1. Applied Materials Division, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439, United States
2. Department of Physics, Informatics and Mathematics, University of Modena and Reggio Emilia, Via Campi 213/A, 41125 Modena, Italy
3. Department of Physics and Astronomy, University of Bologna, 40127 Bologna, Italy
4. Center for Nanoscale Materials, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439, United States