Ultrafast energy transfer across Pd/MXene interface via hot phonon-electron interactions.

The interfacial structure and energy transfer (ET) in heterostructures have attracted tremendous attention for their growing importance in thermal management, catalysis, and optoelectronic applications. However, the role of carrier-lattice interaction in interfacial ET at the nanoscale remains unclear. Here, we construct metal/MXene heterostructures via in situ chemical growth as platforms to study interfacial energy flow. On the basis of femtosecond transient absorption spectroscopic measurements, interfacial ET within ∼1.3 picoseconds is observed in Pd/MXene, which could not be explained by traditional phonon-phonon interaction. Experimental results combined with density functional theory calculations identify an ultrafast ET route involving strong interfacial coupling and high-density-of-state electrons near the Fermi level, enabling hot phonon-driven electron excitation. Distinct from conventional diffusive phonon processes, this ET route exhibits higher ET rate and efficiency with increasing absorbed photon energy and pump fluence. These findings reveal that the tuning of interfacial chemical bonds holds the promise to achieve high-efficiency energy transport across nanoscale interfaces.