1. Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702, South Korea
2. Department of Physics, COMSATS Institute of Information Technology, Lahore 54000, Pakistan
3. Department of Physics, Government College University, Faisalabad 38000, Pakistan
4. Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 15588, South Korea and Department of Electrical and Computer Engineering, MC 0407, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0407, USA