Reflection absorption characteristic measuring method and reflection absorption characteristic evaluating method

Abstract

To provide a method for measuring reflection absorption characteristics capable of effectively utilizing plasmon coupling between metal particles and a metal layer by using a substrate having an MIM structure.SOLUTION: The method for measuring reflection absorption characteristics is provided with a step of measuring reflection absorption characteristics by localized surface plasmon resonance from a surface on the side of a metal layer 11 of an MIM structure substrate 1, by using the MIM structure substrate 1, which includes, in this order, the metal layer 11 having a thickness of less than 30 nm, an insulating film 12 provided on a surface of the metal layer 11, and metal particles 13 provided on a surface of the insulating film 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring reflection / absorption characteristics and a method for evaluating reflection / absorption characteristics. [Background technology]

[0002] In recent years, as an example of a sensor such as a biosensor, a sensor that utilizes surface plasmon resonance (SPR), which occurs when light is irradiated onto the surface of a metal such as gold or silver, has been proposed.

[0003] Surface plasmons are compressional waves based on the collective vibration of free electrons localized on a metal surface. When light is incident on a metal surface, if the conditions are such that the incident light resonates with the surface plasmons localized on the metal surface, the energy of the incident light is transferred to the metal surface. This phenomenon is called surface plasmon resonance. There are two types of surface plasmon resonance: propagation-type surface plasmon resonance, which uses a thin metal film, and localized-type surface plasmon resonance, which uses metal nanoparticles or metal nanostructures.

[0004] For example, when the surface condition of a metal changes due to the adsorption of a substance onto the metal, the refractive index near the metal surface changes, and the resonant wavelength shifts in response to this change in refractive index. Therefore, sensing can be performed based on the change in the resonant wavelength.

[0005] Patent Document 1 discloses an SPR measurement substrate and a method for manufacturing the same that does not require complex patterning techniques for controlling the arrangement of metal particles, is easy to manufacture, and enables the construction of a localized surface plasmon sensor with high detection sensitivity. Specifically, Patent Document 1 discloses an SPR measurement substrate that has a metal layer and an insulating layer formed in that order on an insulating substrate, a single-layer metal colloidal crystal made of metal particles formed on the insulating layer, the metal particles having an average particle size of 50 nm to 500 nm, and the metal particles spaced apart by 50 nm to 1000 nm. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-34543 Summary of the Invention [Problem to be solved by the invention]

[0007] In the SPR measurement substrate described in Patent Document 1, a metal-insulator-metal (MIM) structure is formed on the metal layer by a metal layer, an insulating layer, and metal particles.

[0008] When measuring reflection / absorption characteristics due to surface plasmon resonance using the SPR measurement substrate described in Patent Document 1, plasmon resonance occurs in each metal element of the substrate, but since the distance between the metal particles and the metal layer is generally smaller than the distance between the metal particles, the plasmon resonance between the metal particles and the metal layer is strongest. However, there is room for improvement in terms of effectively utilizing the plasmon coupling between the metal particles and the metal layer.

[0009] The present invention has been made to solve the above problems, and aims to provide a method for measuring reflection / absorption characteristics using a substrate having an MIM structure, which can effectively utilize plasmon coupling between metal particles and a metal layer. Another aim of the present invention is to provide a method for evaluating reflection / absorption characteristics using the above measurement method. [Means for solving the problem]

[0010] The reflection / absorption characteristic measuring method of the present invention includes a step of measuring the reflection / absorption characteristics due to Localized Surface Plasmon Resonance (LSPR) from the surface of the MIM structure substrate facing the metal layer, using an MIM structure substrate including, in this order, a metal layer having a thickness of less than 30 nm, an insulating film provided on the surface of the metal layer, and metal particles provided on the surface of the insulating film.

[0011] The reflection / absorption characteristic evaluation method of the present invention comprises a step of evaluating changes in reflection / absorption characteristics using the reflection / absorption characteristic measurement method of the present invention. [Effects of the Invention]

[0012] According to the present invention, a method for measuring reflection / absorption characteristics using a substrate having an MIM structure can be provided, which can effectively utilize plasmon coupling between metal particles and a metal layer.Furthermore, according to the present invention, a method for evaluating reflection / absorption characteristics using the above measurement method can be provided. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a reflection / absorption characteristic measuring method according to an embodiment within the scope of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of a method for measuring reflection / absorption characteristics according to a comparative example outside the scope of the present invention. [Figure 3] FIG. 3 is a perspective view schematically showing an example of an MIM structure substrate. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an example of an MIM structure substrate. [Figure 5] FIG. 5 is a perspective view schematically showing another example of an MIM structure substrate. [Figure 6] FIG. 6 is a plan view schematically showing yet another example of an MIM structure substrate. [Figure 7] FIG. 7 is an example of a graph showing the results of reflectance obtained using a reflection / absorption characteristic measuring method according to an example within the scope of the present invention. [Figure 8] FIG. 8 is an example of a graph showing the results of reflectance obtained using a reflection / absorption characteristic measuring method according to a comparative example outside the scope of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The reflection / absorption characteristic measuring method and the reflection / absorption characteristic evaluation method of the present invention will be described below. However, the present invention is not limited to the following embodiments and can be appropriately modified and applied within the scope of the present invention. A combination of two or more of the individual preferred configurations of the present invention described in the following embodiments also constitutes the present invention.

[0015] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, and other scales may differ from those of the actual product. In the drawings, the same or equivalent parts will be designated by the same reference numerals. In addition, the same elements will be designated by the same reference numerals in each drawing, and duplicate explanations will be omitted.

[0016] The reflection / absorption characteristic measuring method of the present invention is characterized in that it uses an MIM structure substrate including, in this order, a metal layer having a thickness of less than 30 nm, an insulating film provided on the surface of the metal layer, and metal particles provided on the surface of the insulating film, and measures the reflection / absorption characteristics due to localized surface plasmon resonance from the surface of the MIM structure substrate facing the metal layer.

[0017] Furthermore, the reflection / absorption characteristic evaluation method of the present invention is characterized in that a change in the reflection / absorption characteristic is evaluated using the reflection / absorption characteristic measurement method of the present invention.

[0018] As mentioned above, when the surface state of a metal changes due to, for example, the adsorption of a substance onto the metal, the refractive index near the metal surface changes, and the resonance wavelength shifts accordingly. Therefore, by measuring the reflection / absorption characteristics due to localized surface plasmon resonance using an MIM structure substrate and evaluating the changes in the reflection / absorption characteristics, it can be used as a sensor such as a biosensor.

[0019] In the reflection / absorption property evaluation method of the present invention, the change in the reflection / absorption property may be evaluated by evaluating a change in the resonance peak shift, a change in the resonance peak depth, or both. The resonance peak shift may be a shift to a longer wavelength side or a shift to a shorter wavelength side.

[0020] FIG. 1 is a schematic diagram showing an example of a reflection / absorption characteristic measuring method according to an embodiment within the scope of the present invention.

[0021] The MIM structure substrate 1 shown in FIG. 1 includes a metal layer 11 having a thickness of less than 30 nm, an insulating film 12 provided on the surface of the metal layer 11, and metal particles 13 provided on the surface of the insulating film 12, in this order.

[0022] 1, the MIM structure substrate 1 preferably further includes an insulating substrate 10. In this case, a metal layer 11 is provided between the insulating substrate 10 and an insulating film 12. The insulating substrate 10 is, for example, a glass substrate.

[0023] In the embodiment shown in FIG. 1, a measurement probe 20 is disposed on the surface of the MIM structure substrate 1 facing the metal layer 11 (the bottom surface in FIG. 1). An optical fiber 21 guides light from a light source (not shown) to the measurement probe 20, which then irradiates the metal layer 11 of the MIM structure substrate 1 as incident light LI. The optical fiber 21 receives light reflected by the metal layer 11 as reflected light LR and guides it to a spectrometer (not shown). The reflected light LR separated by the spectrometer is detected by a photodetector. The reflection / absorption characteristics are measured from the light detected by the photodetector. In this way, in the embodiment shown in FIG. 1, the reflection / absorption characteristics are measured from the surface of the MIM structure substrate 1 facing the metal layer 11 (the bottom surface in FIG. 1). Furthermore, by evaluating changes in the reflection / absorption characteristics, the MIM structure substrate 1 can be used as a sensor.

[0024] FIG. 2 is a schematic diagram showing an example of a method for measuring reflection / absorption characteristics according to a comparative example outside the scope of the present invention.

[0025] In the comparative example shown in FIG. 2, a measurement probe 20 is disposed on the surface of the MIM structure substrate 1 facing the metal particles 13 (top surface in FIG. 2). An optical fiber 21 guides light from a light source (not shown) to the measurement probe 20, which then irradiates the metal particles 13 or the metal layer 11 of the MIM structure substrate 1 as incident light LI. The optical fiber 21 receives light reflected by the metal particles 13 or the metal layer 11 as reflected light LR and guides it to a spectrometer (not shown). The reflected light LR dispersed by the spectrometer is detected by a photodetector. The reflection and absorption characteristics are measured from the light detected by the photodetector. Thus, in the comparative example shown in FIG. 2, the reflection and absorption characteristics are measured from the surface of the MIM structure substrate 1 facing the metal particles 13 (top surface in FIG. 2). Furthermore, by evaluating changes in the reflection and absorption characteristics, the MIM structure substrate 1 can be used as a sensor.

[0026] As described above, when measuring the reflection / absorption characteristics due to surface plasmon resonance, plasmon resonance occurs in each metal element of the MIM structure substrate 1, but since the distance between the metal particles 13 and the metal layer 11 is generally smaller than the distance between the metal particles 13, the plasmon resonance between the metal particles 13 and the metal layer 11 is strongest.

[0027] However, it was found that the method of measuring the reflection / absorption characteristics from the surface of the MIM structure substrate 1 on the metal particle 13 side, as in the comparative example shown in Figure 2, does not fully utilize the plasmon coupling between the metal particles 13 and the metal layer 11. The reason for this is presumably that the plasmon resonance between the metal particles 13 and the metal layer 11 is attenuated by the influence of the metal particles 13.

[0028] In contrast, in the example shown in Figure 1, in which the thickness of the metal layer 11 is reduced to less than 30 nm and the reflection / absorption characteristics are measured from the surface of the MIM structure substrate 1 facing the metal layer 11, the method is less affected by the metal particles 13 than in the comparative example shown in Figure 2, and therefore the plasmon coupling between the metal particles 13 and the metal layer 11 can be effectively utilized.

[0029] Fig. 3 is a perspective view schematically showing an example of an MIM structure substrate, and Fig. 4 is a cross-sectional view schematically showing an example of an MIM structure substrate.

[0030] The MIM structure substrate 1 shown in FIGS. 3 and 4 has a common configuration with the MIM structure substrate 1 shown in FIG.

[0031] When the MIM structure substrate 1 includes an insulating substrate 10, the metal layer 11 is preferably provided on one main surface (the upper surface in FIGS. 3 and 4) of the insulating substrate 10. The metal layer 11 may be provided on the entire one main surface of the insulating substrate 10, or may be provided on a part of the one main surface of the insulating substrate 10.

[0032] The metal layer 11 is, for example, a metal film, which can be formed by a method such as vapor deposition, sputtering, or chemical plating.

[0033] The metal layer 11 is made of, for example, gold. The type of metal layer 11 is preferably a noble metal such as gold or silver that can exhibit strong plasmon resonance.

[0034] To facilitate measurement of the reflection / absorption characteristics from the surface of the MIM structure substrate 1 on the metal layer 11 side, the thickness of the metal layer 11 is less than 30 nm, preferably 25 nm or less, and more preferably 20 nm or less. On the other hand, the thickness of the metal layer 11 is, for example, 3 nm or more, preferably 5 nm or more, and more preferably 10 nm or more.

