SEM sample preparation method for micro-nano sample morphology characterization

Abstract

The invention provides an SEM sample preparation method for micro-nano sample morphology characterization. According to the SEM sample preparation method, the adopted solvent is at least one of acetone, ethanol and methanol, and the solvents are liquid with low tension, low boiling point, high vapor pressure and low viscosity; the included angle between the conductive substrate and the horizontal plane is 15-45 degrees; the rapid evaporation effect is achieved by using specific solvents such as acetone, ethanol and methanol, and the micro-nano sample can be uniformly distributed on the conductive substrate in a manner of dropwise adding the dispersion liquid to the surface of the conductive substrate which is obliquely placed at an included angle of 15-45 degrees, so that the coffee ring effect is avoided, and the uniformity and integrity of the surface structure of the micro-nano sample are ensured. The method reduces the particle aggregation of the micro-nano sample, improves the surface quality of the micro-nano sample, is suitable for high-resolution morphology observation, can present a clearer and finer micro-nano structure especially in SEM, AFM and other characterization, and is beneficial to accurate analysis of the structural characteristics of the micro-nano sample.

Description

Technical Field

[0001] The invention belongs to the technical field of surface morphology analysis, and in particular relates to a SEM sample preparation method for characterizing the morphology of micro-nano samples. Background Art

[0002] Scanning electron microscopy (SEM) sample preparation is crucial in scientific research, particularly in the fields of nanomaterials, surface science, microstructure analysis, and material characterization. SEM sample preparation not only provides researchers with a deep understanding of a material's micromorphology, structural properties, and compositional distribution, but also provides reliable data for subsequent experiments and research. Microstructures directly influence a material's physical and chemical properties. By precisely controlling these structures, researchers can tailor material properties to suit specific application requirements.

[0003] Currently, water is usually used as a solvent for SEM sample preparation when characterizing the morphology of micro-nano samples. When water is used as a solvent, a strong coffee ring effect often occurs during the evaporation process, causing the micro-nano sample particles to move to the edge of the substrate and deposit, resulting in uneven distribution of the micro-nano samples, affecting the analysis of the microscopic morphology and structural characteristics of the micro-nano samples during subsequent SEM characterization. Summary of the Invention

[0004] In order to address the defects existing in the prior art, the present invention provides a SEM sample preparation method for characterizing the morphology of micro-nano samples. The method uses liquids with low tension, low boiling point, high vapor pressure, and low viscosity, such as acetone, ethanol, and methanol, as solvents. These solvents have high volatility at room temperature, fast evaporation rate, and low surface tension. When the dispersion liquid is dropped onto the surface of a conductive substrate, it evaporates rapidly, causing the solvent molecules to quickly leave, and the remaining micro-nano samples will leave traces on the surface. Due to the fast evaporation rate of acetone, ethanol, and methanol, the interaction force between the molecules has not yet caused the aggregation of the micro-nano samples, thereby maintaining a uniform distribution of the micro-nano samples.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0007] dispersing the micro-nano sample into a solvent to obtain a dispersion;

[0008] The conductive substrate is placed at an angle of 15 to 45 degrees to the horizontal plane;

[0009] The dispersion was added dropwise onto the surface of a tilted conductive substrate, and after the solvent evaporated, the SEM sample was prepared and the SEM test was performed.

[0010] Wherein, the solvent includes at least one of acetone, ethanol and methanol.

[0011] Preferably, before adding the dispersion dropwise onto the surface of the inclined conductive substrate, the conductive substrate is further plasma cleaned.

[0012] Preferably, the mass fraction of the micro-nano sample in the dispersion is 0.01-0.0001%.

[0013] Preferably, the micro-nano sample includes any one of SiO2 nanospheres, graphene oxide nanosheets, MOF, and MXene-TiO2.

[0014] Preferably, if the micro-nano sample is SiO2 nanospheres, the solvent is acetone;

[0015] If the micro-nano sample is graphene oxide nanosheets, the solvent is ethanol;

[0016] If the micro-nano sample is MOF, the solvent is acetone;

[0017] If the micro-nano sample is MXene-TiO2, the solvent is acetone.

[0018] Preferably, the diameter of the SiO2 nanospheres is 50-500 nm:

[0019] The diameter of the graphene oxide nanosheets is 0.1-6 μm:

[0020] The diameter of the MOF is 1~6 μm:

[0021] The diameter of the MXene-TiO2 is 0.2~10 μm.

[0022] Preferably, the conductive substrate is a silicon wafer with a gold-plated surface.

[0023] Preferably, the plasma cleaning control process is: gas pressure of 0.1~10 Pa, gas flow of 5~50sccm, gas source of one or more of O2, Ar, N2; cleaning time of 10~20 min, cleaning temperature of 30~50℃, power of 50~150W.

[0024] Preferably, the dispersion is added dropwise to the surface of the conductive substrate placed at an angle so that the dispersion spreads evenly on the surface of the conductive substrate, and then the dispersion is added dropwise to the surface of the conductive substrate. After the solvent evaporates, the SEM sample is prepared and the SEM test is performed;

[0025] The volume of the dispersion added each time was 0.5~50 μL.

[0026] The SEM sample preparation method for characterizing the morphology of micro-nano samples of the present invention has the following effects compared with the prior art:

[0027] 1. The SEM sample preparation method for characterizing the morphology of micro-nano samples of the present invention uses at least one solvent selected from acetone, ethanol, and methanol, which are low-tension, low-boiling-point, high-vapor-pressure, and low-viscosity liquids. These solvents are highly volatile at room temperature, evaporate rapidly, and have low surface tension. When the dispersion is added dropwise to the surface of a conductive substrate, it evaporates rapidly, causing the solvent molecules to quickly leave, leaving traces of the remaining micro-nano sample on the surface. Due to the rapid evaporation of acetone, ethanol, and methanol, the interaction between the molecules does not yet cause aggregation of the micro-nano sample, thereby maintaining a uniform distribution of the micro-nano sample and facilitating analysis of the microscopic morphology and structural characteristics of the micro-nano sample during SEM characterization.

[0028] 2. The SEM sample preparation method for characterizing the morphology of micro-nano samples of the present invention has a conductive substrate with an angle of 15 to 45 degrees to the horizontal plane, which has obvious advantages in the field of morphological characterization of micro-nano samples. By using specific solvents such as acetone, ethanol, and methanol to achieve the effect of rapid evaporation, and combining the method of adding the dispersion dropwise to the surface of the conductive substrate tilted at an angle of 15 to 45 degrees, the micro-nano samples can be evenly distributed on the conductive substrate, avoiding the coffee ring effect and ensuring the uniformity and integrity of the surface structure of the micro-nano samples. This method reduces the aggregation of micro-nano sample particles, improves the surface quality of micro-nano samples, and is suitable for high-resolution morphological observation. In particular, in characterizations such as SEM and AFM, it can present clearer and finer micro-nano structures, which helps to accurately analyze the structural characteristics of micro-nano samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0030] Figure 1 Schematic diagram of adding dispersion when the gold-coated silicon wafer is tilted 15 to 45 degrees;

[0031] Figure 2 This is a photo of adding dispersion liquid onto a gold-coated silicon wafer;

[0032] Figure 3 SEM images of dispersions with concentrations of 1 / 100,000 and 1 / 1,000,000 obtained by using ethanol as a solvent according to the method in Example 1 after being dropwise added to an inclined conductive substrate;

[0033] Figures 4 and 5 According to the method in Example 2, acetone or ethanol ( Figures 4 and 5 SEM images at different magnifications after a dispersion with a concentration of 1 / 100,000 (ethanol on the left and acetone on the right) was added dropwise to an inclined conductive substrate;

[0034] Figure 6 SEM images at different viewing angles of a dispersion obtained by using acetone as a solvent and having a concentration of 1 / 100,000 obtained by the method in Example 3 and added dropwise to an inclined conductive substrate;

[0035] Figure 7 In accordance with the method of Example 4, acetone or ethanol ( Figure 7 SEM image of a dispersion with a concentration of 1 / 100,000 obtained by adding ethanol (left side in the middle, acetone (right side)) as a solvent to a conductive substrate placed at an angle;

[0036] Figure 8 SEM images at different magnifications of a dispersion liquid with a concentration of 1 / 100,000 obtained by using water as a solvent according to the method in Comparative Example 1 and added dropwise to an inclined conductive substrate;

[0037] Figure 9 This is a SEM image of the conductive substrate with an angle of 5° to the horizontal plane according to the method in Comparative Example 2, after the dispersion is dropped onto the conductive substrate with an inclination angle of only 5°;

[0038] Figure 10 This is a SEM image of the conductive substrate with an angle of 60° to the horizontal plane according to the method in Comparative Example 2, after the dispersion is dropped onto the conductive substrate with an angle of 60°. DETAILED DESCRIPTION

[0039] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with the specific embodiments. Preferred embodiments of the present invention are provided in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0040] The order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be understood as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0041] The present invention provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0042] S1, dispersing the micro-nano sample into a solvent to obtain a dispersion;

[0043] S2. Place the conductive substrate at an angle of 15 to 45 degrees to the horizontal plane;

[0044] S3, adding the dispersion dropwise to the surface of the conductive substrate placed at an angle, waiting for the solvent to evaporate, completing SEM sample preparation, and performing SEM testing;

[0045] Wherein, the solvent includes at least one of acetone, ethanol and methanol.

[0046] The SEM sample preparation method for characterizing the morphology of micro-nano samples of the present invention uses at least one of acetone, ethanol, and methanol as a solvent, and these solvents are liquids with low tension, low boiling point, high vapor pressure, and low viscosity. These solvents are highly volatile at room temperature, evaporate quickly, and have low surface tension. When a dispersion liquid is dropwise added to the surface of a conductive substrate, it evaporates rapidly, causing the solvent molecules to quickly leave, and the remaining micro-nano sample will leave traces on the surface. Since the evaporation rates of acetone, ethanol, and methanol are very fast, the interaction forces between the molecules have not yet caused the aggregation of the micro-nano sample, thereby maintaining a uniform distribution of the micro-nano sample and facilitating analysis of the microscopic morphology and structural characteristics of the micro-nano sample during SEM characterization.

[0047] If water is used as the solvent, a strong coffee ring effect will be produced during the evaporation process. This is because the surface tension of water is large, the evaporation rate is slower in the center of the dispersion, and the solvent at the edge of the dispersion evaporates faster, causing the particles to move to the edge and deposit, resulting in uneven distribution of micro-nano samples.

[0048] Furthermore, the conductive substrate of the present invention has an angle of 15 to 45 degrees with the horizontal plane. When the dispersion is dropped onto the conductive substrate, the angle of 15 to 45 degrees can make the dispersion diffuse along the surface of the conductive substrate. Compared with the flat spreading method (i.e., the angle is 0 degrees), the inclined angle can better promote the dispersion to spread more widely on the surface of the conductive substrate, thereby avoiding the dispersion from being concentrated in a small area.

[0049] The reason for adding the dispersion dropwise onto the surface of a conductive substrate tilted at an angle of 15 to 45 degrees is that the preparation process is simpler and faster than traditional spin coating, tablet pressing, etc., and it does not damage the sample, and the resulting sample is more uniform. The principle is to regulate the balance between gravity and capillary action: the gravity component drives the flow of the dispersion: after the conductive substrate is tilted, gravity is no longer perpendicular to the surface, but is decomposed into two components: the component perpendicular to the surface: which keeps the dispersion close to the conductive substrate. The component parallel to the surface: this component is the main driving force for the liquid to flow downward along the inclined surface of the conductive substrate. The larger the angle, the larger the parallel component and the stronger the driving force. This angle range of 15 to 45 degrees provides moderate gravity drive.

[0050] 1. Assist and guide capillary spreading: Use gravity to give the dispersion a clear downward direction, guiding the dispersion to flow downward stably and controllably along the surface of the conductive substrate.

[0051] 2. Ensure coverage speed and uniformity: The dispersion liquid is sufficiently driven to evenly cover the entire silicon wafer surface within a few seconds (using low viscosity and high wettability such as acetone or ethanol) under the coordination of capillary action, forming a relatively uniform thin liquid film layer.

[0052] 3. Avoid the problem of excessive flow: Prevent uneven film thickness, particle scouring, increased agglomeration and uncontrolled volatilization caused by excessive dispersion flow rate.

[0053] 4. An angle of 15-45° can also mitigate the "coffee ring effect" to a certain extent: at an angle of 15-45°, the dispersion front advances evenly, and the solvent evaporation front remains parallel to the contact line (the contact line refers to the interface between the solid, gas, and liquid phases, i.e., the boundary between the dispersion, the conductive substrate, and the air). Horizontal dripping of the dispersion can cause pinning of the contact line, pulling the micro-nano sample outward and forming a ring-shaped aggregate.

[0054] The SEM sample preparation method for characterizing the morphology of micro-nano samples of the present invention has significant advantages in the field of micro-nano sample morphology characterization. By using specific solvents such as acetone, ethanol, and methanol to achieve rapid evaporation, and combining the method of adding the dispersion dropwise to the surface of a conductive substrate tilted at an angle of 15 to 45 degrees, the micro-nano sample can be evenly distributed on the conductive substrate, avoiding the coffee ring effect and ensuring the uniformity and integrity of the micro-nano sample surface structure. This method reduces micro-nano sample particle aggregation, improves the surface quality of micro-nano samples, and is suitable for high-resolution morphology observation. In particular, in characterizations such as SEM and AFM, it can present clearer and finer micro-nano structures, facilitating the precise analysis of the structural characteristics of micro-nano samples.

[0055] In some embodiments, before adding the dispersion dropwise onto the surface of the inclined conductive substrate, the method further includes plasma cleaning the conductive substrate.

[0056] In some embodiments, the mass fraction of the micro-nano sample in the dispersion is 0.01-0.0001%. The micro-nano sample is dispersed in a solvent, and the solution is ultrasonically treated using an ultrasonic processor to help the micro-nano sample be completely dispersed in the solution.

[0057] In some embodiments, the micro-nano sample includes any one of SiO2 nanospheres, graphene oxide nanosheets, MOF (metal organic framework material), and MXene-TiO2.

[0058] Specifically, the MOF (metal organic framework material) is ZIS (zinc indium sulfide ZnIn2S4), and its preparation method is:

[0059] 1 mL of 1 mM ZnCl2 aqueous solution, 1 mL of 2 mM InCl3 aqueous solution, and 1 mL of 4 mM thioacetamide aqueous solution were added to a mixed solvent (a mixed solvent of 2.5 mL ethylene glycol and 7.5 mL DMF), heated at 160°C for 12 hours, and washed alternately by centrifugation with deionized water and ethanol. The product was dried in a vacuum drying oven at 60°C overnight to obtain MOF (metal-organic framework material) ZIS.

[0060] In some embodiments, the preparation method of MXene-TiO2 is:

[0061] S1. Add 2 g of LiF to 40 mL of 9 M hydrochloric acid and stir continuously for 30 minutes to obtain an etchant; gradually add 2 g of MAX powder (specifically Ti3AlC2) to the above etchant over 5 minutes, and react at 35°C for 24 hours to obtain a mixture;

[0062] S2. Washing with deionized water: The mixture obtained in step 1) was washed multiple times with deionized water by centrifugation (3500 rpm, 10 min each time); after each wash, the pH of the supernatant was measured until the pH of the supernatant was ≥5, and the supernatant was removed as waste by dumping, and the lower precipitate was collected;

[0063] S3, ethanol sonication: add ethanol to the precipitate obtained in step 2), sonicate for 60 min, centrifuge (10000 rpm, 10 min), remove the supernatant as waste by pouring, and collect the lower precipitate;

[0064] S4. Collect MXene: Deionized water was added to the precipitate obtained in step S3 again, and the mixture was ultrasonicated for 20 min. The mixture was centrifuged at 3500 rpm for 3 min. A dark green supernatant was observed. The supernatant was collected and freeze-dried to obtain powdered MXene.

[0065] S5. Preparation of TiO2-MXene: The powdered MXene obtained in step S4 was placed in a muffle furnace and calcined at 400° C. for 30 min to obtain TiO2-MXene.

[0066] In some embodiments, if the micro-nano sample is SiO2 nanospheres, the solvent is acetone;

[0067] In some embodiments, if the micro-nano sample is graphene oxide nanosheets, the solvent is ethanol;

[0068] In some embodiments, if the micro-nano sample is MOF, the solvent is acetone;

[0069] In some embodiments, if the micro-nano sample is MXene-TiO2, the solvent is acetone.

[0070] For different micro- and nano-samples, the right solvent should be selected. Even acetone and ethanol, both low-tension, low-boiling-point, high-vapor-pressure, and low-viscosity liquids, exhibit varying dispersion effects on different materials. For example, acetone disperses SiO2 nanospheres much better than ethanol. Compared to ethanol, acetone has a lower boiling point and a faster evaporation rate. Rapidly evaporating acetone removes particles more quickly, significantly shortening the window of time during which particles may reaggregate due to capillary forces in a humid state. Ethanol evaporates slowly and remains for a long time, making particles more susceptible to aggregation due to strong capillary forces in the later stages of solvent evaporation. For graphene oxide nanosheets, the more polar ethanol is a desirable solvent.

