1. Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, Massachusetts 01609
2. State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
3. State Key Laboratory on Integrated Optoelectronics, and College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
4. Department of Civil and Environmental Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts 01609
5. Department of Physics, Hampton University, Hampton, Virginia 23668