Research and development of field emission sources to be able to dedicate to operation with high current density and long life time are progressing. In this study, impregnation technology of ruthenium dioxide (RuO2) particles onto nanotube surfaces and rooting technology of carbon nanotubes into the substrate have been developed to ensure the high current and long life time.
Impregnation of nano and subnano-sized RuO2 particles to MWNT emitter surfaces was carried out with utilizing ruthenium tetraoxide. Impregnation to MWNTs was confirmed with a high resolution scanning microscope, an energy dispersive x-ray spectrometer and X-ray photoelectron spectrometer. It turned out that enhancement of emission current density for the MWNTs with RuO2 was a factor of several ten to several hundred depending on parameters and the lowest threshold field for emission from MWNTs impregnated with RuO2 was found to be 0.89V/µm.
The enhancement owing to RuO2 impregnation is explainable based on the good properties of RuO2 such as relatively large electrical conductivity and proper control on both size of the RuO2 particles and surface density of RuO2 particles on MWNT surfaces.
Another key technology is rooting with which randomly oriented MWNTs can be fixed at their ends or sides as metal carbide on a substrate, improving thermal conductivity and tensile rigidity between the MWNTs and the substrate. It was found that the rooting of MWNTs allowed us to achieve a remarkably high DC current more than 300 A/cm2 with several optimization methods such as direct and indirect heat treatments of the MWNTs. |