Field-Emission Study of Carbon Monoxide on Tantalum

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Abstract
Adsorbed carbon monoxide shows three states of binding on tantalum. The weakest of these is desorbed at temperatures above 125°K with no observable surface migration. The bonding with the surface is of the van der Waals type. This is in contrast with the second state, which is desorbed above 650°K. The third state is dissociated before desorption to give the oxygen‐on‐tantalum pattern. Surface migration involving the second adsorbed state occurs with an activation energy of 38 kcal. The work function of a carbon monoxide‐covered tantalum surface, obtained by spreading the carbon monoxide on a shadowed tip at 40°K, is 0.8 eV greater than that of the corresponding clean tantalum. Fowler—Nordheim plots of clean and shadowed tips show that at least under these conditions, the infinite‐field extrapolation of logi/V2 is proportional to the log of the emitting areas.