Diamond-based infrared composite window material and preparation method thereof

Abstract

The application discloses a diamond-based infrared composite window material, which comprises an aluminum oxide substrate, a transition layer and a diamond layer, wherein the transition layer comprises an AlN layer, an Si3N4 layer and an SiC layer; the AlN layer is deposited on the surface of the aluminum oxide substrate, the Si3N4 layer is deposited on the surface of the AlN layer, the SiC layer is deposited on the surface of the Si3N4 layer, and the diamond layer is deposited on the surface of the SiC layer. The diamond-based infrared composite window material has high transmittance, thermal conductivity and interface bonding rate in a middle-wave infrared band (3-5 mu m). The application further discloses a preparation method of the diamond-based infrared composite window material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of infrared and photoelectric guidance materials, and particularly relates to a diamond-based infrared composite window material and a preparation method thereof. BACKGROUND

[0002] Infrared guidance has the advantages of high precision and strong anti-interference capability, and thus is highly valued by countries around the world. The most widely used and most mature scheme of the infrared guidance system in the world at present is mid-wave infrared guidance. The infrared optical materials that can be used in the mid-wave infrared spectrum include sapphire (i.e. Al2O3 single crystal), MgF2, oxide transparent ceramic (such as Y2O3, MgAl2O4, AlON, LiAlON, MgAlON), etc. With the development of super-high-speed aircraft technology, the increase of flight speed will inevitably lead to more serious aerodynamic heating effect. As an infrared window material, when facing a high aerodynamic heating environment, due to the low thermal conductivity of the infrared window material, the aerodynamic heating in high Mach number flight will make the heat unable to conduct quickly and thus more easily concentrate, which will cause a large temperature difference between the stagnation point and the rest of the part, resulting in a large thermal stress and easily causing the rupture and failure of the window. The thermal conductivities of the traditional infrared optical window materials mentioned above are all low (only 10-30 W / m℃). Therefore, there is an urgent need for a scheme to improve their thermal performance and broaden the service limit of the traditional infrared window material.

[0003] Diamond has excellent mechanical, thermal and optical properties, its ultra-high hardness (~100 GPa), ultra-high thermal conductivity (theoretical value ~2000 W / m℃), and ultra-wide light transmission spectrum (from ultraviolet to far infrared and even microwave band), making diamond infrared material an excellent choice for extreme environment applications. However, the diamond bulk material preparation technology is not mature, and it has a strong intrinsic absorption in the mid-infrared (3-5 μm) band, and is not suitable for being used as a mid-wave infrared window in the form of a "thick layer" bulk material. Based on the principle that the optical intrinsic absorption increases with the thickness, the mid-wave infrared intrinsic absorption will also be weakened with the decrease of the thickness of the optical material. Therefore, when a "thin" layer of diamond is coated on the traditional mid-infrared window material, the application of diamond in the mid-infrared band is expected to be realized, and if it is further combined with the traditional low-thermal-conductivity mid-infrared material, good heat dissipation performance can be provided for the traditional infrared window material.

[0004] However, there is a large thermal mismatch and lattice mismatch between diamond and traditional infrared materials, which makes them difficult to be directly and well combined. The current commonly used method is to pre-deposit a transition layer on the substrate, and then grow diamond on the transition layer. The existing research on the composite diamond layer of optical windows mainly focuses on ZnS substrate materials, aiming to improve the mechanical properties of ZnS.

[0005] In general, the main reason that diamond is difficult to be combined with the traditional infrared optical material substrate is that the stress caused by the large difference in thermal expansion coefficient between diamond and the substrate and the lattice mismatch in the thermal expansion and contraction process makes it difficult for diamond to nucleate on the substrate surface, and the cooling process after the growth is easily collapsed. In addition, there is a large difference in refractive index between diamond and substrate. Therefore, a single transition layer cannot meet the requirements of refractive index and thermal expansion coefficient gradient change. SUMMARY

[0006] The present application provides a diamond-based infrared composite window material, which has high transmittance, thermal conductivity and interface bonding rate in the mid-wave infrared band (3-5 μm).

[0007] The embodiment of the present application provides a diamond-based infrared composite window material, which comprises an aluminum oxide substrate, a transition layer and a diamond layer, wherein the transition layer comprises an AlN layer, an Si3N4 layer and an SiC layer.

