1. Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
2. Department of Energy Engineering, Hanyang University, Seoul 133-791, Republic of Korea.
3. Electronics Laboratory, Swiss Federal Institute of Technology, Zurich 8092, Switzerland.
4. Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
5. Departments of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering, Center for Engineering and Health, and Skin Disease Research Center, Northwestern University, Evanston, IL 60208, USA.
6. Applied Mechanics Laboratory, Department of Engineering Mechanics, Center for Mechanics and Materials, Tsinghua University, Beijing 100084, China.
7. Department of Electronic Engineering, Tsinghua University, Beijing 100084, China.
8. Department of Electrical and Computer Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
9. School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, China.
10. Department of Nanoengineering, University of California San Diego, La Jolla, CA 92093, USA.