氢化二维过渡金属硫化物的稳定性和电子特性:第一性原理研究

用氢对单层二维过渡金属硫化物(TMDs)进行功能化是调节单层TMDs电子性质的既有效又经济的方法.采用密度泛函理论,对单层TMDs (MX_2 (M=Mo, W; X=S, Se, Te))的稳定性和电子性质进行理论研究,发现在单层MX_2 的层间有一个比其表面更稳定的氢吸附位点.当同阳离子时,随着阴离子原子序数的增加, H原子与MX_2 层的结合越强,氢化单层MX_2 结构越稳定;相反,同阴离子时,随着阳离子原子序数的增加, H原子与MX_2 层的结合越弱.氢原子从MoS_2的表面经层间穿越到另一表面的扩散势垒约为0.9 eV.氢化对单层MX_2 的电子特性也会产生极大的影响,主要表现在氢化实现了MX_2 体系从无磁性到磁性体系的过渡.表面氢化会使MX_2 层的带隙急剧减小,而层间氢化使MX_2 的电子结构从半导体转变为金属能带.

Stability and electronic structure of hydrogenated two-dimensional transition metal dichalcogenides: First-principles study

Chemical functionalization of two-dimensional transition metal dichalcogenides (TMDs) with hydrogen is an effective and economical method to synthesize monolayer TMDs and tune their electronic properties. We theoretically study the stabilities and electronic properties of chemisorbed H atoms on monolayer TMDs by using density-functional theory calculations. The result shows that there exists a more stable adsorption site in the layers of the monolayer MX₂ (M=Mo, W; X=S, Se, Te) than its surface for hydrogen. In the case of the same cation, with the increase of the anion (X^2-) atomic number, the stronger the bonding between the H atom and the MX₂ layer, the more stable the structure of the hydrogenated monolayer MX₂ is. However, in the case of the same anion, the binding between the H atom and the MX₂ layer becomes weaker as the atomic number of the cations increases. H atoms passes through one surface of the MS₂ to the other surface with a relatively small diffusion barrier of about 0.9 eV. So the H atoms can more easily go through the barrier. And for the H atom to go through the other monolayer MX₂ (M=Mo, W; X=Se, Te), the diffusion barrier is about 1.2 eV. H atoms are difficult to pass through the barrier at this time. The singular diffusion behavior of H atoms in monolayer MX₂ is conducible to understanding the stability of hydrogenated two-dimensional transition metal sulfide system. In addition, the surface hydrogenation and interlaminar hydrogenation have different effects on the electronic properties of monolayer MX₂, and mainly manifest themselves in the fact that the surface hydrogenation induces spontaneous magnetism and sharply reduces the band gap, but still retains the semiconductor properties of the original monolayer MX₂. However, interlaminar hydrogenation enables monolayer MX₂ to directly realize the transition from semiconductor to metal. Interlaminar hydrogenation monolayer MX₂ (M=Mo, W; X=S, Se) make the system generating magnetism, while when the anion is Te^2-, the magnetism almost disappears. These results can provide theoretical guidance in understanding hydrogen functionalization of MX₂ layer, and also present a certain theoretical basis for realizing the application of MX₂ in nano-electronic devices.