1. Department of Engineering, University of Palermo, Viale delle Scienze, Ed. 6, 90128 Palermo, Italy
2. Department of Physics, University of Trento, via Sommarive 14, Povo, 38123 Trento, Italy
3. Department of Industrial and Materials Science, Chalmers University of Technology, Rannvagen 2A, 41258 Gothenburg, Sweden
4. Wallenberg Wood Science Centre, Kemigården 4, 41258 Gothenburg, Sweden