High Selectivity Gas Sensing and Charge Transfer of SnSe₂

Abstract

SnSe 2 is an anisotropic binary-layered material with rich physics, which could see it used for a variety of potential applications. Here, we investigate the gas-sensing properties of SnSe 2 using first-principles calculations and verify predictions using a gas sensor made of few-layer SnSe 2 grown by chemical vapor deposition. Theoretical simulations indicate that electrons transfer from SnSe 2 to NO 2 , whereas the direction of charge transfer is the opposite for NH 3 . Notably, a flat molecular band appears around the Fermi energy after NO 2 adsorption and the induced molecular band is close to the conduction band minimum. Moreover, compared with NH 3 , NO 2 molecules adsorbed on SnSe 2 have a lower adsorption energy and a higher charge transfer value. The dynamicsensing responses of SnSe 2 sensors confirm the theoretical predictions. The good match between the theoretical prediction and experimental demonstration suggests that the underlying sensing mechanism is related to the charge transfer and induced flat band. Our results provide a guideline for designing high-performance gas sensors based on SnSe 2 . KEYWORDS: SnSe 2 , gas sensing, charge transfer, first-principles calculations, selective gas sensing, NO 2 gas sensor, NH 3 gas sensor

First-Principles Study for Gas Sensing of Defective SnSe2 Monolayers

“…The pristine 1T phase SnSe 2 monolayer is a hexagonal crystal structure as shown in Figure 1a. A Sn atom is sandwiched between two Se atoms which form a Se-Sn-Se arrangement with ABC stacking as shown in Figure 1e monolayer has an indirect band gap of 0.78 eV as shown in Figure 2a, which is consistent with the previous reported value [8,20]. In the Se-vacancy SnSe2 monolayer, there are occupied states very near EF as shown in Figure 2b.…”

“…The SnX 2 (X = S, Se)-based gas sensors show a good response to NO 2 at room temperature [6][7][8]. Furthermore, the SnSe 2 monolayer shows a higher sensitivity for NO 2 molecule adsorption than SnS 2 in our related work [7,8]. Also, the charge transfers and the flat band contributed by gas adsorption induces the conductivity difference of the SnSe 2 monolayer reported in our previous study [8].…”

“…The layered SnX 2 (X = S, Se) nanosheets show a significant sensitivity to individual molecules, such as NO 2 and NH 3 [3,[6][7][8]. The SnX 2 (X = S, Se)-based gas sensors show a good response to NO 2 at room temperature [6][7][8]. Furthermore, the SnSe 2 monolayer shows a higher sensitivity for NO 2 molecule adsorption than SnS 2 in our related work [7,8].…”

“…2D-TMDs materials have been applied as gas sensors due to their large surface-area-to-bulk ratio. The layered SnX 2 (X = S, Se) nanosheets show a significant sensitivity to individual molecules, such as NO 2 and NH 3 [3,[6][7][8]. The SnX 2 (X = S, Se)-based gas sensors show a good response to NO 2 at room temperature [6][7][8].…”

“…On the other hand, n-type doping of F, Cl and Br are highly recommended, especially Br, since the states near both the VBM and the conduction band minimum (CBM) result in a high carrier density and conductivity [10][11][12]. For the gas sensor, the SnSe 2 monolayer demonstrates a high sensitivity and charge transfer to NO 2 [8].…”