Micro-nano structure porous silver surface enhanced Raman substrate and preparation method thereof

Abstract

The invention discloses a micro-nano structure porous silver surface enhanced Raman substrate and a preparation method thereof, belongs to the technical field of molecular recognition and nano preparation, and provides a preparation method of a novel silver porous structure based on a silver oxide thermal decomposition principle. According to the method, an atomic layer deposition (ALD) technology is innovatively adopted to construct a protective layer on the surface of a material, the agglomeration behavior of silver particles in the high-temperature process is effectively inhibited, and therefore the original micro-nano structure is completely reserved, the silver micro-nano structure prepared through the technology has excellent SERS performance, and a new solution is provided for preparation of a high-performance SERS substrate.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular recognition and nano-preparation, and in particular relates to a surface-enhanced Raman substrate of micro-nanostructured porous silver and a preparation method thereof. Background Art

[0002] Since Professor C.V. Raman first discovered Raman scattering in 1928, surface-enhanced Raman spectroscopy (SERS) has gradually developed into a highly sensitive analytical method through systematic exploration by researchers such as Van Duyne. The core advantage of SERS lies in its ability to provide "fingerprint" spectral signatures of substances, while also offering non-destructive detection, ultrahigh sensitivity (at the single-molecule level), and rapid response. Therefore, it holds broad application prospects in environmental monitoring, biomedicine, food safety, and other fields. Research has demonstrated that precious metal nanoparticles (such as Au and Ag), subnanometer-scale interstitial structures, or metal substrates with porous morphologies can enhance Raman signal intensity by several orders of magnitude through the localized surface plasmon resonance (LSPR) effect. Consequently, the design and fabrication of efficient metal nanostructured SERS substrates has become a key research focus in this field. Silver oxide readily decomposes to form metallic silver under thermal conditions. However, metallic silver has an inherently low melting point and is prone to melting and agglomeration at high temperatures, making it difficult to maintain its micro-nanostructure. Summary of the Invention

[0003] The present invention provides a surface-enhanced Raman spectroscopy (SERS) substrate of porous silver with a micro-nano structure, as well as a preparation method and application thereof. Atomic layer deposition (ALD) technology is used to construct a protective layer on the surface of the material, effectively inhibiting the agglomeration behavior of silver particles during high-temperature processes, thereby completely preserving the original micro-nano structure. The prepared silver micro-nano structure has excellent SERS performance.

[0004] To achieve the above objectives, the present invention adopts the following technical solutions: A method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver comprises the following steps: Using silver oxide micro-nanostructure as the initial template, ALD technology is used to precisely coat the template surface with a thickness-controlled oxide protective layer. The coated samples were subjected to a high-temperature annealing process, during which the silver oxide core was decomposed into metallic silver by heat, while the ALD protective layer effectively maintained the structural integrity of the material; The surface oxide protective layer is removed to finally obtain porous silver with micro-nano structure.

[0005] In the above steps, the silver oxide micro-nanostructure includes silver oxide materials with nano-pillars, nano-wires, nano-particles and nano-sheet structures; The specific steps of depositing the oxide protective layer by ALD are as follows: transferring the above-mentioned silver oxide material into the ALD reaction chamber, and precisely controlling the thickness by the number of cycles to deposit a 1-15 nm oxide film to form a core-shell structure (Ag2O@oxide) of the oxide film wrapped around the silver oxide; preferably, aluminum oxide or zinc oxide film; The parameters for ALD deposition of aluminum oxide are: Reaction chamber temperature: room temperature ~ 200 ℃; Reaction source: Trimethylaluminum and water were used to deposit aluminum oxide, and the source temperature was room temperature; Pulse and purge time: The pulses of the metal source and water source are both 0.5-5 seconds. Each pulse is followed by a 4-20 second purge with high-purity nitrogen to ensure complete removal of reaction byproducts and residual reaction sources. The parameters for ALD deposition of zinc oxide are: Reaction chamber temperature: room temperature ~ 200 ℃; Reaction source: Diethyl zinc and water are used to deposit zinc oxide, and the source temperature is room temperature; Pulse and purge time: The pulses of the metal source and water source are both 0.5-5 seconds. Each pulse is followed by a 4-20 second purge with high-purity nitrogen to ensure that reaction byproducts and residual reaction sources are flushed away. The high temperature annealing temperature is 400-800°C and the time is 10-120 minutes; The oxide protective layer is removed by selective chemical etching, and the high-temperature annealed material is immersed in an acid or alkaline solution for 30-300 seconds. The acid solution is hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid, and the alkaline solution is sodium hydroxide or potassium hydroxide.

[0006] Beneficial effects: The present invention provides a surface-enhanced Raman substrate of micro-nanostructured porous silver and a preparation method thereof. The micro-nanostructured silver is used as a template, and the precise preparation of micro-nanostructured porous silver is achieved through an ALD-assisted annealing process. The present invention utilizes the three-dimensional conformal deposition characteristics and atomic-level thickness control capabilities of the ALD technology to uniformly coat the surface of the silver oxide template with a nano-scale oxide protective layer, the thickness of which can be precisely controlled by the number of deposition cycles. After the full surface coating is completed, the silver oxide is thermally decomposed by high-temperature annealing treatment to generate elemental silver and release oxygen. Due to the escape of oxygen, pores are formed inside the material, and finally a micro-nanoporous silver material with a complete three-dimensional structure is obtained. Compared with existing preparation technologies, the present invention has the significant advantages of simple process, convenient operation, and good repeatability, and provides an innovative solution for the controllable preparation of high-performance porous silver materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a scanning electron microscope (SEM) image of silver oxide nanorods; Figure 2 The X-ray diffraction (XRD) patterns of silver substrates formed by direct annealing at different temperatures, where I is silver oxide, and the annealing temperatures of II-V are 200℃, 300℃, 400℃, and 500℃, respectively; Figure 3 SEM images of silver substrates formed by direct annealing at different temperatures, where I is 200°C, II is 300°C, III is 400°C, and IV is 500°C; Figure 4 XRD patterns of silver substrates prepared by direct annealing and ALD-assisted annealing in the embodiments of the present invention; Figure 5 This is an SEM image of porous silver prepared by ALD-assisted annealing in an embodiment of the present invention; Figure 6 3. The SERS performance comparison of the porous silver substrate before and after corrosion in the embodiment of the present invention. DETAILED DESCRIPTION

[0008] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments: Example 1

[0009] A method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver comprises the following steps: 1) Using silver oxide nanorods as templates, the microstructure is as follows Figure 1 As shown; 2) The silver oxide nanorods were transferred to the ALD reaction chamber and a 5 nm aluminum oxide film was deposited to form an aluminum oxide-wrapped columnar structure (Ag2O@alumina). The parameters for the ALD deposition of aluminum oxide were: Reaction chamber temperature: 150 °C; Reaction source: Trimethylaluminum and H2O were used to deposit aluminum oxide, and the source temperature was room temperature; Pulse and purge time: The pulse of the metal source and water source is 1 s. Each pulse is followed by a 5 s purge with high-purity nitrogen to flush away reaction byproducts and residual reaction source. 3) The Ag2O@alumina structure was placed in air and annealed at 400℃ for 30 minutes. The XRD pattern and SEM pattern were as follows: Figure 4 and Figure 5 As shown in the figure, the results show that ALD-assisted annealing still forms metallic silver and retains the original columnar structure, obtaining columnar porous silver; 4) The annealed Ag@alumina structure was etched with 1M KOH solution for 60 seconds to remove the surface oxide layer and obtain a pure porous silver structure. Figure 6The comparison pictures of Raman intensity detection of the same concentration of R6G before and after corrosion show that the porous silver substrate formed by ALD-assisted annealing has excellent SERS activity.

[0010] Comparative Example 1 The silver oxide nanorod substrate was directly annealed (200-500℃), and the XRD pattern of the obtained sample was as follows: Figure 2 As shown in Figure 2, it can be found that silver oxide can be decomposed into metallic silver when the annealing temperature is above 400°C. SEM was then used to characterize the corresponding microstructure, as shown in Figure 2. Figure 3 As shown, the results show that although metallic silver was obtained, the original micro-nano structure was lost and transformed into a dense planar structure with weak SERS activity. Example 2

[0011] A method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver comprises the following steps: 1) Using silver oxide nanoparticles as templates; 2) Transfer the silver oxide nanoparticles into the ALD reaction chamber and deposit a 1 nm aluminum oxide film to form an aluminum oxide-encapsulated silver oxide structure (Ag2O@alumina). The parameters for ALD deposition of aluminum oxide are: Reaction chamber temperature: room temperature; Reaction source: Trimethylaluminum and H2O were used to deposit aluminum oxide, and the source temperature was room temperature; Pulse and purge time: The pulses for both the metal source and the water source were 5 s. Each pulse was followed by a 20 s purge with high-purity nitrogen to flush away reaction byproducts and residual reaction sources. 3) Annealing the Ag2O@alumina structure at 800°C for 10 minutes; 4) The annealed silver oxide@aluminum oxide structure was etched with 1 M NaOH solution for 30 seconds to obtain a porous silver structure. Example 3

[0012] A method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver comprises the following steps: 1) Using silver oxide nanowires as templates; 2) The silver oxide nanowires were transferred to the ALD reaction chamber and a 7 nm zinc oxide film was deposited to form a zinc oxide-wrapped silver oxide structure (Ag2O@ZnO). The parameters for ALD zinc oxide deposition were: Reaction chamber temperature: 120 °C; Reaction source: Diethyl zinc and H2O were used to deposit zinc oxide, and the source temperature was room temperature; Pulse and purge time: The pulse of the metal source and water source is 0.5 s. Each pulse is followed by a 4 s purge with high-purity nitrogen to flush away reaction byproducts and residual reaction source. 3) Annealing the Ag2O@ZnO structure at 500°C for 60 minutes; 4) The annealed silver@zinc oxide structure was etched with 1 M KOH solution for 180 seconds to obtain a porous silver structure; Example 4

[0013] A method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver comprises the following steps: 1) Using silver oxide nanosheets as templates; 2) The silver oxide nanosheets were transferred to the ALD reaction chamber and a 15 nm zinc oxide film was deposited to form a zinc oxide-wrapped silver oxide structure (Ag2O@ZnO). The parameters for ALD zinc oxide deposition were: Reaction chamber temperature: 150 °C; Reaction source: Diethyl zinc and H2O were used to deposit zinc oxide, and the source temperature was room temperature; Pulse and purge time: The pulse of the metal source and water source is 1 s. Each pulse is followed by a 5 s purge with high-purity nitrogen to flush away reaction byproducts and residual reaction source. 3) Annealing the Ag2O@ZnO structure at 500°C for 30 minutes; 4) The annealed Ag@ZnO structure was corroded with 1 M HCl solution for 300 seconds to obtain a porous silver structure; Example 5

[0014] A method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver comprises the following steps: 1) Using silver oxide nanowires as templates; 2) The silver oxide nanowires were transferred to the ALD reaction chamber and a 5 nm aluminum oxide film was deposited to form an aluminum oxide-wrapped silver oxide structure (Ag2O@alumina). The parameters for the ALD aluminum oxide deposition were: Reaction chamber temperature: 200 °C; Reaction source: Trimethylaluminum and H2O were used to deposit aluminum oxide, and the source temperature was room temperature; Pulse and purge time: The pulses for both the metal source and the water source are 2 seconds. Each pulse is followed by an 8-second purge with high-purity nitrogen to flush away reaction byproducts and residual reaction sources. 3) Annealing the Ag2O@alumina structure at 400°C for 60 minutes; 4) The annealed Ag@alumina structure was etched with 1 M phosphoric acid solution for 200 seconds to obtain a porous silver structure.

[0015] The above description is only a preferred embodiment of the present invention. It should be pointed out that those skilled in the art can make corresponding changes and adjustments to the technology of the present invention without departing from the basic principles of the present invention. These changes and adjustments are all within the scope of protection of the present invention.

Claims

1. A method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver, characterized in that: The following steps are involved: Using silver oxide micro-nanostructure as template, ALD technology is used to uniformly deposit an oxide protective layer with controllable thickness on the template surface; The coated sample is subjected to high temperature annealing treatment; The surface oxide protective layer of the sample after high-temperature annealing treatment is removed, and finally porous silver with micro-nano structure is obtained.

2. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 1, characterized in that: The silver oxide micro-nano structure is a silver oxide material having a nanocolumn, nanowire, nanoparticle or nanosheet structure.

3. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 1, characterized in that: The thickness of the deposited oxide protective layer is 1-15 nm.

4. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 1 or 3, characterized in that: The oxide protective layer is aluminum oxide or zinc oxide.

5. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 4, characterized in that: The parameters for ALD deposition of aluminum oxide are: Reaction chamber temperature: room temperature ~ 200 ℃; Reaction source: Trimethylaluminum and water were used to deposit aluminum oxide, and the source temperature was room temperature; Pulse and purge time: The pulse of the metal source and water source is 0.5~5 s; each pulse is followed by a 4~20 s purge with high-purity nitrogen to ensure that the reaction by-products and residual reaction source are completely flushed away.

6. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 4, characterized in that: The parameters for ALD deposition of zinc oxide are: Reaction chamber temperature: room temperature ~ 200℃; Reaction source: Diethyl zinc and water are used to deposit zinc oxide, and the source temperature is room temperature; Pulse and purge time: The pulse of the metal source and water source is 0.5~5 s; each pulse is followed by a 4~20 s purge with high-purity nitrogen to ensure that the reaction by-products and residual reaction source are flushed away.

7. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 1, characterized in that: The high temperature annealing temperature is 400-800° C. and the time is 10-120 minutes.

8. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 1, characterized in that: Selective chemical etching is used to remove the oxide protective layer. The high-temperature annealed sample is immersed in an acid or alkaline solution for 30-300 s.

9. The method for preparing a surface-enhanced Raman substrate of micro-nanostructured porous silver according to claim 1, characterized in that: The acid solution is hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid, and the alkali solution is sodium hydroxide or potassium hydroxide.

10. A surface-enhanced Raman substrate of micro-nanostructured porous silver, characterized in that: Porous silver with a micro-nano structure prepared by the method according to any one of claims 1 to 9.

Images