[1] Rostock Univ, Inst Phys, D-18055 Rostock, Germany
[2] Missouri Univ Sci & Technol, Dept Mat Sci & Engn, Rolla, MO 65409 USA
[3] Rutherford Appleton Lab, ISIS Facil, Didcot OX11 0QX, Oxon, England
[4] Deutsch Elektronen Synchrotron DESY, D-22603 Hamburg, Germany