Large-angle broadband antireflection film and manufacturing method thereof

文档序号：1903658 发布日期：2021-11-30 浏览：25次中文

阅读说明：本技术 一种大角度宽波段减反射膜及其制作方法 (Large-angle broadband antireflection film and manufacturing method thereof ) 是由沈伟东王海兰杨陈楹李强张占军金永红章岳光郑婷婷陈潇于 2021-08-17 设计创作，主要内容包括：本发明公开了一种大角度宽波段减反射膜,包括基底,还包括设于基底上的高/低折射率交替膜堆以及设于高/低折射率交替膜堆顶面的纳米结构超低折射率膜层。本发明基于成熟的薄膜沉积技术以及简单快速的水腐蚀法,通过简便的操作控制渐变折射率膜层的厚度以及等效折射率,结合多层膜结构来调整大角度下宽波段的剩余反射率,适于大面积批量化生产,从而使得减反射膜成本大大降低,有望在光学元件、传感器、成像光学系统和太阳能电池等产品中广泛应用,为我国国民经济、社会发展、科学技术和国防建设等领域作出贡献。(The invention discloses a large-angle broadband antireflection film which comprises a substrate, a high/low refractive index alternative film stack arranged on the substrate and a nano-structure ultralow refractive index film layer arranged on the top surface of the high/low refractive index alternative film stack. Based on a mature thin film deposition technology and a simple and rapid water corrosion method, the thickness and the equivalent refractive index of the graded-refractive-index film layer are controlled through simple and convenient operation, the residual reflectivity of a wide band at a large angle is adjusted by combining a multi-layer film structure, and the method is suitable for large-area mass production, so that the cost of the antireflection film is greatly reduced, the antireflection film is expected to be widely applied to products such as optical elements, sensors, imaging optical systems, solar cells and the like, and contributes to the fields of national economy, social development, scientific technology, national defense construction and the like in China.)

1. The wide-angle broadband antireflection film comprises a substrate and is characterized by further comprising a high/low refractive index alternate film stack arranged on the substrate and a nano-structure ultralow refractive index film layer arranged on the top surface of the high/low refractive index alternate film stack.

2. The high-angle broadband antireflection film of claim 1, wherein the nanostructured ultra-low refractive index film layer is a grass-like alumina nanostructure layer.

3. The high-angle broadband antireflection film of claim 1, wherein the nanostructured ultra-low refractive index film layer is a graded refractive index layer obtained by treating an aluminum oxide film with deionized water.

4. The high angle broadband antireflection film of claim 1 wherein said nanostructured ultra-low refractive index film layer provides an equivalent film layer matching a low refractive index film layer.

5. The high-angle broadband antireflection film according to claim 1, wherein the physical thickness of the nanostructure ultra-low refractive index film layer is 200 to 250 nm.

6. The high angle broadband antireflection film of claim 1, wherein said nanostructured ultra-low refractive index film layer is obtained by a method comprising: the alumina film is put into deionized water to be soaked for 30min-5h at the temperature of 60-90 ℃.

7. The high angle broadband antireflection film of claim 1 wherein in the high/low index alternating film stack, the high index material is selected from one or more of titanium dioxide, hafnium oxide, niobium oxide, zirconium oxide, tantalum oxide, silicon nitride, lanthanum titanate, and germanium; the low refractive index material is selected from one or more of silicon oxide, aluminum oxide, fluoride, zinc sulfide and zinc selenide.

8. The high-angle broadband antireflection film according to claim 1, wherein in the high/low refractive index alternating film stack, the number of high refractive index film layers is 1 to 20, and the thickness is 5 to 300 nm; the number of the low refractive index film layers is 1-20, and the thickness is 5-350 nm.

9. The high-angle broadband antireflection film according to any one of claims 1 to 8, wherein when the refractive index of the outermost material of the high/low refractive index alternate film stack is not matched with the refractive index of the nanostructured ultralow refractive index film layer, a buffer layer is arranged between the high/low refractive index alternate film stack and the nanostructured ultralow refractive index film layer.

10. The method for preparing a high-angle broadband antireflection film according to any one of claims 1 to 9, comprising:

(1) after the thickness of the nano-structure ultra-low refractive index film layer is determined, determining the material, the layer number and the thickness of the high/low refractive index alternate film stack by optimizing the thickness of each layer of film according to the bandwidth requirement and the reflectivity requirement of the required antireflection film; when the buffer layer is arranged, determining the material and the thickness of the buffer layer at the same time;

(2) sequentially depositing a high/low refractive index alternate film stack on a substrate by adopting vacuum coating, and covering a precursor film layer corresponding to the nano-structure ultra-low refractive index film layer with a set thickness on the outermost layer of the high/low refractive index alternate film stack; when the buffer layer is arranged, firstly covering the outermost layer of the high/low refractive index alternate film stack with the buffer layer, and then covering the outer surface of the buffer layer with a precursor film layer corresponding to the nano-structure ultra-low refractive index film layer with a set thickness;

(3) and processing the precursor film layer to obtain the nano-structure ultra-low refractive index film layer, and finally obtaining the large-angle broadband antireflection film.

Technical Field

The invention belongs to the technical field of antireflection film processing, and particularly relates to a large-angle broadband antireflection film and a manufacturing method thereof.

Background

The antireflection film is an essential optical element in an optical system, and is an optical thin film with the highest utilization rate at present. With the upgrading of products in application fields such as mobile phones, security protection, vehicles, precision measurement and the like, the requirements on an optical imaging system are higher and higher, the number of lenses in the system is increased, and the large-curvature surface is used, so that the antireflection film with large angle and wide wavelength band becomes one of key factors for reducing the stray light of the system and improving the imaging quality. In the design of broadband antireflection films, there is always a conflict between the bandwidth of the antireflection spectral range and the average residual reflectivity, and the broadening of the spectral range will result in an increase in the average residual reflectivity; meanwhile, as the incident angle increases, the admittance mismatch between the air and the substrate increases, which also results in an increase in reflectivity. According to the thin film optical theory, the refractive index of the outermost thin film has the greatest influence on the residual reflectivity of the broadband multilayer antireflection film, but at present, no natural ultralow-refractive-index material is used for matching in nature, so that the perfect antireflection effect is realized. In order to realize high-efficiency reflection reduction of wide-angle wide wave bands, researchers introduce a low-refractive-index film layer of a bionic micro-nano structure to optimize a reflection reduction film, such as a compound eye structure imitating insects, a butterfly wing structure, a horny layer structure imitating arthropods, a feather structure imitating peacocks or hummingbirds and the like.

Compared with the traditional multilayer film stack antireflection film structure, the antireflection film based on the nano structure has the advantages that 1) the nano structure antireflection film can realize effective regulation and control of structural characteristics such as duty ratio, period, thickness and the like of the film by controlling process conditions, namely, the equivalent refractive index of the film is regulated so as to obtain an ultralow-refractive-index film layer lower than the refractive index of a conventional material, and perfect antireflection is realized. 2) Part of the nano structure is a graded refractive index layer with space change, and the sensitivity to the incident direction and the antireflection wave band of light is obviously reduced, so that the nano structure has important significance in large-angle wide-wave-band antireflection. 3) The surface of the microstructure is uneven, and the rough surface has a hydrophobic characteristic, so that the cleaning work of the film is facilitated.

In recent years, a nanostructure low-refractive-index film layer and a multilayer film stack structure are combined and widely applied to design of an antireflection film, but the design method and the film performance are greatly different. The multilayer film structure mostly adopts modes of electron beam evaporation, magnetron sputtering and the like, and the nanometer low refractive index film layer adopts reactive ion etching, electrostatic self-assembly, a sol-gel method and the like, and most of the methods have complex preparation process, long time consumption and expensive required equipment.

Disclosure of Invention

The invention provides a large-angle broadband antireflection composite film layer based on a nanostructure and high-low refractive index alternate film stack, which is simple to prepare, suitable for large-format and batch production, and also applicable to complex optical surfaces, large-curvature optical elements and the like.

The invention provides a large-angle broadband antireflection composite film layer based on a nanostructure and a high-low refractive index alternate film stack, which is widely applied to optical systems such as security monitoring lenses, vehicle-mounted lenses, mobile phone lenses, microscope precision measuring instruments and the like.

The wide-angle broadband antireflection film comprises a substrate, a high/low refractive index alternate film stack arranged on the substrate and a nano-structure ultralow refractive index film layer arranged on the top surface of the high/low refractive index alternate film stack.

In the present invention, the "bottom surface" refers to the side of the high/low refractive index alternating film stack that is closest to the substrate, and the "top surface" refers to the side that faces away from the bottom surface, i.e., the side that receives incident light.

Preferably, the nanostructure ultralow-refractive-index film layer provides an equivalent film layer matched with the low-refractive-index film layer (preferably, the equivalent refractive index of the bottommost nanostructure ultralow-refractive-index film layer is 1.2-1.25).

Preferably, the nanostructured ultra-low refractive index film layer is a grass-like alumina nanostructure layer. Preferably, the grass-shaped alumina nano-structure layer is a structure with gradually reduced porosity from the outer side to the inner side (close to the top surface of the high/low refractive index alternating film stack).

Preferably, the nano-structure ultra-low refractive index film layer is a structure obtained by treating an alumina film with deionized water. Preferably, the nano-structure ultra-low refractive index film layer structure can be obtained by treating the aluminum oxide film with deionized water heated in a water bath. Preferably, the nano-structure ultra-low refractive index film layer is a graded refractive index layer obtained by treating an alumina film with deionized water.

The invention utilizes the chemical reaction of the alumina film and the high-temperature deionized water to prepare the nanometer alumina structure ultra-low refractive index film layer. In high temperature deionized water, the alumina film undergoes hydration, dynamic dissolution/precipitation and roughening processes. This hydration compounding process ultimately results in the crystallization of amorphous alumina into bayerite and gibbsite with a concomitant increase in the molar volume of the alumina film. The specific reaction principle is as follows:

Al₂O₃(s)+6H⁺(aq)+3H₂O(l)→2[Al(H₂O)₃]³⁺(aq)

Al₂O₃(s)+6OH^-(aq)+3H₂O(l)→2[Al(OH)₄]^-(aq)

it can be seen that alumina reacts with H in water⁺And OH^-The reaction is carried out and water molecules are combined to generate new substances, so that the molar volume of a new film layer is increased, and the increase of the thickness of the nano-structure film is mainly reflected; the porosity of the film layer is increased, a graded refractive index film layer with space change is formed, and the pores are gradually increased from top to bottom.

The grass-shaped alumina nano structure can realize effective regulation and control of the physical thickness and the equivalent refractive index of the nano film layer by controlling the thickness of the initial alumina film and the experimental conditions of subsequent deionized water treatment. The nano structure is combined with a matched multilayer film stack with high refractive index and low refractive index alternately to obtain the antireflection composite film layer with specific wave bands (visible, visible-near infrared, near infrared and the like) and large angles (0-80 degrees).

According to the target antireflection wave band, the thickness of the aluminum oxide film before deionized water treatment can be set to a certain value of 10nm-150nm, and the thickness determines the physical thickness of the grass-shaped aluminum oxide film after deionized water treatment, so that the central wavelength of the antireflection wave band is influenced. Preferably, the physical thickness of the nano-structure ultra-low refractive index film layer is 150nm-300 nm. Preferably, the thickness of the aluminum oxide film is 30nm, the aluminum oxide film with the thickness of 30nm is treated, the physical thickness is 200nm-250nm, the central wavelength is in the range of 550nm-600nm, and the aluminum oxide film is suitable for large-angle antireflection of a visible light wave band.

Preferably, the nanostructured ultra-low refractive index film layer is obtained by a water bath heating method: the alumina film is put into deionized water to be soaked for 30min-5h at the temperature of 60-90 ℃. Preferably, the soaking temperature is 90 ℃, and the soaking time is 1 h. The soaking solution may be selected from deionized water and other solutions containing primarily water.

In the invention, the high/low refractive index alternating film stack is composed of non-absorbing medium materials: the high refractive index material can be selected from oxide (titanium dioxide, hafnium oxide, niobium oxide, zirconium oxide, tantalum oxide, etc.), nitride (silicon nitride, etc.), and mixed material lanthanum titanate (LaTiO)₃For short, H₄) And the infrared band is germanium; the low refractive index material can be selected from oxides (silicon oxide, aluminum oxide and the like) and fluorides (magnesium fluoride, yttrium fluoride, ytterbium fluoride and the like), and sulfides such as zinc sulfide, zinc selenide and the like are selected for the infrared band. The nano-structure ultra-low refractive index film layer is a graded refractive index layer obtained by treating an outermost alumina film layer with deionized water. Preferably, the high refractive index film layer is selected from titanium dioxide and lanthanum titanate, and the low refractive index film layer is selected from silicon dioxide and magnesium fluoride.

As a preferable scheme, a buffer layer may be disposed between the high/low refractive index alternating film stack and the nanostructured ultra-low refractive index film layer as needed. As a further preference, the buffer layer can be made of a silicon dioxide material, the refractive index of which is perfectly matched with that of the grass-like alumina nano structure, and the thickness of which is 10-250 nm.

High and low refractive index alternate film stack can be used (HL)^SB represents a high refractive index film layer, L represents a low refractive index film layer, S represents the number of times of alternation of the high and low refractive index film layers, S is an integer, and B represents a buffer layer between the alternating film stack and the grass-like nano alumina structure (in some cases, the layer may be omitted). The number of times of alternation S is 1 to 20, preferably 2 to 10, and more preferably 3 to 5. The thickness of the high refractive index film layer H is 5-300nm, preferably 10-200nm, and more preferably 15-120 nm. The thickness of the low refractive index film layer L is 5-350nm, preferably 10-250nm, and more preferably 20-150 nm. The buffer layer B is SiO₂，SiO₂The refractive index of the material is perfectly matched with that of the grass-shaped alumina nano structure, and the thickness of the material is 10-250nm, and the thickness of the material is more preferably 20-150 nm.

