1. Department of Physics, Federal University of Pelotas, PO Box 354, Pelotas, Rio Grande do Sul 96010-900, Brazil
2. Institute of Nanotechnology Hermann-von-Helmholtz-Platz, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
3. Chemistry Department, Federal University of Paraná, Curitiba, Paraná 81531-980, Brazil
4. Institute of Physics and International Center of Physics, University of Brasília, Brasília, Federal District 70919-970, Brazil
5. Department of Chemistry, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul 97105-900, Brazil