Plasmon-enhanced second harmonic-based core-shell resonant cavity structure and preparation method thereof

Abstract

The invention provides a core-shell resonant cavity structure based on plasmon enhanced second harmonics, which is characterized in that gold balls of two-dimensional material tungsten disulfide are transferred and wrapped on an ultra-smooth gold film, and the gold film with the thickness of 10 nm is evaporated on the gold balls. And then measuring the second harmonic of the structure on a Raman spectrometer, and comparing the second harmonic with the second harmonic intensity of the gold ball so as to judge the second harmonic enhancement effect of the structure. The main experimental method comprises the following steps: annealing a gold film of 10nm on a silicon oxide substrate to obtain gold balls of about 50nm, evaporating tungsten oxide and sulfur at high temperature, respectively conveying argon and hydrogen to the gold balls, and controlling the time to obtain the core-shell structure of the gold balls wrapped by tungsten disulfide. After the structure is transferred to an ultra-smooth gold film and a 10nm gold film is evaporated, a resonant cavity structure is obtained, and nonlinear characteristics of the resonant cavity structure are represented by a Raman spectrometer.

Description

Technical Field

[0001] The present invention belongs to the technical fields of nanophotonics, nonlinear optics and nanomaterials, and particularly relates to a core-shell resonator structure based on plasmon resonance, which is used to efficiently enhance the second harmonic generation (SHG) of two-dimensional materials. Background Art

[0002] As one of the core technologies of nonlinear optical effects, second harmonic generation (SHG) exhibits key application values in many fields such as laser frequency conversion, super-resolution imaging and optical sensing. However, traditional nonlinear optical materials usually have problems such as low conversion efficiency and limited material selection, which limit the performance improvement in practical applications. In recent years, noble metal nanoparticles (such as gold nanospheres) have shown excellent nonlinear optical response characteristics due to their localized surface plasmon resonance (LSPR) effect, but their second harmonic generation efficiency still needs to be further improved. Summary of the Invention

[0003] Aiming at the problem of insufficient SHG efficiency in the prior art, the present invention provides a core-shell resonator structure and a preparation method thereof, which realize the efficient enhancement of second harmonic waves through the synergistic effect of plasmon resonance and two-dimensional materials.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A core-shell resonator structure based on plasmon-enhanced second harmonic generation, comprising:

[0006] A super-smooth gold film with a thickness of 100 nm and a surface roughness < 1 nm, which is used to reduce light scattering loss;

[0007] A core-shell structure composed of a gold ball (with a diameter of 52 ± 9 nm) and a WS 2 layer (with a thickness of 1-10 nm). The gold ball enhances the local electric field through LSPR, and WS 2 provides a nonlinear response;

[0008] The core-shell structure is located on the surface of the super-smooth gold film, and the outer surfaces of the core-shell structure and the super-smooth gold film are covered with a 10-nm gold film.

[0009] A preparation method of a core-shell resonator structure based on plasmon-enhanced second harmonic generation, comprising the following steps:

[0010] S1: Prepare a super-smooth gold film;

[0011] S2: Prepare a core-shell structure;

[0012] S3: Assemble the resonant cavity;

[0013] S4: Characterize.

[0014] Furthermore, step S1 is specifically as follows:

[0015] First, deposit a 100-nm-thick gold film on the silicon wafer by thermal evaporation, and then stick the transparent glass sheet on the surface of the gold film with ultraviolet curable glue; irradiate with an ultraviolet lamp until the glue cures, and peel the gold film from the silicon wafer with a blade to obtain a super-smooth gold film.

[0016] Furthermore, step S2 is specifically as follows:

[0017] Deposit a gold film with a thickness of about 10 nm on the SiO 2 / Si wafer substrate by thermal evaporation. Place the S powder on the feeding device, and then place the feeding device together with the S powder in the non-heating area of the first high-temperature tube furnace. Place the WO 3 powder in the heating area of the first high-temperature tube furnace. Place the SiO 2 / Si wafer substrate and the gold film in the second high-temperature tube furnace for annealing. Anneal at 750 °C for 10 minutes to obtain gold nanoparticles with a diameter of 52 ± 9 nm. Then connect the first high-temperature tube furnace and the second high-temperature tube furnace, and gradually increase the temperatures of the first high-temperature tube furnace and the second high-temperature tube furnace. As the temperature of the first high-temperature tube furnace gradually increases, the WO 3 powder gradually evaporates. Then use argon to transport the tungsten oxide vapor to the SiO 2 / Si substrate in the second high-temperature tube furnace. When the first high-temperature tube furnace reaches 920 °C and the second high-temperature tube furnace reaches 840 °C, quickly move the S powder to the heating area of the first high-temperature tube furnace with the feeding device. The S powder starts to evaporate and reacts with the WO 3 on the surface of the gold nanoparticles, and finally forms a WS 2 single layer to obtain a core-shell structure with a WS 2 -coated gold ball. By controlling the duration of this process, the number of WS 2 layers can be controlled.

[0018] Furthermore, step S3 is specifically as follows:

[0019] Attach the side of the SiO 2 / Si substrate with the core-shell structure to the super-smooth gold film, and gently press the back of the SiO 2 / Si substrate to transfer the core-shell structure. Then use tweezers to remove the SiO 2 / Si wafer substrate. Subsequently, deposit a 10-nm-thick gold film on the surfaces of the super-smooth gold film and the core-shell structure to form a resonant cavity structure.

[0020] Further, step S4 is specifically as follows:

[0021] First, use a Raman spectrometer to measure the Raman spectrum of the particles on the SiO 2 / Si substrate in dark field mode. If there are characteristic peaks of WS 2 , it proves that the particle is a core-shell structure. Subsequently, measure the second harmonic intensity of the particle and compare the amplification factor with the second harmonic intensity of 100 nm gold particles. Finally, measure the SEM image of the corresponding particle, measure the diameter of the structure, and further determine that the structure is a nearly circular core-shell structure.

[0022] The second harmonic enhancement structure based on tungsten disulfide-coated gold spheres on a super-smooth gold film provided by the present invention has the following advantages:

[0023] 1. High-efficiency second harmonic enhancement: The local surface plasmon resonance effect of the gold sphere can significantly enhance the local electric field. Tungsten disulfide has a high second-order nonlinear susceptibility, and the super-smooth gold film can provide an optical interface with low scattering, thus further optimizing the localization effect of the light field. On this basis, a resonant cavity structure is constructed to achieve a synergistic enhancement effect among the three, thereby significantly improving the efficiency of second harmonic generation.

[0024] 2. Strong controllability: By adjusting parameters such as the size of the gold sphere, the number of layers of tungsten disulfide, and the thickness of the super-smooth gold film, the nonlinear optical properties of the structure can be regulated to meet different application requirements. Description of the Drawings

[0025] Figure 1 is a schematic diagram of the structure of the present invention provided by an embodiment of the present invention.

[0026] Figure 2 is Figure 1 a cross-sectional view of

[0027] Figure 3 is a comparison diagram of the second harmonic intensity of this structure and that of a 100 nm gold sphere. Detailed Embodiments

[0028] The following details the implementation of the present invention. The examples of the implementation are shown in the drawings and are further described in detail for the present invention, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as a limitation to the present invention.

[0029] Embodiment 1

[0030] A core-shell resonant cavity structure based on plasmon-enhanced second harmonic generation, comprising:

[0031] Ultra-smooth gold film, with a thickness of 100 nm and a surface roughness < 1 nm, is used to reduce light scattering loss;

[0032] Core-shell structure, consisting of a gold sphere (diameter 52 ± 9 nm) and a WS layer (thickness 1 - 10 nm) wrapping it. The gold sphere enhances the local electric field through LSPR, and WS provides non-linear response; 2 layer (thickness 1 - 10 nm). The gold sphere enhances the local electric field through LSPR, and WS 2 provides non-linear response;

[0033] The core-shell structure is located on the surface of the ultra-smooth gold film. The outer surfaces of the core-shell structure and the ultra-smooth gold film are covered with a 10-nm gold film, forming a resonant cavity structure.

[0034] Example 2

[0035] A preparation method of a core-shell resonant cavity structure based on plasmon-enhanced second harmonic generation, including the following steps:

[0036] S1: Prepare an ultra-smooth gold film;

[0037] First, deposit a 100-nm-thick gold film on a silicon wafer by thermal evaporation, then stick a transparent glass sheet on the gold film surface with ultraviolet curable glue (Norland optical glue 61); irradiate with an ultraviolet lamp until the glue cures, and use a blade to peel the gold film from the silicon wafer to obtain an ultra-smooth gold film; since the gold film was previously attached to the silicon wafer, it has the same flatness as the silicon wafer.

[0038] S2: Prepare the core-shell structure;

[0039] Deposit a gold film with a thickness of about 10 nm on a SiO 2 / Si wafer substrate by thermal evaporation. Place the S powder on the feeding device, and then place the feeding device together with the S powder in the non-heating zone of the first high-temperature tube furnace. Place the WO 3 powder in the heating zone of the first high-temperature tube furnace. Place the SiO 2 / Si wafer substrate and the gold film in the second high-temperature tube furnace for annealing, anneal at 750 °C for 10 minutes to obtain gold nanoparticles with a diameter of 52 ± 9 nm. Then connect the first high-temperature tube furnace and the second high-temperature tube furnace, and gradually increase the temperatures of the first high-temperature tube furnace and the second high-temperature tube furnace. As the temperature of the first high-temperature tube furnace gradually increases, the WO 3 powder gradually evaporates, and then use argon to transport the tungsten oxide vapor to the SiO 2 / Si substrate in the second high-temperature tube furnace. When the first high-temperature tube furnace reaches 920 °C and the second high-temperature tube furnace reaches 840 °C, use the feeding device to quickly move the S powder to the heating zone of the first high-temperature tube furnace. The S powder starts to evaporate and reacts with the WO 3 on the surface of the gold nanoparticles, and finally form WS2 A single layer is obtained, resulting in WS 2 A core-shell structure encapsulating a gold sphere. By controlling the duration of this process, the number of layers of WS 2 can be controlled.

[0040] S3: Assemble the resonator;

[0041] Attach the side of the SiO 2 / Si substrate with the core-shell structure to the ultrasmooth gold film, and gently press the back of the SiO 2 / Si substrate to achieve the transfer of the core-shell structure. Then, use tweezers to remove the SiO 2 / Si wafer substrate. Subsequently, evaporate a 10-nm-thick gold film on the surface of the ultrasmooth gold film and the core-shell structure to form a resonator structure.

[0042] S4: Characterization;

[0043] First, use a Raman spectrometer to measure the Raman spectrum of the particles on the ultrasmooth gold film in the dark field mode. If there are characteristic peaks of WS 2 , it proves that the particle is a core-shell resonator structure. Subsequently, measure the second harmonic intensity of the particle and compare the amplification factor with the second harmonic intensity of 100-nm gold particles. Finally, measure the SEM image of the corresponding particle, measure the diameter of the structure, and further determine that the structure is a nearly circular core-shell structure.

[0044] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be implemented using existing technologies.

Claims

1. A core-shell resonant cavity structure based on plasmon enhanced second harmonic, characterized in that: include: Ultra-smooth gold film, with a thickness of 100nm and a surface roughness of <1nm, is used to reduce light scattering loss; The core-shell structure consists of a gold ball and a WS2 layer that wraps it. The gold ball enhances the local electric field through LSPR, and WS2 provides a nonlinear response. The core-shell structure is located on the ultra-smooth gold film surface, and the outer surfaces of the core-shell structure and the ultra-smooth gold film surface are covered with a 10nm gold film to form a resonant cavity structure.

2. The method for preparing a core-shell resonant cavity structure based on plasmon enhanced second harmonic as claimed in claim 1, characterized in that: The steps include: S1: Preparation of ultra-smooth gold film; S2: Preparation of core-shell structure; S3: Assemble the resonant cavity; S4: Characterization.

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