Charge Redistribution Mechanisms in SnSe₂ Surfaces Exposed to Oxidative and Humid Environments and Their Related Influence on Chemical Sensing

Abstract

Tin diselenide (SnSe2) is a van der Waals semiconductor, which spontaneously forms a subnanometric SnO2 skin once exposed to air. Here, by means of surface-science spectroscopies and density functional theory, we have investigated the charge redistribution at the SnO2–SnSe2 heterojunction in both oxidative and humid environments. Explicitly, we find that the work function of the pristine SnSe2 surface increases by 0.23 and 0.40 eV upon exposure to O2 and air, respectively, with a charge transfer reaching 0.56 e–/SnO2 between the underlying SnSe2 and the SnO2 skin. Remarkably, both pristine SnSe2 and defective SnSe2 display chemical inertness toward water, in contrast to other metal chalcogenides. Conversely, the SnO2–SnSe2 interface formed upon surface oxidation is highly reactive toward water, with subsequent implications for SnSe2-based devices working in ambient humidity, including chemical sensors. Our findings also imply that recent reports on humidity sensing with SnSe2 should be reinterpreted, considering the pivotal role of the oxide skin in the interaction with water molecules.

Atmospheric pressure chemical vapor deposition growth of vertically aligned SnS2 and SnSe2 nanosheets

“…The Se contribution cannot be attributed to SeO 2 , as this contribution is centered at much higher binding energy, around 59.5 eV. 75,78 Alternatively, the formation of SnSe 2Àx metastable phase can be considered. Indeed, D'Olimpio et al 75 did a careful investigation of SnSe 2 chemistry when exposed to different environment.…”

“…75,78 Alternatively, the formation of SnSe 2Àx metastable phase can be considered. Indeed, D'Olimpio et al 75 did a careful investigation of SnSe 2 chemistry when exposed to different environment. However, this would imply also a contribution on the Sn signal, and this contribution would be between SnSe 2 and SnSe, i.e.…”

Bidimensional Engineered Amorphous a-SnO2 Interfaces: Synthesis and Gas Sensing Response to H2S and Humidity

“…23,24 Spontaneous oxidation of chalcogenides represents, indeed, an excellent opportunity to synthesize new kinds of interfaces comprising thin layers of amorphous metal oxides grown over 2D layered crystalline materials, yielding a-MO/TMD and a-MO/MC heterostructures with unexpected applications in the field of catalysis and gas sensing. 25 On this account, we recently demonstrated by means of experiments and theory that it is possible to synthesize a-SnO 2 /SnSe 2 heterostructures to detect NO 2 , H 2 , NH 3 , and humidity 26,27 by controlled oxidation in air of 2D exfoliated SnSe 2 layers. Besides their excellent gas sensing response, these 2D amorphous/2D crystalline heterostructures unfortunately retain some remarkable limitations.…”

Exploring the optoelectronic properties of SnSe: a new insight

“…55,56 Roy et al 57 have reported 4.6 eV as the work function of SnSe 2 . D'Olimpio et al 58 reported that this discrepancy in the work function values is due to the surface oxidation of SnSe 2 at room temperature, which leads to the formation of SnO 2 . Here we have varied the electron affinity of the SnSe 2 , which is very sensitive to surface oxidation, from 4.4 to 5.0 eV in steps of 0.2 eV as shown in Fig.…”