Effect of oxygen vacancies on electronic structures and field emission properties of TiO2 nanotubes: A density-functional theory investigation

Influence of oxygen vacancies (VO’s) on electronic structures and field emission properties of TiO2 nanotubes (NTs) is investigated by first-principle calculations. It is demonstrated that the formation of 3-fold coordinated VO gives rise to two shallow donor states below the conduction band minimum. Whereas one shallow coupled with another deep donor states appears in the case of a 2-fold bridging vacancy located on the outer side-wall of TiO2 NT. VO’s are found to greatly reduce the barrier for electron extracting. These results can explain why, experimentally, TiO2 NTs with intrinsic VO can overcome the high barrier of electron affinity and exhibit an excellent field-emission performance.