Electric field enhancement element and Raman spectrometer

Abstract

To provide an electric field enhancement element that has high detection sensitivity, can handle multiple wavelengths, and is highly convenient, and a Raman spectrometer equipped with such an electric field enhancement element. [Solution] An electric field enhancing element comprising a substrate, a plurality of conductive microstructures provided on the substrate, and a transparent layer covering the plurality of microstructures and the substrate, wherein the element comprises a first array provided in a first region of the substrate and having the microstructures arranged periodically, and a second array provided in a second region of the substrate different from the first region and having the microstructures arranged periodically, wherein at least one of the diameter of the microstructures, the thickness of the microstructures, and the pitch between adjacent microstructures differs between the first array and the second array.

Description

Technical Field

[0001] The present invention relates to an electric field enhancement element and a Raman spectrometer.

Background Art

[0002] As one of the spectroscopic techniques for detecting low-concentration sample molecules, a Raman spectrometer using Localized Surface Plasmon Resonance (LSPR) is known. In such a Raman spectrometer, an enhanced electric field is formed by an electric field enhancement element having a nanostructured microstructure, and Surface Enhanced Raman Scattering (SERS) in which Raman scattered light is enhanced occurs.

[0003] For example, Patent Document 1 discloses an optical device including a substrate, a metal microstructure composed of a plurality of metal particles formed on the surface of the substrate, and an organic molecular film formed on the metal microstructure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above optical device, further improvement in detection sensitivity is required. In addition, in the above optical device, for example, in the arrangement pattern of the metal microstructure, design is made according to the wavelength of incident light. Therefore, when it is used for incident light having a wavelength different from the design, there is a problem that sufficient detection sensitivity cannot be obtained and the convenience is low.

Means for Solving the Problems

[0006] An electric field enhancing element according to an application example of the present invention is, circuit board and A plurality of conductive microstructures are provided on the substrate, A transparent layer covering a plurality of the aforementioned microstructures and the substrate, Equipped with, A first arrangement is provided in the first region of the substrate, in which the microstructures are arranged periodically, A second array is provided in a second region of the substrate that is different from the first region, and the microstructures are arranged periodically. It has, The first array and the second array differ from each other in at least one of the following: the diameter of the microstructure, the thickness of the microstructure, and the pitch between adjacent microstructures.

[0007] A Raman spectrometer according to an application example of the present invention is, An electric field enhancing element according to an application example of the present invention, A light source that irradiates the aforementioned electric field enhancing element with light, A detector for detecting light from the electric field enhancing element, It is equipped with. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing an electric field enhancing element according to an embodiment. [Figure 2] This is a schematic plan view showing an electric field enhancing element according to the embodiment. [Figure 3] This figure shows an example of the planar shape of a microstructure. [Figure 4] This is a conceptual diagram to explain plasmon resonance in electric field enhancement devices. [Figure 5] This is a conceptual diagram to explain plasmon resonance in electric field enhancement devices. [Figure 6] This diagram illustrates the enhanced electric field generated by the microstructure of an electric field enhancing element. [Figure 7] This is a schematic plan view showing an electric field enhancing element according to a first modified example of the embodiment. [Figure 8] It is a plan view schematically showing an electric field enhancement element according to a second modification of the embodiment. [Figure 9] It is a plan view schematically showing an electric field enhancement element according to a third modification of the embodiment. [Figure 10] It is a graph for explaining the effect brought about by the electric field enhancement element shown in FIG. 9. [Figure 11] It is a plan view schematically showing an electric field enhancement element according to a fourth modification of the embodiment. [Figure 12] It is a graph for explaining the effect brought about by the electric field enhancement element shown in FIG. 11. [Figure 13] It is a cross-sectional view schematically showing an electric field enhancement element according to a fifth modification of the embodiment. [Figure 14] It is a cross-sectional view schematically showing an electric field enhancement element according to a sixth modification of the embodiment. [Figure 15] It is a diagram schematically showing a Raman spectroscopic apparatus according to the embodiment. [Figure 16] It is a diagram for explaining the principle of Raman scattering spectroscopy. [Figure 17] It is a schematic diagram showing an example of a Raman spectrum obtained by Raman scattering spectroscopy. [Figure 18] It is an X-Z cross-sectional view schematically showing a repeating unit of a model used for simulation. [Figure 19] It is an X-Y cross-sectional view schematically showing a model used for simulation. [Figure 20] It is a table comparing main parameters in Examples 1 to 12 and Comparative Example 1. [Figure 21] It is the simulation result of Example 1. [Figure 22] It is the simulation result of Example 2. [Figure 23] It is the simulation result of Example 3. [Figure 24] It is the simulation result of Example 4. [Figure 25] It is the simulation result of Example 5. [Figure 26] This is the simulation result for Example 6. [Figure 27] This is the simulation result for Example 7. [Figure 28] This is the simulation result for Example 8. [Figure 29] This is the simulation result for Example 9. [Figure 30] This is the simulation result for Example 10. [Figure 31] This is the simulation result for Example 11. [Figure 32] This is the simulation result for Example 12. [Figure 33] This is the simulation result for Comparative Example 1. [Modes for carrying out the invention]

[0009] The electric field enhancement element and Raman spectrometer of the present invention will be described in detail below based on the embodiments shown in the accompanying drawings.

[0010] 1. Electric field enhancing element First, the electric field enhancing element according to the embodiment will be described. Figure 1 is a schematic cross-sectional view showing the electric field enhancing element 100 according to this embodiment. Figure 2 is a schematic plan view showing the electric field enhancing element 100 according to this embodiment. Note that Figure 1 is a cross-sectional view taken along line II of Figure 2. In the figures of this application, the X, Y, and Z axes are defined as three mutually orthogonal axes and are indicated by arrows. The tip of the arrow on each axis is called the "positive side," and the base end is called the "negative side." The positive side of the Z axis is also called "up," and the negative side of the Z axis is also called "down."

[0011] 1.1. Structure The electric field enhancing element 100 shown in Figures 1 and 2 comprises a substrate 10, a dielectric layer 20, microstructures 30a and 30b, and a transparent layer 40. Note that the transparent layer 40 is not shown in Figure 2.

[0012] The substrate 10 supports multiple microstructures 30a and 30b via a dielectric layer 20. When light (incident light Lin) from a light source used for Raman scattering is incident from the substrate 10 side in Figure 1, this incident light Lin passes through the substrate 10 and the dielectric layer 20 and reaches the microstructures 30a and 30b. When the incident light Lin is incident from the transparent layer 40 side in Figure 1, this incident light Lin passes through the transparent layer 40 and reaches the microstructures 30a and 30b. In this case, when the incident light Lin is incident from the transparent layer 40 side, the incident light Lin may be reflected by the substrate 10 towards the transparent layer 40 side.

[0013] When incident light Lin reaches the multiple microstructures 30a or 30b, an enhanced electric field is generated. This enhanced electric field may be formed above the microstructures 30a and 30b, but preferably it is maximized in the direction perpendicular to the substrate 10, on the opposite side of the microstructures 30a and 30b from the substrate 10, and at a position away from the multiple microstructures 30a and 30b. With this configuration, the detection signal caused by the target material placed on the transparent layer 40 can be enhanced. As a result, an electric field enhancement element 100 with improved detection sensitivity for the target material can be obtained.

[0014] Furthermore, in the electric field enhancing element 100 shown in Figure 2, when viewed from the direction perpendicular to the substrate 10, a first region 11 and a second region 12 are adjacent to each other via a virtual boundary line BL that runs along the plane of the substrate 10. The first region 11 and the second region 12 are distinct regions set within the plane of the substrate 10. In the case of Figure 2, the upper surface of the dielectric layer 20 is divided into two parts via a boundary line BL parallel to the Y axis, and the first region 11 and the second region 12 are set adjacent in the X axis direction. With such a configuration, multiple regions can be formed relatively easily, thus realizing an electric field enhancing element 100 with excellent manufacturability.

[0015] Furthermore, the first region 11 is provided with a first array 31 in which microstructures 30a are arranged periodically. In addition, the second region 12 is provided with a second array 32 in which microstructures 30b are arranged periodically.

[0016] In the first array 31 and the second array 32, at least one of the following is different: the diameter of the microstructure 30a and the diameter of the microstructure 30b, the thickness of the microstructure 30a and the thickness of the microstructure 30b, and the pitch between adjacent microstructures 30a and the pitch between adjacent microstructures 30b. Hereinafter, such diameter, thickness, and pitch will also be referred to as array elements. In this embodiment, the diameter of the microstructure 30a and the diameter of the microstructure 30b are different. Furthermore, two or more of the array elements may be different, or other elements may be different. Examples of other elements include the thickness of the dielectric layer 20 and the thickness of the transparent layer 40. With this configuration, two regions with different array elements can be placed side by side in a single electric field enhancing element 100.

[0017] When detecting a target substance using the electric field enhancing element 100, the target substance is placed on the upper surface 42 of the transparent layer 40, and the electric field enhancing element 100 is irradiated with incident light Lin. The incident light Lin irradiates an area encompassing the entire electric field enhancing element 100, for example, as shown in Figure 2.

[0018] In the first array 31 and the second array 32, the diameters of the microstructure 30a and the microstructure 30b (array elements) are different from each other. Therefore, the wavelength of incident light Lin when the first array 31 generates plasmon resonance (first excitation wavelength) and the wavelength of incident light Lin when the second array 32 generates plasmon resonance (second excitation wavelength) can be made different. In other words, when the first excitation wavelength is λ1 and the second excitation wavelength is λ2, the electric field enhancing element 100 can generate an enhanced electric field whether incident light Lin with the first excitation wavelength λ1 or incident light Lin with the second excitation wavelength λ2 is used. Thus, an electric field enhancing element 100 that is compatible with multiple wavelengths and highly convenient can be realized. To give a specific example, an electric field enhancement element 100 can be realized in which the first array 31 corresponds to incident light Lin with a wavelength of 550 nm to 660 nm, and the second array 32 corresponds to incident light Lin with a wavelength of 450 nm to less than 550 nm.

[0019] Furthermore, the number of regions (number of arrays) in the electric field enhancing element 100 is not limited to the two mentioned above, and may be three or more. Also, the number of regions and the number of arrays may be different. For example, as will be described later, if the number of regions is four, the number of arrays may be a smaller number, such as three.

[0020] Furthermore, the areas of the first region 11 and the second region 12 may be the same or different. In the latter case, the area ratio may be set according to the first excitation wavelength λ1 and the second excitation wavelength λ2. For example, since the intensity of Raman scattered light is inversely proportional to the fourth power of the wavelength of the incident light Lin, the shorter the wavelength of the incident light Lin, the greater the intensity of the Raman scattered light. Taking this into account, for example, when the second excitation wavelength λ2 is shorter than the first excitation wavelength λ1, it is preferable to make the area of ​​the first region 11 larger than the area of ​​the second region 12. This makes it possible to bring the intensity of Raman scattered light generated by the incident light Lin at the first excitation wavelength λ1 closer to the intensity of Raman scattered light generated by the incident light Lin at the second excitation wavelength λ2. As a result, the difference in the intensity of Raman scattered light between regions is small, and an electric field enhancement element 100 that is easy to use can be realized.

[0021] Examples of substrate 10 include glass substrates and silicon substrates. Examples of constituent materials for glass substrates include SiO2 (quartz glass). Examples of constituent materials for silicon substrates include single-crystal silicon, polycrystalline silicon, and amorphous silicon.

[0022] In Figure 1, Q is the perpendicular line to the top surface of the substrate 10. In Figure 1, the perpendicular line Q is set to be parallel to the Z-axis.

[0023] The dielectric layer 20 shown in Figure 1 is provided between the substrate 10 and the microstructures 30a and 30b. The thickness of the dielectric layer 20 is not particularly limited, but is preferably 1 nm to 2000 nm, and more preferably 10 nm to 1000 nm. The dielectric layer 20 may be omitted.

[0024] The thickness of the dielectric layer 20 is measured from an observation image obtained by observing a cross-section of the dielectric layer 20 with an electron microscope. In the observation image, measurement is performed at 10 or more randomly extracted lengths in the Z-axis direction of the dielectric layer 20, and the average value thereof is defined as the "thickness".

[0025] The dielectric layer 20 is transparent to incident light Lin. Examples of the constituent material of the dielectric layer 20 include Al2O3, TiO2, MgO, LiNbO3, HfO2, Ta2O5, SiON, Si3N4, SiOx (0 < x < 3), PMMA (acrylic resin), PVA (polyvinyl alcohol), polysilazane, polystyrene, and the like. The dielectric layer 20 may be composed of a plurality of layers. In this case, the materials of the plurality of layers may be the same or different.

[0026] The microstructures 30a and 30b shown in FIG. 1 are provided between the dielectric layer 20 and the transparent layer 40. The shapes of the microstructures 30a and 30b are, for example, cylinders, respectively. The diameters of the microstructure 30a and the microstructure 30b are not particularly limited, but are preferably 1 nm or more and 1000 nm or less, more preferably 5 nm or more and 500 nm or less, and still more preferably 10 nm or more and 400 nm or less, respectively.

[0027] Note that the "diameter of the microstructure 30a" is the diameter when the planar shape of the microstructure 30a (the shape when viewed from the perpendicular line Q) is a circle, and is the diameter of the minimum enclosing circle when the planar shape of the microstructure 30a is not a circular shape. As an example of the latter, when the planar shape of the microstructure 30a is a polygon, the smallest circle containing this polygon is the "minimum enclosing circle". Also, when the planar shape of the microstructure 30a is an ellipse, the smallest circle containing this ellipse is the "minimum enclosing circle". The diameter of the microstructure 30b is the same as this.

[0028] The thickness of the microstructures 30a and 30b is not particularly limited, but is preferably 1 nm to 500 nm, more preferably 5 nm to 300 nm, and even more preferably 30 nm to 200 nm, respectively. This allows for a stronger enhanced electric field.

[0029] Multiple microstructures 30a and 30b are provided. The multiple microstructures 30a and 30b are spaced apart from each other. A transparent layer 40 is provided between adjacent microstructures 30a and between adjacent microstructures 30b. The pitch of adjacent microstructures 30a and adjacent microstructures 30b is not particularly limited, but is preferably 20 nm to 1000 nm, and more preferably 100 nm to 900 nm.

[0030] Multiple microstructures 30a and multiple microstructures 30b are arranged periodically. In the example shown in Figure 2, multiple microstructures 30a and multiple microstructures 30b are arranged in a square lattice pattern.

[0031] With this configuration, the electric field enhancing element 100 can reduce variations in the intensity of the enhanced electric field in the in-plane direction. When multiple microstructures are arranged randomly, only microstructures with pitches and diameters matching the wavelength of the incident light Lin induce LSPR. Therefore, there is a risk of variations in the intensity of the enhanced electric field in the in-plane direction. In contrast, by providing the microstructures 30 periodically, it is possible to induce SLR (Surface Lattice Resonance), which will be described later.

[0032] The "pitch of microstructures 30a and 30b" refers to the distance between the centers of adjacent microstructures 30a and 30b in a given direction. The "center of microstructure 30a" is the center of the circle if the planar shape of microstructure 30a is a circle, and the center of the smallest inclusion circle if the planar shape of microstructure 30a is not a circle. The same applies to the "center of microstructure 30b".

[0033] Furthermore, at least one of the multiple microstructures 30a and the multiple microstructures 30b may be arranged in a triangular lattice pattern when viewed from a perpendicular line Q. Although not shown in the figures, the periodicity of the multiple microstructures 30a and 30b may expand or contract at a constant ratio, and the multiple microstructures 30a and 30b may include fractal structures.

[0034] Figure 3 shows examples of the planar shapes of the microstructures 30a and 30b. The planar shape of the microstructures 30a and 30b is not limited to the circular shape described above, but may be elliptical, rectangular, granular, polygonal, ring-shaped, linear, or other shapes, as shown in the microstructure 30 in Figure 3.

[0035] Furthermore, the multiple microstructures 30a and 30b may be combinations of structures with different shapes. This makes it possible to control the intensity and distribution of the enhanced electric field generated by the multiple microstructures 30a and 30b in the in-plane direction perpendicular to the perpendicular line Q.

[0036] Furthermore, the cross-sectional shapes of the microstructures 30a and 30b are not particularly limited and may be trapezoidal, semicircular, circular, inverted tapered, or spherical at the tip. In addition, the shapes of the microstructures 30a and 30b may be truncated square pyramids or cones.

[0037] Although not shown in the figures, a plurality of recesses may be formed on the upper surface of the dielectric layer 20, and microstructures 30a and 30b may be provided within these recesses.

[0038] The microstructures 30a and 30b have conductivity. Examples of the constituent materials of the microstructures 30a and 30b include simple metals or alloys such as Al, Au, Ag, Cu, Pt, Pd, and Ni. Since such metals have particularly good conductivity, the enhanced electric field can be made stronger. Also, the microstructures 30a and 30b may be metal particles. Note that the constituent material of the microstructures 30a and 30b is not particularly limited as long as it has a plasma frequency with respect to the incident light Lin, and may be a transparent electrode material such as ITO (Indium Tin Oxide), a carbon-based material such as a carbon nanotube, or the like.

[0039] The transparent layer 40 is provided on the microstructures 30a and 30b and on the dielectric layer 20. That is, the transparent layer 40 is provided so as to cover the plurality of microstructures 30a, the plurality of microstructures 30b, and the substrate 10. The thickness of the transparent layer 40 is not particularly limited, but is preferably 10 nm or more and 2000 nm or less, more preferably 20 nm or more and 1000 nm or less.

[0040] The thickness of the transparent layer 40 is measured from the observation image obtained by observing the cross-section of the transparent layer 40 with an electron microscope. In the observation image, it is measured at 10 or more randomly extracted lengths in the Z-axis direction of the transparent layer 40, and the average value thereof is defined as the "thickness".

[0041] The transparent layer 40 is transparent to the incident light Lin. Examples of the constituent material of the transparent layer 40 include various dielectrics such as Al2O3, TiO2, MgO, LiNbO3, HfO2, Ta2O5, SiON, Si3N4, and SiOx (0 < x < 3). Also, SiOx (0 < x < 3) is preferably SiOx (1 < x ≤ 2). Note that the constituent material of the transparent layer 40 may be an organic material such as PMMA (acrylic resin), PVA (polyvinyl alcohol), polysilazane, or polystyrene.

[0042] The refractive index of the transparent layer 40 may be different from or the same as that of the dielectric layer 20. If the refractive index of the transparent layer 40 is the same as that of the dielectric layer 20, the Rayleigh anomaly described later is more likely to occur. Also, if the dielectric layer 20 is omitted, the refractive index of the transparent layer 40 may be higher or lower than that of the substrate 10, but preferably the difference between the two is 0.20 or less. If the refractive index difference is within this range, the effect of the refractive index difference is suppressed, and the Rayleigh anomaly described later is more likely to occur regardless of the direction of incident light. This makes it easier to induce SLR, described later. If the refractive index difference falls outside the above range, for example, when light is incident from the substrate 10 side, Fresnel reflection is more likely to occur at the interface between the substrate 10 and the transparent layer 40. As a result, the light energy contributing to the generation of plasmon resonance described later decreases, and the enhanced electric field may decrease.

[0043] The transparent layer 40 has an upper surface 42. The upper surface 42 is, for example, the interface between the transparent layer 40 and the air layer. The upper surface 42 is the surface on which the target substance to be detected is placed. The upper surface 42 shown in Figure 1 is preferably a flat surface. In this case, the target substance can be placed stably.

[0044] 1.2. Enhanced Electric Field Figures 4 and 5 are conceptual diagrams illustrating plasmon resonance in the electric field enhancing element 100. Figure 6 is a diagram illustrating the enhanced electric field generated by the microstructure 30a of the electric field enhancing element 100. The enhanced electric field generated by the microstructure 30b is similar to that generated by the microstructure 30a, so its explanation is omitted.

[0045] In the examples shown in Figures 4 and 5, light incident from the substrate 10 reaches multiple microstructures 30a. The light that reaches the microstructures 30a generates plasmon resonance in the microstructures 30a. The wavelength of the light is, for example, between 350 nm and 850 nm. If the wavelength of the light is within this range, plasmon resonance is more easily generated in the microstructures 30a.

[0046] As shown in Figure 4, when light reaches the microstructure 30a, the aforementioned LSPR is induced. In addition, 90° diffraction, i.e., a Rayleigh anomaly, occurs due to multiple microstructures 30a. The combination of this Rayleigh anomaly and LSPR induces SLR (Surface Lattice Resonance).

[0047] Furthermore, as shown in Figure 5, the incident light is guided through the transparent layer 40. The combination of this guided mode in the transparent layer 40 and LSPR induces a Quasi-Guided Mode (QGM).

[0048] Then, the resonance states of SLR and QGM, etc., combine and cooperate, inducing cooperative plasmon polaritons in the multiple microstructures 30a. As a result of the combination of the resonance states of SLR and QGM, etc., the enhanced electric field E generated by the multiple microstructures 30a has not only a first enhanced field Ea generated at the edge of the microstructure 30a due to LSPR, as shown in Figure 6, but also a second enhanced field Eb generated above the microstructures 30a due to the resonance states of SLR and QGM, etc.

[0049] The enhanced electric field E enhances Raman scattered light and generates SERS. The enhanced electric field E is maximized by the second enhanced field Eb at position S1 or position S2 (in the perpendicular direction, on the opposite side of the substrate 10 from the multiple microstructures 30a, and at a distance from the multiple microstructures 30a) above the multiple microstructures 30a. The fact that the enhanced electric field E is maximized at position S1 or position S2 is characteristic of the cooperative plasmon polariton phenomenon. Positions S1 and S2 shown in Figure 6 are located on the positive Z-axis side of the multiple microstructures 30a.

[0050] This configuration improves the detection sensitivity of the electric field enhancement element 100. For example, if the enhanced electric field E is generated only at the edges of the microstructure 30a due to LSPR, the effect of generating the enhanced electric field E cannot be obtained unless the target material is positioned near the microstructure 30a. Generally, there is variability in the probability that the target material is located near the microstructure, so if the enhanced electric field is generated only at the edges of the microstructure, the detection sensitivity tends to decrease. Furthermore, the reproducibility of detection also decreases. Moreover, if the size of the target material is large, it may not be able to fit between adjacent microstructures, making it difficult to position the target material near the microstructure.

[0051] In contrast, in the electric field enhancing element 100, the enhanced electric field E generated by the multiple microstructures 30a is maximized at a position S1 or S2 in the perpendicular direction, located above the multiple microstructures 30a (a position S1 or S2 that is on the opposite side of the substrate 10 from the multiple microstructures 30a in the perpendicular direction, and is spaced away from the multiple microstructures 30a). Therefore, the detection signal caused by the target substance can be enhanced even without positioning the target substance near the microstructures 30a. As a result, detection sensitivity can be improved. Furthermore, since it is not necessary to position the target substance between adjacent microstructures 30a, various sizes of samples, such as viruses and bacteria, can be freely selected as target substances.

[0052] Furthermore, in the electric field enhancement element 100, since the position S1 or S2 of the maximum point is far from the vicinity of the microstructure 30a, a transparent layer 40 can be provided to cover the microstructure 30a. In other words, even with the transparent layer 40 provided, the enhanced electric field E can be applied to the target substance, and the detection signal caused by the target substance can be amplified. Therefore, unintended chemical changes such as oxidation and sulfidation of the microstructure 30a can be suppressed. In particular, Ag is prone to alteration and deformation due to oxidation, sulfidation, migration, etc. In the electric field enhancement element 100, even if Ag is used as the microstructure 30a, such alteration and deformation can be suppressed. As a result, the durability and reliability of the electric field enhancement element 100 can be improved.

[0053] Furthermore, in the electric field enhancement element 100, the transparent layer 40 can mitigate the irregularities caused by the multiple microstructures 30a. This improves the flatness of the surface in contact with the target material. As a result, variations in the detection signal caused by the target material can be reduced in the in-plane direction.

[0054] The second augmentation field Eb may be separated from the first augmentation field Ea, as shown in Figure 6, or it may be continuous with the first augmentation field Ea.

[0055] Furthermore, in Figure 6, the maximum point where the enhanced electric field E is maximized is located at position S1 or position S2. Of these, position S1 shown in Figure 6 is located within the transparent layer 40. In this case, the distance L1 from the microstructure 30a to position S1 in the perpendicular direction of the upper surface 42 may be less than 100 nm, but is preferably 100 nm or more, and more preferably 200 nm or more. This makes the enhanced electric field E generated above the upper surface 42 stronger, so that even if the target material is not located near the microstructure 30a, in other words, even if the target material is placed on the upper surface 42, the enhanced electric field E acts on the target material and enhances the detection signal caused by the target material.

[0056] Furthermore, in Figure 6, the enhanced electric field E extends across the upper surface 42 to the air layer. The maximum point of the enhanced electric field E may be at position S2 shown in Figure 6. Position S2 shown in Figure 6 is located within the air layer. In other words, the enhanced electric field E may be at a position separated from the transparent layer 40 in the direction perpendicular to the upper surface 42. In this case, the detection signal caused by the target material placed on the upper surface 42 can be further enhanced.

[0057] In this case, the distance L2 from the upper surface 42 (the surface of the transparent layer 40) to position S2 (the maximum point) may be 100 nm or less, or it may be greater than 100 nm.

[0058] If the distance L2 is 100 nm or less, and the size of the target material is 100 nm or less, the probability that position S2 acts on the target material placed on the upper surface 42 increases. Therefore, the detection signal caused by the target material can be particularly enhanced.

[0059] When the distance L2 exceeds 100 nm, the probability that position S2 acts on the target material placed on the upper surface 42 increases, even if the target material is larger than 100 nm. Therefore, even when target materials of various sizes are mixed together, the detection signal caused by the target material can be uniformly amplified.

[0060] 2. Method for manufacturing an electric field enhancing element Next, an example of a method for manufacturing the electric field enhancing element 100 will be described.

[0061] First, a dielectric layer 20 is formed on the substrate 10. The dielectric layer 20 is formed by, for example, vapor deposition, sputtering, CVD (Chemical Vapor Deposition), or ALD (Atomic Layer Deposition).

[0062] Next, multiple microstructures 30a and 30b are formed on the dielectric layer 20. The microstructures 30a and 30b are formed by, for example, depositing a thin film using a vacuum deposition method or sputtering method, and then patterning this thin film. Examples of patterning methods include electron beam lithography, photolithography and etching, microcontact printing, and nanoimprint lithography.

[0063] Next, a transparent layer 40 is formed on the dielectric layer 20 and on the microstructures 30a and 30b. This gives rise to the electric field enhancing element 100. The transparent layer 40 is formed by methods such as vapor deposition, sputtering, CVD, ALD, or sol-gel.

[0064] 3. Modified Examples of Electric Field Enhancing Devices Next, an electric field enhancing element according to a modified embodiment will be described.

[0065] 3.1. First Variation Figure 7 is a schematic plan view showing an electric field enhancing element 100 according to a first modified example of the embodiment.

[0066] The following describes the first modified example, focusing on the differences from the previously described embodiment, and omitting explanations of similar aspects. In Figure 7, components similar to those in the previously described embodiment are denoted by the same reference numerals.

[0067] The first modified example is the same as the above embodiment, except that three types of regions are arranged in a matrix.

[0068] In the electric field enhancing element 100 shown in Figure 7, when viewed from the direction perpendicular to the substrate 10, the first region 11, the second region 12, and the third region 13 are arranged via boundary lines BL that run along the plane of the substrate 10. In Figure 7, the upper surface of the dielectric layer 20 is divided into four sections via boundary lines BL parallel to the X-axis and boundary lines BL parallel to the Y-axis, and the first region 11, two second regions 12, and the third region 13 are arranged in a 2x2 matrix.

[0069] Furthermore, the first region 11 is provided with a first array 31 in which microstructures 30a are arranged periodically. The second region 12 is provided with a second array 32 in which microstructures 30b are arranged periodically. Furthermore, the third region 13 is provided with a third array 33 in which microstructures 30c are arranged periodically.

[0070] In the first array 31, the second array 32, and the third array 33, at least one of the following is different from each other: the diameter of the microstructure 30a, the diameter of the microstructure 30b, and the diameter of the microstructure 30c; the thickness of the microstructure 30a, the thickness of the microstructure 30b, and the thickness of the microstructure 30c; and the pitch between adjacent microstructures 30a, the pitch between adjacent microstructures 30b, and the pitch between adjacent microstructures 30c. In this modified example, the diameters of the microstructure 30a, the diameter of the microstructure 30b, and the diameter of the microstructure 30c are different from each other.

[0071] With this configuration, the wavelength of incident light Lin when the first array 31 generates plasmon resonance (first excitation wavelength λ1), the wavelength of incident light Lin when the second array 32 generates plasmon resonance (second excitation wavelength λ2), and the wavelength of incident light Lin when the third array 33 generates plasmon resonance (third excitation wavelength λ3) can be made different. In other words, an electric field enhancing element 100 that can generate an enhanced electric field can be realized whether incident light Lin with a wavelength corresponding to the first excitation wavelength λ1, the wavelength corresponding to the second excitation wavelength λ2, or the wavelength corresponding to the third excitation wavelength λ3 is used.

[0072] Furthermore, in this modified example, the area of ​​the second region 12 is set to be larger than the area of ​​the first region 11 and the area of ​​the third region 13. In this case, the intensity of the Raman scattered light generated by the incident light Lin at the second excitation wavelength λ2 can be selectively increased. This makes it possible to realize an electric field enhancement element 100 that can handle the incident light Lin at the first excitation wavelength λ1 and the incident light Lin at the third excitation wavelength λ3 while ensuring a particularly high intensity of Raman scattered light for the incident light Lin at the second excitation wavelength λ2.

[0073] Note that the arrangement patterns of each region shown in Figure 7 are examples only and are not limited thereto. For example, in Figure 7, the two second regions 12, 12 are located diagonally opposite each other, but they may also be located along the X or Y axis. Also, the positions of the first region 11 and the third region 13 may be swapped. Furthermore, the same effects as those of the above embodiment can be obtained in the first modified example described above.

[0074] 3.2. Second Variation Figure 8 is a schematic plan view showing an electric field enhancing element 100 according to a second modified example of the embodiment.

[0075] The following describes a second modified example, focusing on the differences from the previously described embodiment, and omitting explanations of similar items. In Figure 8, components similar to those in the previously described embodiment are denoted by the same reference numerals.

[0076] The second modified example is the same as the above embodiment, except that the three types of regions are arranged concentrically.

[0077] In the electric field enhancing element 100 shown in Figure 8, the substrate 10 is circular when viewed from the direction perpendicular to the substrate 10. The first region 11, the second region 12, and the third region 13 are arranged concentrically around the center O of the substrate 10. In the case of Figure 8, the first region 11 is set to include the center O, the second region 12 is set adjacent to the outside of the first region 11, and the third region 13 is set adjacent to the outside of the second region 12.

[0078] Furthermore, the first region 11 is provided with the first array 31 mentioned above. The second region 12 is provided with the second array 32 mentioned above. In addition, the third region 13 is provided with the third array 33 mentioned above. Note that the illustration of the microstructure is omitted in Figure 8.

[0079] Furthermore, the width of the first region 11 in the radial direction of the substrate 10 is denoted as r1, the width of the second region 12 as r2, and the width of the third region 13 as r3. In Figure 8, widths r1, r2, and r3 are set to be equal to each other. In this case, the area of ​​the first region 11 is the smallest, the area of ​​the second region 12 is larger than that of the first region 11, and the area of ​​the third region 13 is the largest. If the in-plane distribution of the light intensity of the incident light Lin is constant, the intensity of the Raman scattered light generated by the incident light Lin at the second excitation wavelength λ2 and the third excitation wavelength λ3 can be made greater than the intensity of the Raman scattered light generated by the incident light Lin at the first excitation wavelength λ1. This makes it possible to realize an electric field enhancement element 100 that can handle the incident light Lin at the first excitation wavelength λ1 while ensuring a particularly high intensity of Raman scattered light for the incident light Lin at the second excitation wavelength λ2 and the third excitation wavelength λ3. Therefore, a user-friendly electric field enhancement element 100 can be realized with a small difference in the intensity of Raman scattered light between regions.

[0080] On the other hand, the in-plane distribution of the light intensity of incident light Lin is often not constant. This case will be discussed in detail later.

[0081] Furthermore, by adjusting the widths r1, r2, and r3 according to the in-plane distribution of the light intensity of the incident light Lin, the ratio of Raman scattered light intensities between regions can be easily adjusted. This makes it possible to realize an electric field enhancement element 100 that can accommodate multiple wavelengths of incident light Lin and optimizes the ratio of Raman scattered light intensities between regions. Furthermore, the same effects as those of the above embodiment can be obtained in the second modified example described above.

[0082] Furthermore, the shape of the substrate 10 is not limited to a circle; for example, it may be an ellipse, an oblong, a polygon, or other shape.

[0083] Furthermore, the outer edges of the first region 11, the second region 12, and the third region 13, which are arranged concentrically, may be perfect circles, ellipses, oblongs, polygons, or the like. Also, the shapes of each outer edge may differ from one another. In this specification, such cases are also included in the definition of concentric circles.

[0084] 3.3. Third Variation Figure 9 is a schematic plan view showing an electric field enhancing element 100 according to a third modified example of the embodiment.

[0085] The third modified example will be described below, focusing on the differences from the second modified example, and similar aspects will be omitted. In Figure 9, components similar to those in the previously described embodiment are denoted by the same reference numerals.

[0086] The third modification is similar to the second modification, except that the widths of the three types of regions are optimized according to the light intensity distribution of the incident light Lin.

[0087] In the electric field enhancing element 100 shown in Figure 9, width r1 is set to be narrower than width r2, and width r3 is set to be wider than width r2. In this case, the area of ​​the first region 11 is even smaller than that of the second modified example, and the area of ​​the third region 13 is even larger than that of the second modified example. By optimizing the widths r1, r2, and r3 in this way, the integral values ​​of the light intensity of incident light Lin in the first region 11, the integral values ​​of the light intensity of incident light Lin in the second region 12, and the integral values ​​of the light intensity of incident light Lin in the third region 13 can be freely adjusted. For example, the integral values ​​of the light intensity of incident light Lin in each region can be made equal to each other, or the difference between them can be reduced.

[0088] Figure 10 is a graph illustrating the effect of the electric field enhancing element 100 shown in Figure 9.

[0089] The light intensity distribution Id shown in Figure 10 represents the distribution of light intensity in the cross-section of the incident light Lin. As shown in Figure 10, the distribution of light intensity in the cross-section of the incident light Lin used in Raman scattering spectroscopy is generally a Gaussian distribution. Therefore, the integrated value of light intensity, i.e., the accumulated light amount, is greater in the central part of the incident light Lin compared to the edges. In Figure 10, the integrated values ​​of light intensity I-1 in the first region 11, I-2 in the second region 12, and I-3 in the third region 13 are represented by the area of ​​the rectangles. The integrated values ​​of light intensity I-1 in the first region 11, I-2 in the second region 12, and I-3 in the third region 13 are all similar. Specifically, although the area of ​​the first region 11 is relatively small, the light intensity irradiated into the first region 11 is relatively large. On the other hand, while the third region 13 has the largest area, the light intensity irradiated to the third region 13 is relatively small. Also, the second region 12 has a relatively medium area, and the light intensity irradiated to the second region 12 is also relatively medium.

[0090] With the above configuration, an electric field enhancing element 100 can be realized that generates an equivalent enhanced electric field regardless of whether the incident light Lin used has a wavelength corresponding to the first excitation wavelength λ1, the second excitation wavelength λ2, or the third excitation wavelength λ3. Therefore, an electric field enhancing element 100 can be realized that has a small difference in the intensity of Raman scattered light between regions and is easy to use. Furthermore, the same effects as those of the above embodiment can be obtained in the third modified example described above.

[0091] 3.4. Fourth Variation Figure 11 is a schematic plan view showing an electric field enhancing element 100 according to a fourth modified example of the embodiment.

[0092] The fourth modified example will be described below, but the following description will focus on the differences from the second modified example, and similar matters will be omitted from the explanation. In Figure 11, the same reference numerals are used for components that are the same as those in the embodiment described above.

[0093] The fourth modification is similar to the second modification, except that the arrangement of the three types of regions is optimized according to the wavelength of the incident light Lin.

[0094] In the electric field enhancement element 100 shown in Figure 11, similar to Figure 9, a first region 11 is set up to include the center O, a second region 12 is set up adjacent to the outside of the first region 11, and a third region 13 is set up adjacent to the outside of the second region 12. Furthermore, the first region 11 is provided with a first array 31 that generates plasmon resonance at a first excitation wavelength λ1, the second region 12 is provided with a second array 32 that generates plasmon resonance at a second excitation wavelength λ2, and the third region 13 is provided with a third array 33 that generates plasmon resonance at a third excitation wavelength λ3. The first excitation wavelength λ1, the second excitation wavelength λ2, and the third excitation wavelength λ3 satisfy the relationship λ3 < λ2 < λ1. This makes it possible to equalize the intensity of Raman scattered light between regions or reduce the difference between them.

[0095] Figure 12 is a graph illustrating the effect of the electric field enhancing element 100 shown in Figure 11.

[0096] The excitation wavelength distribution λd shown in Figure 12 represents the distribution of the first excitation wavelength λ1 set in the first region 11, the second excitation wavelength λ2 set in the second region 12, and the third excitation wavelength λ3 set in the third region 13. Based on the light intensity distribution (Gaussian distribution) of the incident light Lin shown in Figure 10, the light intensity in the first region 11 is relatively the highest, the light intensity in the third region 13 is relatively the lowest, and the light intensity in the second region 12 is relatively moderate.

[0097] On the other hand, the intensity of Raman scattered light in each region is inversely proportional to the fourth power of the wavelength of the incident light Lin. Therefore, the shorter the wavelength of the incident light Lin, the greater the intensity of the Raman scattered light. Thus, it is preferable that the third region 13, which is set to the shortest wavelength, the third excitation wavelength λ3, is located on the outside where the light intensity is smallest; the second region 12, which is set to the next shortest wavelength, the second excitation wavelength λ2, is located in the middle where the light intensity is moderate; and the first region 11, which is set to the longest wavelength, the first excitation wavelength λ1, is located in the center where the light intensity is largeest. This makes it possible to equalize the intensities of Raman scattered light between regions or reduce the difference between them, as described above. As a result, a user-friendly electric field enhancement element 100 can be realized.

[0098] The intensity of Raman scattered light in each region can be adjusted by the widths r1, r2, and r3 of each region, so the intensities of Raman scattered light in each region can be made equal or different as needed. Furthermore, the same effects as those of the above embodiment can be obtained in the fourth modified example described above.

[0099] 3.5. Fifth Variation Figure 13 is a schematic cross-sectional view showing an electric field enhancing element 200 according to a fifth modified example of the embodiment.

[0100] The fifth modified example will be described below, but the following description will focus on the differences from the above embodiment, and similar matters will be omitted from the explanation. In Figure 13, the same reference numerals are used for components that are the same as those in the above embodiment.

[0101] The electric field enhancing element 200 shown in Figure 13 is the same as the electric field enhancing element 100, except that it includes a molecular trapping layer 50.

[0102] The molecular trapping layer 50 is provided on the transparent layer 40 so as to be in contact with the transparent layer 40. The molecular trapping layer 50 is an organic molecular film, for example, a SAM (Self-Assembled Monolayers).

[0103] The thickness of the molecular trapping layer 50 is not particularly limited, but is preferably 0.1 nm or more and 1 nm or less, and more preferably 0.4 nm or less.

[0104] The thickness of the molecular trapping layer 50 is measured by observing a cross-section of the molecular trapping layer 50 with an electron microscope and taking the resulting image. In the observed image, the length of the molecular trapping layer 50 in the Z-axis direction is measured at 10 or more randomly selected locations, and the average value is defined as the "thickness".

[0105] The molecular trapping layer 50 has the function of trapping the target substance. The molecular trapping layer 50 is appropriately selected depending on the type of target substance, but examples include alkanethiol films and silane coupling agents. The molecular trapping layer 50 is formed by, for example, immersion method, vacuum deposition method, MVD (Molecular Vapor Deposition) method, and CVD method.

[0106] In the electric field enhancement element 200, the molecular trapping layer 50 is provided on the transparent layer 40, which can mitigate unevenness in the deposition of the molecular trapping layer 50. For example, if a transparent layer is not provided and the molecular trapping layer is deposited directly on the microstructure and the substrate, unevenness in the deposition of the molecular trapping layer may occur because the physical and chemical states of the surface of the microstructure and the surface of the substrate are different.

[0107] Furthermore, in the electric field enhancement element 200, as described above, the target material does not need to be positioned near the microstructure 30, thus broadening the selectivity of the molecular chain length of the molecular trapping layer 50. Although not shown in the figures, a primer layer may be provided between the transparent layer 40 and the molecular trapping layer 50 to improve their adhesion. Furthermore, the same effects as those of the above embodiment can be obtained in the fifth modified example described above.

[0108] 3.6. Sixth Variation Figure 14 is a schematic cross-sectional view showing an electric field enhancing element 250 according to a sixth modified example of the embodiment.

[0109] The following describes the sixth modified example, focusing on the differences from the previously described embodiment, and omitting explanations of similar matters. In Figure 14, components similar to those in the previously described embodiment are denoted by the same reference numerals.

[0110] The electric field enhancing element 250 shown in Figure 14 is the same as the electric field enhancing element 100, except that the transparent layer 40 is extended in place of the dielectric layer 20 shown in Figure 1. That is, the transparent layer 40 shown in Figure 14 extends to the region where the dielectric layer 20 shown in Figure 1 is extended. As a result, in the cross-section shown in Figure 14, the microstructure 30 is surrounded by the transparent layer 40. Furthermore, the same effects as those of the above-described embodiment can be obtained in the sixth modified example described above.

[0111] 4. Raman spectrometer Next, a Raman spectrometer according to an embodiment will be described. Figure 15 is a schematic diagram showing a Raman spectrometer 300 according to an embodiment.

[0112] 4.1. Composition The Raman spectrometer 300 shown in Figure 15 comprises an electric field enhancement element 100, a light source 310, a collimating lens 320, a polarization control element 330, a dichroic mirror 340, an objective lens 350, a focusing lens 360, and a detector 370. For illustrative purposes, the electric field enhancement element 100 is simplified in Figure 15.

[0113] The target material is introduced into the Raman spectrometer 300 from direction C1 and discharged from direction C2. For example, by driving a fan (not shown), the target material is introduced into the material transport section from the inlet and discharged to the outside of the material transport section from the outlet.

[0114] The light source 310 irradiates the electric field enhancing element 100 with light. The light emitted from the light source 310 has a wavelength that induces resonance such as SLR and QGM in the electric field enhancing element 100. Examples of the light source 310 include lasers and LEDs (Light Emitting Diodes). Examples of lasers include VCSELs (Vertical Cavity Surface Emitting Lasers) and PCSELs (Photonic Crystal Surface Emitting Lasers).

[0115] Light emitted from the light source 310 is, for example, made into parallel light by the collimating lens 320, passes through the polarization control element 330, and is guided towards the electric field enhancing element 100 by the dichroic mirror 340. The light heading towards the electric field enhancing element 100 is focused by the objective lens 350 and incident on the electric field enhancing element 100. At this time, the target material is in contact with the transparent layer 40 of the electric field enhancing element 100.

[0116] When light is incident on the electric field enhancing element 100, an enhanced electric field E is generated by multiple microstructures 30. When the target material is located within the enhanced electric field E, SERS light is generated from it. The SERS light passes through the objective lens 350 and through the dichroic mirror 340, and is guided toward the detector 370. The SERS light heading toward the detector 370 is focused by the focusing lens 360 and incident upon the detector 370.

[0117] Detector 370 detects SERS light from the electric field enhancement element 100. Detector 370 is, for example, a diffraction grating spectrometer. In the Raman spectrometer 300, the SERS light is spectrally decomposed by detector 370, and spectral information is obtained. Detector 370 may also be a Fabry-Perot etalon spectrometer.

[0118] 4.2. Principle Figure 16 is a diagram illustrating the principle of Raman scattering spectroscopy.

[0119] In Figure 16, incident light Lin with wavelength λin is irradiated onto target material X. As a result, scattered light is emitted from target material X. This scattered light includes Rayleigh scattered light Ray with the same wavelength λ1 as the incident light Lin, as well as Raman scattered light Ram with a different wavelength λ2. The energy difference between this Raman scattered light Ram and the incident light Lin corresponds to the energy of the vibrational, rotational, and electronic levels of target material X. Because target material X possesses unique vibrational energies corresponding to its structure, it can be identified from the Raman scattered light Ram by using incident light Lin with wavelength λin.

[0120] Figure 17 is a schematic diagram showing an example of a Raman spectrum obtained by Raman scattering spectroscopy. In Figure 17, the horizontal axis represents the Raman shift. The Raman shift is the difference between the wavenumber (frequency) of the Raman scattered light Ram and the wavenumber of the incident light Lin, and it takes a value specific to the molecular bonding state of the target substance X.

[0121] Comparing the scattered light intensity K1 of Raman scattered light Ram and the scattered light intensity K2 of Rayleigh scattered light Ray shown in Figure 17, it can be seen that the scattered light intensity K1 of Raman scattered light Ram is weaker. Thus, while Raman scattering spectroscopy excels at identifying target substance X, a challenge is its low sensitivity in detecting target substance X. Therefore, the Raman spectrometer 300 uses SERS to improve sensitivity.

[0122] 5. Effects of the above embodiment The electric field enhancing element according to the above embodiment comprises a substrate 10, a plurality of microstructures 30a, 30b, and a transparent layer 40. The microstructures 30a, 30b are provided on the substrate 10 and are conductive. The transparent layer 40 covers the plurality of microstructures 30a, 30b and the substrate 10. The electric field enhancing element according to the above embodiment also has a first array 31 and a second array 32. The first array 31 is provided in a first region 11 of the substrate 10 and consists of periodically arranged microstructures 30a. The second array 32 is provided in a second region 12 of the substrate 10, which is different from the first region 11, and consists of periodically arranged microstructures 30b. The first array 31 and the second array 32 differ from each other in at least one of the following: the diameter of the microstructures 30a, 30b, the thickness of the microstructures 30a, 30b, and the pitch between adjacent microstructures 30a, 30b.

[0123] With this configuration, the detection signal originating from the target substance can be enhanced even without positioning the target substance in the vicinity of the microstructures 30a and 30b. As a result, an electric field enhancement element with improved detection sensitivity can be obtained. Furthermore, since it is not necessary to position the target substance between adjacent microstructures 30a and 30b, various sizes of samples, such as viruses and bacteria, can be freely selected as the target substance. In addition, since the first array 31 and the second array 32 can generate plasmon resonance with incident light Lin of different wavelengths, an electric field enhancement element that can handle multiple wavelengths and offers high convenience can be realized.

[0124] In the electric field enhancing element according to the above embodiment, the first region 11 and the second region 12 may be arranged side by side with a boundary line BL that runs along the plane of the substrate 10.

[0125] With this configuration, two regions with different array elements can be placed side-by-side in a single electric field enhancing element. Furthermore, since multiple regions can be formed relatively easily, an electric field enhancing element with excellent manufacturability can be realized.

[0126] In the electric field enhancing element according to the above embodiment, the areas of the first region 11 and the second region 12 may be different from each other.

[0127] With this configuration, the area ratio can be set according to the wavelength of incident light Lin when the first array 31 generates plasmon resonance (first excitation wavelength) and the wavelength of incident light Lin when the second array 32 generates plasmon resonance (second excitation wavelength). For example, the intensity of Raman scattered light generated by incident light Lin at the first excitation wavelength λ1 can be brought closer to the intensity of Raman scattered light generated by incident light Lin at the second excitation wavelength λ2. This results in a small difference in the intensity of Raman scattered light between regions, making it possible to realize an electric field enhancement element that is easy to use.

[0128] In the electric field enhancing element according to the above embodiment, the first region 11 and the second region 12 may be arranged concentrically.

[0129] This configuration allows for compatibility with multiple incident light wavelengths (Lin) and enables the realization of an electric field enhancement element with optimized ratios of Raman scattered light intensities across different regions.

[0130] In the electric field enhancing element according to the above embodiment, the second region 12 is located outside the first region 11, and the area of ​​the second region 12 may be larger than the area of ​​the first region 11.

[0131] With this configuration, if the in-plane distribution of the incident light intensity Lin is constant, the intensity of the Raman scattered light generated by the incident light Lin at the second excitation wavelength λ2 can be selectively increased. Furthermore, if the in-plane distribution of the incident light intensity Lin is, for example, a Gaussian distribution, the integral values ​​of the incident light intensity Lin in each region can be made equal or their differences reduced.

[0132] In the electric field enhancing element according to the above embodiment, when the wavelength that generates plasmon resonance in the first array 31 is set as the first excitation wavelength λ1, and the wavelength that generates plasmon resonance in the second array 32 is set as the second excitation wavelength λ2, the second excitation wavelength λ2 may be shorter than the first excitation wavelength λ1.

[0133] This configuration allows for equalizing the intensity of Raman scattered light in each region or reducing the differences between them. As a result, a user-friendly electric field enhancement element can be realized.

[0134] In the electric field enhancing element according to the above embodiment, the enhanced electric field E generated by the plurality of microstructures 30a and 30b may be maximized in the direction perpendicular to the substrate 10, above the microstructures 30a and 30b (on the opposite side of the microstructures 30a and 30b from the substrate 10), and at a position separated from the plurality of microstructures 30a and 30b.

[0135] With this configuration, the detection signal originating from the target material located on the opposite side (upper surface 42) of the substrate 10, where the multiple microstructures 30a and 30b are located, can be further enhanced.

[0136] In the electric field enhancing element according to the above embodiment, the enhanced electric field E may reach a position separated from the transparent layer 40 in the perpendicular direction of the substrate 10.

[0137] With this configuration, the probability of the enhanced electric field E acting on the target material placed on the upper surface 42 increases. Therefore, the detection signal originating from the target material can be particularly enhanced.

[0138] In the electric field enhancing element according to the above embodiment, the constituent material of the microstructures 30a and 30b is preferably a metal. With this configuration, the enhanced electric field E can be made stronger.

[0139] The Raman spectrometer according to the above embodiment comprises an electric field enhancing element according to the above embodiment, a light source 310, and a detector 370. The light source 310 irradiates the electric field enhancing element with light. The detector 370 detects the light from the electric field enhancing element.

[0140] This configuration allows for improved detection sensitivity and provides a highly convenient Raman spectrometer 300 that can handle multiple wavelengths.

[0141] Although the electric field enhancement element and Raman spectrometer of the present invention have been described above based on the illustrated preferred embodiments, the present invention is not limited to these embodiments and modifications. For example, the configuration of each part of the above embodiments and modifications may be replaced with any configuration having a similar function, or any other configuration may be added. Furthermore, two or more of the above embodiments and modifications may be combined. [Examples]

[0142] Next, specific embodiments of the present invention will be described. 6. Experimental Examples 6.1. Example 1 Figure 18 is a schematic XZ cross-sectional view showing the iteration unit of Model M used in the simulation. Figure 19 is a schematic XY cross-sectional view showing Model M used in the simulation. Figure 20 is a table comparing the main parameters in Examples 1 to 12 and Comparative Example 1.

[0143] In Model M of Example 1, as shown in Figure 18, the substrate material was quartz glass (SiO2), and the dielectric layer material and the transparent layer material were both Al2O3.

[0144] Furthermore, the thickness B of the transparent layer was set to 360 nm, the constituent material of the microstructure was Al, the diameter D of the microstructure was set to 117 nm, the thickness H of the microstructure was set to 60 nm, and the thickness A of the dielectric layer was set to 20 nm. In Model M, as shown in Figure 19, the arrangement of the microstructure was a square lattice, the shape of the microstructure was cylindrical, and the pitch P of the microstructure was set to 391 nm. In addition, an air layer was provided above the transparent layer.

[0145] Then, light was incident on Model M shown in Figure 18 from the substrate side, and the intensity distribution of the enhanced electric field was calculated. The wavelength of the incident light at which the enhanced electric field was maximum was defined as the excitation wavelength. In Model M of Example 1, the excitation wavelength was 596 nm.

[0146] 6.2. Examples 2-12 In Examples 2 to 12, the intensity distribution of the enhanced electric field was calculated in the same manner as in Example 1, except that the parameters of Model M described above were changed as shown in Figure 20. The excitation wavelengths for Model M in each example are also shown in Figure 20.

[0147] 6.3. Comparative Example 1 In Comparative Example 1, the intensity distribution of the enhanced electric field was calculated in the same manner as in Example 1, except that the thickness B of the transparent layer was set to zero, i.e., no transparent layer was provided, the constituent material of the microstructure was Ag, the diameter D of the microstructure was set to 50 nm, the thickness H of the microstructure was set to 25 nm, the pitch P of the microstructure was set to 250 nm, and the wavelength of the incident light was set to 464 nm.

[0148] 7. Results of the experimental example Simulations were performed to estimate the distribution of the enhanced electric field in each model of Examples 1 to 12 and Comparative Example 1 described above. The FDTD (Finite Difference Time Domain) method was used for the simulations. Synopsys Rsoft was used as the simulation software.

[0149] Figures 21 to 33 show the simulation results for Examples 1 to 12 and Comparative Example 1. Figures 21 to 32 show the distribution α of the normalized enhanced electric field in the XZ cross section, and the distribution β of the normalized enhanced electric field in the XY cross section, with the origin at a position 100 nm above the air interface and corresponding to the center of the microstructure.

[0150] The shades in Figures 21 to 33 indicate the intensity of the enhanced electric field. In distribution α, when the X component of the enhanced electric field is Ex and the Z component of the enhanced electric field is Ez, (Ex 2 +Ez 2 The square root of ) is, that is, √(Ex 2 +Ez 2 ) is reflected in the intensity. In distribution β, when the X component of the enhanced electric field is Ex and the Y component of the enhanced electric field is Ey, (Ex 2 +Ey 2 The square root of ) is, that is, √(Ex 2 +Ey2 ) is reflected in the shades of gray.

[0151] In Figures 21 to 32, the "air interface" refers to the interface between the transparent layer and the air layer. In Figure 33, the "air interface" refers to the interface between the substrate and the air layer.

[0152] In the distributions α shown in Figures 21 to 32, it was observed that the pale color intensified at positions further above the microstructure, and that the pale color extended above the air interface (towards the air layer). In addition, in the distributions β shown in Figures 21 to 32, a predetermined pattern was confirmed at a position 100 nm above the air interface. From these results, it was observed that in Figures 21 to 32, the enhanced electric field was maximized at positions further above the microstructure, and that the enhanced electric field reached above the air interface (towards the air layer). On the other hand, in Figure 33, no enhanced electric field was observed at a distance from the microstructure.

[0153] Furthermore, based on the results shown in Figures 21 to 32, it was also confirmed that the excitation wavelength can be changed by varying the array element (at least one of the following parameters of Model M: the diameter D of the microstructure, the thickness H of the microstructure, and the pitch P between adjacent microstructures).

[0154] For example, in Examples 1 to 3, the diameter D of the microstructures was made different from each other, which allowed the excitation wavelength to be changed.

[0155] Furthermore, in Examples 4-6, the pitch P of adjacent microstructures was made different from each other, which allowed us to change the excitation wavelength.

[0156] Furthermore, in Examples 7-9, the thickness H of the microstructures was varied, which allowed us to change the excitation wavelength.

[0157] Furthermore, in Examples 10 to 12, the thickness B of the transparent layer was varied from one example to the other, which allowed us to change the excitation wavelength.

[0158] Based on these results, it has been confirmed that the excitation wavelength can be changed by differentiating the array elements in the first, second, and third arrays mentioned above. [Explanation of Symbols]

[0159] 10...Substrate, 11...First region, 12...Second region, 13...Third region, 20...Dielectric layer, 30...Microstructure, 30a...Microstructure, 30b...Microstructure, 30c...Microstructure, 31...First array, 32...Second array, 33...Third array, 40...Transparent layer, 42...Top surface, 50...Molecular trapping layer, 100...Electric field enhancement element, 200...Electric field enhancement element, 250...Electric field enhancement element, 300...Raman spectrometer, 310...Light source, 320...Collimating lens, 330...Polarization control element, 340...Dichroic mirror, 350...Objective lens, 360...Focusing lens, 370...Detector, B...Thickness, BL...Boundary Boundary line, D...diameter, E...enhancing electric field, Ea...first enhancement field, Eb...second enhancement field, H...thickness, I-1...integral value, I-2...integral value, I-3...integral value, Id...light intensity distribution, K1...scattered light intensity, K2...scattered light intensity, L1...distance, L2...distance, Lin...incident light, M...model, O...center, P...pitch, Q...perpendicular line, Ram...Raman scattered light, Ray...Rayleigh scattered light, S1...position, S2...position, X...target material, air...air layer, r1...width, r2...width, r3...width, α...distribution, β...distribution, λ1...first excitation wavelength, λ2...second excitation wavelength, λ3...third excitation wavelength, λd...excitation wavelength distribution, λin...wavelength

Claims

1. circuit board and A plurality of conductive microstructures are provided on the substrate, A transparent layer covering a plurality of the aforementioned microstructures and the substrate, Equipped with, A first arrangement is provided in the first region of the substrate, and the microstructures are arranged periodically in a first arrangement, A second arrangement is provided in a second region of the substrate that is different from the first region, and the microstructures are arranged periodically. It has, An electric field enhancing element characterized in that the first array and the second array differ from each other in at least one of the following: the diameter of the microstructure, the thickness of the microstructure, and the pitch between adjacent microstructures.

2. The electric field enhancing element according to claim 1, wherein the first region and the second region are adjacent to each other via a boundary line along the plane of the substrate.

3. The electric field enhancing element according to claim 2, wherein the area of ​​the first region and the area of ​​the second region are different from each other.

4. The electric field enhancing element according to claim 1, wherein the first region and the second region are arranged concentrically.

5. The second region is located outside the first region. The electric field enhancing element according to claim 4, wherein the area of ​​the second region is larger than the area of ​​the first region.

6. The wavelength that generates plasmon resonance in the first array is defined as the first excitation wavelength. When the wavelength that generates plasmon resonance in the second array is defined as the second excitation wavelength, The electric field enhancing element according to claim 5, wherein the second excitation wavelength is shorter than the first excitation wavelength.

7. The electric field enhancing element according to any one of claims 1 to 6, wherein the enhanced electric field generated by the plurality of microstructures is maximized at a position in the perpendicular direction of the substrate, on the opposite side of the microstructures from the substrate, and at a distance from the plurality of microstructures.

8. The electric field enhancing element according to claim 7, wherein the enhanced electric field reaches a position separated from the transparent layer in the perpendicular direction.

9. The electric field enhancing element according to any one of claims 1 to 6, wherein the constituent material of the microstructure is a metal.

10. An electric field enhancing element according to any one of claims 1 to 6, A light source that irradiates the aforementioned electric field enhancing element with light, A detector for detecting light from the electric field enhancing element, A Raman spectrometer characterized by comprising the following features.

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