2D versus 3D-like electrical behavior of MXene thin films: insights from weak localization in the role of thickness, interflake coupling and defects

TL;DR

This study investigates how thickness, interflake coupling, and defects influence the dimensionality of weak localization transport mechanisms in Ti3C2Tx MXene thin films, revealing a crossover from 2D to 3D behavior.

Contribution

It provides a quantitative analysis of the effects of structural parameters on weak localization and dimensionality in MXene thin films, which was previously not well understood.

Findings

Dimensional crossover from 2D to 3D weak localization occurs when film thickness exceeds the dephasing length.

Weak interflake coupling can restore 2D weak localization behavior.

Defects can reduce the phase coherence length to about 10 nm, affecting transport mechanisms.

Abstract

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, Ti$_3$C$_2$T$_x$. Although weak localization (WL) has been proposed as the dominating low-temperature (LT) transport mechanism in Ti$_3$C$_2$T$_x$ thin films, there have been few attempts to model it quantitatively. In this paper, the role of important structural parameters -- thickness, interflake coupling, defects -- on the dimensionality of the LT transport mechanisms in spin-coated Ti$_3$C$_2$T$_x$ 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 $l_\phi$, which is in the $50-100\,\mathrm{nm}$ range. 2D WL can be restored by weakening the coupling between adjacent flakes, the intrinsic thickness of which is lower than $l_\phi$, hence acting as parallel 2D conductors. Alternatively, $l_\phi$ can be reduced down to the $10\,\mathrm{nm}$ range by defects. Our results clearly emphasize the ability of WL quantitative study to give deep insights in the physics of electron transport in MXene thin films.