1. T. S. Ahmadi, T. C. Green, M. A. El-Sayed, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
2. Z. L. Wang, School of Material Sciences and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
3. A. Henglein, Hahn-Meitner Institut, Abteilung Kleinteilchenforschung, 14109 Berlin, Germany.