1. Department of Applied Physics, COMP Centre of Excellence, Aalto University School of Science,
P.O. Box 11100, FI-00076 Aalto, Finland
2. Department of Applied Physics, QTF Centre of Excellence, Aalto University School of Science,
P.O. Box 11100, FI-00076 Aalto, Finland
3. Department of Physics, University of Central Florida, Orlando, Florida 32816, United States
4. Department of Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
5. Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä, Finland