1. Exploratory Research for Advanced Technology (ERATO), Nakamura Functional Carbon Cluster Project, Japan Science and Technology Agency (JST), Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
2. Research Center for Advanced Carbon Materials, National Institute of Advanced Industrial Science and Technology (AIST), Higashi, Tsukuba, Ibaraki 305-8565, Japan.
3. Department of Chemistry, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
4. Precursory Research for Embryonic Science and Technology (PRESTO), JST, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.