1. Department of Chemistry and Biochemistry, University of California, 9500 Gilman Dr, La Jolla, San Diego, California 92093, USA
2. Materials Science and Engineering Program, University of California, 9500 Gilman Dr, La Jolla, San Diego, California 92093, USA
3. IBM T.J. Watson Research Center, PO Box 218, Yorktown Hts., New York 10598, USA