Hydroxylated MgO (111) reconstructions: why the case for clean surfaces does not hold water

TL;DR

This study combines experimental and theoretical methods to analyze MgO (111) surface reconstructions, revealing hydroxyl terminations and proposing a kinetic pathway that favors a specific root(3)xroot(3) structure, challenging previous assumptions about clean surfaces.

Contribution

It provides the first detailed structural framework for MgO (111) reconstructions considering hydroxylation, and introduces a kinetic model explaining surface transformation pathways.

Findings

Surfaces contain significant hydroxyl coverage even after UHV annealing.

A simple structural model fits the 2x2 reconstruction data.

Kinetic analysis suggests only one root(3)xroot(3) structure is feasible.

Abstract

We report an experimental and theoretical analysis of the root(3)xroot(3)-R30 and 2x2 reconstructions on the MgO (111) surface combining transmission electron microscopy, x-ray photoelectron spectroscopy, and reasonably accurate density functional calculations using the meta-GGA functional TPSS. The experimental data clearly shows that the surfaces contain significant coverages of hydroxyl terminations, even after UHV annealing, and as such cannot be the structures which have been previously reported. For the 2x2 surfaces a relatively simple structural framework is detailed which fits all the experimental and theoretical data. For the root(3)xroot(3) there turn out to be two plausible structures and neither the experimental nor theoretical results can differentiate between the two within error. However, by examining the conditions under which the surface is formed we describe a kinetic route for the transformation between the different reconstructions that involves mobile hydroxyl groups and protons, and relatively immobile cations, which strongly suggests only one of the two root(3)xroot(3) structures.