Enhanced field emission properties of thin-multiwalled carbon nanotubes:: Role of SiOx coating

We report the fabrication, characterization, and field emission properties of (silicon oxide) SiOx coated thin-multiwalled carbon nanotubes (t-MWNTs). The coated t-MWNTs show improved field emission behavior. Initially, raw t-MWNTs (diameter similar to 5-8 nm) were functionalized by acid treatment. Using spin on glass as a Si precursor, SiOx was coated on the nanotubes by routine chemical methods. The coated samples were characterized by high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) techniques. The HRTEM results show that the local thickness of the coating varies from similar to 1 to 2 nm. The FTIR investigations show the formation of nanophases, such as Si-C, Si-O-C, and intercalated Si-O, at the coating/nanotube interface. The TGA reveals that the coating prevents the high-temperature oxidation and degradation of the nanotubes. The field emission characteristics of the coated, functionalized, and raw nanotubes show that the turn-on fields and current density are improved for the coated nanotubes. This improvement was attributed to the lowering of the work function and dielectric constant of the C/SiOx interface layer and the localization of the density of states close to the Fermi energy for the coated nanotubes. The analysis of the emission stability spectra shows that the coated nanotubes have a more favorable lifetime. The observed enhancement was attributed to the protection of the nanotubes from the reactive sputter etching during the field emission process. The details of the analysis are presented. (c) 2006 American Institute of Physics.