Fig. 1.

Preparation and characterization of graphene-coated samples. a Illustrative diagram showing PMMA-assisted transfer method used to obtain graphene-coated SiO₂ substrates for present study, b SEM image of single layer graphene (SLG) grown on Cu sample, c large-scale STM topographic image (100 × 100 nm²) of SLG grown on Cu. The filtered atomically resolved image (3.5 × 3.5 nm²) shows the hexagonal lattice of SLG, d optical microscopy image of SLG transferred onto SiO₂, e STM image of SLG transferred onto SiO₂ displays honeycomb lattice and f representative Raman spectra Raman spectra of SLG grown on Cu (up) and SLG transferred onto SiO₂ (down). Background caused by the luminescence of the copper was subtracted in the case of SLG grown and transferred onto Cu. Tunnel current and bias voltages for STM images were between 0.1 and 0.6 nA and 0.1–1 V respectively