Segregation Phenomenon and Its Control in the Catalytic Growth of Graphene

Graphene, a sp(2)-hybridized two-dimensional honeycomb structure of carbon, has attracted great attentions because of its excellent electrical, optical and mechanical properties. One of the major challenges for its various applications is the production of large-area and high-quality graphene. Among the typical approaches reported up to now, catalytic growth on metal surfaces has become the most attractive technique for graphene synthesis with high quality. Segregation, which refers to the enrichment of carbon onto the surface of metals, is one of the key elementary steps for the catalytic growth of graphene on metal surface. In this paper, we will systematically study the segregation phenomenon and the possibility of its control for graphene growth. We will also demonstrate the typical approaches we have developed for growing high-quality graphene by designing and controlling the segregation process, which include segregation technique, co-segregation, synergistic bimetal alloy technique, etc. For instance, with a designed binary alloy, such as Ni/Mo, Co/Mo, or Fe/Mo, we effectively suppressed the carbon precipitation step and achieved perfect single layer graphene with 100% surface coverage by chemical vapor deposition method. With a segregation-only process of carbon atoms predissolved in bulk metals such as Ni, Co, Ni-Cu alloy and Fe, we succeeded in growing wafer-scale high-quality graphene without using extraneous carbon sources. Using co-segregation technique, we could directly grow nitrogen-doped graphene on nickel with controlled dopant concentration and spatial location. These studies will greatly help to understand the catalytic growth process of graphene and further promote its practical applications.