1. Department of Electrical Engineering and Automation, Aalto University, FIN-02150 Aalto, Finland
2. Science Institute and Faculty of Physical Sciences, University of Iceland VR-III, 107 Reykjavík, Iceland
3. Department of Chemistry and Materials Science, Aalto University, FI-00076 Aalto, Finland
4. Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland