1. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, 08193 Barcelona, Spain
2. Centro de Fı́sica de Materiales CFM/MPC (CSIC-UPV/EHU), 20018 Donostia-San Sebastián Spain
3. Department of Materials, ETH Zurich, Hönggerbergring 64, CH-8093 Zurich, Switzerland
4. Istituto di Struttura della Materia (ISM), Consiglio Nazionale delle Ricerche (CNR), I-34149 Trieste, Italy
5. ALBA Synchrotron Light Source, Carretera BP 1413km 3.3, E-08290 Cerdanyola del Vallès, Spain
6. Institució Catalana de Recerca i Estudis Avançats (ICREA), 08070 Barcelona, Spain