The substrate material is not limited, the substrate can be selected from glass materials such as K9, fused quartz, float glass and the like, can also be selected from semiconductor materials such as silicon wafers, germanium sheets and the like, and can also be selected from organic polymer materials such as organic glass (acrylic, PMMA, polymethyl methacrylate and the like), CR-39 (polypropylene-based diglycol carbonate), PC (polyethylene carbonate), PS (styrene) and the like.

The preparation methods of the high-low refractive index film layer and the outermost alumina film layer are not limited, and electron beam evaporation, sputtering, thermal evaporation, atomic layer deposition, electroplating and other chemical methods can be adopted. If the double-sided antireflection effect is realized, the atomic layer deposition technology is preferred, and if the single-sided antireflection effect is realized, the electron beam evaporation is preferred.

Preferably, the antireflection film of the present invention is (H)₄/SiO₂)^SAl₂O₃Or (H)₄/MgF₂)^SSiO₂Al₂O₃Or (TiO)₂/SiO₂)^SAl₂O₃Or (TiO)₂/MgF₂)^S SiO₂Al₂O₃And S is an integer representing the number of alternates. Further preferred isIs (H)₄/SiO₂)^SAl₂O₃。

A method for preparing the high-angle broadband antireflection film comprises the following steps:

(1) after the thickness of the nano-structure ultra-low refractive index film layer is determined, determining the material, the layer number and the thickness of the high/low refractive index alternate film stack by optimizing the thickness of each layer of film according to the bandwidth requirement and the reflectivity requirement of the required antireflection film; when the buffer layer needs to be added, in the step, the material and the thickness of the buffer layer can be determined at the same time;

(2) optionally, the substrate is cleaned: putting the substrate into an acetone solution for ultrasonic treatment, and then cleaning the substrate by using ethanol; then putting the substrate into an ethanol solution for ultrasonic treatment, and then cleaning the substrate by using deionized water; finally, putting the substrate into deionized water for ultrasonic treatment, and then cleaning the substrate again by using the deionized water;

(3) sequentially depositing a high/low refractive index alternate film stack on a substrate by adopting vacuum coating, and covering a precursor film layer corresponding to the nano-structure ultra-low refractive index film layer with a set thickness on the outermost layer of the high/low refractive index alternate film stack; when a buffer layer is needed, firstly covering the outermost layer of the high/low refractive index alternate film stack with the buffer layer, and then covering the outer surface of the buffer layer with a precursor film layer corresponding to the nano-structure ultra-low refractive index film layer with a set thickness;

(4) and processing the precursor film layer to obtain the nano-structure ultra-low refractive index film layer, and finally obtaining the large-angle broadband antireflection film.

Taking a grass-shaped alumina film with a nano structure as an example, the preparation steps of the wide-angle broadband antireflection film provided by the invention during actual processing are as follows:

(1) and analyzing the optical characteristic test result of the single-layer nano aluminum oxide film to obtain the distribution of the refractive index and the thickness, and taking the distribution as the outermost layer structure of the antireflection film system.

(2) Setting an optimization target according to the incident angle, the wave band range and the reflectivity requirement of the antireflection film, and adopting TiO₂/H₄And SiO₂/MgF₂And designing a multi-layer antireflection film by combining the materials to obtain a complete antireflection film system containing the multi-layer film and the nano aluminum oxide film.

(3) The substrate is cleaned with ethanol, acetone, ethyl ether, etc.

(4) And (3) respectively depositing a high-low refractive index film stack and an alumina film layer on the substrate by adopting vacuum coating, wherein the thickness of each layer is consistent with the design parameters obtained in the step (2).

(5) And (3) placing the substrate with the outermost layer covered with the alumina film in heated deionized water for soaking for a period of time, taking out the substrate, washing and soaking the substrate with the deionized water for 30min, taking out the substrate, washing the substrate with absolute ethyl alcohol, and finally drying the substrate with nitrogen.

In the invention, the antireflection film is divided into two parts: by using TiO₂/H₄And SiO₂/MgF₂High-low refractive index alternate film stack and grass-shaped alumina nano structure which are designed by the combination of the materials. The method is characterized in that deionized water is utilized to treat an alumina film with a certain thickness, the volume of the alumina film is increased after the alumina film and the high-temperature deionized water are subjected to chemical reaction, the thickness of the film is increased, and the surface of the film forms a grass-shaped alumina nano structure with an ultralow refractive index. The straw-like alumina nanostructure, in which the porosity gradually increases from the substrate to the air side, is considered to haveThe graded index layer with space variation can control the equivalent refractive index by controlling the diameter, the spacing, the film thickness and the like. In the design of broadband antireflection films, there is always a conflict between the bandwidth of the antireflection spectral range and the average residual reflectivity, and the broadening of the spectral range will result in an increase in the average residual reflectivity; at the same time, as the angle of incidence increases, the admittance mismatch of the air and the substrate/film increases, also resulting in an increase in reflectivity. If the material with the gradually-changed refractive index is used as the outermost layer film and a large-angle wide-waveband composite antireflection film layer is designed by combining with a film stack with alternating high and low refractive indexes, the broadband and angle characteristics of the antireflection film can be greatly improved.

The invention provides a method for preparing a nano aluminum oxide structure by using a wet etching method, namely treating an aluminum oxide film with a certain thickness by using deionized water to obtain an irregular nano structure, and combining the aluminum oxide structure with a high-low refractive index alternate film stack to realize large-angle broadband antireflection.

The wide-angle broadband antireflection film provided by the invention combines the nanostructure and the high-low refractive index alternate film stack, not only fully utilizes the accurate modulation capability of the multilayer film, but also ingeniously combines the continuously-changed nanostructure to realize the low refractive index matching film layer, thereby ensuring the broadband effect of the antireflection film on one hand and meeting the application requirement of large-angle incidence on the other hand. The most main functions of the grass-shaped structure alumina film are as follows: 1) providing an equivalent film layer (equivalent refractive index 1.2-1.25) matched with the low refractive index film layer; 2) a graded index layer with spatial variation is constructed, and interface reflection is reduced, so that the transmittance of the graded index layer is improved.

Based on a mature thin film deposition technology and a simple and rapid water corrosion method, the thickness and the equivalent refractive index of the graded-refractive-index film layer are controlled through simple and convenient operation, the residual reflectivity of a wide band at a large angle is adjusted by combining a multi-layer film structure, and the method is suitable for large-area mass production, so that the cost of the antireflection film is greatly reduced, the antireflection film is expected to be widely applied to products such as optical elements, sensors, imaging optical systems, solar cells and the like, and contributes to the fields of national economy, social development, scientific technology, national defense construction and the like in China.

Drawings

FIG. 1 is a schematic structural diagram of a wide-angle broadband antireflection film according to the present invention;

FIG. 2 is a flow chart of the preparation of a wide-angle broadband antireflection film according to the present invention;

FIG. 3 is a surface and cross-sectional topography of a herb-like alumina nanostructure in a wide-angle broadband antireflection film according to the present invention;

FIG. 4 is a graph showing the actual antireflection effect of a single-layered straw-like alumina nanostructure prepared according to the present invention (without the high and low refractive index film stack);

FIG. 5 is a graph of refractive index as a function of thickness after fitting of single-layered oxalato alumina nanostructures of the present invention;

FIG. 6 is a graph showing the antireflection effect of the multi-layer antireflection film according to the present invention on the visible wavelength band of 420nm to 680nm, wherein the substrate is K9 and the low refractive index material is SiO₂The high refractive index material being TiO₂The deposition thickness of the aluminum oxide film is 30nm, the water corrosion time is 1h, and the chart is a reflectivity curve of the antireflection film deposited on one side;

FIG. 7 is a graph showing the antireflection effect of the multi-layer antireflection film according to the present invention on the visible wavelength band of 420nm to 680nm, wherein the substrate is K9 and the low refractive index material is SiO₂The high refractive index material is H₄The deposition thickness of the aluminum oxide film is 30nm, the water corrosion time is 1h, and the chart is a reflectivity curve of the antireflection film deposited on one side;

FIG. 8 is a graph showing the antireflection effect of the multi-layered antireflection film according to the present invention on the visible wavelength band of 420nm to 680nm, in which the substrate is K9 and the low refractive index material is MgF₂The high refractive index material is H₄The buffer layer is SiO₂The deposition thickness of the aluminum oxide film is 30nm, the water corrosion time is 1h, and the chart is a reflectivity curve of the antireflection film deposited on one side;

FIG. 9 shows the antireflection effect of the multilayered antireflection film according to the present invention on visible-near infrared band of 400nm to 1100nm, in which the substrate is K9 and the low refractive index material is SiO₂The high refractive index material being TiO₂The deposition thickness of the alumina film is 30nm, the water corrosion time is 1h,the chart is a reflectivity curve after the antireflection film is deposited on one side;

FIG. 10 is a graph showing the antireflection effect of the multilayered antireflection film according to the present invention on visible-near infrared wavelength bands of 400nm to 1100nm, wherein the substrate is K9 and the low refractive index material is SiO₂The high refractive index material is H₄The deposition thickness of the aluminum oxide film is 30nm, the water corrosion time is 1h, and the chart is a reflectivity curve of the antireflection film deposited on one side;

