JP2015068663A - Optical element, analysis device, and electronic apparatus - Google Patents

Abstract

An optical element capable of sufficiently enhancing incident light and Raman scattered light even when the Raman shift is large is provided. An optical element according to the present invention includes a metal layer, a dielectric layer provided on the metal layer, a metal particle layer provided on the dielectric layer and arranged with metal particles, The metal particle layer has a metal particle row in which a plurality of the metal particles are arranged at a pitch P1 in the first direction, and the metal particle row is in the second direction intersecting the first direction, A plurality of the dielectric layers are arranged at a pitch P2 larger than the pitch P1, and the thickness d of the dielectric layer satisfies the relationship d2 <d <d1, and is linearly polarized light in the same direction as the first direction, and is incident on the wavelength λi. Light is irradiated. [Where d2 represents mdλi / 2nd (md = 1, nd represents the refractive index of the dielectric layer), and d1 represents the dielectric constant of the metal particle layer at the wavelength λi according to Maxwell-Garnett's. Of the dielectric layer satisfying the conditions of strengthening by secondary interference generated in the structure including the metal layer, the dielectric layer, and the metal particle layer of the optical element when given by the effective dielectric constant obtained by the equation The thickness satisfies d2 <d1. ] [Selection figure] None

Description

  The present invention relates to an optical element, an analyzer, and an electronic apparatus.

  Sensing techniques that detect minute amounts of substances with high sensitivity, high accuracy, speed, and simplicity are required in fields such as the medical and health fields, the environment, food, and public security. There are a wide variety of substances that are subject to sensing. For example, biologically related substances such as bacteria, viruses, proteins, nucleic acids, various antigens and antibodies, and various compounds including inorganic molecules, organic molecules, and polymers. It becomes a target of sensing. Conventionally, detection of trace substances has been performed through sampling, analysis, and analysis. However, since a dedicated device is required and skill of an inspection operator is required, on-site analysis is often difficult. Therefore, it takes a long time (several days or more) to obtain a test result. In the sensing technology, the demand for quick and simple is very strong, and the development of a sensor that can meet the demand is desired. For example, diagnosis of a patient who exhibits vomiting, diarrhea, or fever at an airport or the like is urgent in order to prevent the spread of infection. In addition, in the infectious disease test, treatment is different depending on whether it is a bacterium or a virus, and it is important to quickly identify the type of the bacterium or virus in order to cut off the infection route.

  In response to these demands, various types of sensors have been studied in recent years, including electrochemical techniques. However, surface plasmon resonance (because of the possibility of integration, low cost, and choice of measurement environment) Interest in sensors using SPR (Surface Plasma Resonance) is increasing. For example, there is known one that detects the presence or absence of substance adsorption, such as the presence or absence of antigen adsorption in an antigen-antibody reaction, using SPR generated on a metal thin film provided on the surface of a total reflection prism. In addition, a method of detecting the Raman scattering of a substance attached to a sensor site by using surface enhanced Raman scattering (SERS) and identifying the attached substance has been studied.

  As a structure of such a sensor, for example, in Non-Patent Document 1, in addition to the localized plasmon (LSP: Localized Surface Plasmon) indicated by the Gap type surface plasma polaron (GSPP) model, the XY direction (parallel to the substrate surface) is used. A structure for realizing a hybrid mode in which a propagating surface plasmon (PSP) is generated in the direction) has been proposed.

Non-Patent Document 2 shows an example in which the hybrid mode is used for SERS. SERS effect, E the electric field enhancement at the wavelength of the incident light _i, the degree of electric field enhancement at the wavelength of after Raman scattering and E _s, it is known to be proportional to E _i ² · E _s ^2. E _i and E _s may be enhanced at the same peak or at different peaks, and examples in which E _i and E _s are enhanced at different peaks using two peaks in the hybrid mode are described. Yes.

  Patent Document 1 discloses that an optical resonator is configured by sequentially including a first reflector that is a light scattering surface, a translucent body, and a second reflector having reflectivity. A device for Raman spectroscopy using an electric field enhanced by light absorption by resonance in a body is disclosed. This document describes that multiple interference occurs in the optical resonator, the electric field of the optical resonator is enhanced, and a surface enhanced Raman effect can be obtained. Patent Document 2 describes a resonator structure including a first reflector, a dielectric, and a second reflector in order.

JP 2008-014933 A JP 2009-115492 A

OPTICS LETTERS, Vol.34, No.3,2009,244-246 ACS NANO, Vol.4, No.5,2010,2804-2809

  However, in the case of a structure that realizes the hybrid mode, as described in Non-Patent Document 1, since the enhancement effect due to the resonance between the LSP and the PSP is used, the enhancement effect is obtained when the wavelength difference between the LSP and the PSP is large. Low. For this reason, it is difficult to design the entire wide band so as to provide high enhancement.

  In addition, the structure of metal particles and the like formed on the light scattering surface (sensor portion) of the device disclosed in Patent Document 1 described above is a structure in which metals are arranged at high density (see the same document). (See FIGS. 2 and 4). In the case of such a high-density structure (a structure in which the proportion of metal is large), a light-transmitting body of an optical resonator can be obtained by considering thin-film interference (see equation (1) in paragraph 0025 of the same document). The thickness and refractive index can be designed. The wavelength strengthened by the thin film interference of Patent Document 1 becomes a discrete wavelength. For this reason, it is difficult to adjust the positions of the reinforcing wavelengths in the prior art.

  Further, in the resonator structure of Patent Document 2, it is described that only one coupling mode appears when the localized surface plasmon resonance and the mode of the resonator are coupled. Therefore, if the difference in wave number between incident light and scattered light is large, it is difficult to design an optical element that provides high enhancement for both bands of incident light and scattered light due to thin film interference.

  The present invention has been made to solve at least a part of the above-described problems, and one of the objects according to some aspects thereof is to reduce incident light and Raman scattered light even when the Raman shift is large. An object of the present invention is to provide an optical element, an analysis apparatus, or an electronic apparatus that can be sufficiently enhanced.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

One aspect of the optical element according to the present invention includes a metal layer, a dielectric layer provided on the metal layer, and a metal particle layer provided on the dielectric layer and arranged with metal particles. The metal particle layer has a metal particle array in which a plurality of the metal particles are arranged at a pitch P1 in a first direction, and the metal particle array has the pitch in a second direction intersecting the first direction. A plurality of the dielectric layers are arranged at a pitch P2 larger than P1, and the thickness d of the dielectric layer satisfies the relationship d2 <d <d1, and is linearly polarized light in the same direction as the first direction, and is incident on the wavelength λ _i Light is irradiated.
[Wherein, d2 _{is, m d λ i / 2n d} (m d = 1, n d represents. A refractive index of the dielectric layer) represents, d1, the dielectric of the metal particle layer at the wavelength lambda _i When the ratio is given by the effective dielectric constant obtained by the Maxwell-Garnett equation, a condition that reinforces by secondary interference generated in the structure including the metal layer, the dielectric layer, and the metal particle layer of the optical element And the thickness of the dielectric layer satisfying d2 <d1. ]
According to such an optical element, the LSP is excited in the first direction and the PSP is excited in the second direction. Since the polarization direction of the incident light is the first direction, the hot spot density is higher than that of the hybrid mode (GSPP), and the enhancement of the entire element is strong. In addition, according to such an optical element, the position of the two peaks can be adjusted in the wavelength dependence of the enhancement profile or reflectance, so that even when measuring a sample exhibiting a large Raman shift, Both light and Raman scattered light can be sufficiently enhanced.

One aspect of the optical element according to the present invention includes a metal layer, a dielectric layer provided on the metal layer, and a metal particle layer provided on the dielectric layer and arranged with metal particles. The metal particle layer has a metal particle array in which a plurality of the metal particles are arranged at a pitch P1 in a first direction, and the metal particle array has the pitch in a second direction intersecting the first direction. A plurality of the dielectric layers are arranged at a pitch P2 larger than P1, and the thickness d of the dielectric layer satisfies the relationship d2 <d <d1, and is linearly polarized light in the same direction as the first direction, and is incident on the wavelength λ _i An optical element irradiated with light.
[Wherein, d2 _{is, m d λ s / 2n d} (m d = 1, λ s is the Raman scattering wavelength when irradiated with incident light of wavelength lambda _i, the n _d represents the refractive index of the dielectric layer ), And d1 represents the metal layer and the dielectric layer of the optical element when the dielectric constant of the metal particle layer at the wavelength λ _i is given by the effective dielectric constant obtained by the Maxwell-Garnett equation. And a thickness of the dielectric layer that satisfies a strengthening condition by secondary interference generated in the structure including the metal particle layer, and satisfies d2 <d1. ]
According to such an optical element, the LSP is excited in the first direction and the PSP is excited in the second direction. Since the polarization direction of the incident light is the first direction, the hot spot density is higher than that of the hybrid mode (GSPP), and the enhancement of the entire element is strong. In addition, according to such an optical element, the position of the two peaks can be adjusted in the wavelength dependence of the enhancement profile or reflectance, so that even when measuring a sample exhibiting a large Raman shift, Both light and Raman scattered light can be sufficiently enhanced.

In the optical element according to the present invention, the Raman scattering wavelength λ _s and the incident light wavelength λ _i may satisfy a relationship of 2500 cm ⁻¹ ≦ (1 / λ _i −1 / λ _s ) <3500 cm ^−1. .

