Regulation and control method for friction force of graphene

Abstract

The invention belongs to the technical field of two-dimensional material lubrication, and particularly relates to a regulation and control method for graphene friction force. The preparation method comprises the following steps: performing plasma treatment on a graphene sheet on the surface of a substrate to introduce structural defects to obtain a pretreated graphene sheet; and folding the exposed edge of the pretreated graphene sheet on the surface of the substrate by adopting nano manipulation of an atomic force microscope to obtain a folded pretreated graphene sheet. According to the method, defect structures with different densities are introduced through plasma treatment to weaken and damage a pseudo magnetic field, and effective regulation and control on friction of the edge of the folded graphene are realized. The method provided by the invention is simple to operate, has high regulation and control precision on the friction force of the graphene, and can be widely applied to friction regulation and control of micro-nano devices.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material lubrication technology, specifically relating to a method for regulating the frictional force of graphene. Background Technology

[0002] Friction consumes about one-third of the world's primary energy, and pervasive wear causes 80% of mechanical component failures. Due to weak interlayer van der Waals interactions and excellent in-plane rigidity, two-dimensional materials, such as graphene and molybdenum disulfide, exhibit ultra-low coefficients of friction and can achieve super-lubricating conditions under non-commensurate contact.

[0003] However, the prevalent edge structures in two-dimensional material systems are both a major source of friction and an obstacle to achieving superlubricity. Related experimental and theoretical studies have confirmed that the edge atoms of two-dimensional atomic planes in finite-sized contact surfaces contribute far more to the total frictional force than the internal atoms (approximately 4-5 orders of magnitude higher), resulting in a linear dependence of frictional force on the contact size. Edge pinning and friction can be effectively reduced through edge passivation and annealing reconstruction.

[0004] However, the current demand for friction is no longer limited to achieving ultra-low coefficients of friction, but rather to providing stable and reliable friction control for different application scenarios. Current technology is not yet capable of effectively controlling friction for different application scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling the friction of graphene. The method provided by this invention can achieve precise control of the friction of graphene, thereby enabling the acquisition of graphene with different friction for different application scenarios.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for controlling the frictional force of graphene, comprising the following steps: Pretreated graphene sheets are obtained by introducing structural defects through plasma treatment on the surface of the substrate. The exposed edges of the pretreated graphene sheet located on the substrate surface were folded using nanomanipulation with atomic force microscopy to obtain a folded pretreated graphene sheet.

[0007] Preferably, argon is used as the treatment atmosphere for the plasma treatment.

[0008] Preferably, the conditions for plasma treatment include: pressure of 0.1~0.5 Pa; argon flow rate of 5~15 sccm; radio frequency power of 3~6 W; and treatment time of 0~5 s, which is not 0.

[0009] Preferably, the folding includes the following steps: The morphology of the pretreated graphene sheet is scanned in the tapping mode of an atomic force microscope to determine the position of the exposed edge of the pretreated graphene sheet; the movement trajectory of the atomic force microscope probe is set from the outside to the inside of the pretreated graphene sheet along a direction perpendicular to the exposed edge of the pretreated graphene sheet; then the probe of the atomic force microscope is moved across the pretreated graphene sheet according to the movement trajectory to fold the exposed edge of the pretreated graphene sheet.

[0010] Preferably, the conditions for the atomic force microscope probe to pass over the pretreated graphene sheet include: a normal load of 1~1.5μN and a movement speed of 0.3~0.5μm / s; the material of the atomic force microscope probe used during the folding is single-crystal diamond.

[0011] Preferably, the probe of the atomic force microscope used in the tapping mode is made of silicon.

[0012] Preferably, the ambient atmosphere for nanomanipulation of the atomic force microscope is argon, the ambient humidity is <10%, and the ambient temperature is room temperature.

[0013] Preferably, the graphene sheet has a size of 10~30μm.

[0014] Preferably, the graphene sheet is prepared by mechanical exfoliation.

[0015] Preferably, the substrate material is silicon dioxide; the substrate is sequentially cleaned and dried before use, the cleaning including sequential first cleaning, second cleaning, and third cleaning followed by water washing; the reagents used for the first cleaning are acetone, ethanol, and water, and the first cleaning is performed under ultrasonic conditions; the reagent used for the second cleaning is a mixed solution of H2SO4 and H2O2, and the second cleaning time is 5-15 min; the reagent used for the third cleaning is a mixed solution of NH3 and H2O2, and the third cleaning time is 5-15 min.

[0016] This invention provides a method for controlling the frictional force of graphene, comprising the following steps: introducing structural defects into a graphene sheet located on a substrate surface through plasma treatment to obtain a pretreated graphene sheet; and using nanomanipulation with an atomic force microscope (AFM) to fold the exposed edges of the pretreated graphene sheet on the substrate surface to obtain a folded pretreated graphene sheet. This invention first introduces defect structures into the graphene sheet surface through plasma treatment, and then uses nanomanipulation with an AFM to fold the exposed graphene edges to obtain folded graphene edges. The intrinsically flat two-dimensional honeycomb lattice of graphene undergoes strong stretching at the curved edges, changing the bond lengths and bond angles between carbon atoms, thereby causing changes in electron transition energies within a localized area. This localized strain field can induce a pseudo-magnetic field, causing electrons to move in a ring-like motion as if subjected to a real external magnetic field. This cyclotron motion of charge carriers corresponds to discrete pseudo-Landau levels, significantly altering the material properties. Therefore, this invention, by folding the edges of graphene sheets, effectively reduces friction by generating a pseudo-magnetic field induced by strain at the edges of the folded graphene compared to the edges of exposed graphene of the same height (with the same barrier height). The localized strain-induced pseudo-magnetic field significantly reduces friction to half that of the exposed graphene edge of the same thickness. Since the formation of the pseudo-magnetic field requires ordered, continuously changing lattice deformation, the defects introduced by plasma treatment in this invention can disrupt the strain gradient necessary for generating the pseudo-magnetic field, greatly weakening or even destroying its overall effect. This invention, by first performing plasma treatment and then folding, can generate defect structures of different densities on the inner side of the folded graphene edge, thereby controlling the pseudo-magnetic field strength and achieving effective control of friction at the folded graphene edge. The method provided by this invention is simple to operate, has high precision in controlling the friction of graphene, and can be widely applied to the friction control of micro / nano devices, including lubrication of micro / nano electromechanical systems (requiring reduced friction) and precise control and braking of micro / nano devices (requiring sufficient friction). Attached Figure Description

[0017] Figure 1 This is a schematic diagram of Ar plasma treatment performed on the graphene sheet prepared in this invention. Figure 2 This is the Raman spectrum of the graphene sheet after plasma treatment in this invention; Figure 3 This is an AFM morphology image of the edge of the folded graphene prepared in this invention; Figure 4 The height curve of the edge of the folded graphene prepared in this invention; Figure 5 The scanning tunneling spectrum of the edge of the folded graphene prepared in this invention and the corresponding pseudo-magnetic field strength are shown. Figure 6 The graph shows the friction coefficients of the exposed graphene edges and the folded graphene edges prepared in Examples 1-3. Detailed Implementation

[0018] This invention provides a method for controlling the frictional force of graphene, comprising the following steps: Pretreated graphene sheets are obtained by introducing structural defects through plasma treatment on the surface of the substrate. The exposed edges of the pretreated graphene sheet located on the substrate surface were folded using nanomanipulation with atomic force microscopy (AFM) to obtain a folded pretreated graphene sheet.

[0019] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0020] This invention introduces structural defects into graphene sheets located on the substrate surface through plasma treatment, resulting in pretreated graphene sheets.

[0021] In this invention, the substrate material can be silicon oxide. The silicon oxide substrate used in this invention has a smooth surface and strong mechanical strength, which facilitates the subsequent transfer and spreading of graphene sheets onto it.

[0022] The substrate is preferably cleaned and dried sequentially before use. The cleaning preferably includes a first cleaning, a second cleaning, a third cleaning, and a water rinse sequentially. The reagents used for the first cleaning are preferably acetone, ethanol, and water. The ethanol can be anhydrous ethanol. The water can be deionized water. The first cleaning is preferably performed under ultrasonic conditions. The first cleaning is preferably performed 1 to 3 times. Each first cleaning preferably includes sequential ultrasonic cleaning with acetone, ultrasonic cleaning with ethanol, and ultrasonic cleaning with water. The ultrasonic cleaning time with acetone is preferably 5 to 10 minutes, the ultrasonic cleaning time with ethanol is preferably 5 to 10 minutes, and the ultrasonic cleaning time with water is preferably 5 to 10 minutes. This invention preferably removes organic matter from the substrate surface through the first cleaning.

[0023] In this invention, the reagent used for the second cleaning is preferably a mixed solution of H2SO4 and H2O2. The H2SO4 and H2O2 mixed solution is preferably formed by mixing concentrated sulfuric acid and hydrogen peroxide. The mass content of the concentrated sulfuric acid can be 96-98%. The volume ratio of the concentrated sulfuric acid to hydrogen peroxide is preferably 2-3:1. The second cleaning is preferably an immersion wash. The second cleaning time is preferably 5-15 minutes, and in the example, it can be 10 minutes.

[0024] In this invention, the reagent used for the third cleaning is preferably a mixed solution of NH3 and H2O2. The mixed solution of NH3 and H2O2 is preferably formed by mixing ammonia and hydrogen peroxide. The mass content of the ammonia can be 28-30%. The volume ratio of ammonia to hydrogen peroxide is preferably 1-2:1. The third cleaning is preferably an immersion wash. The time for the third cleaning is preferably 5-15 minutes, and in the example, it can be 10 minutes.

[0025] The present invention preferably removes particulate contaminants from the substrate surface through a second and a third cleaning process. In this invention, deionized water can be used for the water washing. The drying process is preferably nitrogen drying.

[0026] In this invention, the graphene sheets can be prepared by mechanical exfoliation. A specific implementation of the mechanical exfoliation method involves using 3M adhesive tape to mechanically exfoliate the graphene and transfer it onto a substrate. This invention employs a mechanical exfoliation method to ensure the formation of graphene sheets with multiple layers on the surface of the substrate.

[0027] In this invention, the size of the graphene sheet is preferably 10~30μm.

[0028] In this invention, the plasma treatment can be performed in a plasma cleaner. The plasma treatment preferably uses argon gas as the treatment atmosphere (i.e., Ar plasma treatment). During the plasma treatment, it is preferable to first evacuate the plasma cleaner and then introduce argon gas for plasma treatment. The plasma treatment conditions preferably include: a pressure of 0.1~0.5 Pa; an argon gas flow rate of 5~15 sccm, which can be 10 sccm in the embodiment; a radio frequency power of 3~6W, which can be 5W in the embodiment; and a treatment time of 0~5s, and not 0, which can be 3s or 5s in the embodiment.

[0029] This invention, by controlling the conditions of the plasma treatment, including the flow rate of argon gas, the power of the radio frequency power supply, and the treatment time, can introduce defect structures of different densities on the surface of graphene sheets. This allows for the regulation of the intensity of the pseudo-magnetic field through the time of defects of different densities, ultimately controlling the frictional force of the folded pretreated graphene sheets and achieving the controllability of the frictional force of the folded pretreated graphene sheets.

[0030] After obtaining the pretreated graphene sheet, the present invention uses atomic force microscopy (AFM) nanomanipulation to fold the exposed edge of the pretreated graphene sheet located on the substrate surface to obtain a folded pretreated graphene sheet.

[0031] In this invention, the material of the probe of the atomic force microscope used in the tapping mode is preferably silicon.

[0032] In this invention, the folding preferably includes the following steps: The morphology of the pretreated graphene sheet is scanned in the tapping mode of an atomic force microscope to determine the position of the exposed edge of the pretreated graphene sheet; the movement trajectory of the atomic force microscope probe is set from the outside to the inside of the pretreated graphene sheet along a direction perpendicular to the exposed edge of the pretreated graphene sheet; then the probe of the atomic force microscope is moved across the pretreated graphene sheet according to the movement trajectory to fold the exposed edge of the pretreated graphene sheet.

[0033] In this invention, the preferred conditions for the atomic force microscope probe to pass over the pretreated graphene sheet include: a normal load of 1~1.5 μN, which can be 1 μN, 1.2 μN, or 1.5 μN in the embodiments; and a movement speed of 0.3~0.5 μm / s, which can be 0.5 μm / s in the embodiments. The material of the atomic force microscope probe used during the folding process is single-crystal diamond.

[0034] In this invention, the atomic force microscope uses argon gas in a nano-manipulation environment with a humidity of <10% and a room temperature. The room temperature can be 15~30℃, and in this embodiment, it is 25℃.

[0035] Compared to exposed graphene edges of the same height (with the same barrier height), this invention can effectively reduce friction through the pseudo-magnetic field induced by the strain at the edge of the folded graphene. Due to the energy mismatch between phonon energy and the pseudo-Landau level at the edge of the folded graphene, the electronic energy dissipation due to friction, including electron-phonon energy dissipation, is strongly suppressed, and the rate of electron energy dissipation is significantly reduced.

[0036] To further illustrate the present invention, the technical solutions provided by the present invention are described in detail below with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention. The following embodiments are based on... Figure 1 The plasma treatment is performed according to the process shown.

[0037] Example 1 A 1cm × 1cm silica substrate was sequentially ultrasonically cleaned in acetone for 10 minutes, then in anhydrous ethanol for 10 minutes, and finally in deionized water for 10 minutes. The cleaning process was repeated twice. The substrate was then immersed in a 3:1 mixture of concentrated sulfuric acid (98%) and hydrogen peroxide for 10 minutes. Next, it was immersed in a 1:1 mixture of ammonia (28%) and hydrogen peroxide for 10 minutes. Finally, it was rinsed with deionized water and dried with nitrogen.

[0038] Graphene was peeled from bulk graphite onto a cleaned silicon oxide substrate using 3M tape. The morphology was measured using AFM to confirm a 2-layer graphene sheet. The sheet was then placed in a plasma cleaner and evacuated to 10°C. -1 Argon gas was continuously introduced at a flow rate of 10 sccm, the RF power was adjusted to 5W, and the Ar plasma treatment times were 0s, 3s, and 5s, respectively, before the sample was removed.

[0039] The AFM probe was used to fold the plasma-treated graphene sheet: First, the edge position of the 2-layer graphene sheet was determined by tapping mode of AFM. The movement trajectory of the AFM probe was pre-set from the outside to the inside in a direction perpendicular to the exposed edge of the graphene. Then, the AFM probe was moved along the predetermined trajectory with a normal load of 1μN and a movement speed of 0.5μm / s to obtain the edge of the 4-layer folded graphene.

[0040] Example 2 A 1cm × 1cm silica substrate was sequentially ultrasonically cleaned in acetone for 10 minutes, then in anhydrous ethanol for 10 minutes, and finally in deionized water for 10 minutes. The cleaning process was repeated twice. The substrate was then immersed in a 3:1 mixture of concentrated sulfuric acid (98%) and hydrogen peroxide for 10 minutes. Next, it was immersed in a 1:1 mixture of ammonia (28%) and hydrogen peroxide for 10 minutes. Finally, it was rinsed with deionized water and dried with nitrogen.

[0041] Graphene was peeled from bulk graphite onto a cleaned silicon oxide substrate using 3M tape. The morphology was measured using AFM to confirm a 3-layer graphene sheet. The sheet was then placed in a plasma cleaner and evacuated to 10°C. -1 Argon gas was continuously introduced at a flow rate of 10 sccm, the RF power was adjusted to 5W, and the Ar plasma treatment times were 0s, 3s, and 5s, respectively, before the sample was removed.

[0042] The AFM probe was used to fold the plasma-treated graphene sheet: First, the edge position of the 3-layer graphene sheet was determined using the tapping mode of the AFM. The movement trajectory of the AFM probe was pre-set from the outside to the inside along the direction perpendicular to the exposed edge of the graphene. Then, the AFM probe was moved along the predetermined trajectory with a normal load of 1.2 μN and a movement speed of 0.5 μm / s to obtain the edge of the 6-layer folded graphene.

