A full-field super-resolution optical microscopy imaging method based on nanoparticle cracked thin film superlens

Abstract

The present invention provides a full-field super-resolution optical microscopy imaging method based on a nanoparticle self-assembled crack film superlens, which utilizes colloidal self-assembly technology to form a microscopic crack pattern film composed of deep sub-wavelength-sized dielectric nanoparticles on the surface of a target sample, and utilizes the nanoparticle crack film to achieve full-field super-resolution optical imaging of the sample through the dark-field oblique illumination mode of a conventional optical microscope, with a resolution of up to 100nm. The present invention has the advantages of high resolution, high contrast, full field of view and real-time imaging, and the preparation process is simple, the cost is low and the use is convenient. The method has broad application prospects in the fields of nanomaterial surface structure analysis, nano-optical effect exploration and biomedical high-resolution imaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano-optical imaging, and in particular relates to a full-field super-resolution optical microscopic imaging method based on a nanoparticle cracked thin film superlens. Background Art

[0002] Optical microscopes are an important tool for human beings to explore the microscopic world. They use visible light and lens systems to magnify and image tiny objects, and are widely used in modern scientific research and production. However, due to the diffraction limit of light, the upper limit of the resolution of conventional optical microscopes under white light illumination is only half of the wavelength of the illumination light, about 300nm. This resolution can no longer meet the growing demand for fine observation at the nanoscale.

[0003] Breaking through the resolution limit of optical microscopes and achieving super-resolution imaging has become an international frontier research hotspot, and many important advances have been made. At present, super-resolution optical imaging technology is mainly divided into two approaches: far-field and near-field. Usually, the light emitted or reflected by an object contains low-frequency far-field propagation waves and high-frequency near-field evanescent waves. Far-field propagation waves can propagate in free space and are easily captured by the human eye or optical equipment, but are limited by the diffraction limit. Although near-field evanescent waves are not limited by the diffraction limit, they decay exponentially with the propagation distance in the medium and are limited to the sub-wavelength near-field region on the surface of the object, making them difficult to be captured by conventional optical equipment.

[0004] Far-field super-resolution imaging is achieved by reducing or avoiding the diffraction effect between propagating waves, such as the super-resolution fluorescence microscopy technology that won the Nobel Prize in Chemistry in 2014. Near-field super-resolution imaging is achieved by capturing the near-field evanescent waves that carry super-resolution information on the surface of an object, mainly including near-field scanning optical microscopes, silver film flat superlenses, microsphere superlenses, and solid immersion lenses.

[0005] Although existing super-resolution optical imaging technologies have demonstrated unique advantages in different fields, they still face some limitations that need to be addressed. For example, super-resolution fluorescence microscopy has played an important role in biomedical research, but it relies on specific fluorescent probe labeling and is difficult to directly observe non-fluorescent substances. Near-field scanning optical microscopy has broken through the optical diffraction limit and achieved nanoscale resolution, but its light flux is small and the scanning imaging speed is slow, making it difficult to achieve large-field, fast, and high-throughput observation. In addition, near-field scanning microscopy has strict hardware requirements such as needle tip preparation and scanning distance control, resulting in high equipment costs, which limits its promotion and application. Although some emerging near-field super-resolution optical imaging technologies have achieved excellent resolution, they still face challenges in practical application. For example, the silver film superlens uses the surface plasmon effect to collect near-field subwavelength information of the sample, but its working band is mainly in the ultraviolet, and it is still difficult to achieve wide-bandwidth, high-contrast imaging in the visible light band. The microsphere superlens is easy to operate, but its imaging field of view is limited to a small area under a single micron-sized sphere, which is difficult to meet the observation needs of large-area samples. Solid immersion lenses use high refractive index lens materials to increase the numerical aperture of optical microscopes. However, due to the limitations of the selection and processing technology of high refractive index materials, their system construction and optimization still need to be broken through.

[0006] Therefore, it is particularly urgent to develop a new super-resolution optical microscopy technology with strong versatility, simple operation, fast imaging speed and large field of view. This new method should be able to avoid tedious sample pretreatment or fluorescent labeling process, directly realize fast, non-destructive and large-field super-resolution imaging of various material structures, and expand the application field of optical microscopes. At the same time, this new technology should also have the ability to be flexibly integrated with a variety of characterization methods to provide strong support for multimodal correlation studies of complex systems. This is of great significance for promoting cutting-edge research in many fields such as materials science, biomedicine, and micro-nano devices. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the prior art and provide a full-field super-resolution optical microscopy method based on a nanoparticle cracked thin film super-lens. This method uses dielectric nanoparticle materials with high refractive index, low optical absorption loss, and deep subwavelength scale to prepare a thin film flat super-lens with a large coating area and microscopic patterned cracks on the surface of the sample to be observed. This cracked thin film super-lens self-assembled by nanoparticles in a dispersion has the advantages of simple and fast preparation, low cost, and easy operation, and can achieve high-resolution, full-field super-resolution optical microscopy imaging under the dark field illumination mode of a conventional optical microscope. This super-lens will help to explore the microstructure and properties of matter more deeply, and has broad application prospects in scientific and industrial fields such as materials science, biomedicine, nanotechnology, optoelectronics, and semiconductors.

[0008] The present invention provides the following technical solutions:

[0009] The present invention provides a full-field super-resolution optical microscopic imaging method based on a nanoparticle cracked thin film superlens, comprising the following steps:

[0010] (1) A colloidal self-assembly method is used to apply a dispersion of dielectric nanoparticles with deep subwavelength size (i.e., particle size much smaller than the wavelength λ of visible light, usually smaller than λ / 10), high refractive index, and low optical absorption loss on the surface of a sample to be observed and dry the dispersion to form a nanoparticle film; wherein, a low-temperature cooling treatment is used to induce micro cracks inside the nanoparticle film, and finally a number of crack blocks with a size of 1 μm to 50 μm are formed;

[0011] (2) Under the dark-field illumination mode of an optical microscope, the incident light is incident obliquely onto a nanoparticle film with microscopic cracks. The multi-level micro-nanostructure of the nanoparticle film with microscopic cracks and the near-field coupling effect of the oblique light are utilized to achieve full-field capture of the super-resolution detail information of the sample.

[0012] The present invention uses a colloidal self-assembly method to apply a dispersion of dielectric nanoparticle materials with high refractive index, low optical absorption loss, and deep subwavelength scale on the surface of the sample to be observed, and prepares a thin film flat metalens with a large coating area and microscopic patterned cracks. Then, under the dark field illumination mode of the optical microscope, the incident light is obliquely incident on the sample surface, and the multi-level micro-nano structure composed of the densely packed structure of nanoparticles and the micron-scale patterned cracks in the crack film is near-field coupled with the oblique incident light, converting the nano near-field information on the sample surface into a propagable far-field signal, thereby breaking through the optical diffraction limit. At the same time, the enhancement effect of the local electromagnetic field at the edge of the crack can amplify the optical signal, and each crack block also plays the focusing role of a "super lens", ultimately achieving full-field super-resolution imaging.

[0013] Furthermore, the colloidal self-assembly method in step (1) includes any one of spin coating, drop coating, vertical immersion and pulling methods.

[0014] Furthermore, the particle size of the dielectric nanoparticles with deep subwavelength size in step (1) ranges from 1 nm to 50 nm to obtain the best near-field coupling effect and super-resolution imaging performance.

[0015] Furthermore, the dielectric nanoparticles have a refractive index in the visible light band of >1.4, preferably a refractive index >2, and an absorption coefficient in the visible light band of <10 -3 cm -1 .

[0016] Furthermore, the dielectric nanoparticles include any one of titanium dioxide, zirconium dioxide, barium titanate, silicon dioxide, and aluminum oxide.

[0017] Furthermore, the cryogenic cooling treatment includes cooling the nanoparticle film with liquid nitrogen at -196°C or cooling the dispersion with ice water at 0°C, so as to utilize thermal cold stress to induce the formation of micro cracks of appropriate size.

[0018] Furthermore, the size distribution of the crack blocks is regulated by controlling the concentration of the dispersion, the solvent evaporation rate, and the coating process parameters to optimize the super-resolution imaging effect.

[0019] Furthermore, in step (1), the surface of the sample to be observed is subjected to plasma treatment to improve the wettability of the nanoparticle dispersion on the sample surface and the close contact of the nanoparticles on the sample surface, thereby enhancing the near-field coupling optical effect.

[0020] Furthermore, in step (2), the angle between the incident light and the optical axis of the optical microscope objective is 60° to 80°.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. High imaging resolution and large field of view: The current near-field super-resolution imaging technology still has application bottlenecks such as high optical absorption loss, small imaging field of view or low scanning imaging efficiency, making it difficult to have high resolution, full field of view, high contrast and real-time super-resolution imaging performance; the present invention uses high refractive index dielectric nanoparticles to prepare flat film superlenses with surface crack patterning, breaking through the above bottlenecks, thereby achieving high resolution, full field of view, high contrast and real-time super-resolution imaging at the same time, and the imaging resolution can reach 100nm.

[0023] 2. The preparation method is simple, fast and low-cost: This method utilizes the self-assembly drying process of nanoparticle colloidal dispersion. By controlling parameters such as dispersion concentration, solvent evaporation rate, and low-temperature treatment temperature, a nanoparticle film with a microscopic crack pattern can be quickly prepared on the sample surface. No complex micro-nano processing equipment is required, which greatly reduces the difficulty and cost of preparation.

[0024] 3. Good compatibility with conventional optical microscopes: The present invention can achieve super-resolution imaging in the dark field mode of a conventional optical microscope without complicated modification of the microscope hardware. It is easy to operate and easy to promote and apply.

[0025] 4. Fast imaging speed and great potential for dynamic process observation: Compared with traditional point scanning super-resolution microscopy techniques such as near-field scanning optical microscopes, this method can collect full-field super-resolution images of samples in real time at one time, with fast imaging speed, and is expected to achieve high-resolution observation and detection of dynamic processes of nanoparticle samples such as viruses. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a schematic diagram of the optical principle of realizing full-field super-resolution microscopic imaging of the nanoparticle crack film of the present invention under dark-field illumination of a reflective optical microscope;

[0028] Figure 2 This is a schematic diagram of a process of preparing a nanoparticle crack film on the surface of a sample to be observed by spin coating in Example 1 of the present invention;

[0029] Figure 3 The scanning electron microscope (SEM) image of the surface of the blue-ray disc to be observed in Examples 1 to 3 of the present invention (showing that the surface has a parallel line periodic structure consisting of protrusions with a width of 200 nm and grooves with a width of 100 nm);

[0030] Figure 4 The ZrO prepared on the surface of the blue-ray disc by spin coating in Example 1 of the present invention 2 Optical micrograph of the nanoparticle crack film obtained in the dark field illumination mode of an optical microscope with a 100x objective;

[0031] Figure 5 In Example 1 of the present invention, liquid nitrogen at -196°C is used to Figure 4 Medium ZrO 2 After cooling the surface of the nanoparticle crack film, smaller cracks are produced, and the optical micrograph of the 100nm scale pattern on the surface of the blue-ray disc is clearly presented in the dark field illumination mode of the 100x objective lens;

[0032] Figure 6 for Figure 5 A magnified image of a local area in the image;

[0033] Figure 7 The TiO prepared by spin coating method in Example 2 of the present invention 2 The nanoparticle crack film clearly distinguishes the super-resolution imaging of the 100nm spacing structure on the surface of the blue-ray disc under the dark field illumination mode of the 100x objective lens;

[0034] Figure 8 The SiO prepared by spin coating method in Example 3 of the present invention 2 High-magnification SEM image of nanoparticle cracked film;

[0035] Fig. 9The SiO prepared by spin coating method in Example 3 of the present invention 2 Bottom and side SEM images of nanoparticle cracked films;

[0036] Fig.10 The SiO prepared by spin coating method in Example 3 of the present invention 2 The nanoparticle crack film can also distinguish the super-resolution imaging of the 100nm spacing structure on the surface of the blue-ray disc under the dark field illumination mode of the 100x objective lens;

[0037] Fig.11 The ZrO prepared by the drop coating method in Example 4 of the present invention 2 Optical micrograph of the nanoparticle cracked film obtained in dark field illumination mode with a 100x objective;

[0038] Fig.12 ZrO-free 2 Optical micrographs obtained by direct observation in bright field illumination mode with a 100x objective when nanoparticles cracked the film;

[0039] Fig.13 ZrO-free 2 Optical micrographs obtained by direct observation in dark field illumination mode with a 100x objective when nanoparticles cracked the film;

[0040] Fig.14 This is a high-resolution field emission SEM image of the chip surface of Example 4 of the present invention;

[0041] Fig.15 The ZrO prepared by spin coating method in Example 5 of the present invention 2 Nanoparticle crack film Super-resolution imaging of 230nm polymer nanospheres scattered on the surface of a blue-ray disc observed under dark-field illumination mode with a 100x objective lens;

[0042] Fig.16 ZrO-free 2 When nanoparticles crack the film, the imaging image of 230nm polymer nanospheres scattered on the surface of the blue disc is directly observed under the dark field illumination mode of the 100x objective lens. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The embodiment of the present invention provides a full-field super-resolution optical microscopy imaging method based on a nanoparticle cracked thin film superlens, comprising the following steps:

