1. Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana 70148, United States
2. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States
3. Nanoscale Science, University of North Carolina, Charlotte, North Carolina 28223, United States
4. Department of Electrical and Computer Engineering/Optoelectronic Center, University of North Carolina, Charlotte, North Carolina 28223, United States
5. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, 100083 Beijing, China