Nanoscale Evidence of Junction-Limited Transport in Ti₃C₂Tx MXene.

Understanding charge transport in networks of 2D 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 for 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 inter-flake junctions. The chemiresistive response to humidity is further investigated at the single flake, multi-flake and flake network scale, evidencing the crucial impact of junctions on sensing kinetics. These findings underline the dominant role of inter-flake junctions in MXene charge transport and sensing capabilities.