1. Department of Physics, New York University, New York, New York 10003, USA
2. Department of Physics, City College of New York, City University of New York, New York, New York 10031, USA
3. CCDC U.S. Army Research Laboratory, Adelphi, Maryland 20783, USA
4. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA