▎ 摘　　要

The conversion of monolayer graphene grown epitaxially on SiC(0001) into quasi-free standing bilayer graphene (QFSBG) can be achieved by decoupling the buffer layer (BL) from the substrate via an annealing step. We investigated the role of O-2 and H2O (possible agents of this process) by varying the annealing atmosphere and time. Raman spectroscopy reveals a synergistic effect of O-2 and H2O, which promotes a complete BL detachment and thus large-area QFSBG formation. Similar results are obtained in a H2O-rich ambient for longer annealing times. X-ray photoelectron spectroscopy (XPS) revealed that in both cases the observed effect is related to the formation of an oxide layer on the SiC surface during annealing. (C) 2014 Elsevier Ltd. All rights reserved.