Dual Heteroatoms-Induced defect engineering in graphene towards metacomposites with epsilon-near-zero response

In this paper, the effect of diatomic doping on negative permittivity and epsilon-near-zero (ENZ) properties of graphene (GR)/polyvinylidene difluoride (PVDF) composites were investigated for the first time. Nitrogen (N) and phosphorus (P) atoms were doped into the GR lattice, and the doping sites and ratio of N and P atoms in the GR lattice were studied in detail. The results showed that introducing N and P atoms controlled the composite's percolation structure and carrier concentration. The dual atom synergy modulated the value of negative permittivity, and a stable weak negative permittivity between -30 and -40 was obtained. With further regulation of the diatomic doping ratio, an ENZ response in the kHz region was successfully acquired under synergistic effects. The ENZ response appeared at 170 kHz and exhibited a zero-crossing behavior. After the permittivity shifted to negative, the maximum negative permittivity was only -11.92 up to 1 MHz. The negative permittivity obtained for N/P co-doped GR/PVDF composites could all be perfectly fitted by Lorentz and/or Drude model. Further analysis revealed that plasma oscillation and dielectric resonance work in concert were necessary to produce a steady ENZ response in the kHz range.