Diffusion of Xe on Ni(111)

We have measured the diffusion rate D(T) for Xe on Ni(111) from 30 to 60 K at coverages of θ=0.04 and θ=0.16. By fitting D(T) to Arrhenius forms D0 exp(−Ed/RT), we found the diffusion to be characterized by small activation energy and unusually small diffusivity: Ed=0.33±0.02 kcal/mol and D0=2×10−9±0.2 cm2/s at θ=0.04, and Ed=0.40±0.04 kcal/mol and D0=3×10−8±0.3 cm2/s at θ=0.16. We discuss the significance of our result in the light of similar observation of small diffusion barriers and unusually small diffusivities for Xe on W(110) and for Al diffusion on Al(111) and on Au(111) reported recently.