1. M. Bockrath, D. H. Cobden, P. L. McEuen, N. G. Chopra, A. Zettl, Molecular Design Institute, Lawrence Berkeley National Laboratory, and Department of Physics, University of California, Berkeley, CA 94720, USA.
2. A. Thess and R. E. Smalley, Center for Nanoscale Science and Technology, Rice Quantum Institute, and Departments of Chemistry and Physics, Mail Stop 100, Rice University, Post Office Box B1892, Houston, TX 77251, USA.