Chemisorption of Oxygen on Ordered Tungsten Surfaces

Abstract

Chemisorption of oxygen on highly ordered and relatively disordered tungsten surfaces at substrate temperatures of 20° and 300°K has been studied in the field‐emission microscope. Evidence is presented for the chemisorption of a monolayer of gas with a sticking coefficient of unity and the adsorption of a second, initially mobile layer of oxygen, also with a sticking coefficient of unity when the substrate temperature is 20°K. These results are independent of the degree of surface order over the range considered. The second adsorbed layer is not observed at substrate temperatures of 300°K, and use of the Langmuir postulate that only the clean surface contributes to the adsorption allows the definition of a constant sticking coefficient of 0.8 for oxygen on tungsten at 300°K. Variations in the dipole moment per adatom with crystallographic orientation are also reported.