Ultrathin MXene conductive films with percolation-driven electron transport and thickness-dependent microwave absorption/shielding dual functionality†

The microwave interaction of ultrathin Ti₃C₂T_x MXene films is governed by their nanosheet network-modulated conductivity. By integrating a transfer matrix model with the Drude model, this study reveals the dielectric response mechanisms of MXene films under microwave radiation, driven by nanosheet coverage (c) and thickness (t). For monolayer films, coverage-dependent conductivity transitions delineate two distinct regimes: (i) a discontinuous percolation regime (c < 80%) dominated by intra-flake electron transport (|ε_i/ε_r| < 1), resulting in high microwave transparency, and (ii) a metallic-like conduction regime (c > 80%) where synergistic intra-/inter-flake hopping (|ε_i/ε_r| > 1) enhances interfacial polarization and ohmic loss, enabling 27% maximum microwave absorption at a high sheet conductivity of ∼0.001 S (c = 93%). For multilayer continuous films, thickness dictates dual transport dynamics: sub-6.6 nm films exhibit surface/interface scattering-limited bulk conductivity (σ ∼ 3000 S cm⁻¹, τ > 6 ps), while thicker films (t > 6.6 nm) transition to bulk-like metallic conduction (σ ∼ 13 000 S cm⁻¹, τ < 6 ps), achieving concurrent 48% microwave absorption at 6.6 nm and 19 dB shielding at 24 nm. The percolation-governed conductivity scaling and thickness-modulated electron transport establish design principles for optimizing MXene-based ultrathin electromagnetic functional materials in microwave absorption, shielding, and flexible sensing applications, bridging nanoscale structural engineering with macroscopic functionality.