Method for reducing friction on the surface of a single crystal diamond and applications thereof

Abstract

The application relates to a preparation method for reducing the surface friction of single crystal diamond and application, and the preparation method comprises the following steps: step one, determining a predetermined working environment of a single crystal diamond base material; step two, determining a surface energy regulation direction according to the predetermined working environment; when the predetermined working environment is a gas phase environment, the regulation direction is to reduce the surface energy, or when the predetermined working environment is a liquid phase environment, the regulation direction is to increase the surface energy; step three, according to the regulation direction determined in step two, selecting a corresponding surface energy regulation method to modify the friction working surface of the single crystal diamond. The preparation method is combined with the design of the surface energy directional regulation of the single crystal diamond crystal face intrinsic friction characteristic ordering rule, can effectively inhibit the friction failure of micro components, and prolongs the service life of a device.

Description

Technical Field

[0001] This application relates to the field of tribological design and surface engineering technology of microelectromechanical systems (MEMS), and in particular to a preparation method and application for reducing friction on single-crystal diamond surfaces. Background Technology

[0002] As a cutting-edge technology in the 21st century, Microelectromechanical Systems (MEMS) are experiencing a dramatic increase in surface area to volume ratio as device feature sizes continue to shrink to the micrometer / nanometer scale. This leads to surface forces (such as van der Waals forces, capillary forces, and electrostatic forces) becoming dominant in component interactions. This scale effect makes friction, wear, and adhesion problems the main factors affecting the performance, reliability, and lifespan of MEMS devices.

[0003] Single-crystal diamond, with its extremely high hardness, extremely low intrinsic coefficient of friction, excellent chemical stability, and good biocompatibility, is considered an ideal material for manufacturing next-generation high-reliability, long-life MEMS moving parts. It is widely used in precision devices involving relative motion or contact, such as biocompatible probes, micro-bearing gears, RF switch contacts, high-frequency resonators, micromirror torsion hinges, and microfluidic valves. In these applications, the huge surface area-to-volume ratio at the microscale makes surface adhesion and tribological wear effects extremely significant, becoming a core bottleneck leading to device sluggishness, signal drift, a sharp increase in contact resistance, and even eventual failure. Therefore, proactive friction reduction and anti-wear design of the single-crystal diamond friction interface is crucial for improving the working accuracy, reliability, and service life of MEMS moving parts.

[0004] Studies on friction reduction and wear resistance of single-crystal diamond surfaces have been reported, and research has shown that controlling the surface state of diamond through ion implantation, chemical modification, and other methods is an effective way to improve its tribological properties. For example, a study reported that gallium ion beam implantation was used to implant gallium ion beams into the (100) crystal plane of single-crystal diamond. It was found that as the gallium ion implantation concentration increased from 4.65% to 32.26%, the energy reduction of the diamond surface changed from 21.16% to 33.08%, and the droplet contact angle increased from 35.2° to 64.3°. The modified diamond tool had a smaller cutting force and better surface quality during ultra-precision cutting.

[0005] However, the existing technologies still have the following obvious shortcomings: (1) Existing research mainly focuses on the performance of diamond after surface modification under dry friction or cutting conditions, and is designed for a single working condition, without fully considering the diversity of the actual working environment of MEMS devices; (2) Existing surface energy control methods have a single goal, mainly focusing on reducing surface energy to obtain hydrophobic and low adhesion properties; (3) Existing surface energy control methods (such as self-assembled monomolecular films, plasma treatment, layer-by-layer self-assembly, etc.) are mostly developed for silicon or metal materials, and their film formation mechanism, bonding strength and stability on the surface of single crystal diamond are not yet fully studied.

[0006] In summary, there is currently a lack of a preparation method specifically for single-crystal diamond that can actively select the optimal crystal facet or control the surface state according to its predetermined working environment (such as air or water environment) to achieve low friction performance. Summary of the Invention

[0007] Therefore, it is necessary to provide a preparation method and application for reducing the surface friction of single-crystal diamond to address the above problems. The preparation method described in this application combines the sorting law of intrinsic friction characteristics of single-crystal diamond crystal plane with the directional control of surface energy, which can effectively suppress the friction failure of micro-components and extend the service life of devices.

[0008] A method for preparing single-crystal diamond with reduced surface friction includes the following steps:

[0009] Step 1: Determine the intended working environment for the single-crystal diamond substrate;

[0010] Step 2: Determine the surface energy control direction based on the predetermined working environment: when the predetermined working environment is a gas phase environment, the control direction is to reduce the surface energy; or, when the predetermined working environment is a liquid phase environment, the control direction is to increase the surface energy.

[0011] Step 3: Based on the control direction determined in Step 2, select the appropriate surface energy control method to modify the friction working surface of single crystal diamond.

[0012] In one embodiment, the gaseous environment includes at least one of an air environment, a nitrogen environment, an argon environment, or a vacuum environment;

[0013] Alternatively, the liquid environment may include at least one of an aqueous environment, a biological fluid environment, or a lubricating fluid environment.

[0014] In one embodiment, the method for reducing surface energy includes modifying a self-assembled monolayer using an organic molecule with hydrophobic terminal groups, wherein the organic molecule with hydrophobic terminal groups includes at least one of long-chain alkylsilanes, perfluoroalkylsilanes, long-chain alkylthiols, perfluoroalkylthiols, alkyl phosphates or phosphonates, and perfluoroalkyl phosphates or phosphonates.

[0015] In one embodiment, the method for regulating surface energy includes layer-by-layer self-assembly or modification of a self-assembled monolayer using organic molecules with hydrophilic terminal groups.

[0016] In one embodiment, when modifying a self-assembled monolayer using an organic molecule with a hydrophilic terminal group, the organic molecule with the hydrophilic terminal group includes at least one of hydroxyl-terminated silane, amino-terminated silane, carboxyl-terminated thiol, hydroxyl-terminated thiol, phosphoric acid or phosphonic acid compound, phosphorylcholine compound or polyethylene glycol silane.

[0017] In one embodiment, the layer-by-layer self-assembly method includes alternating deposition of polycationic electrolytes and polyanionic electrolytes on the surface of a single-crystal diamond under electrostatic influence to form a multilayer polyelectrolyte film, and satisfying at least one of the following conditions:

[0018] (1) The polycationic electrolyte includes at least one of polydiallyldimethylammonium chloride, polyethyleneimine, chitosan, polyallylamine hydrochloride, or polylysine;

[0019] (2) The polyanionic electrolyte includes at least one of sodium polystyrene sulfonate, polyacrylic acid, polymethacrylic acid or sodium alginate;

[0020] (3) The layer-by-layer self-assembly method includes immersion method, spin coating method or spray method;

[0021] (4) The polyelectrolyte membrane has 8 to 20 layers.

[0022] In one embodiment, after modification, the single-crystal diamond friction working surface is further characterized by at least one of water contact angle testing, surface energy calculation, X-ray photoelectron spectroscopy analysis, or atomic force microscopy morphology characterization.

[0023] In one embodiment, when the control direction is to reduce surface energy, the water contact angle of the friction working surface of the modified single crystal diamond is ≥100°.

[0024] Alternatively, when the control direction is to increase surface energy, the water contact angle of the tribological working surface of the modified single-crystal diamond is ≤35°.

[0025] In one embodiment, the crystal orientation of the single-crystal diamond includes at least one of the (100) crystal plane, the (111) crystal plane, or the (110) crystal plane.

[0026] A single-crystal diamond friction component is prepared by the method described above for reducing the surface friction of single-crystal diamond.

[0027] This application breaks through the conventional thinking of existing technologies that mainly focus on reducing surface energy. Based on a systematic study of the tribological properties of single-crystal diamond with different crystal faces in different environments, it reveals for the first time the rule that "the lower the surface energy in the gas phase environment, the smaller the friction coefficient, and the higher the surface energy in the liquid phase environment, the smaller the friction coefficient." Based on this, it proposes a strategy for bidirectional control of diamond surface energy according to the working environment. By combining the ranking law of intrinsic tribological properties of single-crystal diamond crystal faces with the directional control of surface energy, it "customizes" low-friction interfaces for different working environments, so that the modified surface energy matches the optimal direction for achieving low friction in that environment.

[0028] The preparation method described in this application is applicable to single-crystal diamond with different crystal orientations. The process is simple, compatible with MEMS technology, and easy to promote industrialization. Moreover, the low-friction surface prepared can effectively suppress the frictional failure of micro-components and extend the service life of devices, showing good prospects for industrial applications. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a comparison diagram of the initial contact angles of the three crystal plane samples in Example 1;

[0031] Figure 2 This is a comparison chart of the friction coefficients of single-crystal diamonds with different crystal planes in different environments in Example 1;

[0032] Figure 3 This is a comparison diagram of the frictional forces of single-crystal diamond with the (111) crystal plane in Example 2 under different loading conditions;

[0033] Figure 4 The images show the atomic force microscopy morphology comparison of the single crystal diamond with the (111) crystal plane in Example 3 before and after surface modification, where a is the morphology before surface modification and b is the morphology after surface modification. Detailed Implementation

[0034] To facilitate understanding of this application, it will be described in more detail below. However, it should be understood that this application can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular implementations or embodiments only and is not intended to be limiting of this application. In this application, numerical ranges, unless otherwise specified, are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Furthermore, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0036] Through long-term and in-depth research, the applicant discovered that MEMS devices may operate in air environments (with a certain humidity), vacuum environments, or liquid environments (such as water, biological fluids, lubricants, etc.), and the physicochemical mechanisms of the friction pair interfaces differ significantly in different environmental phases. Therefore, through systematic research on the tribological properties of single-crystal diamond with different crystal planes in various environments, the applicant found that low surface energy is not always the optimal choice under all operating conditions: in certain liquid environments (such as water), moderately increasing the surface energy can actually help form a stable adsorption layer or improve the interfacial contact state, thereby achieving a lower coefficient of friction.

[0037] Based on this, this application provides a method for preparing single-crystal diamond with reduced surface friction, comprising the following steps:

[0038] Step 1: Determine the intended working environment for the single-crystal diamond substrate;

[0039] Step 2: Determine the surface energy control direction based on the predetermined working environment: when the predetermined working environment is a gas phase environment, the control direction is to reduce the surface energy; or, when the predetermined working environment is a liquid phase environment, the control direction is to increase the surface energy.

[0040] Step 3: Based on the control direction determined in Step 2, select the appropriate surface energy control method to modify the friction working surface of single crystal diamond.

[0041] The applicant's research revealed that in micro- and nano-scale friction, the environmental medium determines the dominant friction mechanism. In the gas phase (such as air), friction is primarily driven by the adhesive forces of solid surfaces. Low surface energy (hydrophobic) surfaces have high chemical inertness and weak intermolecular forces with their counterparts, resulting in low adhesion and even lower friction. In the liquid phase (such as water), friction shifts to shear-driven friction at the interface liquid layer. High surface energy (hydrophilic) surfaces adsorb and stabilize water molecules through strong interactions (such as hydrogen bonds), forming a pressure-resistant hydration lubricating film that effectively separates the two surfaces, thereby reducing shear resistance and further lowering friction. Conversely, the unstable interfacial water layer of hydrophobic surfaces is easily crushed under load, leading to direct solid-solid contact and, consequently, high friction. Based on these research mechanisms, the applicant proposes to "customize" low-friction interfaces for different working environments by directionally controlling the surface energy of single-crystal diamond.

