1. Photonic Compounds and Nanomaterials Group, Faculty of Engineering and Natural Sciences, Tampere University, Tampere University, P.O. Box 541, FI-33014, Finland
2. Department of Electronics and Nanoengineering, Aalto University, Tietotie 3, Espoo 02150, Finland
3. Surface Science Group, Faculty of Engineering and Natural Sciences, Tampere University, Tampere University, P.O. Box 692, FI-33014, Finland