Abstract
A nitrogen-doped titania nanotube array vertically aligned on a titanium substrate exhibits efficient electron field emission. Such a titania nanotube array shows very good stability at high field emission current (fluctuation <3% at field emission current of 160 mu A within 4 h) and low turn-on and threshold fields (11.2 and 24.4 V mu m(-1), respectively) because of the coexistence of doped nitrogen and concomitant oxygen vacancies in titania nanotubes. This work demonstrates the possibility of converting pure titania nanotubes without field emission into a favorable and efficient one through the introduction of acceptor states and donor states both above the valence band maximum and below the conduction band minimum in the band gap of titania by the doped nitrogen and concomitant oxygen vacancies, respectively. Application of this doping concept to other transition metal oxides can be expected to broaden the scope of field emission materials.