CN111190031B - Method for correcting friction performance of probe abrasion of atomic force microscope - Google Patents
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Abstract
The invention discloses a friction performance correction method for probe abrasion of an atomic force microscope, which comprises the steps of measuring the adhesion force under the sliding distance by utilizing an AFM (atomic force microscope), measuring the probe tip radius under the sliding distance of a small group by utilizing an SEM (scanning electron microscope), thus obtaining the relation points between the adhesion force and the probe tip radius, and obtaining a relation fitting straight line, a fitting constant and a relation between the adhesion force and the probe tip radius through the relation points; obtaining the corrected tip radius under the sliding distance according to a fitting curve between the sliding distance and the probe tip radius; and finally, correcting the friction force and the adhesion force according to the fitting constant and the corrected radius of the needle point, eliminating or reducing the measurement error of the atomic force microscope on the friction performance of the nano material caused by the abrasion of the needle point, improving the measurement precision and improving the accuracy of the evaluation of the friction performance of the nano material.
Description
Technical Field
The invention belongs to the field of nano science and nano friction interdiscipline, and particularly relates to a friction performance correction method for probe abrasion of an atomic force microscope.
Background
Nanotechnology is known as the science of the 21 st century as one of the most rapidly developing, widely studied, and most invested scientific technologies at present, and is considered as two important antecedents of future science and technology together with bioengineering. From the development of nanotechnology, laser interference nanolithography, nanofabrication, nanometering, nanofabrication, etc. all have considerable status and effect. An Atomic Force Microscope (AFM) is an important tool for researching nanotechnology. The micro-cantilever senses and amplifies the acting force between the probe on the cantilever and the atoms of the material to be detected, so that the purpose of detection is achieved, the micro-cantilever has atomic resolution, the transverse resolution can reach 0.1nm, and the longitudinal resolution can reach 0.01nm.
In recent years, with the development of micro-nano technology, especially the development of atomic force microscope technology, the mechanical property research of nano-scale materials is greatly facilitated. In foreign countries, bhushan B. Et al, ohio State university, studied tribological properties of materials at the nanoscale using AFM (nanotriology and nanomechanics [ J ]. Wear,2005,259 (7-12): 1507-1531); in China, the research on the frictional wear performance of systematic nano materials is carried out by using AFM (nano tribology research progress [ J ], mechanical engineering journal, 2007,43 (10): 1-8.) by thermo Shi cast professor of the national emphasis laboratory of tribology of the university of Qinghua, etc.
AFM has wide application in nano-tribology and nano-mechanics research, researchers can obtain voltage values (Surface science reports,2005,59 (1): 1-152.) related to mechanical properties (such as adhesion and friction) of the Surface of a material to be measured in reaction through an AFM force curve and a friction force module, but voltage signals measured by AFM cannot be directly converted into force by an instrument, and each probe needs to calibrate its own physical parameters before being converted (Langmuir, 2006,22 (5): 2340-2350.). In the microscopic field, the size effect and the surface effect between materials have great effect on the nano friction performance, namely the nano friction performance is related to the contact area, particularly the contact area between a probe and the surface of a measured material in the AFM friction test research. However, AFM probe tip wear is inevitable in testing for contact scanning imaging modalities.
