1. a Department of Physics , Kurukshetra University , Kurukshetra, India
2. b UGC-DAE Consortium for Scientific Research, Mumbai Centre , Bhabha Atomic Research Centre , Mumbai, India
3. c Nano Science and Nano Technology Unit, Department of Chemical Engineering , I.I.T. , Kanpur, India
4. d Material Science Division , Indira Gandhi Centre for Atomic Research , Kalpakkam, India