1. School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu, 273165, P. R. China
2. Department of Electronics and Information Convergence Engineering, Institute for Wearable Convergence Electronics, Kyung Hee University, Yongin-si, Gyeonggi-do 17104, South Korea
3. Department of Physics, Pukyong National University, Busan, 608-737, South Korea