1. Department of Physics North Carolina A&T State University Greensboro NC USA
2. Now at Cooperative Institute for Research in Environmental Sciences University of Colorado Boulder CO USA
3. Now at Chemical Sciences Laboratory National Oceanic and Atmospheric Administration Boulder CO USA
4. Department of Applied Sciences and Technology North Carolina A&T State University Greensboro NC USA
5. Department of Chemistry North Carolina A&T State University Greensboro NC USA
6. ISET Center North Carolina A&T State University Greensboro NC USA