An investigation was made of a bilayer Pd3Ti surface alloy, formed on Pd(100), by using low-energy electron diffraction and angle-resolved photo-electron spectroscopy. The surface alloy had p(2 x 2)-p4g symmetry, and hydrogen adsorption induced a transformation to c(2 x 2) symmetry. On the p(2 x 2)-p4g phase, the first layer was composed of a laterally distorted Pd(100) plane, and the second layer consisted of a c(2 x 2) Pd-Ti alloy. The adsorption of hydrogen removed the first-layer distortion, yielding a surface with c(2 x 2) symmetry that was analogous to the surface of Pd3Ti bulk alloy. Angle-resolved photo-electron spectroscopy band-mapping furnished a rational description of the electronic driving mechanisms. The p(2 x 2)-p4g reconstruction was related to the strong polar interaction between the first-layer Pd and second-layer Ti atoms. Hydrogen-induced lifting of the reconstruction was attributed to repulsion among the first-layer Pd atoms, due to occupation of an in-plane anti-bonding state.

Electronic Driving Mechanisms for Displacive Reconstruction and Its Lifting by Hydrogen Adsorption on a Metallic Surface Alloy. N.Tsuboi, H.Okuyama, M.Nishijima, T.Aruga: Physical Review B, 2003, 68[3], 033408 (4pp)