Raman spectra of a HOPG sample (blue line), the thickest FLG (black line), and the thinnest FLG (red line). The FLG's spectra are extracted from the 16 × 16 μm2 Raman mapping collected in the center of the sample. D band can be seen around 1350 cm-1 indicating the presence of crystalline defects/disorder in the grown FLG. The 2D band around 2750 cm-1 has a single Lorentzian shape that is the fingerprint of a turbostratic stacking. Finally, both G and 2D bands are shifted to high energy compared to the HOPG spectrum. This up shift evidences that FLGs experience a high compressive stress.
Tiberj et al. Nanoscale Research Letters 2011 6:171 doi:10.1186/1556-276X-6-171