependence of Step Stiffness: Failure of SOS and Ising Models to Describe Experimental Data

TL;DR

This study measures the step stiffness on Cu(001) surfaces at various orientations and temperatures, revealing discrepancies with existing SOS and Ising models, which impacts understanding of surface phenomena.

Contribution

It demonstrates the failure of SOS and Ising models to accurately predict experimental step stiffness data for Cu(001) surfaces.

Findings

Experimental stiffness depends strongly on step orientation.

SOS and Ising models underestimate stiffness except along <110>.

Results challenge current theoretical models of surface step behavior.

Abstract

We have investigated the step stiffness on Cu(001) surfaces as a function of step orientation by two independent methods at several temperatures near 300 K. Both sets of data agree well and show a substantial dependence of the stiffness on the angle of orientation. With the exception of steps oriented along $<110>$, the experimental stiffness is significantly larger than the stiffness calculated within the solid-on-solid (SOS) model and the Ising-model, even if next nearest-neighbor interactions are taken into account. Our results have considerable consequences for the understanding and for the theoretical modeling of equilibrium and growth phenomena, such as step meandering instabilities.