Graphene Origami: Evolution of the Morphology of Free-Standing Few-Layer Graphene in Plasma Synthesis

Since discovered, graphene has shown to be a very versatile material due to its unique properties, which makes it suitable to multiple applications, ranging from sensing to batteries. Even though free-standing graphene flakes have traditionally been synthesized using exfoliation techniques, interest on gas-phase synthesis is on the rise due to its suitability for process scale-up and for generating graphene with very low oxygen content. Yet, the growth of free-standing few-layer graphene (FLG) during plasma synthesis leads to a variety of morphologies, such as turbostratic graphene (typically less than ten graphene layers), and the growth mechanism is essentially unknown.<br/><br/>Using spatially resolved thermophoretic sampling directly from the area of the graphene formation zone for transmission electron microscopy (TEM) analysis, we studied the morphology of graphene flakes in different growth stages. Single-layer and few-layer graphene were observed, and a morphology pattern evolution was discerned depending on time and reaction conditions. Based on these investigations, we propose a folding-based growth and structure formation process, leading to a conceptual mechanism of few-layer graphene formation and growth, starting from initial round single-layer graphene to, eventually, carbonaceous nanoparticles. The edges resulting from the folding have also been investigated, revealing that graphene does not seem to break at the bends but fold similar to rolling up carbon nanotubes and without opening new reactive sites for further growth.