1. National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, 077125 Magurele, Romania
2. Faculty of Chemical Engineering and Biotechnologies, University Politehnica of Bucharest, 1-7 Gh. Polizu Street, 011061 Bucharest, Romania
3. Academy of Romanian Scientists, Ilfov No. 3, 050044 Bucharest, Romania
4. Electron Microscopy Laboratory, Department of Physics, Ovidius University of Constanta, 124 Mamaia Avenue, 900591 Constanta, Romania