A method for modifying an atomic force microscope probe tip
By modifying Si-based probe tips with gel-like polymers through oxygen plasma cleaning and contact mode, the problem of difficult modification in existing technologies is solved, and accurate adhesion and mechanical property testing of polymers are achieved, improving the reliability and safety of the probe.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAMEN UNIV
- Filing Date
- 2023-07-11
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technologies make it difficult to modify gel-like polymers onto the tips of ordinary Si-based atomic force microscope probes, and traditional methods cannot effectively test the interfacial mechanical properties between polymers and the test material.
A gel-like polymer was modified onto the tip of a Si-based probe using oxygen plasma cleaning and contact mode. The tip was then pressed into the gel-like polymer using contact mode of atomic force microscopy, and completely solidified by heating in a microgroove to form a polymer film.
It enables accurate modification and adhesion of polymers, allows testing of the adhesion behavior between polymers and analytes, improves the reliability and safety of the probe modification process, and allows direct acquisition of the mechanical properties of polymers and analytes.
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Figure CN116893284B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of atomic force microscopy measurement technology, specifically relating to a method for modifying the tip of an atomic force microscope probe. Background Technology
[0002] Atomic force microscopy (AFM) studies the surface structure and properties of materials by detecting extremely weak interatomic forces between the surface of a sample and a miniature force-sensitive element. A microcantilever, extremely sensitive to these weak forces, is fixed at one end, while a tiny tip at the other end approaches the sample. The tip interacts with the sample surface, causing deformation or changes in the microcantilever's motion. By scanning the sample and detecting these deformations or changes, information about the force distribution can be obtained, leading to ultra-high resolution information on the surface morphology and the interfacial mechanical properties between the tip and the sample. While AFM probes offer excellent accuracy due to their sharp tips, limitations in semiconductor manufacturing processes mean that AFM probes and tips are primarily made of Si-based materials. This limits the characterization of interfacial mechanical properties between Si-based materials such as Si3N4 and the sample, and prevents the characterization of interfacial mechanical properties between two different materials other than Si and Si3N4.
[0003] How to further modify existing Si tips to directly obtain the interfacial mechanical properties between different functional groups and materials on the tip and the object under test is one of the main trends in the development of atomic force microscopy (AFM) technology. Using semiconductor deposition methods, including magnetron sputtering and chemical vapor deposition, is an effective way to modify probe tips. Chinese invention patent CN103665415A utilizes magnetron sputtering to modify AFM probes with Au thin films. At room temperature, Cr and Au films are sequentially deposited on a cleaned AFM probe, ultimately resulting in an AFM probe with a 3–20 nm Cr film and a 30–100 nm Au film coated on the tip surface. Carpick (Carpick RW, Sridharan K, Sumant A V. Diamond-Likecarbon Coated Nanoprobes: US, US20110107473[P].2011) et al. deposited a 5–60 nm thick diamond-like carbon layer on the probe tip using plasma-enhanced chemical vapor deposition to improve the tip's wear resistance. Semiconductor-based deposition methods can rapidly and effectively modify atomic force microscope probe tips with specific materials; almost all metals, Si-based, and C-based semiconductors can be modified onto the tip using this method, and the modification thickness is controllable. However, this method cannot be used to modify polymer solutions or gels containing specific functional groups. Electrochemical polymerization is another method for modifying probe tips. Christine et al. (Christine) Nicolas Willet, Robert et al. Electrografting of polymers onto AFM tips: a novel approach for chemical force microscopy and force spectroscopy[J]. CHEM.COMMUN, 2004, 5(1):147-149) First, an Au film is deposited on the probe tip, and then N-based succinamide polymers are grafted onto the metal probe tip using electrochemical polymerization. By controlling the film thickness through electrochemical polymerization using cyclic voltammetry, polymers such as polyaniline, polypyrrole, and polymethylthiophene can be grafted onto the metal tip. Probe tip modification can also be achieved by immersion method. Chinese invention patent CN 106290989 A completely immerses the entire probe in an aqueous solution of soluble organic matter and stands for 30 minutes. After removal, it is dried, dehydrated and carbonized, and dried to constant weight to obtain a carbon-coated probe tip.
[0004] For gel-like polymers prepared from the stock solution, which are not fully cured and do not form a solid state similar to Cr and Au, it is impossible to modify the probe tip with the gel-like polymer using sputtering in semiconductor coating methods. When modifying ordinary Si-based tips with gel-like polymers, the tip is not metallized, and electrochemical polymerization methods cannot modify the polymer onto ordinary Si-based tips. Furthermore, for gel-like polymers with strong viscosity, if the wetting method is used, the entire probe will be completely embedded in the gel-like polymer and cannot be removed.
