1. Lawrence Berkeley National Laboratory, Molecular Foundry Division, 67 Cyclotron Road, Berkeley, California 94720
2. Italian National Research Council, Institute for Microelectronics and Microsystems, Via P. Castellino 111, 80131 Napoli,
Italy
3. Department of Electrical and Computer Engineering, Boston University, 8 Saint Mary's Street, Boston, Massachusetts 02215
4. Department of Electrical and Computer Engineering, Boston University, 8 Saint Mary's Street, Boston, Massachusetts 02215;
Division of Materials Science and Engineering, Boston University, 15 Saint Mary's Street, Brookline, Massachusetts 02446; and
Department of Physics, Boston University, 590 Commonwealth
Avenue, Boston, Massachusetts 02215