1. Key Laboratory of Optoelectronic Technology & Systems of Ministry of Education International R & D center of Micro‐nano Systems and New Materials Technology Chongqing University Chongqing 400044 P. R. China
2. CAS Center for Excellence in Nanoscience Beijing Key Laboratory of Micro‐nano Energy and Sensor Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 100083 P. R. China
3. Department of Electrical and Computer Engineering Center for Intelligent Sensors and MEMS (CISM) and NUS Graduate School for Integrative Sciences and Engineering National University of Singapore Singapore 117576 Singapore
4. School of Nanoscience and Technology University of Chinese Academy of Sciences Beijing 100049 P. R. China
5. Center on Nanoenergy Research School of Physical Science and Technology Guangxi University Nanning 530004 P. R. China