Adsorption of Oxygen on Tungsten: Field Emission from Single Planes

Abstract

Work‐function and Fowler–Nordheim pre‐exponential changes for incremental oxygen adsorption at 20 and 100°K have been measured on the (120), (111), (100), (211), and (110) planes of a tungsten field emitter. On the (110) plane $\text{Δφ\hspace{0.17em}=\hspace{0.17em}0.6}\mathrm{eV}$ at full coverage, while $\text{Δφ\hspace{0.17em}=\hspace{0.17em}1.2–1.4}\mathrm{eV}$ on most other planes. A model of O adsorption based on the partial filling of an affinity band is presented to account for this and other features of the results. Diffusion into various planes was also investigated. It was found that low‐temperature boundary diffusion at 25°K leaves the (110) plane bare. Diffusion in the chemisorbed layer starts at 400°K on (110) with an activation energy of 15 kcal, and on other planes at temperatures of ∼ 500°K.