Anisotropic surface diffusion of CO on Ni(110)

Anisotropic surface diffusion of CO on Ni(110) has been studied using the newly developed technique of optical second-harmonic diffraction from a laser-induced CO monolayer grating. Two distinct orthogonal diffusion channels, along [11¯0] and [001], were found. The measured diffusion coefficients yield the diffusion activation energies ${\mathit{E}}_{\mathit{d}}$(11¯0)=1.1±0.2 kcal/mol and ${\mathit{E}}_{\mathit{d}}$(001)=3.1±0.4 kcal/mol and the preexponential factors ${\mathit{D}}_0$(11¯0)=(3.8±2.0)×${10}^{\mathrm{-}9}$ ${\mathrm{cm}}^2$/sec and ${\mathit{D}}_0$(001)=(4.8±4.4)×${10}^{\mathrm{-}6}$ ${\mathrm{cm}}^2$/sec. The anisotropy in the surface diffusion appears to cross over at T∼160 K.