Inter-flake transport and humidity response of Ti3C2Tx MXene at the nanoscale

Abstract

Understanding charge transport in networks of two-dimensional crystals is essential for developing reliable applications such as chemiresistors or electromagnetic shields. For this purpose, intra- and inter-flake contributions to the network resistance must be disentangled. MXenes, such as Ti3C2Tx, are prime examples of 2D crystals often employed as thin networks of interconnected flakes deposited on substrates to realize functional devices. While a significant number of studies focused on transport in individual MXene flakes, inter-flake transport remains scarcely explored. Here, we demonstrate that charge transport in multi-flake conductive paths of Ti3C2Tx is dominated by interflake junctions and provide quantitative estimates of junction resistances. Scanning probe measurements reveal that in a MXene multi-flake conductive path, individual flakes behave as isopotential domains, since the voltage drop is localized precisely at the inter-flake junctions. We further investigate the chemiresistive response to humidity at the single flake, multi-flake and flake network scale, evidencing the leading impact of junctions on sensing kinetics. These findings underline the crucial role of junctions in charge transport and sensing capabilities of MXenes.