1. Postgraduate Program in Materials Science and Engineering, University of Caxias do Sul, Francisco Getúlio Vargas 1130, Caxias do Sul, Rio Grande do Sul 95070-560, Brazil
2. Laboratory of Microscope and Microanalysis, Northeast Center for Strategic Technologies (CENETE), Avenida Prof. Luís Freire, 1-Cidade Universitária, Recife, Pernambuco 50740-540, Brazil