1. Department of Nanoscience and Technology, Sri Ramakrishana Engineering College, Affiliated to Anna University, Coimbatore 641 022, Tamilnadu, India
2. Department of Physics, Bharathiar University, Coimbatore 641 046, Tamilnadu, India
3. International and Inter University Centre for Nanoscience and Nontechnology, Mahatma Gandhi University, Kottayam 686 650, Kerala, India