[1] Uzhgorod Natl Univ, Inst Solid State Phys & Chem, Uzhgorod, Ukraine
[2] Rudjer Boskovic Inst, Div Mat Phys, Zagreb 10000, Croatia
[3] Univ Zagreb, Sch Med, Dept Phys & Biophys, Zagreb 10000, Croatia
[4] Elettra Sincrotrone Trieste SCpA, I-34149 Trieste, Italy
[5] Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, CR-18000 Prague, Czech Republic