1. Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
2. Department of Chemistry and Physics, University of Arkansas at Pine Bluff, Pine Bluff, Arkansas 71603, USA
3. Department of Chemistry and Biochemistry, Wichita State University, Wichita, Kansas 67260, USA
4. Materials Science and Engineering Program, Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA
5. Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA