Field emission property of vertically aligned nitrogen-doped multi-walled carbon nanotubes produced by chemical vapor deposition

Abstract

Vertically aligned nitrogen-doped multi-walled carbon nanotubes (N-MWNTs) were synthesized by the chemical vapor deposition (CVD) at 900 °C using imidazole mixed with ferrocene as carbon and nitrogen sources, and catalyst, respectively. The effects of ammonia (NH3) and hydrogen (H2) flow rates on the growth of N-MWNTs were investigated (hereafter referred to A-N-MWNTs and H-N-MWNTs, respectively). Transmission electron microscopy (TEM) revealed the bamboo-like structure of the N-MWNTs, in which the separation between individual bamboo compartments decreased with increasing nitrogen concentration in N-MWNTs. X-ray photoelectron spectroscopy (XPS) analysis results supported that the nitrogen concentrations in N-MWNTs is 0.55 at.%, whereas A-N-MWNTs and H-N-MWNTs with the flow rate at 10 standard cubic centimeters per minute (sccm) (10A-N-MWNTs and 10H-N-MWNTs, respectively) showed 1.14 and 4.06 at.%, respectively. We found that the optimal conditions for the highest nitrogen-doped multi-walled carbon nanotubes (MWNTs) was a flow rate of NH3 and H2 at 10 sccm. Results from field emission measurements indicated that the turn-on fields of N-MWNTs, 10A-N-MWNTs and 10H-N-MWNTs were 6.7, 4.3 and 3.1 V/µm, respectively, while the field enhancement factors (β) were 5230, 10,805 and 20,390, respectively. Furthermore, the current density of N-MNWTs increased with increasing the nitrogen atoms in MWNTs. The results support that field emission based on N-MWNTs is a good emitter with low turn-on field and large field enhancement factor. Nitrogen doping in MWNTs makes them attractive candidates as high-performance field emitters.