Anisotropic trimer chiral plasmonic nanocavity and a preparation method thereof

Abstract

The application belongs to the technical field of micro-nano optics, and discloses a special-shaped trimer chiral plasmonic nanocavity, which comprises, from bottom to top, a substrate, an ultrasmooth metal film and a dielectric layer, and a trimer composed of a metal nanohexagonal plate, a metal nanocube and a metal nanosphere is arranged on the dielectric layer. The trimer structure has a vertical height difference and no symmetry in the horizontal plane, is a three-dimensional chiral structure, has intrinsic chiral response, and has strong CD response. The chiral nanocavity structure is simple and convenient to prepare, and has the characteristics of low price and easy popularization compared with electron beam lithography technology. A preparation method of the special-shaped trimer chiral plasmonic nanocavity is also disclosed, and the three-dimensional chiral nanocavity structure is directly assembled on the substrate in a bottom-up manner, so that the influence of capillary force and Brownian noise on the assembly of the chiral structure in the solution is avoided, and a stable chiral structure can be formed.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optics technology, specifically relating to a heteromorphic trimer chiral plasmon nanocavity and its preparation method. Background Technology

[0002] Chirality is a structural property of a substance that cannot be superimposed on its mirror image through symmetry operations such as translation and rotation. Chirality is ubiquitous in nature, exhibited in everything from small biomolecules like DNA and proteins to certain galaxies in the universe. This widespread phenomenon contains extraordinary biochemical mechanisms. In particular, for many chiral molecules, one enantiomer possesses medicinal properties, while the other has side effects. Therefore, chiral molecules are crucial in the fields of biomedicine and drug engineering. However, because the size of chiral molecules is much smaller than the wavelength of excitation light, their circular dichroism (CD) response is weak, hindering the direct detection of chiral signals.

[0003] Inspired by chiral structures in nature, researchers have designed and fabricated chiral nanostructures that exhibit large chiral optical responses and have been widely applied in chiral catalysis, DNA detection, enantiomeric identification, and chiral fluorescence. Currently, the mainstream methods for constructing chiral nanostructures fall into two main categories: top-down and bottom-up. Top-down methods, represented by electron beam lithography, can directly fabricate three-dimensional chiral nanostructures on substrates, but this method often involves complex fabrication processes and high costs. Bottom-up methods, represented by colloidal chemistry and DNA nanotechnology, can achieve the self-assembly of chiral nanostructures in solution. However, the yield of these structures often depends on effective subsequent separation and purification techniques. Furthermore, solution-based self-assembly methods are affected by Brownian motion of particles, resulting in structural instability and limiting on-chip integration. Therefore, efficient methods for the dynamic assembly and chiral response of chiral nanostructures at arbitrary locations on solid substrates remain scarce. Summary of the Invention

[0004] The purpose of this invention is to provide a heteromorphic trimer chiral plasmon nanocavity and its preparation method, which solves the problem of poor structural stability in solution-based self-assembly methods.

[0005] This invention is achieved through the following technical solution:

[0006] A heteromorphic trimer chiral plasmonic nanocavity includes a substrate, an ultra-smooth metal film, and a dielectric layer arranged sequentially from bottom to top. A trimer composed of metal nanohexagonal plates, metal nanocubes, and metal nanospheres is disposed on the dielectric layer.

[0007] Furthermore, the metal nanohexagonal plates, metal nanospheres, metal nanocubes, and metal films are made of gold or silver.

[0008] Furthermore, the dielectric layer is made of aluminum oxide or silicon dioxide;

[0009] The substrate is made of silicon, quartz, or sapphire.

[0010] Furthermore, the opposite side length of the metal nano-hexagonal plate is 100-300 nm, and the thickness of the metal nano-hexagonal plate is 30-100 nm;

[0011] The diameter of the metal nanospheres is 80-240 nm;

[0012] The side length of the metal nanocubes is 40-200 nm;

[0013] The thickness of the ultra-smooth metal film is 30-150nm;

[0014] The thickness of the dielectric layer is 2-10 nm;

[0015] The substrate has a thickness of 100-5000 μm and a length and width of 0.4-2 cm.

[0016] This invention also discloses a method for preparing a heteromorphic trimer chiral plasmon nanocavity, comprising the following steps:

[0017] Step 1: Deposit metal onto the substrate to form a metal film;

[0018] Step 2: Apply epoxy resin to the substrate with the metal film, attach the new silicon wafer to the epoxy resin, anneal, peel off, and finally obtain an ultra-smooth metal film.

[0019] Step 3: Deposit and grow a dielectric layer on the ultra-smooth metal film obtained in Step 2;

[0020] Step 4: Disperse metal nanoparticles composed of metal nanohexagonal plates, metal nanospheres, and metal nanocubes on the dielectric layer using spin coating;

[0021] Step 5: Perform scattering spectroscopy on the metal nanoparticles from Step 4 to identify individual metal nanohexagonal plates, metal nanocubes, and metal nanospheres.

[0022] Step 6: Assemble individual metal nanohexagonal plates, metal nanocubes, and metal nanospheres to finally obtain a heteromorphic trimer chiral plasmon nanocavity.

[0023] Furthermore, in step six, the assembled trimer is configured such that the three trimers are tightly fitted together or connected end to end.

[0024] Furthermore, in step three, a dielectric material is deposited on the metal film using an atomic layer vapor deposition (ALV) device or a magnetron sputtering coating machine to complete the preparation of the dielectric layer.

[0025] Furthermore, step four specifically involves:

[0026] Metal nano-hexagonal plates, metal nano-cubes, and metal nanosphere colloids are mixed to obtain a mixture. The mixture is then diluted with deionized water at a volume ratio of 0.1-0.2:1, and finally spin-coated onto the medium layer obtained in step three.

[0027] Furthermore, in step six, a tungsten wire probe tip is clamped by a micro-nano manipulation device to assemble individual metal nano-hexagonal plates, metal nano-cubes, and metal nanospheres.

[0028] Furthermore, tungsten wire probe tips were fabricated using an electrochemical etching method with sodium hydroxide solution.

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] This invention discloses a heteromorphic trimer chiral plasmonic nanocavity, comprising a substrate, an ultrasmooth metal film, and a dielectric layer arranged sequentially from bottom to top. A trimer composed of metal nanohexagonal plates, metal nanocubes, and metal nanospheres is disposed on the dielectric layer. This trimer structure exhibits height differences in the vertical direction and lacks symmetry in the horizontal plane, constituting a three-dimensional chiral structure with intrinsic chiral response. It exhibits a strong CD response upon normal incident excitation. The CD response of this invention's structure can be tuned using multiple parameters by adjusting the dimensions of the metal nanohexagonal plates, metal nanospheres, and metal nanocubes, as well as the thickness of the dielectric layer. This invention's structure is simple to fabricate, and the required structural units are readily available and inexpensive. It is small in size, non-biotoxic, and suitable for chiral sensing in the biochemical field.

[0031] This invention also discloses a method for preparing heteromorphic trimer chiral plasmonic nanocavities. By directly assembling three-dimensional chiral nanocavity structures on a substrate in a bottom-up manner, the configuration of the assembled structure can be adjusted, which is more conducive to in-situ tuning of the chiral response of the chiral nanocavity. This method directly assembles the structure on the substrate, avoiding the influence of capillary forces and Brownian noise when assembling chiral structures in solution, and can form stable chiral structures, providing a reliable platform for the detection and identification of chiral molecules.

[0032] Furthermore, by using a micro-nano manipulation device to clamp the tip of a tungsten wire probe, individual metal nanohexagonal plates, metal nanocubes, and metal nanospheres can be assembled. The displacement of the micro-nano manipulation device is at the level of hundreds of nanometers, which can precisely control the movement of the trimer. Attached Figure Description

[0033] Figure 1 SEM image of the heteromorphic trimer chiral plasmon nanocavity structure;

[0034] Figure 2 Front view of the heteromorphic trimer chiral plasmon nanocavity structure;

[0035] Figure 3 for Figure 2 The right view;

[0036] Figure 4 for Figure 2 Top view;

[0037] Figure 5 Top views of the right-handed and left-handed structures of the heteromorphic trimer chiral plasmon nanocavity;

[0038] Figure 6 The scattering spectra of the right-handed structure of the heteromorphic trimer chiral plasmon nanocavity described in Example 1 under normal incident left- and right-handed circularly polarized light excitation;

[0039] Figure 7 The scattering spectra of the heteromorphic trimer chiral plasmonic nanocavity left-handed structure described in Example 1 under normal incident left- and right-handed circularly polarized light excitation;

[0040] Figure 8 The circular difference scattering spectra of the right-handed and left-handed structures of the heteromorphic trimer chiral plasmon nanocavity described in Example 1 are shown.

[0041] Figure 9 The scattering spectra of the right-handed structure of the heteromorphic trimer chiral plasmon nanocavity described in Example 2 under normal incident left- and right-handed circularly polarized light excitation;

[0042] Figure 10 The scattering spectra of the heteromorphic trimer chiral plasmonic nanocavity left-handed structure described in Example 2 under normal incident left- and right-handed circularly polarized light excitation;

[0043] Figure 11 The circular difference scattering spectra of the right-handed and left-handed structures of the heteromorphic trimer chiral plasmon nanocavity described in Example 2 are shown.

[0044] Figure 12 This is a top view of the heteromorphic trimer chiral plasmon nanocavity structure described in Example 3;

[0045] Figure 13 The scattering spectra of the right-handed structure of the heteromorphic trimer chiral plasmon nanocavity described in Example 3 under normal incident left- and right-handed circularly polarized light excitation;

[0046] Figure 14The scattering spectra of the heteromorphic trimer chiral plasmonic nanocavity left-handed structure described in Example 3 under normal incident left- and right-handed circularly polarized light excitation;

[0047] Figure 15 The circular difference scattering spectra of the right-handed and left-handed structures of the heteromorphic trimer chiral plasmon nanocavity described in Example 3 are shown.

[0048] Among them, 1. substrate; 2. ultra-smooth metal film; 3. dielectric layer; 4. metal nano-hexagonal plate; 5. metal nano cube; 6. metal nanosphere. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0050] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0051] It should be noted that the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus. Furthermore, the terms "horizontal" and "vertical" are based on the orientation and positional relationship of the devices or components shown in the accompanying drawings, and are used only for better description of the invention, not to require that the shown devices, components, or apparatus must have that specific orientation, and therefore should not be construed as limiting the invention.

[0052] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0053] Example 1

[0054] like Figures 1-5This invention proposes a heteromorphic trimer chiral plasmon nanocavity based on metal nanoparticles, comprising a substrate 1, an ultrasmooth metal film 2, a dielectric layer 3, metal nanohexagonal plates 4, metal nanocubes 5, and metal nanospheres 6. The substrate 1 is made of silicon, the metal film 2 is made of gold, the dielectric layer 3 is made of aluminum oxide, and the metal nanohexagonal plates 4, metal nanocubes 5, and metal nanospheres 6 are all made of gold.

[0055] The substrate 1 has a thickness of 500 μm, a length of 0.7 cm, and a width of 0.7 cm. The metal film 2 has a thickness of 50 nm, a length of 0.7 cm, and a width of 0.7 cm. The dielectric layer 3 has a thickness of 5 nm, a length of 0.7 cm, and a width of 0.7 cm. The metal nanohexagonal plate 4 has a thickness of 50 nm, is a regular hexagon, and has opposite sides of length d1 = 180 nm. The metal nanocube 5 has a side length d2 = 72 nm. The metal nanosphere 6 has a radius r = 80 nm.

[0056] The preparation method of the above-mentioned heteromorphic trimer chiral plasmon nanocavity structure includes the following steps:

[0057] Step 1: Place the silicon wafer into a vacuum coating machine and deposit gold by vapor deposition to form a gold film;

[0058] Step 2: Apply epoxy resin to the gold film, take a new silicon wafer and stick it on the epoxy resin, anneal, peel it off, and finally obtain an ultra-smooth gold film.

[0059] Step 3: Place the ultra-smooth gold film structure obtained in Step 2 into an atomic layer deposition apparatus to grow an aluminum oxide dielectric layer 3;

[0060] Step 4: Take 40 μl of the metal nano-hexagonal plate 4, metal nano-cube 5 and metal nanosphere 6 colloid using a pipette, dilute with 280 μl of deionized water, and finally spin-coat the mixture onto the aluminum oxide dielectric layer 3 obtained in Step 3.

[0061] Step 5: Perform scattering spectroscopy on the metal nanoparticles from Step 4 to identify individual metal nanohexagonal plates 4, metal nanocubes 5, and metal nanospheres 6.

[0062] Step 6: Use a 2 mol / L sodium hydroxide solution to fabricate the tungsten wire probe tip via electrochemical etching.

[0063] Step 7: Using a micro-nano manipulation device, the needle tip described in Step 6 is clamped and assembled with the individual metal nano-hexagonal plate 4, metal nano-cube 5, and metal nanosphere 6 described in Step 4, ultimately obtaining the following... Figure 1 The heteromorphic trimer chiral plasmon nanocavity structure is shown.

[0064] The CD response of the obtained heteromorphic trimer chiral plasmon nanocavity structure can be characterized by the scattering spectrum of circularly polarized light excited by normal incidence.

[0065] Figure 6 The scattering spectra of the right-handed (RH) structure of the trimer chiral nanocavity under right-circularly polarized (RCP) and left-circularly polarized (LCP) light excitation are presented. It can be clearly seen that the RH structure of the trimer chiral nanocavity has different responses to RCP and LCP.

[0066] Figure 7 The scattering spectra of the left-handed (LH) trimer chiral nanocavity structure under RCP and LCP excitation are shown. The LH trimer chiral nanocavity structure exhibits different responses to RCP and LCP, and these responses are opposite to those of the RH structure, demonstrating that the LH and RH structures are an enantiomeric configuration.

[0067] To more clearly reflect the CD response of the trimer chiral nanocavity, Figure 8 The circular differential scattering (CDS) spectrum of the trimer chiral nanocavity is presented, showing that the trimer chiral nanocavity obtained in this embodiment has a large CD response.

[0068] Example 2

[0069] The substrate 1 is made of silicon, the metal film 2 is made of gold, the dielectric layer 3 is made of aluminum oxide, and the metal nanohexagonal plate 4, metal nanocube 5, and metal nanosphere 6 are all made of gold. The metal nanohexagonal plate 4 has a thickness of 50 nm, is a regular hexagon, and has opposite side lengths d1 = 180 nm. The metal nanocube 5 has a side length d2 = 90 nm. The metal nanosphere 6 has a radius r = 80 nm.

[0070] The preparation method of the above-mentioned heteromorphic trimer chiral plasmon nanocavity structure includes the following steps:

[0071] Step 1: Place the silicon wafer in a vacuum coating machine and deposit gold by vapor deposition; the silicon wafer has a thickness of 500μm, a length of 0.7cm, and a width of 0.7cm.

[0072] Step 2: Apply epoxy resin to the silicon wafer coated with gold film, attach the new silicon wafer to the epoxy resin, anneal, peel off, and finally obtain the ultra-smooth gold film; the ultra-smooth gold film 2 has a thickness of 50nm, a length of 0.7cm, and a width of 0.7cm.

[0073] Step 3: Place the gold film structure obtained in Step 2 into an atomic layer deposition apparatus to grow an aluminum oxide dielectric layer; the dielectric layer 3 has a thickness of 5 nm, a length of 0.7 cm, and a width of 0.7 cm.

[0074] Step 4: Take 55 μl of metal nano-hexagonal plate 4, metal nano-cube 5 and metal nanosphere 6 colloid using a pipette, dilute with 280 μl of deionized water, and finally spin-coat onto the aluminum oxide dielectric layer obtained in step 3.

[0075] Step 5: Perform scattering spectroscopy on the metal nanoparticles from Step 4 to identify individual metal nanohexagonal plates 4, metal nanocubes 5, and metal nanospheres 6.

[0076] Step 6: Use a 2 mol / L sodium hydroxide solution to fabricate the tungsten wire probe tip via electrochemical etching.

[0077] Step 7: Using a micro-nano manipulation device, the needle tip described in Step 6 is used to assemble the single metal nano-hexagonal plate 4, metal nano-cube 5, and metal nanosphere 6 described in Step 4, ultimately obtaining a heteromorphic trimer chiral plasmon nanocavity structure.

[0078] The CD response of the obtained heteromorphic trimer chiral plasmon nanocavity structure can be characterized by the scattering spectrum of circularly polarized light excited by normal incidence. Figure 9 The scattering spectra of the trimer chiral nanocavity RH structure under RCP and LCP excitation are presented. Figure 10 The scattering spectra of the trimer chiral nanocavity LH structure under RCP and LCP excitation are shown.

[0079] Furthermore, in order to more clearly reflect the CD response of the trimer chiral nanocavity, Figure 11 The CDS spectrum of the trimer chiral nanocavity is presented. It can be seen that by changing the side length d2 of the nanocube in the trimer chiral nanocavity, the CD response of the trimer chiral nanocavity can be significantly tuned.

[0080] Example 3

[0081] Unlike Example 1, the single metal nanohexagonal plate 4, metal nanocube 5, and metal nanosphere 6 described in Step 4 are assembled using a micro-nano manipulation device holding the needle tip described in Step 6. The final resulting heteromorphic trimer chiral plasmon nanocavity structure is as follows: Figure 12 As shown, the three are connected end to end.

[0082] Scattering spectroscopic characterization of the heteromorphic trimer chiral plasmon nanocavity structure. Figure 13 The scattering spectra of the trimer chiral nanocavity RH structure under RCP and LCP excitation are presented. Figure 14The scattering spectra of the trimer chiral nanocavity LH structure under RCP and LCP excitation are shown.

[0083] Figure 15 The CDS spectrum of the trimeric chiral nanocavity shows that the trimeric chiral nanocavity in this embodiment has a completely different CD response from that in Examples 1 and 2. This further illustrates that the CD response of the trimeric chiral nanocavity can also be tuned by changing the arrangement of the metal nanohexagonal plate 4, the metal nanocube 5, and the metal nanosphere 6.

[0084] The heteromorphic trimer chiral plasmon nanocavity structure proposed in this invention is simple, easy to prepare, and inexpensive, exhibiting intrinsic chiral response that can be tuned through multiple parameters. The preparation method of the heteromorphic trimer chiral plasmon nanocavity structure proposed in this invention allows for direct in-situ assembly of chiral nanostructures on a substrate, avoiding the influence of capillary forces and Brownian noise during solution assembly. This provides a favorable platform for sensing chiral molecules in the fields of chemistry, biomedicine, and pharmacy.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A heteromorphic trimer chiral plasmon nanocavity, characterized in that, It includes a substrate (1), an ultra-smooth metal film (2) and a dielectric layer (3) arranged sequentially from bottom to top. A trimer composed of a metal nano-hexagonal plate (4), a metal nano cube (5) and a metal nanosphere (6) is provided on the dielectric layer (3). The metal nano-hexagonal plate (4) has a side length of 100-300 nm and a thickness of 30-100 nm. The diameter of the metal nanospheres (6) is 80-240 nm; The side length of the metal nanocube (5) is 40-200 nm; A single metal nano-hexagonal plate (4), a metal nano-cube (5), and a metal nanosphere (6) are assembled by clamping a tungsten wire probe tip using a micro-nano manipulation device.

2. The heteromorphic trimer chiral plasmon nanocavity according to claim 1, characterized in that, The metal nanohexagonal plates (4), metal nanospheres (6), metal nanocubes (5), and metal films are made of gold or silver.

3. The heteromorphic trimer chiral plasmon nanocavity according to claim 1, characterized in that, The dielectric layer (3) is made of aluminum oxide or silicon dioxide; The substrate (1) is made of silicon, quartz or sapphire.

4. The heteromorphic trimer chiral plasmon nanocavity according to claim 1, characterized in that, The thickness of the ultra-smooth metal film (2) is 30-150 nm; The thickness of the dielectric layer (3) is 2-10 nm; The thickness of the substrate (1) is 100-5000µm, and the length and width are 0.4-2 cm.

5. A method for preparing a heteromorphic trimer chiral plasmon nanocavity according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Deposit metal onto the substrate (1) to form a metal film; Step 2: Apply epoxy resin to the substrate (1) with metal film, attach the new silicon wafer to the epoxy resin, anneal, peel off, and finally obtain an ultra-smooth metal film (2). Step 3: Deposit and grow a dielectric layer (3) on the ultra-smooth metal film (2) obtained in step 2; Step 4: Disperse metal nanoparticles composed of metal nanohexagonal plates (4), metal nanospheres (6) and metal nanocubes (5) on the dielectric layer (3) using spin coating; Step 5: Perform scattering spectroscopy on the metal nanoparticles from Step 4 to identify individual metal nanohexagonal plates (4), metal nanocubes (5), and metal nanospheres (6). Step 6: Assemble the individual metal nanohexagonal plates (4), metal nanocubes (5), and metal nanospheres (6) to finally obtain the heteromorphic trimer chiral plasmon nanocavity.

6. The method for preparing the heteromorphic trimer chiral plasmon nanocavity according to claim 5, characterized in that, In step six, the assembled trimer is configured such that the three trimers are tightly joined together or connected end to end.

7. The method for preparing the heteromorphic trimer chiral plasmon nanocavity according to claim 5, characterized in that, In step three, a dielectric material is deposited on the metal film using an atomic layer vapor deposition (ALV) device or a magnetron sputtering coating machine to complete the preparation of the dielectric layer (3).

8. The method for preparing the heteromorphic trimer chiral plasmon nanocavity according to claim 5, characterized in that, Step four is as follows: Metal nano-hexagonal plates (4), metal nano-cubes (5) and metal nanospheres (6) are colloidally mixed to obtain a mixture. The mixture is diluted with deionized water at a volume ratio of 0.1-0.2:1 and finally spin-coated onto the medium layer (3) obtained in step three.

9. The method for preparing the heteromorphic trimer chiral plasmon nanocavity according to claim 5, characterized in that, Tungsten wire probe tips were fabricated using an electrochemical etching method with sodium hydroxide solution.

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