V掺杂二维MoS_2体系气体吸附性能的第一性原理研究

以芥子气和沙林为代表的毒剂具有毒性强、扩散快的特点,是一类杀伤力强、难以防护的化学战剂,对其快速高效检测是一项具有挑战性的课题.本文基于第一性原理计算方法研究了V掺杂对二维MoS_2气敏性能影响的机理,发现V原子向二维MoS_2的掺杂过程为自发的放热反应, V原子可以稳定掺杂于二维MoS_2超胞结构中的S空位上.掺杂进入二维MoS_2体系的V原子作为施主中心向周围Mo原子给出电子,从而提高了材料的导电能力.吸附能、吸附距离和吸附过程中的电子转移计算结果表明V的掺杂提高了二维MoS_2对气体分子的吸附能力,增强了吸附质分子与基底表面的电子相互作用,从而提高了二维MoS_2的气敏性能.

First-principles investigations on gas adsorption properties of V-doped monolayer MoS2

With their high toxicity and fast diffusion,toxic agents such as mustard gas and sarin are chemical warfare agents that are of high lethality and difficult to protect against.Therefore the high-sensitivity detection of toxic agents has become a focus in research on chemical detection in the world.Two-dimensional(2D)MoS2 is at the forefront of research because of its unique structure and promising sensing performance.In this study,theoretical calculations based on the first-principles method are carried out to investigate the structural stability,electronic properties,and gas adsorption of 2D MoS2 before and after V doping in order to explain the gas-sensing mechanism of V-doped 2D MoS2.The binding energy of V atom at the S-vacancy is–6.85 eV,indicating that the V atom can be stably doped into the S vacancy of the 2D MoS2 supercell structure at room temperature due to the strong interaction between the doped V atom and S vacancy of monolayer MoS2.The V atom doped into the 2D MoS2 system gives out electrons to surrounding Mo atoms as a donor center,thus enhancing the electric conductivity of the material.The calculation of adsorption energy indicates that the adsorption process of NO2,NH3,sarin,and mustard gas on the surface of 2D MoS2 are all spontaneous exothermic reactions.The doping of V increases the adsorption capacity of 2D MoS2 for the 4 aforesaid gases,and strengthens the interaction between the electrons of the absorbate molecules and those of substrate surface,thus effectively enhancing the gas-sensitive property of 2D MoS2.This effect occurs due to the strong overlap between the V 3d orbitals and gas molecule orbitals,which promotes the activation of the adsorbed gas molecules.The analysis of Bader charge shows that the charge transfer occurs from V-doped monolayer MoS2 to the oxidizing gas molecules(NO2,sarin,and mustard gas)acting as acceptors.Whereas the direction of charge transfers is reversed for the adsorption of the reducing gas(NH3)behaving as donors,in which 0.11e transfer from adsorbed gas to metal V-doped monolayer MoS2.Our results suggest that V-doped monolayer MoS2 is an ideal candidate for low-cost,highly active,and stable gas sensors,which provides an avenue to the design of high active 2D MoS2-based gas sensors.