Ultrafast Carrier Dynamics in MXene Thin FilmsPublic
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Terahertz (THz) spectroscopy makes it possible to study the interaction between electromagnetic radiation and matter to understand the intrinsic properties of materials and nanostructures. For MXenes, a family of 2D nanomaterials, radiation in the THz range of the electromagnetic spectrum is ideal for the non- invasive characterization of ultrafast charge carrier dynamics. In this paper, time-resolved THz spectroscopy techniques were used to study the carrier dynamics and photoexcitation of two such MXenes, Mo2Ti2C3 and Nb2C. Drude and Drude-Smith conductivity models were used to analyze complex conductivity components (σ1 and σ2) for both materials and were compared to titanium carbide (Ti3C2), a well-studied MXene. We find that while Mo2Ti2C3 has considerable intrinsic conductivity, albeit lower than Ti3C2, the conductivity of Nb2C MXene is negligible. We also establish that effects of photoexcitation on these two MXenes diverge from those of Ti3C2, as they exhibit long-lived positive photoconductivity in contrast with conductivity suppression in Ti3C2. These results demonstrate the wealth of different optoelectronic properties of MXenes and possibility of tailoring these properties with chemical composition and structure.
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