Field emission properties of nanocrystalline chemically vapor deposited-diamond films

We have deposited nanocrystalline diamond films on p-type Si(100) substrates using plasma enhanced chemical vapor deposition (CVD). The diamond films were deposited at substrate temperatures between 950 and 980 degrees C using a high methane concentration of 5% in H-2. The films obtained showed good field emission properties with threshold fields of around 5 V mu m(-1) (for 1 nA emission current). X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy showed that the nanocrystalline films still exhibit the basic electronic features of diamond with a band gap of 5.5 eV and a negative electron affinity when the Surface is hydrogen plasma treated. The Fermi level position in these films is found to be 1+/-0.2 eV above the valence band maximum. The energy resolved field emission measurements show the typical asymmetric peak shape of Fowler-Nordheim (FN) tunneling through a surface potential barrier. The electrons emitted originate from a continuum of electronic states at the Fermi energy of the emitter. From a combined measurement of the field emitted electron energy distribution and the field emission I-V characteristic of an emitter we could independently determine the work function and the local electric field present at the emission site. In the case of nanocrystalline CVD diamond emitters we determined work function values around 5.7 eV and local fields in the range of 2000-3000 V mu m(-1) (for emission currents of 10-1000 pA). The corresponding field enhancement factors can range from 250 to 1700. Simultaneous field and photoelectron emission spectroscopy showed no indication of field penetration. Deviations from the FN law in the high current regime of the I-V plots may be related to an internal resistance of the emitter. (C) 1999 American Vacuum Society. [S0734-211X(99)03205-9].