1. Department of Materials
and Environmental Chemistry, Stockholm University, S-10691 Stockholm, Sweden
2. Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-970 Porto
Alegre, RS, Brazil
3. Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain
4. ICREA, Pg. Lluís
Companys 23, E-08010 Barcelona, Spain
5. Catalan Institute of Nanoscience
and Nanotechnology (ICN2), CSIC, and The Barcelona Institute of Science
and Technology, Campus UAB, Bellaterra, E-08193 Barcelona, Spain