1. P. G. Collins and A. Zettl, Department of Physics, University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
2. H. Bando, Physical Science Division, Electrotechnical Laboratory, Tsukuba, Ibaraki 305, Japan.
3. A. Thess and R. E. Smalley, Center for Nanoscale Science and Technology, and Departments of Chemistry and Physics, Rice University, Houston, TX 77005, USA.