1. Departments of Materials Science and Engineering, Beckman Institute, and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana−Champaign, 1304 West Green Street, Urbana, Illinois 61801
2. Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015, and Centre for Advanced Materials and Nanotechnology, Lehigh University, Bethlehem, Pennsylvania 18015
3. Department of Chemistry, University of Illinois at Urbana−Champaign, Urbana Illinois 61801
4. Department of Electrical and Computer Engineering, Purdue University, 465 Northwestern Avenue, West Lafayette, Indiana 47907
5. Department of Electrical and Computer Engineering, Mechanical Science and Engineering, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801