Modulating nonequilibrium electron-phonon interactions and energy relaxation in MXenes by surface-anchored Mo₃S₇ nanoclusters.

Abstract

Electron-phonon (e-ph) interactions govern photoinduced nonequilibrium dynamics of MXenes, determining hot-carrier relaxation and parasitic heat accumulation. However, strategies to deliberately modulate these interactions through chemical control, together with mechanistic understanding, remain underexplored. Here, we demonstrate the effective modulation of nonequilibrium e-ph interactions in Ti₃C₂T_x MXene via surface-anchored Mo₃S₇ nanoclusters, which introduce a rapid energy harvesting pathway competing with intrinsic e-ph relaxation. Using mild ligand substitution, Mo₃S₇ nanoclusters are densely and homogenously anchored onto Ti₃C₂T_x via coordination bonding between Mo centers and O-terminations. Femtosecond transient absorption and optical-pump terahertz-probe spectroscopy reveal an ultrafast, sub-100 fs nonthermal electron and/or energy extraction, with efficiency increasing from ~28.6 % at 1.55 eV to ~38.2 % at 3.88 eV. This excitation-energy-dependent enhancement is enabled by improved energetic alignment between hot electrons in Ti₃C₂T_x and the conduction-band manifold of Mo₃S₇. The competitive depletion of nonthermal electrons suppresses coherent A_1g phonon excitation, reducing effective e-ph interactions. Our study offers a viable strategy for modulating e-ph interactions in MXenes, advancing hot carrier relaxation and thermal management in next-generation optoelectronic devices.