A polytetrafluoroethylene-based antireflection film suitable for terahertz band 35μm~36μm and a preparation method thereof

Abstract

The invention discloses a polytetrafluoroethylene-based antireflection film suitable for terahertz band 35μm-36μm and a preparation method thereof, wherein the antireflection film is composed of a polytetrafluoroethylene-based substrate and a poly-4-methyl-1-pentene film layer on its surface, and the preparation method is to generate the poly-4-methyl-1-pentene film layer on the surface of the polytetrafluoroethylene-based substrate by ion sputtering coating. Compared with the existing antireflection film, the antireflection film not only reduces the number of film layers, but also simplifies the polytetrafluoroethylene-based substrate material, and the antireflection film has a higher average transmittance in the 35μm-36μm band, a lower average reflectivity, and has better hardness and wear resistance, and can prevent the antireflection film from being easily scratched during use.

Description

Technical Field

[0001] The present invention relates to an antireflection film and a preparation method thereof, in particular to a polytetrafluoroethylene-based antireflection film suitable for the terahertz band of 35 μm to 36 μm and a preparation method thereof, belonging to the technical field of infrared thin films. Background Art

[0002] The terahertz (THz) band lies between infrared and microwaves, forming a transitional frequency band between macroscopic electronics and microscopic photonics. THz wavelengths range from 30μm to 100μm, with frequencies between 0.1THz and 10THz. Due to its advantages of high transmission rates, excellent directionality, high safety, minimal scattering, and excellent penetration, THz waves hold significant scientific value and broad application prospects in fields such as nondestructive testing, satellite communications, medical diagnostics, and satellite communications.

[0003] Functional devices in the terahertz band are often based on silicon. For example, high-resistivity float-zone single-crystal silicon (HRFZ-Si) is an isotropic crystalline dielectric material widely used in the terahertz frequency range. However, due to the refractive index mismatch between silicon and air, the reflectivity at the air-silicon interface reaches 30%, and this introduces Fabry-Perot interference fringes into the transmission spectrum. Therefore, a high-performance anti-reflection coating is required between the air and silicon to increase transmission and reduce reflection.

[0004] In the existing technology, some people have proposed using ultra-thin metals such as ultra-thin chromium, nickel and titanium films as anti-reflection films. The principle is to suppress reflection through impedance matching, but the thickness needs to be controlled very precisely. Some people have also proposed using sub-wavelength anti-reflection structures instead of anti-reflection films to achieve the anti-reflection effect. Its characteristic is that the surface of silicon is made into a relief structure. The transmittance and reflectivity of the relief structure can be changed by changing the characteristic size parameters such as the period size, duty cycle size and height size, so that the refractive index of air and silicon is matched. However, this technology uses micron or millimeter cutting technology to cut or etch the high-resistance silicon surface, which is very difficult to process. Summary of the Invention

[0005] In view of the defects of the prior art, the first object of the present invention is to provide a polytetrafluoroethylene-based antireflection film suitable for the terahertz band of 35μm to 36μm, the antireflection film is based on polytetrafluoroethylene (PTFE) and poly (4-methyl-1-pentene) (C6H 12)n is a film layer having a two-layer structure, which reduces the number of film layers of the antireflection film including the polytetrafluoroethylene-based bottom layer and the air layer, simplifies the polytetrafluoroethylene-based bottom material, and the antireflection film has a high average transmittance in the 35μm to 36μm band and a low average reflectivity, and has good hardness and wear resistance, which can prevent the antireflection film from being easily scratched during use.

[0006] A second object of the present invention is to provide a method for preparing a polytetrafluoroethylene-based antireflection film suitable for use in the terahertz band of 35 μm to 36 μm. The method is simple to operate, has low technical requirements, and is conducive to large-scale production. In addition, the method uses ion sputtering to form a poly(4-methyl-1-pentene) film layer, thereby enhancing the adhesion between the film layer and the substrate and improving the poor film firmness, poor moisture resistance, and film peeling of the antireflection film, thereby reducing the scrap rate and production cost of the antireflection film. In addition, the method improves the average transmittance of the antireflection film in the 35 μm to 36 μm band, reduces the average reflectivity of the antireflection film in the 35 μm to 36 μm band, optimizes the hardness and wear resistance of the antireflection film, and prevents the antireflection film from being easily scratched during use.

[0007] In order to achieve the above technical objectives, the present invention provides a polytetrafluoroethylene-based antireflection film suitable for the terahertz band of 35μm to 36μm, which is composed of a polytetrafluoroethylene substrate and a poly (4-methyl-1-pentene) film layer on its surface.

[0008] As a preferred embodiment, the polytetrafluoroethylene substrate has a refractive index of 1.43 in the 35μm to 36μm spectral range. The antireflection film of the present invention uses polytetrafluoroethylene as a substrate, with a length of 20mm and a width of 1mm. Polytetrafluoroethylene is mainly used for support and, together with poly-4-methyl-1-pentene, forms the antireflection film. Polytetrafluoroethylene is a white solid at room temperature with a density of approximately 2.2g / cm 3 , its melting point is 327 ° C, and its properties remain at a useful level over a wide temperature range of -73 ° C to 204 ° C. It has good transmittance in the range of 35μm to 36μm, and the refractive index in this wavelength range is 1.43.

[0009] As a preferred solution, the 1 / 4 optical thickness of the poly 4-methyl-1-pentene film layer is 6038.6 nm to 6211.2 nm.

[0010] As a preferred solution, the poly-4-methyl-1-pentene film has a refractive index of 1.449 and a transmittance T of 0.99910 within the 35μm to 36μm spectral range. Common film materials in the prior art include Ge, SiO2, and Ta2O5. Testing has shown that antireflection films made from SiO2 exhibit excellent resonant absorption in the 0.21μm to 6.7μm range, but are unsuitable for the terahertz band (35μm to 36μm). Antireflection films made from Ge have a higher refractive index and lower transmittance in the 0.2066μm to 0.8266μm range, making them unsuitable for the 35μm to 36μm terahertz band. The antireflection film prepared by Ta2O5 is suitable for the terahertz band of 35μm~36μm and has a high refractive index n=3.3240, but the transmittance is low at 35μm~36μm in the terahertz band, T=0.35062~0.36927, which is not the best choice. The poly (4-methyl-1-pentene) (C6H 12 )n, its refractive index n = 1.449 and transmittance T = 0.99910 in the terahertz band 35μm ~ 36μm spectral range, which fully meets the application requirements.

[0011] The present invention also provides a method for preparing a polytetrafluoroethylene-based antireflection film suitable for the terahertz band of 35μm to 36μm, wherein the method forms a poly(4-methyl-1-pentene) film layer on the polytetrafluoroethylene-based surface by ion sputtering coating.

[0012] The surface of the poly (4-methyl-1-pentene) film layer generated by the ion sputtering coating method of the technical solution of the present invention is smooth, no splashing occurs during the ion sputtering vacuum coating process, and the continuous decrease in the vacuum chamber pressure during evaporation indicates that no volatile matter and water vapor escape. The generated film layer has excellent adhesion to the substrate and transparency.

[0013] The poly (4-methyl-1-pentene) film coating method of the present invention uses a common existing ion sputtering coating equipment, BSV1030. Specific coating conditions are: poly (4-methyl-1-pentene) deposition rate of 1.5nm / s, using a 16cm RF ion source to bombard the target material, so that the target material particles are deposited on the workpiece disk substrate; wherein, the vacuum chamber pressure of the coating machine is ≤2*10 -6 Tor, argon gas was introduced and the oxygen pressure was set to 30 Pai. The coating time was the film thickness / deposition rate.

[0014] Compared with the existing technology, the technical solution of the present invention brings the following beneficial technical effects:

[0015] The antireflection film provided by the present invention has a two-layer structure, consisting of a polytetrafluoroethylene substrate and a poly(4-methyl-1-pentene) film layer on its surface. Compared with existing antireflection films, this reduces the number of film layers and simplifies the polytetrafluoroethylene substrate material. Furthermore, the antireflection film has a high transmittance (T) of 90.11% and a low reflectivity (R) of 10.19% in the 35-36 μm wavelength band. Furthermore, the poly(4-methyl-1-pentene) film layer, due to its inherent good hardness and wear resistance, prevents the antireflection film from being easily scratched during use.

[0016] The preparation method of the antireflection film provided by the present invention is simple to operate, has low technical requirements, and is conducive to large-scale production.

[0017] The present invention prepares an antireflection film by using a vacuum coating technology, and adopts an ion sputtering coating method to form a poly-4-methyl-1-pentene film layer. This not only enhances the adhesion between the film layer and the substrate, but also improves the poor film firmness, poor moisture resistance and film peeling of the antireflection film, thereby reducing the scrap rate and production cost of the antireflection film. It also improves the average transmittance of the antireflection film in the 35μm to 36μm band, reduces the average reflectivity of the antireflection film in the 35μm to 36μm band, optimizes the hardness and wear resistance of the antireflection film, and prevents the antireflection film from being easily scratched during use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the antireflection film structure prepared in Example 1; 1 is the antireflection film with polytetrafluoroethylene as the substrate; its length is 20 mm and its width is 1 mm; 2 is the poly (4-methyl-1-pentene) film layer, its 1 / 4 optical thickness is 6.133 μm.

[0019] Figure 2 This is a spectrum diagram of the antireflection film prepared in Example 1, a spectrum comparison diagram of the transmittance and reflectance of the antireflection film in the 30μm to 55μm band. It can be seen from the figure that the transmittance and reflectance comparison at 35-36μm in the terahertz band are as follows: transmittance T = 90.11% and reflectance R = 10.19%.

[0020] Figure 3 This is a spectrum comparison of the transmittance and reflectance of the antireflection film prepared in the embodiment in the 30μm to 40μm band. The figure shows the transmittance and reflectance comparison at 35-36μm in the terahertz band, with transmittance T = 90.11% and reflectance R = 10.19%.

[0021] Figure 4 and Figure 5This is a diagram of the refractive index and transmittance of poly (4-methyl-1-pentene) material in the 35μm to 36μm spectral range. The refractive index and transmittance of poly (4-methyl-1-pentene) material are relatively stable at 35μm to 36μm in the terahertz band and tend to be a straight line. The refractive index is 1.449 and the transmittance T = 0.99910. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar numbers throughout represent the same or similar devices or devices with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and are not to be construed as limitations on the present invention. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless defined as such.

[0023] Example 1

[0024] A polytetrafluoroethylene (PTFE) film with a length of 20 mm and a width of 1 mm was selected as the substrate, and a poly (4-methyl-1-pentene) film layer was formed on the substrate by ion sputtering coating. The ion sputtering coating equipment used was BSV1030. The specific coating conditions were as follows: the poly (4-methyl-1-pentene) deposition rate was 1.5 nm / s, and a 16 cm RF ion source was used to bombard the target material, causing the poly (4-methyl-1-pentene) target particles to be deposited on the workpiece disc substrate; wherein, the vacuum chamber of the coating machine Pressure ≤ 2*10 - 6 Torr, the vacuum chamber temperature was set to 300°C, argon was introduced, and the oxygen pressure was set to 30 Pai. During the deposition process, the ion source energy was controlled by adjusting the power required to deposit the film, thereby controlling the speed at which the ion source sputtered the target. By precisely controlling the ion source energy, the uniformity of the film deposition was improved. The deposition time was calculated as the film thickness divided by the deposition rate.

[0025] The prepared antireflection film is made of poly-4-methyl-1-pentene with a 1 / 4 optical thickness of 6.133 μm. The transmittance and reflectance of the polytetrafluoroethylene (PTFE) based antireflection film in the 35-36 μm band were tested. The test results are as follows: Figure 2 and Figure 3 shown.

[0026] Comparative Example 1

[0027] The difference from Example 1 is that Ge, SiO2 or Ta2O5 is used to replace the 4-methyl-1-pentene in Example 1. After testing, the anti-reflection film prepared by SiO2 has good resonant absorption in the range of 0.21μm to 6.7μm, and is not suitable for the terahertz band of 35μm to 36μm. The anti-reflection film prepared by Ge has a high refractive index and low transmittance in the range of 0.2066μm to 0.8266μm, and is not suitable for the terahertz band of 35μm to 36μm. The anti-reflection film prepared by Ta2O5 is suitable for the terahertz band of 35μm to 36μm and has a high refractive index n = 3.3240, but the transmittance is low at 35μm to 36μm in the terahertz band, T = 0.35062 to 0.36927, which is not the best choice.

[0028] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art may still modify or make equivalent substitutions to the specific implementations of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A polytetrafluoroethylene-based antireflection film suitable for terahertz band 35μm~36μm, characterized by: The invention is composed of a polytetrafluoroethylene substrate and a poly-4-methyl-1-pentene film layer on its surface; the 1 / 4 optical thickness of the poly-4-methyl-1-pentene film layer is 6038.6nm to 6211.2nm.

2. The polytetrafluoroethylene-based antireflection film suitable for the terahertz band of 35 μm to 36 μm according to claim 1, characterized in that: The polytetrafluoroethylene substrate has a refractive index of 1.43 in the spectral range of 35 μm to 36 μm.

3. The polytetrafluoroethylene-based antireflection film suitable for the terahertz band of 35 μm to 36 μm according to claim 1, characterized in that: The poly 4-methyl-1-pentene film layer has a refractive index of 1.449 in the spectral range of 35 μm to 36 μm.

4. The polytetrafluoroethylene-based antireflection film suitable for the terahertz band of 35 μm to 36 μm according to claim 1, characterized in that: The poly-4-methyl-1-pentene film layer has a transmittance T of 0.99910 in the spectral range of 35 μm to 36 μm.

5. A method for preparing a polytetrafluoroethylene-based antireflection film suitable for terahertz band 35 μm to 36 μm according to any one of claims 1 to 4, characterized in that: A poly-4-methyl-1-pentene film layer is formed on a polytetrafluoroethylene bottom surface by ion sputtering coating.

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