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 silicon oxide layer covering the plurality of microstructures and the substrate, wherein the enhanced electric field generated by the plurality of microstructures is maximized at a position opposite to the substrate from the microstructures and separated from the plurality of microstructures in the perpendicular direction of the substrate.

Description

Technical Field

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

Background Art

[0002] As one of the spectroscopic techniques for detecting low-concentration sample molecules, a Raman spectroscopic apparatus using Localized Surface Plasmon Resonance (LSPR) is known. In such a Raman spectroscopic apparatus, an enhanced electric field is formed by an electric field enhancement element having a nanostructure on the nanometer scale, 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.

Means for Solving the Problems

[0006] The electric field enhancement element according to an application example of the present invention is a substrate, a plurality of fine structures provided on the substrate and having conductivity, [[ID=5l]] a silicon oxide layer covering the plurality of fine structures and the substrate, Equipped with, The enhanced electric field generated by the multiple microstructures is maximized in the direction perpendicular to the substrate, at a position opposite the microstructures from the substrate and separated from the multiple 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 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 cross-sectional view showing an electric field enhancing element according to a first modified example of the embodiment. [Figure 11] This is a schematic cross-sectional view showing an electric field enhancing element according to a second modified example of the embodiment. [Figure 12]This is a diagram schematically showing a Raman spectroscopic apparatus according to an embodiment. [Figure 13] This is a diagram for explaining the principle of Raman scattering spectroscopy. [Figure 14] This is a schematic diagram showing an example of a Raman spectrum obtained by Raman scattering spectroscopy. [Figure 15] This is an X-Z cross-sectional view schematically showing a repeating unit of a model used in simulation. [Figure 16] This is an X-Y cross-sectional view schematically showing a model used in simulation. [Figure 17] This is a table comparing the main parameters in Examples 1, 2 and Comparative Example 1. [Figure 18] This is the simulation result of Example 1. [Figure 19] This is the simulation result of Example 2. [Figure 20] This is the simulation result of Comparative Example 1.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the electric field enhancement element and the Raman spectroscopic apparatus of the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

[0010] 1. Electric field enhancement element First, the electric field enhancement element according to the embodiment will be described.

[0011] FIG. 1 is a cross-sectional view schematically showing the electric field enhancement element 100 according to the present embodiment. FIGS. 2 to 6 are each a plan view schematically showing the electric field enhancement element 100 according to the embodiment. Note that FIG. 1 is a cross-sectional view taken along line I-I of FIG. 2. Also, in each figure of the present application, the X-axis, Y-axis, and Z-axis are set as three mutually orthogonal axes and are indicated by arrows respectively. And the tip side of the arrow of each axis is referred to as the "plus side", and the base end side is referred to as the "minus side". Also, the Z-axis plus side is also referred to as "up", and the Z-axis minus side is also referred to as "down".

[0012] 1.1. Configuration 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 silicon oxide layer 40. Note that the silicon oxide 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 silicon oxide layer 40 side in Figure 1, the incident light passes through the silicon oxide layer 40 and reaches the microstructures 30. In this case, the incident light may be reflected by the substrate 10 towards the silicon oxide layer 40.

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

[0015] With this configuration, the detection signal originating from the target substance placed on the silicon oxide layer 40 can be amplified. As a result, an electric field enhancement element 100 with improved detection sensitivity for the target substance can be obtained.

[0016] 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.

[0017] 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.

[0018] The dielectric layer 20 shown in Fig. 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 or more and 2000 nm or less, more preferably 10 nm or more and 1000 nm or less. Note that the dielectric layer 20 may be omitted.

[0019] The thickness of the dielectric layer 20 is measured from the obtained observation image by observing the cross-section of the dielectric layer 20 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 dielectric layer 20, and the average value is taken as the "thickness".

[0020] 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 <! [CDATA[3]]>), PMMA (acrylic resin), PVA (polyvinyl alcohol), polysilazane, etc. 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.

[0021] The microstructure 30 shown in Fig. 1 is provided between the dielectric layer 20 and the silicon oxide 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.

[0022] Note that the "diameter of the microstructure 30" is the diameter when the planar shape of the microstructure 30 (the shape when viewed from the Z-axis) is a circle, and is 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".

[0023] The thickness of the microstructure 30 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. This allows for a stronger enhanced electric field.

[0024] Multiple microstructures 30 are provided. The multiple microstructures 30 are spaced apart from each other. A silicon oxide layer 40 is provided between adjacent microstructures 30. The pitch of adjacent microstructures 30 is not particularly limited, but is preferably 20 nm to 1000 nm, and more preferably 100 nm to 900 nm.

[0025] Furthermore, the multiple microstructures 30 are arranged periodically in a predetermined direction when viewed from the Z-axis direction. In the example shown in Figure 2, the multiple microstructures 30 are arranged in a square lattice.

[0026] With this configuration, the electric field enhancement element 100 can reduce variations in the intensity of the enhanced electric field in the in-plane direction of the substrate 10. When multiple microstructures are arranged randomly, only the microstructures with pitch and diameter corresponding to the wavelength of light from the light source induce LSPR. Therefore, there is a risk of variations in the intensity of the enhanced electric field in the in-plane direction. In contrast, the periodically arranged microstructures 30 make it easier to induce SLR (Surface Lattice Resonance), which will be described later.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The silicon oxide layer 40 is provided on the microstructure 30 and on the dielectric layer 20. That is, the silicon oxide layer 40 is provided so as to cover the plurality of microstructures 30 and the substrate 10. The thickness of the silicon oxide 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.

[0034] The thickness of the silicon oxide layer 40 is measured from an observation image obtained by observing the cross section of the silicon oxide layer 40 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 silicon oxide layer 40, and the average value thereof is defined as the "thickness".

[0035] The silicon oxide layer 40 is transparent to light from a light source. The constituent material of the silicon oxide layer 40 is silicon oxide. In this specification, the silicon oxide is a composition represented by SiOx (0 <x <3), but is preferably represented by SiOx (1 <x ≤ 2).

[0036] The refractive index of the silicon oxide layer 40 may be different from or the same as the refractive index of the dielectric layer 20. When the refractive index of the silicon oxide layer 40 is the same as the refractive index of the dielectric layer 20, it is easy to generate the Rayleigh anomaly described later. Further, when the dielectric layer 20 is omitted, the refractive index of the silicon oxide 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. When the refractive index difference is out of 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 silicon oxide 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.

[0037] The silicon oxide layer 40 has an upper surface 42. The upper surface 42 is, for example, the interface between the silicon oxide 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 stably positioned.

[0038] The surface roughness of the upper surface 42 is not particularly limited, but preferably the maximum height Rz is 20 nm or less, and more preferably the maximum height Rz is 15 nm or less. If the surface roughness is within the above range, the smoothness of the upper surface 42 can be sufficiently increased. This makes it easier to homogenize the enhanced electric field formed on the upper surface 42. As a result, the reproducibility of detection can be easily improved. Furthermore, even when target materials of various sizes are mixed, the detection signal caused by the target material can be uniformly amplified.

[0039] The maximum height Rz is determined as follows: First, the upper surface 42 is observed with an atomic force microscope (AFM) to obtain an image. Next, the surface shape of the observed image is cut out along a line passing over the microstructure 30. Then, the maximum height Rz is determined from the obtained line profile.

[0040] 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.

[0041] 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.

[0042] 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).

[0043] Furthermore, as shown in Figure 8, the incident light is guided through the silicon oxide layer 40. The combination of this guided mode in the silicon oxide layer 40 and LSPR induces a Quasi-Guided Mode (QGM).

[0044] 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.

[0045] 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.

[0046] 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.

[0047] In contrast, in the electric field enhancing element 100, 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.

[0048] 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 30, a silicon oxide layer 40 can be provided to cover the microstructure 30. In other words, even with the silicon oxide 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.

[0049] Furthermore, in the electric field enhancement element 100, the silicon oxide layer 40 can mitigate the irregularities caused by the multiple microstructures 30. 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.

[0050] 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.

[0051] 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 silicon oxide 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 close to 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.

[0052] 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 in the air layer. In other words, the enhanced electric field E may be maximum at a position separated from the silicon oxide 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.

[0053] In this case, the distance L2 from the upper surface 42 (the surface of the silicon oxide layer 40) to position S2 (the maximum point) may be 100 nm or less, or it may be greater than 100 nm.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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).

[0058] Next, a plurality of microstructures 30 are formed on the dielectric layer 20. The microstructures 30 are formed, for example, by depositing a thin film using a vacuum deposition method or sputtering method, and then patterning this thin film. Examples of patterning methods include photolithography and etching, microcontact printing, and nanoimprint lithography.

[0059] Next, a silicon oxide layer 40 is formed on the dielectric layer 20 and the microstructure 30. This gives rise to the electric field enhancing element 100. The silicon oxide layer 40 is formed by methods such as vapor deposition, sputtering, CVD, ALD, or sol-gel.

[0060] 3. Modified Examples of Electric Field Enhancing Devices Next, an electric field enhancing element according to a modified embodiment will be described.

[0061] Figure 10 is a schematic cross-sectional view showing an electric field enhancing element 200 according to a first modified example of the embodiment. Figure 11 is a schematic cross-sectional view showing an electric field enhancing element 250 according to a second modified example of the embodiment.

[0062] 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 10 and 11, components similar to those of the electric field enhancing element 100 described above are denoted by the same reference numerals.

[0063] The electric field enhancing element 200 shown in Figure 10 is the same as the electric field enhancing element 100, except that it includes a molecular trapping layer 50 and has a different shape for the microstructure 30.

[0064] The molecular trapping layer 50 is provided on the silicon oxide layer 40 so as to be in contact with the silicon oxide layer 40. The molecular trapping layer 50 is an organic molecular film, for example, a SAM (Self-Assembled Monolayer).

[0065] 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.

[0066] 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".

[0067] 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.

[0068] In the electric field enhancement element 200, the molecular trapping layer 50 is provided on the silicon oxide layer 40, which can mitigate uneven deposition of the molecular trapping layer 50. For example, if the silicon oxide layer is not provided and the molecular trapping layer is deposited directly on the microstructure and the substrate, uneven 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.

[0069] 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 silicon oxide layer 40 and the molecular trapping layer 50 to improve their adhesion.

[0070] The electric field enhancing element 250 shown in Figure 11 is the same as the electric field enhancing element 100, except that the dielectric layer 20 shown in Figure 1 is replaced by an extended silicon oxide layer 40. That is, the silicon oxide layer 40 shown in Figure 11 extends to the region where the dielectric layer 20 shown in Figure 1 is located. As a result, in the cross-section shown in Figure 11, the microstructure 30 is surrounded by the silicon oxide layer 40.

[0071] In the modified examples described above, the same effects as those of the embodiment described above can be obtained.

[0072] 4. Raman spectrometer Next, a Raman spectrometer according to an embodiment will be described. Figure 12 is a schematic diagram showing the Raman spectrometer 300 according to the embodiment.

[0073] 4.1. Composition The Raman spectrometer 300 shown in Figure 12 comprises 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 12.

[0074] 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.

[0075] 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).

[0076] 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 silicon oxide layer 40 of the electric field enhancing element 100 is in contact with the target material.

[0077] 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.

[0078] 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.

[0079] 4.2. Principle Figure 13 is a diagram illustrating the principle of Raman scattering spectroscopy.

[0080] In Figure 13, 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.

[0081] Figure 14 is a schematic diagram showing an example of a Raman spectrum obtained by Raman scattering spectroscopy. In Figure 14, 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.

[0082] 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 14, 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.

[0083] 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 silicon oxide layer 40. The microstructures 30 are provided on the substrate 10 and are conductive. The silicon oxide layer 40 covers the plurality of microstructures 30 and the substrate 10. The enhanced electric field E generated by the plurality of microstructures 30 is maximized in the direction perpendicular to 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.

[0084] 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 microstructure 30. As a result, an electric field enhancement element that can improve detection sensitivity can be obtained. 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 the target substance.

[0085] 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 silicon oxide layer 40 in the perpendicular direction of the substrate 10.

[0086] 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.

[0087] In the electric field enhancing element according to the above embodiment, when the position S2 at which the enhanced electric field E is maximized is defined as the maximum point, the distance from the surface (upper surface 42) of the silicon oxide layer 40 to the maximum point (position S2) may be 100 nm or less.

[0088] With this configuration, the probability that position S2 acts on the target material located on the upper surface 42 increases. Therefore, the detection signal originating from the target material can be particularly enhanced.

[0089] In the electric field enhancing element according to the above embodiment, when the position S2 at which the enhanced electric field E is maximized is defined as the maximum point, the distance from the surface (upper surface 42) of the silicon oxide layer 40 to the maximum point (position S2) may be greater than 100 nm.

[0090] With this configuration, even when target materials of various sizes are mixed together, the detection signal originating from the target material can be uniformly amplified.

[0091] In the electric field enhancing element according to the above embodiment, when the position S1 at which the enhanced electric field E is maximized is defined as the maximum point, the maximum point (position S1) is located inside the silicon oxide layer 40, and the distance from the microstructure 30 to the maximum point (position S1) in the perpendicular direction of the substrate 10 may be 100 nm or more.

[0092] With this configuration, the enhanced electric field E generated above the upper surface 42 can also be strengthened, so even if the target material is not positioned close to the microstructure 30, the enhanced electric field E acts on the target material, and the detection signal originating from the target material can be amplified.

[0093] In the electric field enhancing element according to the above embodiment, it is preferable that the microstructure 30 is arranged periodically.

[0094] 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).

[0095] 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.

[0096] In the electric field enhancing element according to the above embodiment, the surface roughness of the silicon oxide layer 40 is preferably such that the maximum height Rz is 20 nm or less.

[0097] This configuration allows for a sufficiently high degree of smoothness on the upper surface 42. This makes it easier to homogenize the enhanced electric field formed on the upper surface 42. As a result, the reproducibility of detection is improved. Furthermore, even when target materials of various sizes are mixed together, the detection signal caused by the target materials can be uniformly amplified.

[0098] 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.

[0099] 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]

[0100] Next, specific embodiments of the present invention will be described. 6. Experimental Examples 6.1. Example 1 Figure 15 is an XZ cross-sectional view schematically showing the iteration unit of model M used in the simulation. Figure 16 is an XY cross-sectional view schematically showing model M used in the simulation.

[0101] In Model M, as shown in Figure 15, the substrate material was quartz glass (SiO2), and the silicon oxide layer material was SiO2.

[0102] Furthermore, the thickness B of the silicon oxide layer was set to 275 nm, the constituent material of the microstructure was Al, the diameter D of the microstructure was set to 260 nm, and the thickness H of the microstructure was set to 140 nm. In Model M, as shown in Figure 16, the arrangement of the microstructures was a square lattice, the shape of the microstructures was cylindrical, and the pitch P of the microstructures was set to 434 nm. In addition, an air layer was provided above the silicon oxide layer.

[0103] Then, light was incident on the substrate side of Model M shown in Figure 15, and the intensity distribution of the enhanced electric field was calculated. The wavelength of the incident light was set to 434 nm.

[0104] 6.2. Example 2 In Example 2, 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 silicon oxide layer was set to 349 nm, the diameter D of the microstructure was set to 277 nm, the thickness H of the microstructure was set to 139 nm, and the wavelength of the incident light was set to 450 nm, in the aforementioned Model M.

[0105] 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 silicon oxide layer was set to zero, i.e., no silicon oxide 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.

[0106] Figure 17 is a table comparing the main parameters in Examples 1 and 2 and Comparative Example 1.

[0107] 7. Results of the experimental example Simulations were performed to estimate the distribution of the enhanced electric field in each of the models described above in Examples 1 and 2 and Comparative Example 1. The FDTD (Finite Difference Time Domain) method was used for the simulations. Synopsys Rsoft was used as the simulation software.

[0108] Figures 18 to 20 show the simulation results for Examples 1 and 2 and Comparative Example 1, respectively. Figures 18 to 20 show the distribution of the normalized enhanced electric field in the XZ cross-section.

[0109] The shades in Figures 18-20 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 2The square root of ) is, that is, √(Ex 2 +Ez 2 This is reflected in the shading of Figures 18 to 20.

[0110] In Figures 18 and 19, the "air interface" refers to the interface between the silicon oxide layer and the air layer. In Figure 20, the "air interface" refers to the interface between the substrate and the air layer.

[0111] In Figures 18 and 19, the enhanced electric field is maximized slightly above the air interface (on the air layer side). The distance from the air interface to the maximum point S2 shown in Figures 18 and 19 is less than 100 nm in both cases. Furthermore, the enhanced electric field shown in Figures 18 and 19 reaches a position in the air layer that is more than 100 nm away from the air interface. On the other hand, in Figure 20, no enhanced electric field was observed at a distance from the microstructure.

[0112] These results confirm that it is possible to realize an electric field enhancement element in which the enhanced electric field has a maximum at position S2, which is separated from the silicon oxide layer.

[0113] Furthermore, as a separate experimental example from the above, three models were created in which the refractive index of the substrate was changed in the above model M, and the intensity distribution of the enhanced electric field was calculated in the same manner as above.

[0114] The first model lowers the refractive index of the substrate by 0.200 compared to the refractive index of the silicon oxide layer (1.467), resulting in a refractive index of 1.267.

[0115] The second model sets the refractive index of the substrate to be equal to the refractive index of the silicon oxide layer, which is 1.467.

[0116] The third model increases the refractive index of the substrate by 0.200 compared to the refractive index of the silicon oxide layer (1.467), resulting in a refractive index of 1.667.

[0117] Based on the calculation results of the enhanced electric field, the values ​​of the enhanced electric field at a position of 1 nm above the air interface were compared. As a result, when the second model was set as the baseline (100%), the enhanced electric field value of the first model was 86%, and the enhanced electric field value of the third model was 102%. Based on these results, it was found that if the difference between the refractive index of the substrate and the refractive index of the silicon oxide layer is 0.200 or less, it has little effect on the generation of the enhanced electric field. [Explanation of Symbols]

[0118] 10…Substrate, 20…Dielectric layer, 30…Microstructure, 40…Silicon oxide 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, D…Diameter, E…Enhanced electric field, Ea…First enhancement field, Eb…Second enhancement 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

Claims

1. circuit board and A plurality of conductive microstructures are provided on the substrate, Multiple microstructures and a silicon oxide layer covering the substrate, Equipped with, An electric field enhancing element characterized in that the enhanced electric field generated by the plurality of microstructures is maximized at a position opposite to the substrate from the microstructures in the direction perpendicular to the substrate, and at a distance from the plurality of microstructures.

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

3. 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 2, wherein the distance from the surface of the silicon oxide layer to the maximum point is 100 nm or less.

4. 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 2, wherein the distance from the surface of the silicon oxide layer to the maximum point is greater than 100 nm.

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

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

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

8. The electric field enhancing element according to claim 1, wherein the surface roughness of the silicon oxide layer has a maximum height of 20 nm or less.

9. An electric field enhancing element according to any one of claims 1 to 8, 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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