[0008] The AlN layer is deposited on the surface of the aluminum oxide substrate, the Si3N4 layer is deposited on the surface of the AlN layer, the SiC layer is deposited on the surface of the Si3N4 layer, and the diamond layer is deposited on the surface of the SiC layer.

[0009] The present application selects a material with a thermal expansion coefficient between the aluminum oxide substrate and the diamond as the transition layer. Due to the gradient change of the thermal expansion coefficient, the diamond is not easy to fall off in a high aerodynamic heat environment, and has a high interface bonding strength. Since each adjacent layer has the same element, a chemical bond is formed during the deposition process. Since the chemical bond is not easy to break under heat, and the lattice parameters of adjacent layers are relatively close, the interface bonding strength is further enhanced, so that the diamond layer is not easy to fall off in a high aerodynamic heat environment.

[0010] The present application has the same element in each adjacent layer, and the chemical bond is connected by deposition. Therefore, the multi-interface reflection caused by the existence of air between each layer is avoided, and the absorption of the mid-wave infrared band light is further caused, so that the light loss is reduced and the light transmittance is increased.

[0011] Further, the material of the aluminum oxide substrate is sapphire, LiAlON ceramic, MgAlON ceramic or AlON ceramic.

[0012] Further, the size of the aluminum oxide substrate is Ф10-30 mm x 1-3 mm.

[0013] Further, the optical transmittance of the aluminum oxide substrate in the middle wave infrared band is not less than 75%. By obtaining the aluminum oxide substrate with higher optical transmittance in the middle wave infrared band, a basis is provided for obtaining the infrared composite window with higher transmittance in the middle wave infrared band.

[0014] On the basis of ensuring firm physical combination, the optical loss of the interface is optimized to obtain higher transmittance. Based on the optical thin film interference theory, the antireflection thin film design of the diamond and sapphire interface is carried out. Diamond is taken as the light incident medium, sapphire is taken as the light emission medium, SiC, Si3N4 and AlN are taken as the high refractive index medium (H), the medium of medium refractive index (M) and the low refractive index medium (L) respectively. The basic film system structure is: sapphire / L M H / diamond, the reference wavelength is regulated and designed to reduce the reflectivity in 3-5 μm. On this basis, taking the low reflectivity in 3-5 μm as the target, the numerical optimization calculation is further carried out through the film system design to obtain the final film system structure. At this time, the thickness of the AlN layer is 200-400 nm, the thickness of the Si3N4 layer is 200-500 nm, the thickness of the SiC layer is 150-300 nm, and the thickness of the diamond layer is 10-100 μm. The substrate mainly plays a role of main support, and the thickness is not less than 1 mm, and is preferably 1-3 mm.

[0015] The application also provides a preparation method of the diamond-based infrared composite window material, comprising:

[0016] (1) obtaining an aluminum oxide substrate, using a direct current magnetron sputtering method, taking N2 as a reaction gas, taking an Al target as a raw material, sputtering and depositing an AlN layer on the surface of the aluminum oxide substrate in an Ar atmosphere;

[0017] (2) using a radio frequency magnetron sputtering method, taking N2 as a reaction gas, taking a Si target as a raw material, reacting and sputtering 100-200 min on the surface of the AlN layer obtained in step (1) in an Ar atmosphere and at a temperature of 450-500 DEG C to obtain a Si3N4 layer. If the temperature is too high, the deposition rate is too fast, a larger stress is easily formed, and the particles deposited are easy to form voids, causing optical scattering and affecting the optical transmittance. If the temperature is too low, the deposition rate is too slow, the efficiency is low, and the quality of the film layer is also affected. Therefore, a suitable temperature range is set.

[0018] (3) using a radio frequency magnetron sputtering method, taking a SiC target as a raw material, reacting and sputtering 50-100 min on the surface of the Si3N4 layer obtained in step (2) in an Ar atmosphere and at a temperature of 100-150 DEG C to obtain a SiC layer. The temperature setting in this stage is also considered as above;

[0019] (4) through the microwave plasma chemical vapor deposition (MPCVD) method, with CH4 / H2 mixed gas as the reaction gas, at a temperature of 800-900 ℃, the SiC layer surface obtained in step (3) is continuously grown for 10-15 h to obtain a diamond layer, and the diamond layer is polished to obtain a diamond-based infrared composite window material.

