Abstract
MXenes, two-dimensional (2D) layered transition metal carbide/nitride materials with a lot of advantages including high carrier mobility, tunable band gap, favorable mechanical properties and excellent structural stability, have attracted research interest worldwide. It is imperative to accurately understand their electronic and optical properties. Here, the electronic and optical response properties of a Ti2CO2 monolayer, a typical member of MXenes, are investigated on the basis of first-principles calculations including many-body effects. Our results show that the pristine Ti2CO2 monolayer displays an indirect quasi-particle (QP) band gap of 1.32 eV with the conduction band minimum (CBM) located at the M point and valence band maximum (VBM) located at the Γ point. The optical band gap and binding energy of the first bright exciton are calculated to be 1.26 eV and 0.56 eV, respectively. Under biaxial tensile strains, the lowest unoccupied band at the Γ point shifts downward, while the lowest unoccupied band at the M point shifts upward. Then, a direct band gap appears at the Γ point in 6%-strained Ti2CO2. Moreover, the optical band gap and binding energy of the first bright exciton decrease continuously with the increase of the strain due to the increase of the lattice parameter and the expansion of the exciton wave function. More importantly, the absorbed photon flux of Ti2CO2 is calculated to be 1.76–1.67 mA cm−2 with the variation of the strain, suggesting good sunlight optical absorbance. Our work demonstrates that Ti2CO2, as well as other MXenes, hold untapped potential for photo-detection and photovoltaic applications.
Highlights
As a new member of the two-dimensional (2D) material family, MXenes, layered transition metal carbide/nitride materials, have aroused the interest of a great number of researchers, due to their advantages including high carrier mobility, tunable band gap, favorable mechanical properties and excellent structural stability.[1,2,3,4] The rst member of MXenes, Ti3C2Tx nanosheets, was produced by the room temperature exfoliation of Ti3AlC2 in hydro uoric acid.[5]
Most MXenes have exhibited excellent metallic conductivity without an intrinsic bandgap, which limits their applications in laser diode (LD), eld-effect transistor (FET), and light emitting diode (LED) devices
Our results reveal that the rst bright exciton peak of the Ti2CO2 monolayer is located at 1.26 eV with an exciton binding energy as large as 0.54 eV
Summary
As a new member of the two-dimensional (2D) material family, MXenes, layered transition metal carbide/nitride materials, have aroused the interest of a great number of researchers, due to their advantages including high carrier mobility, tunable band gap, favorable mechanical properties and excellent structural stability.[1,2,3,4] The rst member of MXenes, Ti3C2Tx nanosheets, was produced by the room temperature exfoliation of Ti3AlC2 in hydro uoric acid.[5]. 2D MXenes can be denoted as Mn+1XnTx (n 1⁄4 1, 2 and 3), in which M is a transition metal (TM), X is nitrogen and/or carbon and Tx represents surface functional groups The exible tunability of the elemental composition of MXenes leads to plenty of unique physical and chemical properties, which makes them suitable for numerous applications, such as electrodes of lithium/sodium-ion batteries, electrochemical catalysts, supercapacitors, hydrogen storage materials, molecular sensors, and antibacterial and bioimaging probe materials.[2,4,7] most MXenes have exhibited excellent metallic conductivity without an intrinsic bandgap, which limits their applications in laser diode (LD), eld-effect transistor (FET), and light emitting diode (LED) devices
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