1. Center on Nanoenergy Research, School of Physical Science and Technology, School of Resources, Environment and Materials, Guangxi University, Nanning, Guangxi, 530004, China
2. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China
3. School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China