[0020] The present application obtains a diamond-based infrared composite window material with high transmittance, high surface thermal conductivity, high thermal shock resistance and film layer bonding performance by chemically bonding each layer by using a relatively conventional deposition technique.

[0021] In step (1):

[0022] Further, the purity of Ar and N2 is not less than 99.99%, the purity of Al target material is not less than 99.9%, and the flow ratio of the introduced N2 and Ar is 1:2-1:3, wherein the flow of Ar is 10-30 sccm. If the flow or ratio of Ar is too high, the activity or speed of the deposition reaction will be restricted; if it is too low, the growth process will not be easy to control, and defect structures will be easily formed to affect the mechanical, thermal and optical properties.

[0023] Further, the AlN layer is sputter-deposited on the surface of the aluminum oxide substrate, and during the sputtering process, the sputtering power is 100-200 W, and the sputtering gas pressure is 1.0-4.0 Pa.

[0024] Further, in step (2), the purity of the gas N2 is not less than 99.99%, and the flow ratio of the introduced N2 and Ar is 1:1-1:3, wherein the flow of N2 is 5-10 sccm. If the flow or ratio of N2 is too low, the activity or speed of the deposition reaction will be restricted; if it is too high, the growth process will not be easy to control, and defect structures will be easily formed to affect the mechanical, thermal and optical properties. During the reactive sputtering process, the sputtering power is 100-200 W, and the sputtering gas pressure is 0.5-1.0 Pa.

[0025] In step (3):

[0026] Further, the purity of the gas Ar is not less than 99.99%, and the flow of introduced Ar is 10-30 sccm.

[0027] Further, the purity of the SiC target material is not less than 99.9%.

[0028] Further, the SiC layer is obtained by reactive sputtering the Si3N4 layer obtained in step (2) for 50-100 min, and during the reactive sputtering process, the sputtering power is 100-150 W, the sputtering gas pressure is 0.5-1.5 Pa, and the bias voltage is -50 to -80 V.

[0029] In step (4):

[0030] Further, before microwave plasma chemical vapor deposition (MPCVD) is performed, the sample containing the SiC layer obtained in step (3) is placed in a molybdenum holder, and the height of the molybdenum holder is 3-6 mm.

[0031] Further, the ratio of CH4 to H2 is 2:100-4:100, and the flow rate of H2 is 400-600 sccm; the purity of CH4 and H2 is not less than 99.99%.

[0032] Further, the process parameters of the microwave plasma chemical vapor deposition method are as follows: the deposition power is 3.0-4.0 kW, and the deposition gas pressure is 10-15 kPa.

[0033] Further, after the diamond layer is deposited, the cooling rate is controlled to be 5-20 ℃ / min.

[0034] Further, the diamond layer is polished to obtain a diamond-based infrared composite window material, and the diamond powder with an average particle size of 0.5-2.0 μm is used in the polishing process. By using the diamond powder with a smaller particle size to polish, the diamond surface is smooth, which is beneficial to increase the light transmittance of the diamond layer.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] The present application selects a material between the thermal expansion coefficients of the aluminum oxide substrate and the diamond layer as the transition layer, so that the interface bonding strength is high in a high aerodynamic heat environment, and the transition layer is not easy to fall off. In addition, the adjacent layers have the same elements, so that the layers are chemically connected by deposition, and the lattice parameters of the layers are close, which further strengthens the interface bonding strength of each layer. Due to the chemical bonding between the layers, the formation of multiple impurity interfaces is avoided, thereby increasing the transmittance of the middle infrared waveband light to more than 50%. In addition, due to the existence of the diamond layer, the surface thermal conductivity of the obtained infrared window is significantly improved (>1200 W / mK, more than 40 times).

[0037] The present application deposits the transition layer by sputtering, which is simple and efficient, and provides a candidate scheme for a high-speed aircraft infrared window. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The result diagram of the diamond-based infrared composite window material provided by the embodiment of the present application is shown in the following figure:

[0039] Figure 2A preparation method flow chart of the diamond-based infrared composite window material provided by the embodiment of the present application is shown in the figure.

[0040] Figure 3 A Raman spectrum of the diamond-based infrared composite window prepared by the embodiment 1, the embodiment 2 and the embodiment 3 of the present application is shown in the figure. DETAILED DESCRIPTION

[0041] In order to make the purpose, content and advantages of the present application more clear, the specific embodiments of the present application are described in further detail below in combination with the drawings and examples.

[0042] The method of preparing a multi-layer transition layer combination with a certain refractive index, lattice parameter and thermal expansion coefficient gradient on the oxide optical material in advance can effectively reduce the stress between the diamond and the oxide optical material substrate during the growth of the diamond at high temperature (> 800℃). And an AlN / Si3N4 / SiC three-layer transition layer combination is prepared on the substrate by magnetron sputtering, and then a certain thickness of diamond layer is deposited on the transition layer, as shown in the figure. Figure 1 The diamond layer of the obtained composite window is well combined with the substrate, has a transmittance of > 50% in the mid-wave infrared band, and greatly improves the surface thermal conductivity (more than 50 times), which provides a solution for the infrared window material of high-speed aircraft.

[0043] Based on the above research, the present application provides a preparation method of an oxide substrate / transition layer / diamond layer infrared composite material, as shown in the figure. Figure 2 The preparation method comprises the following steps:

[0044] 1) Take an oxide optical material with a certain optical transmittance as a substrate for standby. Further, the oxide optical material is one of sapphire, LiAlON ceramic, MgAlON ceramic and AlON ceramic, the size is Ф10-30mm*1-3mm, and the average value of optical transmittance in the 3-5μm band is not less than 75%.

[0045] 2) A direct current magnetron sputtering method is used, a certain proportion of N2 and Ar is introduced, high-purity Al target is used as raw material, N2 is used as reaction gas, the temperature is raised to 500-600℃ by power and gas pressure adjustment, and a layer of AlN layer is formed on the substrate by reaction sputtering for 100-200min, and then the sample A is taken out after being reduced to room temperature. Further, the purity of the Ar and N2 is not less than 99.99%, the purity of the Al target material is not less than 99.9%, the flow ratio of the introduced N2 and Ar is 1:2-1:3, the flow of Ar is 10-30sccm, the power and gas pressure are set to 100-200W and 1.0-4.0Pa respectively during the sputtering process, and the thickness of the obtained AlN layer is 200-400nm.

[0046] 3) Take sample A, using radio frequency magnetron sputtering, input a certain proportion of N2, Ar, with high-purity Si target as raw material, N2 as reaction gas, adjust the power and gas pressure, heat to 450-500°C, react and sputter for 100-200 min, deposit a layer of Si3N4 on sample A, take out after cooling to room temperature, obtain sample B. Further, the purity of the gas N2 is not less than 99.99%, the flow ratio of input N2, Ar is 1:1-1:3, wherein the flow of N2 is 5-10 sccm; the purity of Si target material is not less than 99.9%; during sputtering, the power and gas pressure are set to 100-200 W and 0.5-1.0 Pa respectively; the thickness of the obtained Si3N4 layer is 200-500 nm.

[0047] 4) Take sample B, using radio frequency magnetron sputtering, input Ar, with high-purity SiC target material as raw material, adjust the power and gas pressure, heat to 100-150°C, apply a certain bias voltage, magnetron sputter for 50-100 min, deposit a layer of SiC on sample B, take out after cooling to room temperature, obtain sample C. Further, the purity of the gas Ar is not less than 99.99%, the flow of input Ar is 10-30 sccm; the purity of SiC target material is not less than 99.9%; during sputtering, the power and gas pressure are set to 100-150 W and 0.5-1.5 Pa respectively; the bias voltage is -50--80V; the thickness of the obtained SiC layer is 150-300 nm.

[0048] 5) Take sample C, place it on a certain thickness of metal molybdenum support, and then place it together in an MPCVD device, use a certain proportion of CH4 / H2 mixed gas as reaction gas, adjust the power and gas pressure, heat to 800-900°C, continue to grow for 10-50 h, deposit a layer of diamond on sample C, take out after slowly cooling to room temperature, obtain sample D. Further, the height of the molybdenum support is 3-6 mm; the ratio of CH4 to H2 is 2:100-4:100, wherein the flow of H2 is 400-600 sccm; the gas purity is not less than 99.99%; the operating power and gas pressure of MPCVD are set to 3.0-4.0 kW and 10.0-15.0 kPa respectively; the cooling rate is controlled at 5-20°C / min; the thickness of the obtained diamond layer is 20-100 μm.

[0049] 6) Take sample D, polish the diamond growth surface to obtain sample E, i.e. oxide substrate / diamond layer infrared composite material (or called diamond-based infrared composite window material). Further, the surface polishing step uses diamond powder with an average particle size of 0.5-2.0 μm as polishing medium; the thickness of the diamond layer on sample E is controlled to 10-50 μm.

