Structure Controlling And Properties Of Vanadium Oxide-Carbon Nanotube Films

The structures,optical and electrical properties of vanadium oxide(VO_x)films prepared by sol-gel method have been extensively studied.However,their low conductivity limits their practical applications.An effective method to improve the electrical properties of VO_x is to combine it with other high conductivity materials,such as carbon nanotubes(CNT)and graphene.Among them,VO_x-CNT composite materials have attracted much attention due to their high TCR and high conductivity.At present,most of the CNTs in the VO_x-CNT composite materials are randomly distributed,which leads to a single photoelectric performance.Compared with the random CNT films,the morphology and arrangement of CNTs in the patterned CNT films are controlled,and its electrical anisotropy is obvious.Although patterned carbon nanotube films have been widely studied,rare results on the preparation and applications of VO_x-aligned CNT composite films have been previously reported.Based on the sol-gel method,VO_x films and various VO_x-aligned CNT composite films were prepared in this work.Moreover,the structures,electrical and optical properties of the as-prepared films were investigated.In addition,the feasibility of applications of VO_x-aligned CNT films in the detectors was investigated.The main contents of this thesis include the following parts:Firstly,the process parameters for the preparation of VO_x thin films by sol-gel were optimized,and the reaction mechanism was investigated.VO_x organic sols were reacted at different temperatures,by which various VO_x thin films were prepared.Results reveal that a moderate temperature of 110 ? prompts both alcoholysis and condensation reactions to produce more VO_x networks(O=V-O-V=O).Consequently,the VO_x films that are produced by the sol reacted at 110 ? possess a low resistivity of 23 ?�cm,a high temperature coefficient resistance(TCR)of-3.2%�K-1,and a low average transmittance of 54% in 580�1100 nm,compared with those prepared by the sols reacted at lower or higher temperatures.Therefore,110 ? is a desirable sol temperature for producing VO_x films serving as high-quality bolometric materials for uncooled infrared detectors.Secondly,based on the optimization of the preparation of VO_x films,VO_x-CNT films with different structures were prepared.The as-prepared films exhibit different optical and electrical properties with the change of the CNT pattern.In addition,the resistance anisotropies of the VO_x-CNT films with different patterned structures were investigated.Moreover,both influences of the dispersion of CNTs and the contact point of CNTs on the electron transports of the composite films were analyzed.Accordingly,a novel method for adjusting the electrical and optical properties of the composite film by designing the CNT pattern was proposed.Finally,in order to achieve well alignment of carbon nanotubes on the micro scale,CNTs that have pre-modified with magnetic nanoparticles were composited with VO_x thin films to prepare VO-magnetic CNT films.Measurement results reveal that the optical properties of VO_x-magnetic CNT films are significantly affected by the magnetic field.Under the magnetic field,the resulting films possess more moderate resistance(6.2 MW),good temperature sensitivity(TCR:-3.3%�K-1)and high optical absorption.Morever,the effects of the interactions among magnetic nanoparticles,carbon nanotubes and VO_x on the photoelectric properties of the films were investigated.Based on these,another new method for adjusting the photoelectric characteristics of VO_x composite films by magnetic field was proposed.