Nitrogen incorporation in monolayer graphene films by atmospheric pressure Townsend dielectric barrier discharge in N₂

Abstract Graphene films grown by chemical vapor deposition and transferred on SiO 2 /Si substrates were treated by a low-frequency dielectric barrier discharge (DBD) operated in N 2 at atmospheric pressure. The discharge conditions were carefully chosen to obtain a weakly-ionized Townsend discharge operated in a diffuse regime and characterized by a neutral gas temperature of 300 K. In such conditions, plasma–graphene interactions are dominated by plasma-generated N atoms and N 2 (A) metastable species, with lower contributions from irradiation by positive ions ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> <mml:mn>4</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> ) and electrons. Defect generation and N incorporation in graphene films were studied using hyperspectral Raman imaging and x-ray photoelectron spectroscopy. Progressive rises in defect concentration and N incorporation were observed with plasma treatment time, with graphene amorphization and nitrogen-to-carbon ratios ∼7% after 60 s. Over the range of experimental conditions investigated, the rate of nitrogen incorporation (mostly pyridine, pyrrole and graphitic) is limited by defect generation in the graphene lattice and not by adsorption and surface diffusion of nitrogen atoms towards defect sites. This work opens a new path to produce large-scale N-graphene by atmospheric-pressure plasma treatments.