1. Department of Materials Science and Engineering; Beckman Institute for Advanced Science and Technologyand Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
2. Department of Electrical Computer, and Energy Engineering; University of Colorado; Boulder CO 80309 USA
3. Department of Civil and Environmental Engineering, and Mechanical Engineering; Northwestern University; Evanston IL 60208 USA
4. Center for Mechanics and Materials; Tsinghua University; Beijing 100084 China
5. State Key Laboratory of Mechanics and Control of Mechanical Structures; Nanjing University of Aeronautics and Astronautics; Nanjing 210016 China
6. Department of Materials Science and Engineering; Department of Energy Engineering; Hanyang University; Seoul 133-791 Republic of Korea
7. Department of Chemistry; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
8. Department of Bioengineering; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
9. Department of Electrical and Computer Engineering; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA