1. Department of Physics, R. K. (PG) College Shamli, C. C. S. University Meerut, UP-247776, India
2. Department of Physics, D. A. V. (PG) College Muzaffarnagar, C. C. S. University Meerut, UP-251001, India
3. Department of Physics, S.G.T.B. Khalsa College, University of Delhi, Delhi-110007, India
4. Advanced Carbon Products and Metrology Section, Advanced Materials and Devices Metrology Division, CSIR-National Physical Laboratory, Delhi-110012, India
5. Indian Reference Materials, CSIR-National Physical Laboratory, New Delhi-110012, India
6. Department of Physics and Astrophysics, University of Delhi, Delhi-110007, India