  Experimental evidence explaining the extremely low-threshold electron
emission from diamond reported in 1996 has been obtained for the first time.
Direct observation using combined ultraviolet photoelectron spectroscopy/field
emission spectroscopy (UPS/FES) proved that the origin of field-induced
electron emission from heavily nitrogen (N)-doped chemical vapour deposited
(CVD) diamond was at conduction band minimum (CBM) utilising negative electron
affinity (NEA). The significance of the result is that not only does it prove
the utilisation of NEA as the dominant factor for the extremely low-threshold
electron emission from heavily N-doped CVD diamond, but also strongly implies
that such low-threshold emission is possible from other types of diamond, and
even other materials having NEA surface. The low-threshold voltage, along with
the stable intensity and remarkably narrow energy width, suggests that this
type of electron emission can be applied to develop a next generation vacuum
nano-electronic devices with long lifetime and high energy resolution.
