AFM (Atomic Force Microscope) microsphere probe based on cage type framework and preparation method of AFM microsphere probe

Abstract

The invention relates to the technical field of AFM (Atomic Force Microscope) probes, and particularly discloses an AFM microsphere probe based on a cage type frame and a preparation method of the AFM microsphere probe. The preparation method comprises the following steps: firstly, preparing a cage type frame, and putting prefabricated microspheres into the frame to realize free rotation in the frame; and firmly bonding the cage-type frame with the AFM cantilever needle tip by using an adhesive, thereby obtaining the cage-type microsphere probe. Through an AFM scratching process based on the probe, rolling and sliding motion between the microspheres and a test sample can be realized. Compared with the technical scheme that the traditional AFM (atomic force microscopy) microsphere probe adopts a consolidation mode to connect the microsphere and the needle tip, only relative slippage between the microsphere and a sample can be realized, and the wear resistance of the microsphere is insufficient, the AFM cage microsphere probe disclosed by the invention not only can improve the nano processing performance of the microsphere needle tip, but also can prolong the service life of the microsphere needle tip; therefore, the nano processing cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of atomic force microscope (AFM) probes, and particularly relates to an AFM microsphere probe based on a cage frame and a preparation method thereof. The invention is applicable to related fields such as nano-scale processing of materials and nano-scale tribology research. Background Art

[0002] An atomic force microscope (AFM) is an important tool capable of achieving nano-scale resolution imaging and mechanical property measurement, and is widely used in fields such as materials science, biomedicine, semiconductor detection, and nano-processing. The performance of the AFM probe directly affects the imaging quality, test accuracy, and nano-processing effect. Therefore, optimizing the design and preparation method of the AFM probe has always been an important research direction in this field.

[0003] Currently, common AFM probes usually adopt bare tips with a conical or pyramidal shape. Their advantages lie in high resolution and good imaging stability. However, when such rigid probes come into contact with the sample, they often introduce large lateral forces and shear stresses, which are likely to cause damage to the sample surface, especially more obvious in the measurement of flexible or biological samples. In addition, since the tip radius of curvature is usually only 1 - 10 nm, it is easy to cause local wear of the probe, thus affecting the measurement accuracy and stability.

[0004] To reduce the damage to the sample by the probe and improve the measurement stability, microsphere probes have emerged as the times require. A microsphere probe refers to fixing a microsphere particle at the end of a conventional bare tip, or directly replacing the bare tip with a microsphere particle. Compared with the traditional bare tip, the radius of curvature of the microsphere probe is increased by about 2 - 3 orders of magnitude (usually between several hundred nanometers and dozens of micrometers), thus significantly increasing the contact area between it and the sample surface. This increased contact area can effectively reduce the local contact pressure, improve the measurement repeatability, and reduce tip wear. Therefore, microsphere probes have been widely used in the research on the surface mechanics and friction characteristics of two-dimensional nanomaterials and the field of nano-scale material processing.

[0005] Currently, the preparation of microsphere probes mainly adopts the method of consolidating microspheres, that is, fixedly connecting the microspheres and the probes. Common methods include the following two categories:

[0006] (1) Glue bonding method: The microsphere is bonded to the end of the probe through an adhesive to construct the microsphere probe.

[0007] Typical examples are as follows:

[0008] Patent 1: CN109521227A uses an AFM equipped with a positive / negative optical imaging system, combines the three-axis motion control of the AFM, and uses adhesives such as DellAB to accurately position and bond microspheres (with a particle size range of 0.2 - 30 μm) such as polystyrene, silicon oxide, and glass to the probe with or without a tip, realizing the preparation of microsphere probes.

[0009] Patent 2: CN111505344A uses an inversion method to consolidate microspheres (with a diameter of 1 - 30 μm) and a cantilever probe without a tip using an ultraviolet curable adhesive, solving the problems of glue content control and microsphere positioning.

[0010] Patent 3: CN110155938A consolidates large-sized microspheres (with a radius of curvature of 50 - 500 μm) and a cantilever probe using adhesives such as AB glue to prepare a receptor platform with a microsphere probe structure.

[0011] Patent 4: CN114236182A uses adhesives such as epoxy resin to bond carbon microspheres (with a particle size of 1 - 20 μm) to the free end of an AFM probe without a tip to obtain a carbon microsphere probe.

[0012] Patent 5: CN118837583A uses adhesives such as epoxy resin, ultraviolet curable glue, or underwater curable glue to fix hydrogel microspheres (polyethylene glycol diacrylate, sodium alginate, or silicone hydrogel, with a particle size of 5 - 100 μm) at the free end of an AFM cantilever beam to obtain a hydrogel microsphere probe.

[0013] (II) Microsphere direct processing method: Use micro-nano processing technology to directly form a microsphere structure at the tip of the AFM probe. For example:

[0014] Literature (A sub-micron spherical atomic force microscopic tip for surface measurements. Langmuir, 2020, 36: 7861 - 7867.), based on a conventional AFM single-crystalline silicon tip, first uses a focused ion beam (FIB) to cut a flat platform at the top of the probe tip. Subsequently, appropriate high-energy helium ion implantation is performed on the material in this platform area to cause it to expand and directly form a silicon microsphere with a diameter of 0.1 - 1 μm, thus realizing the integrated preparation of microsphere probes.

[0015] However, since existing microsphere probes all adopt the method of consolidating microspheres, during AFM testing, the microspheres can only slide on the sample surface and cannot achieve relative rolling and sliding motion. This limitation leads to two main problems: (1) It affects the repeatability and accuracy in tribological experiments and nanomachining. Since the microspheres can only slide, local wear is inevitable, which in turn leads to unstable experimental results. Especially in the research of nanotribology and nanomachining, it will affect the reliability and repeatability of the measurement or processing process, and shorten the service life of the probe. (2) It is difficult to accurately simulate the wear process of real engineering. Currently, AFM experiments based on consolidated microsphere probes can only simulate the two-body abrasive wear process of relative sliding between abrasive grains and samples. However, in the engineering field, three-body abrasive wear is more common than two-body abrasive wear, especially in applications involving friction, lubrication, wear, and micro-nano machining. For example, during Chemical Mechanical Polishing (CMP), a typical three-body abrasive wear state is formed among abrasive grains, polishing pads, and wafers. Compared with abrasive grains that only undergo sliding, abrasive grains with rolling and sliding motion during polishing contribute to improving the material removal efficiency and the surface quality of the workpiece after polishing. However, limited by consolidated microsphere probes, existing AFM research usually simplifies the actual three-body abrasive wear process into a two-body abrasive wear process, ignoring the rotational effect of abrasive grains. This not only reduces the reduction degree of the experiment to the real engineering working conditions but also makes it difficult to comprehensively reveal the key material removal mechanism in practical applications such as CMP. Therefore, how to break through the limitations of consolidated microsphere probes and enable AFM experiments to more accurately simulate the rolling and sliding motion of abrasive grains in three-body abrasive wear is one of the urgent problems to be solved in the current research fields of tribology and nanomachining.

[0016] To solve the above problems, it is urgent to design a microsphere AFM probe that can roll freely, which not only improves the accuracy and stability of measurement but also expands AFM experimental research from two-body abrasive wear to three-body abrasive wear, thereby more accurately simulating the actual wear process in the engineering field and increasing the service life of the probe. However, there are many technical challenges in achieving the free rolling of microspheres: (1) Structural design challenges. Traditional consolidation methods (such as glue bonding or direct machining) will fix the microspheres and limit their free rotation. Therefore, there is an urgent need to develop a new fixation method that enables them to roll freely. (2) Microsphere constraint challenges. In addition to ensuring that the microspheres can roll freely, it is also necessary to prevent them from accidentally falling off or getting out of control during testing. Therefore, the probe structure must provide sufficient binding force on the basis of enabling the microspheres to roll stably within a specified range and ensure the mechanical stability of the overall system. Summary of the Invention

[0017] As described in the background art above, the existing technology lacks an AFM probe with freely rolling microspheres. To overcome the defects of the existing technology, the present invention provides a cage-frame-based AFM microsphere probe with freely rotatable microspheres and a preparation method thereof. The implementation method of the present invention is simple. Only the currently conventional consolidated microsphere tip needs to be replaced with a cage microsphere tip. After calibration, various AFM experiments can be carried out without any modification to the existing consolidated microsphere AFM platform. The object of the present invention can be achieved by the following technical solutions:

[0018] One of the technical solutions of the present invention provides a cage-frame-based AFM microsphere probe for detecting the surface properties of a test sample. Briefly, the microsphere is placed in the cage frame, and then the cage frame with the built-in microsphere is integrally fixed to the AFM tip located at the end of the AFM cantilever. The probe includes:

[0019] Microspheres, cage frames, AFM tips and AFM cantilevers;

[0020] The cage frame is composed of a column upper plate composite substrate and a bottom plate. The column upper plate composite substrate is composed of an upper plate and 4 columns. A spherical through hole is opened at the center of the upper plate. Counterbores are provided at the four corners of the bottom plate, and a spherical pit is provided at the center of the bottom plate. The microsphere is clamped between the spherical through hole and the spherical pit, and the columns are connected to the counterbores, so that the column upper plate composite substrate and the bottom plate are connected to form a cage frame with a built-in microsphere;

[0021] The AFM tip is frustum-shaped. The bottom surface of the frustum is connected to the end of the AFM cantilever, and the top surface of the frustum is connected to the bottom plate;

[0022] The AFM cantilever is connected to the output end of the AFM instrument, driving the cage frame with the built-in microsphere to slide on the surface of the test sample. During the sliding process, the microsphere can rotate.

[0023] Further, the connection method between the column upper plate composite substrate and the bottom plate is adhesive bonding; the connection method between the AFM tip and the bottom plate is adhesive bonding; the connection method between the AFM tip and the AFM cantilever is integral processing;

[0024] The glue used for adhesive bonding is any one of ultraviolet curable glue (i.e., UV glue) and epoxy resin glue;

[0025] Further, the diameter D of the microsphere is 1-10 μm, preferably 5 μm; the microsphere is any one of silica microspheres, silicon microspheres, gold-plated microspheres, polystyrene microspheres or borosilicate microspheres; the material of the cage frame is preferably single crystal silicon, but not limited to single crystal silicon;

[0026] Further, the length and width dimensions of the upper plate and the bottom plate are both 2 to 2.8 times the diameter D of the microsphere; the thickness of the bottom plate is 0.6 to 1 times the diameter D of the microsphere; the thickness of the upper plate is 0.2 to 0.4 times the diameter D of the microsphere; the height of the column is 0.8 to 1 times the diameter D of the microsphere;

[0027] Further, the counterbore is a square counterbore, and the side length of the square counterbore is 0.2 to 0.4 times the diameter D of the microsphere; the depth of the counterbore is 1 to 2 μm; the spherical radius SR1 of the spherical pit is (1.05 to 1.15) / 2 times the diameter D of the microsphere; the spherical crown height h of the spherical pit is 0.2 to 0.3 times the diameter D of the microsphere;

[0028] The size and shape of the column are adapted to the size and shape of the counterbore; for example, when the counterbore is a square counterbore, the column is also a square column, and their side length dimensions are equal; the SR2 of the spherical transition region of the spherical through-hole is (1.05 to 1.15) / 2 times the diameter D of the microsphere, and the lower opening diameter D1 of the spherical through-hole is 0.88 to 0.94 times the diameter D of the microsphere, preferably 0.9 times.

[0029] Further, the diameter D2 of the top surface of the frustum of the AFM tip is 0.6 to 0.8 times the diameter D of the microsphere.

[0030] The second technical solution of the present invention provides a preparation method of an AFM microsphere probe based on a cage frame, including the following steps:

[0031] S1. Process the bottom plate of the cage frame: Select a bottom plate material of a certain size, clean and dry it for standby; Process counterbores and spherical pits at the four corners of the bottom plate material through lithography technology and etching technology; After processing, clean and dry it again for standby;

[0032] S2. Process the column upper plate composite substrate of the cage frame: Select a column upper plate composite substrate material of a certain size, clean and dry it for standby; Process the upper plate, column and spherical through-hole at the four-corner area and the center area through lithography technology and etching technology; After processing, clean and dry it again for standby;

[0033] S3. Assemble the microsphere and the cage frame: Clean and dry the bottom plate and the column upper plate composite substrate for standby; Mix the microsphere dry powder with deionized water to prepare a microsphere dispersion; Place the bottom plate with the spherical pit facing up on a glass slide and place it under a microscope, and drop the microsphere dispersion on the bottom plate to make the microsphere stably placed in the spherical pit; Let it stand still to volatilize the solvent until the microsphere and the spherical pit reach a firm contact; Glue the column and the counterbore together with an adhesive; Clean and dry, and check to ensure that the microsphere can rotate freely to obtain a cage frame with an embedded microsphere;

[0034] S4. Assemble the cage frame and the AFM tip: Take a probe composed of an AFM tip and an AFM cantilever, and grind the AFM tip flat; bond the AFM tip to the bottom plate with an adhesive, clean and dry it to obtain an AFM microsphere probe based on a cage frame.

[0035] Further, the cleaning means: sequentially perform ultrasonic cleaning with acetone, isopropyl alcohol, and deionized water, and the ultrasonic cleaning time is 5 - 10 min; the drying means: let it stand at room temperature until there is no liquid component on the surface;

[0036] Further, the lithography technology is high - resolution lithography technology; the etching technology is reactive ion etching technology (RIE) or deep reactive ion etching technology (DRIE): for the counterbore, it is preferably etched using reactive ion etching technology (RIE); for the spherical pit, the upper plate, the column, and the spherical through - hole, it is preferably etched using deep reactive ion etching technology (DRIE);

[0037] Further, the concentration of the microsphere dispersion liquid in step S3 is 2.5% - 5.0% (w / v).

[0038] Compared with the prior art, the beneficial effects and improvements of the present invention are as follows:

[0039] (1) The present invention solves the problem that the microsphere in the AFM platform with a solidified microsphere tip cannot rotate freely. Replace the existing solidified microsphere tip with the cage - type microsphere tip disclosed in the present invention, and then conduct the AFM scratching experiment on the corresponding sample, and the rolling - sliding motion between the microsphere and the test sample can be realized, so as to simulate the abrasive rolling - sliding motion in three - body abrasive wear and conduct relevant analyses.

[0040] (2) The present invention solves the problem that the microsphere in the AFM platform with a solidified microsphere probe affects the measurement performance and shortens its service life due to wear. In the AFM platform with the existing solidified microsphere tip, since the relative sliding between the microsphere and the test sample, the contact area between the microsphere and the sample is always the same position of the microsphere. As a result, with the accumulation of the AFM operation time, obvious wear areas will appear on the microsphere, which will affect the use performance of the AFM and ultimately lead to the scrapping of the AFM probe. However, for the cage - type microsphere tip disclosed in the present invention, the relative rolling - sliding motion between the microsphere and the sample is maintained, so that the contact area between the microsphere and the sample is no longer a fixed position of the microsphere, which can improve the stability of the AFM use performance and extend the service life of the probe. Description of the Drawings

[0041] Figure 1 It is the overall structure diagram of the AFM experimental platform of the AFM microsphere probe based on a cage frame of the present invention;

[0042] Figure 2 Cross-sectional view of the bottom plate and spherical pit of the cage frame;

[0043] Figure 3 Schematic diagram of the composite substrate of the upper plate of the column of the cage frame and cross-sectional view of the spherical through-hole;

[0044] Figure 4 Schematic diagram of the assembly of the microsphere and the bottom plate of the cage frame;

[0045] Figure 5 Assembly drawing of the cage frame and the microsphere;

[0046] Figure 6 Schematic diagram of the structure of the AFM tip and cantilever;

[0047] Figure 7 Schematic diagram of the structure of the auxiliary boss;

[0048] Figure 8 Installation and positioning drawing of the cage frame containing microspheres on the auxiliary boss;

[0049] Figure 9 Assembly schematic diagram between the cage frame and the AFM probe based on the auxiliary boss;

[0050] Figure 10 AFM microsphere probe structure diagram based on the cage frame;

[0051] Reference numerals:

[0052] 1: Test sample, 2: Microsphere, 3: Composite substrate of the upper plate of the column, 31: Upper plate, 32: Column, 33: Spherical through-hole, 4: Bottom plate, 41: Counterbore, 42: Spherical pit, 5: Adhesive, 6: AFM tip, 7: AFM cantilever;

[0053] SR1: Spherical radius of the spherical pit; h: Spherical crown height of the spherical pit;

[0054] SR2: Radius of the transition region of the spherical through-hole; D1: Diameter of the lower opening of the spherical through-hole;

[0055] D: Microsphere diameter, D2: Diameter of the ground area of the AFM tip;

[0056] G1: First glass slide, G2: Second glass slide. Detailed implementation method

[0057] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below in conjunction with specific embodiments. It should be noted that the following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made. These all belong to the protection scope of the present invention.

[0058] There are no special restrictions on the sources of all raw materials of the present invention (such as microspheres, probes, single crystal silicon wafers, adhesives, etc.), and those purchased on the market or prepared according to the conventional methods well-known to those skilled in the art can be used.

[0059] Embodiment 1: An AFM microsphere probe based on a cage framework

[0060] Reference Figures 1 to 4 , this embodiment provides an AFM microsphere probe based on a cage framework. This microsphere probe is used for the AFM experimental platform to detect the surface properties of test sample 1, such as surface topography, etc.

[0061] The microsphere probe includes the following structures: a microsphere 2, a cage framework, an AFM tip 6 and an AFM cantilever 7. Among them, the cage framework is composed of a bottom plate 4 and a column upper plate composite substrate 3. Reference Figure 2 , the bottom plate 4 is a square single crystal silicon wafer; a square counterbore 41 is provided at each of its four corners, and a spherical pit 42 is provided at the center; reference Figure 3 , the column upper plate composite substrate 3 is a "table" - shaped structure composed of a square single crystal silicon wafer upper plate 31 and four columns 32. The upper plate 31 and the columns 32 are integrally formed; a spherical through - hole 33 is provided at the center position of the upper plate 31; reference Figure 4 , the microsphere 2 is just stuck in the spherical pit 42, and an adhesive 5 is applied at the square counterbore 41 for connecting with the column 32; the adhesive 5 uses an ultraviolet - curable glue (UV glue); the AFM tip 6 is frustum - shaped, the bottom surface of the frustum is connected to the AFM cantilever 7, and the top surface of the frustum is connected to the bottom plate 4; the AFM cantilever 7 is connected to the output end of the AFM instrument.

[0062] Embodiment 2: A preparation method of an AFM microsphere probe based on a cage framework

[0063] Taking the microsphere diameter selected as 5 μm as an example, this embodiment provides the specific preparation steps of an AFM microsphere probe based on a cage framework:

[0064] Step (1) Process the bottom plate 4 of the cage framework

[0065] (1.1) Preparation of the material for the bottom plate 4

[0066] In this embodiment, a single-crystalline silicon wafer is selected as the bottom plate 4 of the cage frame, and the bottom plate 4 is ultrasonically cleaned successively with acetone, isopropyl alcohol, and deionized water. The ultrasonic cleaning time for each step is 5 - 10 minutes. After the cleaning of the bottom plate 4 is completed, it is dried and reserved.

[0067] The selection of the length, width, and thickness dimensions of the bottom plate 4 is considered to match the size of the diameter D of the microspheres 2. In this embodiment, the diameter D of the microspheres 2 is 5 μm. Therefore, the length and width scales of the bottom plate 4 are both 10 - 14 μm, and the thickness is 3 - 5 μm.

[0068] (1.2) Processing the square counterbores 41 at the four corner positions

[0069] Reference Figure 2 , in the four corner regions of the bottom plate 4, first, a pattern of the square counterbores 41 is prepared by a high-resolution lithography process to determine the subsequent etching positions. The side length of the square counterbores 41 is designed to be within the range of 1 - 2 μm. Subsequently, reactive ion etching (RIE) technology is used to precisely process the square counterbores 41 at the corresponding positions, and the etching depth is controlled within 1 - 2 μm to ensure that the sizes and shapes of the square counterbores 41 at the four corners are uniform.

[0070] The side length and the etching depth of the square counterbores 41 do not need to be equal. In this embodiment, for 5-μm microspheres, these two values are exactly similar. The etching depth of 1 - 2 μm is basically fixed and does not change with the diameter of the microspheres 2; while the side length of the square counterbores 41 slightly increases with the increase of the microsphere diameter D. For example, when the microsphere diameter is 10 μm, the side length can be 2.5 μm.

[0071] (1.3) Processing the spherical pit 42 at the central position

[0072] Reference Figure 2 , and then a spherical pit 42 is processed at the central position of the bottom plate 4 by high-resolution lithography technology and deep reactive ion etching (DRIE) technology. The shape of the spherical pit 42 is close to a spherical crown; in this embodiment, the diameter D of the microspheres 2 is selected as 5 μm. Therefore, the spherical crown height (h) of the spherical pit 42 is 1 - 1.5 μm, and the spherical radius (SR1) of the spherical pit 42 is 1.05 - 1.15 times the radius of the microspheres 2 to ensure that the microspheres 2 can be firmly and accurately embedded.

[0073] (1.4) Post-treatment of the bottom plate 4

[0074] The bottom plate 4 processed in the above steps (1.1) - (1.4) is ultrasonically cleaned and dried, and the methods of ultrasonic cleaning and drying are the same as those in step (1.1).

[0075] Step (2) is to process the column upper plate composite substrate 3

[0076] (2.1) Preparation of the material for the composite substrate 3 of the upper plate of the column

[0077] Additionally, select a single crystal silicon wafer with appropriate thickness as the processing material for the composite substrate 3 of the upper plate of the column. After the silicon wafer is selected, it is still ultrasonically cleaned with acetone, isopropyl alcohol, and deionized water, and the cleaning time for each time is 5 - 10 minutes, and then dried for standby;

[0078] The length and width of the silicon wafer described in this step are the same as the length and width dimensions of the bottom plate 4; the thickness of the silicon wafer matches the size of the diameter D of the subsequent microspheres 2. In this embodiment, the diameter D of the microspheres 2 is selected as 5 μm, so the thickness of the silicon wafer of the composite substrate 3 of the upper plate of the column is 5 - 6 μm.

[0079] (2.2) Processing the upper plate 31 and the column 32

[0080] As Figure 3 shown, in the four boundary regions of the silicon wafer, the columns 32 are processed by high - resolution lithography technology and deep reactive ion etching (DRIE) technology, that is, the middle part is etched away, leaving the columns 32; the side length dimension of the columns 32 is the same as that of the square counterbore 41; the etching depth of the upper plate 31 is controlled within 4 - 5 μm, that is, the height of the columns 32 is 4 - 5 μm, ensuring that the remaining thickness of the upper plate 31 is within 1 - 2 μm.

[0081] (2.3) Processing the spherical transition through - hole 33 in the central region of the upper plate

[0082] As Figure 3 shown, in the central region of the upper plate 31, the spherical through - hole 33 is processed by high - resolution lithography technology and deep reactive ion etching (DRIE) technology; the size of the spherical through - hole 33 is precisely matched with the diameter D of the microspheres 2. For the microspheres 2 with a diameter of 5 μm, the lower - mouth diameter of the spherical through - hole 33 can be considered as 4.5 - 4.7 μm, and the radius (SR2) of the transition region of the spherical through - hole 33 is 1.05 - 1.15 times the radius of the microspheres 2 to ensure the accuracy and fitting effect during subsequent assembly. During the etching process, a gradual etching strategy should be considered to precisely control the transition of the hole shape and the size change.

[0083] (2.4) Post - processing

[0084] The processed composite substrate 3 of the upper plate of the column is ultrasonically cleaned and dried, and the methods of ultrasonic cleaning and drying are the same as those in step (1.1).

[0085] Step (3) Assembling the microspheres 2 and the cage - type frame

[0086] (3.1) Material preparation and cleaning

[0087] In the assembly process of this embodiment, a glass slide is required. Before the experiment, the glass slide and each component of the cage frame (including the bottom plate 4 and the column upper plate composite substrate 3) are ultrasonically cleaned (for about 5 - 10 minutes), and then dried. The methods of ultrasonic cleaning and drying are the same as those in step (1.1).

[0088] (3.2) Preparation of the microsphere 2 dispersion

[0089] Prepare dry microspheres with a diameter of about 5 μm. Mix the dry microspheres with deionized water to prepare a dispersion with a concentration of 2.5% - 5.0% (w / v). Use ultrasonic cleaning (for about 10 minutes) to fully disperse the microspheres 2 to ensure that the microspheres 2 are evenly and monodispersed.

[0090] (3.3) Placement of the microspheres 2 at the spherical pits 42

[0091] As Figure 4 and Figure 5 shown, under an optical microscope, place the bottom plate 4 on the glass slide, ensuring that the spherical pits 42 face upward to receive the microspheres 2. Then, use a micropipette (for microspheres 2 with a diameter of 5 μm, the inner diameter of the pipette can be selected to be about 10 - 20 μm) to suck a small amount of solution from the microsphere dispersion, and drop the liquid droplet at a suitable position on the glass slide. Observe under the optical microscope, adjust the focal length, and find the liquid droplet area containing a single or a few microspheres 2. Subsequently, use the micropipette to approach the selected liquid droplet area again, and slowly suck the liquid droplet containing the microspheres 2. Finally, under the microscope, align the micropipette with the position of the spherical pit 42, and slowly squeeze the micropipette to release the liquid droplet, ensuring that at least one microsphere 2 is accurately placed into the spherical pit 42. After observing and confirming that the microspheres 2 have been stably placed in the spherical pits 42, let the solution naturally volatilize for a period of time (about 5 - 10 minutes) to ensure a firm contact is formed between the microspheres 2 and the spherical pits 42.

[0092] (3.4) Assembly of the bottom plate 4 and the column upper plate composite substrate 3

[0093] As Figure 5 shown, drop an appropriate amount of adhesive 5 (UV glue) into the square counterbores 41 at the four corner positions of the bottom plate 4. Then, accurately dock the column 32 with the square counterbores 41 under the microscope, while ensuring that the microspheres 2 in the spherical through-holes 33 can partially protrude correctly. After completing the accurate alignment, use a UV light source to cure the adhesive 5. It is recommended that the curing time be not less than 5 minutes to ensure firm bonding and stable structure.

[0094] (3.5) Overall cleaning of the cage frame

[0095] The assembled cage frame containing the microspheres 2 ( Figure 5) is placed in an ultrasonic cleaner and cleaned with deionized water (mild conditions to avoid glue falling off), and then dried.

