The annealing effect of chemical vapor deposited graphene

Chemical vapor deposited (CVD) graphene is one of the most widely-used methods to get large-area graphene. However, both CVD fabrication process and necessary transfer process will introduce a lot of defects. Therefore, reducing the defects in CVD graphene is a critical problem. In this work, we report the annealing effect to reduce the defects in graphene fabricated by CVD and transferred to Si/SiO₂ substrate. We annealed the CVD samples at five different temperatures in N₂ for 30 s. The Raman spectroscopy shows the defects can be reduced in the range of 200°C to 600°C. Atomic force microscopy (AFM) also indicates a much smoother surface can be reached below 600°C. When the annealing temperature above 800°C, the average carbon-carbon distance increases with the temperature. This will lead to a larger corrugation which is one kind of defects. Thermal expansion generated by high temperature will also damage the graphene lattice structure and therefore produces more disorders.