1. a Polytechnics University of Bucharest , 1-7 Gh. Polizu, P.O. Box 12-134, 011061 , Bucharest , Romania
2. b Department of Solid State and Theoretical Physics , Al. I. Cuza Univ. , 11 Bv. Carol I, 700506 , Iaşi , Romania
3. c Institute of Physical Chemistry Ilie Murgulescu of the Romanian Academy , 202 Spl. Independenţei, 060021 , Bucharest , Romania
4. d S.C. METAV – Research & Development Bucharest , 31 C. A. Rosetti, 020011 , Bucharest , Romania