1. Department
of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, United States
2. Applied
Physics Department, State University of Campinas, Campinas-SP 13083-970, Brazil
3. Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
4. Department
of Chemistry, University of Munich, Butenandtstraße 5-13, 81377 Munich, Germany