1. Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA
2. Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, 04103 Leipzig, Germany
3. U.S. Naval Research Laboratory, Washington, DC 20375, USA
4. Nanoscale Research Facility, University of Florida, Gainesville, Florida 32611, USA
5. Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA