1. Department of Physics and Astronomy; University of Turku; FI-20014 Turku Finland
2. Ioffe Physical-Technical Institute; Russian Academy of Sciences; St. Petersburg 194021 Russian Federation
3. Department of Information Technology; University of Turku; FI-20014 Turku Finland
4. Department of Chemistry; University of Turku; FI-20014 Turku Finland
5. Turku Centre for Materials and Surfaces (MatSurf); Turku Finland
6. Optoelectronics Research Centre; Tampere University of Technology; FI-33101 Tampere Finland