Field Emission From Carbon-doped And Semimetallic TiO₂ Nanotube Ordered Array Films

The key point of the successful application of filed-emission devices is to develop the field-emission cold cathode with low turn-on and threshold electric field, high field-emission current density, good field-emission stability and long operating life. Two kinds of route are used for developing field-emission materials. One of routes is to search new materials; the other is to modify such materials in their morphology structure and electronic structure. As a promising field-emission material, TiO₂ nanotube ordered array films have been caused some attentions in recent years, because of their low work function, wide band-gap, small radius of curvature, strong adhesion to the substrate, excellent structural controllability, chemical and thermal stabilities. However, there are still some common obstacles to overcome for these wide band-gap oxide materials, such as the values of turn-on electric field are somewhat inconsistent and emission current density is relatively low. The study shows that TiO₂ nanotube ordered array films via carbon treatment can modify its morphology structure and electronic structure.This dissertation titled"Field emission from carbon-doped and semimetallic TiO₂ nanotube ordered array films"focuses on the fabrication and field-emission properties of carbon-doped and semimetallic TiO₂ nanotube ordered array films. Mainly works and results are as following:1. The field-emission characteristics of the carbon-doped TiO₂ nanotube ordered array films, which can be obtained by a heat treatment (550°C) of the as-fabricated TiO₂ nanotube ordered array films under a continuous argon and acetylene flux, were investigated. The morphology, crystalline structure, and composition of the as-grown specimens were characterized by using of field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. It was found that the samples'turn-on electric field is reduced from 21.9 to 5.0 V/μm and the field-emission current density rapidly reaches about 9.0 mA/cm2 at 11.8 V/μm after carbon doping. The dramatically improved field-emission characteristics would be mainly attributed to the reduced work function and the enhanced conductivity due to the carbon doping into TiO₂ nanotube ordered array films.2. Semimetallic TiO₂ nanotube ordered array films have been synthesized by a heat treatment (750°C) of the as-fabricated TiO₂ nanotube ordered array films under a continuous argon and acetylene flux. It consists of the TiO₂ phase and TiOxCy phase. And it keeps the fully morphology structure of TiO₂ nanotube ordered array films. Field-emission measurements reveal that semimetallic TiO₂ nanotube ordered array films show improved field-emission performance in contrast to the pure and carbon-doped TiO₂ nanotube ordered array films. Its turn-on electric field is 3.0 V/μm, threshold electric field is 7.0 V/μm. The improved field-emission characteristics would be mainly attributed to the up-shifted Fermi level, the enhanced conductivity and roughness of semimetallic TiO₂ nanotube ordered array films.