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构建范德瓦耳斯异质结是丰富二维材料物性并增强其光电等性能的有效策略. 本文基于第一性原理模拟, 系统地研究了两种不同界面结构的Janus MoSSe/g-C3N4异质结(即SMoSe/g-C3N4和SeMoS/g-C3N4)的电子性质及其双轴应变调控规律. 结果表明, 针对SMoSe/g-C3N4异质结构, MoSSe本征偶极场与界面电场方向一致, 相互叠加形成由g-C3N4指向MoSSe的增强电场, 体系呈现I型能带排列特征; 而在SeMoS/g-C3N4异质结构中, 两者方向相反, 部分相互抵消后形成由MoSSe指向g-C3N4的净电场, 呈现II型能带排列特征, 可促进载流子的分离从而有效提升其光催化分解水活性. 进一步研究发现, 施加双轴应变可有效地调节两种异质结构的电子能带, 尤其在SeMoS/g-C3N4中可实现I型与II型能带结构的可逆转变. 本研究为Janus MoSSe/g-C3N4异质结在光催化与光电器件领域的应用提供了理论依据.Constructing van der Waals (vdW) heterostructures has emerged as an effective strategy for enriching the physical properties of two-dimensional materials and optimizing their optoelectronic performance. In this work, we systematically investigate the electronic properties and biaxial strain modulation of Janus MoSSe/g-C3N4 heterostructures with two distinct interfacial configurations—SMoSe/g-C3N4 and SeMoS/g-C3N4—by means of first-principles simulations. Binding energy comparisons and AIMD simulations are performed to determine the most stable stacking pattern of each type of the heterostructure. The analyses of the electrostatic potential and work function reveal that the intrinsic dipole of MoSSe layer and the interfacial electric field in the SMoSe/g-C3N4 heterostructure undergo a constructive superposition. This enhances the overall built-in electric field, which points from g-C3N4 layer to MoSSe layer, resulting in a type-I band alignment. In contrast, in the SeMoS/g-C3N4 configuration, the two fields oppose each other, leading to a net electric field directed from MoSSe to g-C3N4 layer. This leads to a type-II band alignment, which facilitates spatial carrier separation and significantly enhances photocatalytic water-splitting activity. Furthermore, this study also demonstrates that biaxial strain can effectively modulate the electronic band structures of both types of heterostructures. In particular, the SeMoS/g-C3N4 system exhibits a reversible transition between type-I and type-II band alignments under specific compressive (–4%) and tensile (+5%) strain states. The underlying mechanism is elucidated by the difference charge density calculations. This study provides theoretical insights into the role of interfacial and intrinsic dipoles combined with strain engineering, offering a viable route for designing efficient MoSSe/g-C3N4-based photocatalysts and optoelectronic devices.
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Keywords:
- heterostructure /
- electronic band structure /
- strain engineering /
- first-principles simulations
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图 1 (a) 单层MoSSe和(b) g-C3N4的俯视图和侧视图. 黑色框为MoSSe和g-C3N4的单胞结构; (c) SMoSe/C3N4(A1—A6)和SeMoS/ g-C3N4(B1—B6)不同堆叠构型的俯视图和侧视图, 其中A2—A6, B2—B6分别由A1, B1以60°间隔依次顺时针旋转MoSSe层得到的异质结构(黑色虚线框内为最小超胞, A2和B2上的阴影突出了结合能最低的堆叠构型); (d) A2与(e) B2异质结构声子谱; (f) A2与(g) B2异质结构AIMD模拟的能量变化
Fig. 1. (a) Top and side views of single-layer MoSSe and (b) g-C3N4. The black box indicates the unit-cell structure of MoSSe and g-C3N4; (c) top view and side view of different stacking configurations of SMoSe/g-C3N4 (A1–A6) and SeMoS/g-C3N4 (B1–B6). Among them, A2–A6 and B2–B6 are heterostructures obtained by rotating the MoSSe layers of A1 and B1 clockwise by 60° respectively (the smallest computational supercell is indicated by the black dashed box, and the shadows on A2 and B2 highlight the stacked configuration with the lowest binding energy); Phonon spectrum of (d) A2 and (e) B2 heterostructure; AIMD simulation results for (f) the A2 and (g) B2 heterostructure.
图 2 (a) 单层MoSSe和(b) g-C3N4的能带; (c) A2和(d) B2的投影能带(费米能级均已设为0); (e) A2和(f) B2的投影态密度
Fig. 2. Energy band structures of single-layer (a) MoSSe and (b) g-C3N4; projected energy bands of (c) A2 and (d) B2 (Fermi levels have all been set to 0); projected densities of states of (e) A2 and (f) B2.
图 3 A2差分电荷密度(a) 俯视图 和(c) 侧视图; B2差分电荷密度(b) 俯视图和(d) 侧视图(黄色为正, 代表电子积聚; 蓝色为负, 代表电子消耗); 单层(e) MoSSe和(f) g-C3N4的静电势; A2(g) 和B2(h)的静电势
Fig. 3. Differential charge density diagrams for (a) top view and (c) side view of A2; differential charge density diagrams for (b) top view and (d) side view of B2 (yellow indicates positive, representing electron accumulation; blue indicates negative, representing electron consumption); the electrostatic potential of the single-layer (e) MoSSe and (f) g-C3N4; the electrostatic potentials of (g) A2 and (h) B2.
图 4 MoSSe, g-C3N4, A2和B2异质结在不同PH值下的带边位置
Fig. 4. Band edge positions of MoSSe, g-C3N4, A2 and B2 heterostructures at different PH values.
图 5 (a) A2和(b) B2异质结构带边位置及带隙值随应变的变化
Fig. 5. Dependences of the band edge positions and band gap values of the A2 (a) and B2 (b) heterostructures on the applied biaxial strain.
图 6 (a) B2异质结构在不同拉应变作用下的平面平均差分电荷密度; (b) B2异质结构在不同压应变作用下的平面平均差分电荷密度
Fig. 6. (a) Planar average differential charge density of B2 heterostructure under different tensile strains; (b) planar average differential charge density of B2 heterostructure under different compressive strains.
表 1 SMoSe/g-C3N4(A1—A6)和SeMoS/g-C3N4(B1—B6)不同堆叠构型的黏附功
Table 1. Adhesion energies for different stacking configurations of SMoSe/g-C3N4 (A1–A6) and SeMoS/g-C3N4 (B1–B6).
堆叠类型 A1 A2 A3 A4 A5 A6 黏附功/(J·m–2) 0.135213 0.135218 0.135108 0.135205 0.134514 0.134329 堆叠类型 B1 B2 B3 B4 B5 B6 黏附功/(J·m–2) 0.167633 0.167926 0.167737 0.167705 0.167188 0.167301 
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