SURFACE-DIFFUSION OF K ON PD(111) STUDIED BY PHOTOEMISSION ELECTRON-MICROSCOPY

Surface diffusion of K atoms on Pd(lll) has been measured by photoemis sion electron microscopy in a wide temperature range (150-450 K) for c overages theta < 0.04. Two contributions to the diffusion process have been identified showing different rates and temperature dependences; both are determined by the surface microtopography. In the light of th ese results the discrepancy between microscopic and macroscopic diffus ion constants can be understood.