Polyimide supporting film, electron microscope carrier and preparation method of polyimide supporting film and electron microscope carrier

Abstract

The invention relates to the technical field of transmission electron microscope sample preparation, discloses a polyimide supporting film with the thickness of 5-100 nm, and further discloses a preparation method of the polyimide supporting film and an electron microscope carrier. The preparation method comprises the following steps: carrying out gradient spin-coating on a polyimide precursor diluted solution by utilizing a plurality of spin-coating speeds with gradients, spreading the polyimide precursor diluted solution on a substrate, and increasing the plurality of spin-coating speed gradients in the gradient spin-coating process; the polyimide precursor diluted solution is a mixed solution of a polyimide precursor solution and a diluted solvent; the spread polyimide precursor diluted solution is subjected to imidization treatment to obtain the polyimide supporting film, and the spin-coating speed gradient is increased, so that the nano-scale polyimide supporting film can be obtained, the requirement of a transmission electron microscope on high-resolution imaging can be met, the atomic-scale resolution can be achieved, and the application range is wide. And a more reliable support is provided for microstructure analysis.

Description

Technical Field

[0001] The present application relates to the technical field of transmission electron microscope sample preparation, for example, to a polyimide support film and an electron microscope carrier and a preparation method thereof. Background Art

[0002] Since its invention in the 1930s, electron microscopy (EM) has become an essential tool for analyzing the microstructure of nanomaterials. Breakthroughs in electromagnetic technology, such as spherical aberration correction, have enabled transmission electron microscopy (TEM) to achieve atomic-scale spatial resolution. However, as the resolution of TEMs continues to increase, so too has the demand for sample preparation. Minimizing sample thickness is a prerequisite for obtaining high-resolution images. TEM samples are typically dispersed on the surface of a support film. Thinner films produce less background noise and improve the signal-to-noise ratio (SNR) during imaging. However, excessively thin films also have lower mechanical strength. Therefore, the performance of the support film directly impacts image quality and sample stability. Polymer support films, due to their low electron scattering and chemical modifiability, are ideal support materials for samples such as biomacromolecules and nanoparticles.

[0003] At the same time, with the rapid development of in situ electron microscopy technology, liquid-phase in situ transmission electron microscopy (Liquid-Phase TEM) has become a key means to study processes such as the dynamic evolution of materials and biomolecular interactions. In such applications, the sample support membrane needs to maintain structural integrity in harsh chemical environments (such as strong acids, strong bases, and ionic liquids) and continuous electron beam irradiation, which poses a severe challenge to traditional support membrane systems. Conventional carbon membranes have poor acid and alkali tolerance and are prone to oxidation / hydrolysis reactions in strong acid or strong alkaline environments, leading to membrane structure collapse. The short-range ordered structure of amorphous carbon is difficult to resist chemical corrosion and radiation damage, and the liquid reaction pool has a risk of leakage. When graphene film encapsulates liquid, liquid molecules embedded in the graphene layers can easily cause lateral stress release to produce wrinkles, and even cause the graphene sheets to separate, destroying the liquid layer seal. At the same time, the preparation cost of single-layer graphene is high, and large-scale preparation cannot be achieved. In addition, due to the intrinsic conductivity of carbon films and graphene films, when used as support films for in-situ electrochemical chips, electrochemical signal crosstalk and double-layer shielding will occur, seriously affecting the accuracy of in-situ potential control in the experiment. Silicon nitride films are suitable for high-resolution imaging, but silicon nitride films have weak conductivity and high preparation costs. Although aromatic films have low costs, they are weak in acid and alkali tolerance, conductivity, mechanical strength, and electron beam tolerance, and cannot be used in transmission electron microscopy. Therefore, the above traditional support films are difficult to meet the stringent requirements of in-situ electron microscopy for chemical stability, sub-nanometer surface flatness, and dynamic interface controllability. There is an urgent need to develop new composite membrane material systems to replace existing products.

[0004] Existing conventional methods can achieve thickness control of the support film, especially nanometer-level thickness control. In addition, the surface flatness of the support film obtained by the conventional method is not good, which affects the performance of the support film.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention

[0006] In order to provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. The summary is not an extensive review, nor is it intended to identify key / critical elements or delineate the scope of protection of these embodiments, but rather serves as a prelude to the detailed description that follows.

[0007] The embodiments of the present disclosure provide a polyimide support film and an electron microscope carrier and a preparation method thereof, which can overcome the problem that the polyimide cannot achieve nanoscale thickness control during the formation of agglomerates and the problem that the sub-nanometer surface flatness cannot meet the requirements, and obtain a nanoscale polyimide support film.

[0008] In some embodiments, the polyimide support film has a thickness of 5 to 100 nm and is made of polyimide. This provides a support film with nanometer-level thickness control and subnanometer-level surface flatness, meeting the high-resolution imaging requirements of electron microscopy and achieving atomic-level resolution, providing more reliable support for microstructural analysis.

[0009] In some embodiments, the method for preparing the polyimide support film includes: gradient spin coating a polyimide precursor dilute solution through multiple spin coating speeds with a gradient, spreading the polyimide precursor dilute solution on a substrate, and increasing the gradient of the multiple spin coating speeds during the gradient spin coating process; wherein the polyimide precursor dilute solution is a mixed solution of a polyimide precursor solution and a dilution solvent; and imidization treatment is performed on the spread polyimide precursor dilute solution to obtain a polyimide support film.

[0010] In some embodiments, the electron microscope carrier includes a substrate and a polyimide support film arranged on the surface of the substrate. The polyimide support film is a polyimide support film prepared by the polyimide support film described in any embodiment of the present disclosure or the preparation method of the polyimide support film described in any embodiment of the present disclosure.

[0011] The polyimide support film and electron microscope carrier and their preparation method provided by the embodiments of the present disclosure are such that after spreading a mixed solution of a polyimide precursor and a diluent solvent, the polyimide precursor molecular chains can be orderly oriented on a plane, and then through the imidization process, a controllable preparation of a continuous film of 10 to 100 nm can be achieved, and sub-nanometer surface flatness can be obtained, so that it can be tightly adhered to the electron microscope carrier matrix, forming a transmission electron microscope capable of stably detecting different samples, especially in-situ liquid phase transmission electron microscope detection; the nanometer-scale thickness and surface flatness of the polyimide support film enable it to meet the requirements of the transmission electron microscope for high-resolution imaging, and can also achieve atomic-level resolution, providing more reliable support for microstructure analysis.

[0012] The above general description and the following description are exemplary and explanatory only and are not intended to limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] One or more embodiments are exemplarily described by corresponding drawings. These exemplary descriptions and drawings do not limit the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a scale limitation. In addition,

[0014] Figure 1a A diagram showing a state where a polyimide support film and a glass substrate are separated during a process for preparing a polyimide support film according to Example 1 of the present disclosure;

[0015] Figure 1b A diagram showing a copper mesh placed on a polyimide support film surface during the preparation of an electron microscope carrier according to Example 1 of the present disclosure;

[0016] Figure 1c A physical diagram of an electron microscope carrier showing a process for preparing an electron microscope carrier according to Example 1 of the present disclosure;

[0017] Figure 2a A scanning electron microscope image showing the front side of the electron microscope support according to Example 1 of the present disclosure;

[0018] Figure 2b A scanning electron microscope image showing the front side of an electron microscope carrier according to Example 2 of the present disclosure;

[0019] Figure 3a A transmission electron microscope photograph at a first magnification of a test on iron oxide nanosheets using an electron microscope support according to Example 1 of the present disclosure is shown;

[0020] Figure 3b A transmission electron microscope photograph at a second magnification showing a test on the iron oxide nanosheets in the first region using the electron microscope support according to Example 1 of the present disclosure;

[0021] Figure 3c A fast Fourier transform image of an atomic image of an iron oxide nanosheet in a first region tested using an electron microscope according to Example 1 of the present disclosure is shown, wherein the red circle indicates the maximum resolution that the image can achieve;

[0022] Figure 3d A transmission electron microscope photograph at a second magnification showing a test on the iron oxide nanosheets in the second region using the electron microscope carrier according to Example 1 of the present disclosure;

[0023] Figure 3e A fast Fourier transform image of an atomic image of an iron oxide nanosheet in the second region tested using an electron microscope according to Example 1 of the present disclosure is shown, wherein the red circle indicates the maximum resolution that the image can achieve;

[0024] Figure 4 A flow chart showing a method for preparing a polyimide support film according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0025] In order to be able to understand the features and technical content of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure is described in detail below in conjunction with the accompanying drawings. The accompanying drawings are for reference only and are not used to limit the embodiments of the present disclosure. In the following technical description, for the sake of convenience of explanation, a full understanding of the disclosed embodiments is provided through a number of details. However, one or more embodiments can still be implemented without these details. In other cases, to simplify the drawings, well-known structures, steps, and devices can be simplified for display.

[0026] In the description and claims of the embodiments of the present disclosure, as well as in the accompanying drawings, the terms "first," "second," and the like are used to distinguish similar items and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate to describe the embodiments of the present disclosure herein. In addition, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The term "plurality" means two or more. In the disclosed embodiment, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B. The term "and / or" is a description of the association relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or, three relationships of A and B.

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure can be combined with each other.

[0029] Those skilled in the art will understand that in the methods involved in the specification of this application and other parts, for example, in the methods of each embodiment, example or claim, the writing order of each step does not mean a strict execution order and constitutes any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps A and B, which means that the method may include steps A and B performed sequentially, or steps B and A performed sequentially. For example, it is mentioned that the method may also include step C, which means that step C can be added to the method in any order. For example, the method may include steps A, B and C, or steps A, C and B, or steps C, A and B, etc.

[0030] In this application, open technical features or technical solutions described with words such as "contain," "include," and "includes" do not exclude additional members beyond the listed members unless otherwise specified, and can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may or may not include other members unless otherwise specified. This can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members."

[0031] The "ranges" disclosed herein can be defined in the form of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values, with any end value being independently included or excluded, and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 2000 to 10000 rpm and 3000 to 10000 is listed for a particular parameter, it is understood that a range of 2000 to 10000 rpm and 3000 to 10000 is also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been listed in this document, and "0 to 5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2 to 10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0032] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0033] The present disclosure provides a polyimide support film having a thickness of 5 to 100 nm. The polyimide support film prepared in the present disclosure has a thickness less than or equal to 100 nm, for example, a nanometer-scale thickness such as 50 nm or 80 nm. Preferably, the polyimide support film has a thickness of 5 to 30 nm; more preferably, the polyimide support film has a thickness of 5 to 25 nm.

[0034] Optionally, the polyimide support film has a uniform thickness, and an average thickness deviation of the polyimide support film is 0.7 to 2.15. The polyimide support film disclosed herein does not form aggregates larger than 1 micron and has a sub-nanometer surface flatness, thus meeting the requirements for application in transmission electron microscopy.

[0035] The polyimide support film disclosed herein has a nanometer-scale thickness and subnanometer surface flatness, and can be used in transmission electron microscopy, including liquid-phase in-situ transmission electron microscopy, to improve the resolution of transmission electron microscopy, even reaching atomic-level resolution, providing reliable support for transmission electron microscopy analysis of nanomaterial microstructures. The polyimide support film can closely adhere to the substrate of the electron microscope support, facilitating stable and accurate transmission electron microscopy examination of various samples.

[0036] Optionally, the polyimide support film is obtained by gradient spin coating a polyimide precursor diluted solution at multiple gradient spin coating speeds, which can fully spread the polyimide precursor to obtain a suitable polyimide support film.

