N-Graphene Nanowalls Via Plasma-Assisted Nitrogen Incorporation and Substitution

Abstract

The electronic properties of the graphene materials can be tuned by chemical doping either by the adsorption of foreign molecules into the graphene lattice or by substitutional doping. Among the various chemical and physical doping techniques, plasma-assisted surface treatment techniques are considered as a fast approach to fabricate nitrogen-incorporated graphene with different nitrogen bonding configurations. However, it is still a great challenge to build nitrogen incorporated graphene with controlled nitrogen concentrations and desired nitrogen configurations. Several studies explained the influence of structural defects in graphene for incorporating N-atoms, which has been formulated by DFT theories. However, there is a lack of experimental evidence to bridge the DFT theories for explaining the influence of structural defects for nitrogen incorporation in graphene. Herein, we report a systematic study on the effect of different nitrogen-containing gaseous plasma post-treatment on vertically oriented graphene nanowalls (CNWs) to fabricate N-CNWs with incorporated and substituted nitrogen. A low-pressure inductively coupled radio-frequency plasma is used as the plasma system with ammonia and nitrogen gases as the reactive gases. The structural and morphological analysis describes a remarkable difference in the plasma surface interaction, nitrogen concentration, and nitrogen configurations in CNWs by using different nitrogen-containing plasma. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy studies confirming the formation of structural defects in the graphene lattice during the plasma treatment. Additionally, the absorption spectra obtained from NEXAFS indicates the presence of different nitrogen configurations in the nitrogen incorporated CNWs. Electrical conductivity measurements revealed that the conductivity of the nitrogen incorporated graphene is strongly influenced by the concentration and different configurations of C-N bonding. These findings indicate that the plasma post-treatment can be used as an effective approach for the synthesis of nitrogen incorporated graphene with controlled concentration and specific configuration of incorporated nitrogen for application-oriented properties.