The linear optical diffraction method was used to study the diffusion of H atoms on flat and stepped W(100) surfaces. At an 0.17ML coverage of H, the diffusion coefficient exhibited a strong anomalous dip at the substrate reconstructive phase transition temperature in an Arrhenius plot for diffusion on both surfaces. No anomalous diffusion behavior was observed at a 1.2ML coverage of H, for both surfaces, between 240 and 380K. This was consistent with the absence of the phase transition at this H coverage.The strong reduction in diffusion coefficient could be attributed to the diverging friction damping near to the transition. Steps did not suppress the substrate phase transition, and hardly affected the diffusion anomaly. For both H coverages, the only effect of steps was to introduce a small Schwoebel-Ehrlich barrier (~2.2kcal/mol for 1.2ML and ~2.8kcal/mol for 0.17ML) near to the step edges, which slowed H diffusion perpendicular to the steps. Measurements of H diffusion parallel to steps revealed no obvious enhancement due to step-edge diffusion.

L.Cai, C.Zheng, K.L.Man, M.S.Altman, E.Granato, T.Ala-Nissila, S.C.Ying, X.Xiao: Physical Review B, 2003, 68[7], 075422 (6pp)

Table 329

Parameters for the Diffusion of H Isotopes on (111) W Surfaces