Chemical vapor deposition (CVD) on metals is so far the best suited method to produce high-quality, large-area graphene. We discovered an unprecedentedly large family of small size-selective carbon clusters that form together with graphene during CVD. Using scanning tunneling microscopy (STM) and density functional theory (DFT), we unambiguously determine their atomic structure. For that purpose, we use grids based on a graphene moiré and a dilute atomic lattice that unambiguously reveal the binding geometry of the clusters. We find that the observed clusters bind in metastable configurations on the substrate, while the thermodynamically stable configurations are not observed. We argue that the clusters are formed under kinetic control and establish that the evolution of the smallest clusters is blocked. They are hence products of surface reactions in competition with graphene growth, rather than intermediary species to the formation of extended graphene, as often assumed in the literature. We expect such obstacles to the synthesis of perfect graphene to be ubiquitous on a variety of metallic surfaces.

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尺寸选择性碳簇作为阻碍石墨烯在金属上生长的障碍

迄今为止，在金属上进行化学气相沉积（CVD）是生产高质量大面积石墨烯的最合适方法。我们发现了前所未有的大家族的小尺寸选择性碳簇，这些簇在CVD过程中与石墨烯一起形成。使用扫描隧道显微镜（STM）和密度泛函理论（DFT），我们明确地确定了它们的原子结构。为此，我们使用基于石墨烯云纹和稀薄原子晶格的栅格，这些栅格明确揭示了团簇的结合几何形状。我们发现观察到的簇结合在基板上的亚稳构型，而没有观察到热力学稳定的构型。我们认为这些簇是在动力学控制下形成的，并确定了最小簇的进化受到了阻碍。因此，它们是与石墨烯生长竞争的表面反应的产物，而不是文献中经常假设的形成扩展石墨烯的中间物种。我们期望在各种金属表面上普遍存在这样的阻碍合成完美石墨烯的障碍。