1. Institute for Solid State and Materials Research Dresden e.V., PF 270116,
01171 Dresden, Germany
2. Nanotechnology and Nanometrology
Laboratory, National Institute for Standards (NIS), Giza, Egypt
3. Kirchhoff
Institute for Physics, University of Heidelberg, Im Neuenheimer Feld 227,
D-69120, Heidelberg, Germany
4. Department of Physics, Technische Universität Dresden, D-01062, Dresden,
Germany