[0045] (1) Preparation of nanoparticle cracked thin film superlens: Using colloidal self-assembly methods such as spin coating, drop coating, vertical immersion, and pulling methods, a nanoparticle cracked thin film superlens with high refractive index (refractive index in the visible light band>1.4, preferably refractive index>2.0) and low optical absorption loss (absorption coefficient in the visible light band<10 -3 cm -1 A dispersion of deep sub-wavelength dielectric nanoparticles (such as titanium dioxide, zirconium dioxide, barium titanate, silicon dioxide, aluminum oxide, etc.) with a particle size in the range of 1-50nm is coated on the surface of the sample to be observed and dried to form a nanoparticle self-assembled film composed of densely packed nanoparticles. Through low-temperature treatment such as cooling the dispersion with ice water at 0℃ or cooling the nanoparticle film with liquid nitrogen at -196℃, micro cracks are induced inside the film by using cold and hot shrinkage stress, so that the crack block size is adjusted to a suitable range of 1μm to 50μm.

[0046] Among them, the spin coating method uses high-speed rotation to evenly spread the nanoparticle dispersion added on the surface of the sample to be observed and dry it into a film; the drop coating method uses the natural evaporation of the solvent to dry the dispersion added on the sample surface to form a thin film; the vertical immersion method immerses the sample vertically into the dispersion, and a thin film is deposited on the sample surface as the solvent evaporates and the liquid level drops; the pulling method pulls the sample out of the dispersion at a constant speed, and uses the flow and drying process of the dispersion to form a thin film.

[0047] Preferably, for samples to be observed whose surfaces are hydrophobic, oxygen plasma cleaning can be used to hydrophilize the surfaces, so as to improve the wettability of the nanoparticle aqueous dispersion on the sample surface and enhance the close contact between the self-assembled film and the sample surface. For samples to be observed whose surfaces are already hydrophilic (such as glass, metal, etc.), this step can be omitted.

[0048] (2) Full-field super-resolution optical microscopy imaging is performed using the prepared nanoparticle crack film superlens. In the dark field oblique illumination mode of an optical microscope, high-resolution, full-field, high-contrast, and real-time super-resolution optical microscopy imaging can be achieved by observing the sample covered by the nanoparticle crack film.

[0049] See also Figure 1, is a schematic diagram of the optical principle of the present invention using nanoparticle cracked film to achieve full-field super-resolution imaging under dark-field illumination of an optical microscope. The bottom surface of the nanoparticle film fits tightly with the surface of the sample to be tested, so that the film can accurately match the concave and convex morphology of the sample surface, which is conducive to collecting near-field evanescent waves on the sample surface. In addition, there are a large number of grid-like microscopic cracks distributed in the nanoparticle film, which play a key role in field enhancement and light transmission.

[0050] Under dark field illumination conditions, the incident light is incident on the surface of the nanoparticle film at a large angle of 60° to 80°. When the light wave encounters a crack, strong scattering and diffraction will occur at the edge of the crack, forming a highly localized electromagnetic field. This field enhancement effect can effectively break through the diffraction limit of traditional optical microscopes, allowing the incident light to be focused at a scale much smaller than the wavelength. Each crack block can be regarded as a "super lens" that focuses the incident light to the nanoscale, making the crack block a sub-wavelength point light source.

[0051] When the sample is placed in the near-field region of the nanoparticle crack film, these subwavelength light sources can effectively excite the nanostructure on the sample surface to produce near-field evanescent waves, carrying the super-resolution structural information of the sample. The nanoparticle fragments can not only excite the near-field evanescent waves, but also transform them into scattered waves that can propagate in the far field, so that the super-diffraction sample information can be received and imaged by the objective lens. Since each crack block in the film participates in the excitation, transformation and propagation process of super-resolution details, this scheme realizes full-field super-resolution optical microscopy imaging.

[0052] The present invention will be further described below by means of specific examples.

[0053] Example 1

[0054] The full-field super-resolution optical microscopy imaging method based on the nanoparticle crack film superlens in this embodiment has the following specific process:

[0055] (1) Preparation of nanoparticle dispersion:

[0056] Use commercially available ZrO 2 The aqueous dispersion of nanoparticles (particle size 10 nm) was placed in an open glass bottle and heated in an oven at 60°C to evaporate part of the water, so that the solid content of the dispersion was increased to 25wt%.

[0057] (2) Hydrophilic treatment of sample surface:

[0058] A blue-ray disc with a 100nm line-groove spacing structure on the surface was used as the sample to be observed. The blue-ray disc was cut into small pieces of 2cm×2cm, the protective film on the surface was peeled off, and the surface was placed in a plasma cleaning machine for surface hydrophilization treatment. The treatment conditions were: pure oxygen plasma atmosphere, power 100W, time 2min.

[0059] (3) Assembling nanoparticle cracked film superlenses:

[0060] Fix the Blu-ray disc with hydrophilic surface treatment on the suction cup of the spin coater and add an appropriate amount of nanoparticle aqueous dispersion. Set the spin coating parameters: speed 1500rpm, time 60s. After the spin coating is completed, the nanoparticles can self-assemble on the surface of the Blu-ray disc to form a film with a crack structure. In order to obtain smaller crack blocks, spray -196℃ liquid nitrogen on the surface of the film to quickly cool the film and produce smaller crack blocks.

[0061] (4) Full-field super-resolution optical microscopy:

[0062] The blue-ray disc sample coated with nanoparticle crack film was placed on the stage of a reflective optical microscope (Nikon Eclipse LV-100). First, the crack film was focused with a 100x objective lens (Nikon LU Plan Fluor, numerical aperture NA = 0.9) under bright field illumination. At this time, the 100nm spacing structure on the surface of the blue-ray disc could not be observed. After switching to dark field illumination mode, the incident angle of the oblique light was about 68°. Through each crack block in the crack film, the 100nm spacing structure on the surface of the blue-ray disc could be clearly observed, achieving full-field super-resolution imaging. The incident angle of the oblique light under dark field illumination mainly depends on parameters such as the numerical aperture NA and working distance of the objective lens used. For high-magnification objective lenses (such as 100x, NA is usually between 0.7 and 0.95), the incident angle of the oblique light in dark field illumination is generally set between 60° and 80°, so as to ensure good dark field contrast while taking into account the focusing ability of the objective lens and the working distance limitation.

[0063] In this embodiment, for a 100x objective lens using white light illumination (average light wavelength λ = 550nm), according to the Abbe limit formula d = λ / (2NA), its limit resolution d is about 306nm, so it is impossible to directly distinguish the fine structure of 100nm on the surface of the Blu-ray disc. However, the use of nanoparticle crack film superlens can break through the diffraction limit of conventional optical microscopes and increase the imaging resolution of optical microscopes by 3 times to 100nm.

[0064] In addition, when the surface of the Blu-ray disc is directly observed under an optical microscope or the surface of the Blu-ray disc coated with a crack-free nanoparticle film as a control experiment, the 100nm detailed structure of the Blu-ray disc surface cannot be distinguished. This shows that the synergistic effect of the microscopic crack pattern of the nanoparticle film and the dark field oblique illumination is crucial to achieve full-field super-resolution imaging.

[0065] in, Figure 2 Schematic diagram of the preparation of nanoparticle crack film by spin coating. The nanoparticle aqueous dispersion is added to the surface of the sample to be observed and evenly spread by spin coating. As the water evaporates, the nanoparticles self-assemble under capillary action to form a film with densely packed particles, and the film cracks due to internal stress contraction, forming a network-like crack structure. The morphological characteristics of the crack film, such as the size and thickness of the cracks, can be controlled by optimizing the process parameters such as the concentration of the nanoparticle aqueous dispersion and the spin coating speed.

[0066] Figure 3 This is a SEM image of the surface of a blue-ray disc. It can be clearly observed that the surface has a regular parallel arrangement of concave and convex line periodic structure. The width of the convex part is 200nm, and the width of the groove between two adjacent convex parts is 100nm.

[0067] Figure 4 ZrO prepared on the surface of Blu-ray disc by spin coating 2 Microscopic imaging of a nanoparticle cracked film under dark field illumination mode with a 100x objective lens of an optical microscope. At this time, the size of the crack block in the cracked film is relatively large, and the 100nm spacing structure on the surface of the blue-ray disc can only be observed in the area surrounding the crack.

[0068] Figure 5 For the use of -196℃ medical liquid nitrogen spray Figure 4 ZrO 2 The imaging results of the nanoparticle crack film surface after spraying. After the liquid nitrogen cooled the film and evaporated and dried, the cold and hot shrinkage stress formed a smaller crack block. Under the dark field illumination mode of the 100x objective lens, the 100nm scale pattern on the surface of the blue-ray disc is clearly shown inside each crack block. The field of view of the microscopic image in the figure reaches 103×69μm 2 , i.e. 7107 μm 2 , far exceeding the current range of a single microsphere superlens that can only reach a few square microns to tens of square microns. Therefore, the super-resolution optical microscopy imaging technology based on nanoparticle crack films has obvious advantages in imaging field of view, providing new possibilities for achieving larger-scale and higher-throughput nanostructure characterization.

[0069] Figure 6 yes Figure 5The enlarged image of a local area clearly distinguishes the groove spacing of only 100nm and the convex structure of 200nm on the surface of the Blu-ray disc. 2 The nanoparticle crack film forms a uniform crack structure over a large area, and each crack block can achieve super-resolution imaging, thus achieving full-field nanoscale resolution microscopic imaging under an optical microscope.

[0070] Example 2

[0071] The steps of this embodiment are basically the same as those of embodiment 1, except that: in step (1), the nanoparticle dispersion liquid is commercially available TiO 2 The aqueous dispersion of nanoparticles (particle size 15 nm) is placed in a 60°C oven to heat and evaporate part of the water, thereby increasing the solid content of the dispersion to 20%. In step (3), ice water precooled to 0°C is used to lower the temperature of the dispersion, and then spin coating is performed (spin coating parameters are the same as in Example 1) to directly form a small-sized crack structure.

[0072] Figure 7 The TiO prepared by spin coating in this example is shown 2 The imaging effect of the nanoparticle crack film under an optical microscope. Under a 100x objective lens and dark field illumination mode, the crack block can clearly distinguish the 100nm spacing structure on the surface of the Blu-ray disc, achieving super-resolution imaging.

[0073] Example 3

[0074] The steps of this embodiment are basically the same as those of embodiment 1, except that: in step (1), the nanoparticle dispersion liquid is commercially available SiO 2 The aqueous dispersion of nanoparticles (particle size 15 nm) has a solid content of 20%; in step (3), ice water precooled to 0° C. is used to lower the dispersion temperature, and then spin coating is performed (spin coating parameters are the same as in Example 1) to directly form a small-sized crack structure.

[0075] See also Figure 8 , is SiO prepared by spin coating 2 High-magnification SEM image of the nanoparticle crack film. It can be clearly observed from the figure that the film is composed of a large amount of SiO 2 The nanoparticles are tightly packed and assembled, with uniform particle size and distribution, and the surface of the nanoparticle film is flat. The crack width between two adjacent crack blocks is about 500nm.

[0076] Fig. 9 The spin coating method was used to prepare SiO 2 SEM images of the bottom and side surfaces of the nanoparticle crack film. It can be clearly observed from the bottom surface of the film that SiO 2The bottom surface morphology of the nanoparticle film is completely complementary to the concave-convex structure of the Blu-ray disc surface, confirming that SiO 2 The nanoparticle film fits tightly to the surface of the Blu-ray disc, and the interface is well bonded. The side of the film directly shows the SiO 2 The thickness of nanoparticle films is in the order of hundreds of nanometers. This submicron-level film thickness is conducive to achieving excellent optical and mechanical properties.

[0077] Fig.10 The SiO prepared by spin coating in this example is shown 2 The imaging effect of the nanoparticle crack film under an optical microscope. Under a 100x objective lens and dark field illumination mode, the crack block can also distinguish the 100nm spacing structure on the surface of the Blu-ray disc, achieving super-resolution imaging.

[0078] Generally speaking, the higher the refractive index and the smaller the particle size of the nanoparticles, the better the super-resolution imaging effect of the nanoparticle crack film superlens prepared therefrom. 2 Nanoparticles (refractive index 2.15, particle size 10 nm) and TiO 2 The imaging effect of nanoparticle films (refractive index 2.66, particle size 15nm) is better than that of SiO 2 Imaging effect of nanoparticle (refractive index 1.46, particle size 15nm) film.

[0079] The use of deep subwavelength high-refractive-index nanoparticles to prepare cracked thin-film metalenses has the following main advantages: when the particle size is much smaller than the wavelength of the incident light, the interaction between light and particles is mainly manifested as Rayleigh scattering, and the scattering cross section is proportional to the sixth power of the particle size. Therefore, reducing the particle size can significantly reduce the scattering loss and improve the optical transmittance of the metalens; in addition, nanoparticles have a higher specific surface area and surface energy, which makes it easier to achieve uniform dispersion and dense stacking, and can obtain a more uniform and dense microstructure, reduce defects and inhomogeneities inside the film, and improve the imaging quality of the metalens; high-refractive-index nanoparticles have a strong light field localization effect on near-field light, and can limit the light energy within the nanoscale range. This light field localization enhancement effect can be used to optimize the imaging performance of the metalens; at the same time, the use of high-refractive-index nanoparticles can obtain a higher effective refractive index at a limited filling fraction; the use of inorganic dielectric nanoparticles with good chemical stability and strong corrosion resistance can also improve the material stability and service life of the cracked thin-film metalens.

[0080] Example 4

[0081] This example uses ZrO 2 Aqueous dispersion of nanoparticles was used to prepare ZrO on the surface of semiconductor chips by drop coating and low temperature stress induction. 2Nanoparticle crack film superlens. Using the dark field illumination mode of a conventional optical microscope, full-field super-resolution imaging of periodic nanostructures on the chip surface is achieved.

