Preparation method of highly oriented hydrophobic oxide antireflection film for diamond infrared window

Abstract

The present invention relates to a method for preparing a highly oriented hydrophobic oxide antireflection film for diamond infrared windows, belonging to the field of optical thin film preparation technology. The method includes steps such as precision polishing of the diamond surface, acid boiling of the diamond surface, and magnetron sputtering. The method utilizes a highly oriented oxide composite target material to prepare the highly oriented antireflection film, employing a coating method that alternates low and high temperatures. The resulting antireflection film exhibits both slightly hydrophobic and highly oriented properties. The synthesis process exhibits good process continuity and is simple.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical thin film preparation, and specifically relates to a method for preparing a highly oriented antireflection film with slightly hydrophobic properties for use in diamond infrared windows. The method is characterized by achieving optical antireflection in the diamond mid-infrared band and a surface with hydrophobic properties. Background Art

[0002] Infrared windows are optical windows that transmit ultraviolet, visible, and infrared light. With the advancement of technology, their applications have expanded from infrared imaging systems, infrared thermometers, and night vision devices to CO2 lasers, energy transfer windows, and infrared imaging systems for high-Mach aircraft. This places higher demands on infrared window materials, requiring them to possess high-temperature resistance, high-radiation resistance, high strength, and broadband transmittance. Diamond, the hardest substance on Earth, has become an irreplaceable material in the infrared window field due to its excellent thermal, optical, and chemical stability. Diamond's transmittance range spans X-rays, ultraviolet, visible, infrared, and even microwaves, with transmittance reaching up to 71% in the infrared and microwave bands. Its low atomic number, tight covalent bonds, and cubic atomic structure contribute to its high strength, thermal conductivity, and durability. Currently, synthetic optical-grade single crystals have reached sizes of 1-4 inches, and polycrystalline sizes have reached 2-8 inches, laying the foundation for diamond's applications. However, the theoretical transmittance of diamond is only 71%, while actual transmittance is often less than 70%, affected by the preparation process and surface roughness. This severely limits the application of diamond in optics. Therefore, improving the optical transmittance of diamond has become a critical issue. To meet the requirements of diamond applications in the long-wave infrared band, an antireflection coating is often required. Based on the antireflection mechanism of infrared light, the refractive index that matches the diamond material is approximately 1.55. Currently, commonly used antireflection coatings are mainly oxides such as HfO2 and Y2O3, prepared by methods such as magnetron sputtering. These films have fine grains, uniform density, low roughness, and distinct orientation. They can significantly improve the surface protection of diamond and achieve high transmittance. The structure of oxide antireflection coatings is significantly affected by deposition factors (deposition temperature, oxygen partial pressure, chamber pressure, sputtering power, DC bias), further processing (heat treatment), and surface modification. Currently, antireflection coatings are mainly obtained using metal targets and by adding oxygen, presenting a film structure with multiple crystalline phases coexisting. It is generally believed that cubic oxides offer a higher refractive index and lower AR coating thickness, but their AR efficiency is relatively poor. Monoclinic oxides, on the other hand, offer a more compatible refractive index and are more likely to improve AR performance, but they also exhibit larger grain sizes and greater lattice strain. Furthermore, competitive growth occurs between different crystal structures. Therefore, the performance of multiphase oxide AR coatings is affected by uniformity, as variations in crystal type and content across different regions can pose challenges to achieving uniform AR performance. Summary of the Invention

[0003] To address the above issues, the present invention provides a method for growing a highly oriented antireflection film on a diamond infrared window. Initially, the diamond film is double-sided polished to a surface roughness of less than 1 nm to reduce infrared light scattering. Using a highly oriented oxide target and controlled temperature, a hydrophobic, highly oriented antireflection film is sputtered onto the diamond surface. Highly oriented thin film materials facilitate uniform antireflection performance and can be easily formed into a laminated structure by controlling temperature to balance sputtering rate and antireflection performance. Furthermore, their hydrophobic nature facilitates cleanliness of the entire window.

[0004] The specific technical solutions of the present invention are as follows:

[0005] A method for preparing a highly oriented hydrophobic oxide antireflection film for a diamond infrared window, wherein the growth rate of the antireflection film is controlled by regulating the temperature, thereby preparing a multilayer highly oriented oxide film on the diamond surface, specifically comprising the following steps:

[0006] Step 1: Diamond surface precision polishing

[0007] Stick the diamond film on an automatic polishing machine and polish the diamond with a polishing disk until the diamond surface roughness is less than 1nm. Repeat the above steps and perform the same polishing on the other side of the diamond film.

[0008] Step 2: Acid boiling treatment of diamond surface

[0009] The polished diamond film was acid-boiled to remove the metal debris and non-diamond phase remaining on the surface of the diamond film, and then ultrasonically cleaned in acetone, ethanol, and deionized water in sequence, and then dried.

[0010] Step 3: Magnetron sputtering process

[0011] The oxide target was mounted on the RF target, and then the cleaned diamond film was placed in the magnetron sputtering chamber, and the magnetron sputtering chamber was evacuated to a pressure of 1×10 -4 Pa~9×10 -4 Pa, introduce sputtering gas Ar, adjust the gas pressure to 1~3Pa, adjust the substrate temperature between 25℃~1500℃, and the sample stage speed is 3~15rpm. The sputtering thickness is given by the formula d=λ 介 / 4 is determined to obtain the best anti-reflection effect, where λ 介 It is the wavelength of light that needs to be transmitted in the anti-reflection coating.

[0012] At this point, the preparation of a highly oriented antireflection film on the surface of the diamond film has been achieved. When the contact angle of the sample was subsequently measured, it was found that the sample had a slightly hydrophobic property, which can effectively reduce water erosion and facilitate surface cleaning.

[0013] In the above preparation method, in step one, the polishing process is carried out using an automatic polishing machine, the polishing disk speed can reach 2850r / min, the high-precision mechanical slider drives the grinding head to slide up and down, and the front and rear electrodes drive the grinding head to perform reciprocating feed motion. The front and rear speeds are adjusted according to actual needs, and mechanical pressure is provided to cause friction grinding between the diamond and the grinding disk. The pressure of the automatic grinder can be adjusted in the range of 100~1700N, the front and rear movement of the grinding head is 0~40mm, the grinding monitoring accuracy is 0.02mm, and the grinding flatness is ≤0.02mm.

[0014] In the above preparation method, in the step 2, the acid boiling is preferably performed using a mixed acid of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:1, heated to boiling in an electric furnace, and the acid boiling time is 30 minutes to 1 hour, wherein the concentration of concentrated sulfuric acid is 70% to 98%, and the concentration of concentrated nitric acid is 65% to 68%.

[0015] In the above preparation method, in step 2, the amounts of acetone, ethanol, and deionized water used are all 100-200 ml, the frequency of the ultrasonic machine used is 40 kHz, and the ultrasonic time is 30 min. The sample is then taken out and the surface of the sample is blown dry with nitrogen.

[0016] In the above preparation method, in step three, the oxide composite target material used has a highly oriented crystal structure, and the target material is one or a combination of hafnium oxide, yttrium oxide, erbium oxide, and aluminum oxide.

[0017] In the above preparation method, in step 3, silicon or sapphire or other materials are used as substrates to conduct experiments on the hydrophilic and hydrophobic properties of the thin film.

[0018] In the above preparation method, in step 3, since the film sputtering rate and crystal quality show an approximately linear relationship with the substrate temperature, and the film sputtering rate decreases with increasing temperature while the optical performance is improved, in order to quickly reach the required thickness and ensure the optical performance of the film, the antireflection film is prepared in a fast and slow alternating manner, that is, low temperature and high temperature are alternately performed: sputtering at 25-400°C for 30 minutes to 1 hour, sputtering at 500-1500°C for 30 minutes to 1 hour, and the two are alternately performed until the sputtering thickness reaches d=λ 介 / 4, which can ensure both the growth rate of the antireflection film and the high orientation characteristics of the antireflection film.

[0019] Beneficial effects:

[0020] 1. Using highly oriented oxide composite targets to prepare highly oriented antireflection films can avoid the appearance of multiple crystal phases in the antireflection film structure;

[0021] 2. The growth rate of the antireflection film is controlled by regulating the temperature. The coating method of alternating low temperature and high temperature is adopted, which can not only increase the growth rate of the antireflection film, but also ensure the high orientation characteristics of the antireflection film;

[0022] 3. The prepared antireflection film has a slightly hydrophobic property, which can effectively reduce water erosion and facilitate surface cleaning;

[0023] 4. The entire process is carried out using a magnetron sputtering device, and the synthesis process has good process continuity and is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD measurement diagram of highly oriented oxide film.

[0025] Figure 2 Schematic diagram of the stacked antireflection film.

[0026] Figure 3 The contact angle characteristics before and after coating.

[0027] Figure 4 This is the infrared transmittance spectrum of the sample before and after coating. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to specific examples.

[0029] Example 1

[0030] Silicon wafers were selected to test the hydrophilic and hydrophobic properties of the film. The silicon wafers were placed in acetone, ethanol, and deionized water for ultrasonic cleaning in turn. The frequency of the ultrasonic machine was 40kHz, and the ultrasonic time was 5 to 30 minutes. The sample was then taken out and the surface of the sample was blown dry with nitrogen. The sample was then placed in a magnetron sputtering chamber. The sputtering conditions were an Ar flow rate of 30 to 100 sccm, a sputtering pressure of 1 to 3 Pa, a temperature of 100°C to 1500°C, and a sample stage speed of 3 to 15 rpm. The sputtering thickness is determined according to the formula d = λ medium / 4. In this way, a highly oriented anti-reflective film is obtained. As Figure 1 The XRD pattern of the oxide film on the Si substrate is shown, showing that the film is highly oriented. Figure 3 Shown are the contact angle characteristics of the prepared oxide film, indicating that the film exhibits slightly hydrophobic properties.

[0031] Example 2

[0032] The diamond film is attached to an automatic polishing machine with a polishing disk rotating at 2850 rpm. A high-precision mechanical slider drives the grinding head up and down, while front and rear electrodes drive the grinding head in a reciprocating feed motion. After polishing one side to a roughness of less than 1 nm, the process is repeated to polish the other side of the diamond film. Once both sides of the diamond film are polished, the film is placed in a 1:1 solution of concentrated sulfuric acid and concentrated nitric acid, heated in an electric furnace, and boiled for 30 minutes to 1 hour. The concentrated sulfuric acid concentration is 70%-98%, and the concentrated nitric acid concentration is 65%-68%. The diamond film is then ultrasonically cleaned in 100-200 ml of acetone, ethanol, and deionized water, respectively, at a frequency of 40 kHz for 30 minutes. The sample is then removed and the surface is blown dry with nitrogen. Afterwards, the diamond film was placed in a magnetron sputtering chamber and sputtered at 25-400°C for 30min-1h and at 500-1500°C for 30min-1h alternately. The specific conditions were to adjust the Ar flow rate to 30-70sccm, the sputtering pressure to 1-3Pa, the sample stage speed to 3rpm, and the sputtering time to 30min-1h at each temperature. Thus, a highly oriented diamond anti-reflection film with slight hydrophobicity was obtained. Figure 2 The following is a schematic diagram of the stacked antireflection film: Figure 4 Shown is the infrared transmittance spectrum of the diamond / erbium oxide composite material, which increases the highest point of diamond infrared transmittance from 58% to 73%.

Claims

1. A method for preparing a highly oriented hydrophobic oxide antireflection film for a diamond infrared window, wherein the growth rate of the antireflection film is controlled by regulating the temperature, thereby preparing a multilayer highly oriented oxide film on the diamond surface, comprising the following steps: Step 1: Diamond surface precision polishing Stick the diamond film on an automatic polishing machine and polish the diamond with a polishing disk until the diamond surface roughness is less than 1nm. Repeat the above steps and perform the same polishing on the other side of the diamond film. Step 2: Acid boiling treatment of diamond surface The polished diamond film was acid-boiled to remove the metal debris and non-diamond phase remaining on the surface of the diamond film, and then ultrasonically cleaned in acetone, ethanol, and deionized water in sequence, and then dried. Step 3: Magnetron sputtering process The oxide target was mounted on the RF target, and then the cleaned diamond film was placed in the magnetron sputtering chamber, and the magnetron sputtering chamber was evacuated to a pressure of 1×10 -4 Pa ~9×10 -4 Pa, introduce sputtering gas Ar, adjust the gas pressure to 1~3Pa, adjust the substrate temperature between 25℃~1500℃, and the sample stage speed is 3~15rpm. The sputtering thickness is given by the formula It is determined that the antireflection film is prepared in a fast and slow alternating manner to obtain the best antireflection effect, that is, low temperature and high temperature are carried out alternately: sputtering at 25~400℃ for 30min~1h, sputtering at 500~1500℃ for 30min~1h, and the two are carried out alternately until the sputtering thickness reaches ;in is the wavelength of light that needs to be transmitted in the anti-reflection film; so far, the preparation of a highly oriented anti-reflection film on the surface of the diamond film has been achieved.

2. The method for preparing a highly oriented hydrophobic oxide antireflection film for a diamond infrared window according to claim 1, characterized in that: In the step 1, the polishing process is performed using an automatic polishing machine, the polishing disk speed is 2850r / min, the high-precision mechanical slider drives the grinding head to slide up and down, and the front and rear electrodes drive the grinding head to perform a forward and backward reciprocating feed motion. The front and rear speeds are adjusted according to actual needs, and mechanical pressure is provided to cause friction grinding between the diamond and the grinding disk. The pressure of the automatic grinder can be adjusted in the range of 100 to 1700 N, the forward and backward movement of the grinding head is 0 to 40 mm, the grinding monitoring accuracy is 0.02 mm, and the grinding flatness is ≤0.02 mm.

3. The method for preparing a highly oriented hydrophobic oxide antireflection film for a diamond infrared window according to claim 1, characterized in that: In the step 2, the acid boiling is performed by using a mixed acid of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:1, which is heated to boiling in an electric furnace for 30 minutes to 1 hour. The concentration of the concentrated sulfuric acid is 70% to 98%, and the concentration of the concentrated nitric acid is 65% to 68%.

4. The method for preparing a highly oriented hydrophobic oxide antireflection film for a diamond infrared window according to claim 1, wherein: In step 2, the amount of acetone, ethanol, and deionized water used is 100-200 ml, the frequency of the ultrasonic machine used is 40 kHz, and the ultrasonic time is 30 min. Then, the sample is taken out and the surface of the sample is blown dry with nitrogen.

5. The method for preparing a highly oriented hydrophobic oxide antireflection film for a diamond infrared window according to claim 1, wherein: In the step three, the oxide composite target material used has a highly oriented crystal structure, and the target material is one or a combination of hafnium oxide, yttrium oxide, erbium oxide, and aluminum oxide.

Images