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Graphene, as a perfect two-dimensional crystalline structure, has attracted much attention in the research community, owing its unusual mechanical strength (>1Pa), optical transparency and high carrier mobility for various promising applications. Several methods have been used to develop to obtain graphene, such as mechanical exfoliation, thermal decomposition of SiC and chemical vapor deposition (CVD). Among these methods, CVD is considered to be the most promising way for graphene industrial development and scale-up production due to its convenience and economic efficiency. In a CVD process, growth on Cu substrates is particularly attractive since the growth occurs via a self-limiting mechanism, attributed to the negligible carbon solubility in copper. Yet the CVD graphene shows a lower carrier mobility of a few hundred to a few thousand cm2/(Vs) compared with exfoliated graphene obtained from natural graphite, because of the presence of growth defects and boundaries. In order to attain the predicted theoretical values for graphene, it is critical to improve graphene film quality. Previous studies have shown that seamless merging of graphene domains during CVD is an ideal route to reducing defects and domain boundaries, and produce single crystal graphene to enable further applications. Furthermore, the morphology and edge structure of individual graphene domains strongly influence its properties. It is very important to understand the nucleation stage and the expansion mechanism of the graphene domains to control the morphology of graphene films. Recent advances in the CVD method yields various interesting graphene domain shapes. Pentagonal, triangular, rectangular, snow-like graphene, twelve-pointed and four-lobed, graphene domains have been successfully obtained. The various shapes of these graphene domains can be achieved by optimizing growth parameters, such as precursor composition, flux, and choice of substrate. However, all of these methods either require liquid-state copper as the substrate or yield irregular circular or other shapes with one or very few separate circular graphene domain. Hence, it would be quite advantageous to grow graphene on a solid-state copper substrate via the simultaneous large scale growth and seamless merging of circular-shaped graphene domains. This provides a very good platform to observe and investigate the growth mechanism leading to large area single crystal graphene sheets. In this presentation, I will report the first successful large-scale growth of single-crystal “circular” graphene domains on a solid-state copper substrate during the early stage of CVD operated under atmosphere pressure. The individual circular graphene domains have smooth edges as well as axisymmetric and centrosymmetric shapes which permit seamless merging of adjacent graphene without the effect of orientation. Figure 1 |
