1. Department of Physics Sungkyunkwan University Suwon 16419 Republic of Korea
2. School of Chemical Biological and Environmental Engineering Oregon State University Corvallis OR 97331 USA
3. Department of Physics Pukyong National University Busan 48513 Republic of Korea
4. Department of Energy Science Sungkyunkwan University Suwon 16419 Republic of Korea
5. Graduate School of Semiconductor Materials and Devices Engineering Ulsan National Institute of Science and Technology Ulsan 44919 Republic of Korea
6. Physical Sciences Division Pacific Northwest National Laboratory Richland WA 99254 USA