1. Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland
2. National Institute of Materials Physics, RO-077125 Magurele, Ilfov, Romania
3. National Institute for Laser, Plasma and Radiation Physics, RO-077125 Magurele, Ilfov, Romania
4. Institute for Chemistry and Bioengineering, ETH Zurich, CH-8093 Zurich, Switzerland