Transparent ceramic films with varying Y2O3 composition gradients: preparation methods and applications

Abstract

This invention discloses a transparent ceramic film with a gradient Y2O3 composition, its preparation method, and its applications. The gradient film is deposited on a sapphire substrate using a spin-coating process. The Y2O3 content varies gradually from the sapphire substrate to the film surface, with the Y2O3 content gradually increasing and the Al2O3 content gradually decreasing in the direction away from the substrate, making the composition of the outermost layer close to that of YAG ceramic. The preparation method includes: sequentially depositing sols of different contents onto a sapphire substrate using a spin-coating process; and subjecting the film to isostatic pressing and heat treatment to form the gradient transparent ceramic film structure. This film possesses the characteristics of a gradient composition, transparency, low stress, and high interfacial bonding strength. It can achieve a continuous and gradual change in the coefficient of thermal expansion, thereby effectively alleviating thermal stress at the interface. It has broad application prospects in heterogeneous material combinations requiring high transmission efficiency, such as laser gain media and precision optical devices.

Description

Technical Field

[0001] This invention relates to the field of gradient film technology, specifically to a transparent ceramic film with a gradient change in Y2O3 composition, its preparation method, and its application. Background Technology

[0002] Gradient thin films are composite films formed by depositing materials with different compositions, structures, or properties layer by layer, creating a gradient in composition or structure. They have significant application value and broad prospects in many high-tech fields. For example, in mechanical engineering, multilayer diamond-carbon-based gradient films can reduce friction and energy consumption, and improve the wear resistance and lifespan of components such as gears, cylinder liners, and engines. In the field of optical thin films, gradient refractive index design helps reduce interface reflection, enhance transmittance, and improve the stability of the film under thermal effects.

[0003] However, existing gradient film fabrication technologies face several pressing issues. Most traditional methods struggle to achieve a smooth, continuous transition in performance between layers (e.g., publication number CN121161425A), easily leading to stress concentration and causing interfacial cracking and unstable bonding. Furthermore, gradient films fabricated using common techniques often fail to guarantee high light transmittance (e.g., publication numbers CN120249909A, CN120330669A), hindering efficient light transmission and conversion in optoelectronic devices and impacting overall device performance. Additionally, film thickness uniformity is a critical issue; some processes struggle to precisely control film thickness distribution, resulting in significant thickness variations at different locations and affecting the overall quality and performance consistency of the gradient film.

[0004] In summary, there is currently a lack of thin films that can achieve gradient, low stress, and high optical transparency on the material surface, as well as a preparation method therefor. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a transparent ceramic film with a compositional gradient, transparency, low stress, and a certain strength, as well as its preparation method and application.

[0006] This invention discloses a transparent ceramic film with a gradient Y2O3 composition. The transparent ceramic film is a multilayered compositional gradient film deposited on a sapphire substrate (Al2O3) by a spin coating process. The Y2O3 content in the compositional gradient film changes in a gradient from the sapphire substrate to the film surface. The Y2O3 content gradually increases and the Al2O3 content gradually decreases in the direction away from the sapphire substrate, so that the composition content of the outermost layer is close to that of YAG ceramic (5Al2O3·3Y2O3).

[0007] As a further improvement of the present invention, the total thickness of the composition-gradient film is 200-500 nm.

[0008] This invention discloses a method for preparing a transparent ceramic film with a Y2O3 composition gradient, comprising the following steps: Step 1, Substrate Pretreatment: Cut, polish and clean the sapphire substrate; Step 2: Preparation of sol: Prepare various sols with different a and b ratios according to preset parameters. The composition of the sols includes a%Al2O3 and b%Y2O3, so that the Y2O3 content from the sapphire substrate (Al2O3) to the surface of the sol layer is distributed in a gradient. Step 3: Preparation of gradient film using spin coating process: Sapphire is fixed in a spin coating machine, and the machine speed is controlled to deposit sol sequentially on the sapphire substrate. After each layer is deposited, it is dried in a gradient manner before depositing the next layer. This process is repeated until all layers are deposited. The Y2O3 content in the deposited sol changes in a gradient from the sapphire substrate to the film surface, that is, the Y2O3 content gradually increases and the Al2O3 content gradually decreases, so that the composition of the outermost layer is close to that of YAG ceramic (5Al2O3·3Y2O3). Step 4, Isostatic pressing: The sapphire substrate with the deposited multilayer prefabricated structure is placed in an isostatic pressing equipment and a cold isostatic pressing process is adopted. The pressure is controlled at 100-200MPa and the holding time is 10-30 minutes. The uniform pressure is used to eliminate the micropores and cracks inside the film layer, and improve the density and structural uniformity of the film layer. Step 5, Heat treatment: The sapphire substrate that has undergone isostatic pressing is placed in a vacuum or inert atmosphere and subjected to annealing and high-temperature sintering in sequence. Annealing removes residual organic matter in the film and promotes the densification of the amorphous alumina network. High-temperature sintering causes interdiffusion and reaction between the layers, completely eliminating residual pores and defects, and finally forming a transparent ceramic film with a gradient of Y2O3 content. Step 6: Polish the transparent ceramic film.

[0009] As a further improvement of the present invention, in steps 1 and 6, the polishing requires that the surface flatness be better than λ / 20 and the roughness Ra < 0.5 nm, where λ = 632.8 nm.

[0010] As a further improvement of the present invention, in step 2, the first layer of sol used for deposition on the sapphire substrate has the lowest Y2O3 content and the highest Al2O3 content; as the number of coating layers increases, the Y2O3 content in the sol used in subsequent layers gradually increases and the Al2O3 content gradually decreases until the composition ratio of the outermost sol is close to the stoichiometric ratio of YAG (62.5% Al2O3 + 37.5% Y2O3); the sol contains a sintering aid, which includes at least one of MgO, SiO2, Y2O3 and La2O3.

[0011] As a further improvement of the present invention, in step 3, the spin coating process adopts a combination of "low-speed leveling + high-speed spin coating". Through the coordinated control of rotation speed and time, the film thickness and uniformity can be precisely controlled. The low speed is 500-1000 rpm for 5-10 seconds; the high speed is 3000-6000 rpm for 30-60 seconds, ensuring that the thickness of each film layer is 50-100 nm. The temperature of the gradient drying is 80-100℃, and the holding time is 1-2 hours.

[0012] As a further improvement of the present invention, in step 5, the annealing temperature for removing impurities is 400-600℃ and the holding time is 1-2 hours; the high-temperature sintering temperature is 1100-1900℃ and the holding time is 2-5 hours.

[0013] This invention discloses a sapphire substrate, wherein the surface of the sapphire substrate has a transparent ceramic film with a gradient change in Y2O3 composition, and the transparent ceramic film is prepared by the above-described preparation method.

[0014] This invention discloses a laser gain medium comprising the aforementioned sapphire substrate.

[0015] This invention discloses a solid-state laser comprising the laser gain medium described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The gradient transparent ceramic film prepared by this invention has high optical transparency. Through composition gradient design, a continuous transition of refractive index is achieved, eliminating optical loss caused by abrupt changes in refractive index. It is suitable for scenarios with stringent requirements for light transmittance, such as laser transmission and precision optics.

[0017] 2. This invention prepares a gradient film through a spin coating process, followed by isostatic pressing and heat treatment, which causes interdiffusion and reaction between the layers, ultimately forming a ceramic thin film with a continuously varying coefficient of thermal expansion. This can eliminate the stress caused by the mismatch in the coefficients of thermal expansion between heterogeneous materials.

[0018] 3. This invention employs a spin coating process, which achieves precise control over film thickness and uniformity through coordinated regulation of rotation speed and time.

[0019] 4. The thin film prepared by this invention has the characteristics of compositional gradient, low stress, high optical transparency and high interfacial bonding strength, and is suitable for application scenarios with strict requirements for thermal stress management, optical transmittance and interfacial bonding strength. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope (SEM) image showing the content distribution of Y, Al, and O at different locations along the thickness direction after high-temperature sintering of a gradient thin film.

[0021] Figure 2 These are images of gradient films under an optical microscope. The left side shows the coated area, and the right side shows the uncoated area.

[0022] Figure 3 The film is prepared on a sapphire substrate through a spin coating and high-temperature sintering process. The transmittance curves of the film for different wavelengths of light are detected by a spectrophotometer.

[0023] Figure 4 It is a thin film prepared on a sapphire substrate, and its surface shape is detected using a Zygo interferometer. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The present invention will now be described in further detail with reference to the accompanying drawings: This invention provides a transparent ceramic film with a gradient Y2O3 composition. The transparent ceramic film is a multilayered composition-gradient thin film deposited on a sapphire substrate (Al2O3) using a spin coating process. In the composition-gradient thin film, the Y2O3 content changes in a gradient from the sapphire substrate to the film surface, with the Y2O3 content gradually increasing and the Al2O3 content gradually decreasing in the direction away from the sapphire substrate, so that the composition content of the outermost layer is close to that of YAG ceramic (5Al2O3·3Y2O3). The total thickness of the composition-gradient thin film is 200-500 nm.

[0026] This invention discloses a method for preparing a transparent ceramic film with a Y2O3 composition gradient, comprising the following steps: Step 1, Substrate Pre-treatment: The sapphire is precisely cut, annealed to relieve stress, and ground and polished to make its surface surface accuracy better than λ / 20 and roughness Ra < 0.5nm, where λ = 632.8nm; it is then ultrasonically cleaned with organic solvent and deionized water, and then hydrophilic treatment is performed to remove surface impurities. Step 2: Sol preparation: Prepare various sols with different a and b ratios according to preset parameters. The composition of the sols includes a% Al2O3 and b% Y2O3, so that the Y2O3 content from the sapphire substrate (Al2O3) to the sol surface is distributed in a gradient. Specifically, the first layer of sol used for deposition on the sapphire substrate side has the lowest Y2O3 content and the highest Al2O3 content. As the number of coating layers increases, the Y2O3 content in the sols used in subsequent layers gradually increases, and the Al2O3 content gradually decreases, until the composition ratio of the outermost sol is close to the stoichiometric ratio of YAG (62.5% Al2O3 + 37.5% Y2O3). The sols contain sintering aids, which include at least one of MgO, SiO2, Y2O3, and La2O3. Step 3: Preparation of gradient films using spin coating process: Sapphire is fixed on a spin coating machine, and the machine's rotation speed is controlled to sequentially deposit sol on the sapphire substrate. After each layer is deposited, gradient drying is performed before depositing the next layer, repeating this process until all layers are deposited. The Y2O3 content in the deposited sol changes gradient from the sapphire substrate to the film surface, i.e., the Y2O3 content gradually increases and the Al2O3 content gradually decreases, making the composition of the outermost layer close to that of YAG ceramic (5Al2O3·3Y2O3). The spin coating process employs a combination of "low-speed leveling + high-speed spin coating," achieving precise control of film thickness and uniformity through coordinated regulation of rotation speed and time. The low speed is 500-1000 rpm for 5-10 seconds; the high speed is 3000-6000 rpm for 30-60 seconds, ensuring that each film layer thickness is 50-100 nm. The gradient drying temperature is 80-100℃, and the holding time is 1-2 hours. Step 4, Isostatic pressing: The sapphire substrate with the deposited multilayer prefabricated structure is placed in an isostatic pressing equipment and a cold isostatic pressing process is adopted. The pressure is controlled at 100-200MPa and the holding time is 10-30 minutes. The uniform pressure is used to eliminate the micropores and cracks inside the film layer, and improve the density and structural uniformity of the film layer. Step 5, Heat Treatment: The isostatically pressed sapphire substrate is placed in a vacuum or inert atmosphere and subjected to annealing and high-temperature sintering in sequence. Annealing removes residual organic matter in the film and promotes the densification of the amorphous alumina network. High-temperature sintering causes interdiffusion and reaction between the layers, completely eliminating residual porosity and defects, and finally forming a transparent ceramic film with a gradient of Y2O3 content. The annealing temperature is 400-600℃, and the holding time is 1-2 hours. The high-temperature sintering temperature is 1100-1900℃, and the holding time is 2-5 hours. Step 6: Polish the transparent ceramic film to make its surface shape accuracy better than λ / 20 and roughness Ra < 0.5nm, where λ = 632.8nm.

[0027] This invention discloses a sapphire substrate, wherein the surface of the sapphire substrate has a transparent ceramic film with a gradient change in Y2O3 composition, and the transparent ceramic film is prepared by the above-described preparation method.

[0028] This invention discloses a laser gain medium comprising the aforementioned sapphire substrate.

[0029] This invention discloses a solid-state laser comprising the laser gain medium described above.

[0030] The transparent ceramic film with Y2O3 composition gradient variation of the present invention is characterized by: Regarding gradient properties, low stress, and strength: This gradient film is deposited on a sapphire substrate using a spin coating process. The Y2O3 content gradually increases and the Al2O3 content gradually decreases in the direction away from the sapphire substrate (Al2O3), resulting in an outermost layer composition close to that of YAG ceramic (5Al2O3·3Y2O3). After isostatic pressing and heat treatment, interdiffusion and reaction occur between the layers, forming a good bond between the gradient film and the sapphire substrate with high interfacial bonding strength. Simultaneously, the coefficient of thermal expansion transitions smoothly and continuously from the substrate to the film surface, effectively mitigating the thermal stress concentration problem caused by the discontinuity of the coefficient of thermal expansion in traditional gradient films.

[0031] Regarding optical transparency: This invention uses high-purity Y₂O₃ and Al₂O₃ to prepare a sol, and the ceramic prepared from it is an isotropic material. After isostatic pressing and high-temperature sintering, the gradient film is transformed into a transparent ceramic film. This invention utilizes the crystal structure compatibility of Y₂O₃ and Al₂O₃ during the high-temperature sintering process: Y₂O₃... 3+The gradient diffusion of ions into the Al2O3 lattice and the formation of the YAG phase (cubic crystal system, optically isotropic) do not disrupt the overall crystal structure symmetry of the film, ensuring its optical isotropic properties throughout the compositional gradient process. This lays the physical foundation for achieving high transparency. Based on this, the present invention guarantees high optical transparency of the film through the following three aspects: First, isostatic pressing and heat treatment highly densify the film, completely eliminating porosity and thus pore scattering; second, compositional gradient design ensures a continuous and smooth transition of refractive index from the substrate to the film surface, eliminating interface reflection loss caused by abrupt changes in refractive index; third, the addition of sintering aids inhibits abnormal grain growth, forming a uniform and fine grain structure, while simultaneously purifying grain boundaries, thereby reducing grain boundary scattering.

[0032] The ceramic film prepared by this invention has the characteristics of compositional gradient, transparency, low stress and high interfacial bonding strength. The gradual change of composition in each layer avoids optical loss caused by abrupt change in refractive index, making it suitable for scenarios with strict requirements for light transmittance, such as laser transmission and precision optics. Example

[0033] This invention provides a method for preparing a transparent ceramic film with a gradient of Y2O3 composition, comprising: S1. Substrate pretreatment: The sapphire substrate is precisely cut to a size of 17mm×17mm×2mm. The sapphire substrate is then cleaned with acetone, anhydrous ethanol, and deionized water in sequence, and ultrasonically cleaned for 1 hour each time. Finally, it is dried with nitrogen.

[0034] S2. Preparation of Sol: Four-layer gradient sol was prepared according to preset ratio parameters: The parameters for the first sol layer are 99.5% Al2O3 + 0.5% MgO; The second layer consists of 90% Al₂O₃ + 9.5% Y₂O₃ + 0.5% MgO; The third layer consists of 80% Al₂O₃ + 19.5% Y₂O₃ + 0.5% MgO; The fourth layer consists of 70% Al₂O₃ + 29.5% Y₂O₃ + 0.5% MgO; The composition ratio is distributed in a gradient from the sapphire (Al2O3) side to the YAG (62.5%Al2O3+37.5%Y2O3) side.

[0035] S3. Preparation of gradient films using spin coating process: A sapphire substrate is fixed to the suction cup of a spin coater. 150 μl of sol is dropped onto the center of the sapphire substrate and allowed to stand for 10 seconds. The substrate is then spread at a low speed of 800 rpm for 8 seconds, followed by spin coating at a high speed of 6000 rpm for 60 seconds to form a 100 nm thick film. The substrate is then placed in an oven and heated to 100 °C at 20 °C room temperature, with the temperature increased at 0.5 °C / min, and held for 2 hours. After cooling, another layer of sol is deposited, and the above operation is repeated until four layers are coated.

[0036] S4. Isostatic pressing: The substrate with the multilayer prefabricated structure deposited is placed in an isostatic pressing device and a cold isostatic pressing process is adopted. The pressure is controlled at 200MPa and the holding time is 30 minutes. The uniform pressure eliminates the micropores and cracks inside the film layer, and improves the density and structural uniformity of the film layer.

[0037] S5. Heat treatment: The prepared gradient film samples were subjected to annealing and high-temperature sintering treatment in sequence. The substrate was transferred into a muffle furnace and heated to 500℃ at 1℃ / min and held at that temperature for 1 hour for annealing; finally, the temperature was increased to 1700℃ at 1℃ / min and held at that temperature for 2 hours, and then allowed to cool naturally to room temperature.

[0038] S6. Polish the gradient film: Ensure that the flatness of the gradient film is better than λ / 20 and the surface roughness Ra < 0.5nm, where λ = 632.8nm.

[0039] Gradient membrane performance testing: 1. Measurement of the content of Y, Al, and O elements: by Figure 1 As can be seen, line scanning analysis of the cross-section of the heat-treated gradient thin film using scanning electron microscopy (SEM), by detecting the count intensity of characteristic X-rays of each element, combined with ZAF correction and normalization, yielded the atomic percentage distribution of each element, thus achieving quantitative characterization of the content of Y, Al, and O elements. The results show that in the range of approximately 0-200 nm, the substrate is sapphire, where the Y content is approximately 0, while the Al and O contents remain constant; in the range of approximately 200-600 nm, the heat-treated gradient transparent ceramic film is represented. As the measurement position moves away from the substrate, the Y content gradually increases to 15%, the Al content decreases accordingly, while the O content remains essentially constant throughout the range. Near 600 nm, the proportions of each element are close to those of YAG ceramic. The concentration curves of each element show a continuous and smooth transition without significant abrupt changes. This atomic-level interdiffusion phenomenon proves the effectiveness of this process: during heat treatment, Y... 3+Ions orderly enter the alumina lattice for substitution or gradually transform into the optically isotropic YAG cubic crystal system. Because this compositional gradient process does not disrupt the overall symmetry of the crystal structure, the film maintains optical isotropy throughout its thickness. Comparing this experimental data with the preset four-layer gradient sol parameters in step two, the increasing trend of composition shown in the experimental curves is highly consistent with the process design.

[0040] 2. Optical performance testing: such as Figure 2 As shown in the figure, the obtained film layer is continuous and uniform as observed by an optical microscope. The transmittance of the sample in the wavelength range of 450-2000 nm was measured using a spectrophotometer, and the results are as follows. Figure 3 As shown, the transmittance in this band ranges from 85.17% to 87.38%, exhibiting high transmittance with minimal fluctuation. Figure 1 Analysis shows that the high transmittance is achieved due to two factors: as mentioned earlier, Y 3+ The gradient introduction of ions and their transformation to the YAG phase maintain structural symmetry, minimizing scattering losses at grain boundaries and within the internal structure. Heat treatment eliminates defects and scattering centers in the film, resulting in densification and a continuously gradient compositional structure. Experimental results confirm that the gradient transparent ceramic film prepared using this process possesses excellent optical transmittance.

[0041] 3. Surface Shape and Stress Assessment: The surface shape of the sample was tested using a Zygo laser interferometer. (See reference...) Figure 4 The results showed that the surface accuracy of the film region was better than 0.05λ, indicating that the stress of the film layer was small after sintering and did not cause obvious warping of the substrate.

[0042] The gradient transparent ceramic film prepared by this invention has been verified to have good optical transmittance and low residual stress. It can achieve a continuous and smooth transition of thermal expansion coefficient and refractive index between heterogeneous materials, effectively relieving thermal stress. It provides a generalized and high-performance technical solution for the connection of heterogeneous materials and can be widely used in basic science, industrial processing and national defense construction.

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A transparent ceramic film with a gradient Y₂O₃ composition, characterized in that, The transparent ceramic film is a multi-layered compositional gradient film deposited on a sapphire substrate using a spin coating process. The Y2O3 content in the compositional gradient film changes in a gradient from the sapphire substrate to the film surface, with the Y2O3 content gradually increasing and the Al2O3 content gradually decreasing in the direction away from the sapphire substrate, so that the compositional content of the outermost layer is close to that of YAG ceramic.

2. The transparent ceramic film according to claim 1, characterized in that, The total thickness of the composition-gradient film is 200-500 nm.

3. A method for preparing a transparent ceramic film according to claim 1 or 2, characterized in that, Includes the following steps: Step 1, Substrate Pretreatment: Cut, polish and clean the sapphire substrate; Step 2: Preparation of sol: Prepare various sols with different a and b ratios according to preset parameters. The composition of the sols includes a% Al2O3 and b% Y2O3, so that the Y2O3 content from the sapphire substrate to the surface of the sol layer is distributed in a gradient. Step 3: Preparation of gradient film by spin coating process: Sapphire is fixed on a spin coating machine, and the machine speed is controlled to deposit sol sequentially on the sapphire substrate. After each layer is deposited, gradient drying is performed before depositing the next layer. This process is repeated until all layers are deposited. The Y2O3 content in the deposited sol changes in a gradient from the sapphire substrate to the film surface, that is, the Y2O3 content gradually increases and the Al2O3 content gradually decreases, so that the composition of the outermost layer is close to that of YAG ceramic. Step 4, Isostatic pressing: Place the sapphire substrate with the deposited multilayer prefabricated structure into the isostatic pressing equipment, and use the cold isostatic pressing process, controlling the pressure to be 100-200MPa and the holding time to be 10-30 minutes. Step 5, Heat treatment: The sapphire substrate that has undergone isostatic pressing is placed in a vacuum or inert atmosphere and subjected to annealing and impurity removal and high-temperature sintering in sequence to finally form a transparent ceramic film with a gradient of Y2O3 content. Step 6: Polish the transparent ceramic film.

4. The preparation method according to claim 3, characterized in that, In steps 1 and 6, polishing requires a surface flatness better than λ / 20 and a roughness Ra < 0.5 nm, where λ = 632.8 nm.

5. The preparation method according to claim 3, characterized in that, In step 2, the first sol layer used for deposition on the sapphire substrate has the lowest Y2O3 content and the highest Al2O3 content. As the number of coating layers increases, the Y2O3 content in the sol layer used in subsequent layers gradually increases, and the Al2O3 content gradually decreases, until the composition ratio of the outermost sol layer is close to the stoichiometry of YAG. The sol layer contains sintering aids, which include at least one of MgO, SiO2, Y2O3, and La2O3.

6. The preparation method according to claim 3, characterized in that, In step 3, the spin coating process adopts a combination of "low-speed leveling + high-speed spin coating". Through the coordinated control of rotation speed and time, the film thickness and uniformity are precisely controlled. The low speed is 500-1000 rpm for 5-10 seconds; the high speed is 3000-6000 rpm for 30-60 seconds, ensuring that the thickness of each film layer is 50-100 nm. The gradient drying temperature is 80-100℃, and the holding time is 1-2 hours.

7. The preparation method according to claim 3, characterized in that, In step 5, the annealing temperature for removing impurities is 400-600℃, and the holding time is 1-2 hours; the high-temperature sintering temperature is 1100-1900℃, and the holding time is 2-5 hours.

8. A sapphire substrate, characterized in that, The surface of the sapphire substrate has the transparent ceramic film as described in claim 1 or 2, and the transparent ceramic film is prepared by any one of claims 3 to 7.

9. A laser gain medium, characterized in that, It includes the sapphire substrate as described in claim 8.

10. A solid-state laser, characterized in that, It includes the laser gain medium as described in claim 9.

Images