The migration of H upon the (100) surface was studied by linearly diffracting a laser-beam probe from a monolayer grating of adsorbed H. It was found that, at between 110 and 161K, the Arrhenius plot revealed a marked levelling-off of the diffusion coefficient at about 144K (figure 19). This deviation was attributed to the appearance of quantum diffusion. It was suggested that the underlying surface diffusion was governed by an activation energy of 3.5kcal/mol.

Surface Diffusion of Hydrogen on Ni(100): an Experimental Observation of Quantum Tunneling Diffusion. X.D.Zhu, A.Lee, A.Wong, U.Linke: Physical Review Letters, 1992, 68[12], 1862-5