Metal free, end-opened, selective nitrogen-doped vertically aligned carbon nanotubes by a single step in situ low energy plasma process

Abstract

We report a novel single step in situ process of growth and nitrogen-electron cyclotron resonance plasma treatment of vertically aligned multi walled carbon nanotubes (VA-MWCNTs) that leads to concurrent end opening by metal cap removal, nitrogen incorporation and intercalation along with substitution at graphitic sites resulting in n-type electronic doping. Microscopic and spectroscopic evaluations of the nitrogen treated MWCNTs reveal negligible iron content with significant conservation of both structure and alignment. The nitrogen induced electronic change increases distinct π* states as evidenced by Near Edge X-ray Absorption Fine Structure (NEXAFS) and 5 cm⁻¹ downshift of G-band, as observed from Raman spectroscopy, confirm n-type doping. The combined effect of plasma activation (both cavities and surface of the end opened VA-MWCNTs) and n-type doping enhances the field emission performance of the CNTs resulting in high current density (15 mA cm⁻²) at low applied voltage of 1.5 V μm⁻¹ with low turn on and threshold electric fields (E_to-0.52 and E_th-0.76 V μm⁻¹). This low energy highly controllable plasma has great implications not only in the fabrication of various n-type materials and bio related application but also many other interesting areas for cost effective energy related applications.