[1] IMT Bucharest, Natl Inst Res & Dev Microtechnol, Ctr Nanotechnol, 126 A Erou Iancu Nicolae, Bucharest 077190, Romania
[2] IMT Bucharest, Natl Inst Res & Dev Microtechnol, Res Ctr Nanotechnol & Carbon Based Nanomat, 126 A Erou Iancu Nicolae, Bucharest 077190, Romania
[3] Natl Inst Res & Dev Elect Engn ICPE CA, 313 Splaiul Unirii, Bucharest 030138, Romania
[4] Univ Bucharest, Fac Phys, 405 Atomistilor, Bucharest 077125, Romania