1. School
of Physics, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
2. Beijing
Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, National Center for Nanoscience and Technology (NCNST), Beijing 100083, China
3. Multidisciplinary
Nanotechnology Centre, College of Engineering, Swansea University, Swansea, SA1 8EN, U.K.
4. School of
Material Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States