1. Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, P. O. Box 70377, San Juan, Puerto Rico 00936-8377, USA
2. ASEE Research Fellow at U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington DC 20375, USA
3. School of Chemistry and Physics, St. Andrews University, St. Andrews, Scotland KY16 9ST, United Kingdom