1. Department of Chemistry, Boston University, Boston, MA 02215, USA.
2. Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
3. National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA.
4. Department of Physics, Florida State University, Tallahassee, FL 32306, USA.
5. Division of Materials Science and Engineering, Boston University, Boston, MA 02215, USA.
6. Department of Physics, Boston College, Chestnut Hill, MA 02467, USA.
7. Department of Electrical and Computer Engineering, Boston University, Boston, MA 02215, USA.
8. Department of Physics, Boston University, Boston, MA 02215, USA.
9. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
10. The Photonics Center, Boston University, Boston, MA 02215, USA.