Exceptional piezoelectricity, high thermal conductivity and stiffness and promising photocatalysis in two-dimensional MoSi2N4 family confirmed by first-principles

Manipulable Electronic and Optical Properties of Two-Dimensional MoSTe/MoGe2N4 van der Waals Heterostructures

“…Its CBM is located at the K point and is mainly contributed from Mo-d orbitals, while the VBM is located in the K-Γ path in the 2D hexagonal Brillouin zone and mainly comes from strong hybridization between Mo-d, N-p, and Ge-s orbitals. These results are consistent with the previously reported results [22].…”

“…At present, people have revealed the physical properties of the MA 2 Z 4 monolayer through first principles calculations, such as structural stability, electronic properties, visible absorption coefficient, Rashba spin splitting, carrier mobility, and so on. These findings revealed that the fascinating MA 2 Z 4 families are promising 2D materials for many applications due to their outstanding properties [21][22][23][24][25]. Transition metal nitride (TMN) monolayers in this family, such as MoSi 2 N 4 and MoGe 2 N 4 , are promising candidates for optoelectronic nanodevices [26][27][28][29].…”

Novel Two-Dimensional Layered MoSi2Z4 (Z = P, As): New Promising Optoelectronic Materials

“…Motivated by the exciting properties of MoSi 2 N 4 and WSi 2 N 4 , some theoretical works have been carried out to further explore the mechanical and physical properties of their family by using the first-principles calculation method [19,20]. The lattice thermal conductivity, piezoelectric and flexoelectric response, and photocatalytic and electronic feature of monolayer MA 2 Z 4 (M = Cr, Mo, W; A = Si, Ge; Z = N, P) were systematically calculated.…”

“…They show diverse electronic properties from antiferromagnetic metal to half metal and semiconductor with band gaps ranging from 0.31 to 2.57 eV. Monolayer MoSi 2 N 4 and WSi 2 N 4 were predicted to show outstandingly high lattice thermal conductivity of 440 and 500 W/mK, respectively [19]. The piezoelectricity property was calculated for six different configurations of MSi 2 N 4 (M = Mo, W) which are built through translation, mirror and rotation operations.…”

Plane Strain on Band Structures and Photoelectric Properties of 2D Monolayer MoSi2N4

“…Key words: two-dimensional material; plane strain; photoelectric property; first-principles calculations 通过微机械剥离技术获得石墨烯以来 [1] ，二维 (2D)材料凭借优异的光学、电学、热学等特性在诸 多领域掀起了研究热潮 [2−4] 。近几年，以 二硫化钼为 代表的二维过渡金属硫化物(TMDs)因具有稳定的 类石墨烯层状结构、超大比表面积与高热导率而广 泛应用于光催化 [5] 、太阳能电池 [6] 、传感器 [7] 和超级 电容器 [8] 等前沿领域。尤其是片层状二硫化钼结构 适配性强且能带结构易于调控，可以实现可见光至 近红外的连续探测光谱响应，使其在纳米光电子器 件领域具有极大的应用潜力 [9] 。但众多研究显示单 层二硫化钼的器件响应速度并不高，主要原因在于 其较高的光生电子−空穴复合率和较低的载流子输 运能力。 新近，通过化学气相沉积法首次制备出结构稳 定的二维单层 MoSi2N4 薄膜，其本征光生载流子迁 移率为单层 MoS2 的 4 至 6 倍 [10][11] 。随后，研究人 员开展了大量工作以探索其力学、热学等方面的性 质。单层 MoSi2N4 具有出色的机械性能，拥有比石 墨烯更大的泊松比且在双轴应变下可以承受高达 50. 6 GPa 的拉伸强度 [12][13] 。通过迭代求解玻尔兹曼 输运方程发现其在室温下的固有晶格热导率为 224 W/mK，远高于部分常见的半导体材料 [14] 。垂直压 缩应变驱动双层 MoSi2N4 内部界面处不对称性电荷 的重新分布，使其由半导体性质过渡为金属性质， 为其可调谐电子性质的理论研究提供了重要指导 [15] 。此外，在 MoSi2N4/NbS2 异质结构中还观察到较 低的肖特基势垒高度，将为构建全新的范德瓦尔斯 异质结构器件创造更多的可能性 [16] 。这些进展主要 集中在材料固有性质的探索与改性等方面 [17][18] ，但 其平面应变对能带结构与光电性质影响的系统研究 尚未展开，所表现出较高的载流子迁移率和较强的 光吸收能力的物理机理仍有待深入分析。另外，上 述研究中常通过构建具有特殊基底材料的悬臂装置 达到施加应变的目的，但实际探测过程复杂且结果 分析周期较长 [19][20][21] [22] 。 通过广义梯度近似(GGA)的 PBE 方案 [23] 处理 电子间相互作用的交换关联能，计算不同程度平面 应变下单层 MoSi2N4 总能量的变化情况时还考虑了 局域密度近似(LDA)的 CA−PZ 方案 [24] 。 在描述离子 实与价电子之间的相互作用时， 选取价电子组态为： N: 2s 2 2p 2 、Si: 3s 2 3p 2 、Mo: 4s 2 4p 6 4d 5 5s 1 ，其他轨道视 为芯电子进行计算。为了提高计算精度，平面波截 断能取为 320 eV。自洽精度设为每个原子能量收敛 至 2.0×10 -6 eV，第一布里渊区按 8×8×1 进行分格， 达到收敛性要求。采用 BFGS 算法对结构模型进行 优化，每个原子能量收敛至 5.0×10 -6 eV 内，原子受 力不超过 0.01 eV/nm ，原子的最大位移不超过 5×10 −4 nm。 所有计算均通过 CASTEP 软件完成 [25]…”