单层W_(x)Mo_(1-x)S_(2)合金电子和光学性质的第一性原理研究

Electronic and Optical Properties of Monolayer W_(x)Mo_(1-x)S_(2) Alloys:a First-principles Study

采用基于密度泛函理论(DFT)的第一性原理方法对W_(x)Mo_(1-x)S_(2)(x=0,0.25,0.5,0.75,1)单层合金的电子结构和光学性质进行了较为系统的研究。计算结果表明:合金的带隙都为直接带隙,随着W含量增加可由1.802 eV增加至1.940 eV,但并不是线性增加。电荷差分密度图计算结果显示,随着W含量的增加,Mo原子失电子数逐渐增加,W原子得电子数逐渐增加。合金的光学性质可随着W含量的变化调谐。随着W含量的增加,W_(x)Mo_(1-x)S_(2)合金的静态介电常数逐渐减小,虚部吸收阈值逐渐增大,吸收边向高能区移动。与本征Mo_(16)S_(32)相比W_(x)Mo_(1-x)S_(2)合金在紫外光区域(6~8.5 eV)表现出更强的紫外吸收能力,而W_(12)Mo_(4)S_(32)和W_(16)S_(32)合金在可见光区域(~3 eV)有着更高的吸收系数,这在理论上表明此类单层合金在可见光及近紫外光区域可应用于光电信号的探测。

First-principles calculations are employed on the electronic and optical properties of W_(x)Mo_(1-x)S_(2)(x=0,0.25,0.5,0.75,1)monolayer alloys under the direction of density functional theory calculations.The calculated results indicate that the band gaps of the alloys,which will be increased nonlinearly from 1.802 eV to 1.940 eV with the increase of W content,are all direct band gaps.It is shown in the calculated results of charge differential density that both the number of electrons lost by Mo atom and that of electrons gained by W atom increase gradually as W content climbs.The optical properties of the alloys can be tuned with the change of W content.With the increase of W content,the static dielectric constant gradually decreases,the absorption threshold of the imaginary part gradually increases,and the absorption edge moves to the high energy range.Compared with original Mo_(16)S_(32),W_(x)Mo_(1-x)S_(2) alloys have stronger absorption ability in the ultraviolet range(6—8.5 eV),while W_(12)Mo_(4)S_(32) and W_(16)S_(32) alloys have higher absorption coefficient in the visible range(~3 eV),indicating in theory that the sort of the monolayer alloys can be applied to the detection of photoelectric signals in visible light and near ultraviolet range.