1. State Key Laboratory for Mechanical Behavior of Materials School of Electronic and Information Engineering Xi'an Jiaotong University Xi'an 710049 China
2. Department of Materials Science and Engineering and Shenzhen Engineering Research Center for Novel Electronic Information Materials and Devices Southern University of Science and Technology Shenzhen 518055 China
3. State Key Lab. of Electrical Insulation and Power Equipment Xi'an Jiaotong University Xi'an 710049 China
4. Department of Materials Science and Engineering The Pennsylvania State University University Park PA 16802 USA