Yu Ye, Lun Dai*, Lin Gan, Hu Meng, Yu Dai, Xuefeng Guo and Guogang Qin*
* Corresponding authors: Lun Dai lundai@pku.edu.cn - Guogang Qin qingg@pku.edu.cn
Nanoscale Research Letters 2012, 7:218 doi:10.1186/1556-276X-7-218