1. Research Center for Computational Design of Advanced Functional Materials, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Tsukuba, Ibaraki 305-8568, Japan
2. TASC Graphene Division, Tsukuba, Ibaraki 305-8565, Japan
3. Max Planck Institute for the Structure and Dynamics of Matter and Center for Free-Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany
4. Nano-Bio Spectroscopy Group and ETSF, Universidad del País Vasco, CSIC-UPV/EHU-MPC, 20018 San Sebastián, Spain