1. Research Center for Nano Biomaterials, Analytical & Testing Center, Sichuan University, Chengdu 610064, P. R. China
2. Analytical & Testing Center, Sichuan University, Chengdu 610064, P. R. China
3. Department of Mechanical Engineering, Union College, 807 Union St., Schenectady, NY 12308, USA
4. Sichuan Institute of Atomic Energy, Chengdu, 610101, P. R. China