JP2014228320A - Optical enhancement element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical enhancement element capable of stably securing a high optical enhancement effect.SOLUTION: The optical enhancement element comprises a substrate and an enhanced strong electromagnetic field formation layer in which a large number of silver particulates are dispersedly arranged on the surface of the substrate independently of each other. The enhanced strong electromagnetic field formation layer has a gold film on a surface of each of the large number of silver particulates out of contact with the substrate, the gold film being dispersedly arranged.

Description

  The present invention relates to a light enhancement element using localized surface plasmons of metal fine particles and a method for manufacturing the same.

  Raman spectroscopy, which obtains a spectrum of Raman scattered light by dispersing Raman scattered light obtained by irradiating an analysis target with light of a single wavelength (laser light), is used for identification of substances. However, the Raman scattered light obtained from the analysis object is usually difficult to detect with high sensitivity because the signal is weak.

  Therefore, in recent years, a laser beam is emitted to an object to be analyzed adsorbed on the surface of the metal fine particle by utilizing the localized surface plasmon effect of the metal fine particle (also referred to as “metal nanoparticle”). Research on surface-enhanced Raman scattering (SERS: Surface Enhanced Raman Scattering) in which Raman scattered light is detected by dramatically increasing the intensity is being promoted (see, for example, Patent Documents 1 and 2).

  FIG. 10A is a schematic diagram showing the configuration of the light enhancement element disclosed in Patent Document 1. FIG. The light enhancement element 100 shown in FIG. 10A includes a flat substrate 111, a high reflection layer 112 formed on the surface of the substrate 111, and a dielectric formed on the surface of the high reflection layer 112. It has a multilayer structure including a layer 113 and an enhanced electromagnetic field forming layer 115 made up of a large number of silver fine particles 114 formed on the surface of the dielectric layer 113.

  FIG. 10B is a schematic diagram showing the configuration of the light enhancement element disclosed in Patent Document 2. As shown in FIG. The light enhancement element 101 shown in FIG. 10B is formed so as to cover the outer surface of many silver fine particles 114 and the entire surface of the substrate 111 in addition to the light enhancement element 100 shown in FIG. A gold film 116 is provided.

JP 2012-132804 A International Publication No. 2012/085586

  Such a light enhancement element has an effect of enhancing Raman scattered light and fluorescence. For this reason, an object to be inspected is placed on the upper surface of the light enhancement element, and excitation light is irradiated to perform spectrum analysis of Raman scattered light and fluorescence, so that applications such as identification and inspection of the substance of the object to be inspected are considered. It is done. As one of such application examples, utilization for examination of biological samples such as various cells, biological tissue sections, and antibodies / antigens is considered.

  However, when such a biological sample is assumed as the test object, the biological sample contains halide ions. For this reason, when such a specimen is placed on the light enhancement element 100 as shown in FIG. 10A, the halide ions and the silver fine particles immediately undergo a chemical reaction and change, and the silver fine particles are detached or dissolved. This causes a problem that the light enhancement effect cannot be obtained.

  In addition, as a result of the silver fine particles being exposed to the air, the silver fine particles are oxidized over time, so that the light enhancement effect cannot be obtained.

  Since the surface of the silver fine particles is covered with a gold film in the light enhancement element 101 shown in FIG. 10B, even if an inspection object made of a biological substance as described above is placed on the light enhancement element. There is no direct contact between halide ions and silver fine particles. Therefore, it was thought that this element can be used to inspect biological samples. Further, since the silver fine particles are not exposed to the atmosphere, the stability of the silver fine particles can be maintained and the maintenance of the light enhancement effect over time can be ensured as compared with the light enhancement element 100 shown in FIG. It was thought.

  However, according to the earnest study of the present inventor, as shown in FIG. 10B, it was found that covering the substrate with a gold film attenuates the light enhancement effect possessed by many silver fine particles. . That is, when the Raman scattering light is received by irradiating the excitation light with the inspection object placed on the light enhancement element, the light reception intensity in the configuration of FIG. 10B is higher than that in the configuration of FIG. Will drop significantly.

  An object of this invention is to implement | achieve the optical enhancement element which can ensure the high optical enhancement effect stably in view of said subject.

The light enhancement element of the present invention is a light enhancement element comprising a substrate and an enhanced electromagnetic field forming layer in which a large number of silver fine particles are dispersedly arranged independently of each other on the surface of the substrate,
The enhanced electromagnetic field forming layer has a gold film on a surface that is not in contact with the substrate of each of the silver fine particles,
The gold film is dispersedly arranged.

  According to this configuration, since the gold film is dispersedly arranged, compared with the configuration in which the gold film is entirely covered, the enhanced electromagnetic field forming layer in which a large number of silver fine particles are dispersedly arranged has a high light enhancement effect. It is fully demonstrated. In addition, since a gold film is formed on the surface (outer surface) of each of the many silver fine particles that is not in contact with the substrate, even if a test object made of a biological sample is placed on the light enhancement element, Halide ions do not come into direct contact with the silver fine particles, and oxidation by oxygen contained in the atmosphere is prevented.

  That is, it is possible to achieve both of the light enhancement effect of the enhanced electromagnetic field forming layer and the protection of the silver fine particles.

  Here, the gold film may be dispersed and arranged in association with each of the large number of silver fine particles.

  In other words, in this configuration, a gold film is formed on the outer surface of the silver fine particle at a place where a large number of silver fine particles are dispersed and arranged, that is, a place where a silver fine particle is not formed on the substrate, that is, a large number of silver A gold film is not formed in the region between the fine particles. As a result, the presence of the gold film makes it possible to suppress as much as possible the rate of reducing the light enhancement effect of the enhanced electromagnetic field forming layer composed of a large number of silver fine particles.

  The gold film may be formed so as to completely cover the surface of each of the silver fine particles that is not in contact with the substrate.

  As a result, the outer surface of each of the many silver fine particles formed on the light enhancement element is completely coated with a gold film, so that the reaction with halide ions or the like and the light enhancement effect due to oxidation are reduced for a long time. Can be protected over. That is, the function of maintaining a high light enhancement effect for a considerably long time is exhibited.

  Here, the thickness of the gold film is more preferably 1 nm or more and 5 nm or less. If the film thickness is less than 1 nm, the function of protecting the silver fine particles from reaction with halide ions or oxidation or oxidation cannot be sufficiently exhibited. On the other hand, if the film thickness is thicker than 5 nm, the content ratio of the gold film increases, and as a result, the light enhancement effect of the strong electromagnetic field forming layer composed of a large number of silver fine particles is reduced. By making the film thickness of the gold film within the above range, it is possible to maximize the compatibility between ensuring the light enhancement effect of the enhanced electromagnetic field forming layer and protecting the silver fine particles.

In addition to the above features, the light enhancement element of the present invention has the following features:
Another feature is that a protective layer is formed on the substrate and the enhanced electromagnetic field forming layer.

  By having this protective layer in addition to the gold film, it is possible to further enhance the function of protecting the silver fine particles from reaction with halide ions and oxidation. Further, unlike the case where the gold film is formed with a thick film, when this protective layer is formed, a strong light enhancement effect can be exerted on the upper surface of the protective layer through the protective layer. Therefore, by placing the inspection object on the upper surface of the protective layer and irradiating the excitation light, Raman scattered light and fluorescence obtained from the inspection object (or its label) can be remarkably enhanced. That is, according to this configuration, the effect of maintaining a high light enhancement effect for a considerably long time can be further enhanced.

  Here, the protective layer may have a structure having an orientation in relation to the large number of metal fine particles. More specifically, the protective layer may be composed of an inorganic substance having orientation in connection with the large number of metal fine particles or a polymer of organic substance having orientation.

  With this configuration, an enhanced electromagnetic field caused by the localized surface plasmon effect in the enhanced electromagnetic field forming layer can be transmitted to the surface of the protective layer with high efficiency.

  The protective layer may contain a halogen element.

  With this configuration, the enhanced electromagnetic field caused by the localized surface plasmon effect in the enhanced electromagnetic field forming layer can be transmitted to the surface of the protective layer with higher efficiency. Note that this configuration is different from the case where halide ions are directly brought into contact with the exposed silver fine particles in the configuration having no protective layer, and therefore a material containing a halogen element is used as the protective layer. Similarly, the function of protecting the silver fine particles from damage caused by halide ions is secured.

In addition, the method for manufacturing the light enhancement element of the present invention includes:
Preparing a substrate (a),
A step (b) of depositing a large number of fine silver particles dispersed on the substrate;
And it has the process (c) which forms the said gold film on the surface which is not contacting the said board | substrate of each of these many silver fine particles by vapor-depositing a gold film and performing heat processing.

  According to this method, it is possible to manufacture a light enhancement element capable of ensuring both the light enhancement effect of the enhanced electromagnetic field forming layer and the protection of silver fine particles.

  Here, in the step (c), the heat treatment can be performed under a temperature condition in which the gold film and the large number of silver fine particles are not alloyed.

  According to this method, since the silver component contained in the silver fine particles can be covered with the gold film without exposing it, a light enhancement element capable of maintaining a high light enhancement effect for a long time can be manufactured.

  According to the light enhancement element of the present invention, a high light enhancement effect can be stably secured. Moreover, according to the manufacturing method of this invention, such a light enhancement element can be manufactured.

It is the schematic which shows the structure of the optical enhancement element of 1st Embodiment of this invention. FIG. 6 is a schematic diagram illustrating a configuration of elements of Comparative Example 1 and Comparative Example 2. It is a conceptual diagram of the measuring apparatus for verifying the performance of a light enhancement element. It is a graph which shows an example of the Raman spectrum received by the light-receiving part when irradiating excitation light with respect to the optical enhancement element. It is a graph which shows the relationship between the intensity | strength of the Raman scattered light received by the light-receiving part when each element of Example 1 and Comparative Example 2 was irradiated with excitation light, and NaCl aqueous solution processing time. It is the schematic which shows the structure of the optical enhancement element of 2nd Embodiment of this invention. FIG. 6 is a schematic diagram illustrating a configuration of elements of Comparative Example 3 and Comparative Example 4. It is a graph which shows the relationship between the intensity | strength of the Raman scattered light received by the light-receiving part when each element of Example 2 and Comparative Example 3 was irradiated with excitation light, and NaCl aqueous solution processing time. It is a graph which shows the Raman spectrum received by the light-receiving part when irradiating each element of the comparative example 3 and the verification example 1 with excitation light. It is the schematic which shows the structure of the conventional light enhancement element.

[First Embodiment]
A first embodiment of the present invention will be described with reference to the drawings. In each figure, the dimensional ratio in the drawing does not necessarily match the actual dimensional ratio.

<Element structure>
FIG. 1 is a schematic diagram showing the configuration of the light enhancement element of the first embodiment. The light enhancement element 1 shown in FIG. 1 includes a substrate 7 and an enhanced electromagnetic field forming layer 9.

  The material of the board | substrate 7 is not specifically limited, For example, glass, ceramics, resin etc. can be used. As will be described later, when heat treatment (for example, heating at 100 ° C. or higher) is performed in the manufacturing process of the light enhancement element 1, it is preferable to have heat resistance such as glass or polyimide resin.

  The enhanced electromagnetic field forming layer 9 is configured by a large number of silver fine particles 2 being dispersedly arranged on the surface of the substrate 7 independently of each other. A gold film 3 is formed on the surface of each silver fine particle 2 that is not in contact with the substrate 7, and the gold film 3 is arranged in a dispersed manner in the same manner as the silver fine particle 2.

  As the shape of the silver fine particles 2, those having shape anisotropy such as a flat hemispherical shape and a flat plate shape can be suitably used. Note that it is desirable that all the silver fine particles 2 have a uniform size and shape, but there may be some variation in size and shape.

  Moreover, it is preferable that the particle diameter of the silver fine particles 2 is not larger than the wavelength of the excitation light. Here, in the present specification, “particle size” refers to a projected area equivalent circle diameter measured by microscopy. Specifically, it is obtained as follows. A field of view of a scanning electron microscope (for example, 1.5 μm × 2 μm) in which a line segment having a length of 2 μm is observed to be expanded to a length of 6 cm (magnification of 30000 times) in an arbitrarily selected region on the surface of the sensor chip 3 ) As an imaging region, a secondary electron image of the region in the sensor chip 3 is obtained. At this time, the diameter of a perfect circle having the same area as that of the silver fine particles 2 is obtained as the particle size of the silver fine particles 2 for each of the metal fine particles having a brightness index (256 steps) of about 100 or more.

The particle diameter of the silver fine particles 2 is in the range of, for example, 5 to 300 nm, and the thickness is in the range of, for example, 5 to 70 nm. Moreover, the density of the silver fine particles 2 constituting the enhanced electromagnetic field forming layer 9 can be, for example, about 10 ⁸ to 10 ¹¹ particles / cm ² .

  In the present embodiment, the gold film 3 is formed on the surface (outer surface) of each silver fine particle 2 that is not in contact with the substrate 7 and is formed so as to completely coat the outer surface of each silver fine particle 2. Has been. As shown in FIG. 1, in the present embodiment, the gold film 3 is dispersed and arranged in association with each of a large number of silver fine particles 2. That is, in a place where a large number of silver fine particles 2 are dispersedly arranged, the gold film 3 is formed on the outer surface of the silver fine particle 2, while on the substrate 7 the silver fine particles 2 are not formed, that is, a large number of places. A gold film is not formed in the region 5 between the silver fine particles 2.

  The film thickness of the gold film 3 is, for example, 4 to 10% of the thickness of the silver fine particles 2. When the thickness of the silver fine particles 2 is in the range of 5 to 70 nm, the thickness of the gold film 3 can be 1 nm or more and 5 nm or less.

<Production method>
A substrate 7 is prepared, and a dispersion liquid in which a precursor of silver fine particles 2 is dispersed in an appropriate solvent is applied to the surface of the substrate 7 by a spin coating method and heated. As a result, a large number of silver fine particles 2 dispersedly arranged independently of each other are formed on the surface of the substrate 7. In addition, as another method, the method of dipping the precursor of the silver fine particle 2 on the surface of the substrate 7 and heating, the method of vacuum-depositing the silver fine particle 2 on the surface of the substrate 7, the silver fine particle 2 on the surface of the substrate 7 A sputter deposition method or the like can be used.

  Next, a precursor of the gold film 3 is deposited on the surface of the substrate 7 on which the silver fine particles 2 are formed, for example, by sputtering deposition. Thereafter, by performing heat treatment under a predetermined temperature condition, the precursor of the gold film 3 moves to the silver fine particle 2 side due to the effect of surface tension, and adheres to the outer surface of the silver fine particle 2. Thereby, the gold film 3 covering the outer surface of the silver fine particles 2 is formed.

<Performance evaluation>
Hereinafter, the point that the light enhancement effect can be stably realized by the light enhancement element 1 of the present embodiment will be described with reference to Examples.

Example 1
A slide glass of several cm square is prepared as the substrate 7. Then, a large number of silver fine particles 2 dispersed and arranged independently of each other were formed on the surface of the glass slide by depositing a silver fine particle film using a direct current sputtering vapor deposition method. The silver fine particles 2 in the silver fine particle monolayer film have a particle size of 40 to 100 nm, a particle thickness (height) of 5 to 30 nm, and a density of the silver fine particles 2 of 10 ¹⁰ to 10 ¹¹ particles / cm ² .

  Next, a gold thin film having a thickness of 1 nm or more and 5 nm or less is deposited on the surface of the slide glass on which the silver fine particles 2 are formed by using a direct current sputtering deposition method. Furthermore, annealing is performed at about 200 ° C. ± 10 ° C. in the atmosphere for 5 to 10 minutes, and the gold thin film deposited on the glass surface in the gaps between the many silver fine particles 2 is moved to the silver fine particle 2 side. Thereby, a fine particle layer having a half core shell type structure in which the outer surface of the silver fine particles 2 was coated with a gold film 3 having a thickness of 1 nm to 5 nm was produced.

  The annealing time and annealing temperature are set under conditions such that the gold thin film does not remain on the glass surface in the gaps between the many silver fine particles 2 and the silver fine particles 2 and the gold thin film are not alloyed. did. In order to move the gold thin film toward the silver fine particles 2 in a short time, it is effective to set the annealing temperature high. However, if the temperature is too high, the gold thin film and the silver fine particles 2 are alloyed. Therefore, in the above embodiment, a temperature setting of about 200 ° C. ± 10 ° C. is set as a temperature at which the gold thin film can be moved to the silver fine particle 2 side in a short time of about 5 to 10 minutes under a temperature condition where alloying is not performed. did.

(Comparative Example 1)
FIG. 2A shows a schematic configuration of the element 21 prepared as the first comparative example. The element 21 of Comparative Example 1 was produced by the same method as that of Example 1 except that the gold film 3 was not formed.

(Comparative Example 2)
FIG. 2B shows a schematic configuration of the element 22 prepared as Comparative Example 2. The element 22 of Comparative Example 2 was produced by depositing a gold thin film on the entire surface of the substrate 7 on which the silver fine particles 2 were formed. That is, compared with the structure of Example 1 shown in FIG. 1, the point by which the gold film 3 is formed also on the board | substrate 7 of the clearance gap between many silver fine particles 2 differs.

(Method of verification)
Next, a performance verification method for each element (1, 21, 22) manufactured as Example 1, Comparative Example 1, and Comparative Example 2 will be described. Each element was immersed in a 0.2 mol / L NaCl aqueous solution (concentration about twice that of physiological saline) at a temperature of 40 ° C. for an arbitrary time, and then washed with running pure water. Then, at each elapsed time, a spin solution of a diluted ethanol solution (100 μmol / L) of rhodamine 6G dye (Rh6G: luminescence quantum yield of about 1) is spin-coated at 3000 revolutions on the surface of the element, so that the dye molecule is placed on the surface of the element. It was made to carry on. The relationship between the density of dye molecules supported on the surface of the light enhancement element 1 and the dye concentration of the solution used for spin coating is that the amount of dye molecules supported is 3 when the concentration of rhodamine 6G dye is 1 μM. × 10 ¹¹ pieces / cm ²

  And the intensity | strength of the Raman scattered light emitted from a sample (pigment molecule | numerator) by irradiating excitation light with respect to each element was measured with the measuring apparatus shown in FIG. FIG. 3 is a conceptual diagram of a measuring apparatus for verifying the performance of the light enhancement element. A light source unit 41 is configured by an excitation light source 50 and a filter 51 configured by a He—Ne laser (wavelength 632.8 nm) with an output of less than 1 mW, and excitation light is incident on the light enhancement element 1 from the light source unit 41 to enhance the light. Raman scattered light from the dye molecules carried on the surface of the element 1 is received by the light receiving unit 43. The light receiving unit 43 is configured by a photodetector 55 including a condenser lens 52, a filter 53, a light receiving head 54, and an electronically cooled diode array.

More specifically, the light emitted from the excitation light source 50 composed of a He—Ne laser (wavelength 632.8 nm) is not condensed (energy density is about 30 mW / cm ² ) or decondensed (energy) through the filter 51. (Density: about 10 mW / cm ² or less) The excitation light is incident on the light enhancement element 1 at an angle of about 45 °. Then, the light scattered in the 90 ° angle direction by the dye molecules carried on the light enhancement element 1 was condensed by the condenser lens 52 onto the light receiving head 54 of the photodetector 55 via the filter 53.

FIG. 4 is an example of a Raman spectrum measured by the light receiving unit 43 by irradiating the element with excitation light. A peak at 1510 cm ⁻¹ attributed to the rhodamine 6G molecule was taken out as a representative value and used as an index of Raman intensity. At this time, since Raman was included in the Raman spectrum as a background, it was subtracted assuming a straight line. In the example of FIG. 4, the Raman scattered light intensity is about 500 cps. In the verification based on the following examples and comparative examples, the relationship between the signal intensity and the treatment time of the NaCl aqueous solution is measured based on the peak of 1510 cm ⁻¹ .

(inspection result)
When the element 21 of Comparative Example 1 was immersed in a 0.2 mol / L NaCl aqueous solution (40 ° C.), silver corrosion that could be easily discerned with the naked eye immediately started, and the silver fine particles 2 on the substrate 7 immediately dissolved. The Raman signal could not be detected.

FIG. 5A shows the relationship between the signal intensity of the Raman spectrum received by the light receiving unit when the light enhancement element 1 of Example 1 is irradiated with excitation light and the NaCl aqueous solution treatment time. FIG. 5B shows the relationship between the signal intensity of the Raman spectrum received by the light receiving unit when the element 22 of Comparative Example 2 is irradiated with excitation light and the NaCl aqueous solution treatment time. In the graph of FIG. 5, the vertical axis indicates the Raman scattering intensity (cps) of 1510 cm ⁻¹ (see FIG. 4), and the horizontal axis indicates the treatment time of the 0.2 mol / L NaCl aqueous solution (40 ° C.).

  When the element 22 of Comparative Example 2 is immersed in a 0.2 mol / L NaCl aqueous solution (40 ° C.), corrosion of the film that can be easily discerned with the naked eye starts with immersion for about 5 minutes, and almost complete after about 15 minutes immersion. Corrosion progressed, and the silver fine particle 2 film was lost from the substrate 7 at this point. As shown in FIG. 5B, the enhanced Raman signal lasts for 15 minutes, which coincides with the time when the silver fine particle 2 film is lost.

  On the other hand, when the light enhancement element 1 of Example 1 is immersed in a 0.2 mol / L NaCl aqueous solution (40 ° C.), an extremely longer time (about 5 hours) elapses than the case of the element 22 of Comparative Example 2. At this stage, corrosion of the film, which can be easily identified with the naked eye, began. As shown in FIG. 5A, the enhanced Raman signal is still maintained even after 5 hours. Although not shown in FIG. 5 (a), it was 10 hours after the start of the experiment that the enhanced Raman signal was not completely confirmed.

  5A and 5B, it can be seen that the intensity of the enhanced Raman signal is higher in Example 1 than in Comparative Example 2.

  In the case of an element in which the gold film 3 is not formed on the silver fine particles 2 as in Comparative Example 1 (element 21), when an aqueous solution containing halide ions is immersed in the element, the silver fine particles 2 are directly applied to the halide ions. It will be exposed. For this reason, it is considered that the silver fine particles 2 immediately reacted with halide ions, dissolved and desorbed from the substrate 7, and lost the light enhancement effect. That is, it can be said that a biological sample containing halide ions cannot be inspected using such an element 21.

  In Comparative Example 2 (Element 22), resistance to halide ions is increased as compared with Comparative Example 1. This is because the gold film 3 composed of gold that is chemically more stable than silver is formed around the silver fine particles 2, so that the halide ions proceed to the silver fine particle 2 side as compared with Comparative Example 1. This is probably because it takes time.

  In Example 1 (light enhancement element 1), resistance to halide ions is further increased as compared with Comparative Example 2. This is because, in the manufacturing process of Example 1, the annealing process was performed to move the gold thin film to the silver fine particle 2 side, and as a result, the outer surface of the silver fine particle 2 was particularly close to the surface of the substrate 7. This is because the gold film 3 having a sufficient thickness is also formed on the outer surface having an angle (region 2A: see FIG. 1).

  On the other hand, in Comparative Example 2, only a gold thin film was deposited on the entire surface, and the annealing process performed in the manufacturing process of Example 1 was not performed. For this reason, with respect to the outer surface of the silver fine particles 2, the gold film 3 having a certain thickness is formed on a surface substantially parallel to the surface of the substrate 7, but has an angle close to perpendicular to the surface of the substrate 7. Only an extremely thin gold film 3 is formed on the outer surface (region 2A: see FIG. 2 (b)), or in some cases, the gold film 3 is hardly formed, and the outer surface of the silver fine particles 2 is substantially not formed. It is inferred that the surface is exposed. For this reason, in the element 22 of Comparative Example 2, when immersed in the NaCl aqueous solution, halide ions proceed from the portion of the region 2A to the silver fine particle 2 side in a short time, and as a result, the light enhancement of Example 1 It is considered that the resistance to halide ions is lower than that of element 1.

  Further, in the element 22 of the comparative example 2, the gold film 3 is also formed in the region on the substrate 7 located in the gaps between the many silver fine particles 2. Gold, together with silver, is a material that has an enhanced Raman effect, but its effect is lower than silver. For this reason, it is considered that the Raman enhancement effect is lower than that of the light enhancement element 1 of Example 1 due to the presence of the gold film 3 located in the gap between the silver fine particles 2.

  That is, as in the light enhancement element 1 of the first embodiment, the gold film 3 is formed so as to cover the outer surface of each of the many silver fine particles 2, and further, in the region of the gap between the many silver fine particles 2. By adopting a configuration in which the gold film 3 is not formed, a high Raman enhancement effect can be maintained for a long time. Therefore, according to such a light enhancement element 1, it is possible to inspect a biological sample stably. Moreover, since it is covered with the gold film 3, it can be protected from the oxidation reaction caused by the silver fine particles 2 being exposed to the atmosphere.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to the drawings. In addition, about the component same as 1st Embodiment, the same code | symbol is attached | subjected on drawing, and description is abbreviate | omitted.

<Element structure>
FIG. 6 is a schematic diagram illustrating the configuration of the light enhancement element of the second embodiment. The light enhancement element 1A shown in FIG. 6 further includes a protective layer 11 in addition to the element 1 of the first embodiment.

  The protective layer 11 is formed in the upper layer of the enhanced electromagnetic field forming layer 9 including the surface of the substrate 7 exposed in the gaps between the many silver fine particles 2. Examples of the material constituting the protective layer 11 include silicon oxide, titanium oxide, cerium oxide, boron oxide, phosphorus oxide, magnesium oxide, calcium oxide, aluminum oxide, gallium oxide, germanium oxide, and zinc oxide.

The average thickness of the protective layer 11 is preferably 50 to 250 nm, for example. In particular, when the thickness of the protective layer 11 is 85 nm or more, resistance to halide ions (for example, Cl ⁻ ) can be further increased. This point will be described later with reference to an embodiment.

<Production method>
After manufacturing the light enhancement element 1 of the first embodiment, the outer surface of the enhanced electromagnetic field forming layer 9 including the surface of the substrate 7 exposed in the gaps between the many silver fine particles 2 is deposited on the outer surface of the gold film 3 by vapor deposition. The protective layer 11 having a columnar structure is formed by growing the protective layer in the thickness direction starting from the silver fine particles 2 covered with silver. The thickness of the protective layer 11 can be adjusted by appropriately changing the growth conditions and time. Moreover, as a formation method of the protective layer 11, methods, such as a radio frequency (RF) sputter vapor deposition method, an electron beam vapor deposition method, or an electron cyclotron resonance (ECR) sputter vapor deposition method, can be selected suitably and can be utilized.

<Performance evaluation>
Hereinafter, the fact that the light enhancement effect can be stably realized by the light enhancement element 1A of the present embodiment will be described with reference to examples.

(Example 2)
A light enhancement element 1 was produced in the same manner as in Example 1. Thereafter, using an RF sputtering apparatus “RFS-200 type” (manufactured by Ulvac), sputtering is performed under the following conditions using silicon oxide (SiO ₂ ) as a target, whereby the substrate exposed in the gaps between the many silver fine particles 2. On the surface of the enhanced electromagnetic field forming layer 9 including the surface of 7, a protective layer 11 having a thickness of 100 nm was formed to produce a light enhancing element 1A.

The sputtering conditions are as follows.
-Distance from the target to the surface of the enhanced electromagnetic field forming layer 9: 45 mm
・ Atmosphere: Ar 3.0Pa (during discharge)
・ Discharge output: 100W
・ RF frequency: 13.6MHz
-Growth rate of the protective layer 11: 10 nm / min

(Comparative Example 3)
FIG. 7A shows a schematic configuration of an element 21A prepared as Comparative Example 3. The element 21A of Comparative Example 3 was produced by forming the protective layer 11 by the same method as that of Example 2 with respect to the element 21 of Comparative Example 1.

(Comparative Example 4)
FIG. 7B shows a schematic configuration of an element 22A prepared as Comparative Example 4. The element 22A of Comparative Example 4 was produced by forming the protective layer 11 with respect to the element 22 of Comparative Example 2 by the same method as in Example 2.

(Method of verification)
Verification was performed by the same method as described above in the first embodiment.

(inspection result)
When the element 22A of Comparative Example 4 was immersed in a 0.2 mol / L NaCl aqueous solution (40 ° C.), the silver fine particles 2 were peeled off from the substrate 7 together with the protective layer 11 immediately. The Raman signal could not be detected.

FIG. 8A shows the relationship between the signal intensity of the Raman spectrum received by the light receiving unit when the light enhancement element 1A of Example 2 is irradiated with excitation light and the NaCl aqueous solution treatment time. FIG. 8B shows the relationship between the signal intensity of the Raman spectrum received by the light receiving portion when the element 21A of Comparative Example 3 is irradiated with excitation light and the NaCl aqueous solution treatment time. In the graph of FIG. 8, the vertical axis of 1510 cm ⁻¹ indicates the Raman scattering intensity (cps) (see FIG. 4), and the horizontal axis of the 0.2 mol / L NaCl aqueous solution (40 ° C.) is the same as the graph of FIG. 5. Indicates processing time.

  The element 21A of Comparative Example 3 dropped to about ½ of the maximum Raman intensity in about 2 hours after starting to be immersed in a 0.2 mol / L NaCl aqueous solution (40 ° C.), and about 4 hours. Decreased to about 1/3. If the time until the Raman intensity decreases to ½ of the maximum value of Raman intensity is defined as the lifetime, the lifetime of the element 21A of Comparative Example 3 is determined to be about 2 hours.

  On the other hand, when the light enhancement element 1A of Example 2 was immersed in a 0.2 mol / L NaCl aqueous solution (40 ° C.), the Raman intensity reached a maximum value after about 40 hours had elapsed since the start of the immersion. Reduced to 1/2. Further, even after about 80 hours have passed since the start of immersion, the Raman intensity of 1/3 of the maximum value is still realized. Further, comparing FIG. 5A corresponding to the measurement result of Example 1 and FIG. 8A corresponding to the measurement result of Example 2, the Raman intensity itself is higher in Example 2 than in Example 1. It can be seen that the lifetime is very long.

  When the protective layer 11 is formed in the upper layer of the element 22 having the gold film 3 formed on the entire surface as in the comparative example 4 (element 22A), the protective layer 11 ( The region 11A portion (see FIG. 7B) is also formed on the upper surface of the gold film 3 without being formed on the surface of the substrate 7. In general, adhesion (bonding force) between many substrates (surface) or the protective film and particularly gold is poor, and as a result, when the protective layer 11 is formed, between the gold film 3 and the protective layer 11. It is considered that residual stress is generated. When the element 22A is immersed in a NaCl aqueous solution in such a state, the stress is released by the action of the ionic species that have entered through a slight gap, and as a result, the protective layer 11 is immediately separated from the gold film 3. Conceivable.

  Further, since the protective layer 11 is much thicker than the silver fine particles 2 and the gold film 3, the substrate 7 is pushed out to the protective layer 11 during the peeling process of the protective layer 11 from the gold film 3. It is considered that both the gold film 3 and the silver fine particles 2 having poor adhesion to the substrate 7 are detached from the substrate 7. This suggests that in the configuration of Comparative Example 4 (element 22A), the protective layer 11 is not stably formed on the substrate 7 and is formed in a state where it is easily peeled off.

  On the other hand, in Comparative Example 3 (Element 21A), the time for showing higher Raman scattered light is longer than in Comparative Example 4 (Element 22A). This is considered to be because the protective layer 11 is formed on the substrate 7 in the element 21 </ b> A, and thus the protective layer 11 does not peel from the substrate 7 even when immersed in the NaCl aqueous solution. Further, when Comparative Example 1 (element 21) and Comparative Example 3 (element 21A) are compared, silver fine particles 2 are immediately dissolved and desorbed in Comparative Example 1, whereas such a phenomenon does not occur in Comparative Example 3 for 12 hours. The Raman scattering signal can be confirmed even at the elapsed stage (see FIG. 8B). Thereby, it was suggested that the formation of the protective layer 11 as in Comparative Example 3 did not cause the halide ions contained in the NaCl aqueous solution to directly contact the silver fine particles 2 and increased the resistance to the halide ions. The

  According to the configuration of Example 2, the resistance to halide ions is higher than that of Example 1. In addition to the gold film 3 that coats the outer surface of the silver fine particles 2, the protective layer 11 is further formed, so that the effect of delaying the progress of halide ions with respect to the silver fine particles 2 can be realized. It is thought that it is because.

  Furthermore, according to the configuration of the second embodiment, the Raman scattering intensity itself is higher than that of the first embodiment. This is presumably due to the following reasons. The protective layer 11 includes a surface of the substrate 7 exposed in a space between a large number of silver fine particles 2 whose outer surface is covered with the gold film 3, and an outer surface of the silver fine particles 2 (more precisely, the silver fine particles 2). The surface of the gold film 3 covering the outer surface of the film is different from the film formation state. As a result, a so-called grain boundary occurs between the portion of the protective layer 11 deposited on the surface of the substrate 7 and the portion of the protective layer 11 deposited on the surface of the gold film 3 covering the outer surface of the silver fine particles 2, Thereby, the protective layer 11 has orientation (anisotropy). In this situation, the plasmon electric field generated on the surface of the light enhancement element 1A is not disturbed and reaches the surface of the protective layer 11 without loss.

  Therefore, according to the light enhancement element 1A of the present embodiment, it is possible to realize a function of maintaining a higher Raman enhancement effect for a long time than the light enhancement element 1 of the first embodiment.

  In the present embodiment, the protective layer 11 may be composed of an organic polymer having crystallinity (orientation). As the organic polymer, an acrylic polymer such as polymethyl methacrylate, polyvinyl alcohol, or the like can be used. In this case, the protective layer 11 is formed by dropping or applying the protective layer forming liquid onto the substrate 7 using a spin coat method, a dip coat method, a spray coat method, a slit coat method, a bar coat method, or the like. However, the spin coating method can be suitably used as a method for forming the protective layer 11 having the most uniform thickness.

  The solvent for preparing the protective layer forming liquid is appropriately selected according to the polymer used. Specifically, any material that can dissolve the polymer to be used may be used. For example, when a water-soluble polymer such as polyvinyl alcohol is used as the polymer, water can be used as the solvent. Further, when a water-insoluble polymer such as polymethyl methacrylate is used as the polymer, a protective layer forming solution can be prepared by using, for example, cyclohexanone as a solvent for preparing the polymer solution.

  The content ratio of the polymer in the protective layer forming liquid is determined by the combination of the coating method and the target protective film thickness. For example, when a polyvinyl alcohol film is formed from the aqueous solution by using a spin coating method (3000 rpm), the content of the polymer necessary for adjusting the film thickness to 100 nm is about 4.5% by mass.

[Third Embodiment]
A third embodiment of the present invention will be described with reference to the drawings. In addition, about the component same as 1st Embodiment, the same code | symbol is attached | subjected on drawing, and description is abbreviate | omitted.

  The configuration of this embodiment is different only in that a halogen element is previously contained in the protective layer 11 in the light enhancement element 1A shown in the second embodiment. As a method for adding a halogen element to the protective layer 11, a method of immersing the light enhancing element 1A in a state where the protective layer 11 is formed in an aqueous solution of a halide salt can be used. For example, when the concentration of the halide salt aqueous solution is 0.1 to 0.3 mol / L, the maximum effect can be obtained by room temperature immersion for about 5 to 30 minutes, but the concentration of the aqueous solution is higher than that. On the other hand, if it is low, the same effect can be obtained by adjusting the immersion time according to the concentration. In addition, it is preferable that the content rate of the halogen element in the protective layer 11 is 0.002 mass%-0.05 mass%.

Specific examples of the halide salt include alkali metal salts such as sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), and potassium iodide (KI), and calcium chloride (CaCl ₂ ). And alkaline earth metal salts.

  Thus, even when the light enhancement element 1A is immersed in the halide salt aqueous solution in advance, if the immersion is performed for about 5 to 30 minutes, a high Raman scattering intensity can be realized as shown in FIG. . As will be described later with reference to the verification example, the light enhancement effect can be further enhanced by preliminarily containing the halogen element in the protective layer 11.

  The following verification was performed using an element (hereinafter referred to as “Verification Example 1”) formed by containing a halogen element in the element 21A of Comparative Example 3 shown in FIG. 7A. . This element is not an element in which the gold film 3 is formed on the outer surface of the silver fine particles 2 as the light enhancement element of the present embodiment assumes. However, since the difference between the element 21A of the comparative example 3 and the element of the verification example 1 is the same as the difference between the light enhancement element 1A of the second embodiment and the light enhancement element of this embodiment, the comparative example 3 and the verification example By comparing and verifying the experimental results of 1, it is possible to verify the comparison between the light enhancement element 1A of the second embodiment and the light enhancement element of the present embodiment.

(Verification example 1)
A device 21A was produced in the same manner as in Comparative Example 3. Thereafter, the element 21A is immersed in an aqueous NaCl solution having a chloride ion concentration of 0.2 to 0.3 mol / L for about 30 minutes, and then washed with pure water and dried, whereby the protective layer 11 is filled. The device of Verification Example 1 was obtained by containing halide ions in Although the content of the halogen element contained in the protective layer 11 in the device of Verification Example 1 is difficult to determine accurately, it is estimated to be on the order of approximately 0.01% by mass.

(Method of verification)
For the element 21A of Comparative Example 3 and the element of Verification Example 1, spin molecules are coated on the surface of the protective layer 11 by spin-coating a diluted ethanol solution of rhodamine 6G dye at 3000 revolutions on the upper surface of the protective layer 11. It was supported at a density of 3 × 10 ¹¹ pieces / cm ² . Then, in the same manner as in the first embodiment and the second embodiment, the element was irradiated with excitation light, and the spectrum of Raman scattered light received by the light receiving unit 43 was measured.

(inspection result)
FIG. 9 is a graph showing Raman spectra received by the light receiving unit when each element of Comparative Example 3 and Verification Example 1 is irradiated with excitation light. In FIG. 9, the vertical axis indicates the Raman scattering intensity (cps), and the horizontal axis indicates the Raman shift (cm ⁻¹ ).

  According to FIG. 9, the verification example 1 in which the halide ions are immersed has a more remarkable Raman signal than the comparative example 3 in which the halide ions are not immersed, and the light enhancement effect is enhanced. It is suggested that

  In Verification Example 1, a NaCl aqueous solution having a chloride ion concentration of 0.2 to 0.3 mol / L was immersed, but instead, the chloride ion concentration was 0.2 mol / L. An element formed by immersing an aqueous potassium chloride solution, an element formed by immersing an aqueous sodium bromide solution having a bromide ion concentration of 0.2 mol / L, and an iodide having an iodide ion concentration of 0.2 mol / L As a result of performing the same measurement on an element formed by immersing a potassium aqueous solution and an element formed by immersing a calcium chloride aqueous solution having a chloride ion concentration of 0.2 mol / L, the same results were obtained. As compared with the above, the verification example 1 was able to receive higher Raman scattered light. On the other hand, when the same measurement was performed on an element formed by immersing a sodium sulfate aqueous solution having a sulfate ion concentration of 0.2 mol / L instead of a sodium chloride aqueous solution, the intensity of the received Raman scattered light was low. there were.

  Thereby, it can be seen that when a halogen element is added to the protective layer 11, the light enhancement effect can be further enhanced. That is, it is suggested that the light enhancement element of this embodiment in which the protective layer 11 contains a halogen element has a higher light enhancement effect than the light enhancement element 1A of the second embodiment. And also in the light enhancement element of this embodiment, since the gold film 3 is formed on the outer surface of the silver fine particles 2 and the protective layer 11 is further formed thereon, Similarly, it is considered that a high light enhancement effect can be maintained for a long time.

  Even when the protective layer 11 is composed of an organic polymer having crystallinity (orientation), the light enhancement effect can be further enhanced by containing a halogen element in the same manner as described above. . In this case, as the protective layer forming liquid, a predetermined polymer and a metal salt of a halogen are dissolved in a solvent, or a polymer solution in which a predetermined polymer is dissolved in a solvent, and a halogen in the solvent. It can be prepared by mixing with a metal salt solution in which the metal salt is dissolved.

  The solvent for preparing the protective layer forming liquid is appropriately selected according to the polymer and metal salt used. Specifically, any polymer that can dissolve the polymer and metal salt used may be used. For example, when a water-soluble polymer such as polyvinyl alcohol is used as the polymer, water can be used as the solvent. When a polymer insoluble in water such as polymethyl methacrylate is used as the polymer, for example, cyclohexanone is used as a solvent for preparing the polymer solution, and water and acetone are used as the solvent for preparing the metal salt solution. A protective layer forming solution can be prepared by mixing a polymer solution and a metal salt solution using a mixed solvent. The ratio of the metal salt in the protective layer forming liquid is set according to the content ratio of the halogen element in the target protective layer 11 and the content ratio of the polymer in the protective layer forming liquid.

[Another embodiment]
Another embodiment will be described below.

  <1> In the above embodiment, when the gold film 3 is formed on the outer surface of the silver fine particles 2, it is assumed that annealing is performed under a temperature condition in which the silver fine particles 2 and the gold thin film are not alloyed. However, the present invention is not intended to exclude an element in which a part of the gold film 3 is alloyed with silver during the manufacturing process from the scope of rights.

  Similarly, in the above-described embodiment, the gold film 3 has been described as being dispersedly arranged in relation to each of the many silver fine particles 2. However, according to the present invention, the gold film 3 is formed in the region 5 between the two adjacent specific silver fine particles 2 so that the specific two silver fine particles 2 are connected by the gold film 3. It is not intended to exclude existing devices from the scope of rights.

  Further, in the above-described embodiment, the description has been given on the assumption that the gold film 3 realizes a half-core shell structure in which the outer surfaces of the many silver fine particles 2 are completely covered. However, the present invention is not intended to exclude an element in which a region not covered with the gold film 3 exists on a part of the outer surface of the silver fine particles 2 from the scope of rights.

  According to the light enhancement element of the present invention, which has a region where the gold film 3 is not formed on the substrate in the space between the many silver fine particles 2 and the gold film 3 is formed on the outer surface of the silver fine particles 2. Compared with Comparative Example 1 (Element 21) and Comparative Example 2 (Element 22), the ability to stably maintain the light enhancement effect can be enhanced. Of course, the gold film 3 is formed on the outer surface of a large number of silver fine particles 3 without being alloyed, so that the ability is further enhanced, and the gold film 3 is dispersed in relation to each of the large number of silver fine particles 2. The ability is further enhanced by the arrangement, and the ability is further enhanced by forming the gold film 3 so as to completely cover the outer surfaces of the many silver fine particles 2.

  <2> In each of the above embodiments, similarly to the element shown in FIG. 10, it may be formed in a multilayer structure that additionally includes a highly reflective layer 112 and a dielectric layer 113. In such a structure, the highly reflective layer 112 and the dielectric layer 113 are formed in this order on the surface of the substrate 7, and the enhanced electromagnetic field forming layer 9 is formed on the surface of the dielectric layer 113.

  <3> In the above embodiment, excitation light is applied to the light enhancement element (1, 1A) on which the sample is placed, and the spectral intensity of the Raman scattered light received by the light receiving unit 43 is analyzed. Explained. However, it is confirmed that the effect of enhancing fluorescence can be obtained by appropriately setting the excitation light source 50 and the sample and analyzing the fluorescence spectrum by the same method using the measuring apparatus of FIG. That is, according to the light enhancement element of the present invention, it is possible to enhance the ability to stably maintain not only the Raman scattered light but also the fluorescence enhancement effect.

DESCRIPTION OF SYMBOLS 1,1A: Light enhancement element of this invention 2: Silver fine particle 2A: Area | region 3: Gold film 5: Area | region on the board | substrate in which the gold film is not formed 7: Board | substrate 9: Enhanced electromagnetic field formation layer 11: Protection layer 11A: Area | region 21: Element of Comparative Example 21A: Element of Comparative Example 3 22: Element of Comparative Example 2 22A: Element of Comparative Example 4 41: Light Source Unit 43: Light Receiving Unit 50: Excitation Light Source 51: Filter 52: Condensing Lens 53: Filter 54: Light receiving head 55: Photo detector 100: Conventional light enhancement element 101: Conventional light enhancement element 111: Substrate 112: High reflection layer 113: Dielectric layer 114: Silver fine particle 115: Enhancement electromagnetic field forming layer 116: Gold film

Claims (10)

A light enhancement element comprising a substrate and an enhanced electromagnetic field forming layer in which a large number of silver fine particles are dispersed and arranged independently of each other on the surface of the substrate,
The enhanced electromagnetic field forming layer has a gold film on a surface that is not in contact with the substrate of each of the silver fine particles,
The light enhancement element, wherein the gold film is dispersedly arranged.   The light enhancement element according to claim 1, wherein the gold film is dispersedly arranged in association with each of the plurality of silver fine particles.   The light enhancement element according to claim 1, wherein the gold film is formed so as to completely cover a surface of each of the plurality of silver fine particles that is not in contact with the substrate.   The light enhancement element according to claim 1, wherein the gold film has a thickness of 1 nm to 5 nm.   The light enhancement element according to claim 1, further comprising a protective layer formed on the substrate and the enhanced electromagnetic field forming layer.   6. The light enhancement element according to claim 5, wherein the protective layer has a structure having an orientation in relation to the large number of metal fine particles.   The inspection method according to claim 6, wherein the protective layer is made of an inorganic substance having an orientation or a polymer of an organic substance having an orientation in relation to the large number of metal fine particles.   The inspection method according to claim 5, wherein the protective layer contains a halogen element. A method of manufacturing a light enhancement element,
Preparing a substrate (a),
A step (b) of depositing a large number of fine silver particles dispersed on the substrate;
And a step (c) of forming the gold film on a surface of each of the silver fine particles that is not in contact with the substrate by performing a heat treatment by depositing a gold film. A method for manufacturing an enhancement element.   10. The method of manufacturing a light enhancement element according to claim 9, wherein in the step (c), the heat treatment is performed under a temperature condition in which the gold film and the large number of silver fine particles are not alloyed.

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