1. Physics Department, Faculty of Science, Ain Shams University, Khalifa El-Maamon Street, 11566 Cairo, Egypt
2. Bioelectronics (IBI-3), Forschungszentrum Jülich, D-52425 Jülich, Germany
3. Nanotechnology Research Center (NTRC), The British University in Egypt, P.O. Box 43, Suez Desert Road, El-Shorouk City, Cairo 11837, Egypt