[0096] (3.6) Microsphere 2 free rotation test

[0097] Observe under a microscope and gently move the protruding part of the microsphere 2 in the upper plate 31 to ensure that the microsphere 2 can rotate freely in the cage frame. At this point, all the assembly steps of the microsphere and the cage frame are completed.

[0098] If it is found that the microsphere 2 is not flexible in rotating freely, it is necessary to soften and remove the adhesive 5 (UV glue), disassemble the assembled frame, and reassemble the microsphere 2 and the cage frame according to steps 3.1 to 3.6.

[0099] Step (4) Assembling the cage frame and the AFM tip 6

[0100] (4.1) AFM tip 6 pretreatment

[0101] like Figure 6 As shown, an AFM cantilever 7 with an AFM tip 6 attached is taken and the AFM tip 6 is ground flat. The diameter of the ground area is It should be adjusted accordingly according to the specific cage frame size. For a frame containing microspheres 2 with a diameter of 5μm, The polished AFM tip 6 and AFM cantilever 7 are ultrasonically cleaned with acetone, isopropanol and deionized water (5 to 10 minutes) and then dried.

[0102] (4.2) Preparation of bosses for auxiliary positioning

[0103] like Figure 7 As shown, take a first glass slide G1, clean it, and drip adhesive 5 (UV glue) on its surface in a square layout. Then, place four small square second glass slides G2 at the glue drops for curing to form four bosses, whose size matches the position of the four columns 32 of the cage frame. And the height of the boss should be greater than the height of the microsphere 2 protruding from the central through hole 33 of the upper plate of the frame, so that the microsphere 2 does not contact the first glass slide G1.

[0104] (4.3) Cage frame and boss docking

[0105] like Figure 8 As shown, under a microscope, the upper plate of the cage frame containing the microspheres 2 is placed downward on the boss of the slide, so that the four corners of the upper plate (positions 32 of the columns) fall on the boss formed by four second slides G2, and the microspheres 2 are suspended in the air without contacting the first slide G1.

[0106] (4.4) Cage frame and AFM tip 6 fixed

[0107] As Figure 9 shown, apply the adhesive 5 (UV glue) to the central area of the frame bottom plate 4, and then dock the polished AFM tip 6 with this area. Subsequently, use a UV light source for curing, and the curing time shall not be less than 5 minutes to ensure that the glue is fully cured. Finally, integrate the cage frame containing the microspheres 2 with the AFM tip 6. Thus, an AFM microsphere probe based on the cage frame is prepared, as Figure 10 shown.

[0108] (4.5) Final cleaning and calibration of the microsphere probe

[0109] Perform ultrasonic cleaning (under mild conditions to avoid the glue falling off) and drying on the fabricated cage microsphere probe. Replace the conventional solidified microsphere tip on the AFM experimental platform with the cage microsphere probe provided by this application, and for the newly prepared microsphere probe, refer to the probe calibration procedure provided by the AFM equipment manufacturer, mainly using the method based on standard samples, to calibrate and calibrate the stiffness, displacement sensitivity, etc. of the probe. After calibration, the new probe can be used for AFM scratching experiments or nanomachining to achieve the rolling and sliding motion between the microspheres and the sample, as Figure 1 shown.

[0110] The above description of the embodiments is for those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A cage-frame-based AFM microsphere probe, characterized in that The probe includes: a microsphere (2), a cage frame, an AFM tip (6), and an AFM cantilever (7); The cage frame is composed of a column upper plate composite substrate (3) and a bottom plate (4). The column upper plate composite substrate (3) is composed of an upper plate (31) and 4 columns (32). A spherical through hole (33) is provided at the center of the upper plate (31). Counterbores (41) are provided at the four corners of the bottom plate (4), and a spherical pit (42) is provided at the center of the bottom plate (4). The microsphere (2) is clamped between the spherical through hole (33) and the spherical pit (42), and the columns (32) are connected to the counterbores (41), thereby connecting the column upper plate composite substrate (3) and the bottom plate (4) to form a cage frame with the microsphere (2) inside; The AFM tip (6) is frustum-shaped, the bottom surface of the frustum is connected to the end of the AFM cantilever (7), and the top surface of the frustum is connected to the bottom plate (4); The AFM cantilever (7) is connected to the output end of the AFM instrument and is used to drive the cage frame with the microsphere (2) inside to slide on the surface of the test sample (1). During the sliding process, the microsphere (2) can rotate.

2. The AFM microsphere probe based on a cage frame according to claim 1, characterized in that, The connection method between the column upper plate composite substrate (3) and the bottom plate (4) is bonding; the connection method between the AFM tip (6) and the bottom plate (4) is bonding; the AFM tip (6) and the AFM cantilever (7) are integrally formed.

