Self-Assembled Titanium Oxide Composite Nanoscale Films for Terahertz EMI Shielding

Titanium oxide (TiO_x) composite thin films are developed via a solid-state disproportionation process that spontaneously forms conductive TiO nanocrystallites embedded within an insulating amorphous TiO_2−δ matrix. This self-organized composite architecture enables tunable terahertz (THz) electromagnetic interference (EMI) shielding by allowing the simultaneous modulation of absorption and reflection. The submicron-thick films exhibit low transmittance (∼0.05), high absorptance (∼0.20), and a shielding effectiveness (SE) of ∼13 dB across 0.2–1.3 THz, corresponding to an SE per unit thickness of ∼25.5 ± 0.5 dB/μm, one of the highest values reported for composite-based THz shielding films. Systematic comparisons show that the electrodynamic response is dictated by the size and crystallinity of TiO nanocrystallites. S1017, containing larger crystallites, exhibits higher σ_DC (∼6.5 × 10⁴ S/m) and a longer scattering time (τ ≈ 135 fs), leading to stronger conduction-driven shielding. In contrast, S1018, with smaller crystallites and greater interfacial area, shows reduced σ_DC and τ but a more negative Drude–Smith parameter (c₁ = −0.45 vs −0.34), indicative of enhanced backscattering and partial carrier localization. These combined trends clarify why S1017 yields stronger Joule absorption, while S1018 more effectively suppresses reflection through interface-induced scattering. These findings demonstrate that the solid-state disproportionation route not only simplifies fabrication but also provides deterministic control over carrier dynamics and interfacial scattering, enabling tunable THz absorption and positioning TiO_x composites as a scalable platform for next-generation EMI shielding technologies.