Method and device for preparing artificial speckles of amorphous nanocarbon particles for microscopic DIC

Abstract

The invention discloses a method and a device for preparing artificial speckles of amorphous nano carbon particles for microscopic DIC (Digital Integrated Circuit). According to the method, a high-purity carbon material is used as a carbon target, and operation parameters of plasma physical vapor deposition equipment are reasonably regulated and controlled; and the artificial speckles which are strong in adhesive force, uniform, dispersed in distribution and high in resolution ratio and can be combined with an electron backscatter diffraction (EBSD) technology can be prepared. The technology is good in stability and high in repeatability, the speckle size can be adjusted according to requirements, the requirements of the high-resolution micro-scale digital image correlation technology (DIC) can be met, and the defects of six micro-scale speckle preparation methods in the prior art are overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of digital image correlation method, and particularly relates to a preparation method and device of artificial non-crystalline nanoparticle speckle for micro-DIC. BACKGROUND

[0002] Digital image correlation (DIC) is a non-contact optical measurement method. A computer image processing software or program is used to analyze image sequences of an object in a deformation process, so as to realize full-field and dynamic measurement of physical quantities such as displacement and strain. The DIC technology has the advantages of high measurement accuracy and non-contact, and can be applied to extreme environments such as high temperature, low temperature and high speed, and has been widely applied and developed in the fields of material science and engineering structure. Taking material science as an example, the DIC technology can be used to measure the strain field of metals, ceramics and polymers from a macro scale to a micro scale.

[0003] A key technology of the DIC technology is the preparation of feature speckles, because the computer image processing software mainly calculates the displacement or strain of each sub-region based on the feature speckles. Therefore, the quality of the feature speckles directly affects the measurement accuracy of the DIC technology and the spatial resolution of the strain map. Since the feature speckle contrast of the material or structure itself is small, it is not conducive to image processing software analysis, and artificial feature speckles need to be prepared. Image acquisition at a macro scale usually uses various optical cameras, and the magnification is relatively low, so the requirement for feature recognition speckles is relatively low. Therefore, the preparation of recognition speckles for macro scale strain measurement is relatively easy, and there are many technologies related to the preparation method and device of macro scale speckles. The strain distribution at a micro scale is often used to study the strain partition behavior and damage nucleation mechanism of materials in a deformation process. Image acquisition at a micro scale usually uses an optical microscope (the magnification can be up to 2 k times) or a scanning electron microscope (the magnification can be up to 50 k times). For high-resolution micro DIC technology, a scanning electron microscope must be used, and the magnification is usually greater than 10 k. At a high magnification, the number density of the feature recognition speckles and whether they are uniformly and evenly distributed are key factors to determine the resolution of the micro scale DIC strain map. Therefore, the requirements for artificial speckles for micro scale DIC analysis are as follows: (1) high adhesion to the material surface; (2) uniform and even distribution; (3) high resolution, that is, the speckle size is as small as possible, and the spacing between the speckles is also as small as possible; and (4) not affecting the backscattering signal, so as to be combined with electron backscattering diffraction (EBSD) technology to obtain microstructure and crystallographic orientation information.

[0004] The existing micro-scale speckle preparation methods mainly include the following six methods. The first method is to use chemical etching method to obtain microstructure morphology, and to use the microstructure of the material itself as a characteristic spot. The advantages of this method are simple and easy to operate, and the disadvantages are low resolution and not suitable for materials with large grain size. The second method is to use non-crystalline nano-SiO2 particles as characteristic spots, and to use spin coating method to spin coat non-crystalline SiO2 particles with a size of about 20-50 nm on the sample surface. The advantages of this method are high resolution and do not affect the backscattering signal, and the disadvantages are that it is difficult to achieve uniform dispersion of SiO2 particles. The third method is to use chemical electroplating method to electroplate some metal or alloy (such as metal indium) particles as marker spots. The disadvantage of this method is that the electroplated metal particles will affect the electron backscattering signal and cannot be used with EBSD technology. The fourth method is gold particle deposition method, which can obtain extremely high resolution, but the process of preparing gold particles needs to be carried out in a water vapor atmosphere, the temperature of the sample surface is about 300°C, and the holding time is relatively long, which will change the microstructure of most materials. The fifth method is indentation method. The nanoindentation technology is used to prepare indentation array on the sample surface, and the indentations are used as identification points. This technology not only has low resolution, but also destroys the original surface structure of the sample, which will affect the stress state of the sample surface layer. The sixth method is focused ion beam marking method. The focused ion beam (FIB) technology is used to mark a grid on the sample surface, and the grid is used as a characteristic spot. This method also destroys the original surface of the sample.

[0005] Therefore, the existing micro-scale speckle preparation methods in the prior art all have many disadvantages, and there is no micro-scale speckle preparation process that can stably obtain high resolution, strong adhesion, uniform and stable dispersion, and does not affect the electron backscattering signal without changing the microstructure of the material or destroying the surface state of the material (such as surface integrity, influence on backscattering signal and influence on stress state, etc.). SUMMARY

[0006] The embodiments of the present application provide a kind of micro-DIC of amorphous nano-carbon particle artificial speckle preparation method and device, to solve the traditional micro-scale speckle preparation method has not been able to stably obtain high resolution, strong adhesion, uniform and stable dispersion, and does not affect the electron backscattering signal without changing the microstructure of the material or destroying the surface state of the material.

[0007] In the first aspect of the application, a micro-DIC amorphous nano-carbon particle artificial speckle preparation method is provided, which uses plasma assisted physical vapor deposition technology to deposit carbon on the sample surface to form artificial speckles, which are composed of a large number of amorphous nano-carbon particles.

[0008] The carbon atoms are mainly in the form of neutral atoms, and the carbon atom flow is deposited on the sample surface to form uniformly dispersed nano-amorphous carbon particles when the sample surface temperature is not too high. The process does not change the microstructure of the sample and does not damage the surface state of the sample material (such as surface integrity, influence on backscattering signal and influence on stress state, etc.), and the size of the carbon particles can be precisely controlled by controlling the power and deposition time, so that various sizes of artificial speckles are obtained.

[0009] Preferably, the method comprises the following steps: 1) installing a carbon target on the cathode of a plasma physical vapor deposition device; 2) placing a polished and dried sample into the vacuum chamber of the plasma physical vapor deposition device; 3) starting vacuumizing, and after the vacuum degree reaches the requirement, introducing argon into the vacuum chamber; 4) after the argon partial pressure stabilizes, energizing to excite the plasma and start deposition; 5) when the deposition is completed, de-energizing to stop exciting the plasma, and after the sample is cooled in the vacuum and argon-protected atmosphere, taking out the sample.

[0010] In the above process, taking a graphite rod as an example, after energizing, the argon is ionized to form free electrons, argon ions (Ar⁺), excited argon atoms (Ar), metastable argon atoms (Ar m ), and a large number of un-ionized neutral argon atoms. Among them, the positively charged Ar + ions are accelerated in the electric field between the positive electrode and the negative electrode (graphite rod target), and bombard the target to make the carbon atoms separate from the surface of the graphite rod.

[0011] Preferably, the carbon target is a graphite rod or a synthetic product mainly composed of carbon elements. For example, the purity of the graphite rod is higher than 99.9%.

[0012] Preferably, the carbon target comprises a plurality of carbon targets, and the plurality of carbon targets are arranged in an array around the sample. For example, the carbon target comprises 9 graphite rods, and is arranged in a 3x3 array directly above the sample.

[0013] Preferably, the carbon target is uniformly distributed around the sample surface; in particular, when the sample size is large, in order to uniformly deposit on each surface of the sample, the carbon target is arranged to be uniformly distributed around the sample.

[0014] Preferably, the position of the carbon target closest to the surface of the sample is 3mm-10mm, for example 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, from the surface of the sample.

[0015] Preferably, the vacuum chamber has a sample holder for holding the sample, and the sample holder has a cooling system.

[0016] Preferably, the vacuum degree is less than 5x10 -4 Pa.

[0017] Preferably, the purity of the argon gas is >99.99%.

[0018] Preferably, the argon gas partial pressure is considered stable when it reaches 15Pa-30Pa, for example 15Pa, 18Pa, 20Pa, 22Pa, 25Pa, 28Pa, 30Pa.

[0019] Preferably, the working power of the plasma physical vapor deposition device is less than 2 kW, for example 0.3KW, 0.5KW, 0.8KW, 1.0KW, 1.2KW, 1.5KW, 1.8KW, 1.9KW, which is determined by the current and voltage, i.e. the working power of the plasma device = working current x working voltage.

[0020] Preferably, the working current of the plasma physical vapor deposition device is in the range of 0.2A-2.0A, for example 0.2A, 0.4A, 0.6A, 0.8A, 1.0A, 1.5A, and the plasma physical vapor deposition device uses constant current mode.

[0021] Preferably, the working voltage of the plasma physical vapor deposition device is automatically adjusted according to the set current to maintain a constant current, and the working voltage is preferably in the range of 300V-800V, for example 300V, 350V, 400V, 450V, 500V, 550V, 600V, 650V, 700V, 750V, 800V.

[0022] Preferably, the deposition time is 5-15 minutes, for example 5 minutes, 6.5 minutes, 8 minutes, 9 minutes, 10 minutes, 12 minutes, 13.5 minutes, 15 minutes.

[0023] Preferably, the method further comprises: when the size and distribution density of the carbon particles deposited on the surface of the sample taken out are less than the preset requirement, the sample is put back into the vacuum chamber, and the above steps (3-5) are repeated again until the size and distribution density of the carbon particles on the surface of the sample taken out meet the preset requirement.

[0024] Preferably, the method further comprises: A transparent window and a cold light source are arranged on the vacuum chamber, wherein the outside of the transparent window is configured with a CMOS camera with a long-distance microscope lens, and the cold light source provides cold light irradiated on the sample surface. A software is configured to control the COMS camera to take pictures of the sample surface in the vacuum chamber from the outside of the transparent window after the deposition starts, and to identify whether the carbon particles on the sample surface meet the preset requirements according to the images obtained by the taking, and to control power-off when the preset requirements are met. Preferably, the software is further configured to receive a speckle preset requirement input by a user, to output deposition process parameters adapted to the speckle preset requirement by using a pre-trained machine learning model, and to control the plasma physical vapor deposition equipment to perform deposition according to the deposition process parameters.

[0025] In a second aspect of the present application, a device for preparing artificial speckles of amorphous nanometer carbon particles for micro-DIC is provided, comprising a physical vapor deposition equipment, wherein The physical vapor deposition equipment is configured with a vacuum chamber, and a transparent window and a cold light source are arranged on the vacuum chamber, wherein the outside of the transparent window is configured with a CMOS camera with a long-distance microscope lens, and the cold light source provides cold light irradiated on the sample surface. The physical vapor deposition equipment is configured with a software for controlling the COMS camera to take pictures of the sample surface in the vacuum chamber from the outside of the transparent window after the deposition starts, and for identifying whether the carbon particles on the sample surface meet the preset requirements according to the images obtained by the taking, and for controlling power-off when the preset requirements are met.

[0026] Preferably, the software is further configured to receive a speckle preset requirement input by a user, to output deposition process parameters adapted to the speckle preset requirement by using a pre-trained machine learning model, and to control the plasma physical vapor deposition equipment to perform deposition according to the deposition process parameters.

[0027] Advantages: The present application is based on a plasma-assisted physical vapor deposition equipment, and a method and device for preparing artificial speckles of amorphous nanometer carbon particles are developed for the first time. The method uses a carbon target as a target material, and by reasonably adjusting the operating parameters of the plasma physical vapor deposition equipment, artificial speckles with strong adhesion, uniform and dispersed distribution, high resolution, and the ability to be used with electron backscatter diffraction (EBSD) technology can be prepared. The technology has good stability, high repeatability, and the speckle size can be adjusted according to requirements, which can meet the needs of high-resolution micro-scale digital image correlation technology (DIC) and solve the deficiencies of the six existing micro-scale speckle preparation methods. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application and are incorporated herein for a purpose of explanations and of Complement to the application without limiting the present application. In the drawings: Figure 1 is the morphology and distribution of the artificial speckle of amorphous nanometer carbon particles prepared on a silicon wafer observed under a scanning electron microscope in Embodiment Six of the present application.

[0029] Figure 2 is the morphology and distribution of the artificial speckle of amorphous nanometer carbon particles prepared on low carbon steel observed under a scanning electron microscope in Embodiment Seven of the present application.

[0030] Figure 3 is the morphology and distribution of the artificial speckle of amorphous nanometer carbon particles prepared on low carbon steel through two rounds of repeated deposition observed under a scanning electron microscope in Embodiment Eight of the present application.

[0031] Figure 4 is the morphology and distribution of the artificial speckle of amorphous nanometer carbon particles observed under a scanning electron microscope in Embodiment Nine of the present application. DETAILED DESCRIPTION

[0032] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, “clockwise”, “counterclockwise” and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated by the terms must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms “first” and “second” are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by “first” and “second” can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of “multiple” is two or more, unless otherwise specifically limited.

[0034] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0035] The embodiment of the present application is to obtain high resolution, strong adhesion, uniform and dispersed distribution stability and not affect the electron backscattering signal without changing the microstructure of the material and without damaging the surface state of the material (such as surface integrity, influence on backscattering signal and influence on stress state, etc.).

[0036] Based on the existing microscale speckle manufacturing process, the above effects cannot be achieved. The applicant turns to other possible means to find a way to achieve the above effects, and finally successfully prepares an artificial speckle that meets the above effects by improving the existing technology of plasma assisted physical vapor deposition.

[0037] Physical vapor deposition is a series of technologies that vaporize solid materials into atomic, molecular or ionic state in vacuum environment, and then deposit them on the surface of workpiece to form thin films with special properties. The evaporation vaporization method mainly includes vacuum evaporation coating method using thermal energy, sputtering coating method using momentum transfer, and arc ion plating method using arc energy, including but not limited to resistance heating, high frequency induction heating, electron beam, laser beam, ion beam high energy bombardment, etc. Plasma assisted physical vapor deposition method has the advantages of not changing the microstructure of the material and not damaging the surface state of the material (such as surface integrity, influence on backscattering signal and influence on stress state, etc.). However, in the prior art, the plasma assisted physical vapor deposition method can only obtain dense thin film.

[0038] The embodiment of the application adopts plasma assisted physical vapor deposition method, which bombards the carbon target with high energy Ar + ions, and the gas phase carbon atoms bombarded out are deposited on the surface of the sample. Through the control of specific process, the deposition process and environment are changed, so that uniform and dispersed distribution of microscale carbon particle speckles are formed on the surface of the sample instead of dense thin film.

[0039] Plasma-assisted physical vapor deposition (PVA) is a technique that utilizes plasma to enhance or optimize traditional physical vapor deposition processes; it belongs to the sputtering deposition method. Films prepared using this technique exhibit high density, strong adhesion, low impurity content, and controllable structure and properties, and can deposit high-performance films on low-temperature substrates. In existing technologies, this method is primarily used for the deposition of dissimilar thin film materials, with applications including: preparation of coatings for tools and cutting tools; key thin film deposition in integrated circuit manufacturing; preparation of conductive and functional layers for liquid crystal displays, OLED displays, and touchscreens; optical coatings for lenses (cameras, microscopes, telescopes), spectacle lenses, filters, laser mirrors, reflectors, and architectural glass; preparation of thermal barrier coatings, wear-resistant coatings, and antioxidant coatings for aerospace and turbine engines; and preparation of coatings in the field of medical implants and devices to improve the biocompatibility, osseointegration, wear resistance, and corrosion resistance of implants. All of these applications utilize plasma-assisted physical vapor deposition to obtain a dense coating, with coating thickness ranging from nanometers to micrometers depending on the specific requirements.

[0040] Based on the aforementioned characteristics of plasma-assisted physical vapor deposition (PPVD), this technology is advantageous for obtaining deposited coatings with strong adhesion, which is one of the characteristics required for the artificial speckle pattern in this embodiment. Furthermore, the plasma operating temperature is relatively low, and the atomic release from the target material is mainly through a momentum transfer collision process, i.e., "physical sputtering." This produces a gaseous particle stream primarily composed of neutral atoms. The low plasma operating temperature, combined with the sample stage cooling system, ensures that the microstructure of the sample remains unchanged. This is also one of the requirements for the artificial speckle preparation method in this embodiment. Considering that the artificial speckle pattern required in this embodiment also possesses the characteristics of nanometer-sized diameter, amorphous structure, and uniform dispersion, this embodiment proposes process improvements to PPVD. Specifically, these improvements include precise control of deposition process parameters such as argon partial pressure, plasma operating current, and deposition time to obtain uniformly and dispersedly distributed nano-sized particles, and the use of carbon targets instead of metal targets to obtain amorphous carbon particles. These process improvements all contribute to the deposition of the desired artificial speckle pattern.

[0041] Example 1 This embodiment provides an artificial speckle preparation device for amorphous carbon nanoparticles used in micro-DIC, including a physical vapor deposition (PVD) device. The PVD device typically includes six modules: a vacuum chamber module, a vacuum system module, a plasma source and power supply module, a gas path and control system module, a substrate processing and temperature control module, and a control module.

[0042] The vacuum chamber module provides a clean, atmosphere-pollution-free working environment for the deposition process; the vacuum system module evacuates and maintains the vacuum chamber at a high vacuum or ultra-high vacuum state required for work; the plasma source and power supply module generates and maintains plasma for heating, sputtering or evaporating the target material; the gas path and control system module can accurately deliver and control the working gas and reaction gas into the vacuum chamber; the substrate processing and temperature control module can carry and move the sample and control its temperature to obtain the best deposition effect; the control module can automate the entire process and ensure the safety of the equipment and operators.

[0043] Embodiment Two In order to accurately control the deposition process, unlike the above-mentioned embodiment one, this embodiment is provided with a transparent window and a cold light source on the vacuum chamber, wherein the transparent window can be made of high optical quality materials such as fused quartz, which has high light transmittance and low fluorescence characteristics, and the cold light source provides cold light irradiation on the sample surface, which has the characteristics of extremely low heat generation, long service life, high brightness and stability. Specifically, the light can be guided into the vacuum chamber through an optical fiber light guide arm and irradiated onto the sample through a dedicated vacuum feedthrough interface. The transparent window is externally configured with a CMOS camera with a long-distance microscope lens, and a narrow-band filter is installed in front of the light source or the camera to allow only specific wavelengths of light to pass through. At the same time, a corresponding band-pass filter is installed in front of the CMOS camera, which can greatly suppress the background light emitted by the plasma, thereby obtaining a clear image with high signal-to-noise ratio.

[0044] Embodiment Three Although the amorphous carbon particles deposited on the sample surface are very small in size and need to be observed with a scanning electron microscope, the reflection effect of the sample surface on visible light will change at the macro scale with the change of the density of the carbon particles deposited on the sample surface. The higher the density of the deposited carbon particles, the worse the reflection effect of the sample surface, and the rougher the surface. Therefore, based on the influence law of the micro-scale sample surface amorphous carbon particle density on the macro-scale sample surface reflection effect, the carbon particle density deposited can be inferred by detecting the reflection effect of the sample surface with an optical camera. Specifically, a model of micro-scale particle density and macro-scale surface optical effect can be established through machine learning training to preliminarily detect the speckle effect of the deposition.

[0045] Therefore, on the basis of the above-mentioned embodiment two, the control module in this embodiment integrates a software for controlling the COMS camera to take pictures of the sample surface from the inside of the vacuum chamber to the outside of the transparent window after the deposition starts and identifying whether the carbon particles on the sample surface meet the preset requirements according to the images obtained by the shooting, and controlling the power-off when the preset requirements are met. Thus, the automation degree of the above-mentioned deposition process is higher.

[0046] Specifically, in the embodiments of the present application, by pre-adopting the conditions under which the COMS camera is located to take images of the surfaces of a large number of samples to obtain surface images, and by using a high-magnification scanning electron microscope to obtain microscopic images corresponding to the surface images to confirm the carbon particle parameters, a data set composed of the surface images and the carbon particle parameters (such as average diameter, density) is used as a training set to train a machine learning model to establish a relationship between the surface images and the carbon particle parameters, and then in the subsequent deposition process, by inputting the real-time obtained surface images into the machine learning model to output the corresponding carbon particle parameters, it is possible to realize the identification of whether the carbon particles on the surface of the sample meet the preset requirements according to the images obtained by shooting.

[0047] Embodiment Four In order to improve the automation of the deposition process, on the basis of the above-mentioned embodiment one, the control module in this embodiment integrates a software for receiving the speckle preset requirements input by the user, outputting the deposition process parameters adapted to the speckle preset requirements by using the pre-trained machine learning model, and controlling the plasma physical vapor deposition equipment to deposit according to the deposition process parameters.

[0048] The above-mentioned scheme relies on a pre-trained machine learning model, which is obtained by collecting historical data formed during the deposition process of a plurality of samples in advance and using the historical data as training materials for training. All parameters (including vacuum degree, gas pressure, inert gas concentration content, working current, working voltage, power, deposition time, sample table temperature, etc.) and final results (particle size, density, thickness, dispersion uniformity, etc. measured by a scanning electron microscope) of each deposition process are recorded. The machine learning model (such as random forest, neural network) is trained by using these historical data. After the training converges, the user only needs to input the target requirements (such as "I need a speckle with an average diameter of 150 nm and a density of 25 / μm²"), and the system can call the model, automatically calculate and recommend a set of optimal process parameters, and automatically control the operation according to the process parameters.

[0049] Embodiment Five Different from the above-mentioned embodiments, the control module in this embodiment integrates the functions of the control modules in embodiments three and four, that is, the control module in this embodiment integrates a software, which is used for receiving the speckle preset requirements input by the user, outputting the deposition process parameters adapted to the speckle preset requirements by using the pre-trained machine learning model, and controlling the plasma physical vapor deposition equipment to deposit according to the deposition process parameters, and on the other hand, after the deposition starts, controlling the COMS camera to take images of the sample surface in the vacuum chamber from outside the transparent window and identifying whether the carbon particles on the surface of the sample meet the preset requirements according to the images obtained by shooting, and controlling the power-off when the preset requirements are met.

[0050] The non-crystalline nanometer carbon particle artificial speckle preparation device of any one of the above embodiments 1 to 5 is used for artificial speckle preparation, which can at least include the following steps: 1) A carbon target is installed on the cathode of the plasma physical vapor deposition device, which is a high-purity graphite rod or a synthetic product mainly composed of carbon elements; 2) The polished and dried sample is placed in the vacuum chamber of the plasma physical vapor deposition device; 3) Start vacuumizing, when the vacuum degree reaches the required value, generally less than 5x10 -4 Pa, argon is introduced into the vacuum chamber, the higher the purity of argon, the better the quality of the obtained artificial speckle, therefore the purity of argon is preferably >99.99%; 4) After the argon partial pressure is stable, for example, reaches 15Pa-30Pa, the plasma working mode is selected as constant current mode, power on and control the working current in the range of 0.2A-2.0 A, the voltage and power will be automatically adjusted to maintain a constant working current (the working voltage is preferably in the range of 300V-800 V, and the power needs to be less than 2 kW), in this state, the plasma is excited, and the deposition is started; 5) Set the deposition time to 5-15 minutes, when the deposition is completed, the power is turned off to stop the excitation of the plasma, and after the sample is cooled in the vacuum and argon protection atmosphere, the sample is taken out.

[0051] In the above process, the control of the carbon atom escape rate is the key to the successful preparation of high-quality artificial speckles, and the carbon atom escape rate is directly affected by the concentration of high-energy Ar + ions in the plasma. The above combination of deposition process parameters can make the carbon atoms in the carbon target be bombarded out of the surface of the carbon target by high-energy Ar + ions in a relatively mild manner and gradually and uniformly deposited on the sample surface. Compared with the traditional process for obtaining dense films, the deposition speed is slower due to the lower working current and smaller power of the plasma, so the precise control of the deposition process can be realized.

[0052] In the above process, taking the graphite rod as an example, the number of graphite rods can be arranged as needed, for example, 9 graphite rods are arranged on the cathode in a 3x3 array.

[0053] Especially in the case of a larger sample volume, the graphite rods are preferably uniformly distributed around the sample surface.

[0054] The distance between the lowermost end of the graphite rod and the upper surface of the sample to be deposited can also be set as needed, which is set to 5 mm in this embodiment.

[0055] The carbon target is arranged to help ensure that the carbon atoms scattered by the bombardment are uniformly deposited on the sample surface, and to ensure uniform distribution of artificial speckles in a larger area.

[0056] In the above embodiments, the vacuum chamber has a sample holder for holding the sample, and the sample holder has a cooling system, such as a water-cooled cooling system. During deposition, cooling water is supplied to the sample holder to remove the heat transferred from the plasma to the sample, thereby preventing changes in the microstructure caused by excessive sample temperature.

[0057] In the above process, the operator can set the process parameters based on experience to control the deposition process. In order to effectively control the speckle effect and avoid excessive speckles, multiple short-time depositions can be used to gradually approach the preset requirements of the speckles. Therefore, the method further comprises: when the size and distribution density of the carbon particles deposited on the surface of the sample taken out are less than the preset requirements, the sample is placed back into the vacuum chamber, and steps 3-5) are repeated again until the size and distribution density of the carbon particles on the surface of the sample taken out meet the preset requirements.

[0058] For embodiments using devices provided with COMS cameras and corresponding control software as in Embodiments 2, 3, and 5, the control system can be used to automatically control vacuum pumping, gas supply, discharge, and after the deposition starts, the COMS camera can be controlled to take pictures of the sample surface from outside the transparent window into the vacuum chamber, and based on the images obtained by the taking, it can be determined whether the carbon particles on the sample surface meet the preset requirements, and when the preset requirements are met, the power supply can be controlled to be turned off, and when the sample cools to room temperature, the internal pressure can be restored to atmospheric pressure and the vacuum chamber can be opened.

[0059] For embodiments using devices as in Embodiments 4 and 5, the deposition process can also be controlled based on the deposition process parameters recommended by the machine learning model provided by the control system. In this way, the micro-DIC artificial speckle preparation device receives the preset requirements of the speckles through an interactive panel or the like, uses a pre-trained machine learning model to output deposition process parameters that are adapted to the preset requirements of the speckles, and controls the plasma physical vapor deposition equipment to deposit according to the deposition process parameters. This approach has less dependence on human experience and can efficiently obtain the desired speckles.

[0060] Embodiment 6 In this embodiment, a clean experimental silicon wafer is selected as the target sample.

[0061] 1) Install a graphite rod on the electrode of the plasma heating physical vapor deposition equipment; 2) Place the silicon wafer sample on the sample holder of the plasma heating physical vapor deposition equipment, close the vacuum chamber door, and start the vacuum pump and molecular pump in sequence to perform vacuum pumping; 3) When the vacuum degree is lower than 5*10 -4 Pa, open the argon switch, and introduce high-purity argon (content > 99.99%) into the vacuum chamber, adjust the argon flow rate, and ensure that the argon partial pressure in the vacuum chamber reaches 15 Pa; 4) After the argon partial pressure is stable, select the plasma working mode as the constant current mode, set the plasma working current to 0.5 A, open the plasma power switch, and start timing after the plasma is stable. At this time, the automatically matched working voltage is about 350 V.

[0062] 5) When the deposition time reaches 5 minutes, turn off the plasma device power, let the sample cool in the vacuum and argon-protected atmosphere, and after the vacuum chamber temperature drops to room temperature, turn off the argon switch and the vacuum pump group, and take out the sample.

[0063] The morphology and distribution of the artificial speckle of amorphous nanocarbon particles were observed under a scanning electron microscope, as shown in FIG. 1. Figure 1

[0064] Example Seven In this example, low-carbon steel is selected as the target sample.

[0065] 1) Install the graphite rod on the electrode of the plasma heating physical vapor deposition device; 2) After polishing the low-carbon steel sample with 200#, 800#, and 2000# sandpaper in turn, polish the sample with 1 μm diamond polishing paste. Then clean the sample surface with alcohol and acetone in turn to remove organic matter and other impurities on the sample surface, and then blow dry the residual liquid on the sample surface with cold air; 3) Place the polished low-carbon steel sample on the sample table of the plasma heating physical vapor deposition device, close the vacuum chamber door, and start the vacuum pump and molecular pump in turn to perform vacuum pumping; 4) When the vacuum degree is lower than 5*10 -4 Pa, open the argon switch, and introduce high-purity argon (content > 99.99%) into the vacuum chamber, adjust the argon flow rate, and ensure that the argon partial pressure in the vacuum chamber reaches 20 Pa; 5) After the argon partial pressure is stable, set the plasma working current to 0.8 A, open the plasma power switch, and start timing after the plasma is stable. At this time, the automatically matched working voltage is about 400 V.

[0066] 6) When the deposition time reaches 8 minutes, turn off the plasma device power, let the sample cool in the vacuum and argon-protected atmosphere, and after the vacuum chamber temperature drops to room temperature, turn off the argon switch and the vacuum pump group, and take out the sample.

[0067] ​The morphology and distribution of the amorphous nanocarbon particle artificial speckle were observed under a scanning electron microscope, as shown in Figure 2 .

[0068] Example Eight In this example, low carbon steel was selected as the target sample, and two rounds of repeated deposition were performed.

[0069] 1) Install a graphite rod on the electrode of the plasma heating physical vapor deposition device; 2) Grind the low carbon steel sample with 200#, 800#, and 2000# sandpaper in turn, then polish it with 1 μm diamond polishing paste. Clean the sample surface with alcohol and acetone in turn to remove organic matter and other impurities on the sample surface, then blow dry the residual liquid on the sample surface with cold air; 3) Place the polished low carbon steel sample on the sample stage of the plasma heating physical vapor deposition device, close the vacuum chamber door, and start the vacuum pump and molecular pump in turn to perform vacuum pumping; 4) After the vacuum degree is lower than 5×10 -4 Pa, open the argon switch, introduce high-purity argon (content > 99.99%) into the vacuum chamber, adjust the argon flow to ensure that the argon partial pressure in the vacuum chamber reaches 30 Pa; 5) After the argon partial pressure stabilizes, set the plasma working current to 1.0 A, turn on the plasma power switch, and start timing after the plasma stabilizes. The automatically matched working voltage is about 400 V at this time; 6) When the deposition time reaches 6 minutes, turn off the plasma device power, and let the sample cool in a vacuum and argon protective atmosphere; 7) After the vacuum chamber temperature drops to room temperature, repeat steps 5-6); 8) After the vacuum chamber temperature drops to room temperature, turn off the argon switch and the vacuum pump set, and take out the sample.

[0070] The morphology and distribution of the amorphous nanocarbon particle artificial speckle were observed under a scanning electron microscope, as shown in Figure 3 .

[0071] Example Nine In this example, low carbon steel was selected as the target sample.

[0072] 1) Install a graphite rod on the electrode of the plasma heating physical vapor deposition device; 2) Grind the low carbon steel sample with 200#, 800#, and 2000# sandpaper in turn, then polish it with 1 μm diamond polishing paste. Clean the sample surface with alcohol and acetone in turn to remove organic matter and other impurities on the sample surface, then blow dry the residual liquid on the sample surface with cold air; 3) Place the polished low-carbon steel sample onto the sample stage of the plasma-heated physical vapor deposition equipment, close the vacuum chamber door, and start the vacuum pump and molecular pump in sequence to evacuate the vacuum. 4) When the vacuum degree is lower than 5×10 -4 After Pa, turn on the argon gas switch and introduce high-purity argon gas (content >99.99%) into the vacuum chamber. Adjust the argon gas flow rate to ensure that the argon gas partial pressure in the vacuum chamber reaches 30 Pa. 5) After the partial pressure of argon gas stabilizes, set the plasma working current to 2.0 A, turn on the plasma power switch, and start timing after the plasma stabilizes. At this time, the automatically matched working voltage is about 400 V.

[0073] 6) When the deposition time reaches 15 minutes, turn off the power of the plasma equipment and allow the sample to cool in a vacuum and argon-protected atmosphere. After the temperature of the vacuum chamber drops to room temperature, turn off the argon switch and the vacuum pump group, and take out the sample.

[0074] The morphology and distribution of artificial speckle patterns on amorphous carbon nanoparticles were observed under a scanning electron microscope, such as... Figure 4 As shown.

[0075] Depend on Figures 1-4 It is known that plasma operating power, deposition time, and argon partial pressure all have a significant impact on the carbon particle density and particle diameter of speckle. Based on a large number of experimental results, we found that the carbon particle density (or particle diameter) of speckle roughly satisfies the following empirical formula with respect to plasma operating power, deposition time, and argon partial pressure: (1) In formula (1), p The density of carbon particles representing speckle patterns is expressed in units of (particles / μm). 2 ); P The plasma working power is determined by both the plasma working current and the working voltage (plasma working power = working voltage × working current). Indicates the partial pressure of argon gas; t Indicates the deposition time.

