1. Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104
2. Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104
3. Department of Physics and Electronics, University of Puerto Rico, Humacao, Puerto Rico 00791
4. Vagelos Integrated Program for Energy Research, University of Pennsylvania, Philadelphia, Pennsylvania 19104
5. Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104