Abstract

 The morphology of as-grown graphene in chemical vapor deposition (CVD) experiments is sensitive to the reaction environment. Understanding the mechanism of formation of different graphene morphologies is essential to achieve controlled graphene CVD growth. Here we report the growth and formation mechanism of adlayer graphene spirals. An adlayer graphene spiral is formed by fast propagation of the tips of spiral arms along the edge of the first graphene layer. The driving force to form spirals is the limited availability of carbon diffusing from the Cu surface through the edge of the first graphene layer. In addition, we find that graphene onions are formed by overlapping graphene spirals with clockwise and anticlockwise arms. Based on these features, we demonstrate a kinetic Monte Carlo (kMC) method using which we successfully reproduced all the observed graphene spiral structures at the atomic level. This study thus unravels the hither-to unresolved mechanism of graphene onion growth and paves the way to the controllable growth of few-layer graphene by increasing the carbon supply at the edge of the first layer graphene.