1. Faculty of Physics and Center for Nanointegration, CENIDE; University of Duisburg-Essen; 47048 Duisburg Germany
2. Department of Materials Science and Engineering; Texas A&M University; College Station TX 77845 USA
3. Institute of Materials Science; University of Connecticut; Storrs CT 06269 USA
4. IFW Dresden; P.O. Box 270116 01171 Dresden Germany
5. Condensed Matter Physics; Chelyabinsk State University; 454001 Chelyabinsk Russia