Probing copper and copper-gold surfaces with space-quantized oxygen molecular beams

空間量子化された酸素分子ビームによる銅および銅金合金表面のプロービング

津田 泰孝   ; Gueriba, J. S.*; 植田 寛和   ; Dio, W. A.*; 倉橋 光紀*; 岡田 美智雄*

Tsuda, Yasutaka; Gueriba, J. S.*; Ueta, Hirokazu; Dio, W. A.*; Kurahashi, Mitsunori*; Okada, Michio*

The interaction of O with various metal surfaces induces changes in its chemical stability and reactivity. And the ability to control such processes bears on the chemical economy. Alloying of pristine metals provides one of the simplest and oldest way to do so. Unraveling the stereochemistry of the processes involved would be imperative for understanding the mechanisms behind of these interactions. The dynamics of reactant molecules (esp., the orientation and the movement of molecules in 3D space) plays an important role in reactions. The small rotational energy excitations involved (ca. less than a few meV) render the reactants susceptible to dynamical steering. This makes direct comparison with theory rather challenging. To directly probe and observe the (polar and azimuthal) orientation dependence of O adsorption on Cu(110) and CuAu(110), we prepared space quantized O molecular beams by sorting the quantum states of the O via Richtungsquantelung (space quantization, as first introduced by the 1922 Stern-Gerlach experiment). We found that chemisorption proceeded rather favorably with the O-O bond axis oriented parallel (vs. perpendicular) to the surface, and also for O-O bond axis oriented along [001] (vs. along [-110]). Alloying with Au introduced a higher activation barrier to chemisorption. This hinders the surface from further oxidation, and azimuthal anisotropy becomes almost negligible. The presence of Au also prevented cartwheel-like rotating O from further reactions.