Superior Gas Sensing Properties of Monolayer PtSe₂

Abstract

non-self-consistent calculation, respectively. We study a 4 × 4 supercell of monolayer PtSe 2 with one gas molecule adsorbed, which eliminates intermolecular interaction. Specifically, we employ the optimized in-plane lattice parameter of 3.72 Å and add a vacuum slab of 20 Å thickness in the out-of-plane direction for our slab model. The structural relaxation is assumed to be converged when the Hellmann-Feynman forces have dropped below 0.005 eV Å −1 for all atoms.Monolayer PtSe 2 consists of Pt atoms sandwiched between Se atoms such that a top view shows a hexagonal structure with Pt and Se atoms located at alternating corners and an additional Se atom in the center of each hexagon. To determine the favorable adsorption sites for gas molecules, we consider adsorption (1) on top of the center of a hexagon (H-site), (2) on top of a Se atom (Se-site), (3) on top of a Pt atom (Pt-site), and (4) on top of a PtSe bond (B-site). Initially the center of mass of the molecule is positioned at these sites and different orientations are assessed. For example, for NO the molecular axis can be oriented parallel to the monolayer or perpendicular with the N or O atom pointing to the monolayer. A quantitative assessment of the adsorption strength is possible by means of the adsorption energy E a = E(PtSe 2 + molecule) − E(PtSe 2 ) − E(molecule), where the individual terms represent the total energies of monolayer PtSe 2 with adsorbed gas molecule, pristine monolayer PtSe 2 , and an isolated gas molecule, respectively. Negative values of E a reflect exothermic adsorption.For each gas molecule and adsorption site the calculated adsorption energy and relaxed height of the molecule above the monolayer are given in Table 1. While adsorption energies can vary for different exchange correlation functionals, we are here only interested in relative adsorption energies to identify the most favorable geometry. For this reason our analysis is also not limited by the fact that discrepancies persist in the adsorption energies calculated with different methods to model the van der Waals interaction. [28][29][30] We note that the adsorption energies in Table 1 compare well to both MoS 2 and graphene, [15,21] 2D materials have huge potential in future nanodevices, particularly transition metal dichalcogenides (TMDCs), which therefore are studied extensively in recent years. [1][2][3][4][5] TMDCs can have diverse electronic properties (metallic, [6] half-metallic, [7] semiconducting, [8] and superconducting [9] ), depending on the number of transition metal d electrons and the structural polytype. [10] However, intrinsic limitations such as the relatively low carrier mobility in MoS 2[8] call for further research. Monolayer PtSe 2 can provide an enhanced mobility and thus is of great interest for electronic applications. [11] Sensing of toxic gases is a critical task, for example, in pollution monitoring. [12] 2D materials are ideal for such purposes because of their high surface-to-volume ratio and the often strong charge transfer to/from adsor...

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