[0035] The insulating film 12 is provided on the surface of the metal layer 11. When the MIM structure substrate 1 includes an insulating substrate 10, the insulating film 12 is provided on the surface of the metal layer 11 opposite to the insulating substrate 10. The insulating film 12 may be provided on the entire surface of the metal layer 11, or on a part of the surface of the metal layer 11. The insulating film 12 may be provided on the main surface of the insulating substrate 10 on the side where the metal layer 11 is provided (the top surface in FIGS. 3 and 4), as well as on the main surface of the insulating substrate 10 on the side where the metal layer 11 is not provided (the bottom surface in FIGS. 3 and 4).

[0036] The insulating film 12 preferably has a surface with a positive or negative charge.

[0037] 4, the surface of the insulating film 12 has a positive charge. An example of the insulating film 12 having a positive charge is a silica film having an amino group.

[0038] The insulating film 12 having a positive charge can be formed, for example, by forming a silica layer on the surface of the metal layer 11 using a first silane coupling agent having a mercapto group such as 3-mercaptopropyltrimethoxysilane (MEPTMS), and then bonding an amino group to the silane layer using a second silane coupling agent such as 3-aminopropyltriethoxysilane (APTES), or by adsorbing a polymer having a cationic group such as polyethyleneimine or poly(2-vinylpyridine) onto the surface.

[0039] The thickness of the insulating film 12 is not particularly limited, and may be smaller than the thickness of the metal layer 11, may be the same as the thickness of the metal layer 11, or may be larger than the thickness of the metal layer 11.

[0040] The metal particles 13 are provided on the surface of the insulating film 12. Specifically, the metal particles 13 are provided on the surface of the insulating film 12 opposite to the metal layer 11. The metal particles 13 may be provided on the entire surface of the insulating film 12, or may be provided on only a part of the surface of the insulating film 12.

[0041] The metal particles 13 are preferably arranged in a single layer on the surface of the insulating film 12. In other words, the metal particles 13 are preferably arranged two-dimensionally on the surface of the insulating film 12. In this case, it is sufficient that the metal particles 13 are arranged in a single layer in at least a partial region of the surface of the insulating film 12.

[0042] For example, when observing the MIM structure substrate 1 using a microscope such as an optical microscope or an electron microscope, if the metal particles 13 are observed only when the height of the sample stage is set to a certain height, it can be confirmed that the metal particles 13 are arranged in a single layer on the surface of the insulating film 12.

[0043] In the MIM structure substrate 1 shown in Figures 3 and 4, when a metal layer 11 is provided on a portion of one main surface of the insulating substrate 10, it is preferable that the metal particles 13 are selectively provided only on the surface of the insulating film 12 on the metal layer 11.

[0044] The metal particles 13 preferably have a charge of the opposite sign to the surface charge of the insulating film 12. In the example shown in Figure 4, the surfaces of the metal particles 13 have a negative charge.

[0045] 4, for example, when the surface of insulating film 12 has a positive charge and the surfaces of metal particles 13 have a negative charge, metal particles 13 are arranged at intervals on the surface of insulating film 12 due to electrostatic repulsion acting between metal particles 13. On the other hand, since the surface of insulating film 12 has a positive charge, negatively charged metal particles 13 are adsorbed to the surface of insulating film 12 by electrostatic attraction.

[0046] 3, two-dimensional colloidal crystals in which metal particles 13 are regularly arranged are preferably formed on the surface of the insulating film 12. In this case, the metal particles 13 are preferably arranged two-dimensionally and regularly on the surface of the insulating film 12 with spaces between them.

[0047] The metal particles 13 are, for example, gold particles. The type of metal particles 13 is preferably a noble metal such as gold or silver, which can exhibit strong plasmon resonance.

[0048] The average particle size of the metal particles 13 is not particularly limited, but is, for example, 50 nm or more and 200 nm or less. The average particle size of the metal particles 13 may be 100 nm or more, or may be 150 nm or less.

[0049] The average particle size of the metal particles 13 is measured as the average value of particle sizes (diameters) of 100 to 200 metal particles 13 when the MIM structure substrate 1 is viewed in a plan view in the thickness direction.

