1. Spin Convergence Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea
2. School of Nano-Bioscience and Chemical Engineering, KIER-UNIST Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea
3. KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 136-701, Korea
4. Creative Electrotechnology Research Center, Korea Electrotechnology Research Institute, Changwon 642-120, Korea