1. Department of Physics & Engineering Physics, Morgan State University, Baltimore, MD 21251, USA
2. Weapons & Materials Research Directorate, Army Research Laboratory, APG, MD 21005, USA
3. Department of Material & Metallurgical Engineering, SDSMT, Rapid City, SD 57701, USA
4. Department of Physics & Astronomy, West Virginia University, Morgantown, WV 26506, USA