A Field Ion Investigation of Oxygen on Tungsten

Abstract

The adsorption of oxygen on tungsten was investigated with a field ion microscope. Two experimental procedures were followed. In the first, a tungsten tip previously annealed to 973 or 1173 °K was held at 78 °K while exposed to oxygen. Coverages ranged from less than a monolayer to saturation. After the ambient oxygen was removed, the tip was heated to the annealing temperature. In the second, oxygen adsorption occurred on a hot tip held at 973 °K. Estimated coverages were significantly less than a monolayer.Results reveal a dramatic difference in the extent of surface diffusion, rearrangement, disruption, and oxygen penetration for the two procedures, the latter producing more extensive effects. Possible explanations for these differences are considered.