1. Institute of Electron Devices and Circuits; University of Ulm; 89081 Ulm Germany
2. Third Institute of Physics; University of Stuttgart; 70569 Stuttgart Germany
3. Department of Physics; La Trobe University; Victoria 3086 Australia
4. Bio21 Institute; University of Melbourne; Parkville Victoria 3010 Australia
5. Institute for Applied Physics and Metrology LRT2; University of the Federal Armed Forces Munich; 85577 Neubiberg Germany