Molecular Dynamics Simulation Of Gas Adsorption Properties On The Zinc Oxide Surface

At present,the research on the gas adsorption of gas sensing materials is mainly based on the first principles method.But this method can only calculate the ground state and small system,it can not observe the temperature,defects,stress and other factors on the impact of the gas adsorption on the material.The molecular dynamics method can simulate a large system,and it can be used to simulate the dynamics of the system under different conditions.It can model chemical reactions because of the requirement of breaking and forming bonds which traditional force field can't.At present,ReaxFF is widely used to study the simulation of combustion and explosion.The gas sensor works by oxidation-reduction reaction between thin film material and gas.However,there is nearly no report on the study of the interaction between gas and gas sensing film based on Reax FF molecular dynamics.This paper attempts to simulate the impact of temperature,defects and stress using ReaxFF molecular dynamics method about reaction between Zinc Oxide film and hydrogen,oxygen and water molecules.The reaction of hydrogen molecules,oxygen molecules and water molecules on the surface of Zinc Oxide films was observed.We found that the hydrogen molecules didn't adsorb on the surface of the film,and observed the adsorption of oxygen molecules and water molecules on the film of ZnO.The adsorption configuration of the gas molecule adsorbed on thin film was presented and bond length was given by radial distribution function.Meanwhile,the adsorption rate of gas molecules on the surface and the relationship between the adsorption energy and the temperature are studied.It is found that the increase of temperature leads to the decrease(increase)of the adsorption rate of oxygen molecular(water molecular)on the surface of the film.Adsorbtion of multiple type gas molecular on surface was observed.We found hydrogen can be adsorbed on the surface in the presence of oxygen.It is considered that there is a competitive adsorption between water molecules and oxygen molecules according to the relationship between the multiple type adsorption energy and the adsorption configuration.The increase of temperature will cause the oxygen molecule and the hydrogen molecule to break the bond and reorganization.This paper studied adsorption of gas molecular on surface with point defects and line defect.It is found that the oxygen molecules and the water molecules will fill the oxygen vacancies and oxygen crack,while no gas molecular was found in the zinc vacancies and zinc crack.Finally,through the simulation of the stress applied to the film,it is found that the application of stress will enhance the adsorption of gas molecules on the surface of the film.