1. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439,
United States
2. Center for
Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439,
United States
3. IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, United
States
4. IBM Semiconductor Research and Development Center, Hopewell Junction,
New York 12533, United States
5. Department of Physics, University of California San Diego,
San Diego, California 92093, United States