The diffusion of oxygen on W(110) revisited

The diffusion of oxygen on the (110) plane of tungsten has been reexamined via the field emission fluctuation method, using a digital correlation apparatus. Measurements were carried out over a coverage range of 0.13⩽O/W⩽0.79. Where overlap exists activation energies agree well with previous work; there is qualitative but not quantitative agreement with prefactors D0. Mean-square fluctuations show very little temperature dependence. The present results show that E rises almost linearly from 14 kcal/mol at O/W⩽0.2 to 23 kcal/mol at O/W=0.4, then shows a slight dip at O/W=0.56 and then rises again to 27 kcal/mol at O/W=0.79. D0=4×10−8 cm2/s at O/W=0.13, and rises by six orders of magnitude to 5×10−2 cm2/s at O/W=0.79. It is postulated that the increases in E and D0 with coverage have their origin in polaronic effects, to wit the participation of substrate atoms in the diffusion process and a progressive stiffening of the substrate by O atoms as coverage increases.