Sol-gel method for preparing optical antireflection film at room temperature

Abstract

The invention relates to a method for preparing an optical antireflection film through sol-gel at room temperature, and belongs to the technical field of optical antireflection films / sol-gel. According to the low-temperature crystallization preparation method of the sol-gel oxide optical antireflection film, in the low-temperature oxygen plasma treatment process of the oxide film, reactive ions and free radicals diffuse into the film, organic functional groups in the gel are oxidized, further condensation and densification of the gel are promoted, and therefore the stability of the film is improved. And a high-density metal-oxygen-metal (M-O-M) network is formed. In addition, high-energy electrons in the plasma provide extra energy for ordered arrangement of atoms in the oxide, and crystallization is promoted. Therefore, for the oxide with low crystallization activation energy, crystallization is realized in the plasma treatment process, and the function of an optical antireflection film is realized.

Description

Technical Field

[0001] The invention relates to a method for preparing an optical anti-reflection film by sol-gel at room temperature, belonging to the technical field of optical anti-reflection film / sol-gel. Background Art

[0002] Optical anti-reflection film anti-reflection coatings are widely used in architectural windows, video display panels, solar panels and other fields. The ideal combination of functional properties of increased transmittance, high scratch resistance and self-cleaning ability further expands its industrial application. The technologies for preparing optical anti-reflection film coatings include sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD) and sol-gel method. Among them, the sol-gel method shows unique advantages. Solution chemistry gives purity, uniformity and stoichiometric control, and solution processing makes low-cost, easy-to-operate, large-scale and irregular substrate coating possible.

[0003] The sol-gel process usually involves the hydrolysis and polycondensation of inorganic salts or metal alcohol oxides, followed by the use of heat treatment (generally 500°C) to remove organic ligands to obtain glassy or crystalline materials with desired optical properties. However, thermal diffusion at the interface can deteriorate the expected optical properties, while high temperatures limit their application on heat-sensitive substrates. Therefore, several methods have emerged to try to synthesize at low temperatures. From the perspective of precursor design, the introduction of suitable ligands can form functional groups with low decomposition temperatures and adjust the interatomic distances to make them very similar to the MOM network, thereby providing a lower synthesis temperature. In addition, researchers have found that ultraviolet irradiation can photolyze organic residues to obtain inorganic highly condensed oxide films with good electrical properties. This method has also been verified to reduce the subsequent crystallization temperature. Nevertheless, the general applicability of the above methods and the reduction of heat treatment temperatures are limited. Therefore, low temperature preparation of sol-gel derived films is required.

[0004] The prior art uses sintering as a post-processing solution for preparing optical anti-reflection films by sol-gel method, which has the following problems:

[0005] 1. Thermal diffusion problem: Thermal diffusion at the interface may lead to deterioration of the expected optical performance, especially when preparing AR coatings, thermal diffusion will affect the light transmittance of the coating.

[0006] 2. High temperature limitation: High temperature sintering limits the application of sol-gel method on heat-sensitive substrates because high temperature may damage the substrate or affect the performance of the substrate. Summary of the invention

[0007] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and to propose a sol-gel method for preparing an optical anti-reflection film at room temperature. In view of the problem of low-temperature crystallization that needs to be solved when preparing an optical anti-reflection film by the sol-gel method, the present invention provides a method for achieving crystallization by treating an organic gel with the assistance of low-temperature plasma. Titanium dioxide and silicon dioxide, two commonly used thin film materials for optical anti-reflection films, were treated with microwave-excited oxygen plasma (the highest temperature was about 35°C), and organic matter removal, gel condensation and film densification were achieved during the treatment process. Glassy SiO2 and crystalline TiO2 were obtained during the plasma treatment process, and preparation was achieved under conditions close to room temperature. The present invention uses common microwaves as a plasma excitation source to treat and prepare single-layer and multi-layer optical anti-reflection films, and develops a simple and universal low-temperature preparation method for optical anti-reflection films.

[0008] The technical solution of the present invention is:

[0009] A method for preparing an optical anti-reflection film by sol-gel at room temperature, the method comprising the steps of:

[0010] (1) mixing a metal alkoxide, a complexing agent, a pH regulator and a solvent uniformly, and aging for 24 h to 72 h to obtain a sol;

[0011] (2) using ethanol to ultrasonically clean the substrate, and after drying, using argon plasma to clean the substrate;

[0012] (3) using a spin coater to spin-coat the sol obtained in step (1) onto the surface of the substrate treated in step (2), and allowing it to stand in the air for curing for 10-24 hours to obtain a dry and formed film;

[0013] (4) placing the substrate with the thin film obtained in step (3) into a microwave plasma chamber with the thin film facing upward, and treating it with oxygen plasma to obtain a ceramicized optical anti-reflection film.

[0014] A method for treating a sol-gel optical anti-reflection film with low-temperature plasma, wherein the plasma is microwave-excited oxygen plasma, the vacuum degree is 700-200000 mTorr, and the treatment time is 6 hours; the sol is composed of a metal alkoxide, a complexing agent, a pH regulator and a solvent.

[0015] A sol-gel low-temperature crystallization method for preparing an optical anti-reflection film comprises the following steps:

[0016] The optical anti-reflection film material sol is spin-coated on the surface of the substrate to obtain a thin film, the thickness of the film after drying is 200 to 400 nm, and after microwave plasma treatment (about 35° C.), a ceramicized optical anti-reflection film is obtained;

[0017] Furthermore, in step (1), magnetic stirring is used to mix to obtain a uniform solution, wherein the stirring rate is 250 rpm and the stirring time is 30 min.

[0018] Furthermore, in step (2), microwave argon plasma cleaning is used, the power is 700 W, the chamber pressure is 700-200000 mTorr, and the cleaning time is 3 min.

[0019] Furthermore, in step (3), the spin coating speed is 1000 to 8000 rpm, and the spin coating time is 10 to 30 s.

[0020] Furthermore, in step (4), microwave oxygen plasma is used with a power of 700 W and a chamber pressure of 700 to 200,000 mTorr.

[0021] Beneficial Effects

[0022] (1) The present invention provides a method for preparing a sol-gel oxide optical anti-reflection film by low-temperature crystallization. During the low-temperature oxygen plasma treatment of the oxide film, reactive ions and free radicals diffuse into the film, oxidize the organic functional groups in the gel, promote further condensation and densification of the gel, and form a high-density metal-oxygen-metal (MOM) network. In addition, the high-energy electrons in the plasma provide additional energy for the ordered arrangement of atoms in the oxide, promoting crystallization. Therefore, for oxides with low crystallization activation energy, crystallization is achieved during the plasma treatment process, realizing the function of an optical anti-reflection film.

[0023] (2) The present invention provides a method for preparing an optical anti-reflection film with low cost, simple process and wide adaptability. By selecting common microwaves as the plasma excitation source, maintaining low temperature by adjusting the power and pressure, and combining the advantages of the sol-gel method of adjustable components and easy large-area preparation, the universal preparation of high-quality optical anti-reflection films can be achieved.

[0024] (3) The SiO2 and TiO2 ceramics were realized by plasma technology at a temperature close to room temperature (35°C), and single-layer and multi-layer AR films with anti-reflection effects were obtained, eliminating the problems of thermal diffusion and thermal stress cracking. Compared with the traditional sintering with slow heating rate and long processing time, this technology greatly shortens the processing time, does not need to consider the problem of temperature cracking, and can be used immediately, shortening the processing time of a single-layer film to 6 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the X-ray diffraction spectrum of the TiO2 single-layer oxide film prepared in Example 1;

[0026] Figure 2is the X-ray diffraction spectrum of the SiO2 single-layer oxide film in Example 2;

[0027] Figure 3 is the transmittance curve of the TiO2 single-layer anti-reflection film prepared in Example 1;

[0028] Figure 4 is the transmittance curve of the SiO2 single-layer anti-reflection film prepared in Example 2;

[0029] Figure 5 This is the transmittance curve of the TiO2-SiO2 double-layer V-type anti-reflection film prepared in Example 3. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments, wherein the methods are conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0031] A method for preparing an optical anti-reflection film by sol-gel low-temperature crystallization comprises the following steps:

[0032] The deposited sol-gel film is treated by low-temperature oxygen plasma to obtain a ceramicized optical anti-reflection film; or after multiple plasma treatments, an optical anti-reflection film with multiple layers of different materials stacked on top of each other is obtained.

[0033] The metal oxide sol comprises metal alkoxide, a complexing agent, a pH regulator and a solvent.

[0034] Thin film deposition methods include brush coating, spin coating or dip coating.

[0035] The thickness of the deposited film is ≤300nm.

[0036] The drying temperature of the deposited film is room temperature to 120°C.

[0037] The plasma is oxygen plasma, and the temperature is ≤35°C.

[0038] In the following embodiments:

[0039] Transmittance characterization: The optical transmittance of the sample to be tested was characterized using the UV-3600plus spectrophotometer produced by Shimadzu China Co., Ltd.

[0040] XRD characterization: The crystal structure of the sample to be tested was characterized using a SmartLab grazing incidence X-ray diffractometer from Rigaku Corporation of Japan;

[0041] Tetrabutyl titanate: 99% purity, Shanghai MacLean Biochemical Technology Co., Ltd.;

[0042] Tetraethyl orthosilicate: 98% purity, Shanghai MacLean Biochemical Technology Co., Ltd.;

[0043] Hydrochloric acid: AR 36-38%, Beijing Tongguang Fine Chemical Company;

[0044] Acetic acid: 99.5% purity, Beijing Tongguang Fine Chemical Company;

[0045] Nitric acid: AR 65-68%, Beijing Tongguang Fine Chemical Company;

[0046] N,N-dimethylacetamide: 99.8% purity, Shanghai MacLean Biochemical Technology Co., Ltd.;

[0047] Microwave plasma cleaning machine: Plasma-PreenⅡ-862, Plasmatic Systems Co., Ltd.

