CN114325884B - Cantilever circular dichroism micro-nano structure and preparation method thereof - Google Patents
Cantilever circular dichroism micro-nano structure and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the field of chiral micro-nano structure preparation, in particular to a cantilever-shaped circular dichroism micro-nano structure and a preparation method thereof. On one hand, charge vibration on the noble metal film is regulated and controlled through the height difference of the first cantilever and the second cantilever, so that strong circular dichroism is caused; on the other hand, the invention can be obtained by only one-time electron beam etching and combining with the electron beam evaporation inclined coating technology, and has simple manufacturing flow and good application prospect compared with other preparation methods of double-layer three-dimensional structures.
Description
Technical Field
The invention relates to the field of chiral micro-nano structure preparation, in particular to a cantilever circular dichroism micro-nano structure and a preparation method thereof.
Background
Distinguishing the polarization state of circularly polarized light is a fundamental problem in optics. The traditional method for distinguishing left-handed circularly polarized light and right-handed circularly polarized light generally uses a quarter wave plate to convert the circularly polarized light into linearly polarized light with different polarization directions, and then uses a polarization analyzer to filter according to the required polarization directions. The large size of the components required for such conventional methods is disadvantageous for miniaturization and integration of the device.
The chiral micro-nano structure is prepared to distinguish left circularly polarized light and right circularly polarized light, so that the defects are overcome, and the chiral micro-nano structure has good application prospect in the aspects of circularly polarized light judgment and the like.
Three-dimensional chiral micro-Nano structures have stronger circular dichroism, such as three-dimensional helices (j.k.gansel, science,325,1513,2009) and bilayer structures (y.cui, nano lett.14,1021, 2014). Because laser direct writing or multiple exposure is needed for preparing the three-dimensional structure, the preparation process is complex and the preparation difficulty is high.
Disclosure of Invention
In order to solve the problems, the invention provides a cantilever-shaped circular dichroism micro-nano structure and a preparation method thereof.
In one aspect, the invention provides a cantilever-shaped circular dichroism micro-nano structure, which comprises a substrate layer and a micro-nano structure layer, wherein the micro-nano structure layer is arranged on the substrate layer, the micro-nano structure layer comprises chiral units which are periodically arranged, the chiral units comprise a dielectric layer and a noble metal film, the noble metal film is arranged on the dielectric layer, holes are formed in the dielectric layer and the noble metal film, the chiral units further comprise a first cantilever and a second cantilever, the first cantilever and the second cantilever are adhered to part of side walls of the holes, materials of the first cantilever and the second cantilever are the same as those of the noble metal film, and heights of the first cantilever and the second cantilever are different.
Further, the substrate layer is made of transparent material.
Further, the substrate layer is conductive glass.
Further, the noble metal film is made of gold or silver.
Further, the holes are circular.
Further, the symmetry axis of the first cantilever and the second cantilever are both along the periodic direction of the chiral unit.
On the other hand, the invention also provides a preparation method of the cantilever-shaped circular dichroism micro-nano structure, which comprises the following steps:
step 1, preparing a substrate layer: according to actual needs, cutting the conductive glass into small squares with the side length of 1cm by using a glass cutter, and keeping the integrity of the corners of each small square, so that the calibration work in the subsequent exposure process is convenient, and the exposure position is convenient to select; the next is to clean the substrate layer, firstly, respectively ultrasonically clean the substrate layer for 15 minutes by using acetone and alcohol, then ultrasonically clean the substrate layer for 3 minutes by using deionized water, and finally, blow-dry the cleaned substrate layer by using nitrogen for standby;
Step 5, developing and fixing: the exposed sample is put into a developing solution and stays for 60s; then, the fixing solution was put into the sample box, and left for 30 seconds, and then taken out and put into the sample box.
Step 6, coating: before coating, the substrate layer is attached to a sample tray in an electron beam evaporation coating instrument and then vacuumized, when the pressure in the cavity reaches 4 multiplied by 10 -6 the torr side can start to coat films twice; the inclination angles of the two coating films are respectively a first inclination angle and a second inclination angle, and the first inclination angle and the second inclination angle are different; the difference of the direction angles of the two coating films is larger than 60 degrees.
The invention has the beneficial effects that: the invention provides a cantilever-shaped circular dichroism micro-nano structure, which comprises a substrate layer and a micro-nano structure layer, wherein the micro-nano structure layer is arranged on the substrate layer, the micro-nano structure layer comprises chiral units which are periodically arranged, each chiral unit comprises a dielectric layer and a noble metal film, each noble metal film is arranged on the dielectric layer, holes are formed in the dielectric layer and each noble metal film, the chiral units further comprise a first cantilever and a second cantilever, the first cantilever and the second cantilever are adhered to part of side walls of the holes, materials of the first cantilever and the second cantilever are the same as those of the noble metal films, and heights of the first cantilever and the second cantilever are different. On one hand, the charge vibration on the noble metal film is regulated and controlled through the height difference of the first cantilever and the second cantilever, so that the whole micro-nano structure generates two different charge vibration modes when the different circularly polarized lights are irradiated, and strong circular dichroism is caused; on the other hand, the preparation method is obtained only by one-time electron beam etching and then by utilizing the inclined angle deposition technology in the electron beam evaporation coating, and has simple preparation flow compared with other preparation methods of double-layer three-dimensional structures, and good application prospect in the field of three-dimensional chiral micro-nano structure preparation.
The present invention will be described in further detail with reference to the accompanying drawings.
Drawings
Fig. 1 is a top view of a cantilever-shaped circular dichroism micro-nano structure.
Fig. 2 is a transmission spectrum (a) and a circular dichroism spectrum (b) of a cantilever-shaped circular dichroism micro-nano structure.
FIG. 3 is a graph showing the charge distribution on chiral units at an incident light wavelength of 830 nm.
Fig. 4 is an SEM image of the prepared cantilever-shaped circular dichroism micro-nano structure.
FIG. 5 is a graph of experimentally measured transmission spectra and circular dichroism spectra.
In the figure: 1. a noble metal film; 2. a hole; 3. a first cantilever; 4. and a second cantilever.
Detailed Description
For the purposes of making the objects, technical solutions and advantages of the present application more apparent, the present application will be described in further detail below with reference to the accompanying drawings and examples.
Example 1
The invention provides a cantilever-shaped circular dichroism micro-nano structure. The cantilever-type circular dichroism micro-nano structure comprises a substrate layer and a micro-nano structure layer. The material of the substrate layer is a transparent material. Preferably, the material of the substrate layer is conductive glass. The micro-nano structure layer is arranged on the substrate layer. The micro-nano structure layer comprises chiral units which are periodically arranged. Fig. 1 is a top view of one periodic unit of a micro-nanostructure layer. The arrangement period of the period units can be rectangular period or square period. The chiral unit comprises a dielectric layer and a noble metal film 1, wherein the noble metal film 1 is arranged on the dielectric layer, and holes 2 are formed in the dielectric layer and the noble metal film 1. The shape of the hole 2 is square. The chiral unit further comprises a first cantilever 3 and a second cantilever 4, the first cantilever 3 and the second cantilever 4 being adhered to a part of the side wall of the hole 2. Specifically, the first cantilever 3 and the second cantilever 4 are adhered to adjacent sidewalls of the hole 2. The first cantilever 3 and the second cantilever 4 are different in height, that is, the first cantilever 3 and the second cantilever 4 have different depths in a direction perpendicular to the paper surface. The material of the first cantilever 3 and the second cantilever 4 is the same as that of the noble metal film 1. The materials of the first cantilever 3, the second cantilever 4, and the noble metal film 1 may be different from each other in terms of realizing circular dichroism, and the technical effects of the present invention can be realized. However, for ease of preparation, the first cantilever 3, the second cantilever 4, the noble metal film 1 are the same material, and the noble metal film 1 is gold or silver.
When the circular dichroism detection device is applied, circular polarized light with different polarization states irradiates one side of the noble metal film 1, and circular dichroism detection is realized by detecting transmitted light. In the invention, on one hand, the charge vibration on the noble metal film 1 is regulated and controlled through the height difference of the first cantilever 3 and the second cantilever 4, so that the whole micro-nano structure generates two different charge vibration modes when the different circularly polarized lights are irradiated, and strong circular dichroism is caused; on the other hand, the preparation method is obtained by only one-time electron beam etching and combining with an electron beam evaporation inclined coating technology, has simple preparation flow compared with other preparation methods of a double-layer three-dimensional structure, and has good application prospect in the field of three-dimensional chiral micro-nano structure preparation.
The invention is provided with the holes 2, and a strong electric field and a chiral field are formed in the holes 2, which is favorable for arranging chiral molecules in the holes for chiral molecule detection.
Example 2
Based on example 1, the holes 2 are circular. This is because for the square hole 2, an accurate coating angle is ensured to attach the first cantilever 3 and the second cantilever 4 to the adjacent sides. However, the circular hole 2 is different, and the first cantilever 3 and the second cantilever 4 are attached to the side wall of the hole 2, regardless of the coating angle.
Example 3
On the basis of examples 1-2, the directions of the symmetry axes of the first cantilever 3 and the second cantilever 4 are both along the periodic direction of the chiral unit. That is, for the square hole 2, the normal directions of the first cantilever 3 and the second cantilever 4 are along the periodic direction of the chiral unit, i.e. the horizontal or vertical direction in fig. 1; for the circular hole 2, the first cantilever 3 and the second cantilever 4 are arc-shaped, and the angular bisector of the arc is along the periodic direction of the chiral unit. Since the periodic direction of the chiral unit is the vibration direction of the surface plasmon polariton on the noble metal film 1, the first cantilever 3 and the second cantilever 4 can regulate and control the vibration of the surface plasmon polariton on the noble metal film 1 more, thereby generating stronger circular dichroism.
Example 4
The invention also designs a cantilever-shaped circular dichroism micro-nano structure with specific morphological parameters, and circular dichroism spectrum and charge distribution of the micro-nano structure are calculated by using COMSOL finite element software, so as to explain the core principle of the invention.
The material of the noble metal film 1 is silver, the material of the first cantilever 3 and the second cantilever 4 is silver, the material of the medium is PMMA, the material of the substrate layer is glass, and the thickness of the noble metal film 1 is 80 nanometers; the holes 2 are round, and the diameter of the holes 2 is 500 nanometers; the height of the first cantilever 3 is 200 nanometers, and the height of the second cantilever 4 is 100 nanometers; the first cantilever 3 has a corresponding arc of 120 degrees, and the second cantilever 4 has a corresponding arc of 120 degrees. The thickness of the first cantilever 3 and the second cantilever 4 is 30 nm.
In fig. 2, the square lines represent the line patterns of left-handed circularly polarized Light (LCP) irradiated on the cantilever-shaped nanostructures, and the dot lines represent the line patterns of right-handed circularly polarized light (RCP) irradiated on the cantilever-shaped nanostructures. As shown in fig. 2, the transmission coefficient (t++) of transmission was 27% under the irradiation of RCP, the transmitted intensity (t—) was almost zero and the Circular Dichroism (CD) was 27% under the irradiation of LCP, and strong circular dichroism was achieved.
FIG. 3 shows the charge distribution on chiral units at an incident light wavelength of 830 nm. FIGS. 3a and 3c are top views of charge distributions of cantilever-shaped micro-nanostructures; fig. 3b and 3d are three-dimensional perspective views of the charge distribution of the cantilever-shaped micro-nano structure. Since the charge is mainly distributed on the noble metal structure, the dielectric layer and the substrate layer are not shown in the figure. When LCP light irradiates, a surface plasmon polariton mode is excited on the noble metal film 1, and local surface plasmon resonance is formed between the first cantilever 3, the second cantilever 4 and the noble metal film 1, so that strong absorption and low transmission coefficient of incident light are caused; when RCP light is irradiated, localized surface plasmon resonance modes are generated on the noble metal film 1, and coupling between the first cantilever 3, the second cantilever 4 and the noble metal film 1 is weak, resulting in weak absorption of incident light and a high transmission coefficient. In summary, the difference in coupling between the charge vibrations on the first cantilever 3, the second cantilever 4 and the noble metal film 1 under different circularly polarized light illumination results in strong circular dichroism, and the present invention provides a novel structure for realizing circular dichroism.
Example 5
The invention also provides a preparation method of the cantilever circular dichroism micro-nano structure, which comprises the following steps:
step 1, preparing a substrate layer: according to actual needs, cutting the conductive glass into small squares with the side length of 1cm by using a glass cutter, and keeping the integrity of the corners of each small square, so that the calibration work in the subsequent exposure process is convenient, and the exposure position is convenient to select; the next is to clean the substrate layer, firstly, respectively ultrasonically clean the substrate layer for 15 minutes by using acetone and alcohol, then ultrasonically clean the substrate layer for 3 minutes by using deionized water, and finally, blow-dry the cleaned substrate layer by using nitrogen for standby;
step 5, developing and fixing: the exposed sample is put into a developing solution and stays for 60s; then placing the fixing solution, staying for 30s, and then taking out and placing the fixing solution in a sample box;
step 6, coating: before coating, the substrate layer is attached to a sample tray in an electron beam evaporation coating instrument and then vacuumized, when the pressure in the cavity reaches 4 multiplied by 10 -6 the torr side can start to coat films twice; the inclination angles of the two coating films are respectively a first inclination angle and a second inclination angle, and the first inclination angle and the second inclination angle are different; the difference of the direction angles of the two coating films is larger than 60 degrees. In the process of twice coating, a material is deposited on the PMMA surface to form a noble metal film 1, the thickness of the two times coating forms the thickness of the noble metal film 1, and a first cantilever 3 and a second cantilever 4 are respectively formed.
After coating, the micro-nano structure can be obtained without removing the glue, the glue removing link is reduced, and the success rate of sample preparation is high.
Example 6
Cantilever-shaped micro-nano structures were prepared by the method of application example 4, and SEM pictures thereof are shown in fig. 4. The scale bar is 1 micron in the figure. The brighter areas of the left and upper borders of the circular hole 2 in the figure are a first cantilever 3 and a second cantilever 4. The inclination angles when preparing the first cantilever 3 and the second cantilever 4 are 27 degrees and 13 degrees respectively, so as to ensure that the heights of the first cantilever 3 and the second cantilever 4 are 200 nanometers and 100 nanometers respectively; the direction angles at the time of preparing the first cantilever 3 and the second cantilever 4 are different by 120 degrees. Fig. 5 is a graph of transmission spectrum and circular dichroism spectrum of the above sample, from which it can be seen that the structure achieves strong circular dichroism, confirming the core principle or concept of the present invention.
The foregoing description of the preferred embodiments of the present invention is not intended to limit the invention to the precise form disclosed, and any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention are intended to be included within the scope of the present invention.
Claims (6)
1. The cantilever-shaped circular dichroism micro-nano structure is characterized by comprising a substrate layer and a micro-nano structure layer, wherein the micro-nano structure layer is arranged on the substrate layer, the micro-nano structure layer comprises chiral units which are periodically arranged, each chiral unit comprises a medium layer and a noble metal film, each noble metal film is arranged on the medium layer, holes are formed in the medium layer and the noble metal films, each chiral unit further comprises a first cantilever and a second cantilever, the first cantilever and the second cantilever are adhered to part of side walls of the holes, materials of the first cantilever and the second cantilever are the same as those of the noble metal films, and heights of the first cantilever and the second cantilever are different.
2. The cantilever-shaped circular dichroism micro-nano structure of claim 1, wherein: the substrate layer is a transparent material.
3. The cantilever-shaped circular dichroism micro-nano structure of claim 1, wherein: the substrate layer is conductive glass.
4. The cantilever-shaped circular dichroism micro-nano structure of claim 1, wherein: the noble metal film is made of gold or silver.
5. The cantilever-shaped circular dichroism micro-nano structure of claim 1, wherein: the holes are round.
6. The cantilever-shaped circular dichroism micro-nano structure of claim 1, wherein: the symmetry axis directions of the first cantilever and the second cantilever are along the periodic direction of the chiral unit.
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| CN109116462A (en) * | 2018-10-29 | 2019-01-01 | 中山科立特光电科技有限公司 | A kind of micro-nano structure of adjustable circular dichroism signal |
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