1. Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
2. Electronics Laboratory; Swiss Federal Institute of Technology; Zurich 8092 Switzerland
3. Department of Civil and Environmental Engineeringand Mechanical Engineer; Center for Engineering and Health and Skin Disease Research Center; Northwestern University; Evanston IL 60208 USA
4. Department of Chemistry; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
5. Department of Chemical and Biomolecular Engineering; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
6. Department of Materials Science and Engineering; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
7. Department of Materials Science and Engineering; Korea University; Seoul 136-713 Republic of Korea
8. Department of Engineering Mechanics; Center for Mechanics and Materials; Tsinghua University; Beijing 100084 China
9. Laboratory of Nano-Optoelectronics; Institute of SemiconductorsChinese Academy of Sciences; Beijing 100083 China
10. Department of Materials Science and Engineering Chemistry, Mechanical Science, and Engineering Electrical, and Computer Engineering; Beckman Institute for Advanced Science and Technology and Frederick Seitz Materials, Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA