1. Center for Functional Nanomaterials, Brookhaven National Laboratory, 735 Brookhaven Avenue, Upton, NY 11973, USA.
2. Department of Electrophysics, National Chiao Tung University, 1001 University Road, Hsinchu City, Taiwan 300, R.O.C.
3. Solid State Physics, Lund University, Box 118, S-221 00 Lund, Sweden.
4. IBM Research Division, T. J. Watson Research Center, Yorktown Heights, NY 10598, USA.
5. Polymer & Materials Chemistry, Lund University, Box 124, S-221 00 Lund, Sweden.