Modified Carbon Nanotubes And Their Field Emission Performances

Carbon nanotubes (CNTs) have drawn tremendous interest from fields ranging from condensed-matter physics to chemistry, and from both academia and industry, especially as cold cathode electron source. Up to date, however, field emission properties of CNTs are not satisfied for applications. There also are numerous argues in the understanding of emission mechanism. The purposes of this work are to understand emission mechanism of CNTs, and hence modify CNTs to improve their field emission performances. In this thesis, carbon nanotube is the common thread tying together diverse topics, ranging from materials synthesis to materials modification to device fabrication.A multifunctional ultrahigh vacuum system was built for CNTs growth, field emission characterization, surface treatment, vacuum sealing and anneal. High quality CNT films and aligned CNT arrays were obtained using plasma enhanced chemical vapor deposition (PECVD). In addition, we have controlled deposition parameters to grow some novel materials such as Y-junction, spinose CNTs and carbon nanospring. Low temperature growth of CNTs on glass was also available.Effect of plasma treatment on the microstructure and field emission of screen-printed CNTs was studied systematically. A novel configuration of CNTs was discovered. We attributed the improvement of field emission to the changing of the electronic and/or geometrical structure of the local emission region in CNTs. It was proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment,electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips.For PECVD CNT films, two approaches were used to improve their field emission performances. Hafnium coated and successively anneal could enhance the emission properties due to lower surface work function and hence lower barrier height. Additionally, formation of conductive carbide on the interface between the substrate and CNTs also enhanced emission current because of thin or remove contact barrier. According to a two-barrier model, we attributed the knee on the Fowler-Nordheim (F-N) plots to thechange of tunneling mechanism-from direct tunneling in the low field region to F-Ntunneling in the high field region.Full sealed large area prototype FEDs based on CNT were demonstrated, which showed good emission characteristics. In addition, we integrated CNT emitters with metal-oxide-semiconductor field effect transistor (MOSFET) for high performance display application. A LDMOSFET controlled CNT FEA based on SOI was fabricated. This may pave a new road for CNT-FED devolopment.