Photoemission enhancement of nanodiamond particles by treatment in H2 or N2 plasmas

Generally materials, having a low/negative electron affinity (NEA) and/or a low work function which facilitate the electron escape from their surfaces, exhibit good photo- and thermo-emission properties. From this point of view, natural and synthetic diamond is an interesting material because possesses a low EA that becomes negative when the surface is treated in H2 plasma. Moreover, as-grown diamond films produced by microwave plasma enhanced chemical vapour deposition and starting from CH4:H2 (1:99%) gas mixture exhibit hydrogenated surfaces, suitable for photocathodes, neutralizer cathode, energy converters and so on. Very recently the authors of this contribution have patented a new methodology (easy, inexpensive and working at temperature of 120°C) to fabricate layers of nanodiamond (ND) particles. In the present work, the photoemission behaviour of ND layers produced by this new methodology i.e. the pulsed spray technique is presented. Commercial (Diamonds & Tools srl) ND particles, 250 nm in size, were utilized. Layers of untreated and treated (in pure H2 or N2 plasmas) NDs were produced. The photoemission quantum efficiency (QE), a merit figure for photocathode applications, was assessed in the UV range (140-210 nm), showing a QE enhancement for both hydrogenated and nitrogenated ND particles.