[1] Seoul Natl Univ, Sch Phys, Seoul 151747, South Korea
[2] Seoul Natl Univ, Nanosyst Inst, Natl Core Res Ctr, Seoul 151747, South Korea
[3] Renmin Univ China, Dept Chem, Beijing, Peoples R China
[4] Russian Acad Sci, AF Ioffe Phys Tech Inst, St Petersburg 194021, Russia
[5] Univ Tsukuba, Inst Mat Sci, Tsukuba Ctr Interdisciplinary Mat Sci, TIMS, Tsukuba, Ibaraki 3508573, Japan