In the optical element according to the present invention, the thickness d of the dielectric layer may be 60 nm or more.
According to such an optical element, when measuring a sample exhibiting a large Raman shift of 2500 cm ⁻¹ or more, such as a CH ₂ group or a CH ₃ group, using incident light having a wavelength λ _i of 400 nm or more, the incident light is incident. Both light and Raman scattered light can be sufficiently enhanced.

In the optical element according to the present invention, the thickness d of the dielectric layer may be 145 nm or more.
According to such an optical element, when measuring a sample exhibiting a large Raman shift of 2500 cm ⁻¹ or more, such as a CH ₂ group or a CH ₃ group, using incident light having a wavelength λ _i of 600 nm or more, the incident light is incident. Both light and Raman scattered light can be sufficiently enhanced.

In the optical element according to the present invention, the material of the dielectric layer may be SiO ₂ .
According to such an optical element, when measuring a sample exhibiting a large Raman shift using incident light having a wavelength λ _i of 400 nm or more, both incident light and Raman scattered light can be sufficiently enhanced. .

In the optical element according to the present invention, the pitch P1 may satisfy 6 nm <P1 <535 nm.
According to such an optical element, it is possible to sufficiently enhance both incident light and Raman scattered light when measuring a sample exhibiting a large Raman shift using incident light having a wavelength λ _i of less than 1100 nm. .

In the optical element according to the present invention, the material of the metal layer may be Au, and the pitch P2 may satisfy 480 nm <P2 <1840 nm.
According to such an optical element, when a sample having a structure with a Raman shift of 2500 cm ⁻¹ or more and less than 3500 cm ⁻¹ is measured using incident light having a wavelength λ _i of 600 nm or more and less than 1100 nm, incident light and Raman are measured. Both of the scattered light can be sufficiently enhanced.

In the optical element according to the present invention, the material of the metal particles may be Au or Ag.
Since such an optical element exhibits stronger LSP resonance, the enhancement of the entire element is strong.

In the optical element according to the present invention, the wavelength λ _{i of the} incident light may be not less than 630 nm and not more than 1070 nm.
According to such an optical element, when measuring a sample exhibiting a large Raman shift using incident light having a wavelength λ _i of 630 nm or more and 1070 nm or less, both incident light and Raman scattered light are sufficiently enhanced. Can do.

One aspect of the analysis apparatus according to the present invention includes the above-described optical element, a light source that irradiates the optical element with the incident light, and a detector that detects light emitted from the optical element.
According to such an analyzer, an optical element having a high hot spot density and a strong enhancement of the entire element is used, and even a sample exhibiting a large Raman shift sufficiently absorbs both incident light and Raman scattered light. Therefore, it is possible to qualitatively analyze and / or quantitatively analyze various substances with high sensitivity.

One aspect of the electronic device according to the present invention includes the above-described analyzer, a calculation unit that calculates health and medical information based on detection information from the detector, a storage unit that stores the health and medical information, and the health A display unit for displaying medical information.
According to such an electronic device, an optical element having a high hot spot density and a high enhancement factor of the entire element is used, and even a sample exhibiting a large Raman shift sufficiently absorbs both incident light and Raman scattered light. Since it can be enhanced, detection of trace substances can be easily performed, and highly accurate health care information can be provided.

The perspective view which shows the optical element of embodiment typically. The schematic diagram which looked at the optical element of embodiment planarly from the thickness direction of the metal layer. The schematic diagram of the cross section perpendicular | vertical to the 1st direction of the optical element of embodiment. The schematic diagram of the cross section perpendicular | vertical to the 2nd direction of the optical element of embodiment. The schematic diagram which looked at the optical element of embodiment planarly from the thickness direction of the metal layer. A graph of dispersion relation showing dispersion curves of incident light and gold. The graph which shows the dielectric constant and wavelength of Ag. The graph which shows the dispersion | distribution relationship of a metal dispersion curve, localized plasmon, and incident light. Schematic of the analyzer of the embodiment. Schematic of the electronic device of the embodiment. The figure which shows the model which concerns on an experiment example typically. The reflection spectrum of the model which concerns on an experiment example. The intensity distribution of the electric field Ex on the XZ plane of the model according to the experimental example. The reflection spectrum of the model which concerns on an experiment example. The reflection spectrum of the model which concerns on an experiment example. The graph of the dispersion | distribution relationship which concerns on an experiment example.

  Several embodiments of the present invention will be described below. Embodiment described below demonstrates an example of this invention. The present invention is not limited to the following embodiments, and includes various modified embodiments that are implemented within a range that does not change the gist of the present invention. Note that not all of the configurations described below are essential configurations of the present invention.

1. Optical Element FIG. 1 is a perspective view schematically showing an optical element 100 of the present embodiment. FIG. 2 is a schematic view of the optical element 100 according to the present embodiment viewed in plan (viewed from the thickness direction of the dielectric layer). 3 and 4 are schematic views of a cross section of the optical element 100 of the present embodiment. FIG. 5 is a schematic view of the optical element 100 of this embodiment as viewed from the thickness direction of the dielectric layer.
The optical element 100 according to the present embodiment includes a metal layer 10, a dielectric layer 20 provided on the metal layer 10, and a metal particle layer 30 provided on the dielectric layer 20.

1.1. Metal Layer The metal layer 10 is not particularly limited as long as it provides a metal surface that does not transmit light. For example, the metal layer 10 may have a plate shape or a film, layer, or film shape. Also good. The metal layer 10 may be provided on the substrate 1, for example. The substrate 1 in this case is not particularly limited, but a substrate that does not easily affect the propagation plasmon excited by the metal layer 10 is preferable. Examples of the substrate 1 include a glass substrate, a silicon substrate, and a resin substrate. The shape of the surface on which the metal layer 10 of the substrate 1 is provided is not particularly limited. When a regular structure is formed on the surface of the metal layer 10, it may have a surface corresponding to the regular structure, and when the surface of the metal layer 10 is a plane, it may be a plane. In the example of FIGS. 1 to 5, the metal layer 10 is provided on the surface (plane) of the substrate 1.

  Here, the expression “plane” is used, but this expression does not indicate a mathematically exact plane whose surface is flat (smooth) without slight unevenness. For example, the surface may have unevenness due to constituent atoms and unevenness due to secondary structure of the constituent substances (crystals, grain clumps, grain boundaries, etc.). If it sees, it may not be an exact plane. However, even in such a case, when viewed from a more macroscopic viewpoint, these irregularities become inconspicuous and are observed to the extent that the surface may be referred to as a plane. Therefore, in this specification, if it can be recognized as a plane when viewed from such a macroscopic viewpoint, this is referred to as a plane.

  In the present embodiment, the thickness direction of the metal layer 10 coincides with the thickness direction of the dielectric layer 20 described later. In this specification, the thickness direction of the metal layer 10 or the thickness direction of the dielectric layer 20 is sometimes referred to as a thickness direction, a height direction, or the like when describing the metal particle layer 30 or the metal particles 40 described later. is there. For example, when the metal layer 10 is provided on the surface of the substrate 1, the normal direction of the surface of the substrate 1 may be referred to as a thickness direction or a height direction.

  The metal layer 10 can be formed, for example, by a technique such as vapor deposition, sputtering, casting, or machining. When the metal layer 10 is provided on the substrate 1, it may be provided on the entire surface of the substrate 1 or may be provided on a part of the surface of the substrate 1. The thickness of the metal layer 10 is not particularly limited as long as propagating plasmons can be excited in the metal layer 10. For example, the thickness is 10 nm to 1 mm, preferably 20 nm to 100 μm, more preferably 30 nm to 1 μm. it can.

The metal layer 10 is a metal having an electric field in which an electric field given by incident light and a polarization induced by the electric field vibrate in opposite phases, that is, when a specific electric field is given, The real part has a negative value (has a negative dielectric constant), and the imaginary part is made of a metal that can have a dielectric constant smaller than the absolute value of the dielectric constant of the real part. Examples of metals that can have such a dielectric constant in the visible light region include gold, silver, aluminum, copper, platinum, and alloys thereof. Of these, the material of the metal layer 10 is more preferably gold, silver, copper, or aluminum. Further, the surface (end surface in the thickness direction) of the metal layer 10 may or may not be a specific crystal plane.

  The metal layer 10 has a function of generating propagating plasmons in the optical element 100 of the present embodiment. Propagation-type plasmons are generated near the surface of the metal layer 10 (end surface in the thickness direction) when light is incident on the metal layer 10 under the conditions described later. Further, in this specification, the quantum of vibration in which the vibration of electric charges near the surface of the metal layer 10 and the electromagnetic wave are combined is referred to as a surface plasmon polariton (SPP). Propagation-type plasmons generated in the metal layer 10 can interact (hybridize) with localized plasmons generated in the metal particles 40 described later under certain conditions.

1.2. Dielectric Layer The optical element 100 of the present embodiment has a dielectric layer 20 for separating the metal layer 10 and the metal particle layer 30 (metal particles 40). The dielectric layer 20 is provided on the metal layer 10 as shown in FIGS. Thereby, the metal layer 10 and the metal particle 40 of the metal particle layer 30 can be separated. The dielectric layer 20 can have the shape of a film, layer or film.

  In this specification, for example, the expression “the member B is provided on the member A” means that the member B is provided in contact with the member A and other members or spaces are provided on the member A. And the case where the member B is disposed.

  The dielectric layer 20 can be formed by, for example, techniques such as vapor deposition, sputtering, CVD, and various coatings. The dielectric layer 20 may be provided on the entire surface of the metal layer 10 or may be provided on a part of the surface of the metal layer 10.

The dielectric layer 20 only needs to have a positive dielectric constant, and can be formed of, for example, SiO ₂ , Al ₂ O ₃ , TiO ₂ , polymer, ITO (Indium Tin Oxide), or the like. The dielectric layer 20 may be composed of a plurality of layers made of different materials. Of these, the material of the dielectric layer 20 is more preferably SiO ₂ . In this way, when measuring a sample exhibiting a large Raman shift using incident light having a wavelength λ _i of 400 nm or more, both incident light and Raman scattered light can be sufficiently enhanced.

The dielectric layer 20 has a refractive index n _d. When the dielectric layer 20 is configured to include a case and a plurality of materials consisting of multiple layers, the effective refractive index of the entire dielectric layer 20 and the refractive index n _d.

The thickness d of the dielectric layer 20 is designed in consideration of the wavelength λ _{i of} incident light irradiated on the optical element 100, the wavelength λ _s of Raman scattered light when light having the wavelength λ _i is incident, and the like. The relationship d <d1 is satisfied.

Here, d2 is an expression (1).
d2 = m _d λ / 2n _d (1)
(M _d = 1, λ represents the wavelength λ _{i of the} incident light or the wavelength λ _s of the Raman scattered light, and n _d represents the refractive index of the dielectric layer 20).
Further, d1 represents the metal layer 10 of the optical element 100, the dielectric constant when the dielectric constant ε _m of the metal particle layer 30 at the wavelength λ _i is given by the effective dielectric constant ε (ω) obtained by the Maxwell-Garnett equation. This is the thickness of the dielectric layer 20 that satisfies the conditions for strengthening by secondary interference generated in the structure including the body layer 20 and the metal particle layer 30. In addition, d1 and d2 are the expressions (2)
d2 <d1 (2)
Satisfy the relationship.

  In the optical element 100 of the present embodiment, both the incident light and the Raman scattered light are measured even when a sample exhibiting a large Raman shift is measured when the thickness d of the dielectric layer 20 satisfies such a relationship. Can be sufficiently enhanced. Details of the mechanism will be described later.

1.3. Metal Particle Layer As shown in FIGS. 1 to 5, the metal particle layer 30 has a metal particle row 41 in which a plurality of metal particles 40 are arranged at a pitch P1 in the first direction, and the metal particle row 41 is In the second direction intersecting the first direction, a plurality of structures are arranged at a pitch P2 larger than the pitch P1. As shown in FIGS. 3 and 4, the metal particle layer 30 is a layer containing the metal particles 40, but other substances such as dielectrics and metals may be disposed in portions other than the metal particles 40, Preferably gas is arranged. In this specification, the metal particle layer 30 refers to a region between the upper surface of the dielectric layer 20 and the surface in contact with the tip of the metal particle 40 on the side away from the dielectric layer 20. For example, the upper surface of the metal particle layer 30 is an imaginary surface when the metal particle layer 30 includes the metal particles 40 and a gas, and the metal particle layer 30 has side surfaces of the metal particles 40. Included gas shall also be included.

(Metal particles)
The metal particles 40 are provided away from the metal layer 10 in the thickness direction due to the presence of the dielectric layer 20. The metal particles 40 are disposed on the metal layer 10 via the dielectric layer 20. In the example of FIGS. 1 to 5 of the present embodiment, the dielectric layer 20 is provided on the metal layer 10, and the metal particles 40 are formed thereon, whereby the metal layer 10 and the metal particles 40 are thick. The metal particle layer 30 is formed so as to be spaced apart in the vertical direction.

  The shape of the metal particle 40 is not particularly limited. For example, the shape of the metal particles 40 may be a circle, an ellipse, a polygon, an indeterminate shape or a combination of them when projected in the thickness direction of the metal layer 10 or the dielectric layer 20 (in plan view from the thickness direction). Even when projected in a direction orthogonal to the thickness direction, the shape may be a circle, an ellipse, a polygon, an indeterminate shape, or a combination thereof. 1 to 5, the metal particles 40 are all drawn in a columnar shape having a central axis in the thickness direction of the dielectric layer 20, but the shape of the metal particles 40 is not limited to this.

  The size T in the height direction of the metal particles 40 refers to the length of a section in which the metal particles 40 can be cut by a plane perpendicular to the height direction, and is 1 nm or more and 300 nm or less. The size in the first direction perpendicular to the height direction of the metal particles 40 refers to the length of a section in which the metal particles 40 can be cut by a plane perpendicular to the first direction, and is 5 nm to 300 nm. For example, when the shape of the metal particles 40 is a cylinder having the height direction as a central axis, the size of the metal particles 40 in the height direction (the height of the cylinder) is 1 nm or more and 300 nm or less, preferably 2 nm or more. It is 100 nm or less, More preferably, it is 3 nm or more and 50 nm or less, More preferably, it is 4 nm or more and 40 nm or less. When the shape of the metal particle 40 is a cylinder having the height direction as the central axis, the size of the metal particle 40 in the first direction (diameter of the bottom surface of the cylinder) is 10 nm to 300 nm, preferably 20 nm to 200 nm. Hereinafter, it is more preferably 25 nm or more and 180 nm or less.

The shape and material of the metal particles 40 are arbitrary as long as localized plasmons can be generated by irradiation with incident light. Examples of materials that can generate localized plasmons by light in the vicinity of visible light include gold, silver, aluminum, copper, platinum, and alloys thereof. Among these, the material of the metal particles 40 is more preferably Au or Ag. In this way, stronger LSP resonance can be obtained and the enhancement of the entire device can be increased.

  The metal particles 40 can be formed by, for example, a patterning method after forming a thin film by sputtering, vapor deposition, or the like, a microcontact printing method, a nanoimprinting method, or the like. The metal particles 40 can be formed by a colloidal chemical technique, and may be arranged at a position separated from the metal layer 10 by an appropriate technique.

  The metal particles 40 have a function of generating localized plasmons in the optical element 100 of the present embodiment. By irradiating the metal particles 40 with incident light under the conditions described later, localized plasmons can be generated around the metal particles 40. Localized plasmons generated in the metal particles 40 can interact (hybridize) with propagation plasmons generated in the metal layer 10 under certain conditions.

(Arrangement of metal particles)
As shown in FIGS. 1 to 5, a plurality of metal particles 40 form a metal particle row 41. The metal particles 40 are arranged side by side in a first direction orthogonal to the thickness direction of the metal layer 10 in the metal particle array 41. In other words, the metal particle row 41 has a structure in which a plurality of metal particles 40 are arranged in a first direction orthogonal to the height direction. The first direction in which the metal particles 40 are arranged does not have to coincide with the longitudinal direction when the metal particles 40 have a longitudinal shape (an anisotropic shape). The number of the metal particles 40 arranged in one metal particle row 41 may be plural, and is preferably 10 or more.

  Here, the distance between the centers of gravity of the metal particles 40 in the first direction in the metal particle array 41 is defined as a pitch P1 (see FIGS. 2 to 5). The distance between the two metal particles 40 in the metal particle array 41 is a length obtained by subtracting the diameter of the cylinder from the pitch P1 when the metal particle 40 is a cylinder having the thickness direction of the metal layer 10 as a central axis. Equal to When the distance between the particles is small, the intensity of the localized plasmon acting between the particles tends to increase. The interparticle distance is 1 nm or more and 530 nm or less, preferably 5 nm or more and 200 nm or less, more preferably 5 nm or more and 150 nm or less.

  The pitch P1 of the metal particles 40 in the first direction in the metal particle row 41 is 6 nm or more and 535 nm or less, preferably 10 nm or more and 400 nm or less, more preferably 20 nm or more and 350 nm or less.

When the pitch P1 of the metal particles 40 in the first direction in the metal particle array 41 is 6 nm or more and 535 nm or less, when measuring a sample exhibiting a large Raman shift using incident light having a wavelength λ _i of less than 1100 nm. Both incident light and Raman scattered light can be sufficiently enhanced.

When the pitch P1 of the metal particles 40 in the first direction in the metal particle array 41 is 20 nm or more and 350 nm or less, a sample exhibiting a large Raman shift is measured using incident light having a wavelength λ _i of 400 nm or more and less than 700 nm. In this case, both incident light and Raman scattered light can be sufficiently enhanced.

  The metal particle array 41 is composed of a plurality of metal particles 40 arranged at a pitch P1 in the first direction. The distribution / strength of localized plasmons generated in the metal particles 40 depends on the arrangement of the metal particles 40. Also depends. Therefore, the localized plasmon that interacts with the propagation plasmon generated in the metal layer 10 takes into account the arrangement of the metal particles 40 in the metal particle array 41 as well as the localized plasmon generated in the single metal particle 40. It is a localized plasmon.

  As shown in FIGS. 1-5, the metal particle row | line | column 41 is arrange | positioned along with the pitch P2 in the 2nd direction which cross | intersects the thickness direction of the metal layer 10, and a 1st direction. The number of the metal particle rows 41 may be a plurality, preferably 10 rows or more.

  Here, the distance between the centroids in the second direction of the adjacent metal particle rows 41 is defined as the pitch P2. When the metal particle row 41 is composed of a plurality of rows, the pitch P2 is the position of the center of gravity in the second direction of the plurality of rows and the center of gravity in the second direction of the plurality of rows of the adjacent metal particle row 41. And the distance between.

  The pitch P <b> 2 between the metal particle rows 41 is larger than the pitch P <b> 1 between the metal particles 40. That is, there is a relationship of P1 <P2 between the pitch P1 and the pitch P2. By having such a relationship, the arrangement of the metal particles 40 in the optical element 100 has anisotropy when viewed from the thickness direction of the dielectric layer 20.

  The pitch P2 between the metal particle rows 41 can be set according to the conditions described in “1.4. Propagation type plasmon and localized type plasmon” below, but is, for example, 10 nm or more and 10 μm or less, preferably 100 nm or more and 2 μm or less. More preferably, they are 300 nm or more and 1900 nm or less, More preferably, they are 400 nm or more and 1850 nm or less, Especially preferably, they are 480 nm or more and 1840 nm or less.

When the pitch P2 between the metal particle rows 41 is 480 nm or more and 1840 nm or less, a sample having a structure with a Raman shift of 2500 cm ⁻¹ or more and less than 3500 cm ⁻¹ using incident light having a wavelength λ _i of 600 nm or more and less than 1100 nm. In measurement, both incident light and Raman scattered light can be sufficiently enhanced.

  An angle formed by a line extending in the first direction of the metal particle row 41 and a line connecting two metal particles 40 belonging to the adjacent metal particle row 41 and connecting the two metal particles 40 closest to each other. Is not particularly limited and may or may not be a right angle. For example, as shown in FIG. 2, the angle between the two may be a right angle, or as shown in FIG. 5, the angle between the two may not be a right angle. That is, when the arrangement of the metal particles 40 viewed from the thickness direction is regarded as a two-dimensional lattice with the position of the metal particles 40 as a lattice point, the irreducible basic unit lattice is parallel even if it is a rectangular shape. It may be a quadrilateral shape. In addition, an angle formed by a line extending in the first direction of the metal particle row 41 and a line connecting the two metal particles 40 belonging to the adjacent metal particle row 41 and closest to each other. Is not a right angle, the distance between the two metal particles 40 belonging to the adjacent metal particle rows 41 and closest to each other may be the pitch P2.

1.4. Propagation-type plasmon and localized-type plasmon First, the propagation-type plasmon will be described. FIG. 6 is a graph of dispersion relation showing dispersion curves of incident light and gold. Usually, even if light is incident on the metal layer 10 at an incident angle (irradiation angle θ) of 0 to 90 degrees, no propagation plasmon is generated. For example, when the metal layer 10 is made of Au, as shown in FIG. 6, the dispersion curve of the light line (LightLine) and the SPP of Au has no intersection. Even if the refractive index of the medium through which the light passes changes, the Au SPP also changes according to the refractive index of the surroundings, so that there is no intersection. In order to create a propagation type plasmon by having an intersection, a metal layer is provided on the prism as in the Kretschmann arrangement, and the wave number of the light line is increased by a diffraction grating. There are ways to increase it. FIG. 6 is a graph showing a so-called dispersion relationship (vertical axis is angular frequency [ω (eV)] and horizontal axis is wave vector [k (eV / c)]).

  Further, the angular frequency ω (eV) on the vertical axis of the graph of FIG. 6 has a relationship of wavelength λ (nm) = 1240 / ω (eV) and can be converted into a wavelength. Further, the wave vector k (eV / c) on the horizontal axis of the graph has a relationship of k (eV / c) = 2π · 2 / [wavelength λ (nm) / 100]. Therefore, for example, when the wavelength λ = 600 nm, k = 2.09 (eV / c). The irradiation angle is an incident angle of incident light, and is an inclination angle from the thickness direction of the metal layer 10 or the dielectric layer 20 or the height direction of the metal particles 40.

FIG. 6 shows the dispersion curve of the SPP of Au. In general, the angular frequency of incident light incident on the metal layer 10 is ω _i , the speed of light in vacuum is c, and the metal constituting the metal layer 10 is shown in FIG. When the dielectric constant is ε ₁ (ω) and the peripheral dielectric constant is ε ₂ , the dispersion curve of the SPP of the metal is expressed by the equation (3).
K _SPP = ω _i / c [ε ₂ · ε ₁ (ω _i ) / (ε ₂ + ε ₁ (ω _i ))] ^1/2 (3)
Given in.

On the other hand, the angle of incidence of incident light, which is the inclination angle from the thickness direction of the metal layer 10 or the dielectric layer 20 or the height direction of the metal particles 40, is θ, and passes through a virtual diffraction grating having an interval Q The wave number K of the measured light is given by equation (4)
K = n ₂ · (ω _i / c) · sin θ + m · 2π / Q (m = ± 1, ± 2,...) (4)
This relationship appears as a straight line instead of a curve on the dispersion relationship graph.

Note that n ₂ is the peripheral refractive index, and if the extinction coefficient is κ, the real part ε ₂ ′ and the imaginary part ε ₂ ″ of the relative permittivity ε _{2 at} the light frequency are ε ₂ ′ = If n ₂ ² −κ ₂ ² , ε ₂ ″ = 2n ₂ κ ₂ and the surrounding material is transparent, it is κ _{2 to} 0, so ε ₂ is a real number and ε ₂ = n ₂ ² , N ₂ = ε ₂ ^1/2 . m represents the order of the diffracted light.

In the graph of dispersion relation, when the dispersion curve of the metal SPP (the above formula (3)) and the straight line of diffracted light (the above formula (4)) have an intersection, the propagation plasmon is excited. That is, when the relationship of K _SPP = K is established, the propagation plasmon is excited in the metal layer 10.

Therefore, from the above equations (3) and (4), the following equation (5) is obtained:
(Ω _i / c) · {ε ₂ · ε ₁ (ω _i ) / (ε ₂ + ε ₁ (ω _i ))} ^1/2 = ε ₂ ^1/2 · (ω _i / c) · sin θ + 2mπ / Q ( m = ± 1, ± 2,) (5)
It is understood that the propagation type plasmon is excited in the metal layer 10 when the relationship of the formula (5) is satisfied. In this case, in the example of the Au SPP in FIG. 6, the inclination and / or intercept of the write line can be changed by changing θ and m, and the write line is compared with the dispersion curve of the Au SPP. Can be crossed.

Next, localized plasmons will be described.
The condition for generating localized plasmons in the metal particles 40 depends on the real part of the dielectric constant:
Real [ε ₁ (ω)] = − 2ε ₂ (6)
Given in. If the peripheral refractive index n ₂ is 1, ε ₂ = n ₂ ² −κ ₂ ² = 1, so that Real [ε ₁ (ω)] = − 2.

FIG. 7 is a graph showing the relationship between the dielectric constant of Ag and the wavelength. For example, the dielectric constant of Ag is as shown in FIG. 7, and localized plasmons are excited at a wavelength of about 400 nm or more. However, when a plurality of Ag particles approach in the nano order, or Ag particles and metal When the layer 10 (Au film or the like) is disposed separated by the dielectric layer 20 (SiO ₂ or the like), the excitation peak wavelength of the localized plasmon is red-shifted (to the longer wavelength side) due to the influence of the gap. shift. Although this shift amount depends on dimensions such as Ag diameter, Ag thickness, Ag particle spacing, and dielectric layer thickness, it shows a wavelength characteristic in which the localized plasmon peaks at, for example, 500 nm to 900 nm.

  Unlike the propagation plasmon, the localized plasmon is a plasmon that has no velocity and does not move. When plotted on a graph of the dispersion relationship, the slope is zero, that is, ω / k = 0.

  FIG. 8 is a graph showing an example of a dispersion relationship between a metal dispersion curve, localized plasmons, and incident light. The optical element 100 of the present embodiment obtains an extremely large increase in electric field by electromagnetically coupling propagating plasmons and localized plasmons (Electromagnetic Coupling). That is, the optical element 100 according to the present embodiment does not set the intersection of the straight line of the diffracted light and the dispersion curve of the metal SPP as an arbitrary point in the graph of the dispersion relationship, but the metal particle 40 (metal particle array 41). One of the features is that the two are crossed in the vicinity of a point giving the maximum or maximum enhancement in the localized plasmon generated in () (see FIG. 8).

  In other words, in the optical element 100 of the present embodiment, in the graph of the dispersion relation, the maximum or maximum enhancement is given in the dispersion curve of the metal SPP and the localized plasmon generated in the metal particle 40 (metal particle array 41). It is designed so that the straight line of the diffracted light passes through the vicinity of the intersection with the angular frequency of the incident light (a line parallel to the horizontal axis attached to LSP on the dispersion relation graph in FIG. 8).

  Here, the vicinity of the intersection is within a wavelength range having a length of about ± 10% of the wavelength of the incident light when converted into a wavelength, or ± P1 of the wavelength of the incident light (of the metal particles 40). It is within a wavelength range of a length of about the pitch P1) in the metal particle array 41.