[0005] Therefore, it is necessary to develop a new method for modifying the tip of an atomic force microscope probe. Summary of the Invention
[0006] The purpose of this invention is to overcome the defects of the existing technology and provide a method for modifying the tip of an atomic force microscope probe.
[0007] To achieve the above objectives, one of the technical solutions of the present invention is: a method for modifying the tip of an atomic force microscope probe, specifically including the following steps:
[0008] S1: The stock solution for preparing the polymer is synthesized to obtain a pre-solidified gel-like polymer.
[0009] S2: Place the atomic force microscope probe into the microgroove in the silicon wafer fixture, clean the atomic force microscope probe with oxygen plasma, and achieve hydrophilic treatment of the probe tip;
[0010] S3: Based on the contact mode of atomic force microscopy, the cleaned and hydrophilicated probe is loaded into the gas phase fixture of the atomic force microscope, and the probe tip is pressed into the gel-like polymer for modification after force is applied.
[0011] Atomic force microscopy (AFM) has three basic testing modes: contact, tapping, and force curve. Based on these modes, AFM can be further expanded to characterize mechanical, electrical, and magnetic properties. The contact mode, one of the basic modes, involves making full contact between the probe tip and the sample, applying pressure, and scanning back and forth across the sample surface. This invention, based on the contact mode, applies pressure to the probe tip, pressing in a polymer so that the polymer "sticks" to the tip. The difference between this and the contact mode is that it does not involve scanning back and forth across the sample surface.
[0012] S4: The modified atomic force microscope probe is placed into the microgroove in the silicon wafer fixture, heated to achieve complete solidification, and finally coated with a layer of polymer film at the tip of the probe.
[0013] In a preferred embodiment of the present invention, the probe is a common silicon (Si)-based probe.
[0014] In a preferred embodiment of the present invention, the polymer stock solution in step S1 comprises bis(4-tert-butylcyclohexyl) peroxide dicarbonate, 1,4-butanediol diacrylate, styrene methacrylate, styrene acrylate, and 2-ethoxyethyl methacrylate, wherein the mass percentages of the above five materials in the polymer stock solution are 1wt%–3wt%, 2wt%–6wt%, 35wt%–40wt%, 35wt%–40wt%, and 18wt%–22wt%, respectively.
[0015] In a preferred embodiment of the present invention, the preliminary solidification synthesis process of the polymer stock solution in step S1 involves a vacuum degree of 0.01–0.05 Pa, a temperature of 25–35 °C, and a time of 2–8 hours to initially solidify, forming a gel-like polymer. Compared to a fully solidified polymer, the gel-like polymer facilitates component transfer to the tip of an atomic force microscope probe; compared to the stock solution, the gel-like polymer can be easily fixed onto a specially designed magnetic plate of the atomic force microscope, accurately achieving effective contact between the probe tip and the polymer, thereby realizing the transfer of polymer components.
[0016] In a preferred embodiment of the present invention, in steps S2 and S4, microgrooves are formed in the silicon wafer fixture using semiconductor processes to hold probes. The semiconductor processing mainly includes photolithography and deep silicon etching. The depth of the microgrooves is 150–250 μm, the width of the microgrooves is 50–150 μm greater than the width of the probes, and the length of the microgrooves is 100–150 μm greater than the length of the probes.
[0017] An atomic force microscope (AFM) probe consists of three parts: a support base, a cantilever beam, and a tip. The cantilever beam is connected to the support base, and its head forms the tip. The cantilever beam is typically 2–4 μm thick, making it highly susceptible to breakage during probe clamping and transfer, leading to probe failure. During cleaning and curing, placing the probe within a specially designed microgroove not only reduces the number of clamping and transfer operations but also prevents crosstalk from external airflow onto the probe fixed within the microgroove, especially to the cantilever beam, thus effectively preventing its breakage.
[0018] In a preferred embodiment of the present invention, the oxygen plasma cleaning in step S2 has a power of 100–300 W, a gas pressure of 0.3–1 Pa, a gas flow rate of 0.5–1 sccm, and a cleaning time of 0.5–4 min. The needle tip after oxygen plasma cleaning has a hydrophilic interface, which is beneficial for improving the adhesion between the needle tip and the polymer during subsequent modification.
[0019] In a preferred embodiment of the present invention, the pressure applied by the probe tip to the gel-like polymer in step S3 is 1.5 to 6.5 μN, and the time is 5 to 15 min.
[0020] In a preferred embodiment of the present invention, in step S4, the modified atomic force microscope probe is inserted into a microgroove in a specially made silicon wafer fixture and heated to completely solidify the polymer at a temperature of 55-65°C for 0.5-3.5 hours.
[0021] To achieve the above objectives, the second technical solution of the present invention is: an atomic force microscope probe prepared by the above modification method.
[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0023] 1. This invention can modify polymer components onto ordinary Si-based probe tips using atomic force microscopy contact mode, without the need for metallization of the probe or additional processing equipment to complete the main modification process, and the modification process is simple to operate.
[0024] 2. This invention enables the modification of ordinary Si-based probe tips with the same components of polymers, and can accurately test the adhesion behavior between polymers and proteins, providing a method for determining the interaction between polymers and other substances;
[0025] 3. The present invention uses a silicon wafer with microgrooves as the carrier plate of the probe, which can not only reduce the number of probe clamping and transfer, but also avoid crosstalk of external airflow to the probe fixed in the microgrooves, especially to the cantilever beam, thereby effectively avoiding the breakage of the cantilever beam and improving the reliability and safety of the probe modification process.
[0026] 4. The modification method of this invention successfully transfers the same components of a completely solidified polymer to the tip of an atomic force microscope probe. The modified probe can be used for subsequent atomic force microscopy morphology characterization and force curve testing and analysis. It can accurately locate the object under test and truly reflect the mechanical behavior between the solidified polymer and the object under test, thereby directly obtaining the mechanical properties between the completely solidified polymer and the sample under test, providing a method for determining the interaction between polymers and other substances. Attached Figure Description
[0027] Figure 1 This is a specially designed silicon wafer for placing probes, as described in Example 1.
[0028] Figure 2 This is a schematic diagram of the polymer being heated and solidified on a modified probe placed in a silicon wafer microgroove in Example 1.
[0029] Figure 3 This is a scanning electron microscope image of the atomic force microscope probe tip before modification in Example 1;
[0030] Figure 4 This is a scanning electron microscope image of the modified atomic force microscope probe tip from Example 1.
[0031] Figure 5 Energy dispersive spectroscopy (EDS) elemental analysis of the atomic force microscope probe tip before modification, as shown in Example 1.
[0032] Figure 6 Energy dispersive spectroscopy (EDS) elemental analysis of the modified atomic force microscope probe tip in Example 1;
[0033] Figure 7 The infrared spectrum of the needle tip and the infrared spectrum of the polymer are shown in Example 1.
[0034] Figure 8 This is a morphology image of bovine serum albumin scanned by an atomic force microscope probe tip before modification, as shown in Example 1.
[0035] Figure 9 The mechanical curves of the atomic force microscope probe tip and bovine blood protein before modification in Example 1 are shown.
[0036] Figure 10 This is a morphology image of bovine serum albumin scanned by the atomic force microscope probe tip after modification in Example 1.
[0037] Figure 11 The mechanical curves of the modified atomic force microscope probe tip and bovine serum albumin are shown in Example 1. Detailed Implementation
[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of this invention is not limited to these embodiments. The same reference numerals throughout the text always represent the same elements, and similar reference numerals represent similar elements.
[0039] A method for modifying the tip of an atomic force microscope probe, specifically including the following steps:
[0040] S1: The stock solution for preparing the polymer is synthesized to obtain a pre-solidified gel-like polymer.
[0041] S2: Place the atomic force microscope probe into the microgroove in the silicon wafer fixture, clean the atomic force microscope probe with oxygen plasma, and achieve hydrophilic treatment of the probe tip;
[0042] S3: Based on the contact mode of atomic force microscopy, the cleaned and hydrophilized probe tip is pressed into a gel-like polymer for modification;
[0043] S4: The modified atomic force microscope probe is placed into the microgroove in the silicon wafer fixture, heated to achieve complete solidification, and finally coated with a layer of polymer film at the tip of the probe.
[0044] The probe is a common silicon (Si)-based probe.
[0045] The polymer stock solution in step S1 comprises bis(4-tert-butylcyclohexyl) peroxide dicarbonate, 1,4-butanediol diacrylate, styrene methacrylate, styrene acrylate, and 2-ethoxyethyl methacrylate, with the above five materials accounting for 1wt%–3wt%, 2wt%–6wt%, 35wt%–40wt%, 35wt%–40wt%, and 18wt%–22wt% of the polymer stock solution, respectively.
[0046] The preliminary solidification synthesis process of the polymer stock solution in step S1 is carried out under a vacuum of 0.01 to 0.05 Pa, a temperature of 25 to 35 °C, and a time of 2 to 8 hours, forming a gel-like polymer.
[0047] In steps S2 and S4, the microgrooves in the silicon wafer fixture are created using semiconductor processing technology to hold the probes. The semiconductor processing technology mainly includes photolithography and deep silicon etching. The depth of the microgrooves is 150-250 μm, the width of the microgrooves is 50-150 μm greater than the width of the probes, and the length of the microgrooves is 100-150 μm greater than the length of the probes.
[0048] In step S2, the atomic force microscope probe is cleaned with oxygen plasma at a power of 100–300 W, a gas pressure of 0.3–1 Pa, a gas flow rate of 0.5–1 sccm, and a cleaning time of 0.5–4 min.
[0049] In step S3, the pressure applied by the probe tip to the gel-like polymer is 1.5–6.5 μN, and the time is 5–15 min.
[0050] In step S4, the modified atomic force microscope probe is placed into a microgroove in a specially designed silicon wafer fixture and heated to completely solidify the polymer at a temperature of 55–65°C for 0.5–3.5 hours.
[0051] An atomic force microscope probe prepared by a method for modifying the probe tip.
[0052] Example 1
[0053] An atomic force microscope (AFM) probe is prepared by a method for modifying the probe tip. The modification method includes the following steps:
[0054] (1) Preparation of polymer stock solution: Weigh 0.06g of bis(4-tert-butylcyclohexyl) peroxide dicarbonate, 0.16g of 1,4-butanediol diacrylate, 1.49g of phenethyl methacrylate, 1.49g of phenethyl acrylate, and 0.8g of 2-ethoxyethyl methacrylate, mix and stir evenly to obtain stock solution; place stock solution in vacuum oven with vacuum degree of 0.02Pa and temperature of 30℃, polymerize for 6h, and obtain gel-like polymer through preliminary solidification;
[0055] (2) Three microgrooves for placing probes were fabricated on a 4-inch silicon wafer using photolithography and deep silicon etching processes in semiconductor fabrication. The grooves were 4 mm long, 2.2 mm wide, and 200 μm deep. Figure 1 As shown;
[0056] (3) Insert the probe Figure 1 The probe of an atomic force microscope was cleaned in a microgroove on a specially made silicon wafer using oxygen plasma at a power of 200W, a gas pressure of 0.8Pa, a gas flow rate of 0.8sccm, and a time of 2min.
[0057] (4) The cleaned probe is placed into the gas phase holder of the atomic force microscope. Based on the contact mode of the atomic force microscope, the tip is pressed into the gel-like polymer. The pressure is 4 μN and the application time is 10 min.
[0058] (5) The modified atomic force microscope probe is placed into the microgroove of the specially made silicon wafer fixture, and heated to achieve complete solidification. The heating temperature is 60℃ and the time is 2 hours. Figure 2 As shown; after complete solidification, a layer of polymer film will be coated on the tip of the probe.
[0059] Characterization of the modified atomic force microscope probe:
[0060] First, morphological characteristics: Figure 3 The scanning electron microscope (SEM) image of the atomic force microscope (AFM) probe tip before modification shows a smooth sidewall with no surface coating. The tip is sharp with a radius of curvature of approximately 10 nm. Figure 4 This is a scanning electron microscope image of the modified atomic force microscope probe tip, compared to... Figure 4 The sidewalls of the probe tip, coated with the polymer, exhibit an undulating pattern, with a significantly wider tip and a radius of curvature of approximately 30 nm. Morphological characterization indicates that the probe tip has been modified with the polymer.
[0061] Secondly, elemental characterization: the main element of the polymer is C. Figure 5 The elemental analysis spectrum of the atomic force microscope probe tip before modification shows that the weight percentage of C is 15.7% and the weight percentage of Si is 66.4%. Figure 6Energy dispersive spectroscopy (EDS) elemental analysis of the modified atomic force microscope (AFM) probe tip revealed that the weight percentage of carbon (C) increased from 15.7% to 39.21%, while the weight percentage of silicon (Si) decreased from 66.4% to 45.71%. Modification of the probe tip with a polymer significantly increased the C content while significantly decreasing the proportion of intrinsic Si. Therefore, the elemental analysis of the probe tip before and after modification further validates that this method successfully modifies polymers onto the tip of an AFM probe.
[0062] Finally, infrared spectral characterization: Figure 7 The images show the infrared spectra of the modified needle tip and the original polymer, respectively, at 2955 cm⁻¹. -1 The peak at 1726 cm⁻¹ is the characteristic stretching vibration peak of CH(CH₃,CH₂). -1 The peak at 1160 cm⁻¹ represents the characteristic stretching vibration of the carbonyl group in acrylates. -1 The asymmetric stretching peak of -COC is 691 cm⁻¹. -1 The peak at position 1 is a characteristic peak of the benzene ring CH. The infrared spectrum shows that the characteristic peaks of the polymer adhered to the probe are basically consistent with those of the original polymer, further proving that the method described in this invention patent has successfully modified the polymer onto the tip of the atomic force microscope probe.
[0063] Figure 8 To obtain morphology images of bovine serum albumin (BSA) using a standard Si-based unmodified probe via atomic force microscopy, the unmodified probe tip was moved onto the BSA and a pressure of up to 1 μN was applied. The mechanical properties of the unmodified probe tip against the protein were then obtained, as shown in the figure. Figure 9 As shown. By calculating the area of the closed curve formed by probe indentation and extraction, the adhesion energy between the ordinary Si-based unmodified probe and bovine serum albumin was found to be 4.71 × 10⁻⁶. -14 J.
[0064] Figure 10 To scan bovine serum albumin with the modified probe described in this invention using atomic force microscopy, based on the obtained morphology image, the modified probe tip is moved onto the bovine serum albumin, and a pressure of up to 1 μN is applied to obtain the mechanical curve of the modified probe tip and the protein, as shown in the figure. Figure 11 As shown, the curves for needle tip insertion and extraction basically overlap, with an adhesion energy of 4.52 × 10⁻⁶. -16 J shows that the adhesion energy between the polymer and the protein is reduced by two orders of magnitude compared to the unmodified tip, indicating that there is a repulsion between the polymer and the protein, which is a characterization effect that the unmodified Si-based tip cannot achieve.
[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for modifying the tip of an atomic force microscope probe, characterized in that, Includes the following steps: S1: The original solution of the polymer is synthesized to obtain a pre-solidified gel-like polymer. The gel-like polymer can accurately achieve effective contact between the probe tip and the polymer, thereby realizing the transfer of polymer components. S2: The atomic force microscope probe is placed into the microgroove in the silicon wafer fixture. The microgroove is created by photolithography and deep silicon etching. The atomic force microscope probe is cleaned by oxygen plasma and the tip is made hydrophilic. S3: Based on the contact mode of atomic force microscopy, the probe tip, which has been cleaned and hydrophilized in step S2, is pressed into a gel-like polymer for modification; based on the contact mode, a pressure of 1.5 to 6.5 μN is applied to the tip for 5 to 15 min to press in the polymer and allow the polymer to adhere to the tip. S4: The modified atomic force microscope probe from step S4 is placed into a microgroove in a silicon wafer fixture and heated to achieve complete solidification. Finally, a layer of polymer film is coated on the tip of the probe.
2. The modification method as described in claim 1, characterized in that, The probe is a silicon (Si) based probe.
3. The modification method as described in claim 1, characterized in that, The polymer stock solution in step S1 comprises, by mass percentage, 1 wt% to 3 wt% bis(4-tert-butylcyclohexyl) peroxide dicarbonate, 2 wt% to 6 wt% 1,4-butanediol diacrylate, 35 wt% to 40 wt% styrene methacrylate, 35 wt% to 40 wt% styrene acrylate, and 18 wt% to 22 wt% 2-ethoxyethyl methacrylate.
4. The modification method as described in claim 1, characterized in that, The vacuum degree of synthesis in step S1 is 0.01-0.05 Pa, the temperature is 25-35 °C, and the time is 2-8 h.
5. The modification method as described in claim 1, characterized in that, The depth of the microgroove is 150–250 µm, the width of the microgroove is 50–150 µm greater than the width of the probe, and the length of the microgroove is 100–150 µm greater than the length of the probe.
6. The modification method as described in claim 1, characterized in that, In step S2, the oxygen plasma cleaning power is 100-300W, the gas pressure is 0.3-1Pa, the gas flow rate is 0.5-1sccm, and the cleaning time is 0.5-4min.
7. The modification method as described in claim 1, characterized in that, In step S4, the heating temperature is 55–65°C and the heating time is 0.5–3.5 h.
8. An atomic force microscope probe prepared by the modification method according to any one of claims 1-7.