1. Department
of Physics, Inha University, Incheon 402-751, Republic of Korea
2. Department of Physics and
Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749, Republic of Korea
3. School of Engineering, Brown University, Providence, Rhode Island 02912, United States
4. Department of Physics, Hallym University, Gangwondo 200-702, Republic of Korea