Field emission of different oriented carbon nanotubes

Field emission data from aligned high-density carbon nanotubes (CNTs) with orientations parallel, 45 degrees, and perpendicular to the substrate have been obtained. The large-area uniformly distributed CNTs were synthesized o n smooth nickel substrates via dc plasma-assisted hot filament chemical vap or deposition. CNTs with diameters in the range of 100-200 nm were employed in this study. The different orientations were obtained by changing the an gle between the substrate and the electrical field direction. The growth me chanism for the alignment and orientation control of CNTs has been discusse d. The CNTs oriented parallel to the substrate have a lower onset applied f ield than those oriented perpendicular to the substrate. This result indica tes that electrons can emit from the body of the CNT, which means that the CNT can be used as a linear emitter. The small radius of the tube wall and the existence of defects are suggested as the reasons for the emission of e lectrons from the body of the tubes. (C) 2000 American Institute of Physics . [S0003-6951(00)01817-9].