作者机构:College of Physics and Optoelectrical Engineering, Dalian University of Technology, Dalian, 116023, China
相关基金:The authors would like to thank the financial supports from the National Nature Science Foundation of China (Grant Nos. 61137005 and 60977055) and the Ministry of Education of China (Grant Nos.NCET-09-0255 and SRFDP 20120041110040).