1. Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
2. Department of Chemistry, Sungkyunkwan University, 440-746 Suwon, South Korea
3. Center for Free-Electron Laser Science/DESY, D-22607 Hamburg, Germany
4. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
5. Department of Materials Science and Engineering, National University of Singapore, Singapore 117575