Field emission from combined structures of carbon nanotubes and carbon nanofibers

A convenient and inexpensive approach to producing carbonaceous field emitters has been developed. Combined structures of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were grown on graphitic substrates with an improved chemical vapor deposition (CVD) method. The fabrication featured a high reaction temperature and a rapid temperature rising. In each combined structure, a CNT with good crystallinity was surrounded by a cone-shaped CNF. The CNTs and the bases of the CNFs were less than 0.1 and 10 μm in diameter, respectively. These combined CNT/CNF structures, several ten microns in length, had an upward orientation from the substrate and an appropriate separation between each other, which are believed to be two favorable factors to the field emission. Electron current was readily extracted from them. Current densities of 10 μA/cm2 and 1 mA/cm2 were obtained when the average fields between the anode and the cathode were 2.3 and 3.9 V/μm, respectively.