Self-organized graphene crystal patterns

Abstract

The phenomenon of ordered pattern formation is universal in nature but involves complex non-equilibrium processes that are highly important for both fundamental research and applied materials systems. Among countless pattern systems, a snowflake is possibly the most fascinating example offered by nature. Here, we report that single-layered and single-crystalline graphene flakes (GFs) with highly regular and hexagonal symmetric patterns can be grown on a liquid copper surface using a CH4 chemical vapor deposition (CVD) method. The different morphologies of these GFs can be precisely tailored by varying the composition of the inert gas/H2 carrier gas mixture used to produce the GFs, and the GF edges can be continuously tuned over the full spectrum from negative to zero to positive curvature in a controllable way. The family of GF crystal patterns is remarkably analogous to that of snowflakes, representing an ideal two-dimensional (2D) growth system. Pattern formations from compact to dendritic GFs can be explained by the continuous modulation of the competition between adatom diffusion along island edges or corners and surface diffusion processes. The formation of specific patterns during the growth of materials is both intriguing from a fundamental perspective and useful for practical applications. A team of researchers in China, led by Yunqi Liu, have now described the controlled formation of snowflake-like crystals of graphene — the one-atom-thick layer of carbon atoms that has attracted a great deal of attention across the scientific and technology communities in recent years. The highly regular and symmetric graphene flakes were grown by chemical vapor deposition: gaseous methane was transported over a liquid copper surface by means of a carrier gas (a mixture of hydrogen and an inert gas, argon or helium). The resulting single-layer, single-crystal flakes exhibited snowflake-like patterns that can be controlled by tuning the composition of the carrier gas. These chiseled structures are not only aesthetically appealing, but also represent an attractive platform for studying growth and nucleation processes and exploring structure–property relationships. We report that single-layered and single-crystalline graphene flakes (GFs) with highly regular and hexagonal symmetric patterns can be grown on a liquid copper surface using a CH4 chemical vapor deposition (CVD) method. Different morphologies of these GFs can be precisely tailored by varying the composition of inert gas/H2 carrier gas mixture, and the GF edges can be continuously tuned over the full spectrum from negative to zero to positive curvature in a controllable way. This study provides a well-behaved two-dimensional crystal growth system mimicking snowflakes, opening rich opportunities for engineering graphene patterns and studying graphene structure/property relationships.