1. Dipartimento di Chimica IFM and NIS Centre of Excellence INSTM-UdR, Università di Torino, via Pietro Giuria 7/9, I-10125 Turin, Italy
2. Departament de Fisica, Universitat Autonoma de Barcelona, E-08193 Bellaterra, Spain
3. ID11, European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France
4. Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1 D-76344 Eggenstein-Leopoldshafen, Germany