The electron-field-emission sEFEd behavior of the nanodiamond films was observed to be
pronouncedly superior to that of the diamond films with micrometer- or submicrometer-sized grains, which is ascribed to the presence of abundant grains boundaries with sp2 bonds. Incorporation of boron species into the nanodiamond films further improves the EFE properties for the films. The best EFE properties achieved are turn-on field E0=18 V/mm with EFE capacity J=0.7 mA/cm2 at
around 30 V/mm applied field. However, boron doping into the nanodiamond films does not result in consistent boron-content dependence of the EFE properties for the films as those in conventional micrometer-sized diamonds. The complication is explained by the fact that the small size of the diamond grains s,20 nmd may not be able to accommodate the boron species into the lattices to effectively act as acceptor dopants. Moreover, the formation of aggregates of the nanosized diamond
grains may alter the local field enhancement factor, which further complicates the correlation of the field-emission behavior with the boron-doping concentration for the nanodiamond films.