1. Department of Physics and Astronomy; Ohio University; Athens OH 45701 USA
2. Department of Electrical and Computer Engineering; Laboratory for Nanophotonics; Rice University; Houston TX 77005 USA
3. Institut Charles Delaunay; LNIO; Université de Technologie de Troyes; CNRS UMR 6281; Troyes Cedex CS 42060 - 10004 France
4. School of Chemistry; Raymond and Beverly Sackler Faculty of Exact Sciences; Tel Aviv University; Tel Aviv 6997801 Israel
5. Institute of Fundamental and Frontier Sciences; University of Electronic Science and Technology of China; Chengdu 610054 P. R. China
6. State Key Laboratory of Electronic Thin Films and Integrated Devices; University of Electronic Science and Technology of China; Chengdu 610054 P. R. China