Use of gallium-incorporated zinc-oxide for coating of carbon nanotubes and characterization of field-emission properties

Abstract

Carbon nanotubes (CNTs) were coated with zinc oxide (ZnO) and gallium-doped ZnO (GZO) using various deposition conditions. Multi-walled CNTs were directly grown on conical-type tungsten (W) substrates at 700°C via inductively coupled plasma-chemical vapor deposition before they were coated with ZnO or GZO. The pulsed laser deposition technique was used to produce ZnO or GZO thin films with very low stress. Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) were used to monitor the variations in the morphology and microstructure of CNTs before and after ZnO or GZO coating. The formation of the ZnO or GZO films on CNTs was confirmed using energy-dispersive x-ray spectroscopy (EDX). Furthermore, the measurement of the field emission characteristics of all the fabricated CNT emitters showed that the emitter that was coated with a 10 nm-thick ZnO film with a gallium doping concentration of 5 wt% (5GZO) had the best performance, such as a maximum emission current of 325 μA (at an applied voltage of 1 kV), a threshold field of 1.96 V/μm (at an emission current of 0.1 μA), and an emission current with long-term (up to 40 h) stability.