1. Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York 11794-2275, Department of Physics, Yeshiva University, New York, New York 10016, Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973-5000, and Department of Materials Science and Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261