Diamond infrared window film and preparation method thereof

Abstract

According to the diamond infrared window thin film and the preparation method thereof, the rare earth metal oxide thin film is arranged on the surface of the diamond substrate, firstly, the average transmittance of a target wave band is remarkably improved by selecting the rare earth oxide with the refractive index between that of diamond and that of air and utilizing the destructive interference principle; and the problem of high reflection loss is efficiently solved. And secondly, the compact oxide film forms a physical and chemical barrier on the surface of the diamond, and direct contact between high-temperature oxygen and a substrate is effectively blocked, so that the oxidation reaction at 700-800 DEG C is inhibited, and the high-temperature oxidation problem of the diamond is fundamentally solved. Finally, the thin film has high anti-reflection performance, strong oxidation resistance and excellent film-substrate binding force, so that the diamond window thin film can still keep stable optical performance and complete structure after bearing severe thermal shock.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to the field of optical thin film technology, and in particular to a diamond infrared window thin film and a preparation method thereof. BACKGROUND

[0002] Diamond has high long-wave infrared (7.5 μm~14 μm) transparency, as well as ultra-high hardness (~80 GPa), thermal conductivity (~2000 W / mK) and bending strength (~400 MPa), and is the best infrared optical material in terms of heat shock resistance, and is expected to be applied to infrared optoelectronic systems under high temperature and high heat conditions as an infrared optical window.

[0003] However, its two inherent defects seriously restrict its practical application: first, the high refractive index (~2.4) of diamond leads to serious Fresnel reflection on its surface, so that the transmittance of the uncoated window is only about 70%, causing a huge signal loss. Second, diamond will oxidize in an oxygen-containing environment above 700℃, which not only further reduces the transmittance, but also etches the surface, weakens the strength, and increases the risk of window cracking under thermal shock. At present, there is an urgent need in the art for a solution that can overcome both the high reflection and the easy oxidation of the two major bottlenecks, and the existing single-function thin films or traditional preparation techniques are difficult to achieve effective compatibility of high transmittance and high heat shock resistance / oxidation resistance. SUMMARY

[0004] In view of the above-mentioned defects or shortcomings in the prior art, it is desirable to provide a diamond infrared window thin film and a preparation method thereof to solve the above-mentioned problems.

[0005] In a first aspect, the present application provides a diamond infrared window thin film, comprising: The basic film system structure of the diamond infrared window thin film is: S / L / Air Wherein, S represents a diamond substrate, Air represents air, and L represents a rare earth metal oxide material.

[0006] According to the technical scheme provided by the embodiments of the present application, the rare earth metal oxide material is any one of yttrium oxide, ytterbium oxide and neodymium oxide.

[0007] According to the technical scheme provided by the embodiments of the present application, the rare earth metal oxide material is deposited on the surface of the diamond substrate by ion-assisted thermal evaporation.

[0008] In a second aspect, the present application provides a preparation method of the diamond infrared window thin film as described above, comprising the following steps: S100. Obtain the target waveband and the heat resistance temperature; S200. Selecting a rare earth metal oxide material according to the target waveband and the heat resistance temperature, and the selected rare earth metal oxide material is denoted as a coating material; S300. Obtaining a simulated physical thickness according to the target waveband, the coating material and the simulated maximum average transmittance obtained by the basic mode system simulation; S400. Coating the coating material on the surface of the diamond substrate by the ion-assisted thermal evaporation method according to the simulated physical thickness, to obtain a diamond infrared window film.

[0009] According to the technical scheme provided in the embodiments of the present application, step S300 comprises the following steps: S310. Determining a center wavelength according to the target waveband; S320. Obtaining a refractive index of the coating material at the center wavelength; S330. Calculating an initial physical thickness according to the center wavelength and the refractive index; S340. Fine-tuning the initial physical thickness, calculating a simulated average transmittance and a physical thickness corresponding thereto; S350. Setting the simulated average transmittance with the highest value as the simulated maximum average transmittance, and setting the expected corresponding physical thickness as the simulated physical thickness.

[0010] According to the technical scheme provided in the embodiments of the present application, step S400 further comprises the following steps: S402. Cleaning the diamond substrate.

[0011] According to the technical scheme provided in the embodiments of the present application, step S402 further comprises the following steps: S401. Oxidizing the diamond substrate.

[0012] According to the technical scheme provided in the embodiments of the present application, step S400 further comprises the following steps: S500. Obtaining a measured average transmittance of the impact-resistant film; S600. Judging whether the difference between the measured average transmittance and the simulated maximum average transmittance is less than a preset threshold value; if greater than or equal to the preset threshold value, adjusting the refractive index and repeating steps S300-S600.

[0013] Compared with the prior art, the application has the beneficial effects that: by arranging the rare earth metal oxide film on the surface of the diamond substrate, firstly, by selecting the rare earth oxide with the refractive index between the diamond and the air, the average transmittance of the target waveband is significantly improved by using the interference cancellation principle, and the high reflection loss problem is efficiently solved. Secondly, the dense oxide film forms a physical and chemical barrier on the surface of the diamond, effectively blocking the direct contact of high-temperature oxygen and the substrate, thereby inhibiting the oxidation reaction at 700-800 DEG C, and fundamentally solving the high-temperature oxidation problem of the diamond. Finally, the film has high transmittance, strong oxidation resistance and excellent film-substrate adhesion, so that the diamond window film can still maintain stable optical performance and complete structure after suffering severe thermal shock. BRIEF DESCRIPTION OF DRAWINGS

[0014] Other features, objects and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments made with reference to the accompanying drawings: Figure 1 The transmittance diagram of the uncoated diamond infrared window; Figure 2 The transmittance diagram of the uncoated diamond infrared window film; Figure 3 The surface microscope photo of the uncoated diamond infrared window film after thermal shock; Figure 4 The transmittance diagram of the uncoated diamond infrared window film after thermal shock; Figure 5 The transmittance diagram of the coated diamond infrared window film; Figure 6 The surface microscope photo of the coated diamond infrared window film after thermal shock; Figure 7 The transmittance diagram of the coated diamond infrared window film after thermal shock. DETAILED DESCRIPTION

[0015] The application will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and are not a limitation on the application. In addition, it should be noted that, for the convenience of description, only the parts related to the application are shown in the drawings.

[0016] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. The application will be described in detail below with reference to the accompanying drawings and embodiments.

[0017] Embodiment 1 The present application provides a diamond infrared window film, the basic film system structure of the diamond infrared window film is: S / L / Air Wherein, S represents a diamond substrate, Air represents air, and L represents a rare earth metal oxide material.

[0018] The impact-resistant film realizes effective compatibility of high transmittance and heat shock resistance / oxidation resistance. The refractive index of diamond is relatively high (about 2.4) in the long-wave infrared segment. When it is in direct contact with air (the refractive index is about 1.0), due to the refractive index mutation, according to the Fresnel reflection formula, a single surface will produce about 17% of reflection loss, resulting in that the theoretical transmittance of a double-side polished diamond window is only about 70%. The rare earth metal oxide layer (L) introduced in the present application has a refractive index (for example, Y2O3 is about 1.67 at a wavelength of 8.6 μm) that is just between diamond and air. By accurately designing the optical thickness of the layer to be one quarter (λ / 4) of the center wavelength of the target waveband, the light interference effect can be utilized to make the amplitude of the light reflected from the upper surface of the film (L / Air interface) similar to that of the light reflected from the lower surface of the film (S / L interface) and the phase opposite (the optical path difference is half a wavelength), so that destructive interference occurs, and the overall reflectivity is significantly reduced. This makes the average transmittance of the diamond window in the target waveband greatly improved.

[0019] In addition, the rare earth metal oxide material itself has excellent physical and chemical properties and firm combination with the substrate. First, the rare earth metal oxide is an extremely stable high-temperature ceramic material, and its melting point is much higher than the oxidation temperature of diamond (>700℃). When it forms a dense and continuous film on the surface of the diamond, it is equivalent to building a physical and chemical barrier that can effectively block the direct contact of oxygen in the environment with the diamond substrate, thereby fundamentally inhibiting the oxidation process of the diamond at high temperature. Second, the film can obtain low internal stress and excellent film-substrate adhesion through an optimized deposition process (such as ion-assisted deposition). Ion bombardment not only makes the film layer denser, but also enhances the chemical bonding between the film and the surface of the diamond subjected to a specific pre-treatment (such as non-high-temperature oxidation treatment) at the interface. When the film is subjected to severe temperature changes (thermal shock), it can resist cracks, peeling or falling due to thermal stress, thereby ensuring the long-term stability of the optical performance in extreme environments.

[0020] In a preferred embodiment, the rare earth metal oxide material is any one of yttrium oxide, ytterbium oxide and neodymium oxide.

[0021] Yttria (Y2O3), Ytterbia (Yb2O3) and Neodymia (Nd2O3) have refractive indices of about 1.67, 1.70 and 1.76 in the long-wave infrared (LWIR) band (8-12 μm), respectively. Although they all fall within the ideal refractive index range (1.5-1.8) required for antireflection coatings, different values mean they can be combined with different thicknesses to precisely match a specific target band, or to achieve the best balance between bandwidth and center transmittance. For example, for diamond samples with higher refractive index or specific bands, Y2O3 with slightly lower refractive index may be a better choice. All three oxides have extremely high melting points (Y2O3: 2425℃, Yb2O3: 2355℃, Nd2O3: 2233℃) and excellent high-temperature phase stability, ensuring that the film itself remains structurally intact and chemically inert in the temperature range where diamond is significantly oxidized (greater than 700℃), so that it does not easily undergo phase transition, decomposition or softening, thereby providing durable and reliable high-temperature protection.

[0022] In a preferred embodiment, the rare earth metal oxide material is deposited on the surface of the diamond substrate using ion-assisted thermal evaporation.

[0023] The method comprises the following steps: The diamond substrate is placed in a coating machine and the vacuum pump is turned on to create a vacuum. The temperature of the diamond substrate is set to 300℃. The pressure in the vacuum chamber is reduced to 2×10 -3 Pa; The rare earth metal oxide material is selected to have a mass purity of not less than 99.9%; A Kaufman ion source is selected for ion-assisted deposition. The ion source is filled with working gas Ar. Oxygen can also be filled as a reaction gas. The pressure in the vacuum chamber is not higher than 2.0×10 -2 Pa. The voltage of the ion source screen is 450V and the ion beam current is 100mA.

[0024] The electron gun beam current is adjusted to sufficiently and uniformly pre-melt the film material. The shutter is opened and the crystal thickness controller is observed to control the evaporation rate of the film layer to be 0.1 nm / s. When the pre-set film thickness is reached, the shutter is closed and the preparation of the film layer is completed.

[0025] Ion-assisted deposition enhances the atomic mobility of the film material through ion bombardment, forms a dense film layer and strengthens the chemical bonding between the film and the substrate, improves the adhesion and thermal shock resistance. At the same time, it reduces scattering and absorption in the film, ensures high transmittance, and can also adjust the stress to further optimize the crack resistance.

[0026] Example 2 Based on example 1, the application provides a method for preparing a diamond infrared window film, comprising the following steps: S100. Obtain the target band and heat-resistant temperature; Wherein, the target waveband is, for example, 7.5 μm~9.7 μm or 8.0 μm~12.0 μm; the heat resistance temperature is, according to actual requirements, optionally 800℃.

[0027] S200. Selecting a rare earth metal oxide material according to the target waveband and the heat resistance temperature, and recording the selected rare earth metal oxide material as a plating material; Wherein, the melting point of the material is determined whether it meets the heat resistance temperature requirement, for example, if the heat resistance temperature requirement is extremely high (not less than 800℃), the Y2O3 with the highest melting point can be selected as the plating material.

[0028] S300. Obtaining a simulation physical thickness corresponding to a simulation maximum average transmittance according to the target waveband, the plating material and the basic mode system structure simulation; including the following steps: S310. Obtaining a center wavelength according to the target waveband; Wherein, the target waveband is 7.5 μm~9.7 μm, and the center wavelength λ0=8.6 μm; the target waveband is 8.0 μm~12.0 μm, and the center wavelength λ0=10.0 μm.

[0029] S320. Obtaining a refractive index of the plating material at the center wavelength; The refractive index can be obtained by consulting an authoritative optical material manual or a database provided by a supplier, for example, the refractive index of Y2O3 at 8.6 μm is 1.67.

[0030] S330. Calculating an initial physical thickness according to the center wavelength and the refractive index; Wherein, the initial physical thickness is calculated by the following formula:

[0031] Wherein, d is the initial physical thickness, and n is the refractive index.

[0032] Taking the target waveband as 7.5 μm~9.7 μm, the center wavelength λ0=8.6 μm and n=1.67, the initial physical thickness is 1.287 μm.

[0033] S340. Fine-tuning the initial physical thickness, calculating a simulation average transmittance and a physical thickness corresponding thereto; S350. Setting the simulation average transmittance with the highest value as the simulation maximum average transmittance, and setting the expected corresponding physical thickness as the simulation physical thickness.

[0034] In steps S340 and S350, calculations are performed using film system design software to establish a thickness-transmittance response curve. Optionally, the software is Essential Macleod. The highest simulated average transmittance is selected from the thickness-transmittance response curves as the simulated maximum average transmittance, and the corresponding value is the simulated physical thickness. Taking a target wavelength range of 7.5 μm to 9.7 μm and a coating material of Y2O3 as an example, the simulated maximum average transmittance is 81.5%.

[0035] In a preferred embodiment, the following steps are included before step S400: S402. Clean the diamond substrate.

[0036] Specifically, before placing the diamond substrate into the coating machine, wipe the surface of the diamond substrate with a degreased cotton cloth soaked in anhydrous ethanol or a mixture of anhydrous ethanol and ether until it is clean. This effectively removes physically adsorbed contaminants such as dust, fingerprints, and grease from the surface of the diamond substrate, achieving basic surface cleaning.

[0037] In a preferred embodiment, the following steps are included before step S402: S401. The diamond substrate is subjected to oxidation treatment.

[0038] Specifically, the diamond substrate is immersed in a strong oxidizing solution, which can be composed of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 7:3, for 30 hours. After the immersion time is met, the diamond is removed and ultrasonically cleaned with deionized water.

[0039] Strong oxidizing solutions can completely decompose and remove organic contaminants and non-diamond carbon that are difficult to wipe off the surface of diamond substrates. The oxidation process introduces a large number of polar oxygen-containing functional groups such as hydroxyl groups (-OH) into the surface of diamond substrates, transforming them from chemically inert low-energy surfaces into chemically active high-energy surfaces. The activated surface energy forms strong chemical bonds (such as COY bonds) with the deposited rare earth oxide materials, rather than just physical adhesion.

[0040] S400. The coating material is deposited on the surface of the diamond substrate using the ion-assisted thermal evaporation method according to the simulated physical thickness, to obtain a diamond infrared window film. This is prepared using ion-assisted deposition as described above.

[0041] Depend on Figure 2 Calculations show that after cleaning, the average transmittance of the diamond substrate coated with the film in the 7.5μm~9.7μm range is 81%, which is consistent with... Figure 1 Compared to before coating, there is a significant improvement. (From...) Figure 3 It can be seen that after a thermal shock of 700℃ (30s), the film surface remained smooth, without cracks or delamination.Figure 4 It can be seen that the transmittance does not decrease significantly compared with that before the heat shock. Figure 5 It can be calculated that the average transmittance of the diamond substrate after the additional oxidation treatment and the coating is 81% at 7.5 μm-9.7 μm, which is obviously improved compared with that before the coating. Figure 1 It can be seen that the transmittance does not decrease significantly compared with that before the heat shock. Figure 6 It can be seen that after the heat shock (30 s) at 800 °C, the surface of the coating layer is flat, and no cracks or delamination occurs. Figure 7 It can be seen that the transmittance does not decrease significantly compared with that before the heat shock. The oxidation treatment of the substrate can effectively improve the heat shock resistance of the diamond infrared window anti-reflective film.

[0042] In a preferred embodiment, the step S400 is followed by the following steps: S500. Obtaining the measured average transmittance of the diamond infrared window; The prepared diamond infrared window is taken out of the coating machine, and is measured using a Fourier transform infrared spectrometer (FTIR).

[0043] S600. Determining whether the difference between the measured average transmittance and the simulated maximum average transmittance is less than a preset threshold value; if greater than or equal to the preset threshold value, adjusting the refractive index and repeating steps S300-S600.

[0044] Alternatively, if the difference is greater than the preset threshold value, it is determined that the product performance is not optimal, and an optimization program is started. The low transmittance and the low measured average transmittance may be related to a small deviation between the material optical constants (refractive index) used in the software and the effective refractive index of the film deposited under actual process conditions. Therefore, the refractive index is adjusted in the film system design software. Using the adjusted parameters, steps S330 to S400 are repeated.

[0045] The established feedback optimization mechanism automatically compensates for the effects of process fluctuations through the iterative process of "measurement-judgment-adjustment", significantly improving the consistency of product performance, process stability and process yield.

[0046] The above description is only a preferred embodiment of the present application and a description of the principles of the technology used. Those skilled in the art should understand that the scope of the invention disclosed in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features can be replaced with technical features disclosed in the present application (but not limited to) having similar functions to form technical solutions.

Claims

1. A diamond infrared window film, characterized by, The basic film system structure of the diamond infrared window film is: S / L / Air Wherein, S represents a diamond substrate, Air represents air, and L represents a rare earth metal oxide material.

2. The diamond infrared window film of claim 1, wherein, The rare earth metal oxide material is any one of yttrium oxide, ytterbium oxide, and neodymium oxide.

3. The diamond infrared window film of claim 1, wherein, The ion-assisted thermal evaporation method is used to plate the rare earth metal oxide material on the surface of the diamond substrate.

4. A method of making a diamond infrared window film as claimed in claim 3, wherein, The method comprises the following steps: S100. Obtain a target waveband and a heat resistance temperature; S200. Select a rare earth metal oxide material according to the target waveband and the heat resistance temperature, and the selected rare earth metal oxide material is denoted as a plating material; S300. Simulate a simulation physical thickness corresponding to a simulation maximum average transmittance according to the target waveband, the plating material, and the basic mode system structure; S400. Plate the plating material on the surface of the diamond substrate by the ion-assisted thermal evaporation method according to the simulation physical thickness, to obtain a diamond infrared window film.

5. The method of claim 4, wherein the diamond infrared window film is prepared by a process comprising: Step S300 comprises the following steps: S310. Determine a center wavelength according to the target waveband; S320. Obtain a refractive index of the plating material at the center wavelength; S330. Calculate an initial physical thickness according to the center wavelength and the refractive index; S340. Fine-tune the initial physical thickness, calculate a simulation average transmittance and a physical thickness corresponding thereto; S350. Set the simulation average transmittance with the highest value as the simulation maximum average transmittance, and set the expected corresponding physical thickness as the simulation physical thickness.

6. The method of claim 4, wherein the diamond infrared window film is prepared by a process comprising: Step S400 further comprises the following step: S402. Clean the diamond substrate.

7. The method for preparing a diamond infrared window film according to claim 5, characterized in that, Step S402 further comprises the following step: S401. Perform an oxidation treatment on the diamond substrate.

8. The method of claim 5, wherein the diamond infrared window film is prepared by a process comprising: Step S400 further comprises the following step: ​ S500. Obtain an actual average transmittance of the diamond infrared window; S600. Determine whether a difference between the actual average transmittance and the simulation maximum average transmittance is less than a preset threshold value; if greater than or equal to the preset threshold value, adjust the refractive index, and repeat steps S300-S600.

Images