Growth of graphene nanowalls in low-temperature plasma: Experimental insight in initial growth and importance of wall conditioning

Plasma-enabled growth of vertically aligned graphene nanowalls (CNWs) and the influence of plasma parameters are widely investigated to produce high-quality CNWs. The initial growth steps of CNWs and the impact of the plasma chamber condition still need to be explored. This work investigates the initial growth steps of CNWs and the influence of plasma chamber conditions using advanced spectroscopic and microscopic techniques. The changes in substrate surfaces and CNW growth were studied in two steps: pre-treatment and plasma deposition. Angle-resolved NEXAFS observations on the samples produced during both stages suggest that growth starts horizontally on the substrate and changes to vertical in one critical moment. Also, we observed that CNW growth occurs not only at the deposition stage but also during the pre-treatment stage, indicating the influence of the chamber wall during the growth. Switching from horizontal to vertical orientation could be explained by the surface energy disbalance during the initial growth stages. The pre-treatment and conditioning of the chamber control the oxygen presence and provide a higher amount of carbon precursor for a fast, stable and controllable growth process. These results will direct the future possibilities of upscaling plasma systems for large-scale growth of CNWs for commercial applications by considering the influence of plasma and chamber conditions.