1. PLASMANT, Department of Chemistry, University of Antwerp, Antwerp 2610, Belgium
2. Department of Physics, University of Antwerp, Antwerp 2020, Belgium
3. NANOlab Center of Excellence, University of Antwerp, Belgium
4. Departamento de Fisica, Caixa Postal 6030, Universidade Federal do Ceará, Fortaleza 60455-70, Ceará, Brazil