Two-dimensional MXene/MMT composite metafilms with negative permittivity

The applications of metamaterials in the field of electromagnetic devices have put forward requirements on their size and flexibility, the development of metamaterials has gradually shifted to two-dimensional (2D) systems, and further exploration is needed for 2D random metamaterials. Herein, MXene and montmorillonite (MMT) are stacked layer by layer to construct the MXene/MMT composite metafilms which has good flexibility and ultra-thin thickness. With the increase of the volume fraction of MXene, the conductive mechanism of the metafilms changes from hopping conduction to metal-like conduction which proves the occurrence of percolation, and the percolation threshold is 8.69 vol%. The negative permittivity is obtained in the material due to the plasma oscillations of free electrons explained by Drude model, which can be regulated by changing the layer spacing between MXene nanosheets. Besides, the electromagnetic interference (EMI) shielding effectiveness (SET) of the metafilms is more than 30 dB in the frequency range of 8.2-12.4 GHz when the volume fraction of MXene is greater than 31.25 vol%, and reached 48.6 dB at 8.2 GHz when the MXene volume fraction is 47.62 vol%. This work fills the gap in study of the 2D random metamaterials and can expand the potential applications of metamaterials.