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 [110BAR] and [001], were found. The measured diffusion coefficients yield the diffusion activation energies E(d)(110BAR) = 1.1 +/- 0.2 kcal/mol and E(d)(001) = 3.1 +/- 0.4 kcal/mol and the preexponential factors D0(110BAR) = (3.8 +/- 2.0) X 10(-9) cm2/sec and D0(001) = (4.8 +/- 4.4) X 10(-6) cm2/sec. The anisotropy in the surface diffusion appears to cross over at T approximately 160 K.