The Modification Research Of Field Emission Properties Of SnO₂ And TiO₂ Nanoarray Structures

The key point of the successful applications of vacuum microelectronics devices based on field emission lies in the preparation of the field-emission cold cathode with low turn-on and threshold electric field, high field-emission current density, good field-emission stability, long operating life and low cost. The SnO₂ and TiO₂ nanostructure arrays with lower work function, controllable morphology, simple preparation and low cost of raw materials, are kinds of extensively researched field emisison materials, which enjoy great potential and vast development prospects. The difficulties faced by the current research for SnO₂ and TiO₂ nanostructure arrays field emitter are to further reduce the turn-on and threshold electric field, to improve the field emission current density, and to improve the field emission stability. In this paper, on the basis of summary and analysis of existing work we forward new ideas and new ways to overcome these problems. This dissertation titled ―The modification research of field emission prope rties of Sn O₂ and TiO₂ nanoarray structures‖ focuses on the fabrication and investigation of field emission properties of SnO₂ nanoparticle and TiO₂ nanotube arrays. And the main works and results are shown as following:（1） For the first time, uniformly dispersed SnO₂ nanoparticle arrays were prepared via a catalytic reduction of FTO glass in hydrogen atmosphere. By controlling the hydrogenation temperature, the dispersed SnO₂ nanoparticles were uniformly embedded in the TiO₂ film. Particle density and size were optimized, which allowed significant reduction in the field-screen effect. Furthermore, hydrogenation can introduce oxygen vacancies, thereby reducing the work function and improving conductivity of the SnO₂ nanoparticles. All these factors result in the enhancement of FE performance. Notably, the SnO₂ nanoparticle arrays at 500 °C showed a low turn-on field of ³.81 V/μm and excellent FE stability.（2） With the in-depth investigation of SnO₂ nanoparticle arrays’ growth mechanism we find that the amount of TiO₂ catalyst for the growth of SnO₂ nanoparticle arrays is also another important factor. By adjusting the amount of catalyst over the range of 6.5⁴5.5 μL, the SnO₂ nanoparticle arrays are uniformly embedded in TiO₂ films and display the controllable density, size and conductivity. Also, the growth mechanism of SnO₂ nanoparticle arrays is analyzed in detail based on the experimental results. The optimized SnO₂ nanoparticle arrays prepared with 32.5 μL TiO₂ sol show excellent field emission performances, with both a low turn-on field of 3.86 V/μm and remarkable field emission stability. Therefore, t he reported uniformly dispersed and protuberant SnO₂ nanoparticles with excellent field emission properties, may serve as one of promising candidates for application in flat panel displays and nanoelectronics building blocks.（3） In this part, a mass of oxygen vacancies are successfully introduced into TiO₂ nanotube arrays using low-cost Na BH4 as a reductant in a liquid-phase environment. By controlling and adjusting the reduction time over the range of 0-24 h, the doping concentration of the oxygen vacancy realizes controllable and eventually reaches saturation. Meanwhile, the thermal stability of oxygen vacancies is also investigated, indicating that part of oxygen vacancies remain stable up to 250 °C. In addition, this liquid-phase reduction strategy significantly lowers the requirements of instruments and cost. More interesting, reduced TiO₂ nanotube arrays show drastically enhanced field emission performances including substantially decreased turn-on field from 25.01 to 2.65 V/μm, a high current density of 3.5 mA/cm2 at an applied field of 7.2 V/μm and an excellent field emission stability and repeatability. These results are attributed to the oxygen vacancies obtained by reducing, resulting in a reduced effective work function and an increased conductivity.（4） With the in-depth investigation of partially reduced TiO₂ nanotube arrays growth mechanism, we find that the reduction temperature for the generation of oxygen vacancy is also important factor, which can manipulate morphology of TiO₂ nanotube arrays to obtain a large field enhancement factor besides introducing oxygen vacancies into samples by transforming and controlling the reduction temperature from 30 to 90 °C. Meanwhile, the thermal and long-term stability of oxygen vacancy are also investigated, indicating that the oxygen vacancies remain long-term stability from room temperature up to 150 °C. More interesting, partially reduced TiO₂ nanotube arrays show drastically enhanced field emission performances including substantially decreased turn-on field from 18.86 to 1.53 V/μm, a high current density of 4.00 mA/cm2 at 4.52 V/μm, and an excellent field emission stability and repeatability.