1. Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan
2. Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
3. Department of Material Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
4. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
5. Department of Chemistry, University College of Science, Osmania University, Hyderabad, Telangana 500007, India