1. Grup de Caracterització de Materials, Departament de Física, EEBE, and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Campus Diagonal-Besòs, Av. Eduard Maristany, 10-14, 08019 Barcelona, Catalonia, Spain
2. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
3. Department of Physics, Southern Illinois University, Carbondale, Illinois 62901, USA