Theoretical Study On The Electronic Structure And Gas Sensing Properties Of Two-Dimensional Graphyne Adsorbed By NO Small Molecule

In recent years,as a new type of two-dimensional carbon allotrope,graphyne has attracted extensive attention from researchers because of its excellent electrical conductivity,large specific surface area and abundant unsaturated chemical bonds.Because of these excellent properties,it has the potential to be a gas sensitive material.In this paper,the first-principles calculation method based on density functional theory is used to study the adsorption behavior of NO gas on the surface of intrinsic graphyne.The metal adsorption method is used to improve the sensitivity of graphyne to NO and accelerate the adsorption and separation of NO gas on the surface of metal modified graphyne by applying electric field,in order to contribute to the application of graphyne materials in gas detection.The main research contents and conclusions of the thesis are as follows:Firstly,the adsorption properties of NO molecule on the intrinsic two-dimensional graphyne surface were studied.The interaction between NO molecule and intrinsic two-dimensional graphyne was analyzed from the aspects of adsorption configuration,adsorption energy,electronic structure,carrier mobility and conductivity.The results show that when NO adsorbs to the C atom at the T2 position,the adsorption energy of the system is the largest（-0.080 eV）,and the structure is the most stable,which is physical adsorption.The energy band structure of NO adsorption two-dimensional graphyne system is a simple superposition of isolated NO and intrinsic two-dimensional graphyne energy bands.The NO molecules provide a small amount of electrons to the graphyne system,and the state density of the adsorption system shifts to a low energy direction.However,after NO adsorption,the electron mobility and hole mobility of the adsorption system decrease.In the x direction,the mobility of electrons of GY and GY_NO are 1.51×10⁴ and 0.63×10⁴ cm²V^-1s^-1,respectively;the mobility of holes of them are 1.07×10⁴ and 0.60×10⁴ cm²V^-1s^-1,respectively.In the y direction,the mobility of electrons of GY and GY_NO are 1.11×10⁴ and 0.58×104 cm²V^-1s^-1,respectively;the mobility of holes is 0.73×10⁴ and 0.67×10⁴cm²V^-1s^-1.The relative conductivity of the system before and after NO adsorption was calculated to be 1.71 and 1.37 along the x direction and the y direction,respectively,indicating that the introduction of NO significantly reduced the conductivity of the system.Secondly,the electronic structure and adsorption characteristics of NO molecules adsorption on graphyne decorated by Ca and Co atoms were studied.Research indicates:（1）The Ca atom tends to adsorb at the out-of-plane position of the graphyne,and the adsorption energy is 3.04 eV,which is much larger than the cohesive energy of the Ca cluster of 1.84 eV.Thus,the Ca atom can diffuse freely on the graphyne material.The NO molecule tends to adsorb to the surface of the Ca atom-modified graphyne at the N-terminus.There is a strong coupling between NO and Ca,and the adsorption energy is about 1.50 eV,which is chemical adsorption.NO acts as an electron acceptor in the system,trapping electrons from GY_Ca,and reducing the electron concentration of the graphyne sheet.However,the electron mobility of GY_Ca/NO is significantly higher than that of GY_Ca.The relative electrical conductivity of GY_Ca and GY_Ca/NO in the x and y directions are:0.34 and 0.35,respectively.This indicates that the Ca modification can effectively improve the gas sensitivity of the graphyne to NO.（2）The Co atom tends to adsorb in the center of the triangular mesh of the graphyne,and the adsorption energy is 5.16 eV,which is much larger than the cohesive energy of the cluster of 3.88 eV.Therefore,the Co atom can diffuse freely on the graphyne material as well.The NO molecule tends to adsorb on the surface of the Co atom-modified graphyne at the N-terminus.There is a strong coupling between NO and Co,and the adsorption energy is about 1.67 eV,which is chemical adsorption.The Co atom itself is magnetic,and the introduction of Co also brings magnetism to the GY_Co system with a total magnetic moment of 1.08μB.NO acts as an electron donor in the system,and the electron concentration of the graphyne sheet increases.The electron mobility of GY_Co and GY_Co/NO in the x direction were 4.31×10⁴and 0.26×10⁴ cm²V^-1s^-1,respectively,and the electron mobility in the y direction was3.75×10⁴ and 1.07×10⁴ cm²V^-1s^-1,respectively.The relative conductivity of GY_Co and GY_Co/NO along the x and y directions are 15.91 and 3.36,respectively.This indicates that Co modification can effectively improve the gas sensitivity of graphyne to NO.Finally,the adsorption behavior of NO on the surface of metal modified graphyne was studied under an electric field of-0.1-0.1 V/?.Studies have shown that the applied electric field causes a change in the charge amount and adsorption spacing between the metal and NO,thereby linearly changing the adsorption energy of NO on the metal modified graphyne.Compared with GY_Co/NO,the adsorption energy of GY_Ca/NO is more obvious to the electric field under electric field.