In the above formulas (3), (4) and (5), the angular frequency of incident light incident on the metal layer 10 is ω _i , and the conditions for exciting the propagation plasmon are shown. In order to generate a hybrid (interaction) between a type plasmon and a propagation type plasmon, in the optical element 100 of this embodiment, ω _i in the above formulas (3), (4), and (5) is a metal In the localized plasmon generated in the particle 40 (metal particle array 41), the angular frequency of the incident light that gives the maximum or maximum enhancement is the angular frequency in the vicinity thereof.

  Therefore, when the angular frequency of the localized plasmon excited by the metal particle array 41 is ω, if the above formula (5) is satisfied, a hybrid of the localized plasmon and the propagating plasmon may be generated. it can.

Therefore, the angular frequency of the localized plasmon generated in the metal particle array 41 in which the metal particles 40 are arranged at the pitch P1 is ω, and in the graph of the dispersion relationship, in the vicinity of the position of ω in the dispersion curve of the metal SPP, If a straight line of diffracted light (order m _diff ) diffracted by being incident on a virtual diffraction grating with an irradiation angle θ at an interval Q passes through (if Expression (5) is satisfied), the localized plasmon And a propagation type plasmon can be produced, and an extremely large enhancement can be obtained. In other words, in the graph of the dispersion relation shown in FIG. 8, by changing the light line inclination and / or intercept and changing the light line so as to pass near the intersection of the SPP and the LSP, A hybrid of plasmons and propagating plasmons can be generated, and an extremely large enhancement can be obtained.

The pitch P2 between the metal particle rows 41 is set as follows. When normal incidence (incident angle θ = 0) and primary diffraction light (m = 1) are used, Equation (5) can be satisfied if the pitch P2 is the interval Q. However, the interval Q that can satisfy Equation (5) has a width depending on the incident angle θ and the order m of the diffracted light. In this case, the incident angle θ is preferably an inclination angle from the thickness direction to the second direction, but may be an inclination angle to the direction including the component in the first direction.

Therefore, in consideration of being in the vicinity of the intersection point (the width of ± P1), the range of the pitch P2 in which the hybrid of the localized plasmon and the propagation plasmon can be generated is expressed by the following equation (7):
Q−P1 ≦ P2 ≦ Q + P1 (7)
It becomes.

  On the other hand, the pitch P2 is the pitch in the second direction between the metal particle rows 41, but the pitch between the two metal particles 40 belonging to the adjacent metal particle rows 41 depends on how the two metal particles 40 are selected. Can be tilted with respect to the second direction. That is, the two metal particles 40 belonging to the adjacent metal particle rows 41 can be selected so as to have a longer interval than the pitch P2. In FIG. 2, an auxiliary line for explaining this is drawn, and two metal particles 40 separated by a distance longer than the pitch P2 along a direction inclined with respect to the second direction are adjacent to each other. The particle row 41 can be selected. As already described, since the adjacent metal particle rows 41 are the same metal particle row 41, the arrangement of the metal particles 40 viewed from the thickness direction is a two-dimensional lattice with the position of the metal particles 40 as a lattice point. Can be considered. As a result, this two-dimensional grating has an interval (diffraction grating) longer than the pitch P2.

  Therefore, the matrix of the metal particles 40 arranged at the pitch P1 and the pitch P2 can be expected to be diffracted light by the diffraction grating having an interval larger than the pitch P2. Therefore, the inequality on the left side of Equation (7) can be P1 <P2. In other words, in the equation (7), even when the pitch P2 is smaller than Q-P1, there can be a diffraction grating having an interval Q that can satisfy the equation (5). Hybrids with plasmons can be generated. Therefore, the pitch P2 may be a value smaller than Q−P1, and it is sufficient if the relationship of P1 <P2 is satisfied.

From the above, the pitch P2 between the metal particle rows 41 in the optical element 100 of the present embodiment is expressed by the following formula (8).
P1 <P2 ≦ Q + P1 (8)
If this relationship is satisfied, a good hybrid of localized plasmons and propagating plasmons can be generated.

1.4. Incident Light The wavelength λ _{i of} incident light incident on the optical element 100 is not limited as long as it produces localized plasmons and can satisfy the relationship of the above-described formula (5). It can be electromagnetic waves including light and infrared light. In the present embodiment, the incident light is linearly polarized light in the same direction as the first direction and is light having a wavelength λ _i . In the present embodiment, the incident light is linearly polarized light whose electric field is in the same direction as the first direction of the optical element 100 (the direction in which the metal particle row 41 extends). In this way, the optical element 100 can obtain a very large light enhancement.

The wavelength λ _{i of the} incident light can be, for example, 400 nm or more and 1070 nm or less, preferably 500 nm or more and 1070 nm or less, more preferably 630 nm or more and 1070 nm or less. In this way, when measuring a sample exhibiting a large Raman shift such as a methyl group, the enhancement of both incident light and Raman scattered light can be further increased.

1.5. Increase Strength The relationship between the magnitude of the electric field Ex in the X direction (first direction) and the electric field Ez in the Z direction (thickness direction), that is, the vector changes depending on the mesh position of the FDTD calculation. When linearly polarized light in the X direction is used as excitation light, the electric field Ey in the Y direction (second direction) can be almost ignored. Therefore, the enhancement can be grasped using the square root of the square sum of Ex and Ez, that is, SQRT (Ex ² + Ez ² ). In this way, they can be compared with each other as a scalar of the local electric field.

  In the experimental examples and drawings of the present specification, the first direction may be referred to as the X direction, and the direction may be represented by the notation “X”. Further, the second direction may be referred to as the Y direction, and the direction may be expressed by the notation “Y”. Further, the thickness direction of the element may be referred to as a Z direction, and the direction may be expressed by the notation “Z”.

The SERS (Surface Enhancement Raman Scattering) effect is SERS EF (Enhancement Factor), where the electric field enhancement at the wavelength of the excitation light is Ei, the electric field enhancement at the wavelength after Raman scattering is Es, and the hot spot density (HSD) is used. The following formula (a)
SERS EF = Ei ² · Es ² · HSD (a)
It is represented by

When considering the enhancement of the optical element 100, it is necessary to consider so-called hot spot density (HSD). That is, the light enhancement intensity by the optical element 100 depends on the number of metal particle layers 30 per unit area of the optical element 100. In the optical element 100 of the present embodiment, the pitch P1 and the pitch P2 are arranged so that the relationship of the above formulas (1) and (2) is satisfied. Therefore, considering HSD, the SERS enhancement of the optical element 100 is proportional to (Ei ² + Es ² ) / (P1 · P2). In the experimental examples described later, for comparison in the same HSD, the above formula (a) is defined as SERS EF = Ei ² · Es ² for simplicity.

1.6. Design of Optical Element When the optical element 100 of this embodiment is used for SERS, the wavelength λ _{i of the} incident light, the thickness d of the dielectric layer 20, the structure of the metal particle layer 30 is taken into consideration, and the measurement target The structure is optimized to obtain a high enhancement against the Raman shift of the sample.

  The wavelength or wave number of Raman scattered light generally covers a wide band. In such a wide band, it is difficult to cover a region with high enhancement at one peak in the enhancement profile. However, if the wavelength characteristic of enhancement or reflectance is designed to have two or more peaks, one peak is used to enhance the incident light and the other peak is used to enhance the Raman scattered light. Analysis is possible. Furthermore, if one peak is used to enhance the incident light and the Raman scattered light having a small amount of Raman shift, and the other peak is used to enhance the Raman scattered light having a large amount of Raman shift, a more sensitive analysis can be performed.

The thin-film interference model (see equation (1)), at the interface of the dielectric layer 20 and the metal particle layer 30, a condition where the incident light is constructive, when the refractive index n _d is constant, wherein the light of the wavelength lambda ( The thickness d2 satisfies 9).
d2 = m _d λ / 2n _d (9)
(Where λ represents the wavelength λ _{i of the} incident light or the wavelength λ _s of the Raman scattered light, m _d represents a positive integer, and n _d represents the refractive index of the dielectric layer 20).
However, in this case, since m _d takes discrete values such as 1, 2, 3,..., The wavelength strengthened by the thin film interference is the discrete wavelength even if the thickness d2 is changed. It becomes. Also In this case, changing the thickness d2, wavelength constructive corresponding to each m _d is, for interlocking, it is difficult to adjust the respective positions of the constructive wavelength.

  On the other hand, if interference based on the Maxwell-Garnett model is used in combination, two peaks can be generated in the optical element, and the positions of the respective peaks can be individually changed.

Maxwell-Garnett's equation is the following equation (10):
(Ε (ω) −ε ₂ ) / (ε (ω) + 2ε ₂ ) = f (ε ₁ (ω) −ε ₂ ) / (ε ₁ (ω) + 2ε ₂ ) (10)
It is represented by Here, ε (ω) is the effective dielectric constant of the metal particle layer 30, ε ₂ is the dielectric constant of the portion (medium) other than the metal particles 40 of the metal particle layer 30, and ε ₁ (ω) is the metal particle layer. 30 is a dielectric constant of the metal particles 40, and f is a fill-factor of the metal particles 40 in the metal particle layer 30. Since ε ₁ (ω) is a complex number, ε (ω) is also a complex number. Therefore, if ε ₁ (ω) is given the complex dielectric constant of the metal particle 40 at a specific wavelength, ε (ω) can be obtained.

