High-temperature contact potential difference measurement of surface work function using in vacuo Kelvin probe

Characterization of the work function of emitting surfaces represents an important contribution to thermionic emission research today. This is because materials that exhibit lower work functions are capable of thermionically emitting higher current densities at lower operating temperatures, which ultimately means longer lifetimes for the vacuum electron devices that make use of thermionic emitters. One widely used technique to characterize a material's work function is the measurement of contact potential difference using a Kelvin probe system. When applied in the traditional mode, this technique fails to produce meaningful results in situations where a sufficiently hot sample under inspection and the cooler Kelvin probe are in thermal disequilibrium. However, as this paper will outline, the standard application of a Kelvin probe system can be amended to facilitate meaningful asymmetric contact potential difference measurements, and consequently, obtain values of work function for samples at high temperatures, including relevant operating temperatures for thermionic emitters (>1000 °C).