Lifting of Ir{100} reconstruction by CO adsorption: An ab initio study

TL;DR

This study uses ab initio methods to analyze how CO adsorption influences the stability of Ir{100} surface reconstructions, revealing critical coverage thresholds and interaction effects.

Contribution

It provides a detailed thermodynamic and electronic analysis of CO's impact on Ir{100} surface reconstruction, including coverage-dependent stability and molecular interactions.

Findings

CO coverage above 0.09 ML destabilizes the reconstructed surface at zero temperature.

Repulsive CO interactions on reconstructed surfaces explain high coverage on (1X1) islands.

Only two stable states exist across conditions: a CO overlayer and the reconstructed surface.

Abstract

The adsorption of CO on unreconstructed and reconstructed Ir{100} has been studied, using a combination of density functional theory and thermodynamics, to determine the relative stability of the two phases as a function of CO coverage, temperature and pressure. We obtain good agreement with experimentaldata. At zero temperature, the (1X5) reconstruction becomes less stable than the unreconstructed (1X1) surface when the CO coverage exceeds a critical value of 0.09 ML. The interaction between CO molecules is found to be repulsive on the reconstructed surface, but attractive on the unreconstructed, explaining the experimental observation of high CO coverage on growing (1X1) islands. At all temperatures and pressures, we find only two possible stable states: 0.05 ML CO c(2X2) overlayer on the (1X1) substrate, and the clean (1$\times$5) reconstructed surface.