CN114252952B - Double-layer chiral micro-nano structure and preparation method thereof - Google Patents

Abstract

The application relates to the field of chiral micro-nano structure preparation, in particular to a double-layer chiral micro-nano structure and a preparation method thereof, wherein the upper layer is a first noble metal layer provided with L-shaped holes, the lower layer is a second noble metal layer provided with nanorods, and when different circularly polarized lights irradiate, different couplings are generated between the L-shaped holes and the nanorods, so that resonance intensity is different and transmissivity is different, and strong circular dichroism is generated. In the application, the double-layer chiral micro-nano structure can be prepared by only one time of electron beam etching and one time of noble metal material evaporation, so that the materials and time are saved, and the preparation process steps are simplified. In addition, dynamic regulation and control of circular dichroism can be realized, secondary evaporation can be performed on the basis of the structure, regulation and control of the thickness of a structural film and the thickness of a nanorod are realized, application is flexible and convenient, and the method has good application prospect in the field of chiral micro-nano structure preparation.

Description

A double-layer chiral micro-nano structure and its preparation method

Technical field

The invention relates to the field of preparation of chiral micro-nano structures, and in particular to a double-layer chiral micro-nano structure and a preparation method thereof.

Background technique

Artificial chiral surface plasmon micro-nano structures have stronger interactions with light and have important applications in many fields such as analytical chemistry, biosensing, and circular polarization devices.

At present, the main technologies for preparing artificial chiral surface plasmon micro-nano structures include electron beam etching, laser direct writing, and molecular self-assembly. Electron beam etching can be used to prepare planar artificial chiral surface plasmon micro-nano structures with high precision dimensions. The laser direct writing method can be used to prepare micron-level three-dimensional artificial chiral surface plasmon micro-nanostructures, such as spirals or conical metal spirals. The molecular self-assembly method links molecules and metal nanostructures through chemical bonds to form chiral surface plasmon micro-nanostructures. For example, researchers used DNA double helices as templates to assemble multiple gold nanospheres into double helix-arranged artificial hands. Characteristic surface plasmon micro-nano structures.

The double-layer chiral micro-nano structure has stronger circular dichroism than the single-layer chiral micro-nano structure. For example, the circular dichroism of a double-layered Greek cross nanostructure is much greater than that of a single-layered Greek cross nanostructure. Double-layer chiral micro-nano structures have received widespread attention from researchers.

In the preparation of double-layer chiral micro-nano structures, the molecular self-assembly method cannot be completed, and the laser direct writing method cannot prepare nanometer-sized structural features. This is because the laser wavelength of the laser direct writing method determines the artificial chiral surface plasmon microstructure. The collective size of nanostructures, but the laser wavelength is limited by optical diffraction, making it difficult to prepare nanoscale artificial chiral surface plasmon structures. In the traditional application of electron beam etching, two electron beam etchings are required, and overlay etching is required. The preparation is difficult, takes a long time, and is costly. Therefore, exploring double-layer structures with strong signals and their preparation methods are important research contents in this field.

Contents of the invention

In order to solve the above problems, the present invention provides a double-layer chiral micro-nano structure and a preparation method thereof.

On the one hand, the present invention provides a two-layer chiral micro-nano structure, including a substrate, a second noble metal layer, a transparent dielectric layer, and a first noble metal layer. The transparent dielectric layer is placed on the substrate, and the first noble metal layer is placed on the substrate. On the transparent medium layer, there are penetrating L-shaped holes in the first precious metal layer and the transparent medium layer. The L-shaped holes are arranged periodically. The L-shaped holes include a first arm of the hole and a second arm of the hole. The second precious metal layer includes a periodic arrangement. The nanorods are placed in the second arm of the hole on the substrate.

Furthermore, the material of the substrate is conductive glass.

Furthermore, the L-shaped hole is a right-angled L-shape.

Furthermore, the material of the first precious metal layer and the second precious metal layer is gold or silver.

Furthermore, the thickness of the nanorods is smaller than the thickness of the transparent dielectric layer.

Furthermore, the material of the transparent dielectric layer is PMMA.

Furthermore, the periodic arrangement of the L-shaped holes is a rectangular periodicity.

Furthermore, the directions of the first arm of the hole and the second arm of the hole are parallel to both sides of the rectangular period.

On the other hand, the present invention also provides a preparation method of a double-layer chiral micro-nano structure, which preparation method includes the following steps:

Step 1. Prepare the substrate: According to actual needs, use a glass knife to cut the conductive glass into small squares with a side length of 1cm, paying attention to maintaining the integrity of the corners of each small square; the next step is to clean the substrate. , first ultrasonically clean it with acetone and alcohol for 15 minutes, then ultrasonically clean it with deionized water for 3 minutes, and finally blow dry the cleaned substrate with nitrogen for later use;

Step 2. Spinning the glue: Turn on the power of the glue leveling machine, set the time to 60s and the rotation speed to 4000rpm. Use a multimeter to measure the front and back sides of the substrate, and attach it face up to the sample plate of the glue leveling machine; take out the PMMA ( AR-P 672.03), suck up a drop of PMMA with a straw, drop it on the center of the substrate, turn on the switch of the glue leveler to spin the glue;

Step 3. Heating: Turn on the power of the heating plate, set the temperature to 150°C, take out the PMMA substrate from the glue homogenizer and place it on the heating plate for heating. The purpose is mainly to dry the PMMA on the substrate. After 3 minutes Take out the substrate layer and place it in the sample box;

Step 4. Electron beam exposure: Set Spot to 3, HV to 15KV, exposure dose to 100μC/cm ² , adjust astigmatism, perform calibration work, select the exposure position, and start to process the pre-designed L-shaped holes Graphics are exposed;

Step 5. Development and fixing: Put the exposed sample into the developer and stay for 60 seconds; then put the fixer into the solution and stay for 30 seconds, then take it out and place it in the sample box;

Step 6. Coating: Before coating, the substrate is attached to the sample plate in the electron beam evaporation coating instrument and then evacuated. Coating can only begin when the pressure in the cavity reaches 4×10 ^-6 torr; the deposition direction is θ = 89.3° and φ=0° or 90°, where θ represents the polarization angle, which refers to the angle between the normal direction of the sample stage and the precious metal evaporation beam; φ represents the azimuth angle, which refers to the direction of the precious metal evaporation beam on the sample. The angle between the projection on the table and the horizontal coordinate axis.

Beneficial effects of the present invention: The present invention provides a double-layer chiral micro-nano structure and a preparation method thereof. The upper layer is a first noble metal layer provided with L-shaped holes, and the lower layer is a second noble metal layer provided with nanorods. When irradiated with different circularly polarized lights, different couplings occur between the L-shaped holes and the nanorods, resulting in different resonance strengths and transmittances, resulting in strong circular dichroism. In the present invention, the double-layer chiral micro-nano structure only needs one electron beam etching and one evaporation of precious metal materials, which saves materials and time and simplifies the preparation process steps. In addition, dynamic control of circular dichroism can be achieved: Generally, after the micro-nano structure is prepared, the parameters of the micro-nano structure cannot be changed after preparation, especially the parameters of the lower layer, but the second layer can be modified based on the structure of the present invention. Secondary evaporation can realize the control of structural film thickness and nanorod thickness. It is flexible and convenient to use and has good application prospects in the field of chiral micro-nano structure preparation.

The present invention will be further described in detail below with reference to the accompanying drawings.

Description of the drawings

Figure 1 is a schematic diagram of a double-layer chiral micro-nano structure.

Figure 2 is a schematic structural diagram of the first precious metal layer.

Figure 3 is the transmission spectrum and circular dichroism spectrum of a double-layer chiral micro-nano structure.

Figure 4 is a diagram of the electric field and charge distribution at the resonance mode.

Figure 5 is a schematic diagram of the deposition angle of another double-layer chiral micro-nano structure.

In the picture: 1. Substrate; 2. Second precious metal layer; 3. Transparent dielectric layer; 4. First precious metal layer; 5. L-shaped hole; 6. Triangular ring hole; 51. First arm of the hole; 52. Hole The second arm; 61, the first arm of the triangle; 62, the second arm of the triangle; 63, the third arm of the triangle.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below with reference to the accompanying drawings and examples.

Example 1

The invention provides a two-layer chiral micro-nano structure, as shown in Figure 1, including a substrate, a second noble metal layer, a transparent dielectric layer, and a first noble metal layer. The transparent dielectric layer is placed on the substrate. The material of the substrate is conductive glass, which facilitates conduction during electron beam etching, so that charges can be conducted without irregularities in the etched sample caused by charge accumulation. The material of the transparent medium layer is PMMA. The first precious metal layer is placed on the transparent dielectric layer, and the material of the first precious metal layer is silver or gold. As shown in Figure 2, the first noble metal layer and the transparent dielectric layer are provided with penetrating L-shaped holes. That is to say, the L-shaped holes penetrate the first noble metal layer and the transparent dielectric layer and reach the surface of the substrate. The L-shaped holes are arranged periodically, and the period of the L-shaped holes is a rectangular period. The L-shaped hole is a right-angled L-shape, and the L-shaped hole includes a first arm of the hole and a second arm of the hole. The second noble metal layer includes periodically arranged nanorods, and the nanorods are placed in the second arm of the hole on the substrate. The material of the nanorods is gold or silver. The directions of the first arm of the hole and the second arm of the hole are parallel to both sides of the rectangular period. In this way, when the surface plasmon polariton is formed on the first noble metal layer, the direction of the surface plasmon polariton is along Periodic direction, thereby forming charge accumulation on both sides of the first arm of the hole and the second arm of the hole, which not only enhances the charge vibration intensity on both sides of the first arm of the hole and the second arm of the hole, but also enhances the interaction between the first noble metal layer and the nanorods coupling between.

In the present invention, the upper layer is a first noble metal layer provided with L-shaped holes, and the lower layer is a second noble metal layer provided with nanorods. When different circularly polarized lights are irradiated, different couplings occur between the L-shaped holes and the nanorods. , leading to differences in resonance intensity and transmittance, resulting in strong circular dichroism. In the present invention, the double-layer chiral micro-nano structure only needs one electron beam etching and one evaporation of precious metal materials, which saves materials and time and simplifies the preparation process steps. In addition, dynamic control of circular dichroism can be achieved: Generally, after the micro-nano structure is prepared, the parameters of the micro-nano structure cannot be changed after preparation, especially the parameters of the lower layer, but the second layer can be modified based on the structure of the present invention. Secondary evaporation realizes the regulation of the thickness of the structural film and the thickness of the nanorods. Moreover, in the present invention, changes in the thickness of the film and the thickness of the nanorods directly affect the coupling strength between the two. The sensitivity of dynamic regulation is very high, and the application is flexible and convenient. , has good application prospects in the field of chiral micro-nano structure preparation.

Example 2

On the basis of Embodiment 1, the thickness of the nanorods is smaller than the thickness of the transparent dielectric layer so that there is a certain distance between the lower surface of the first noble metal layer and the upper surface of the nanorods. The coupling between them produces circular dichroism of transmitted light. Preferably, the distance between the lower surface of the first noble metal layer and the upper surface of the nanorod is greater than 10 nanometers and less than 240 nanometers, so that coupling between the film and the nanorods can be achieved.

Example 3

On the basis of Example 2, a two-layer chiral micro-nano structure with specific morphological parameters was designed, and the transmission spectrum, circular dichroism spectrum and The charge distribution at the resonance mode is used to illustrate and illustrate the core principles of the invention.

The material of the first precious metal layer and the second precious metal layer is silver. The transparent medium layer is PMMA. The material of the substrate is conductive glass with a refractive index of 1.45. The thickness of the first precious metal layer is 60 nanometers. The length of the first arm of the hole is 260 nm and the width is 80 nm. The length of the second arm of the hole is 320 nm and the width is 80 nm. The L-shaped holes have periods of 600 nm and 600 nm. The thickness of the transparent dielectric layer is 60 nanometers. The thickness of the nanorods is the same as the thickness of the first noble metal layer. The length and width of the nanorod are the same as the length and width of the second arm of the hole.

Figure 3. The transmission spectrum and circular dichroism spectrum of the double-layer chiral micro-nano structure. It can be seen from the figure that there is a difference in the transmission spectrum under the irradiation of left and right circularly polarized light at wavelengths of 800 nanometers and 1380 nanometers, resulting in a circular dichroism effect. in. The circular dichroism signal at the wavelength of 800 nanometers is more obvious, reaching 20%. Figure 4(a) is the electric field distribution of the resonance mode at a wavelength of 800 nanometers. It can be seen from the figure that when left-handed circularly polarized light is incident, a strong resonance coupling occurs between the double-layer chiral micro-nano structures; right-handed When circularly polarized light is incident, weak resonance coupling occurs between the double-layer chiral micro-nano structures. The main reason is whether there are nanorods directly below the L-shaped hole, which leads to different coupling strengths between the two L-shaped holes and the lower layer. Figure 4(b) shows the electric field distribution of the resonance mode at a wavelength of 800 nanometers. It can also be seen from the figure that when left-handed circularly polarized light is incident, the electric field intensity in the first arm of the hole is weak. When right-handed circularly polarized light is incident, , the electric field intensity in the first arm of the hole is stronger, further proving the different coupling strengths between the two layers. Since the coupling between the nanorod and the first noble metal layer is different when left-hand circularly polarized light is incident and when right-hand circularly polarized light is incident, a strong circular dichroism (CD) signal is generated.

Example 4

The invention also provides a method for preparing a double-layer chiral micro-nano structure. The preparation method includes the following steps:

Step 1. Prepare the substrate: According to actual needs, use a glass knife to cut the conductive glass into small squares with a side length of 1cm, paying attention to maintaining the integrity of the corners of each small square; the next step is to clean the substrate. , first ultrasonically clean it with acetone and alcohol for 15 minutes, then ultrasonically clean it with deionized water for 3 minutes, and finally blow dry the cleaned substrate with nitrogen for later use;

Step 2. Spinning the glue: Turn on the power of the glue leveling machine, set the time to 60s and the rotation speed to 4000rpm. Use a multimeter to measure the front and back sides of the substrate, and attach it face up to the sample plate of the glue leveling machine; take out the PMMA ( AR-P 672.03), suck up a drop of PMMA with a straw, drop it on the center of the substrate, turn on the switch of the glue leveler to spin the glue;

Step 3. Heating: Turn on the power of the heating plate, set the temperature to 150°C, take out the PMMA substrate from the glue homogenizer and place it on the heating plate for heating. The purpose is mainly to dry the PMMA on the substrate. After 3 minutes Take out the substrate layer and place it in the sample box;

Step 4. Electron beam exposure: Set Spot to 3, HV to 15KV, exposure dose to 100μC/cm ² , adjust astigmatism, perform calibration work, select the exposure position, and start to process the pre-designed L-shaped holes Graphics are exposed;

Step 5. Development and fixing: Put the exposed sample into the developer and stay for 60 seconds; then put the fixer into the solution and stay for 30 seconds, then take it out and place it in the sample box;

Step 6. Coating: Before coating, the substrate is attached to the sample tray in the electron beam evaporation coating instrument and then evacuated. Coating can only begin when the pressure in the cavity reaches 4×10 ^-6 torr; the deposition direction is θ = 0° and φ=89.3°, where θ represents the polarization angle, which refers to the angle between the normal direction of the sample stage and the noble metal evaporation beam; φ represents the azimuth angle, which refers to the angle of the noble metal evaporation beam on the sample stage. The angle between the projection and the horizontal axis. In this way, due to the shadow effect, metal will only be multiplied in the second arm of the hole, but not in the first arm of the hole, thus forming a double-layer chiral structure of L-shaped holes and metal rods.

Example 5

On the basis of Example 4, in "Step 4", the exposure pattern is a triangular ring hole, as shown in Figure 5. The triangular ring hole is surrounded by the first arm of the triangle, the second arm of the triangle and the third arm of the triangle. In "Step 6", the deposition directions are θ = 89.3° and φ = 0°. In this way, nanorods will be formed directly below the first arm, the second arm and the third arm of the triangle. The three nanorods are not connected to each other, and due to the different angles between the three corners of the triangle, The distance between the three nanorods is also different. Since the three nanorods will also form couplings between each other, gathering a strong electric field, and then generating a strong coupling with the upper metal film, resulting in a greater difference in transmittance under left- and right-handed light excitation, This enables the structure prepared in this example to produce strong circular dichroism. In addition, due to the different angles between the three corners of the triangle, the spacing between the three nanorods is also different, which will cause the coupling strength between the nanorods to be different, resulting in different positions with the upper metal film. The coupling increases the asymmetry of the coupling, resulting in a greater difference in transmittance under left- and right-handed light excitation, making the circular dichroism signal stronger. Compared with the structure in Embodiment 2, this structure has the characteristics of stronger coupling between the double-layer metals and higher coupling asymmetry, thereby generating a larger circular dichroism signal.

The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the present application. within the scope of protection.

Claims (7)

1. The utility model provides a double-deck chiral micro-nano structure, its characterized in that includes substrate, second noble metal layer, transparent dielectric layer, first noble metal layer, transparent dielectric layer is arranged in on the substrate, first noble metal layer is arranged in on the transparent dielectric layer, first noble metal layer with be equipped with L shape hole that runs through in the transparent dielectric layer, L shape hole period is arranged, L shape hole includes hole first arm and hole second arm, the second noble metal layer includes the nanorod of period arrangement, the nanorod is arranged in on the substrate in the hole second arm.

2. The bilayer chiral micro-nano structure of claim 1, wherein: the substrate is made of conductive glass.

3. The bilayer chiral micro-nano structure of claim 1, wherein: the L-shaped hole is in a right-angle L shape.

4. The bilayer chiral micro-nano structure of claim 1, wherein: the first noble metal layer and the second noble metal layer are made of gold or silver.

5. The bilayer chiral micro-nano structure of claim 1, wherein: the thickness of the nanorods is smaller than that of the transparent medium layer.

6. The bilayer chiral micro-nano structure of claim 1, wherein: the transparent dielectric layer is made of PMMA.

7. The bilayer chiral micro-nano structure of claim 1, wherein: the period of the arrangement of the L-shaped holes is a rectangular period.