Field Assisted Photoemission from Nanocrystalline Diamond and Diamond Field Emitter Arrays

Field emission from nanocrystalline diamond and especially from diamond field emitters is known to have an onset at low electric fields of a few MV/m, although the discussion on the agreement of the results with the classical Fowler-Nordheim model is still pending. While measurements of pure photoemission from flat nanocrystalline diamond agree reasonably well with the 3-step photoemission model for the wide bandgap semiconductor with low electron affinity, we are not aware of systematic studies of photoemission in the ~0.1-5 MV/ m range, where the electron emission mechanism is expected to be affected by the Schottky effect and crossover with the field emission. In order to understand applicability of field enhanced photoemission from diamond to generation of bright coherent photo-gated electron beams suitable for dielectric laser accelerators, we have designed a system to measure spectral response (quantum efficiency vs wavelength) of ~mm-sized samples with up to 5 MV/ m electric field in the anode-cathode gap. The system is based on an incoherent Xe lamp-based tunable ultaviolet light source, therefore relatively large and dense diamond field emitter arrays are required for comparative studies of arrays versus flat nanocrystalline diamond samples. We present the results of our original measurements in the range between 195 nm and 270 nm. Potential schemes of laser-triggered photoemission from a single diamond field emitter tip are discussed in view of the obtained results.