JP2020153892A - Optical device, analyzer, and method of manufacturing optical device - Google Patents

Abstract

To provide an optical device with a simple structure that can further enhance Raman scattering light obtained from a sample using surface plasmon and thereby can achieve a more highly sensitive measurement of the surface-enhancement Raman scattering light when incorporated to an analyzer.SOLUTION: An optical device 7, used in an analyzer 1 for performing sample analysis by measuring surface-enhancement Raman scattering light L3, comprises a substrate 21 having a first surface 21a and a second surface 21b opposed to the first surface. The second surface has a rough surface in at least its partial region and a plurality of metallic nanoparticles 22 are fixed to at least a protruding end of the rough surface.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical device, an analyzer, and a method for manufacturing the optical device, and the optical device is suitable for application to, for example, an analyzer that measures surface-enhanced Raman scattered light and performs sample analysis.

In surface-enhanced Raman scattering (hereinafter, also referred to as SERS (Surface Enhanced Raman Scattering)), the intensity of Raman scattered light emitted by molecules existing on the metal surface is enhanced by several orders of magnitude by the electric field generated by the surface plasmon excited on the metal surface. It is a phenomenon. Surface plasmons are coarse and dense waves of free electrons in a metal that are excited when the metal is irradiated with light. Such SERS can be applied to the analysis of the molecular structure near the sample surface, and can increase the measurement sensitivity of Raman scattered light in the conventional Raman spectroscopy by about two orders of magnitude or more.

Patent Document 1 is known as an analyzer using such surface-enhanced Raman spectroscopy. Patent Document 1 has a configuration in which a plurality of spherical metal particles are dispersed inside the probe and the plurality of metal particles are exposed on the surface of the probe. An analyzer using such a probe injects excitation light into the probe with the probe tip close to the sample, excites the electric field of the surface plasmon by the excitation light, and emits Raman from the sample. It is possible to enhance the scattered light and measure the surface-enhanced Raman scattered light.

Japanese Unexamined Patent Publication No. 2008-281530

Compared to the analyzer disclosed in Patent Document 1, there is a demand for the emergence of an analyzer capable of performing structural analysis of a sample with higher sensitivity by further enhancing the Raman scattered light emitted by the sample by surface plasmon.
In view of the above requirements, the present invention has an optic having a simple structure capable of further enhancing Raman scattered light from a sample by surface plasmon and realizing measurement of surface enhanced Raman scattered light with higher sensitivity when incorporated into an analyzer. The present invention provides a device, an analyzer including the optical device, and a method for manufacturing the optical device.

The optical device according to one embodiment is used in an analyzer that measures surface-enhanced Raman scattered light to perform sample analysis, and has a first surface and a second surface opposite to the first surface. The second surface is a rough surface at least in a part, and a plurality of metal nanoparticles are fixed to at least the tip of the convex portion of the rough surface.

The analyzer according to one embodiment is such that the optical device, a light source that emits excitation light, an imaging means, and the excitation light are transmitted to the sample after being transmitted through the optical device, or the sample is irradiated after being transmitted through the sample. It is provided with a light guide means for irradiating an optical device and guiding the surface-enhanced Raman scattered light emitted from the sample to the imaging means.

Further, the method for manufacturing an optical device according to one embodiment includes a base material having a first surface and a second surface opposite to the first surface, and the second surface is at least a part of a region. Is a rough surface, and a plurality of metal nanoparticles are fixed to the rough surface. The method for manufacturing an optical device used in an analyzer that measures surface-enhanced Raman scattered light and performs sample analysis. A step of sandblasting a region including a part of the region of the second surface of the base material to form the rough surface, and sputtering a metal on the rough surface to perform the metal nanoparticles on the rough surface. Includes a step of fixing the.

It is the schematic which shows the whole structure of the analyzer which includes the optical device which concerns on this embodiment. It is a schematic diagram which shows the state which a part region (the region including the protruding tip) of the base material of the optical device which concerns on this Embodiment is close to a sample surface. (A) is a schematic view showing the excited state of surface plasmon when hemispherical metal nanoparticles are point-contacted with the sample surface, and (b) is a schematic view showing the excited state of surface plasmon, and (b) is surface contact of hemispherical metal nanoparticles with the sample surface. It is the schematic which shows the excited state of the surface plasmon when it was made. It is the schematic which shows the other arrangement of an optical device and a sample in the analyzer which concerns on this embodiment. It is the schematic which shows the other structure of the optical device which concerns on this embodiment. It is a schematic diagram which shows the other structure of an optical device and a sample in the analyzer which concerns on this embodiment. It is a scanning electron micrograph which shows the rough surface of the 2nd surface of the base material of the optical device which concerns on Example 1. FIG. It is a graph which shows the Raman spectrum of the surface of the zinc dialkyldithiophosphate (ZDTP) thin film measured using the optical device which concerns on Example 1 and Comparative Example 1. 6 is a scanning electron micrograph showing a state in which metal nanoparticles are fixed on the rough surface of the second surface of the base material of the optical device according to the fourth embodiment. It is a graph which shows the Raman spectrum of the surface of the Fe ₂ O ₃ thin film measured using the optical device which concerns on Example 2. FIG. It is a graph which shows the relationship between the arithmetic average roughness Ra of the 2nd surface of the base material of the optical device which concerns on Examples 2-4 and Comparative Examples 2 and 3 and an intensity ratio.

The analyzer according to this embodiment will be described with reference to FIG.
FIG. 1 is a schematic view showing an overall configuration of an analyzer 1 including an optical device 7 according to the present embodiment. The analyzer 1 has a light source 2 that irradiates the excitation light L1. The excitation light L1 emitted from the light source 2 is configured to be able to reach the sample S by sequentially passing through the objective lens 6 and the optical device 7 after being incident on the half mirror (light guide means) 4 through the optical fiber 3a. Has been done.

The optical device 7 according to the present embodiment includes a base material 21, for example, the base material 21 is formed of a transparent member capable of transmitting light. The base material 21 has a first surface 21a and a second surface 21b opposite to the first surface 21a. The second surface 21b is curved in a convex shape toward the direction opposite to the first surface 21a side. The base material 21 has, for example, a disk shape, is curved in a convex shape with the central portion of the second surface 21b as the protruding tip, and when placed on the sample S, the protruding tip is closer to the sample S than the peripheral portion.

Here, attention is paid to a region including a protruding tip of the base material 21 of the optical device 7. FIG. 2 is a schematic view showing a state in which a part of a region (region including a protruding tip) of the base material 21 of the optical device 7 according to the present embodiment is close to the sample surface. As shown in FIG. 2, the second surface 21b of the base material 21 has a rough surface at least a part of the region (the region including the protruding tip) and has an uneven structure. Metal nanoparticles 22 are fixed to at least the tip T1 of the convex portion of the rough surface. Therefore, in the region including the protruding tip, the single or a plurality of metal nanoparticles 22 fixed to at least the convex tip T1 of the rough surface are the surface of the sample S to be analyzed (simply referred to as the sample surface) S1. Can be in close proximity to or in contact with.

In the optical device 7, the curved curvature of the second surface 21b of the base material 21 is adjusted, and the region near the protruding tip in contact with the sample surface S1 is the beam diameter of the excitation light L1 (circular irradiation of the excitation light L1). It is smaller than the diameter of the region), and as a result, the surface resolution due to the surface-enhanced Raman scattered light L3 can be improved.

In the optical device 7, the excitation light L1 is transmitted through the base material 21 from the first surface 21a toward the convex tip tip T1 in the region including the protruding tip of the second surface 21b, and is further arranged at the tip T1. The sample S is irradiated and focused by passing through the metal nanoparticles 22. At this time, the metal nanoparticles 22 can excite surface plasmons on a surface close to the sample surface S1. At this time, Raman scattered light is emitted from the sample S by the excitation light L1, and the intensity of the Raman scattered light of the molecules existing in the sample S is increased by several orders of magnitude due to the electric field generated by the surface plasmon P excited by the optical device 7. SERS (Surface-enhanced Raman scattering) is generated, and surface-enhanced Raman scattered light L3 is emitted.

The analyzer 1 is provided with an imaging optical system of an optical filter 13, an aperture 14, a diffraction grating 15, and an imaging means 16, and the imaging optical system and the light source 2 are orthogonal to each other about the half mirror 4. Is arranged. The analyzer 1 irradiates the half mirror 4 with the reflected light L2 including the surface-enhanced Raman scattered light L3 generated in the sample S via the objective lens 6, and reflects the reflected light L2 by the half mirror 4 to generate light. It is guided to the optical filter 13 through the fiber 3b, and further passes through the aperture 14 and the diffraction lattice 15 in order to reach the imaging means 16 such as a CCD (Charge Coupled Device).

In the imaging optical system, only the surface-enhanced Raman scattered light L3 is extracted from the reflected light L2 by filtering with an optical filter 13, and the light passing through the aperture 14 is separated as a spectrum by a diffraction grating 15 and used as an imaging means 16. Can be reached. In this way, the analyzer 1 spectroscopically measures the Raman spectrum from the image obtained by the imaging means 16 and identifies the molecular structure of the sample S from the intensity of the Raman spectrum.

