1. Department of Physics and Center for Energy Science, Indian Institute of Science Education and Research, Pune 411008, Maharashtra, India
2. Departamento de Física, Universidade Federal de São Carlos, 13560-905 São Carlos, SP, Brazil
3. School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
4. UNESCO-UNISA Africa Chair in Nanoscience and Nanotechnology Laboratories, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, P.O. Box 392, Pretoria, South Africa