Micro-nano structure for regulating and controlling resonance wavelength of surface plasmon based on laser induction and preparation method of micro-nano structure

Abstract

The invention discloses a micro-nano structure for regulating and controlling surface plasmon resonance wavelength based on laser induction and a preparation method of the micro-nano structure. According to the technology, an M-SAM-M structure composed of a metal substrate, a self-assembled monomolecular layer (SAM) and metal nano-particles is constructed through molecular interface engineering, selected molecules such as 4-fluorothiophenol, 4-chlorophenylmercaptan and 4-bromophenylmercaptan serve as gap materials for accurately defining the size of a nano gap in the assembling process, and due to the fact that the molecules are short in length, the size of the nano gap can be accurately defined. Compared with the prior art, the method has the characteristics that a compact single layer is easily formed and the static polarizability is relatively large, a dipole layer is formed under the action of a local electric field, the optical force is enhanced, gold atoms on the surfaces of nano-particle gaps are induced to migrate, and then non-contact and rapid (1-10 seconds) regulation and control of resonant wavelength are realized. By adopting a laser irradiation technology at normal temperature and pressure, the method provided by the invention not only overcomes the limitation of a traditional adjustment method depending on a geometric structure and reduces the preparation difficulty, but also realizes high-precision, large-scale and low-cost preparation of the metal nanostructure, and provides powerful support for development of novel optical electronic devices.

Description

Technical Field

[0001] The present invention relates to a method for dynamically regulating the surface plasmon resonance wavelength in metal nanogaps based on molecular interface engineering by laser. This method belongs to the technical field of surface plasmon photonic devices and also covers multiple interdisciplinary fields such as semiconductors, nanomaterials, and optics. Background Art

[0002] Surface plasmon resonance refers to the phenomenon that free electrons in metal nanostructures undergo collective oscillations under the excitation of an optical field, and its resonance wavelength is affected by a variety of factors. In the resonance state, the local electric field intensity can reach 10 2 to 10 4 times that of the incident light intensity, while in the non-resonance state, the enhancement effect is significantly weakened. Therefore, precisely regulating the resonance wavelength is of great significance for improving the performance of photonic devices and catalytic efficiency. Existing regulation methods mostly rely on changing the geometric morphology of metal materials, such as inherent parameters like shape and size. This method not only has a low adjustment efficiency, but also the preparation of metal nanostructures is difficult. Even after precise design, it is difficult to avoid the resonance wavelength deviation caused by nanoscale structural errors. In view of the above deficiencies, the present invention proposes a micro-nano structure for regulating the surface plasmon resonance wavelength by laser induction under normal temperature and pressure. This structure consists of a metal substrate, a self-assembled monolayer (SAM), and metal nanoparticles, forming an M-SAM-M heterostructure. Among them, the molecules used (such as 4-fluorobenzenethiol, 4-chlorobenzenethiol, and 4-bromobenzenethiol, etc.) not only form a molecular layer as the gap material, support the nanoparticles and determine the gap size, but also due to their short molecular length, easy formation of a dense monolayer, and large static polarizability, they can undergo electron rearrangement to form a dipole layer under the action of the local field in the nanogap, thereby enhancing the optical force, causing the gold atoms on the surface of the nanoparticle gap to be pulled out, resulting in an increase in the gap cross-section and realizing the regulation of the resonance wavelength. Experimental results show that this structure can achieve non-contact and rapid response (1 - 10 seconds) resonance wavelength regulation, providing a new idea for the large-scale and high-efficiency preparation of metal nanostructures with specific resonance wavelengths. Summary of the Invention

[0003] The present invention discloses an M-SAM-M micro-nano structure based on laser-induced dynamic regulation and its preparation method. This structure consists of a metal substrate, a self-assembled monolayer (SAM), and metal nanoparticles to form a three-layer heterogeneous system, where the metal substrate and nanoparticles can adopt homogeneous or heterogeneous combinations of Ag / Au. In particular, molecules such as 4-fluorobenzenethiol, 4-chlorobenzenethiol, and 4-bromobenzenethiol selected in the molecular layer, while stabilizing the structure as a spacer material, have the characteristics of short molecules, easy formation of a dense monolayer, and a large static polarizability, enabling the formation of a dipole layer under the action of a local electric field, thereby enhancing the magnitude of the optomechanical force during laser regulation and pulling out the atoms on the surface of the nanoparticle gap to achieve the purpose of regulating the resonance wavelength. By performing laser irradiation in a normal temperature and atmospheric environment, this structure can achieve non-contact precise regulation of the surface plasmon resonance wavelength in the range of 10 - 50 nm. This method not only breaks through the limitations of traditional lithography processes but also combines solution self-assembly technology to achieve the controllable preparation of three-dimensional plasmonic structures, which not only has the advantage of low cost but is also suitable for mass production. Detailed implementation mode

[0004] The preparation process of the structure includes the following steps: Film deposition: Deposit an Ag / Au film with a thickness of 200 ± 10 nm on the surface of a silicon substrate using a magnetron sputtering process. Self-assembled monolayer assembly: Immerse the pretreated metal substrate in an ethanol solution of thiol molecules (such as 4-fluorobenzenethiol, 4-chlorobenzenethiol, or 4-bromobenzenethiol) with a concentration of 4 mM, and let it stand for about 12 hours to allow the molecules to bind to the metal surface through Au–S / Ag–S bonds to form a dense and ordered molecular layer. This molecular layer not only acts as a spacer material to support the metal nanoparticles and accurately determine the size of the nano-gap but is also the key to subsequent laser regulation of the resonance wavelength. Nanoparticle deposition: Drop a metal nanoparticle solution with a diameter of 60 nm on the surface of the molecular layer and rinse it with distilled water to remove the excess particles, finally forming a stable M-SAM-M structure. Optical regulation mechanism

[0005] Using a fiber laser with a wavelength of 633 nm, it is focused onto the target area (spot radius is about 360 nm) through an objective lens with a magnification of 100× and a numerical aperture of 0.9. Under the condition of a laser power of 0.1 mW, by controlling the irradiation time (1 - 10 seconds), a linear redshift of the resonance wavelength can be achieved. The principle lies in that for the used molecular layer, due to its characteristic of a large static polarizability, electron rearrangement occurs in the local field of the nano-gap to form a dipole layer, significantly enhancing the optical force, thereby inducing the gold atoms on the surface of the nano-particle gap to be pulled out, increasing the gap cross-section, and finally realizing the regulation of the resonance wavelength. The experimental results show that this method can achieve a resonance wavelength shift of 10 - 20 nm; when the laser power is increased, the displacement range can be further expanded. Calculation Advantages and Applications

[0006] This technology has the advantages of a simple preparation process, without complex steps such as lithography or etching, and can achieve large-scale and highly reproducible preparation of samples. The used molecules and nano-particle solutions are highly commercialized, with low costs and are convenient for popularization and application. From the perspective of the regulation mechanism, the role of the molecular layer is crucial: on the one hand, as the gap material, it not only stably supports the nano-particles but also precisely defines the nano-gap size; on the other hand, the dipole layer formed in the local field enhances the optical force, causing the gold atoms on the surface of the nano-particle gap to be pulled out, thus changing the gap cross-section and achieving precise regulation of the resonance wavelength. The laser regulation method, due to its advantages of non-contact, high-speed response (1 - 10 seconds), and strong environmental adaptability (room temperature atmosphere), provides a new technical approach for the large-scale preparation of micro-nano structures with a predetermined resonance wavelength, facilitating the development and integration of new optoelectronic devices. Description of the Drawings

[0007] Figure 1 It is a schematic diagram of the M-SAM-M structure in the present invention, showing a three-layer structure of a metal substrate, a self-assembled monolayer, and metal nano-particles; Figure 2 It is an SEM image of the sample.; Figure 3 It is the scattering spectrum measured before and after laser irradiation for different metal combination structures; Figure 4 It is the influence of different laser irradiation times on the resonance wavelength shift under the same laser power (0.3 mW); Figure 5 It is the regulation effect of different laser powers on the resonance wavelength shift under a fixed laser irradiation time (30 s); Figure 6 It is the influence of different molecular layer types on the resonance wavelength shift under the same laser parameters (0.5 mW, 30 s). Specific Implementation Cases

[0008] The following will, in conjunction with the attached Figure 1 , provide a detailed description of the specific implementation manners of the present invention.

[0009] Example: Material preparation: Select a silicon substrate, an Ag / Au alloy target, a 4-bromobenzenethiol ethanol solution (concentration 4 mM), and a 60-nm metal nanoparticle solution (Au particle product number: BBI solution EM.GC60, Ag particle product number: Sigma-Aldrich 730785); Preparation steps: First, deposit an Ag / Au thin film (2) with a thickness of about 200 on the surface of the silicon substrate (1) by magnetron sputtering; Subsequently, place the deposited metal substrate into the 4 mM thiol molecule ethanol solution and let it stand at room temperature for 12 hours. After taking it out, carefully rinse the excess solution with ethanol and dry it with nitrogen to form a dense monolayer (3); Finally, uniformly drop the metal nanoparticle solution on the surface of the monolayer, let it stand, and then rinse with distilled water to remove the excess particles, and deposit a single nanoparticle above the molecular layer (4); Laser regulation: Use a 633-nm fiber laser to focus and irradiate the target area (5) through a 100×0.9NA objective lens, and achieve different degrees of red shift of the resonance wavelength by adjusting the laser power and irradiation time.

[0010] Figure 2 The SEM images of the samples are shown. Figure 2 (a) shows that multiple nanoparticles are assembled above the molecular layer at a low magnification, forming multiple M-SAM-M structures; Figure 2 (b) shows a single M-SAM-M structure at a high magnification.

[0011] Figure 3 The scattering spectra measured before and after laser irradiation for different metal combination structures are shown. Specifically, Figure 3 (a) is the scattering spectrum of the AgM-4-bromobenzenethiol SAM-AgM structure before and after 30 s of laser irradiation with 0.3 mW; Figure 3 (b) is the AgM-4-bromobenzenethiol SAM-AuM structure; Figure 3 (c) is the scattering spectrum of the AuM-4-bromobenzenethiol SAM-AgM structure under the same laser conditions; Figure 3 (d) is the scattering spectrum of the AuM-4-bromobenzenethiol SAM-AuM structure before and after 30 s of laser irradiation with 0.5 mW. The results show that different metal material combinations and different molecular layers can all achieve laser regulation of the resonance wavelength.

[0012] Figure 4The influence of different laser irradiation times on the resonance wavelength shift at the same laser power (0.3 mW) is shown (the structure is AgM-4-bromobenzenethiol SAM-AgM, with about 40 samples in each group). The results show that the reaction is completed within 20 s, and the resonance wavelength shift is about 20–30 nm.

[0013] Figure 5 The regulation effect of different laser powers on the resonance wavelength shift at a fixed laser irradiation time (30 s) is shown (the structure is AgM-4-bromobenzenethiol SAM-AgM, with about 40 samples in each group). The results show that the resonance wavelength shift varies with the laser power and can reach up to 50 nm.

[0014] Figure 6 The influence of different molecular layer types on the resonance wavelength shift at the same laser parameters (0.5 mW, 30 s) is shown (the structure is AgM-SAM-AgM). Among them, M1 is 4-fluorobenzenethiol, M2 is 4-chlorobenzenethiol, and M3 is 4-bromobenzenethiol. As can be seen from the figure, various thiol molecules can be used as self-assembled monolayers (SAMs) to construct this structure.

[0015] It is not limited to the disclosed embodiments, but is intended to cover equivalent methods within the spirit and scope of the appended claims.

Claims

1. A M-SAM-M micro-nano structure based on laser-induced dynamic regulation, characterized in that This structure is composed of a metal substrate, a self-assembled monolayer (SAM), and metal nanoparticles. The metal substrate and nanoparticles can be selected from heterogeneous or homogeneous combinations of Ag / Au.

2. The structure according to claim 1, wherein Deposit an Ag or Au thin film (200 ± 10 nm) on a silicon substrate by magnetron sputtering to form the metal substrate.

3. The structure according to claim 1, characterized in that, Immerse the metal substrate in an ethanol solution of thiol molecules to form the self-assembled monolayer.

4. The structure according to claim 1, wherein, Drop the metal nanoparticle solution onto the surface of the molecular layer and remove the excess particles by rinsing to form a stable M-SAM-M structure.

5. The structure according to claim 1, characterized in that, Under normal temperature and pressure, use laser irradiation to achieve non-contact regulation of the resonance wavelength according to the regulation parameters (laser power, irradiation time).

6. The molecular layer according to claim 3, wherein The molecular layer is composed of molecules such as 4-fluorobenzenethiol, 4-chlorobenzenethiol, and 4-bromobenzenethiol. These molecules have the characteristics of short molecular length, easy formation of self-assembled monolayers, and large static polarizability. The molecular layer with the above characteristics can undergo electron rearrangement in the local field of the gap to form a dipole layer, increasing the magnitude of the optical force, thereby inducing the migration of gold atoms between nanoparticles, resulting in an increase in the gap cross-section and achieving resonance wavelength regulation.

7. The laser control method according to claim 5, wherein The laser irradiation uses a fiber laser with a wavelength of 633 nm, which is focused by a high-power objective lens (spot radius of about 360 nm). At a laser power of 0.1 mW and an irradiation time of 1 - 10 seconds, a linear redshift of the resonance wavelength is achieved, and the displacement range is 10 - 20 nm. Further increasing the laser power can increase the displacement range.

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