A gold nanoparticle island array surface plasmon resonant cavity and its preparation method

Abstract

The present invention discloses a gold nanoparticle island array surface plasmon resonant cavity and a method for preparing the same. The gold nanoparticle island array surface plasmon resonant cavity comprises a porous alumina template prepared on an aluminum substrate, and a gold nanoparticle island array layer formed on the surface of the alumina template. The preparation method uses an aluminum sheet as a substrate, forms the alumina template through two anodization processes, and then modifies the alumina template surface with ion sputtering to form the gold nanoparticle island array. The gold nanoparticle island array surface plasmon resonant cavity exhibits excellent performance, and the preparation method is more convenient and faster than conventional methods for preparing structures such as nanorods and nanospheres.

Description

Technical Field

[0001] The present invention relates to the field of surface plasmons, and in particular to a gold nanoparticle island array surface plasmon resonant cavity and a preparation method thereof. Background Art

[0002] When light shines on a metal nanostructure, free electrons on the metal surface are excited and produce resonant oscillations called surface plasmons. Surface plasmons include two major aspects: localized surface plasmons and surface plasmon polaritons.

[0003] Localized surface plasmons (LSPs) are generated by the collective oscillation of free electrons on the metal surface, driven by an electromagnetic field. The shape and size of metal nanoparticles influence this collective oscillation. At specific resonant wavelengths, this electron resonance excites the electromagnetic field, creating a resonance known as LSPR. When this LSPR occurs at the interface between a metal structure and the surrounding medium, an enhanced electromagnetic field is generated on the surface of the structure.

[0004] Surface plasmon polaritons (SPPs) are electromagnetic waves in the infrared or visible wavelengths that propagate along metal-dielectric or metal-air interfaces. Surface plasmon polaritons exhibit excellent spatial localization and high local field strength. However, due to the dispersion relation, they cannot be directly excited by light incident directly from air on the surface of a metal film. Successful excitation requires external devices or the satisfaction of wave-vector matching conditions.

[0005] In addition to the localized surface plasmon modes and surface plasmon polaritons mentioned above, when the gap between two or more metal nanostructures is small enough to form a surface plasmon resonant cavity, the surface plasmons formed on these metal nanostructures can interact with each other, generating strong near-field coupling, a so-called strong coupling surface plasmon resonance mode. In recent years, research has begun to focus on these strongly coupled surface plasmon resonance modes, with the near-field coupling generated by fabricating periodic noble metal nanostructures as nanocavities to excite surface plasmon resonances being of particular interest. A variety of nanostructures have been studied, including spheres, nanorods, cubes, metal nanorings, nanoprisms, nanoshell core-shell structures, and alloy nanostructures. Noble metal nanostructures have been used to design highly sensitive micro- and nanophotonic devices, including biosensors, nanolight sources, optical switches, and medical testing instruments.

[0006] Although the fabrication of nanorods and nanospheres is relatively simple, the resulting surface plasmon resonant cavities still have significant shortcomings. For example, the nanospheres are not arranged regularly, and the nanorods are of varying lengths. This results in the resonance peaks exhibiting wide half-widths and low intensities, indicating high losses. Furthermore, the fabrication process is often criticized for its long preparation time and low success rate. Summary of the Invention

[0007] The present invention provides a gold nanoparticle island array surface plasmon resonant cavity and a preparation method thereof, so as to solve the problem of poor performance of the nano-localized surface plasmon resonant cavity in the prior art, simplify the tedious and complicated preparation method and shorten the production cycle.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A gold nanoparticle island array surface plasmon resonant cavity comprises a porous alumina template prepared on an aluminum substrate. The surface of the alumina template is modified to form a gold nanoparticle island array layer. The gold nanoparticle island array layer is composed of multiple gold nanoparticle islands distributed in an array, and each gold nanoparticle island is formed by stacking gold nanoparticles.

[0010] Furthermore, a dot matrix consisting of a number of gold nanoparticle islands is distributed around each hole of the alumina template, and each dot matrix is ​​distributed in an array along with the hole.

[0011] Furthermore, the lattice is a hexagonal lattice formed by six gold nanoparticle islands.

[0012] A method for preparing the gold nanoparticle island array surface plasmon resonant cavity comprises the following steps:

[0013] Step 1: Using an aluminum sheet as a substrate, an aluminum oxide template with a porous structure is formed on the aluminum substrate through two anodizing treatments;

[0014] Step 2: performing ion sputtering on the surface of the alumina template obtained in step 1 under a gold evaporation environment, thereby modifying the surface of the alumina template to form a gold nanoparticle island array.

[0015] In a further step 1, the clean aluminum is annealed and placed in an electrolytic cell, and an oxalic acid solution with a concentration of 0.25 to 0.35 mol / L is added to the electrolytic cell. Then, the aluminum sheet is used as an anode and a graphite electrode is used as a cathode, and oxidation is performed at a DC voltage of 40 to 50 V and a temperature of 11 to 13° C. for 20 to 24 hours to complete the first anodization treatment.

[0016] Then, an acid is used to remove the oxide layer formed on the surface of the aluminum substrate after the first anodizing treatment;

[0017] Finally, the aluminum substrate after the oxide layer was removed was placed in the electrolytic cell again, and an oxalic acid solution with a concentration of 0.25-0.35 mol / L was added to the electrolytic cell. With the aluminum sheet as the anode and the graphite electrode as the cathode, the aluminum substrate was oxidized at a DC voltage of 40-50 V and a temperature of 11-13°C for 1 minute and 10 seconds to complete the second anodization, thereby forming a porous alumina template on the aluminum substrate.

[0018] Furthermore, when annealing the aluminum substrate, the aluminum substrate is placed at 10 -3 The aluminum substrate was annealed at 500°C for 5 hours under an atmosphere of 1.5 Pa to remove the internal stress of the aluminum substrate.

[0019] Furthermore, phosphochromic acid is used to remove the oxide layer formed on the surface of the aluminum substrate after the first anodizing treatment.

[0020] Furthermore, the aluminum substrate after the first anodizing treatment is placed in phosphochromic acid and heated at 60° C. for 40 to 48 hours to remove the oxide layer.

[0021] Furthermore, in the phosphochromic acid, the mass percentage of phosphoric acid is 5-8%, the mass percentage of chromic acid is 1.6-2.0%, and the rest is deionized water.

[0022] Furthermore, in step 2, an ion sputtering instrument is used for ion sputtering. The working pressure of the ion sputtering instrument is set to 0.05~0.06MPa and the working current is set to 10~40mA DC current in a gold evaporation environment. The surface of the alumina template is ion sputtered for 40~200 seconds, thereby modifying the surface of the alumina template to form a gold nanoparticle island array.

[0023] In the present invention, metallic aluminum is used as a substrate, which is subjected to secondary anodization to form an ultra-thin alumina template, and then gold is evaporated on this basis by ion sputtering to conveniently prepare a surface plasmon resonant cavity.

[0024] The surface plasmon resonance cavity of the present invention is distributed in a hexagonal lattice around the holes on the surface of an ultra-thin alumina template. Each lattice contains six independent gold nanoparticle islands, and each gold nanoparticle island is composed of stacked gold nanoparticles. Because it is based on the ultra-thin alumina template, the entire array exhibits good periodicity. Through the enhancement effect of the array, the surface plasmon resonance peak is excited.

[0025] The preparation method of the present invention can significantly shorten the sample preparation cycle and improve the success rate of sample preparation. The prepared surface plasmon resonant cavity has excellent performance. By controlling the parameters of ion sputtering and the variation of gold evaporation conditions, surface plasmon resonant cavities with different surface plasmon modes can be easily and effectively prepared.

[0026] The localized surface plasmon resonance of gold nanostructures can effectively confine the incident field energy to the surface of the structure, resulting in a significant local field enhancement. This, to a certain extent, increases the intensity of the interaction between light and matter, which has profound and positive implications for research directions such as biosensing and nano-localized optical imaging. Aluminum sheets can form highly ordered porous structures after secondary anodization, which lays the foundation for assisting the assembly of ordered arrays of gold nanoparticle islands. The surface plasmon resonance cavity of the gold nanoparticle island array prepared by ion sputtering and evaporating gold on the surface of an alumina template can exhibit excellent performance with a narrower half-width at half-maximum resonance peak and higher intensity, while greatly improving preparation efficiency and shortening the cycle time.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The present invention uses a highly ordered porous template formed by anodizing aluminum sheets, a structure with excellent performance. On this basis, a highly ordered array of gold nanoparticle islands is prepared by gold vaporization, resulting in a gold nanoparticle island array surface plasmon resonant cavity. This preparation method is more convenient and faster than previous methods for preparing structures such as nanorods and nanospheres, and offers better performance. Furthermore, the performance of the surface plasmon resonant cavity can be manipulated by simply changing the gold vaporization conditions. This has significant implications for research in areas such as biosensing and nano-localized optical imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an electron microscope image of the ultrathin alumina template of the present invention.

[0030] Figure 2 3 and 4. These are electron micrographs of the gold nanoparticle island array assembled with the aid of an alumina template in an embodiment of the present invention, wherein (a) is a low-magnification electron micrograph and (b) is a high-magnification electron micrograph.

[0031] Figure 3 It is the change in the resonance peak position of the surface plasmon resonance cavity of the gold nanoparticle island array in the embodiment of the present invention when the gold evaporation time is in the range of 40 to 200 seconds. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and examples.

[0033] Example 1

[0034] like Figure 2 As shown, this embodiment discloses a gold nanoparticle island array surface plasmon resonator cavity, comprising a porous alumina template fabricated on an aluminum substrate. The alumina template is surface-modified to form a gold nanoparticle island array layer, which is composed of multiple gold nanoparticle islands arranged in an array. Specifically, each hole in the alumina template is surrounded by a hexagonal lattice consisting of six gold nanoparticle islands, each hexagonal lattice arranged in an array along the hole, and each gold nanoparticle island is composed of a stack of gold nanoparticles.

[0035] Example 2

[0036] This embodiment discloses a method for preparing the gold nanoparticle island array surface plasmon resonant cavity described in Example 1, comprising the following steps:

[0037] Step 1: Using an aluminum sheet as a substrate, a porous alumina template is formed on the aluminum substrate through two anodizing processes. The process is as follows:

[0038] (1.1) Use an aluminum sheet with a purity of 99.999% and a thickness of 0.3-0.5 mm as the aluminum substrate. Cut the aluminum substrate into discs with a diameter of 20-25 mm. Flatten the aluminum substrate with organic glass and soak it in acetone for 24-48 hours to remove surface oil stains and dust.

[0039] (1.2) Take out the aluminum substrate treated in step (1.1) and place it in anhydrous ethanol. Shake gently to wash away the residual acetone solution, oil stains and dust. Then take out the aluminum substrate and place it in deionized water to clean it in the same way. Repeat this sequence and wash it again. Then take out the aluminum substrate piece by piece and place it on filter paper. Cover it with a layer of filter paper and dry it for 48 hours to ensure that the aluminum sheet is clean and dry.

[0040] (1.3) Place the aluminum substrate treated in step (1.2) into a vacuum annealing furnace and set it to 10 -3 Pa pressure conditions, annealed in a vacuum annealing furnace at 500 ° C for 5 hours to remove the internal stress of the aluminum substrate, and then placed in a sample bag for storage after cooling;

[0041] (1.4) Place the aluminum substrate annealed in step (1.3) in an electrolytic cell and add a 0.25-0.35 mol / L oxalic acid solution sufficient to submerge the aluminum substrate. Then, oxidize the aluminum substrate for 20-24 hours at a DC voltage of 40-50 V and a temperature of 11-13°C, using the aluminum sheet as the anode and the graphite electrode as the cathode, to complete the first anodization treatment. Rinse the aluminum substrate after the first anodization treatment with deionized water for 3-4 hours and then, with the oxidized surface facing downward, place it in a Petri dish filled with deionized water and soak for 24-48 hours.

[0042] (1.5) After drying the aluminum substrate after the first anodizing treatment in step (1.4) on filter paper, soak it in phosphochromic acid, where the mass percentage of phosphoric acid is 5-8%, the mass percentage of chromic acid is 1.6-2.0%, and the remainder is deionized water. The phosphochromic acid-soaked aluminum substrate is heated in an oven at 60°C for 40-48 hours to remove the oxide layer formed by oxidation. The aluminum substrate is then placed in a petri dish and rinsed with deionized water several times until the solution no longer turns yellow. The aluminum substrate is then placed face down in a petri dish filled with deionized water and soaked for 24-48 hours.

[0043] (1.6) Place the aluminum substrate treated in step (1.5) on filter paper and dry it, then place it in an electrolytic cell, and add an oxalic acid solution with a concentration of 0.25~0.35mol / L to the electrolytic cell, which is sufficient to submerge the aluminum substrate. Then, under conditions of a DC voltage of 40~50V and a temperature of 11~13°C, use the aluminum sheet as the anode and the graphite electrode as the cathode, and oxidize for 1 minute and 10 seconds to complete the second anodizing treatment, thereby forming an ultra-thin porous alumina template on the aluminum substrate. Then, place the aluminum substrate after the second anodizing treatment in a culture dish and wash it with deionized water for 3~4 times, and place the oxidized surface of the aluminum substrate facing down in a culture dish filled with deionized water and soak it for 24 hours. Observe under a scanning electron microscope, and the electron microscope image of the ultra-thin alumina template is as follows Figure 1 shown.

[0044] Step 2: Set the ion sputtering instrument to a gold vaporization environment with a working pressure of 0.05-0.06 MPa and a working current of 10-40 mA DC current, and perform ion sputtering on the surface of the alumina template formed on the aluminum substrate in step 1 for 40-200 seconds, thereby modifying the surface of the alumina template to form a gold nanoparticle island array.

[0045] In this embodiment, the size of the formed gold nanoparticle islands is 40-50 nm, and the distance between the gold nanoparticle islands is 10-20 nm.

[0046] The thickness of the oxide layer of the anodized aluminum template will change with the change of oxidation time, and the primary oxidation will retain scratches and defects on the surface of the aluminum sheet. After the primary oxidation, using phosphochromic acid to remove the primary oxidation layer can play a certain role in removing scratches and defects and forming a uniformly arranged oxide lattice, such as Figure 1 As shown, secondary oxidation on this basis will produce a very regular ultra-thin alumina template.

[0047] like Figure 2As shown, the template is evaporated with gold using ion sputtering. When the evaporation current is larger, the sputtered gold nanoparticles will be larger. When the evaporation time is longer, a thicker gold nanoparticle island array will be formed. When a certain thickness is reached, a gold film will be formed.

[0048] Surface plasmons in metallic nanostructures are generated at the interface between the metal structure and the surrounding medium, creating a region of enhanced electromagnetic field on the surface of the structure. This effect can be stimulated by a surface plasmon resonator (SPR) using a gold nanoparticle island array, fabricated by evaporating gold onto an alumina template. Using a near-infrared-visible-ultraviolet spectrophotometer, the reflectance spectrum of the SPR is measured at an 8° diffuse reflectance angle, thereby characterizing the surface plasmon modes.

[0049] from Figure 3 As can be seen in the figure, the surface plasmon resonance modes of a gold nanoparticle island array surface plasmon resonator change with the gold evaporation time. This is essentially because the evaporation time alters the size of the gold nanoparticle islands within the array, which in turn affects the thickness of the array. Under conditions of 0.05–0.06 MPa and a gold evaporation current of 10–40 mA, increasing the evaporation time increases the thickness of the gold nanoparticle island array, and the longitudinal surface plasmon resonator modes of the same order blueshift. Here, we fabricated surface plasmon resonators of gold nanoparticle island arrays with evaporation times of 40–200 s. The corresponding resonance peaks are at 708 nm, 669 nm, 631 nm, 602 nm, and 593 nm, respectively. This demonstrates the high regularity of the surface plasmon resonators of the gold nanoparticle island arrays fabricated using this method and demonstrates their practical value for future research.

[0050] The preferred embodiments of the present invention are described in detail above with reference to the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner unless there is any contradiction. Such combinations should also be regarded as the contents disclosed in this disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0051] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by those skilled in the art should fall within the scope of protection of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A gold nanoparticle island array surface plasmon resonant cavity, characterized in that: The invention comprises an alumina template with a porous structure prepared on an aluminum substrate, wherein the surface of the alumina template is modified to form a gold nanoparticle island array layer, wherein the gold nanoparticle island array layer is composed of a plurality of gold nanoparticle islands distributed in an array, and each gold nanoparticle island is respectively formed by stacking gold nanoparticles; A dot matrix consisting of a number of gold nanoparticle islands is distributed around each hole in the alumina template, and each dot matrix is ​​distributed in an array along the hole; The lattice is a hexagonal lattice formed by six gold nanoparticle islands; The method for preparing the gold nanoparticle island array surface plasmon resonant cavity comprises the following steps: Step 1: Using an aluminum sheet as a substrate, an aluminum oxide template with a porous structure is formed on the aluminum substrate through two anodizing treatments; Step 2: performing ion sputtering on the surface of the alumina template obtained in step 1 under a gold evaporation environment, thereby modifying the surface of the alumina template to form a gold nanoparticle island array; In step 1, the clean aluminum is annealed and placed in an electrolytic cell, and an oxalic acid solution with a concentration of 0.25-0.35 mol / L is added to the electrolytic cell. Then, the aluminum sheet is used as the anode and the graphite electrode is used as the cathode. The aluminum sheet is oxidized at a DC voltage of 40-50 V and a temperature of 11-13° C. for 20-24 hours to complete the first anodization treatment. Then, an acid is used to remove the oxide layer formed on the surface of the aluminum substrate after the first anodizing treatment; Finally, the aluminum substrate after the oxide layer was removed was placed in an electrolytic cell again. An oxalic acid solution with a concentration of 0.25-0.35 mol / L was added to the electrolytic cell. With the aluminum sheet as the anode and the graphite electrode as the cathode, oxidation was performed at a DC voltage of 40-50 V and a temperature of 11-13° C. for 1 minute and 10 seconds to complete a second anodization, thereby forming an alumina template with a porous structure on the aluminum substrate. When annealing the aluminum substrate, place the aluminum substrate at 10 -3 The aluminum substrate was annealed at 500°C for 5 hours under an atmosphere of 1.5 Pa to remove the internal stress of the aluminum substrate.

2. The gold nanoparticle island array surface plasmon resonant cavity according to claim 1, characterized in that: Phosphochromic acid is used to remove the oxide layer formed on the surface of the aluminum substrate after the first anodizing treatment.

3. The gold nanoparticle island array surface plasmon resonant cavity according to claim 2, characterized in that: The aluminum substrate after the first anodizing treatment is placed in phosphochromic acid and heated at 60°C for 40-48 hours to remove the oxide layer.

4. The gold nanoparticle island array surface plasmon resonant cavity according to claim 2 or 3, characterized in that: In the phosphochromic acid, the mass percentage of phosphoric acid is 5-8%, the mass percentage of chromic acid is 1.6-2.0%, and the rest is deionized water.

5. The gold nanoparticle island array surface plasmon resonant cavity according to claim 1, characterized in that: In step 2, ion sputtering is performed using an ion sputtering instrument. The working pressure of the ion sputtering instrument is set to 0.05~0.06MPa and the working current is set to 10~40mA DC current in a gold vaporization environment. The surface of the alumina template is ion sputtered for 40~200 seconds, thereby modifying the surface of the alumina template to form a gold nanoparticle island array.

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