Atomic Defects in Monolayer Titanium Carbide (Ti₃C₂T_x) MXene

Area of Science:

• Materials Science
• Nanotechnology
• Energy Storage

Background:

• Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are promising materials for energy storage applications like lithium-ion batteries and supercapacitors.
• Characterization and properties of single-layer MXenes remain underexplored, limiting their full potential.

Purpose of the Study:

• To determine the atomic structure of freestanding monolayer Ti3C2Tx flakes.
• To characterize point defects prevalent in monolayer MXenes.
• To investigate the influence of defects and layer number on MXene conductivity.

Main Methods:

• Scanning transmission electron microscopy (STEM) for atomic structure determination.
• Minimally intensive layer delamination (MILD) for preparing freestanding monolayer Ti3C2Tx flakes.
• Density functional theory (DFT) calculations for defect analysis.
• Fabrication of devices from single- and few-layer Ti3C2Tx flakes to study conductivity.

Main Results:

• The atomic structure of monolayer Ti3C2Tx was determined, revealing prevalent point defects.
• Titanium (Ti) vacancy concentration can be controlled by adjusting etchant concentration during preparation.
• DFT calculations confirmed defect structures and predicted minimal impact on metallic conductivity, though surface morphology and termination groups are influenced.
• Experimental devices showed conductivity is affected by the number of layers in Ti3C2Tx flakes.

Conclusions:

• Freestanding monolayer Ti3C2Tx flakes possess controllable defects that influence their properties.
• These findings advance the understanding of MXene properties at the atomic level, crucial for optimizing their use in energy storage devices.