[0043] Example 3 A 1cm × 1cm silica substrate was sequentially ultrasonically cleaned in acetone for 10 minutes, then in anhydrous ethanol for 10 minutes, and finally in deionized water for 10 minutes. The cleaning process was repeated twice. The substrate was then immersed in a 3:1 mixture of concentrated sulfuric acid (98%) and hydrogen peroxide for 10 minutes. Next, it was immersed in a 1:1 mixture of ammonia (28%) and hydrogen peroxide for 10 minutes. Finally, it was rinsed with deionized water and dried with nitrogen.

[0044] Graphene was peeled from bulk graphite onto a cleaned silicon oxide substrate using 3M tape. The morphology was measured using AFM to confirm a 4-layer graphene sheet. The sheet was then placed in a plasma cleaner and evacuated to 10°C. -1 Argon gas was continuously introduced at a flow rate of 10 sccm, the RF power was adjusted to 5W, and the Ar plasma treatment times were 0s, 3s, and 5s, respectively, before the sample was removed.

[0045] The AFM probe was used to fold the plasma-treated graphene sheet: First, the edge position of the 4-layer graphene sheet was determined using the tapping mode of the AFM. The movement trajectory of the AFM probe was pre-set from the outside to the inside along the direction perpendicular to the exposed edge of the graphene. Then, the AFM probe was moved along the predetermined trajectory with a normal load of 1.5 μN and a movement speed of 0.5 μm / s to obtain the edge of the 8-layer folded graphene.

[0046] Characterization test Defect characterization: Figure 2 This is the Raman spectrum of the graphene sheet after plasma treatment in this invention. The D peak in the graphene Raman spectrum originates from a defect-triggered double-resonance Raman scattering process, where the ratio of the D peak intensity to the G peak intensity can semi-quantitatively assess the defect density and disorder of the graphene. With increasing plasma treatment time, the ratio of the D peak intensity to the G peak intensity in the Raman spectrum increases, indicating a greater defect density introduced into the graphene. The Raman spectra of the two-layer graphene sheet in Example 1 after Ar plasma treatment for 0s, 3s, and 5s are shown below. Figure 2 As shown, I D / I G The values ​​are 0.05, 0.12 and 0.26, respectively, indicating that the graphene was introduced with defects of different densities after plasma treatment, and the atomic-scale resolution map shows that the graphene lattice was damaged to some extent after plasma treatment.

[0047] Figure 3 This is an AFM morphology image of the edge of the folded graphene prepared after Ar plasma treatment for 3 seconds in Example 1 of this invention. Figure 3It can be seen that the bilayer graphene sheet becomes four layers after folding, and the height changes from 7.25nm to 1.52nm. Furthermore, there is a curvature structure at the folded edge, resulting in a tubular-like edge.

[0048] Figure 4 for Figure 3 The corresponding height map, Figure 4 This is the height curve of the edge of the folded graphene after Ar plasma treatment for 3 seconds in Example 1.

[0049] Pseudo-magnetic field characterization: Scanning tunneling spectra of the edges of folded graphene were measured using scanning tunneling microscopy at 77.5 K. Figure 5 As shown, Figure 5 Discrete electron energy peaks appear in the graphene, and calculations show that the pseudomagnetic field strength at the edge of the folded graphene is approximately 27.02 T. Figure 5 The results show that the strain field at the edge of folded graphene can induce a pseudo magnetic field.

[0050] Friction test: Friction tests were performed using the transverse force mode of the AFM probe at a scan rate of 2 μm / s along the direction perpendicular to the edge of the folded graphene. The friction coefficients of the folded graphene edges obtained in Examples 1-3 were evaluated and compared with those of exposed graphene edges of the same thickness. During the test, the normal load of the AFM probe was increased from 0 nN to 20 nN, and six sets of friction force data were measured at equal intervals. The friction coefficients are shown below. Figure 6 As shown, compared to the friction coefficient of 0.127 for the edge of exposed graphene with a thickness of 4 layers, the friction coefficients of the edge of folded graphene of the same thickness after plasma treatment for 0s, 3s, and 5s are 0.056, 0.100, and 0.149, respectively; compared to the friction coefficient of 0.189 for the edge of exposed graphene with a thickness of 6 layers, the friction coefficients of the edge of folded graphene of the same thickness after plasma treatment for 0s, 3s, and 5s are 0.067, 0.171, and 0.216, respectively; compared to the friction coefficient of 0.257 for the edge of exposed graphene with a thickness of 8 layers, the friction coefficients of the edge of folded graphene of the same thickness after plasma treatment for 0s, 3s, and 5s are 0.076, 0.173, and 0.311, respectively. Based on the above data, it can be seen that after introducing defects into the edge of the folded graphene prepared in this invention through plasma treatment, the pseudo-magnetic field strength is effectively controlled, thereby effectively adjusting the friction force.

