Defects in the surface regions

We have ...carried out an experimental and analytical study of field emission from both undoped and p-type doped diamond produced by chemical vapor deposition (CVD). The study demonstrated a strong correlation between the emission properties and the defect densities in diamond. This letter further confirms the role of defects by reporting the effects of ion bombardment on the field emission characteristics of CVD diamond.

...The energetic ion implantation, even at the moderate doses used here, is known to cause structural damage and defect generation in the surface region of various materials, including diamond. Raman spectroscopy indicated that the full width at half-maximum (FWHM) of the diamond peak at 1332 cm21 increased after the ion implantation, suggesting that defects were generated in diamond.


....the defects near the surface region were annealed-out, while the dopants (boron or sodium) were still not effectively activated, resulting in relatively insulating
films.

...When the ion-implanted samples were annealed at high temperatures in order to anneal out the implantation-induced defects, the low-field electron emission capability of diamond disappeared.

These results suggest that the defects introduced in the surface regions by ion implantation increased the conductivity and altered the work function of as-grown diamond samples, thus directly affecting their field emission properties. While the exact nature of the responsible defects is yet to be identified, the types of defects formed can include vacancies, dislocations, stacking faults, and second phases such as graphite and amorphous carbon components. When the number of these defects is significant, the electronic states of defects could form a band or bands within the bulk diamond band gap. Electrons can be emitted directly into vacuum
from these band~s! or be transported to the surface states for emission. This is consistent with our earlier findings about the roles of defects in a field emission process from diamond. In essence, the formation of these defects and their associated electronic structures elevates the Fermi level, and consequently, the energy barrier that the electrons must tunnel through is reduced.

....The results suggest that the broad types of defects created by the ion implantation are responsible for electron emission at low electric

Electron field emission from ion-implanted diamond,1995 American Institute of Physics, AT&T Bell Laboratories, http://ora.ouls.ox.ac.uk
W. Zhu, G. P. Kochanski, S. Jin, and L. Seibles, J. Appl. Phys. 78, 2707
(1995).