[0050] Example 1

[0051] 1) Take the size specification of Ф10mm x 1mm sapphire as a substrate, ready for use. Among them, the average value of optical transmittance in the 3-5μm band is 82%.

[0052] 2) Using the method of direct current magnetron sputtering, a certain proportion of N2, Ar is introduced, using high-purity Al target as raw material, N2 as reaction gas, adjusting the power and gas pressure, heating to 500℃, reacting and sputtering for 200min, forming an AlN layer on the substrate, taking out after cooling to room temperature, obtaining sample A1.

[0053] Further, the purity of Ar and N2 is 99.99%, the purity of Al target material is 99.9%; the flow ratio of introduced N2, Ar gas is 1:2, wherein the flow of Ar is 30sccm; during sputtering, the power and gas pressure are set to 100W and 4.0Pa respectively; the thickness of the obtained AlN layer is 220nm.

[0054] 3) Take sample A1, use radio frequency magnetron sputtering, introduce a certain proportion of N2, Ar, use high-purity Si target as raw material, N2 as reaction gas, adjust the power and gas pressure, heat to 500℃, react and sputter for 100min, deposit a layer of Si3N4 on sample A1, take out after cooling to room temperature, obtain sample B1.

[0055] Further, the purity of the gas N2 is 99.99%, the flow ratio of introduced N2, Ar gas is 1:1, wherein the flow of N2 is 10sccm; the purity of Si target material is 99.9%; during sputtering, the power and gas pressure are set to 150W and 0.7Pa respectively; the thickness of the obtained Si3N4 layer is 205nm.

[0056] 4) Take sample B1, use radio frequency magnetron sputtering, introduce Ar, use high-purity SiC target material as raw material, adjust the power and gas pressure, heat to 150℃, apply a certain bias voltage, magnetron sputter for 100min, deposit a layer of SiC on sample B1, take out after cooling to room temperature, obtain sample C1.

[0057] Further, the purity of the gas Ar is 99.99%, the flow of introduced Ar is 10sccm; the purity of SiC target material is 99.99%; during sputtering, the power and gas pressure are set to 150W and 0.5Pa; the bias voltage is -50V; the thickness of the obtained SiC layer is 346nm.

[0058] 5) Take sample C1, place it on a certain thickness of metal molybdenum support, and then place it together in the MPCVD equipment, use a certain proportion of CH4 / H2 mixed gas as the reaction gas, adjust the power and gas pressure, heat to 800℃, continue to grow for 10h, deposit a layer of diamond on sample C1, slowly cool to room temperature, take out, obtain sample D1.

[0059] Further, the molybdenum support height is 3 mm; the ratio of CH4 to H2 is 2:100, wherein the flow rate of H2 is 400 sccm; the gas purity is 99.99%; the MPCVD operating power and gas pressure are set to 3.1 kW and 10.0 kPa, respectively; the cooling rate is controlled at 20 ℃ / min; and the obtained diamond layer is 22 μm thick.

[0060] 6) Sample D1 is taken, and the diamond growth surface is polished to obtain sample E1, i.e., a sapphire substrate / diamond layer infrared composite material (or referred to as a diamond-based infrared composite window material).

[0061] Further, the surface polishing step uses diamond powder with an average particle size of 2.0 μm as the polishing medium; and the diamond layer on sample E1 is 12 μm thick.

[0062] Example 2

[0063] 1) A LiAlON ceramic with a size specification of Ф20 mm x 2 mm is taken as a substrate for standby use. The average optical transmittance in the 3-5 μm band is 75%.

[0064] 2) A direct current magnetron sputtering method is used, a certain ratio of N2 and Ar is introduced, high-purity Al target is used as a raw material, N2 is used as a reaction gas, the power and gas pressure are adjusted, the temperature is raised to 550 ℃, and a layer of AlN is formed on the substrate by reaction sputtering for 150 min. After being cooled to room temperature, sample A2 is taken out.

[0065] Further, the purity of Ar and N2 is 99.999%, and the purity of the Al target material is 99.95%; the flow rate ratio of introduced N2 and Ar is 2:5, wherein the flow rate of Ar is 20 sccm; during the sputtering process, the power and gas pressure are set to 200 W and 2.3 Pa, respectively; and the obtained AlN layer is 303 nm thick.

[0066] 3) Sample A2 is taken, a radio frequency magnetron sputtering method is used, a certain ratio of N2 and Ar is introduced, high-purity Si target is used as a raw material, N2 is used as a reaction gas, the power and gas pressure are adjusted, the temperature is raised to 450 ℃, and a layer of Si3N4 is deposited on sample A2 by reaction sputtering for 200 min. After being cooled to room temperature, sample B2 is taken out.

[0067] Further, the purity of the gas N2 is 99.999%, the flow rate ratio of introduced N2 and Ar is 1:2, wherein the flow rate of N2 is 7 sccm; the purity of the Si target material is 99.99%; during the sputtering process, the power and gas pressure are set to 100 W and 1.0 Pa, respectively; and the obtained Si3N4 layer is 302 nm thick.

[0068] 4) Take sample B2, using radio frequency magnetron sputtering, input Ar, using high-purity SiC target material as raw material, adjusting power and gas pressure, heating to 120°C, applying a certain bias, magnetron sputtering for 70 min, depositing a layer of SiC on sample B2, taking it out after cooling to room temperature, and obtaining sample C2.

[0069] Further, the purity of the gas Ar is 99.999%, the flow rate of the input Ar is 20 sccm; the purity of the SiC target material is 99.9%; during sputtering, the power and gas pressure are set to 122 W and 1.0 Pa; the bias value is -65 V; and the thickness of the obtained SiC layer is 253 nm.

[0070] 5) Take sample C2, place it on a certain thickness of metal molybdenum support, and then place it together in the MPCVD device, using a certain proportion of CH4 / H2 mixed gas as the reaction gas, adjusting the power and gas pressure to raise the temperature to 850°C, continuously growing for 24 h, depositing a layer of diamond on sample C2, slowly cooling to room temperature, and taking it out to obtain sample D2.

[0071] Further, the height of the molybdenum support is 4 mm; the proportion of CH4 to H2 is 4:100, with the flow rate of H2 being 500 sccm; the gas purity is 99.999%; the MPCVD operating power and gas pressure are set to 3.5 kW and 12.3 kPa, respectively; the cooling rate is controlled at 10°C / min; and the thickness of the obtained diamond layer is 58 μm.

[0072] 6) Take sample D2, polish the diamond growth surface to obtain sample E2, i.e., a LiAlON-based substrate / diamond layer infrared composite material (or referred to as a diamond-based infrared composite window material).

[0073] Further, the surface polishing step uses diamond powder with an average particle size of 1.0 μm as the polishing medium; and the thickness of the diamond layer on sample E2 is 32 μm.

[0074] Example 3

[0075] 1) Take MgAlON ceramic with a size specification of Ф30 mm x 3 mm as the substrate for standby use. The average optical transmittance in the 3-5 μm band is 77%.

[0076] 2) Use the method of direct current magnetron sputtering, input a certain proportion of N2 and Ar, use high-purity Al target as raw material, use N2 as reaction gas, adjust power and gas pressure, heat to 600°C, react and sputter for 100 min, form an AlN layer on the substrate, take it out after cooling to room temperature, and obtain sample A3.

[0077] Further, the purities of Ar and N2 are 99.999% and 99.99% respectively, and the purity of Al target is 99.99%; the flow ratio of the input N2 and Ar is 1:3, wherein the flow of Ar is 10sccm; during the sputtering process, the power and the gas pressure are set as 150W and 1.0Pa respectively; the thickness of the obtained AlN layer is 395nm.

[0078] 3) Sample A3 is taken, and radio frequency magnetron sputtering is adopted, a certain proportion of N2 and Ar is input, high-purity Si target is used as raw material, N2 is used as reaction gas, the power and the gas pressure are adjusted, the temperature is raised to 470℃, a layer of Si3N4 is deposited on sample A3 by reaction sputtering for 150min, and sample B3 is obtained after being taken out after being reduced to room temperature.

[0079] Further, the purity of the gas N2 is 99.99%, the flow ratio of the input N2 and Ar is 1:3, wherein the flow of N2 is 5sccm; during the sputtering process, the power and the gas pressure are set as 200W and 0.5Pa respectively; the thickness of the obtained Si3N4 layer is 488nm.

[0080] 4) Sample B3 is taken, and radio frequency magnetron sputtering is adopted, Ar is input, high-purity SiC target is used as raw material, the power and the gas pressure are adjusted, the temperature is raised to 100℃, a certain bias voltage is applied, a layer of SiC is deposited on sample B3 by magnetron sputtering for 50min, and sample C3 is obtained after being taken out after being reduced to room temperature.

[0081] Further, the purity of the gas Ar is 99.999%, the flow of Ar is 30sccm; the purity of SiC target is 99.99%; during the sputtering process, the power and the gas pressure are set as 100W and 1.5Pa respectively; the bias voltage value is -80V; the thickness of the obtained SiC layer is 155nm.

[0082] 5) Sample C3 is taken, and placed on a certain thickness of metal molybdenum support, and then placed in an MPCVD device, a certain proportion of CH4 / H2 mixed gas is used as reaction gas, the power and the gas pressure are adjusted, the temperature is raised to 900℃, a layer of diamond is deposited on sample C3 by continuous growth for 50h, and sample D3 is obtained after being taken out after being slowly reduced to room temperature.

[0083] Further, the height of the molybdenum support is 6mm; the ratio of CH4 to H2 is 3:100, wherein the flow of H2 is 600sccm; the gas purity is 99.999%; the running power and the gas pressure of MPCVD are set as 4.0kW and 15.0kPa respectively; the cooling rate is controlled at 5℃ / min; the thickness of the obtained diamond layer is 96μm.

[0084] 6) Sample D3 was taken, and the diamond growth surface was ground and polished to obtain sample E3, i.e., MgAlON substrate / diamond layer infrared composite material (or diamond-based infrared composite window material).

[0085] Furthermore, the surface polishing step uses diamond powder with an average particle size of 0.5 μm as the polishing medium; the thickness of the diamond layer on sample E3 is 48 μm.

[0086] Performance Analysis

[0087] Figure 1 The schematic diagram of the present invention is a composite structure formed by depositing an AlN layer, a Si3N4 layer, a SiC layer, and finally a diamond layer on an aluminum oxide substrate (sapphire, LiAlON ceramic, MgAlON ceramic, or AlON ceramic). The specific implementation process is as follows: Figure 2 shown.

[0088] The Raman spectra of the diamond layer on the surface of the diamond / multi-layer transition layer / oxide substrate composite window samples D1, D2, and D3 obtained in Examples 1, 2, and 3 of the present invention are as follows: Figure 3 As shown in the Raman shift and intensity relationship test results, we can see that they have very good crystal quality, the characteristic peak of diamond (1332cm -1 ) is obvious, there is no obvious other impurities, and the half-maximum width is narrow (FHWM is 2.6-2.9). The sharper the Raman characteristic peak and the narrower the half-maximum width, the better the diamond quality.

[0089] The average transmittances of diamond / multi-layer transition layer / oxide substrate composite window material samples E1, E2, and E3 obtained in Examples 1, 2, and 3 of the present invention in the mid-wave infrared band (3–5 μm) are shown in Table 1. It can be seen that the obtained samples have high optical transmittance.

[0090] In order to analyze the heat shock resistance and the film layer bonding effect of the composite structure, first, we test the surface thermal conductivity of the composite structure. The laser pulse calorimetry method is used for testing, and the test results are shown in Table 2. For samples E1, E2 and E3, the surface thermal conductivities are 1680 W / mK, 1232 W / mK and 1480 W / mK respectively, while the thermal conductivity of the comparative sample 2 is only 13 W / mK. Since the thermal conductivity of the selected substrate (sapphire, LiAlON ceramic, MgAlON ceramic or AlON ceramic) is generally lower than 30 W / mK, the surface thermal conductivity is increased by more than 40 times based on the substrate. The higher the thermal conductivity, the better the material can transfer heat when subjected to high heat flow, and the less likely it is to form local heat accumulation, resulting in large thermal stress and structural rupture. Secondly, we characterize the heat shock resistance of the material. The method and test results are shown in Table 3. Compared with the comparative sample 2, i.e. LiAlON (size Ф20mmx2mm. The average optical transmittance in the 3-5μm band is 75%), the composite structure withstands the heat shock test without breaking or film peeling. The above results show that the composite structure sample provided by the present application has excellent heat shock resistance.

[0091] Table 1. Optical transmittance of the samples obtained in the examples

[0092] Performance Sample E1 Sample E2 Sample E3 Transmittance (%) 60.1％ 50.2％ 53.5％

[0093] Table 2. Surface thermal conductivity of the samples obtained in the examples

[0094] Performance Sample E1 Sample E2 Sample E3 Comparative Sample 2 Thermal Conductivity (W / mK) 1680 1232 1480 13 W / mK

[0095] Table 3. Heat shock resistance of the samples obtained in the examples

[0096]

[0097] The above only describes the preferred embodiments of the present application. It should be noted that for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A diamond-based infrared composite window material, characterized in that: It includes an aluminum oxide substrate, a transition layer and a diamond layer, wherein the transition layer includes an AlN layer, a Si3N4 layer and a SiC layer; Wherein, an AlN layer is deposited on the surface of the aluminum oxide substrate, a Si3N4 layer is deposited on the surface of the AlN layer, a SiC layer is deposited on the surface of the Si3N4 layer, and a diamond layer is deposited on the surface of the SiC layer; The material of the aluminum oxide substrate is sapphire, LiAlON ceramic, MgAlON ceramic or AlON ceramic.

2. The diamond-based infrared composite window material according to claim 1, characterized in that: The optical transmittance of the aluminum oxide substrate in the mid-wave infrared band is not less than 75%.

3. The diamond-based infrared composite window material according to claim 1, characterized in that: The thickness of the AlN layer is 200-400 nm, the thickness of the Si3N4 layer is 200-500 nm, the thickness of the SiC layer is 150-350 nm, the thickness of the diamond layer is 10-100 μm, and the thickness of the aluminum oxide substrate is not less than 1 mm.

4. A method for preparing a diamond-based infrared composite window material according to any one of claims 1 to 3, characterized in that: include: (1) Obtaining an aluminum oxide substrate, using a DC magnetron sputtering method, using N2 as a reaction gas and an Al target as a raw material, in an Ar atmosphere, sputtering and depositing an AlN layer on the surface of the aluminum oxide substrate; (2) using radio frequency magnetron sputtering, using N2 as the reaction gas and Si target as the raw material, in an Ar atmosphere at a temperature of 450-500 °C, the surface of the AlN layer obtained in step (1) was reactively sputtered for 100-200 min to obtain a Si3N4 layer; (3) using RF magnetron sputtering, with SiC target as raw material, in an Ar atmosphere at 100–150 °C, reactive sputtering was performed on the surface of the Si3N4 layer obtained in step (2) for 50–100 min to obtain a SiC layer; (4) A diamond layer is obtained by continuously growing the SiC layer obtained in step (3) for 10-15 hours on the surface of the SiC layer obtained in step (3) at a temperature of 800-900°C using a microwave plasma chemical vapor deposition method with a CH4 / H2 mixed gas as a reaction gas, and polishing the diamond layer to obtain a diamond-based infrared composite window material.

5. The method for preparing a diamond-based infrared composite window material according to claim 4, characterized in that: In step (1), the purity of the Ar and N2 is not less than 99.99%, the purity of the Al target is not less than 99.9%, and the flow ratio of the N2 and Ar gases is 1:2-1:3, wherein the flow rate of Ar is 10-30 sccm.

6. The method for preparing a diamond-based infrared composite window material according to claim 4, wherein: The AlN layer is sputtered and deposited on the surface of the aluminum oxide substrate. During the sputtering process, the sputtering power is 100-200 W and the sputtering gas pressure is 1.0-4.0 Pa.

7. The method for preparing a diamond-based infrared composite window material according to claim 4, wherein: In step (2), the purity of the N2 is not less than 99.99%, and the flow ratio of the N2 and Ar gases is 1:1–1:3, wherein the flow rate of N2 is 5–10 sccm. During the reactive sputtering process, the sputtering power is 100–200 W, and the sputtering pressure is 0.5–1.0 Pa.

8. The method for preparing a diamond-based infrared composite window material according to claim 4, wherein: The surface of the Si3N4 layer obtained in step (2) is reactively sputtered for 50–100 min to obtain a SiC layer. During the reactive sputtering process, the sputtering power is 100–150 W, the sputtering gas pressure is 0.5–1.5 Pa, and the bias value is -50–-80 V.

9. The method for preparing a diamond-based infrared composite window material according to claim 4, wherein: The process parameters of the microwave plasma chemical vapor deposition method are: deposition power of 3.0-4.0 kW, and deposition gas pressure of 10-15 kPa.

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