1. Institute of Solid State Physics, University of Latvia, Kengaraga str. 8, LV-1063 Riga, Latvia
2. Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania
3. State Research Institute Center for Physical Sciences and Technology, Saulėtekio av. 3, LT-10257 Vilnius, Lithuania