Roughness simulation method for ion implantation based on molecular dynamics

Abstract

The present invention discloses a roughness simulation method for ion implantation of materials based on molecular dynamics, including: S1. constructing a surface point height matrix M of the research material according to the value of the set three-dimensional roughness parameter Sq; S2. constructing a smooth surface target model of the research material, and changing the smooth surface target model into a rough surface target model according to the surface point height matrix M of the research material; S3. reading the rough surface target model, and then constructing a molecular dynamics model for ion implantation of the rough surface target model and performing simulation calculation; S4. extracting the target surface morphology of the rough surface target model during the ion implantation process, and calculating the surface roughness change trend according to the target surface morphology. The present invention can predict the change of the roughness of the surface of the research material under ion implantation while considering the initial surface roughness of the research material, and further provide theoretical guidance for the evolution mechanism of the surface roughness of the material under ion implantation, and is simple to operate and low in cost.

Description

Technical Field

[0001] The invention relates to the technical field of material ion implantation, and in particular to a roughness simulation method for ion implantation of materials based on molecular dynamics. Background Art

[0002] Roughness is one of the important parameters to characterize the surface state of parts. Reducing the roughness will reduce stress concentration, reduce the friction coefficient, and significantly improve the contact performance. The ion implantation process uses high-energy ions to bombard the surface of parts, and reduces the surface roughness of parts through surface atomic sputtering, viscous flow and diffusion. In recent years, it has received more and more attention and is widely used in various industries.

[0003] In the prior art, the roughness of the material under ion implantation is generally detected by white light interferometer or atomic force microscope. However, detection by white light interferometer or atomic force microscope is not only cumbersome and costly, but also inconvenient to predict the change of the surface roughness of the material under ion implantation. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a roughness simulation method for ion implantation of materials based on molecular dynamics, which can predict the change of the roughness of the surface of the material under ion implantation while considering the initial surface roughness of the material under study, and further provide theoretical guidance for studying the evolution mechanism of the surface roughness of the material under ion implantation. Moreover, compared with the existing detection method using a detector, the operation is simpler and the cost is lower.

[0005] According to the first aspect of the present invention, a roughness simulation method for ion implantation of materials based on molecular dynamics comprises the following steps:

[0006] According to some embodiments of the present invention, the following steps are included:

[0007] S1. Construct the surface point height matrix M of the research material according to the set value of the three-dimensional roughness parameter Sq;

[0008] S2. constructing a smooth surface target model of the research material, and changing the smooth surface target model to a rough surface target model according to the surface point height matrix M of the research material;

[0009] S3. Reading the rough surface target model, and then constructing a molecular dynamics model for ion implantation into the rough surface target model and performing simulation calculations;

[0010] S4. Extracting the target surface morphology of the rough surface target model during the ion implantation process, and calculating the surface roughness variation trend based on the target surface morphology.

[0011] The roughness simulation method for ion implantation of materials based on molecular dynamics according to an embodiment of the present invention has at least the following beneficial effects:

[0012] In the present invention, the roughness of the initial surface of the research material is first considered, and a surface point height matrix M of the research material is constructed. Then, the surface point height matrix M of the research material and a smooth surface target model established according to the research material are combined to obtain a rough surface target model. Then, a molecular dynamics model of ion implantation into the rough surface target model is constructed and simulation calculations are performed. Finally, the target surface morphology of the rough surface target model during the ion implantation process is extracted. The surface roughness variation trend can be calculated according to the target surface morphology, thereby providing theoretical guidance for studying the evolution mechanism of the surface roughness of the material under ion implantation. Moreover, compared with the existing detection method using a detector, the operation is simpler and the cost is lower.

[0013] According to some embodiments of the present invention, in step S1, the three-dimensional roughness parameter Sq represents the point height h of the surface of the object. i The root mean square of the distance to the reference plane, the height of the reference plane is the height h of all points on the surface of the object i The average value of .

[0014] According to some embodiments of the present invention, in step S1, the surface of the research material is decomposed into n sub-surfaces, and the surface point height matrix M of the research material satisfies the relationship:

[0015]

[0016] Where, d sur is the distance between adjacent surface points on the surface of the studied material, is the distance between adjacent surface points of the sub-surface, M i ′ is the surface point height matrix of each sub-surface, and the weight factor k i The sum of (i=1, 2, ..., n) is 1.

[0017] According to some embodiments of the present invention, in step S1, the surface point height matrix M of the sub-surface i The construction method of ′ is: using Python's random function to convert the initial height matrix M of the surface points of all the sub-surfaces i Assign random values ​​to the initial height matrix M of all surface points of the sub-surface i Obey Gaussian distribution, that is, M i ~N i (0,k i Sq 2 );

[0018] Use Python's interpolate function to calculate the initial height matrix M of the surface points of the sub-surface i Interpolate and construct it into the surface point height matrix M of the sub-surface i ′.

[0019] According to some embodiments of the present invention, in step S1, the number of rows and columns of the surface point height matrix M of the research material are both set to m, where m is expressed as:

[0020]

[0021] Where D is the side length of the surface of the research material, d sur is the distance between adjacent surface points on the surface of the studied material.

[0022] According to some embodiments of the present invention, step S2 specifically includes the following steps:

[0023] Step S201: construct the smooth surface target model and store the three-dimensional coordinate values ​​(x i ,y i , z i ), where i is the atomic number;

[0024] Step S202. The atoms on the same vertical line in the smooth surface target model are matched with an element in the surface point height matrix M of the research material, and the coordinate values ​​(x i ,y i ), calculate the row number row of the corresponding element in the surface point height matrix M of the research material i and column number col i ;

[0025] Step S203. Use row number row i and column number col i , read the value of the corresponding element in the surface point height matrix M of the research material:

[0026] H i =M(row i ,col i );

[0027] Step S204: Determine the height z of atoms on the same vertical line i and the value H of the corresponding element i The size of z i ≤H i , keep the corresponding atom, otherwise, delete the corresponding atom;

[0028] Step S205: construct the rough surface target model according to the relevant information of all retained atoms.

[0029] According to some embodiments of the present invention, in step S3, the rough surface target model is read, and the x-direction and y-direction are set as periodic boundary conditions for the rough surface target model, the positive z direction is set as a free boundary condition, and the negative z direction is set as a fixed boundary condition, and the rough surface target model is divided into a boundary layer, a constant temperature layer and a Newtonian layer from bottom to top, wherein the Newtonian layer is an ion implantation area.

[0030] According to some embodiments of the present invention, in the molecular dynamics model, the ion implantation method is set as follows:

[0031] Ions are generated from random positions in the vacuum region at a set height above the rough surface target model. The ion injection direction is at an angle to the z direction. The ions are injected into the rough surface target model in sequence according to a set time interval. The ion injection speed is:

[0032]

[0033] Where E is the implantation energy, in J; m is the mass of the implanted ions, in kg.

[0034] According to some embodiments of the present invention, step S4 specifically includes the following steps:

[0035] Step S401. Construct a matrix S m , and initialize it to a zero matrix, where the element in the pth row and qth column is denoted by S m (p,q);

[0036] Step S402. The three-dimensional coordinate values ​​of the atoms in the rough surface target model are (x i ′,y i ′,z i ′), the atoms located on the same vertical line in the rough surface target model and the matrix S m The coordinates of the projections of the atoms on the same vertical line on the horizontal plane (x i ′,y i '), calculate the matrix S m The row number of the corresponding element in row i ' and column number col i ′;

[0037] Step S403. Compare the value S of the element m (row i ′,col i′) and the height value z of the corresponding atom i ′, if S m (row i ′,col i ′) <z i ′, then let S m (row i ′,col i ′)=z i ', otherwise, keep S m (row i ′,col i ')constant;

[0038] Step S404. Until all atoms are iterated, the matrix S m The target surface morphology is used as the rough surface target model during ion implantation.

[0039] According to some embodiments of the present invention, step S4 further includes the following steps:

[0040] Step S405. Using the matrix S obtained in step S404 m , calculate the values ​​of the three-dimensional roughness parameters Sa and Sq of the rough surface target model during ion implantation, where:

[0041] The three-dimensional roughness parameter Sa is the arithmetic mean of the distance from the surface point height of the object to the reference plane. The calculation formula of Sa is:

[0042]

[0043] The three-dimensional roughness parameter Sq represents the root mean square of the distance from the point height of the object surface to the reference plane. The calculation formula of Sq is:

[0044]

[0045] In the formula, h i is the surface point height of the object, is the height of the reference plane, For all h i The average value of .

[0046] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0048] Figure 1is a schematic diagram of the initial surface of the rough surface target model;

[0049] Figure 2 Schematic diagram of molecular dynamics model;

[0050] Figure 3 Schematic diagram of the evolution of vacancies and interstitial atoms;

[0051] Figure 4 Schematic diagram of the surface roughness evolution of the rough surface target model under ion implantation. DETAILED DESCRIPTION

[0052] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0053] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, inside, outside, top, bottom, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0054] In the description of the present invention, "a plurality" refers to two or more than two. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0055] In the description of the present invention, unless otherwise clearly defined, words such as setting and establishing should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0056] Reference below Figures 1 to 4 A roughness simulation method for ion implantation of materials based on molecular dynamics according to an embodiment of the present invention is described.

[0057] The roughness simulation method for ion implantation of materials based on molecular dynamics according to an embodiment of the present invention comprises the following steps:

[0058] S1. Construct the surface point height matrix M of the research material according to the set value of the three-dimensional roughness parameter Sq;

[0059] S2. construct a smooth surface target model of the research material, and change the smooth surface target model into a rough surface target model according to the surface point height matrix M of the research material;

[0060] S3. Read the rough surface target model, then construct a molecular dynamics model for ion implantation into the rough surface target model and perform simulation calculations;

[0061] S4. Extract the target surface morphology of the rough surface target model during ion implantation, and calculate the surface roughness variation trend based on the target surface morphology.

[0062] The roughness simulation method for ion implantation of materials based on molecular dynamics in an embodiment of the present invention first considers the roughness of the initial surface of the research material, constructs a surface point height matrix M of the research material, then combines the surface point height matrix M of the research material and a smooth surface target model established according to the research material to obtain a rough surface target model, then constructs a molecular dynamics model for ion implantation of the rough surface target model and performs simulation calculations, and finally extracts the target surface morphology of the rough surface target model during the ion implantation process, and calculates the surface roughness change trend based on the target surface morphology, thereby providing theoretical guidance for studying the evolution mechanism of the surface roughness of the material under ion implantation, and compared with the existing method of detecting through a detector, the operation is simpler and the cost is lower.

[0063] The following is a more detailed description of steps S1 to S4 of the roughness simulation method for ion implantation of materials based on molecular dynamics according to an embodiment of the present invention, taking chromium ions implanted into single crystal iron as a research object.

[0064] In some embodiments of the present invention, step S1. constructing a surface point height matrix M of the research material according to the set value of the three-dimensional roughness parameter Sq specifically includes the following process:

[0065] The three-dimensional roughness parameter Sq represents the point height h on the surface of the object. i The root mean square of the distance to the reference plane, the height of the reference plane is the height h of all points on the surface of the object i The average value of .

[0066] The point height distribution of the rough surface is mainly affected by the roughness parameter Sq value and the distance d between adjacent surface points. sur In this embodiment, the surface of the research material is decomposed into n sub-surfaces, and the surface point height matrix M of the research material satisfies the relationship:

[0067]

[0068] Where, d sur is the distance between adjacent surface points on the surface of the studied material, is the distance between adjacent surface points of the sub-surface, M i ′ is the surface point height matrix of each sub-surface, and the weight factor k iThe sum of (i=1, 2, ..., n) is 1.

[0069] Among them, the number of rows and columns of the surface point height matrix M of the research material can be set to m, and m can be calculated by the following formula:

[0070]

[0071] Where D is the side length of the surface of the material under study.

[0072] It should be noted that in this embodiment, chromium ion implantation single crystal iron is used as the research object, the research material is single crystal iron, and the distance d between adjacent surface points on the surface of the research material is sur is the lattice constant L c half of , that is:

[0073] d sur =L c / 2;

[0074] Lattice constant of iron Therefore, the distance between adjacent surface points on the surface of the studied material is When the side length of the surface of the studied material is set to , m=100.

[0075] Among them, the surface point height matrix M of the sub-surface is constructed i The construction method of ' is:

[0076] First, use Python's random function to get the initial height matrix M of all sub-surface points i Assign random values ​​to the initial height matrix M of all sub-surface surface points i Obey Gaussian distribution, that is, M i ~N i (0,k i Sq 2 );

[0077] Then use Python's interpolate function to interpolate the surface point height matrix M of the sub-surface i ′ is interpolated to construct the surface point height matrix M of the sub-surface i ′;

[0078] It should be noted that the sub-surface surface point height matrix M i The number of rows and columns of ′ is the same as the number of rows and columns of the surface point height matrix M of the research material. For example, when the number of rows and columns of the surface point height matrix M of the research material is 100×100, the interpolate function of Python is used to interpolate the initial height matrix M of the sub-surface surface points. iInterpolation, constructing a surface point height matrix M of a 100×100 sub-surface i ′.

[0079] In this embodiment, the value of the roughness parameter Sq can be set to The number of sub-surfaces may be set to 3, that is, n=3.

[0080] The specific parameters of each sub-surface can be referred to in Table 1 below:

[0081] Table 1

[0082]

[0083] Referring to the above parameters, use Python's interpolate function to calculate the initial height matrix M of the surface points of the sub-surface i By interpolation, the surface point height matrix M of each sub-surface can be constructed i ′, then the surface point height matrix M of all sub-surfaces i ′After weighted addition, add the height of the reference plane The surface point height matrix M of the research material can be obtained.

[0084] In some embodiments of the present invention, S2. constructing a smooth surface target model of the research material, and changing the smooth surface target model into a rough surface target model according to the surface point height matrix M of the research material, specifically includes the following process;

[0085] Step S201: Construct a smooth surface target model and store the three-dimensional coordinate values ​​(x i ,y i , z i ), where i is the atomic number.

[0086] Specifically, the smooth surface target model can be constructed using Lammps software. Since the present embodiment takes chromium ion implantation into single crystal iron as the research object, the smooth surface target model can be a smooth surface single crystal iron model. Then, the lmp type file of Lammps software is output to store the three-dimensional coordinate values ​​(x i ,y i , z i ), where i is the atomic number.

[0087] It should be noted that other suitable software may also be used to construct a smooth surface target model.

[0088] In addition, the model size of the smooth surface target model can be set as: Of course, the model size of the smooth surface target model can also be set to other appropriate sizes. Specifically, as long as the height size of the smooth surface target model is greater than or equal to the maximum height size of the rough surface target model to be constructed. The coordinates of the lowest point of the smooth surface target model in the vertical direction can be set to The smooth surface target model can use a body-centered cubic lattice, and the lattice constant can be set to

[0089] Step S202. The atoms on the same vertical line in the smooth surface target model are matched to an element in the surface point height matrix M of the research material, and the coordinate values ​​(x i ,y i ), calculate the row number of the corresponding element in the surface point height matrix M of the research material i and column number col i .

[0090] row number i It is expressed as:

[0091]

[0092] Column number col i It is expressed as:

[0093]

[0094] It should be noted that since all atoms in the smooth surface target model are arranged in three dimensions, all atoms can include multiple groups of atoms. The same group of atoms is located on the same vertical line, and the coordinate values ​​of the projections of the same group of atoms on the horizontal plane (x i ,y i ), therefore, the row number and column number of an element in the surface point height matrix M of the studied material can be calculated based on the coordinate value (x i ,y i ) for calculation.

[0095] Step S203. Use row number row i and column number col i , read the value of the corresponding element in the surface point height matrix M of the research material:

[0096] H i =M(row i ,col i );

[0097] Since the coordinate value of the projection of the atom on the horizontal plane (x i ,y i) corresponds to the position of one of the elements in the surface point height matrix M of the research material. Once the position of the atom corresponding to the element in the surface point height matrix M of the research material is known, the specific value H of the corresponding element can be known. i .

[0098] It should be noted that the coordinate values ​​of the projections of a group of atoms on the same vertical line on the horizontal plane (x i ,y i ), therefore, a group of atoms located on the same vertical line correspond to the same values ​​of the elements in the surface point height matrix M of the studied material.

[0099] Step S204: Determine the height z of atoms on the same vertical line i and the value H of the corresponding element i The size of z i ≤H i , keep the corresponding atom, otherwise, delete the corresponding atom.

[0100] Specifically, the height values ​​z of a group of atoms on the same vertical line are i The value of the corresponding element H i Compare the size and keep z i The value is less than or equal to the value of the corresponding element H i atoms, so that among the retained atoms, the height of the highest atom in a group of atoms located on the same vertical line is close to the height of the surface point of the research material.

[0101] Step S205: Construct a rough surface target model based on the relevant information of all retained atoms.

[0102] Since the height of the highest atom in a group of atoms located on the same vertical line among the retained atoms is close to the surface point height of the research material, a rough surface target model can be constructed based on the relevant information of all the retained atoms, and the surface of the rough surface target model corresponds to the surface of the research material.

[0103] It should be noted that the relevant information of all retained atoms can be written into a new lmp type file of the Lammps software to generate a rough surface target model.

[0104] Finally, the point height of the initial surface of the rough surface target model is as follows: Figure 1 Distribution shown.

[0105] In some embodiments of the present invention, S3. reading the rough surface target model, then constructing a molecular dynamics model for ion implantation into the rough surface target model and performing simulation calculations, specifically includes the following process:

[0106] The read_data command of Lammps software can be used to read the rough surface target model in the lmp type file as the rough surface target model of the molecular dynamics model.

[0107] Then, the rough surface target model is set to periodic boundary conditions in the x and y directions to reduce the scale effect, the positive z direction is a free boundary condition, and the negative z direction is a fixed boundary condition. The rough surface target model is divided into a boundary layer, a constant temperature layer, and a Newton layer from bottom to top. In order to prevent the target body of the rough surface target model from being moved by force during ion implantation, the boundary layer is set to be completely fixed. After the injected ions contact the target body of the rough surface target model, their kinetic energy will be converted into heat energy through continuous collisions, and then a thermostat can be applied to the constant temperature layer to ensure reasonable heat dissipation. The thermostat can be a Berendsen thermostat or other suitable thermostat. The Newton layer is the ion implantation area, which conforms to Newton's law and can be calculated using the NVE system of Lammps software.

[0108] In the molecular dynamics model, the interaction potential of atoms can be selected. For example, the interaction potential between the injected chromium ions and the iron atoms in the target of the rough surface target model can be set to the Tersoff / ZBL potential function, the interaction between chromium ions can be described by the lj potential function, and the interaction between iron atoms can be described by the eam / fs potential function which is more suitable for intermetallic interactions.

[0109] When simulating the molecular dynamics model, it can be divided into three stages: energy minimization, relaxation, and ion injection. The time step can be set to 0.001ps, and the Velocity-Verlet integration algorithm can be used.

[0110] Specifically, since the initial configuration of the target we constructed only meets the requirements of the lattice structure and is far from the equilibrium state, some atoms are too close or the forces are unbalanced, which will cause the simulation to crash. Using the Minimize command of Lammps software to optimize the initial configuration can minimize the potential energy of the system and avoid bad contact between atoms.

