1. Plasma Processing Laboratory, Lithuanian Energy Institute, Breslaujos 3, LT44403 Kaunas, Lithuania
2. Institute of Materials Science, Kaunas University of Technology, K. Baršausko 59, LT51423 Kaunas, Lithuania
3. Department of Physics, Kaunas University of Technology, Studentų 50, LT-51368 Kaunas, Lithuania