Electric field enhancement element and Raman spectrometer

Abstract

To provide an electric field enhancement element that can improve detection sensitivity, 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 transparent layer has an uneven surface on the surface opposite to the microstructures, and the enhanced electric field generated by the plurality of microstructures is maximized in the perpendicular direction of the substrate, on the side of the microstructures opposite to the substrate, and at a position separated from the plurality of microstructures.

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

[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 is a schematic plan view showing an electric field enhancing element according to the embodiment. [Figure 4] This is a schematic plan view showing an electric field enhancing element according to the embodiment. [Figure 5] This is a schematic plan view showing an electric field enhancing element according to the embodiment. [Figure 6] This is a schematic plan view showing an electric field enhancing element according to the embodiment. [Figure 7] This is a conceptual diagram to explain plasmon resonance in electric field enhancement devices. [Figure 8] This is a conceptual diagram to explain plasmon resonance in electric field enhancement devices. [Figure 9] This diagram illustrates the enhanced electric field generated by the microstructure of an electric field enhancing element. [Figure 10] This is a schematic top view showing an electric field enhancing element according to the embodiment. [Figure 11] This is a schematic cross-sectional view showing an electric field enhancing element according to an embodiment. [Figure 12] It is a cross-sectional view schematically showing an electric field enhancement element according to an embodiment. [Figure 13] It is a cross-sectional view schematically showing an electric field enhancement element according to an embodiment. [Figure 14] It is a cross-sectional view schematically showing an electric field enhancement element according to a first modification of an embodiment. [Figure 15] It is a cross-sectional view schematically showing an electric field enhancement element according to a second modification of an embodiment. [Figure 16] It is a diagram schematically showing a Raman spectroscopic apparatus according to an embodiment. [Figure 17] It is a diagram for explaining the principle of Raman scattering spectroscopy. [Figure 18] It is a schematic diagram showing an example of a Raman spectrum obtained by Raman scattering spectroscopy. [Figure 19] It is an X-Z cross-sectional view schematically showing a repeating unit of a model used in simulation. [Figure 20] It is an X-Y cross-sectional view schematically showing a model used in simulation. [Figure 21] It is a table comparing main parameters in Example 1, Reference Example 1, and Comparative Example 1. [Figure 22] It is a simulation result of Example 1 in Experimental Example A. [Figure 23] It is a simulation result of Reference Example 1 in Experimental Example A. [Figure 24] It is a simulation result of Comparative Example 1 in Experimental Example A. [Figure 25] [[ID=4l]]It is a simulation result of Example 1 in Experimental Example B. [Figure 26] It is a simulation result of Example 2 in Experimental Example B. [Figure 27] It is a simulation result of Example 3 in Experimental Example B. [Figure 28] It is a simulation result of Reference Example 2 in Experimental Example B.

MODE 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.

[0011] Figure 1 is a schematic cross-sectional view of the electric field enhancing element 100 according to the embodiment. Figures 2 to 6 are schematic plan views of the microstructure 30 of the electric field enhancing element 100 according to the embodiment. 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."

[0012] 1.1. Structure The electric field enhancing element 100 shown in Figures 1 and 2 comprises a substrate 10, a dielectric layer 20, a microstructure 30, and a transparent layer 40. Note that the transparent layer 40 is not shown in Figures 2 to 6.

[0013] The substrate 10 supports multiple microstructures 30 via a dielectric layer 20. When light from a light source used for Raman scattering is incident from the substrate 10 side in Figure 1, the incident light passes through the substrate 10 and the dielectric layer 20 and reaches the microstructures 30. When light is incident from the transparent layer 40 side in Figure 1, the incident light passes through the transparent layer 40 and reaches the microstructures 30. In this case, the incident light may be reflected by the substrate 10 towards the transparent layer 40 side.

[0014] When incident light reaches the multiple microstructures 30, an enhanced electric field is generated. This enhanced electric field is maximized at a position above the microstructures 30, that is, on the opposite side of the microstructures 30 from the substrate 10 in the perpendicular direction of the substrate 10, and at a position away from the multiple microstructures 30.

[0015] Furthermore, the upper surface 42 of the transparent layer 40 (the surface opposite to the microstructure 30) has an uneven surface 44. This uneven surface 44 weakens the refractive index gradient on the upper surface 42, reducing the probability that light will be trapped inside the transparent layer 40. This makes it possible to strengthen the enhanced electric field at positions above the upper surface 42.

[0016] With this configuration, the detection signal originating from the target substance placed on the transparent layer 40 can be amplified. This results in an electric field enhancement element 100 with improved detection sensitivity for the target substance.

[0017] 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.

[0018] In Figure 1, Q is defined as 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.

[0019] The dielectric layer 20 shown in Figure 1 is provided between the substrate 10 and the microstructure 30. 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.

