Effect of catalytic layer thickness on growth and field emission characteristics of carbon nanotubes synthesized at low temperatures using thermal chemical vapor deposition

The direct synthesis of carbon nanotubes (CNTs) on substrates by chemical vapor deposition (CVD) is a highly promising route for their application to field emission displays. Several stringent requirements have to be met for this purpose, including low-temperature growth below 600degreesC to utilize glass substrates and large-area deposition for practical use. In this study, we carried out the synthesis of CNTs by thermal CVD on glass substrates at temperatures as low as 500-550degreesC. CNTs were grown by thermal decomposition of CO and H-2 gases at atmospheric pressure for different thicknesses of Invar (Fe-Ni-Co alloy) catalytic layers. The CNT growth was strongly correlated with the preparation conditions of the catalytic layers. The diameters and heights of as-grown CNTs increased with the catalytic layer thickness from 2 nm to 30 nm. Measurements of the field emission properties of the CNTs showed that the threshold electric fields decreased with increasing thickness of the catalytic layers. Uniform electron emission was observed over a large area of 150 x 150 mm(2) with high emission current and high brightness.