[0042] This application breaks through the conventional thinking of existing technologies that mainly focus on reducing surface energy. Based on a systematic study of the tribological properties of single-crystal diamond with different crystal faces in different environments, it reveals for the first time the rule that "the lower the surface energy in the gas phase environment, the smaller the friction coefficient, and the higher the surface energy in the liquid phase environment, the smaller the friction coefficient." Based on this, it proposes a strategy for bidirectional control of diamond surface energy according to the working environment. By combining the ranking law of intrinsic tribological properties of single-crystal diamond crystal faces with the directional control of surface energy, it "customizes" low-friction interfaces for different working environments, so that the modified surface energy matches the optimal direction for achieving low friction in that environment.

[0043] In one embodiment of this application, the predetermined working environment in step one includes a gaseous environment or a liquid environment. Specifically, the gaseous environment includes at least one of an air environment, a nitrogen environment, an argon environment, or a vacuum environment; the liquid environment includes at least one of a water environment, a biological fluid environment, or a lubricating fluid environment.

[0044] In one embodiment of this application, the surface of the single-crystal diamond substrate is preferably cleaned and dried. Specifically, the cleaning process includes ultrasonic cleaning using at least one of organic solvents, acids, alkalis, or deionized water.

[0045] In step two of this application, the determination of the control direction is based on a pre-established correspondence between "single-crystal diamond surface energy - working environment - friction coefficient." This correspondence is established in advance by the following method: selecting single-crystal diamond samples with different surface physicochemical properties, conducting tribological performance tests in different working environments to obtain the friction coefficient of each sample in different environments; simultaneously characterizing the surface energy of each sample, establishing the correspondence between surface energy and friction coefficient, and determining the trend of friction coefficient changing with surface energy in each working environment. The different surface physicochemical properties include at least one of different crystal orientations, different surface terminations, different surface roughness, or different surface modification treatments.

[0046] Through long-term and in-depth research, the applicant discovered the following relationship between "surface energy of single-crystal diamond - working environment - coefficient of friction": In a gaseous environment, the coefficient of friction of single-crystal diamond is positively correlated with its surface energy, meaning the lower the surface energy, the smaller the coefficient of friction; in a liquid-phase environment, the coefficient of friction of single-crystal diamond is negatively correlated with its surface energy, meaning the higher the surface energy, the smaller the coefficient of friction. Based on this, in step two of this application, the direction of surface energy control is determined to be either reducing the surface energy if the predetermined working environment is a gaseous environment, or increasing the surface energy if the predetermined working environment is a liquid-phase environment.

[0047] In one embodiment of this application, the method for reducing surface energy in step three includes, but is not limited to, at least one of self-assembled monolayer modification, fluorocarbon polymer coating grafting, ion implantation, or layer-by-layer self-assembly. Self-assembled monolayer modification involves forming an ordered molecular film on the surface of a single-crystal diamond and introducing hydrophobic groups, thereby reducing surface energy. Step three preferably uses organic molecules with hydrophobic terminal groups for self-assembled monolayer modification. One end of the organic molecule contains an active group that can form a chemical bond with the diamond surface, and the other end contains a hydrophobic terminal group.

[0048] Specifically, the hydrophobic terminal group includes, but is not limited to, at least one of alkyl, fluoroalkyl, or perfluoroalkyl groups; the active group includes, but is not limited to, at least one of silyl, thiol, phosphate, phosphonic acid, or carboxylic acid groups.

[0049] Preferably, the organic molecule having hydrophobic terminal groups includes at least one of long-chain alkylsilanes, perfluoroalkylsilanes, long-chain alkylthiols, perfluoroalkylthiols, alkyl phosphates or phosphonates, and perfluoroalkyl phosphates or phosphonates.

[0050] In one embodiment of this application, before performing self-assembled monolayer modification, the single-crystal diamond substrate is pretreated to introduce active groups on the diamond surface and enhance the chemical bonds of organic molecules. The pretreatment preferably includes at least one of oxygen plasma treatment, ultraviolet ozone treatment, and chemical oxidation treatment.

[0051] In one embodiment of this application, the self-assembled monolayer modification can be achieved by a liquid-phase immersion method, specifically including the following steps: immersing a pretreated single-crystal diamond substrate in a solution containing organic molecules, reacting at a predetermined temperature for a predetermined time, allowing the organic molecules to self-assemble on the diamond surface through chemical bonding. The degree of surface energy reduction can be controlled by adjusting the solution concentration and immersion time; the solvent of the solution is selected from at least one of toluene, ethanol, isopropanol, acetone, chloroform, n-hexane, cyclohexane, and tetrahydrofuran; the solution concentration is preferably 0.1 mM to 10 mM; the immersion time is preferably 10 minutes to 72 hours; and the reaction temperature is preferably 10°C to 80°C.

[0052] In one embodiment of this application, the self-assembled monolayer modification can also be achieved by vapor deposition, specifically including the following steps: placing the pretreated single-crystal diamond substrate in a sealed container, heating and evaporating the solution or solid containing organic molecules, so that the organic molecules are deposited on the diamond surface in gaseous form and chemically bonded; wherein, the deposition temperature is preferably 50℃~180℃; the deposition time is preferably 30 minutes~12 hours.

[0053] In one embodiment of this application, after the self-assembled monomolecular membrane modification is completed, post-processing steps such as solvent cleaning and nitrogen drying are also included to remove physically adsorbed organic molecules and obtain a uniform and dense monomolecular membrane.

[0054] In one embodiment of this application, the method for regulating surface energy in step three includes layer-by-layer self-assembly or modification with a self-assembled monolayer using organic molecules with hydrophilic end groups. The self-assembled monolayer modification is achieved by forming an ordered molecular film on the surface of a single-crystal diamond and introducing hydrophilic groups, thereby increasing the surface energy. One end of the organic molecule contains an active group that can form a chemical bond with the diamond surface, and the other end contains a hydrophilic end group.

[0055] Specifically, the hydrophilic terminal groups include, but are not limited to, at least one of hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), phosphate (-PO3H2), sulfonic acid (-SO3H), phosphorylcholine, or polyethylene glycol (PEG); the active groups include, but are not limited to, at least one of silyl, thiol, phosphate, phosphonic acid, or carboxylic acid.

[0056] Preferably, the organic molecule having hydrophilic terminal groups includes at least one of hydroxy-terminated silanes, amino-terminated silanes, carboxyl-terminated thiols, hydroxy-terminated thiols, phosphoric acid or phosphonic acid compounds, phosphorylcholine compounds, or polyethylene glycolated silanes.

[0057] In one embodiment of this application, before performing self-assembled monolayer modification, the single-crystal diamond substrate is pretreated to introduce active groups on the diamond surface and enhance the chemical bonds of organic molecules; the self-assembled monolayer modification can be achieved by liquid phase immersion or vapor phase deposition.

[0058] It is understandable that the difference between the self-assembled monomolecular film modification process for increasing surface energy and the self-assembled monomolecular film modification process for reducing surface energy lies in whether the organic molecules used are hydrophilic or hydrophobic, and the process parameters can be flexibly adjusted and optimized.

[0059] In one embodiment of this application, the method for controlling surface energy improvement in step three further includes a layer-by-layer self-assembly method. Specifically, the layer-by-layer self-assembly method involves alternating deposition of positively charged polycationic electrolytes and negatively charged polyanionic electrolytes on the surface of a single-crystal diamond under electrostatic influence to form a multilayer polyelectrolyte film, thereby introducing hydrophilic groups and improving surface energy. It is understood that the driving force for the layer-by-layer self-assembly is electrostatic interaction; by alternating deposition of polyelectrolytes with opposite charges, charge reversal is utilized to achieve the layer-by-layer growth of the multilayer film.

[0060] In one embodiment of this application, the polycationic electrolyte includes, but is not limited to, at least one of polydiallyldimethylammonium chloride (PDDA), polyethyleneimine (PEI), chitosan, polyallylamine hydrochloride (PAH), and polylysine (PLL); the polyanionic electrolyte includes, but is not limited to, at least one of sodium polystyrene sulfonate (PSS), polyacrylic acid (PAA), polymethacrylic acid (PMAA), and sodium alginate.

[0061] In one embodiment of this application, the polyelectrolyte is preferably a strongly hydrophilic polyelectrolyte, including but not limited to PDDA, PSS, PAA, etc. By introducing a large number of hydrophilic groups with strong hydration ability, such as quaternary ammonium salt groups, sulfonic acid groups, and carboxyl groups, into the multilayer film, it is beneficial to further enhance the stability of the formed water film.

[0062] In one embodiment of this application, before performing layer-by-layer self-assembly, the single-crystal diamond substrate is pretreated. The pretreatment introduces charges on the surface, which is beneficial to enhance the adsorption of the first layer of polyelectrolyte.

[0063] Specifically, the pretreatment method preferably includes at least one of plasma treatment, ultraviolet ozone treatment, and chemical oxidation treatment.

[0064] In one embodiment of this application, the layer-by-layer self-assembly method can be achieved by immersion, spin coating or spraying, with immersion being preferred.

[0065] In one embodiment of this application, the immersion method includes the following steps: the pretreated single-crystal diamond substrate is sequentially and alternately immersed in a polycationic solution and a polyanionic solution, and a cleaning step is performed after each immersion in a solution. The above cycle is repeated until the desired number of layers of multilayer polyelectrolyte membrane is obtained.

[0066] Preferably, the process parameters of the impregnation method include: the concentration of the polyelectrolyte solution is 0.1 mg / mL to 10 mg / mL, preferably 0.5 mg / mL to 5 mg / mL, and more preferably 1 mg / mL to 3 mg / mL; the pH value of the solution is adjusted according to the type of polyelectrolyte, usually 3 to 9, and can be adjusted by acid or alkali to ensure that the polyelectrolyte is in the optimal ionization state; the ionic strength can be adjusted by adding salts such as NaCl and KCl, with a concentration of less than 1 M, preferably 0.1 M to 0.5 M, which is beneficial for controlling the conformation and adsorption amount of the polyelectrolyte chain; the soaking time is 5 minutes to 60 minutes each time, preferably 10 minutes to 30 minutes; the soaking temperature is room temperature or heated to 30°C to 60°C; the cleaning step is to wash with deionized water or buffer solution for 1 minute to 5 minutes after each soaking to remove the excess physically adsorbed polyelectrolyte, which can be repeated 2 to 3 times; the drying method is nitrogen blowing or vacuum drying.

[0067] In one embodiment of this application, the polyelectrolyte membrane preferably has 8 to 20 layers, more preferably 8 to 12 layers. By optimizing the number of layers in the self-assembly process, on the one hand, it can avoid the problem that if the number of layers is too small, the polyelectrolyte membrane cannot completely cover the diamond substrate, leaving exposed areas on the substrate surface, resulting in insignificant improvement in surface energy and limited improvement in tribological properties. On the other hand, it can also avoid the problem that if the number of layers is too large, the polyelectrolyte membrane will be too thick, introducing a large interfacial impedance and affecting the microscale structural accuracy and motion accuracy of the MEMS device, or even causing the device to jam or fail.

[0068] It is understood that the number of layers of the polyelectrolyte membrane is the total number of layers of the polycationic electrolyte layer and the polyanionic electrolyte layer; when the polycationic electrolyte layer and the polyanionic electrolyte layer are used as a single circulating layer, the number of circulating layers of the polyelectrolyte membrane is half of the total number of layers, that is, 4 to 10 circulating layers, more preferably 4 to 6 circulating layers.

[0069] In one embodiment of this application, for the classic PDDA / PSS system, preparing 4 to 6 cycling layers is more conducive to forming a uniform, dense, and completely substrate-covering multilayer polyelectrolyte membrane. At the same time, controlling the membrane thickness within the range of 5 nm to 30 nm is not only conducive to the formation of a stable hydration layer with high surface energy, but also ensures that it will not affect the microscale movement of MEMS devices.

[0070] In one embodiment of this application, during the layer-by-layer self-assembly process, a quartz crystal microbalance, elliptic polarization spectroscopy, ultraviolet-visible spectroscopy, and zeta surface potential can be used to monitor the film growth, which helps to ensure the quality and uniformity of the multilayer film and avoid problems such as incomplete coverage due to too few layers or uncontrolled film thickness due to too many layers.

[0071] In one embodiment of this application, when the control direction is to reduce surface energy, the water contact angle of the friction working surface of the modified single crystal diamond is greater than the water contact angle of the friction working surface of the single crystal diamond before modification. Preferably, the water contact angle of the friction working surface of the modified single crystal diamond is ≥100°.

[0072] In one embodiment of this application, when the control direction is to increase the surface energy, the water contact angle of the friction working surface of the modified single crystal diamond is smaller than the water contact angle of the friction working surface of the single crystal diamond before the modification treatment. Preferably, the water contact angle of the friction working surface of the modified single crystal diamond is ≤35°.

[0073] In one embodiment of this application, after modification treatment, the single-crystal diamond friction working surface is further characterized by testing to confirm that its surface energy has changed along a predetermined control direction and that its tribological properties have reached the expected target. Specifically, the characterization test includes at least one of water contact angle testing, surface energy calculation, X-ray photoelectron spectroscopy analysis or atomic force microscopy morphology characterization.

[0074] In one embodiment of this application, the crystal orientation of the single-crystal diamond includes at least one of the (100) crystal plane, the (111) crystal plane, or the (110) crystal plane.

[0075] Preferably, when the single-crystal diamond substrate has a specific crystal orientation, the selection of the surface energy control method in step three can be optimized in combination with the crystal characteristics, which is beneficial to improving the control efficiency or control effect.

[0076] This application provides a scientific scheme for the systematic design of micromechanical single-crystal diamond interfaces that is predictable and precisely controllable. The preparation method is applicable to single-crystal diamonds with different crystal orientations. The process is simple and can be realized on conventional surface treatment equipment without the need for special devices. It is not only compatible with MEMS processes and easy to promote industrialization, but also the low-friction surface prepared can effectively suppress the frictional failure of micro-components, which can significantly improve the reliability and service life of related devices under complex working conditions and has good prospects for industrial application.

[0077] This application also provides a single-crystal diamond friction component, prepared using the method described above for reducing surface friction of single-crystal diamond, which can be used as an independent friction component in MEMS devices. It is understood that in other applications, the surface-modified single-crystal diamond prepared using the method provided in this application can also be assembled into the friction pair of a MEMS device.

[0078] The following specific embodiments will further illustrate the preparation method and application of reducing surface friction of single-crystal diamond. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0079] Example 1

[0080] This embodiment aims to establish the relationship between surface energy and friction coefficient by testing the tribological properties of single-crystal diamond with different crystal orientations in different environments, providing a basis for subsequent surface energy control.

[0081] (1) Sample preparation: Select CVD-synthesized single-crystal diamond samples with three crystal orientations (100), (110) and (111), each with a size of 4mm×4mm×0.3mm. Place the samples in acetone, ethanol and deionized water for ultrasonic cleaning for 10 minutes each, and then dry them with high-purity nitrogen gas for later use.

[0082] (2) Surface Energy Characterization: The surface contact angle of each sample was measured at room temperature using a static contact angle meter. Five different locations were measured for each sample, and the average value was taken as the contact angle value for that sample. The contact angle qualitatively reflects the surface energy: the larger the contact angle, the lower the surface energy; the smaller the contact angle, the higher the surface energy. The contact angle measurement results for initial water and hexadecane for the three crystal plane samples are shown below. Figure 1 As shown. From Figure 1 It can be seen that the (111) crystal plane has the largest water contact angle, that is, the lowest surface energy; the (110) crystal plane has the smallest contact angle and the highest surface energy; and the (100) crystal plane is in the middle.

[0083] (3) Tribological Performance Testing: The tribological properties of three crystal surface samples in different environments were tested using the friction mode of atomic force microscopy (AFM). The test conditions were as follows: silicon microcantilever probe, elastic constant 2 N / m, load 0.5 mV, scanning speed 2.5 Hz, scanning range 2 μm × 2 μm; test environment: conducted in atmospheric environment (relative humidity 45% ± 5%) and deionized water environment. Each sample was tested at least 3 times in different environments, and the average friction coefficient was taken. The results are as follows: Figure 2 As shown.

[0084] (4) Correlation analysis between surface energy and tribological properties: combined with Figure 1 and Figure 2 Analysis of the data revealed that in an air environment, the friction coefficient decreased in the order of (110) > (100) > (111), meaning that the lower the surface energy (the larger the contact angle) of the crystal face, the smaller the friction coefficient. This indicates that in an air environment, the friction coefficient is positively correlated with surface energy. In a water environment, the friction coefficient decreased in the order of (111) > (100) > (110), meaning that the higher the surface energy (the smaller the contact angle) of the crystal face, the smaller the friction coefficient. This indicates that in a water environment, the friction coefficient is negatively correlated with surface energy. These patterns reveal that the tribological properties of single-crystal diamond in different environmental phases are closely related to its surface energy, and the optimal surface energy requirement varies depending on the environment. Liquid phase environments require high surface energy, while gas phase environments require low surface energy. This finding lays the theoretical foundation for the subsequent technical solution of actively regulating surface energy based on the working environment in this application.

[0085] This embodiment uses the crystal plane as an example of changing surface energy. In fact, surface energy can also be controlled by other means (such as surface termination, modification treatment, etc.), but the revealed law has universality. That is, no matter how the surface energy is changed, its tribological properties change trend in a specific environment conforms to the above relationship.

[0086] Example 2

[0087] This embodiment takes (111) crystal plane single crystal diamond as the research object, and examines the influence of different loads on its friction force in air and water environments, further verifying the relationship between surface energy and friction performance, and providing load adaptability basis for subsequent surface energy control application scenarios.

[0088] (1) Sample preparation: A CVD-synthesized single-crystal diamond sample with (111) crystal plane orientation was selected, with a size of 4mm×4mm×0.3mm. The sample was ultrasonically cleaned in acetone, ethanol and deionized water for 10 minutes each, and then dried with high-purity nitrogen gas for later use. The initial water contact angle of the sample was tested to be 59.8°, indicating a low surface energy.

[0089] (2) AFM friction test under different loads: The friction mode of AFM was used to conduct friction tests on the samples in an air environment (relative humidity 45%±5%) and a deionized water environment. The test conditions were as follows: silicon micro cantilever probe, elastic constant 2N / m, scanning speed 2.5Hz, scanning range 2μm×2μm; load settings: 0.5mV, 1mV and 1.5mV loads were applied respectively; at least 3 tests were conducted under each load, and the average friction force was taken (unit is mV, directly obtained from AFM friction signal for easy comparison).

[0090] (3) Test results: The test results of the friction force of the (111) crystal plane in air and water environments under different loads are as follows: Figure 3 As shown. From Figure 3 The data reveals the following pattern: under the same load, the frictional force in the water environment is always greater than that in the air environment, which is consistent with the trend in Example 1 where the friction coefficient of the (111) crystal plane is higher in the water environment than in the air environment. As the load increases, the difference in frictional force between the two environments becomes more pronounced: at 0.5 mV, the frictional force in the water environment is about 1.2 times that in the air environment; at 1.5 mV, the frictional force in the water environment has reached nearly 1.5 times that in the air environment.

[0091] The microscopic mechanism of the above phenomenon is analyzed as follows: In an air environment, friction behavior is mainly controlled by interfacial shear, and the frictional force increases linearly with the load, conforming to the classical friction law. In an aquatic environment, friction behavior is transformed into shear-dominated by the interfacial liquid layer. Single-crystal diamond (111) crystal planes have low surface energy and are relatively hydrophobic. Near hydrophobic surfaces, water molecules are loosely arranged and structurally unstable, making it difficult to form a continuous and ordered hydration layer. When a load is applied, this unstable interfacial water layer is easily crushed, leading to local solid-solid direct contact and thus generating high frictional resistance. As the load increases, the degree of water layer crushing intensifies, the proportion of solid-solid contact increases, and therefore the frictional force exhibits an exponential rapid increase. In contrast, high surface energy (hydrophilic) surfaces can adsorb and stabilize water molecules through strong interactions (such as hydrogen bonds), forming a dense, ordered, and pressure-resistant hydration lubricating film. This hydration film can effectively separate the two surfaces, maintaining structural integrity under load, thereby reducing shear resistance and achieving lower friction.

[0092] The test results of this embodiment further verify the law disclosed in this application: surface energy not only directly affects the magnitude of the friction coefficient, but also determines the sensitivity of friction behavior to load. In a liquid environment, the friction performance of low surface energy surfaces is more sensitive to load, and friction increases sharply under high load; while high surface energy surfaces can maintain lower friction through a stable hydration lubricating film.

[0093] Example 3

[0094] In this embodiment, a self-assembled monolayer was constructed on the surface of single-crystal diamond using heptadecafluorodecyltrimethoxysilane via vapor deposition to reduce surface energy. The tribological properties of the modified sample in air and water environments were investigated to verify the effect of reducing surface energy on improving liquid phase friction.

[0095] (1) Sample preparation: A single-crystal diamond sample with (111) crystal plane orientation was selected, with a size of 4mm×4mm×0.3mm. The sample was ultrasonically cleaned in acetone, ethanol and deionized water for 10 minutes each, and then dried with nitrogen. The initial water contact angle of the sample was tested to be 59°, and the initial surface energy was relatively low.

[0096] (2) Surface pretreatment: To enhance the bonding between the self-assembled monolayer and the diamond surface, the sample was first subjected to oxygen plasma activation treatment. After treatment, a large number of hydroxyl active groups were introduced into the sample surface, the water contact angle was reduced to 10°, and the surface energy was significantly improved, which is beneficial to the subsequent chemical bonding of silane molecules.

[0097] (3) Vapor-phase deposition of self-assembled monolayer: The pretreated diamond sample was placed in a sealed vacuum desiccator and an open container containing 50 μL of heptadecafluorodecyltrimethoxysilane (purity ≥97%) was placed in it. The container was then heated in an oven at 150°C for 3 hours to allow the silane molecules to volatilize and undergo chemical adsorption and self-assembly on the diamond surface.

[0098] (4) Characterization of modified samples: The water contact angle of the modified samples was measured using a static water contact angle meter. The results showed that after modification with the heptadecafluorodecyltrimethoxysilane self-assembled film, the water contact angle of the diamond surface was significantly increased to 114°, indicating that the surface energy was successfully reduced. AFM was used to characterize the morphology of single-crystal diamond before and after the self-assembled film modification, such as... Figure 4 As shown, a is the morphology before surface modification, and b is the morphology after surface modification. The thickness of the self-assembled monolayer film is at the nanometer level and does not affect the original performance of the MEMS.

[0099] (5) Tribological Performance Testing: Friction tests were conducted on the modified samples in air (relative humidity 45% ± 5%) and deionized water environments using AFM friction mode. The load was 0.5 mV, the scanning speed was 2.5 Hz, and the scanning range was 2 μm × 2 μm. Each condition was tested three times, and the average friction coefficient was taken. The results showed that in air, after modifying the surface energy with a self-assembled film, the friction coefficient of the diamond surface decreased from 0.015 to 0.01, indicating that reducing surface energy had a significant effect on friction reduction in the liquid environment. In water, the friction coefficient increased from 0.019 to 0.022 after modification, indicating that reducing surface energy was not conducive to friction reduction in the liquid environment and may even have a negative effect.

[0100] (6) Applicability verification of different crystal planes: In order to verify the universality of the method described in this embodiment on single crystal diamond with different crystal plane orientations, single crystal diamond samples with (100) and (110) crystal planes were selected respectively, and self-assembled monolayers were modified using the same process steps as those for the (111) crystal plane.

[0101] a. Processing and testing of (100) crystal plane samples

[0102] A single-crystal diamond sample with a (100) crystal plane, measuring 4 mm × 4 mm × 0.3 mm, was selected, with an initial water contact angle of 54.7° ± 1.5°. Oxygen plasma pretreatment and heptadecafluorodecyltrimethoxysilane vapor deposition modification were performed according to steps (2) to (4) of this embodiment. The water contact angle of the treated sample was measured to be 108° ± 2.0°.

[0103] The tribological properties of the modified (100) crystal plane sample were tested using the AFM tribological mode with a load of 0.5 mV and a scan rate of 2.5 Hz, in both air and water environments.

[0104] b. (110) Processing and testing of crystal plane samples

[0105] A single-crystal diamond sample with a (110) crystal plane, measuring 4 mm × 4 mm × 0.3 mm, was selected. The initial water contact angle was 47.2° ± 1.8°. After modification using the same method, the water contact angle was measured to be 114.5° ± 1.9°. Subsequently, AFM friction tests were performed under the same conditions.

[0106] c. Results Analysis

[0107] The results show that after modification with heptadecafluorodecyltrimethoxysilane, the water contact angle of the samples with the three crystal faces all reached over 100°, successfully constructing a low surface energy surface, proving that the method of the present invention has good applicability to single-crystal diamond with different crystal facet orientations; the friction coefficient of the three crystal faces in the air environment was reduced to below 0.02 after modification, with a significant friction reduction effect; the friction coefficient of the three crystal faces in the liquid phase environment was increased (0.02~0.03), consistent with the pattern revealed in Example 1.

[0108] The above results show that the self-assembled monolayer modification method described in this application is not limited by crystal orientation and can achieve consistent surface energy reduction and tribological property improvement on single-crystal diamond with different crystal planes, thus having good versatility.

[0109] Example 4

[0110] In this embodiment, polyelectrolyte multilayer film was constructed on the surface of single-crystal diamond using a layer-by-layer self-assembly method with polydiallyldimethylammonium chloride and sodium polystyrene sulfonate to improve surface energy. The tribological properties of the modified sample in air and water environments were investigated to verify the effect of improving surface energy on gas phase friction.

[0111] (1) Sample preparation: A single-crystal diamond sample with (111) crystal plane orientation was selected, with a size of 4mm×4mm×0.3mm. The sample was ultrasonically cleaned in acetone, ethanol and deionized water for 10 minutes each, and then dried with nitrogen. The initial water contact angle of the sample was tested to be 59°, indicating a low surface energy.

[0112] (2) Surface pretreatment: To enhance the adsorption of the first layer of polyelectrolytes, the sample was subjected to oxygen plasma activation treatment to make the surface negatively charged. The negatively charged sample surface after treatment is conducive to the adsorption of the first layer of polycations.

[0113] (3) Preparation of polyelectrolyte solution

[0114] Polycationic solution: Dilute polydiallyldimethylammonium chloride (PDDA, molecular weight 200,000, 20wt% aqueous solution) with deionized water to a concentration of 2 mg / mL, and add NaCl to adjust the ionic strength to 0.5 M, and stir well.

[0115] Polyanionic solution: Dissolve sodium polystyrene sulfonate (PSS, molecular weight 70,000) in deionized water to a concentration of 2 mg / mL, and add NaCl to adjust the ionic strength to 0.5 M, then stir until homogeneous.

[0116] (4) Layer-by-layer self-assembly deposition

[0117] The layer-by-layer self-assembly deposition was performed using the impregnation method, and the specific operational steps are as follows:

[0118] a. Immerse the pretreated diamond sample in PDDA solution for 15 minutes, allowing PDDA to form the first layer on the surface through electrostatic adsorption.

[0119] b. Take out the sample and immerse it in deionized water to wash twice, 1 minute each time, to remove the excess polyelectrolytes that are physically adsorbed.

[0120] c. Immerse the sample in the PSS solution for 15 minutes to allow the PSS to be adsorbed onto the PDDA layer;

[0121] d. Remove the sample and rinse it twice more in deionized water, 1 minute each time;

[0122] e. Repeat steps a~d, and perform cyclic deposition 4.5 times to obtain PDDA / PSS multilayer film;

[0123] (f) Finally, dry the sample surface with nitrogen gas.

