WO2021017331A1 - 一种实现锥形针尖的afm探针与石墨表面之间超滑的方法 - Google Patents

一种实现锥形针尖的afm探针与石墨表面之间超滑的方法 Download PDF

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WO2021017331A1
WO2021017331A1 PCT/CN2019/120657 CN2019120657W WO2021017331A1 WO 2021017331 A1 WO2021017331 A1 WO 2021017331A1 CN 2019120657 W CN2019120657 W CN 2019120657W WO 2021017331 A1 WO2021017331 A1 WO 2021017331A1
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probe
graphite
tip
graphite surface
friction
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French (fr)
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刘大猛
庞华
沙田东
房亮
李津津
雒建斌
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Tsinghua University
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Tsinghua University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
    • G01Q60/38—Probes, their manufacture, or their related instrumentation, e.g. holders
    • G01Q60/42—Functionalisation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
    • G01Q60/26—Friction force microscopy
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
    • G01Q60/38—Probes, their manufacture, or their related instrumentation, e.g. holders

Definitions

  • the invention relates to the field of nanotribology, and in particular to a method for achieving super-slip between an atomic force microscopy (AFM) needle with a tapered tip and a graphite surface.
  • AFM atomic force microscopy
  • Graphite is a layered material, each layer is composed of sp 2 hybrid type carbon atoms, with high strength and good stability; the layers are connected by van der Waals force, and the shear force between the layers is small, so the graphite slides between layers The resistance is very small.
  • researchers have used spherical tip AFM probes to measure the friction force on the graphite surface. The friction coefficient is in the range of 0.0003 to 0.003, indicating that the AFM probe tip and the graphite surface are in a "super slippery" state.
  • the first method is too expensive to use CVD to deposit graphene, and the obtained graphene usually contains many defects; the second method is because the real contact area between the spherical tip of the probe and the graphite surface is very large and the contact pressure is very low. Therefore, it is difficult to wear the graphite surface. If the graphite surface is not worn, no graphene nanosheets will be produced, and no graphene nanosheets will be transferred to the surface of the spherical tip. In order to cause the graphite surface to wear and transfer the graphene nanosheets to the spherical tip surface, the spherical tip requires multiple and long-term friction measurements to damage the graphite surface, resulting in low experimental efficiency.
  • the most commonly used probe tip of the atomic force microscope is a cone, and the radius of curvature of the tip does not exceed 10 nanometers.
  • the probe with the tapered tip has a higher contact pressure under the same normal load, which is easier to cause wrinkles and abrasion on the surface of the material, and peel off the nanosheet from the surface of the material.
  • the tapered tip probe has high versatility, high measurement sensitivity, and easy lateral force calibration in atomic force microscope experiments. Therefore, the tapered tip probe is an ideal tool for studying the super-slip of graphite and other materials.
  • the method is to make the probe rub on the graphite surface for a long time.
  • the disadvantage is that the transfer of graphene debris to the tapered tip surface is a small probability event. , This method takes a long time.
  • This application provides a method for achieving ultra-slip between an AFM probe with a tapered tip and a graphite surface, which includes the following steps:
  • the elastic coefficient of the first probe is smaller than the elastic coefficient of the second probe.
  • the elastic coefficient of the first probe is 3.5 N/m
  • the elastic coefficient of the second probe is 34 N/m.
  • the scanning range of the second probe is greater than 50 ⁇ m ⁇ 50 ⁇ m, and a square area with a side length of 20 ⁇ m-30 ⁇ m is selected from the scanning range as the subsequent etching area.
  • the trajectory of the needle tip of the second probe on the graphite surface is consistent with the path drawn by the atomic force microscope.
  • the shape of the etching path is arbitrary.
  • the shape formed by the etching path is two concentric circles with different diameters, and the diameter of the two concentric circles ranges from 27 to 28 ⁇ m.
  • the normal load applied to the tip of the second probe can satisfy the requirement of damaging the graphite surface.
  • step S30 the current setting value in the atomic force microscope is 8-10 nA, and the corresponding normal load of the tip of the second probe is 4000-7000 nN.
  • the first probe and the second probe are both silicon probes.
  • the current setting value is changed in the atomic force microscope to change the normal load of the first probe.
  • the measurement of the first sample area in different methods A lateral force signal under a forward load to obtain the first friction force under different loads, and the first friction coefficient is the slope of the curve of the first friction force changing with the normal load.
  • a surface with a size of 600 nm ⁇ 600 nm in the first sample area is selected as the scanning area for the friction test.
  • the preset threshold is 0.001.
  • the present invention has the following technical effects:
  • the shape of the etching path is two concentric circles with different diameters, so that the nanosheets are not only distributed along the track of the score, but also there are more nanosheets inside and outside the circular score, which greatly improves the graphite The probability of debris transfer to the tip of the silicon probe, and it takes a short time.
  • the needle tip still maintains ultra-low friction after the scanning distance on the graphite surface exceeds 10,000 microns, which shows that the needle tip-graphite super-slip friction pair prepared by the method of the present invention has good stability.
  • the friction pair prepared by the preparation method of the present invention can greatly reduce the friction force and the friction coefficient (that is, the slope of the fitting straight line of the relationship between the friction force and the normal load), and the friction coefficient of the probe A before the friction score It is 0.00213, and the friction coefficient after friction scoring is as low as 0.0007, reaching a super-slip state, which is of great significance to the study of nanotribology.
  • the preparation method of the super-slip friction pair provided by the present invention is not only suitable for graphite, but also suitable for materials such as molybdenum disulfide and boron nitride.
  • the homogenous friction pair or the heterogeneous friction pair prepared by the method of the present invention has the characteristics of quickly entering the super-slip state, good stability and the like.
  • Figure 1 is a flow chart of the preparation method of the present invention.
  • Fig. 2 is a 200 times optical microscope image of the scratches on the graphite surface of the present invention, with 1# ⁇ 5# being the inspection points.
  • Fig. 3 is the Raman spectrum of the five points in Fig. 2 of the present invention.
  • Fig. 4 is a graph showing the relationship between the friction force of the silicon probe of the present invention before and after the scratch rubbing on the graphite surface with the normal load.
  • Fig. 5 is a graph showing the relationship between the friction force of the silicon probe before and after the scratch rubbing on the graphite surface with the scanning distance of the tip (the normal load is always 422.6 nN).
  • Fig. 6 is an illustration of a method for using a silicon probe with a tapered tip to achieve super-slip on the surface of a two-dimensional material.
  • a method for achieving ultra-slip between the tapered tip of the atomic force microscope probe and the graphite surface, as shown in FIG. 1, includes the following steps:
  • 3M Scotch TM transparent tape can be used to cleave the ZYA grade graphite surface to obtain a clean and smooth graphite surface.
  • sample area 1 A first sample area (sample area 1) that is smooth, wrinkle-free and free of impurities is selected on the graphite surface through the optical microscopic imaging system of the atomic force microscope, and the first probe (probe A) is installed on the atomic force microscope , And then move probe A to sample area 1.
  • the scanning range of the probe A should be as large as possible, preferably above 10 ⁇ m ⁇ 10 ⁇ m.
  • the obtained surface topography may contain multiple atomic steps, and an area without atomic steps is selected as the friction test area.
  • the size of the scanning area used as the friction test in the sample area 1 is 600 nm ⁇ 600 nm.
  • the slope of the friction force versus load curve is the friction coefficient.
  • the elastic modulus of probe A is 3.5 N/m.
  • the elastic modulus of the second probe (probe B) is 34 N/m.
  • the probe B with the elastic coefficient of 34N/m is installed on the probe holder of the atomic force microscope, and the position of the end of the probe microcantilever relative to the graphite surface is changed with the optical microscopic imaging of the atomic force microscope as a reference.
  • the tapping mode is used to measure the surface topography in the selected sample area 2, and the scanning range of the probe is above 50 ⁇ m ⁇ 50 ⁇ m.
  • a square area with a side length of 20 ⁇ m-30 ⁇ m is selected from the obtained surface morphology, which is required to be as flat as possible but not necessarily the entire area is on an atomic step surface.
  • the probe B draws an etching path on the area of the surface topography measured the second time.
  • the shape of the etching path in this embodiment is circular.
  • the process of nano-etching the trajectory of the tip of the probe B on the graphite surface is consistent with the path drawn by the user on the control software of the atomic force microscope.
  • the normal load imposed by the tip of the probe B by the atomic force microscope should be as large as possible ( Thousands of nano cattle). Specifically, in this embodiment, the normal load of the probe tip of the atomic force microscope is about 4000-7000 nN. Because the tip of the probe B is very sharp, the width of the notch left by the probe is nanometer scale.
  • the optical display of the atomic force microscope does not observe the existence of nicks. Only by scanning the topography of the sample surface in tap mode again can the topography of the nicks be obtained. The surface morphology of the nicked area on the graphite surface can be seen around the nicks Many debris was peeled off the graphite surface by the needle tip during the nano-etching process.
  • the probe of the atomic force microscope was replaced again with the previously used probe A with an elastic coefficient of 3.5N/m, the working mode of the atomic force microscope was changed to contact mode, and the morphology of the nicks were measured.
  • the notch left on the surface is a circle with a diameter of about 27 ⁇ m.
  • the measurement signal can be arbitrary.
  • the purpose of this step is to make the probe tip fully contact the graphite debris produced by nano-etching, and to increase the probability of the graphite debris being transferred to the probe tip.
  • a sample area 3 (third sample area) with no nicks, no debris, and a smooth surface is selected on the sample surface, and the size is preferably 5 ⁇ m ⁇ 5 ⁇ m or more.
  • an atomic step surface is selected to measure the second friction force under multiple normal loads. The slope of the second friction force versus load curve is the second friction coefficient.
  • the preset threshold is 0.001. If the second friction force is less than the first friction force and the second friction coefficient is less than the preset threshold, the super-slip friction pair is successfully prepared; otherwise, steps S40 and S50 are repeated until the tip of the probe A and the graphite surface are super-slip .
  • the morphology of the nicked area on the graphite surface was measured by an atomic force microscope. After the probe was etched on the graphite surface, an obvious circular nick was left, destroying the original surface of the graphite; at the same time, the surrounding area of the nick There are many debris, and the size of these debris can be judged to be in the range of tens of nanometers to hundreds of nanometers according to the ruler, so these debris are called "nanoplates".
  • the comparison of the friction force and the friction coefficient measured in steps S20 and S50 is shown in FIG. 4.
  • the normal load applied by the tip of the probe A on the graphite surface is controlled by changing the setting value in the control software of the atomic force microscope. According to the result of the probe calibration, the normal load in the experiment can be converted into a range of 0 ⁇ 1370nN. It can be seen from Fig. 4 that the friction force after the probe A has rubbed the score is reduced compared with before, and the greater the friction force decreases when the normal load is larger.
  • the friction coefficient is the slope of the fitted line of the relationship between the friction force and the normal load.
  • the friction coefficient of the probe A before the friction score is 0.00213, and the friction coefficient after the friction score is as low as 0.0007, reaching a super-slip state.
  • the transmission electron microscope can see the nano-level fine structure, and the present invention uses the transmission electron microscope to observe the surface morphology of the tip of the atomic force microscope probe A and B.
  • the tip of the probe A can see a clear layered structure, and the transfer layer has more than 10 layers, so only the rubbing process can induce the transfer of the graphite nanosheets.
  • the present invention also measures the relationship between the frictional force between the probe tip and the graphite surface and the scanning distance of the probe on the graphite surface.
  • the frictional force is still The measurement was performed on the atomic step surface of the score. Under a constant normal load of 422.6nN, the relationship between the friction force before and after the tip friction score with the scanning distance was measured, as shown in Figure 5. Under a normal load of 422.6nN, the friction force of the silicon probe tip after rubbing the score is an order of magnitude smaller than before, and the tip of the graphite surface still maintains ultra-low friction even after the scanning distance exceeds 10,000 microns.
  • the tip-graphite super-slip friction pair prepared by the method of the invention has good stability.
  • the silicon probe tip that has not been repeatedly scanned in the nick area does not enter the super-slip state even after rubbing 10,000 microns on the graphite surface, which indicates that the method of the present invention has the ability to quickly enter a stable super-smooth state of the silicon tip-graphite Features.
  • Fig. 6 is an illustration of a method for using a silicon probe with a tapered tip to achieve super-slip on the surface of a two-dimensional material.
  • a silicon probe with a lower coefficient of elasticity probe A in the figure
  • probe B uses a silicon probe with a higher elastic coefficient
  • probe B performs nano-etching on the surface of the two-dimensional material sample to form a circular nick.
  • probe A Use probe A to make a nick area on the sample surface Repeatedly and reciprocally rub.
  • the preparation method of the super-slip friction pair provided by the present invention is not only suitable for graphite, but also suitable for materials such as molybdenum disulfide and boron nitride.
  • the homogenous friction pair or the heterogeneous friction pair prepared by the method of the present invention has the characteristics of quickly entering the super-slip state, good stability and the like.

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Abstract

一种实现锥形针尖的AFM探针与石墨表面之间超滑的方法，通过弹性系数较高的探针在石墨表面进行纳米刻蚀从而剥离出石墨纳米片，再采用弹性系数较低的探针在刻痕区域通过摩擦转移使石墨纳米片包裹于探针针尖表面，提供的超滑摩擦副的制备方法不仅适用于石墨，还适用于二硫化钼、氮化硼等材料，通过该方法制备的同质摩擦副或异质摩擦副具有进入超滑状态快、稳定性好等特点。

Description

一种实现锥形针尖的AFM探针与石墨表面之间超滑的方法 技术领域
本发明涉及纳米摩擦学领域，具体而言，涉及一种实现锥形针尖的原子力显微镜探(AFM)针与石墨表面之间超滑的方法。
背景技术
石墨是一种层状材料，每一层均由sp 2杂化类型的碳原子构成，强度高、稳定性好；层间靠范德华力连接，层间剪切力很小，因此石墨层间滑动的阻力很小。目前已有学者使用球形针尖的原子力显微镜探针测量石墨表面的摩擦力，摩擦系数在0.0003～0.003范围内，说明原子力显微镜探针针尖与石墨表面之间处于“超滑”状态。实现球形针尖的原子力显微镜探针与石墨表面之间超滑的方法有两种：一是通过化学气相沉积法(CVD)在球形针尖表面沉积石墨烯，避免了在摩擦力测试过程中探针针尖与石墨表面的直接接触，降低了摩擦力；二是将球形探针在石墨表面反复摩擦，一段时间后石墨表面破损产生的石墨烯碎屑粘附在球形探针表面，摩擦过程变成了石墨烯碎屑与石墨表面的摩擦(即石墨的层间滑动摩擦)，因此摩擦力很小。但这两种方法都存在一定的局限性。第一种方法使用CVD沉积石墨烯的成本太高，而且得到的石墨烯通常含有较多缺陷；第二种方法因为探针的球形针尖与石墨表面的真实接触面积非常大导致接触压强很低，所以很难使石墨的表面发生磨损。如果石墨表面没有磨损，就不会产生石墨烯纳米片，更不会有石墨烯纳米片转移到球形针尖的表面。为了使石墨表面发生磨损并且使石墨烯纳米片转移到球形针尖表面，球形针尖需要进行多次且长时间的摩擦测量才能使石墨表面破损，造成实验效率低下。
无论是表征材料的形貌还是测量材料的摩擦力，原子力显微镜最常用的探针针尖为锥形，尖端的曲率半径不超过10纳米。和球形针尖的探针相比，锥形针尖的探针在相同的法向载荷下具有更高的接触压强，更容易使材料表面产生褶皱和磨损，并从材料表面剥离出纳米片。而且锥形针尖的探针在原子力显微镜实验中通用性高、测量灵敏度高、容易进行侧向力标定，所以具有锥形针尖的探针是研究石墨等材料超滑的理想工具。
目前已有人实现了锥形针尖的探针与石墨表面之间的超滑，方法是使探针在石墨表面进行长时间的摩擦，缺点是石墨烯碎屑转移至锥形针尖表面是小概率事件，该方法耗时较长。
发明内容
本申请提供一种实现锥形针尖的AFM探针与石墨表面之间超滑的方法，包括如下步骤：
S10.对石墨表面进行解理；
S20.在解理后的所述石墨表面选择一块没有褶皱且没有杂质的第一样品区域，将第一探针安装到原子力显微镜上，选择所述第一样品区域作为摩擦力测试区域，调整原子力显微镜的工作模式为侧向力模式，在所述第一样品区域获取正向侧向力信号和反向侧向力信号，通过所述正向侧向力信号和反向侧向力信号获得所述第一探针的针尖与石墨表面之间的第一摩擦力和第一摩擦系数；
S30.将第二探针安装到原子力显微镜上，选择一个表面没有褶皱及杂质的第二样品区域，在原子力显微镜的工作模式为轻敲模式下测量所述第二样品区域的表面形貌；将原子力显微镜的工作模式切换至接触模式，控制所述第二探针在所述第二样品区域表面进行刻蚀，获得纳米片；刻蚀过程中可切换至轻敲模式，再次测量所述第二样品区域的表面形貌，在所述第二样品区域的表面形貌显示出刻痕后停止刻蚀；
S40.将原子力显微镜的所述第二探针更换为所述第一探针，变更原子力显微镜的工作模式为接触模式，所述第一探针在刻痕区域来回扫描；
S50.在样品表面选择一个没有刻痕及碎屑的第三样品区域，在侧向力模式下，获得所述第一探针的针尖与石墨表面之间的第二摩擦力和第二摩擦系数；
S60.判断是否所述第二摩擦力远小于所述第一摩擦力且所述第二摩擦系数小于预设阈值；如果否，重复S40及S50，直至所述第一探针的针尖与石墨表面实现超滑；
其中，所述第一探针的弹性系数小于所述第二探针的弹性系数。
一实施例中，所述第一探针的弹性系数为3.5N/m，所述第二探针的弹性系数为34N/m。
一实施例中，在S30中，所述第二探针的扫描范围在50μm×50μm以上，从所述扫描范围中选取一个边长为20μm～30μm的正方形区域作为后续的刻蚀区域。
