Controllable graphene synthesis in an oxygen-free environment

Surface oxidation of copper substrates prior to chemical vapor deposition (CVD) graphene growth has proven to significantly alter the nucleation density, grain size, and defect concentration of the resulting film. Here we discuss the role of trace oxygen in gas feedstocks on graphene growth kinetics and overall film uniformity. We can eliminate these oxidizing impurities to obtain fast, repeatable growth without the reliance of a hydrogen-rich environment. The O₂/H₂ ratio was explored to understand the balance between grain growth and oxygen-based etching in a phase space analysis. This study sets the maximum oxygen concentration with respect to hydrogen to overcome graphene etching reactions. We have modelled our CVD graphene growth rate using a Langmuir adsorption isotherm for varied methane and hydrogen flow rates. Our findings highlight the competitive nature of absorbed methane intermediate species as carbon precursors and trace surface oxide as the growth inhibitor and set the limit between impurities limited growth and methane adsorption-dissociation limited growth. We assert that CVD graphene growth in standard ultra-high purity gas feedstock without downstream purification falls within the impurities limited growth regime, thus is held at the mercy of etching reactions.