1. College of Information and Communication Engineering and Sungkyunkwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 16419, Korea
2. Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 44610, Korea
3. ICT Components and Materials Technology Research Division, Electronics and Telecommunications Research Institute, Daejeon 34129, Korea