1. Aalto University, Department of Electrical Engineering and Automation, P.O. Box 13500, FIN-00076 Aalto, Espoo, Finland
2. Aalto University, Nanomicroscopy Center, P.O. Box 15100, FIN-00076 Aalto, Espoo, Finland
3. Fraunhofer Institute for Microstructure of Materials and Systems IMWS, Walter-Huelse-Str. 1, 06120 Halle, Germany
4. University of Jyvaskyla, Department of Physics, P.O. Box 35, FIN-40014, Jyvaskyla, Finland