1. Chemistry Division, U.S. Naval Research Laboratory, Code 6177, Washington, DC 20375, USA.
2. School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.
3. School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
4. School of Chemical Engineering and Materials Science, Chung Ang University, Seoul 156-756, Republic of Korea.
5. Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
6. CNRS-Institut Néel, BP166, 38042 Grenoble Cedex 9, France.