1. Department
of Physics and Astronomy and Wright Center for Photovoltaic Innovation
and Commercialization, The University of Toledo, Toledo, Ohio 43606, United States
2. School
of Physics and Technology, Center for Electron Microscopy, MOE Key
Laboratory of Artificial Micro- and Nano-structures, and Institute
for Advanced Studies, Wuhan University, Wuhan 430072, China
3. Science
and Technology of High Strength Structural Materials Laboratory, Central South University, Changsha 410083, China
4. Department
of Mechanical Engineering and Materials Science and Department of
Chemistry, Duke University, Durham, North Carolina 27708, United States