Optical film-thinning of few-layer graphene epitaxially grown on 4H-SiC(0001) surface : Robustness of monolayer-graphene against the photoexcitation.

As the properties of graphene films depend on their stacked atomic layers, their thickness should be accurately controlled to improve their specific properties. However, by existing methods, controlling the homogeneity of graphene films at the atomic level remains difficult. In this work, photo-stimulated structural modifications of few-layer graphene epitaxially grown on 4H-SiC(0001) were studied using Raman scattering spectroscopy and core-level photoemission spectroscopy. Iterative excitation with laser pulses (800nm, 100fs, p-polarized, 250mJ/cm2) changed the graphene-related 2D Raman line, which is composed of three components characterized by their different responses upon photoexcitation: two components decaying at fast and slow rates, and a component highly resistant to excitation. Core-level photoemission spectroscopy revealed that the observed decay of the 2D line was associated with the elimination of carbon atoms from the graphene layers, finally leaving the robust thin film of single-layer graphene by prolonged excitation. Therefore, this work clearly demonstrates the thickness-dependent structural stability of graphene to optical excitation and opens a promising new method for thinning graphene. An underlying mechanism for the photo-stimulated modifications was also proposed.