Structure of monolayer tin oxide films on Pt(111) formed using NO2 as an efficient oxidant -: art. no. 245402

Submonolayer Sn deposits on Pt(111) and Sn incorporated in a (root3 x root3)R30degrees Sn/Pt(111) Surface alloy were oxidized by NO2 under ultrahigh-vacuum conditions. The oxide films formed were characterized by Auger-electron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Four different surface morphologies were identified, depending on the preparation conditions, each of them exhibiting a distinct LEED pattern. STM revealed two ordered epitaxial overlayers. One is interpreted its the adsorption of SnO pseudomolecules at preferential sites to form a (4 x 4) coincidence lattice with the substrate. The other structure forms an incommensurate tin oxide overlayer, exhibiting a long-range Moire pattern. The remaining LEED patterns are associated with the formation of a regular stress-relief pattern that can transform into an ordered array of tin oxide islands upon repeated oxidation. This ordered island array exhibited a (5 x 5) superlattice with respect to the Pt(111) substrate. The variety of SnOx overlayer morphologies is attributed to subtle differences in the oxide stoichiometry and alterations in the oxide/metal interface, in particular Pt-Sn alloying.