Polybenzimidazole copolymer derived lacey carbon film for graphene transfer and contamination removal strategies for imaging graphene nanopores

The study of the nanometer-scale vacancy defects (nanopores) in graphene by transmission electron microscopy (TEM) is severely hindered by the presence of polymeric residues originating from the graphene-transfer-step to the TEM grid. The state-of-the-art transfer strategies yield contamination-free pristine graphene specimens but do not work well for the nanoporous graphene. This is because of the relatively high energy of the vacant nanopores which makes it difficult to remove the residues without altering the structure of nanoporous graphene. Herein, we present a novel strategy to fabricate a sub-100-nm-thick lacey polymer film hosting see-through windows (10–900 nm) by using a facile nonsolvent-induced phase separation (NIPS). The polymer film is transformed into a lacey carbon film that reinforces graphene and allows residue-free transfer to the TEM grid as one avoids the direct contact between the polymer and the nanopores within a window. Finally, atmospheric-, graphene-synthesis-, and transfer-bath-related contaminants are removed by annealing the specimen inside an activated carbon bed at 900 °C in a reducing atmosphere. The method results in samples with large contamination-free areas which are easy to find during aberration-corrected high-resolution TEM (AC-HRTEM) imaging, enabling high throughput structural analysis of graphene nanopores.