A method for constructing sub-nanometer plasmonic nanocavity

Abstract

The application discloses a method for constructing sub-nanometer plasmonic nanocavity, comprising the following steps: (1) preparing a flexible metal nanometer array film; (2) constructing a spacing layer on the exposed metal side of a flexible metal nanometer array film, and then placing another flexible metal nanometer array film on the exposed metal side of the spacing layer, so that the two flexible metal nanometer array films are adsorbed and attached by Van der Waals force, thereby obtaining a plasmonic nanocavity, which allows polarized excitation, realizes the enhancement of molecular signal and carries out the research on adsorption form. Compared with the chemical synthesis method, the application is more accurate and easy to realize in the control of structure gap, and the substrate is more uniform; compared with the nanometer gap prepared by photolithography and ion beam, the substrate process of the application is simple, easy to operate and short in time consumption, and the structure has a controllable sub-nanometer gap. The method has simple preparation process, high repeatability and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for three-dimensional micro-nano processing, in particular to a method for constructing sub-nanometer plasmonic nanocavity. BACKGROUND

[0002] In the field of micro-nano materials, noble metal (gold, silver, etc.) materials have attracted extensive attention due to their special surface plasmon resonance. Under the excitation of incident light of a certain wavelength, the free electrons on the surface of noble metal undergo collective oscillation, producing localized surface plasmon resonance (LSPR), which can localize electromagnetic field on the surface. When the excitation frequency approaches the oscillation frequency, the localized electromagnetic field of plasmonic coupling is generated, greatly improving the electromagnetic field intensity. These micro-nano metal structures with significant electromagnetic field enhancement have important significance and strong practical value in the field of nano-photonics, and can be used in related fields such as sensor devices, optical trapping, optical catalysis, and surface-enhanced spectroscopy.

[0003] Surface-enhanced Raman spectroscopy of noble metal is a technology that mainly uses the electromagnetic field enhancement generated by noble metal to enhance the Raman signal of the molecules to be detected. (This enhancement is also known as the electromagnetic field enhancement mechanism.) For a long time, the research on the detection capability of surface-enhanced Raman spectroscopy has mainly focused on improving the electromagnetic field intensity in noble metal micro-nano structures, and introducing a nanogap into these structures is an effective means. The nanogap refers to the formation of a nanoscale gap between adjacent metal nanostructures. According to Maxwell's equations, the smaller the nanogap, the stronger the electromagnetic field enhancement. When the gap is less than 10 nm, the electromagnetic field in the noble metal micro-nano structure is significantly enhanced, and when a sub-nanometer gap is formed, the light intensity can be enhanced by millions of times.

[0004] The methods for manufacturing such small-gap metal nanocavity structures in the past are generally divided into two categories: "bottom-up" chemical synthesis and "top-down" ion beam etching. The chemical synthesis method can achieve a metal gap of several nanometers or even sub-nanometers, but this method has a high degree of randomness and cannot be accurately controlled. The ion beam lithography method can accurately control the size of the gap, but it cannot be used to prepare structures with a gap smaller than 5 nm. Using this technology to prepare substrates is complex and costly. Controlling the gap distance between nanostructures to be within the sub-nanometer length range is still a challenge for nanofabrication technology. Further, some probe molecules such as benzene ring derivatives are usually similar in size to small gaps or even larger, and it is difficult to insert these molecules into ultra-small gaps to obtain effective Raman signal enhancement. SUMMARY

[0005] The purpose of the present application is to provide a method for constructing sub-nanometer plasmonic nanocavity with low equipment requirements and simple process.

[0006] Technical scheme: The method for constructing sub-nanometer plasmonic nanocavity comprises the following steps:

[0007] (1) preparing a flexible metal nanometer array film;

[0008] (2) constructing a spacing layer on the metal-exposed side of a flexible metal nanometer array film, and then placing another flexible metal nanometer array film on the metal-exposed side on the spacing layer, and the two flexible metal nanometer array films are adsorbed and attached by Van der Waals force, so as to obtain a plasmonic nanocavity.

[0009] In step (2), the method for constructing the spacing layer is that molecules are self-assembled into a monolayer on the metal surface or a metal stripping two-dimensional material method.

[0010] In step (2), the molecules in the monolayer are easy to bond with the metal surface to form a self-assembled monolayer adsorption layer under thermodynamic equilibrium. The method for constructing the monolayer is that the metal-exposed side of a flexible metal nanometer array film is in contact with a solution of molecules to perform monolayer adsorption of the molecules.

[0011] In step (2), the method for constructing the two-dimensional material as the spacing layer is that the metal nanometer array is constructed on a substrate with two-dimensional material transferred thereon, then wrapped with a polymer, and the substrate is removed to obtain a flexible metal nanometer array film with two-dimensional material attached to one side.

[0012] In step (2), the spatial three-dimensional size of the molecules in the monolayer is 0.3-5 nm.

[0013] In step (2), the two-dimensional material is one of monolayer or few-layer graphene, molybdenum disulfide, rhenium disulfide or black scale.

[0014] In step (1), the metal is one of gold, silver, copper, aluminum, platinum and palladium.

[0015] In step (1), the method for preparing the flexible metal nanometer array film is that a transparent polymer is spin-coated to wrap a metal plasmonic nanometer array on a substrate, and then heated and solidified, and then the sample is heated in an etching solution to remove the substrate.

[0016] The substrate is one of a quartz sheet, a silicon sheet, silicon oxide, titanium oxide, a metal sheet, or a functionalized substrate plated on the substrate, and the plating material is one of an oxide, a nitride, carbon and a metal.

[0017] The corrosion solution is one of sodium hydroxide, potassium hydroxide, ferric chloride, copper chloride and oxygen-free water, or a mixture thereof.

[0018] The polymer is one of polymethyl methacrylate, polyethylene terephthalate, polydimethylsiloxane or hydrogel.

[0019] The polymer is one of polymethyl methacrylate, polyethylene terephthalate, polydimethylsiloxane or hydrogel.

[0020] The molecule in the molecular solution is one of rhodamine, 4-aminobenzene sulfenol, 4-nitrobenzene sulfenol, benzene sulfenol and 1,4 benzene dithiol; the molecule is a molecule chemisorbed on the metal surface.

[0021] Advantages: Compared with the prior art, the present application has the following remarkable effects: (1) Compared with the technology of preparing a metal nanometer small gap by photolithography or focused ion beam etching, the present application has the advantages of low dependence on high-end equipment, simple process, stable performance and easy engineering; (2) The sub-nanometer plasmonic nanocavity prepared by the present application provides a solution to the simple and rapid preparation of sub-nanometer gaps, and solves the difficulty of effectively enhancing the Raman signal of molecules using a nanometer gap with a size comparable to that of the molecule; (3) The sub-nanometer plasmonic nanocavity prepared by the present application is supported by a flexible material, has great flexibility, can arbitrarily adjust the spatial relative angle of the nanocavity, allows the cavity to be polarized excited, can realize the enhancement of molecular signal and the research of adsorption form, and has important reference significance for the design and preparation of high-efficiency charge transfer optoelectronic devices, the design of high-performance catalysts and the like. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The core preparation flow chart of the plasmonic nanocavity is shown in the figure;

[0023] Figure 2 The side view of the sub-nanometer plasmonic nanocavity is shown in the figure;

[0024] Figure 3 The method flow chart of the plasmonic nanocavity with two-dimensional material as a spacer layer is shown in the figure;

[0025] Figure 4 The scanning electron microscope picture of the metal nanometer array obtained by the template method using electron beam deposition is shown in the figure;

[0026] Figure 5The electric field distribution diagram of the plasmonic nanocavity obtained by the finite-difference time-domain method;

[0027] Figure 6 The Raman enhancement diagram of the plasmonic nanocavity;

[0028] Figure 7 The Raman enhancement spectrum diagram of the Rhodamine molecules with the incident light relative polarization angle changed;

[0029] Figure 8 The photo of the plasmonic nanocavity with the spacer layer being molybdenum disulfide.

[0030] Figure 9 The Raman enhancement spectrum diagram of the plasmonic nanocavity with the spacer layer being molybdenum disulfide under the incident laser at different angles. DETAILED DESCRIPTION

[0031] The application will be further described in detail below.

[0032] Example 1

[0033] The application provides a method for constructing a sub-nanometer plasmonic nanocavity, which specifically comprises the following steps.

[0034] (1) Preparing a flexible plasmonic nanometer array film:

[0035] The gold nanometer array is obtained on the surface of a hard substrate quartz by using a template method and electron beam deposition, and a transparent polymer polymethyl methacrylate is spin-coated on the surface of the metal nanometer array for protection, the parameter setting of the film applicator is 300 r / s, after the film application is completed, the sample is placed on a heating table at 110 DEG C and baked for 20 min, then the sample is completely immersed in a sodium hydroxide solution with a mass fraction of 6%, the heating temperature is set to 100 DEG C, so that the gold nanoparticles are separated from the quartz, and finally a flexible gold nanometer array film supported by a polymer is obtained, which is transferred to deionized water for rinsing and temporary storage;

[0036] (2) Preparing a plasmonic nanocavity: two pieces of the flexible plasmonic nanometer array film obtained in step 1 are used, one of which is first floated on the surface of a Rhodamine solution, so that the exposed metal side contacts the solution for single-layer adsorption of molecules, then the other flexible plasmonic nanometer array film is placed with the metal side upward, and the layer with the adsorbed molecules is covered thereon, the molecules are sandwiched between the two flexible plasmonic nanometer arrays, the two flexible plasmonic nanometer arrays are tightly adhered by van der Waals force, and the gap formed therebetween is only nanoscale in size of the size of the adsorbed molecules. Figure 1 The preparation flowchart of the application. Figure 2 The side view schematic diagram of the final product of the application, wherein 1 is a polymer, 2 is a spacer layer, which can be a monolayer or a two-dimensional material, and 3 is a metal particle.Figure 4 is a scanning electron microscope photo of the top view of the metal nanoarray. Figure 5 is a finite-difference time-domain simulation data graph of the electric field of the final product of the present application. It can be seen that the electric field intensity in the plasmonic nanocavity of the present application is very strong, and the electric field intensity in the nanocavity is also enhanced when the polarization angle of the incident laser relative to the nanocavity is changed. Figure 6 is a comparison graph of the Raman spectrum of rhodamine molecules with a concentration of -6M in the nanocavity and the Raman spectrum of rhodamine with a concentration of -2M on a silicon wafer, which highlights the Raman enhancement capability of the plasmonic nanocavity. Figure 7 is a Raman enhancement spectrum of rhodamine molecules under the condition that the incident laser is parallel to the normal direction of the nanocavity and at an angle of 80° to the normal direction. It can be seen that the relative intensities of different Raman vibration modes, such as the Raman peaks at 774 cm -1 and 1649 cm -1 , are different. According to the surface enhancement rule, the relative orientation of the molecules on the metal surface can be determined.

[0037] Example 2

[0038] (1) Preparation of flexible plasmonic nanometer array film:

[0039] Silver nanometer arrays are obtained on the surface of a hard substrate quartz by using a template method with electron beam deposition, and a hydrogel is spin-coated on the surface of the metal nanometer array for protection. The parameter setting of the spin coater is 300 r / s. After the spin coating is completed, the sample is placed on a heating table at 100°C and baked for 20 min. Then the sample is completely immersed in a potassium hydroxide solution with a mass fraction of 7%, and the heating temperature is set to 80°C to separate the silver nanoparticles from the quartz. Finally, a flexible metal nanometer array film supported by a polymer is obtained, which is transferred to deionized water for rinsing and temporary storage;

[0040] (2) Preparation of plasmonic nanocavity: Two pieces of flexible plasmonic nanometer array films obtained in step 1 are used in this step. First, one of them is floated on the surface of a 1,4-benzenedithiol molecular solution, so that the exposed metal side contacts the solution for single-layer adsorption of the molecules. Then the other layer of the flexible plasmonic film is placed with the metal side facing up, covering the layer with adsorbed molecules. The molecules are sandwiched between the two layers of flexible plasmonic nanometer arrays, which are tightly adhered by van der Waals force. The gap formed in the middle is only sub-nanometer in size, which is the size of the adsorbed molecules.

[0041] Example 3

[0042] (1) Preparation of flexible plasmonic nanometer array film:

[0043] Silver nanoarrays were deposited on a hard quartz substrate using electron beam deposition via a template method. A transparent polymer, polydimethylsiloxane, was spin-coated onto the surface of the silver nanoarrays for protection. The spin coater parameters were set to 300 r / s. After spin coating, the sample was placed on a heating stage and baked at 80°C for 30 min. Then, the entire sample was immersed in a 5% sodium hydroxide solution and the heating temperature was set to 150°C to separate the silver nanoparticles from the quartz. Finally, a flexible metal nanoarray film supported by the polymer was obtained. The film was then transferred to deionized water for rinsing and temporary storage.

[0044] (2) Preparation of plasmonic nanocavities: In this step, two identical flexible plasmonic nanoarray films obtained in step 1 are used. First, one of the films is floated on the surface of the 4-aminothiophenol molecular solution, so that the exposed metal side is in contact with the solution for monolayer adsorption of molecules. Then, the metal side of the other flexible plasmonic film is placed upward, and the layer with adsorbed molecules is placed on top of it. The molecules are sandwiched between the two flexible plasmonic nanoarrays. The two flexible plasmonic layers are tightly bonded by van der Waals forces, and the gap formed in the middle is only the sub-nanometer size of the adsorbed molecules.

[0045] Example 4

[0046] (1) Preparation of flexible plasmonic nanoarray thin films:

[0047] Gold nanoarrays were deposited on a hard quartz substrate using electron beam deposition via a template method. A transparent polymer, polymethyl methacrylate (PMMA), was spin-coated onto the surface of the gold nanoarrays for protection. The spin coater parameters were set to 1000 r / s. After spin coating, the sample was placed on a heating stage and baked at 150°C for 30 min. Then, the entire sample was immersed in a 5% sodium hydroxide solution at a constant temperature and the heating temperature was set to 100°C to separate the gold nanoparticles from the quartz. Finally, a flexible nanoarray film supported by the polymer was obtained. The film was then transferred to deionized water for rinsing and temporary storage.

[0048] (2) Preparation of plasmonic nanocavities: A gold nanoarray was constructed on a substrate with transferred graphene, then coated with a polymer. The quartz substrate was removed to obtain a flexible metal nanoarray film with graphene attached to one side. This flexible gold nanoarray film was then placed on top of the flexible gold nanoarray film obtained in step 1, with the graphene sandwiched in between. Annealing was then performed at 150°C for 6 hours. The two flexible gold nanoarrays were tightly bonded together by van der Waals forces, forming a sub-nanometer plasmonic nanocavity with graphene as the spacer layer. The specific preparation process is as follows: Figure 3 As shown. Among them, as Figure 3As shown in the first image on the left, a metal nanoarray is deposited on the surface of a flat graphene material. The relative positions of the metal and graphene are fixed to ensure the uniformity and relative flatness of the graphene in the nanocavity.

[0049] Example 5

[0050] (1) Preparation of flexible plasmonic nanoarray thin films:

[0051] Gold nanoarrays were deposited on a hard quartz substrate using electron beam deposition via a template method. A transparent polymer, polymethyl methacrylate, was spin-coated onto the surface of the gold nanoarrays for protection. The spin coater parameters were set to 1000 r / s. After spin coating, the sample was placed on a heating stage and baked at 100°C for 30 min. Then, the entire sample was immersed in a sodium hydroxide solution and the heating temperature was set to 150°C to separate the metal nanoparticles from the quartz. Finally, a flexible nanoarray film supported by the polymer was obtained. The film was then transferred to deionized water for rinsing and temporary storage.

[0052] (2) Preparation of plasmonic nanocavities: A gold nanoarray was constructed on a quartz substrate with a transferred monolayer of molybdenum disulfide, and then a polymer was wrapped around it. The quartz substrate was removed to obtain a flexible gold nanoarray film with molybdenum disulfide attached to one side. This flexible gold nanoarray film was then placed on top of the flexible gold nanoarray film obtained in step 1, with the molybdenum disulfide sandwiched in between. Annealing was performed at 120°C for 8 hours, and the two layers of flexible gold nanoarrays were tightly bonded together by van der Waals forces to form a sub-nanometer-scale plasmonic nanocavity with a monolayer of molybdenum disulfide as the spacer layer.

[0053] Specific physical images are provided by Figure 8 As shown in the photo, the darker part in the middle is the plasmonic nanocavity with molybdenum disulfide as the spacer layer.

[0054] Figure 9 This is the Raman-enhanced spectrum of molybdenum disulfide under the conditions of incident laser light parallel to the normal direction of the nanocavity and at an angle of 80° to the normal direction. The out-of-plane vibrational mode A of molybdenum disulfide can be seen from the figure. 1g and E 2g The relative intensities of the Raman peaks are different. Since molybdenum disulfide has a definite lattice orientation, the electric field orientation in the plasmonic nanocavity under different incident lasers can be determined.

Claims

1. A method for constructing sub-nanometer-scale plasmonic nanocavities, characterized in that, Includes the following steps: (1) Preparation of flexible plasmonic nanoarray thin films: Gold nanoarrays were deposited on a hard quartz substrate using electron beam deposition via a template method. A transparent polymer, polymethyl methacrylate, was spin-coated onto the surface of the metal nanoarrays for protection. The spin coater parameters were set to 300 r / s. After spin coating, the sample was placed on a heating stage and baked at 110°C for 20 min. Then, the entire sample was immersed in a 6% sodium hydroxide solution and the heating temperature was set to 100°C to separate the gold nanoparticles from the quartz. Finally, a flexible gold nanoarray film supported by the polymer was obtained. The film was then transferred to deionized water for rinsing and temporary storage. (2) Preparation of plasmonic nanocavities: In this step, two identical flexible plasmonic nanoarray films obtained in step 1 are used. First, one of the films is floated on the surface of the rhodamine solution so that the exposed metal side is in contact with the solution for monolayer adsorption of molecules. Then, the metal side of the other flexible plasmonic film is placed upwards, and the layer with adsorbed molecules is placed on top of it. The molecules are sandwiched between the two flexible plasmonic nanoarrays. The two flexible plasmonic layers are tightly bonded by van der Waals forces, and the gap formed in the middle is only nanometer-sized in size of the adsorbed molecules.

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