FIG. 11 is a graph showing the antireflection effect of the multilayered antireflection film according to the present invention on the visible-near infrared wavelength region of 400nm to 1100nm, in which the substrate is K9 and the low refractive index material is MgF₂The high refractive index material being TiO₂The buffer layer is SiO₂The deposition thickness of the aluminum oxide film is 30nm, the water corrosion time is 1h, and the chart is a reflectivity curve of the antireflection film deposited on one side;

FIG. 12 is a graph showing the measured antireflection effect of the multilayer antireflection film shown in FIG. 6, wherein the substrate is K9 and the low refractive index material is SiO₂The high refractive index material being TiO₂The deposition thickness of the aluminum oxide film is 30nm, the water corrosion time is 1h, and the chart is a reflectivity curve obtained by testing after the antireflection film is deposited on one side;

FIG. 13 is a graph showing the measured antireflection effect of the multilayer antireflection film shown in FIG. 9, wherein the substrate is K9 and the low refractive index material is SiO₂The high refractive index material being TiO₂The deposition thickness of the aluminum oxide film is 30nm, the water corrosion time is 1h, and the chart is a reflectivity curve obtained by testing after the antireflection film is deposited on one side.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings.

As shown in fig. 1, the wide-angle broadband antireflection film provided by the present invention is composed of a substrate 1, a stack 2 with alternating high and low refractive indexes, a buffer layer 3, and a grass-shaped alumina nanostructure 4.

The material of the substrate 1 is not limited, and the substrate can be selected from K9, glass materials such as fused silica and float glass, plastic materials such as polymethyl methacrylate and polycarbonate, and semiconductor materials such as silicon wafers and germanium wafers. The film stack 2 with the high refractive index and the low refractive index alternated is formed by alternately stacking high refractive index medium film layers and low refractive index medium film layers, wherein the high refractive index medium material can be titanium dioxide, hafnium oxide, tantalum oxide, silicon nitride and the like, the thickness of the high refractive index medium film layers is 5 nm-300nm, the low refractive index medium material can be magnesium fluoride, silicon oxide, yttrium fluoride and the like, and the thickness of the low refractive index medium film layers is 5 nm-350 nm. The buffer layer 3 can be made of silicon dioxide material, the refractive index of which is perfectly matched with that of the grass-shaped alumina nano structure, and the thickness of which is 10-250 nm. The grass-shaped alumina nano structure 4 is obtained by treating an alumina film with deionized water, the thickness of the film is 10nm-150nm, the volume of the alumina film is increased after the alumina film and the high-temperature deionized water are subjected to chemical reaction, the thickness of the film is increased, and the surface of the film forms a random nano structure similar to weeds.

As shown in fig. 2, the preparation steps of the large-angle broadband antireflection composite film layer based on the grass-shaped alumina structure and the high-low refractive index alternate film stack are as follows:

(3) The substrate is cleaned with ethanol, acetone, ethyl ether, etc.

(5) And (3) placing the substrate with the outermost layer covered with the alumina film in heated deionized water (at the temperature of 60-90 ℃) for soaking for a period of time (30min-5h), taking out, washing and soaking for 30min by using the deionized water, taking out, washing by using absolute ethyl alcohol, and finally drying by using nitrogen.

The specific embodiments are described by taking the preparation of an alumina film and a high-low refractive index film stack by electron beam evaporation as examples:

(1) cleaning a substrate: when the substrate is cleaned, the substrate can be wiped by using an ethanol/diethyl ether mixed solution, and the substrate can also be cleaned by using a solution ultrasonic method; for example, the substrate may be first placed in an acetone solution for ultrasonic treatment, and then washed with ethanol; then putting the substrate into an ethanol solution for ultrasonic treatment, and then cleaning the substrate by using deionized water; finally, the substrate is placed into deionized water for ultrasonic treatment, and then the substrate is washed again by the deionized water.

(2) Preparing an alumina film with the thickness of 30nm on a substrate by utilizing electron beam evaporation (coating equipment); the film deposition temperature was 230 ℃ and the deposition rate was 0.5 nm/s.

(3) Wiping a sample plated with a 30nm aluminum oxide film by using an ethanol/ether mixed solution, soaking the sample in deionized water at 90 ℃ for 1h, taking out the sample, washing and soaking the sample in the deionized water for 30min, soaking the sample in absolute ethanol for 10min, and drying the sample by using nitrogen.

(4) The reflectances of p light and s light at 6 °, 20 °, 40 °, and 60 ° were measured using a cary7000 spectrophotometer, and the single-side reflectances thereof were calculated, and the results were introduced into a thin film design software OptiLayer, and the refractive index and thickness were optimized on the basis of the initial structure, whereby the grass-like alumina structure could be equivalent to a multilayer film structure with a varying refractive index.