[0020] The thickness of the dielectric layer 20 is measured by observing a cross-section of the dielectric layer 20 with an electron microscope and taking the resulting image. In the observed image, the length of the dielectric layer 20 in the Z-axis direction is measured at 10 or more randomly selected locations, and the average value is defined as the "thickness".

[0021] The dielectric layer 20 is transparent to light from a light source. 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, and the like. The dielectric layer 20 may be composed of a plurality of layers. In this case, the constituent materials of the plurality of layers may be the same as each other or different from each other.

[0022] The microstructure 30 shown in FIG. 1 is provided between the dielectric layer 20 and the transparent layer 40. The shape of the microstructure 30 is, for example, a cylinder. The diameter of the microstructure 30 is not particularly limited, but is 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.

[0023] Note that the "diameter of the microstructure 30" means the diameter when the planar shape of the microstructure 30 (the shape when viewed from the Z-axis) is a circle, and the diameter of the minimum enclosing circle when the planar shape of the microstructure 30 is not a circular shape. As an example of the latter, when the planar shape of the microstructure 30 is a polygon, the smallest circle containing this polygon is the "minimum enclosing circle". Also, when the planar shape of the microstructure 30 is an ellipse, the smallest circle containing this ellipse is the "minimum enclosing circle".

[0024] The thickness of the microstructure 30 is not particularly limited, but is preferably 1 nm or more and 500 nm or less, more preferably 5 nm or more and 300 nm or less, and still more preferably 30 nm or more and 200 nm or less. Thereby, the enhanced electric field can be made stronger.

[0025] A plurality of microstructures 30 are provided. The plurality of microstructures 30 are separated from each other. A transparent layer 40 is provided between adjacent microstructures 30. The distance between adjacent microstructures 30 is not particularly limited, but is preferably 20 nm or more and 1000 nm or less, more preferably 100 nm or more and 900 nm or less.

[0026] The multiple microstructures 30 are arranged in a predetermined direction and at a predetermined pitch when viewed from the Z-axis direction. In other words, the microstructures 30 are arranged periodically. In the example shown in Figure 2, the multiple microstructures 30 are arranged in a square lattice.

[0027] 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 of the substrate 10. If multiple microstructures are arranged randomly, only the microstructures with a diameter matching the wavelength of light from the light source will 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.

[0028] The "pitch of the microstructure 30" is the distance between the centers of adjacent microstructures 30 in a given direction. The "center of the microstructure 30" is the center of the circle if the planar shape of the microstructure 30 is a circle, and the center of the smallest inclusion circle if the planar shape of the microstructure 30 is not a circle.

[0029] Furthermore, when viewed from the Z-axis direction, the multiple microstructures 30 may be arranged in a triangular lattice pattern, as shown in Figure 3. Although not shown in the figures, the periodicity of the multiple microstructures 30 may expand or contract at a constant ratio, and the multiple microstructures 30 may include fractal structures.

[0030] The planar shape of the microstructure 30 is not limited to a circle. For example, the planar shape of the microstructure 30 may be an ellipse as shown in Figure 4, a rectangle as shown in Figure 5, or a granular, polygonal, ring-shaped, linear, or other shape as shown in Figure 6. Furthermore, multiple microstructures 30 may be a combination of different shapes. This makes it possible to control the intensity and distribution of the enhanced electric field generated by multiple microstructures 30 in the in-plane direction perpendicular to the perpendicular line Q.

[0031] Furthermore, the cross-sectional shape of the microstructure 30 is not particularly limited and may be trapezoidal, semicircular, circular, inverted tapered, or spherical at the tip. In addition, the shape of the microstructure 30 may be a truncated square pyramid or a cone.

[0032] Although not shown in the diagram, a plurality of recesses may be formed on the upper surface of the dielectric layer 20, and the microstructure 30 may be provided within these recesses.

[0033] The microstructure 30 is electrically conductive. Examples of constituent materials for the microstructure 30 include elemental metals or alloys such as Al, Au, Ag, Cu, Pt, Pd, and Ni. Such metals have particularly good conductivity, which allows for a stronger enhanced electric field. The microstructure 30 may also consist of metal particles. The constituent material of the microstructure 30 is not particularly limited as long as it is a material that has a plasma frequency with respect to light from a light source, and may include transparent electrode materials such as ITO (Indium Tin Oxide), carbon-based materials such as carbon nanotubes, etc.

[0034] The transparent layer 40 is provided on the microstructure 30 and the dielectric layer 20. In other words, the transparent layer 40 is provided so as to cover the multiple microstructures 30 and the substrate 10. The thickness of the transparent layer 40 is not particularly limited, but is preferably 10 nm to 2000 nm, and more preferably 20 nm to 1000 nm.

[0035] The thickness of the transparent layer 40 is measured by observing a cross-section of the transparent layer 40 with an electron microscope and taking the resulting image. In the observed image, the length of the transparent layer 40 in the Z-axis direction is measured at 10 or more randomly selected locations, and the average value is defined as the "thickness".

