1. Istituto Nanoscienze-CNR, Via Campi 213a, Modena I-41125, Italy
2. Wigner Research Centre for Physics, PO Box 49, Budapest H-1525, Hungary
3. Department of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, Budapest H-1111, Hungary
4. Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, Mons 7000, Belgium