[1] Univ Fed Rio Grande do Sul, Escola Engn, Dept Met, BR-91501970 Porto Alegre, RS, Brazil
[2] Univ Fed Rio Grande do Sul, Inst Fis, BR-91501970 Porto Alegre, RS, Brazil
[3] Res Ctr Rossendorf Inc, Inst Ion Beam Phys & Mat Res, D-01314 Dresden, Germany