[0050] The distance between the metal particles 13 is not particularly limited.

[0051] The distance between the metal particles 13 is measured as the average value of the interparticle distances of 100 to 200 metal particles 13 in plan view of the MIM structure substrate 1 in the thickness direction.

[0052] FIG. 5 is a perspective view schematically showing another example of an MIM structure substrate.

[0053] The MIM structure substrate 1A shown in FIG. 5 has a common configuration with the MIM structure substrate 1 shown in FIG. 3, except that it further includes a base metal layer 14 provided on the surface of the insulating substrate 10 on the metal layer 11 side.

[0054] The metal underlayer 14 is, for example, a metal film, which can be formed by a method such as vapor deposition, sputtering, or chemical plating.

[0055] The metal base layer 14 is made of, for example, chromium (Cr), titanium (Ti), or aluminum (Al). These metals may be a single metal or an alloy. The type of the metal base layer 14 is preferably different from the type of the metal layer 11.

[0056] The thickness of the metal base layer 14 is preferably smaller than the thickness of the metal layer 11. The thickness of the metal base layer 14 is, for example, 3 nm or less, and preferably 1 nm or less. On the other hand, the lower limit of the thickness of the metal base layer 14 is not particularly limited, but is, for example, 0.1 nm or more.

[0057] FIG. 6 is a plan view schematically showing yet another example of an MIM structure substrate.

[0058] As in the MIM structure substrate 1B shown in FIG. 6, the metal particles 13 may be in a polycrystalline state where regions (domains) in which the metal particles 13 are regularly arranged two-dimensionally change direction and aggregate.

[0059] When a two-dimensional colloidal crystal of metal particles 13 is formed on the surface of insulating film 12, there may be only a region where metal particles 13 are regularly arranged, or in addition to the region where metal particles 13 are regularly arranged, there may be a region where metal particles 13 are irregularly arranged.

[0060] The present specification discloses the following:

[0061] <1> A method for measuring reflection and absorption characteristics, comprising a step of measuring reflection and absorption characteristics due to localized surface plasmon resonance from a surface of the MIM structure substrate that faces the metal layer, the surface of the MIM structure substrate including, in this order, a metal layer having a thickness of less than 30 nm, an insulating film provided on the surface of the metal layer, and metal particles provided on the surface of the insulating film.

[0062] <2> The thickness of the metal layer is 25 nm or less. <1> The reflection / absorption characteristic measuring method according to claim 1.

[0063] <3> The thickness of the metal layer is 5 nm or more and 25 nm or less. <1> or <2> The reflection / absorption characteristic measuring method according to claim 1.

[0064] <4> the metal layer is made of gold, The metal particles are gold particles. <1> ~ <3> 10. The reflection / absorption characteristic measuring method according to claim 9, wherein the reflection / absorption characteristic measuring method is a reflection / absorption characteristic measuring method.

[0065] <5> The MIM structure substrate further includes an insulating substrate, the metal layer is provided between the insulating substrate and the insulating film; <1> ~ <4> 10. The reflection / absorption characteristic measuring method according to claim 9, wherein the reflection / absorption characteristic measuring method is a reflection / absorption characteristic measuring method.

[0066] <6> The MIM structure substrate further includes a base metal layer provided on the surface of the insulating substrate on the metal layer side. <5> The reflection / absorption characteristic measuring method according to claim 1.

[0067] <7> The thickness of the base metal layer is 3 nm or less. <6> The reflection / absorption characteristic measuring method according to claim 1.

[0068] <8> The thickness of the base metal layer is 1 nm or less. <6> or <7> The reflection / absorption characteristic measuring method according to claim 1.

[0069] <9> The base metal layer is made of chromium, titanium, or aluminum. <6> ~ <8> 10. The reflection / absorption characteristic measuring method according to claim 9, wherein the reflection / absorption characteristic measuring method is a reflection / absorption characteristic measuring method.

