Low-threshold electron emission from diamond

We have studied the photoassisted electron emission of single-crystal diamo nd (111) for photon energies from just above the diamond band gap of 5.5 eV well into-the sub-band-gap regime (hv approximate to 2.8 eV). As an indepe ndent parameter, the electron affinity was varied between -1.27 eV [negativ e electron affinity (NEA)] and +0.35 eV [positive electron affinity (PEA)] by changing the hydrogen coverage of the surface. A substantial sub-band-ga p emission band with constant intensity: is observed in all cases. Except f or the NEA surfaces, it dominates the electron flux. We attribute this inte nse band to nanometer-size graphitic patches which cover less than 1% of th e surface area. The low-energy threshold for this emission band is, however , not determined by intrinsic properties of graphite, but controlled by the work function of the surrounding diamond matrix. The details of this inhom ogeneous emission model, which may have implications for the field emission from nanocrystalline diamond films, are discussed. [S0163-1829(99)08647-6] .