[0036] The transparent layer 40 is transparent to the light from the light source. 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). Further, 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.

[0037] Also, the transparent layer 40 may be composed of a plurality of layers. In this case, the constituent materials of the plurality of layers may be the same as each other or different from each other.

[0038] The refractive index of the transparent layer 40 may be different from or the same as that of the dielectric layer 20. When the refractive index of the transparent layer 40 is the same as that of the dielectric layer 20, it is easy to generate the Rayleigh anomaly described later. Also, when the dielectric layer 20 is omitted, the refractive index of the transparent layer 40 may be higher or lower than the refractive index 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 influence due to the refractive index difference is suppressed, and regardless of the incident direction of light, the Rayleigh anomaly described later is likely to occur. As a result, the SLR described later is likely to be induced. Note that when the refractive index difference is outside the above range, for example, when light is incident from the substrate 10 side, Fresnel reflection is 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 the surface plasmon resonance described later may decrease, and the enhanced electric field may decrease.

[0039] 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. And the upper surface 42 is the surface on which the target substance to be detected is disposed.

[0040] The upper surface 42 shown in Figure 1 has an uneven structure 44. By providing such an uneven structure 44, the refractive index in the direction crossing the upper surface 42 (the direction of the perpendicular Q) changes gradually along the perpendicular Q. For example, when light is incident from the substrate 10 side in Figure 1, the incident light passes through the substrate 10 and the dielectric layer 20 and reaches the microstructure 30. In addition, some of the light reaches the upper surface 42 and, due to the effect of the gentle refractive index gradient, seeps out above the upper surface 42. This makes it possible to strengthen the enhanced electric field above the upper surface 42. Also, for example, when light is incident from the transparent layer 40 side in Figure 1, the incident light passes through the transparent layer 40 and reaches the microstructure 30. In addition, some of the light is reflected by the substrate 10 and returns to the upper surface 42. In this case as well, some of the light seeps out above the upper surface 42 due to the effect of the gentle refractive index gradient. In this way, the enhanced electric field at positions above the upper surface 42 can be made stronger.

[0041] Furthermore, the uneven structure 44 may have the function of holding the target substance placed on the upper surface 42. This allows the target substance to be stably positioned and suppresses a decrease in detection sensitivity. The uneven structure 44 will be described in detail later.

[0042] 1.2. Enhanced Electric Field Figures 7 and 8 are conceptual diagrams illustrating plasmon resonance in the electric field enhancing element 100. Figure 9 is a diagram illustrating the enhanced electric field E generated by the microstructure 30 of the electric field enhancing element 100.

[0043] In the examples shown in Figures 7 and 8, light incident from the substrate 10 reaches multiple microstructures 30. The light that reaches the microstructures 30 generates plasmon resonance in the microstructures 30. 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 30.

[0044] As shown in Figure 7, when light reaches the microstructure 30, the aforementioned LSPR is induced. In addition, 90° diffraction, i.e., a Rayleigh anomaly, occurs due to multiple microstructures 30. The combination of this Rayleigh anomaly and LSPR induces SLR (Surface Lattice Resonance).

[0045] Furthermore, as shown in Figure 8, 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).

[0046] Then, the resonance states of SLR and QGM, etc., combine and cooperate, inducing cooperative plasmon polaritons in the multiple microstructures 30. 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 30 has not only a first enhanced field Ea generated at the edge of the microstructure 30 due to LSPR, as shown in Figure 9, but also a second enhanced field Eb generated above the microstructures 30 due to the resonance states of SLR and QGM, etc.

[0047] The enhanced electric field E enhances Raman scattered light and generates SERS. The enhanced electric field E reaches a maximum at position S1 or S2 (on the opposite side of the substrate 10 from the multiple microstructures 30 in the Z-axis direction, and at a distance from the multiple microstructures 30) due to the second enhanced field Eb. The fact that the enhanced electric field E reaches a maximum at position S1 or S2 is characteristic of the cooperative plasmon polariton phenomenon. Positions S1 and S2 shown in Figure 9 are located on the positive Z-axis side of the multiple microstructures 30.

[0048] Furthermore, in the electric field enhancing element 100 shown in Figure 9, the upper surface 42 of the transparent layer 40 has an uneven structure 44. Due to this uneven structure 44, the refractive index does not change discontinuously between the transparent layer 40 and the air layer, but rather a pseudo-gradient in the refractive index is created. As a result, light incident on the transparent layer 40 seeps out upward from the upper surface 42. Therefore, in the electric field enhancing element 100, the uneven structure 44 allows for a stronger enhanced electric field above the upper surface 42.

[0049] 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 30 due to LSPR, the effect of generating the enhanced electric field E cannot be obtained unless the target material is positioned near the microstructure 30. In general, 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.