[0051] As shown in the above embodiments, this invention provides a method for controlling the frictional force of graphene. This invention uses nanomanipulation via atomic force microscopy to fold the edges of exposed graphene, resulting in folded graphene edges. The pseudo-magnetic field induced by local strain significantly reduces the frictional force to half that of exposed graphene edges of the same thickness. Before folding the exposed graphene edges using atomic force microscopy, this invention pre-treats the edges with Ar plasma to introduce defect structures of different densities, thereby weakening and destroying the pseudo-magnetic field caused by the folding, achieving effective control of the frictional force of the folded graphene edges. The method provided by this invention is simple to operate, has high precision in controlling the frictional force of graphene, and can be widely applied to the frictional control of micro / nano devices.

[0052] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for controlling the frictional force of graphene, characterized in that, Includes the following steps: Pretreated graphene sheets are obtained by introducing structural defects through plasma treatment on the surface of the substrate. The exposed edges of the pretreated graphene sheet located on the substrate surface were folded using nanomanipulation with atomic force microscopy to obtain a folded pretreated graphene sheet.

2. The method for controlling the frictional force of graphene according to claim 1, characterized in that, Argon gas was used as the treatment atmosphere for the plasma treatment.

3. The method for controlling the frictional force of graphene according to claim 2, characterized in that, The conditions for plasma treatment include: pressure of 0.1~0.5 Pa; argon flow rate of 5~15 sccm; radio frequency power of 3~6 W; and treatment time of 0~5 s, which is not 0.

4. The method for controlling the frictional force of graphene according to claim 1, characterized in that, The folding process includes the following steps: The morphology of the pretreated graphene sheet is scanned in the tapping mode of an atomic force microscope to determine the position of the exposed edge of the pretreated graphene sheet; the movement trajectory of the atomic force microscope probe is set from the outside to the inside of the pretreated graphene sheet along a direction perpendicular to the exposed edge of the pretreated graphene sheet; then the probe of the atomic force microscope is moved across the pretreated graphene sheet according to the movement trajectory to fold the exposed edge of the pretreated graphene sheet.

5. The method for controlling the frictional force of graphene according to claim 4, characterized in that, The conditions for the atomic force microscope probe to pass over the pretreated graphene sheet include: a normal load of 1~1.5μN and a movement speed of 0.3~0.5μm / s; the material of the atomic force microscope probe used during the folding is single-crystal diamond.

6. The method for controlling the frictional force of graphene according to claim 4, characterized in that, The probe of the atomic force microscope used in the tapping mode is made of silicon.

7. The method for controlling the frictional force of graphene according to any one of claims 1, 4 to 6, characterized in that, The atomic force microscope is used to manipulate nanoscale environments with argon gas, humidity <10%, and room temperature.

8. The method for controlling the frictional force of graphene according to claim 1, characterized in that, The graphene sheets have a size of 10~30μm.

9. The method for controlling the frictional force of graphene according to claim 1 or 8, characterized in that, The graphene sheet is prepared by mechanical exfoliation.

10. The method for controlling the frictional force of graphene according to claim 1, characterized in that, The substrate material is silicon dioxide; the substrate is cleaned and dried sequentially before use. The cleaning includes a first cleaning, a second cleaning, a third cleaning, and a water wash. The reagents used for the first cleaning are acetone, ethanol, and water, and the first cleaning is performed under ultrasonic conditions. The reagent used for the second cleaning is a mixed solution of H2SO4 and H2O2, and the second cleaning time is 5-15 minutes. The reagent used for the third cleaning is a mixed solution of NH3 and H2O2, and the third cleaning time is 5-15 minutes.

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