3. The AFM microsphere probe based on a cage frame according to claim 1, wherein The diameter D of the microsphere (2) is 1 - 10 μm; the microsphere (2) is any one of a silica microsphere, a silicon microsphere, a gold-plated microsphere, a polystyrene microsphere, or a borosilicate microsphere; the material of the cage frame is single-crystalline silicon.

4. The AFM microsphere probe based on a cage frame according to claim 1, characterized in that, The length and width dimensions of the upper plate (31) and the bottom plate (4) are both 2 - 2.8 times the diameter D of the microsphere (2); the thickness of the bottom plate (4) is 0.6 - 1 times the diameter D of the microsphere (2); the thickness of the upper plate (31) is 0.2 - 0.4 times the diameter D of the microsphere (2); the height of the column (32) is 0.8 - 1 times the diameter D of the microsphere (2).

5. The AFM microsphere probe based on a cage frame according to claim 1, characterized in that, The counterbore (41) is a square counterbore, and its side length is 0.2 - 0.4 times the diameter D of the microsphere (2); the depth of the counterbore (41) is 1 - 2 μm; the spherical radius SR1 of the spherical pit (42) is (1.05 - 1.15) / 2 times the diameter D of the microsphere (2); the spherical crown height h of the spherical pit (42) is 0.2 - 0.3 times the diameter D of the microsphere (2).

6. The AFM microsphere probe based on a cage frame according to claim 1, characterized in that, The size and shape of the column (32) are adapted to the size and shape of the counterbore (41); the SR2 of the spherical transition region of the spherical through hole (33) is (1.05 - 1.15) / 2 times the diameter D of the microsphere (2), and the lower opening diameter D1 of the spherical through hole (33) is 0.88 - 0.94 times the diameter D of the microsphere (2).

7. The AFM microsphere probe based on a cage frame according to claim 1, wherein The diameter D2 of the top surface of the frustum of the AFM tip (6) is 0.6 - 0.8 times the diameter D of the microsphere (2).

8. A preparation method of the AFM microsphere probe based on a cage framework as described in claim 1, characterized in that, Including the following steps: S1. Process the bottom plate (4) of the cage frame: Select bottom plate materials of a certain size, clean and dry them for standby; Process counterbores (41) and spherical pits (42) at the four corners of the bottom plate materials through photolithography and etching techniques; After processing, clean and dry them again for standby; S2. Process the column upper plate composite substrate (3) of the cage frame: Select column upper plate composite substrate materials of a certain size, clean and dry them for standby; Process the upper plate (31), columns (32) and spherical through-holes (33) at the four corner regions and the central region through photolithography and etching techniques; After processing, clean and dry them again for standby; S3. Assemble the microspheres (2) with the cage frame: Clean and dry the bottom plate (4) and the column upper plate composite substrate (3) for standby; Mix the dry powder of microspheres (2) with deionized water to prepare a dispersion of microspheres (2); Place the bottom plate (4) with the spherical pits (42) facing up on a glass slide and place it under a microscope, and drop the dispersion of microspheres (2) on the bottom plate (4) to make the microspheres (2) stably placed in the spherical pits (42); Let it stand still to allow the solvent to volatilize until there is a firm contact between the microspheres (2) and the spherical pits (42); Glue the columns (32) and the counterbores (41) together with an adhesive (5); Clean and dry, and check to ensure that the microspheres (2) can rotate freely to obtain a cage frame with embedded microspheres (2); S4. Assemble the cage frame with the AFM tip: Take a probe composed of an AFM tip (6) and an AFM cantilever (7), and grind the AFM tip (6) flat; Glue the AFM tip (6) and the bottom plate (4) together with an adhesive (5), clean and dry to obtain an AFM microsphere probe based on the cage frame.

9. The preparation method of an AFM microsphere probe based on a cage frame according to claim 8, characterized in that, The cleaning mentioned above means: Perform ultrasonic cleaning successively with acetone, isopropanol and deionized water, and the time of ultrasonic cleaning is 5 - 10 min; The drying mentioned above means: Let it stand at room temperature until there is no liquid component on the surface; The photolithography technique is a high-resolution photolithography technique; The etching technique is a reactive ion etching technique or a deep reactive ion etching technique: For the counterbores (41), use the reactive ion etching technique for etching; For the spherical pits (42), upper plate (31), columns (32) and spherical through-holes (33), use the deep reactive ion etching technique for etching.

10. The preparation method of an AFM microsphere probe based on a cage frame according to claim 8, wherein, The concentration of the dispersion of microspheres (2) described in step S3 is 2.5% - 5.0% (w / v).

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