Protective film of infrared anti-reflection coating and preparation method of protective film

Abstract

The invention discloses a protective film of an infrared anti-reflection coating and a preparation method of the protective film. The protective film is made of an acid-resistant and alkali-resistant MgF2 material, and has good light transmission in the middle infrared range of 3000-5000nm. Through a magnetron sputtering method, the surface of the ZnO antireflection film is covered with a layer of compact MgF2 material, and the protective film has excellent acid and alkali resistance. The MgF2 thin film is coated on the anti-reflection coating through a magnetron sputtering method, the parameters of magnetron sputtering are regulated, the thickness of the MgF2 thin film is regulated to be 100-300 nm, the refractive index of the MgF2 thin film is regulated to be 1.30-1.35, the anti-reflection performance of the original anti-reflection coating at the wave band of 3000-5000 nm is not reduced, and meanwhile the effect of protecting the anti-reflection coating is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetron sputtering plasma coating, and in particular relates to a protective film of an infrared anti-reflection coating and a preparation method thereof. Background Art

[0002] CdSe crystal is an infrared window material with a wide transmittance wavelength in the infrared band. It also has the advantages of good stability and moisture resistance, so it is often used in infrared equipment materials. However, the refractive index of CdSe crystal is as high as 2.49. According to the Fresnel reflection law, it can be calculated that the crystal will reflect about 20% of the incident light.

[0003] Anti-reflective coatings can reduce light reflection and increase light transmittance based on the principle of light interference. However, the thickness and refractive index of the coating need to meet the conditions of interference. This limits many materials as infrared anti-reflective coatings. At present, ZnO material is used as an anti-reflective coating for CdSe crystals because of its suitable refractive index and adjustable thickness, which can obtain excellent anti-reflective performance (High-quality ZnO anti-reflective coatings for CdSe crystal in the infraredwavelength. Infrared Physics&Technology 135(2023)104963). However, ZnO is an amphoteric oxide and is not resistant to acid and alkali, so its application is limited. It is necessary to cover its surface with an acid- and alkali-resistant protective film. The addition of a protective film may greatly reduce the original anti-reflective effect due to the influence of the thickness, refractive index and transmittance of the protective film. Summary of the invention

[0004] Based on the above shortcomings of the prior art, the present invention provides a protective film for infrared anti-reflection coating and a preparation method thereof. The protective film is made of acid-resistant and alkali-resistant MgF2 material. By magnetron sputtering, a layer of dense MgF2 material is covered on the surface of the ZnO anti-reflection film, which has excellent acid and alkali resistance. By adjusting the thickness and refractive index of the MgF2 film, the anti-reflection performance can be maintained without weakening, while protecting the anti-reflection film.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A protective film for infrared anti-reflection coating:

[0007] The protective film material is MgF2, which is coated on the anti-reflective coating by magnetron sputtering. The anti-reflective coating is ZnO material, which is coated on CdSe crystal. The anti-reflective band of the ZnO coating is 3000-5000nm.

[0008] MgF2 material is resistant to acid and alkali, and does not absorb light in the 3000-5000nm band, so covering the ZnO coating with MgF2 can slow down its corrosion by acid and alkali. The light absorbed by MgF2 can be ignored. The introduction of the new coating may interfere with the anti-reflection performance of the original anti-reflection coating, so there are certain requirements for the thickness and refractive index of MgF2.

[0009] As a further step of protecting the infrared anti-reflection coating.

[0010] Preferably, the thickness of the anti-reflection coating is 460-780 nm, and the refractive index is 1.60; the thickness of the protective film is 100-300 nm, and the refractive index is 1.30-1.35.

[0011] Preferably, the protective film has a thickness of 100 to 150 nm and a refractive index of 1.30 to 1.32.

[0012] When the MgF2 film is introduced, it is equivalent to coating the CdSe crystal with two layers of coating. For a single-layer antireflection film, it only needs to meet the following requirements:

[0013] n1d=λ0 / 4 (1)

[0014] n1=(n0×n s ) 1 / 2 (2)

[0015] d is the physical thickness of the film, n1, n0, n s are the refractive indices of the film, air and substrate respectively, and λ0 is the wavelength of the incident light.

