Abstract
By using a rapid heating and cooling system (RHCS), several kinds of carbon nanotubes (CNTs) were synthesized in a thermal chemical vapor deposition (CVD) chamber. The process for grown positioning CNT and the applications of synthesized vertical CNTs array were discussed in this work. Vertically aligned CNTs were synthesized on a lithographically patterned silicon/silica substrate coated with an ultra thin iron film. The length of CNTs array could be grown up to 500 um and the profile was controlled by the thickness of catalytic film. To improve to field emission properties of CNTs array, a process for transferring CNT array from silicon wafer to alumina substrate coated with Ag-paste was proposed. A current density of 325 mA/cm2 was attained with an applied electric field of 2.4 V/um and the turn-on field was only 0.55 V/um. With this method, the adhesion between CNTs and substrate was enhanced and the current density and turn-on voltage were also improved. Effects of microstructure of the emitting sites at CNT tip on the current density were also studied. On the process for fabricating directional single-walled carbon nanotubes (SWNTs), an electric field was applied during the CVD process. The electric field affected significantly the CNTs direction during growth on multi-layered substrate. The sharp edge of Cr electrode yielded an enhanced electric field, which promoted the growth of SWNTs between the two tips. A theoretical modeling was proposed to predict the electric field, and the simulated pattern was quite consistent with the SWNT growth region around the tips. High quality and high purity SWNTs on Fe-Mo catalysts were synthesized by thermal chemical vapor deposition. The catalysts were prepared by using co-sputtering and multilayer pre-coating methods. Morphologies and microstructure of the synthesized SWNTs were examined. Peaks of the radial breathing mode (RBM) in the Raman spectrum demonstrated that highly pure SWNTs had been synthesized when the co-sputtered Fe-Mo catalysts were used. The CNT bulb was also made by the SWNTs filament which was synthesized by the floating catalyst method.