X-ray truncation rod analysis of the reversible temperature-dependent [001] surface structure of LaAlO3

Abstract

A reversible change in the [001] surface structure of ${\mathrm{LaAlO}}_{3}$ has been studied using x-ray truncation rod analysis. Crystal truncation rod profiles in the $00L,$ $10L,$ and $20L$ directions have been recorded on [001]-oriented single crystals at both room temperature and approximately 670 K under UHV conditions. Modeling of these data has enabled a detailed picture of the surface structure at both room and high temperature to be determined. At room temperature the surface is found to be terminated by aluminum, and a fairly minor structural rearrangement relative to the ideally terminated surface is found to occur, involving a relaxation of the surface oxygen atoms away from the surface and a small relaxation of the aluminum atoms into the surface. At the higher temperature a much more significant and reversible structural transformation occurs involving the top four atomic surface layers. This is primarily characterized by a substantial vertical movement of the top surface oxygen atoms and a concomitant relaxation of the aluminum atom into the surface, together with appreciable lateral movements of the oxygen atoms in the top two layers. The lanthanum and oxygen atoms in the third and fourth atomic layers also show clearly discernible movements.