1. Nano
Electronics Lab. Samsung Advanced Institute of Technology, Suwon, Gyeonggi-Do 446-712, South Korea
2. Department
of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, South Korea
3. School
of Integrative Engineering, Chung-Ang University, Seoul 156-756, South Korea