[0048] Spin coater: KW-4A, Institute of Microelectronics, Chinese Academy of Sciences.

[0049] Example 1

[0050] (1) 0.01 mol of tetrabutyl titanate, 0.1 mol of ethanol, 0.05 mol of N,N-dimethylacetamide, 0.022 mol of nitric acid, 0.005 mol of acetic acid and 0.1 mol of deionized water were mixed, and magnetic stirring was used for mixing at a speed of 250 rpm for 30 min, and aging for 24 h to obtain a sol;

[0051] (2) The substrate was ultrasonically cleaned with ethanol for 10 min. The substrate was dried with a hair dryer and placed in a microwave plasma chamber. The substrate was cleaned with argon plasma at a power of 700 W, a chamber pressure of 18000 mTorr, and a cleaning time of 7 min.

[0052] (3) A thin film was prepared on the substrate surface by spin coating, wherein the sol was dripped onto the substrate surface using a dropper, the spin coating speed was 6000 rpm, the spin coating time was 20 s, and the film was allowed to stand in the air for 12 h to solidify.

[0053] (4) The sample was placed in a microwave plasma chamber with the film side facing upward and treated with oxygen plasma at a power of 700 W, a chamber pressure of 200,000 mTorr, and a treatment time of 6 h.

[0054] The prepared TiO2 film has been obviously crystallized, the film quality is good, dense and without cracks.

[0055] Figure 1 The XRD test results show that anatase TiO2 is formed; Figure 3Spectrometer characterization shows that the film has an antireflection effect.

[0056] Example 2

[0057] (1) 0.04 mol of tetraethyl silicate, 0.08 mol of ethanol, 0.04 mol of N,N-dimethylacetamide, 0.004 mol of hydrochloric acid and 0.16 mol of deionized water were mixed and mixed by magnetic stirring at a speed of 250 rpm for 30 min. After aging for 72 h, a sol was obtained. Before use, 0.4 mol of ethanol was added for dilution and mixed again by magnetic stirring at a speed of 250 rpm for 15 min.

[0058] Steps (2) to (4) are the same as steps (2) to (4) in Example 1;

[0059] Figure 2 The XRD test results show that glassy SiO2 is formed; Figure 4 The mesophotometer characterization shows that the film has an antireflection effect.

[0060] Example 3

[0061] (1) A single-layer TiO2 film was prepared by the method in Example 1;

[0062] (2) Based on the prepared single-layer TiO2 film, a second SiO2 film was prepared according to steps (3) to (4) in Example 2.

[0063] Figure 5 Spectrometer characterization shows that the TiO2-SiO2 double-layer film has an anti-reflection effect.

[0064] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an optical anti-reflection film at room temperature by sol-gel, characterized in that The steps of the method include: (1) mixing the raw material metal alkoxide, complexing agent, pH adjuster and solvent uniformly, and aging for 24h-72h to obtain a sol; (2) using ethanol to ultrasonically clean the substrate, and after drying, using argon plasma to clean the substrate; (3) using a spin coater to spin-coat the sol obtained in step (1) onto the surface of the substrate treated in step (2), and allowing it to stand in the air for curing for 10-24 hours to obtain a dry and formed film; (4) placing the substrate with the thin film obtained in step (3) into a microwave plasma chamber with the thin film facing upward, and treating it with oxygen plasma to obtain a ceramicized optical anti-reflection film.

2. The method for preparing an optical anti-reflection film by sol-gel at room temperature according to claim 1, characterized in that: In the step (1), the raw materials are tetrabutyl titanate, ethanol, N,N-dimethylacetamide, nitric acid, acetic acid and deionized water.

3. The method for preparing an optical anti-reflection film by sol-gel at room temperature according to claim 1, characterized in that: In the step (1), the raw materials are tetraethyl silicate, ethanol, N,N-dimethylacetamide, hydrochloric acid and deionized water.

4. A sol-gel method for preparing an optical anti-reflection film at room temperature according to claim 2 or 3, characterized in that: In the step (1), magnetic stirring is used to mix to obtain a uniform solution, wherein the stirring rate is 250 rpm and the stirring time is 30 min.

5. The method for preparing an optical anti-reflection film by sol-gel at room temperature according to claim 2 or 3, characterized in that: In the step (2), microwave argon plasma cleaning is used, the power is 700 W, the chamber pressure is 700-200000 mTorr, and the cleaning time is 3 minutes.

6. The method for preparing an optical anti-reflection film by sol-gel at room temperature according to claim 2 or 3, characterized in that: In the step (3), the spin coating speed is 1000 to 8000 rpm, and the spin coating time is 10 to 30 seconds.

7. The method for preparing an optical anti-reflection film by sol-gel at room temperature according to claim 2 or 3, characterized in that: In the step (4), microwave oxygen plasma is used with a power of 700 W, a chamber pressure of 700-200000 mTorr, and a processing temperature of 30-35°C.

8. The method for preparing an optical anti-reflection film by sol-gel at room temperature according to claim 2 or 3, characterized in that: The thickness of the film after drying is 200-400nm.

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