1. Department of Nanoparticle Technology and Electron Microscopy Group, Center of Advanced European Studies and Research (CAESAR), 53175 Bonn, Germany, Departamento de Química Física and Unidad Asociada CSIC, Universidade de Vigo, 36310 Vigo, Spain, and Fachbereich Physik and Centre for Nano Integration (CeNIDE), Universität Duisburg-Essen, 47048 Duisburg, Germany