Substitutional Coinage Metals as Promising Defects for Adsorption and Detection of Gases on MoS 2 Monolayers: A Computational Approach.

Defective molybdenum disulfide (MoS 2 ) monolayers (MLs) modified with coinage metal atoms (Cu, Ag and Au) embedded in sulfur vacancies are studied at a dispersion-corrected density functional level. Atmospheric constituents (H 2 , O 2 and N 2 ) and air pollutants (CO and NO), known as secondary greenhouse gases, are adsorbed on up to two atoms embedded into sulfur vacancies in MoS 2 MLs. The adsorption energies suggest that the NO (1.44 eV) and CO (1.24 eV) are chemisorbed more strongly than O 2 (1.07 eV) and N 2 (0.66 eV) on the ML with a cooper atom substituting for a sulfur atom. Therefore, the adsorption of N 2 and O 2 does not compete with NO or CO adsorption. Besides, NO adsorbed on embedded Cu creates a new level in the band gap. In addition, it was found that the CO molecule could directly react with the pre-adsorbed O 2 molecule on a Cu atom, forming the complex OOCO, via the Eley-Rideal reaction mechanism. The adsorption energies of CO, NO and O 2 on Au 2S2 , Cu 2S2 and Ag 2S2 embedded into two sulfur vacancies were competitive. Charge transference occurs from the defective MoS 2 ML to the adsorbed molecules, oxidizing the later ones (NO, CO and O 2 ) since they act as acceptors. The total and projected density of states reveal that a MoS 2 ML modified with copper, gold and silver dimers could be used to design electronic or magnetic devices for sensing applications in the adsorption of NO, CO and O 2 molecules. Moreover, NO and O 2 molecules adsorbed on MoS 2 - Au 2 s 2 and MoS 2 - Cu 2 s 2 introduce a transition from metallic to half-metallic behavior for applications in spintronics. These modified monolayers are expected to exhibit chemiresistive behavior, meaning their electrical resistance changes in response to the presence of NO molecules. This property makes them suitable for detecting and measuring NO concentrations. Also, modified materials with half-metal behavior could be beneficial for spintronic devices, particularly those that require spin-polarized currents.