[0071] The advantage of choosing a low-tension, low-boiling-point, high-vapor-pressure, low-viscosity liquid as a solvent is that after drying, no residue remains on the silicon wafer, ensuring the purity of the test sample and preventing any impact on the imaging of micro- and nano-sample morphologies. However, using polymers (including polyvinylpyrrolidone, sodium carboxymethylcellulose, and polyvinylidene fluoride) as solvents does not evaporate after drying, and residues remain on the conductive substrate, resulting in a decrease in overall conductivity and significantly affecting SEM imaging quality.

[0072] In some embodiments, the diameter of the SiO2 nanospheres is 50-500 nm:

[0073] The diameter of graphene oxide nanosheets is 0.1~6 μm:

[0074] The diameter of MOF is 1~6 μm:

[0075] The diameter of MXene-TiO2 is 0.2~10 μm.

[0076] In some embodiments, the conductive substrate is a silicon wafer with a gold-plated surface (ie, a gold-plated silicon wafer). The gold-plated silicon wafer is not the only selectable material. Any material with a smooth surface and a certain degree of conductivity can be used as the substrate.

[0077] In some embodiments, the plasma cleaning control process is: gas pressure of 0.1~10 Pa, gas flow of 5~50sccm, gas source of one or more of O2, Ar, and N2; cleaning time of 10~20 min, cleaning temperature of 30~50°C, and power of 50~150W.

[0078] Specifically, a square gold-plated silicon wafer with a size of 5 mm × 5 mm (i.e., both length and width are 5 mm) is removed from the packaging film and cleaned using a plasma cleaning machine to obtain a clean, flat, and well-wettable surface.

[0079] Reasons for using gold-coated silicon wafers as substrates and plasma cleaning:

[0080] Gold-coated silicon wafers have very high electrical conductivity, providing stable and uniform conductivity during experiments. This is crucial for studying the electrical properties of micro- and nanoscale samples, such as charge transport and conductivity measurements. Furthermore, gold-coated silicon wafers are chemically stable and do not react readily with atmospheric substances (such as oxygen and moisture). Therefore, they provide a stable surface that is relatively unaffected by environmental influences, avoiding the problem of silicon surface oxidation. Gold's chemical inertness makes it less reactive with substances in solution. This is particularly true when dispersing micro- and nanoscale samples. The gold surface exhibits minimal adsorption of solvents and micro- and nanoscale samples, which helps achieve uniform distribution of micro- and nanoscale samples. Commercial gold-coated silicon wafers are typically bonded to the encapsulating film using an adhesive. Removal of the film may leave residual adhesive or other organic matter, which can affect subsequent experimental results. Plasma cleaning is commonly used to ensure a clean, flat, and free surface free of organic impurities. Plasma cleaning involves inducing discharges in a gas, generating reactive particles such as ions, electrons, and free radicals. These reactive particles react with the silicon wafer surface, removing contaminants, residual adhesive, and organic matter. Furthermore, plasma treatment enhances the wettability of the gold-coated silicon wafer surface, allowing the ethanol solution to spread more easily across the surface, ensuring uniform distribution of micro- and nano-samples.

[0081] In some embodiments, the dispersion is added dropwise to the surface of a conductive substrate placed at an angle so that the dispersion spreads evenly on the surface of the conductive substrate. Then, the dispersion is added dropwise to the surface of the conductive substrate. After the solvent evaporates, SEM sample preparation is completed and SEM testing is performed.

[0082] The volume of the dispersion added each time was 0.5~50 μL.

[0083] Use a pipette to take 0.5~50 μL of dispersion each time, twice in total, and tilt the cleaned gold-coated silicon wafer at 15~45 degrees. The dispersion is dripped from the top of the silicon wafer. At this time, the dispersion will quickly cover the entire silicon wafer. Then quickly titrate the dispersion for the second time. After the dispersion is completely evaporated, SEM testing can be performed.

[0084] Furthermore, a single drop of 2.5 μL ensures that the dispersion covers the entire substrate without causing uneven distribution of the solution on the silicon wafer. Adding too much solution can cause surface aggregation and uneven edges, while too little may not cover the entire substrate. By adding 2.5 μL droplets in two steps, the spreading and evaporation of the dispersion can be more precisely controlled. The first 2.5 μL droplet will partially cover the silicon wafer surface, while the second 2.5 μL droplet further smoothes and evenly distributes the solution, ensuring that the micro-nano sample is evenly distributed on the substrate surface.

[0085] Specifically, such as Figure 1As shown, it shows a schematic diagram of adding dispersion liquid when the gold-coated silicon wafer is tilted 15~45°.

[0086] like Figure 2 As shown, it is a real picture of adding dispersion liquid on the gold-coated silicon wafer.

[0087] The following further illustrates the SEM sample preparation method for characterizing the morphology of micro- and nano-samples of the present invention using specific examples. This section further illustrates the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means employed in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment employed in the present invention are conventional in the art.

[0088] The gold-plated silicon wafers in the following examples and comparative examples were purchased from Harbin Tebo Technology Co., Ltd. and had a size of 5 mm × 5 mm (i.e., both the length and width were 5 mm);

[0089] SiO2 nanospheres were purchased from Jiangsu Yuante New Material Technology Co., Ltd. with a diameter of 50-500 nm.

[0090] Graphene oxide nanosheets were purchased from Sanya Hanxi Graphene Technology Research Institute Co., Ltd., with a diameter of 0.1~6μm:

[0091] The MOF (metal organic framework material) is ZIS (zinc indium sulfide ZnIn2S4), prepared as above, with a diameter of 1~6 μm;

[0092] The preparation method of MXene-TiO2 is the same as above, and its diameter is 0.2~10 μm.

[0093] In the following examples and comparative examples, the plasma cleaning process was controlled as follows: gas pressure of 2 Pa, gas flow of 10 sccm, Ar gas source; cleaning time of 10 min, cleaning temperature of 30° C., and power of 80 W.

[0094] Example 1

[0095] This embodiment provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0096] S1. Dispersing graphene oxide sheets in ethanol to obtain a dispersion; the mass fraction of the graphene oxide sheets in the dispersion is 1 / 100000 or 1 / 1000000;

[0097] S2. Plasma cleaning the conductive substrate (specifically, a gold-plated silicon wafer);

[0098] The plasma-cleaned conductive substrate is placed at an angle of 40° to the horizontal plane;

[0099] S3. Add 2.5 μL of dispersion onto the surface of an inclined conductive substrate (add the dispersion from the highest end of the conductive substrate). The dispersion will quickly cover the entire silicon wafer. Then add another 2.5 μL of dispersion onto the surface of the conductive substrate. Wait for the solvent to evaporate, complete the SEM sample preparation, and perform SEM testing.

[0100] like Figure 3 As shown, it is an SEM picture of dispersions with concentrations of 1 / 100000 and 1 / 1000000 obtained by using ethanol as a solvent according to the method in Example 1 and then added dropwise to a conductive substrate placed at an angle.

[0101] from Figure 3 It can be seen that graphene oxide is evenly dispersed and no coffee rings appear.

[0102] Example 2

[0103] This embodiment provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0104] S1. Dispersing SiO2 nanoparticles in acetone (or ethanol) to obtain a dispersion; the mass fraction of SiO2 nanoparticles in the dispersion is 1 / 100000;

[0105] S2. Plasma cleaning the conductive substrate (specifically, a gold-plated silicon wafer);

[0106] The plasma-cleaned conductive substrate is placed at an angle of 40° to the horizontal plane;

[0107] S3. Add 2.5 μL of dispersion onto the surface of an inclined conductive substrate (add the dispersion from the highest end of the conductive substrate). The dispersion will quickly cover the entire silicon wafer. Then add another 2.5 μL of dispersion onto the surface of the conductive substrate. Wait for the solvent to evaporate, complete the SEM sample preparation, and perform SEM testing.

[0108] like Figures 4 and 5 As shown, it is SEM images at different magnifications after a dispersion with a concentration of 1 / 100000 obtained by using acetone or ethanol as a solvent according to the method in Example 2 is added dropwise to a conductive substrate placed at an angle.

[0109] Figures 4 and 5 The left side of the figure shows ethanol as the solvent, and the right side shows acetone as the solvent.

[0110] from Figures 4 and 5It can be seen that for SiO2 nanospheres, the dispersion effect of acetone solvent is much better than that of ethanol. Compared with ethanol, acetone has a lower boiling point and a faster volatilization rate. The rapidly evaporating acetone can be removed from between the particles more quickly, greatly shortening the time window in which the particles may re-aggregate due to capillary forces in a humid state; while ethanol evaporates slowly and has a long residual time, and the particles are more easily pulled together by the strong capillary force in the later stage of solvent evaporation.

[0111] Example 3

[0112] This embodiment provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0113] S1. Dispersing MOF (specifically ZIS (zinc indium sulfide ZnIn2S4)) in acetone to obtain a dispersion; the mass fraction of MOF in the dispersion is 1 / 100000;

[0114] S2. Plasma cleaning the conductive substrate (specifically, a gold-plated silicon wafer);

[0115] The plasma-cleaned conductive substrate is placed at an angle of 40° to the horizontal plane;

[0116] S3. Add 2.5 μL of dispersion onto the surface of an inclined conductive substrate (add the dispersion from the highest end of the conductive substrate). The dispersion will quickly cover the entire silicon wafer. Then add another 2.5 μL of dispersion onto the surface of the conductive substrate. Wait for the solvent to evaporate, complete the SEM sample preparation, and perform SEM testing.

[0117] like Figure 6 As shown, it is SEM images at different viewing angles of a dispersion liquid with a concentration of 1 / 100000 obtained by using acetone as a solvent according to the method in Example 3 and then added dropwise to a conductive substrate placed at an angle.

[0118] from Figure 6 It can be seen that the MOF is evenly dispersed and no coffee rings appear.

[0119] Example 4

[0120] This embodiment provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0121] S1. Dispersing MXene-TiO2 in acetone (or ethanol) to obtain a dispersion; the mass fraction of MXene-TiO2 in the dispersion is 1 / 100000;

[0122] S2. Plasma cleaning the conductive substrate (specifically, a gold-plated silicon wafer);

[0123] The plasma-cleaned conductive substrate is placed at an angle of 40° to the horizontal plane;

[0124] S3. Add 2.5 μL of dispersion onto the surface of an inclined conductive substrate (add the dispersion from the highest end of the conductive substrate). The dispersion will quickly cover the entire silicon wafer. Then add another 2.5 μL of dispersion onto the surface of the conductive substrate. Wait for the solvent to evaporate, complete the SEM sample preparation, and perform SEM testing.

[0125] like Figure 7 As shown, it is a SEM picture of a dispersion liquid with a concentration of 1 / 100000 obtained by using acetone or ethanol as a solvent according to the method in Example 4 and then added dropwise to a conductive substrate placed at an angle.

[0126] Figure 7 The left side of the figure shows ethanol as the solvent, and the right side shows acetone as the solvent.

[0127] from Figure 7 It can be seen that when ethanol is used as the solvent, MXene-TiO2 undergoes significant agglomeration, while when acetone is used as the solvent, there is no obvious agglomeration.

[0128] Comparative Example 1

[0129] This comparative example provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0130] S1. Dispersing graphene oxide sheets in water to obtain a dispersion; the mass fraction of the graphene oxide sheets in the dispersion is 1 / 100000;

[0131] S2. Plasma cleaning the conductive substrate (specifically, a gold-plated silicon wafer);

[0132] The plasma-cleaned conductive substrate is placed at an angle of 40° to the horizontal plane;

[0133] S3. Add 2.5 μL of dispersion onto the surface of an inclined conductive substrate (add the dispersion from the highest end of the conductive substrate). The dispersion will quickly cover the entire silicon wafer. Then add another 2.5 μL of dispersion onto the surface of the conductive substrate. Wait for the solvent to evaporate, complete the SEM sample preparation, and perform SEM testing.

[0134] like Figure 8 As shown, it is SEM images at different magnifications after a dispersion liquid with a concentration of 1 / 100000 is obtained by using water as a solvent according to the method in Comparative Example 1 and is added dropwise to a conductive substrate placed at an angle.

[0135] As can be seen from Figure 8, water as a solvent often produces a strong coffee ring effect during the evaporation process. This is because the surface tension of water is large, the evaporation rate is slower in the center of the droplet, and the solvent at the edge of the droplet evaporates faster, causing the particles to move to the edge and deposit.

[0136] Comparative Example 2

[0137] This comparative example provides a SEM sample preparation method for characterizing the morphology of micro-nano samples, comprising the following steps:

[0138] S1. Dispersing graphene oxide sheets in ethanol to obtain a dispersion; the mass fraction of the graphene oxide sheets in the dispersion is 1 / 100000;

[0139] S2. Plasma cleaning the conductive substrate (specifically, a gold-plated silicon wafer);

[0140] Place the plasma-cleaned conductive substrate at an angle of 5° (or 60°) to the horizontal plane;

[0141] S3. Add 2.5 μL of dispersion onto the surface of an inclined conductive substrate (add the dispersion from the highest end of the conductive substrate). The dispersion will quickly cover the entire silicon wafer. Then add another 2.5 μL of dispersion onto the surface of the conductive substrate. Wait for the solvent to evaporate, complete the SEM sample preparation, and perform SEM testing.

