Surface diffusion of hydrogen on Ni(100): An experimental observation of quantum tunneling diffusion

Abstract
We studied the surface diffusion of hydrogen on Ni(100) by linearly diffracting a probe laser beam from a monolayer grating of adsorbed hydrogen. In the temperature range from 110 to 161 K the Arrhenius plot shows a significant leveling off of the diffusion coefficient D(T) at around 144 K. Such a deviation from the behavior of thermally activated diffusion suggests the onset of quantum tunneling diffusion.