Polaron Dynamics Controlled by Tunable Surface Plasmons in MXenes

MXenes have garnered significant interest in energy conversionand catalysis due to their exceptional optical and electronic properties.The extended lifetime of photocarriers and high carrier mobility canbe attributed to large polarons in MXenes. Therefore, it is crucialto comprehend the fundamental dynamics of polarons in MXenes. Here,we report a comprehensive analysis of the small polarons using ultrafastspectroscopy. Small polarons are found to form efficiently under transversalsurface plasmon (SP) excitation. Under interband transition (IBT)and longitudinal SP excitation, small polaron formation is less efficient.In the thermal migration stage, multipolar surface plasmon excitationmeasurements reveal that heat flows both vertically and laterallyacross the flakes under transversal SP and IBT excitation and predominantlymigrates laterally in plane under longitudinal SP excitation. Ourfindings offer critical insights into the polaron dynamics of MXenesand are valuable in the advancement of MXene-based devices.