Results are reported on microscopic study of electronic and structural prop
erties of field emission centers for chemical vapor deposition diamond film
s. The field electron emission (FEE) for the best films studied was observe
d at >3 V mu m(-1), and ultralow (<0.1 eV) values of effective work functio
n derived from Fowler-Nordheim plot fitting are discussed. A specially desi
gned high vacuum scanning tunneling-field emission microscope was applied f
or simultaneous mapping of FEE intensity, morphology, work function and loc
al electroconductivity evaluation. It was found that the emission centers w
ere not associated with sharp morphology protrusions. On the contrary, they
correspond to morphology pits (grain boundaries) which also show a low val
ue of the work function. A mechanism of the low-FEE near grain boundaries i
ncluding field enhancement of narrow conductive channels between insulating
diamond grains is discussed. (C) 1999 Elsevier Science S.A. All rights res
erved.