Ding Yi-Min, Nie Xiaomin, Dong Huilong, Rujisamphan Nopporn, Li Youyong
Institute of Functional Nano & Solf Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University Suzhou Jiangsu 215123 China
School of Chemistry and Materials Engineering, Changshu Institute of Technology Changshu Jiangsu 215500 China.
Nanoscale Adv. 2020 May 6;2(6):2471-2477. doi: 10.1039/c9na00632j. eCollection 2020 Jun 17.
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 TiCO 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 TiCO 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 TiCO. 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 TiCO is calculated to be 1.76-1.67 mA cm with the variation of the strain, suggesting good sunlight optical absorbance. Our work demonstrates that TiCO, as well as other MXenes, hold untapped potential for photo-detection and photovoltaic applications.
MXenes是具有诸多优势的二维（2D）层状过渡金属碳化物/氮化物材料，包括高载流子迁移率、可调节带隙、良好的机械性能和出色的结构稳定性，已引起全球研究关注。准确理解其电子和光学性质势在必行。在此，基于包括多体效应的第一性原理计算，研究了典型的MXenes成员TiCO单层的电子和光学响应特性。我们的结果表明，原始TiCO单层显示出间接准粒子（QP）带隙为1.32 eV，导带最小值（CBM）位于M点，价带最大值（VBM）位于Γ点。计算得出第一亮激子的光学带隙和结合能分别为1.26 eV和0.56 eV。在双轴拉伸应变下，Γ点处的最低未占据能带向下移动，而M点处的最低未占据能带向上移动。然后，在6%应变的TiCO中，Γ点处出现直接带隙。此外，由于晶格参数增加和激子波函数扩展，第一亮激子的光学带隙和结合能随应变增加而持续降低。更重要的是，计算得出TiCO的吸收光子通量随应变变化为1.76 - 1.67 mA cm，表明具有良好的太阳光光吸收性能。我们的工作表明，TiCO以及其他MXenes在光探测和光伏应用方面具有尚未开发的潜力。
