Roles of H2 in annealing and growth times of graphene CVD synthesis over copper foil

Abstract

Single-layer and high-quality graphene was synthesized over Cu foil by atmospheric pressure chemical vapor deposition (CVD) without additionally introducing H₂ gas during the growth time. We compared the Cu surface morphology and graphene growth evolution as a function of time, with and without H₂ gas supply during the growth time, by AFM, SEM, EBSD, and Raman spectroscopy. The comparison results suggested that the absence of H₂ gas supply during the growth time caused the orientated wrinkles, small grain size, more grain boundaries on the Cu surface, as well as high graphene quality and a rapid growth rate. The cross sectional TEM, HR-TEM, and SAED indicated the homogeneity and high quality, which was also confirmed by the low sheet resistance of 710 Ω sq⁻¹. To elucidate the roles of H₂ in the annealing and growth times, we introduced H₂ at the individual stages of heating, growth, and cooling steps. The data showed that graphene could be grown only when H₂ was introduced during the growth time, indicating that the H₂ from CH₄ pyrolysis was not responsible for graphene growth. Therefore, the existence of H₂ during the growth time was essential for graphene growth. This result led us to infer that the H₂ introduced during the annealing time could be released from the bulk Cu to promote graphene growth. The release process was further confirmed by the detection of H₂ concentrations using a hydrogen analyzer. The results are beneficial to highlight the roles of H₂ in the individual reaction steps for the controllable synthesis of graphene.