1. Department of Physics; Shanghai University, 99 Shangda Road, 200444 Shanghai; P.R. China
2. Institute of NanoMicroEnergy; Shanghai University, 99 Shangda Road, 200444 Shanghai; P.R. China
3. Department of Chemical and Materials Engineering; University of Alberta, Alberta T6G 2V4, Edmonton; Canada
4. School of Materials Science and Engineering; Shanghai University, 99 Shangda Road, 200444 Shanghai; P.R. China
5. National Key Laboratory of Science and Technology on Micro/Nano Fabrication; Shanghai Jiao Tong University, 800 Dongchuan Road, 200240 Shanghai; P.R. China
6. Department of Micro/Nano Electronics; Shanghai Jiao Tong University, 800 Dongchuan Road, 200240 Shanghai; P.R. China