Improved Charge Transfer for NO2 Gas Sensors by Using 0D SnS Quantum Dot/2D WSe2 Heterostructures

A highlysensitive array of two-dimensional (2D) WSe2 nanosheetsintegrated with zero-dimensional (0D) SnS quantum dotswas synthesized by combining liquid-phase exfoliation and wet chemicalsynthesis methods. The characterization results of scanning electronmicroscopy (SEM), transmission electron microscopy (TEM), and X-raydiffraction (XRD) revealed the formation of WSe2/SnS heterostructures,which enable a cyclic and reproducible high gas sensing response.The role allocation of SnS on WSe2 was verified by usingdensity functional theory (DFT) calculations. The result indicatesthat the top alignment of SnS and the bottom layer of WSe2 act as a gas adsorption layer and carrier conduction layer, respectively.The charge interactions of the heterostructures were systematicallyexplored by monitoring changes in the transferred characteristicsat room temperature (27 degrees C) after introducing 25-100 ppbNO(2). The highest sensing response of WSe2/SnSheterostructures toward the NO2 gas was found to be 1.08at 25 ppb with a LOD of 10.6 ppb. The experimental and simulationresults revealed that the charge transfer across the active sitesincreased after incorporating SnS in the WSe2. The sensingresults showed an abrupt and reliable gas response under periodicNO(2) gas injection unambiguously achieved by such heterostructures.The sensor also exhibited satisfactory stability and accuracy in selectivityand is not affected by humidity at room temperature. DFT calculationswere also used to explain the sensing mechanism and heterojunctionfor such nanocomposites.