1. Helmholtz-Zentrum Dresden-Rossendorf, Institute for Ion Beam Physics and Materials Research, 01328 Dresden, Germany.
2. Faculty of Electrical and Computer Engineering, Technical University of Dresden, 01062 Dresden, Germany.
3. Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
4. Faculty of Physics, Technical University of Dresden, 01062 Dresden, Germany.
5. Institute of Physics, Technical University of Chemnitz, 09107 Chemnitz, Germany.