2D versus 3D-Like Electrical Behavior of MXene Thin Films: Insights from Weak Localization in the Role of Thickness,...

MXenes stand out from other 2D materials because they combine very good electrical conductivity with hydrophilicity, allowing cost-effective processing as thin films. Therefore, there is a high fundamental interest in unraveling the electronic transport mechanisms at stake in multilayers of the most conducting MXene, Ti₃C₂T_x. Although weak localization (WL) has been proposed as the dominating low-temperature (LT) transport mechanism in Ti₃C₂T_x thin films, there have been few attempts to model it quantitatively. In this work, the role of important structural parameters - thickness, interflake coupling, defects - on the dimensionality of the LT transport mechanisms in spin-coated Ti₃C₂T_x thin films is investigated through LT and magnetic field dependent resistivity measurements. A dimensional crossover from 2D to 3D WL is clearly evidenced when the film thickness exceeds the dephasing length l_ϕ, estimated here in the 50-100 nm range. 2D WL can be restored by weakening the coupling between adjacent flakes, the intrinsic thickness of which is lower than l_ϕ, hence acting as parallel 2D conductors. Alternatively, l_ϕ can be reduced down to the 10 nm range by defects. These results clearly emphasize the ability of WL quantitative study to give deep insights in the physics of electron transport in MXene thin films.