1. National Institute for Research and Development in Microtechnologies, Erou Iancu Nicolae 126 A, 077190 Voluntari, Romania
2. Faculty of Exact Sciences and Engineering, Hyperion University, Calea Călărașilor 169, Bucharest, Romania
3. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136, USA
4. National Institute for Laser, Plasma and Radiation Physics, 077125 Bucharest, Romania
5. Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580, Japan