Raman spectroscopy study of annealed incommensurate graphene bilayer on SiO2 substrate

• A twisted bilayer graphene (tBLG) was grown by chemical vapor deposition and deposed on SiO2 substrate.
• The Raman spectra of the tBLG allowed us to determine the incommensurate nature of the tBLG and the value of the twist angle.
• The incommensurate tBLG was annealed at 1050 °C and studied by Raman spectroscopy.
• The effects of doping and of strain are qualitatively quantified by comparing the Raman spectra before and after annealing.

A Raman study of a twisted bilayer graphene grown by chemical vapor deposition (CVD) and transferred on SiO2 substrate is presented. The Raman spectra show the G and 2D peaks at 1582 cm−1 and 2683 cm−1 respectively. The presence of the interlayer Raman band (I band) in the range 1374 cm−1 - 1440 cm−1 and of the R band at 1484 cm−1, as well as the single-Lorentzian line shape of the 2D peak, reveals the incommensurate stacking of the two graphene layers. From the R band, we determined that the twist angle (θ = 13.9°) is close to the critical angle θc (11.9° for the excitation photon energy of 2.33 eV). The effect of annealing at 1050 °C of the incommensurate twisted bilayer graphene (ItBLG) structure is then studied. The analysis of the Raman spectra allows us to directly quantify the effects of doping and of strain on each graphene layer.