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

The microwave interaction of ultrathin Ti₃C₂T_<i>x</i> 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 (<i>c</i>) and thickness (<i>t</i>). For monolayer films, coverage-dependent conductivity transitions delineate two distinct regimes: (i) a discontinuous percolation regime (<i>c</i> < 80%) dominated by intra-flake electron transport (|<i>ε</i>_i/<i>ε</i>_r| < 1), resulting in high microwave transparency, and (ii) a metallic-like conduction regime (<i>c</i> > 80%) where synergistic intra-/inter-flake hopping (|<i>ε</i>_i/<i>ε</i>_r| > 1) enhances interfacial polarization and ohmic loss, enabling 27% maximum microwave absorption at a high sheet conductivity of ∼0.001 S (<i>c</i> = 93%). For multilayer continuous films, thickness dictates dual transport dynamics: sub-6.6 nm films exhibit surface/interface scattering-limited bulk conductivity (<i>σ</i> ∼ 3000 S cm^-1, <i>τ</i> > 6 ps), while thicker films (<i>t</i> > 6.6 nm) transition to bulk-like metallic conduction (<i>σ</i> ∼ 13 000 S cm^-1, <i>τ</i> < 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.