Direct observation of space charge dynamics by picosecond low-energy electron scattering C. Cirelli, M. Hengsberger, A. Dolocan, H. Over, J. Osterwalder and T. Greber EPL, 85 1 (2009) 17010 Published online: 19 January 2009 DOI: 10.1209/0295-5075/85/17010