1. Department of Physics, Periyar University, Salem, Tamil Nadu636 011, India
2. Department of Physics and Astronomy, The University of Texas at San Antonio, San Antonio, Texas78249-1644, United States
3. Department of Physics and Astronomy, University of Texas at Rio Grande Valley, Brownsville, Texas78520, United States
4. Centre for Nanotechnology Research, Vellore Institute of Technology, Vellore, Tamil Nadu632014, India
5. Department of Biotechnology, Bharathiar University, Coimbatore, Tamil Nadu641 046, India