Electronic and Mechanical Properties of MXenes Derived from Single-Flake Measurements

Abstract

MXenes are a large class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides that show a great promise for a broad spectrum of applications. More than 25 different MXenes have been already experimentally demonstrated, and many others have been studied theoretically; however, their intrinsic physical properties remain largely unexplored. Here we review the electrical measurements of bulk assemblies of MXene sheets and demonstrate that the results strongly depend not only on the MXene’s chemical composition and structure but also on the form of assembly (a filtered, spin-casted, or sprayed film, a pressed disc, a particle, etc.), as well as on the preparation and postprocessing methods and measurement conditions, which dictate the stacking of individual MXene sheets and the interflake resistances. These results show the importance of single-flake measurements for revealing the intrinsic properties of various MXene materials and their comparison with each other. Single-flake measurements have been shown imperative for a variety of other 2D materials but remain scarce for MXene monolayers and so far have been limited only to Ti3C2Tx. Electrical measurements of individual Ti3C2Tx monolayers showed their high conductivity of 4600 ± 1100 S/cm and field-effect electron mobility of 2.6 ± 0.7 cm2/ V · s. These measurements were further proved to be useful for comparing the efficiencies of different synthetic methods for preparing high-quality MXene materials and investigating the environmental stability and kinetics of oxidation of Ti3C2Tx flakes in humid air. Mechanical measurements of Ti3C2Tx monolayers revealed their high Young’s modulus of 0.33 ± 0.03 TPa, establishing their enormous potential for mechanically reinforced composites, protective coatings, and nanoresonators. These examples demonstrate the importance of single-flake physical measurements, which expand our understanding of MXenes and broaden the already impressive range of their potential applications.