Some studies have been conducted by researchers regarding the effect of AFM probe radius on tribological performance, yoon et al, using several borosilicate glass spheres of different radii attached to the AFM probe tip to measure the frictional force (Wear, 2005,259 (7-12): 1424-1431.); bhushan et al used several probes of different radii (Acta Materialia,1998,46 (11): 3793-3804.) to study the effect of tip radius on tribological performance; fang et al measured friction using a pre-ground AFM probe to avoid the effect of sharp changes in radius of the tip at the beginning of wear on the accuracy of the friction performance measurements (Nanotechnology, 2017,28 (24): 2457703.); patent document with application number of CN201710324292.8 and name of a method for measuring ultimate shear stress of a nano material discloses a method for measuring the ultimate shear stress of a material by measuring the surface friction force and the adhesive force of the measured material by applying normal load by using AFM, and finds that the friction force obtained by comparing probe tips with different abrasion degrees has certain difference. However, for the same probe, the above experimental study does not give a quantitative description and rule of the change of the radius of the tip with the sliding distance, and the key factor of the change of the radius of the tip cannot be processed to reduce the error of the measurement value caused by the abrasion of the tip in the experiment, which is important for the accuracy of the nano-friction performance result.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a friction performance correction method for probe abrasion of an atomic force microscope, which describes the friction performance of a measured material through the adhesive force and the friction force between a probe tip and a measured sample under each sliding distance, and corrects the adhesive force and the friction force according to the relationship between the radius change of the probe tip and the adhesive force under each sliding distance so as to solve the measurement error caused by the probe tip abrasion and improve the measurement accuracy.
The invention solves the technical problems through the following technical scheme: a friction performance correction method for abrasion of an atomic force microscope probe comprises the following steps:
step 1: applying normal load by using an atomic force microscope to enable the probe tip to slide on the surface of the measured sample, and measuring an AFM (atomic force microscope) measured value of the friction force and an AFM measured value of the adhesion force between the probe tip and the surface of the measured sample at each sliding distance; the sliding distance refers to the total length of the sliding line of the probe tip on the surface of the measured sample in each AFM scanning image;
step 2: selecting a plurality of sliding distances from all the sliding distances in the step 1, and measuring SEM (Scanning Electron microscope) measurement values of the radius of the needle tip at the plurality of sliding distances by using a Scanning Electron Microscope (SEM);
and step 3: obtaining relation points between the AFM measured values of the adhesion force and the SEM measured values of the radius of the needle tip under a plurality of sliding distances according to the relation between the sliding distance and the AFM measured value of the adhesion force in the step 1 and the relation between the sliding distance and the SEM measured value of the radius of the needle tip in the step 2, and performing linear fitting on the relation points to obtain a relation fitting straight line;
and 4, step 4: obtaining a fitting constant according to the relation fitting straight line in the step 3, wherein the fitting constant is the slope of the relation fitting straight line; obtaining a relational expression between the AFM measured value of the adhesion and the radius of the needle point according to the fitting constant;
and 5: obtaining the radius of the needle tip at each sliding distance according to the relation between the AFM measured value of the adhesive force and the radius of the needle tip in the step 4, wherein the radius of the needle tip is the radius of the needle tip obtained by using an atomic force microscope;
step 6: fitting all the sliding distances and the needle point radiuses under all the sliding distances to obtain a fitting curve between the sliding distances and the needle point radiuses, and obtaining the corrected needle point radiuses under the sliding distances according to the fitting curve;
and 7: and correcting the friction force and the adhesive force according to the fitting constant and the corrected radius of the needle tip under the sliding distance so as to eliminate or reduce the measurement error caused by the abrasion of the needle tip.
Because the radius of the probe tip is directly measured by using the SEM for at least more than 30min each time, the measurement efficiency is low, the radius of the probe tip cannot be directly obtained by using the conventional AFM, and the measurement of the adhesive force at each sliding distance only needs a few seconds, the frictional property correction method of the invention measures the adhesive force at the sliding distance by using the AFM, and then measures the radii of the probe tips at a few groups of sliding distances by using the SEM, thereby obtaining the relation points between the adhesive force and the radius of the probe tip, and obtaining the relation fitting straight line, the fitting constant and the relation between the adhesive force and the radius of the probe tip through the relation points; obtaining the corrected tip radius at any sliding distance according to a fitting curve between the sliding distance and the probe tip radius; and finally, correcting the friction force and the adhesion force according to the fitting constant and the corrected radius of the needle point, eliminating or reducing the measurement error of the atomic force microscope on the friction performance of the nano material caused by the abrasion of the needle point, improving the measurement precision and improving the accuracy of the evaluation of the friction performance of the nano material.
Further, in the step 1, the probe tip slides on a designated area of the surface of the measured sample, wherein the designated area refers to any area of the surface of the measured sample.
Further, in the step 1, the sliding mode of the probe tip on the surface of the measured sample is as follows: the probe tip slides from left to right or from right to left on the surface of the measured sample, then slides from right to left or slides from left to right after parallel movement, and so on until completing the sliding distance once, and the length of each sliding line is equal to the sliding distance divided by 512.
Further, in step 1, each sliding distance is equal.
Further, in the step 1, a specific measurement method of the AFM measurement value of the friction force is as follows: and scanning the friction electric signals of all points in the designated area on the surface of the measured sample by using a transverse force module of the AFM, and converting the friction electric signals into AFM measured values of friction force by using the friction force calibration coefficient of the probe.
Further, in the step 1, a specific measurement method of the AFM measurement value of the adhesion force is as follows: dotting the probe tip in a designated area of the surface of the measured sample, measuring the adhesive force of at least 1024 points in the designated area by using an AFM force diagram module, and obtaining the average value of the adhesive force of the designated area through Gaussian statistics, wherein the average value of the adhesive force is the AFM measured value of the adhesive force of the probe tip and the surface of the measured sample at the sliding distance.
Further, in step 2, the number of the sliding distances spaced among the plurality of selected sliding distances is equal.
Further, in step 4 or 5, the relationship between the AFM measurement of the adhesion force and the tip radius is:
F AFM ＝k ad R AFM
wherein, F AFM For AFM measurement of adhesion, k ad As fitting constant, R AFM Is the tip radius obtained using an atomic force microscope.
Further, in the step 6, a numerical integral is obtained for the atomic wear model by using Matlab and adopting a dragon lattice-kutta method to obtain a relational expression between the radius of the needle tip and the sliding distance, and then the sliding distance and the radius of the needle tip are fitted by using Matlab and adopting a least square method to obtain a fitting curve;
the atomic wear model is:
wherein R is the radius of the needle tip, d is the sliding distance, theta is the opening angle of the needle tip, and f a For probe phonon frequency, b is the lattice constant, v 0 At nominal slip speed, E eff For effective activation energy, V an To activate the volume effectively, F n Is a normal load, k ad As fitting constant, k B Boltzmann constant, T is test ambient temperature.
Further, in step 7, the correction formulas of the friction force and the adhesion force are respectively as follows:
F f ＝μ(F n +k ad R d )
F ad ＝k ad R d
wherein, F f For the corrected friction, μ is the coefficient of friction, F n For normal loading, F ad For corrected adhesion, k ad As fitting constant, R d Is the corrected tip radius.
Advantageous effects
Compared with the prior art, the method for correcting the friction performance of the probe abrasion of the atomic force microscope provided by the invention has the advantages that the AFM is used for measuring the adhesion force under the sliding distance, the SEM is used for measuring the probe tip radius under a few groups of sliding distances, so that the relation points between the adhesion force and the probe tip radius are obtained, and the relation fitting straight line, the fitting constant and the relation between the adhesion force and the probe tip radius are obtained through the relation points; obtaining the corrected tip radius at any sliding distance according to a fitting curve between the sliding distance and the probe tip radius; and finally, correcting the friction force and the adhesion force according to the fitting constant and the corrected radius of the needle point, eliminating or reducing the measurement error of the atomic force microscope on the friction performance of the nano material caused by the abrasion of the needle point, improving the measurement precision and improving the accuracy of the evaluation of the friction performance of the nano material. The method provides a new method for atomic force microscope needle point abrasion evaluation and nano material friction performance correction, and the method is simple to operate and easy to implement.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only one embodiment of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a schematic diagram illustrating a probe tip sliding manner according to an embodiment of the present invention;
FIG. 2 is a graph of sliding distance versus adhesion for an embodiment of the present invention;
FIG. 3 is a schematic diagram of a relationship-fitting straight line in an embodiment of the present invention;
FIG. 4 is a schematic view of a fitted curve in an embodiment of the present invention;
FIG. 5 is an AFM topography of molybdenum disulfide in an embodiment of the present invention;
FIG. 6 is a Raman spectrum of molybdenum disulfide according to an example of the present invention;
FIG. 7 is an SEM image of a tip at 10 different stages in an embodiment of the present invention, the 10 different stages being SEM images of the tip at 10 sliding distances selected from 2000 sliding distances, FIG. 7 (a) is an SEM image of the tip when the tip of the probe is unworn, FIG. 7 (b) is an SEM image of the tip at 1 st sliding distance selected from 2000 sliding distances, FIG. 7 (c) is an SEM image of the tip at 2 nd sliding distance selected from 2000 sliding distances, FIG. 7 (d) is an SEM image of the tip at 3 rd sliding distance selected from 2000 sliding distances, FIG. 7 (e) is an SEM image of the tip at 4 th sliding distance selected from 2000 sliding distances, FIG. 7 (f) is an SEM image of the tip at 5 th sliding distance selected from 2000 sliding distances, FIG. 7 (g) is an SEM image of the tip at 6 th sliding distance selected from 2000 sliding distances, FIG. 7 (h) is an SEM image of the tip at 7 th sliding distance selected from 2000 sliding distances, FIG. 7 (i) is an SEM image of the tip at 2000 sliding distances selected from 2000 sliding distances, and FIG. 7 (j) is an SEM image of the tip at 2000 sliding distances selected from 2000 sliding distances;
FIG. 8 is a graph comparing a corrected friction force to a test friction force in an example of the invention;
FIG. 9 is a graph comparing corrected adhesion to test adhesion for an example of the present invention;
wherein 1-designated area, 2-sample tested, 3-sliding direction.
Detailed Description
The technical solutions in the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a method for correcting the friction performance of the abrasion of an atomic force microscope probe, which comprises the following steps:
1. and applying normal load by using an atomic force microscope to enable the probe tip to slide on the surface of the measured sample, and measuring the AFM measurement value of the friction force and the AFM measurement value of the adhesion force between the probe tip and the surface of the measured sample at each sliding distance.
The probe tip slides in a designated area of the surface of the measured sample, and each sliding distance is equal, the sliding distance refers to the total length of a slide line of the probe tip on the surface of the measured sample in each AFM scanning picture, the designated area refers to any area of the surface of the measured sample, in the embodiment, the area of the surface of the measured sample is not more than 10 microns multiplied by 10 microns, and the area of the designated area is not more than 1 micron multiplied by 1 micron. As shown in fig. 1, a designated area 1 is arbitrarily selected on the surface of a measured sample 2, a probe tip slides on the designated area 1, the probe tip slides from left to right (or slides from right to left) on the designated area 1, the probe tip slides from right to left (or slides from left to right) after moving in parallel, and so on until completing a sliding distance, the sliding distance is equal to the total length of the slide lines in the designated area 1, the distance between two adjacent slide lines is equal, and the length of each slide line is equal. For each 256 × 2 slide line, the AFM scan of the designated area and one AFM scan is obtained, i.e., the slide distance is equal to 256 × 2 × the length of each slide line. In this embodiment, each sliding distance is 0.13mm.
Every time the probe tip finishes sliding distance on the surface of the measured sample, scanning friction electric signals of each point in a specified area of the surface of the measured sample by using a transverse force module of an AFM (atomic force microscope), and converting the friction electric signals into AFM (atomic force microscope) measured values of friction force (namely the friction force measured by the AFM) by using a friction force calibration coefficient of the probe; and dotting the probe tip in a designated area of the surface of the measured sample, measuring the adhesive force of at least 1024 points in the designated area by using an AFM force diagram module, and obtaining the average value of the adhesive force of the designated area through Gaussian statistics, wherein the average value of the adhesive force is the AFM measured value (namely the adhesive force obtained by AFM measurement) of the adhesive force of the probe tip and the surface of the measured sample under the sliding distance, and is shown in figure 2. The number of AFM scans, the number of sliding distances, the number of AFM measurements of friction and the number of AFM measurements of adhesion were all equal.
2. Selecting n sliding distances from all the sliding distances in the step 1, and measuring SEM measured values of the radius of the needle tip at the n sliding distances by using a scanning electron microscope.
Since the conventional AFM cannot directly obtain the radius of the probe tip, it takes at least 30min or more to directly measure the radius of the probe tip by using the SEM each time, and thus the measurement efficiency is low, in the present application, a few SEM measurements (the number is relative to the number of all the sliding distances) of the radius of the probe tip at the sliding distance (that is, the radius of the probe tip obtained by SEM measurement) are measured by using the SEM, and an AFM measurement (only a few seconds) of the adhesion force at each sliding distance is measured by using the AFM, so that a few relationship points between the SEM measurements of the radius of the probe tip at the sliding distance and the AFM measurement of the adhesion force are obtained. SEM measurements of probe tip radius at sliding distances are performed using SEM in order to obtain a fitting constant between the probe tip radius and the AFM measurement of adhesion, and in order to improve the measurement efficiency, SEM measurements of probe tip radius at a plurality of sliding distances are selected from all sliding distances and measured, instead of SEM measurements of probe tip radius at each sliding distance. For example, the number of sliding distances is N, the number of selected sliding distances is N, and N < N (N =2000, N =9, N is much smaller than N in this embodiment). In order to obtain a more accurate fitting constant, the selected N sliding distances are dispersed as much as possible, the number of the sliding distances spaced among the N sliding distances is equal, that is, the 1 st sliding distance is selected from the N sliding distances, the 2 nd sliding distance is selected from the N-1 sliding distances, the m sliding distances are spaced between the 1 st sliding distance and the 2 nd sliding distance, the 3 rd sliding distance is selected from the N-2 sliding distances, the m sliding distances are spaced between the 2 nd sliding distance and the 3 rd sliding distance, and so on until the N th sliding distance is selected from the N-1 sliding distances, and the m sliding distances are spaced between the N-1 st sliding distance and the N th sliding distance. In this embodiment, the N sliding distances are arranged according to the order in which the tips of the probes slide on the surface of the sample to be measured.
3. From the relationship between the sliding distance in step 1 and the AFM measurement of adhesion, and from the SEM measurement R of the sliding distance and tip radius in step 2 SEM The relation between the AFM measurement values of the adhesive force at the n sliding distances and the SEM measurement value of the tip radius is obtained, and the relation between the AFM measurement values of the adhesive force at the n sliding distances and the SEM measurement value of the tip radius is linearly fitted to obtain a relation fitting straight line, as shown in fig. 3.
AFM measurements based on the N sliding distances and adhesion in FIG. 2, and SEM measurements R of the N sliding distances and tip radius SEM The relationship between (N sliding distances are N of the N sliding distances), it can be concluded that the AFM measurement of the adhesion force at the N sliding distances and the SEM measurement R of the tip radius SEM For simplicity of calculation, AFM measurements of adhesion at n sliding distances are compared with SEM measurements of tip radius SEM The relation points are subjected to linear fitting to obtain a relation fitting straight line, and the fitting constant is the slope of the relation fitting straight line, so that the relation between the AFM measured value of the adhesion and the radius of the needle tip can be deduced:
F AFM ＝k ad R AFM (1)
wherein, F AFM For AFM measurement of adhesion, k ad As fitting constant, R AFM Is the tip radius obtained using an atomic force microscope.
4. Obtaining a fitting constant k according to the relation fitting straight line in the step 3 ad According to the fitting constant k ad AFM measurement F of adhesion AFM Radius of needle tip R AFM The relationship between them is shown in formula (1).
5. According to the fitting constant k in the step 4 ad And obtaining the radius R of the needle tip under N-N sliding distances by the formula (1) AFM I.e. the radius of the tip obtained with AFM.
SEM measured value R of the radius of the needle tip under n sliding distances is measured by SEM SEM And the remaining N-N sliding distances are equal to the radius R of the lower needle tip AFM This can be obtained by the formula (1).
6. N sliding distances and N needle tip radii (N R) at the N sliding distances SEM N-N R AFM ) And fitting to obtain a fitting curve between the sliding distance and the radius of the needle tip, and obtaining the corrected radius of the needle tip at any sliding distance according to the fitting curve as shown in FIG. 4.
Utilizing Matlab to calculate numerical product of atomic abrasion model (namely formula (2)) by adopting Runge-Kutta methodObtaining a relational expression between the needle point radius R and the sliding distance d, but the needle point radius R cannot be solved, fitting the sliding distance and the needle point radius R by using Matlab and a least square method to obtain a fitting curve, and obtaining the corrected needle point radius R under any different sliding distances through the fitting curve d 。
The atomic wear model formula is:
in the formula (2), R is the radius of the needle tip, d is the sliding distance, theta is the opening angle of the needle tip, f a For probe phonon frequency, b is the lattice constant, v 0 At nominal sliding speed, E eff For effective activation energy, V an To activate the volume effectively, F n Is a normal load, k ad As fitting constant, k B Boltzmann constant, T test ambient temperature, E eff And V an Can be found by the lsqnolin function of Matlab. Formula (2) is prior art and can be referred to [ Physical review letters,2008,101 (12): 125501.]
7. According to the fitting constant and the corrected needlepoint radius R under any sliding distance d The friction and adhesion forces are corrected to eliminate or reduce measurement errors due to wear of the needle tip.
According to the Amontons law under the nanometer scale, the correction formula of the friction force and the adhesion force is as follows:
F f ＝μ(F n +k ad R d ) (3)
F ad ＝k ad R d (4)
in formulae (3) and (4), F f For the corrected friction, μ is the coefficient of friction, F n As normal load, k ad As fitting constant, R d To correct the tip radius, F ad Is the corrected adhesion.
The method can obtain the change value of the radius of the probe tip through test fitting, and under the condition of a large number of change values of the radius of the probe tip, the method avoids the problem of low efficiency of directly measuring the radius of the probe tip by adopting SEM, corrects the friction force and the adhesive force through a fitting constant and the corrected radius of the probe tip, eliminates or reduces the measurement error of the atomic force microscope on the friction performance of the nano material caused by the abrasion of the probe tip, improves the measurement precision and improves the accuracy of the atomic force microscope on the evaluation of the friction performance of the nano material.
Example 1
And (3) test environment: an ultra-clean laboratory with an ambient temperature of 23 ℃ and a humidity of 45%; the model of the atomic force microscope is as follows: cypher ES, ashylum Research, CA, the type of a probe used for measuring the friction force is AC240TS-R3, olympus, the elastic modulus is 190GPa, and the calibration coefficient of the friction force is 566.33Nm/v; the measured sample is MoS 2 Nanosheets having an elastic modulus of 270GPa.
Placing the silicon wafer deposited with the MoS2 nanosheets on a sample stage of an atomic force microscope, scanning the sample to obtain a molybdenum disulfide morphology graph with the morphology area less than or equal to 10 microns multiplied by 10 microns in a tapping mode, and analyzing the morphology and the cross-section height, as shown in FIG. 5; and the samples and their layer thicknesses were characterized by Raman spectroscopy (InVia Raman microscopie, renishaw, UK) as shown in fig. 6. From the cross-sectional heights at the locations of the solid lines in FIG. 5, it can be seen that the cross-sectional heights are 2.7nm, respectively, because of the single-layer MoS 2 The thickness is about 0.65nm, so MoS in FIG. 5 2 The nanoplatelets are inferred to be 4 layers, and it can be seen from fig. 5 that the sample surface is relatively flat. The two characteristic peaks of the curve in FIG. 6 appear at 380cm -1 Near and 410cm -1 In the vicinity, therefore, it can be judged that the nanosheet in FIG. 6 is MoS 2 The distance between characteristic peaks of the curve in FIG. 6 is 23.6cm -1 Therefore, it was judged that the MoS2 nanosheet was 4-layered.
Normal load F at 38nN according to step 1 n Then, every time the probe tip finishes sliding distance of 0.13mm in the designated area of the sample, the measurement of the adhesive force and the frictional force is carried out, the sliding distance is 2000, and the measurement can be correspondingly carried outAFM measurement F of 2000 adhesion forces AFM And AFM measurements of friction.
According to step 2, SEM measurement R of the radius of the needle tip at 9 sliding distances was obtained by SEM SEM The probe tip was analyzed for wear by SEM, as shown in fig. 7. In fig. 7 (a), SEM characterization is performed before the probe is worn, and it can be seen that the tip is very sharp, i.e., the tip radius is very small. From fig. 7 (b) to fig. 7 (j), it is apparent that the wear of the needle tip during the test is still relatively large. The analysis of fig. 7 (a) revealed that the opening angle θ =16 ° of the probe. The data in table 1 are specific values of the tip radius obtained by analysis of fig. 7.
TABLE 1 specific values of the radius of the tip at different stages of wear
Fitting constant k obtained according to step 3 ad =0.99, the relational expression between the probe tip R and the sliding distance d can be obtained from the expression (2):
the corrected radius R of the needle tip at each sliding distance can be obtained through the step 6 d According to k again ad 、R d And the frictional force F after correction can be obtained by the equations (3) and (4) f And adhesion force F ad Corrected friction force F f Comparison with the test Friction force, corrected adhesion force F ad Adhesion to test F AFM As shown in fig. 8 and 9, respectively, it can be seen that the test adhesion force F is obtained at the initial stage of the probe sliding AFM And the friction force changes more sharply in the test, namely the radius of the needle tip is increased more quickly, namely the abrasion rate of the needle tip is high, and the adhesion force F measured at the moment AFM The value is also increasing continuously, and the radius R of the needle tip reaches the later stage of the test AFM I.e. number of adhesionValue F AFM And tends to be stable. Under the condition that the friction force and the adhesion force are not corrected, the friction performance data measured by using the AFM has larger error; the relationship between the corrected sliding distance and the radius of the probe is a smooth curve, and the adhesion force F is measured relative to the AFM test AFM R obtained by conversion AFM Closer to the true radius R of the tip as measured by SEM SEM (ii) a And the corrected frictional force F f And corrected adhesion force F ad With respect to the friction and adhesion forces F measured by the test AFM The method has no large fluctuation, which shows that the AFM is used for measuring the friction performance data under the condition that the friction force and the adhesion force are corrected, so that the method has high measurement precision, and the measurement error of the atomic force microscope on the friction performance of the nano material caused by the abrasion of the needle point is eliminated or reduced.
The above disclosure is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or modifications within the technical scope of the present disclosure may be easily conceived by those skilled in the art and shall be covered by the scope of the present invention.
