[1] Ecole Polytech Fed Lausanne, Inst Microengn IMT, Photovolta & Thin Film Elect Lab, Rue Maladiere 71B, CH-2000 Neuchatel, Switzerland
[2] Univ Basel, Dept Phys, Klingelbergstr 82, CH-4056 Basel, Switzerland
[3] Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany
[4] Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany
[5] Nanyang Technol Univ, Sch Mat Sci & Engn, 50 Nanyang Ave, Singapore, Singapore