1. Department of Physics, Federal University of São Carlos, 13565-905, São Carlos, São Paulo, Brazil
2. University of Brasília, Institute of Physics and International Center of Physics, Brasília 70919-970, DF, Brazil
3. Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, United States
4. São Carlos Institute of Chemistry, University of São Paulo, P.O. Box 780, 13560-970, São Carlos, São Paulo, Brazil