Electron field emission properties of carbon nanotubes grown on nickel caps

Carbon nanotubes (CNTs) were grown on Ni caps, possessing good electron field emission properties and exhibiting good potential for the applications as the electron sources in cathode ray tubes. The characteristics of the CNTs grown on Ni caps vary with the synthesis processes markedly. For the gas-phase-formed CNTs, which were grown on ferrocene-derived Fe clusters via a gas-phase-nucleation process, the CNTs are uniformly small in diameter and of high purity. In contrast, for the surface-grown CNTs, which were formed on Fe(C7H17COO)(3)-derived Fe clusters, the CNTs are large in diameter, containing large proportion of carbon soots. However, the surface-grown CNTs exhibit markedly better electron field emission capacity (J(e))(s) = 4.4 mA/cm(2), than the gas-phase-formed CNTs, (J(e))(g) = 1.5 mA/cm(2) at 22.5 V/mum, even though the latter possess a smaller effective work function [(Phi(e)),=0.114 eV and (Phi(e))(g)=0.034 eV]. Such phenomenon is presumably ascribed to the better CNT-to-substrate contact properties for the CNTs grown directly on the Fe clusters coated on Ni caps. (C) 2003 American Vacuum Society.