Theoretical Studying On Gas Sensing Properties Of Two-Dimensional Layered M₂CO₂ And GeS

With the development of industry and technology,the amount of toxic gases NO₂ and SO₂ have been significantly increased and air pollution has become an urgent global problem,which pollute the environmen and harm the human body.It has important scientific significance and application value that searching for suitable materials for toxic detection at low temperature with simple manufacture.Due to the abundant electronic structures,great physical and chemical characters,the two-dimensional（2D）layered MXenes and phosphorene-like GeS materials present potential applications in energy storage and conversion,gas sensing and catalyst.In experiments,more than 30 MXenes materials have been successfully synthesized by chemical etching.And the GeS nanosheet is synthesized through vapor-liquid-solid technique.In theories,a lot of studies of MXenes and GeS materials are focused on the mechanical,electronic,optical and transport properties.However,these works should be further studied in the further.In this thesis,the adsorption of a series of gas molecules on MXenes and GeS monolayers have been studied systematically based on first-principles calculation,to explore their potential applications as gas sensor.The gaseous selectivity,sensitivity,structure stability and the underlying mechanism were elaborated based on the analysis of the adsorption strength and optimized geometries,electronic structures and current-voltage transport properties for these systems.Moreover,the effects of in-plane strain and out-of-plane electric field on the adsorption properties were addressed in more details.The present study reveals interesting insights into the gas sensing features of 2D layered O-terminated MXenes and GeS,which may facilitate the design of two-dimensional MXenes-and GeS-based gas sensor devices.The main findings are concluded as follows:1.Among the O-terminated M₂CO₂（M=Hf,Zr,Ti）nanosheets,the Sc₂CO₂ monolayer has the highest selectivity and sensibility toward SO₂ molecule,suitable for SO₂ gas sensor.Moreover,the interaction strength between SO₂ and Sc₂CO₂ can be efficiently modulated by biaxial strain and external electric field,which are effective routes to realize the capture and reversible release of SO2.These characteristics embody monolayer Sc2CO2 a promising candidate as SO₂ gas sensor and capture.2.The adsorption of NO₂ molecule on GeS monolayer is the strongest among the gas molecules considered,in combination with more sensitive change in the electronic band structure and charge transfer,suggesting that GeS is more sensitive to this toxic gas.The adsorption-induced current change of GeS exhibits strong anisotropic characteristics along the armchair or zigzag directions of GeS monolayer.The controllable capture and releasing of gaseous NO₂ could be realized on GeS nanosheet by applying biaxial strains and vertical electric fields.Such sensitivity and selectivity to NO2 gas molecule adsorption make phosphorene a desirable candidate as a superior gas sensor and storage.