Samples were maintained at cryogenic temperatures during transfer and analysis using an Elsa™ cryo-transfer holder and temperature controller (Gatan). Imaging was performed on a JEOL 2100F FEG-TEM operating at 200kV and recorded on a K3 direct electron detection camera (Gatan), nominal defocus was applied and an objective aperture inserted to improve image quality. A sample temperature of -172 o C (±0.5 o C) was maintained during imaging.