Enhanced field emission properties of electrochemically synthesized self-aligned nitrogen-doped TiO ₂ nanotube array thin films

Vertically aligned TiO _2-δ and TiO _2-3yN2y nanotube array thin films were synthesized electrochemically in a single step. N-Doping at different levels was achieved by using different concentrations of urea, as nitrogen precursor, in the electrolyte. The GIXRD and Raman studies revealed that the nanotube arrays are of anatase phase. The field emission measurements showed low turn-on fields of 10, 9.21, and 6.54 V/μm at 3.88, 4.12, and 4.74 at% of N-doping, respectively, implying enhanced field emission upon N-doping as well as an increase in electron emission with increase in N-doping. The electron emission current was found to be stable for a period of 5 h. The high electron emission current and low threshold field on N-doping is due to the presence of localized donor states below the conduction band minimum, as a result of oxygen vacancies, created by N-doping, and introduction of localized N 2p states above the valence band minimum by the doped nitrogen.