A method to control phonon friction by changing the mismatch angle between black phosphorus layers

Abstract

The present invention relates to a method for regulating phonon friction by changing the mismatch angle between black phosphorus layers, the method comprising the following steps: (1) a black phosphorus film is selected as a probe, and another black phosphorus film supported by a rigid body is used as a substrate. Initially, the probe and the substrate are in commensurate contact. After rotating a certain angle, the probe and the substrate are in non-commensurate contact, and the size of the probe and the substrate in the sliding direction is always the same; (2) a molecular dynamics friction model composed of a probe and a substrate is established; (3) the energy quantization analysis of the friction interface is performed, the phonon spectrum at the interface is extracted, the frequency mode distribution of the probe and the substrate phonon spectrum is analyzed, and the energy dissipation efficiency is explored; further, the friction interface excitation phonons are extracted, and the friction energy dissipation and friction force are quantitatively analyzed by the number of excitation phonons; (4) a simulation process is performed and data is processed. The present invention can analyze the influence of different angles and speeds on the magnitude of the friction force between black phosphorus layers, as well as the influence of different normal loads on the friction force between black phosphorus layers.

Description

Technical Field

[0001] The present invention relates to the field of molecular dynamics technology, and in particular to a method for regulating phonon friction by changing the mismatch angle between black phosphorus layers. Background Art

[0002] Black phosphorus (BP) is one of the most stable allotropes of phosphorene and has recently (since 2014) been re-evaluated as an important layered material, in which each layer is vertically stacked by van der Waals forces and the black phosphorus flakes are easy to shear. Black phosphorus has a wrinkled orthorhombic crystal structure that is different from other two-dimensional materials such as graphene and MoS2. In addition to its special structure, black phosphorus also has physical properties such as limited direct band gap and high carrier mobility at ambient temperature, high light and UV absorption; and in a dark environment, phosphorus-based field effect transistors show bipolar behavior, while when illuminated, black phosphorus transistors show excitation response wavelengths from visible light to 940nm, and the luminescence time rises by about 1ms. Therefore, the bipolar characteristics coupled with fast and broadband light detection make few-layer black phosphorus a promising material for detecting visible and near-infrared light in the electromagnetic spectrum. In addition, the angle-dependent anisotropy makes black phosphorus have better conductivity than other two-dimensional materials. The combination of these unique and outstanding properties makes black phosphorus an ideal material with great application prospects. It has been deeply studied in the fields of mechanics, electronics, electricity, transportation, thermoelectricity, optics, biomedicine, etc., and has been widely used in the fields of semiconductors and optoelectronics.

[0003] In recent years, black phosphorus has been further studied using molecular dynamics and experimental methods. Lubricants containing P elements can effectively inhibit the rapid increase in friction under high loads. In addition, even under high-pressure contact (>1GPa), black phosphorus modified with hydroxyl groups or partially oxidized can obtain stable lubrication properties, and the friction coefficient decreases with the increase of normal load after the hydrophobic BP-oleylamine group is added to hexadecylamine, which shows that chemically modified black phosphorus has great potential as a lubricant in the extreme pressure application of lubricating oils. At the same time, after inserting a layer of interfacial flowing water layer at the interface between the degraded black phosphorus flakes and the SiO2 / Si substrate, it was found that super-lubricity degradation existed at the sliding interface. This finding shows that there is a strong interaction between the degraded BP and water molecules, which provides support for the widespread application of few-layer BP nanomaterials in biolubrication.

[0004] Research on the friction properties of black phosphorus has not only made progress in chemical modification, but also attracted widespread attention on the characteristics of the material itself. The study of the anisotropy of black phosphorus found that the friction of the probe along the armchair direction is greater than the friction along the zigzag direction. Supported by the theoretical prediction of the 2D-Tomlinson model, this phenomenon can be explained by the anisotropy of the bending deformation amplitude induced by the tip of the BP flake. Further research on the friction of black phosphorus with different layer thicknesses found that BP flakes with a thickness greater than about 5 layers showed almost the same friction as bulk BP, and the friction of black phosphorus within 5 layers decreased with the increase in the number of layers. The friction of phosphorene under pre-strain also shows significant anisotropy. The friction increases with pre-strain along the zigzag direction and decreases with pre-strain in the armchair direction. The increase in friction is attributed to the increase in the potential barrier, and the decrease in friction is caused by the reduction in contact area. The diamond probe found an interesting "M-shaped" friction curve when sliding on a silicon-supported black phosphorus substrate at different angles, that is, the friction force at 15° and 75° relative to the zigzag direction is the largest. This is due to the potential energy difference between different orientations caused by the unique structure of phosphorene and the heterogeneous interaction with the substrate. Regarding the effect of normal load on the friction between black phosphorus layers, the researchers found different results from two-dimensional materials such as graphene and molybdenum disulfide: BP effectively suppresses the rapid increase of friction under high load, and has significant high-load friction insensitivity, but the friction performance under zero load is relatively poor. Studies have shown that the friction between double-layer black phosphorus is usually determined by the stacking method (zigzag-zigzag, armchair-armchair and zigzag-armchair) and the torsion angle.

[0005] Although relevant studies have shown that black phosphorus has excellent friction properties and the friction between black phosphorus layers is determined by its stacking method, these studies only focus on the anisotropy of the probe sliding on black phosphorus along the zigzag and armchair directions, and lack the exploration of the anisotropy of interlayer friction when the black phosphorus / black phosphorus layers are in contact at different mismatch angles. Since the friction process and energy dissipation are inseparable, and related properties such as friction energy dissipation have an important impact on the preparation, life, energy saving and wider application of graphene-based nanodevices, therefore, the friction properties of black phosphorus are urgently needed. In-depth research is needed. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for regulating phonon friction by changing the mismatch angle between black phosphorus layers.

[0007] In order to solve the above problems, the present invention provides a method for regulating phonon friction by changing the mismatch angle between black phosphorus layers, comprising the following steps:

[0008] (1) A black phosphorus film is selected as a probe, and another black phosphorus film supported by a rigid body is selected as a substrate. Initially, the probe and the substrate are in commensurate contact. After the probe black phosphorus film is rotated by a certain angle, there is a certain mismatch angle between the probe and the substrate black phosphorus layer, so that the probe and the substrate are in non-commensurate contact, and the size of the probe and the substrate in the sliding direction is always the same;

[0009] (2) Establishing a molecular dynamics friction model consisting of the probe and the substrate:

[0010] Each atom in the black phosphorus film probe is x , y , z Springs are set in the x direction respectively; among which: the spring in the x direction connects the probe film with the sliding speed The virtual slider is connected to guide the uniform sliding of the probe relative to the substrate, so as to obtain sliding friction; the spring applied in the y direction is used to eliminate the translation of the probe along the y axis and the rotation around the y and z axes; the spring applied in the z axis is used to apply the normal load during the sliding process and maintain the dynamic balance of the distance between the probe and the substrate, thereby ensuring that the position of the friction system does not shift during the sliding process; periodic boundary conditions are set in the x-axis and y-axis directions, and free boundary conditions are set in the z-axis direction;

[0011] The system simulation was carried out in a microcanonical ensemble and the temperature was controlled by a Berendsen thermostat. The Stillinger-Weber (SW) potential was used for the interaction between all phosphorus atoms, and the Lennard–Jones (LJ) potential was used for the interaction between black phosphorus layers.

[0012] ⑶ Quantize the energy of the friction interface, extract the phonon spectrum at the interface, analyze the frequency mode distribution of the probe and substrate phonon spectra, and explore the energy dissipation efficiency; further extract the excited phonons at the friction interface, and quantitatively analyze the friction energy dissipation and friction force through the number of excited phonons;

[0013] ⑷Execute the simulation process and process the data:

[0014] ① Maintain normal load f n The sliding speed is set to 10m / s and 50m / s respectively, the temperature is set to 300K, and the simulation process is performed respectively after changing the mismatch angle; the friction between the black phosphorus layers under different sliding states is calculated, and then used to analyze the influence of different angles and speeds on the friction between the black phosphorus layers;

[0015] ② Keeping the sliding speed constant, different normal loads ranging from 0.001nN / atom to 0.03nN / atom were set for the black phosphorus / black phosphorus friction system with a 0° mismatch angle and a 90° mismatch angle. f n , and calculate the friction between black phosphorus layers under different normal loads, which is then used to analyze the effect of changing the normal load on the friction between black phosphorus layers under different contact states, namely commensurate contact and incommensurate contact.

[0016] The step (4) of executing the simulation process and processing the data also includes: statistically analyzing the potential barrier and temperature standard deviation between black phosphorus layers under different contact states, and using the relationship between the potential barrier and temperature under different contact states to analyze the influence of thermal excitation and thermal vibration on the friction between atomic layers.

[0017] The step (4) of executing the simulation process and processing the data also includes: selecting areas containing sixteen phosphorus atoms on the substrate and the probe respectively, and calculating the state density of atoms adjacent to the friction interface in the area; and analyzing the energy dissipation efficiency of the friction interface at different angles from the perspective of state density.

[0018] The step (4) of executing the simulation process and processing the data also includes: selecting a region containing sixteen phosphorus atoms on the substrate, calculating the number of excited phonons on different layers of atoms in the region; and analyzing the amount of energy dissipation of the friction interface and the magnitude of the friction force under different contact states from the perspective of the number of excited phonons.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The present invention finds that the friction between black phosphorus layers presents a 180° periodicity under room temperature conditions, and then keeps the sliding speed unchanged. When the mismatch angles between the probe and the substrate are 0° and 90° respectively, the system temperature is changed and the normal load is gradually increased. The effects of the normal load and temperature on the friction between black phosphorus layers under different sliding states are calculated, which is used to analyze the effects of changing temperature and load on the friction between black phosphorus layers under different mismatch angles.

[0021] 2. The present invention uses the potential barrier height and the temperature standard deviation to analyze the reasons for the change of friction between black phosphorus layers at different mismatch angles. The results show that: at 0°, i.e., commensurate contact, the sliding interface has a strong potential barrier constraint and a large friction force. When the temperature rises, the thermal excitation effect will provide some atoms with the energy required to cross the potential energy, thereby reducing the friction between black phosphorus layers. However, at 90°, i.e., non-commensurate contact, the potential barrier constraint of the sliding interface is very weak. Once an external force is applied, the black phosphorus film can easily move relative to each other. When the temperature rises, the higher temperature will cause the thermal vibration between atoms on the contact surface to intensify, which will lead to an increase in atomic collisions and increase friction.

[0022] 3. In order to clarify the energy dissipation mechanism during black phosphorus / black phosphorus friction under different contact states, the state density of atoms on the relative contact surfaces is analyzed, that is, the phonon spectra excited on the P1 atoms of the probe and the P2 atoms of the substrate are extracted. The results show that: at 0° contact, the atoms in contact between the probe and the substrate have a highly unified phonon mode, which will form an energy dissipation channel between the surfaces, promote the transmission of excited phonons during relative motion, and improve the energy transfer efficiency; at 90° contact, there is no unified phonon mode between the atoms on the contact surfaces of the probe and the substrate, and no energy dissipation channel can be formed, which reduces the efficiency of energy dissipation.

[0023] 4. In order to quantify the number of phonons excited in the friction process, the present invention counted the number of phonons excited on atoms when the probe slides, and the results show that: in commensurate contact and incommensurate contact, the phonons excited on the P1 atom adjacent to the contact interface are more than the phonons excited on the non-adjacent interface atom P2, which indicates that the contribution of the adjacent contact interface atoms to the friction force is higher than the contribution of the non-adjacent interface atoms to the friction force; in addition, the research results show that in the lower acoustic mode, the number of phonons excited on the P1 atom is slightly higher than the number of phonons excited on the P2 atom in commensurate contact, and in incommensurate contact, the number of phonons excited on the P1 atom is significantly higher than the number of phonons excited on the P2 atom, therefore, there is a slight difference in the contribution of the non-adjacent interface atoms and the adjacent contact atoms to the friction force in commensurate contact, and a significant difference in the contribution of the non-adjacent interface atoms and the adjacent contact atoms to the friction force in incommensurate contact. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0025] Figure 1 The black phosphorus structure model (a) and the black phosphorus probe film / black phosphorus substrate sheet friction model (b) in the present invention.

[0026] Figure 2 The friction force curve (a) between the friction force and the mismatch angle at the same sliding speed in the present invention and the relationship curve (b) between the friction force and different normal loads at 0° and 90° contact states.

[0027] Figure 3 For the present invention v s =10m / s, 0° contact with different temperatures and potential barriers (a), v s =10m / s, the relationship between different temperatures and potential barriers when contacting at 90° (b), v s =10m / s, change in temperature standard deviation when contacting at 0° (c), v s=10m / s, change in temperature standard deviation when contact is at 90° (d).

