[1] Univ Duisburg Essen, Inst Mat Sci, Ctr Nanointegrat Duisburg Essen CENIDE, D-45141 Essen, Germany
[2] Univ Picardie Jules Verne, Lab Phys Matiere Condensee UR2081, F-80039 Amiens, France
[3] Univ Duisburg Essen, Elect Mat & Nanostruct & Ctr Nanointegrat Duisbur, D-47057 Duisburg, Germany
[4] Univ Cologne, Inst Phys Chem, D-50939 Cologne, Germany
[5] Univ Duisburg Essen, Inst Technol Nanostruct, Ctr Nanointegrat Duisburg Essen CENIDE, D-47057 Duisburg, Germany