Dynamics of Long-lived Carriers in Molybdenum Carbide Nanosheets

TL;DR

This study investigates the long-lived carrier dynamics in molybdenum carbide nanosheets using spectroscopy and calculations, revealing slow hot carrier cooling due to phonon decay restrictions, which benefits device performance.

Contribution

It provides new insights into the carrier relaxation processes in MoC nanosheets and explains the origin of their long carrier lifetimes through phonon dispersion analysis.

Findings

Long carrier lifetimes compared to other transition metal carbides

Restricted phonon decay pathways due to mass difference between C and Mo

Potential for improved hot carrier-based device performance

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.