[0111] The relaxation stage allows the molecular dynamics model to gradually reach the set temperature and pressure state. In this embodiment, the temperature of the molecular dynamics model can be set to 293K, that is, set to room temperature, until the molecular dynamics model reaches a dynamic equilibrium process with relatively stable total energy.

[0112] During the ion implantation phase, ions are generated from random positions in the vacuum region at a set height above the rough surface target model. The ion implantation direction is at an angle to the z direction, and the ions are injected into the rough surface target model in sequence according to the set time interval. For example, it can be set that ions are injected from above the rough surface target model. The ions are generated at random positions in the vacuum region. The angle between the ion injection direction and the z direction can be set to 7°. The time interval between two adjacent ion injections can be set to 20 ps. The ion injection speed is:

[0113]

[0114] Where, E is the implantation energy, in J; m is the mass of the implanted ions, in kg. For example, in this embodiment, E = 2keV = 3.204 × 10 -16 J, the ion can be a chromium ion, whose mass

[0115] The molecular dynamics model can store data every 30,000 steps, and the rough surface target can be

[0116] ″′

[0117] The three-dimensional coordinates (x i ,y i , z i ) is recorded in the dump file, where i represents the atomic number.

[0118] The final molecular dynamics model is as follows Figure 2 shown.

[0119] After ion implantation, the atoms in the target model with a rough surface will gain energy. When the accumulated energy is greater than the lattice binding energy, point defects such as vacancies and interstitial atoms will be formed. Figure 3 As shown, with the increase of the dose of implanted ions, both the vacancy type point defects and the interstitial atom type interstitial atoms will increase. In this case, the atoms are no longer arranged strictly according to the lattice parameter rules.

[0120] In some embodiments of the present invention, S4. extracting the target surface morphology of the rough surface target model during ion implantation, and calculating the surface roughness variation trend according to the target surface morphology, specifically comprises the following steps:

[0121] Step S401. Construct a matrix S m , and initialize it to a zero matrix, where the element in the pth row and qth column is denoted by S m (p,q).

[0122] Matrix S mIt is used to record the surface point height of the rough surface target model when ion implantation is performed. The matrix S m The number of rows and columns can be the same as the number of rows and columns of the surface point height matrix M of the research material, for example, both are 100×100.

[0123] Step S402. The three-dimensional coordinate values ​​of the atoms in the rough surface target model are (x i ′,y i ′,z i ′), the atoms on the same vertical line in the rough surface target model and the matrix S m The coordinates of the projections of the atoms on the same vertical line on the horizontal plane (x i ′,y i ′), calculate the matrix S m The row number of the corresponding element in row i ' and column number col i ′;

[0124] row number i ′ is expressed as:

[0125]

[0126] Column number col i ′ is expressed as:

[0127]

[0128] Among them, round() is Python's rounding function, so when or When the value is not an integer, an integer value can be obtained, which makes it easier to calculate the row number row i ' and column number col i ′.

[0129] It should be noted that since all atoms in the rough surface target model are arranged in three dimensions, all atoms may include multiple groups of atoms. The same group of atoms is located on the same vertical line, and the coordinate values ​​of the projections of the same group of atoms on the horizontal plane (x i ′,y i ′), so the matrix S m The row and column numbers of the elements in the image can be determined based on the coordinates of the projection of the corresponding set of atoms on the horizontal plane (x i ′,y i ′) for calculation.

[0130] Step S403. Compare the value S of the element m (row i ′,coli ′) and the height value z of the corresponding atom i ′, if S m (row i ′,col i ′) <z i ′, then let S m (row i ′,col i ′)=z i ', otherwise, keep S m (row i ′,col i ')constant;

[0131] Specifically, the height value z of one of the atoms in the same group of atoms is i ′ and the value S of the corresponding element m (row i ′,col i ′) compared to the initial state, the matrix S m It is a zero matrix, that is, the initial value of the element is 0, and then the value S of the corresponding element can be m (row i ′,col i ′) is equal to the height value z of the atom i ', and then the height values ​​z of the remaining atoms in the group of atoms i ′ and the value S of the element m (row i ′,col i ′) for comparison, if S m (row i ′,col i ′) <z i ′, then let S m (row i ′,col i ′)=z i ', otherwise, keep S m (row i ′,col i ′) remains unchanged until all atoms are compared and judged.

[0132] Step S404. Until all atoms are iterated, the matrix S m Target surface morphology as a model for a rough surface target during ion implantation.

[0133] After all atoms are iterated, the height value z of the highest atom in each group of atoms can be i ′Assign matrix S m The corresponding elements in the matrix S mThat is, the rough surface point height matrix of the rough surface target model during ion implantation, and then the matrix S m The target surface morphology is used as the rough surface target model in the ion implantation process. During the ion implantation process, the surface of the rough surface target model changes, and the matrix S m The values ​​of the elements in will also change accordingly.

[0134] Step S405. Using the matrix S obtained in step S404 m , calculate the values ​​of the three-dimensional roughness parameter Sa and the three-dimensional roughness parameter Sq of the rough surface target model during ion implantation.

[0135] The three-dimensional roughness parameter Sa is the surface point height h of the object i The arithmetic mean of the distance to the reference plane, Sa, is calculated as:

[0136]

[0137] The three-dimensional roughness parameter Sq represents the point height h on the surface of the object. i The root mean square of the distance to the reference plane, the height of the reference plane is the height h of all points on the surface of the object i The average value of

[0138] The calculation formula of the three-dimensional roughness parameter Sq is:

[0139]

[0140] In the formula, h i is the surface point height of the object, is the height of the reference plane, For all h i The average value of .

[0141] The calculation results are as follows Figure 4 As shown, it can be known that with the increase of the dose of ion implantation, the values ​​of the three-dimensional roughness parameter Sq and the three-dimensional roughness parameter Sa are generally on a downward trend, that is, the surface roughness of the research material is generally on a downward trend, which matches the conclusions of the experiment and instrument detection, that is, ion implantation will reduce the surface roughness of the material, thereby improving the density, reducing the stress concentration factor, and strengthening the fatigue resistance of the matrix. It can be understood that the three-dimensional roughness parameter Sq mentioned in step S1 is artificially set, while the three-dimensional roughness parameter Sq in step S4 is calculated by the above-mentioned formula for calculating the three-dimensional roughness parameter Sq based on the actual target plate surface morphology during the ion implantation process, and the two are not consistent.

[0142] It can be seen from the above that the present invention can predict the roughness change trend of the material surface during ion implantation, and further provide theoretical guidance for studying the evolution mechanism of the material surface roughness under ion implantation. Moreover, compared with the existing detection method using a detector, the operation is simpler and the cost is lower.

