Strain relaxation in small adsorbate islands: O on W(110)

TL;DR

This study investigates how small oxygen islands on W(110) relax strain, revealing size-dependent mismatch behaviors along different crystallographic directions, modeled by a Frenkel-Kontorova approach and supported by ab-initio calculations.

Contribution

It provides a quantitative analysis of strain relaxation in small adsorbate islands using a combined experimental, theoretical, and computational approach.

Findings

Mismatch scales as 1/L along [1-10] for all coverages.

Mismatch along [001] significant only for small islands, scales with higher inverse power.

Surface stress change estimated and confirmed by ab-initio calculations.

Abstract

The stress-induced lattice changes in a p(1x2) ordered oxygen layer on W(110) are measured by low-energy electron diffraction. We have observed that small oxygen islands show a mismatch with the underlying lattice. Our results indicate that along [1-10] the average mismatch scales inversely with the island size as 1/L for all oxygen coverages up to 0.5 ML, while along [001] it is significant only for the smallest oxygen islands and scales as a higher power of the inverse island size. The behaviour along [1-10] is described by a one-dimensional finite-size Frenkel-Kontorova model. Using this model, together with calculated force constants, we make a quantitative estimate for the change of surface-stress upon oxygen adsorption. The result is consistent with our ab-initio calculations, which give a relative compressive stress of -4.72 N/m along [1-10] and a minute relative tensile stress of 0.15 N/m along [001]. The scaling along [001] is qualitatively explained as an effect induced by the lattice relaxation in the [1-10] direction.