[0016] According to these two formulas, the thickness and refractive index of the ZnO coating in the 3000-5000nm band can be calculated. When the thickness of the anti-reflection coating is 460-780nm and the refractive index is 1.60, it is close to the result calculated by the formula and has a good anti-reflection effect. However, the introduction of MgF2 will destroy the original optimal conditions.

[0017] According to the experiment, when the thickness of MgF2 film is 100-300nm and the refractive index is 1.30-1.35, it has little effect on the overall transmittance. It is also found that when the thickness of the protective film is 100-150nm and the refractive index is 1.30-1.32, the transmittance of light can be further increased.

[0018] The present invention also provides a method for preparing a protective film of an infrared anti-reflection coating, comprising the following steps:

[0019] S1. Install the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflection film on the sample stage, and adjust the distance between the substrate and the target to 5-8 cm;

[0020] S2, evacuate the magnetron sputtering chamber to 10 -3 -10 -4 After 0.05 Pa, argon gas is then filled in, the working gas pressure is controlled at 0.3-0.6 Pa, and the sputtering power is set at 150-250 W;

[0021] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 1 to 3 hours;

[0022] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0023] In the magnetron sputtering process, the thickness and refractive index of the MgF2 film that meet the requirements can be obtained by adjusting the above parameters, which can ensure that the film has protective properties and does not affect the transmittance of the original material.

[0024] The method for preparing a protective film as an infrared anti-reflection coating is further preferred.

[0025] Preferably, the purity of the MgF2 target is greater than 99.99%.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Compared with the original ZnO anti-reflective coating, after being covered with the MgF2 film, the MgF2 material is resistant to acid and alkali, and does not absorb light in the 3000-5000nm band, which can slow down its corrosion by acid and alkali and improve the stability of its ZnO anti-reflective coating.

[0028] (2) Compared with general protective films, the MgF2 protective film in the present invention is controlled by controlling the parameters of magnetron sputtering, thereby controlling its thickness and refractive index. According to the combination of thickness and refractive index, the increase of the protective film has less impact on the overall anti-reflection effect, and even increases the overall transmittance within a certain thickness and refractive index range.

[0029] (3) Compared with the original anti-reflection coating, when the thickness of MgF2 in the present invention is 100-150 nm and the refractive index is 1.30-1.32, the covering protective film not only does not reduce the transmittance, but on the contrary increases the original transmittance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a scanning electron microscope photograph of the protective film prepared in Example 1;

[0031] Figure 2Spectra of transmittance of samples in Examples 1 to 3 and Comparative Example 1;

[0032] Figure 3 : are the transmittance spectra of the samples in Example 4 and Comparative Example 2;

[0033] Figure 4 Spectra of transmittance of samples in Example 4, Example 5 and Comparative Example 3;

[0034] Figure 5 Spectra of the transmittance of the samples in Example 1, Comparative Example 1 and Comparative Example 4. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail in combination with the embodiments below. The following content is only an example and explanation of the concept of the present invention. The technicians in the relevant technical field make various modifications or supplements to the specific implementation cases described or replace them with similar methods. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all belong to the protection scope of the present invention.

[0036] The above-mentioned preparation method of the present invention is described below through specific examples and comparative examples.

[0037] Example 1

[0038] This embodiment provides a protective film of an infrared anti-reflection coating and a preparation method thereof.

[0039] Preparation method:

[0040] S1. Mount the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflective coating on the sample stage, wherein the thickness of the ZnO coating is 650nm, and adjust the distance between the substrate and the target to 5cm;

[0041] S2, evacuate the magnetron sputtering chamber to 10 -4 After 0.05 Pa, argon gas was filled in, the working gas pressure was controlled at 0.3 Pa, and the sputtering power was set at 250 W;

[0042] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 1h;

[0043] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0044] According to the above method, a protective film of an infrared anti-reflection coating is obtained, wherein the thickness of the protective film is 100 nm and the refractive index is 1.30.

[0045] Example 2

[0046] This embodiment provides a protective film of an infrared anti-reflection coating and a preparation method thereof.

[0047] Preparation method:

[0048] S1. Mount the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflective coating on the sample stage, wherein the thickness of the ZnO coating is 650nm, and adjust the distance between the substrate and the target to 5cm;

[0049] S2, evacuate the magnetron sputtering chamber to 10 -4 After 0.05 Pa, argon gas was filled in, the working gas pressure was controlled at 0.3 Pa, and the sputtering power was set at 250 W;

[0050] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 1.5h;

[0051] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0052] According to the above method, a protective film of an infrared anti-reflection coating is obtained, wherein the thickness of the protective film is 150 nm and the refractive index is 1.32.

[0053] Example 3

[0054] This embodiment provides a protective film of an infrared anti-reflection coating and a preparation method thereof.

[0055] Preparation method:

[0056] S1. Mount the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflective coating on the sample stage, wherein the thickness of the ZnO coating is 650nm, and adjust the distance between the substrate and the target to 5cm;

[0057] S2, evacuate the magnetron sputtering chamber to 10 -4 After 0.05 Pa, argon gas was filled in, the working gas pressure was controlled at 0.3 Pa, and the sputtering power was set at 250 W;

[0058] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 3h;

[0059] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0060] According to the above method, a protective film of an infrared anti-reflection coating is obtained, wherein the thickness of the protective film is 300 nm and the refractive index is 1.35.

[0061] Example 4

[0062] This embodiment provides a protective film of an infrared anti-reflection coating and a preparation method thereof.

[0063] Preparation method:

[0064] S1. Mount the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflective coating on the sample stage, wherein the thickness of the ZnO coating is 460 nm, and adjust the distance between the substrate and the target to 8 cm;

[0065] S2, evacuate the magnetron sputtering chamber to 15 -3 Pa, then fill with argon, control the working gas pressure at 0.4Pa, and set the sputtering power at 200W;

[0066] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 1.1h;

[0067] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0068] According to the above method, a protective film of an infrared anti-reflection coating is obtained, wherein the thickness of the protective film is 100 nm and the refractive index is 1.30.

[0069] Example 5

[0070] This embodiment provides a protective film of an infrared anti-reflection coating and a preparation method thereof.

[0071] Preparation method:

[0072] S1. Mount the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflective coating on the sample stage, wherein the thickness of the ZnO coating is 780 nm, and adjust the distance between the substrate and the target to 6 cm;

[0073] S2, evacuate the magnetron sputtering chamber to 10 -3 After 0.05 Pa, argon gas was then filled in, the working gas pressure was controlled at 0.3 Pa, and the sputtering power was set at 150 W;

[0074] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 1h;

[0075] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0076] According to the above method, a protective film of an infrared anti-reflection coating is obtained, and the thickness of the protective film is 130 nm and the refractive index is 1.32.

[0077] Example 6

[0078] This embodiment provides a protective film of an infrared anti-reflection coating and a preparation method thereof.

[0079] Preparation method:

[0080] S1. Mount the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflective coating on the sample stage, wherein the thickness of the ZnO coating is 780 nm, and adjust the distance between the substrate and the target to 6 cm;

[0081] S2, evacuate the magnetron sputtering chamber to 10 -3 After 0.05 Pa, argon gas was then filled in, the working gas pressure was controlled at 0.3 Pa, and the sputtering power was set at 150 W;

[0082] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 1.2h;

[0083] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0084] According to the above method, a protective film of an infrared anti-reflection coating is obtained, wherein the thickness of the protective film is 150 nm and the refractive index is 1.32.

[0085] Comparative Example 1

[0086] The sample without protective film, in which the thickness of ZnO coating is 650nm.

[0087] Comparative Example 2

[0088] The sample without protective film, in which the thickness of the ZnO coating is 460nm.

[0089] Comparative Example 3

[0090] The sample without protective film, in which the thickness of the ZnO coating is 780nm.

[0091] Comparative Example 4

[0092] This comparative example provides a protective film of an infrared anti-reflection coating and a preparation method thereof.

[0093] Preparation method:

[0094] S1. Mount the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflection film on the sample stage, wherein the thickness of the ZnO coating is 650nm, and adjust the distance between the substrate and the target to 5cm;

[0095] S2, evacuate the magnetron sputtering chamber to 10 -3 After 0.05 Pa, argon gas was then filled in, the working gas pressure was controlled at 0.3 Pa, and the sputtering power was set at 150 W;

[0096] S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 10h;

[0097] S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

[0098] According to the above method, a protective film of an infrared anti-reflection coating is obtained, wherein the thickness of the protective film is 1000 nm and the refractive index is 1.36.

[0099] Figure 1 This is a scanning electron microscope photo of the protective film prepared in Example 1. It can be seen that the MgF2 coating prepared by magnetron sputtering is dense and the film layer is uniform and flat, which can effectively protect the inner coating.

[0100] Figure 2 The transmittance spectra of the samples in Examples 1 to 3 and Comparative Example 1 are shown. From the transmittance, it can be seen that in the 3000-5000nm nanometer mid-infrared band, the transmittance of the sample does not decrease significantly after being covered with the protective film. This shows that the prepared protective film can protect the film layer and has little effect on the transmittance of the original anti-reflection coating.

[0101] Figure 3 Spectra of the transmittance of the samples in Example 4 and Comparative Example 2. Figure 4is the transmittance spectrum of the samples in Example 4, Example 5 and Comparative Example 3. Figure 3 and Figure 4 It can be seen from the transmittance spectrum that when the thickness of MgF2 is between 100 and 150 nm and the refractive index is between 1.30 and 1.32, the covering protective film not only does not reduce the transmittance, but on the contrary increases the original transmittance.

[0102] Figure 5 The transmittance spectra of the samples in Example 1, Comparative Example 1 and Comparative Example 4. It can be seen that when the thickness of MgF2 is 1000nm and the refractive index is 1.36, the transmittance in the 3000-5000nm band is significantly reduced when it is covered on the anti-reflection coating.

[0103] In summary, the present invention prepares the MgF2 protective film by controlling the parameters of magnetron sputtering, thereby controlling its thickness and refractive index. According to the combination of thickness and refractive index, the increase of the protective film has less impact on the overall anti-reflection effect, and even increases the overall transmittance within a certain thickness and refractive index range.

[0104] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A protective film for an infrared anti-reflection coating, characterized in that: The protective film material is MgF2, which is coated on the anti-reflective coating by magnetron sputtering. The anti-reflective coating is ZnO material, which is coated on CdSe crystal. The anti-reflective band of the ZnO coating is 3000-5000nm.

2. The protective film of the infrared anti-reflection coating according to claim 1, characterized in that: The thickness of the anti-reflection coating is 460-780 nm, and the refractive index is 1.60; The protective film has a thickness of 100-300 nm and a refractive index of 1.30-1.

35.

3. The protective film of the infrared anti-reflection coating according to claim 2, characterized in that: The protective film further preferably has a thickness of 100 to 150 nm and a refractive index of 1.30 to 1.

32.

4. A method for preparing a protective film of an infrared antireflection coating according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Install the MgF2 target on the target holder of the magnetron sputtering equipment, place the CdSe crystal with ZnO anti-reflection film on the sample stage, and adjust the distance between the substrate and the target to 5-8 cm; S2, evacuate the magnetron sputtering chamber to 10 -3 -10 -4 After 0.05 Pa, argon gas is then filled in, the working gas pressure is controlled at 0.3-0.6 Pa, and the sputtering power is set at 150-250 W; S3, turn on the magnetic field, control the inert gas flow rate to 2000sccm, argon is ionized into plasma, bombarding the MgF2 target, sputtering a large number of Mg and F atoms, deposited on the ZnO surface, the sputtering time is 1 to 3 hours; S4. After the sputtering is completed, the sample is slowly cooled to room temperature in a vacuum or low pressure environment, and then the sample is taken out.

5. The method for preparing a protective film of an infrared antireflection coating according to claim 4, characterized in that: The purity of the MgF2 target material is greater than 99.99%.

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