Thin-walled conical silver nanoarray based on nested structure and preparation method and application thereof

Abstract

The application belongs to the technical field of metal dot array, and provides a thin-wall conical silver nano array based on a nested structure, a preparation method and application thereof, and comprises the following steps: pretreatment of an aluminum sheet; nano-imprinting and anodic oxidation; etching of a nested anodic aluminum oxide structure in a phosphoric acid solution; preparation of a nested anodic aluminum oxide template; and preparation of a noble metal dot array. The application is used to overcome the problems of complex process, single preparation structure, long preparation period, and single optical mode of the structure that can be selected in the preparation process of the noble metal dot array. The application adopts a combination of under-voltage anodic oxidation and chemical etching to prepare a noble metal array with a special thin-wall conical structure and multiple optical modes. The preparation method is more convenient, the preparation time is shorter, the preparation area is larger, and the prepared sample and derived structure can be used as a resonant cavity of a micro laser, and have a wide application prospect in the field of micro-nano optics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal array, and particularly relates to a thin-wall conical silver nanoarray based on a nested structure and a preparation method and application thereof. BACKGROUND

[0002] Plasmon is a quasi-particle phenomenon formed by collective oscillation of free electrons in metals or semiconductors, has two core characteristics of breaking through the optical diffraction limit and local field enhancement, and is widely applied to biological sensing and photo-thermal catalysis, and the characteristic of breaking through the diffraction limit also enables the development of nanophotonic devices and quantum information technology.

[0003] Surface plasmon resonance (SPR) is an important branch of plasmon, and the surface plasmon resonance effect can produce extremely strong electromagnetic field enhancement and special optical response at the metal-dielectric interface, and the physical nature is derived from the coherent oscillation of free electrons in the metal under the action of the electromagnetic field of light waves. According to the geometric morphology of the nanostructure, surface plasmons are mainly divided into two categories: propagating surface plasmon polaritons and localized surface plasmon resonances. When propagating surface plasmon polaritons propagate along the metal-dielectric surface, the energy is quickly attenuated due to ohmic loss and radiation loss of the metal, which limits the application in long-distance photon integration, and the problem of momentum matching also increases the complexity of device design and process difficulty; while the localized surface plasmon polaritons can produce strong hot spot effect at the tip of the metal nanostructure, thereby realizing the confinement of subwavelength scale light field, and only through the regulation of the structure morphology can multi-band adjustment be realized, without phase matching, simplifying the device design.

[0004] Localized surface plasmons are derived from the collective oscillation of free electrons in metal nanoparticles under the action of light field, and can produce strong local electric field enhancement, but the resonance peak is usually wide, and the quality factor is limited. When the nanoparticles are arranged in a periodic manner, the structure will introduce a Rayleigh anomaly caused by Bragg diffraction, and the extended state mode has high coherence and narrow linewidth characteristics. When the localized surface plasmon and the diffraction mode are matched in frequency and wave vector, the two can form a new hybrid optical mode through coherent coupling, i.e. surface lattice resonance. This resonance has strong local field characteristics, narrow spectrum and high quality factor, realizes the effective transformation from local resonance to collective optical response, and provides an important platform for high-sensitivity sensing, narrow-linewidth nanolaser and optical regulation.

[0005] Based on the characteristics of narrow linewidth, direction adjustable and multi-mode selection of surface lattice resonance, when the surface lattice resonance of metal particle array is coupled with the fluorescent light of dye, it is easier to realize low threshold, narrow linewidth and high quality factor of nanometer laser. Metal particles exist as the resonant cavity in the three elements of laser, which solves the problem of metal loss by using the way of spatial localization of light, breaks through the diffraction limit, so as to achieve the purpose of smaller volume, lower power and faster response of plasmonic nanolaser. The fine tuning of the structure and morphology of metal particles will present different modulation effects on light. Through the structure design of metal particles, the optical cavity structure which is beneficial to realize the excellent performance of nanolaser can be prepared.

[0006] At present, the commonly used preparation methods of metal point array mainly include two categories of "top-down" and "bottom-up". The top-down methods such as electron beam lithography, focused ion beam etching and photolithography all have problems such as high cost, low efficiency and small structure area, which are difficult to be widely applied in various fields. The bottom-up self-assembly method also has problems such as poor process stability, many array defects and poor repeatability. SUMMARY

[0007] The embodiment of the application aims to provide a preparation method of thin-walled conical silver nanoarray based on nested structure, and aims to solve the problems in the above background art.

[0008] The embodiment of the application is implemented in the following way: the preparation method of thin-walled conical silver nanoarray based on nested structure includes the following steps:

[0009] Pretreatment of aluminum sheet: after cutting the high-purity aluminum foil, it is cleaned, then chemical polishing and cleaning are carried out to obtain a polished aluminum sheet for standby;

[0010] Nanoimprinting and anodic oxidation: the convex side of the nickel film is covered on the smooth surface of the polished aluminum sheet, pressure is applied to form nanoindentation, and 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 an initial form of anodic aluminum oxide;

[0011] Etching of nested anodic aluminum oxide structure in phosphoric acid solution: the initial form of anodic aluminum oxide is placed in a 5% mass fraction 30 DEG C constant temperature phosphoric acid solution for chemical etching, the time is 30 min, and the anodic aluminum oxide structure is obtained after cleaning and standby;

[0012] Preparation of nested anodic aluminum oxide template: drop a small amount of PMMA solution on the nested anodic aluminum oxide structure, perform spin coating operation, then drop the same amount of concentrated PMMA solution, perform spin coating operation, remove the aluminum substrate, obtain the nested anodic aluminum oxide template supported by PMMA, and then put the PMMA side up into the acetone solution, after the PMMA is completely dissolved, the nested anodic aluminum oxide template is obtained;

[0013] Preparation of noble metal dot array: the nested anodic aluminum oxide template is put into a physical vapor deposition system, silver is deposited after taking out, and then the surface silver film is removed, cleaned, and a thin-walled conical silver nano array based on the nested structure is obtained.

[0014] Another purpose of the embodiment of the present application is a thin-walled conical silver nano array based on the nested structure, which is prepared by the above preparation method.

[0015] Another purpose of the embodiment of the present application is the application of a thin-walled conical silver nano array based on the nested structure in the field of micro-nano optics.

[0016] The nested anodic aluminum oxide template is prepared by the method of under-voltage anodization in the embodiment of the present application, and based on the structural characteristics of the template itself, the template realizes the preparation of a higher efficient silver metal nano array with simplified steps through physical vapor deposition and chemical etching, and the structure prepared inherits the characteristics of the nested structure, realizes the generation of more selectable optical mode characteristics based on a single structure, and the existence of the anodic aluminum oxide template in the array not only realizes the plasticity of the particles, but also realizes the rapid heat dissipation of the array area, which helps to prolong the service life of the array; in addition, the embodiment of the present application can prepare a centimeter-level sample, which can save the cost to the greatest extent, and is carried out at room temperature, which protects the operator safety to the greatest extent, and has a broad prospect in the fields of biosensing, nano photonic devices and quantum. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The preparation process of the nested anodic aluminum oxide provided for the embodiment 1 of the present application is provided;

[0018] Figure 2 The basic morphology of the nested anodic aluminum oxide provided for the embodiment 1 of the present application is provided;

[0019] Figure 3 The preparation process of the nested anodic aluminum oxide template provided for the embodiment 1 of the present application is provided;

[0020] Figure 4 The morphology of the nested anodic aluminum oxide template provided for the embodiment 1 of the present application is provided;

[0021] Figure 5 The preparation process of the nested silver metal dot array provided for the embodiment 1 of the present application is provided;

[0022] Figure 6 The morphology of the nested silver metal dot array provided for the embodiment 1 of the present application is provided;

[0023] Figure 7 The optical property diagram of the thin-walled conical silver nano array based on the nested structure prepared for the embodiment 1 of the present application is provided.

[0024] In the drawing: 1-polished aluminum sheet; 2-nickel film; 3-anodic aluminum oxide; 4-PMMA support; 5-cover glass; 6-silver film. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0026] A thin-walled conical silver nano array based on a nested structure, the preparation method comprising the following steps:

[0027] (1) Pretreatment of aluminum sheet: first cut high-purity aluminum foil into uniform 2 cm circular aluminum sheets, and sequentially place the aluminum sheets into beakers containing anhydrous ethanol, ultrapure water, and anhydrous ethanol in an ultrasonic machine for cleaning, then perform chemical polishing on the aluminum sheets by electrochemical method, and clean the polished aluminum sheets after polishing for use;

[0028] (2) Nanoimprinting and anodic oxidation: cover the raised side of the nickel film with a square 600 nm periodic protrusion on the smooth surface of the polished aluminum foil, apply a certain pressure using a hydraulic press, and maintain, forming square 600 nm recesses on the polished sheet, place the nanoimprinted aluminum sheet in an electrolyte environment at 4°C, apply the oxidation voltage and current corresponding to the nested structure, and obtain the initial morphology of anodic aluminum oxide;

[0029] (3) Etching of nested anodic aluminum oxide structure in phosphoric acid solution: place the prepared initial morphology of anodic aluminum oxide in a constant-temperature phosphoric acid solution for chemical etching, and clean for use, thereby obtaining the desired morphology of the nested anodic aluminum oxide structure;

[0030] (4) Preparation of nested anodic aluminum oxide template: drop a certain amount of dilute polymethyl methacrylate (PMMA) solution on the nested anodic aluminum oxide structure three times, spin coat it on a spin coater to ensure that the solution enters the aluminum oxide pores, then drop the same amount of concentrated PMMA solution three times, spin coat and dry to serve as a support skeleton, then place the spin-coated sheet aluminum substrate downward into a mixed copper chloride hydrochloride solution, after the aluminum substrate is completely corroded, remove the substrate by placing the spin-coated sheet in a copper chloride solution, obtain the nested anodic aluminum oxide template with PMMA support, and finally place the PMMA side upward into an acetone solution, after the PMMA is completely dissolved, transfer the nested anodic aluminum oxide template to a cover glass, and obtain the template.

[0031] (5) Preparation of noble metal dot array: Put the cover glass fixed with nested anodic aluminum template into a physical vapor deposition system, deposit a certain amount of silver, and then take it out. Then use a cotton swab to dip a mixed solution of hydrochloric acid and copper chloride to chemically remove the silver film on the surface of the template. After ultrapure water cleaning, the metal nanodot array with the original nested anodic aluminum template still retained on the cover glass can be obtained.

[0032] The specific implementation of the present application is described in detail below in combination with specific examples.

[0033] Example 1, a thin-walled conical silver nanometer array based on a nested structure, the preparation method comprising the following steps:

[0034] (1) Pretreatment of aluminum sheet, as shown in Figure 1 : Cut high-purity aluminum foil into uniform 2 cm circular aluminum sheets, and place the aluminum sheets in beakers containing absolute ethanol, ultrapure water, and absolute ethanol in sequence, and clean them in an ultrasonic machine for 7 minutes each time. Then, use electrochemical method to chemically polish the aluminum sheets by placing them in an electrolyte (100 mL of perchloric acid and 700 mL of absolute ethanol) in an ice water bath, applying a current of 30 V and 2 A to each sheet, and observing the polishing condition of the aluminum sheet after 6-7 minutes. Turn off the power, take out the polished aluminum sheet 1, and clean it with absolute ethanol and ultrapure water for use;

[0035] (2) Nanoimprint and anodization, as shown in Figure 1 : Cover the convex side of the nickel film 2 with a periodic convexity of 600 nm square with the smooth surface of the polished aluminum sheet 1, apply a pressure of 4 MPa using a hydraulic press, and maintain for 2 minutes. Take out the polished aluminum sheet 1, and observe that a 600 nm square concave is formed on the smooth surface. Place the nanoimprinted polished aluminum sheet 1 in a 4°C electrolyte (0.3 mol / L phosphoric acid solution) environment, apply the oxidation voltage corresponding to the nested structure, 140 V, and a current of 0.5 A, and oxidize for 10 minutes to obtain the initial form of anodic aluminum 3;

[0036] (3) Nested anodic aluminum structure phosphoric acid solution etching: Place the prepared initial form of anodic aluminum 3 in a 30°C constant temperature phosphoric acid solution (5% by mass fraction) for chemical etching, and etch for 30 minutes. After completion, clean with ultrapure water for use, and the nested anodic aluminum structure with the required morphology can be obtained. The sample morphology is as shown in Figure 2As shown, it can be seen that the structure is mainly divided into two parts of the upper nested anodic aluminum oxide structure and the lower aluminum substrate. The nested structure is observed from the top view. The pores are mainly divided into main holes and auxiliary holes. The main holes are larger. The bottom is divided into four parts with a protrusion in the middle. The auxiliary holes are composed of four shallow small holes symmetrically distributed. The existence of the aluminum substrate can protect the bottom of the nested structure. After etching in the phosphoric acid solution, the overall void of the upper structure increases, and the structure is clearer. The nested aluminum oxide containing impurities is partially dissolved during etching. The optical mode of the structure after etching is clearer. At the same time, the increase in void also facilitates the preparation of a complete support skeleton during template preparation, which plays a better supporting and protecting role.

[0037] (4) Preparation of the nested structure anodic aluminum oxide template, as shown in Figure 3 : First, 450 μl of dilute PMMA solution (PMMA powder 0.5 g, dichloromethane 15 mL) is added dropwise on the aluminum oxide sheet. It is spin-coated on a spin coater at 1800 r / min for 20 s. The solution is repeated three times to ensure that it enters the aluminum oxide hole. Then the same amount of concentrated PMMA solution (PMMA powder 1 g, dichloromethane 20 mL) is added dropwise. The same spin-coating parameters are used for spin-coating. After the PMMA is dried, it plays a supporting skeleton role. Then the spin-coated sheet is placed aluminum substrate down into a copper chloride hydrochloric acid mixed solution (3.4 g of copper chloride dihydrate, 100 mL of hydrochloric acid, 100 mL of ultrapure water). After the aluminum substrate is completely corroded, the spin-coated sheet is placed into a copper chloride solution (3.4 g of copper chloride dihydrate, 200 mL of ultrapure water) for complete removal of the substrate. A nested anodic aluminum oxide template with PMMA support 4 is obtained. Finally, the PMMA side is placed into an acetone solution for 30 min. After the PMMA is completely dissolved, the nested anodic aluminum oxide template is transferred to a cover glass 5. The template is obtained. The template morphology is shown in Figure 4 : The template pores are placed upward on the glass substrate. At this time, the template only has the nested anodic aluminum oxide structure. After removing the aluminum substrate, the optical mode of the substrate no longer has an impact. At this time, the optical mode of the complete nested anodic aluminum oxide template is obtained, which is convenient for analysis and application.

[0038] (5) Preparation of noble metal dot array, as shown in Figure 5 : The cover glass 5 with the nested anodic aluminum oxide template fixed thereon is placed into a physical vapor deposition system. After depositing 200 nm of silver at a speed of 0.2 nm / s, the cover glass 5 is taken out. Then a cotton swab is used to dip into a copper chloride hydrochloric acid mixed solution (3.4 g of copper chloride dihydrate, 100 mL of hydrochloric acid, 100 mL of ultrapure water) to chemically remove the silver film 6 on the surface of the template. After ultrapure water cleaning, a metal nanodot array (thin-walled conical silver nanometer array based on the nested structure) that still retains the original nested anodic aluminum oxide template on the cover glass is obtained, as shown in Figure 6As shown, at this time, the structure is composed of three parts, the nested anodic aluminum oxide structure, the silver nanodot array in the nested structure aperture and the glass substrate, based on the unique morphology of the nested structure, the silver metal entering the main aperture is attached to the top of the central convex, and gradually forms a thin-walled conical silver particle with the deposition, the whole template forms a metal array, which breaks the diffraction limit as a laser resonant cavity, and can be applied to the field of nanolaser based on the principle of plasmon.

[0039] Example 2, compared with example 1, the difference is only that the dilute PMMA solution in step (4) is adjusted to PMMA powder 0.7g, dichloromethane 20mL, and the concentrated PMMA solution is adjusted to PMMA powder 0.96g, dichloromethane 20mL.

[0040] Example 3, compared with example 1, the difference is only that the dilute PMMA solution in step (4) is adjusted to PMMA powder 0.68g, dichloromethane 20mL, and the concentrated PMMA solution is adjusted to PMMA powder 0.98g, dichloromethane 20mL.

[0041] The optical properties of the thin-walled conical silver nanometer array based on the nested structure prepared by example 1 are analyzed, and the EK dispersion diagram of the thin-walled conical silver nanometer array based on the nested structure prepared by example 1 under white light at 0° azimuth angle is as shown in Figure 7 As shown, the unique structure of the nested structure makes the originally single scattering center split into four adjacent scatterers, which introduces additional diffraction paths, thereby affecting the surface lattice resonance distribution of the nanometer array, and multiple surface lattice resonance modes appear. Through the composition analysis of the structure and the calculation of the duty cycle, the nanometer array prepared in the embodiment of the application is composed of triple surface lattice resonance, and has more high symmetry points and high symmetry paths.

[0042] In summary, the nested anodic aluminum oxide with main and auxiliary holes is obtained by the process of under-voltage oxidation, wherein the main holes are distributed with X-shaped columnar convexes, and a group of small holes (four in a group) are symmetrically distributed between the surface main holes, and the nanometer metal point array can be directly obtained by using the template. Due to the structural characteristics of the template itself, the metal deposited into the main hole will be deposited on the convex in the hole, forming a thin-walled conical silver metal nanometer array. Compared with the ordinary structure, the array has more selectable optical modes and can be applied in the field of micro-nano optics. The method bypasses the complex process of preparing a double-pass anodic aluminum oxide template and avoids the loss caused by preparing a double-pass template.

[0043] The above only describes the preferred embodiments of the present application and should not be used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

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 corresponding to the nested structure is 140 V, the current is 0.5 A, and the oxidation time is 10 min 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, the nested anodic aluminum oxide structure was obtained. The morphology of the nested structure can be observed from above. The pores are divided into main pores and secondary pores. The bottom is divided into four parts with a protrusion in the middle. The secondary pores are composed of four shallow pores that are symmetrically distributed. 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 the structure and spin-coated again. 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. The solvent for both the dilute and concentrated PMMA solutions 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. Preparation of precious metal dot array: A nested anodic aluminum oxide template is placed in a physical vapor deposition system, metallic silver is deposited and then removed. The surface silver film is then removed and the array is cleaned to obtain a thin-walled conical silver nanoarray based on the nested structure. Based on the morphology of the nested structure, the silver metal that enters the main pore is attached to the top of the central protrusion and gradually forms thin-walled conical silver particles as deposition proceeds.

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 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.

5. 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 1-4.

6. An application of the thin-walled conical silver nanoarray based on a nested structure as described in claim 5 in the field of micro-nano optics.

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