1. Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, USA
2. A.J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, USA
3. Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden
4. Physics Department, Nuclear Research Centre - Negev, PO Box 9001, 84190 Beer-Sheva, Israel