The investigation of elastic anisotropy can significantly advance the understanding and application of the mechanical properties in two-dimensional transition metal dichalcogenides superlattices. Here, we illustrate the utilization of elastic properties-dependent strain to manipulate the anisotropy of MoS2/MoSe2 lateral superlattice (LS). We conduct a comprehensive analysis of the structural and elastic characteristics of MoS2/MoSe2 LS under uniaxial zigzag strain, uniaxial armchair strain, and plane biaxial strain. Through first-principles calculations, we compute the elastic constants over a comprehensive strain series (from-0.06 to 0.06 in increments of 0.02) using the strain-stress relationship. Based on calculated elastic parameters, the shear anisotropy factor, as well as the Young's modulus and Poisson's ratio, indicate pronounced anisotropic behavior in MoS2/MoSe2 LS under uniaxial strains. In contrast, plane biaxial strain does not induce this behavior. These findings demonstrate strain-tuned elastic anisotropy in MoS2/MoSe2 LS not only provides a theoretical foundation for experimental exploration, but also unlocks new opportunities in functional device design-particularly for direction-sensitive strain sensors and advanced nanoelectronic strain engineering.

This study investigates the structural, electronic, and elastic properties of commensurate twisted MoS 2 /MoSe 2 heterobilayers across five specific twist angles through first-principles calculations. We identify a critical angle (30°) that yields an exceptionally flat interface, characterized by a minimal interlayer spacing variation of only 0.017 Å. This distinctive planar morphology originates from a high-symmetry moiré superlattice with spatially uniform stacking configurations. Furthermore, we reveal that the variation in interlayer binding energy is governed by the lattice corrugation, reflected by a larger difference between maximum and minimum bilayer thicknesses. A more pronounced corrugation enables the system to maximize the fractional area of strongly coupled, low-energy stacking domains (e.g., AB-1) while minimizing that of weakly coupled, high-energy regions (e.g., AA). Electronically, the system exhibits a twist-angle-dependent transition between direct and indirect band gaps, while maintaining a robust type-II band alignment across all angles, with band edges localized in the MoSe 2 and MoS 2 layers, respectively. Elastic properties remain nearly unchanged at twist angles greater than 9°. But the Young's moduli of these heterobilayers surpass those of silicene and phosphorene. These findings highlight the potential of twisted MoS 2 /MoSe 2 heterobilayers as a tunable platform for advanced optoelectronic devices.

Manipulating interlayer twist angle represents a potent approach for tuning properties of layered twodimensional crystals. However, limited attention has been given to explore the impact of twist angle on elastic properties. We employ first-principles calculations to investigate how twist angles affect the structure as well as mechanical and thermal characteristics of bilayer MoS2. The in-plane elastic constants of seven twisted structures are determined by fitting the stress-strain relationship linearly. The results indicate all structures exhibit both mechanical stability and elastic isotropy, with exceptional rigidity compared to other twodimensional materials. Based on calculated elastic constants, the thermal parameters, including sound velocities, Gr & uuml;neisen parameter, and Debye temperature are obtained. Moreover, we investigate how tuning the twist angle affects thermal conductivity and observe a decreasing trend with an increase in the moire lattice constant due to the increase of acoustic branches. Notably, at twist angle of 60 degrees, we find a thermal conductivity value of 93.57 Wm-1K-1, whereas at an angle of 9.43 degrees, it reaches 9.09 Wm-1K-1, representing an approximate reduction of 90 % in the thermal conductivity. These findings offer valuable insights into understanding how twisting influences the properties of bilayer MoS2 and establish its potential as a promising material for thermoelectric devices.

The thermal expansion coefficient of two-dimensional (2D) materials is a very important physical parameter when forming heterostructures. Here, we have established a method that can be employed to evaluate the thermal expansion coefficient of 2D hexagonal materials by the computationally feasible elastic parameters, where the monolayer MoS2 is chosen as an example. Using the first-principles calculations, we calculate the elastic constants under different strains from the strain–stress relationship. Then, based on the calculated elastic parameters, the mechanical and thermal parameters of the monolayer MoS2, including bulk moduli, shear moduli, sound velocities, Debye temperature, heat capacity and thermal expansion coefficient, are obtained. The calculation results are in good agreement with those determined by quasi-harmonic phonon calculations and the experimental results. The monolayer WS2 is employed to further confirm the validity of the methodology. This method can also be widely used to investigate the thermal properties of other 2D materials and thin films.

The thermal expansion coefficient of two-dimensional (2D) materials is a very important physical parameterwhen forming heterostructures. However, the thermal expansion coefficient evaluation of 2D materials evaluatedusing elastic properties is not clear. Here, we have established a method that can be employed to evaluate thethermal expansion coefficient of 2D hexagonal materials by the computationally feasible elastic parameters,where the monolayer MoS 2 is chosen as an example. Using the first-principles calculations, we calculate theelastic constants under different strains from the strain-stress relationship. Then, based on the calculated elasticparameters, we obtain the sound velocities, Debye temperature, heat capacity, and thermal expansion coefficientof the monolayer MoS 2 . The calculation results are in good agreement with those determined by quasi-harmonicphononcalculationsandtheexperimentalresults. ThemonolayerWS 2 isemployedtofurtherconfirmthevalidityof the methodology. This method can also be widely used to investigate the thermal properties of other 2Dmaterials and thin films.

基于Python及OpenCV、Matplotlib和Pygame等库开发了一款在三线摆实验中集周期测量、图像绘制、数据处理及实验仿真等功能于一体的软件.实验时用摄像头模块记录下盘标志物运动,在软件内用OpenCV识别并解析数据、Matplotlib绘制实时运动图像、两套独立算法计算周期.此外自制数据记录板块可辅助学生数据处理,以Pygame搭建的二维实验仿真系统可辅助学生学习实验操作.

MoS2/MoSe2 superlattice is a potential candidate for thermoelectric materials. We have theoretically constructed MoS2/MoSe2 vertical and lateral superlattices based on the density functional theory. Here, five possible stacking structures of MoS2/MoSe2 vertical superlattice are considered. The optimized energy of AA1 structure is the lowest. The structural stability, electronic and mechanical properties of AA1 structure and lateral superlattice (LS) are studied. The results shows that AA1 and LS are thermodynamically, dynamically and mechanically stable. The calculated band structures display AA1 is an indirect bandgap semiconductor, while LS is a direct bandgap semiconductor. Furthermore, the sound speed of LS is slightly lower than that of AA1. The sound velocity of LS has a little anisotropy and is minimum in the [01] direction.

为提高TiO2光电极的光电化学性能,采用水热/溶剂热两步法在TiO2纳米棒阵列上合成Bi2MoO6/TiO2异质结构.通过XRD、SEM、TEM、HRTEM、XPS、UV-Vis、PL对样品的物相、形貌、微结构、元素价态和光学性能进行分析,结果表明成功制备了Bi2MoO6/TiO2纳米棒阵列异质结构,Bi2MoO6修饰TiO2拓宽了光谱响应范围.电化学工作站测试表明,Bi2MoO6与TiO2形成异质结构有利于光生载流子的有效分离,获得了增强的光电化学性能.Bi2MoO6/TiO2异质结构(样品BMT-3)具有最大的光电流密度为2.589 mA/cm2,约为TiO2(0.143 mA/cm2)的18倍,具有最大的光转换效率0.287％和最小的电荷转移电阻.能带结构表明,TiO2的导带和价带电位比Bi2MoO6的导带和价带更正.TiO2和Bi2MoO6形成的type II型能带结构与可见光的扩展吸收之间的协同作用是光电化学性能提升的内在机理.

We investigate the influence of biaxial strain on the electronic and thermoelectric properties of Sb2Te3 monolayer by first-principles calculation and semiclassical Boltzmann transport theory. The calculated results of formation energy and phonon spectrum suggest there is a limited strain for Sb2Te3 monolayer. The effective mass of hole increases with the increase of tensile strain, but decreases with the increase of compressive strain. However, the change trend of electron effective mass with strain is opposite to that of hole effective mass. The results of energy band structures show that the Sb2Te3 monolayer is an indirect energy gap semiconductor. Three conduction band valleys almost degenerate together at 5% compressive strain. At this strain, Seebeck coefficient and power factor are improved for n-type doped Sb2Te3 monolayer, suggesting that strain engineering is an effective way to improve the thermoelectric properties of Sb2Te3 monolayer.

本文以不同堆垛方式,构建了5种双层MoSe2结构,分别记为AA、AA1、A1B、AB、AB1.基于第一性原理计算,对5种结构进行结构优化,优化结果显示AA1堆垛方式最为稳定.为探究应变对AA1结构的电子特性的调控作用,对AA1结构施加了-10％～10％的平面双轴应变.能带结构的计算结果表明压缩应变和拉伸应变分别可以改变价带顶和导带底的位置,但是不能让双层MoSe2从间接能隙半导体变成直接能隙半导体.在应变作用下(2.5％压缩应变外),AA1结构的能隙值不断减小.在10％的拉伸应变作用下,能隙值甚至减小到0,让双层MoSe2变为了金属.投影态密度结果表明价带顶和导带底处主要是Mo d和Se p轨道的杂化作用.而双层Mo与Mo原子间距dMo-Mo,Mo与Se原子间的键长dMo-Se,Se-Mo-Se间的夹角α对投影态密度分布都有调控作用.

In order to obtain a recyclable photocatalyst for efficient degradation of organic pollutants under visible light, TiO2 nanorod arrays were modified with Bi2 MoO6 nanosheets by hydrothermal solvothermal two-step method to obtain Bi2 MoO6/TiO2 composite. The morphology, structure, chemical element composition and optical properties of Bi2 MoO6/TiO2 photocatalyst were analyzed, and the photoelectrochemical and photocatalytic properties of Bi2 MoO6/TiO2 photocatalyst were tested with the help of electrochemical workstation in order to analyze the mechanism of enhanced photocatalytic activity. The results show that modification of TiO2 nanorod arrays by Bi2 MoO6 with narrow gap broadens the spectral response range, promotes the effective separation and transfer of photogenerated carriers, and obtains significantly enhanced photocatalytic degradation efficiency of methylene blue. The energy band structure diagram shows that type II heterojunction is formed between TiO2 and Bi2 MoO6 , which promotes the separation and transfer of photogenerated electron holes. The synergistic effect between type II band structure of Bi2 MoO6/TiO2 and the extended absorption of visible light is the internal mechanism for the improvement of photocatalytic properties.

The effects of Zn atoms on the electronic and optical properties of CuGaSe2 have been investigated by the first-principles calculations. In this work, we discuss three possible substitution ways for Cu and Ga atoms of CuGaSe2 substituted by Zn atoms. First, we estimate the formation energies of Zn-substituted CuGaSe2. And then the energy band structures, densities of state and optical properties are calculated with MBJ-LDA. The spectra of reflectivity and absorption coefficients show that the participation of Zn can reduce the reflectivity of CuGaSe2 in the range 1–5 eV, and improve the absorption coefficients of solar cells in the low energy range.

The electronic and optical properties of CuGaSe2 with different anion positions have been investigated by the first principles calculations. The crystal structures are optimized by two different methods, namely fixing the tetragonal distortion and constraining the fractional position of anion only. The optimized lattice parameters are slightly inconsistent with the results proposed by Abrahams and Bernstein. The band structure, density of states, dielectric functions, absorbance and reflectivity are calculated, using the modified Becke Johnson (mBJ) potential. CuGaSe2 with different anion positions are direct-gap semiconductors. When the anion position changes from 0.2 to 0.3, CuGaSe2 has strong absorption capacity, low reflectivity in visible light range and wide adjustable band gap, which means we can optimize the properties of CuGaSe2 by controlling the fractional position of anion.

Recently, many monolayer materials have been reported as a kind of potential thermoelectric materials. And motivated by the idea of improving thermoelectric performance via strain-induced band degeneracy, we investigate the influence of strain on the electronic and thermoelectric properties of Sb2Te3 monolayer by first-principles calculations and semiclassical Boltzmann transport theory. The results of calculated energy band structures demonstrate that three valence and three conduction band valleys almost degenerate together at 0.075 tensile strain and 0.05 compressive strain, respectively. At these strains, the increase of Seebeck coefficients and power factors are obtained for the p-type and n-type doped Sb2Te3 monolayer at room temperature, suggesting that strain is an effective way to improve the thermoelectric properties of Sb2Te3 monolayer.

