1. Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
2. School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
3. Institute of Solid Mechanics, Beihang University, Beijing 100191, China
4. Department of Electrical Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
5. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
6. Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA
7. Department of Engineering Mechanics and Soft Matter Research Center, Zhejiang University, Hangzhou 310027, China
8. Department of Civil and Environmental Engineering, Department of Mechanical Engineering, Center for Engineering and Health, and Skin Disease Research Center, Northwestern University, Evanston, Illinois 60208, USA