Second-harmonic diffraction, from a one-dimensional laser-induced monolayer grating, was used to probe the anisotropic surface diffusion of adsorbates. The 2 orthogonal and independent CO diffusion tensor components were measured along the [1¯10] and [001] directions of the (110)Ni surface. It was found that the results could be described by the expressions:

[1¯10]     D(cm2/s) = 3.8 x 10-9exp[-1.1(kcal/mol)/RT]

[001]     D(cm2/s) = 4.8 x 10-6exp[-3.1(kcal/mol)/RT]

thus revealing the existence of a marked anisotropy in both the activation energy and the frequency factor. The diffusion parameters were related by the Meyer-Neldel effect. The results suggested that the (110)Ni surface, as seen by CO, was much smoother than the (111) and (100) Ni surfaces.

X.D.Xiao, X.D.Zhu, W.Daum, Y.R.Shen: Physical Review B, 1992, 46[15], 9732-43