Oxygen-induced reconstruction of a Pt-Rh(100) alloy surface was studied using scanning tunnelling microscopy. When a clean Pt-enriched Pt---Rh(100) surface was exposed to O2 at more than 600K, oxygen-induced reconstruction took place with segregation of Rh atoms to the surface. Depending upon the oxygen coverage, two types of reconstruction on the Pt-Rh(100) alloy surface were induced. A p(3 x 1)-O structure appeared at relatively low oxygen coverage, and the TPD spectrum of the p(3 x 1)-O surface gave a desorption peak of O2 at about 930K. The p(3 x 1)-O structure showed several different scanning tunnelling microscopic images depending on the tip condition, from which it was possible to distinguish the two component metals, Rh-O rows and Pt rows. Based upon this, a model structure was deduced. At a high oxygen coverage, more Rh atoms were segregated to the surface and the scanning tunnelling microscopic image suggested a c(2 x 20)-O structure. The c(2 x 20)-O surface changed into the p(3 x 1)-O by heating with the concomitant desorption of O2 at about 830K. The scanning tunnelling microscopy images for this c(2 x 20)-O surface was analogous to the arrangement of Rh atoms on the top layer of a Rh(111) hexagonal lattice. Due to the lattice mismatch between the quasi-Rh(111) overlayer and Pt-Rh(100) substrate, a moire pattern with 20 times periodicity along the <111> directions was observed. Both the p(3 x 1)-O and c(2 x 20)-O surfaces were easily reduced by H2 even at room temperature.

STM Studies of Oxygen-Induced Reconstruction on a Pt-Rh(100) Alloy Surface. Y.Matsumoto, Y.Aibara, K.Mukai, K.Moriwaki, Y.Okawa, B.E.Nieuwenhuys, K.Tanaka: Surface Science, 1997, 377-379, 32-7