应变对Mo2C(001)表面电子结构及光学性质的影响

采用第一性原理方法研究应变对Mo₂C(001)表面电子结构及光学性质的影响。研究表明,在应变作用下Mo₂C(001)表面均为间接带隙半导体,带隙随着压应变和拉应变的增加而减小。当应变为-20%时,Mo₂C(001)表面由间接带隙半导体转变为金属性质。当应变为-20%、-15%、-10%、-5%、0%、5%、10%、15%、20%时,其带隙分别为0 eV、0.162 eV、0.376 eV、0.574 eV、0.696 eV、0.708 eV、0.604 eV、0.437 eV、0.309 eV。带隙变化的原因主要是Mo 4p、4d、5s态电子和C 3p态电子对应变敏感,在应变作用下受激发,活性增强导致价带顶在布里渊区G、A、L、M点之间变化,导带底在K、H点之间变化;当应变由-15%逐渐变化到20%时,吸收谱的第一峰逐渐减弱,并且第一峰对应的光电子能量减小,吸收带边向低能方向移动,表明光吸收随着压应变增大而增加,吸收带边随着拉应变增加向低能方向移动。其他光学性质表现出类似的变化规律,光学性质计算结果表明应变能够有效调节光吸收特性,增强光学利用率,研究结果为Mo₂C(001)作为新型光电子材料的应用提供理论支撑。

Effects of Strain on Electronic Structure and Optical Properties of Mo2C (001) Surface

The effect of strain on the electronic structure and optical properties of Mo₂C(001) surface were studied by the first-principles method. The band structure results show that Mo₂C(001) surface is an indirect band gap semiconductor, and the band gap decreases with compressive strain and tensile strain increasing. When the strain is -20%, Mo₂C surface (001) changes from an indirect band gap semiconductor to metal. When the strain is -20%, -15%, -10%, -5%, 0%, 5%, 10%, 15% and 20%, the band gap is 0 eV, 0.162 eV, 0.376 eV, 0.574 eV, 0.696 eV, 0.708 eV, 0.604 eV, 0.437 eV and 0.309 eV, respectively. The reason for the change of band gap is mainly that, the electrons of Mo 4p, 4d, 5s and C 3p states become sensitive to each other are excited under difference strains, and the activity is enhanced. The results valence band top is changed among the points of G, A, L and M, and the conduction band bottom is changed between the points K and H in Brillouin region. When the strain gradually changes from -15% to 20%, the first peak of the absorption spectrum gradually decreases, the photoelectron energy corresponding to the first peak decreases, and the absorption band edge moves to the low energy direction, indicating that the optical absorption increases with the increase of compressive strain, and the absorption band edge moves to the low energy direction with the increase of tensile strain. At the same time, other optical properties show similar changes with the strain change. The calculation results of optical properties show that the strain effectively adjust the optical absorption characteristics. The research results provide theoretical support for the application of Mo₂C (001) as new optoelectronic material.