An investigation of the surface reactivity of diamond photocathodes with molecular and atomic oxygen species

Abstract

The surface reactivity of CVD diamond films, which function as UV photocathodes, with thermal and electronically excited O 2, as well as atomic oxygen, has been explored. The CVD films show a low, but measurable reactivity with O 2, which increases markedly with electronic excitation, to form dilute oxygen adlayers which are stable thermally to 800 K. In contrast, reaction with atomic O produces significantly higher surface concentrations of oxygen, although these adlayers decompose thermally below 500 K, evolving CO 2. Greater surface reaction probabilities are observed if the diamond surface is pre-hydrogenated before interaction with oxygen. The consequences of these observations for the stable operation of H-terminated diamond photocathodes are discussed.