In situ TEM investigation of nickel catalytic graphitization

With the increasing demand for production of graphitic materials for various applications, it becomes crucial to get a fundamental understanding of how graphene layers grow on metal catalysts. Here, we performed an in situ heating transmission electron microscopy (TEM) study to understand the mechanism of graphitization of amorphous carbon (a-C) on Ni catalyst by following graphene growth at atomic resolution in real time. By discerning the Ni3C phase from the pure Ni phase during the graphitic carbon growth process, we demonstrate that growth occurs through the carbide graphitization of Ni3C. Additionally, during the graphitization, Ni diffusion has a crucial effect on the structure of the resulting graphene. Under our experimental conditions, we observed graphene contains islands of multilayers. Based on our in situ experimental results, we suggest a mechanism for graphitization of the a-C/Ni system and explain the dynamics resulting from Ni diffusion. Our study can contribute to the control of graphitization by using Ni catalyst in the production of graphene and other graphitic materials.