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; therefore, a comprehensive understanding of its carrier dynamics is demanded for advancing the synthesis strategy and implementation of MoC. In this work, the carrier relaxation in MoC nanosheets is investigated by combining femtosecond transient reflection spectroscopy with first-principles calculations. The measured processes of electron–electron, electron–phonon, and phonon–phonon scattering show significantly longer lifetimes compared with those of other transition-metal carbides. Based on the analysis of calculated phonon dispersion, the nanosecond-carrier lifetime is consistent with the restricted phonon decay pathways, which is induced by the large mass difference between Mo and C atoms. The observed slow carrier cooling rate in our study offers a straightforward approach for effectively utilizing hot carriers, which is expected to improve the performance of photothermal and photovoltaic devices.