  An example of a method for calculating a condition in which incident light is strengthened by interference based on the Maxwell-Garnett model is a method using a transfer matrix.

  In the optical element 100 of the present embodiment, two peaks are designed with a free wavelength difference using both the thin film interference model and the Maxwell-Garnett model (MG model).

Note that, as described above, in the thin film interference model, the wavelength with high enhancement depends on the thickness d of the dielectric layer 20 and the wavelength λ _{i of} incident light or the wavelength λ _s of Raman scattered light. In the MG model, the wavelength of high enhancement depends on the size and dielectric constant of the metal particles 40 of the metal particle layer 30 in addition to the thickness d of the dielectric layer 20 and the wavelength λ _{i of the} incident light. Therefore, in the present embodiment, by considering the MG model, the wavelengths of the two peaks in the wavelength characteristic of the enhancement or reflectance can be tuned separately.

  Although the presence of the metal particle layer 30 and the metal layer 10 is not considered in the condition of the thin film interference of the formula (9), the region of the metal particle layer 30 other than the metal particle 40 (the region where the upper surface of the dielectric layer 20 is exposed) It is considered that the interference that occurs in (1) can be designed by considering thin film interference. The light enhanced by the thin film interference can propagate through the dielectric layer 20 and can be combined with the surface plasmon wave of the metal layer 10.

  The thickness d2 of the dielectric layer 20 when the short wavelength side peak and the long wavelength side peak are strengthened by thin film interference, and the thickness of the dielectric layer 20 when the short wavelength side peak is strengthened by the Maxwell-Garnett effect They are different from d1. Therefore, the thickness d of the dielectric layer 20 is between the thickness d1 of the dielectric layer 20 strengthened by thin film interference and the thickness d2 of the dielectric layer 20 when strengthened by the interference effect of the Maxwell-Garnett model. By setting this value, the two peaks can be strengthened with a good balance. That is, the thickness d of the dielectric layer 20 may satisfy the relationship d2 <d <d1.

  Thereby, sufficiently high enhancement can be obtained in both bands corresponding to incident light and scattered light. In the optical element 100 according to the present embodiment, two peaks in the wavelength characteristic of the enhancement or reflectance can be designed as follows.

For example, when the optical element 100 of the present embodiment is used for detection of a known substance, the peaks of the two enhancement profiles are increased in the wavelength or wave number region of the incident light and the Raman scattered light of the substance, respectively. Set to. In this way, the substance can be detected with high sensitivity. Further, for example, when the optical element 100 of the present embodiment is used for detection and identification of an unknown substance, two peaks in the wavelength characteristic of enhancement or reflectance are set so as to be large in as wide a band as possible. In this way, the substance can be detected and identified with high sensitivity.

1.8. Effects The optical element 100 of the present embodiment has the following characteristics.
By further strengthening the enhanced electric fields of LSP and PSP by the interference effect, an extremely large electric field enhancing effect can be obtained. That is, a strong enhanced electric field can be obtained with both excitation and scattering wavelengths.

  Using an excitation wavelength linearly polarized in the X direction, metal particles are formed in the first direction at a pitch P1, and hot spots of LSP can be obtained at a high density, so that a higher enhancement effect than the hybrid structure (GSPP) is obtained. be able to.

  When the thickness d of the dielectric layer is increased, the electric field enhancement due to the interference effect can be used, and the dispersion curve of the SPP can be on the low energy side (long wavelength side). Thereby, when the SPP has the same energy (wavelength), the wave number increases as the thickness d of the dielectric layer increases, and the pitch P2 can be shortened. Thereby, the hot spot density in the incident light irradiation region can be increased.

  By these actions, strong enhancement is obtained at both the excitation wavelength and the scattering wavelength, and molecules with a large Raman shift can be sensed with high sensitivity.

  According to the optical element 100 of the present embodiment, the position of the two peaks can be adjusted in the wavelength dependence of the enhancement intensity or reflectance, so that incident light can be measured even when measuring a sample exhibiting a large Raman shift. And both of the Raman scattered light can be sufficiently enhanced.

  Since the optical element 100 of the present embodiment has a high strength enhancement, for example, in the fields of medical / health, environment, food, public security, etc., bio-related substances such as bacteria, viruses, proteins, nucleic acids, various antigens / antibodies, In addition, various compounds including inorganic molecules, organic molecules, and polymers can be used as sensors for detecting with high sensitivity, high accuracy, quickness and simpleness. For example, an antibody is bound to the metal particle 40 of the optical element 100 of the present embodiment to determine the enhancement at this time, and the presence / absence or amount of the antigen is determined based on the change in the enhancement when the antigen is bound to the antibody. Can be examined. In addition, the enhancement of light of the optical element 100 of the present embodiment can be used to enhance Raman scattered light of a trace substance.

2. Analysis Device FIG. 9 is a diagram schematically showing the analysis device 1000 of the present embodiment. The analysis apparatus 1000 according to the present embodiment includes the optical element 100 described above, a light source 300 that irradiates the optical element 100 with incident light, and a detector 400 that detects light emitted from the optical element 100.

2.1. Optical Element The optical element 100 has a function of enhancing light in the analyzer 1000. The optical element 100 may be used in contact with a sample to be analyzed by the analyzer 1000. The arrangement of the optical element 100 in the analyzer 1000 is not particularly limited, and may be installed on a stage or the like whose installation angle can be adjusted. The optical element 100 is as described above.

2.2. Light Source The analysis apparatus 1000 according to this embodiment includes a light source 300. The light source 300 is the optical element 10.
0 is irradiated with incident light. The light source 300 emits light linearly polarized (linearly polarized light in the same direction as the first direction) in the first direction of the optical element 100 (the direction in which the metal particles 40 are arranged and the metal particle rows 41 extend). be able to.

  The inclination angle θ of the incident light irradiated from the light source 300 from the thickness direction of the dielectric layer 20 may be appropriately changed according to the excitation condition of the surface plasmon of the optical element 100. The light source 300 may be installed in a goniometer or the like.

  The light emitted from the light source 300 is not particularly limited as long as the surface plasmon of the optical element 100 can be excited, and can be an electromagnetic wave including ultraviolet light, visible light, and infrared light. The light emitted from the light source 300 may or may not be coherent light. Specifically, examples of the light source 300 include a semiconductor laser, a gas laser, a halogen lamp, a high-pressure mercury lamp, a xenon lamp, and the like provided with a wavelength selection element, a filter, a polarizer, and the like as appropriate.

  In the case of using a polarizer, a known one can be used, and a mechanism for appropriately rotating the polarizer may be provided. Light from the light source 300 becomes excitation light, and enhanced light is emitted from the optical element 100. As a result, the Raman scattered light of the sample is amplified, and the substance interacting with the optical element 100 can be detected.

2.3. Detector The analysis apparatus 1000 of this embodiment includes a detector 400. The detector 400 detects light emitted from the optical element 100. As the detector 400, for example, a CCD (Charge Coupled Device), a photomultiplier tube, a photodiode, an imaging plate, or the like can be used.

  The detector 400 may be provided at a position where the light emitted from the optical element 100 can be detected, and the positional relationship with the light source 300 is not particularly limited. The detector 400 may be installed in a goniometer or the like. Further, the analysis apparatus 1000 of the present embodiment may include other appropriate configurations (not shown) such as a casing and input / output means.

  According to the analyzer 1000 described above, the optical element 100 that can adjust the positions of the two peaks in the wavelength dependence of the enhancement profile or the reflectance is provided, so that it is a case where a sample exhibiting a large Raman shift is measured. However, it is possible to easily and highly sensitively detect and measure a wide range of trace substances.

  In addition, since the analyzer 1000 of the present embodiment has high strength, for example, in the fields of medical / health, environment, food, public security, etc., biologically related substances such as bacteria, viruses, proteins, nucleic acids, and various antigens / antibodies In addition, various compounds including inorganic molecules, organic molecules, and macromolecules can be detected with high sensitivity, high accuracy, speedy and simple. For example, the Raman scattered light of a trace substance can be enhanced by using the light enhancement of the analyzer 1000 of the present embodiment.

3. Electronic Device An electronic device 2000 according to the present embodiment includes the above-described analyzer 1000, a calculation unit 2010 that calculates health and medical information based on detection information from the detector 400, a storage unit 2020 that stores health and medical information, A display unit 2030 for displaying health care information.

  FIG. 10 is a schematic diagram of a configuration of the electronic device 2000 of the present embodiment. The analysis apparatus 1000 is the analysis apparatus 1000 described above in “2. Analysis apparatus”, and detailed description thereof is omitted.

  The calculation unit 2010 is, for example, a personal computer or a personal digital assistant (PDA), receives detection information (signals and the like) sent from the detector 400, and performs a calculation based on the detection information. Further, the arithmetic unit 2010 may control the analysis apparatus 1000. For example, the arithmetic unit 2010 may perform control of the output and position of the light source 300 of the analyzer 1000, control of the position of the detector 400, and the like. The calculation unit 2010 can calculate health care information based on the detection information from the detector 400. The health care information calculated by the calculation unit 2010 is stored in the storage unit 2020.

  The storage unit 2020 is, for example, a semiconductor memory, a hard disk drive, or the like, and may be configured integrally with the calculation unit 2010. The health care information stored in the storage unit 2020 is sent to the display unit 2030.

  The display unit 2030 includes, for example, a display board (liquid crystal monitor or the like), a printer, a light emitter, a speaker, and the like. The display unit 2030 displays or issues information based on the health care information calculated by the calculation unit 2010 so that the user can recognize the contents.

  The presence or absence of at least one compound selected from the group consisting of bacteria, viruses, proteins, nucleic acids, and antigens / antibodies, or at least one compound selected from inorganic and organic molecules is included as health care information Or information about the quantity can be included.

4). Experimental Examples The experimental examples are shown below to further explain the present invention, but the present invention is not limited to the following examples. The following example is a computer simulation.

4.1. Summary of calculation The calculation was performed using FDTD soft Fullwave of Rsoft (currently Cybernet System Co., Ltd.). The incident light was linearly polarized light in the X direction (first direction) and perpendicular incidence parallel to the thickness direction of the metal layer. The mesh conditions used were a 2 nm minimum mesh for comparison within the same HSD, a 1 nm minimum mesh for increase calculation, and a calculation time cT of 10 μm.

In the present experimental example, the increase in intensity is represented by SQRT (Ex ² + Ez ² ) at the maximum enhancement position. Here, Ex represents the electric field strength in the polarization direction (first direction) of the incident light, and Ez represents the electric field strength in the thickness direction. In this case, the electric field strength in the second direction is small and is not considered.

FIG. 11 is a schematic diagram showing a basic structure of a model used for simulation of an experimental example.
The structure parameters in this experimental example are expressed in the order of “metal layer / dielectric layer / metal particle layer”, and the size parameters are the X direction (first direction) period Xp (pitch P1), the Y direction. The period Yp (pitch P2) in the (second direction), the diameter D of the metal particles, the height T of the metal particles, and the thickness d of the dielectric layer are represented in this order. The metal particle model of the metal particle layer was a cylinder. For example, if Xp = 140 nm, Yp = 600 nm, D = 80 nm, T = 30 nm, d = 150 nm in the layer of Au film / SiO ₂ film / Ag particles, it is expressed as “Au / SiO ₂ / Ag X140Y600D80T30d150” or the like. .

4.2. Results From the results of the FDTD calculation and the calculation results of the interference equation, the interference effect occurs in the optical element of this experimental example, and the SERS EF is maximum at the dielectric thickness d satisfying d2 <d <d1. Explain that

<Experimental example 1>
In the structure of this experimental example, Au / SiO ₂ / Au X200Y600D110T30, when the excitation wavelength is 630 nm and the scattering wavelength is 780 nm, the SiO ₂ film thickness strengthened by the interference effect was obtained from the equations (9) and (10), respectively.

Specifically, n = 1.46, λ _i = 630, and λ _s = 770 (nm) were substituted into Equation (9) of the thin film interference model, respectively. Further, ε ₂ = 1 (dielectric constant of air) is substituted into Maxwell-Garnett equation (10), Au complex permittivity is substituted for ε ₁ (ω), and energy of wavelength 630 nm is substituted for ω, and ε (ω) And the thickness d strengthened by interference was calculated (interference order m was set to m = 2). Note that f (fill factor) is a volume filling factor, and f = (volume of one metal particle) / (X pitch × Y pitch × metal particle height T), so that f = π × (110/2). ² × 30 / (200 × 600 × 30) = 0.079.

  The calculation results are shown in Table 1 below.

Table 1 shows the thickness d of SiO ₂ (dielectric layer) strengthened by the interference effect of the model Au / SiO ₂ / Au X200Y600D110T30.

FIG. 12 is a reflection spectrum when the thickness d of SiO ₂ (dielectric layer) in the Au / SiO ₂ / Au X200Y600D110T30 model is changed from 250 nm to 370 nm in increments of 20 nm. d> When _{d2 = m d λ i / 2n} d = 216nm, 2 peaks is expressed, it is possible to enhance both the incident light and the Raman scattered light.

When the peak is strengthened by interference, the shape of the peak becomes sharp. The peak on the long wavelength side is sharpest at SiO ₂ = 270 nm, and the reflectance is lowered. The peak on the short wavelength side is broad, but the shape is sharpest at SiO ₂ = 350 nm.

FIG. 13 is a cross section of the chain line I of the model shown in FIG. 11 and shows the intensity distribution of the electric field Ex on the XZ plane of the portion surrounded by the chain line II. The excitation wavelength was set to 630 nm and the thickness d of the dielectric layer was set to 350 nm. The portion of the SiO ₂ layer in FIG. 13 is marked with an arrow, indicating a region with high strength.

Referring to FIG. 13, in the distribution of the electric field Ex on the XZ plane, there are two strong electric field portions (arrows) in the SiO ₂ layer. That is, at d = 350 nm, it can be seen that the secondary interference occurs with two antinodes of amplitude.

Therefore, when d = 350 nm, it can be described by the MG equation. On the other hand, in the case of the first-order thin film interference formula, the thickness d = 630 / (2 × 1.46) = SiO ₂ layer =
In the case of 215.7 (nm) and the second order, the thickness of the SiO ₂ layer is d = 2 × 630 / (2 × 1.46) = 431.5 (nm), which cannot be explained.

  From the results of Table 1 and FIGS. 12 and 13, it can be said that the peak on the long wavelength side was strengthened by thin film interference, and the peak on the short wavelength side was strengthened by interference of the Maxwell-Garnett model.

  From Table 1, the thickness d2 of the dielectric layer when the peak on the long wavelength side is strengthened by thin film interference, and the thickness d1 of the dielectric layer when the peak on the short wavelength side is strengthened by the effect of Maxwell-Garnett Found different from each other.

The enhanced electric field of plasmon has a large drop in reflectivity, and it is considered that the stronger the electric field strength is, the sharper the peak is. Therefore, the thickness d of SiO ₂ (dielectric layer) satisfies the relationship of d2 <d <d1. , Strong SERS EF can be obtained. Here is a _{d2 = m d λ s / 2n} d. From FIG. 12, it is considered that d = 310 nm is suitable in the range of d2 <d <d1, that is, in the range of 263 nm <d <350 nm.

  Next, the near-field enhanced electric field was obtained by FDTD calculation with d = 310 nm, d1 = 350 nm, and d2 = 270 nm. The mesh used for the calculation has a minimum mesh size of 2 nm. Table 2 shows the enhancement and SERS enhancement effects.

Table 2 shows the calculation results of FDTD, and describes the enhancement of the peak of 2800 cm ⁻¹ or more on the 633 nm excitation substrate.

Table 2 shows that the highest enhancement effect was obtained at d = 310 nm. For this reason, it has been found that when the thickness d of the dielectric layer satisfies d2 <d <d1, a high enhancement can be obtained. Here, a _{d2 = m d λ i / 2n} d, more preferably _{d2 = m d λ s / 2n} d.

Table 3 shows the increase in intensity (SQRT (Ex ² + Ez ² )) obtained by FDTD calculation when incident light having a wavelength of 630 nm and 780 nm is incident on an optical element having a dimension of X200Y600D110T30d310. The calculation mesh has a minimum mesh size of 1 nm.

From Table 3, it was found that SERS EF = (97.8) ² × (100.8) ² = 9.7 × 10 ⁷ , and a strong SERS enhancement effect on the order of about 10 ⁸ can be obtained.

The material of the dielectric layer is not limited to SiO ₂ , and TiO ₂ , Al ₂ O ₃ , ITO, etc. can be used. The refractive index n of these substances is about 1.46 or more and 3 or less. Further, the excitation wavelength (incident light wavelength λ _i ) and the Raman scattered light wavelength λ _s are not limited.

<Experimental example 2>
In this experimental example, the dielectric layer is made of TiO ₂ (refractive index: 2.71). FIG. 14 is a reflection spectrum of a model of Au / TiO ₂ / Au X200Y500D80T30d150. Table 4 shows the film thickness (thickness d) of TiO ₂ obtained from the equations (9) and (10) at wavelengths of 630 nm and 780 nm.

From Table 4, d2 = 144 nm and d1 = 200 nm. It can be seen that the thickness d of TiO ₂ satisfying d2 <d <d1 is between 144 nm and 200 nm.

FIG. 14 shows that there are two peaks at 630 nm and 800 nm. Since the wavelength corresponding to 2800 cm ⁻¹ is 780 nm, two peaks separated by 2800 cm ⁻¹ or more are obtained. From these results, it can be seen that even if the material of the dielectric layer is TiO ₂ , the effect of the present invention is exhibited, and the material of the dielectric layer is not limited.

<Experimental example 3>
FIG. 15 is a reflectance spectrum of an optical element having a dimension of X200Y750D160T30d390 designed to have an excitation wavelength of 785 nm based on FDTD calculation.

FIG. 15 shows that there are two peaks at 760 nm and 1020 nm. A wavelength corresponding to 2800 cm ^-1 is so 1006Nm, it was possible to obtain two peaks separated 2800 cm ^-1 or more. It can also be seen that the peak at 760 nm covers 785 nm. At any peak, the reflectance is sufficiently small and high enhancement can be expected.

From this result, in the structure of the present invention, the pitch, size, material, dielectric type, incident wavelength, etc. of the metal particles are not limited, and the wave number difference of 2800 cm ⁻¹ or more is obtained in the wavelength characteristic of the enhancement or reflectance. It turns out that two peaks can be made.

<Experimental example 4>
This experimental example shows a method of adjusting the PSP resonance wavelength by changing the Y-direction pitch Yp (P2).
The peak wavelength on the short wavelength side can be adjusted by changing the LSP resonance wavelength. The LSP resonance wavelength is the type, shape, diameter, height, distance between adjacent metal particles (period Xp (pitch P1) in the X direction (first direction)), surrounding dielectric constant, etc. Depends on. On the other hand, the peak wavelength on the long wavelength side is determined by the resonance wavelength of LSP and PSP. When Yp is changed, the wave number k which is the horizontal axis of the SPP dispersion curve is changed. FIG. 16 is a graph of the dispersion relationship when the metal layer is Au and the dielectric layer is SiO ₂ or air. FIG. 16 shows SPP dispersion curves and corresponding light lines generated at the Au / air (n = 1) interface and the Au / SiO ₂ (n = 1.46) interface. The SPP dispersion curve generated at the metal / dielectric layer interface is expressed by equation (3).
K _SPP = ω _i / c [ε ₂ · ε ₁ (ω _i ) / (ε ₂ + ε ₁ (ω _i ))] ^1/2 (3)
(K _SPP is the wave number of SP, ω _i is the energy of SPP, c is the speed of light, ε ₁ (ω _i ) is the dielectric constant of the metal, and ε ₂ is the dielectric constant of the dielectric layer. ₂ = n ² ).
Equation (3) assumes that the thickness of the dielectric layer is infinite, but for a dielectric layer of finite thickness, the SPP dispersion curve is the SPP of the metal / air interface and the SPP of the metal / dielectric layer interface. Intermediate. As the thickness d of the dielectric layer increases, the SPP dispersion curve at the metal / dielectric interface approaches, ie, the wavelength of the SPP becomes longer.

Since the PSP propagates in the Y direction (second direction), the wave number k of the PSP can be controlled by the period Yp (pitch P2) in the Y direction. The relationship between wave number k and Yp is
k = m * 2π / Yp [nm] * 100 (11)
(M is a positive integer). For example, when Yp = 600 nm, m = 2 and k = 2.09. In the case of normal incidence, the wave number of PSP can be represented by a line parallel to the vertical axis, as shown in FIG. In the case of FIG. 16, when Yp = 600 nm, the wavelength range of SPP generated at the Au / SiO ₂ interface is between 625 nm and 900 nm (the range of the arrow in FIG. 16). When the thickness d of SiO ₂ (dielectric layer) is changed, the peak on the long wavelength side can be changed between 625 nm and 900 nm. However, if the thickness d of SiO ₂ (dielectric layer) is changed, the strength of the enhanced electric field may not be increased because it may deviate from the condition of the interference effect. For this reason, the adjustment of the peak on the long wavelength side may be performed by changing Yp.

  As described above, when the LSP resonance wavelength is changed, both of the two peaks change. Therefore, the PSP resonance wavelength is adjusted by changing Yp (pitch P2).

-CH ₂ the sample molecules -, - if there is a structure of CH _3, i.e., if there is a methylene group or a methyl group, a peak of the Raman scattering of these groups are mainly 2800cm ^-1 ~3500cm ^-1 between.

When the metal layer is Au and the material of the dielectric layer is SiO ₂ , Yp (pitch P2) for detecting a Raman shift of 2500 cm ⁻¹ to 3500 cm ⁻¹ by excitation with incident light having a wavelength of 600 nm to 1100 nm. ) Is as follows.

480 nm <Yp <1840 nm
This lower limit of 480 nm is a condition under which a scattering wavelength of 748 nm of 2500 cm ⁻¹ can be detected at an excitation wavelength of 600 nm. From the SPP dispersion curve of the Au / SiO ₂ interface, k = 2.58 and Yp = 486 nm.

The upper limit of 1840 nm is a condition under which a scattering wavelength of 1815 nm at 3500 cm ⁻¹ can be detected at an excitation wavelength of 1100 nm. From the SPP dispersion curve of the Au / SiO ₂ interface, k = 0.68 and Yp = 1737 nm.

Further, the structure of the optical element of this experimental example can prevent PSP from occurring in the X direction. The condition that PSP does not propagate is Xp <λ / 2, where λ is the excitation wavelength. When the excitation wavelength is 1064 nm, Xp = 532 nm at λ = 1064 nm, and if the excitation wavelength is 1064 nm or less, it can be understood that Xp <535 nm. Although the lower limit of Xp is not particularly limited, since LSP is generated, if the diameter of the metal particles is 5 nm and the distance (interval or gap) between the metal particles is 1 nm, Xp = 6 nm can be set as the lower limit. In this way, it can be seen that both incident light and Raman scattered light can be sufficiently enhanced when a sample exhibiting a large Raman shift is measured using incident light having a wavelength λ _i of less than 1100 nm.

  In each of the above experimental examples, the metal layer and the metal particles are exemplified by Au and Ag, but the same applies even when Au, Ag, Cu, Al, or an alloy thereof is employed. In the above experimental example, the arrangement of the metal particles is the GSPP model, but the same applies to D2PA (Disk-coupled dots-on-pillar antenna model). In the above experimental example, the shape of the metal particles is exemplified as a columnar shape, but the same applies to any shape such as a hemispherical shape or a prismatic shape. Furthermore, in the above experimental example, the excitation wavelengths are exemplified for 633 nm and 785 nm, but the same can be applied to other excitation wavelengths.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 10 ... Metal layer, 20 ... Dielectric layer, 30 ... Metal particle layer, 40 ... Metal particle, 41 ... Metal particle row | line | column, 100 ... Optical element, 300 ... Light source, 400 ... Detector, 1000 ... Analyzer , 2000 ... electronic device, 2010 ... calculation unit, 2020 ... storage unit, 2030 ... display unit

Claims (12)

A metal layer, a dielectric layer provided on the metal layer, and a metal particle layer provided on the dielectric layer and arranged with metal particles,
The metal particle layer has a metal particle array in which a plurality of the metal particles are arranged at a pitch P1 in a first direction, and the metal particle array is formed from the pitch P1 in a second direction intersecting the first direction. Are arranged at a large pitch P2,
The thickness d of the dielectric layer satisfies the relationship d2 <d <d1,
An optical element that is irradiated with incident light having a wavelength λ _i that is linearly polarized light in the same direction as the first direction.
[Wherein, d2 _{is, m d λ i / 2n d} (m d = 1, n d represents. A refractive index of the dielectric layer) represents, d1, the dielectric of the metal particle layer at the wavelength lambda _i When the ratio is given by the effective dielectric constant obtained by the Maxwell-Garnett equation, a condition that reinforces by secondary interference generated in the structure including the metal layer, the dielectric layer, and the metal particle layer of the optical element And the thickness of the dielectric layer satisfying d2 <d1. ] A metal layer, a dielectric layer provided on the metal layer, and a metal particle layer provided on the dielectric layer and arranged with metal particles,
The metal particle layer has a metal particle array in which a plurality of the metal particles are arranged at a pitch P1 in a first direction, and the metal particle array is formed from the pitch P1 in a second direction intersecting the first direction. Are arranged at a large pitch P2,
The thickness d of the dielectric layer satisfies the relationship d2 <d <d1,
An optical element that is irradiated with incident light having a wavelength λ _i that is linearly polarized light in the same direction as the first direction.
[Wherein, d2 _{is, m d λ s / 2n d} (m d = 1, λ s is the Raman scattering wavelength when irradiated with incident light of wavelength lambda _i, the n _d represents the refractive index of the dielectric layer ), And d1 represents the metal layer and the dielectric layer of the optical element when the dielectric constant of the metal particle layer at the wavelength λ _i is given by the effective dielectric constant obtained by the Maxwell-Garnett equation. And a thickness of the dielectric layer that satisfies a strengthening condition by secondary interference generated in the structure including the metal particle layer, and satisfies d2 <d1. ] In claim 2,
The Raman scattering wavelength λ _s and the incident light wavelength λ _i are:
2500 cm ⁻¹ ≦ (1 / λ _i −1 / λ _s ) <3500 cm ⁻¹
An optical element that satisfies the above relationship. In any one of Claims 1 thru | or 3,
The thickness d of the said dielectric material layer is an optical element which is 60 nm or more. In any one of Claims 1 thru | or 3,
An optical element having a thickness d of the dielectric layer of 145 nm or more. In any one of Claims 1 thru | or 5,
An optical element in which the material of the dielectric layer is SiO ₂ . In any one of Claims 1 thru | or 6,
The pitch P1 is an optical element satisfying 6 nm <P1 <535 nm. In any one of Claims 1 thru | or 7,
The material of the metal layer is Au,
The pitch P2 is an optical element satisfying 480 nm <P2 <1840 nm. In any one of Claims 1 thru | or 8,
An optical element in which the material of the metal particles is Au or Ag. In claim 8,
The optical element having a wavelength λ _{i of the} incident light of 630 nm to 1070 nm. The optical element according to any one of claims 1 to 10,
A light source for irradiating the optical element with the incident light;
A detector for detecting light emitted from the optical element;
Analytical device equipped with.   12. The analyzer according to claim 11, a calculation unit that calculates health and medical information based on detection information from the detector, a storage unit that stores the health and medical information, and a display unit that displays the health and medical information. And electronic equipment.