High Quantum Efficiency Ultrananocrystalline Diamond Photocathode:   Negative Electron Affinity Meets $n$-doping
  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 QE of $\sim$10$^{-3}$ ($\sim$0.1%) at 254 nm. Moreover, (N)UNCD:H was sensitive in visible light with a QE of $\sim$5$\times$10$^{-8}$ at 405 nm and $\sim$5$\times$10$^{-9}$ at 436 nm. After growth and prior to QE measurements, samples were exposed to air for about 2 hours for transfer and loading. Such design takes advantage of a key combination: 1) H-termination inducing negative electron affinity (NEA) on the (N)UNCD and stabilizies its surface against air exposure; and 2) N-incorporation inducing $n$-type conductivity in intrinsically insulating UNCD. 
K.J. P\'erez Quintero, S. Antipov, A.V. Sumant, C. Jing, A.D.   Kanareykin, S.V. Baryshev
cond-mat.mtrl-sci cond-mat.mes-hall