Electronic properties of the emission sites of low-field emitting diamond films

Using the functional capabilities of a special scanning tunneling field emi ssion microscope (STFEM), a new measuring procedure for studying the electr onic properties of the emission sites of low-held emitting materials has be en developed. The position of intensive, separately situated emission sites ('individual' emission centres) was determined over a large surface area, whereupon both an electron escape and a surface electron potential at the ' individual' centre were investigated in detail. We report on the experiment al results of the STFEM study of electronic properties of low-field emittin g diamond films which have a composite structure consisting of diamond and nanocrystalline graphite phases, and show stable electron emission at field s 3-8 V/mu,. We observed a non-monotonous dependence of the electron escape from the emission site on the bias voltage - i.e, in a certain voltage ran ge, the electron escape decreased with increasing voltage. Also. in the sam e voltage range, the effective surface potential barrier at the emission si te shows a peak value. It is supposed that such anomalous electronic proper ties are due to resonant tunneling through the grain boundary region near t he interface of the diamond and graphite phases. In addition, the results o f energy resolved electron emission measurements are analyzed. The emission spectra show a cut-off at high energies and a tail towards low energies. T he best approximation of the spectrum tail is reached if electron tunneling through a triangular potential barrier of 0.1-0.2 eV relative to the Fermi level of the diamond film substrate, and the emission field of 50-100 V/mu m are taken into account. It thus can be supposed that the electrons are e mitted from the valence band, and the electric field at the emission site i s enhanced. A possible mechanism for the low-held electron emission from ch emical vapor deposited (CVD) diamond films, including both the geometric fi eld enhancement and the quantum well effect at the grain boundary, is discu ssed. (C) 2000 Elsevier Science S.A. All rights reserved.