[1] Univ Antwerp, Dept Phys, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
[2] Univ Fed Ceara, Dept Fis, Caixa Postal 6030, BR-60455760 Fortaleza, Brazil
[3] Univ Antwerp, NANOlab Ctr Excellence, B-2020 Antwerp, Belgium
[4] Univ Fed Mato Grosso, Inst Fis, BR-78060900 Cuiaba, MT, Brazil