[1] Natl Inst Laser Plasma & Radiat Phys, 409 Atomistilor, Magurele 077125, Romania
[2] CNR, ISC, Area Ric Roma Tor Vergata, Via Fosso del Cavaliere 100, I-00133 Rome, Italy
[3] Natl Inst Mat Phys, 105 BisAtomistilor, Magurele 077125, Romania
[4] CNR, IMM, Via Fosso del Cavaliere 100, I-00133 Rome, Italy