The anisotropic migration of CO on the (110) plane of Ni was studied by using a new method which involved the monitoring of optical second-harmonic diffraction from a laser-induced CO monolayer grating. It was found that 2 distinct orthogonal diffusion channels existed along the [1¯10] and [001] directions. The measurements indicated that the diffusivity along these directions could be described by:

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

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

The anisotropy of the surface diffusivity appeared to exhibit a crossover at about 160K.

X.D.Xiao, X.D.Zhu, W.Daum, Y.R.Shen: Physical Review Letters, 1991, 66[18], 2352-5