Abstract
When a clean Pt-Rh(100) alloy surface was exposed to NO at T>440 K, the LEED pattern changed sequentially as p(1x1)→c(2x2)→c(2x2)+p(3x1)→p(3x1), where the c(2x2) pattern appeared immediately after the exposure to NO. In contrast to this, the appearance time for the p(3x1) depends strongly on the initial Rh concentration on the surface adjusted by annealing. When the p(3x1) surface was exposed to H 2 by mixing H 2 into NO gas, the AES intensity of O(a) decreased and of N(a) increased markedly and the LEED pattern changed from p(3x1) to c(2x2). These results suggest that N(a) has equal affinity to Pt and Rh atoms so that the N(a) does not distinguish the Pt and Rh sites on the alloy surface. On the other hand, O(a) makes a stronger bond with Rh atoms so that Rh atom segregation onto the surface is induced. By reacting randomly distributed Rh atoms on the Pt-Rh(100) surface with oxygen, a surface compound in a p(3x1) arrangement is built on the surface.
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