A refractive index sensor based on structural color and a manufacturing method and a testing system thereof

Abstract

The application discloses a refractive index sensor based on structural color and a manufacturing method and a testing system thereof, and belongs to the technical field of sensors. The refractive index sensor is prepared by burning a polymer film to generate amorphous carbon material through the thermal effect of a laser. The polymer film is a polyimide film. The refractive index sensor takes an F-P cavity based on amorphous carbon as a reflection structure. The F-P cavity structure comprises a first amorphous carbon thin layer and a second amorphous carbon layer. An air layer is arranged between the first amorphous carbon thin layer and the second amorphous carbon layer. The application generates amorphous carbon through a laser, changes the color of the surface of the amorphous carbon by controlling laser parameters, and generates a wide color gamut of structural color. The method is simple, efficient, low in cost, and green and environment-friendly. Meanwhile, the generated air layer is used to add liquid with different refractive indexes, so as to cause the change of reflected light on the surface and realize the structural color of the refractive sensor.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically relating to a refractive index sensor based on structural color, its fabrication method, and testing system. Background Technology

[0002] Color serves as a simple and direct means of information transmission. Electromagnetic waves within the visible light range can be reflected, transmitted, or absorbed by objects. This results in different colors, creating a colorful world for us. Pigments and structural colors are the main sources of color in nature. Compared to pigment colors, structural colors offer advantages such as long-term stability, sustainable production, and even multifunctionality, environmental friendliness, and dynamic adjustability. Due to their unique properties, structural colors can be applied in fields such as sensing, anti-counterfeiting, and displays.

[0003] In recent years, with the advancement of micro-nano fabrication technology, structural color sensors based on mechanisms such as plasmonic nanoantennas, metasurfaces, and scattering have been reported. However, these methods often require expensive fabrication processes such as ultraviolet lithography and chemical deposition, as well as complex pattern design, resulting in high manufacturing costs and unsuitability for mass production. In contrast, the simple one-dimensional FP cavity structure offers a feasible solution for mass production of structural colors. FP cavities typically employ a two-layer thin-film structure, generating interference between the top and bottom layers, leading to strong resonance of incident light and thus producing color on the surface. However, existing structural color sensors based on FP cavities also suffer from cumbersome fabrication processes and inflexible devices. Therefore, providing a simple, low-cost, and mass-producible solution has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a refractive index sensor based on structural color, as well as its fabrication method, testing system, and testing method, to solve the problems mentioned in the background art.

[0005] The objective of this invention is achieved as follows: a material for preparing a refractive index sensor, characterized in that the material is prepared by means of atomizing a polymer film with the thermal effect of a laser to generate an amorphous carbon material.

[0006] Preferably, the polymer film is a polyimide film.

[0007] Preferably, the laser is a carbon dioxide laser with a power range of 0-30W and a scanning speed range of 0-1000 mm / s.

[0008] A refractive index sensor based on structural color, characterized in that it is made of amorphous carbon material;

[0009] The amorphous carbon material has a three-dimensional porous structure, and the refractive index sensor is constructed using a three-dimensional porous structure.

[0010] The refractive index sensor includes a first amorphous carbon thin layer and a second amorphous carbon layer, and the first amorphous carbon thin layer and the second amorphous carbon layer form an FP cavity reflector; the FP cavity reflector is an air layer, and a refractive index liquid is added in the air layer.

[0011] Preferably, the first amorphous carbon layer and the second amorphous carbon layer are not the same, the thickness of the first amorphous carbon layer is 100 nm, and the thickness of the second amorphous carbon layer is in the range of 40-100 μm.

[0012] A method for fabricating a refractive index sensor based on structural color is characterized by the following steps: Selecting a polyimide film of a certain thickness, placing the polyimide film at the focal point of a laser, and controlling the laser to etch rectangular amorphous carbon cubes onto the surface of the polyimide film. During the laser ablation of the polyimide film, controlling the scanning speed and power of the laser allows for control over the internal structure of the generated amorphous carbon material. Different laser parameters cause differences in the internal structure of the amorphous carbon, resulting in selective reflection of visible light by the amorphous carbon, allowing for the observation of multiple colors on the surface of the amorphous carbon material.

[0013] Preferably, the polyimide film has a thickness of 50 μm, and the laser is controlled to etch 1cm*1cm rectangular amorphous carbon blocks on the surface of the polyimide film.

[0014] A testing system for a liquid refractive index sensor is characterized by employing a test system generated by a refractive index sensor based on structural color; the test system includes a microscopic imaging system and image processing software, the microscopic imaging system including an optical camera with recording function and a display, and the image processing software using Photoshop.

[0015] Preferably, the optical camera is replaced by a mobile phone lens with microscopic function combined with a mobile phone.

[0016] Compared with the prior art, the present invention has the following improvements and advantages: 1. Amorphous carbon is generated by laser induction, and the color of the amorphous carbon surface is changed by controlling the laser parameters. The generated structural color has a wide color gamut distribution. This method is simple, efficient, low cost, and environmentally friendly. At the same time, the generated air layer is used to add liquids with different refractive indices, which causes changes in the surface reflected light, thereby realizing the structural color of the refractive sensor.

[0017] 2. By analyzing the refractive index sensor, various colors are selected to analyze the change of Hue value with refractive index, further improving the sensing efficiency and sensitivity of the refractive index sensor; by combining mobile phones and lenses, the refractive index sensor detection can be made portable; the structured color generated by laser induction can not only be used in the field of sensing, but also has great application potential in the fields of information encryption and anti-counterfeiting. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

[0019] Figure 2 These are Raman spectra of amorphous carbon materials of different colors used in the invention.

[0020] Figure 3 SEM images of the surface and side views of the colored and silver amorphous carbon in the invention.

[0021] Figure 4 This is a schematic diagram of the structural color reflection spectrum and the refractive index of the added liquid in the invention.

[0022] Figure 5 The invention relates to the CIE Yxy diagrams showing the changes in the refractive index of liquid for the three colors of violet, blue, and green.

[0023] Figure 6 This is a graph showing the relationship between the purple Hue value and the refractive index of the liquid in the invention.

[0024] Figure 7 This is a schematic diagram of a portable refractive index sensor using a mobile phone in the invention.

[0025] Figure 8 This is a schematic diagram illustrating the color characteristics of amorphous carbon generated under different laser scanning speeds and powers in the invention.

[0026] Among them, 1-first layer of amorphous carbon thin layer; 2-air layer; 3-second layer of amorphous carbon layer. Detailed Implementation

[0027] The invention will be further summarized below with reference to the accompanying drawings.

[0028] like Figure 1 As shown, a material for fabricating a refractive index sensor is prepared by ablation of a polymer film using a laser to generate an amorphous carbon material. The polymer film is a polyimide (PI) film.

[0029] The laser used is a carbon dioxide laser with a power range of 0-30W and a scanning speed range of 0-1000 mm / s.

[0030] A refractive index sensor based on structural color is fabricated using amorphous carbon material. The amorphous carbon material has a three-dimensional porous structure, and the refractive index sensor is constructed using this three-dimensional porous structure. The refractive index sensor includes a first amorphous carbon thin layer 1 and a second amorphous carbon layer 3, with an FP cavity reflector formed between the first amorphous carbon thin layer 2 and the second amorphous carbon layer 3. The FP cavity reflector is an air layer 2, and a refractive index liquid is added within the air layer 2.

[0031] Furthermore, the thickness of the first amorphous carbon layer 1 is 100 nm, the thickness of the second amorphous carbon layer 3 is arbitrary in the range of 40-100 μm, and the thickness of the air layer 2 is less than 1 μm.

[0032] When a broadband light source illuminates the surface of the refractive index sensor, air layers 2 of varying thicknesses cause the amorphous carbon material surface to reflect light of different wavelengths. This corresponds to the laser-induced generation of amorphous carbon, where the internal cavity sizes differ due to effects such as laser thermal diffusion, resulting in different colors of light reflected from the surface. By adding liquids of different refractive indices to the air layers 2 of a specific color, the color reflected from the surface changes accordingly, thus achieving refractive index sensing based on structural color.

[0033] A method for fabricating a refractive index sensor based on structural color involves selecting a 50 μm thick polyimide film and controlling a laser to etch 1cm*1cm rectangular amorphous carbon cubes on the surface of the polyimide film. During the laser ablation of the polyimide film, controlling the scanning speed and power of the laser can control the internal structure of the generated amorphous carbon material.

[0034] Different laser parameters cause differences in the internal structure of amorphous carbon, which in turn causes the surface of amorphous carbon to selectively reflect visible light, allowing a variety of colors to be observed on the surface of amorphous carbon.

[0035] A testing system for liquid refractive index sensors is disclosed, used to test refractive index sensors based on structural colors. The testing system includes a microscopic imaging system and image processing software. The microscopic imaging system includes an optical camera with recording capabilities and a display. The image processing software uses Photoshop.

[0036] Furthermore, a microscopic imaging system can utilize a mobile phone lens with microscopic capabilities. This lens can be mounted on the built-in camera of a mobile phone and combined with the phone to serve as a portable microscopic imaging system.

[0037] A verification method for a liquid refractive index sensor, specifically for verifying a refractive index sensor based on structural color, includes the following steps:

[0038] Step S1: Place the amorphous carbon cube with structural color under the microscopic imaging system;

[0039] Step S2: Select the purple, green and blue color regions in the structural color respectively, and then drop liquids with different refractive indices onto the first amorphous carbon thin layer 1 through a capillary tube so that they penetrate into the air layer 2;

[0040] Step S3: Photograph the color change of the surface of the first amorphous carbon thin layer (1) when liquids with different refractive indices are dropped, and save the photos;

[0041] Step S4: Input the stored photo into Photoshop software for processing, select the area in the amorphous carbon cube with the initial colors of purple, green and blue, extract the Hue values ​​of these three colors under different refractive indices, record them multiple times and take the average value, plot them on the CIE1931 coordinate system, and judge the color change.

[0042] Step S5: Analyze the sensor sensitivity under the three color conditions, and finally select the color with the highest sensitivity and draw the relationship between its color Hue value and the refractive index of the liquid;

[0043] Step S6: Then, the liquid to be tested is added to the purple sample surface, and the color of the amorphous carbon surface is recorded. The Hue value is extracted by inputting it into Photoshop. The relationship between the liquid refractive index and the Hue value is compared to obtain the refractive index corresponding to this Hue value, thus realizing refractive index sensing. Example 1

[0044] A method for fabricating a refractive index sensor based on structural color: A polyimide film with a thickness of 50 μm is selected, and then a carbon dioxide laser with a wavelength of 10.6 μm is used. The scanning speed, power, scanning linewidth and other parameters of the laser are controlled by computer software to control the degree of carbonization of the polyimide by laser ablation. Different laser parameters result in different colors of amorphous carbon.

[0045] A multicolored structural color was fabricated using a carbon dioxide laser with a scanning speed of 40 mm / s and a power of 1.2 W; a blue color was fabricated at a scanning speed of 40 mm / s and a power of 1.8 W; and a silver structural color was fabricated at a scanning speed of 50 mm / s and a power of 2.7 W. Subsequently, a microscopic imaging system was used to observe the amorphous carbon materials fabricated with different laser parameters. Figure 8 As shown, Figure 8The amorphous carbon generated under the laser parameters corresponding to the region marked "(1)" has a silver microstructure. The amorphous carbon generated under the laser parameters corresponding to the region marked "(2)" has a blue microstructure in most areas. The amorphous carbon generated under the laser parameters corresponding to the region marked "(3)" has a microstructure in various colors such as purple, green, and yellow. Figure 8 Under the laser parameters corresponding to the upper left corner marked "(4)", the laser power density acting on the PI film surface is relatively large, which makes the PI film easy to break during the processing, the device cannot be used, and there is no color. Figure 8 The area marked "(4)" in the lower right corner corresponds to the laser parameters. Due to the low laser power, the PI film is not carbonized and there is no color. That is, a refractive index sensor can only be fabricated within the appropriate laser parameter range.

[0046] like Figure 2 As shown, the Raman spectra of samples in silver, colored, and PI conditions were tested. The figure shows three typical characteristic peaks: the D peak, the G peak, and the 2D peak. The D peak (~1350 cm⁻¹) represents a defect peak, reflecting structural defects or edges. The G peak (~1580 cm⁻¹) reflects its symmetry and crystallinity, generated by the stretching motion of all sp² atom pairs in the carbon ring or long chain. Typically, the intensity ratio of the D and G peaks is used to measure the disorder of carbon materials. The 2D peak (~2700 cm⁻¹) describes the number of graphene layers; the fewer the layers, the sharper the peak and the smaller its half-width. By comparing the Raman spectra of silver and colored samples with those of PI, it is shown that as the laser energy gradually increases, the material generated by laser-induced PI gradually transforms from amorphous carbon into graphene, while the structural color gradually changes from colored to silver.

[0047] like Figure 3 As shown, Figure 3 (a) and Figure 3 (b) are images of the surfaces of the silver sample and the colored sample under an electron microscope. By comparison, it can be seen that the surface of the colored sample is relatively smooth, but there are also some small pores, which facilitates the addition of liquid into the interior of the amorphous carbon material. Figure 3 (c) and Figure 3(d) are electron microscope images of the sides of the silver and multicolored samples, respectively. Both the multicolored and silver amorphous carbon materials contain numerous pores. However, by comparison, the multicolored sample contains a cavity structure with a size of approximately 1 μm. Because the surface of the amorphous carbon material is relatively smooth and contains numerous pores, it is believed that the surface and interior form a FP cavity structure, selectively reflecting visible light and thus producing multicolored structural colors. Different colors indicate different cavity lengths. The presence of pores both inside and on the surface of the amorphous carbon material facilitates the inflow of liquids; by adding liquids with different refractive indices, the color of the structural color surface can be altered. Example 2

[0048] An analysis method based on a structural color refractive index sensor includes the following steps:

[0049] like Figure 4 As shown, in Figure 4 (a) Purple, green, blue, and yellow regions were selected from the amorphous carbon with multicolored structural colors, and their spectra were measured using a spectrometer. The measurement results are as follows: Figure 4 As shown in (d). Based on the FP cavity theory, the reflection spectra of purple, green, blue, and yellow were simulated using MATLAB software. The simulation results are shown in (d). Figure 4 As shown in (c), the simulated and experimental spectra are in good agreement, confirming that the structural color is caused by FP cavity interference. After the FP cavity is fixed, liquids with different refractive indices are added to the surface, and the reflected light changes with the refraction of the liquid. Subsequently, amorphous carbon regions with initial colors of purple, green, and blue were selected, and liquids with different refractive indices were added to their surfaces to analyze the color changes.

[0050] like Figure 5 As shown, three samples with initial colors of blue, purple, and green were selected in the experiment. When liquids with different refractive indices were added to their surfaces, the reflectance spectra of their surface colors were plotted on a CIE-Yxy coordinate graph, where the initial colors were ① purple, ② blue, and ③ green. Figure 5 As can be seen, the purple sensor has the widest color gamut distribution, so purple samples can be selected for practical applications. For example... Figure 6 As shown, Figure 6 (a) shows the surface color as the refractive index changes from the initial purple color captured in the experiment. Figure 6 (b) is a graph showing the change of Hue value for purple liquid with the refractive index of the liquid. Example 3

[0051] An analytical method based on a structural color refractive index sensor is proposed, which is portable, simple, and universally applicable to refractive index sensor analysis through a microscope, a mobile phone, and the mobile phone's built-in light source. First, data on the changes in color with refractive index under three conditions—purple, green, and blue—based on a magnifying lens, a mobile phone camera, and a light source, are input into software and compiled into a small program installed on a mobile phone. The mobile phone's built-in camera and light source, combined with a commercially available microscope, are directly attached to the surface of the structural color sample, and the sample is kept stationary. Then, a liquid is added, and the mobile phone software can directly calculate the refractive index and other relevant parameters of the liquid by identifying the color of the reflected light.

[0052] The above description is merely an embodiment of the present invention and is not intended to limit the 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 principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A refractive index sensor based on structural color, characterized in that: It is made from amorphous carbon materials; The amorphous carbon material has a three-dimensional porous structure, and the refractive index sensor is constructed using a three-dimensional porous structure. The refractive index sensor includes a first amorphous carbon thin layer (1) and a second amorphous carbon layer (3), and the first amorphous carbon thin layer (1) and the second amorphous carbon layer (3) form an FP cavity reflector; the FP cavity reflector is an air layer (2), and a refractive index liquid is added in the air layer (2); The method for fabricating a refractive index sensor is as follows: A polyimide film of a certain thickness is selected and placed at the focal point of a laser. The laser is controlled to etch rectangular amorphous carbon blocks on the surface of the polyimide film. During the laser ablation of the polyimide film, the scanning speed and power of the laser can be controlled to control the internal structure of the generated amorphous carbon material.

2. A refractive index sensor based on structural color according to claim 1, characterized in that: The laser is a carbon dioxide laser with a power range of 0-30W and a scanning speed range of 0-1000 mm / s.

3. The refractive index sensor based on structural color according to claim 1, characterized in that: The first amorphous carbon thin layer (1) and the second amorphous carbon layer (3) are not the same. The thickness of the first amorphous carbon thin layer (1) is 100 nm, and the thickness of the second amorphous carbon layer (3) is in the range of 40-100 μm.

4. A refractive index sensor based on structural color according to claim 1, characterized in that: The polyimide film is selected with a thickness of 50μm, and the laser is controlled to etch 1cm*1cm rectangular amorphous carbon blocks on the surface of the polyimide film.

5. A test system for a liquid refractive index sensor based on a refractive index sensor generated according to any one of claims 1-4, characterized in that: The testing system includes a microscopic imaging system and image processing software. The microscopic imaging system includes an optical camera with recording function and a display. The image processing software is Photoshop.

6. The testing system for a liquid refractive index sensor according to claim 5, characterized in that: The optical camera is replaced by a mobile phone lens with microscopic function combined with a mobile phone.

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