1. Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland, Department of Physical Chemistry & Nanomaterials Research Centre, Palacky University, Svobody 26, 77146 Olomouc, Czech Republic, and Solid State Chemistry and Analyses Laboratory EMPA, the Swiss Federal Laboratories for Materials Testing and Research EMPA, CH-8600 Duebendorf, Switzerland