Yang Jia-Shu, Zhao Luneng, Li Shi-Qi, Liu Hongsheng, Wang Lu, Chen Maodu, Gao Junfeng, Zhao Jijun
Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), Ministry of Education, School of Physics, Dalian 116024, China.
Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, China.
Nanoscale. 2021 Mar 18;13(10):5479-5488. doi: 10.1039/d0nr09146d.
Two-dimensional MA2Z4 (M = Mo, W, V, Nb, Ta, Ti, Zr, Hf, or Cr; A = Si or Ge; Z = N, P, or As) is a new lead in the 2D family, because it exhibits versatile properties by tuning the components M, A and Z. However, theoretical studies on MA2Z4 are quite limited, and electronic properties are mainly studied by standard DFT levels, which seriously underestimates the band gap. Here, we systematically investigated the electronic properties and nonlinear optical response of MA2Z4 using a hybrid HSE06 functional. It was found that replacing component Z changes the lattice constant most, while the lattice influence by component M substitution is only slight. We showed that the gap difference between PBE and HSE06 is generally about 30% but can be up to 101%. (MIV = Hf, Ti, or Zr)Si2N4 possesses multi-valley characteristics. Furthermore, the second-harmonic generation (SHG) responses of various MA2Z4 composites were also calculated. Three non-zero elements of second order non-linear susceptibilities are revealed for MA2Z4 with the relationship: d16 = d21 = d22, indicating that MA2Z4 belongs to the D3H1 space group. HfSi2N4 possesses a multi-valley characteristic, and exhibits the largest susceptibility under broad wavelengths and the value of d21 reaches 3697.04 pm V-1 at band gap resonance energy. Intriguingly, the non-linear coefficients of MoSi2P4 and MoSi2As4 in the IR region are two orders of magnitude larger than those of other well-known non-linear crystals, such as LiGaS2 and BaAl4S7. We further explored the anisotropic SHG response by the polar plot of intensity under different incident light into MA2Z4. Our work provides theoretical guidelines for further experimental explorations of MA2Z4 and paves the way for its utilization in non-linear optic devices.
二维MA2Z4（M = 钼、钨、钒、铌、钽、钛、锆、铪或铬；A = 硅或锗；Z = 氮、磷或砷）是二维材料家族中的一个新成员，因为通过调整组分M、A和Z，它展现出了多样的性质。然而，关于MA2Z4的理论研究相当有限，并且电子性质主要是在标准密度泛函理论（DFT）水平上进行研究的，这严重低估了带隙。在此，我们使用杂化HSE06泛函系统地研究了MA2Z4的电子性质和非线性光学响应。研究发现，替换组分Z对晶格常数的改变最大，而组分M的替换对晶格的影响较小。我们表明，PBE和HSE06之间的带隙差异通常约为30%，但最高可达101%。（四价M = 铪、钛或锆）Si2N4具有多谷特性。此外，还计算了各种MA2Z4复合材料的二次谐波产生（SHG）响应。对于MA2Z4，揭示了二阶非线性极化率的三个非零元素，其关系为：d16 = d21 = d22，这表明MA2Z4属于D3H1空间群。HfSi2N4具有多谷特性，并且在宽波长范围内表现出最大的极化率，在带隙共振能量处d21的值达到3697.04 pm V-1。有趣的是，MoSi2P4和MoSi2As4在红外区域的非线性系数比其他著名的非线性晶体，如LiGaS2和BaAl4S7大两个数量级。我们通过不同入射光下MA2Z4强度的极坐标图进一步探索了各向异性的SHG响应。我们的工作为MA2Z4的进一步实验探索提供了理论指导，并为其在非线性光学器件中的应用铺平了道路。
