| An ideal material for field emission should have low work function, good chemical stability high aspect ratio etc. In recent years, many kinds of materials such as metal, semiconductor, carbon and oxide are commonly used for field emission. Yet, most materials possess more or less defects like high work function, high chemical activity, low emission current, etc. The emitters need high driving voltage and easily degrade. Thereby, 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 structure and the chemical composition. Fortunatly, TiO2 nanotube arrays with low work function possess high aspect ratio opened tips which can efficiently improve the field enhancement factor. They also can easily modify into composite materials for their larger specific surface area. Furthermore, they can be prepared by simple methods. There is no double that TiO2 nanotube arrays would be suitable for electron emitter applications. However, few works of their field emission have been reported.This dissertation titled"Field emission from TiO2 nanotube arrays"focuses on the fabrication and field emission properties of TiO2/Ti nanotube arrays. Mainly works and results are as following:1. The devices of anodization (which can be used to synthesis AAO, TiO2 nanotube arrays or porous TiO2 and electrochemically deposition) have been improved. A low press chemical vapor deposition system (LCVD) (the utmost temperature and pressure is 1000℃and 10 Pa, respectively) and a field emission measurement system (the utmost pressure is 10-6 Pa) have been set up.2. Highly ordered and uniform TiO2 nanotube arrays are fabricated by anodic oxidation of titanium foil in HF aqueous solution. The structure parameters such as tube diameter, density, length and wall thickness can be controlled effectively by varying anodization parameters including anodization voltage. Also, the field emission properties can be adjusted by such anodization parameters. With increasing of anodization voltage appropriately, the field emission properties of TiO2 nanotube arrays are optimized including lower turn-on field and higher field enhancement factor. 3. Carbon nanotubes and diamond nanorods are respectively fabricated by chemical vapor deposition in nanotube of TiO2 at low pressure in order to modify TiO2 nanotube arrays. As a result, composite nanostructure of CNTs/TiO2/Ti and DNRs/TiO2/Ti are synthesis and their field emission properties are studied. The results revealed that field emission properties of TiO2 nanotube arrays modified by CNTs or DNRs are remarkably enhanced and the turn-on field is declined from 11.5 V/μm to 1.2 V/μm and 3.0 V/μm, respectively. The field emission stability is also improved. |
