Direct Observation of Electron-Vibration Coupling at MXene-Solvent Interface

MXenes,a new family of two-dimensional(2D)materials,have received extensive interest due to their fascinating physicochemical properties,such as outstandinglight-to-heat conversion efficiency.However,the photothermal conversion mechanism of MXenes is still poorly understood.Here,by using femtosecond visible and mid-infrared transient absorption spectroscopy,the electronic energy dissipation dynamics of MXene(Ti_(3)C_(2)T_(x))nanosheets dispersed in various solvents are carefully studied.Our results indicate that the lifetime of photoexcited MXene is strongly dependent on the surrounding environment.Especially,the interfacial electron-vibration coupling between the MXene nanosheets and the adjacent solvent molecules is directly observed following the ultrafast photoexcitation of MXene.It suggests that the interfacial interactions at the MXene-solvent interface play a critical role in the ultrafast energy transport dynamics of MXene,which offers a potentially feasible route for tailoring the light conversion properties of 2D systems.

Unveiling Defect-Mediated Carrier Dynamics in Few-Layer MoS2 Prepared by Ion Exchange Method via Ultrafast Vis-NIR-MIR Spectroscopy

Defect-mediated processes in two-dimensional transition metal dichalcogenides have a significant influence on their carrier dynamics and transport properties,however,the detailed mechanisms remain poorly understood.Here,we present a comprehensive ultrafast study on defect-mediated carrier dynamics in ion exchange prepared few-layer MoS2 by femtosecond time-resolved Vis-NIR-MIR spectroscopy.The broadband photobleaching feature observed in the near-infrared transient spectrum discloses that the mid-gap defect states are widely distributed in few-layer MoS2 nanosheets.The processes of fast trapping of carriers by defect states and the following nonradiative recombination of trapped carriers are clearly revealed,demonstrating the mid-gap defect states play a significant role in the photoinduced carrier dynamics.The positive to negative crossover of the signal observed in the mid-infrared transient spectrum further uncovers some occupied shallow defect states distributed at less than0.24 e V below the conduction band minimum.These defect states can act as effective carrier trap centers to assist the nonradiative recombination of photo-induced carriers in few-layer MoS2 on the picosecond time scale.