Ultra-black film and preparation method and application thereof

Abstract

The invention relates to an ultra-black film and a preparation method and application thereof. The ultra-black thin film comprises a TiAlC thin film and a low-refractive-index dielectric thin film which are alternately deposited on the surface of a substrate, and the material of the dielectric film with low refractive index comprises at least one of SiO2, CaF2 and MgF2.

Description

Technical Field

[0001] The invention relates to an ultra-black film and a preparation method and application thereof, and in particular to an ultra-black film applied to a surface of a complex structure and a preparation method thereof, and belongs to the field of precision optics. Background Art

[0002] Ultra-black materials have excellent light absorption properties and have broad application prospects in the fields of precision optics, space detection, and solar energy conversion. As the precision of optical systems continues to increase, the adverse effects of stray light on detection sensitivity, imaging contrast, and picture quality are becoming increasingly prominent, so the need to suppress stray light is very urgent. Stray light is other non-imaging light that reaches the detector surface in addition to normal imaging light in an optical system, as well as imaging light that reaches the detector through an abnormal optical path. If it cannot be effectively suppressed, the background noise of the detector will be very high, which will directly affect the sensitivity of the optical instrument. Ultra-black coatings or films applied to specific positions of the optical system can strongly absorb light within a certain wavelength range, thereby effectively eliminating or suppressing stray light. In view of this, ultra-black coatings and film materials have been widely studied and applied in recent years.

[0003] The coatings with high absorption and stray light elimination mainly include vertical carbon nanotubes, black anodized coatings, organic black paints, etc. For example, Vantablack developed by Surrey Nanosystems in the UK is composed of carbon nanotubes with an absorption rate of more than 99%, but it is expensive, and carbon nanotubes have shortcomings such as poor mechanical stability and substrate dependence; black anodized coatings have advantages such as mature technology, but they have to go through two main processes of anodization and coloring, and the aluminum alloy composition and anodized film have a great influence on the coloring quality of the film layer; spraying organic black paint has the advantages of simple process and a wide range of substrate selection, but there may be condensable volatiles in the black paint, and their volatilization may affect the optical system. At present, the application of ultra-black coatings is hindered by complex preparation processes, insufficient material stability, and difficulty in achieving strong absorption in a wide band. In addition, considering the practicality of ultra-black coatings on complex optical components with large curvature, it is necessary to achieve uniform coating of ultra-black coatings on complex three-dimensional structures, and traditional methods such as spraying, sputtering, and evaporation are difficult to meet the above requirements.

[0004] Atomic layer deposition (ALD) is a technique that alternately passes gaseous precursor pulses into a reaction chamber, adsorbs and reacts on the substrate surface to form a thin film. Compared with traditional methods, the atomic layer deposition process has outstanding advantages: 1) The self-limiting nature of the reaction enables it to form a uniform film on the surface of a three-dimensional complex structure; 2) The film is dense and pinhole-free; 3) Controllable coating can be achieved at the atomic level with good repeatability. Therefore, the advantages of this technology can be used to prepare ultra-black films for use in a new generation of high-precision, high-resolution optical systems. Summary of the invention

[0005] To this end, the present invention provides an ultra-black film and a preparation method and application thereof.

[0006] On the one hand, the present invention provides an ultra-black film, comprising: a TiAlC film and a low-refractive index dielectric film alternately deposited on the surface of a substrate; the material of the low-refractive index dielectric film comprises at least one of SiO2, CaF2 and MgF2. In the art, TiAlC is mainly used in the field of mechanical manufacturing, and there are few reports on its optical properties. The inventors first discovered that the average absorption rate of TiAlC with a thickness of 200nm can reach more than 0.7, and has good light absorption characteristics; and then synergistically with a low-refractive index dielectric film with an anti-reflection effect, an ultra-black film is finally obtained.

[0007] Preferably, the ratio of Ti element: Al element and C element in the TiAlC film is (4-7):1:(2-8); Preferably, the phase composition of the TiAlC film includes Ti 4.3 AlC 7.1 、Ti 5.5 AlC7、Ti 7.5 At least one of AlC2.

[0008] Preferably, the total number of layers of the TiAlC film and the low refractive index dielectric film in the ultra-black film is 4 to 10. In the present invention, the application field is the field of precision optics. In order to achieve the effect of eliminating stray light, the absorption rate must be at least 98%. Therefore, the present invention needs to adopt a multilayer super-absorption structure consisting of at least 4 layers of absorption layers and anti-reflection layers alternately, so that its absorption rate is as high as 98% or more, preferably as high as 99.3%.

[0009] Preferably, the thickness of each TiAlC film is 10-200 nm.

[0010] Preferably, the thickness of each layer of low refractive index dielectric film is 10-100 nm.

[0011] Preferably, the total thickness of the ultra-black film is 200nm to 800nm; the average absorptivity of the ultra-black film in the wavelength range of 400nm to 1000nm is ≥98%, preferably up to 99.3%.

[0012] Preferably, the material of the substrate includes quartz, glass, metal and ceramic; the shape of the substrate is a plane, a curved surface (for example, an arch, a cylinder, etc.) or other complex three-dimensional structure; the surface of the substrate is smooth or rough.

[0013] On the other hand, the present invention provides a method for preparing an ultra-black film, using atomic layer deposition technology to alternately deposit TiAlC film and low refractive index dielectric film on the surface of a substrate to obtain the ultra-black film. The optical devices in the application field of the present invention are often complex three-dimensional structures such as arched and cylindrical. Therefore, the present invention innovatively adopts atomic layer deposition means, and through specific embodiments, it is confirmed that it can evenly cover the inner and outer surfaces of curved surfaces or other three-dimensional complex structures with ultra-black films; while the ultra-black film prepared by magnetron sputtering process cannot evenly cover the inner and outer surfaces of curved surfaces or three-dimensional complex structures.

[0014] Preferably, a titanium-containing precursor and an aluminum-containing precursor are used as precursors for depositing TiAlC, an inert gas is used as a purge gas, and the TiAlC film is prepared using atomic layer deposition technology. Preferably, the titanium-containing precursor is titanium tetrachloride (TiCl4), the aluminum-containing precursor is trimethylaluminum (TMA), and the purge gas is nitrogen (N2).

[0015] Preferably, a silicon-containing precursor and ozone (O3) are used as precursors for depositing SiO2, an inert gas is used as a purge gas, and an atomic layer deposition technique is used to prepare a SiO2 film. Preferably, the silicon-containing precursor is diisopropylamine silane (DIPAS), and the purge gas is nitrogen (N2).

[0016] Preferably, the deposition process of TiAlC film includes: setting the film forming temperature to 200-450°C; introducing trimethylaluminum TMA into the reaction chamber for 0.1-1s, then introducing N2 to purge for 2-10s; then introducing TiCl4 into the reaction chamber for 0.1-2s, then introducing N2 to purge for 2-10s. The deposition process of SiO2 film includes: setting the film forming temperature to 200-450°C; introducing DIPAS into the reaction chamber for 0.1-2s, then introducing N2 to purge for 2-10s; then introducing O3 into the reaction chamber for 1-4s, then introducing N2 to purge for 2-10s.

[0017] In yet another aspect, the present invention provides an application of an ultra-black film in the field of precision optics.

[0018] Beneficial effects of the present invention: 1. The present invention can evenly form an ultra-black film on the inner and outer surfaces of a three-dimensional complex structure; 2. The ultra-black film prepared by the present invention has an absorption rate of up to 99.3% in the 400-1000nm band, and the film has high bonding strength with the substrate, no pinholes, and high mechanical strength; 3. The ultra-black film prepared by the present invention has excellent environmental adaptability, and its performance remains stable after wet-heat aging and thermal cycle performance assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is the XPS image of the TiAlC film prepared in Example 1; Figure 2 The performance characterization results of the ultra-black film deposited on the surface of the quartz glass in Example 1, wherein (a) is a microscopic structure photo of the ultra-black film cross section (scale 200nm), (b) is a macroscopic photo of the quartz glass before and after coating, and (c) is an absorptivity curve after the ultra-black film is deposited on the surface of the quartz glass; Figure 3 This is a photo of the ultra-black film bonding test in Example 1; Figure 4 The test results of the abrasion resistance of the ultra-black film in Example 1 are as follows; Figure 5 The results of the wet heat aging and thermal cycle tests of the ultra-black film in Example 1; Figure 6 The performance characterization results of the ultra-black film deposited on the surface of the quartz glass tube in Example 2, wherein (a) is a macroscopic photograph before and after coating, and (b) is an absorptivity curve of the ultra-black film on the inner and outer surfaces; Figure 7 This is a photo of the ultra-black film deposited on the surface of the complex structure alloy component in Example 3; Figure 8 The film absorption rate curves in Example 4, Comparative Example 1 and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0020] The present invention is further described below by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0021] In the present disclosure, an ultra-black film applied to a surface of a complex structure and a preparation method thereof are provided, which are used to eliminate interference of stray light and the like on an optical system.

[0022] In the present invention, the ultra-black film is composed of TiAlC and a low-refractive index dielectric film alternately, wherein TiAlC is used as a light absorption layer and the low-refractive index dielectric film is used as an anti-reflection layer. Preferably, the total number of film layers of the ultra-black film can be 4 to 10 layers, and the total thickness can be 200nm to 800nm. The ultra-black film has an average absorption rate of 99.3% in the 400nm to 1000nm band, and has excellent film-base bonding, abrasion resistance, resistance to wet and hot aging and thermal cycling performance.

[0023] The present invention adopts an atomic layer deposition method to prepare an ultra-black film, and the preparation process is simple and controllable. The obtained ultra-black film has a wide light absorption range and stable mechanical and environmental properties.

[0024] The following is an exemplary description of the process of preparing an ultra-black film with alternating TiAlC and low refractive index dielectric layers using atomic layer deposition technology. After a precursor is introduced into the reaction chamber, it is purged with an inert gas to remove excess precursor; then another precursor is introduced into the reaction chamber and reacted, and then purged with an inert gas to remove unreacted precursor and reaction byproducts, which is a cycle. The thickness of the film can be controlled by controlling the number of cycles.

[0025] The substrate is ultrasonically cleaned and dried, and then placed in the reaction chamber of the atomic layer deposition equipment. The substrate material can be quartz, glass, metal, ceramic, etc., and the substrate shape can be a plane, a curved surface or other complex three-dimensional structure. The substrate surface can be smooth or rough. The substrate used in the present invention does not need sandblasting, and an ultra-black film can be prepared on a smooth surface.

[0026] The TiAlC film is deposited on the substrate surface by atomic layer deposition process. Titanium tetrachloride or titanium tetraisopropoxide can be used as a titanium source precursor, and trimethylaluminum can be used as an aluminum source precursor to react to form TiAlC. The film forming temperature is 200-450°C.

[0027] The low refractive index dielectric film is deposited by atomic layer deposition process. The low refractive index dielectric film can be SiO2. Furthermore, diisopropylamine silane or tri(dimethylamino)silane and ozone can be used as precursors to form SiO2. The film forming temperature is 200-450°C.

[0028] Repeat the above steps to form a structure of substrate / TiAlC / low-refractive-index medium layer / TiAlC / low-refractive-index medium layer… / TiAlC / low-refractive-index medium layer, wherein the layer close to the substrate is TiAlC, and the layer close to the air is the low-refractive-index medium layer.

[0029] In the prior art, ultra-black materials are often prepared by roughening the surface of the material to enhance its ultra-black effect, while the ultra-black film in the present invention can be applied to a substrate with a smooth surface.

[0030] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples in a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0031] Example 1 This embodiment relates to an ultra-black film applied on a flat quartz glass surface and a preparation method thereof, comprising: A quartz glass substrate with a surface roughness of less than 1nm and a size of 20mm×20mm×0.5mm was ultrasonically cleaned with ethanol, acetone, and deionized water in sequence, then dried and placed in the reaction chamber of the atomic layer deposition equipment. The vacuum was evacuated to 6-8mbar, and the substrate was heated to 400℃ to prepare the TiAlC and SiO2 film layers; Titanium tetrachloride (TiCl4) and trimethylaluminum (TMA) are used as precursors for depositing TiAlC, and diisopropylamine silane (DIPAS) and ozone (O3) are used as precursors for depositing SiO2. Nitrogen (N2) with a purity higher than 99.99% is used as the purge gas. A growth cycle of atomic layer deposition reaction mainly includes four steps. Taking TiAlC as an example, its deposition process is as follows: 1) TMA is introduced into the reaction chamber (0.3s); 2) N2 is introduced for purge (5s); 3) TiCl4 is introduced into the reaction chamber (0.6s); 4) N2 is introduced again for purge (5s). Similarly, the deposition process of SiO2 includes 1) DIPAS is introduced into the reaction chamber (0.1s); 2) N2 is purged (5s); 3) O3 is introduced into the reaction chamber (2s); 4) N2 is purged (5s). The total number of layers of the ultra-black film is 6, which are TiAlC (193nm) / SiO2 (15nm) / TiAlC (31nm) / SiO2 (51nm) / TiAlC (15nm) / SiO2 (88nm). The scanning electron microscope photo of the cross section of the multilayer film is shown in the figure. Figure 2 As shown in (a). Figure 2 (b) is a photo of the quartz glass substrate before and after coating. Figure 2 (c) is the measured absorptivity data after the ultra-black film is deposited on the surface of the quartz glass substrate. The average absorptivity of the ultra-black film in the 400 to 1000 nm band reaches 99.3%. In the TiAlC film prepared in this embodiment 1, the ratio of Ti element: Al element and C element is 4.3:1:7.1.

[0032] Referring to the ASTM D3359 standard test method, the cross-cut tape test was used to evaluate the bonding between the ultra-black film and the substrate. Specifically, the film layer was cross-cut in a vertical grid shape, and the cuts penetrated the film layer to the substrate. Subsequently, the tape was pressed against the cross-cut area, and the air bubbles between the tape and the sample were removed. The tape was quickly torn off at an angle as close to 180° as possible to observe whether the film layer fell off. Figure 3 The following are photos of the experimental process and results. After the test, the cut edge of the cross-cut remained intact and smooth, and no peeling of the cross-cut area was observed, proving that the ultra-black film has good bonding strength.

[0033] The film surface was rubbed 20 times with an eraser and 500-grit sandpaper (pressure was about 10 N) respectively, and the damage of the film was observed to evaluate the mechanical stability of the ultra-black film. Figure 4The following are photos of the samples before and after the test and the measured absorption rate data. After the sample surface was rubbed with rubber, no significant appearance change was observed, and the measured absorption rate curve was almost the same as before the test. After the sample was rubbed with 500-mesh sandpaper, fine scratches appeared on the surface, but the average absorption rate in the 400-1000nm band remained at 98.3%. The friction test results confirmed that the ultra-black film has good mechanical stability.

[0034] In order to investigate the performance stability of the ultra-black film in harsh environments, the samples were subjected to a wet heat aging test and a thermal cycle test. The wet heat aging test conditions were to place the sample in an environment with a temperature of 50°C and a humidity of 95±5%RH for 24 hours, and the thermal cycle test conditions were to place the sample in a thermal cycle from -100°C (maintained for 5 minutes) to 100°C (maintained for 5 minutes), and repeated 100 cycles in total. Figure 5 The following are the photos of the samples before and after the test and the measured absorption rate data. The ultra-black film was subjected to a 24-hour wet heat aging test and After 100 thermal cycle tests, the appearance of the film layer did not change significantly. The average absorption rate test results in the 400-1000nm band showed that the absorption rate of the sample decreased to 99.2% after the wet heat aging test, and the absorption rate remained at 99.3% after the thermal cycle test, confirming that the ultra-black film has excellent environmental stability.

[0035] Example 2 This embodiment relates to an ultra-black film applied to the inner and outer surfaces of a quartz tube and a preparation method thereof. This embodiment is basically the same as Embodiment 1, except that the substrate is a quartz tube with a length to diameter ratio of 2:1. Figure 6 The following are photos of the quartz tube before and after coating and the measured absorption rate data of the inner and outer surfaces. It can be seen that the ultra-black film can evenly cover the inner and outer walls of the quartz tube, and the measured absorption rates are similar, which reflects the uniform coverage ability of the ultra-black film prepared by the atomic layer deposition process for the surface of the cavity with a high aspect ratio.

[0036] Example 3 This embodiment relates to an ultra-black film applied to a metal component with a complex structure and a preparation method thereof. This embodiment is basically the same as Embodiment 1, except that: the substrate is an alloy component with a complex three-dimensional structure. Figure 7 The photos are of metal parts before and after coating. It can be seen that the ultra-black film in the present invention can evenly cover complex three-dimensional structures.

[0037] Example 4 The preparation process of the ultra-black film in this embodiment 4 is similar to that in embodiment 1, except that the total number of layers of the ultra-black film is 4, which is TiAlC (193nm) / SiO2 (51nm) / TiAlC (15nm) / SiO2 (88nm). The average absorption rate of the obtained ultra-black film in the wavelength range of 400 to 1000nm reaches 98.7%.

[0038] Comparative Example 1 The preparation process of the ultra-black film in this comparative example 1 is similar to that in Example 1, except that only one layer of TiAlC film is prepared, with a thickness of 193 nm. The average absorption rate of the obtained film in the wavelength range of 400 to 1000 nm is only 68%.

[0039] Comparative Example 2 The preparation process of the ultra-black film in this comparative example 2 is similar to that in Example 1, except that only one layer of SiO2 film is prepared, with a thickness of 51 nm. The average absorption rate of the obtained film in the wavelength range of 400 to 1000 nm is close to 0%.

[0040] Comparative Example 3 The preparation process of the ultra-black film in this comparative example 3 is similar to that in Example 1, except that the total number of ultra-black film layers is only 2, which is TiAlC (193nm) / SiO2 (88nm). The average absorption rate of the obtained film in the wavelength range of 400 to 1000nm is only 89.6%.

Claims

1. An ultra-black film, characterized in that: include: TiAlC thin films and low-refractive-index dielectric thin films are alternately deposited on the substrate surface; The material of the low refractive index dielectric film includes at least one of SiO2, CaF2 and MgF2.

2. The ultra-black film according to claim 1, characterized in that: The ratio of Ti element: Al element and C element in the TiAlC film is (4-7): 1: (2-8); preferably, the phase composition of the TiAlC film includes Ti 4.3 AlC 7.1 、Ti 5.5 AlC7、Ti 7.5 At least one of AlC2.

3. The ultra-black film according to claim 1, characterized in that: The total number of layers of the TiAlC film and the low-refractive-index medium film in the ultra-black film is 4 to 10 layers.

4. The ultra-black film according to claim 1, characterized in that: The thickness of each TiAlC film is 10 to 200 nm.

5. The ultra-black film according to claim 1, characterized in that: The thickness of each layer of low refractive index dielectric film is 10 to 100 nm.

6. The ultra-black film according to claim 1, characterized in that: The total thickness of the ultra-black film is 200nm-800nm; the average absorption rate of the ultra-black film in the waveband range of 400nm to 1000nm is ≥98%.

7. The ultra-black film according to any one of claims 1 to 6, characterized in that: The material of the substrate includes quartz, glass, metal and ceramic; the shape of the substrate is a plane, a curved surface or other complex three-dimensional structure; the surface of the substrate is smooth or rough.

8. A method for preparing an ultra-black film as claimed in any one of claims 1 to 7, characterized in that: The ultra-black film is obtained by alternately depositing a TiAlC film and a low-refractive-index medium film on the surface of a substrate using an atomic layer deposition technique.

9. The preparation method according to claim 8, characterized in that: A titanium-containing precursor and an aluminum-containing precursor are used as precursors for depositing TiAlC, an inert gas is used as a purge gas, and an atomic layer deposition technique is used to prepare a TiAlC film; preferably, titanium tetrachloride (TiCl4) and trimethylaluminum (TMA) are used as precursors for depositing TiAlC, and nitrogen (N2) is used as a purge gas; Alternatively, a silicon-containing precursor and ozone (O3) are used as precursors for depositing SiO2, an inert gas is used as a purge gas, and an atomic layer deposition technique is used to prepare a SiO2 film; preferably, diisopropylamine silane (DIPAS) and ozone (O3) are used as precursors for depositing SiO2, and nitrogen (N2) is used as a purge gas.

10. The preparation method according to claim 8 or 9, characterized in that: The deposition process of the TiAlC film includes: setting the film forming temperature to 200-450° C.; introducing trimethylaluminum (TMA) into the reaction chamber for 0.1-1s, and then introducing N2 for purging for 2-10s; then introducing TiCl4 into the reaction chamber for 0.1-2s, and then introducing N2 for purging for 2-10s; Alternatively, the deposition process of the SiO2 film includes: setting the film forming temperature to 200-450°C; introducing DIPAS into the reaction chamber for 0.1-2s, and then introducing N2 for purging for 2-10s; then introducing O3 into the reaction chamber for 1-4s, and then introducing N2 for purging for 2-10s.

11. Use of the ultra-black film according to any one of claims 1 to 7 in the field of precision optics.

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