[0050] In contrast, in the electric field enhancement element 100 shown in Figure 9, the enhanced electric field E generated by the multiple microstructures 30 is maximized at a position S1 or S2 located above the multiple microstructures 30 in the perpendicular direction (a position S1 or S2 located on the opposite side of the multiple microstructures 30 from the substrate 10 in the Z-axis direction, and separated from the multiple microstructures 30). Therefore, the detection signal caused by the target substance can be enhanced even without positioning the target substance near the microstructures 30. As a result, detection sensitivity can be improved. Furthermore, since it is not necessary to position the target substance between adjacent microstructures 30, various sizes of samples, such as viruses and bacteria, can be freely selected as target substances.

[0051] Furthermore, in the electric field enhancement element 100, since the position S1 or position S2 of the maximum point is far from the vicinity of the microstructure 30, a transparent layer 40 can be provided to cover the microstructure 30. 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 30 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 30, such alteration and deformation can be suppressed. As a result, the durability and reliability of the electric field enhancement element 100 can be improved.

[0052] Furthermore, in the electric field enhancement element 100, since the transparent layer 40 has an uneven structure 44, the enhanced electric field E can be strengthened even more, especially above the upper surface 42. In other words, the probability of the enhanced electric field E reaching a maximum at position S2 increases. This significantly improves detection sensitivity.

[0053] Furthermore, the uneven structure 44 makes it easier to hold the target substance placed on the upper surface 42. This allows the target substance to be placed stably, suppressing a decrease in detection sensitivity.

[0054] The second augmentation field Eb may be separated from the first augmentation field Ea, as shown in Figure 9, or it may be continuous with the first augmentation field Ea.

[0055] Furthermore, in Figure 9, the maximum point where the enhanced electric field E is at its maximum is located at position S1 or position S2. Of these, position S1 shown in Figure 9 is located within the transparent layer 40. In this case, the distance L1 from the microstructure 30 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 30, 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 9, 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 9. Position S2 shown in Figure 9 is 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] Distance L2 is the distance in the perpendicular direction between the lowest point 46 on the upper surface 42 that is closest to the substrate 10 and position S2. The lowest point 46 is defined as the point where the upper surface 42 slopes down the lowest when viewing a cross-section of a repeating unit containing any one microstructure 30, as shown in Figure 9. The cross-section shown in Figure 9 can be obtained, for example, by cutting the electric field enhancing element 100 so as to include the perpendicular Q, and observing the resulting cross-section with an electron microscope.

[0061] 1.3.Concave and convex structure The uneven structure 44 may be offset from the microstructure 30 when viewed from the perpendicular direction of the substrate 10, but preferably it is provided in a position that overlaps with the microstructure 30, as shown in Figure 1. In this case, the enhanced electric field distribution distributed starting from the microstructure 30 and the position of the uneven structure 44 are aligned, so the strength of the enhanced electric field E formed above the upper surface 42 can be made uniform. As a result, the detection signal caused by the target substance can be uniformly amplified.

[0062] Furthermore, the overlap between the uneven structure 44 and the microstructure 30 refers to a state in which, when viewed from the perpendicular direction, the area occupied by the uneven structure 44 and the area occupied by the microstructure 30 overlap in at least a portion of the same area.

[0063] The height h of the uneven structure 44 shown in Figure 9 is preferably 1 nm to 500 nm, more preferably 1 nm to 200 nm, and even more preferably 1 nm to 40 nm. If the height h of the uneven structure 44 is within the above range, the gradient of the refractive index on either side of the upper surface 42 can be optimized. As a result, the enhanced electric field E formed above the upper surface 42 can be particularly strengthened.

[0064] The height h is calculated from the perpendicular lengths between the lowest point 46 closest to the substrate 10 and the highest point 443 furthest from the substrate 10 in a repeating unit containing any one uneven structure 44, as shown in Figure 9. Specifically, these lengths are measured in 10 or more repeating units, and the average value is defined as the "height h".

[0065] The shape of the uneven structure 44 is not particularly limited, but as shown in Figure 1, it may have a shape having multiple protrusions 442 that project upward, or, although not shown, it may have a shape having multiple recesses that are concave downward.

[0066] Furthermore, the convex portion 442 shown in Figure 1 is hemispherical. This makes the pseudo-gradient of the refractive index formed between the transparent layer 40 and the air layer gentler. As a result, the enhanced electric field E formed above the upper surface 42 can be strengthened. Note that a hemispherical shape refers to a convex curved surface that protrudes upward. The convex curved surface may be a perfect sphere or an aspherical surface.

[0067] When the protrusions 442 are hemispherical, the radius of curvature of the protrusions 442 is preferably 125 μm or less, more preferably 1 μm to 100 μm, and even more preferably 3 μm to 50 μm. With such a configuration, it becomes easier to optimize the pitch between the protrusions 442 and the height h of the protrusions 442. For this reason, when the protrusions 442 are provided in positions that overlap with the microstructure 30, the independence of the protrusions 442 is ensured, making it easier to control the shape of the uneven structure 44, and also reducing the difficulty of manufacturing the uneven structure 44.

[0068] Figure 10 is a schematic top view showing the electric field enhancing element 100 according to the embodiment. In the electric field enhancing element 100 shown in Figure 10, multiple protrusions 442 are arranged along the plane (XY plane) where the substrate 10 extends. This allows for the uniform formation of a refractive index gradient along the XY plane. As a result, the enhanced electric field E can be strengthened over a wide area of ​​the upper surface 42.

[0069] In the example shown in Figure 10, the microstructures 30 (not shown) are arranged in a square grid, and the protrusions 442 are also arranged in a square grid accordingly. However, the arrangement pattern of the protrusions 442 is not limited to this. For example, the protrusions 442 may be arranged in a triangular grid, similar to the microstructures 30 shown in Figure 3, or they may be arranged in other arrangement patterns.

[0070] Figures 11 to 13 are schematic cross-sectional views of the electric field enhancing element 100 according to the embodiment. The cross-sectional shape of the protrusion 442 is not limited to the hemispherical shape shown in Figure 1, but may be other shapes as shown in Figures 11 to 13.

[0071] The uneven structure 44 shown in Figure 11 has protrusions 442 with a triangular cross-sectional shape. When the protrusions 442 shown in Figure 11 are viewed from the direction perpendicular to the substrate 10, the planar shape of the protrusions 442 is, for example, circular. In this case, the protrusions 442 shown in Figure 11 are conical. This widens the gaps between the protrusions 442, making it easier for the target substance to enter these gaps. In addition, the pseudo-gradient of the refractive index formed between the transparent layer 40 and the air layer becomes gentler. Note that the protrusions 442 shown in Figure 11 may also be pyramidal.

[0072] The uneven structure 44 shown in Figure 12 has protrusions 442 with a rectangular cross-sectional shape. When the protrusions 442 shown in Figure 12 are viewed from the direction perpendicular to the substrate 10, the planar shape of the protrusions 442 is, for example, circular or square. In this case, the protrusions 442 shown in Figure 12 are cylindrical or rectangular prisms. This makes it easier for the target substance to enter the gaps between the protrusions 442. Note that the protrusions 442 shown in Figure 12 may be prisms other than rectangular prisms.

[0073] Furthermore, the planar shape of the protrusion 442 may be a shape other than those described above, for example, a ring shape, a linear shape, etc.

[0074] The uneven structure 44 shown in Figure 13 has random heights h and arrangement patterns of the protrusions 442. Random means that adjacent protrusions 442 have different heights h, or that the pitch of the protrusions 442 differs in at least two places. Such an uneven structure 44 contributes to reducing the difficulty of manufacturing the electric field enhancing element 100.

[0075] The diameter of the protrusion 442 is not particularly limited, but is preferably 1 nm to 1000 nm, more preferably 5 nm to 500 nm, and even more preferably 10 nm to 400 nm.

[0076] The diameter of the protrusion 442 is the diameter if the planar shape of the protrusion 442 (shape viewed from the Z-axis) is a circle, and the diameter of the smallest inclusion circle if the planar shape of the protrusion 442 is not a circle.

[0077] The pitch of the protrusions 442 is not particularly limited, but is preferably 20 nm to 1000 nm, and more preferably 100 nm to 900 nm.

[0078] The pitch of the protrusions 442 is the distance between the centers of adjacent protrusions 442. The center of a protrusion 442 is the center of the circle if the planar shape of the protrusion 442 is a circle, and the center of the smallest inclusion circle if the planar shape of the protrusion 442 is not a circle.

[0079] 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.

[0080] 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).

[0081] Next, a plurality of microstructures 30 are formed on the dielectric layer 20. The microstructures 30 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.

[0082] Next, a transparent layer 40 is formed on the dielectric layer 20 and the microstructure 30. 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.

[0083] Furthermore, by adjusting the thickness and deposition rate of the transparent layer 40 according to the thickness and pitch of the microstructure 30, it is possible to form a bumpy structure 44 that matches the position of the microstructure 30. For example, by increasing the thickness of the microstructure 30 or widening the pitch, the height h of the protrusions 442 can be increased.

[0084] On the other hand, by using EB (electron beam) lithography, photolithography and etching, microcontact printing, nanoimprinting, mask deposition, lift-off, etc., it is possible to form protrusions 442 that satisfy any shape, arrangement pattern, height h, pitch, etc.

[0085] 3. Modified Examples of Electric Field Enhancing Devices Next, an electric field enhancing element according to a modified embodiment will be described.

[0086] Figure 14 is a schematic cross-sectional view showing an electric field enhancing element 200 according to a first modified example of the embodiment. Figure 15 is a schematic cross-sectional view showing an electric field enhancing element 250 according to a second modified example of the embodiment.

[0087] The following description focuses on the differences between the electric field enhancing element 200, according to the first modified embodiment, and the electric field enhancing element 100 described above, while descriptions of similar components are omitted. In Figures 14 and 15, components similar to those of the electric field enhancing element 100 described above are denoted by the same reference numerals.

[0088] The electric field enhancing element 200 shown in Figure 14 is the same as the electric field enhancing element 100 except that it has a molecular trapping layer 50.

[0089] 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).

[0090] 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.

[0091] 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".

[0092] 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.

[0093] 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.

[0094] 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.

[0095] The electric field enhancing element 250 shown in Figure 15 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 15 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 15, the microstructure 30 is surrounded by the transparent layer 40. In the modified examples described above, the same effects as those of the embodiment described above can be obtained.

[0096] 4. Raman spectrometer Next, a Raman spectrometer according to an embodiment will be described. Figure 16 is a schematic diagram showing the Raman spectrometer 300 according to the embodiment.

[0097] 4.1. Composition The Raman spectrometer 300 shown in Figure 16 includes an electric field enhancing 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 enhancing element 100 is simplified in Figure 16.

[0098] 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.

[0099] 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).

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 4.2. Principle Figure 17 is a diagram illustrating the principle of Raman scattering spectroscopy.

[0104] In Figure 17, 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.

[0105] Figure 18 is a schematic diagram showing an example of a Raman spectrum obtained by Raman scattering spectroscopy. In Figure 18, 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.

[0106] Comparing the scattered light intensity K1 of Raman scattered light Ram and the scattered light intensity K2 of Rayleigh scattered light Ray, as shown in Figure 18, 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.

[0107] 5. Effects of the above embodiment The electric field enhancing element according to the above embodiment comprises a substrate 10, a plurality of microstructures 30, and a transparent layer 40. The microstructures 30 are provided on the substrate 10 and are conductive. The transparent layer 40 covers the plurality of microstructures 30 and the substrate 10. The transparent layer 40 also has an uneven structure 44 on its upper surface 42 (the surface opposite to the microstructures 30). The enhanced electric field E generated by the plurality of microstructures 30 is maximized in the perpendicular direction of the substrate 10, on the opposite side of the plurality of microstructures 30 from the substrate 10, and at a position separated from the plurality of microstructures 30.

[0108] With this configuration, the detection signal originating from the target substance can be amplified even without positioning the target substance in the vicinity of the microstructure 30. As a result, an electric field augmentation element with improved detection sensitivity can be obtained. Furthermore, since it is not necessary to position the target substance between adjacent microstructures 30, various samples such as viruses and bacteria can be freely selected as the target substance. In addition, because the transparent layer 40 has an uneven structure 44, the augmented electric field E can be strengthened even more, especially above the upper surface 42. This allows for a particularly improved detection sensitivity.

[0109] In the electric field enhancing element according to the above embodiment, it is preferable that the uneven structure 44 is provided at a position that overlaps with the microstructure when viewed from the perpendicular direction of the substrate 10.

[0110] With this configuration, the enhanced electric field distribution originating from the microstructure 30 aligns with the position of the uneven structure 44, thus uniformizing the strength of the enhanced electric field E formed above the upper surface 42. This allows for uniform enhancement of the detection signal caused by the target substance.

[0111] In the electric field enhancing element according to the above embodiment, it is preferable that the height h of the uneven structure 44 is 1 nm or more and 500 nm or less.

[0112] With this configuration, the refractive index gradient across the upper surface 42 (the surface opposite to the microstructure 30) can be optimized. As a result, the enhanced electric field E formed above the upper surface 42 can be particularly strengthened.

[0113] In the electric field enhancing element according to the above embodiment, the uneven structure 44 has a plurality of protrusions 442 arranged along the surface on which the substrate 10 expands, and these protrusions 442 may be hemispherical in shape.

[0114] With this configuration, the pseudo-gradient in the refractive index formed between the transparent layer 40 and the air layer becomes gentler. As a result, the enhanced electric field E formed above the upper surface 42 can be strengthened.

[0115] In the electric field enhancing element according to the above embodiment, it is preferable that the radius of curvature of the protrusion 442 is 125 μm or less.

[0116] This configuration makes it easier to optimize the pitch between the protrusions 442 and the height h of the protrusions 442. Therefore, when the protrusions 442 are placed in positions that overlap with the microstructure 30, the independence of the protrusions 442 can be ensured, making it easier to control the shape of the uneven structure 44, and also reducing the difficulty of manufacturing the uneven structure 44.

[0117] In the electric field enhancing element according to the above embodiment, the uneven structure 44 has a plurality of protrusions 442 arranged along the surface on which the substrate 10 expands, and these protrusions 442 may be conical in shape.

[0118] With this configuration, the gaps between the protrusions 442 become wider, making it easier for the target material to enter these gaps. In addition, the pseudo-gradient in the refractive index formed between the transparent layer 40 and the air layer becomes gentler.

[0119] In the electric field enhancing element according to the above embodiment, the uneven structure 44 has a plurality of protrusions 442 arranged along the surface on which the substrate 10 extends, and the cross-sectional shape when these protrusions 442 are cut by a plane including the perpendicular Q of the substrate 10 may be rectangular. With this configuration, the target substance can easily enter the gaps between the protrusions 442.

[0120] In the electric field enhancing element according to the above embodiment, when the position S1 where the enhanced electric field E is maximized is defined as the maximum point, the distance L1 from the microstructure 30 to position S1 (maximum point) in the perpendicular direction of the substrate 10 may be 100 nm or more.

[0121] With this configuration, even when a target material is placed on the upper surface 42, the enhanced electric field E acts on the target material, thereby enhancing the detection signal caused by the target material.

[0122] In the electric field enhancing element according to the above embodiment, the enhanced electric field E may be maximized at a position S2 located away from the transparent layer 40 in the perpendicular direction of the substrate 10.

[0123] With this configuration, the detection signal originating from the target material located on the opposite side (upper surface 42) of the substrate 10 of the multiple microstructures 30 can be further enhanced.

[0124] In the electric field enhancing element according to the above embodiment, it is preferable that the microstructure 30 is arranged periodically.

[0125] This configuration reduces variations in the intensity of the enhanced electric field E in the in-plane direction. Furthermore, the periodic arrangement of the microstructures 30 facilitates the induction of straight-line resistance (SLR).

[0126] In the electric field enhancing element according to the above embodiment, the constituent material of the microstructure 30 is preferably a metal. This configuration allows for a stronger augmented electric field.

[0127] 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. With this configuration, a Raman spectrometer 300 with improved detection sensitivity can be obtained.

[0128] 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]

[0129] Next, specific embodiments of the present invention will be described. 6. Experimental Example A 6.1. Example 1 Figure 19 is an XZ cross-sectional view schematically showing the iteration units of model M used in the simulation. Figure 20 is an XY cross-sectional view schematically showing model M used in the simulation.

[0130] In Model M, as shown in Figure 19, the substrate material was quartz glass (SiO2), and the reflective layer material was Al2O3. The thickness B of the transparent layer was 360 nm, the material of the microstructure was Al, the diameter D of the microstructure was 156 nm, and the thickness H of the microstructure was 60 nm. In Model M, as shown in Figure 20, the arrangement of the microstructure was a square lattice, the shape of the microstructure was cylindrical, and the pitch P of the microstructure was 391 nm. An air layer was provided above the transparent layer. Furthermore, the height h of the uneven structure (convex part) was 50 nm, the shape of the convex part was a hemispherical shape with a diameter of 156 nm, and the convex part was provided directly above the microstructure.

[0131] Then, light was incident on the substrate side of Model M shown in Figure 19, and the intensity distribution of the enhanced electric field was calculated. The wavelength of the incident light was set to 476 nm.

[0132] 6.2. Reference example 1 In Reference Example 1, the height h of the uneven structure was set to zero in the aforementioned Model M, i.e., the uneven structure was omitted. Furthermore, the thickness B of the transparent layer was set to 275 nm, the diameter D of the microstructure to 260 nm, the thickness H of the microstructure to 140 nm, the pitch of the microstructure to 434 nm, and the wavelength of the incident light to 434 nm. Aside from these, the intensity distribution of the enhanced electric field was calculated in the same manner as in Example 1.

[0133] 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.

[0134] Figure 21 is a table comparing the main parameters in Example 1, Reference Example 1, and Comparative Example 1.

[0135] 7. Results of Experiment Example A Simulations were performed to estimate the distribution of the enhanced electric field in each of the models described above: Example 1, Reference Example 1, and Comparative Example 1. The FDTD (Finite Difference Time Domain) method was used for the simulations. Synopsys' Rcost software was used for the simulations.

[0136] Figures 22 to 24 show the simulation results for Example 1, Reference Example 1, and Comparative Example 1 in Experimental Example A, respectively. Figures 22 to 24 show the distribution of the normalized enhanced electric field in the XZ cross-section.

[0137] The shades in Figures 22-24 indicate the intensity of the enhanced electric field in the XZ cross-section. Specifically, 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 ) that is, √(Ex 2 +Ez 2 This is reflected in the shading of Figures 22 to 24.

[0138] In Figures 22 and 23, the "air interface" refers to the interface between the transparent layer and the air layer. In Figure 24, the "air interface" refers to the interface between the substrate and the air layer.

[0139] In Figure 22, the enhanced electric field is maximized at position S2, which is sufficiently far above the air interface (on the air layer side). Furthermore, a clearer maximum point is observed at position S2 compared to Figure 23, indicating that the enhanced electric field is sufficiently strong. The distance from the air interface to the maximum point S2 shown in Figure 22 is less than 100 nm. Additionally, the enhanced electric field shown in Figure 22 reaches positions in the air layer that are more than 100 nm away from the air interface. Furthermore, in Figure 24, no enhanced electric field was observed at a distance from the microstructure.

[0140] These results confirm that it is possible to realize an electric field enhancement element that has a maximum enhanced electric field at position S2, which is sufficiently far from the transparent layer.

[0141] 8. Experimental Example B 8.1. Example 2 In Example 2, the same model as in Example 1 was fabricated, except that the shape of the protrusion was made into a cone with a diameter of 156 nm.

[0142] 8.2. Example 3 In Example 3, a model similar to that in Example 1 was fabricated, except that the shape of the convex portion was made into a rectangular prism with a square base having sides of 156 nm.

[0143] 8.3.Reference example 2 In Reference Example 2, a model similar to that in Example 1 was created, except that the uneven structure was omitted.

[0144] 9. Results of Experimental Example B In each of the models described in Examples 1-3 and Reference Example 2, simulations were performed to determine the distribution of the enhanced electric field. The FDTD (Finite Difference Time Domain) method was used for the simulations. Synopsys' Rcost software was used for the simulations.

[0145] Figures 25 to 28 show the simulation results for Examples 1 to 3 and Reference Example 2 in Experimental Example B. Figures 25 to 28 show the distribution of the normalized enhanced electric field in the XY plane at a position 1 nm above the center of the uneven structure.

[0146] The shades in Figures 25-28 indicate the intensity of the enhanced electric field in the XY plane. Specifically, when the X component of the enhanced electric field is Ex and the Y component is Ey, (Ex 2 +Ey 2 The square root of ) that is, √(Ex 2 +Ey 2 This is reflected in the shading of Figures 25 to 28.

[0147] As shown in Figures 25 to 28, in Examples 1 to 3, which have an uneven structure, the enhanced electric field formed in the air layer is stronger compared to Reference Example 2, which does not have an uneven structure.

[0148] These results confirm that providing an uneven structure in the transparent layer can further strengthen the enhanced electric field formed in the air layer. [Explanation of Symbols]

[0149] 10...Substrate, 20...Dielectric layer, 30...Microstructure, 40...Transparent layer, 42...Top surface, 44...Rough structure, 46...Lowest point, 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, 442...convex part, 443...highest point, B...thickness, D...diameter, E...enhanced electric field, Ea...first enhanced field, Eb...second enhanced field, H...thickness, K1...scattered light intensity, K2...scattered light intensity, L1...distance, L2...distance, Lin...incident light, M...model, P...pitch, Q...perpendicular, Ram...Raman scattered light, Ray...Rayleigh scattered light, X...target material, air...air layer, h...height

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, The transparent layer has an uneven surface on the surface opposite to the microstructure, An electric field enhancing element characterized in that the enhanced electric field generated by the plurality of microstructures is maximized at a position in the direction perpendicular to the substrate, on the opposite side of the microstructure from the substrate, and at a distance from the plurality of microstructures.

2. The electric field enhancing element according to claim 1, wherein the uneven structure is provided at a position that overlaps with the microstructure when viewed from the perpendicular direction.

3. The electric field enhancing element according to claim 1 or 2, wherein the height of the uneven structure is 1 nm or more and 500 nm or less.

4. The aforementioned uneven structure has a plurality of protrusions arranged along the surface on which the substrate expands, The electric field enhancing element according to claim 1 or 2, wherein the convex portion is hemispherical.

5. The electric field enhancing element according to claim 4, wherein the radius of curvature of the convex portion is 125 μm or less.

6. The aforementioned uneven structure has a plurality of protrusions arranged along the surface on which the substrate expands, The electric field enhancing element according to claim 1 or 2, wherein the convex portion is cone-shaped.

7. The aforementioned uneven structure has a plurality of protrusions arranged along the surface on which the substrate expands, The electric field enhancing element according to claim 1 or 2, wherein the cross-sectional shape when the protrusion is cut by a plane including a perpendicular line of the substrate is rectangular.

8. When the position where the aforementioned enhanced electric field is at its maximum is defined as the maximum point, The electric field enhancing element according to claim 1 or 2, wherein the distance from the microstructure to the maximum point in the perpendicular direction is 100 nm or more.

9. The electric field enhancing element according to claim 1 or 2, wherein the enhanced electric field is maximized at a position separated from the transparent layer in the perpendicular direction.

10. The electric field enhancing element according to claim 1 or 2, wherein the microstructures are arranged periodically.

11. The electric field enhancing element according to claim 1 or 2, wherein the constituent material of the microstructure is a metal.

12. An electric field enhancing element according to claim 1 or 2, 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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