Preparation method and application of hard and wear-resistant zinc sulfide anti-reflection protective film

Abstract

The application discloses a preparation method and application of a hard and wear-resistant zinc sulfide anti-reflection protective film. The substrate is germanium, and the film is zinc sulfide. The working wave band of the film layer is 8-12 microns. In order to enhance the hardness and wear resistance of the zinc sulfide film, the germanium substrate needs to be kept at a specific high temperature during the film preparation, electron beam evaporation technology is selected to keep a specific deposition rate, and an alternating high-voltage electric field needs to be arranged in a vacuum chamber. After the film preparation, high-temperature annealing treatment needs to be conducted in air. The substrate temperature is set to 220 DEG C, the film deposition rate is about 10 nm / s, the voltage of the alternating high-voltage electric field is 3400 V, the current is zero, and the frequency is 50 Hz. The high-temperature annealing treatment temperature in air is 350 DEG C, and the constant temperature time is 6 hours. Through the superposition and joint action of the above multiple measures, the hardness and wear resistance of the zinc sulfide film are enhanced, and the zinc sulfide film can meet the actual use requirements.

Description

Technical Field

[0001] This invention relates to a method for preparing a hard and wear-resistant zinc sulfide antireflective protective film, which is used in infrared photoelectric monitoring or surveillance instruments and belongs to the field of optical thin films. Background Technology

[0002] The mid-infrared band with wavelengths of 3–5 μm and the far-infrared band with wavelengths of 8–12 μm are two important infrared atmospheric windows, which have extremely important application value in the monitoring and surveillance of the sea surface and land.

[0003] Due to the good refractive index matching between germanium (Ge) substrates and zinc sulfide (ZnS) films, they are widely used in photoelectric monitoring or surveillance instruments in the two infrared bands mentioned above. Because of this, many research results have been reported, including antireflection effects, film structures under different processes, and the moisture resistance, chemical properties, and mechanical properties of the film. However, there is little research on the preparation process for improving the hardness and wear resistance of ZnS films. ZnS films are widely used as low-refractive-index materials in the infrared band, and can also be used as high-refractive-index materials. It is a typical soft film material, so the hardness and wear resistance of its film have always been a focus of attention. Early on, Yu Juxian of the Kunming Institute of Physics disclosed a high-strength antireflection film (CN 87102489A) on a single layer of zinc sulfide on a germanium substrate. This involved a strengthening process of heat treatment at a specific temperature after the ZnS film was prepared using conventional cold substrate processes, which greatly improved the mechanical strength of the ZnS film, achieving significant progress. Summary of the Invention

[0004] This invention provides a method for preparing and applying a hard and wear-resistant zinc sulfide antireflective protective film.

[0005] A robust and wear-resistant zinc sulfide antireflective protective film is needed for far-infrared marine surface monitoring instruments with wavelengths of 8–12 μm. The Ge substrate and ZnS film located on the outermost layer of the instrument lens need to withstand long-term sand and dust abrasion in the windy and dusty weather of northern my country (such as the Bohai Bay). Therefore, this invention specifically proposes preparation techniques and process factors to enhance the hardness and wear resistance of the ZnS film. Multiple techniques and process factors are combined during and after preparation. Through the superposition and synergistic effect of multiple measures, the hardness and wear resistance of the ZnS film are effectively enhanced to meet practical application requirements. Clearly, this ZnS film on a Ge substrate has two functions: it serves as both an antireflective film for Ge and a wear-resistant protective film.

[0006] A hard and wear-resistant zinc sulfide antireflective protective film is composed of a germanium (Ge) substrate and a zinc sulfide (ZnS) thin film. The only way to obtain a hard and wear-resistant ZnS film is to increase the kinetic energy of the evaporating particles during deposition: E = 3kT / 2, where E is the kinetic energy of the evaporating particles during deposition, and k is the Boltzmann constant (= 8.62 x 10⁻⁶). -5 (eV / °K), where T is the Kelvin temperature at which the thin film material evaporates. Given that the evaporation temperature of ZnS material is 1373°K, its kinetic energy E can be calculated to be only 0.18 eV. Clearly, this kinetic energy is too low; therefore, ZnS films prepared using conventional processes cannot be hard and wear-resistant.

[0007] To this end, this invention proposes the following three concepts: First, during thin film preparation, the Ge substrate needs to be maintained at a specific high temperature. To achieve this, a specific evaporation method and a specific deposition rate must be selected for the ZnS film. This represents a crucial first step towards growing a hard and wear-resistant ZnS film on a high-temperature substrate. Second, a new AC high-voltage electric field needs to be introduced into the vacuum chamber of a commercial coating machine to further increase the kinetic energy of the ZnS evaporation particles during their journey from the evaporation source to the substrate, thereby enhancing the hardness and wear resistance of the ZnS film. Third, after thin film preparation, a high-temperature annealing treatment is performed in air to further improve the film density and reduce film stress. These are elaborated below.

[0008] 1. Using specific high-temperature substrates and deposition rates

[0009] As is well known, the hardness or wear resistance of a thin film strongly depends on the substrate temperature during film deposition, because a high-temperature substrate can significantly increase the energy of the deposited molecules and increase the migration rate of the deposited molecules on the substrate surface, resulting in preferential orientation growth of the film layer and the formation of a dense, hard and wear-resistant thin film structure.

[0010] The substrate temperature during deposition is particularly sensitive to the growth of ZnS thin films. ZnS films deposited on cold substrates (room temperature) are very soft and have very poor adhesion. Therefore, this invention proposes the use of high-temperature substrates for deposition. Unfortunately, as the substrate temperature increases, the back-evaporation of ZnS films (i.e., the film molecules deposited on the substrate evaporate away from the substrate) makes deposition very difficult, and may even result in the inability to deposit a film at all. This is what is commonly referred to as "ZnS films cannot be deposited on high-temperature substrates," which is why existing ZnS films are often deposited on cold or low-temperature substrates. Pulker also pointed out earlier that when the substrate temperature reaches 300°C, ZnS films at conventional deposition rates will completely stop depositing.

[0011] By the way, what is a high-temperature substrate? Room temperature usually refers to a cold substrate, meaning the substrate is not heated during film deposition. Low-temperature substrate deposition refers to substrate temperature below 150°C, while high-temperature substrate deposition refers to substrate temperature above 150°C. For high-temperature substrate deposition, experiments have confirmed that when the substrate temperature exceeds 250°C, not only is reverse evaporation severe and deposition difficult, but the ZnS film structure also becomes coarser, and scattering increases. Therefore, the so-called high-temperature substrate deposition of ZnS films actually refers to the 150–250°C range.

[0012] So, how can we overcome the bottleneck of difficulty in depositing ZnS films on high-temperature substrates? To this end, this invention first studied the relationship between the deposition rate of ZnS films and the substrate temperature, proposed the concept of deposition coefficient, and expressed the deposition coefficient α as:

[0013]

[0014] In the formula, N + and N - These represent the number of atoms or molecules of ZnS that evaporated onto the substrate and those that desorbed away from the substrate, respectively. C depends on N. + A quantity, N + The larger the value, the smaller C, and the larger α. U represents the adsorption energy, k is the Boltzmann constant, and T is the substrate temperature. Clearly, and The relationship is linear within a certain range, and the slope of the line is... This indicates that the deposition coefficient α of the thin film depends not only on the substrate temperature but also on the deposition rate. To investigate the relationship between the deposition coefficient of ZnS films and the substrate temperature and deposition rate, this invention conducted experimental studies, obtaining [results] at two specific deposition rates of 0.97 nm / s and 9.5 nm / s. Figure 2 The relationship between the deposition coefficient α of the ZnS film and the substrate temperature T is shown. From... Figure 2 As can be seen, at the same substrate temperature, different deposition rates result in drastically different deposition coefficients. For clarity, the experimental results are presented in Table 1. Table 1 shows that at a substrate temperature of 200°C, using a conventional deposition rate of 0.97 nm / s yields a deposition coefficient of only 0.33. This not only makes ZnS film deposition difficult but also wastes a significant amount of ZnS evaporation material. However, by increasing the ZnS deposition rate from 0.97 nm / s to 9.5 nm / s, the deposition coefficient increases to 0.68. This means that the bottleneck of ZnS film deposition on high-temperature substrates can be significantly alleviated by increasing the deposition rate. This invention presents a novel method for depositing ZnS films on high-temperature substrates, making ZnS film deposition on high-temperature substrates possible.

[0015] Table 1

[0016]

[0017] Figure 2 The relationship between the deposition coefficient α and the substrate temperature T shown was tested using the following method: [Select...] Figure 1 The quartz crystal control plate 12 controls the film thickness. The crystal control plate is water-cooled to maintain room temperature. Then, the coating substrate 5 (5′) on the workpiece holder 4 is heated to 100℃, 150℃, 200℃, and 250℃ respectively, and ZnS films of the same thickness are deposited on the thickness control plate at the same deposition rate of 0.97nm / s. Finally, the ZnS film thickness on the substrate at each temperature is measured by photometry or other thickness gauges. The deposition coefficient α is obtained by measuring the ratio of the thickness on the substrate at each temperature to the thickness at room temperature. Figure 2 Curve 1. The deposition rate of 9.5 nm / s was tested again using the same method, and the results were obtained. Figure 2 Curve 2.

[0018] It should be noted that the deposition rates of ZnS are 0.97 nm / s and 9.5 nm / s. In the visible light region, with a center wavelength λ0 = 550 nm and a ZnS film refractive index of 2.35, for an optical thickness of λ0 / 4, the geometric thickness is 59 nm. The evaporation time using conventional processes is approximately 1 minute, resulting in a deposition rate of approximately 1 nm / s, while the actual experiment controlled the rate at 0.97 nm / s. In the infrared band, with a center wavelength λ0 = 10 μm and a ZnS film refractive index of 2.2, again for an optical thickness of λ0 / 4, the geometric thickness is 1136 nm. The evaporation time using conventional processes is 19 minutes. To improve the deposition rate, this invention shortens the evaporation time to approximately 2 minutes, resulting in a deposition rate of approximately 10 nm / s, while the actual experiment controlled the rate at 9.5 nm / s.

[0019] It should also be noted that although existing technologies often use crucible heating to evaporate ZnS materials, this invention, in order to achieve a deposition rate 10 times higher than existing technologies on high-temperature substrates, must employ electron beam heating evaporation technology. This invention has found that crucible heating evaporation has several drawbacks: firstly, the evaporation rate is very slow, far below the required deposition rate of approximately 10 nm / s; secondly, the resulting ZnS film is a mixture of zincblende and wurtzite, which is prone to transformation into ZnO under prolonged ultraviolet radiation during use, and the film layer is relatively soft, while the ZnS film generated by electron beam evaporation has a stable cubic zincblende structure and is relatively hard; furthermore, when ZnS is evaporated using a crucible, the material decomposes severely, leaving a large amount of decomposed black zinc residue at the bottom of the crucible, especially at faster evaporation rates, leading to a significant increase in ZnS film absorption. This indicates that electron beam heating evaporation technology must be used when depositing ZnS films on high-temperature substrates.

[0020] II. Introduction of AC high-voltage electric field

[0021] ZnS is a very unique thin film material that completely sublimates during vacuum evaporation and undergoes ionization: Zn + and S - During the thin film deposition process, Zn + and S - The molecules will recombine on the substrate, thus still yielding a film with stoichiometry identical to that of ZnS. This mechanism of deposition in elemental form can well explain the phenomenon that the deposition coefficient of ZnS film decreases rapidly with increasing substrate temperature.

[0022] Based on the ionization that occurs during the evaporation of ZnS materials, this invention proposes that if an AC high-voltage electric field is installed in the vacuum chamber of a commercial coating machine, the ionized ZnS... + and S - During their journey from the evaporation source to the substrate, the ions are inevitably subjected to a strong electric field, which will greatly increase the kinetic energy of the ions and improve the hardness and wear resistance of the film.

[0023] So how can an AC high-voltage electric field be introduced into the vacuum chamber? The introduced AC high-voltage electric field must not affect the original functions of the commercial coating machine. Therefore, this invention conceives the following configuration scheme: Figure 1 As shown, a pair of electrodes 7 and 7' are positioned close to the workpiece holder 4 within the vacuum chamber electron beam evaporation source 10. Electrodes 7 and 7' are composed of two semi-circular rings made of pure aluminum plates. The distance between them and the workpiece holder varies depending on the size of the vacuum chamber, generally ranging from 20 to 100 mm, with 50 mm being preferred in this invention. The width (i.e., height) of the two semi-circular ring electrodes is 10 to 40 mm, with 20 mm being preferred in this invention. When evaporating ZnS material under high vacuum conditions, an AC high voltage of 3.2 to 3.6 kV with a frequency of 50 Hz is applied to electrodes 7 and 7', with 3.4 kV being preferred in this invention. Because no glow discharge is generated in the high-voltage electric field under high vacuum conditions, the current is zero. The two pure aluminum semi-circular ring electrodes 7 and 7' are supported by stainless steel high-voltage introduction electrodes 8 and 8', connected to the high-voltage transformer 16, and insulated from the high voltage of the coating machine.

[0024] The diameter of the ring formed by the two semicircular rings is similar to the diameter of the workpiece holder, generally 200–1200 mm, but preferably 400 mm in this invention (see [reference]). Figure 3 The radius of the two semicircular rings is preferably 200mm. Both semicircular rings are cut from pure aluminum plates approximately 1.2mm thick. Because the two semicircular rings need to be insulated from each other, they are separated by 40mm. Simultaneously, both semicircular rings are wrapped with clean pure aluminum foil 0.01mm thick, and the aluminum foil is replaced after each ZnS film preparation to reduce contamination of the ZnS film by the coating material deposited on the electrodes.

[0025] Experiments have shown that the above assumptions are feasible and the concept is correct.

[0026] III. Implement high-temperature annealing treatment

[0027] After ZnS film preparation, high-temperature annealing in air is required. This method is simple and easy to implement, so existing technologies all adopt this method. The only difference lies in the process parameters, which vary depending on the equipment and the shape and size of the sample. The process parameters mainly include: first, the average temperature during isothermal treatment; second, time, including heating time, isothermal time, cooling time, and the time from sample removal from the vacuum chamber to the oven; third, the atmosphere, commonly air, but nitrogen can also be used; fourth, the placement method of the ZnS film sample, including horizontal or vertical placement; and fifth, the material and shape of the sample placement fixture. High-temperature annealing after ZnS film preparation not only alters the microstructure of the ZnS film, making it denser, but also reduces film stress. This is particularly important for the zinc sulfide film of this invention, which operates in the 8μm–12μm wavelength range, corresponding to a very thick film with very high compressive stress. In terms of high-temperature annealing, this invention mainly optimizes the process parameters and designs a dedicated sample fixture (see...). Figure 4 ).

[0028] The above three measures are all important for preparing a hard and wear-resistant zinc sulfide antireflective protective film. Only when multiple technologies and processes are used in combination can the hardness and wear resistance of the ZnS film be effectively improved to meet the requirements of actual use.

[0029] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0030] A hard and wear-resistant zinc sulfide antireflective protective film consists of two parts: a substrate and a film. The substrate is germanium and the film is zinc sulfide.

[0031] A method for preparing a hard and wear-resistant zinc sulfide antireflective protective film includes the following steps:

[0032] S1: During the preparation of ZnS thin films, the substrate needs to be kept at a high temperature, and a specific evaporation method needs to be selected to maintain a high deposition rate. At the same time, an AC high-voltage electric field is set in the vacuum chamber to increase the kinetic energy of the deposited particles on the substrate.

[0033] Furthermore, during the thin film preparation, a germanium substrate was used, and an AC high-voltage electric field of 3000V to 3800V was set in a vacuum chamber. The zinc sulfide antireflection protective film was evaporated using an electron beam evaporation source, maintaining a deposition rate of 6nm / s to 15nm / s.

[0034] S2: After preparation of zinc sulfide antireflective coating, it is annealed in air to obtain a hard and wear-resistant zinc sulfide antireflective coating on a germanium substrate.

[0035] Furthermore, the substrate temperature is set to 200℃~240℃, and the holding time is 1~3 hours.

[0036] Furthermore, the thin-film evaporation method employs electron beam evaporation technology.

[0037] Furthermore, the thin film deposition rate is 8 nm / s to 12 nm / s.

[0038] Furthermore, the voltage of the AC high-voltage electric field is 3200V~3600V, the current is zero, and the frequency is 50Hz.

[0039] Furthermore, the high-temperature annealing treatment in air is carried out at a temperature of 330℃~370℃ for 4~8 hours.

[0040] Furthermore, the temperature of the high-temperature substrate is 215℃~225℃. The optimal substrate temperature is 220℃, and the holding time is 2 hours.

[0041] Furthermore, electron beam evaporation technology is used to maintain a deposition rate of 9 nm / s to 11 nm / s, and most preferably, the film deposition rate reaches about 10 nm / s.

[0042] Furthermore, the voltage of the AC high-voltage electric field is 3300V to 3500V, and the most preferred voltage of the AC high-voltage electric field is 3400V.

[0043] Furthermore, the annealing conditions are: high-temperature annealing at 345℃~355℃ for 5~7 hours. The optimal annealing temperature for the film in air is 350℃, with a holding time of 6 hours.

[0044] Finally, the zinc sulfide film on the germanium substrate operates in the wavelength range of 8 μm to 12 μm. The refractive index of the germanium substrate in the operating wavelength range is 4.0, the refractive index of the zinc sulfide film in the operating wavelength range is 2.2, and its geometric thickness is 1136 nm.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] Given the specific characteristics of ZnS materials, existing techniques often employ cold substrate deposition of ZnS films to avoid the bottleneck problem of difficult deposition on high-temperature substrates. However, due to the evaporation of Zn... + and S -If the ion energy is too low, the migration rate of the precipitated molecules or atoms after reaching the substrate surface is almost zero, resulting in a very soft ZnS film. Even after high-temperature annealing in air following preparation, the final ZnS film's hardness and wear resistance still fail to meet the application requirements.

[0047] To obtain a hard and wear-resistant ZnS film, the measures taken during film preparation are far more important than the post-preparation treatment. Therefore, this invention employs a high-temperature substrate and introduces an alternating high-voltage electric field during film preparation, significantly improving the deposition efficiency of ZnS. + and S - The energy of the ions. In this way, the deposited particles with sufficient energy collide with the surface of the deposited film, generating a sufficiently large momentum transfer, and the deposited particles obtain a sufficiently large mobility. The film exhibits sufficient preferential growth, and its diffraction spectrum shows a sharp and strong (111) diffraction peak near the diffraction angle of 28°. This film has sufficient hardness and wear resistance. Since the ZnS film of the present invention has already formed sufficient hardness and wear resistance during the deposition process, further high-temperature annealing in air is carried out to achieve the purpose of adding icing on the cake, obtaining hardness and wear resistance that fully meet practical requirements, and withstanding long-term abrasion from sand and dust. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the configuration of the vacuum evaporation system of a commercial coating machine and the AC high-voltage electrode of the present invention.

[0049] Figure 2 This is a curve showing the relationship between the deposition coefficient of the ZnS film of this invention and the substrate temperature at different deposition rates.

[0050] Figure 3 This is a schematic diagram of an electrode pair consisting of two semi-circular pure aluminum rings in this invention.

[0051] Figure 4 This is a sample annealing fixture diagram used in this invention.

[0052] Figure 5 This is the spectral transmittance curve of a hard and wear-resistant ZnS antireflective protective film of the present invention. Detailed Implementation

[0053] Before presenting the concept of this invention, it is necessary to first explain the vacuum evaporation system of a commercial coating machine, such as... Figure 1As shown, it mainly includes a vacuum chamber 1, which obtains a high vacuum by exhausting air through a suction port 2. Inside the vacuum chamber, a substrate heating system 3 is installed to heat the substrate to a specific temperature before coating. Below the heating system 3 is a workpiece holder 4 for placing the substrates. The workpiece holder is a disc capable of holding many substrates (such as 5, 5'), and it rotates uniformly and rapidly during coating. A film thickness monitoring plate box 6 (i.e., a monitoring plate) is placed at the center of the disc. The thin film material evaporation source consists of a crucible-heated evaporation source 9 and an electron beam-heated evaporation source 10, which can be selected according to different evaporation materials. Above each evaporation source is a baffle 11, 11' to control the vapor of the evaporating material, so as to precisely control the thickness of each film layer. The film thickness monitoring system can use a quartz crystal control plate 12, or a light control system can be selected. The light control system consists of a light source 13, a filter 14, a monitoring plate, and a photodetector 15.

[0054] use Figure 1 The commercial vacuum coating machine vacuum evaporation system shown, along with the AC high-voltage electrode added in this invention, deposits a zinc sulfide film on a germanium substrate, operating in the wavelength range of 8 μm to 12 μm. The refractive index of the germanium substrate in the operating wavelength range is 4.0, the refractive index of the zinc sulfide film in the operating wavelength range is 2.2, the center wavelength λ0 = 10 μm, the optical thickness of the zinc sulfide film is λ0 / 4, and the corresponding geometric thickness is 1136 nm.

[0055] The added AC high-voltage electrodes 7 and 7' are located between the thin film material evaporation source 9 and 10 and the Ge substrate workpiece holder 4, such as Figure 1 As shown. Electrodes 7 and 7' are composed of two semi-circular rings made of pure aluminum plates. The distance between them and the workpiece holder 4 varies depending on the size of the vacuum chamber, generally 20–100 mm, and preferably 40 mm in this invention. The width (i.e., height) of the two semi-circular ring electrodes is 10–40 mm, and preferably 20 mm in this invention. When evaporating ZnS material under high vacuum conditions, an AC high voltage of 50 Hz and 3.2–3.6 kV is applied to electrodes 7 and 7', with 3.4 kV being preferred in this invention. The two pure aluminum semi-circular ring electrodes 7 and 7' are supported by stainless steel high-voltage electrode supports 8 and 8' and connected to the high-voltage transformer 16. Figure 3This is a schematic diagram of the electrode pair composed of two semicircular pure aluminum rings according to the present invention. The separation of the two semicircular rings is approximately 40mm to effectively prevent arcing under high vacuum conditions. The size of the rings varies depending on the size of the workpiece holder 4, and generally the diameter of the rings is approximately the same as the diameter of the workpiece holder, such as 200-1200mm, with 400mm being preferred in this invention. Electrodes 7 and 7' are directly cut from pure aluminum plates with a thickness of 0.5-2mm, with 1.2mm being preferred in this invention. The electrode manufacturing steps are as follows: 1. Cut two electrode plates from a 1.2mm thick pure aluminum plate according to a semicircular circumference πR equal to 628mm and a width of 20mm; 2. Bend the two electrode plates into two semicircular rings according to R=200mm and assemble them into a circle; 3. To prevent the two semicircular rings from arcing with each other, cut off 20mm at the contact area, ultimately forming... Figure 3 It looks like that.

[0056] Before preparing the ZnS thin film, the germanium substrate was gradually heated to 220°C and held at that temperature for 2 hours. Then, the ZnS crystalline bulk material was heated and evaporated using an electron beam. At the same time, an AC voltage of 3.4 kV was applied to the high-voltage electrodes 7 and 7'.

[0057] Depend on Figure 2 It is known that at a substrate temperature of 220℃, if evaporation is carried out at a conventional deposition rate of approximately 1 nm / s, the deposition coefficient of the ZnS film is only 0.22, meaning that 78% of the deposited molecules are re-evaporated. This not only results in a significant loss of ZnS material but also leads to an extremely slow increase in film thickness. Ultimately, all the ZnS material added by the electron beam evaporation source evaporates, but the film thickness is still less than λ0 / 4. Therefore, a high deposition rate of approximately 10 nm / s must be chosen for evaporation. Figure 2 It can be seen that the deposition coefficient of the ZnS film can reach 0.6, thus successfully completing the deposition of a ZnS film with an optical thickness of λ0 / 4, that is, a geometric thickness of 1136 nm.

[0058] After ZnS film deposition, the substrate heating system and 3.4KV AC high voltage are turned off, and the coated sample is cooled. Once the sample temperature is below 60℃, the coated sample is removed from the vacuum chamber and transferred to an oven for high-temperature annealing in air. The annealing temperature is 330℃~370℃, preferably 350℃; the annealing holding time is 4~8 hours, preferably 6 hours. During annealing, the oven needs to be slowly heated for about 2 hours, then held at that temperature for 6 hours, and finally slowly cooled for more than 12 hours. Due to differences in oven models and specifications, the heating and cooling times vary greatly, but most ovens suffer from the problem of heating and cooling too quickly. Therefore, this invention designs... Figure 4The sample fixture shown is made of stainless steel. Because stainless steel has a low thermal conductivity of only about 20 W / (mK), this fixture can both increase heat capacity and slow down heating and cooling times, thus overcoming problems such as excessively rapid heating and cooling times and large temperature fluctuations during constant temperature operation. Figure 4 In the diagram, 1 is a stainless steel fixture, 2 is aluminum foil, and 3 is the annealed sample. The ZnS film is placed flat on a 0.05mm thick aluminum foil with the ZnS film facing upwards. During annealing, another fixture identical to 1 with a concave hole facing downwards is used to cover the sample. Figure 4 Above 1.

[0059] Finally, the ZnS antireflective protective film was subjected to spectroscopic characteristic tests, as well as hardness and abrasion resistance tests. Figure 5 The solid line shown is the spectral transmittance curve of the sample after being coated with a ZnS film, and the dashed line is the transmittance curve of a single Ge surface without a ZnS film. It can be seen that the ZnS film has an excellent broad-spectrum anti-reflection effect on the Ge surface. Regarding the film hardness and abrasion resistance tests, this invention mainly adopts a simple and easy-to-implement relative comparison method, using pencils of different hardness to repeatedly scratch the film surface. Currently, hard-core pencils with hard leads from 1H to 10H are commercially available; the higher the number, the higher the hardness. Generally, ZnS films produced by conventional processes can only withstand repeated scratching with 1H to 2H pencils, while this invention showed no damage after repeated scratching with 9H or 10H pencils.

Claims

1. A method for preparing a hard and wear-resistant zinc sulfide antireflective protective film, characterized in that, Includes the following steps: S1: During film preparation, a germanium substrate is used. The germanium substrate is a high-temperature substrate with a temperature of 200℃~240℃. An AC high-voltage electric field of 3000V~3800V is set in a vacuum chamber. The zinc sulfide antireflection protective film is evaporated by an electron beam evaporation source, maintaining a deposition rate of 6nm / s~15nm / s. S2: After the zinc sulfide antireflective coating is prepared, it is annealed in air to obtain a hard and wear-resistant zinc sulfide antireflective coating on a germanium substrate.

2. The method for preparing the hard and wear-resistant zinc sulfide antireflective protective film according to claim 1, characterized in that, In step S1, the temperature of the high-temperature substrate is 215℃~225℃.

3. The method for preparing the hard and wear-resistant zinc sulfide antireflective protective film according to claim 1, characterized in that, In step S1, the heating time of the high-temperature substrate is 1 to 3 hours.

4. The method for preparing the hard and wear-resistant zinc sulfide antireflective protective film according to claim 1, characterized in that, In step S1, the voltage of the AC high-voltage electric field is 3200V~3600V.

5. The method for preparing the hard and wear-resistant zinc sulfide antireflective protective film according to claim 4, characterized in that, In step S1, the voltage of the AC high-voltage electric field is 3300V~3500V.

6. The method for preparing the hard and wear-resistant zinc sulfide antireflective protective film according to claim 1, characterized in that, In step S1, maintain a deposition rate of 8 nm / s to 12 nm / s.

7. The method for preparing the hard and wear-resistant zinc sulfide antireflective protective film according to claim 6, characterized in that, In step S1, maintain a deposition rate of 9 nm / s to 11 nm / s.

8. The method for preparing the hard and wear-resistant zinc sulfide antireflective protective film according to claim 1, characterized in that, In step S2, the annealing conditions are: high-temperature annealing at 330℃~370℃ for 4~8 hours.

9. An infrared monitoring instrument, characterized in that, A hard and wear-resistant zinc sulfide antireflective protective film prepared by the preparation method according to any one of claims 1 to 8.

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