▎ 摘　　要

As the graphene is transforming from a laboratory niche material into a mass-produced industrial commodity, maintaining high quality standard across different chemical vapor deposition (CVD) systems becomes the first priority. In this paper, we investigated the carbon diffusion behavior involving two kinds of annealing gases, which reduced the nucleation density in different rate. Compared to the time-consuming and hazardous high-pressure H-2 annealing, O-2 annealing represents a more efficient route to reduce the nucleation density down to similar to 10 nuclei cm(-2) in half an hour. We also proposed a well-defined carbon depletion and refilling mechanism, with which we can precisely gauge the minute carbon concentration inside Cu (less than 10 ppm), and control the nucleation density in a reproducible manner. Moreover, we find that O-2 displays an impressive carbon depletion activity, similar to 6 order more efficient than H-2. The graphene single crystals' quality was confirmed with Raman spectroscopy and field effect transistor (FET) devices. (C) 2017 Elsevier Ltd. All rights reserved.