Oxygen Annealing Induced Defect Generation in Monolayer and Bilayer Graphene

In this work, O2 annealing triggered defect generation within monolayer (MLG) and bilayer graphene (BLG) was studied using Raman spectroscopy and atomic force microscopy. Above a critical temperature (denoted as the infection point), the activation energies for defect generation in MLG and BLG upon O2 annealing were found to be 1.2 and 2.3 eV, respectively. Such defect generation was proposed to be mainly dominated by chemical reactions between graphene and oxygen, and the difference of the activation energies within MLG and BLG is attributed to a difference in van der Waals interactions with the supporting substrates. Besides, the infection point for MLG is also different from that for BLG; the former is 400 °C, while the latter is 550 °C. We also found that both MLG and BLG are insensitive to defect generation with a characteristic of very small activation energy for O2 annealing treatment below the infection point, which may be ascribed to the thermal mismatch between graphene and the underlying substrate.