1. Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstrasse
20, 01069 Dresden, Germany
2. Brazilian Nanotechnology National Laboratory, CNPEM, PO Box 619, 13083-970 Campinas, Brazil
3. Semiconductor Physics, Chemnitz University of Technology, Reichenhainerstrasse 70, 09107 Chemnitz, Germany
4. Institute for Solid State Research, IFW Dresden, Helmholtzstrasse
20, 01069 Dresden, Germany
5. Material Systems for Nanoelectronics, Chemnitz University of Technology, Reichenhainerstrasse 70, 09107 Chemnitz, Germany