The impact of surface hydrogenation on the thermionic electron emission from polycrystalline diamond films

Abstract

In this work, thermionic electron emission (TEE) from hot filament chemical vapour deposition polycrystalline diamond films deposited on p‐type silicon substrates was recorded in the 25–650 °C temperature range. The studied surfaces were as deposited, as well as hydrogenated by atomic hydrogen under ultra‐high vacuum conditions. The impact of substrate temperature during hydrogenation, TH, on TEE was studied. For TH = 25 °C the TEE was found to display a broad maximum at substrate temperature around 300 °C followed by an exponential increase. Annealing at 700 °C results in irreversible changes in surface conditioning, and drastic reduction of TEE yield at low temperatures. For samples that underwent hydrogenation at TH = 300 and 500 °C, the TEE yield is significant at higher temperatures only. The TEE from these samples is stable also after 700 °C annealing treatment. We associate these effects with irreversible thermal induced physicochemical changes of the hydrogen bonding configuration adsorbed on the polycrystalline diamond surface resulting in changes in its surface electronic structure which occur upon annealing to ∼300 °C.