Intermediate infrared molecular sensor with ultrathin gold micro-nano structure and preparation method of intermediate infrared molecular sensor

Abstract

The invention discloses a preparation method of an intermediate infrared molecular sensor with an ultrathin gold micro-nano structure. The preparation method comprises the following steps: S1, spin-coating a substrate with photoresist; s2, evaporating a metal film on the surface of the photoresist; s3, exposing the metal film to form a preset structure pattern which is a haplotype nanorod array antenna structure or a dimer type nanorod array antenna structure; s4, after the metal film is removed through corrosive liquid, low-temperature developing and fixing treatment is carried out on the structure pattern; and S5, evaporating an ultrathin gold film with the thickness of less than 10nm on the structural pattern, and then stripping the photoresist and the metal layer covering the photoresist, thereby obtaining the intermediate infrared molecular sensor with the ultrathin gold micro-nano structure. The sensor can realize molecular sensing detection of mid-infrared broadband response, and the highest detection sensitivity can reach single-layer molecules.

Description

Technical Field

[0001] The invention relates to a mid-infrared molecular sensor with an ultra-thin gold micro-nano structure and a preparation method thereof, and belongs to the technical field of infrared spectrum testing. Background Art

[0002] An infrared sensor is a device that can detect infrared radiation and convert it into an electrical signal. These sensors are usually based on the principle of the photoelectric effect, that is, when infrared radiation shines on the sensitive element of the sensor, it excites electrons, resulting in a change in current or voltage. Other infrared sensors use the thermal effect, where the infrared radiation is absorbed and converted into heat energy, causing a change in the sensor's temperature, which in turn generates an electrical signal. They are widely used in many fields such as environmental monitoring, industrial automation, medical diagnosis, military and security.

[0003] Mid-infrared molecular sensors are specially designed devices that are specifically used to detect radiation in the mid-infrared region (wavelength range is approximately 2~20 microns), which is also called the "molecular fingerprint region". In this specific wavelength range, many gas molecules absorb light waves of specific wavelengths due to their molecular vibrations, such as carbon dioxide (CO2) at 4.5 microns, methane (CH4) at 3.25~3.45 microns, hydrogen fluoride (HF) at 2.33~2.78 microns, sulfur dioxide (SO2) at 7.14~7.52 microns, etc. Therefore, mid-infrared molecular sensors can be used to detect and analyze the composition and concentration of these gases.

[0004] However, the response range of existing mid-infrared molecular sensors is relatively narrow, usually only tens to hundreds of wave numbers, which makes it difficult for them to cover the entire mid-infrared band. In addition, the detection sensitivity of these sensors is limited, making it quite difficult to detect single-layer molecules. Summary of the invention

[0005] The present invention provides a mid-infrared molecular sensor with an ultrathin gold micro-nano structure and a preparation method thereof, which can effectively solve the above problems.

[0006] The present invention is achieved in that: A method for preparing a mid-infrared molecular sensor with an ultrathin gold micro-nano structure comprises the following steps: S1, spin coating the photoresist on the substrate; S2, evaporating a metal film on the surface of the photoresist; S3, exposing the metal film to form a preset structural pattern, wherein the structural pattern is a monomeric nanorod array antenna structure or a dimer nanorod array antenna structure; S4, after removing the metal film using an etching solution, performing low-temperature development and fixing treatment on the structure pattern; S5, vapor-depositing an ultra-thin gold film with a thickness of less than 10 nm on the structural pattern, and then stripping off the photoresist and the metal layer covering it, thereby obtaining the ultra-thin gold micro-nanostructure mid-infrared molecular sensor.

[0007] In some embodiments, the substrate includes one or more of calcium fluoride, barium fluoride, magnesium fluoride, gallium nitride, silicon carbide, silicon nitride, silicon oxide, and silicon.

[0008] In some embodiments, the photoresist is electron beam photoresist or ultraviolet photoresist, and the thickness of the photoresist is 80-120 nm.

[0009] In some embodiments, the metal of the metal film includes one of gold, aluminum, and chromium, and the thickness of the metal film is 10-20 nm.

[0010] In some embodiments, the corrosive liquid includes one or more of a sodium hydroxide solution, a potassium hydroxide solution, a tetramethylammonium hydroxide solution, aqua regia, and a cerium ammonium nitrate solution.

[0011] In some embodiments, the structural unit parameters of the monomeric nanorod array antenna structure pattern are: length 750nm, width 50nm, thickness 3nm, array unit spacing 100nm, and array area 100μm×100μm.

[0012] In some embodiments, the structural unit parameters of the dimer-type nanorod array antenna structure pattern are: length 750nm, width 50nm, thickness 3nm, dimer unit spacing 10nm, array unit spacing 100nm, and array area 100μm×100μm.

[0013] In some embodiments, the step of evaporating an ultra-thin gold film on the structure pattern comprises placing a sample of the structure pattern in an electron beam evaporation system, wherein the vacuum degree of the cavity to be evaporated is less than 9×10 -8 torr, a copper film with a thickness of 0.5nm to 1nm is deposited by evaporation. After the deposition is completed, the sample is placed in the atmosphere for natural oxidation. The sample is then placed in an electron beam evaporation system until the vacuum degree of the evaporation chamber is less than 9×10 -8 torr, an ultra-thin gold film with a thickness of less than 10nm is deposited by evaporation.

[0014] In some embodiments, the temperature of the low-temperature development and fixing is -20 to -15°C.

[0015] A mid-infrared molecular sensor with an ultrathin gold micro-nanostructure prepared by the above method.

[0016] The beneficial effects of the present invention are: The enhanced infrared range of the mid-infrared molecular sensor of the ultra-thin gold micro-nanostructure of the present invention covers 1000-4000cm -1 , with the characteristics of wide-band enhanced infrared.

[0017] The ultra-thin gold micro-nanostructured mid-infrared molecular sensor of the present invention has a strong ability to enhance molecular infrared absorption, has high detection sensitivity, and can detect the infrared absorption spectrum of a single layer of molecules at most.

[0018] The thickness of the ultra-thin gold film of the mid-infrared molecular sensor with an ultra-thin gold micro-nano structure of the present invention is less than 10 nm, which is much smaller than the common surface enhanced infrared sensor, and is conducive to the integration and miniaturization of the sensor device. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 The flowchart of the preparation of the ultra-thin gold micro-nanostructure mid-infrared molecular sensor of the embodiment of the present invention is shown in FIG. 1 , wherein the symbol 1 represents the substrate; the symbol 2 is the photoresist with a predefined structure pattern; the symbol 3 is the conductive layer metal; the symbol 4 is the copper seed layer (adhesion layer) required to construct the ultra-thin gold film; and the symbol 5 is the ultra-thin gold film with a thickness of less than 10 nm.

[0021] Figure 2 The figure is a schematic diagram of the process of self-assembling a monolayer on an ultra-thin gold micro-nanostructured mid-infrared molecular sensor. In which, the symbol 1 is the substrate required for the sensor; the symbols 2 and 3 are the materials Cu and Au used to construct the ultra-thin gold micro-nanostructured mid-infrared molecular sensor, and 2 and 3 together constitute a nanostructure with a specific enhancement effect; 4 is a monolayer self-assembled on the ultra-thin gold micro-nanostructured mid-infrared molecular sensor.

[0022] Figure 3 Scanning electron microscope imaging of a mid-infrared molecular sensor with an ultrathin gold micro-nano monomer structure prepared under the specific parameters of Example 1.

[0023] Figure 4 Scanning electron microscope imaging of the ultrathin gold micro-nano dimer structure infrared sensor prepared under the specific parameters of Example 2.

[0024] Figure 5 The concentration is 10 -9Comparison of the infrared absorption signals of octadecanethiol (ODT) molecules on a clean calcium fluoride substrate and adsorbed on a 3nm flat ultra-thin gold film surface.

[0025] Figure 6 It is the infrared absorption signal of a 3nm thick flat ultra-thin gold film prepared under specific parameters and a 3nm ultra-thin gold micro-nano monomer structure mid-infrared molecular sensor prepared under specific parameters after simultaneously assembling a single layer of ODT molecules.

[0026] Figure 7 The ultrathin gold micro-nano monomer structure mid-infrared molecular sensor and the ultrathin gold micro-nano dimer structure mid-infrared molecular sensor are at 1460cm -1 and 2800-3000cm -1 The two bands simultaneously enhance the contrast of the infrared absorption signal intensity of the methylene functional groups of the monolayer ODT molecules.

[0027] Figure 8 It is a signal diagram of the ultra-thin gold micro-nanostructure mid-infrared molecular sensor for enhanced infrared testing of ODT molecules of different concentrations and the infrared testing of ODT molecules without enhancement as a reference example.

[0028] Fig. 9 This is the signal diagram of the ultra-thin gold micro-nanostructure mid-infrared molecular sensor for enhanced infrared testing of mercaptopropionic acid (3-MPA) molecules of different concentrations and the infrared test of 3-MPA molecules without enhancement as a reference example.

[0029] Fig.10 (a) is a comparison of the vibration signal intensity of the ultrathin gold micro-nano dimer structure infrared sensor with different dimer structure unit spacing at a thickness of 3nm, a length of 750nm, and a width of 50nm to enhance the infrared vibration absorption of the ODT monolayer; (b) is a schematic diagram of the mid-infrared molecular sensor with an ultrathin gold micro-nano dimer structure.

[0030] Fig.11 (a) is a comparison chart of the vibration signal intensity of the mid-infrared molecular sensor with ultra-thin gold micro-nano monomer structure under the unit structure of the figure, which enhances the infrared vibration absorption of the ODT monolayer; (b) is a schematic diagram of the mid-infrared molecular sensor with ultra-thin gold micro-nano monomer structure.

[0031] Fig.12 This is a scanning electron microscope image of a mid-infrared molecular sensor of ultrathin gold micro-nano dimer structure with different dimer structural unit spacing sizes prepared under specific parameters as shown in the figure.

[0032] Fig.13 Scanning electron microscope imaging of mid-infrared molecular sensors with ultrathin gold micro-nano monomer structures of different structural unit sizes prepared under specific parameters as shown in the figure. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] The embodiment of the present invention provides a method for preparing a mid-infrared molecular sensor of an ultrathin gold micro-nanostructure, which involves a series of delicate steps to ensure the performance and accuracy of the final product. The specific steps are as follows: S1, first, a layer of photoresist with a specific thickness is evenly spin-coated on a suitable substrate at a specific spin-coating speed and a specific spin-coating acceleration. The thickness must not only ensure the exposure accuracy, but also facilitate the final metal stripping step.

[0035] S2, then, a metal film is evaporated on the surface of the spin-coated photoresist, which will serve as a conductive layer in the subsequent steps. The material selection and thickness control of the metal film are crucial to the performance of the entire sensor.

[0036] S3, then, performing an exposure operation on the metal film to form a predefined structural pattern. These structural patterns can be monomeric nanorod array antenna structural patterns or dimer nanorod array antenna structural patterns. The design and layout of these patterns have a direct impact on the sensitivity and selectivity of the sensor.

[0037] S4, after the exposure is completed, a specific etching solution is used to remove the metal film portion not covered by the pattern. Subsequently, the structural pattern is subjected to low-temperature development and fixing treatment to ensure the accuracy and stability of the pattern.

[0038] S5, then, evaporate a layer of ultra-thin gold film on the formed structure pattern. The thickness of this gold film must be less than 10nm to ensure that it has special optical and electrical properties. Finally, by stripping off the photoresist and the metal covering the photoresist, the desired ultra-thin gold micro-nanostructure mid-infrared molecular sensor can be obtained.

[0039] The key to the present invention is to expose a predefined structural pattern on the metal film, which allows the ultra-thin metal film to be precisely designed and cut to form a specific nanostructure. This structured metal film can effectively localize infrared light on its surface, thereby amplifying the intensity of the local infrared optical electric field. This enhanced localized optical electric field significantly enhances the interaction between infrared light and the substance to be tested, thereby improving the sensitivity of infrared spectroscopy detection.

[0040] In addition, when the thickness of the ultra-thin gold film is less than 10nm, the gold film will exhibit some special optical and electrical properties, such as high broadband infrared absorption, electrically adjustable plasmons, nonlinear optical response, and quantum optical effects. By further designing and cutting the ultra-thin metal film, these special properties can be optimized and regulated, thereby further improving the performance of the sensor. This ultra-thin gold micro-nanostructure only needs to be adjusted within the above-mentioned parameter range to achieve mid-infrared wide-band response.

[0041] The ultrathin gold micro-nanostructured mid-infrared molecular sensor of the present invention performs well in enhancing the infrared range, covering 1000-4000cm -1 This wide-band enhanced infrared property enables the sensor to have a strong ability to enhance molecular infrared absorption, thereby achieving high-sensitivity detection. Under optimal conditions, the sensor can even detect the infrared absorption spectrum of a single layer of molecules, which has important application value in the field of molecular detection.

[0042] In some specific embodiments, the substrate material may include one or more of calcium fluoride, barium fluoride, magnesium fluoride, gallium nitride, silicon carbide, silicon nitride, silicon oxide, and silicon. Before the substrate material is used in a specific application, it needs to be thoroughly cleaned. The cleaning step includes the following steps: First, the substrate material is placed in two organic solvents, acetone and ethanol, and ultrasonic cleaning is performed respectively, each lasting for 5 minutes. Ultrasonic cleaning helps to remove tiny particles and organic pollutants on the surface of the substrate. Next, the substrate material is thoroughly rinsed with a large amount of deionized water to remove residual organic solvents and other soluble impurities. After rinsing, the substrate material is blown dry with nitrogen to ensure that there is no moisture remaining on the surface. Finally, the cleaned substrate material is placed on a hot plate at 180°C and baked for 5 minutes, in order to further remove residual water vapor and other volatile substances on the surface of the substrate, and ensure the purity and reliability of the substrate material in subsequent processes. Through this series of cleaning steps, it can be ensured that the substrate material reaches the required cleanliness and surface quality before use.

[0043] In some specific embodiments, the photoresist used may be an electron beam photoresist or an ultraviolet photoresist. For the electron beam photoresist, it may be a material such as polymethyl methacrylate (PMMA) or styrene methacrylate (ZEP520). For the ultraviolet photoresist, it may be a positive-negative switchable photoresist (e.g., AZ5214E). In addition, the thickness of these photoresists is usually controlled between 80nm and 120nm to ensure that high-precision and high-resolution patterns can be obtained during the photolithography process.

[0044] In some embodiments, the metal of the metal film includes one of gold, aluminum, and chromium, and is a conductive layer. The thickness of the metal film is 10-20 nm.

[0045] In some embodiments, the corrosive liquid includes one or more of a sodium hydroxide solution, a potassium hydroxide solution, a tetramethylammonium hydroxide solution, aqua regia, and a cerium ammonium nitrate solution.

[0046] In some embodiments, the structural unit parameters of the monomer nanorod array antenna structure pattern are: length 750nm, width 50nm, thickness 3nm, array unit spacing 100nm, array area 100μm×100μm. Through this fine cutting and design, the obtained ultra-thin gold micro-nano monomer structure mid-infrared molecular sensor has shown a significant improvement in detection performance, and its detection sensitivity has been significantly enhanced.

[0047] In some embodiments, the structural unit parameters of the dimer-type nanorod array antenna structure pattern are: length 750nm, width 50nm, thickness 3nm, dimer unit spacing 10nm, array unit spacing 100nm, array area 100μm×100μm. Compared with the ultra-thin gold micro-nano monomer structure mid-infrared molecular sensor designed under specific parameters, the ultra-thin gold micro-nano dimer structure infrared sensor with further optimized design has been significantly improved in performance. This further enhancement of performance fully demonstrates the optimization and improvement of micro-nano optical design in enhancing sensing detection performance.

[0048] In some embodiments, the process of evaporating an ultra-thin gold film on the structure pattern includes placing a sample of the structure pattern in an electron beam evaporation system, and waiting for the evaporation cavity to reach a volume of less than 9×10 -8 After the vacuum degree of 100 torr is reached, a copper film with a thickness of 0.5nm to 1nm is first deposited by evaporation as a seed layer. After the deposition is completed, the sample is moved to the atmosphere for natural oxidation treatment; then, the sample is placed in the electron beam evaporation system again until the vacuum degree of the evaporation chamber reaches less than 9×10 -8torr, an ultra-thin gold film with a thickness of less than 10nm is deposited by evaporation. The seed layer is crucial to the formation of the ultra-thin gold film thickness, which makes it possible to prepare ultra-thin metal micro-nano devices with a thickness of less than 10nm. By combining semiconductor process technology, we have explored related preparation processes, so that the structural style of ultra-thin metal devices can be freely defined, and the preparation area of ​​ultra-thin metal films is only limited by the size of the evaporation chamber, thereby enabling the preparation of large-area ultra-thin metal devices.

[0049] In some embodiments, the temperature of the low temperature development and fixing is -20-15°C.

[0050] A mid-infrared molecular sensor with ultrathin gold micro-nanostructures prepared by a specific method. This sensor utilizes the unique optical properties of gold micro-nanostructures and can achieve high-sensitivity detection of molecules in the mid-infrared band. By precisely controlling the size and shape of the gold micro-nanostructures, its response characteristics to specific molecules can be further optimized, thereby improving the accuracy and reliability of detection. This sensor has broad application prospects in environmental monitoring, medical diagnosis, food safety and other fields.

[0051] The embodiment of the present invention relates to an infrared spectrum test method for a mid-infrared molecular sensor of an ultra-thin gold micro-nano structure. The method comprises immersing the mid-infrared sensor of an ultra-thin gold micro-nano structure in a solution containing thiol molecules (the solution may contain one or more of octadecyl mercaptan, hexadecanethiol, 3-mercaptopropionic acid, cysteine, thioglycolic acid, N-acetylcysteine, mercaptobenzoic acid, mercaptopropanol, and 2-mercaptoethanol) to achieve self-assembly, thereby obtaining an ultra-thin gold micro-nano structure infrared sensor loaded with a monolayer of molecules. In addition, a molecular solution of a specific concentration may be added dropwise to the surface of the ultra-thin gold micro-nano structure infrared sensor by titration. Subsequently, an infrared spectrum test is performed on the ultra-thin gold micro-nano structure infrared sensor loaded with a monolayer of molecules.

[0052] Example 1 This example introduces a method for preparing a wide-band mid-infrared molecular sensor based on an ultrathin gold micro-nanostructure, and the specific steps are as follows: Step 1: The calcium fluoride substrate was ultrasonically treated in acetone and ethanol for 5 minutes each, then thoroughly rinsed with a large amount of deionized water and dried with nitrogen. After that, the substrate was placed on a hot plate at 180°C and baked for 5 minutes to remove residual moisture on the surface.

[0053] Step 2: Spin-coat a 100 nm thick layer of polymethyl methacrylate electron beam photoresist (PMMA) on the treated calcium fluoride substrate and bake it on a hot plate at 180 °C for 3 min to cure the PMMA and remove excess solvent.

[0054] Step 3: Evaporate a 15nm thick aluminum film on the PMMA-coated substrate as a conductive layer.

[0055] Step 4: Expose the designed monomeric nanorod array antenna structure pattern using an electron beam lithography system. The structural unit parameters are set as follows: length 750nm, width 50nm, thickness 3nm, array unit spacing 100nm, and array area 100μm×100μm. Under specific exposure parameters, the exposure dose is 25C / m². After exposure, the sample is immersed in a sodium hydroxide solution with a mass fraction of 1% and ultrasonically treated to corrode the aluminum film. Next, the sample needs to be rinsed with deionized water several times and blown dry with nitrogen. Then, the sample is placed in a low-temperature developer (methyl isobutyl ketone: isopropanol = 1:3 mixture) and a fixer (isopropanol) at −16°C for low-temperature development and fixing. Finally, the sample is blown dry with nitrogen to obtain a photoresist pattern structure with a monomeric nanorod array.

[0056] Step 5: Place the structured photoresist pattern into the electron beam evaporation system and place it in a vacuum chamber with a degree of less than 9×10 -8 After 100 torr, a 1nm thick copper film was deposited as a seed layer. After the deposition was completed, the sample was taken out and placed in the atmosphere for natural oxidation for 10 minutes. Subsequently, the sample was placed in the electron beam evaporation system again and an ultra-thin gold layer with a thickness of 3nm was evaporated under the same vacuum degree.

[0057] Step 6: Place the sample with the evaporated ultra-thin metal film in a photoresist stripping solution and let it stand to remove the photoresist and the metal layer thereon, and finally obtain a mid-infrared molecular sensor with an ultra-thin gold micro-nano monomer structure.

[0058] The prepared ultra-thin gold micro-nano monomer structure mid-infrared molecular sensor was tested by microscopic infrared spectroscopy. The specific steps are as follows: The sensor was immersed in an ethanol solution of 1mM octadecyl mercaptan molecules, taken out after 12 hours of self-assembly, and physically adsorbed octadecyl mercaptan molecules were washed away with a large amount of ethanol (more than 500mL). After washing, it was dried with nitrogen to obtain a mid-infrared molecular sensor with an ultra-thin gold micro-nano monomer structure loaded with an octadecyl mercaptan monolayer.

[0059] The sensor loaded with monolayer molecules was tested by microscopic infrared spectroscopy. A Bruker Lumos II Fourier transform microscopic infrared spectrometer was used, the detection aperture size was set to 50 μm × 50 μm, the detector was a mercury cadmium telluride (MCT) detector equipped with liquid nitrogen cooling, and the resolution was selected to be 8 cm -1 , the background is a structureless blank calcium fluoride substrate.

[0060] In Example 1, the preparation and self-assembly process of the ultrathin gold micro-nano monomer structure mid-infrared molecular sensor is as follows: Figure 1 , 2 The surface morphology scanning electron microscope characteristic diagram is shown in Figure 3 shown.

[0061] Comparative Example 1 The difference from Example 1 is that the electron beam lithography system is not used to expose the designed monomeric nanorod array antenna structure pattern to prepare a 3 nm thick flat ultra-thin gold film, and other operations are the same as Example 1.

[0062] like Figure 6 As shown, the infrared absorption signal comparison of a 3nm thick flat ultra-thin gold film (Comparative Example 1) prepared under specific parameters and a 3nm ultra-thin gold micro-nanostructure infrared sensor (Example 1) prepared under the same parameters after assembling a single layer of ODT molecules is shown. It can be observed that compared with the 3nm flat ultra-thin gold film without any micro-nanostructure, the carefully designed ultra-thin gold micro-nano monomer structure mid-infrared molecular sensor performs better in detection sensitivity. Specifically, the sensor detects the 2800-3000cm -1 The absorption peak of the methylene functional group (stretching vibration) showed a higher signal intensity and the ODT molecule could be detected at 1460 cm -1 The absorption peak of (bending vibration of methylene functional group) is detected, but this signal cannot be detected on the surface of 3nm flat ultra-thin gold film.

[0063] Example 2 This example introduces a method for preparing a wide-band mid-infrared molecular sensor based on an ultrathin gold micro-nanostructure, and the specific steps are as follows: Step 1: Immerse the calcium fluoride substrate in acetone and ethanol successively, perform ultrasonic treatment for 5 minutes each, then rinse thoroughly with a large amount of deionized water and blow dry with nitrogen. Next, bake the cleaned substrate on a hot plate at 180°C for 5 minutes to remove residual moisture on the surface.

[0064] Step 2: Spin-coat a 100 nm thick layer of polymethyl methacrylate electron beam photoresist (PMMA) on the treated calcium fluoride substrate and bake it on a hot plate at 180 °C for 3 min to cure the PMMA and remove excess solvent.

[0065] Step 3: Evaporate a 15nm thick aluminum film on the PMMA-coated substrate as a conductive layer.

[0066] Step 4: In order to contrast with the mid-infrared molecular sensor with ultrathin gold micro-nano monomer structure, the designed dimer nanorod array antenna structure pattern with enhanced effect was exposed using an electron beam lithography system. The structural unit parameters were set as follows: length 750nm, width 50nm, thickness 3nm, dimer unit spacing 10nm, array unit spacing 100nm, and array area 100μm×100μm. Under specific exposure parameters, the exposure dose was 22C / m². After exposure, the sample was ultrasonically etched in a 1% sodium hydroxide solution to remove the aluminum film on the surface of the photoresist. Subsequently, the sample was rinsed with deionized water several times and dried with nitrogen. Next, the sample was low-temperature developed and fixed in a low-temperature developer (methyl isobutyl ketone: isopropanol = 1:3 mixture) and a fixer (isopropanol) at −16°C. Finally, the sample was dried with nitrogen to obtain a photoresist pattern structure with a dimer nanorod array.

[0067] Step 5: Place the sample in the electron beam evaporation system and set the vacuum degree of the evaporation chamber to 9×10 -8 After 0.1 torr, a 1nm thick copper film was deposited as a seed layer. After the deposition was completed, the sample was taken out and placed in the atmosphere for natural oxidation for 10 minutes, and then put into the electron beam evaporation system again to evaporate a 3nm thick ultra-thin gold layer under the same vacuum degree.

[0068] Step 6: Place the sample with the evaporated ultra-thin metal film in a photoresist stripping solution and let it stand to remove the photoresist and the metal layer on it, and finally obtain a mid-infrared molecular sensor with an ultra-thin gold micro-nano dimer structure.

[0069] The ultrathin gold micro-nano dimer structure mid-infrared molecular sensor loaded with octadecanethiol monolayer was tested by microscopic infrared spectroscopy. A Bruker Lumos II Fourier transform microscopic infrared spectrometer was used, the detection aperture size was set to 50μm×50μm, the detector was a liquid nitrogen cooled mercury cadmium telluride (MCT) detector, and the resolution was selected to be 8cm -1 , a blank calcium fluoride substrate with no structure was used as the background.

[0070] In Example 2, the preparation and self-assembly process of the ultrathin gold micro-nano dimer structure mid-infrared molecular sensor is as follows: Figure 1 , 2 The surface morphology scanning electron microscope characteristic diagram is shown in Figure 4 shown.

[0071] Figure 7 The ultrathin gold micro-nano monomer structure mid-infrared molecular sensor (Example 1) and the ultrathin gold micro-nano dimer structure mid-infrared molecular sensor (Example 2) were demonstrated at 1460cm -1 and 2800-3000cm -1Comparison of the infrared absorption signal intensity of the methylene functional group of the monolayer ODT molecule in the two bands. Compared with the mid-infrared molecular sensor with ultra-thin gold micro-nano monomer structure designed under specific parameters, the enhancement factor of the mid-infrared molecular sensor with further optimized ultra-thin gold micro-nano dimer structure is increased by nearly 2.6 times, which fully proves the optimization effect of micro-nano optical design in improving sensing detection performance.

[0072] Comparative Example 2: Infrared test of different concentrations of ODT molecules dripped on a clean calcium fluoride substrate Step 1: Place the calcium fluoride substrate in acetone and ethanol, respectively, and ultrasonically treat for 5 minutes each. After being thoroughly cleaned with a large amount of deionized water, blow dry with nitrogen, and bake on a hot plate at 180°C for 5 minutes to remove residual moisture on the surface.

[0073] Step 2: Pipette 20 μL of octadecyl mercaptan ethanol solution of a specific concentration and titrate it onto a clean blank calcium fluoride substrate, and allow the droplet to air dry naturally.

[0074] Step 3: Microscopic infrared spectroscopy test of calcium fluoride substrate carrying octadecyl mercaptan molecules was performed using a Bruker Lumos II Fourier transform microscopic infrared spectrometer, with the detection aperture size set to 50 μm × 50 μm, and the detector being a liquid nitrogen cooled mercury cadmium telluride (MCT) detector with a resolution of 8 cm -1 , a clean blank calcium fluoride substrate without molecules was used as the background.

[0075] Comparative Example 2 shows the infrared test results of different concentrations of ODT molecules dripped on a clean calcium fluoride substrate. -1 The intensity of the infrared characteristic peak increases with the increase of concentration, such as Figure 8 As shown in the right figure. This comparative example serves as a control for dropping ODT molecules on the ultra-thin gold micro-nanostructure mid-infrared molecular sensor, verifying the enhanced detection capability of the ultra-thin gold micro-nanostructure mid-infrared molecular sensor.

[0076] Comparative Example 3: Infrared test of different concentrations of 3-MPA molecules dropped on a clean calcium fluoride substrate Step 1: Place the calcium fluoride substrate in acetone and ethanol, respectively, and ultrasonically treat for 5 minutes each. After being thoroughly cleaned with a large amount of deionized water, blow dry with nitrogen, and bake on a hot plate at 180°C for 5 minutes to remove residual moisture on the surface.

[0077] Step 2: Pipette 20 μL of 3-mercaptopropionic acid ethanol solution of a specific concentration and titrate it onto a clean blank calcium fluoride substrate, and allow the droplet to air-dry naturally.

[0078] Step 3: Perform microscopic infrared spectroscopy on the calcium fluoride substrate carrying 3-mercaptopropionic acid molecules. A Bruker Lumos II Fourier transform microscopic infrared spectrometer was used, with the detection aperture size set to 50 μm × 50 μm, and the detector was a liquid nitrogen cooled mercury cadmium telluride (MCT) detector with a resolution of 8 cm -1 , a clean blank calcium fluoride substrate without molecules was used as the background.

[0079] Comparative Example 3 shows the infrared test results of different concentrations of 3-MPA molecules dropped on a clean calcium fluoride substrate. -1 The intensity of the infrared characteristic peak increases with the concentration, such as Fig. 9 As shown in the right figure. This comparative example is used as a control for the addition of 3-MPA molecules onto the ultra-thin gold micro-nanostructured mid-infrared molecular sensor, verifying the universality of the ultra-thin gold micro-nanostructured mid-infrared molecular sensor in enhancing the infrared absorption signals of different molecules.

[0080] Comparative Example 4 verifies the enhancement effect of 3nm ultra-thin gold film The preparation steps of 3nm ultra-thin gold film are as follows: Step 1: Place the calcium fluoride substrate in acetone and ethanol, respectively, and ultrasonically treat for 5 minutes each. After being thoroughly cleaned with a large amount of deionized water, blow dry with nitrogen, and bake on a hot plate at 180°C for 5 minutes to remove residual moisture on the surface.

[0081] Step 2: The vacuum degree of the deposition chamber is reduced to 9×10 -8 Below torr, a 1nm thick copper film was deposited as a seed layer. After the deposition was completed, the sample was taken out and placed in the atmosphere for natural oxidation for 10 minutes. Subsequently, the sample was put back into the electron beam evaporation system and a 3nm thick ultra-thin gold film was evaporated under the same vacuum.

[0082] The detection method steps are as follows: The 3nm ultra-thin gold film was immersed in a 1mM ethanol solution of octadecyl mercaptan molecules and taken out after 12 hours of self-assembly. More than 500mL of ethanol was used to rinse off the physically adsorbed octadecyl mercaptan molecules, and then dried with nitrogen gas to obtain a 3nm ultra-thin gold film loaded with an octadecyl mercaptan monolayer.

[0083] Microscopic infrared spectroscopy was performed on the 3nm ultrathin gold film loaded with a monolayer of octadecyl mercaptan. A Bruker LumosII Fourier transform microscopic infrared spectrometer was used, with the detection aperture size set to 50μm×50μm, and the detector was a liquid nitrogen cooled mercury cadmium telluride (MCT) detector with a resolution of 8cm -1 , a blank calcium fluoride substrate with no structure was used as the background.

[0084] The 3 nm ultra-thin flat gold film prepared in Comparative Example 4 also showed the ability to enhance infrared detection, and was able to detect the single-layer ODT molecules at 2800-3000 cm -1 The infrared characteristic peak of the band is 10 -9 Compared with the mol / LODT molecular solution (on a clean calcium fluoride substrate), the detection signal is significantly enhanced. Figure 5 shown.

[0085] Comparative Example 5 Different structural unit parameters of the monomeric nanorod array antenna structure pattern and different structural unit parameters of the dimer nanorod array antenna structure pattern were set, and other operations were the same as in Example 1. The experimental results are as follows: Figure 10-13 shown.

[0086] like Fig.10 As shown, (a) is a comparison chart of the vibration signal intensity of the infrared vibration absorption of the enhanced ODT monolayer by the ultrathin gold micro-nano dimer structure infrared sensor with different dimer structure unit spacings at a thickness of 3nm, a length of 750nm, and a width of 50nm. It can be seen that as the dimer structure unit spacing of the ultrathin gold micro-nano dimer structure mid-infrared molecular sensor further decreases, the infrared vibration signal of the ODT monolayer is further enhanced; (b) is a schematic diagram of the mid-infrared molecular sensor with an ultrathin gold micro-nano dimer structure, the yellow structure is a schematic diagram of the dimer-type nanorod array antenna structure pattern, and the blue below is the substrate of the sensor.

[0087] like Fig.11 As shown in the figure, (a) this is a comparison of the vibration signal intensity of the ultra-thin gold micro-nano monomer structure mid-infrared molecular sensor under different size unit structures (monomer structure unit length, thickness) to enhance the infrared vibration absorption of the ODT monolayer; (b) is a schematic diagram of the ultra-thin gold micro-nano monomer structure mid-infrared molecular sensor, the yellow structure is the monomer nanorod array antenna structure pattern, the blue below is the sensor substrate, L is the length of the monomer structure unit, and t is its thickness. It can be seen that as the arrangement of the nanorod array increases, the infrared detection intensity of the infrared sensor becomes stronger and stronger.

[0088] like Fig.12As shown, this is the scanning electron microscope imaging of the mid-infrared molecular sensor of the ultrathin gold micro-nano dimer structure with different dimer structure unit spacing sizes prepared under specific parameters. In the figure (a), the scanning electron microscope imaging of the mid-infrared molecular sensor of the ultrathin gold micro-nano dimer structure with a dimer structure unit spacing of 10nm; in the figure (b), the scanning electron microscope imaging of the mid-infrared molecular sensor of the ultrathin gold micro-nano dimer structure with a dimer structure unit spacing of 15nm; in the figure (c), the scanning electron microscope imaging of the mid-infrared molecular sensor of the ultrathin gold micro-nano dimer structure with a dimer structure unit spacing of 20nm.

[0089] like Fig.13 As shown, this is the scanning electron microscope imaging of the mid-infrared molecular sensor of ultrathin gold micro-nano monomer structure with different structural unit sizes (monomer structure unit length, thickness) prepared under specific parameters. In the figure (a), the scanning electron microscope imaging of the mid-infrared molecular sensor of ultrathin gold micro-nano monomer structure with a monomer structure unit length of 500nm and a thickness of 3nm; in the figure (b), the scanning electron microscope imaging of the mid-infrared molecular sensor of ultrathin gold micro-nano monomer structure with a monomer structure unit length of 1000nm and a thickness of 6nm; in the figure (c), the scanning electron microscope imaging of the mid-infrared molecular sensor of gold micro-nano monomer structure with a monomer structure unit length of 1500nm and a thickness of 30nm.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a mid-infrared molecular sensor with an ultrathin gold micro-nanostructure, characterized in that: The following steps are involved: S1, spin coating the photoresist on the substrate; S2, evaporating a metal film on the surface of the photoresist; S3, exposing the metal film to form a preset structural pattern, wherein the structural pattern is a monomeric nanorod array antenna structure or a dimer nanorod array antenna structure; S4, after removing the metal film using an etching solution, performing low-temperature development and fixing treatment on the structure pattern; S5, vapor-depositing an ultra-thin gold film with a thickness of less than 10 nm on the structural pattern, and then stripping off the photoresist and the metal layer covering it, thereby obtaining the ultra-thin gold micro-nanostructure mid-infrared molecular sensor.

2. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The substrate includes one or more of calcium fluoride, barium fluoride, magnesium fluoride, gallium nitride, silicon carbide, silicon nitride, silicon oxide, and silicon.

3. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The photoresist is electron beam photoresist or ultraviolet photoresist, and the thickness of the photoresist is 80-120nm.

4. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The metal of the metal film includes one of gold, aluminum and chromium, and the thickness of the metal film is 10-20 nm.

5. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The corrosive liquid includes one or more of sodium hydroxide solution, potassium hydroxide solution, tetramethylammonium hydroxide solution, aqua regia, and cerium ammonium nitrate solution.

6. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The structural unit parameters of the monomeric nanorod array antenna structure pattern are: length 750nm, width 50nm, thickness 3nm, array unit spacing 100nm, and array area 100μm×100μm.

7. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The structural unit parameters of the dimer-type nanorod array antenna structure pattern are: length 750nm, width 50nm, thickness 3nm, dimer unit spacing 10nm, array unit spacing 100nm, and array area 100μm×100μm.

8. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The method of evaporating the ultra-thin gold film on the structure pattern comprises placing the sample of the structure pattern in an electron beam evaporation system, wherein the vacuum degree of the cavity to be evaporated is less than 9×10 -8 torr, a copper film with a thickness of 0.5nm to 1nm is deposited by evaporation. After the deposition is completed, the sample is placed in the atmosphere for natural oxidation. The sample is then placed in an electron beam evaporation system until the vacuum degree of the evaporation chamber is less than 9×10 -8 torr, an ultra-thin gold film with a thickness of less than 10nm is deposited by evaporation.

9. The method for preparing the ultrathin gold micro-nanostructure mid-infrared molecular sensor according to claim 1, characterized in that: The temperature of the low-temperature developing and fixing is -20~-15°C.

10. A mid-infrared molecular sensor with an ultrathin gold micro-nanostructure prepared by the method according to any one of claims 1 to 9.

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