Molecular Dynamics Study On Low-energy Radiation Effects On SiO₂ Sol-gel Films

Optical thin films are widely used in inertial confinement fusion(ICF)drivers,solar cells and other optical devices due to their advantages for improving laser transmission efficiency.Silicon dioxide chemical film is the prior choice for coating optical elements in laser ICF drivers.However,the chemical films could be damaged under multiple transient radiation environments.This thesis focuses on the microcosmic process of chemical membrane structure change under low-energy neutron irradiation,using the molecular dynamics methods on chemical membrane materials.Effects on microstructure variation of chemical membranes caused by the interaction between neutrons and chemical membrane materials were also discussed under different atom types,atom numbers,and recoil energies.The micro-evolution rules of chemical film bond length,bond angle,atom coordination number and ring size distribution with the atomic species,atomic number and recoil energy in the system are expounded in detail.It provides a theoretical basis for controlling the structural damage and performance degradation of materials under the combination of radiation environment and strong laser.The main research contents and conclusions of the paper are as follows:1.The establishment of micro-physical structure system of chemical film was described in the first place.The charge scaling method and the volume scaling method were used to establish the microstructure model of the chemical membrane,the feasibility of the molecular dynamics method was confirmed,and the differences between the two methods in simulating the chemical membrane structure were discussed.2.The chemical film structure system under of low-energy neutron irradiation was established.Through the discussion of potential function and atomic threshold displacement energy,the LAMMPS platform was used to construct atomic systems with different atom types,different atom numbers,and different recoil energies.3.Using the established chemical membrane structure system,the structural calculation simulation of chemical membranes with different porosities was performed.The physical structure parameters of chemical membranes under different porosities were analyzed,and the porosity parameters which can be used in neutron irradiation simulation were obtained.The laws of chemical membrane structure changes with different porosities were discussed.4.The limitations of the Teter potential function were found during the simulation of the construction of the neutron-irradiated chemical film system.The new potential function ReaxFF force field was analyzed and introduced.The simulation confirmed the advantages of the ReaxFF force field in chemical bonding.5.The molecular dynamics of low-flux neutron-irradiated chemical membrane structures under different atom types,different atom numbers,and different recoil energies were simulated.The effects of the number of silicon oxygen species and the recoil energy on the microstructure of the chemical film were discussed,and the structure evolution law was obtained.6.In terms of theoretical calculations,the influence of neutron beam radiation on the physical structure of silicon dioxide chemical films is explored,which provides a theoretical basis for mastering the structural damage and performance degradation of materials under the combined effect of radiant environment and intense laser.