采用第一性原理方法,研究了高压下黄铜矿半导体CuInS2的电子结构、弹性参数、热学和电学性质.研究结果表明CuInS2是直接能隙半导体,其能隙值随着压强的增大而增大,能隙随压强变化的一阶系数值为54.31 meV/GPa;其弹性参数满足高压下的机械稳定性的条件,并且材料的韧性随着压强的增加而增强.基于弹性参数计算了体系的德拜温度和最小热导率,德拜温度随着压强的增大而逐渐减小,而最小热导率随着压强的增加而增大.通过对塞贝克系数和功率因子比弛豫时间的研究,发现增加压强和调节载流子的浓度可以改善CuInS2的电学性能.

The influence of vacancy on electronic, mechanical and thermal properties of CuGaTe2 are investigated by first-principle calculations. The calculated formation energies are found to be lowest for vacancy at Cu site. The electronic properties display the energy gap, effective mass and density of states for CuGaTe2 with Cu vacancy at the Fermi energy level are increased. The results of elastic constants show that CuGaTe2 with Cu vacancy is mechanical stability. Based on the calculated elastic constants, the bulk modulus, shear modulus, sound velocities, Grunesian parameter and Debye temperature are estimated. By combining these calculated results and few well established models, low thermal conductivity is predicted. The analytical calculations reveal the reduction of Cu can effectively reduce the thermal conductivity, which may be the one way to enhance the thermoelectric properties of CuGaTe2.

The effects of copper-vacancy on the electrical, optical and thermoelectric properties of CuInTe2 have been investigated by the first-principles calculations and semi-classical Boltzmann theory. The estimated results of copper vacancy formation energies for Cu(1-x)nTe(2) (x = 0, 1/16, 1/8 and 1/4) showed it is more difficult to prepare the sample with higher copper vacancy concentration. From the calculated energy band structures with MBJ-GGA, it can be seen that they are p-type semiconductors and the energy gap values increase with the vacancy concentration increasing. The wavelength is smaller than 460 nm, and the high copper vacancy concentration (x = 1/4) is helpful to the values of absorption coefficient, while above 460 nm, the lower copper vacancy concentration (x = 1/16) is able to enhance the absorption coefficient. The lower copper vacancy concentration (x = 1/16) is more favorable to improve the power factor in low or middle temperature. However, the high copper vacancy concentration (x = 1/4) is better in high temperature. These results give hints for the design of CuInTe2 as the good photovoltaic and thermoelectric materials.

The effects of various anion displacements (u) on electronic structures, elastic constants, Debye temperature and the minimum thermal conductivity of CuInS2 are studied by first-principles calculation. The lattice constant couples with the anion displacement, however, they are not consistent with the relation proposed by Abrahams and Bernstein. When the anion displacement varies from 0.2 to 0.3, the Cu-S bond length is elongated, while the In-S bond length is shortened, which cause the increase of band gap with anion displacement. The anisotropies of sound velocities and lattice thermal conductivities are also discussed. The results imply that the lattice thermal conductivity along [110] direction is the smallest and decreases with u. These research findings shed light on improving the thermoelectric properties by manipulating u and the direction of propagation.

本文以我校湖北科技学院光电专业新实践课程的教学目标,培养学生思考能力、动手能力、分析和解决问题的能力为出发点,从实践课程的选题、指导方式、考核标准三个方面进行改革探索,初步建立光电专业实践课程的新模式,使学生能更清楚地掌握光电专业相关专业知识,提高学生们的综合素质,为以后工作奠定基础.

Based on the density functional theory, the influences of strain on structural, elastic, thermal and optical properties of CuGaTe 2 are discussed in detail. It is found that the tensile strain on CuGaTe 2 is beneficial to the decrease of lattice thermal conductivity by reducing the mean sound velocity and Debye temperature. Moreover, all strained and unstrained CuGaTe 2 exhibit rather similar optical characters. But the tensile strain improves the ability to absorb sunlight in the visible range.These research findings can give hints for designing thermoelectric and photovoltaic devices.