Investigations on the Stability Enhancement of the Field Emission Device Based on Hybrid Nanostructures of Ultrananocrystalline Diamond Films

• Main Authors: Chang, Ting Hsun, 張庭熏
• Other Authors: Tai, Nyan Hwa
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/32057836872913960016

博士 === 國立清華大學 === 材料科學工程學系 === 104 === Growth, microstructure and electron field emission (EFE) characteristics of diamond films were investigated in this research work. A facile and reproducible way was developed to enhance the stability of EFE properties of diamond films. Firstly, hybrid granular structured diamond (HiD) films, which were nanocrystalline diamond/ultrananocrystalline diamond (UNCD) films, were coated on Si tips by a two-step microwave plasma enhanced chemical vapor deposition (MPE-CVD) process to synthesize the high performance EFE emitters. Secondly, the integration of the diamond films with high robustness and the carbon nanotubes (CNTs) with marvelous EFE properties that yielded highly stable electron sources was demonstrated. Lastly, high conductivity diamond-graphite nano-carbon composite (DGC) films were utilized to modify the granular structure of UNCD/CNTs films to form needle-like diamond grains encased in nano-graphitic layers, which possess high conductivity and improve EFE properties. The feasible mechanisms will be discussed. In the development of the nano-EFE emitters via the preparation of HiD on Si tip templates using a two-step MPE-CVD process, the mechanism which improved EFE properties were investigated. The superior EFE properties of the HiD films can be attributed to the formation of unique granular structure of the films. The transmission electron microscopic investigations revealed that the HiD films consisted of abundant graphitic phases, which were located at the periphery of large diamond aggregates and at the boundaries between the ultra-small diamond grains. The development of the CNTs-based EFE emitters, the enhanced lifetime stability for the CNTs by coating HiD films on nanodiamond particulates decorated CNTs/Si-based emitters using a two-step MPE-CVD process was reported, overcoming the drawback of short lifetime of the CNTs-based EFE-emitters. The use of CNTs effectively suppresses the presence of amorphous carbon in the diamond-to-Si interface that enhances the transport of electrons from Si, across the interface, to diamond. The two-step MPE-CVD process results in the coalescence of the small grains in UNCD films and the formation of abundant graphitic phases in these films. All these factors contribute toward the enhancement on the EFE process for the HiD/CNTs/Si-based emitters. Finally, we integrated high conductivity DGC films and CNTs and demonstrated the potential applications for EFE emitters as well as triode vacuum field emission transistor. The growth of high conductivity DGC films on CNTs were achieved by (i) strengthening the CNTs for directly growth of DGC films on CNTs in CH4/N2 plasma and (ii) lower growth temperature for DGC films by bias-enhanced plasma post-treatment process.