Atomic force microscope probe and method of evaluating steel materials

Abstract

To provide an atomic force microscope probe which enables material surface characteristics evaluation, including friction force measurement and adhesion force measurement, in an environmental close to an actual system in which a steel material is used.SOLUTION: An atomic force microscope probe 1 disclosed herein comprises a sample-contacting portion having a curvature radius R of 0.5 μm or greater, and a metal vapor deposition film 21 having a thickness in a range of 20-100 nm on a surface thereof. The atomic force microscope prober may have a tabular lever portion 10 and a tip portion 20 provided on the lever portion 10. The tip portion 20 may be sphere-shaped.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a probe for an atomic force microscope and a method for evaluating a steel material. [Background technology]

[0002] Steel materials are widely used in industrial products such as automobile parts, railway vehicle parts, building materials, pipes, etc. In particular, alloy steels for machine construction and carbon steels for machine construction are often used as materials for sliding parts, such as gears and shafts, which are typical of parts in power transmission systems (mechanical systems), due to their high mechanical strength.

[0003] The biggest issue with sliding parts is friction and wear between parts, which are thought to be the cause of malfunctions and low efficiency in the entire mechanical system. In the future, as mechanical systems become smaller and lighter, the environment for sliding parts is expected to become even harsher. For example, for crankshafts, which are engine parts for automobiles, improving the seizure resistance of sliding parts is a permanent issue, along with making them smaller and lighter. To solve these issues, it is necessary to develop steel materials with better sliding properties than current products, in preparation for the miniaturization and weight reduction of mechanical systems.

[0004] One of the problems that steel materials for sliding parts must solve is the improvement of seizure resistance from the viewpoint of improving the life and reliability of parts. Seizure refers to a phenomenon in which sliding surfaces are fixed, welded, or adhered to each other, and the occurrence of seizure leads to failure of mechanical systems. Regarding the improvement of the seizure resistance of steel materials, methods of controlling adhesion by controlling precipitates and components in the steel materials have been studied. For example, JP 2013-227674 A describes that adhesion is suppressed and seizure resistance is improved by controlling the carbide and nitrogen concentrations on the surface.

[0005] Since the mechanical properties of steel are easily affected by its structure, microstructural control is important for improving its sliding properties. In order to find the optimal structure, it is necessary to accurately evaluate the surface properties of the steel. One method for evaluating the surface properties of steel is the atomic force microscope.

[0006] Japanese Patent Laid-Open Publication No. 6-300315 discloses a probe for a scanning probe microscope. This probe for a scanning probe microscope is made of a cantilever with a sharpened metal or semiconductor tip that is coated with an insulator. The publication also describes that a 200 nm-thick Au thin film is evaporated onto the surface of the cantilever that does not have a tip.

[0007] Japanese Patent Laid-Open Publication No. 6-96714 discloses a surface processing device, which is characterized in that in a scanning probe microscope, in order to supply electric charge to an insulating probe, the probe has a multi-layer structure with a conductor layer on the surface, and voltage application means is provided for applying a voltage between the tip of the probe and the sample surface, thereby processing the sample surface.

[0008] Japanese Patent Laid-Open Publication No. 2006-71448 discloses a probe for a near-field microscope. This probe for a near-field microscope is used in a near-field microscope in which a probe is inserted into an evanescent field generated on a sample surface, and the evanescent field is scattered at the tip of the probe to detect scattered light, and at least a part or all of the probe caused by the interaction of the evanescent field is coated with a metal having a particle size with a radius of curvature of 10 nm to 50 nm so that the metal does not adhere to each other.

[0009] JP 2021-25995 A discloses a cantilever for use in a scanning probe microscope. In a cross-sectional view, the cantilever has a vertex portion that is a portion that can be brought close to a sample and is covered with a metal film, a ridge line that is connected to the vertex portion and is covered with a metal film, and an upper corner portion that is connected to the ridge line. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2013-227674 A [Patent Document 2] Japanese Patent Application Publication No. 6-300315 [Patent Document 3] Japanese Patent Application Publication No. 6-96714 [Patent Document 4] JP 2006-71448 A [Patent Document 5] Patent Publication No. 2021-25995 Summary of the Invention [Problem to be solved by the invention]

[0011] An atomic force microscope (AFM) is a type of scanning probe microscope (SPM) that obtains images by detecting the force acting between atoms on a sample surface and a probe. An AFM probe is also called a cantilever, and has a needle-shaped or spherical tip formed at the tip of a cantilever. Although the term "probe" is sometimes used to refer to only the tip portion, in this specification, the whole, including the lever-shaped portion (hereinafter referred to as the "lever portion") and the tip portion (hereinafter referred to as the "tip portion"), is referred to as the "probe."

[0012] This probe is attached to the AFM's XY plane direction drive device. The lever of the probe is equipped with a laser receiving surface, and the Z direction displacement is measured by an electrical signal corresponding to the reflected laser light. When the tip approaches the sample surface, it is attracted to the sample surface by atomic force. This makes it possible to observe the surface condition (unevenness) of the sample.

[0013] When the probe is slid horizontally with the tip in contact with the sample, the lever twists. By measuring the amount of this twist, the frictional force between the tip and the surface of the sample can be measured (contact mode measurement). In addition, by measuring the amount of deflection of the lever when the tip is brought into vertical contact with the sample, the adhesive force between the tip and the surface of the sample can be measured (force mode measurement). The amount of deflection is recorded as a piezoelectric displacement, and the adhesive force of the sample at the contact point can be calculated from the obtained force-distance curve.

[0014] Most of the friction, wear, and seizure that are problems with sliding parts made of steel materials occur at the interface between metals. Therefore, in order to evaluate the surface characteristics of steel materials for sliding parts, it is considered desirable to measure friction and adhesion forces using a probe with a metal tip. On the other hand, the materials of AFM probes that are generally available are limited, and there are almost no metal ones. Metal colloidal probes manufactured by agglomerating metal particles exist, but the types of metals that can be manufactured by agglomeration are limited. In addition, it is difficult to make a metal colloidal probe have a smooth surface, and there are cases where the measurement values ​​vary widely.

[0015] An object of the present invention is to provide a probe for an atomic force microscope capable of evaluating material surface characteristics, including friction force measurement and adhesion force measurement, in an environment approximating the actual system in which steel is used. Another object of the present invention is to provide a method for evaluating steel material, capable of evaluating material surface characteristics, including friction force measurement and adhesion force measurement, in an environment approximating the actual system in which steel is used. [Means for solving the problem]

[0016] The atomic force microscope probe according to one embodiment of the present invention has a curvature radius of 0.5 μm or more at a portion that comes into contact with a sample, and has a metal vapor deposition film with a thickness of 20 to 100 nm on the surface.

[0017] An atomic force microscope probe according to one embodiment of the present invention may have a plate-shaped lever portion and a tip portion provided on the lever portion.

[0018] A method for evaluating steel material according to one embodiment of the present invention is a method for evaluating a sample made of steel material using an atomic force microscope equipped with the above-mentioned atomic force microscope probe, and comprises at least one of the steps of measuring the friction force between the tip and the surface of the sample by moving the atomic force microscope probe horizontally with the tip in contact with the sample, and measuring the adhesion force between the tip and the surface of the sample by moving the atomic force microscope probe vertically from a state in which the tip is in contact with the sample. Effect of the Invention

[0019] According to the present invention, it is possible to evaluate the surface characteristics of materials, including friction force and adhesion force, in an environment approximating the actual system in which steel materials for sliding parts are used. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a probe for an atomic force microscope according to one embodiment of the present invention. [Figure 2A] FIG. 2A is a cross-sectional view that illustrates a schematic configuration of a modified example of the probe of FIG. [Figure 2B] FIG. 2B is a cross-sectional view that illustrates a schematic configuration of another modified example of the probe of FIG. [Figure 2C] FIG. 2C is a cross-sectional view that illustrates a schematic configuration of still another modified example of the probe of FIG. [Figure 3A] FIG. 3A is an optical micrograph of the probe before deposition. [Figure 3B] FIG. 3B is an optical microscope photograph of the probe before deposition. [Figure 4A] FIG. 4A is an optical microscope image of the probe after deposition. [Figure 4B] FIG. 4B is an optical microscope image of the probe after deposition. [Diagram 5] Figure 5 shows an SEM image of a ready-made Au colloidal probe. [Figure 6] Figure 6 is an SEM image of a probe on which a metal deposition film was formed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The inventors have found that a metal film deposited on the surface of a probe having a tip of a shape other than a needle is suitable as a probe for evaluating the surface characteristics of steel materials for sliding parts by AFM. With this method, the film thickness can be controlled by controlling the deposition conditions, and a wide variety of metal deposition films can be formed relatively inexpensively.

[0022] The above-mentioned Patent Documents 2 to 5 also disclose probes for scanning probe microscopes in which a metal vapor deposition film is formed on the surface of a base material. However, these probes are not intended to measure frictional force or adhesive force, and are not intended to have their tips slide over the sample surface.

[0023] For example, the probe disclosed in JP-A-6-300315 (Patent Document 2) is intended for microfabrication of samples. Specifically, the purpose is to apply a pulse voltage between the probe and the sample to form pits or mounds with a diameter of several nm on the surface of the sample. This probe has a sharpened tip. The publication describes that the back surface of the probe is coated with a thin film of Au, which is said to be "so that the deflection of the cantilever 2 can be known by the optical lever method or the like."

[0024] The probe disclosed in JP-A-6-96714 (Patent Document 3) is also intended for use in surface processing. This publication describes coating the probe with a conductive material such as Au or Ga in order to supply an electric charge to the tip of the probe.

[0025] The probe disclosed in JP 2006-71448 A (Patent Document 4) is a probe used in a scanning near-field optical microscope. The publication describes coating the surface of the probe with silver particles in order to excite surface plasmons. The publication describes a probe-attached cantilever having a quadrangular pyramid-shaped probe with a tip radius of about 10 nm and a height of 20 μm at the tip of the cantilever, coated with silver particles with a radius of curvature of 10 nm to 50 nm.

[0026] The probe disclosed in JP 2021-25995 A (Patent Document 5) is also a probe used in a scanning near-field optical microscope, and it is described that the surface of the probe is coated with a metal to excite surface plasmons.

[0027] When it is assumed that the tip will slide over the sample surface, it is preferable that the tip shape is other than needle-like. Specifically, it is preferable that the radius of curvature of the tip where it comes into contact with the sample surface is 0.5 μm or more. If the radius of curvature of the tip where it comes into contact with the sample surface is too small, the deposited film may peel off early due to sliding, making it impossible to perform stable measurements.

[0028] In order to perform stable measurements, it is preferable to adjust the thickness of the deposited film to an appropriate value. If the deposited film is too thick or too thin, the deposited film may peel off early.

[0029] The present invention has been completed based on the above findings. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and their description will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0030] [Atomic force microscope probes] 1 is a cross-sectional view showing a schematic configuration of an atomic force microscope probe 1 (hereinafter simply referred to as "probe 1") according to one embodiment of the present invention. Probe 1 comprises a plate-shaped lever portion 10 and a tip portion 20 provided on lever portion 10. A metal vapor deposition film 21 is formed on the surface of tip portion 20.

[0031] The probe 1 is a probe for an atomic force microscope (AFM). The probe 1 is attached to an XY plane direction driving device of the AFM. The AFM is preferably capable of at least one of measuring the frictional force between the tip 20 and the surface of the sample by moving the probe 1 in the horizontal direction with the tip 20 in contact with the sample (contact mode measurement) and measuring the adhesive force between the tip 20 and the surface of the sample by moving the probe 1 in the vertical direction from the state where the tip 20 is in contact with the sample (force mode measurement).

[0032] In FIG. 1, the tip 20 is shown as being spherical, but the shape of the tip 20 may be any shape other than needle-like. FIGS. 2A to 2C are cross-sectional views that show the configurations of probes 1A to 1C, which are modifications of the probe 1. The tip 20 may be shaped such that the portion in contact with the sample is curved as shown in FIG. 2A, or may be shaped such that the portion in contact with the sample is flat (e.g., block-shaped) as shown in FIG. 2B. The tip 20 may also be shaped like a cone (e.g., pyramid-shaped) as shown in FIG. 2C, so long as the portion in contact with the sample has a predetermined radius of curvature R.

[0033] More specifically, the tip 20 has a shape in which the radius of curvature R of the portion in contact with the sample is 0.5 μm or more. If the radius of curvature R of the portion in contact with the sample is too small, the deposition film 21 may peel off early due to sliding with the sample, making it impossible to perform a stable measurement. The radius of curvature R is preferably 0.8 μm or more, and more preferably 1.0 μm or more. Note that, as shown in FIG. 2B, when the portion of the tip 20 in contact with the sample is flat, the radius of curvature R of the portion in contact with the sample can be considered to be infinite.

