1. Department of Physics, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand
2. Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
3. Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan