CN114214101A - Method for regulating friction force of molybdenum disulfide by constructing interface liquid drops - Google Patents

Method for regulating friction force of molybdenum disulfide by constructing interface liquid drops Download PDF

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CN114214101A
CN114214101A CN202111628833.9A CN202111628833A CN114214101A CN 114214101 A CN114214101 A CN 114214101A CN 202111628833 A CN202111628833 A CN 202111628833A CN 114214101 A CN114214101 A CN 114214101A
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molybdenum disulfide
pmma
substrate
annealing
friction force
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CN114214101B (en
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李强
许铭源
张德良
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Shandong University
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M103/00—Lubricating compositions characterised by the base-material being an inorganic material
    • C10M103/06—Metal compounds
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M177/00—Special methods of preparation of lubricating compositions; Chemical modification by after-treatment of components or of the whole of a lubricating composition, not covered by other classes
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2201/00—Inorganic compounds or elements as ingredients in lubricant compositions
    • C10M2201/06—Metal compounds
    • C10M2201/065—Sulfides; Selenides; Tellurides
    • C10M2201/066—Molybdenum sulfide
    • C10M2201/0663—Molybdenum sulfide used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
    • C10N2030/06—Oiliness; Film-strength; Anti-wear; Resistance to extreme pressure
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2050/00—Form in which the lubricant is applied to the material being lubricated
    • C10N2050/14—Composite materials or sliding materials in which lubricants are integrally molded
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The invention provides a method for adjusting friction force of molybdenum disulfide by constructing interface liquid drops. The method of the invention comprises the following steps: uniformly coating a polymethyl methacrylate solution on a molybdenum disulfide surface on which a single-layer molybdenum disulfide silicon substrate grows, and then annealing to obtain PMMA/molybdenum disulfide/silicon substrate; etching with etching solution, washing to obtain PMMA/molybdenum disulfide composite membrane, and storing in deionized water; transferring the composite film to a substrate for annealing treatment; and then removing the PMMA film, and annealing to obtain the molybdenum disulfide/substrate. The method can realize the adjustment of the deformation performance and the in-plane stress of the monolayer molybdenum disulfide atomic thickness by constructing interface liquid drops with different sizes, thereby effectively controlling the friction performance of the monolayer molybdenum disulfide, reducing the friction force of the monolayer molybdenum disulfide and enhancing the lubricating performance.

Description

Method for regulating friction force of molybdenum disulfide by constructing interface liquid drops
Technical Field
The invention relates to a method for adjusting friction force of molybdenum disulfide by constructing interface liquid drops, belonging to the technical field of nano material lubrication.
Background
Friction is almost unavoidable in all kinematic systems and generally leads to energy dissipation (e.g. vibration of surface atoms, chemical interactions, electronic excitation upon electron-hole coupling, etc.), which determines the efficiency and lifetime of the mechanical system. Particularly for a micro-nano electromechanical system with high specific surface area, friction is a main factor for restricting the development of the micro-nano electromechanical system. Fortunately, two-dimensional layered materials with excellent lubricity and mechanical properties (e.g., ultra-strong breaking strength and high young's modulus) are used as effective solid lubricants and are increasingly used in many engineering applications to effectively reduce the coefficient of friction to 0.05-0.2. Therefore, the research on the friction performance of the two-dimensional layered material is of great significance. At present, the two-dimensional nano material as a lubricating and antiwear additive has also become one of the hot spots of current scientific research and industrial application.
Molybdenum disulfide is an important member of a two-dimensional layered material, is composed of a sandwich structure formed by sandwiching a single-layer transition metal molybdenum atom between two layers of sulfur atoms, has good/adjustable mechanical and electronic properties, is an important substitute material for constructing high-performance electronic and optoelectronic devices, and has excellent tribological properties. Molybdenum disulfide exhibits very low friction and good antiwear properties in terms of lubrication. Currently, molybdenum disulfide has been successfully used as a solid lubricant (especially for extremely demanding aerospace components), as an additive to liquid lubricants, or as a component of composite coatings. In addition, molybdenum disulfide shows various characteristics in the aspect of tribology at a micro-nano scale, such as dependence on the number of layers, friction anisotropy, friction hysteresis, structural super-lubrication and the like, but the characteristics are difficult to control, control and in many cases minimize friction, which has been a long-sought goal, and today, no simple and effective method for controllably adjusting the friction force of molybdenum disulfide exists. In addition, compared with the bulk molybdenum disulfide, the single-layer molybdenum disulfide is more suitable for application in micro-nano devices due to smaller size, but the single-layer molybdenum disulfide has deformation capacity and shrinkage effect, so that the friction force is increased, and therefore controllable adjustment and reduction of the friction force of the single-layer molybdenum disulfide are problems to be solved urgently.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for adjusting the friction force of molybdenum disulfide by constructing interface liquid drops. The method can realize the adjustment of the deformation performance and the in-plane stress of the monolayer molybdenum disulfide atomic thickness by constructing interface liquid drops with different sizes, thereby effectively controlling the friction performance of the monolayer molybdenum disulfide, reducing the friction force of the monolayer molybdenum disulfide and enhancing the lubricating performance.
The technical scheme of the invention is as follows:
a method for regulating friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: uniformly coating a polymethyl methacrylate (PMMA) solution on a molybdenum disulfide surface on which a single-layer molybdenum disulfide silicon substrate grows, and then annealing to obtain PMMA/molybdenum disulfide/silicon substrate;
(2) etching: immersing the PMMA/molybdenum disulfide/silicon substrate obtained in the step (1) in etching liquid for etching, so that the PMMA film attached with a single layer of molybdenum disulfide is separated from the silicon substrate; immersing the PMMA film attached with the single-layer molybdenum disulfide in etching liquid, washing with deionized water to obtain a PMMA/molybdenum disulfide composite film, and storing the PMMA/molybdenum disulfide composite film in the deionized water;
(3) transferring and removing glue: transferring the PMMA/molybdenum disulfide composite film in the deionized water obtained in the step (2) onto a substrate, and carrying out annealing treatment to obtain PMMA/molybdenum disulfide/substrate; and then removing the PMMA film, and carrying out annealing treatment to obtain molybdenum disulfide/substrate, thereby realizing the adjustment of the friction force of the molybdenum disulfide by constructing interface liquid drops.
According to the invention, in the step (1), the preparation method of the silicon substrate with the single-layer molybdenum disulfide grown is carried out according to the prior art. Preferably, the preparation method of the silicon substrate with the single-layer molybdenum disulfide grown thereon comprises the following steps: taking sulfur powder and molybdenum trioxide as a sulfur source and a molybdenum source respectively, taking argon as a carrier gas, and growing a single-layer molybdenum disulfide on a silicon substrate by a chemical vapor deposition method; reference is made to "SCIENCE CHINA Materials 59,182 (2016)".
Preferably, according to the invention, in step (1), the relative molecular mass of the polymethyl methacrylate is 800-1200K, preferably 950K; the polymethyl methacrylate (PMMA) solution is an anisole solution of polymethyl methacrylate (PMMA), and the mass concentration of the polymethyl methacrylate (PMMA) solution is 3-6%, preferably 4.5%.
Preferably, in step (1), the polymethyl methacrylate (PMMA) solution is coated as follows: and uniformly coating the molybdenum disulfide surface on which the single-layer molybdenum disulfide silicon substrate grows by adopting a spin coating method.
Preferably, the rotation speed of the spin coating is 500-; further preferably, the spin coating step is: the spin coating is performed at 500-1200 rpm for 5-15 seconds, and then at greater than 1200 rpm for 90-115 seconds. By controlling the spin-coating rotation speed, the thickness of the spin-coated PMMA film can be controlled.
Preferably, according to the present invention, in the step (1), the amount of the Polymethylmethacrylate (PMMA) solution is 10 to 40 microliters per square centimeter.
Preferably, according to the invention, in step (1), the annealing temperature is 80-120 ℃, preferably 90 ℃; the annealing time is 2-10 minutes, preferably 3 minutes; the annealing atmosphere was air.
Preferably, in the step (2), the etching solution is a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution, and the concentration of the etching solution is 3-4 mol/L.
Preferably, in step (2), the etching temperature is 90-180 ℃; the immersion treatment temperature is 90-180 ℃, and the immersion treatment time is 0.5-3 h.
Preferably, in step (2), the washing is performed with deionized water.
Preferably, in step (3), the substrate is a conductor device or a semiconductor device; preferably, the substrate is a highly oriented pyrolytic graphite device. The shape and size of the PMMA/molybdenum disulfide composite film are determined according to the size and shape of the new substrate and actual requirements, and the shape and size of the molybdenum disulfide in the single-layer molybdenum disulfide silicon substrate grown in the step (1) can be adjusted to realize the shape and size of the molybdenum disulfide.
Preferably, in step (3), the transfer method is as follows: flatly placing the PMMA/molybdenum disulfide composite film on a substrate; one side of molybdenum disulfide in the PMMA/molybdenum disulfide composite film is tightly attached to the substrate; preferably, the transfer method is as follows: and fishing up the PMMA/molybdenum disulfide composite film in the deionized water by using the substrate, so that the PMMA/molybdenum disulfide composite film is flatly loaded on the substrate.
Preferably, in the step (3), annealing treatment is carried out to obtain PMMA/molybdenum disulfide/substrate, wherein the annealing temperature is 80-120 ℃, and preferably 90 ℃; the annealing time is 2-10 minutes, preferably 3 minutes; the annealing atmosphere was air.
According to a preferred embodiment of the present invention, in the step (3), the method for removing the PMMA film is as follows: the PMMA/molybdenum disulfide/substrate is immersed in an organic solvent at 50-120 ℃ for 2-5 hours, preferably 3 hours.
Preferably, the method for removing the PMMA film is as follows: soaking PMMA/molybdenum disulfide/substrate in acetone at 50-70 ℃ for half an hour, and then soaking in N-methylpyrrolidone at 100 ℃ and 120 ℃ for half an hour; repeat the above step 2 times.
Preferably, in the step (3), after the PMMA film is removed, the temperature of the annealing treatment is 200-500 ℃; the time of the annealing treatment is 4-8h, preferably 6 h; the atmosphere for the annealing treatment was argon.
Preferably, according to the invention, in step (3), in the molybdenum disulfide/substrate, an interfacial droplet is formed between the molybdenum disulfide and the substrate; the height of the interface liquid drop is 5-20 nanometers; the lateral dimension of the interface droplet is 100-500 nm.
According to the invention, the method can be used for reducing the friction force of the monolayer molybdenum disulfide; or can be used to reduce the friction of the new substrate surface in step (3); or the molybdenum disulfide/substrate obtained by the invention is used as a semiconductor/conductor heterojunction device as a whole to reduce the friction force of the surface of the heterojunction device, namely the surface of the molybdenum disulfide.
The invention has the technical characteristics and beneficial effects that:
1. the method provides a new regulation strategy for regulating the friction characteristic of the molybdenum disulfide, namely interface liquid drops with different sizes are constructed between a substrate and a single layer of molybdenum disulfide by a wet transfer method, so that the single layer of molybdenum disulfide generates self-maintained in-plane stress with different sizes, and experimental tests show that the friction force of the molybdenum disulfide can be effectively regulated and controlled by introducing the interface liquid drops with different sizes, the friction force of the single layer of molybdenum disulfide can be reduced, and the lubricating property is enhanced. The wet transfer method used in the method is simple and convenient to operate, relatively low in cost and high in success rate.
2. The invention uses PMMA as a transfer medium, has good flexibility, stability and proper viscosity, and can be effectively adhered to the surface of the single-layer molybdenum disulfide; and can be removed under the treatment of acetone and N-methyl pyrrolidone (NMP), and has good application prospect. The PMMA is preferably coated by adopting a specific spin coating method and specific concentration, so that a PMMA film with uniform thickness can be obtained; the thickness of the PMMA film is controlled by controlling a spin coating method, namely the rotating speed; and the thickness of the PMMA film needs to be proper, the PMMA film is too large and difficult to remove, the thickness is too small, the viscosity and the flexibility of the PMMA film are not good, and the transfer of the single-layer molybdenum disulfide is influenced.
3. The single-layer molybdenum disulfide obtained after the transfer by the method can keep the original shape structure on the macroscopic size, has clean surface without folds, still keeps the original physical and chemical properties, can realize atomic-level cleaning on the microcosmic aspect, and can carry out atomic-level lattice imaging. The friction force adjusting strategy provided by the invention has a good development prospect, and has a potential practical application value in the field of molybdenum disulfide-based micro-nano devices.
4. In the process of transferring the PMMA/molybdenum disulfide composite film to the substrate, deionized water droplets exist between the PMMA/molybdenum disulfide composite film and the substrate, and interface droplets are finally formed at the interface between the molybdenum disulfide and the substrate after subsequent annealing, PMMA removal and annealing treatment. According to the invention, after the PMMA/molybdenum disulfide composite film is transferred to the substrate, the interface liquid drop can be smoothly generated between the substrate and the single-layer molybdenum disulfide interface by controlling the annealing treatment condition and the annealing treatment condition after the PMMA film is removed, and the size of the interface liquid drop is regulated, so that the effect of reducing the friction force of molybdenum disulfide is realized. The method uses the specific substrate to facilitate the appearance of interface liquid drops between the substrate and the single-layer molybdenum disulfide interface, thereby realizing the effect of reducing the friction force of the molybdenum disulfide. In conclusion, the method of the invention is taken as a whole, and the conditions and steps have complex interaction and can be combined to realize the effect of the invention.
Drawings
FIG. 1 is an optical microscope image of a silicon wafer grown with a monolayer of molybdenum disulfide prepared in example 1;
figure 2 is an optical microscope image of the molybdenum disulfide/substrate prepared in example 1;
figure 3 is an atomic force microscope image of the molybdenum disulfide/substrate prepared in example 1;
FIG. 4 is a graph of the friction test of molybdenum disulfide/substrate prepared in example 1 with smooth molybdenum disulfide;
figure 5 is an atomic force microscopy contrast image of molybdenum disulfide/substrate prepared in example 3 before and after increasing the annealing temperature;
figure 6 is a graph of the friction test before and after raising the annealing temperature for the molybdenum disulfide/substrate prepared in example 3;
figure 7 is an optical microscope image of the molybdenum disulfide/substrate prepared in comparative example 3;
figure 8 is an atomic force microscope image of the molybdenum disulfide/substrate prepared in comparative example 5;
figure 9 is an optical microscope image of the molybdenum disulfide/substrate prepared in comparative example 7.
Detailed Description
The present invention is described in detail below with reference to examples, but the present invention is not limited thereto.
The methods described in the examples are conventional methods unless otherwise specified; the reagents used are commercially available without further indication.
Example 1
A method for adjusting the friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: 10 microliters of polymethyl methacrylate (PMMA) anisole solution (mass concentration: 4.5%, PMMA relative molecular mass: 950K) was uniformly spin-coated on the molybdenum disulfide surface of a silicon wafer (0.5 cm. times.0.5 cm) on which a monolayer of molybdenum disulfide had grown, and after 10 seconds of spin-coating at 500rpm, one and a half minutes of spin-coating at 2000rpm was performed. And then annealing in air at 90 ℃ for 3 minutes to cure the PMMA, thus obtaining PMMA/molybdenum disulfide/silicon wafer.
(2) Etching: and (3) immersing the PMMA/molybdenum disulfide/silicon wafer in 3mol/L KOH aqueous solution for etching, wherein the etching temperature is 160 ℃. After etching is finished, the PMMA film attached with molybdenum disulfide is separated from the silicon wafer, the separated PMMA film is placed in a KOH aqueous solution with the temperature of 160 ℃ and the mol/L ratio of 3, the etching is continued for 1 hour, the etching temperature is 160 ℃, then the PMMA film is cleaned by deionized water for 3 times, and each time lasts for 15 minutes, so that a PMMA/molybdenum disulfide composite film is obtained; the PMMA/molybdenum disulfide composite membrane is not taken out in deionized water.
(3) Transferring: and fishing out the PMMA film by using new substrate highly oriented cracked graphite (HOPG), flatly loading the composite film on the substrate, and annealing for 3min at the temperature of 90 ℃ in an atmospheric environment to obtain the PMMA/molybdenum disulfide/substrate.
(4) Removing glue: the PMMA/molybdenum disulfide/substrate is immersed in acetone at 60 ℃ for 0.5h and N-methyl pyrrolidone (NMP) at 110 ℃ for 0.5h in sequence; the above step was repeated 2 times to remove the PMMA film. And then, annealing for 6h at 300 ℃ in an argon atmosphere to obtain molybdenum disulfide/substrate, so that the friction force of the molybdenum disulfide is adjusted by constructing interface liquid drops.
In this embodiment, optical micrographs of the silicon wafer with a single layer of molybdenum disulfide grown in step (1) and the molybdenum disulfide/substrate in step (4) are shown in fig. 1 and 2, and the single layer of molybdenum disulfide transferred in fig. 2 maintains the original triangular shape, and has a clean and pollution-free surface.
Fig. 3 shows an atomic force microscope image of the molybdenum disulfide/substrate obtained in step (4) of this embodiment, as can be seen from image 3, the light color part is HOPG, the dark color part is molybdenum disulfide, and the dotted line part in fig. 3 is a boundary between molybdenum disulfide and HOPG. In FIG. 3, the raised part is a constructed interface liquid drop which is formed by covering a monolayer of molybdenum disulfide on the liquid drop. The height of the interface liquid drop is 5-20 nanometers; the lateral dimension of the interface droplet is 100-500 nm.
The molybdenum disulfide/substrate molybdenum disulfide friction test chart obtained in step (4) of this embodiment is shown in fig. 4, and 3 curved molybdenum disulfides (droplet 1, droplet 2, droplet 3) covered with an interface droplet and a flat molybdenum disulfide (molybdenum disulfide) not covered with a droplet portion are randomly selected to perform a test, and it is found that the curved molybdenum disulfide covered with an interface droplet has a smaller friction and has a better lubricating effect, which indicates that the interface droplet has an adjusting effect on the friction of a monolayer of molybdenum disulfide.
Example 2
A method for adjusting the friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: 20 microliters of a polymethyl methacrylate (PMMA) anisole solution (mass concentration: 4.5%, PMMA relative molecular mass: 950K) was uniformly spin-coated on the molybdenum disulfide surface of a silicon wafer (1 cm. times.1 cm) on which a monolayer of molybdenum disulfide had grown, and after 10 seconds of spin-coating at 500rpm, one and a half minutes of spin-coating at 2000 rpm. And then annealing in air at 90 ℃ for 3 minutes to cure the PMMA, thus obtaining PMMA/molybdenum disulfide/silicon wafer.
(2) Etching: and (3) immersing the PMMA/molybdenum disulfide/silicon wafer in 4mol/L NaOH aqueous solution for etching, wherein the etching temperature is 160 ℃. After etching, separating the PMMA film attached with molybdenum disulfide from the silicon wafer, placing the separated PMMA film in a NaOH aqueous solution with the temperature of 160 ℃ and the mol/L of 4, continuously etching for 1h, and then cleaning the PMMA film with deionized water for 3 times, wherein each time lasts for 15 minutes, so as to obtain a PMMA/molybdenum disulfide composite film; the PMMA/molybdenum disulfide composite membrane is not taken out in deionized water.
(3) Transferring: and fishing out the PMMA film by using new substrate highly oriented cracked graphite (HOPG), flatly loading the composite film on the substrate, and annealing for 3min at the temperature of 90 ℃ in an atmospheric environment to obtain the PMMA/molybdenum disulfide/substrate.
(4) Removing glue: the PMMA/molybdenum disulfide/substrate is immersed in acetone at 60 ℃ for 0.5h and N-methyl pyrrolidone (NMP) at 110 ℃ for 0.5h in sequence; the above step was repeated 2 times to remove the PMMA film. And then, annealing for 6h at 300 ℃ in an argon atmosphere to obtain molybdenum disulfide/substrate, so that the friction force of the molybdenum disulfide is adjusted by constructing interface liquid drops.
Example 3
A method for adjusting the friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: 20 microliters of a polymethyl methacrylate (PMMA) anisole solution (mass concentration: 4.5%, PMMA relative molecular mass: 950K) was uniformly spin-coated on the molybdenum disulfide surface of a silicon wafer (1 cm. times.1 cm) on which a monolayer of molybdenum disulfide had grown, and after 10 seconds of spin-coating at 500rpm, one and a half minutes of spin-coating at 2000 rpm. And then annealing in air at 90 ℃ for 3 minutes to cure the PMMA, thus obtaining PMMA/molybdenum disulfide/silicon wafer.
(2) Etching: and (3) immersing the PMMA/molybdenum disulfide/silicon wafer in 3mol/L KOH aqueous solution for etching, wherein the etching temperature is 160 ℃. After etching, separating the PMMA film attached with molybdenum disulfide from the silicon wafer, placing the separated PMMA film in a KOH aqueous solution with the temperature of 160 ℃ and the mol/L of 3, continuously etching for 1h, and then cleaning the PMMA film with deionized water for 3 times, wherein each time lasts for 15 minutes, so as to obtain a PMMA/molybdenum disulfide composite film; the PMMA/molybdenum disulfide composite membrane is not taken out in deionized water.
(3) Transferring: and fishing out the PMMA film by using new substrate highly oriented cracked graphite (HOPG), flatly loading the composite film on the substrate, and annealing for 3min at the temperature of 90 ℃ in an atmospheric environment to obtain the PMMA/molybdenum disulfide/substrate.
(4) Removing glue: the PMMA/molybdenum disulfide/substrate is immersed in acetone at 60 ℃ for 0.5h and N-methyl pyrrolidone (NMP) at 110 ℃ for 0.5h in sequence; the above step was repeated 2 times to remove the PMMA film. And then annealing for 3h at 300 ℃ in an argon atmosphere, and annealing for 3h at 480 ℃ in the argon atmosphere to obtain molybdenum disulfide/substrate, so that the friction force of the molybdenum disulfide is adjusted by constructing interface droplets.
A comparison graph of the atomic force microscope of the molybdenum disulfide/substrate after the annealing treatment at 300 ℃ and the annealing treatment at 480 ℃ in the step (4) of this embodiment is shown in fig. 5, in this embodiment, an interface droplet is successfully constructed between the molybdenum disulfide and the highly oriented pyrolytic graphite, and the size of the droplet is reduced by controlling the annealing treatment conditions.
As shown in fig. 6, compared with the flat molybdenum disulfide (molybdenum disulfide) not covered by the droplet portion, the friction of the curved molybdenum disulfide (after annealing at 300 ℃, i.e., before temperature rise, and after annealing at 480 ℃, i.e., after temperature rise) covered by the interface droplet is smaller, and the droplet becomes smaller and the friction force increases after the annealing temperature is raised, which indicates that the size of the interface droplet has an adjusting effect on the friction of the monolayer molybdenum disulfide, and the droplet size can be adjusted by controlling the annealing condition.
Example 4
A method for adjusting the friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: uniformly spin-coating 20 microliters of polymethyl methacrylate (PMMA) anisole solution (the mass concentration is 4.5 percent, and the relative molecular mass of PMMA is 950K) on the molybdenum disulfide surface of a silicon wafer (1cm multiplied by 1cm) with a monolayer of molybdenum disulfide, after 10 seconds of spin-coating at 800rpm, spin-coating at 2000rpm for one and a half minutes, and then annealing in air at 90 ℃ for 3 minutes to solidify PMMA, thereby obtaining the PMMA/molybdenum disulfide/silicon wafer.
(2) Etching: and (3) immersing the PMMA/molybdenum disulfide/silicon wafer in 3mol/L KOH aqueous solution for etching, wherein the etching temperature is 90 ℃. After etching, separating the PMMA film attached with molybdenum disulfide from the silicon wafer, placing the separated PMMA film in a KOH aqueous solution with the temperature of 160 ℃ and the mol/L of 3, continuously etching for 1h, and then cleaning the PMMA film with deionized water for 3 times, wherein each time lasts for 15 minutes, so as to obtain a PMMA/molybdenum disulfide composite film; the PMMA/molybdenum disulfide composite membrane is not taken out in deionized water.
(3) Transferring: and fishing out the PMMA film by using new substrate highly oriented cracked graphite (HOPG), flatly loading the composite film on the substrate, and annealing for 3min at the temperature of 90 ℃ in an atmospheric environment to obtain the PMMA/molybdenum disulfide/substrate.
(4) Removing glue: the PMMA/molybdenum disulfide/substrate is immersed in acetone at 60 ℃ for 0.5h and N-methyl pyrrolidone (NMP) at 110 ℃ for 0.5h in sequence; the above step was repeated 2 times to remove the PMMA film. And then, annealing for 6h at 300 ℃ in an argon atmosphere to obtain molybdenum disulfide/substrate, so that the friction force of the molybdenum disulfide is adjusted by constructing interface liquid drops.
In the embodiment, the etching temperature in the step (2) is changed, the etching time at 90 ℃ is prolonged, and interface liquid drops are successfully constructed between the molybdenum disulfide and the highly oriented cracked graphite.
Example 5
A method for adjusting the friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: uniformly spin-coating 30 microliters of polymethyl methacrylate (PMMA) anisole solution (the mass concentration is 4.5 percent, and the PMMA has a relative molecular mass of 950K) on a molybdenum disulfide surface of a silicon wafer (1.5cm multiplied by 1.5cm) with a monolayer of molybdenum disulfide, after 10 seconds of spin-coating at 800rpm, spin-coating at 2000rpm for one and a half minutes, and then annealing in air at 90 ℃ for 3 minutes to solidify PMMA, thereby obtaining the PMMA/molybdenum disulfide/silicon wafer.
(2) Etching: and (3) immersing the PMMA/molybdenum disulfide/silicon wafer in 4mol/L KOH aqueous solution for etching, wherein the etching temperature is 160 ℃. After etching, separating the PMMA film attached with molybdenum disulfide from the silicon wafer, placing the separated PMMA film in a KOH aqueous solution of 4mol/L at 160 ℃ for continuously etching for 1h, and then cleaning the PMMA film with deionized water for 3 times, wherein each time lasts for 15 minutes, so as to obtain a PMMA/molybdenum disulfide composite film; the PMMA/molybdenum disulfide composite membrane is not taken out in deionized water.
(3) Transferring: and fishing out the PMMA film by using new substrate highly oriented cracked graphite (HOPG), flatly loading the composite film on the substrate, and annealing for 3min at the temperature of 90 ℃ in an atmospheric environment to obtain the PMMA/molybdenum disulfide/substrate.
(4) Removing glue: the PMMA/molybdenum disulfide/substrate is immersed in acetone at 60 ℃ for 0.5h and N-methyl pyrrolidone (NMP) at 110 ℃ for 0.5h in sequence; the above step was repeated 2 times to remove the PMMA film. And then, annealing for 6h at 300 ℃ in an argon atmosphere to obtain molybdenum disulfide/substrate, so that the friction force of the molybdenum disulfide is adjusted by constructing interface liquid drops.
Example 6
A method for adjusting the friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: uniformly spin-coating 30 microliters of polymethyl methacrylate (PMMA) anisole solution (the mass concentration is 4.5 percent, and the PMMA has a relative molecular mass of 950K) on a molybdenum disulfide surface of a silicon wafer (0.5cm multiplied by 0.5cm) with a monolayer of molybdenum disulfide, after 10 seconds of spin-coating at 800rpm, spin-coating at 2000rpm for one and a half minutes, and then annealing in air at 110 ℃ for 3 minutes to solidify PMMA, thereby obtaining the PMMA/molybdenum disulfide/silicon wafer.
(2) Etching: and (3) immersing the PMMA/molybdenum disulfide/silicon wafer in 4mol/L NaOH aqueous solution for etching, wherein the etching temperature is 160 ℃. After etching, separating the PMMA film attached with molybdenum disulfide from the silicon wafer, placing the separated PMMA film in a NaOH aqueous solution with the temperature of 160 ℃ and the mol/L of 4, continuously etching for 1h, and then cleaning the PMMA film with deionized water for 3 times, wherein each time lasts for 15 minutes, so as to obtain a PMMA/molybdenum disulfide composite film; the PMMA/molybdenum disulfide composite membrane is not taken out in deionized water.
(3) Transferring: and fishing out the PMMA film by using new substrate highly oriented cracked graphite (HOPG), flatly loading the composite film on the substrate, and annealing for 3min at 110 ℃ in an atmospheric environment to obtain the PMMA/molybdenum disulfide/substrate.
(4) Removing glue: the PMMA/molybdenum disulfide/substrate is immersed in acetone at 60 ℃ for 0.5h and N-methyl pyrrolidone (NMP) at 110 ℃ for 0.5h in sequence; the above step was repeated 2 times to remove the PMMA film. And then, annealing for 6h at 300 ℃ in an argon atmosphere to obtain molybdenum disulfide/substrate, so that the friction force of the molybdenum disulfide is adjusted by constructing interface liquid drops.
Comparative example 1
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (1), 10 microliters of methyl methacrylate (PMMA) anisole solution (the mass concentration is 4.5 percent, and the PMMA relative molecular mass is 950K) is spin-coated on the molybdenum disulfide surface of a silicon wafer (0.5cm multiplied by 0.5cm) with a single layer of molybdenum disulfide, the molybdenum disulfide is spin-coated for one and a half minutes at 2000rpm, and then the PMMA is cured by annealing in air at 90 ℃ for 3 minutes to obtain the PMMA/molybdenum disulfide/silicon wafer.
The other steps and conditions were identical to those of example 1.
In the process, the step of low-speed spin coating is omitted, the thickness of the PMMA film obtained by direct high-speed spin coating is not uniform, and the whole area on the silicon wafer cannot be covered.
Comparative example 2
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (1), 10 microliters of an anisole solution of polymethyl methacrylate (the mass concentration is 4.5%, and the relative molecular mass of PMMA is 950K) is spin-coated on a molybdenum disulfide surface of a silicon wafer (0.5cm multiplied by 0.5cm) on which a single layer of molybdenum disulfide grows, after 10 seconds of spin-coating at 500rpm, one and a half minutes of spin-coating at 1000rpm, and then annealing is carried out in air at 90 ℃ for 3 minutes to solidify PMMA, so that the PMMA/molybdenum disulfide/silicon wafer is obtained.
The other steps and conditions were identical to those of example 1.
In the process, the PMMA film obtained by spin coating at the speed of 1000rpm is too thick, so that PMMA residual glue is left on the surface of finally obtained molybdenum disulfide, and the friction test cannot be carried out.
Comparative example 3
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (1), 10 microliters of an anisole solution of polymethyl methacrylate (the mass concentration is 4.5%, and the relative molecular mass of PMMA is 950K) is spin-coated on a molybdenum disulfide surface of a silicon wafer (0.5cm multiplied by 0.5cm) on which a single layer of molybdenum disulfide grows, after 10 seconds of spin-coating at 500rpm, one and a half minutes of spin-coating at 4000rpm, and then annealing is carried out in air at 90 ℃ for 3 minutes to solidify PMMA, so that the PMMA/molybdenum disulfide/silicon wafer is obtained.
The other steps and conditions were identical to those of example 1.
An optical microscope image of the molybdenum disulfide/substrate prepared in this comparative example is shown in fig. 7, in the process, the PMMA film obtained by 4000rpm spin coating is too thin and has poor flexibility, and the PMMA film is cracked during the transfer process, so that the molybdenum disulfide after the transfer is cracked.
Comparative example 4
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (2), the step of washing is omitted, and the concrete steps are as follows: and (3) immersing the PMMA/molybdenum disulfide/silicon wafer in 3mol/L KOH aqueous solution for etching, wherein the etching temperature is 160 ℃. After the etching is finished, the PMMA film attached with the molybdenum disulfide is separated from the silicon wafer, and the separated PMMA film is placed in a KOH aqueous solution with the temperature of 160 ℃ and the mol/L ratio of 3 and continuously etched for 1 hour to obtain a PMMA/molybdenum disulfide composite film; the PMMA/molybdenum disulfide composite membrane is not taken out in KOH aqueous solution.
The other steps and conditions were identical to those of example 1.
The process eliminates the pure water washing step, resulting in crystallization of residual potassium hydroxide after annealing. The monolayer molybdenum disulfide surface after transfer was not amenable to tribological testing due to the presence of potassium hydroxide crystals.
Comparative example 5
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (3), the annealing treatment is replaced by natural air drying for 24 hours.
The other steps and conditions were identical to those of example 1.
The atomic force microscope image of the molybdenum disulfide/substrate obtained in the comparative example is shown in fig. 8, and no interface droplet appears between the substrate and the monolayer of molybdenum disulfide, and wrinkles are generated on the monolayer of molybdenum disulfide.
Comparative example 6
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (4), only acetone is used for soaking, and the specific method is as follows: immersing PMMA/molybdenum disulfide/substrate in acetone at 60 ℃ for 0.5 h; the above procedure was repeated 4 times to remove the PMMA film. Subsequently, annealing was carried out at 300 ℃ for 6h under an argon atmosphere to obtain molybdenum disulfide/substrate.
The other steps and conditions were identical to those of example 1.
In the process, only acetone with the temperature of 60 ℃ is used for soaking, so that PMMA remains. The remaining PMMA affected the friction test.
Comparative example 7
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (4), annealing operation is not carried out, and PMMA/molybdenum disulfide/substrate are immersed in acetone at 60 ℃ for 0.5h and N-methylpyrrolidone (NMP) at 110 ℃ for 0.5h in sequence; and repeating the step for 2 times to remove the PMMA film, thereby obtaining the molybdenum disulfide/substrate.
The other steps and conditions were identical to those of example 1.
An optical microscope image of the molybdenum disulfide/substrate prepared in the comparative example is shown in fig. 9, and annealing operation is not performed after soaking in the process, so that more pollutants such as PMMA residual glue and organic solvent are attached to the surface of the molybdenum disulfide.
Comparative example 8
A method of constructing an interface droplet to modulate friction of molybdenum disulfide, as described in example 1, except that: in the step (3), the substrate is a silicon wafer (the surface of which is provided with silicon dioxide with the thickness of 300 nm).
The other steps and conditions were identical to those of example 1.
In the process, a silicon wafer is used as a new substrate, and consequently, no interface liquid drop appears between the silicon wafer and a single layer of molybdenum disulfide.

Claims (10)

1. A method for regulating friction force of molybdenum disulfide by constructing interface liquid drops comprises the following steps:
(1) gluing: uniformly coating a polymethyl methacrylate (PMMA) solution on a molybdenum disulfide surface on which a single-layer molybdenum disulfide silicon substrate grows, and then annealing to obtain PMMA/molybdenum disulfide/silicon substrate;
(2) etching: immersing the PMMA/molybdenum disulfide/silicon substrate obtained in the step (1) in etching liquid for etching, so that the PMMA film attached with a single layer of molybdenum disulfide is separated from the silicon substrate; immersing the PMMA film attached with the single-layer molybdenum disulfide in etching liquid, washing with deionized water to obtain a PMMA/molybdenum disulfide composite film, and storing the PMMA/molybdenum disulfide composite film in the deionized water;
(3) transferring and removing glue: transferring the PMMA/molybdenum disulfide composite film in the deionized water obtained in the step (2) onto a substrate, and carrying out annealing treatment to obtain PMMA/molybdenum disulfide/substrate; and then removing the PMMA film, and carrying out annealing treatment to obtain molybdenum disulfide/substrate, thereby realizing the adjustment of the friction force of the molybdenum disulfide by constructing interface liquid drops.
2. The method for building an interface droplet to regulate friction force of molybdenum disulfide according to claim 1, wherein step (1) comprises one or more of the following conditions:
i. the relative molecular mass of the polymethyl methacrylate is 800-1200K, preferably 950K; the polymethyl methacrylate (PMMA) solution is an anisole solution of polymethyl methacrylate (PMMA), and the mass concentration of the polymethyl methacrylate (PMMA) solution is 3-6%, preferably 4.5%;
ii. The amount of polymethyl methacrylate (PMMA) solution is 10-40 microliter per square centimeter;
iii, the annealing temperature is 80-120 ℃, preferably 90 ℃; the annealing time is 2-10 minutes, preferably 3 minutes; the annealing atmosphere was air.
3. The method for constructing an interface drop for regulating the friction force of molybdenum disulfide according to claim 1, wherein in the step (1), the polymethyl methacrylate (PMMA) solution is coated as follows: uniformly coating the molybdenum disulfide surface on which a single-layer molybdenum disulfide silicon substrate grows by adopting a spin coating method;
preferably, the rotation speed of the spin coating is 500-; further preferably, the spin coating step is: the spin coating is performed at 500-1200 rpm for 5-15 seconds, and then at greater than 1200 rpm for 90-115 seconds.
4. The method for building an interface droplet to regulate friction force of molybdenum disulfide according to claim 1, wherein step (2) comprises one or more of the following conditions:
i. the etching solution is a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution, and the concentration of the etching solution is 3-4 mol/L;
ii. The etching temperature is 90-180 ℃; the immersion treatment temperature is 90-180 ℃, and the immersion treatment time is 0.5-3 h;
and iii, washing by using deionized water.
5. The method for building an interface droplet to regulate friction force of molybdenum disulfide according to claim 1, wherein in step (3), the substrate is a conductor device or a semiconductor device; preferably, the substrate is a highly oriented pyrolytic graphite device.
6. The method for building an interface liquid drop to regulate the friction force of molybdenum disulfide according to claim 1, wherein in the step (3), the transferring method is as follows: flatly placing the PMMA/molybdenum disulfide composite film on a substrate; one side of molybdenum disulfide in the PMMA/molybdenum disulfide composite film is tightly attached to the substrate; preferably, the transfer method is as follows: and fishing up the PMMA/molybdenum disulfide composite film in the deionized water by using the substrate, so that the PMMA/molybdenum disulfide composite film is flatly loaded on the substrate.
7. The method for constructing the interface liquid drop friction force for adjusting the molybdenum disulfide is characterized in that in the step (3), annealing treatment is carried out to obtain PMMA/molybdenum disulfide/substrate, and the annealing temperature is 80-120 ℃, preferably 90 ℃; the annealing time is 2-10 minutes, preferably 3 minutes; the annealing atmosphere was air.
8. The method for constructing an interface liquid drop for regulating the friction force of molybdenum disulfide according to claim 1, wherein the method for removing the PMMA film in step (3) is as follows: immersing PMMA/molybdenum disulfide/substrate in an organic solvent at 50-120 ℃ for 2-5 hours, preferably 3 hours;
preferably, the method for removing the PMMA film is as follows: soaking PMMA/molybdenum disulfide/substrate in acetone at 50-70 ℃ for half an hour, and then soaking in N-methylpyrrolidone at 100 ℃ and 120 ℃ for half an hour; repeat the above step 2 times.
9. The method for droplet adjustment of friction force of molybdenum disulfide for construction interface as claimed in claim 1, wherein in step (3), after removing PMMA film, the temperature of annealing treatment is 200-; the time of the annealing treatment is 4-8h, preferably 6 h; the atmosphere for the annealing treatment was argon.
10. The method for constructing an interfacial droplet to adjust frictional force of molybdenum disulfide according to claim 1, wherein in step (3), an interfacial droplet is formed between molybdenum disulfide and a substrate in molybdenum disulfide/substrate; the height of the interface liquid drop is 5-20 nanometers; the lateral dimension of the interface droplet is 100-500 nm.
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US20180345316A1 (en) * 2010-03-30 2018-12-06 Nantero, Inc. Ordered Nanotube Fabrics
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