High quantum efficiency ultrananocrystalline diamond photocathode for photoinjector applications

We report results of quantum efficiency (QE) measurements carried out on a 150 nm thick nitrogen-incorporated ultrananocrystalline diamond terminated with hydrogen; abbreviated as (N)UNCD:H. (N)UNCD:H demonstrated a remarkable QE of ∼10−3 (∼0.1%) at 254 nm. Moreover, (N)UNCD:H was sensitive in visible light with a QE of ∼5 × 10−8 at 405 nm and ∼5 × 10−9 at 436 nm. Importantly, after growth and prior to QE measurements, samples were exposed to air for about 2 h for transfer and loading. Such design takes advantage of a key combination: (1) H-termination proven to induce negative electron affinity on the (N)UNCD and to stabilize its surface against air exposure; and (2) N-incorporation inducing n-type conductivity in intrinsically insulating UNCD.