1. i3N - Institute for Nanostructures, Nanomodelling and Nanofabrication, Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal
2. Phantom-G, CICECO—Aveiro Institute of Materials, and Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal
3. Walter Schottky Institut and Physik-Department, Technische Universität München, Am Coulombwall 4, Garching D-85748, Germany
4. Institute for Combustion and Gasdynamics − Reactive Fluids−and CENIDE, Center for Nanointegration Duisburg-Essen, Universität Duisburg-Essen, Carl-Benz-Straße 199, 47057 Duisburg, Germany