[0124] (5) Characterization of modified samples: The water contact angle of the modified sample after layer-by-layer self-assembly was measured to be 33° using a static water contact angle meter, indicating that the surface energy has been successfully improved. The film thickness was measured using an ellipsometry and found to be 9.2 nm. This film thickness can completely cover the substrate without being too thick to affect the microscale motion accuracy of the MEMS device.

[0125] (6) Micro-nano tribological performance testing: AFM tribological mode was used to test the modified samples in air (relative humidity 45%±5%) and deionized water environments. The load was 0.5mV (consistent with Example 3), the scanning speed was 2.5Hz, and the scanning range was 2μm×2μm. Each condition was tested 3 times, and the average friction coefficient was taken. The results showed that in the water environment, after layer-by-layer self-assembly to increase the surface energy, the friction coefficient of the diamond surface decreased from 0.019 to 0.01, indicating that increasing the surface energy has a significant effect on reducing friction in the liquid phase environment. The modification of the polyelectrolyte multilayer film not only increases the surface energy, but PDDA also has a strong ability to resist ion hydration, which is conducive to locking water molecules to form a stable hydration layer to separate the friction pairs, thereby significantly reducing its friction coefficient and improving the friction reduction performance. In the air environment, the friction coefficient after modification increased from 0.015 to 0.035, indicating that increasing the surface energy is not conducive to friction reduction in the gas phase environment, and may even have a negative effect. This result perfectly matches the pattern revealed in Example 1: increasing surface energy is suitable for gaseous environments, while decreasing surface energy is necessary for liquid environments. Furthermore, this example contrasts with the effect of self-assembled film modification in Example 3, which reduced surface energy: in Example 3, reducing surface energy increased friction in water and decreased friction in air; in this example, increasing surface energy increases friction in air and decreases friction in water. The two sets of experiments corroborate each other, fully demonstrating the correctness and necessity of the strategy proposed in this application for actively regulating the direction of surface energy based on the working environment.

[0126] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing single-crystal diamond with reduced surface friction, characterized in that, Includes the following steps: Step 1: Determine the intended working environment for the single-crystal diamond substrate; Step 2: Determine the surface energy control direction based on the predetermined working environment: when the predetermined working environment is a gas phase environment, the control direction is to reduce the surface energy; or, when the predetermined working environment is a liquid phase environment, the control direction is to increase the surface energy. Step 3: Based on the control direction determined in Step 2, select the appropriate surface energy control method to modify the friction working surface of single crystal diamond.

2. The preparation method for reducing surface friction of single-crystal diamond according to claim 1, characterized in that, The gaseous environment includes at least one of an air environment, a nitrogen environment, an argon environment, or a vacuum environment; Alternatively, the liquid environment may include at least one of an aqueous environment, a biological fluid environment, or a lubricating fluid environment.

3. The preparation method for reducing surface friction of single-crystal diamond according to claim 1, characterized in that, The method for reducing surface energy includes modifying a self-assembled monolayer using organic molecules with hydrophobic terminal groups, wherein the organic molecules with hydrophobic terminal groups include at least one of long-chain alkylsilanes, perfluoroalkylsilanes, long-chain alkylthiols, perfluoroalkylthiols, alkyl phosphates or phosphonates, and perfluoroalkyl phosphates or phosphonates.

4. The preparation method for reducing surface friction of single-crystal diamond according to claim 1, characterized in that, Methods to improve surface energy include layer-by-layer self-assembly or modification of monolayers using organic molecules with hydrophilic terminal groups.

5. The preparation method for reducing surface friction of single-crystal diamond according to claim 4, characterized in that, When modifying a self-assembled monolayer using an organic molecule with a hydrophilic terminal group, the organic molecule with the hydrophilic terminal group includes at least one of hydroxyl-terminated silane, amino-terminated silane, carboxyl-terminated thiol, hydroxyl-terminated thiol, phosphoric acid or phosphonic acid compound, phosphorylcholine compound, or polyethylene glycol silane.

6. The preparation method for reducing surface friction of single-crystal diamond according to claim 4, characterized in that, The layer-by-layer self-assembly method includes alternating deposition of polycationic electrolytes and polyanionic electrolytes on the surface of a single-crystal diamond under electrostatic action to form a multilayer polyelectrolyte film, and satisfies at least one of the following conditions: (1) The polycationic electrolyte includes at least one of polydiallyldimethylammonium chloride, polyethyleneimine, chitosan, polyallylamine hydrochloride, or polylysine; (2) The polyanionic electrolyte includes at least one of sodium polystyrene sulfonate, polyacrylic acid, polymethacrylic acid or sodium alginate; (3) The layer-by-layer self-assembly method includes immersion method, spin coating method or spray method; (4) The polyelectrolyte membrane has 8 to 20 layers.

7. The preparation method for reducing surface friction of single-crystal diamond according to claim 1, characterized in that, After modification, the process also includes characterization tests on the single-crystal diamond friction working surface, including at least one of water contact angle testing, surface energy calculation, X-ray photoelectron spectroscopy analysis, or atomic force microscopy morphology characterization.

8. The preparation method for reducing surface friction of single-crystal diamond according to claim 1 or 7, characterized in that, When the control direction is to reduce surface energy, the water contact angle of the friction working surface of the modified single crystal diamond is ≥100°. Alternatively, when the control direction is to increase surface energy, the water contact angle of the tribological working surface of the modified single-crystal diamond is ≤35°.

9. The preparation method for reducing surface friction of single-crystal diamond according to claim 1, characterized in that, The crystal orientation of single-crystal diamond includes at least one of the (100) crystal plane, (111) crystal plane, or (110) crystal plane.

10. A single-crystal diamond friction component, characterized in that, It is prepared by the method for reducing surface friction of single-crystal diamond as described in any one of claims 1 to 9.

Images