[0028] Figure 4 The potential energy surfaces of the probe and the substrate at 0° contact (a), 90° contact (b), 90° contact (c), and 180° contact (d) in the present invention are shown.

[0029] Figure 5 For the present invention v s =10m / s, f n =0.05nN / atom. Analysis of the phonon spectrum of atoms excited on the surface of the probe when the contact angle is 0° with the substrate (a). Analysis of the phonon spectrum of atoms excited on the surface of the probe when the contact angle is 90° with the substrate (b).

[0030] Figure 6 For the present invention v s =10m / s, f n =0.05nN / atom. Analysis of the number of phonons excited by interface atoms when the probe contacts the substrate at 0° (a). Analysis of the number of phonons excited by interface atoms when the probe contacts the substrate at 90° (b). DETAILED DESCRIPTION

[0031] A method for regulating phonon friction by changing the mismatch angle between black phosphorus layers comprises the following steps:

[0032] ⑴ Select a black phosphorus film as a probe and another black phosphorus film supported by a rigid body as a substrate. Initially, the probe and the substrate are in commensurate contact. After the probe black phosphorus film is rotated by a certain angle, there is a certain mismatch angle between the probe and the substrate black phosphorus layer, so that the probe and the substrate are in non-commensurate contact. The size of the probe and the substrate in the sliding direction is always the same. Figure 1 As shown in (a), the upper atom of each layer of black phosphorus in the black phosphorus structure model is labeled P2, and the lower atom is labeled P1.

[0033] ⑵Establish a molecular dynamics friction model consisting of a probe and a substrate:

[0034] Each atom in the black phosphorus film probe is x , y , z Springs are set in the x direction respectively; among which: the spring in the x direction connects the probe film with the sliding speed The virtual slider is connected to guide the uniform sliding of the probe relative to the substrate, so as to obtain sliding friction; the spring applied in the y direction is used to eliminate the translation of the probe along the y axis and the rotation around the y and z axes; the spring applied in the z axis is used to apply a normal load during the sliding process and maintain the dynamic balance of the distance between the probe and the substrate, thereby ensuring that the position of the friction system does not shift during the sliding process; periodic boundary conditions are set in the x-axis and y-axis directions, and a free boundary condition is set in the z-axis direction.

[0035] The system simulation was carried out in a microcanonical ensemble and the temperature was controlled by a Berendsen thermostat; the Stillinger-Weber (SW) potential was used for the interaction between all phosphorus atoms, and the Lennard–Jones (LJ) potential was used between black phosphorus layers.

[0036] ⑶ Quantize the energy of the friction interface, extract the phonon spectrum at the interface, analyze the frequency mode distribution of the probe and substrate phonon spectra, and explore the energy dissipation efficiency; further extract the excited phonons at the friction interface, and quantitatively analyze the friction energy dissipation and friction force through the number of excited phonons;

[0037] ⑷Execute the simulation process and process the data:

[0038] ① Maintain normal load f n The sliding speed is set to 10m / s and 50m / s respectively, the temperature is set to 300K, and the simulation process is performed respectively after changing the mismatch angle; the friction between the black phosphorus layers under different sliding states is calculated, and then used to analyze the influence of different angles and speeds on the friction between the black phosphorus layers;

[0039] ② Keeping the sliding speed constant, different normal loads ranging from 0.001nN / atom to 0.03nN / atom were set for the black phosphorus / black phosphorus friction system with a 0° mismatch angle and a 90° mismatch angle. f n , and calculate the friction between black phosphorus layers under different normal loads, which is then used to analyze the effect of changing the normal load on the friction between black phosphorus layers under different contact states, namely commensurate contact and incommensurate contact.

[0040] The present invention also includes one of the following steps:

[0041] The standard deviations of the potential barriers and temperatures between black phosphorus layers under different contact states were statistically analyzed, and the relationship between the potential barriers and temperatures under different contact states was used to analyze the effects of thermal excitation and thermal vibration on the friction between atomic layers.

[0042] Regions containing sixteen phosphorus atoms were selected on the substrate and the probe respectively, and the state density of the atoms adjacent to the friction interface in this region was calculated. The energy dissipation form of the friction interface at different angles was analyzed from the perspective of state density, that is, the friction energy was quantized and the phonon spectrum of the excited atoms on the contact surface was analyzed. The degree of coupling of the phonon spectrum was used to determine whether the energy dissipation channel could be established at different angles, and the friction energy dissipation efficiency was analyzed.

[0043] A region containing sixteen phosphorus atoms was selected on the substrate, and the number of excited phonons on different layers of atoms in this region was calculated. From the perspective of the number of excited phonons, the amount of energy dissipated at the friction interface and the magnitude of the friction force under different contact states were analyzed, and then the contribution of adjacent contact surface atoms and non-adjacent contact surface atoms to the friction force under different mismatch angles was proved.

[0044] Embodiment The present invention takes black phosphorus, a special two-dimensional material composed of a wrinkled orthogonal structure, as a research object, and explores a research method for the angle dependence of phonon friction between black phosphorus layers.

[0045] The specific process is as follows:

[0046] 1. Establish molecular dynamics model

[0047] refer to Figure 1 The molecular dynamics model shown in the figure uses non-equilibrium molecular dynamics to simulate the friction process of the black phosphorus system under the microcanonical ensemble. The model includes a probe and a substrate. The probe is a black phosphorus film obtained by shearing after rotating at different angles (black phosphorus film probes at different angles are executed separately during simulation), and the substrate is a black phosphorus sheet supported by a rigid body. The graphene on the substrate is used to simulate the cantilever beam probe of the atomic force microscope.

[0048] In order to accurately simulate the stable sliding process of the AFM cantilever beam, springs with large stiffness were applied to the three directions of the film. The springs with a stiffness of 6000nN / nm were applied in the x and y directions. The spring in the x direction separated the probe film from the sliding speed of The virtual slider is connected to guide the probe to slide at a uniform speed relative to the substrate, thereby obtaining sliding friction; the spring applied in the y direction is used to eliminate the translation of the probe along the y axis and the rotation around the y and z axes; the spring stiffness applied to the z axis is 4000nN / nm, which is used to apply the normal load during the sliding process and maintain the dynamic balance between the probe and the substrate, further ensuring that the position of the friction system does not shift during the sliding process. The degrees of freedom of all the black phosphorus atoms in the bottom layer and the atoms at the boundary of the upper black phosphorus are fixed, and the atoms close to the fixed edge are set as Berendsen thermostats. The entire simulation first undergoes a 100 ps relaxation process to allow the system temperature to reach the set temperature, and the ambient temperature of the system is considered to be constant during the entire calculation process.

[0049] The interaction between all phosphorus atoms is described by SW potential. In addition, the interaction between black phosphorus layers is described by van der Waals potential, where: =1.594 meV, equilibrium constant =0.3438nm, cutoff radius =0.8938nm. The initial size of the model probe is 16.8×16.3nm 2 (7252 atoms), the substrate size is 16.8×40.1nm (36480 atoms).

[0050] The x-axis and y-axis directions are set as periodic boundary conditions, and the z-axis direction is set as a free boundary condition. Therefore, the atoms between the probe and the substrate are always in a state of mutual excitation in the sliding direction. Finally, a region containing 16 phosphorus atoms is selected on the probe and the substrate black phosphorus, respectively, and the probe sliding time step is set to 0.5fs, which is much lower than the fastest annihilation time of phonons, so that all information about phonons generated by dynamic excitation can be extracted.

[0051] , analyze the influence of different angles, sliding speeds and temperatures on the friction between black phosphorus layers

[0052] according to Figure 1 (b) The friction model established is calculated as follows Figure 2 (a) shows the friction curve. The figure shows that at room temperature, the friction between black phosphorus layers shows a 180° periodicity, and the maximum friction is near 0° and 180°, that is, the friction is maximum when the probe and the substrate are in contact, and when the probe is rotated by a certain angle, the friction between the layers gradually decreases, and when the probe is rotated 90° and slides along the substrate, the friction reaches the minimum.

[0053] Further research is conducted on the effects of different loads and temperatures on friction when the mismatch angle is 0° and 90°. The results are as follows: Figure 2 (b) As shown in the figure, it can be clearly seen that: in commensurate contact, as the normal load increases, the sliding friction increases significantly, while in non-commensurate contact, as the normal load increases, the trend of friction gradually increasing is no longer significant. In the 90° contact state, the friction also increases with the increase in temperature, which deviates from the existing thermal excitation effect.

[0054] , Analyze the influence of thermal excitation and thermal vibration on the friction between atomic layers from the relationship between potential barrier and temperature at different mismatch angles

[0055] Regarding the difference in the friction between BP layers with increasing temperature under commensurate and incommensurate contact, it may be that the temperature increase under different contact states not only provides energy for the probe to cross the potential barrier, but also causes the thermal excitation effect to no longer apply after the temperature increases in incommensurate contact. Therefore, the potential barrier height and temperature standard deviation (TSD) under different normal loads at 0° and 90° contact were calculated for verification. The potential barrier is used to reflect the difficulty of the probe atom to overcome the obstacle, and the temperature standard deviation is used to reflect the atomic vibration amplitude when the atom is subjected to high temperature. Figure 3 (a) shows that the surface potential barrier is very high at 0° contact, while Figure 3 (b) shows that the surface barrier is extremely low at 90° contact and the barrier is even lower at 0 K; Figure 3 (c) and (d) show the temperature standard deviations at 0° and 90° contact. The results show that there is no significant difference between the values ​​for commensurate and non-commensurate contact, that is, the thermal vibrations caused by temperature rise under different contact conditions are almost the same.

[0056] Combining the high potential barrier during commensurate contact and the low potential barrier during incommensurate contact, we can know that at 0 K, the strong constraint of the higher potential barrier under commensurate contact seriously hinders the relative motion between black phosphorus layers, while the low potential barrier under incommensurate contact has less hindrance to atomic motion; once the temperature rises, the system energy and thermal amplitude increase. Therefore, during commensurate contact, the increased temperature provides additional energy to promote atoms to overcome the high potential barrier, making the probe easy to slide relative to 0 K. However, under incommensurate contact, the probe itself can easily slide under the action of external force due to its smaller constraint, but the energy added by the system after the temperature rises is much higher than the energy required to overcome the potential barrier, so the thermal vibration of the atoms increases, which leads to an increase in the frequency of collisions between atoms, and thus an increase in friction.

[0057] , Analyze the energy dissipation form of friction interface at different angles from the perspective of state density

[0058] (41) Potential energy surface analysis at different mismatch angles

[0059] To further prove that the friction force between black phosphorus layers exhibits a 180° periodicity, the potential energy surface of the substrate and the probe at different mismatch angles was calculated through the interlayer contact state of black phosphorus / black phosphorus, as shown in Figure 2. Figure 4 shown.

[0060] and Figure 1 The difference between the computational friction model and the conventional friction model is that both the probe and the substrate are set as rigid bodies, which can accurately describe the contact pattern between the relative sliding surfaces when the probe is scanned on the substrate. Figure 4 It can be seen that when the probe is rotated 0° and 180° relative to the substrate, the results of the potential energy surface expression are consistent. The distance between the probe atom when it crosses the two potential energy peaks is a and bremains unchanged, so it can be proved that Figure 1 The obtained 180° period is reasonable, and the length of the potential energy period does not change. However, a different potential energy surface is obtained after the probe is rotated 90°. Figure 4 (b) shows the potential energy surface of the substrate. Figure 4 (c) is the potential energy surface of the probe. It can be seen from the figure that the potential energy period of the interaction between the probe and the substrate has changed. Compared with the initial 0°, it is found that the potential energy period values ​​along the armchair direction and the zigzag direction are interchanged, that is, after rotating 90°, the period length of the probe affected by the substrate along the armchair direction is b , the period length along the zigzag direction is a .

[0061] (42) Analysis of energy dissipation forms of friction interfaces at different angles from the perspective of state density

[0062] The energy in the friction process is quantized, and friction is the process of converting the kinetic energy of mechanical motion into heat energy carried by phonons. Therefore, the energy of the friction interface exists in the form of phonons, and the transport of these phonons depends on the specific energy transfer channels between the contact surfaces. Therefore, the phonon spectrum of the contact surface excitation is further studied based on this characteristic.

[0063] Since the thermal phonons excited by the background temperature will mask the phonon information related to friction, only the phonon spectrum excited at 0 K is extracted to avoid the entanglement of thermal phonons and friction excited phonons. In order to facilitate the comparison of the results, the larger normal load is extracted. f n = 0.05nN / atom, such as Figure 5 As shown in the figure. The figure shows that the friction-excited phonons are distributed in different frequency modes. Figure 4 As we know, the potential energy period changes when the probe slides in different directions, and the atoms in contact with the surface are subjected to forces from the atoms on the opposite side. Therefore, the washboard frequency of the probe and the substrate at 0° is calculated to be f s and f t The values ​​of v s / a , and after the probe rotates 90°, the probe's washboard frequency f s = v s / a , the washboard frequency of the base f t = v s / b . Figure 5The dashed lines shown represent the frequency distribution of the washboard frequency and its harmonics. It can be seen from the figure that the friction-excited phonons are distributed exactly at the frequencies where these dashed lines are located, that is, the friction-excited phonons are distributed at the washboard frequency and its harmonics.

[0064] When the black phosphorus layers in 0° contact move relative to each other, the phonon modes excited by the contact surface atoms, i.e., the P1 atoms of the probe and the P2 atoms of the substrate, are distributed in the same way, thus establishing a special phonon transport channel and improving the energy dissipation efficiency. Figure 5 (a); at 90°, the phonon modes excited on the contact surface atoms are located at different vibration frequencies, so there is no definite energy dissipation channel, which in turn leads to the obstruction of energy transfer efficiency, as shown in Figure 5 (b) shown.

[0065] , from the perspective of the number of excited phonons, analyze the amount of energy dissipation of the friction interface and the magnitude of the friction force under different contact states

[0066] In order to quantify the amount of friction energy dissipated and the magnitude of friction force during the friction process, the number of excited phonons on the adjacent contact interface atoms (P1) and non-adjacent contact interface atoms (P2) of the probe black phosphorus during the friction process was counted, such as Figure 6 First, the results show that the frequencies of concentrated phonon excitation in commensurate contact are more than 6, while the concentrated phonon excitation in incommensurate contact is only distributed in the first two frequencies. Therefore, the number of interface excited phonons in commensurate contact is greater than that in incommensurate contact. This is because the bending and deformation of the interface in commensurate contact is greater than that in incommensurate contact, so that the commensurate contact accumulates more energy converted into anharmonic phonons.

[0067] In addition, the number of phonons excited on the P1 atom under different contact states is always greater than that on the P2 atom. Therefore, the contribution of the upper and lower atoms of black phosphorus to the friction force is inconsistent, and the contribution of atoms close to the interface to the friction force is greater than that of atoms not close to the interface. This can be understood through the dynamic stick-slip process of atomic motion. Since all mechanical energy is converted into the internal potential energy of the atoms in the stick stage, and this accumulated energy will be dissipated in the form of atomic vibration in the slip stage, the probe in this simulation is a non-rigid body with a spring applied, so it satisfies the stick-slip state, that is, the P1 atom close to the interface will undergo significant vibration dissipation energy in the slip stage, while the vibration transmitted from the P1 atom to the P2 atom is relatively weak, resulting in a large number of phonons excited on the P1 atom.

[0068] In addition to the above results, it is also found that when the commensurate contact occurs, the contribution of the P2 atom at low frequencies is slightly weaker than that of the P1 atom, e.g. Figure 6 (a); in the case of incommensurate contact, the contribution of the P2 atom at low frequency is very weak compared to the contribution of the P1 atom, as shown in Figure 6 (b) As shown. Combined Figure 3 From (a) and (b), we can see that the energy accumulated in the sticking stage during commensurate contact is much greater than the energy accumulated in the sticking stage during incommensurate contact. Therefore, in the sliding stage, the atomic vibration amplitude caused by energy dissipation during commensurate contact is much higher than the atomic vibration during the incommensurate sliding stage. Therefore, the strong vibration of P1 atoms during commensurate contact will trigger a stronger vibration of P2 atoms, so the number of phonons excited on P2 atoms is slightly smaller than the number of phonons excited on P1 atoms. In incommensurate contact, the weak vibration of P1 atoms causes a weaker vibration of P2 atoms, so the number of phonons excited on P2 atoms is significantly less than the number of phonons excited on P1 atoms. And because the vibration caused by friction is mainly dominated by the excitation and dissipation of acoustic mode phonons, this difference is reflected at a smaller frequency.

[0069] In summary, the present invention is based on the combination of molecular dynamics and quantum theory, revealing the angle dependence mechanism of phonon friction between black phosphorus layers. The friction between black phosphorus layers shows a periodicity of 180°, with the maximum friction at relative angles of 0° and 180°, and the minimum friction at 90°. The difference in the effect of high temperature on friction during commensurate and non-commensurate contact is explained. After quantizing the friction energy, the phonon spectrum is extracted and analyzed. When the probe and the substrate atoms are in commensurate contact, an effective energy transfer channel can be established between the probe and the substrate atoms, which improves the energy transfer efficiency. When the commensurate contact is not achieved, a good energy transport channel cannot be established, so the energy dissipation efficiency decreases. Finally, by extracting the number of interface excitation phonons, it is found that the number of atomic excitation phonons adjacent to the contact interface is greater than the number of atomic excitation phonons adjacent to the interface, so the contribution of atoms adjacent to the contact interface to the friction force is higher than that of atoms adjacent to the interface.

[0070] The technical solution provided by the present invention is described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for regulating phonon friction by changing the mismatch angle between black phosphorus layers, comprising the following steps: (1) A black phosphorus film is selected as a probe, and another black phosphorus film supported by a rigid body is selected as a substrate. Initially, the probe and the substrate are in commensurate contact. After the probe black phosphorus film is rotated by a certain angle, there is a certain mismatch angle between the probe and the substrate black phosphorus layer, so that the probe and the substrate are in non-commensurate contact, and the size of the probe and the substrate in the sliding direction is always the same; (2) Establishing a molecular dynamics friction model consisting of the probe and the substrate: Each atom in the black phosphorus film probe is x , y , z Springs are set in the x direction respectively; among which: the spring in the x direction connects the probe film with the sliding speed The virtual slider is connected to guide the uniform sliding of the probe relative to the substrate, so as to obtain sliding friction; the spring applied in the y direction is used to eliminate the translation of the probe along the y axis and the rotation around the y and z axes; the spring applied in the z axis is used to apply the normal load during the sliding process and maintain the dynamic balance of the distance between the probe and the substrate, thereby ensuring that the position of the friction system does not shift during the sliding process; periodic boundary conditions are set in the x-axis and y-axis directions, and free boundary conditions are set in the z-axis direction; The system simulation was carried out in a microcanonical ensemble and the temperature was controlled by a Berendsen thermostat. The Stillinger-Weber potential was used for the interaction between all phosphorus atoms, and the Lennard–Jones potential was used for the interaction between black phosphorus layers. ⑶ Quantize the energy of the friction interface, extract the phonon spectrum at the interface, analyze the frequency mode distribution of the probe and substrate phonon spectra, and explore the energy dissipation efficiency; further extract the excited phonons at the friction interface, and quantitatively analyze the friction energy dissipation and friction force through the number of excited phonons; ⑷Execute the simulation process and process the data: ① Maintain normal load f n The sliding speed is set to 10m / s and 50m / s respectively, the temperature is set to 300K, and the simulation process is performed respectively after changing the mismatch angle; the friction between the black phosphorus layers under different sliding states is calculated, and then used to analyze the influence of different angles and speeds on the friction between the black phosphorus layers; ② Keeping the sliding speed constant, different normal loads ranging from 0.001nN / atom to 0.03nN / atom were set for the black phosphorus / black phosphorus friction system with a 0° mismatch angle and a 90° mismatch angle. f n , and calculate the friction between black phosphorus layers under different normal loads, which is then used to analyze the effect of changing the normal load on the friction between black phosphorus layers under different contact states, namely commensurate contact and incommensurate contact.

2. The method for regulating phonon friction by changing the mismatch angle between black phosphorus layers according to claim 1, characterized in that: The step (4) of executing the simulation process and processing the data also includes: statistically analyzing the potential barrier and temperature standard deviation between black phosphorus layers under different contact states, and using the relationship between the potential barrier and temperature under different contact states to analyze the influence of thermal excitation and thermal vibration on the friction between atomic layers.

3. The method for regulating phonon friction by changing the mismatch angle between black phosphorus layers according to claim 1, characterized in that: The step (4) of executing the simulation process and processing the data also includes: selecting areas containing sixteen phosphorus atoms on the substrate and the probe respectively, and calculating the state density of atoms adjacent to the friction interface in the area; and analyzing the energy dissipation efficiency of the friction interface at different angles from the perspective of state density.

4. The method for regulating phonon friction by changing the mismatch angle between black phosphorus layers according to claim 1, characterized in that: The step (4) of executing the simulation process and processing the data also includes: selecting a region containing sixteen phosphorus atoms on the substrate, calculating the number of excited phonons on different layers of atoms in the region; and analyzing the amount of energy dissipation of the friction interface and the magnitude of the friction force under different contact states from the perspective of the number of excited phonons.

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