1. Fachbereich Physik and Forschungszentrum
OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
2. Graduate School of Excellence Materials Science in Mainz, Gottlieb-Daimler-Strasse
47, 67663 Kaiserslautern, Germany
3. Department of Physics and Astronomy, Uppsala University, Box
516, SE-75120, Uppsala, Sweden
4. IMM-Instituto de Microelectronica de Madrid (CNM-CSIC), Isaac Newton 8, PTM, Tres Cantos, E-28760 Madrid, Spain