1. Department of Physics, University of Konstanz 1 , Konstanz, Germany
2. Department of Physics, University of Vermont 2 , Burlington, Vermont 05405, USA
3. Materials Science Program, University of Vermont 3 , Burlington, Vermont 05405, USA
4. Hasselt University, Institute for Materials Research (IMO) 4 , Wetenschapspark 1, 3590 Diepenbeek, Belgium
5. Energyville 5 , Thorpark, 3600 Genk, Belgium