1. Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland
2. Dept. Mathematics and Natural Sciences, College of Science, Cardinal S. Wyszyński University, Warsaw, Poland
3. Groupe d'Etudes de la Matière Condensée, CNRS-Université de Versailles, 45 avenue des Etats-Unis, 78035 Versailles, France
4. Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, P.O. Box 6100, 02015 Espoo, Finland
5. FEI Co, 5600 MD Eindhoven, Netherlands