An STM study of the oxidation of Mg(0001)

We have studied the oxidation of Mg(0 0 0 1) using electron stimulated desorption ion angular distributions, low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Two structures associated with the oxidation were observed by STM and are identified as a suboxide, consisting of incorporated oxygen, and ionic MgO. We observed that both the clean step edges and oxygen adsorbed on the terraces were highly mobile and interact with the STM tip at room temperature. Ionic oxide is observed to form first at defect sites along step edges and grows as an elongated pillar, These ionic oxide nucleation sites a pear to be point defects that pin two terraces forming a double p step. A form of suboxide characterized by broad bumps 1.2 Angstrom across and 3.6 Angstrom in height were observed on the terraces. The bumps increase in number and the pillars grow in area and height with increased oxygen exposure. At 12 L (Langmuir = 1 x 10(-6) Torr s), the bumps coalesce to completely cover the surface, LEED shows a diffuse 1 x 1 pattern indicating that this coalesced phase is in registry with the Mg Substrate. At 14 L, protrusions begin to form on the terraces and an upward inflection point is observed in the ESD ion yield, indicating that the oxide is now on the surface. At higher oxygen exposures, these protrusions continue to grow in size leading to an increased coverage of the ionic oxide. (C) 2001 Elsevier Science B.V. All rights reserved.