[0037] Optionally, the polyimide precursor concentration in the polyimide precursor dilution solution is 0.6 to 3 wt %. Controlling the polyimide precursor concentration in the polyimide precursor dilution solution within 3 wt % allows the polyimide precursor dilution solution to have good spreadability, which is conducive to spreading film formation with a small film thickness. In this embodiment, the polyimide precursor dilution solution is a mixed solution of a polyimide precursor solution and a diluting solvent. By adjusting parameters such as the concentration of the polyimide precursor solution and the volume ratio of the precursor solution to the diluent, a polyimide precursor dilution solution with a preset polyimide precursor concentration can be obtained.

[0038] Optionally, the polyimide precursor is polyamic acid (PAA).

[0039] Optionally, in the polyimide precursor diluted solution, the polyimide precursor includes aromatic polyamic acid.

[0040] Optionally, the aromatic polyamic acid is obtained by polycondensation of aromatic diamine monomers and aromatic dianhydride.

[0041] Optionally, the aromatic diamine includes terephthalic acid or isophthalic acid, and the aromatic dianhydride includes p-phenylenediamine or m-phenylenediamine. For example, pyromellitic dianhydride (PMDA) and an aromatic diamine (such as ODA) are condensed to form a homophenylene polyamic acid, which is then subjected to an imidization reaction to form a polyimide. The choice of polyimide precursor helps to exhibit good spreadability after spin coating, allowing for orderly orientation along the substrate plane.

[0042] Optionally, the aromatic polyamic acid is an aromatic fluorinated polyamic acid.

[0043] Optionally, the aromatic fluorinated polyamic acid is obtained by polycondensation of an aromatic fluorinated diamine monomer and an aromatic fluorinated dianhydride, wherein the aromatic fluorinated diamine monomer is an aromatic diamine containing a fluorine atom or a fluorinated group on the molecular chain, and the aromatic fluorinated dianhydride is an aromatic dianhydride containing a fluorine atom or a fluorinated group on the molecular chain. The fluorine atoms and fluorine-containing functional groups introduced into the aromatic fluorinated polyamic acid molecular chain significantly optimize the film forming process through multiple mechanisms. First, the high electronegativity of the fluorine atom and its excellent compatibility with low polarity solvents (such as γ-butyrolactone and hexafluoroisopropanol) significantly improve the dilution efficiency of the precursor polyamic acid solution, so that it can be stably dispersed in a dilute solution with a concentration of less than 2wt%, thereby laying the foundation for the preparation of ultra-thin films (5-10nm). Secondly, the steric hindrance effect generated by the fluorine-containing groups (such as trifluoromethyl, -CF3) works synergistically with the rigidification of the molecular chain to effectively inhibit the physical entanglement of the PAA molecular chains (the entanglement density is reduced by about 40%), and promote the formation of a monolayer or a few-layer ordered structure in the film formation process. In addition, the spontaneous enrichment behavior of the fluorine-containing groups on the film surface can significantly reduce the interfacial energy (reduced surface tension), thereby improving the wettability of the solution on the substrate surface, inhibiting the edge stacking effect in the spin coating process (reduced thickness deviation), and achieving uniform and controllable deposition of nanometer-level thickness. After the substrate tiling process of this application, it is easier to obtain a thin film with a smooth surface.

[0044] Combine Figure 4 As shown, the embodiment of the present disclosure provides a method for preparing a polyimide support membrane, comprising:

[0045] S10, gradient spin coating the polyimide precursor diluted solution using multiple gradient spin coating speeds to spread the polyimide precursor diluted solution on the substrate; the multiple spin coating speeds during the gradient spin coating process are increased in a gradient. The polyimide precursor diluted solution is a mixed solution of a polyimide precursor solution and a dilution solvent. The gradient increase in the spin coating speed can make the polyimide precursor uniformly distributed, control the thickness of the film, avoid the formation of agglomerates, and obtain nanometer-level thickness and subnanometer-level surface flatness; the substrate is used as a support to enable the polyimide precursor to spread to form a film.

[0046] S20, performing imidization treatment on the spread polyimide precursor diluted solution to obtain a polyimide support film. The imidization process allows the polyimide precursor to react to obtain polyimide.

[0047] Optionally, the solvent of the polyimide precursor solution may be a polar solvent, for example, γ-butyrolactone, hexafluoroisopropanol, etc.

[0048] Optionally, in step S10 , the concentration of the polyimide precursor solution is 3 wt % to 5 wt %.

[0049] Optionally, the dilution solvent is N,N-dimethylacetamide (DMAC) or N-methylpyrrolidone; the volume ratio of the polyimide precursor solution to the dilution solvent is 1:1 to 1:20; preferably, the volume ratio of the polyimide precursor solution to the dilution solvent is 1:1 to 1:5. The addition of a diluent can reduce the viscosity and rheological properties of the polyimide precursor solution, allowing it to spread better. N,N-dimethylacetamide and the polyimide precursor are combined to orient the polyimide precursor molecular chains in an orderly manner along the plane of the substrate, avoiding the entropy-driven spontaneous entanglement and stacking to form micron-sized agglomerates during the heating reaction, so as to ensure the sub-nanometer surface flatness of the polyimide support film, so that the polyimide support film can form a nanometer thickness and sub-nanometer surface flatness.

[0050] The polyimide precursor in the polyimide precursor solution in step S10 is described in the aforementioned related content and will not be described again here.

[0051] Optionally, the substrate may be a glass substrate, a metal substrate or other substrate with a smooth and flat surface.

[0052] Optionally, the polyimide precursor solution and the dilution solvent are mixed by dripping the dilution solvent into the polyimide precursor solution. Optionally, the rate of dripping the dilution solvent into the polyimide precursor solution is 0.1 to 5 mL / min; preferably, the rate of dripping the dilution solvent into the polyimide precursor solution is 0.1 to 2 mL / min. This allows the dilution solvent and the polyimide precursor solution to be fully mixed and dispersed. After adding the dilution solvent to the polyimide precursor solution, the stirring speed is 500 to 3000 rpm and the stirring time is 5 to 30 minutes. There are various stirring methods.