[0143] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A roughness simulation method for ion implantation materials based on molecular dynamics, characterized in that: The following steps are involved: S1. Construct the surface point height matrix M of the research material according to the set value of the three-dimensional roughness parameter Sq; S2. constructing a smooth surface target model of the research material, and changing the smooth surface target model to a rough surface target model according to the surface point height matrix M of the research material; S3. Reading the rough surface target model, and then constructing a molecular dynamics model for ion implantation into the rough surface target model and performing simulation calculations; S4. extracting the target surface morphology of the rough surface target model during ion implantation, and calculating the surface roughness change trend according to the target surface morphology; In step S1, the three-dimensional roughness parameter Sq represents the point height of the object surface The root mean square of the distance to the reference plane, the height of the reference plane is the height of all points on the surface of the object The average value of In step S1, the surface of the research material is decomposed into n sub-surfaces, and the surface point height matrix M of the research material satisfies the relationship: ， In the formula, is the distance between adjacent surface points of the studied material, is the distance between adjacent surface points of the sub-surface, is the surface point height matrix of each sub-surface, and the weight factor The sum of (i=1, 2, ..., n) is 1, the surface point height matrix M of the research material and the surface point height matrix of the sub-surface The number of rows and columns is the same; In step S1, the surface point height matrix of the sub-surface The construction method is: Use Python's random function to generate the initial height matrix of all the sub-surface points Assign random values ​​to the initial height matrix of all surface points of the sub-surface It obeys Gaussian distribution, that is ; Use Python's interpolate function to generate the initial height matrix of the surface points of the sub-surface Interpolate and construct it as the surface point height matrix of the sub-surface ; Step S2 specifically includes the following steps: Step S201. Construct the smooth surface target model and store the three-dimensional coordinate values ​​of all atoms in the smooth surface target model ( ); Step S202. The atoms on the same vertical line in the smooth surface target model are matched with an element in the surface point height matrix M of the research material, and the coordinate values ​​of the projections of the atoms on the same vertical line on the horizontal plane are calculated according to the coordinate values ​​of the projections of the atoms on the same vertical line on the horizontal plane ( ), calculate the row number of the corresponding element in the surface point height matrix M of the research material and column number ; Step S203. Using row numbers and column number Read the value of the corresponding element in the surface point height matrix M of the research material ， ）； Step S204: Determine the height values ​​of atoms on the same vertical line The value of the corresponding element The size of , keep the corresponding atom, otherwise, delete the corresponding atom; Step S205. constructing the rough surface target model according to the relevant information of all retained atoms; Step S4 specifically includes the following steps: Step S401. Construct a matrix , and initialize it to a zero matrix, where the element in the pth row and qth column is represented as ; Step S402. The three-dimensional coordinate values ​​of the atoms in the rough surface target model are ( ), the atoms located on the same vertical line in the rough surface target model and the matrix Corresponding to an element in the , according to the coordinate value of the projection of the atom on the same vertical line on the horizontal plane ( ), calculate the matrix The row number of the corresponding element in and column number ; Step S403. Compare the values ​​of the elements The height value of the corresponding atom The size of , then let Otherwise, keep constant; Step S404. Until all atoms are iterated, the matrix The target surface morphology is used as the rough surface target model during ion implantation.

2. The roughness simulation method for ion implantation of materials based on molecular dynamics according to claim 1, characterized in that: In step S1, the number of rows and columns of the surface point height matrix M of the research material are both set to m, where m is expressed as: ， In the formula, is the side length of the surface of the studied material, is the distance between adjacent surface points of the studied material.

3. The roughness simulation method for ion implantation material based on molecular dynamics according to claim 1, characterized in that: In step S3, the rough surface target model is read, and the x-direction and y-direction are set as periodic boundary conditions, the positive z-direction is set as a free boundary condition, and the negative z-direction is set as a fixed boundary condition. The rough surface target model is divided into a boundary layer, a constant temperature layer and a Newtonian layer from bottom to top, wherein the Newtonian layer is an ion implantation area.

4. The roughness simulation method for ion implantation of materials based on molecular dynamics according to claim 3, characterized in that: In the molecular dynamics model, the ion implantation method is set as: Ions are generated from random positions in the vacuum region at a set height above the rough surface target model. The ion injection direction is at an angle to the z direction. The ions are injected into the rough surface target model in sequence according to a set time interval. The ion injection speed is: ， Where E is the implantation energy and m is the mass of the implanted ions.

5. The roughness simulation method for ion implantation of materials based on molecular dynamics according to claim 1, characterized in that: The step S4 also includes the following steps: Step S405. Using the matrix obtained in step S404 , calculate the values ​​of the three-dimensional roughness parameters Sa and Sq of the rough surface target model during ion implantation, where: The three-dimensional roughness parameter Sa is the arithmetic mean of the distance from the surface point height of the object to the reference plane. The calculation formula of the three-dimensional roughness parameter Sa is: ， The calculation formula of the three-dimensional roughness parameter Sq is: ， In the formula, is the point height on the surface of the object, is the height of the reference plane, For all The average value of .

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