A method for generating amorphous silica chemical film models of different porosities to evaluate irradiation effects

Abstract

The application discloses a method for generating amorphous silicon dioxide chemical film models with different porosities to evaluate irradiation effects. The method utilizes charge scaling and combines molecular dynamics and first principle calculation means to generate amorphous silicon dioxide chemical film atomic structure models with different porosities, calculates basic physical properties (elastic modulus, thermal conductivity and light transmittance) of the models, and provides effective and reliable models and theoretical methods for subsequent theoretical research on irradiation effects of the chemical films.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of irradiation effects of optical materials, and particularly relates to a method for generating amorphous silicon dioxide chemical film models with different porosities to evaluate irradiation effects. BACKGROUND

[0002] Sol-gel chemical films have the advantages of simple preparation process, low cost, easy realization of large-area preparation, adaptability to various irregularly-shaped substrates, and high laser damage threshold, and are widely used in the surface coating of ICF drivers and solar cells, energy converters, electronic components, sensor devices, and the like. Since the mid-1980s, the LLNL laboratory in the United States has pioneered the application of sol-gel chemical films to high-power solid laser devices. Since the application of sol-gel chemical films on the NOVA device, high-power solid laser devices in various countries have adopted sol-gel chemical films as high-threshold antireflection optical films. For example, the CEL-V laboratory in France, the AWE laboratory in the United Kingdom, Osaka University in Japan, and research teams in China have all utilized the antireflection properties of sol-gel chemical films to coat sol-gel antireflection films on the surfaces of transmissive optical elements in high-power laser systems.

[0003] With the in-depth development of ICF physical experiments, a large amount of high-energy radiation is released after deuterium-tritium fusion reactions, so that the environment of the chemical film element is no longer single laser irradiation, but laser and various types of prompt radiation, which causes the originally high laser damage threshold of the sol-gel chemical film to begin to have problems such as large-area peeling and falling off of the film layer itself in the actual operating environment. Due to the protection of the shielding sheet (the shielding sheet is replaced every time), the expensive fused quartz lenses, KDP frequency-doubling crystals, and the like in the terminal optical assembly are not affected by X-ray radiation and debris impact, and are not responsive to electromagnetic pulses, and are mainly affected by penetrating neutrons and gamma rays, which cause defects in the chemical film and aggravate the damage in the subsequent laser irradiation. Therefore, neutrons and gamma rays are two types of radiation sources of concern.

[0004] However, there is no literature report on the peeling phenomenon of the chemical film in the ICF device at home and abroad. Therefore, the damage behavior, damage law, and generation mechanism of the chemical film in the deuterium-tritium fusion reaction environment are unknown, and it is necessary to study the damage law and mechanism of the chemical film in the multiple prompt radiation environment. However, there is little experimental and theoretical research on the chemical film, and the relationship between the porosity of the chemical film and the degradation degree caused by high-energy irradiation is unknown.

[0005] Existing research methods for multi-void chemical films only focus on structural characteristics, and there is a gap in the study of physical properties for evaluating the performance of chemical films. The performance degradation, peeling, and damage of the silicon dioxide chemical film caused by irradiation effects are imminent. SUMMARY

[0006] The present application provides a method for generating different porosity amorphous silicon dioxide chemical film model to evaluate irradiation effects, the steps are as follows:

[0007] 1. Generate amorphous silicon dioxide film structure: first, silicon atoms (initial ion charge is +0.48e) and oxygen atoms (initial ion charge is-0.24e) are randomly inserted into the supercell containing a certain number of oxygen-silicon atoms constructed in advance, and the density is adjusted to 1.1g / cm3 (the density of the chemical film commonly used in experiments is 50% porosity); the system is fully relaxed in the NVT ensemble, and due to the limited Coulomb interaction between the atoms in the system, the ion charges of silicon atoms and oxygen atoms are gradually increased to +2.4e and-1.2e, respectively. Then the system is further relaxed and balanced at 300K and 0GPa, and finally a stable silicon dioxide chemical film atomic structure is obtained.

[0008] 2. Generate amorphous silicon dioxide chemical film structure with different porosities: first, remove a certain number of oxygen atoms and silicon atoms from the stable amorphous chemical film structure to generate amorphous chemical film structures with different porosities (generally, the porosity is controlled at 30% to 80%). Then repeat step 1 and optimize these structures using first-principles calculation method to a certain convergence standard, and obtain stable amorphous silicon dioxide chemical film structures with different porosities. The obtained different porosity chemical film structures are optimized using VASP software, and the required stable structure is obtained after optimization. The conjugate gradient algorithm (IBRION = 2) is used for the relaxation of atoms in the structure. The atoms in the structure can move freely. Sampling is performed using a first Brillouin zone with a 2x2x2k point grid. The specific precision parameters are set as follows: the energy broadening (SIGMA) is 0.14eV. The SCF energy convergence (EDIFF) is 1x10-4eV, the ion convergence (EDFFG) is The cutoff energy of the plane wave basis set (ENCUT) is 550eV, and the time step of ion relaxation (POTIM) is 0.2fs. The maximum ion SCF step number (NSW) is 500 steps, and all ion relaxation processes can be converged within 300 steps.

[0009] 3. Assess the influence of different porosities on the physical properties of the chemical film: (1) Use the first-principle calculation method to obtain the electronic properties of the amorphous chemical film structure with different porosities, such as the band gap, charge density, and electronic state density. (2) Perform statistical calculations on the structural parameters of the amorphous chemical film structure with different porosities, such as bond angle distribution, radial distribution function, and atomic coordination number. (3) Finally, simulate the optical properties (dielectric function, absorption coefficient, refractive index, reflectivity, etc.) of these amorphous structures by combining the many-body theory and considering the exciton effect. (4) Calculate the thermal conductivity and elastic modulus of the chemical film with different porosities using the EMD (equilibrium molecular dynamics) method and the pressure-energy method, respectively.

[0010] The beneficial effects of the present application are:

[0011] 1) The present application generates amorphous silicon dioxide chemical film atomic structure models with different porosities using the charge scaling method. This is different from existing methods of generating amorphous structures;

[0012] 2) The present application can generate amorphous silicon dioxide chemical film structures with various porosities by adjusting the ratio of oxygen atoms to silicon atoms in the model (the density of the molecular model). This is different from methods of generating amorphous chemical film structures with fixed porosities;

[0013] 3) The present application can obtain physical property parameters that are close to experimental results through molecular dynamics and first-principle calculation methods. This is different from general calculation methods that have large calculation errors;

[0014] The present application combines various simulation methods and theories to generate amorphous silicon dioxide chemical film atomic structure models with different porosities to evaluate the performance degradation caused by irradiation effects. This method can effectively analyze and evaluate the physical performance degradation of chemical films under irradiation effects in combination with related topics, thereby identifying suitable porosities and exploring the irradiation damage mechanism of chemical films. The application range of the present application is wide, the simulation results are basically consistent with experiments, and the present application has high adaptability and accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The flowchart of the present application;

[0016] Figure 2 Molecular structure of a 50% porosity chemical film of Example 1;

[0017] Figure 3 Si-O-Si bond angle distribution function of the chemical film with different porosities of Example 1;

[0018] Figure 4Example 1. Pair distribution function of Si-O bond of chemical films with different porosities.

[0019] Figure 5 Example 1. Young's modulus of chemical films with different porosities.

[0020] Figure 6 Example 1. Refractive index of chemical films with different porosities.

[0021] Figure 7 Example 1. Light transmittance of chemical films with different porosities. DETAILED DESCRIPTION

[0022] The method for generating a model of amorphous silicon dioxide chemical film with different porosities to evaluate irradiation effects is further described in conjunction with the accompanying drawings.

[0023] The method for generating a model of amorphous silicon dioxide chemical film with different porosities to evaluate irradiation effects of the present application has the following steps:

[0024] Example 1

[0025] The amorphous silicon dioxide chemical film models with different porosities were simulated to analyze the influence of porosity on the physical properties of the chemical film. First, based on the charge calibration method, molecular dynamics and first-principle calculation method, amorphous silicon dioxide chemical film models with porosities of 40%-70% were constructed, and the model with a porosity of 50% is shown in Figure 1 Subsequently, various calculation methods were used to calculate the structural parameters, elastic modulus, thermal conductivity and light transmittance of the silicon dioxide chemical film. Figure 2 and 3 respectively show the O-Si-O bond angle distribution and Si-O pair distribution function of the chemical film under different porosities. It can be seen from the figure that the bond angle distribution and Si-O bond of the chemical film are mainly concentrated around 110 degrees and respectively, which is consistent with the experimental results. Subsequently, we also calculated the Young's modulus of the chemical film under different porosities, which is shown in Figure 4 From which it can be seen that there is a linear relationship between the Young's modulus of the chemical film and the porosity, and as the porosity increases, the chemical film appears to be softening. This is caused by the reduction of chemical bonds and the increase of defects due to the reduction of the number of atoms in the structure. We calculated the optical properties of the chemical film using the GW method. Figure 5 and Figure 6The refractive index and transmittance of the chemical film with different porosities are shown respectively. When the porosity is between 40% and 50%, the refractive index is around 1.2. According to the test results, the refractive index of the 50% chemical film is generally between 1.2 and 1.25, which indicates that this result is more reliable. As can be seen from the figure, the greater the porosity, the lower the refractive index, indicating that the porosity can modulate the refractive index. For the transmittance, in the range of 3-4 ev, the transmittance of the chemical film is mainly above 98%, which is consistent with the experimental results. The transmittance of the fused quartz substrate is about 95%, which is mainly attributed to the loose and porous structure of the chemical film. In addition, for the 355 nm wavelength laser, the lower the porosity of the chemical film, the better the transmittance. The transmittance of the 40% porosity is 99.8%, while that of the 70% porosity can be improved to 99.2%.

