1. Laboratoire Photonique Numérique et Nanosciences, Univ. Bordeaux, UMR 5298, F-33400 Talence, France
2. Institut d’Optique & CNRS, LP2N UMR 5298, F-33400 Talence, France
3. Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
4. Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 United States
5. Maryland NanoCenter, University of Maryland, College Park, Maryland 20742, United States