1. Center on Nanoenergy Research School of Physical Science and Technology Guangxi University Nanning 530004 P. R. China
2. Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 100083 P. R. China
3. School of Electronic Communication Technology Shenzhen Institute of Information Technology Shenzhen 518172 P. R. China
4. Mechanical and Materials Engineering Western University London N6A 3K7 Canada
5. School of Materials Science and Engineering Georgia Institute of Technology Atlanta GA 30332 USA