Identifying the surface properties of Ti3C2Tx MXene through transmission electron microscopy

The titanium carbide Ti3C2Tx (Tx = surface functional groups) MXene exhibits promising physical properties and chemical activity as one of the most commonly and extensively investigated materials, but the participating surface structures and properties have yet to be clarified. Here, we reveal the superficial nature of etching-processed Ti3C2Tx using transmission electron microscopy/spectroscopy, first -principles calculation, and molecular dynamics simulation. An O-rich, but C-deficient, diffusion layer (approximately 3 nm) with an inverse gradient distribution is identified. Associated with the superficial substitution of O for C, an amorphous overlayer (approx-imately 2 nm) containing oxyfluoride of Ti, Al, and C is also revealed. The stable diffusion layer has a high density of states at the Fermi level and a low shear modulus to bulk modulus ratio, implying that the formation of the diffusion layer is not detrimental to Ti3C2Tx's conductivity and ductility. These findings are significant for improving oxidation strategies and understanding the structural properties of this material.