Low-temperature growth of nitrogen-doped nanocrystalline graphene films by cold-wall plasma assisted chemical vapor deposition for gas sensor application

Abstract

Our surrounding is containing high mixture of hazardous gases which had brought severe problem environment and human’s health. Recently, nanomaterial particularly graphene has been extensively studied as one of the promising materials due its excellent sensing capabilities. Nevertheless, due to the physisorption of adsorbates which lead to false alarm detection and the absence of bandgap in most of the graphene devices, nitrogen (N) heteroatoms substitution is introduced. The specific bonding configuration in N-Gr i.e., pyridinic-N is believed have predominant effect on chemisorption between CO and the surface due to the presence of single lone pair which resulting highly selective and sensitive CO sensors. Whereas, predominant pyrrolic-N is experimentally approved for enhancement of NO2 detection. The substitution of N atoms also will tune the band gap of the graphene. Thus, we report a viable method to produce nanocrystalline graphene films on polycrystalline nickel (Ni) with enhanced N doping at low temperatures by a cold-wall plasma-assisted chemical vapor deposition (CVD) method. The growth of nanocrystalline graphene films was carried out in a benzene/ammonia/argon (C6H6/NH3/Ar) system, in which the temperature of the substrate heated by Joule heating can be further lowered to 100 °C to achieve a low sheet resistance of 3.3 kΩ sq–1 at a high optical transmittance of 97.2%. The morphological, structural, and electrical properties and the chemical compositions of the obtained N-doped nanocrystalline graphene films can be tailored by controlling the growth parameters. An increase in the concentration of atomic N from 1.42 to 11.28 atomic percent (at. %) is expected due to the synergetic effects of a high NH3/Ar ratio and plasma power (RF). The possible growth mechanism of nanocrystalline graphene films is also discussed to understand the basic chemical reactions that occur at such low temperatures with the presence of plasma as well as the formation of pyridinic-N- and pyrrolic-N-dominated nanocrystalline graphene. In this work, the N-doped nanocrystalline graphene films dominated by pyridinic-N and pyrrolic-N exhibit n-type semiconductor behaviour with a strong asymmetry in electron–hole conduction under ambient air conditions. The realization of nanocrystalline graphene films with enhanced N doping at 100 °C may open great potential in developing future transparent nanodevices.