[0082] The specific process is as follows:

[0083] (1) ZrO 2 Preparation of Nanoparticle Dispersion:

[0084] The commercially available ZrO 2 The aqueous dispersion of nanoparticles (particle size 10 nm) was placed in an open glass bottle and heated in an oven at 60° C. to evaporate part of the water, thereby increasing the solid content of the dispersion to 25 wt %.

[0085] (2) Hydrophilic treatment of sample surface:

[0086] A chip with a periodic nanostructure on its surface was used as the sample to be observed. The chip was cut into small pieces of 2 cm × 2 cm and placed in a plasma cleaning machine for surface hydrophilization treatment. The treatment conditions were: pure oxygen plasma atmosphere, power 100 W, time 2 min.

[0087] (3) Assembly of ZrO by drop coating 2 Nanoparticle Cracked Thin Film Metalenses:

[0088] Use a dropper to add an appropriate amount of ZrO 2 The nanoparticle aqueous dispersion is added dropwise to the surface of the chip after the surface hydrophilic treatment, so that the aqueous dispersion forms a liquid film on the chip surface, and then the chip is tilted to pour off the excess aqueous dispersion. Then the aqueous dispersion on the chip surface is allowed to dry naturally or with an electric hair dryer. 2 Nanoparticles can self-assemble on the chip surface to form crack films. In order to obtain smaller crack blocks, ZrO 2 -196℃ liquid nitrogen is sprayed on the surface of the nanoparticle film to quickly cool the film, thereby producing a smaller crack structure.

[0089] (4) Full-field super-resolution optical microscopy:

[0090] The ZrO 2 The chip sample of the nanoparticle crack film was placed on the stage of a reflective optical microscope (Nikon Eclipse LV-100), and the sample was imaged and observed in dark field illumination mode using a 100x objective lens (NA = 0.9), with the incident angle of the oblique light being about 68°. Fig.11 As shown, through ZrO 2 The nanoparticle crack film can clearly observe the 3×3 lattice structure inside the square array on the right side of the chip.

[0091] To further prove that ZrO2 We conducted a series of control experiments to demonstrate the unique advantages of nanoparticle crack films in imaging the internal structure of chips. 2 In the case of nanoparticle crack films, the same optical microscope and 100x objective were used, regardless of whether brightfield illumination mode ( Fig.12 ) or dark field illumination mode ( Fig.13 ), we were unable to observe the fine lattice structure inside the square array. This shows that conventional optical microscopes are limited by resolution and it is difficult to image the micro-nanostructure inside the chip at high magnification. We also used a field emission SEM with higher resolution to image the exposed chip surface ( Fig.14 ). However, due to the transparent coating layer on the chip surface, even field emission SEM cannot penetrate the coating layer and directly observe the 3×3 lattice structure inside the block. This further highlights that ZrO 2 The nanoparticle crack film has significant advantages and unique functions in achieving high-resolution imaging of the internal structure of the chip. Therefore, this method provides a simple and efficient solution for super-resolution optical non-destructive testing of chip surface structures.

[0092] Example 5

[0093] In this study, ZrO was prepared on the surface of a blue-ray disc coated with monodisperse polystyrene (PS) nanospheres with a particle size of 230 nm by spin coating and low-temperature stress induction. 2 Nanoparticle crack film superlens, and through the dark field illumination mode of a conventional optical microscope, full-field super-resolution imaging detection of 230nm polymer nanospheres was achieved.

[0094] The specific process is as follows:

[0095] (1) ZrO 2 Preparation of Nanoparticle Dispersion:

[0096] The commercially available ZrO 2 The aqueous dispersion of nanoparticles (particle size 10 nm) was placed in an open glass bottle and heated in an oven at 60° C. to evaporate part of the water, thereby increasing the solid content of the dispersion to about 25 wt %.

[0097] (2) Hydrophilic treatment of sample surface:

[0098] The blue-ray disc with a 100nm line width groove periodic structure on the surface was cut into small pieces of 2cm×2cm, the protective film was peeled off, and the surface was put into a plasma cleaning machine for surface hydrophilization treatment. The treatment conditions were: pure oxygen plasma atmosphere, power 100W, time 2min.

[0099] (3) Coating of PS nanospheres:

[0100] The hydrophilic surface treated Blu-ray disc was fixed on the suction cup of the spin coater, and a low concentration of 230nm PS nanosphere aqueous dispersion was added. The spin coating was performed at 1500rpm for 60s to make the nanospheres scattered on the surface of the Blu-ray disc.

