1. Instituto de Física, Universidade Federal de Uberlândia, C.P. 593, Uberlândia 38400-902, Minas Gerais, Brazil
2. Brazilian Nanotechnology National Laboratory (LNNano), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, São Paulo 13083-970, Brazil
3. Center for Natural and Human Sciences, Federal University of ABC, Santo André, São Paulo 09210-580, Brazil