Anisotropic charge transport in few-layer 2D crystals: the case of Ti3C2Tx MXenes

Charge transport in two-dimensional (2D) crystals is critical for a large variety of future applications, and it is therefore highly desirable to get a better understanding of the underlying mechanisms. While the in-plane resistivity of 2D crystals is usually relatively easy to extract, the out-of-plane component is much more difficult to access, especially at the flake-scale. Here, we focus on individual metallic single crystal Ti ₃ C ₂ T _x flakes. Ti ₃ C ₂ T _x belongs to the MXenes family, which has recently garnered significant attention for excellent prospects of applications in printable electronics, energy storage and electromagnetic interference shielding, for which electrical properties play a leading role. To answer the need for experimental data on charge transport in Ti ₃ C ₂ T _x , we combine local-probe measurements (Conductive AFM), conventional four-contact measurements, finite element and ab initio simulations on individual few-layer flakes of Ti ₃ C ₂ T _x . This effort establishes new methods to study charge transport both in in-plane and out-of-plane directions and yields consistent quantitative value of resistivity anisotropy in individual Ti ₃ C ₂ T _x flakes, an essential ingredient in the understanding and modeling of charge transport in MXenes, in particular considering the role of interlayer interactions and surface functionalization in these materials.