1. Walter Schottky Institut and Physics Department, Technische Universität München, Am Coulombwall 4, 85748 Garching, Germany
2. Institute for Combustion and Gas Dynamics—Reactive Fluids—and CENIDE, Center for Nanointegration Duisburg-Essen, Universität Duisburg-Essen, Carl-Benz-Straße 199, 47057 Duisburg, Germany
3. I3N - Institute for Nanostructures, Nanomodelling and Nanofabrication, Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal