Light-absorbing black film, preparation method and application thereof

Abstract

The application relates to an optical film technology field and solves the problem that the light absorption performance and material strength of an existing light absorption material are difficult to be considered simultaneously. The light absorption black film comprises a substrate and a metal layer and first and second absorption layers which are sequentially deposited on the substrate; the substrate material is metal, alloy or optical glass; the metal layer is a Ti and Cr alloy material; the first absorption layer is an alternating stack of a metal material and an oxide material; the metal material is a Ti and Cr alloy material; the second absorption layer comprises a superlattice superlattice structure metal layer and an oxide material; the superlattice superlattice structure comprises periodically alternating nanoscale Ti / Cr metal layers, and each group of layers comprises a nanometer-thick Ti layer and a nanometer-thick Cr layer. The application has excellent mechanical properties and process compatibility while maintaining the high absorption characteristics of an ultrabroad spectrum, and provides an ideal light absorption solution for a high-performance optical system.

Description

Technical Field

[0001] This invention relates to the field of optical thin film technology, specifically to a light-absorbing black film, its preparation method, and its application. Background Technology

[0002] In optical systems such as cameras, there is always some unusable light generated by processes such as beam splitting and scattering. This light often forms stray light that negatively impacts the system's imaging. When dealing with this stray light, it is necessary to prevent it from reflecting to other areas that affect the system's imaging quality. Therefore, it is necessary to prepare a light-absorbing material with low transmittance, high cutoff depth, low reflectance, and high absorptivity.

[0003] There are generally two methods for preparing light-absorbing materials suitable for high-precision optical systems such as cameras. One method involves preparing coatings with a microporous structure composed of special fine particles. The principle is that incident light is repeatedly reflected within the micropores, and the light is absorbed by the special material forming the micropores. This type of material has the highest absorption limit. For example, Koyo Orient Japan's "Musou Black," touted as the "world's blackest" water-based acrylic coating, boasts an absorption rate of 99.2%, and Surrey Nanosystems of the UK has developed Vantablack, claiming to be the world's blackest coating with a Guinness World Record of 99.965% absorption rate. However, light-absorbing materials prepared using this method have lower material strength due to their loose and porous structure. They are easily damaged during the installation and debugging of optical systems and may shed residue during subsequent use, affecting the operation of the optical system.

[0004] Another method is optical coating, which utilizes the light absorption capacity of metals such as titanium and chromium. By designing a suitable film system, this light absorption capacity can be amplified. While this method has a lower limiting absorbance than microporous structures, it is less prone to shedding and contamination, making it more practical than microporous coatings in high-precision optical systems. Although Chinese patent document CN119861478A, published in April 2025, has a high cutoff depth above OD2, its reflectivity and absorbance were not tested. Chinese patent document CN109738976A, published in May 2019, exhibits low reflectivity in the 400-700nm visible light band, but significantly increases reflectivity and decreases absorbance in the 300-400nm ultraviolet and 700-1100nm near-infrared bands commonly used in optical cameras. Summary of the Invention

[0005] To address the challenge of balancing light absorption performance and material strength in existing optical systems, this invention proposes a light-absorbing black film, its preparation method, and its applications.

[0006] The specific technical solution of the present invention is as follows:

[0007] A light-absorbing black film, the light-absorbing black film comprising a substrate and a metal layer, a first absorption layer and a second absorption layer sequentially deposited on the substrate;

[0008] The substrate is made of metal, alloy, or optical glass;

[0009] The metal layer is a mixed alloy of Ti and Cr, with a thickness of 50~300nm;

[0010] The first absorption layer is an alternating stack of metal and oxide materials, with 2 to 10 stacks; the metal material is a mixed alloy of Ti and Cr, and the mixing ratio varies in a gradient in different stacks;

[0011] The second absorption layer includes a metal layer with a superlattice structure and an oxide material; wherein the metal layer with the superlattice structure includes 3 to 15 groups of periodically alternating nanoscale Ti / Cr metal stacks, each group of stacks including a nanometer-thick Ti layer and a nanometer-thick Cr layer.

[0012] Preferably, the mass percentage of Ti in the metal layer is 30% to 70%.

[0013] Preferably, the first absorber layer has 5 stacked layers;

[0014] The gradient variation of the mixing ratio of Ti and Cr in different stacks is specifically as follows:

[0015] The mass percentages of Ti in the five stacks from bottom to top are 25%~35%, 35%~45%, 45%~55%, 55%~65%, and 65%~75%, respectively.

[0016] Preferably, the nanometer thickness is 2~10 nm.

[0017] Preferably, the oxide material is SiO2 or Al2O3.

[0018] The present invention also provides a method for preparing the above-mentioned light-absorbing black film, which employs electron beam evaporation deposition and includes the following steps:

[0019] Cleaning the substrate: Use an ion source to bombard the substrate for ion cleaning. The bombardment voltage is 100~200V, the current is 1~10A, and the bombardment time is 5~30min.

[0020] Metal plating: Two electron guns are used to simultaneously evaporate Ti film and Cr film. The electron gun current is 100~1000mA. The mass ratio of Ti metal in the film is controlled by adjusting the magnitude of the two electron gun currents.

[0021] Depositing the first absorption layer: Ti and Cr metal films and oxide films are evaporated alternately. When depositing the metal layer, the mass ratio of Ti metal is gradually adjusted by increasing the electron gun current corresponding to the Ti film. The electron gun current is 200~800mA.

[0022] Depositing the second absorption layer: Using Ti and Cr metal film materials and oxide film materials, a metal layer with a superlattice structure is deposited with an electron gun current of 200~800mA, and then an oxide layer is deposited.

[0023] Preferably, the vacuum degree during the coating process is 5×10⁻⁶. -3 Pa ~ 1×10 -4 Pa, workpiece disc rotation speed 5~30 rpm, purity of each film material above 99.99%.

[0024] The present invention also provides a method for preparing the above-mentioned light-absorbing black film, which employs magnetron sputtering deposition and includes the following steps:

[0025] Cleaning the substrate: Apply a negative bias voltage to the substrate for bias cleaning. High-purity Ar2 gas is introduced into the vacuum chamber at a flow rate of 1~30 sccm. The substrate bias voltage is -200~-1000V, and the bias cleaning time is 5~30min.

[0026] Metal layer deposition: Ti and Cr targets are co-sputtered with a power supply of 0.1~1.5kW. The mass ratio of Ti metal in the film is controlled by adjusting the power supply of the Ti and Cr targets.

[0027] Depositing the first absorption layer: Alternately use metal targets such as Ti and Cr with oxide targets, with a power supply of 0.3~2kW. When depositing the metal layer, the mass ratio of Ti metal is gradually adjusted by increasing the power supply of the Ti target.

[0028] Depositing the second absorption layer: Using metal targets such as Ti and Cr and oxide targets, first deposit a metal layer with a superlattice structure, with a power supply of 0.3~2kW, and then deposit an oxide layer.

[0029] Preferably, the vacuum degree during the coating process is 5×10⁻⁶. -3 Pa ~ 1×10 -4 Pa, workpiece disc rotation speed 5~30 rpm, purity of each film material above 99.99%.

[0030] The present invention also provides an application of the above-mentioned light-absorbing black film in an optical system.

[0031] Compared with the prior art, the specific beneficial effects of the present invention are as follows:

[0032] The light-absorbing black film provided by this invention exhibits superior optical performance in an ultra-wide spectral range of 300-1100 nm, with an average absorbance exceeding 99% and extremely low reflectance, demonstrating groundbreaking broadband absorption characteristics. In the visible light band (400-780 nm), it possesses an ultra-high cutoff depth (OD>6), equivalent to a transmittance of less than 0.0001%, achieving near-perfect light absorption. In the near-infrared band (780-1100 nm), it maintains an excellent cutoff depth (OD>4), with a transmittance of less than 0.01%, significantly superior to conventional light-absorbing materials. It also exhibits excellent spectral stability throughout the entire operating wavelength range, with no significant absorption fluctuations, ensuring reliable application in complex optical environments.

[0033] The use of advanced PVD coating technology enables the thin film to form a strong bonding interface with the substrate, which is compatible with a variety of substrate materials, including but not limited to metals and optical glass, thus expanding the application scenarios of the product.

[0034] The light-absorbing black film of this invention, through innovative material system and structural design, maintains ultra-wide spectrum and high absorption characteristics while possessing excellent mechanical properties and process compatibility, providing an ideal light absorption solution for high-performance optical systems. Attached Figure Description

[0035] Figure 1 A schematic diagram of the light-absorbing black film structure provided by the present invention;

[0036] Figure 2 The light-absorbing black film's reflectance spectrum in Example 1;

[0037] Figure 3 The absorbance of the light-absorbing black film in Example 1;

[0038] Figure 4 The cutoff depth of the light-absorbing black film in Example 1;

[0039] Figure 5 The reflectance of the light-absorbing black film in the comparative example is given. Detailed Implementation

[0040] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0041] Example 1.

[0042] Figure 1 This is a schematic diagram of a light-absorbing black film structure in this embodiment.

[0043] The light-absorbing black film mainly comprises four parts: a substrate, a metal layer, a first absorption layer, and a second absorption layer. The metal layer is disposed on the substrate, the first absorption layer is disposed on the metal layer, and the second absorption layer is disposed on the first absorption layer. The metal layer, together with the first and second absorption layers, works to reduce reflectivity and increase light absorption.

[0044] The substrate can be made of metal, alloy, or various types of glass. In this embodiment, a titanium alloy substrate commonly used in aerospace is used.

[0045] The metal layer uses a mixed alloy of Ti and Cr, which has the following advantages compared to a pure Ti or Cr metal layer: First, the alloy film material has good light absorption properties, and together with the absorption layer, it can achieve high light absorption; second, it has high adhesion to the substrate, ensuring that the film does not detach during use; third, it has high density; and fourth, it has good chemical stability. The thickness of the metal layer is 50~300nm.

[0046] The first absorption layer consists of five stacks of Ti / Cr alloy materials and SiO2 thin films. The thickness of the metal layer in the stack ranges from 10 to 50 nm. By adjusting the electron gun power corresponding to the Ti film material, the mass percentage of Ti metal in the metal layer is controlled. From bottom to top, the mass percentages of Ti metal in the five stacks are 25%–35%, 35%–45%, 45%–55%, 55%–65%, and 65%–75%, respectively. The thickness of each SiO2 thin film is 50–150 nm.

[0047] The second absorption layer consists of a Ti / Cr metal stack with a superlattice structure and a SiO2 thin film. The Ti / Cr metal stack with the superlattice structure includes 5 groups of Ti / Cr stacks. In each group of stacks, the thickness of the Ti metal layer is 3~7nm, the thickness of the Cr metal layer is 3~7nm, and the thickness of the SiO2 thin film is 50~150nm.

[0048] In this embodiment, the light-absorbing black film mainly comprises a metal layer, a first absorption layer, and a second absorption layer. Through the combined effect of these three layers, it achieves the function of reducing reflectivity and increasing light absorption. Testing showed that the reflectivity of the film is as follows: Figure 2 As shown, the average reflectance of this thin film is less than 1% in the wavelength range of 300–1100 nm. The absorbance of the thin film is as follows: Figure 3 As shown, its average absorbance is above 99%. This thin film can be applied to metals, alloys, and various types of glass in optical systems to absorb stray light. The cutoff depth of the light-absorbing black film is as follows: Figure 4As shown, below 820nm wavelength, the film almost completely absorbs light. In the range below 1100nm wavelength, the cutoff depth OD > 4, meaning the transmittance is less than 0.1% and the absorptivity is higher than 99.9%. Using PVD coating can increase the adhesion between the film and various substrates, preventing film failure and detachment during optical assembly and use.

[0049] Comparative example.

[0050] The comparative example of the light-absorbing black film mainly comprises a substrate, a metal layer, and a first absorption layer. The metal layer is disposed on the substrate, and the first absorption layer is disposed on the metal layer. The substrate is a titanium alloy substrate commonly used in aerospace, the metal layer is a Ti metal material, and the first absorption layer is a stack of 5 groups of Ti metal materials and SiO2 thin films.

[0051] Tests showed that the reflectivity of the black film was as follows: Figure 5 As shown, the average reflectivity in the 300~1100nm range is still 7%, which is much higher than that of the light-absorbing black film in Example 1.

[0052] In summary, the light-absorbing black film provided by this invention can achieve an average reflectance of less than 1% and an average absorbance of more than 99% within a wide spectral range from 300 to 1100 nm ultraviolet to near infrared. Furthermore, the fabrication process of this film ensures high adhesion to the substrate, resistance to delamination and breakage, and high applicability on various substrates.

[0053] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A light-absorbing black film, characterized in that, The light-absorbing black film includes a substrate and a metal layer, a first absorption layer and a second absorption layer sequentially deposited on the substrate. The substrate is made of metal, alloy, or optical glass; The metal layer is a mixed alloy of Ti and Cr; The first absorption layer is an alternating stack of metal and oxide materials, with 2 to 10 stacks; the metal material is a mixed alloy of Ti and Cr, and the mixing ratio varies in a gradient in different stacks; The second absorption layer includes a metal layer with a superlattice structure and an oxide material; wherein the metal layer with the superlattice structure includes 3 to 15 groups of periodically alternating nanoscale Ti / Cr metal stacks, each group of stacks including a nanometer-thick Ti layer and a nanometer-thick Cr layer.

2. The light-absorbing black film according to claim 1, characterized in that, The mass percentage of Ti in the metal layer is 30% to 70%.

3. The light-absorbing black film according to claim 1, characterized in that, The first absorption layer has 5 stacked layers; The gradient variation of the mixing ratio of Ti and Cr in different stacks is specifically as follows: The mass percentages of Ti in the five stacks from bottom to top are 25%~35%, 35%~45%, 45%~55%, 55%~65%, and 65%~75%, respectively.

4. The light-absorbing black film according to claim 1, characterized in that, The nanometer thickness is specifically 2~10nm.

5. The light-absorbing black film according to claim 1, characterized in that, The oxide material is SiO2 or Al2O3.

6. A method for preparing a light-absorbing black film as described in any one of claims 1 to 5, characterized in that, The electron beam evaporation deposition method includes the following steps: Cleaning the substrate: Use an ion source to bombard the substrate for ion cleaning. The bombardment voltage is 100~200V, the current is 1~10A, and the bombardment time is 5~30min. Metal plating: Two electron guns are used to simultaneously evaporate Ti film and Cr film. The electron gun current is 100~1000mA. The mass ratio of Ti metal in the film is controlled by adjusting the magnitude of the two electron gun currents. Depositing the first absorption layer: Ti and Cr metal films and oxide films are evaporated alternately. When depositing the metal layer, the mass ratio of Ti metal is gradually adjusted by increasing the electron gun current corresponding to the Ti film. The electron gun current is 200~800mA. Depositing the second absorption layer: Using Ti and Cr metal film materials and oxide film materials, a metal layer with a superlattice structure is deposited with an electron gun current of 200~800mA, and then an oxide layer is deposited.

7. The method for preparing the light-absorbing black film according to claim 6, characterized in that, The vacuum degree during the coating process is 5×10 -3 Pa ~ 1×10 -4 Pa, workpiece disc rotation speed 5~30 rpm, purity of each film material above 99.99%.

8. A method for preparing a light-absorbing black film as described in any one of claims 1 to 5, characterized in that, The magnetron sputtering deposition method includes the following steps: Cleaning the substrate: Apply a negative bias voltage to the substrate for bias cleaning. High-purity Ar2 gas is introduced into the vacuum chamber at a flow rate of 1~30 sccm. The substrate bias voltage is -200~-1000V, and the bias cleaning time is 5~30min. Metal layer deposition: Ti and Cr targets are co-sputtered with a power supply of 0.1~1.5kW. The mass ratio of Ti metal in the film is controlled by adjusting the power supply of the Ti and Cr targets. Depositing the first absorption layer: Alternately use metal targets such as Ti and Cr with oxide targets, with a power supply of 0.3~2kW. When depositing the metal layer, the mass ratio of Ti metal is gradually adjusted by increasing the power supply of the Ti target. Depositing the second absorption layer: Using metal targets such as Ti and Cr and oxide targets, first deposit a metal layer with a superlattice structure, with a power supply of 0.3~2kW, and then deposit an oxide layer.

9. The method for preparing the light-absorbing black film according to claim 8, characterized in that, The vacuum degree during the coating process is 5×10 -3 Pa ~ 1×10 -4 Pa, workpiece disc rotation speed 5~30 rpm, purity of each film material above 99.99%.

10. The application of a light-absorbing black film as described in any one of claims 1 to 5 in an optical system.

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