Anisotropy of Surface Diffusion Determined by Study of Ordering Kinetics: Oxygen on (011) Molybdenum
Kinetics of ordering in one-firth-monolayer oxygen film adsorbed on Mo(011) is studied to derive data on surface diffusion. Evolution of the c(2×2) domain average size occuring after upquench of the overlayer preliminarily deposited at low temperature is investigated by video LEED. The two-dimensional diffraction intensity profile is monitored in a wide range of times at different ordering temperatures and corresponding average domain sizes are calculated. Time dependence of the domain size fits the power law 〈L〉=At x +B with the growth exponent x=1/2 and the rate constant A dependent on ordering temperature. The growth exponent proves to be of the same value in any direction. However the domain growth rate is found to be different along the 〈011〉 and 〈001〉 axes. The diffusion coefficient D is considered to relate to A as D x ∝ A. The diffusion anisotropy ratio can be thus determined: D 011/D 001=0.45. This ratio turns out constant, independent of temperature, showing the equality of the activation energie E d =1.76 eV for the two directions. The results are discussed in comparison with the data on E d and model calculations of diffusion anisotropy obtained for the considered system in other works.
KeywordsSurface Diffusion Diffusion Parameter Anisotropy Ratio Antiphase Boundary Distortion Model
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