1. School of Basic Sciences and Humanities; German Jordanian University; Amman 11180 Jordan
2. Physics Department; Al al-Bayt University; Mafraq 25113 Jordan
3. Department of Electrical Engineering; University of Arkansas; Fayetteville AR 72701 USA
4. Institute for Nanoscience and Engineering; University of Arkansas; Fayetteville AR 72701 USA
5. Physics Department; University of Arkansas; Fayetteville AR 72701 USA