1. Fakultät für Physik Universität Duisburg-Essen 47057 Duisburg Germany
2. Institute for Research in Electronics and Applied Physics University of Maryland College Park MD 20740 USA
3. U.S. Army Research Laboratory Adelphi MD 20783 USA
4. Institut für Ionenstrahlphysik und Materialforschung Helmholtz-Zentrum Dresden-Rossendorf 01328 Dresden Germany
5. Fakultät für Physik Universität Bielefeld 33615 Bielefeld Germany
6. Department of Physics, Guwahati Indian Institute of Technology Guwahati Guwahati Assam 781039 India
7. U.S. Naval Research Laboratory Washington DC 20375 USA
8. Department of Electrical and Computer Engineering University of Maryland College Park MD 20740 USA
9. Center for Nanophysics and Advanced Materials University of Maryland College Park MD 20740 USA