[0142] like Figure 9 As shown, it is an SEM image after the conductive substrate is tilted at an angle of 5° (less than 15°) to the horizontal plane according to the method in Comparative Example 2, and the dispersion is dropped onto the conductive substrate with an inclination angle of only 5° (SEM comparison images of graphene oxide sheets on the upper and lower parts of the silicon wafer);

[0143] like Figure 10 As shown, it is an SEM image after the dispersion is dropped onto a conductive substrate with an inclination angle of 60° (greater than 45°) according to the method in Comparative Example 2 (SEM comparison images of graphene oxide sheets on the upper and lower parts of the silicon wafer).

[0144] from Figure 9 It can be seen that when the conductive substrate is tilted at an angle less than 15° (specifically 5°), most of the graphene oxide nanosheets are deposited on the upper part of the silicon wafer, and a certain degree of coffee rings are formed, in which the graphene oxide nanosheets are stacked together, while only a few graphene oxide nanosheets are scattered on the lower part of the silicon wafer.

[0145] from Figure 10 It can be seen that when the conductive substrate is tilted at an angle greater than 45° (specifically 60°), only a small amount of graphene oxide nanosheets are distributed on the upper part of the silicon wafer, while agglomerates are formed on the lower part.

[0146] It can be understood that the various technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0147] The above are merely preferred embodiments of the present application and only specifically describe the technical principles of the present application. These descriptions are intended only to explain the principles of the present application and should not be construed in any way as limiting the scope of protection of the present application. Based on the explanations herein, any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application, as well as other specific implementations of the present application that can be conceived by those skilled in the art without inventive effort, shall be included within the scope of protection of the present application.

Claims

1. A SEM sample preparation method for characterizing the morphology of micro-nano samples, characterized in that: The following steps are involved: dispersing the micro-nano sample into a solvent to obtain a dispersion; The conductive substrate is placed at an angle of 15 to 45 degrees to the horizontal plane; The dispersion was added dropwise onto the surface of a tilted conductive substrate, and after the solvent evaporated, the SEM sample was prepared and the SEM test was performed. Wherein, the solvent includes at least one of acetone, ethanol and methanol.

2. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 1, characterized in that: Before adding the dispersion dropwise onto the surface of the conductive substrate placed obliquely, the method further includes plasma cleaning the conductive substrate.

3. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 1, characterized in that: The mass fraction of the micro-nano sample in the dispersion is 0.01-0.0001%.

4. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 1, characterized in that: The micro-nano sample includes any one of SiO2 nanospheres, graphene oxide nanosheets, MOF, and MXene-TiO2.

5. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 1, characterized in that: If the micro-nano sample is SiO2 nanospheres, the solvent is acetone; If the micro-nano sample is graphene oxide nanosheets, the solvent is ethanol; If the micro-nano sample is MOF, the solvent is acetone; If the micro-nano sample is MXene-TiO2, the solvent is acetone.

6. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 5, characterized in that: The diameter of the SiO2 nanospheres is 50-500 nm; The diameter of the graphene oxide nanosheets is 0.1-6 μm; The diameter of the MOF is 1 to 6 μm; The diameter of the MXene-TiO2 is 0.2~10 μm.

7. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 1, characterized in that: The conductive substrate is a silicon wafer with a gold-plated surface.

8. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 2, characterized in that: The plasma cleaning control process is as follows: gas pressure of 0.1-10 Pa, gas flow of 5-50 sccm, gas source of one or more of O2, Ar, and N2; cleaning time of 10-20 min, cleaning temperature of 30-50°C, and power of 50-150W.

9. The SEM sample preparation method for micro-nano sample morphology characterization according to claim 1, characterized in that: The dispersion is added dropwise onto the surface of a tilted conductive substrate so that the dispersion spreads evenly over the surface of the conductive substrate. Then, more dispersion is added dropwise onto the surface of the conductive substrate. After the solvent evaporates, the SEM sample preparation is completed and the SEM test is performed. The volume of the dispersion added each time was 0.5~50 μL.

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