1. Departamento
de Física, Universidade Federal de Santa Catarina−UFSC, 88040-900 Florianópolis, SC, Brazil
2. Department
of Electronic Materials, Institute of Materials Science, Technical University of Darmstadt, Petersenstrasse 23, D-64287, Darmstadt, Germany
3. Instituto
de Física de São Carlos, Universidade de São Paulo, 13560-970 São Carlos, SP, Brazil
4. Centre de Recherche Paul Pascal, Université de Bordeaux & CNRS, 115 Avenue Schweitzer, 33600 Pessac, France