Impact of short duration, high-flow H₂ annealing on graphene synthesis and surface morphology with high spatial resolution assessment of coverage

Treatment of graphene growth substrates with H₂ has long been known to impact the quality of deposited graphene. However, the parameters for hydrogen treatment that are considered the optimum – very long anneals under low hydrogen concentrations – are often undesirable for practical reasons. In this paper we optimize anneal parameters for fast anneals of <1 h, via investigation of both substrate surface modification and graphene growth quality using a number of traditional and novel experimental techniques. Our results indicate a dual effect of H₂ annealing on the surface morphology of the copper substrate, and consequent graphene growth quality, whereby H₂ passivates and smoothens the Cu surface, causing it to become morphologically more favorable for graphene growth, but may in large quantities make the surface less chemically favorable, limiting the quality of grown graphene. Moreover, we use a novel method based on Atomic Force Microscopy (AFM) for higher spatial resolution analysis of the homogeneity of graphene using maps of the Hamaker coefficient.