Preparation and characterization of MgO(100) surfaces

Abstract

The preparation of crystalline magnesium oxide surfaces by means of mechanical polishing, acid etching, oxidative annealing and vacuum annealing has been studied on an atomic scale using low energy electron diffraction (LEED) and ultrahigh vacuum (UHV) atomic force microscopy (AFM). Mechanical polishing results in a microscopically smooth and an atomically disordered surface. Although acid etching of the magnesium oxide surface results in LEED patterns indicating a crystalline nature, AFM characterization of these surfaces reveals that surface layers are removed in an anisotropic fashion resulting in a surface roughness on the order of 100 Å (which is not probed by the LEED studies). Annealing this same surface in vacuum only modestly reduces the surface roughness while high temperature anneals of an acid etched surface in a 1 atm oxygen environment produces a well ordered surface characterized by 1000 Å terraces separated by single and double layer step heights. Further annealing these terraced surfaces to 1000°C under vacuum produced well-ordered and crystallographic surfaces on an atomic scale. Topographic images of the MgO(100) surface obtained under UHV conditions reveal rows of oxygen atoms oriented in a 〈110〉 direction with a spacing of 3.0 Å and indicate that this surface preparation results in an unreconstructed, bulk termination of the rock salt structure.