A method for preparing a periodic array of nano-needle tip open ring 3D structure

Abstract

This invention belongs to the field of micro-nanostructures and relates to a method for preparing a periodic array of nanotip open-ring 3D structures. This method involves self-assembling polystyrene nanospheres after depositing a reflective layer and a support layer on a silicon substrate. Reactive ion etching is then used to reduce the nanosphere volume. Subsequently, two tilted magnetron sputtering steps are performed. The deposited noble metal is etched using a reactive ion etcher. After removing the nanosphere mask, a periodic array of nanotip open-ring 3D structures is obtained. This method features a simple preparation process, good uniformity, high order, and strong repeatability, and has broad application potential in fields such as SERS and photoelectric performance testing.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano structures and relates to a method for preparing a periodic array of nano-needle tip open ring 3D structures. Background Art

[0002] In recent years, the surface plasmon resonance (SPR) effect has attracted considerable attention due to its unique light-matter interaction properties, demonstrating its enormous potential for improving photocatalytic energy conversion efficiency. The SPR phenomenon occurs on the surface of metals (such as gold, silver, copper, and aluminum), where valence electrons collectively oscillate under the influence of an external field (e.g., light). By adjusting the size, composition, and morphology of metal nanoparticles, their absorption properties from the visible to near-infrared region can be precisely controlled, potentially expanding the range of light capture. In 2004, Stockman proposed the concept of nanofocusing, a key characteristic of surface plasmons. This describes the phenomenon in which the energy of surface plasmons is highly concentrated at the tip of a cone as they propagate along a conical metal nanostructure. This nanofocusing effect enables the formation of a remotely excited and propagating electromagnetic field "hotspot" at the tip of the nanostructure, with the focus size exceeding the nanometer scale. This has sparked a surge of international research in recent years. Regarding enhancing light-matter interactions, when SPPs propagate along a conical nanostructure, their energy converges at the tip, forming an electromagnetic field "hotspot." This focusing effect not only achieves breakthrough nanoscale precision but also maintains a high-intensity electromagnetic field during remote excitation and propagation, enabling highly sensitive detection at the molecular level. In the field of spectral scanning detection, nanotip arrays, as probes, enable remote excitation of molecules and precise spectral analysis, greatly improving detection accuracy and sensitivity.

[0003] The nanotip split ring structure exhibits unique advantages in near-field optics and nanophotonics. Its ring structure effectively localizes and enhances electromagnetic fields, forming a highly concentrated near-field hotspot, providing an ideal platform for high-sensitivity sensing and super-resolution imaging. Leveraging the electromagnetic field enhancement effect of the nanotip split ring, ultrasensitive detection of single molecules or nanoparticles can be achieved, opening new possibilities for breakthroughs in technologies such as surface-enhanced Raman spectroscopy (SERS) and fluorescence enhancement.

[0004] Compared to traditional nanoantenna structures, nanotip split rings offer superior field enhancement properties and more flexible light field manipulation capabilities, making them particularly suitable for nonlinear optics and quantum optics research. However, the precise fabrication of nanotip split rings currently faces significant challenges. Their complex geometric structure requires extremely high machining precision, and ensuring uniformity and consistency in large-scale fabrication is difficult. These issues have severely hampered their widespread adoption in industrial applications. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention proposes a method for preparing periodic arrays of nanotip split-ring 3D structures. This method aims to produce smaller nanotip structures with more pronounced focusing and field enhancement effects, while also providing a simple, cost-effective preparation process. The resulting periodic arrays of nanotip split-ring 3D structures exhibit large-scale, controllable fabrication, good uniformity, high order, and strong repeatability, and exhibit excellent localized surface plasmon resonance (LSPR) performance and increased specific surface area.

[0006] During the preparation process, the optical loss is effectively reduced by depositing an aluminum (Al) reflective layer on the silicon wafer. Due to the high lattice matching between aluminum and silicon, its adhesion to the silicon wafer is excellent, making the open ring structure not easy to fall off during the subsequent mechanical peeling of the polystyrene (PS) balls. At the same time, the characteristics of silicon dioxide (SiO2) with a small dielectric constant and high transparency are utilized as a structural support layer to further improve the optical performance of the nano-needle tip open ring array. In addition, sulfur hexafluoride (SF6) gas is used to anisotropically etch the SiO2 support layer, so that the nano-needle tip open ring forms a semi-suspended state, which significantly reduces the dielectric loss, thereby further optimizing the optical performance of the structure. In order to achieve the above purpose, the present application is implemented through the following technical solutions:

[0007] A method for preparing a periodic array of nano-needle tip open ring 3D structures comprises the following steps:

[0008] S1 deposits Al as a reflective layer on a silicon wafer, then deposits SiO2 as a support layer, and then self-assembles nanospheres on the support layer as a mask;

[0009] S2 reduces the volume of the nanospheres by reactive ion etching, and obtains a nanosphere mask with reduced volume on the surface of the silicon wafer;

[0010] S3 places the silicon wafer with the nanosphere mask surface on a magnetron sputtering sample stage tilted at a certain angle α to deposit the precious metal;

[0011] S4: After rotating the silicon wafer with the nanosphere mask surface on the sample stage by a certain angle γ, repeat step S3 to deposit the noble metal again;

[0012] S5 uses reactive ion etching to etch the precious metal that is not blocked by the nanosphere mask using argon gas;

[0013] After S6 etching is completed, the nanospheres are physically peeled off to obtain a periodic array of nanotip open ring 3D structure.

[0014] Preferably, in S2, the reactive ion etching is specifically to perform O2 etching on the polystyrene nanospheres using a reactive ion etching method, with an etching power of 125 W, an oxygen pressure of 20 Pa, a gas flow rate of 50 sccm, and an etching time of 40 s.

[0015] Preferably, S3 specifically includes: placing the silicon wafer on a sample table inclined at 60°, and evacuating the sample to a vacuum of 5×10 -4 Pa, argon gas was passed to adjust the sputtering pressure to 0.6 Pa, the Au sputtering power was 0.01 KW, the sputtering time was 90 s, and a 60 nm gold film was deposited.

[0016] Preferably, in S1, the thickness of the deposited Al is 100 nm; the thickness of the deposited SiO2 is 100 nm, and the deposition rate is 0.2 Å / s; the nanospheres are polystyrene nanospheres with a diameter of 500 nm.

[0017] Preferably, in S5, the etching power is 150 W, the pressure is 20 Pa, the gas flow rate is 50 sccm, and the etching time is 180 s.

[0018] Preferably, in S6, the nanospheres are physically peeled off using polyimide tape.

[0019] Preferably, after S6, the method further includes: step S7, using sulfur hexafluoride gas to etch silicon dioxide to achieve a semi-suspended state of the structure, thereby reducing dielectric loss.

[0020] Preferably, S7 specifically includes the following steps:

[0021] The etching power was 125 W, the pressure was 20 Pa, the gas flow rate was 65 sccm, and the etching times were 60 s, 180 s, and 420 s, respectively.

[0022] In the present invention, a periodic array of 3D structures of nano-needle tip open rings is prepared. The periodic array has high order, good uniformity, and strong repeatability. The preparation method is relatively simple and the preparation cycle is short. It can be effectively replicated and applied on a large scale, which broadens the operational space for subsequent nanostructures. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the preparation process of nanotip open ring.

[0024] Figure 2 SEM comparison of polystyrene nanospheres before and after reactive ion etching.

[0025] Figure 3 This is an SEM image of a periodic array obtained by Ar ion etching after one deposition.

[0026] Figure 4This is the SEM image of the periodic array obtained by Ar ion etching after two depositions.

[0027] Figure 5 is the reflectance spectrum of the fabricated array.

[0028] Figure 6 The structural hot spot distribution obtained by COMSOL simulation. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, the method for preparing the periodic array of nano-tip open ring 3D structure of this embodiment includes the following steps:

[0031] 1) Using electron beam evaporation, 100 nm of aluminum and 100 nm of silicon dioxide were deposited on a silicon substrate at a rate of 0.2 Å / s.

[0032] 2) Using polystyrene nanospheres as a mask, a single-layer hexagonal close-packed array is formed by self-assembly and then the nanosphere mask is transferred to the substrate;

[0033] 3) Use reactive ion etching, introduce oxygen, set the flow rate to 50sccm, the pressure to 20Pa, the power to 125W, and the RF time to 40s. After the etching is completed, use nitrogen to break the vacuum and obtain a nanosphere mask with a reduced volume, such as Figure 2 As shown;

[0034] 4) Use magnetron sputtering or electron beam evaporation for deposition, fix the silicon wafer on a sample stage tilted 60°, and pump the vacuum to 5×10 -4 Pa, argon gas, power setting to 10W, 60nm gold deposition;

[0035] 5) Rotate the wafer 90° and repeat the above steps;

[0036] 6) Place the silicon wafer with the deposited precious metal into a reactive ion etcher and introduce argon gas with a flow rate of 50 sccm, a pressure of 20 Pa, a power of 150 W, and an RF time of 180 s. After the etching is completed, nitrogen is used to break the vacuum. Due to the blocking of the nanosphere mask, the exposed precious metal is etched, while the precious metal in the nanosphere orthographic projection area is retained.

[0037] 7) The nanosphere mask was physically peeled off using polyimide tape, and a periodic array of nanotip open ring 3D structure was obtained on the silicon wafer, such as Figure 4 As shown;

[0038] 8) Use SF6 in reactive ion etching to etch the SiO2 substrate with a flow rate of 65 sccm, a pressure of 20 Pa, a power of 125 W, and etching times of 60 s, 180 s, and 420 s, respectively, to reduce dielectric loss.

[0039] With the development of advanced nanofabrication technologies, a variety of nanostructures can be used to design and fabricate nanoscale plasmon devices. The fundamental properties of surface plasmons (SPPs) and localized surface plasmons (LSPs) provide new insights and understandings for the study of optoelectronic devices. Nanostructures such as plasmon tips, gaps, and cavities have been widely studied due to their high-intensity localized fields and their strongly enhanced optical response. Unlike the widely studied nanopores, the nanotip open ring structure has two nanometer-scale tips, and there is a strong coupling between the surface plasmons (SPPs) propagating along the structure and the localized surface plasmon resonances (LSPRs) at the open tips, which can be used for SERS and optoelectronic performance detection.

[0040] The reflection spectra of samples with different SiO2 etching times were tested, such as Figure 5 As shown in the figure, in addition to the reflection valley generated by the interband transition of gold at 500nm, two more reflection valleys are generated near 600nm and 900nm. Moreover, as the etching time of SiO2 increases, the reflection spectrum has a significant blue shift. In addition, COMSOL Multiphysics was used to simulate the sample with the etching time of SiO2 of 420s, as shown in the figure. Figure 6 As shown in the figure, two high-energy hot spots are generated at the nanotip. Therefore, this structure has good potential in SERS detection and photoelectric performance detection.

Claims

1. A method for preparing a periodic array of nano-tip open ring 3D structures, characterized in that: The following steps are involved: S1, depositing Al as a reflective layer on a silicon wafer, then depositing SiO2 as a support layer, and then self-assembling nanospheres on the support layer as a mask; S2, reducing the volume of the nanospheres by reactive ion etching, thereby obtaining a nanosphere mask with a reduced volume on the surface of the silicon wafer; S3, placing the silicon wafer with the nanosphere mask surface on a magnetron sputtering sample stage tilted at a certain angle α, and depositing the noble metal; S4, rotating the silicon wafer with the nanosphere mask surface on the sample stage by a certain angle γ, and repeating step S3 to deposit the noble metal again; S5, using reactive ion etching to etch the noble metal that is not blocked by the nanosphere mask using argon gas; S6. After etching is completed, the nanospheres are physically peeled off to obtain a periodic array of nanotip open ring 3D structure; S7. Use sulfur hexafluoride gas to etch silicon dioxide to achieve a semi-suspended state of the structure and reduce dielectric loss.

2. The method for preparing a periodic array of nano-tip open ring 3D structures according to claim 1, characterized in that: In S2, the reactive ion etching is specifically to perform O2 etching on the polystyrene nanospheres using a reactive ion etching method, with an etching power of 125 W, an oxygen pressure of 20 Pa, a gas flow rate of 50 sccm, and an etching time of 40 s.

3. The method for preparing a periodic array of nano-tip open ring 3D structures according to claim 1, characterized in that: S3 specifically includes: placing the silicon wafer on a sample stage tilted at 60°, and evacuating the sample to 5×10 -4 Pa, argon gas was passed to adjust the sputtering pressure to 0.6 Pa, the Au sputtering power was 0.01 KW, the sputtering time was 90 s, and a 60 nm gold film was deposited.

4. The method for preparing a periodic array of nano-tip open ring 3D structures according to claim 1, wherein: In S1, the thickness of the deposited Al is 100 nm; the thickness of the deposited SiO2 is 100 nm, and the deposition rate is 0.2 Å / s; the nanospheres are polystyrene nanospheres with a diameter of 500 nm.

5. The method for preparing a periodic array of nano-tip open ring 3D structures according to claim 1, characterized in that: In S5, the etching power is 150 W, the pressure is 20 Pa, the gas flow rate is 50 sccm, and the etching time is 180 s.

6. The method for preparing a periodic array of nano-tip open ring 3D structures according to claim 1, characterized in that: In S6, the nanospheres were physically exfoliated using polyimide tape.

7. The method for preparing a periodic array of nano-tip open ring 3D structures according to claim 1, characterized in that: In S7, the etching power is 125 W, the pressure is 20 Pa, the gas flow rate is 65 sccm, and the etching time is 420 s.

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