Claims (9)
1. A method for correcting the abrasion friction performance of an atomic force microscope probe is characterized by comprising the following steps:
step 1: applying normal load by using an atomic force microscope to enable the probe tip to slide on the surface of the measured sample, and measuring an AFM (atomic force microscope) measured value of the friction force and an AFM measured value of the adhesion force between the probe tip and the surface of the measured sample at each sliding distance; the sliding distance refers to the total length of a sliding line of the probe tip on the surface of the measured sample in each AFM scanning picture;
and 2, step: selecting a plurality of sliding distances from all the sliding distances in the step 1, and measuring SEM measured values of the needle tip radiuses at the plurality of sliding distances by using a scanning electron microscope;
and 3, step 3: obtaining relation points between the AFM measured values of the adhesion force and the SEM measured values of the radius of the needle tip under a plurality of sliding distances according to the relation between the sliding distance and the AFM measured value of the adhesion force in the step 1 and the relation between the sliding distance and the SEM measured value of the radius of the needle tip in the step 2, and performing linear fitting on the relation points to obtain a relation fitting straight line;
and 4, step 4: obtaining a fitting constant according to the relation fitting straight line in the step 3, wherein the fitting constant is the slope of the relation fitting straight line; obtaining a relational expression between the AFM measured value of the adhesion and the radius of the needle point according to the fitting constant;
and 5: obtaining the radius of the needle tip at each sliding distance according to the relational expression between the AFM measured value of the adhesive force and the radius of the needle tip in the step 4, wherein the radius of the needle tip is the radius of the needle tip obtained by using an atomic force microscope;
step 6: fitting all the sliding distances and the needle point radiuses under all the sliding distances to obtain a fitting curve between the sliding distances and the needle point radiuses, and obtaining the corrected needle point radiuses under the sliding distances according to the fitting curve;
and 7: correcting friction force and adhesive force according to the fitting constant and the corrected radius of the needle point under the sliding distance so as to eliminate or reduce measurement errors caused by abrasion of the needle point;
the correction formulas of the friction force and the adhesion force are respectively as follows:
F f ＝μ(F n +k ad R d )
F ad ＝k ad R d
wherein, F f For the corrected friction, μ is the coefficient of friction, F n As normal load, F ad For corrected adhesion, k ad As fitting constant, R d Is the corrected tip radius.
2. The frictional property correction method of claim 1, wherein in the step 1, the probe tip slides on a designated area of the surface of the measured sample, and the designated area refers to an arbitrary area of the surface of the measured sample.
3. The method for correcting friction performance according to claim 1, wherein in the step 1, the probe tip slides on the surface of the sample to be measured in a manner that: the probe tip slides from left to right or from right to left on the surface of the measured sample, then slides from right to left or from left to right after parallel movement, and so on until completing one sliding distance, and the length of each sliding line is equal to the sliding distance divided by 512.
4. The frictional property correction method as set forth in claim 1, wherein in said step 1, each sliding distance is equal.
5. A friction property correction method as described in any one of claims 1 to 4, wherein in step 1, AFM measurement of friction force is measured by: and scanning the friction electric signals of all points in the designated area on the surface of the measured sample by using a transverse force module of the AFM, and converting the friction electric signals into AFM measured values of friction force by using the friction force calibration coefficient of the probe.
6. A friction property correction method as described in any one of claims 1 to 4, wherein in step 1, the specific measurement method of AFM measurement of adhesion is: dotting the probe tip in a designated area of the surface of the measured sample, measuring the adhesive force of at least 1024 points in the designated area by using an AFM force diagram module, and obtaining the average value of the adhesive force of the designated area through Gaussian statistics, wherein the average value of the adhesive force is the AFM measured value of the adhesive force of the probe tip and the surface of the measured sample at the sliding distance.
7. The frictional property correction method according to any one of claims 1 to 4, wherein in the step 2, the number of the sliding distances spaced between the plurality of sliding distances selected is equal.
8. A method of modifying friction properties according to any of claims 1 to 4 wherein in step 4 or 5 AFM measurements of adhesion are related to tip radius by:
F AFM ＝k ad R AFM
wherein, F AFM As AFM measurement of adhesion, k ad As fitting constant, R AFM Is the tip radius obtained using an atomic force microscope.
9. A friction performance correcting method according to any one of claims 1 to 4, wherein in the step 6, numerical integration is performed on the atomic wear model by using Matlab and a Runge-Kutta method to obtain a relational expression between the radius of the needle tip and the sliding distance, and then fitting is performed on the sliding distance and the radius of the needle tip by using Matlab and a least square method to obtain a fitting curve;
the atomic wear model is:
wherein R is the radius of the needle tip, d is the sliding distance, theta is the opening angle of the needle tip, and f a For probe phonon frequency, b is the lattice constant, v 0 At nominal slip speed, E eff For effective activation energy, V an To activate the volume effectively, F n Is a normal load, k ad As fitting constant, k B Boltzmann constant, T is test ambient temperature.
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