Theory of adsorbate induced surface reconstruction on W(100)

TL;DR

This paper presents a theoretical study of hydrogen-induced surface reconstruction on W(100), revealing a temperature-dependent phase transition characterized by Monte Carlo simulations and an XY model analogy.

Contribution

It introduces a novel effective Hamiltonian model for hydrogen-induced surface reconstruction and analyzes the transition order using Monte Carlo renormalization group methods.

Findings

Transition is second order at high temperatures

Transition is first order at low temperatures

Phase diagrams are compared with mean field theory

Abstract

We report results of a theoretical study on an adsorbate induced surface reconstruction. Hydrogen adsorption on a W(100) surface causes a switching transition in the symmetry of the displacements of the W atoms within the ordered c(2x2) phase. This transition is modeled by an effective Hamiltonian, where the hydrogen degrees of freedom are integrated out. Based on extensive Monte Carlo renormalisation group calculations we show that the switching transition is of second order at high temperatures and of first order at low temperatures. This behavior is qualitatively explained in terms of an XY model where there is an interplay between four and eight fold anisotropy fields. We also compare the calculated phase diagrams with a simple mean field theory.