Interface-Tailored Secondary Excitation and Ultrafast Charge/Energy Transfer in Ti₃C₂T_<i>x</i>-MoS₂ Heterostructure Films

Charge/energy separation across interfaces of plasmonic materials is vital for minimizing plasmonic losses and enhancing their performance in photochemical and optoelectronic applications. While heterostructures combining plasmonic two-dimensional transition metal carbides/nitrides (MXenes) and semiconducting transition metal dichalcogenides (TMDs) hold significant potential, the mechanisms governing plasmon-induced carrier dynamics at these interfaces remain elusive. Here, we uncover a distinctive secondary excitation phenomenon and an ultrafast charge/energy transfer process in heterostructure films composed of macro-scale Ti₃C₂T_<i>x</i> and MoS₂ films. Using Rayleigh-Bénard convection and Marangoni effect-induced self-assembly, we fabricate large-scale (square centimeters) Ti₃C₂T_<i>x</i> and MoS₂ films composed of edge-connected monolayer nanoflakes. These films are flexibly stacked in a controlled sequence to form macroscopic heterostructures, enabling the investigation and manipulation of excited-state dynamics using transient absorption and optical pump-terahertz probe spectroscopy. In the Ti₃C₂T_<i>x</i>-MoS₂ heterostructure, we observe a secondary excitation in MoS₂ driven by the surface plasmon resonance of Ti₃C₂T_<i>x</i>. This phenomenon, with a characteristic rise time constant of ∼70 ps, is likely facilitated by acoustic phonon recycling across the interface. Further interfacial thermal transport engineering─achieved by tailoring the sequence and combination of interfaces in trilayer heterostructures─allows extending the characteristic time to ∼175 ps. Furthermore, we identify a sub-150 fs ultrafast charge/energy transfer process from Ti₃C₂T_<i>x</i> to MoS₂. The transfer efficiency is strongly dependent on the excitation photon energy, resulting in amplified photoconductivity in MoS₂ by up to ∼180% under 3.10 eV excitation. These insights are crucial for developing plasmonic MXene-based heterostructures, paving the way for advancements in photochemical and optoelectronic applications.