1. Institute of Scientific Instruments of the Czech Academy of Sciences , Královopolská 147 , Brno , Czech Republic
2. Department of Microelectronics , Brno University of Technology , Technologická 10 , Brno , Czech Republic
3. Institute of Materials Science , Brno University of Technology , Purkyňova 464 , Brno , Czech Republic
4. Department of Physics , Brno University of Technology , Technologická 8 , Brno , Czech Republic