Optical micrographs of freestanding membranes (M1, M2) spanning circular apertures with a diameter of ∼105 µm and ∼84 µm are shown in Figure ,b. These membranes were used for the AFM bulge tests presented below. The optical micrographs reveal a fairly homogeneous morphology of the hybrid membranes. Bright spots, however, indicate the deposition of TNR aggregates. Figure shows the SEM images of the remaining parts of a hybrid membrane after a burst experiment (see below). These images clearly reveal the different textures of the bottom and the top surface of the freestanding membrane. On the top surface the morphology is characterized by the TNRs covered with GO sheets while the first deposited layers of GO/SF form a smooth bottom surface. The higher magnification inset indicates a rather homogeneous distribution of TNRs in the upper layers of the hybrid membrane.