(5) By using TiO₂And SiO₂Designing a high-low refractive index film stack, taking the fitted film system structure as an outermost film, and designing a wide-band large-angle antireflection film at the incidence of 0-60 degrees in wave bands of 420-680nm and 400-1100nm by using optical film design software.

(6) According to the multilayer film scheme designed by the software, after the substrate is cleaned, a film stack with high and low refractive indexes alternated and an alumina film with the thickness of 30nm are prepared on the substrate by using electron beam evaporation.

(7) Wiping a sample of the multilayer antireflection film by using an ethanol/ether mixed solution, soaking the sample in deionized water at 90 ℃ for 1h to enable an outermost 30nm aluminum oxide film to react with pure water to generate a nanostructure, taking out the nanostructure, washing and soaking the nanostructure with the deionized water for 30min, finally washing the nanostructure with absolute ethanol, and drying the nanostructure with nitrogen to obtain the wide-angle and wide-waveband antireflection film designed by software.

As can be seen from the above, short term immersion of the alumina film into heated deionized water results in the formation of nanostructures with antireflective effect. Specifically, in pure water, the membrane undergoes hydration, dynamic dissolution/precipitation and roughening. This hydration compounding process ultimately results in the crystallization of amorphous alumina into bayerite and gibbsite with a concomitant increase in the molar volume of the alumina film. The specific reaction principle is as follows:

Al₂O₃(s)+6H⁺(aq)+3H₂O(l)→2[Al(H₂O)₃]³⁺(aq)

Al₂O₃(s)+6OH^-(aq)+3H₂O(l)→2[Al(OH)₄]^-(aq)

it can be seen that alumina reacts with H in water⁺And OH^-A reaction occurs and combines water molecules to form a new species, which produces a dramatic change in the smooth alumina surface, as shown in figure 3. After the reaction, the molar volume of the aluminum oxide film increases, resulting in an increase in the physical thickness of the film; the porosity of the film layer is increased along with the increase of the film layer, and a random grass-shaped structure is formed, so that the gradient refractive index film layer matched with the low refractive index film layer is constructed.

Preparation of monolayer grass-shaped alumina nano-structured film example 1, 30nm alumina (substrate K9) prepared by electron beam evaporation technology was treated with deionized water at 90 ℃ for 1 hour, taken out and dried. The reflectance in the 420nm-680nm band was measured as shown in FIG. 4. The average reflectance over the entire wavelength band was 0.35% at an incident angle of 6 °, and 1.55% at an incident angle of 60 °.

Then, the measured reflectivities at the respective angles are introduced into a film fitting software OptiLayer to perform fitting of the refractive index and the thickness, and a multilayer film equivalent structure of the nano-structured alumina film shown in fig. 5 can be obtained.

Example 1: taking the grass-shaped alumina nano-structure film treated by deionized water as an outermost layer film, and taking TiO₂And SiO₂The material is a multilayer antireflection film designed in a 420nm-680nm wave band by way of example, and the structure is as follows: substrate | TiO₂(8.0nm)|SiO₂(54.5nm)|TiO₂(27.3nm)|SiO₂(35.7nm)|TiO₂(36.3nm)|SiO₂(46.9nm)|TiO₂(11.2nm)|SiO₂(39.2nm)|Al₂O₃(30nm), depositing each film layer by electron beam evaporation and using high-temperature water for treatment to realize the antireflection effect of a large-angle wide band, wherein the antireflection effect under each incident angle is shown in figure 6, and the average reflectivity of 0 degree, 20 degree, 40 degree and 60 degree is 0.07%, 0.06%, 0.07% and 0.55% in the visible light band of 420-680 nm.

Example 2: taking the grass-shaped alumina nano-structure film treated by deionized water as an outermost layer film, and taking H as₄(lanthanum titanate) and SiO₂The material is a multilayer antireflection film designed in a 420nm-680nm wave band by way of example, and the structure is as follows: base | H₄(15.3nm)|SiO₂(46.8nm)|H₄(41.6nm)|SiO₂(21.1nm)|H₄(181.5nm)|SiO₂(33.8nm)|H₄(15.0nm)|SiO₂(40.0nm)|Al₂O₃(30nm), depositing each film layer by electron beam evaporation and treating by using high-temperature water to realize the antireflection effect of a large-angle wide band, wherein the antireflection effect under each incident angle is shown in figure 7, and the average reflectivity of 0, 20, 40 and 60 degrees is 0.04%, 0.04%, 0.04% and 0.54% in a visible light band of 420-680 nm.

Example 3: taking the grass-shaped alumina nano-structure film treated by deionized water as an outermost layer film, and taking H as₄Lanthanum titanate, MgF₂And SiO₂The material is a multilayer antireflection film designed in a 420nm-680nm wave band by way of example, and the structure is as follows: base | H₄(13.3nm)|MgF₂(50.2nm)|H₄(33.7nm)|MgF₂(48.3nm)|H₄(34.9nm)|MgF₂(31.1nm)|H₄(15.0nm)|MgF₂(32.2nm)|H₄(40.4nm)|MgF₂(34.3nm)|H₄(58.1nm)|MgF₂(38.2nm)|H₄(19.1nm)|SiO₂(41.3nm)|Al₂O₃(30.0nm), the wide angle is realized by adopting electron beam evaporation to deposit each film layer and using high-temperature water for treatmentThe antireflection effect of the wavelength band at each incident angle is shown in fig. 8, and the average reflectivities at 0 °, 20 °, 40 °, and 60 ° are 0.05%, 0.04%, 0.04%, and 0.57% in the visible light wavelength band of 420-680 nm.

Example 4: taking the aluminum oxide film treated by deionized water as the outermost layer film, and taking TiO as₂And SiO₂The material is a multilayer antireflection film designed in 400nm-1100nm wave band, and the structure is as follows: substrate | TiO₂(11.0nm)|SiO₂(47.2nm)|TiO₂(29.3nm)|SiO₂(21.7nm)|TiO₂(141.0nm)|SiO₂(23.3nm)|TiO₂(20.1nm)|SiO₂(90.4nm)|Al₂O₃(30nm), each film layer is evaporated and deposited by adopting an electron beam, and the film layers are treated by using high-temperature water to realize the antireflection effect of a large-angle wide band, the antireflection effect of the film layers under each incident angle is shown in figure 9, and the average reflectivity of 0 degree, 20 degrees, 40 degrees and 60 degrees is 0.22 percent, 0.21 percent, 0.25 percent and 1.44 percent in a visible-near infrared band of 400-1100 nm.

Example 5: taking the aluminum oxide film treated by deionized water as an outermost layer film, and taking H as₄(lanthanum titanate) and SiO₂The material is a multilayer antireflection film designed in 400nm-1100nm wave band, and the structure is as follows: base | H₄(11.8nm)|SiO₂(47.7nm)|H₄(33.1nm)|SiO₂(23.1nm)|H₄(158.9nm)|SiO₂(22.4nm)|H₄(20.6nm)|SiO₂(82.6nm)|Al₂O₃(30nm), depositing each film layer by electron beam evaporation and using high-temperature water for treatment to realize the antireflection effect of a large-angle wide band, wherein the antireflection effect under each incident angle is shown in figure 10, and the average reflectivity of 0 degree, 20 degree, 40 degree and 60 degree is 0.05%, 0.04%, 0.10% and 1.37% in a visible-near infrared band of 400-1100 nm.

Example 6: taking the aluminum oxide film treated by deionized water as the outermost layer film, and taking TiO as₂、MgF₂And SiO₂The material is a multilayer antireflection film designed in 400nm-1100nm wave band, and the structure is as follows: substrate | TiO₂(6.0nm)|MgF₂(50.6nm)|TiO₂(15.0nm)|MgF₂(37.6nm)|TiO₂(15.0nm)|MgF₂(18.7nm)|TiO₂(15.0nm)|MgF₂(15.0nm)|TiO₂(28.4nm)|MgF₂(15.0nm)|TiO₂(51.9nm)|MgF₂(15.8nm)|TiO₂(38.5nm)|MgF₂(31.9nm)|TiO₂(15.0nm)|SiO₂(85.4nm)|Al₂O₃(30.0nm), each film layer is evaporated and deposited by adopting an electron beam, and the film layers are treated by using high-temperature water to realize the antireflection effect of a large-angle wide band, the antireflection effect of the film layers under each incident angle is shown in figure 11, and the average reflectivity of 0 degrees, 20 degrees, 40 degrees and 60 degrees is 0.07 percent, 0.06 percent, 0.13 percent and 1.48 percent in a visible-near infrared band of 400-1100 nm.

In example 1, after depositing each film layer on a single-polished K9 substrate by electron beam evaporation and treating with high-temperature water, the actual reflectance at each incident angle is measured by a cary7000 spectrophotometer as shown in fig. 12, and the average reflectance at the wavelength of 420-680nm is 0.08%, 0.08%, 0.15%, 1.22% at 6 °, 20 °, 40 °, 60 °.

In example 4, after depositing each film layer on a single-throw K9 substrate by electron beam evaporation and treating with high-temperature water, the actual reflectance at each incident angle was measured using a cary7000 spectrophotometer and the average reflectances at 6 °, 20 °, 40 °, and 60 ° in the 400-1100nm visible-near infrared band were 0.25%, 0.24%, 0.35%, and 1.98%, as shown in fig. 13.

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Large-angle broadband antireflection film and manufacturing method thereof

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