Control of MXenes’ electronic properties through termination and intercalation

Abstract

MXenes are an emerging family of highly-conductive 2D materials which have demonstrated state-of-the-art performance in electromagnetic interference shielding, chemical sensing, and energy storage. To further improve performance, there is a need to increase MXenes’ electronic conductivity. Tailoring the MXene surface chemistry could achieve this goal, as density functional theory predicts that surface terminations strongly influence MXenes' Fermi level density of states and thereby MXenes’ electronic conductivity. Here, we directly correlate MXene surface de-functionalization with increased electronic conductivity through in situ vacuum annealing, electrical biasing, and spectroscopic analysis within the transmission electron microscope. Furthermore, we show that intercalation can induce transitions between metallic and semiconductor-like transport (transitions from a positive to negative temperature-dependence of resistance) through inter-flake effects. These findings lay the groundwork for intercalation- and termination-engineered MXenes, which promise improved electronic conductivity and could lead to the realization of semiconducting, magnetic, and topologically insulating MXenes.

Surface Modification of a MXene by an Aminosilane Coupling Agent

“…SEM is used widely to observe the sheet‐like structure of MXenes . Here, we conducted SEM on the cross‐section of AEAPTMS‐Ti 3 C 2 T x and found that the layered structure of the pristine MXene stays intact even after the functionalization reaction.…”

“…To evaluate the different types and strengths of bonding between AEAPTMS and Ti 3 C 2 T x , TGA and MS of pristine and AEAPTMS‐Ti 3 C 2 T x were performed and presented in Figure . The thermogram of pristine MXene indicates the dehydration of the material from 25 °C up to ≈300 °C, which correlates to the water ( m / z = 18) curve in the MS shown in Figure 4B. High temperatures are required to dehydrate free‐standing MXene films due to the intercalation of water in small interlayer spacing of ≈10 Å.…”

Electromagnetic Shielding of Monolayer MXene Assemblies

“…Initially, there are four deconvoluted peaks corresponding to the surface functional groups including –OH, –O, and trapped water molecules, which are inevitably formed during the chemical etching of parental Ti 3 AlC 2 . After thermal treatment, peak intensities for Ti‐OH and Ti‐H 2 O are significantly reduced, confirming that reduction in gallery spacing between MXene layers upon thermal treatment is not due to the phase transformation to TiO 2 or oxidation of MXene, but due to the removal of intercalants, such as absorbed H 2 O and partial loss of surface terminations such as –OH, –F, and –O …”

High‐Efficiency Thermoelectric Power Generation Enabled by Homogeneous Incorporation of MXene in (Bi,Sb)2Te3 Matrix

“…[15,16,26] Therefore, the Ti 3 C 2 T x /BST interface in the composite can be deemed as a typical metal-semiconductor contact, which could lead to the formation of interface potential (V) due to the difference of work function for the two materials. [15,16,26] Therefore, the Ti 3 C 2 T x /BST interface in the composite can be deemed as a typical metal-semiconductor contact, which could lead to the formation of interface potential (V) due to the difference of work function for the two materials.…”