1. CAS Center for Excellence in NanoscienceBeijing Key Laboratory of Micro‐Nano Energy and SensorBeijing Institute of Nanoenergy and NanosystemsChinese Academy of Sciences Beijing 100083 P. R. China
2. School of Nanoscience and TechnologyUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China
3. College of ScienceNanjing University of Aeronautics and Astronautics Nanjing 211106 P. R. China
4. College of Physics and Optoelectronic EngineeringShenzhen University Shenzhen 518060 P. R. China
5. Center on Nanoenergy ResearchSchool of Physical Science and TechnologyGuangxi University Nanning Guangxi 530004 P. R. China
6. School of Materials Science and EngineeringGeorgia Institute of Technology Atlanta GA 30332‐0245 USA