1. Fujian Key Laboratory of Semiconductor Materials and Applications CI center of OSED College of Physical Science and Technology Xiamen University Xiamen 361005 P. R. China
2. School of Mechanical Engineering Shanghai Jiao Tong University Shanghai 200240 P. R. China
3. Xiamen University Affilicated Keji High School Xiamen 361005 P. R. China
4. College of Ocean and Earth Sciences Xiamen University Xiamen 361005 P. R. China