KINETICS OF OXYGEN ADSORPTION ON (112) AND (110) PLANES OF TUNGSTEN

The kinetics of oxygen adsorption on the (112) and (110) planes of tungsten at coverages below a monolayer have been studied in detail by LEED and work function measurements during adsorption. On both surfaces the oxygen appears to adsorb first in a weakly bound molecular state and chemisorption occurs at the edges of growing islands of previously chemisorbed oxygen atoms. The sticking coefficient is found to be independent of coverage on the (112) surface indicating that the inter-island distance is sufficiently small that every adsorbed molecule reaches an island in its diffusion lifetime. On the (110) surface the sticking coefficient is found to be proportional to the square-root of the coverage indicating that the islands are so far apart that only those molecules adsorbed sufficiently close to the edge of an island become chemisorbed. The question of reconstruction of substrate atoms is considered in some detail in view of these and other recently published1) findings. It is shown that the experimental data is consistent with a simple chemisorption model which does not involve reconstruction. © 1969.