Cryo-SEM was carried out using a FEI Quanta 3D and a Gatan LTO2500 cryo-unit. The hybrid structure was cut and mounted onto the holder and flash frozen in slushy nitrogen. The sample was then transferred to the LTO2500 cryo-unit cooled to -140 o C and freeze-fractured using a cold scalpel to produce a freshly cut surface. The frozen water was sublimed off at -90 o C for 5 min, and the sample was sputter-coated with palladium. Afterward, the sample was transferred to the cryo-stage (-140 o C) for imaging.