[0101] (4) Spin coating method to assemble ZrO 2 Nanoparticle Cracked Thin Film Metalenses:

[0102] Fix the blue disc coated with 230nm nanospheres on the suction cup of the spin coater and add appropriate amount of ZrO 2 Nanoparticles aqueous dispersion. Spin coating at 1500 rpm for 60 s to make ZrO 2 Nanoparticles self-assemble on the surface of blue-ray discs and PS nanospheres to form a film with a crack structure. 2 -196℃ liquid nitrogen is sprayed on the surface of the nanoparticle film to quickly cool the film and produce smaller crack structures.

[0103] (5) Full-field super-resolution optical microscopy:

[0104] The samples were imaged and observed using a 100x objective lens (NA = 0.9) in dark field illumination mode of a reflective optical microscope (Nikon Eclipse LV-100), with the incident angle of oblique light being approximately 68°. 2 The nanoparticle crack film superlens successfully observed the clear outline of polymer nanospheres with a diameter of only 230nm, and the fine groove structure with a period of 100nm on the surface of the blue-ray disc ( Fig.15 ). In contrast, in the absence of ZrO 2 In the case of nanoparticle cracked films, the outline of the nanospheres becomes blurred due to the optical diffraction limit, and obvious diffraction rings appear around them. At the same time, the 100nm sub-wavelength structure on the surface of the Blu-ray disc cannot be distinguished ( Fig.16 ). This comparison result strongly demonstrates the remarkable ability of nanoparticle crack film superlens to break through the optical diffraction limit and achieve high-resolution imaging of subwavelength nanostructures.

[0105] It can be seen that the nanoparticle crack film superlens technology provides a new approach to the field of optical microscopy, allowing people to break through the resolution limit of traditional optical microscopes and achieve high-resolution imaging of sub-wavelength nanostructures. This technology is expected to be widely used in high-throughput optical detection and imaging analysis of nanoscale samples such as nanoparticles and virus particles, providing a novel, simple and efficient means for the characterization of nano-fine structures in the fields of materials science and biomedicine, and has important scientific significance and application value.

[0106] In summary, the present invention uses dielectric nanoparticles with deep subwavelength size, high refractive index and low optical loss, and prepares a cracked thin film superlens by a dispersion self-assembly method. The superlens cleverly utilizes the near-field coupling effect of nanoparticles and the field localization characteristics of cracks, providing new ideas and solutions for achieving low-loss, large field of view and high-resolution optical imaging. It is worth mentioning that the preparation process is simple and easy, and the crack structure can be flexibly adjusted by adjusting the experimental parameters, laying the foundation for the industrial application of the device. This superlens technology based on nanoparticle cracked thin films has broad application prospects in many fields such as super-resolution imaging, lithography, and sensing, and is expected to promote innovation and development in related fields.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A full-field super-resolution optical microscopy imaging method based on nanoparticle cracked thin film superlens, characterized in that: The following steps are involved: (1) Preparation of nanoparticle dispersion: A commercially available aqueous dispersion of ZrO2 nanoparticles was used, the dispersion was placed in an open glass bottle, and heated in an oven at 60°C to evaporate part of the water, so that the solid content of the dispersion was increased to 25wt%; the particle size of the ZrO2 nanoparticles was 10nm; (2) Hydrophilic treatment of sample surface: A blue-ray disc with a line-groove spacing of 100 nm was used as the sample to be observed; the blue-ray disc was cut into small pieces of 2 cm × 2 cm, the protective film on the surface was peeled off, and the surface was placed in a plasma cleaning machine for surface hydrophilic treatment; the treatment conditions were: pure oxygen plasma atmosphere, power 100 W, time 2 min; (3) Assembling nanoparticle crack thin film superlens: fix the surface hydrophilic treated Blu-ray disc on the suction cup of the spin coater, and add an appropriate amount of nanoparticle aqueous dispersion; set the spin coating parameters: speed 1500rpm, time 60s; after the spin coating, the nanoparticles can self-assemble on the surface of the Blu-ray disc to form a thin film with a crack structure; then, in order to obtain smaller crack blocks, spray -196℃ liquid nitrogen on the surface of the film to quickly cool the film, generating a number of crack blocks with a size of 1μm to 50μm; In the dark field illumination mode of the optical microscope, the incident light is incident obliquely onto the nanoparticle film with microscopic cracks. The multi-level micro-nanostructure of the nanoparticle film with microscopic cracks and the near-field coupling effect of the oblique light are used to achieve full-field capture of the super-resolution detail information of the sample. The angle between the incident light and the optical axis of the optical microscope objective is 68°.

Images