An Oxford EDX system in combination with a Sigma VP Field Emission Scanning Electron Microscope was used to analyse the samples. For cross-section samples the membranes were fractured in liquid nitrogen to preserve their microstructures. Afterwards, the samples were fixed to carbon adhesive discs and a small amount of conductive silver paint was added to ensure good conductivity. Finally, the samples were coated with Pt (5 nm) in a high vacuum sputter coater (Safematic CCU-O10 HV) to avoid charging effects. The SEM micrographs were obtained from a Sigma VP field Emission Scanning Electron Microscope (Carl-Zeiss AG, Germany). SEM micrographs were performed with an acceleration voltage of 6 -8 kV an emission current of 271 -289 pA and using SE2 and InLens detectors. EDX samples were prepared as mentioned above but using a coating of Pt (8 nm). EDS investigations were performed with an Oxford system and a 50 mm 2 XMax detector with a resolution of 127 eV.