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基于第一性原理计算方法, 设计出了一种新型二维半导体材料TiO 2, 并进一步研究了其结构稳定性, 电子结构, 载流子迁移率和光学性质等. 二维TiO 2的形成能、声子谱、分子动力学、弹性常数表明, 二维TiO 2具有较好的动力学, 热力学和机械稳定性, 具备实验制备的条件, 且能够稳定存在于常温条件下. 电子结构分析表明, 二维TiO 2是一种间接带隙半导体, 在GGA+PBE和HSE06算法下的能隙分别为1.19 eV和2.76 eV, 其价带顶和导带底能级分别由Ti-3d和Ti-4s态电子构成, O原子的电子态在费米能级附近贡献很小, 主要分布在深处能级. 载流子迁移率显示, 二维TiO 2的迁移率比单层MoS 2要小, 其电子和空穴迁移率分别为31.09和36.29 cm 2·V –1·s –1. 由于空穴迁移率和电子迁移率的各向异性, 电子-空穴复合率较低, 使得单层TiO 2的使用寿命更长, 光催化活性更好. 在应变调控下, 二维TiO 2的能隙发生明显响应, 以适用于各种半导体器件的需要. 半导体的带边势和光学性质显示, 在–5%—2%单/双轴应变下, 二维TiO 2能够光裂水制H 2, 在–5%—5%单/双轴应变下, 能够光裂水制O 2, H 2O 2和O 3等. 此外, 二维TiO 2对可见光和紫外光具有较高的吸收系数, 说明其在未来光电子器件和光催化材料领域有着潜在的应用前景.By means of state-of-the-art density functional theory (DFT) computations, We designed a new two-dimensional material TiO 2. We further investigated the stability, electronic structure, carrier mobility, and optical properties of monolayer TiO 2. Our results show that monolayer TiO 2has good kinetic, thermodynamic and mechanical stability and can exist stably at room temperature. The results were demonstrated using the binding energy, phonon spectrum, molecular dynamics simulation, and elastic constant calculation. The band structure indicates that the monolayer TiO 2is an indirect bandgap semiconductor with energy gaps of 1.19 eV (GGA+PBE) and 2.76 eV (HSE06), respectively. The results of state density show that the Ti-3d state electrons constitute the top of the valence band and Ti-4s state electrons constitute the bottom of the conduction band. The electron states of O atoms contribute very little near the Fermi energy level and are mainly distributed in the deep energy level. In addition, the carrier mobility of monolayer TiO 2is smaller than monolayer MoS 2, and the electron and hole mobility can reach 31.09 cm 2·V –1·s –1and 36.29 cm 2·V –1·s –1, respectively. Due to the anisotropy of hole mobility and electron mobility, the composite rate of electrons and holes is relatively low. This ensures longer service life and better photocatalytic activity of monolayer TiO 2. Furthermore, under the condition of uniaxial strain and biaxial strain, the energy gap of monolayer TiO 2has a clear response. The energy gap is more sensitive to biaxial strain than uniaxial strain, indicating that monolayer TiO 2can be applied to various semiconductor devices. The band-edge potential and optical properties of semiconductors indicate that two-dimensional TiO 2is capable of photo-splitting water production, H 2at –5~2% single/biaxial strain, and O 2, H 2O 2, O 3, etc. at –5~5% single/biaxial strain. Moreover, the monolayer TiO 2has a high absorption coefficient for visible and ultraviolet light. In conclusion, the monolayer TiO 2has a potential application prospect in the field of optoelectronic devices and photocatalytic materials in the future.
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Material a/b/Å ${\theta _1}$/($^ \circ $) ${\theta _2}$/($^ \circ $) l/Å $\sigma $/Å Ef/eV TiO2 2.89 91.66 68.16 2.01 2.26 –8.11 MoS2 3.18 82.58 80.74 2.41 3.14 –7.35 
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Carrier type $m_a^ * $/${m_{\rm{e}}}$ $m_b^ * $/${m_{\rm{e}}}$ $m_l^ * $/${m_{\rm{e}}}$ $\left| {{E_{la}}} \right|$/ eV $\left| {{E_{lb}}} \right|$/ eV $C_a^{2{\rm{D}}}$/ N·m–1 $C_b^{{\rm{2 D}}}$/ N·m–1 $\mu _a^{2{\rm{D}}}$/ cm2·V–1·s–1 $\mu _b^{2{\rm{D}}}$/ cm2·V–1·s–1 Electrons 3.21 1.39 2.11 3.43 3.38 21.27 21.28 12.92 30.75 Holes 4.73 4.12 4.41 1.26 1.25 21.27 21.28 31.09 36.29 下载:
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