Modulating the work function of carbon by N or O addition and nanotip fabrication

A model is presented for the lowering of the work function for high-efficiency electron emission. It is suggested that: (i) an oxide or nitride tetrahedron formation creates nonbonding lone pairs that induce the anti-bonding dipoles associated with density of states added above the Fermi level and; (ii) that nanofabrication could densitify the charges in the confined region due to the coordination number (CN)-imperfection-induced bond contraction. However, over dosing N or O may cause hydrogen-like bond formation with a ‘dipole/+’ valence state which could explain the reduced work function. Closely packed nanotips also reproduce the work function of a flat surface. It is anticipated that the work function of a surface can be lowered by proper co-doping O or N with metals of low-work function to the miniaturized tips. Predictions agree with various experimental observations.