Prior to transmission electron microscopy (TEM) measurements, samples were suspended in water and drop-casted onto 200-mesh copper grids coated with carbon film. TEM was measured at the Electron Microscopy Facility at IST (Austria) using a Phillips Tecnai 12 (120kV) TEM equipped with a CMOS TVIPS TemCam-F216 camera. The resulting pictures were processed with Gatan Micrograph software and analyzed with TVIPS EM Measure beta 0.85.