1. Department of Applied Physics, Aalto University, Puumiehenkuja 2, FI-00076 Espoo, Finland
2. Nanomicroscopy Center, Aalto University, Puumiehenkuja 2, FI-00076 Espoo, Finland
3. Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
4. Université Grenoble Alpes, Université Savoie Mont-Blanc, CNRS, Grenoble INP, LEPMI, 38000 Grenoble, France