Field Emission from Titanium-Coated Carbon Nanotubes Grown on Micron-Sized Silicon Pillar Arrays

Abstract

Carbon nanotubes (CNTs) have attracted great attention because of their unique physical properties such as high mechanical strength, thermal stability and electrical properties[1]. Because CNTs have high electron emission efficiency at low voltage due to their high aspect ratio, CNTs have been regarded as the most efficient electron emitter among various materials such as metal, semiconductor. However, the electric-field-screening effect of the dense CNTs and relatively high work function of CNTs (~ 5 eV) degrades the emission performance significantly[2,3]. CNTs grown on uneven substrate can reduce electric-field-screening effect and coating of CNTs with lower work function leads to enhanced field emission. In particular, it is reported that the coating Titanium (Ti) on CNTs affects the work function and the substantial change in surface morphology of CNTs most significantly[4].In this paper, we report the combined effect of suppression of electric-field-screening and lower work function on field emission characteristics by Ti-coated CNTs on micron-sized silicon (Si) pillar arrays. Micron-sized Si pillar arrays are formed using conventional photolithography process including reactive ion etching by mixture gas of SF6 and Ar. CNTs are grown on Invar(52% Fe-42% Ni-6% Co alloy) catalyst using C2H2 as a source gas by inductively-coupled plasma-enhanced chemical vapor deposition. Then, Ti with 5 nm thickness is optionally coated on CNTs by sputtering method and field emission behaviors are investigated in a diode configuration in the vacuum of ~10-7 Torr.Field enhancement factor for CNTs on Si pillar arrays was higher by 15% compared with that of CNTs on Si. The application of Ti on CNT surface reduced turn-on field by 30% further compared with that of pristine CNTs. In addition, coating of CNTs also improved emission stability by strengthening the adhesion between CNTs and substrate. We expect that the Ti-coated CNTs grown on micron-sized silicon pillar arrays can be excellent electron sources, providing a very stable current at very low fields by reduction of electric-field-screening effect and effective work function of emitters..