1. Department of Physics, University of Puerto Rico, Mayaguez, Puerto Rico 00681, USA
2. Department of Physics, Astronomy, and Geosciences, Towson University, Towson, Maryland 21252, USA
3. Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
4. Department of Chemistry, University of Puerto Rico, Mayaguez, Puerto Rico 00681, USA