1. Department of Chemistry, University of California, Irvine, California 92697, USA
2. Department of Physics and Astronomy, Ball State University, Muncie, Indiana 47306, USA
3. Qld Micro- and Nanotechnology Centre, Griffith University, Nathan, Qld 4111, Australia
4. CNR-Istituto di Nanoscienze, Via Campi 213A, I-41125 Modena, Italy