Vertically aligned carbon nanotube field emitter arrays with Ohmic base contact to silicon by Fe-catalyzed chemical vapor deposition

Abstract

In this study, dense arrays of aligned carbon nanotubes are obtained by thermal catalytic chemical vapor deposition, using Fe catalyst dispersed on a thin Ta layer. Alignment of the carbon nanotubes depends on the original Fe layer thickness from which the catalyst dispersion is obtained by thermal treatment prior to the synthesis step, as well as on the synthesis temperature, which in this study was varied between 680 and 740°C. For the intended application of the nanotubes as field emitters, it is essential that electrical conductivity between the tubes and the substrate is guaranteed. In a novel approach, a noble metal layer, of 100nm Pt or Au, was applied between the Ta layer and the support, which ensures an Ohmic contact throughout the metal multilayer which connects the silicon substrate with the CNT fibers, because oxidation of Ta at its interface with Si is prevented. For optimized dense arrays of aligned nanotubes with low Ohmic resistance, field emission in nitrogen atmosphere is demonstrated, with field enhancement factors of up to ca. 2000 for nanotubes grown using Fe/Ta catalyst deposited on Au and Pt.