Screening effect and reliability are two of the most important issues in carbon nanotube-based field-emission devices. A thin Ti capping layer has been deposited on the hydrogen-pretreated catalytic iron nanoparticles to control the density of subsequently grown carbon nanotubes. In this way, the screening effect can be remarkably reduced due to the density of carbon nanotubes down to 107 from 109cm−2 as compared to the control specimens. Thus, the turn-on field can be improved to be 2.1 from 3.8V∕μm at the emission current density of 10μA∕cm2 . Furthermore, the electrical breakdown field can be increased to more than 7V∕μm and the lifetime of carbon nanotubes at high electric field (10V∕μm) can be greatly prolonged from a few seconds to more than 1h . This can be attributed to better adhesion and lower contact resistance between the carbon nanotubes and the substrate.

A multilayer catalyst, Co/Cr/Al, was employed to synthesize carbon nanotubes (CNTs) at atmospheric pressure by thermal chemical vapor deposition (thermal CVD). The relative growth rates, calculated on the basis of the average lengths of nanotubes grown at different temperatures, were utilized to estimate an activation energy of 0.84 eV for the multilayer catalyst. Such a low activation energy implies that the nucleation and growth of nanotubes could be effectively enhanced via the multilayer catalyst due to the well-distributed small catalytic nanoparticles by Al supporting layer and higher activity by Cr co-catalyst layer. It was also found that nanotubes grown using this configuration at 500 C exhibited excellent field emission characteristics, and showed a highly uniform emission image in a phosphor-coated anode plate.

We found out the promising catalyst materials(NiPd). The NiPd not only has the low melting point but also has the Pd enhancing the surface diffusion at low temperatures(<500'c ). With the Pd film thickness increasing, we could control the CNT density and synthesize more aligned and uniform CNTs. We also obtained the better electrical properties including lower turn-on field (3.4 V/um) and higher current density (34.3 mA/cm2) for NiPd as catalyst. For the advantages described above, we believe that the difficulty of low temperature on FED can be overcome. Further, the large area field emission display might be fabricated in the future.