1. Department of Physics, University of Azad Jammu and Kashmir, Muzaffarabad 13100, Pakistan
2. National Center for Physics, Quaid-i-Azam University, Islamabad 44000, Pakistan
3. Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 OldFaure Road, Somerset West 7129, POBox 722, Somerset West, Western Cape Province, south africa