DIFFUSION OF RH OVERLAYERS GROWN ON A PT(110) SURFACE

The kinetics of Rh diffusion were investigated on an abrupt interface of Rh/Pt(110) which was artifically created by using molecular beam epitaxy evaporation of 0.5 or 1 monolayer Rh on a reconstructed Pt(110)(1 x 2) substrate. The kinetics of Rh overlayer diffusion were monitored by AES as a function of time and up-quenching temperature. The AES measurements were further compared with a phenomenological model for diffusion of overlayers into a bulk substrate. The barrier height of Rh diffusing into Pt has been determined to be 2.69 +/- 0.55 eV. Various equilibrium structural phases, c(2 x 2), (1 x 3) and (1 x 2), associated with certain Rh concentrations during diffusion were observed by using high-resolution LEED. In addition, excess surface segregation of Pt occurs at temperatures above 870 +/- 10 K, about 70 K higher than the onset temperature in a bulk Pt-Rh alloy.