Affiliation: | a School of Advanced Materials Science and Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do, 440-746, South Korea b Department of Electrical Engineering, Yale University, New Haven, CT 06520, USA c School of Advanced Materials Engineering, Chonbuk National University, Jeonju 561-756, South Korea |