1. DST Unit on Nanoscience, Department of Chemistry and Sophisticated Analytical Instrument Facility, Indian Institute of Technology Madras, Chennai 600 036, India, College of Science, California State University, East Bay, Hayward, California 94542, Chemistry and Material Science Directorate, Lawrence Livermore National Laboratory, P.O. Box 808 L-268, Livermore, California 94550, and Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720