First-principles Investigation On Adsorption,Sensing And Catalytic Properties Of AlN Monolayer

Recently,Two-dimensional materials have attracted extensive attentions in materials science due to their unique physical and chemical properties.AIN monolayer as a member of III-V Two-dimensional materials has been investigated through theoretical calculations has made some progress in synthesis because of its particular properties different from wurtzite AIN.Because of its huge surface-to-volume ratio,AIN monolayer has wide application prospects in sensing,filtering materials and as the matrix of supported monoatomic catalysts.Thus,in this paper,the first-principles calculation based on density functional theory with Van der Waals force correction are used to investigate the adsorption,sensing and catalytic characteristics of various AIN monolayer by doping,decorating or defects.This paper comprises the following research results:"When CO molecule adsorbed on pristine AIN monolayer,the most stable configuration is that C atom is that the C atom is located above the A1 atom with the C-O bond perpendicular to the substrate.The adsorption energy is-3.874 eV with a binding distance of 2.240 A.The band gap shrinks from 2.943 eV to 2.593 eV,and there are 0.126 e transferring from the substrate to the molecule.CO molecule is adsorbed on C-doped AIN monolayer with an adsorption energy of-5.192 eV larger than that of pristine system.The band gap decreases from 3.048 eV to 0.490 eV after adsorption,and 0.367 e charge transfers from the substrate to the molecule.N-vacancy defected AIN monolayer is a p-type semiconductor.The adsorption energy of CO on it is-4.959 eV with band gap sharply decreases from 2.907 eV to 1.366 eV.There are 0.996 e transferring from the substrate to the molecule.C-doping and N-vacancy can increase the band gap changes after adsorption on the basis of increasing adsorption energies.Therefore,C-doping and N-vacancy defected AIN monolayer can be excellent candidate sensing materials for CO detection.Vacancy defects can significantly increase the adsorption energy of SO2 and NO2 on AIN monolayer and change the configurations of gas molecules adsorbed on the substrates.Divacancy defected AlN monolayer can decompose the adsorbed SO2 or NO2.There are some atoms around the vacancy with unsaturated bond in the systems of N-vacancy and divacancy defected AlN monolayer,which can greatly increase the charge transfer number between SO2 or NO2 molecules and the substrates.The charge transfer number of divacancy defected system is more than 1 e indicating that the interactions between molecules and substrates are obviously enhanced.The band structure of SO2 and NO2 adsorbed on vacancy defected AlN changes more remarkably with the appearance,combining and disappearance of deep energy level.Meanwhile,the change of band gap before and after adsorption is also increased.The work function of N-vacancy and divacancy defected AlN monolayer changes obviously after SO2 and NO2 adsorption indicating the stronger interactions between molecules and substrates.Therefore,AlN monolayer with vacancy defects is suitable for SO2 and NO2 filter materials.The structure of Pt atom adsorbed on AlN monolayer is Pt atom on the top of N atom.The adsorptive energy is-3.30 eV and the charge transfer quantity are 0.60 e from monolayer AlN to Pt atom.The diffusion barrier of Pt atom from a N atom to the adjacent N atom is 1.21 eV implying that Pt clusters are not easy to form and that Pt atoms can exist stably on monoalyer AlN.The adsorption energies of CO,O2,O and CO2 on Pt-decorated monolayer AlN surface,the adsorption energies are-5.77 eV,-3.90 eV,-7.41 eV and-3.30 eV,respectively.This indicates that the products of CO oxidation are easier to desorb than the reactants and intermediates,which is conducive to the reaction.The CO oxidation catalyzed by Pt-decorated monolayer AlN can take place via Eley-Rideal mechanism.Two steps of this reaction are CO(ads)+ O2(ads)CO2(gas)+ O(ads)and CO+O(ads)?CO2(gas).The potential barriers of the two steps of reaction are 0.61 eV and 0.49 eV with 3.56 eV and 2.42 eV heat releasing.respectively.In a brief summary,Pt-decorated monolayer AlN can be used as an efficient catalyst for CO oxidation.In the system of Fe-doped monolayer AlN.the bond length of Fe-N is 1.875 A.with a formation energy of 2.16 eV.After doping.Fe atom loses the charge of 1.34 e,which indicates that the interaction between Fe atom and the substrate is strong.The magnetic moment of the whole system originating from the 3d electrons of the Fe atom is 5.00 ?B,which is the largest among the systems doped with Cr,Mn,Fe,Co or Ni atom.The magnetic moments of the Fe-doped monolayer AIN remain unchanged after various non-magnetic gas(CO,CO2,H2,H2S,NH3 and SO2)molecules adsorption.Except for the system of SO2 adsorption,the amount of charge transfer is small indicating that the interactions between the substrates and gas molecules are weak.At the same time,the band gaps change a little after adsorption of these gas molecules.Thus,the Fe-doped monolayer AIN is not suitable for the sensor of the above gases.After various paramagnetic gases(NO,NO2 or O2)adsor:ption,the magnetic moments of the systems decrease from 5.00 ?B to 2.00.b,0.00 ?B and 3.00?B.Compared to the non-magnetic gas adsor:ption systems,the adsorption energies are larger with bigger band gap changes and the larger amount of charge transfer.The Fe-doped monolayer AIN is sensitive to paramagnetic gases and can be a potential sensor material.