Nanometer thick layers of Mg metal vapor deposited onto a polycrystalline gold substrate at 22 K with and without O-2 multilayers were examined after annealing. Auger electron spectroscopy and temperature programmed desorption of N-2 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 02, Mg oxidizes and forms an MgO film having a high surface area (similar to700 m(2)/g). The surface area decreases upon annealing, approaching that of a well-ordered MgO(100) surface by 500 K. On thinner O-2 multilayers, both oxidized and metallic Mg are observed at 22 K. Mild thermal annealing (200-400 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 N-2 binding sites, similar to well-ordered MgO(100). The film sublimes above 1000 K when heated.