1. National Institute of Standards and Technology; Gaithersburg; Maryland; 20899
2. Karlsruhe Institute of Technology, Institute of Applied Materials; 76131 Karlsruhe; Germany
3. LARMAUR, ERL 6274 (CNRS University of Rennes 1); 35042 Rennes; France
4. Laboratoire PPMD/SIMM, UMR 7615 (CNRS, UPMC, ESPCI Paristech) 10 rue Vauquelin; 75005 Paris; France