1. Departamento de Física, Universidad de Santiago de Chile (USACH), Av. Ecuador 3493, 9170124 Santiago, Chile
2. Institute of Nanostructure and Solid State Physics, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
3. Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Valparaíso, Chile
4. Center for the Development of Nanoscience and Nanotechnology (CEDENNA), Av. Ecuador 3493, 9170124 Santiago, Chile