[0026] The above description is merely preferred embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art without creative efforts should fall within the protection scope of the present application.

Claims

1. A method for evaluating the irradiation effect by generating amorphous silica chemical film models with different porosities, characterized in that, The method comprises the following steps: S1, generating an amorphous silicon dioxide film structure S11, randomly inserting silicon and oxygen atoms into the supercell containing a certain number of oxygen-silicon atoms constructed in advance, the density is adjusted to 1.1 g / cm 3 ; S12, the system is fully relaxed in the NVT ensemble, due to the finite Coulomb interaction between atoms in the system, the ionic charges of silicon atoms and oxygen atoms are gradually increased, and then the system is further relaxed and balanced at 300K and 0GPa, and finally a stable atomic structure of a silicon dioxide chemical film is obtained; S2, generating amorphous silicon dioxide chemical film structures with different porosities S21, removing a certain number of oxygen atoms and silicon atoms from the stable amorphous chemical film structure obtained in S12, thereby generating amorphous chemical film structures with different porosities; S22, repeating step S1, and using a first-principles calculation method to fully optimize these structures, and after the energy reaches a certain convergence standard, stable amorphous silicon dioxide chemical film structures with different porosities are obtained; S3, evaluating the influence of different porosities on the physical properties of the chemical film S31, using a first-principles calculation method, the electronic properties of the amorphous chemical film structures with different porosities are obtained; S32, statistical calculation is performed on the structure parameters of the amorphous chemical film structures with different porosities; S33, combined with many-body theory and considering the exciton effect, the optical properties of these amorphous structures are simulated and calculated; S34, using the equilibrium molecular dynamics EMD method and the pressure-energy method, the thermal conductivity and the elastic modulus of the chemical film with different porosities are calculated.

2. The method for generating a model of different porosity amorphous silica chemical films to evaluate irradiation effects according to claim 1, characterized in that: In step S11, the initial ionic charge of the silicon atom is +0.48e, and the initial ionic charge of the oxygen atom is -0.24e.

3. The method of claim 1, wherein the method further comprises: determining the irradiation effect of the amorphous silica chemical film model with different porosities. In step S12, the ionic charges of silicon atoms and oxygen atoms are gradually increased to +2.4e and -1.2e, respectively.

4. The method for generating a model of amorphous silica chemical films of different porosities to evaluate irradiation effects according to claim 1, characterized in that: In step S21, the porosity is controlled to be 30% to 80%.

5. The method for generating different porosity amorphous silica chemical film model to evaluate irradiation effects according to claim 1, characterized in that: In step S22, the obtained amorphous silicon dioxide chemical film structures with different porosities are optimized using VASP software, and the required stable structure can be obtained after optimization is completed; The conjugate gradient algorithm, IBRION = 2, is used for the relaxation of the atoms in the structure, which can move freely, and the first Brillouin zone with a 2x2x2 k-point mesh is used for sampling, with the following specific precision parameters: energy broadening SIGMA of 0.14 eV, SCF energy convergence EDIFF of 1x10-4 eV, and ion convergence EDFFG of The cutoff energy of the plane wave basis set ENCUT is 550 eV, the time step of the ion relaxation POTIM is 0.2 fs, the maximum number of SCF steps NSW is 500 steps, and all the ion relaxation processes can converge within 300 steps.

6. The method for generating different porosity amorphous silica chemical film model to evaluate irradiation effects according to claim 1, characterized in that: The electronic properties obtained in step S31 include band gap, charge density and electronic state density.

7. The method for generating different porosity amorphous silica chemical film model to evaluate irradiation effects according to claim 1, characterized in that: In step S32, the structure parameters include bond angle distribution, radial distribution function and atomic coordination number.

8. The method for generating a model of amorphous silica chemical films of varying porosity to evaluate radiation effects according to claim 1, wherein: In step S33, the simulated and calculated optical properties include dielectric function, absorption coefficient, refractive index and reflectivity.

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