1CAS 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, PR China
2School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, PR China
3Center on Nanoenergy Research, School of Physical Science and Technology, Guangxi University, Nanning, 530004, China
4Division of Solid-State Electronics, Department of Electrical Engineering, Uppsala University, SE-75103, Uppsala, Sweden