一实施例中，在S30中，在所述刻蚀的过程中，所述第二探针的针尖在所述石墨表面运动的轨迹与通过原子力显微镜画出的路径一致。
一实施例中，在S30中，刻蚀路径形成的形状是任意的。
一实施例中，刻蚀路径形成的形状为两个直径不同的同心圆，两个同心圆的直径范围为27～28μm。
一实施例中，在S30中，对所述第二探针的针尖施加的法向载荷能够满足使所述石墨表面破损。
一实施例中，在步骤S30中，原子力显微镜中的电流设定值为8～10nA，对应的所述第二探针的针尖的法向载荷为4000～7000nN。
一实施例中，所述第一探针和所述第二探针均为硅探针。
一实施例中，在S20中，在原子力显微镜中更改电流设定值从而改变所述第一探针的法向载荷，在侧向力力模式下，测量所述第一样品区域在不同法向载荷下的侧向力信号，从而获得不同载荷下的所述第一摩擦力，所述第一摩擦系数为所述第一摩擦力随法向载荷变化的曲线的斜率。
一实施例中，在S20中，选择所述第一样品区域中尺寸为600nm×600nm的一表面作为摩擦力测试的扫描区域。
一实施例中，所述预设阈值为0.001。
与现有技术相比较，本发明具有如下技术效果：
1、采用不同弹性系数的探针B和A，分别进行刻蚀和摩擦转移，且通过透射电子显微镜来观测原子力显微镜探针A、B针尖的表面形貌，在石墨表面进行纳米刻蚀的探针B的针尖上没有任何转移层，证明了纳米刻蚀并不会使石墨纳米片转移到探针针尖上；而在石墨表面刻痕区域进行反复多次摩擦的探针A的针尖可以看到清晰的层状结构，本发明发现只有摩擦过程才会诱发石墨纳米片的转移。
2、刻蚀路径形状为两个直径不同的同心圆，使得纳米片不仅沿着刻痕的轨迹分布，而且在圆形刻痕的内部和外部也存在较多的纳米片，极大地提高了石墨碎屑转移到硅探针针尖上的概率，且耗时短。
3、通过拉曼光谱检测，纳米刻蚀过程中锐利的探针针尖将石墨表面划破并剥离了大量的石墨纳米片，这些石墨纳米片没有发生其他的物理变化或化学反应，具有较高的纯净度，为向探针针尖的摩擦转移提供了良好的条件。
4、针尖在石墨表面扫描距离超过1万微米后依然保持着超低摩擦力，这表明用本发明方法制备的针尖-石墨超滑摩擦副具有很好的稳定性。
5、采用本发明制备方法制得的摩擦副能够大大减小摩擦力和摩擦系数(即是摩擦力随法向载荷变化关系的拟合直线斜率)，探针A在摩擦刻痕之前的摩擦系数为0.00213，而摩擦刻痕之后的摩擦系数低至0.0007，达到了超滑状态，对纳米摩擦学的研究具有重要意义。
6、本发明所提供的超滑摩擦副的制备方法不仅适用于石墨，还适用于二硫化钼、氮化硼等材料。本发明方法制备的同质摩擦副或异质摩擦副具有进入超滑状态快、稳定性好等特点。
本申请的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本申请的实践了解到。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对实施例中所需要使用的附图作简单地介绍，应当理解，以下附图仅示出了本申请的某些实施例，因此不应被看作是对范围的限定，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他相关的附图。
图1为本发明制备方法的流程图。
图2为本发明石墨表面刻痕的200倍光学显微镜图像，1#～5#为检测点。
图3为本发明图2中5个点的拉曼光谱图。
图4为本发明硅探针在石墨表面刻痕摩擦之前和摩擦之后的摩擦力随法向载荷的变化关系图。
图5为本发明硅探针在石墨表面刻痕摩擦之前和摩擦之后的摩擦力随针尖扫描距离的变化关系图(法向载荷始终是422.6nN)。
图6为使用锥形针尖的硅探针在二维材料表面实现超滑的方法图解。
具体实施方式
为使本申请实施例的目的、技术方案和优点更加清楚，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。通常在此处附图中描述和示出的本申请实施例的组件可以以各种不同的配置来布置和设计。
因此，以下对在附图中提供的本申请的实施例的详细描述并非旨在限制要求保护的本申请的范围，而是仅仅表示本申请的选定实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
应注意到：相似的标号和字母在下面的附图中表示类似项，因此，一旦某一项在一个附图中被定义，则在随后的附图中不需要对其进行进一步定义和解释。
根据本申请一种实现锥形针尖的原子力显微镜探针与石墨表面之间超滑的方法，如图1所示，包括如下步骤：
S10.对石墨表面进行解理。
一实施例中，可以使用3M Scotch TM透明胶带对ZYA级石墨表面进行解理，得到一个干净、平滑的石墨表面。
S20.在解理后的所述石墨表面选择一块没有褶皱且没有杂质的第一样品区域，将第一探针安装到原子力显微镜上，选择所述第一样品区域作为摩擦力测试区域，调整原子力显微镜的工作模式为侧向力模式，在所述第一样品区域获取正向侧向力信号和反向侧向力信号，通过所述正向侧向力信号和反向侧向力信号获得所述第一探针的针尖与石墨表面之间的第一摩擦力和第一摩擦系数；
通过原子力显微镜的光学显微成像系统在所述石墨表面选择一块光滑、没有褶皱且没有杂质的第一样品区域(样品区域1)，将第一探针(探针A)安装到原子力显微镜上，然后将探针A移动到样品区域1。
在选定的样品区域1，使原子力显微镜工作在接触模式下测量表面形貌，探针A扫描范围要尽可能大，最好在10μm×10μm以上。获得的表面形貌图中可能会包含多个原子台阶，选择其中的一块没有原子台阶的区域作为摩擦力的测试区域。优选的，样品区域1中作为摩擦力测试的扫描区域尺寸为600nm×600nm。
调整原子力显微镜工作模式为侧向力测量模式，在刚刚选定的扫描区域获取探针A正向和反向两个方向的侧向力信号，从而获得探针A针尖与样品表面间的摩擦力。之后在原子力显微镜的控制软件中更改电流设定数值从而改变探针的法向载荷，在不同法向载荷下测量选定的样品区域1的摩擦力，摩擦力随载荷变化曲线的斜率即为摩擦系数。
一实施例中，探针A的弹性系数为3.5N/m。
S30.将第二探针安装到原子力显微镜上，选择一个表面没有褶皱及杂质的第二样品区域，在原子力显微镜的工作模式为轻敲模式下测量所述第二样品区域的表面形貌；将原子力显微镜的工作模式切换至接触模式，控制所述第二探针在所述第二样品区域表面进行刻蚀，获得纳米片；刻蚀过程中可切换至轻敲模式，再次测量所述第二样品区域的表面形貌，在所述第二样品区域的表面形貌显示出刻痕后停止刻蚀；
一实施例中，第二探针(探针B)的弹性系数为34N/m。
具体实施时，将弹性系数为34N/m的探针B安装到原子力显微镜的探针座上，以原子力显微镜的光学显微成像为参照，更改探针微悬臂梁末端相对于石墨表面的位置， 再次选择一个表面平滑、没有褶皱且没有杂质的样品区域(第二样品区域)2。在选定的样品区域2使用轻敲模式测量表面形貌，探针扫描范围在50μm×50μm以上。从获得的表面形貌中选取一个边长为20μm～30μm的正方形区域，要求尽可能平坦但不一定整个区域都在一个原子台阶面上。
将原子力显微镜的工作模式切换至接触模式，探针B在第二次测得的表面形貌的区域上画出刻蚀路径，本实施例的刻蚀路径形状为圆形，纳米刻蚀的过程中，探针B针尖在石墨表面运动的轨迹与用户在原子力显微镜的控制软件上画出的路径一致，为了使石墨表面破损，原子力显微镜对探针B针尖施加的法向载荷应该尽可能大(几千纳牛)。具体的，本实施例中，原子力显微镜的探针针尖法向载荷约为4000～7000nN，由于探针B针尖非常尖锐，所以探针留下的刻痕宽度是纳米尺度的，原子力显微镜的光学显微成像系统观察不到刻痕的存在，只有再次在轻敲模式下扫描样品表面的形貌才能获得刻痕的形貌图，通过石墨表面刻痕区域的表面形貌可以看到刻痕周围存在许多碎屑，是在纳米刻蚀过程中被针尖从石墨表面剥离下来的。
S40.将原子力显微镜的所述第二探针更换为所述第一探针，变更原子力显微镜的工作模式为接触模式，所述第一探针在刻痕区域来回扫描；
具体地，再次将原子力显微镜的探针更换为之前使用过的弹性系数为3.5N/m的探针A，变更原子力显微镜的工作模式为接触模式，测量刻痕的形貌，本实施例在石墨表面留下的刻痕为直径27μm左右的圆形。接下来以圆周的一小段为中心扫描1μm×1μm范围内的形貌或摩擦力，只要是接触模式下针尖在刻痕处反复地扫描即可，测量信号可以随意。该步骤的目的是使探针针尖与纳米刻蚀产生的石墨碎屑充分接触，提高石墨碎屑转移到探针针尖上的概率。
S50.在样品表面选择一个没有刻痕及碎屑的第三样品区域，在侧向力模式下，获得所述第一探针的针尖与石墨表面之间的第二摩擦力和第二摩擦系数；
具体地，在样品表面选择一个没有刻痕、没有碎屑并且表面平滑的样品区域3(第三样品区域)，尺寸最好在5μm×5μm以上。探针A在接触模式下获取表面形貌后，选取一个原子台阶面测量多个法向载荷下的第二摩擦力，第二摩擦力随载荷变化曲线的斜率即为第二摩擦系数。
S60.判断是否所述第二摩擦力远小于所述第一摩擦力且所述第二摩擦系数小于预设阈值；如果否，重复S40及S50，直至所述第一探针的针尖与石墨表面实现超滑；
一实施例中，预设阈值为0.001。第二摩擦力小于所述第一摩擦力且第二摩擦系数小 于预设阈值，那么超滑摩擦副制备成功；否则重复步骤S40、S50，直至所述探针A的针尖与石墨表面实现超滑。
在纳米刻蚀之后，石墨表面刻痕区域的形貌由原子力显微镜测得，探针在石墨表面刻蚀之后留下了明显的圆形刻痕，破坏了石墨原来的表面；同时，刻痕周围存在许多碎屑，根据标尺可以判断出这些碎屑的尺寸在十几纳米到几百纳米的范围内，因此这些碎屑被称为“纳米片”。
在完成步骤S10-S60后，使用扫描电子显微镜获取了石墨表面刻痕区域的形貌图，可以观察到，碎屑不仅沿着刻痕的轨迹分布，而且在圆形刻痕的内部和外部也存在较多的碎屑。这是因为探针针尖在刻痕区域反复摩擦的过程中，针尖划破了刻痕的边缘，加剧了刻痕周围的破损，产生了更多的碎屑，并将部分碎屑“推”到了离刻痕轨迹较远的区域。石墨表面有如此多可观测的碎屑，也极大地提高了石墨碎屑转移到硅探针针尖上的概率。
通过拉曼光谱检测，如图2所示，在石墨表面刻痕区域选择了5个检测点，如图3所示，根据G峰和2D峰的波数和形状可以判断这5条谱线都是石墨的谱线，而且没有其他材料的特征峰，所以1#～4#位置的碎屑都是石墨碎屑。另外，石墨碎屑位置(1#～4#)的拉曼谱线都出现了D峰(1350cm-1)而无碎屑区域(5#)的谱线没有。D峰的出现通常是因为石墨表面的缺陷使石墨露出了边界，破坏了原有晶格的对称性。而纳米刻蚀留下的刻痕使石墨表面出现了边界，刻蚀产生的石墨纳米片也存在边界，因此1#～4#的拉曼谱线出现了D峰。根据拉曼光谱检测的结果可知，即纳米刻蚀过程中锐利的探针针尖将石墨表面划破并剥离了大量的石墨纳米片，没有发生其他的物理变化或化学反应。这说明石墨表面的这些石墨纳米片具有较高的纯净度，这也为向探针针尖的摩擦转移提供了良好的条件。
步骤S20和S50测量的摩擦力和摩擦系数对比如图4所示。通过更改原子力显微镜控制软件中的设定值来控制探针A针尖施加在石墨表面的法向载荷，根据探针标定的结果可以换算出实验中法向载荷的变化范围在0～1370nN之间。从图4可以看出，探针A摩擦过刻痕后的摩擦力较之前有所减小，当法向载荷越大时摩擦力减小的幅度越大。摩擦系数为摩擦力随法向载荷变化关系的拟合直线斜率，探针A在摩擦刻痕之前的摩擦系数为0.00213，而摩擦刻痕之后的摩擦系数低至0.0007，达到了超滑状态。
由此可知，石墨纳米片使针尖-石墨摩擦副实现超滑的机理主要有两点：一是石墨纳米片防止了探针针尖的粗糙峰与石墨表面的直接接触；二是针尖上粘附的石墨纳米片与 石墨表面处于非公度接触状态，这也被证明是实现超滑的必要条件之一。
透射电子显微镜可以看到纳米级细微结构，本发明通过透射电子显微镜来观测原子力显微镜探针A、B针尖的表面形貌。在石墨表面进行纳米刻蚀的探针B的针尖上没有任何转移层，证明了纳米刻蚀并不会使石墨纳米片转移到探针针尖上；而在石墨表面刻痕进行反复多次摩擦的探针A的针尖可以看到清晰的层状结构，转移层有10层以上，因此只有摩擦过程才会诱发石墨纳米片的转移。
本发明为了检测上述方法制备的针尖-石墨超滑摩擦副的稳定性，还测量了探针针尖与石墨表面之间摩擦力随探针在石墨表面扫描距离的变化关系，摩擦力仍然是在无刻痕的原子台阶面上进行测量，在恒定的法向载荷422.6nN下，分别测量了针尖摩擦刻痕之前和之后的摩擦力随扫描距离的变化关系，如图5所示。在422.6nN的法向载荷下，硅探针针尖摩擦过刻痕之后的摩擦力比之前小了一个数量级，并且针尖在石墨表面扫描距离超过1万微米后依然保持着超低摩擦力，这表明用本发明方法制备的针尖-石墨超滑摩擦副具有很好的稳定性。此外，未在刻痕区域反复扫描的硅探针针尖即使在石墨表面摩擦了1万微米，仍未进入超滑状态，这表明本发明方法具有使硅针尖-石墨快速进入稳定的超滑状态的特点。
图6为使用锥形针尖的硅探针在二维材料表面实现超滑的方法图解。图6中，(a)使用弹性系数较低的硅探针(图中探针A)测量二维材料样品表面与探针A的针尖之间的摩擦力和摩擦系数。(b)使用弹性系数较高的硅探针(图中探针B在二维材料样品表面进行纳米刻蚀，形成一个圆形刻痕。(c)用探针A在样品表面的刻痕区域多次、往复地摩擦。(d)在样品表面选取一个没有刻痕的原子台阶面用探针A测量其摩擦力和摩擦系数。
本发明所提供的超滑摩擦副的制备方法不仅适用于石墨，还适用于二硫化钼、氮化硼等材料。本发明方法制备的同质摩擦副或异质摩擦副具有进入超滑状态快、稳定性好等特点。
需要说明的是，在不冲突的情况下，本申请中的实施例中的特征可以相互结合。
以上所述仅为本申请的优选实施例而已，并不用于限制本申请，对于本领域的技术人员来说，本申请可以有各种更改和变化。凡在本申请的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。

