第一性原理研究MoS2/WS2异质结构的界面电子性质

摘要

构建异质结构是提高光催化材料量子效率的有效策略,而二维材料最重要的特征是平面内极高的载流子迁移率,将上述二者优势结合是设计高效光催化材料体系的热点.二维过渡金属硫化物MoS2和WS2较小的晶格失配和完全相同的晶体结构,使得它们在结合形成不同异质结构时具有极小的界面弛豫和界面结合能.当二者结合形成平面内无缝异质结构时,几乎保留了各自单分子层时的电子结构特征,而界面处能带的相对移动和界面内建电场的产生将有利于光生电子-空穴对的异向转移,从而能够提高光催化的量子效率.当二者以垂直堆垛方式形成双层异质结构时,由于层间较弱的范德瓦尔斯相互作用保证了二维晶体面内的稳定性,使得对应的异质结构呈现出类似体相时的电子结构.构建垂直堆垛的范德瓦尔斯异质结构虽然不能利用二维材料平面内极高的载流子迁移率,但是这种方式结合形成的异质结构能带有明显的下移,这将有利于氧化还原电势的明显增强.计算结果能够加深对以二维材料为基础构建高效、具有异质结构的光催化材料的理解,并对进一步开发高效光催化材料和器件提供有价值的参考.%Construction of heterogeneous structure is an effective stratagem to improve the quantum efficiency of photocatalytic materials.On the other hand,the outstanding characteristic of two dimensional materials is the ultra-high mobility of carrier in the crystal plane.To combine above advantages is the hot-spot subj ect in the field of high efficient photocatalysts.The small lattice mismatch and the identical crystal structure of MoS2 and WS2 in the present work make them possess very insignificant interface relaxation and interface binding energy, when they are combined together to form six different hetero-structures.When they are combined to form the seamless in-plane hetero-structures,they almost retain the electronic structure characteristics of each single mo-lecular layer.Moreover,the relative band-shifting and built-in electric field at the interface is very benefit for the anisotropic transfer of photo-generated electron-hole pairs,leading to enhance the photocatalytic quantum efficiency.When they are combined to form vertical stacking double hetero-structure,they present the similar e-lectronic structure characteristics with each bulk phase,due to the interlayer weak Van Der Waals interaction that ensure the stability of two-dimensional crystal plane.Although vertical stacking Van Der Waals hetero-structures between MoS2 and WS2 cannot use the advantages of ultra-high mobility of carriers,but the energy bands of this type of hetero-structure are obviously down-shifting,resulting in the enhancement of redox poten-tial.These results can enhance the understanding for the high efficient photocatalyst based on two-dimensional materials,and is helpful to the further development of novel photocatalytic materials and devices.