An infrared antireflection coating with a protective film and a preparation method thereof

Abstract

The present invention discloses a protective film for an infrared antireflection coating and a preparation method thereof. The protective film selects MgF2 material resistant to acids and alkalis and has good light transmittance in the mid-infrared range of 3000-5000 nm. By means of magnetron sputtering, a dense layer of MgF2 material is covered on the surface of the ZnO antireflection film. The protective film has excellent acid and alkali resistance. It is coated on the antireflection coating by magnetron sputtering, and the parameters of magnetron sputtering are adjusted to adjust the thickness of the MgF2 thin film to be 100-300 nm and the refractive index to be 1.30-1.35, so that the antireflection performance of the original antireflection coating in the 3000-5000 nm band can be not reduced, and at the same time, the antireflection film can be protected.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetron sputtering plasma coating, and particularly relates to a protective film for an infrared antireflection coating and a preparation method thereof. Background Art

[0002] CdSe crystal is an infrared window material, which has a wide transmittance wavelength band in the infrared range. Moreover, it has advantages such as good stability and resistance to moisture, so it is commonly used as a material for infrared devices. However, the refractive index of CdSe crystal is as high as 2.49. According to the Fresnel reflection law, it can be calculated that this crystal will reflect about 20% of the incident light.

[0003] Anti-reflection coatings can reduce light reflection and increase light transmission according to the principle of destructive interference of light. However, the thickness and refractive index of the coating need to meet the conditions of destructive interference. This limits many materials as infrared antireflection coatings. Currently, ZnO materials are used as antireflection coatings for CdSe crystals because of their appropriate refractive index and adjustable thickness, and excellent antireflection performance can be obtained (High-quality ZnO anti-reflective coatings for CdSe crystal in the infrared wavelength. Infrared Physics & Technology 135 (2023) 104963). However, ZnO is an amphoteric oxide and is not resistant to acids and alkalis, so its application is limited. It is necessary to cover a layer of acid- and alkali-resistant protective film on its surface. The addition of the protective film may cause a significant reduction in the original antireflection effect due to the influence of the thickness, refractive index, and light transmittance of the protective film. Summary of the Invention

[0004] Based on the deficiencies of the above-mentioned existing technologies, the present invention provides a protective film for an infrared antireflection coating and a preparation method thereof. The protective film selects acid- and alkali-resistant MgF2 material, and a dense MgF2 material is covered on the surface of the ZnO antireflection film by magnetron sputtering method, which has excellent acid- and alkali-resistant properties. By adjusting the thickness and refractive index of the MgF2 thin film, the antireflection performance can be not weakened, and at the same time, the antireflection film can be protected.

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

[0006] A protective film for an infrared antireflection coating:

[0007] The material of the protective film is MgF2, which is coated on the antireflection coating by magnetron sputtering method. The antireflection coating is made of ZnO material, and the antireflection coating is coated on the CdSe crystal. The antireflection 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 thickness of the protective film is further preferably 100 to 150 nm, and the refractive index is 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] (1)

[0014] (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 Pa, then fill it with argon, control the working pressure at 0.3 - 0.6 Pa, and set the sputtering power at 150 - 250 W;

[0021] S3. Turn on the magnetic field, control the gas flow rate of the inert gas to be 2000 sccm, argon is ionized into plasma, bombards the MgF2 target, sputters a large number of Mg and F atoms, and deposits on the ZnO surface. The sputtering time is 1 - 3 h;

[0022] S4. After sputtering, slowly cool the sample to room temperature in a vacuum or low - pressure environment, and then take out the sample.

[0023] During the magnetron sputtering process, by adjusting the above - mentioned parameters, the thickness and refractive index of the qualified MgF2 film can be obtained. It can not only ensure that the film has protection, but also ensure that it does not affect the transmittance of the original material.

[0024] As a further preference for the preparation method of the protective film of an infrared antireflection coating,

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

[0026] The beneficial effects of the present invention compared with the prior art are as follows:

[0027] (1) Compared with the original ZnO antireflection coating, after covering the MgF2 film, the MgF2 material has acid and alkali resistance and does not absorb light in the 3000 - 5000 nm band, which can slow down its corrosion by acid and alkali and improve the stability of the ZnO antireflection coating.

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

[0029] (3) Compared with the original antireflection coating, when the thickness of MgF2 in the present invention is 100 - 150 nm and the refractive index is 1.30 - 1.32, the covered protective film not only does not reduce the transmittance, but on the contrary, increases the original transmittance. Description of the Drawings

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

[0031] Figure 2Transmittance spectra of the samples in Examples 1 to 3 and Comparative Example 1;

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

[0033] Figure 4 Transmittance spectra of the samples in Example 4, Example 5 and Comparative Example 3;

[0034] Figure 5 Transmittance spectra of the samples in Example 1, Comparative Example 1 and Comparative Example 4. Detailed implementation manners

[0035] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific implementation manners of the present invention will be given in conjunction with the embodiments. The following content is only an example and explanation of the concept of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific implementation cases or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims of the present invention, they should all fall within the protection scope of the present invention.

[0036] The above preparation method of the present invention will be described below through specific examples and comparative examples.

[0037] Example 1

[0038] This example provides a protective film for an infrared antireflection coating and a preparation method thereof.

[0039] Preparation method:

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

[0041] S2. After evacuating the magnetron sputtering chamber to 10 -4 Pa, then fill it with argon, control the working pressure at 0.3 Pa, and set the sputtering power at 250 W;

[0042] S3. Turn on the magnetic field, control the gas flow rate of the inert gas to be 2000 sccm, the argon is ionized into plasma, bombards the MgF2 target, sputters a large number of Mg and F atoms, and deposits them on the ZnO surface, and the sputtering time is 1 h;

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

[0044] According to the above method, a protective film for an infrared antireflection coating is obtained. The thickness of the protective film is 100 nm, and the refractive index is 1.30.

[0045] Example 2

[0046] This example provides a protective film for an infrared antireflection coating and a preparation method thereof.

[0047] Preparation method:

[0048] S1. Install the MgF2 target on the target seat of the magnetron sputtering equipment, place the CdSe crystal with a ZnO antireflection coating on the sample stage, where the thickness of the ZnO coating is 650 nm, and adjust the distance between the substrate and the target to 5 cm;

[0049] S2. After evacuating the magnetron sputtering chamber to 10 -4 Pa, then fill it with argon, control the working pressure at 0.3 Pa, and set the sputtering power at 250 W;

[0050] S3. Turn on the magnetic field, control the gas flow rate of the inert gas at 2000 sccm, ionize the argon into plasma, bombard the MgF2 target, sputter out a large number of Mg and F atoms, deposit them on the ZnO surface, and the sputtering time is 1.5 h;

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

[0052] According to the above method, a protective film for an infrared antireflection coating is obtained. The thickness of the protective film is 150 nm, and the refractive index is 1.32.

[0053] Example 3

[0054] This example provides a protective film for an infrared antireflection coating and a preparation method thereof.

[0055] Preparation method:

[0056] S1. Install the MgF2 target on the target seat of the magnetron sputtering equipment, place the CdSe crystal with a ZnO antireflection coating on the sample stage, where the thickness of the ZnO coating is 650 nm, and adjust the distance between the substrate and the target to 5 cm;

[0057] S2. After evacuating the magnetron sputtering chamber to 10 -4 Pa, then fill it with argon, control the working pressure at 0.3 Pa, and set the sputtering power at 250 W;

[0058] S3. Turn on the magnetic field, control the gas flow rate of the inert gas to be 2000 sccm, ionize argon into plasma, bombard the MgF2 target, sputter out a large number of Mg and F atoms, deposit them on the ZnO surface, and the sputtering time is 3 h;

[0059] S4. After sputtering, slowly cool the sample to room temperature in a vacuum or low-pressure environment, and then take out the sample.

[0060] According to the above method, a protective film for an infrared antireflection coating is obtained. The thickness of the protective film is 300 nm and the refractive index is 1.35.

[0061] Example 4

[0062] This example provides a protective film for an infrared antireflection coating and a preparation method thereof.

[0063] Preparation method:

[0064] S1. Install the MgF2 target on the target seat of the magnetron sputtering device, place the CdSe crystal with the ZnO antireflection coating on the sample stage, where the thickness of the ZnO coating is 460 nm, and adjust the distance between the substrate and the target to 8 cm;

[0065] S2. Pump the magnetron sputtering chamber to a vacuum of 15 -3 Pa, then fill it with argon, control the working pressure at 0.4 Pa, and set the sputtering power at 200 W;

[0066] S3. Turn on the magnetic field, control the gas flow rate of the inert gas to be 2000 sccm, ionize argon into plasma, bombard the MgF2 target, sputter out a large number of Mg and F atoms, deposit them on the ZnO surface, and the sputtering time is 1.1 h;

[0067] S4. After sputtering, slowly cool the sample to room temperature in a vacuum or low-pressure environment, and then take out the sample.

[0068] According to the above method, a protective film for an infrared antireflection coating is obtained. The thickness of the protective film is 100 nm and the refractive index is 1.30.

[0069] Example 5

[0070] This example provides a protective film for an infrared antireflection coating and a preparation method thereof.

[0071] Preparation method:

[0072] S1. Install the MgF2 target on the target seat of the magnetron sputtering device, place the CdSe crystal with the ZnO antireflection coating on the sample stage, where the thickness of the ZnO coating is 780 nm, and adjust the distance between the substrate and the target to 6 cm;

[0073] S2. After evacuating the magnetron sputtering chamber to 10 -3 Pa, then fill it with argon, control the working pressure at 0.3 Pa, and set the sputtering power at 150 W;

[0074] S3. Turn on the magnetic field, control the gas flow rate of the inert gas at 2000 sccm, argon is ionized into plasma, bombards the MgF2 target, sputters a large number of Mg and F atoms, and deposits on the ZnO surface. The sputtering time is 1 h;

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

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

[0077] Example 6

[0078] This example provides a protective film for an infrared antireflection coating and a preparation method thereof.

[0079] Preparation method:

[0080] S1. Install the MgF2 target on the target seat of the magnetron sputtering equipment, place the CdSe crystal with the ZnO antireflection coating on the sample stage, where the thickness of the ZnO coating is 780 nm, and adjust the distance between the substrate and the target to 6 cm;

[0081] S2. After evacuating the magnetron sputtering chamber to 10 -3 Pa, then fill it with argon, control the working pressure at 0.3 Pa, and set the sputtering power at 150 W;

[0082] S3. Turn on the magnetic field, control the gas flow rate of the inert gas at 2000 sccm, argon is ionized into plasma, bombards the MgF2 target, sputters a large number of Mg and F atoms, and deposits on the ZnO surface. The sputtering time is 1.2 h;

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

[0084] According to the above method, a protective film for an infrared antireflection coating is obtained. The thickness of the protective film is 150 nm and the refractive index is 1.32.

[0085] Comparative Example 1

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

[0087] Comparative Example 2

[0088] A sample without a protective film, where the thickness of the ZnO coating is 460 nm.

[0089] Comparative Example 3

[0090] A sample without a protective film, where the thickness of the ZnO coating is 780 nm.

[0091] Comparative Example 4

[0092] This comparative example provides a protective film for an infrared antireflection coating and a preparation method thereof.

[0093] Preparation method:

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

[0095] S2. After evacuating the magnetron sputtering chamber to 10 -3 Pa, then fill it with argon, control the working pressure at 0.3 Pa, and set the sputtering power at 150 W;

[0096] S3. Turn on the magnetic field, control the gas flow rate of the inert gas to be 2000 sccm, the argon gas is ionized into plasma, bombards the MgF2 target, sputters a large number of Mg and F atoms, and deposits them on the ZnO surface. The sputtering time is 10 h;

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

[0098] According to the above method, a protective film for an infrared antireflection coating is obtained. The thickness of the protective film is 1000 nm, and the refractive index is 1.36.

[0099] Figure 1 It is a scanning electron microscope photograph 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 It is the transmittance spectrum of the samples in Examples 1 to 3 and Comparative Example 1. From the transmittance, it can be seen that in the 3000 - 5000 nm mid-infrared band, after covering the protective film, the transmittance of the sample does not decrease significantly. This shows that the prepared protective film can not only protect the film layer, but also has little effect on the transmittance of the original antireflection coating.

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

[0102] Figure 5 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 1000 nm and the refractive index is 1.36, when coated on the antireflection coating, the transmittance in the wavelength range of 3000 - 5000 nm is significantly reduced.

[0103] In summary, the MgF2 protective film prepared in the present invention controls its thickness and refractive index by controlling the parameters of magnetron sputtering. According to the combination of thickness and refractive index, the addition of the protective film has little influence on the overall antireflection effect, and even within a certain range of thickness and refractive index, the overall light transmittance is increased.

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

Claims

1. An infrared antireflection coating with a protective film, characterized in that, The protective film material is MgF2, which is coated on the antireflection coating by magnetron sputtering. The antireflection coating is made of ZnO material, and the antireflection coating is coated on the CdSe crystal. The antireflection band of the antireflection coating is 3000 - 5000 nm; The thickness of the antireflection 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.

2. The protective film of the infrared antireflection coating according to claim 1, wherein The thickness of the protective film is 100 - 150 nm, and the refractive index is 1.30 - 1.

32.

3. A method for preparing an infrared antireflection coating with a protective film according to any one of claims 1 to 2, characterized in that, It includes the following steps: S1. Install the MgF2 target on the target seat of the magnetron sputtering equipment, place the CdSe crystal with the antireflection coating 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 Pa, then fill it with argon, control the working pressure at 0.3 - 0.6 Pa, and set the sputtering power at 150 - 250 W; S3. Turn on the magnetic field, control the gas flow rate of the inert gas to be 2000 sccm, ionize argon into plasma, bombard the MgF2 target, sputter out a large number of Mg and F atoms, and deposit them on the ZnO surface. The sputtering time is 1 - 3 h; S4. After sputtering, slowly cool the sample to room temperature in a vacuum or low-pressure environment, and then take out the sample.

4. The preparation method of the infrared antireflection coating with a protective film according to claim 3, characterized in that, The purity of the MgF2 target is greater than 99.99%.

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