1. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics (NLB2), The Ohio State University, 201 West 19th Avenue, Columbus, Ohio 43210-1142
2. Mechanical Engineering, Harbin Institute of Technology, Harbin 150001, P.R. China
3. Centre de Physique Moleculaire Optique et Hertzienne, University Bordeaux I 351 cours de la Liberation, F-33405 Talence, France