Thin-wall conical silver nano array based on nested structure as well as preparation method and application of thin-wall conical silver nano array

Abstract

The invention is suitable for the technical field of metal dot arrays, and provides a thin-wall conical silver nano array based on a nested structure and a preparation method and application of the thin-wall conical silver nano array based on the nested structure. Nanoimprinting and anodic oxidation are carried out; etching the nested anodic aluminum oxide structure by using a phosphoric acid solution; preparing a nested anodic aluminum oxide template; and preparing the precious metal dot array. In order to solve the problems of complex process, single preparation structure, long preparation period, single optical mode for selection of the structure and the like in the preparation process of the precious metal dot array at present, the special thin-wall conical multi-optical mode precious metal array is prepared by adopting a mode of combining undervoltage anodic oxidation and chemical corrosion; the preparation method is more convenient, the preparation time is shorter, the preparation area is larger, and the prepared sample and the derivative structure thereof can be used as resonant cavities of micro lasers, and have wide application prospects in the fields of micro-nano optics and the like.

Description

Technical Field

[0001] This invention belongs to the field of metal dot array technology, and particularly relates to thin-walled conical silver nanoarrays based on nested structures, their preparation methods, and applications. Background Technology

[0002] Plasmons are quasi-particle phenomena formed by the collective oscillation of free electrons in metals or semiconductors. They have two core characteristics: breaking the optical diffraction limit and enhancing the local field. They are widely used in biosensing and photothermal catalysis. Their ability to break the diffraction limit also empowers the development of nanophotonic devices and quantum information technology.

[0003] Surface plasmon resonance (SPR) is an important branch of plasmons. The SPR resonance effect can generate extremely strong electromagnetic field enhancement and unique optical responses at metal-dielectric interfaces. Its physical essence originates from the coherent oscillation of free electrons within the metal under the influence of the electromagnetic field of light waves. Based on the geometry of the nanostructure, SPRs are mainly divided into two categories: propagating SPRs and localized SPR resonances. When propagating SPRs propagate along the metal-dielectric surface, their energy decays rapidly due to ohmic and radiative losses, limiting their application in long-distance photonic integration. Furthermore, the need for momentum matching increases the complexity of device design and fabrication. In contrast, localized SPRs can generate strong hotspot effects at the tips of metal nanostructures, achieving subwavelength-scale optical field confinement. Multi-band modulation can be achieved simply by controlling the structural morphology, without phase matching, simplifying device design.

[0004] Localized surface plasmons originate from the collective oscillation of free electrons in metallic nanoparticles under the influence of an optical field, generating strong localized electric field enhancement. However, their resonance peaks are typically broad, and their quality factors are limited. When nanoparticles are arranged periodically, Rayleigh anomalies generated by Bragg diffraction are introduced into the structure. These extended modes exhibit high coherence and narrow linewidth characteristics. When localized surface plasmons and diffraction modes match in frequency and wave vector, they can coherently couple to form new hybrid optical modes, namely surface lattice resonances. This resonance simultaneously possesses strong localized field characteristics, narrow spectral width, and a high quality factor, achieving an effective transition from localized resonance to collective optical response. It also provides an important platform for applications such as high-sensitivity sensing, narrow-linewidth nanolasers, and optical manipulation.

[0005] Based on the narrow linewidth, tunable orientation, and multi-mode selection characteristics of surface lattice resonance, low-threshold, narrow-linewidth, and high-quality-factor nanolasers are readily achieved when the surface lattice resonance of a metal particle array is coupled with the fluorescence emission of a dye. Metal particles, acting as the resonant cavity in the three essential elements of laser technology, utilize spatial localization of light to address metal loss issues and overcome the diffraction limit. This allows for smaller size, lower power, and faster response in plasmonic nanolasers. Fine-tuning the morphology of the metal particles exhibits different modulation effects on light. Through structural design of the metal particles, optical cavity structures conducive to achieving superior nanolaser performance can be fabricated.

[0006] Currently, the commonly used methods for fabricating metal dot arrays are mainly divided into two categories: "top-down" and "bottom-up". Top-down methods such as electron beam lithography, focused ion beam etching, and photolithography all face problems such as high cost, low efficiency, and small structural area, making it difficult to be widely used in various fields. Bottom-up self-assembly methods, on the other hand, face problems such as poor process stability, many array defects, and poor repeatability. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing thin-walled conical silver nanoarrays based on nested structures, thereby addressing the problems mentioned in the background art.

[0008] The present invention is implemented as follows: a method for fabricating a thin-walled conical silver nanoarray based on a nested structure includes the following steps: Pretreatment of aluminum sheets: After cutting high-purity aluminum foil, it is cleaned, then chemically polished and cleaned to obtain polished aluminum sheets for later use; Nanoimprinting and anodizing: The raised side of the nickel film is covered on the smooth surface of the polished aluminum sheet, pressure is applied to form nano-depressions, the imprinted aluminum sheet is placed in an electrolyte environment, and the oxidation voltage and current corresponding to the nested structure are applied to obtain the initial morphology of anodized aluminum. Embedding of nested anodic aluminum oxide structure with phosphoric acid solution: The initial anodic aluminum oxide was placed in a 5% (w / w) phosphoric acid solution at 30°C for chemical etching for 30 min. After cleaning, it was ready for use to obtain the nested anodic aluminum oxide structure. Preparation of nested anodized aluminum oxide template: A dilute PMMA solution is dropped onto the nested anodized aluminum oxide structure and spin-coated. Then, the same amount of concentrated PMMA solution is dropped onto it and spin-coated. The aluminum substrate is then removed to obtain a nested aluminum oxide template supported by PMMA. The PMMA side is then placed in an acetone solution. After the PMMA is completely dissolved, the nested anodized aluminum oxide template is obtained. Preparation of noble metal dot array: A nested anodic aluminum oxide template was placed in a physical vapor deposition system, metallic silver was deposited, and then the template was removed. The surface silver film was then removed and the template was cleaned to obtain a thin-walled conical silver nanoarray based on a nested structure.

[0009] Another objective of this invention is to provide a thin-walled conical silver nanoarray based on a nested structure, which is prepared using the above-described method.

[0010] Another objective of this invention is the application of a thin-walled conical silver nanoarray based on a nested structure in the field of micro-nano optics.

[0011] This invention utilizes undervoltage anodizing to prepare nested anodic aluminum oxide templates. Based on the template's structural characteristics, a simplified and more efficient silver metal nanoarray fabrication process is achieved using physical vapor deposition and chemical etching. The resulting structure inherits the characteristics of nested structures, enabling the generation of more selectable optical modes based on a single structure. The presence of the anodic aluminum oxide template in the array not only achieves particle plasticity but also facilitates rapid heat dissipation in the array region, contributing to extended array lifetime. Furthermore, this invention can prepare centimeter-scale samples, maximizing cost savings and allowing for operation at room temperature, thus ensuring operator safety. It holds broad promise in biosensing, nanophotonic devices, and quantum computing. Attached Figure Description

[0012] Figure 1 The preparation process of nested anodized aluminum oxide provided in Embodiment 1 of the present invention; Figure 2 This is a basic morphological diagram of the nested anodized aluminum provided in Embodiment 1 of the present invention; Figure 3 The preparation process of the nested anodized aluminum template provided in Embodiment 1 of the present invention; Figure 4 This is a topographic image of the nested anodized aluminum template provided in Embodiment 1 of the present invention; Figure 5 The fabrication process of the nested silver metal dot array provided in Embodiment 1 of the present invention; Figure 6 This is a topographic diagram of the nested silver metal dot array provided in Embodiment 1 of the present invention; Figure 7 The optical properties of the thin-walled conical silver nanoarray based on a nested structure prepared in Example 1 of this invention are shown.

[0013] In the attached diagram: 1-polished aluminum sheet; 2-nickel film; 3-anodized aluminum; 4-PMMA support; 5-cover glass; 6-silver film. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0015] A thin-walled conical silver nanoarray based on a nested structure is prepared by the following steps: (1) Pretreatment of aluminum sheets: First, cut high-purity aluminum foil into uniform 2 cm circular aluminum sheets, and put the aluminum sheets into beakers containing anhydrous ethanol, ultrapure water and anhydrous ethanol in sequence according to time. Then, clean them in an ultrasonic machine. After that, use electrochemical method to chemically polish the aluminum sheets. After polishing, clean the polished aluminum sheets for later use. (2) Nanoimprinting and anodizing: The protruding side of a nickel film with a periodic 600 nm square protrusion is covered on the smooth surface of the polished aluminum foil. A certain pressure is applied using a hydraulic press and held to form a 600 nm square depression on the polished sheet. The nanoimprinted aluminum sheet is placed in an electrolyte environment at 4°C, and the oxidation voltage and current corresponding to the nested structure are applied to obtain the initial morphology of anodized aluminum. (3) Embedding of nested anodic aluminum oxide structure with phosphoric acid solution: The prepared initial morphology of anodic aluminum oxide is placed in a constant temperature phosphoric acid solution for chemical etching, cleaned and ready for use, and the desired morphology of nested anodic aluminum oxide structure can be obtained. (4) Preparation of nested anodic aluminum oxide template: A certain amount of dilute polymethyl methacrylate (PMMA) solution is added to the nested anodic aluminum oxide structure in three batches and then spin-coated on a spin coater to ensure that the solution enters the pores of the aluminum oxide. Then, the same amount of concentrated PMMA solution is added in three batches. After spin-coating and drying, it plays the role of supporting the skeleton. Then, the aluminum substrate of the spin-coated sheet is placed in a mixture of hydrochloric acid and copper chloride solution with the aluminum substrate facing down. After the aluminum substrate is completely corroded, the spin-coated sheet is placed in a copper chloride solution to completely remove the substrate, and a nested aluminum oxide template with PMMA support is obtained. Finally, the PMMA side is placed in an acetone solution. After the PMMA is completely dissolved, the nested aluminum oxide template is transferred to a coverslip to obtain the template. (5) Preparation of precious metal dot array: The coverslip with the nested anodic aluminum oxide template is placed in the physical vapor deposition system. After depositing a certain amount of silver, it is taken out and then the silver film on the surface of the template is chemically removed by using a cotton swab dipped in a mixture of hydrochloric acid and copper chloride. After washing with ultrapure water, the metal nano dot array on the coverslip that still retains the original nested aluminum oxide template can be obtained.

[0016] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0017] Example 1: A thin-walled conical silver nanoarray based on a nested structure, the preparation method of which includes the following steps: (1) Perform pretreatment on the aluminum sheet, such as... Figure 1 As shown: High-purity aluminum foil was cut into uniform 2 cm circular aluminum sheets. The aluminum sheets were then placed in beakers containing anhydrous ethanol, ultrapure water, and anhydrous ethanol in sequence according to time. They were cleaned in an ultrasonic cleaner for 7 min each. Subsequently, the aluminum sheets were chemically polished by electrochemical means. The aluminum sheets were placed in an electrolyte (100 mL perchloric acid and 700 mL anhydrous ethanol) in an ice-water bath. A current of 30 V and 2 A was applied to each sheet. After 6-7 min, the polishing condition of the aluminum sheets was observed. The power was turned off, the polished aluminum sheet 1 was taken out and cleaned with anhydrous ethanol and ultrapure water for later use. (2) Nanoimprinting followed by anodizing, such as Figure 1 As shown: The raised side of the nickel film 2 with tetragonal 600 nm periodic protrusions was covered on the smooth surface of the polished aluminum sheet 1. A pressure of 4 MPa was applied using a hydraulic press and held for 2 min. The polished aluminum sheet 1 was then removed, and a tetragonal 600 nm depression was observed to form on the smooth surface. The nano-imprinted polished aluminum sheet 1 was placed in an electrolyte environment (0.3 mol / L phosphoric acid solution) at 4 °C. An oxidation voltage of 140 V and a current of 0.5 A corresponding to the nested structure were applied, and the oxidation time was 10 min to obtain the initial morphology of anodic aluminum oxide 3. (3) Etching of nested anodic aluminum oxide structure with phosphoric acid solution: The prepared initial morphology anodic aluminum oxide 3 was placed in a 30℃ constant temperature phosphoric acid solution (mass fraction of 5%) for chemical etching for 30 min. After etching, it was rinsed with ultrapure water and ready for use. The desired morphology of the nested anodic aluminum oxide structure can be obtained. The morphology of the sample is as follows: Figure 2 As shown, the structure is mainly divided into two parts: an upper nested anodic aluminum oxide structure and a lower aluminum substrate. Observing the morphology of the nested structure from above, the pores are mainly divided into main pores and secondary pores. The main pores are larger, and the bottom is divided into four parts with a protrusion in the middle. The secondary pores consist of four symmetrically distributed shallow pores. The presence of the aluminum substrate can protect the bottom of the nested structure. After etching with phosphoric acid solution, the overall porosity of the upper structure increases, and the structure becomes clearer. The nested aluminum oxide containing impurities dissolves with the etched parts. The optical mode of the etched structure is clearer. At the same time, the increased porosity also facilitates the preparation of a complete support skeleton during template preparation, playing a better supporting and protective role. (4) Preparation of nested structure anodic aluminum oxide templates, such as Figure 3As shown: First, 450 μl of dilute PMMA solution (0.5 g PMMA powder, 15 mL dichloromethane) was dropped onto an alumina sheet. The sheet was then spin-coated at 1800 r / min for 20 s, repeated three times to ensure the solution entered the alumina pores. Next, the same amount of concentrated PMMA solution (1 g PMMA powder, 20 mL dichloromethane) was added, and the same spin-coating parameters were used. After drying, the PMMA acted as a supporting framework. Then, the spin-coated sheet was placed aluminum-substrate-side down in a mixture of hydrochloric acid and copper chloride (3.4 g copper chloride dihydrate, 100 mL hydrochloric acid, 100 mL ultrapure water). After the aluminum substrate was completely etched, the spin-coated sheet was placed in a copper chloride solution (3.4 g copper chloride dihydrate, 200 mL ultrapure water). The substrate was thoroughly removed in (mL ultrapure water) to obtain a nested alumina template supported by PMMA 4; finally, the PMMA side was placed in acetone solution for 30 min until the PMMA was completely dissolved. The nested alumina template was then transferred onto coverslip 5 to obtain the template, the morphology of which is as follows. Figure 4 As shown, the template is placed on the glass substrate with the pores facing upwards. At this time, the template only has a nested anodized aluminum structure. After removing the aluminum substrate, the optical mode of the substrate no longer has an impact. At this time, the complete optical mode of the nested anodized aluminum template is obtained, which is convenient for analysis and application. (5) Fabrication of noble metal dot arrays, such as Figure 5 As shown: A coverslip 5 with a nested alumina template is placed in a physical vapor deposition system. 200 nm of metallic silver is deposited at a velocity of 0.2 nm / s. The coverslip is then removed, and a cotton swab dipped in a mixed solution of hydrochloric acid and copper chloride (3.4 g copper chloride dihydrate, 100 mL hydrochloric acid, 100 mL ultrapure water) is used to chemically remove the silver film 6 on the template surface. After rinsing with ultrapure water, a metal nanodot array (a thin-walled conical silver nanoarray based on a nested structure) is obtained on the coverslip, still retaining the original nested alumina template. Figure 6 As shown, the structure consists of three parts: a nested anodic aluminum oxide structure, a silver nanoparticle array within the pores of the nested structure, and a glass substrate. Based on the unique morphology of the nested structure, the silver metal entering the main pore is attached to the top of the central protrusion. As the deposition proceeds, it gradually forms thin-walled conical silver particles. The entire template forms a metal array, which serves as a resonant cavity for lasers, breaking the diffraction limit. Based on the principle of plasmon resonance, it can be applied to the field of nanolaser applications.

[0018] Example 2: Compared with Example 1, the only difference is that the dilute PMMA solution in step (4) is adjusted to 0.7g of PMMA powder and 20mL of dichloromethane, and the concentrated PMMA solution is adjusted to 0.96g of PMMA powder and 20mL of dichloromethane.

[0019] Example 3: Compared with Example 1, the only difference is that the dilute PMMA solution in step (4) is adjusted to 0.68g of PMMA powder and 20mL of dichloromethane, and the concentrated PMMA solution is adjusted to 0.98g of PMMA powder and 20mL of dichloromethane.

[0020] The optical properties of the thin-walled conical silver nanoarray based on a nested structure prepared in Example 1 were analyzed, and its EK dispersion diagram at a 0° azimuth angle under white light was obtained as follows: Figure 7 As shown, the unique structure of the nested structure used to characterize its optical properties causes the originally single scattering center to split into four adjacent scatterers. This "composite" introduces additional diffraction paths, which in turn affects the surface lattice resonance distribution of the nanoarray, resulting in multiple surface lattice resonance modes. Through compositional analysis of the structure and calculation of the duty cycle, the nanoarray prepared in the embodiment of the present invention is composed of triple surface lattice resonances, with more high symmetry points and high symmetry paths.

[0021] In summary, this invention provides a nested anodic aluminum oxide with main and secondary holes obtained through undervoltage oxidation. The main holes contain X-shaped columnar protrusions, and a group of small holes (four in a group) are symmetrically distributed between the main holes on the surface. A nano-metal dot array can be directly obtained using this template. Due to the structural characteristics of the template itself, the metal deposited into the main holes will be deposited on the protrusions in the holes, forming a thin-walled conical silver metal nanoarray. At the same time, this array provides more selectable optical modes compared to ordinary structures, and can be applied in fields such as micro-nano optics. This method bypasses the complex process of preparing a double-pass anodic aluminum oxide template, avoiding the losses caused by preparing a double-pass template.

[0022] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating thin-walled conical silver nanoarrays based on a nested structure, characterized in that, Includes the following steps: Pretreatment of aluminum sheets: After cutting high-purity aluminum foil, it is cleaned, then chemically polished and cleaned to obtain polished aluminum sheets for later use; Nanoimprinting and anodizing: The raised side of the nickel film is covered on the smooth surface of the polished aluminum sheet, pressure is applied to form nano-depressions, the imprinted aluminum sheet is placed in an electrolyte environment, and the oxidation voltage and current corresponding to the nested structure are applied to obtain the initial morphology of anodized aluminum. Embedding of nested anodic aluminum oxide structure with phosphoric acid solution: The initial anodic aluminum oxide was placed in a 5% (w / w) phosphoric acid solution at 30°C for chemical etching for 30 min. After cleaning, it was ready for use to obtain the nested anodic aluminum oxide structure. Preparation of nested anodized aluminum oxide template: A dilute PMMA solution is dropped onto the nested anodized aluminum oxide structure and spin-coated. Then, the same amount of concentrated PMMA solution is dropped onto it and spin-coated. The aluminum substrate is then removed to obtain a nested aluminum oxide template supported by PMMA. The PMMA side is then placed in an acetone solution. After the PMMA is completely dissolved, the nested anodized aluminum oxide template is obtained. Preparation of noble metal dot array: A nested anodic aluminum oxide template was placed in a physical vapor deposition system, metallic silver was deposited, and then the template was removed. The surface silver film was then removed and the template was cleaned to obtain a thin-walled conical silver nanoarray based on a nested structure.

2. The method for preparing a thin-walled conical silver nanoarray based on a nested structure according to claim 1, characterized in that, In the pretreatment step of the aluminum sheet, the chemical polishing operation specifically involves placing the cut high-purity aluminum foil in an electrolyte bath and applying an electric current. The electrolyte includes perchloric acid and anhydrous ethanol.

3. The method for preparing a thin-walled conical silver nanoarray based on a nested structure according to claim 1, characterized in that, In the step of nanoimprinting and anodizing, the nickel film is a nickel film with tetragonal nano-periodic protrusions; the electrolyte is a phosphoric acid solution.

4. The method for preparing a thin-walled conical silver nanoarray based on a nested structure according to claim 1, characterized in that, In the step of preparing the nested anodic aluminum oxide template, the solvent for the dilute PMMA solution and the concentrated PMMA solution is dichloromethane, the concentration of the dilute PMMA solution is 0.033-0.035 g / mL, and the concentration of the concentrated PMMA solution is 0.048-0.05 g / mL.

5. The method for preparing a thin-walled conical silver nanoarray based on a nested structure according to claim 1, characterized in that, In the step of preparing the nested anodized aluminum template, the operation of removing the aluminum substrate specifically involves: placing the aluminum substrate of the spin-coated sheet face down in a mixture of hydrochloric acid and copper chloride; after the aluminum substrate is completely corroded, placing the spin-coated sheet into a copper chloride solution to completely remove the substrate.

6. A thin-walled conical silver nanoarray based on a nested structure, characterized in that, It is prepared using the preparation method described in any one of claims 1-5.

7. An application of the thin-walled conical silver nanoarray based on a nested structure as described in claim 6 in the field of micro-nano optics.

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