1. Department of Nuclear Physics University of Madras Guindy Campus Chennai 600 025 India
2. Centre for Nanoscience and Technology Anna University Chennai 600 025 India
3. Department of Physics Ethiraj College for Women Egmore Chennai 600 008 India
4. Nanostructures and Functional Materials Centre for Materials Science and Nanotechnology Department of Chemistry University of Oslo Po Box 1033 N-0315 Oslo Norway