1. School of Electrical Engineering, Korea University, Seoul 02841, Republic of Korea
2. Department of Applied Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
3. Department of Physics, Sookmyung Women's University, Seoul 04310, Republic of Korea
4. Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
5. Institute of Advanced Materials and Systems, Sookmyung Women's University, Seoul 04310, Republic of Korea