Preparation method of broadband antireflection film

Abstract

The invention belongs to the technical field of optical thin films, and particularly relates to a preparation method of a broadband antireflection film, and the film system structure of the broadband antireflection film is S (HL) nL 'A, wherein S is a glass substrate; a is air; h is a high refractive index material; l is a low-refractive-index material; l'is a matched membrane stack formed by silicon oxide microspheres; and (HL) n is a basic film stack formed by alternately stacking high-refractive-index materials H and low-refractive-index materials L. The preparation method comprises the following steps: plating a basic membrane stack (HL) n on a glass substrate in a vapor deposition manner, and then coating a matched membrane stack on the basic membrane stack; and the matching membrane stack adopts a silicon oxide microsphere layer. According to the invention, the antireflection bandwidth can be expanded, the environmental stability is good, the mechanical strength is high, the preparation process is simplified, scratches and wear can be reduced, and the optical performance can be ensured.

Description

Technical Field

[0001] This invention belongs to the field of optical thin film technology, specifically relating to a method for fabricating a broadband antireflective filter based on a combination of multilayer films and silicon oxide microsphere nanostructures. This method achieves wide-band (B=2.75) low reflectivity (R<0.5%) optical performance by optimizing the film structure and material combination, while simultaneously improving the mechanical strength and environmental stability of the film layer, making it suitable for the field of precision optical instruments. Background Technology

[0002] Antireflective coatings are among the most widely used optical thin films. Their principle utilizes the interference effect of optical thin films, employing multiple layers of films with different refractive indices to achieve antireflection effects across specific wavelengths. Antireflective coatings are typically manufactured using techniques such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). Based on extensive design results, Willey summarized an empirical formula for the lowest achievable average reflectivity of broadband antireflective coatings:

[0003]

[0004] In the formula, B = λ max / λ min λ represents the anti-reflection bandwidth. max λ is the maximum value in the anti-reflection wavelength region. min The minimum value is given by L; the refractive index of the outermost film is given by T; and the total optical thickness of the film system is given by T.

[0005]

[0006] D is the difference between the high and low refractive indices of the film layers other than the outermost layer.

[0007] Currently, the design method for anti-reflective filters is typically based on (HL). n Based on the basic membrane system, and using software optimization methods, a visible region bandwidth B = λ was prepared. max / λ min A conventional antireflective coating with a refractive index (B) of 1.7 can achieve an R < 0.5% in practical fabrication. To obtain an antireflective coating with a wider bandwidth, a lower refractive index material is usually deposited on the outermost layer. For example, depositing MgF2 on the outermost layer can achieve a bandwidth of B = 2.25 and R < 0.5% in practical fabrication. However, the outermost MgF2 film is more susceptible to the influence of ambient humidity than the SiO2 film, which leads to a decrease in transmittance. Summary of the Invention

[0008] The present invention aims to overcome the shortcomings of the prior art and provide a method for preparing a broadband antireflection film with scalable antireflection bandwidth, good environmental stability, high mechanical strength, simplified preparation process, reduced scratches and wear, and guaranteed optical performance.

[0009] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0010] A method for preparing a broadband antireflective coating, the structure of which is as follows:

[0011] S|(HL) n L′|A

[0012] Where: S is the glass substrate; A is air; H is a high refractive index material; L is a low refractive index material; L' is a matched film stack composed of silica microspheres; (HL) n It is a basic film stack consisting of alternating layers of high-refractive-index material H and low-refractive-index material L.

[0013] Furthermore, the microspheres have a diameter of 100–150 nm and a refractive index of 1.2–1.5.

[0014] Furthermore, the high refractive index material is Ta2O5, and the low refractive index material is SiO2.

[0015] Furthermore, the silica microspheres are synthesized via a modified Stober method, comprising the following steps:

[0016] a. Using tetraethyl orthosilicate as the silicon source and polyacrylic acid as the template agent;

[0017] b. Under the catalysis of ammonia, hydrolysis is carried out in a mixed solvent of ethanol and water to form microspheres with uniform diameter.

[0018] Furthermore, the base film stack is deposited by PVD process with a deposition rate of 0.5-1 nm / s and a substrate temperature of 150-300℃.

[0019] Furthermore, the matching film stack uses silica microspheres, and the coating process is spin coating or spray coating.

[0020] The broadband antireflective film prepared by the above method has a bandwidth of B = 2.75 and an average reflectivity of R < 0.5%.

[0021] The membrane structure of this invention is: S|(HL) n L′|A,(HL) n The base film stack is fabricated using a PVD process, while L′ represents the matching film stack, achieved through a coating process using arranged silica nanospheres. This invention combines (HL)... n A base film stack and a matching film stack (L') with silica microspheres achieve wide-band (B=2.75) low reflectivity (R<0.5%), while improving mechanical strength and environmental stability. The base film stack is fabricated using alternating Ta2O5 / SiO2 deposition, and the matching film stack is coated with silica microspheres (diameter 100-150nm, n=1.21) using a solution method.

[0022] (1) Membrane system design:

[0023] Based on the target bandwidth (B = 2.75) and reflectivity (R < 0.5%), the optical thickness of each layer (T = 10–130 nm) was optimized using optical simulation software.

[0024] Calculate the diameter (d = 100-150 nm) and wall thickness of the silica microspheres in the matching film stack to ensure that their effective refractive index matches that of air and the base film stack.

[0025] (2) Preparation of basic membrane stack:

[0026] Ta2O5 and SiO2 layers were deposited sequentially using PVD process, with the deposition rate (0.5–1 nm / s) and substrate temperature (150–300 °C) controlled.

[0027] (3) Matching film stack coating:

[0028] Silica microspheres were synthesized using a modified Stobol method: Tetraethyl orthosilicate (TEOS) was used as a precursor, polyacrylic acid (PAA) as a template agent, ammonia was used for catalytic hydrolysis, and ethanol / water was used as a solvent to prepare microspheres with uniform diameter. The microsphere dispersion was then spin-coated or sprayed onto the surface of a base film stack to form a nanostructure layer with a thickness of 100–150 nm.

[0029] This invention's filter utilizes two materials with different refractive indices (high and low) and a type of silica microsphere with an adjustable refractive index, achieving a broadband antireflection effect (B = 2.75, R < 0.5%) and exhibiting a certain degree of fabrication feasibility. Furthermore, the ordered nano-optical structure formed by the silica microspheres possesses high mechanical strength, reducing scratches and wear while ensuring optical performance. Compared with existing technologies, this invention has the following characteristics:

[0030] (1) Broadband antireflection: B = 2.75, average reflectance R < 0.5% (compared to the traditional method B = 2.25). Broadband antireflection with B = 2.75 (R < 0.5%) was achieved by introducing silica microsphere nanostructures as matching film stacks (L').

[0031] (2) High environmental stability: Silica microspheres (n=1.21) are used instead of traditional MgF2 to avoid performance degradation caused by humidity.

[0032] (3) Excellent mechanical properties: The nano-ordered structure formed by the microspheres has high hardness, reducing scratches and wear. Attached Figure Description

[0033] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0034] Figure 1 This is a schematic diagram of the membrane system structure of the present invention.

[0035] Figure 2 This is the reflectance spectrum of the film system of the present invention. Detailed Implementation

[0036] See Figures 1-2 As shown, the first step is to design the membrane system. Based on the spectral requirements, the software is used to design the system: simulate the number of layers and thickness of the basic membrane stack; design the refractive index and thickness of the required matching membrane stack; and design the silica microspheres, calculating the required microsphere diameter and wall thickness.

[0037] After theoretical verification, actual deposition was carried out: the (HL)n basic membrane stack was deposited using PVD deposition process; the silica microspheres required for the L′ matching membrane stack were prepared by modified Stober synthesis. The materials used are shown in Table 1. Silica microspheres with a certain thickness and diameter were prepared and coated on the antireflection membrane.

[0038] Table 1. Materials used in the preparation of silica microspheres

[0039]

[0040] Example 1:

[0041] (HL) is deposited on a glass substrate (n = 1.55). 3 The base film stack is then coated with a layer of silicon oxide microspheres with a diameter of 128 nm, ultimately achieving an average reflectivity R<0.5% in the 400–1100 nm wavelength band.

[0042]

[0043]

[0044] Silica microspheres size: diameter d = 128 nm, refractive index n = 1.21 (achieved by adjusting the microsphere porosity).

[0045] The content of this invention is not limited to the embodiments listed. Any equivalent modifications made by those skilled in the art to the technical solutions of this invention by reading this specification are covered by the claims of this invention.

Claims

1. A method for preparing a broadband antireflective coating, characterized in that, Its membrane structure is as follows: S|(HL) n L′|A Where: S is the glass substrate; A is air; H is a high refractive index material; L is a low refractive index material; L' is a matched film stack composed of silica microspheres; (HL) n It is a basic film stack consisting of alternating layers of high-refractive-index material H and low-refractive-index material L.

2. The method for preparing the broadband antireflective coating according to claim 1, characterized in that: The silica microspheres have a diameter of 100–150 nm and a refractive index n = 1.2–1.

5.

3. The method for preparing the broadband antireflective coating according to claim 2, characterized in that: The high refractive index material H is Ta2O5, and the low refractive index material L is SiO2.

4. The method for preparing the broadband antireflective coating according to claim 3, characterized in that: The silica microspheres were synthesized via a modified Stober method, comprising the following steps: a. Using tetraethyl orthosilicate as the silicon source and polyacrylic acid as the template agent; b. Under the catalysis of ammonia, hydrolysis is carried out in a mixed solvent of ethanol and water to form microspheres with uniform diameter.

5. The method for preparing the broadband antireflective coating according to claim 4, characterized in that: The base film stack is deposited by physical vapor deposition (PVD) at a deposition rate of 0.5–1 nm / s and a substrate temperature of 150–300 °C.

6. The method for preparing the broadband antireflective coating according to claim 5, characterized in that: The coating process is either spin coating or spray coating.

7. The broadband antireflective coating prepared by the method according to any one of claims 1 to 6, characterized in that: Bandwidth B = 2.75, average reflectivity R < 0.5%.

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