[0076] Since the adjustable range of argon partial pressure is small, the main factors affecting the density and diameter of speckled carbon particles are plasma operating power and deposition time. The density of speckled carbon particles is directly proportional to both plasma operating power and deposition time. The higher the power and the longer the deposition time, the higher the density of speckled carbon particles and the larger the diameter of carbon particles.

[0077] Using the above empirical formula, the ratio of each parameter on the right side of the formula can be quickly obtained by comparing the target carbon particle density with historical carbon particle densities. For example, if the target carbon particle density is... p 1. Select historical carbon particle densities slightly less thanp 1 and slightly more than p If the result of the combination of each parameter on the right side of the two corresponding empirical formulas of 1 and slightly more than 1 is A1 and A2, then the result of the combination of each parameter on the right side of the empirical formula corresponding to the target carbon particle density is between A1 and A2, and preferably the result of the combination of parameters is closer to A1 to start with.

[0078] The above merely provides an example of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

1. A method for preparing artificial speckle patterns using amorphous carbon nanoparticles for microscopic DIC, characterized in that, Artificial speckle patterns are formed by depositing carbon onto the sample surface using plasma-assisted physical vapor deposition (PEPV).

2. The method according to claim 1, characterized in that, Includes the following steps: 1) Mount the carbon target onto the cathode of the plasma physical vapor deposition equipment; 2) Place the polished and dried sample into the vacuum chamber of the plasma physical vapor deposition equipment; 3) Begin evacuating the vacuum chamber. Once the required vacuum level is reached, introduce argon gas into the vacuum chamber. 4) After the partial pressure of argon gas stabilizes, the plasma is excited by electricity, and deposition begins; 5) After deposition is complete, power off to stop plasma excitation. After the sample has cooled in a vacuum and argon-protected atmosphere, remove the sample.

3. The method according to claim 2, characterized in that, The carbon target is a graphite rod or a synthetic product mainly composed of carbon. Preferably, the carbon targets include multiple carbon targets, and the multiple carbon targets are arranged in an array distributed near the sample; Preferably, the carbon target is uniformly distributed around the sample surface; Preferably, the carbon target is located at a distance of 3mm-10mm from the sample surface.

4. The method according to claim 2, characterized in that, The vacuum chamber has a sample stage for supporting the sample, and the sample stage has a cooling system.

5. The method according to claim 2, characterized in that, The vacuum level is less than 5×10 -4 Pa; Preferably, the purity of the introduced argon gas is >99.99%; Preferably, the argon partial pressure is considered stable when it reaches 15Pa-30Pa.

6. The method according to claim 2, characterized in that, The power of the plasma physical vapor deposition equipment is less than 2 kW; The operating current of the plasma physical vapor deposition equipment is in the range of 0.2A-2.0A; Preferably, the operating voltage of the plasma physical vapor deposition equipment is in the range of 300V-800V.

7. The method according to claim 2, characterized in that, The deposition time is 5-15 minutes.

8. The method according to claim 3, characterized in that, The method further includes: when the size and distribution density of carbon particles deposited on the surface of the removed sample are less than the preset requirements, the sample is put back into the vacuum chamber and the above steps 3-5 are repeated until the size and distribution density of carbon particles on the surface of the removed sample meet the preset requirements.

9. The method according to claim 3, characterized in that, Also includes: A transparent viewing window and a cold light source are provided on the vacuum chamber, wherein a CMOS camera with a long-distance microscope lens is disposed outside the transparent viewing window, and the cold light source provides cold light illuminating the sample surface; and, The system is equipped with software that controls the CMOS camera to take pictures of the sample surface in the vacuum chamber from outside the transparent window after the deposition begins, and identifies whether the carbon particles on the sample surface meet the preset requirements based on the acquired images, and controls the power to be cut off when the preset requirements are met. Preferably, the software is also used to receive speckle preset requirements input by the user, output deposition process parameters adapted to the speckle preset requirements using a pre-trained machine learning model, and control the plasma physical vapor deposition equipment to perform deposition according to the deposition process parameters.

10. A device for preparing artificial speckle patterns of amorphous carbon nanoparticles for micro-DIC, characterized in that, Including physical vapor deposition equipment, among which, The physical vapor deposition apparatus is equipped with a vacuum chamber, on which a transparent window and a cold light source are provided. A CMOS camera with a long-distance microscope lens is arranged outside the transparent window, and the cold light source provides cold light to illuminate the sample surface. The physical vapor deposition equipment is equipped with software for controlling the CMOS camera to take pictures of the sample surface in the vacuum chamber from outside the transparent window after the deposition begins, and to identify whether the carbon particles on the sample surface meet the preset requirements based on the acquired images, and to control the power off when the preset requirements are met. Preferably, the software is also used to receive speckle preset requirements input by the user, output deposition process parameters adapted to the speckle preset requirements using a pre-trained machine learning model, and control the plasma physical vapor deposition equipment to perform deposition according to the deposition process parameters.

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