PNNL

Abstract

Nanometer thick layers of Mg metal vapor deposited onto a polycrystalline gold substrate at 22 K with and without O2 multilayers were examined after annealing. Auger electron spectroscopy and temperature programmed desorption of N2 were used to determine the Mg oxidation state and the surface area of the deposits immediately after deposition at 22 K, and following annealing. Deposited on 20 layers of O2, Mg oxidizes and forms an MgO film having a high surface area (~700 m2/g). The surface area decreases upon annealing, approaching that of a well-ordered MgO(100) surface by 500 K. On thinner O2 multilayers, both oxidized and metallic Mg are observed at 22 K. Mild thermal annealing (200 to 400 K) results in transport of the excess metallic Mg to, and alloy formation with, the underlying Au substrate. MgO films annealed to 1000 K display a narrow distribution of N2 binding sites, similar to well-ordered MgO(100). The film sublimes above 1000 K when heated.