Dynamics of Long-lived Carriers in Molybdenum Carbide Nanosheets

Abstract

Molybdenum carbide (MoC) is a promising candidate for substituting expensive platinum-group metals in many applications owing to its low cost and excellent properties. A comprehensive understanding of the carrier dynamics in MoC facilitates its implementations and helps designing synthesis strategies. In this work, the carrier relaxation in MoC nanosheets is investigated by combining femtosecond transient reflection spectroscopy with first-principles calculations. The observed processes of electron-electron, electron-phonon, and phonon-phonon scattering show longer lifetimes compared to those of other transition metal carbides. The nanosecond carrier lifetime is explained by the restricted phonon decay pathways induced by the large mass difference between C and Mo atoms, which is revealed through the analysis of calculated phonon dispersion. The slow cooling of hot carriers in MoC nanosheets offers a simple approach for designing devices that effectively utilize hot carriers, which are expected to improve photothermal and photovoltaic performances.