[0034] The tip 20 preferably has a width W of 0.5 to 30.0 μm. When the surface of the tip 20 in contact with the sample is a curved surface, the width W is the maximum dimension in the width direction (direction parallel to the measurement plane) of a curved surface (surface having the same radius of curvature) continuous with the curved surface. When the tip 20 is spherical, the width W is equal to the diameter of the tip 20. When the surface of the tip 20 in contact with the sample is flat, the width W is the maximum dimension in the width direction (direction parallel to the measurement plane) of the flat surface.

[0035] If the width W is too small, the deposited film may peel off early even if the radius of curvature R is large. Also, if the width W is increased, the area that interacts with the sample increases, making it possible to evaluate the surface-averaged characteristics of the sample. On the other hand, this also means that the resolution decreases. Furthermore, if the width W is increased, the vibration of the lever portion 10 tends to increase, resulting in greater variation in the measurement. The lower limit of the width W is more preferably 1.0 μm, and even more preferably 2.0 μm. The upper limit of the width W is more preferably 25.0 μm, and even more preferably 20.0 μm.

[0036] In calculating the above-mentioned radius of curvature R and width W, the thickness of the deposited film 21 is not included.

[0037] It is particularly preferable that the tip portion 20 is spherical. As described above, when the tip portion 20 is spherical, the width W coincides with the diameter of the tip portion 20. Since the radius of curvature R of the tip portion is 0.5 μm or more, when the tip portion 20 is spherical, the preferred range of the width W (i.e., the diameter of the tip portion) is 1.0 to 30.0 μm.

[0038] As described above, a metal vapor-deposited film 21 is formed on the surface of the tip portion 20. The thickness of the vapor-deposited film 21 is 20 to 100 nm. If the vapor-deposited film 21 is too thick or too thin, the vapor-deposited film may peel off early. The lower limit of the thickness of the vapor-deposited film is preferably 30 nm, and more preferably 40 nm. The upper limit of the thickness of the vapor-deposited film is preferably 95 nm.

[0039] The metal constituting the vapor-deposited film 21 is not particularly limited as long as it can be formed by vapor deposition. Examples of the metal constituting the vapor-deposited film include Au, Al, and Cu. The vapor deposition method is also not particularly limited, but physical vapor deposition such as vacuum deposition, ion plating, and sputtering can be used, and vacuum deposition is particularly preferred.

[0040] The deposited film 21 may be formed at least on the portion that comes into contact with the sample. However, from the viewpoint of ease of manufacture, it is preferable that the deposited film 21 is formed on the entire tip portion 20.

[0041] A vapor-deposited film may or may not be formed on the surface of the lever portion 10. When a vapor-deposited film is formed on the surface of the lever portion 10, the vapor-deposited film formed on the lever portion 10 and the vapor-deposited film formed on the tip portion 20 may be films of the same metal or films of different metals. However, from the viewpoint of ease of manufacture, it is preferable that a vapor-deposited film of the same metal is formed on the entire lever portion 10 and the tip portion 20. Note that by forming a vapor-deposited film on the lever portion 10, the rigidity of the lever portion 10 is increased, and vibration is reduced, which may reduce variation in measurement.

[0042] The material of the portions (base) other than the evaporated film of the lever portion 10 and the tip portion 20 is not particularly limited. In AFM probes, the lever portion and the tip portion are generally manufactured by processing a silicon or silicon nitride substrate. Furthermore, when the tip portion is spherical, it is manufactured by adhering a spherical piece of SiO2 or borosilicate glass (BSG) to the lever portion. The probe 1 according to this embodiment can be manufactured by forming a evaporated metal film on the surface of a probe manufactured by such a general method.

[0043] [Steel evaluation method] A method for evaluating steel according to one embodiment of the present invention is a method for evaluating a sample made of steel using an AFM equipped with the above-mentioned probe 1, and includes at least one of the steps of measuring the frictional force between tip 20 and the surface of the sample by moving probe 1 horizontally while keeping tip 20 in contact with the sample (contact mode measurement), and measuring the adhesive force between tip 20 and the surface of the sample by moving probe 1 vertically while keeping tip 20 in contact with the sample (force mode measurement).

[0044] This measurement (a process of performing at least one of contact mode measurement and force mode measurement) is preferably performed in a low-oxygen atmosphere with an oxygen concentration lower than that of the air atmosphere. In the steel evaluation method according to this embodiment, a probe with a metal vapor-deposited on its surface is used. If the measurement is performed in an atmosphere containing oxygen, corrosion (oxidation) of the metal vapor-deposited on the probe surface may progress during the measurement. By performing the measurement in a low-oxygen atmosphere, the progress of oxidation can be suppressed, the measurement accuracy is improved, and the life of the probe can be extended.

[0045] Measurement in a low-oxygen atmosphere can be achieved, for example, by placing the AFM in a glove box and replacing the atmosphere in the glove box with an inert gas such as argon. The oxygen concentration in the measurement atmosphere is preferably 100 ppm by volume or less, and more preferably 50 ppm by volume or less.

[0046] The above describes the probe 1 according to one embodiment of the present invention, and the method for evaluating steel materials using the probe 1. The probe 1 according to this embodiment has a metal vapor deposition film 21 formed on the surface of the tip 20. This makes it possible to evaluate friction and adhesion that occur at the interface between metals for metal samples. In addition, since a wide variety of metals can be formed, it is possible to perform measurements that are close to actual sliding conditions. In other words, it becomes possible to evaluate material surface characteristics, including friction force measurements and adhesion force measurements, in an environment that is close to the actual system in which steel materials are used. EXAMPLES

[0047] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0048] A Cu deposition film was formed by vacuum deposition on a commercially available AFM probe (CP-NCH-BSG manufactured by s-Qube. BSG colloid was attached to the end of the lever. The diameter of the BSG is about 20 μm.) A vacuum deposition device manufactured by ULVAC was used for the vacuum deposition, and the vacuum degree was several × 10 -7 The experiment was carried out under conditions of 1000 Torr.

[0049] Figures 3A and 3B show optical microscope photographs of the probe before deposition, and Figures 4A and 4B show optical microscope photographs of the probe after deposition. For the 20 μm diameter probe, it was confirmed evenly that the deposition film was formed on the probe. It was also confirmed that deposition films could be formed similarly with Au and Al.

[0050] Similarly, an Al deposition film was formed by vacuum deposition on an AFM probe (CP-FM-SiO manufactured by s-Qube, with SiO2 colloid attached to the end of the lever) with a tip diameter of 2.0 μm. Figure 5 is an SEM image of a ready-made Au colloidal probe (CP-FM-Au manufactured by s-Qube, diameter 1.5-3.0 μm). Figure 6 is an SEM image of a probe on which a metal deposition film was formed by the above-mentioned vacuum deposition. The magnifications of both images were 40,000 times. As shown in Figures 5 and 6, the probe on which the metal deposition film was formed (Figure 6) had a smoother surface than the ready-made Au colloidal probe (Figure 5).

[0051] Next, a number of probes were manufactured by changing the deposition conditions, etc., and the durability of the probes and the degree of variation in the measured values ​​were evaluated.

[0052] In Table 1 below, the probe with test number 1 is a ready-made Au colloidal probe (CP-FM-Au manufactured by s-Qube, diameter 1.5 to 3.0 μm). The probes with test numbers 2 to 8 are probes (CP-FM-SiO manufactured by s-Qube) with a SiO2 colloid of diameter 2.0 μm (curvature radius 1.0 μm) on which an Au, Al or Cu vapor deposition film is formed. The probe with test number 9 is a probe with a needle-shaped tip with a curvature radius of 15 nm or less on which an Au vapor deposition film is formed. The thickness of the vapor deposition film was adjusted by changing the vapor deposition time. The thickness of the vapor deposition film was estimated from the film thickness when the film was formed on a flat substrate under the same conditions.

[0053] The durability (lifespan) of the probe was evaluated by repeatedly measuring the friction force with an AFM and counting the number of measurements (i.e., the number of two-dimensional images that could be measured normally) until the friction force measurement value fluctuated (the acquired image became distorted) or the measurement became impossible. The AFM used was a Cypher ES manufactured by Oxford Instruments. The measurement object was pure iron, and the friction test was performed with a measurement range of 10 μm × 10 μm (measurement points: 256 points × 256 points) and a load of approximately 3000 nN. The number of measured images was limited to 30, with 20 or more being considered as passing and less than 20 being considered as failing. In addition, a point analysis of the apex of the probe was performed by SEM-EDS analysis immediately after the measured friction force value fluctuated, and it was confirmed that the deposition film had peeled off on the probe.

[0054] The measurement error (variation in the measured values) was evaluated by measuring the friction force and the adhesion force with an AFM. The friction force measurement was performed under the same conditions as above. The adhesion force measurement was performed with a load of approximately 50 nN. Within the measurement range, the larger of (maximum friction force obtained - minimum friction force obtained) / average friction force and (maximum adhesion force obtained - minimum adhesion force obtained) / average adhesion force was taken as the measurement error (variation in the measured values). A measurement error of 0.130 or less was considered to be acceptable.

[0055] As a general evaluation, a product that passed both the life evaluation and the measurement error evaluation was deemed to have passed. The measurement results in air are shown in Table 1.

[0056] [Table 1]

[0057] The probes of test numbers 2 to 6 and 10 had smaller variations in the measured values ​​than the probe of test number 1. The probes of test numbers 2 to 6 and 10 also had excellent durability.

[0058] The probes of test numbers 7 and 11 showed a large variation in the measured values ​​and were also poor in durability. This is believed to be because the deposited film was too thick. The probe of test number 8 showed poor durability. This is believed to be because the deposited film was too thin. The probe of test number 9 showed poor durability. This is believed to be because the tip was needle-shaped (the radius of curvature of the part in contact with the sample was too small).

[0059] Next, the AFM was placed in a glove box, and the atmosphere in the glove box was replaced with argon gas to control the oxygen concentration to 50 ppm by volume or less, and similar measurements were performed in this environment. In the measurements in the low-oxygen atmosphere, a product with 25 or more measured images was rated as passing for the evaluation of life, and a product with a measurement error of 0.120 or less was rated as passing for the evaluation of measurement error. The results are shown in Table 2.

[0060] [Table 2]

[0061] A comparison of Tables 1 and 2 shows that performing measurements in a low-oxygen atmosphere improves measurement accuracy and extends the life of the probe.

[0062] Although the embodiment of the present invention has been described above, the above-mentioned embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-mentioned embodiment, and the above-mentioned embodiment can be appropriately modified and carried out within the scope of the invention.

Claims

1. The radius of curvature of the portion in contact with the sample is 0.5 μm or more, A probe for an atomic force microscope, having a metal vapor deposition film with a thickness of 20 to 100 nm on its surface.

2. 2. The atomic force microscope probe according to claim 1, A plate-shaped lever portion, and a tip portion provided on the lever portion.

3. 3. The atomic force microscope probe according to claim 2, The probe for an atomic force microscope, wherein the tip portion has a spherical shape.

4. 4. The atomic force microscope probe according to claim 3, The probe for an atomic force microscope, wherein the tip has a diameter of 1.0 to 30.0 μm.

5. 3. The atomic force microscope probe according to claim 2, The material of the substrate of the tip is SiO ２ A probe for atomic force microscopes.

6. 3. The atomic force microscope probe according to claim 2, A probe for an atomic force microscope, wherein the tip portion that comes into contact with the sample is a curved surface, and the maximum dimension W in the width direction of a curved surface continuous with the curved surface is 0.5 to 30 μm.

7. 3. The atomic force microscope probe according to claim 2, A probe for an atomic force microscope, wherein the portion of the tip that comes into contact with the sample is flat, and the maximum dimension W of the flat surface in the width direction is 0.5 to 30 μm.

8. A method for evaluating a sample made of a steel material by using an atomic force microscope equipped with the atomic force microscope probe according to any one of claims 2 to 7, comprising the steps of: A method for evaluating steel materials, comprising at least one of the steps of measuring the frictional force between the tip and the surface of the sample by moving an atomic force microscope probe in a horizontal direction while keeping the tip in contact with the sample, and measuring the adhesive force between the tip and the surface of the sample by moving the atomic force microscope probe in a vertical direction from a state where the tip is in contact with the sample.

9. The method for evaluating a steel material according to claim 8, A method for evaluating steel products, comprising the steps of: measuring the frictional force between the tip and the surface of the sample by moving the atomic force microscope probe in a horizontal direction while keeping the tip in contact with the sample; and measuring the adhesive force between the tip and the surface of the sample by moving the atomic force microscope probe in a vertical direction from a state where the tip is in contact with the sample, in a low-oxygen atmosphere having an oxygen concentration lower than that of the air atmosphere.

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