Fig. 2
SEM images of the graphene directly grown on silica at 1150 °C for growth time of a 2 h, b 4 h, c 8 h, and d 10 h. Their representative Raman spectra are shown in e–h. The I2D/IG ratio for 4-h-, 8-h-, and 10-h-grown graphene is estimated to be 1.56, 1.47, and 1.39, respectively. Bottom panel i presents some high-magnification SEM images of bilayer and trilayer graphene flakes taken from d. The grains with larger in size and lower contrast are first graphene layers, and those with smaller in size and higher contrast correspond to the second and third layers. The scale bar is the same for all