1. School of Material Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212100, China
2. Department of Chemistry and Physics, University of Arkansas at Pine Bluff, Pine Bluff, AR 71601, USA
3. Department of Physics, University of North Texas, Denton, TX 76203, USA
4. Department of Electrical Engineering, University of North Texas, Denton, TX 76207, USA