[0053] Alternatively, the mixing of the polyimide precursor solution and the dilution solvent may be performed at room temperature.

[0054] Optionally, in step S10, the polyimide precursor dilution solution is gradient-spin-coated using a plurality of gradient spin-coating speeds, including: applying the polyimide precursor dilution solution to a substrate, and gradient-spin-coating the polyimide precursor dilution solution at a plurality of gradient spin-coating speeds that generally increase from low to high, to obtain a substrate covered with the polyimide precursor dilution solution.

[0055] Optionally, "gradient spin coating the polyimide precursor dilution solution at multiple spin coating speeds with a gradient and an overall trend from low to high" can be understood as spin coating at two or more spin coating speeds, and the multiple spin coating speeds have an overall trend from low to high from front to back.

[0056] Optionally, the plurality of spin coating speeds may have an overall trend from low to high from front to back, including a plurality of spin coating speeds that increase in trend from low to high, such as 200 rpm, 2000 rpm, or 200 rpm, 1000 rpm, and 4000 rpm.

[0057] Optionally, the plurality of spin coating speeds may have an overall trend from low to high from the beginning to the end, including three or more spin coating speeds, wherein the three or more spin coating speeds exhibit a zigzag upward trend. That is, the intermediate spin coating speed is lower than the previous spin coating speed, but the overall trend is upward. For example, 200 rpm, 2000 rpm, 100 rpm, and 5000 rpm.

[0058] Optionally, the polyimide precursor diluted solution is gradient-spin-coated at multiple spin-coating speeds with a gradient and an overall trend from low to high, including: spin-coating at a first rotation speed, and then spin-coating at a second rotation speed; wherein the first rotation speed is less than or equal to 1000 rpm, and the second rotation speed is greater than the first rotation speed. During the spin-coating process of the spin coater, the solution is first spread by rotating at a low speed to remove excess solution, and then spin-coating is performed at a high speed to thin the film, thereby controlling the thickness of the support film to prepare a nanoscale support film. The rotation speed of the spin coater can match the spreading process of the polyimide precursor solution, which is conducive to obtaining a nanoscale support film and also helps to improve the surface flatness of the polyimide support film.

[0059] Optionally, the speed ratio of the first speed to the second speed is 1:3-15.

[0060] Optionally, the first rotational speed is greater than or equal to 200 rpm. Optionally, the first rotational speed is 200 rpm to 800 rpm; Optionally, the first rotational speed is 200 rpm to 500 rpm.

[0061] Optionally, the second rotational speed is 2000-10000 rpm; optionally, the second rotational speed is 3000-10000 rpm; optionally, the second rotational speed is 5000-10000 rpm; optionally, the second rotational speed is 8000-10000 rpm.

[0062] Optionally, the spin coating time at the first rotation speed is 10 to 80 seconds, the spin coating time at the second rotation speed is 10 to 200 seconds, and further preferably, the spin coating time at the first rotation speed is 20 to 60 seconds, and the spin coating time at the second rotation speed is 30 to 180 seconds.

[0063] Optionally, before "spin coating at a second speed", it also includes spin coating with one or more intermediate gradient speeds; one or more intermediate gradient speeds are greater than the first speed and less than the second speed; when multiple intermediate gradient speeds are used for spin coating, the multiple intermediate gradient speeds have a gradient and show a trend change from low to high as a whole. In the process of spin coating by the spin coater, the solution is first spread by rotating at a low speed to remove excess solution, and then the speed is increased, and then spin coating is performed at a medium speed, which can fully spread the polyimide precursor, and finally spin coating is performed at a high speed to thin the film, so that the thickness of the support film can be controlled to prepare a nanoscale support film. The speed of the spin coater can match the spreading process of the polyimide precursor solution, which is conducive to obtaining a nanoscale support film and is also conducive to improving the surface smoothness of the polyimide support film. In this embodiment, the understanding of "the overall trend change from low to high" in the multiple intermediate gradient speeds having a gradient and showing a trend change from low to high is the same as the understanding of the aforementioned "the overall trend change from low to high from front to back".

[0064] Optionally, the plurality of intermediate gradient rotational speeds have a gradient and show an overall trend change from low to high, including a plurality of intermediate gradient rotational speeds having a larger gradient trend from low to high.

[0065] Optionally, a rotational speed ratio of the first rotational speed, the intermediate gradient rotational speed, and the second rotational speed is 1:2-6:3-15.

[0066] Optionally, one or more intermediate gradient speeds between the first speed and the second speed may range from 1000 to 9000 rpm. It is sufficient to ensure that the maximum intermediate gradient speed is less than the second speed. Optionally, the intermediate gradient speeds may range from 1000 to 8000 rpm, optionally from 1000 to 6000 rpm, optionally from 1000 to 5000 rpm, or optionally from 1000 to 3000 rpm.

[0067] Optionally, the number of the plurality of intermediate gradient rotational speeds is two, and the two intermediate gradient rotational speeds may be 1000-1500 rpm and 2000-3000 rpm respectively.

[0068] Optionally, the time for spin coating at each intermediate gradient speed is 10 to 60 seconds. Further preferably, the time for spin coating at each intermediate gradient speed is 20 to 60 seconds.

[0069] Optionally, in step S20, the spread polyimide precursor dilute solution is subjected to imidization treatment to obtain a polyimide support film, including: heating the substrate on which the polyimide precursor dilute solution is spread, so that the polyimide precursor dilute solution on the surface of the substrate forms a polyimide film; wet separation of the polyimide film and the substrate to obtain a polyimide support film. By heating the substrate, the temperature of the polyimide precursor solution and the dilution solvent increases, the solvent is gradually evaporated, and the polyimide precursor can be further dehydrated and condensed, and an imidization reaction occurs to form a polyimide, which is gradually solidified into a nanoscale film. Therefore, the preparation method disclosed in the present invention can achieve the controllable preparation of continuous films of 5 to 100 nm.

[0070] Optionally, by heating the substrate, the polyimide precursor diluted solution on the surface of the substrate forms a polyimide film, including: heating the substrate is divided into two heating stages, heating the substrate at a first temperature to evaporate the solvent of the polyimide precursor diluted solution, and then heating the substrate at a second temperature to cause the polyimide precursor diluted solution to undergo an imidization reaction to obtain polyimide, and solidify into a polyimide film.

[0071] Optionally, the first temperature is 40-130°C, and the second temperature is 250-360°C. Further preferably, the first temperature is 50-120°C, and the second temperature is 280-350°C. The first temperature is used to evaporate excess solvent from the polyimide precursor dilution solution. The film is then sintered and cured at a high temperature to complete imidization.

[0072] Optionally, the heating time at the first temperature is 1 to 15 minutes; more preferably, the heating time at the first temperature is 2 to 10 minutes. In some embodiments, the heating time at the second temperature is 2 to 20 minutes; more preferably, the heating time at the second temperature is 5 to 15 minutes.

[0073] Alternatively, separating the polyimide film from the substrate to obtain a polyimide support film comprises soaking the substrate in an acid solution, then placing the soaked substrate in water to remove the film, thereby obtaining the polyimide support film. While the substrate is soaked in the acid solution, the acid corrodes the substrate, separating the film. The film is then separated by placing the substrate in water, causing the exfoliated polyimide film to float on the surface of ultrapure water. The acid solution is selected based on the substrate material.

[0074] Optionally, the acid solution may be a hydrofluoric acid solution, which can corrode the glass substrate, thereby achieving demolding of the polyimide film using the glass substrate as the substrate.

[0075] Optionally, the acid solution may be hydrochloric acid, etc. The hydrochloric acid can corrode the metal substrate, thereby achieving demoulding of the polyimide film using the metal substrate as the substrate.

[0076] Optionally, the substrate soaked in the hydrofluoric acid solution is placed in ultrapure water.

[0077] Optionally, the concentration of the acid solution is 3 to 30 vol%, and the immersion time in the acid solution is 1 to 10 seconds. Further preferably, the concentration of the acid solution is 5 to 25 vol%, and the immersion time in the acid solution is 1 to 5 seconds. The specific acid solution concentration can be determined based on the type of acid and the substrate material. For example, the concentration of hydrofluoric acid solution is relatively low and can be obtained by diluting it with ultrapure water. The substrate is immersed in the hydrofluoric acid solution for a short time, and controlling the immersion time allows for better separation of the film and the substrate.

[0078] An embodiment of the present disclosure also provides an electron microscope carrier, which includes a substrate and a polyimide support film arranged on the surface of the substrate. The polyimide support film is a polyimide support film prepared by the polyimide support film of any embodiment of the present disclosure or the preparation method of the polyimide support film of any embodiment of the present disclosure.

[0079] Optionally, the electron microscope may include a scanning electron microscope and / or a transmission electron microscope, and in particular may include a liquid phase in situ transmission electron microscope in a transmission electron microscope.

[0080] Optionally, the substrate may be a metal mesh or a chip. Further, the metal mesh may be made of copper, nickel, molybdenum, titanium, or gold, etc.; the chip may be a silicon nitride chip, etc.

[0081] The embodiments of the present disclosure also provide a method for preparing an electron microscope carrier, which includes: applying a diluted polyimide precursor solution to a substrate, wherein the diluted polyimide precursor solution is a mixed solution of a polyimide precursor solution and a dilution solvent, and spreading the diluted polyimide precursor solution by spin coating; heating the substrate so that the diluted polyimide precursor solution on the surface of the substrate forms a polyimide film; wet-separating the polyimide film and the substrate to obtain a polyimide support film floating in water; placing a substrate on the polyimide support film, and removing the polyimide support film to obtain an electron microscope carrier with a polyimide support film.

[0082] After the substrate is placed on the polyimide support film, the polyimide support film is attached to the substrate. When removing the film, be careful to control the pulling speed to avoid mechanical stress that may cause the film to break or wrinkle.

[0083] The following specific examples are provided to illustrate a polyimide support film and electron microscope carrier according to the embodiments of the present disclosure, and their preparation methods, in order to more clearly illustrate the technical problems, technical solutions, and beneficial effects solved by the present application. Obviously, the described embodiments are only some of the embodiments of the present application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and in no way limits the present application and its applications.

[0084] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0085] In the following examples, the reagents involved are:

[0086] Serial number name CAS number / brand factory 1 4,4'-Diaminodiphenyl ether 101-80-4 Maclean 2 N,N-Dimethylacetamide 127-19-5 Maclean 3 hydrofluoric acid 7664-39-3 Maclean

[0087] The preparation process of polyimide precursor solution is as follows:

[0088] Under dry nitrogen, 2,2'-bis(trifluoromethyl)benzidine (TFDB) (0.01 mol, 3.68 g) was dissolved in 80 mL of N-methylpyrrolidone (NMP) and magnetically stirred at 40°C for 2 hours until completely dissolved, resulting in a light yellow, transparent solution. 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA) (0.0099 mol, 4.44 g) was vacuum-dried at 150°C for 4 hours, cooled, and ground into a powder for later use. A gradient polycondensation reaction was then performed. The reaction system was placed in an ice bath (0-5°C). 6FDA powder was slowly added to the TFDB solution in four batches, with 15-minute intervals between each batch, maintaining the temperature at ≤10°C. After the first batch of 6FDA was added, stirring was continued at 200 rpm for 30 minutes. The temperature of subsequent batches was gradually raised to 25°C, and the stirring rate was increased to 500 rpm. The total reaction time was 6 hours. Aniline (0.0002 mol, 18.6 mg) was added and the reaction continued at 25°C for 1 hour to terminate chain growth. Perfluorooctyltriethoxysilane (PFO-TES) (0.1 wt%) was added and ultrasonic dispersion (40 kHz, 300 W) was applied for 30 minutes to promote surface enrichment of fluorinated groups. Unreacted monomers and gel particles were removed by filtration through a 0.1 μm PTFE filter. The solids content was adjusted by vacuum rotary evaporation (40°C, 10 kPa).

[0089] The polyimide precursor solution prepared above was used in the following examples.

[0090] The absolute thickness of the polyimide support film is measured as follows:

[0091] First, the thickness (t) of the polyimide support film is measured using a step profiler. The thickness result obtained is compared with the result (t / λ) obtained by electron energy loss spectroscopy (EELS) to obtain the mean free path (λ) of electron inelastic scattering in the polyimide film. In subsequent examples, the absolute thickness of the polyimide support film can be calculated using the mean free path of electron inelastic scattering and EELS.

[0092] The above-mentioned method for measuring the absolute thickness of the polyimide support film was applied to the following examples.

[0093] Example 1

[0094] A polyimide support film having a thickness of 20.8 nm and an average thickness deviation of 2.11.

[0095] The preparation method of the polyimide support film comprises:

[0096] (1) The polyimide precursor solution and N,N-dimethylacetamide were mixed in a volume ratio of 1:1 to obtain a polyimide precursor diluted solution with a concentration of 1.5 wt% to 2.5 wt%. The mixture was stirred at a speed of 3000 rpm for 5 minutes.

[0097] (2) The diluted polyimide precursor solution was added dropwise to the surface of the glass substrate. The solution was first spin-coated at 300 rpm for 30 seconds to remove excess solution. The speed was then increased to 8500 rpm and the solution was spin-coated for 120 seconds to thin the film.

[0098] (3) The spin-coated glass substrate was heated at 100°C for 5 minutes to evaporate the excess solvent. The temperature was then raised to 350°C and sintered for 10 minutes to complete the imidization of the film.

[0099] (4) The sample was completely immersed in a 20 vol% hydrofluoric acid solution, taken out immediately after soaking for 2 seconds, and then transferred to a container filled with ultrapure water for demolding. After demolding, the membrane floated on the surface of the ultrapure water.

[0100] An electron microscope support, comprising a method for preparing the electron microscope support, comprising: in step (4) of preparing the transmission electron microscope support membrane, after the membrane floats on the surface of ultrapure water, placing a copper mesh on the membrane, removing a glass slide, and air-drying the membrane. The preparation process is shown in Figures 1(a), 1(b), and 1(c).

[0101] Figure 1(a) shows that the glass substrate and polyimide support film are completely separated in ultrapure water. Figure 1(b) shows that the copper mesh is completely adhered to the polyimide support film in ultrapure water. Figure 1(c) shows that the polyimide support film is adhered to the copper mesh after removal.

[0102] Example 2

[0103] A polyimide support film has a thickness of 8.21 nm and an average thickness deviation of 0.83.

[0104] The preparation method of the polyimide support film comprises:

[0105] (1) The polyimide precursor solution and N,N-dimethylacetamide were mixed in a volume ratio of 1:2 to obtain a polyimide precursor diluted solution with a concentration of 1 wt% to 1.5 wt%. The mixture was stirred at a speed of 500 rpm for 5 minutes.

[0106] (2) The diluted polyimide solution was added dropwise to the surface of the glass substrate. The film was first spin-coated at 500 rpm for 60 s to remove excess solution. The speed was then increased to 8000 rpm and the film was spin-coated for 60 s to thin the film.

[0107] (3) Heat the spin-coated glass substrate at 100°C for 3 minutes to evaporate excess solvent. Then continue heating to 320°C and sinter for 5 minutes to complete the imidization of the film.

[0108] (4) The sample was completely immersed in a 10 vol% hydrofluoric acid solution, taken out immediately after soaking for 3 seconds, and then transferred to a container filled with ultrapure water for demolding. After demolding, the membrane floated on the surface of the ultrapure water.

[0109] An electron microscope carrier, the preparation method of the electron microscope carrier comprises: in the step (4) of the transmission electron microscope support film, after the film floats on the surface of ultrapure water, a silicon nitride chip is placed on the film, and the chip carrying the polyimide film is fished out and dried.

[0110] Example 3

[0111] A polyimide support film has a thickness of 20.1 nm and an average thickness deviation of 1.78.

[0112] The difference between this embodiment and embodiment 1 lies in step (2). Step (2) of this embodiment is: the diluted polyimide precursor solution is added dropwise to the surface of the glass substrate, firstly spin-coated at a speed of 300 rpm for 30 seconds to remove excess solution, then the speed is increased to 2500 rpm, spin-coated for 40 seconds, and finally the speed is increased to 8500 rpm, spin-coated for 120 seconds to thin the film.

[0113] Example 4

[0114] This embodiment differs from Example 1 in that, in step (1) of the method for preparing a polyimide support film, a polyimide precursor solution and N,N-dimethylacetamide are mixed in a volume ratio of 1:4, and the concentration of the resulting polyimide precursor diluted solution is 0.6 wt % to 1 wt %. The remaining steps and parameters are the same.

[0115] The thickness of the polyimide support film obtained in Example 4 was 3.8 nm, and the average thickness deviation was 0.73.

[0116] The thickness of the polyimide support film obtained in Example 4 is smaller than that of the polyimide support film obtained in Example 1.

[0117] Example 5

[0118] This embodiment is different from step (2) of embodiment 1. Step (2) of this embodiment is: the diluted polyimide precursor solution is added dropwise to the surface of the glass substrate, first spin-coated at a speed of 300 rpm for 30 seconds to remove excess solution, then the speed is increased to 1500 rpm, spin-coated for 20 seconds, then increased to 2500 rpm, spin-coated for 30 seconds, and finally increased to 8500 rpm, spin-coated for 120 seconds to thin the film.

[0119] The thickness of the polyimide support film obtained in Example 5 was 19.9 nm.

[0120] Application Examples

[0121] Scanning electron microscopy images of the electron microscopy supports obtained in Example 1 and Example 2 are shown in Figures 2(a) and 2(b) , respectively, showing the front views of the electron microscopy supports. Figures 2(a) and 2(b) demonstrate that the polyimide support film can be evenly and completely applied to the surface of the metal mesh or chip, with the polyimide support film being tightly bonded to the metal mesh or chip.

[0122] The electron microscope carrier prepared in Example 1 was used in a transmission electron microscope, and the sample to be tested in the transmission electron microscope was an iron oxide nanosheet. The test results of the electron microscope carrier prepared in Example 1 are as follows: Figure 3a 、 Figure 3b and Figure 3d shown. Figure 3a The boundary lines between iron oxide nanosheets can be clearly seen. Figure 3b and Figure 3d Compared to Figure 3a The image is partially enlarged, and the boundary between the iron oxide nanosheets can still be clearly seen after enlargement. Figure 3c and Figure 3eClear images of the source atoms of the iron oxide nanosheets can be seen. Therefore, the electron microscope carrier disclosed in the present invention can be used for transmission electron microscopy detection of zinc oxide particles, and the detection results can reach atomic-level resolution.

[0123] Example 6

[0124] The difference from Example 1 is the type of dilution solvent. The dilution solvent of this example is N-methylpyrrolidone.

[0125] The thickness of the transmission electron microscope support film obtained in this example was 24.2 nm, with an average thickness deviation of 2.15. Compared to the transmission electron microscope support film obtained in Example 1, the transmission electron microscope support film of Example 7 was thicker, indicating that the polyimide precursor and N,N-dimethylacetamide disclosed in this disclosure have a better effect as a diluent.

[0126] Comparative Example 1

[0127] The difference from Example 1 is step (2). Step (2) of this comparative example is: adding the diluted polyimide solution dropwise to the surface of the glass substrate, increasing the rotation speed to 8500 rpm using a spin coater, and spin coating for 120 seconds.

[0128] In Comparative Example 1, the TEM support film obtained by direct spin coating at the second rotation speed of 8500 rpm had a thickness of 21.1 nm and an average thickness deviation of 2.21. Thus, compared to the polyimide support film obtained in Example 1, the thickness of the polyimide support film in Comparative Example 1 is similar, but the uniformity is poor.

[0129] Comparative Example 2

[0130] The difference between this comparative example and Example 1 is that in the preparation method of the polyimide support film, a polyimide precursor (solid content of 3% to 5%) is directly used and dropped onto the surface of the glass substrate. The remaining parameters and steps are the same as those in Example 1.

[0131] The thickness of the polyimide support film obtained in Comparative Example 2 was 39.3 nm, and the average thickness deviation was 2.15.

[0132] Comparative Example 3

[0133] The difference between this comparative example and Example 1 is that the polyimide precursor is different. The polyimide precursor in this comparative example is polyamide ester.

[0134] The thickness of the polyimide support film obtained in Comparative Example 3 was 36.9 nm, and the average thickness deviation was 2.29.

[0135] Fluorinated polyimide films have high transmittance in the visible light region and good transparency. Due to the presence of fluorine atoms, they have good chemical stability and can resist corrosion from a wider range of chemical substances. In some harsh chemical environments, such as those with organic solvents, acids, and alkalis, they can better maintain their performance. The films obtained using polyamide ester as a precursor are usually yellow and transparent. Compared with fluorinated polyimide films, they may have slightly worse optical transparency and their applications are subject to certain limitations.

[0136] Flatness measurement: The measurement method includes: using the thickness measurement method described above to measure the thickness of the transmission electron microscope support film prepared in each embodiment and comparative example at 12 different locations. The thickness values ​​are shown in Table 1. The average thickness deviation can be calculated using the following formula: Among them, n is the number of data, x i represents the i-th data value, The sum of the absolute values ​​of the differences between each data value xi and the average value is shown in Table 1.

[0137] Table 1 Thickness values ​​and average deviations of transmission electron microscope support films of different embodiments and comparative examples

[0138]

[0139] As shown in Table 1, the transmission electron microscope support films prepared in Examples 1, 2, 3, 4, 5, and 6 have uniform thickness and good surface flatness. Therefore, the preparation method disclosed herein can produce support films with submicron surface flatness and no micron-sized aggregates. Therefore, the diluent and gradient spin coating method disclosed herein facilitate the production of polyimide support films with improved flatness.

[0140] From the average deviation of Comparative Example 1, it can be seen that during the spin coating process, if the spin coating is directly performed by high-speed spin coating, the polyimide precursor cannot be well oriented and cannot be fully spread, so the flatness of the obtained film is poor.

[0141] It can be seen from the average deviation of Comparative Example 2 that if the concentration of the polyimide precursor in the polyimide precursor dilution solution is too high, it cannot be spread well during the spin coating process, so the obtained film is thicker.

[0142] It can be seen from the average deviation and thickness of Comparative Example 3 that the polyimide precursor of the present application is conducive to obtaining a polyimide support film with uniform thickness and an appropriate thickness range.

[0143] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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.

[0144] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A polyimide support membrane, characterized in that The thickness of the polyimide support film is 5 to 100 nm, and the material of the polyimide support film is polyimide.

2. The polyimide support film according to claim 1, characterized in that The average deviation of the thickness of the polyimide support film is 0.7 to 2.15 nm.

3. The polyimide support film according to claim 1, wherein The polyimide support film is obtained by gradient spin coating a polyimide precursor diluted solution at multiple gradient spin coating speeds; Preferably, in the polyimide precursor diluted solution, the mass concentration of the polyimide precursor is 0.6 wt % to 3 wt %; Preferably, in the polyimide precursor diluted solution, the polyimide precursor comprises polyamic acid; Preferably, in the polyimide precursor diluted solution, the polyimide precursor comprises aromatic polyamic acid; Preferably, the aromatic polyamic acid is obtained by polycondensation of aromatic diamine monomer and aromatic dianhydride; Preferably, the aromatic diamine comprises terephthalic acid or isophthalic acid, and the aromatic dianhydride comprises p-phenylenediamine or m-phenylenediamine; Preferably, the aromatic polyamic acid is an aromatic fluorinated polyamic acid; Preferably, the aromatic fluorinated polyamic acid is obtained by condensation polymerization of an aromatic fluorinated diamine monomer and an aromatic fluorinated dianhydride, wherein the aromatic fluorinated diamine monomer is an aromatic diamine containing fluorine atoms or fluorinated groups on the molecular chain, and the aromatic fluorinated dianhydride is an aromatic dianhydride containing fluorine atoms or fluorinated groups on the molecular chain.

4. The method for preparing a polyimide support membrane according to any one of claims 1 to 3, wherein: The preparation method comprises: Spin coating the polyimide precursor dilute solution at multiple gradient spin coating speeds to spread the polyimide precursor dilute solution on the substrate, wherein the multiple spin coating speeds in the gradient spin coating process increase in gradient; wherein the polyimide precursor dilute solution is a mixed solution of the polyimide precursor solution and a dilution solvent; The spread polyimide precursor diluted solution is subjected to imidization treatment to obtain a polyimide support membrane.

5. The preparation method according to claim 4, characterized in that The polyimide precursor diluted solution is subjected to gradient spin coating at a plurality of gradient spin coating speeds, including: The polyimide precursor diluted solution is applied to the substrate, and the polyimide precursor diluted solution is gradient-spin-coated at multiple spin-coating speeds with a gradient and an overall trend from low to high to obtain a substrate covered with the polyimide precursor diluted solution.

6. The preparation method according to claim 5, characterized in that Gradient spin coating of a polyimide precursor dilute solution at multiple spin coating speeds with a gradient and an overall trend from low to high includes: spin coating at a first spin speed and then spin coating at a second spin speed; wherein the first spin speed is less than or equal to 1000 rpm and the second spin speed is greater than the first spin speed; Preferably, the speed ratio of the first speed to the second speed is 1:3-15; Preferably, the time at the first speed is 10 to 80 seconds; Preferably, the time for performing the operation at the second speed is 10 to 200 seconds; Preferably, the first rotational speed is greater than or equal to 200 rpm; or, the first rotational speed is 200 rpm to 800 rpm; or, the first rotational speed is 200 rpm to 500 rpm; and / or The second rotational speed is 2000-10000 rpm; or, the second rotational speed is 3000-10000 rpm; or, the second rotational speed is 5000-10000 rpm; or, the second rotational speed is 8000-10000 rpm.

7. The preparation method according to claim 6, characterized in that The preparation method further includes: before "spin coating at a second speed", further including spin coating at one or more intermediate gradient speeds; the one or more intermediate gradient speeds are greater than the first speed and less than the second speed; when the multiple intermediate gradient speeds are used for spin coating, the multiple intermediate gradient speeds have a gradient and generally change from low to high; Preferably, the speed ratio of the first speed, the intermediate gradient speed and the second speed is 1:2-6:3-15; Preferably, the time at the first speed is 10 to 80 seconds; Preferably, the time for performing the operation at the second speed is 10 to 200 seconds; Preferably, the time for each intermediate gradient speed is 10 to 60 seconds; Preferably, the speed range of the intermediate gradient speed is 1000-3000 rpm.

8. The preparation method according to any one of claims 4 to 7, characterized in that The polyimide support film is obtained by imidization treatment of the spread polyimide precursor diluted solution, comprising: heating the substrate on which the polyimide precursor diluted solution is spread, so that the polyimide precursor diluted solution on the surface of the substrate forms a polyimide film; The polyimide film and the substrate are separated by a wet method to obtain a polyimide support membrane.

9. The preparation method according to claim 8, characterized in that Heating a substrate on which a polyimide precursor dilute solution is spread so that the polyimide precursor dilute solution on the surface of the substrate forms a polyimide film, comprising: Heating the substrate at a first temperature to evaporate the solvent of the polyimide precursor diluted solution, and then heating the substrate at a second temperature to cause the polyimide precursor diluted solution to undergo an imidization reaction to obtain polyimide, which is then cured into a polyimide film; wherein the second temperature is greater than the first temperature; Preferably, the first temperature is 40-130°C; and / or the second temperature is 250-360°C.

10. The preparation method according to any one of claims 4 to 7, characterized in that: Separating the polyimide film and the substrate to obtain a polyimide support film, comprising: soaking the substrate in an acid solution, and then placing the soaked substrate in water to remove the film to obtain the polyimide support film; Preferably, the concentration of the acid solution is 3 to 30 vol%; and / or the soaking time in the acid solution is 1 to 10 seconds.

11. The preparation method according to any one of claims 4 to 7, characterized in that: The diluting solvent is N,N-dimethylacetamide or N-methylpyrrolidone; and / or, The concentration of the polyimide precursor in the polyimide precursor diluted solution is 0.6 wt % to 3 wt %; and / or, The volume ratio of the polyimide precursor solution to the dilution solvent is 1:1 to 1:

20.

12. An electron microscope carrier, characterized in that include: matrix; and A polyimide support film is provided on the surface of the substrate; the polyimide support film is a polyimide support film according to any one of claims 1 to 3 or a polyimide support film prepared by the method for preparing a polyimide support film according to any one of claims 4 to 11; Preferably, the substrate comprises a metal mesh or a chip.

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