1. School of Materials Science and Engineering; Georgia Institute of Technology; Atlanta GA 30332-0245 USA
2. Institute of Photonics and Optoelectronics & Department of Electrical Engineering; National Taiwan University; Taipei 10617 Taiwan ROC
3. Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division; King Abdullah University of Science & Technology (KAUST); Thuwal 23955-6900 Saudi Arabia
4. State Key Laboratory for Advanced Metals and Materials; School of Materials Science and Engineering; University of Science and Technology Beijing; Beijing 100083 China
5. Beijing Institute of Nanoenergy and Nanosystems; Chinese Academy of Sciences; Beijing China