Claims (12)

  1. 一种实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，包括如下步骤：
    S10.对石墨表面进行解理；
    S20.在解理后的所述石墨表面选择一块没有褶皱且没有杂质的第一样品区域，将第一探针安装到原子力显微镜上，选择所述第一样品区域作为摩擦力测试区域，调整原子力显微镜的工作模式为侧向力模式，在所述第一样品区域获取正向侧向力信号和反向侧向力信号，通过所述正向侧向力信号和反向侧向力信号获得所述第一探针的针尖与石墨表面之间的第一摩擦力和第一摩擦系数；
    S30.将第二探针安装到原子力显微镜上，选择一个表面没有褶皱及杂质的第二样品区域，在原子力显微镜的工作模式为轻敲模式下测量所述第二样品区域的表面形貌；将原子力显微镜的工作模式切换至接触模式，控制所述第二探针在所述第二样品区域表面进行刻蚀，获得纳米片；刻蚀过程中可切换至轻敲模式，再次测量所述第二样品区域的表面形貌，在所述第二样品区域的表面形貌显示出刻痕后停止刻蚀；
    S40.将原子力显微镜的所述第二探针更换为所述第一探针，变更原子力显微镜的工作模式为接触模式，所述第一探针在刻痕区域来回扫描；
    S50.在样品表面选择一个没有刻痕及碎屑的第三样品区域，在侧向力模式下，获得所述第一探针的针尖与石墨表面之间的第二摩擦力和第二摩擦系数；
    S60.判断是否所述第二摩擦力远小于所述第一摩擦力且所述第二摩擦系数小于预设阈值；如果否，重复S40及S50，直至所述第一探针的针尖与石墨表面实现超滑；
    其中，所述第一探针的弹性系数小于所述第二探针的弹性系数。
  2. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，所述第一探针的弹性系数为3.5N/m，所述第二探针的弹性系数为34N/m。
  3. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，在S30中，所述第二探针的扫描范围在50μm×50μm以上，从所述扫描范围中选取一个边长为20μm～30μm的正方形区域作为后续的刻蚀区域。
  4. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，在S30中，在所述刻蚀的过程中，所述第二探针的针尖在所述石墨表面运动的轨迹与通过原子力显微镜画出的路径一致。
  5. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，在S30中，刻蚀路径形成的形状是任意的。
  6. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，刻蚀路径形成的形状为两个直径不同的同心圆，两个同心圆的直径范围为27～28μm。
  7. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，在S30中，对所述第二探针的针尖施加的法向载荷能够满足使所述石墨表面破损。
  8. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，在步骤S30中，原子力显微镜中的电流设定值为8～10nA，对应的所述第二探针的针尖的法向载荷为4000～7000nN。
  9. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，所述第一探针和所述第二探针均为硅探针。
  10. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，在S20中，在原子力显微镜中更改电流设定值从而改变所述第一探针的法向载荷，在侧向力力模式下，测量所述第一样品区域在不同法向载荷下的侧向力信号，从而获得不同载荷下的所述第一摩擦力，所述第一摩擦系数为所述第一摩擦力随法向载荷变化的曲线的斜率。
  11. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，在S20中，选择所述第一样品区域中尺寸为600nm×600nm的一表面作为摩擦力测试的扫描区域。
  12. 根据权利要求1所述的实现锥形针尖的AFM探针与石墨表面之间超滑的方法，其特征在于，所述预设阈值为0.001。
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