1. Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
2. UNAM − National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent University, Ankara, TR 06800, Turkey
3. Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, United States
4. Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
5. Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
6. Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States