1. Department of Materials Science and Engineering and A. J. Drexel Nanomaterials InstituteDrexel University 3141 Chestnut Street Philadelphia PA 19104 USA
2. Department of Physics and AstronomyUniversity of Pennsylvania 209 South 33rd Street Philadelphia PA 19104 USA
3. Department of Chemical EngineeringDrexel University 3141 Chestnut Street Philadelphia PA 19104 USA