1. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, 08193 Barcelona, Spain
2. ALBA Synchrotron, 08290 Cerdanyola del Vallès, Barcelona, Spain
3. ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain