[1] Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons ER C, Wilhelm Johnen Str, D-52428 Julich, Germany
[2] Rhein Westfal TH Aachen, Inst Phys 2, Templergraben 55, D-52062 Aachen, Germany
[3] Ludwig Maximilians Univ Munchen, Dept Chem, Butenandtstr 5-13, D-81377 Munich, Germany
[4] Helmholtz Zentrum Munchen, Inst Biol & Med Imaging, D-85764 Neuherberg, Germany