Ultrathin nitrogen-doping graphene films for flexible and stretchable EMI shielding materials

Ultrathin, flexible and highly conductive materials that possess excellent electromagnetic interference (EMI) shielding performance are greatly needed, especially for the fabrication of stretchable shielding materials in practical applications such as wearable and foldable electronics. Graphene oxide (GO) sheets are modified with ethylenediamine to prepare cross-linked graphene films using a pressure-assisted self-assembly technique. FTIR and XPS results demonstrate that amine monomers are chemically bonded to GO sheets, with simultaneous reduction of GO sheets. After thermal annealing and followed with compression, the 6.6-μm-thick nitrogen-doping graphene film (rGO-EDA-2) is obtained with ultrahigh electrical conductivity of 8796 S cm⁻¹. The excellent electrical conductivity is mainly attributed to nitrogen-doping effect, defects repair during chemical functionalization and removal of oxygenated groups. Ultrahigh electrical conductivity, multilayer structure and modified electronic structure with nitrogen doping lead to outstanding shielding performance for the rGO-EDA-2 film, with excellent shielding effectiveness (SE) of 58.5 dB and the specific SE/thickness of 43902 dB cm² g⁻¹, respectively. By fixing the rGO-EDA-2 film on the pre-stretched wavy substrate, the stretchable shielding composite is obtained, with constant EMI SE of 56.3 dB after repeated stretching. The pre-stretched wavy substrate allows the multilayer graphene film to achieve wavy structure after strain release, which is capable of bearing tensile strain up to 32.6%. This study could be significant in the applications of stretchable and wearable electronic devices.