In-situ RHEED study on graphene growth during chemical vapor deposition

Abstract

Chemical vapor deposition (CVD) of graphene was investigated by using an in-situ reflection high-energy electron diffraction (RHEED). A Si wafer covered with a 150 nm thick of SiO2 was used as a substrate, on which a 100 to 600 nm thick of metal (Cu, Co, Ni) was deposited as a catalyst (Cu is known as a metal with low carbon solid solubility, Co and Ni are known as metals with high carbon solid solubility). The substrate was heated up to 900°C and 0.1 Pa of ethanol was introduced as a source gas, and the RHEED pattern was monitored during the CVD process. As the result, a streak pattern, which was originated from 2-dimensional graphene, appeared immediately after the start of the growth for all kinds of catalysts. It was also revealed that the streak appearance time depends only on catalyst material, but not depends on their thickness. Therefore, even on the high carbon solid solubility catalysts, it was considered that graphene nucleation occurred directly on the catalyst surface without solution-segregation process of carbon atoms.