1. School of Electromechanical Engineering, Guangdong University of Technology, 510006 Guangzhou, China
2. Thin Film Physics Division, Department of Physics, Linköping University, SE-581 83 Linköping, Sweden
3. Frederick Seitz Materials Research Laboratory and Materials Science Department, University of Illinois, 104 South Goodwin, Urbana, Illinois 61801
4. Materials Science Department, National Taiwan University of Science and Technology, Taipei 10607, Taiwan