1. Department of Physics, Applied Physics
and Astronomy, Binghamton University, Binghamton, New York 13902, United States
2. Department of Physics, Chung-Ang University, Seoul 06974, South Korea
3. Department of Physics, Pusan National University, Busan 46241, South Korea
4. Department of Measurement & Analysis, National NanoFab Center, Dajeon 34141, South Korea