1. Flexible Electronics Research CenterSchool of Mechanical Science and EngineeringHuazhong University of Science and Technology Wuhan Hubei 430074 China
2. Beijing Institute of Nanoenergy and NanosystemsChinese Academy of Sciences Beijing 100083 China
3. School of Nanoscience and TechnologyUniversity of Chinese Academy of Sciences Beijing 100049 China
4. School of Materials Science and EngineeringGeorgia Institute of Technology Atlanta GA 30332‐0245 USA