Tin Diselenide (SnSe 2 ) Van der Waals Semiconductor: Surface Chemical Reactivity, Ambient Stability, Chemical and Optical Sensors.

Tin diselenide (SnSe 2 ) is a layered semiconductor with broad application capabilities in the fields of energy storage, photocatalysis, and photodetection. Here, we correlate the physicochemical properties of this van der Waals semiconductor to sensing applications for detecting chemical species (chemosensors) and millimeter waves (terahertz photodetectors) by combining experiments of high-resolution electron energy loss spectroscopy and X-ray photoelectron spectroscopy with density functional theory. The response of the pristine, defective, and oxidized SnSe 2 surface towards H 2 , H 2 O, H 2 S, NH 3 , and NO 2 analytes was investigated. Furthermore, the effects of the thickness were assessed for monolayer, bilayer, and bulk samples of SnSe 2 . The formation of a sub-nanometric SnO 2 skin over the SnSe 2 surface (self-assembled SnO 2 /SnSe 2 heterostructure) corresponds to a strong adsorption of all analytes. The formation of non-covalent bonds between SnO 2 and analytes corresponds to an increase of the magnitude of the transferred charge. The theoretical model nicely fits experimental data on gas response to analytes, validating the SnO 2 /SnSe 2 heterostructure as a suitable playground for sensing of noxious gases, with sensitivities of 0.43, 2.13, 0.11, 1.06 [ppm] -1 for H 2 , H 2 S, NH 3 , and NO 2, respectively. The corresponding limit of detection is 5 ppm, 10 ppb, 250 ppb, and 400 ppb for H 2 , H 2 S, NH 3 , and NO 2, respectively. Furthermore, SnSe 2 -based sensors are also suitable for fast large-area imaging applications at room temperature for millimeter waves in the THz range.