[0070] <10> The average particle size of the metal particles is 50 nm or more and 200 nm or less. <1> ~ <9> 10. The reflection / absorption characteristic measuring method according to claim 9, wherein the reflection / absorption characteristic measuring method is a reflection / absorption characteristic measuring method.

[0071] <11> <1> ~ <10> 10. A reflection / absorption characteristic evaluation method, comprising: evaluating a change in the reflection / absorption characteristic by using the reflection / absorption characteristic measurement method according to any one of the above items. [Example]

[0072] Hereinafter, examples will be given that more specifically disclose the reflection / absorption characteristic measuring method and reflection / absorption characteristic evaluating method of the present invention, but the present invention is not limited to these examples.

[0073] The refractive index of the ethylene glycol-water mixed solvent was measured and the reflectance was calculated using the method of the example shown in Fig. 1 or the method of the comparative example shown in Fig. 2. The refractive index of water was 1.33, and the refractive index of ethylene glycol was 1.45, and the refractive index was adjusted by changing the concentration of ethylene glycol.

[0074] Fig. 7 is an example of a graph showing the results of reflectance measurements using a reflection / absorption characteristic measurement method according to an example within the scope of the present invention, and Fig. 8 is an example of a graph showing the results of reflectance measurements using a reflection / absorption characteristic measurement method according to a comparative example outside the scope of the present invention.

[0075] 7 and 8, a resonance peak due to localized surface plasmon resonance can be confirmed in both methods. It can also be confirmed that the resonance peak shifts due to the change in refractive index accompanying the change in the ethylene glycol (EG) ratio.

[0076] In particular, the amount of shift in the resonance peak is larger in Fig. 7 than in Fig. 8. Comparing Fig. 7 and Fig. 8, it is considered that the method of the example shown in Fig. 1 has improved measurement sensitivity compared to the method of the comparative example shown in Fig. 2. [Explanation of symbols]

[0077] 1, 1A, 1B MIM structure board 10. Insulating substrate 11 Metal layer 12 insulating film 13 Metal particles 14 Undercoat metal layer 20 Measuring Probes 21 Optical Fiber LI incident light LR reflected light

Claims

1. A method for measuring reflection and absorption characteristics, comprising a step of measuring reflection and absorption characteristics due to localized surface plasmon resonance from a surface of the MIM structure substrate facing the metal layer, the surface of the MIM structure substrate including, in this order, a metal layer having a thickness of less than 30 nm, an insulating film provided on the surface of the metal layer, and metal particles provided on the surface of the insulating film.

2. 2. The reflection / absorption characteristic measuring method according to claim 1, wherein the thickness of the metal layer is 25 nm or less.

3. 2. The reflection / absorption characteristic measuring method according to claim 1, wherein the thickness of the metal layer is 5 nm or more and 25 nm or less.

4. the metal layer is made of gold; 2. The reflection / absorption characteristic measuring method according to claim 1, wherein the metal particles are gold particles.

5. The MIM structure substrate further includes an insulating substrate; 5. The reflection / absorption characteristic measuring method according to claim 1, wherein the metal layer is provided between the insulating substrate and the insulating film.

6. 6. The reflection / absorption characteristic measuring method according to claim 5, wherein the MIM structure substrate further includes an underlying metal layer provided on the surface of the insulating substrate on the side of the metal layer.

7. 7. The reflection / absorption characteristic measuring method according to claim 6, wherein the thickness of the underlying metal layer is 3 nm or less.

8. 7. The reflection / absorption characteristic measuring method according to claim 6, wherein the thickness of the underlying metal layer is 1 nm or less.

9. 7. The reflection / absorption characteristic measuring method according to claim 6, wherein the underlying metal layer is made of chromium, titanium, or aluminum.

10. 5. The reflection / absorption characteristic measuring method according to claim 1, wherein the metal particles have an average particle size of 50 nm or more and 200 nm or less.

11. A reflection / absorption characteristic evaluation method, comprising the step of evaluating a change in reflection / absorption characteristics using the reflection / absorption characteristic measurement method according to any one of claims 1 to 4.

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