In addition to the above-described configuration, the analyzer 1 includes a base 12 on which the sample S is placed, and the base 12 moves in the triaxial direction to excite the sample S. The focus of the light L1 can be adjusted in the depth direction z and the plane direction (x-axis direction and y-axis direction orthogonal to the depth direction z) of the sample S. Practically, the base 12 has a first piezo stage 10 that moves in the x-axis direction in the plane direction and the y-axis direction in the same plane direction that is orthogonal to the x-axis direction, and in the x-axis direction and the y-axis direction. It has a second piezo stage 11 that moves in the orthogonal depth direction z, and the focal position is positioned in the plane direction and the depth direction z in Å (ongstrom) units by the first piezo stage 10 and the second piezo stage 11. It is adjustable.

In the present embodiment, by moving the base 12 on which the sample S is placed in the triaxial direction, the focal point of the excitation light L1 focused by the objective lens 6 is focused on the surface direction and the depth direction of the sample S. Although the case where the objective lens 6 is moved to z has been described, in the analyzer 1, the objective lens 6 is provided with the piezo actuator 5, so that the piezo actuator 5 can also move the objective lens 6 in the depth direction z. It is configured. As a result, in the analyzer 1, the objective lens 6 can be moved in the depth direction z by the piezo actuator 5 while fixing the base 12 on which the sample S is placed, and the excitation focused by the objective lens 6 can be performed. The focus of the light L1 can be moved in the depth direction z of the sample S.

The electric field of the excitation light L1 focused by the objective lens 6 (hereinafter referred to as the excitation light electric field) is enhanced by the surface plasmon. For example, when the focal point is in the sample S, it is maximized at the focal position and centered on the focal position. It can be a steep electric field gradient. Therefore, in this analyzer 1, the focal position of the excitation light L1 is moved in the depth direction z of the sample S, and the focal position is adjusted to, for example, a predetermined interface S2 in the sample S to bring it to the focal position (interface S2). The maximum surface-enhanced Raman scattered light L3 is obtained, the Raman spectrum is spectroscopically measured from the surface-enhanced Raman scattered light L3 obtained from the interface S2, and the molecular structure of the interface S2 in the sample S is specified from the intensity of the Raman spectrum. be able to.

An example in which metal nanoparticles 22 fixed to the convex tip T1 of the concave-convex structure constituting the rough surface of the second surface 21b are brought into contact with the sample surface S1 in the region including the protruding tip of the base material 21 of the optical device 7. explain. FIG. 3A is a schematic view showing the excited state of the surface plasmon P when the hemispherical metal nanoparticles 22 are brought into point contact with the sample surface S1. On the other hand, FIG. 3B is a schematic view showing the excited state of the surface plasmon P when the hemispherical metal nanoparticles 22 are brought into surface contact with the sample surface S1.

As shown in FIG. 3A, the metal nanoparticles 22 are hemispherical and have a structure in which the flat surface is fixed to the convex tip tip T1 of the rough surface of the second surface 21b. In the metal nanoparticles 22, the apex of the curved surface is in point contact with the sample surface S1. In this state, when the excitation light L1 vibrating in the electric field vibration direction is vertically incident from the flat surface side toward the sample S via the curved surface apex, the surface plasmon P is excited to the curved surface apex in point contact with the sample surface S1. .. As a result, the electric field of the surface plasmon P excited in the sample surface S1 or the sample S (also simply referred to as a plasmon electric field) enhances the intensity of Raman scattered light from the molecule of the sample S by several orders of magnitude. Raman scattering) occurs, and surface-enhanced Raman scattered light L3 is obtained.

On the other hand, as shown in FIG. 3B, the flat surface of the metal nanoparticles 22 is fixed to the tip T1 of the convex portion of the rough surface of the second surface 21b, and is strongly pressed against the sample surface S1 against the sample surface S1. There is surface contact. Even in this state, when the excitation light L1 vibrating in the electric field vibration direction is vertically irradiated from the flat surface side toward the curved surface apex in surface contact, the surface plasmon P is excited to the curved surface apex in surface contact with the sample surface S1. As a result, the electric field of the surface plasmon P (plasmon electric field) generates SERS (surface-enhanced Raman scattering) in which the intensity of Raman scattered light from the molecule of sample S is increased by several orders of magnitude, and the surface-enhanced Raman scattered light L3 is generated. can get.
As shown in FIG. 3B, when the metal nanoparticles 22 are brought into surface contact with the sample surface S1, the metal nanoparticles 22 shown in FIG. 3A are brought into point contact with the sample surface S1. The strength of the plasmon electric field is about three times that of the above.

As described above, in the optical device 7 according to the present embodiment, the metal nanoparticles 22 fixed to at least the convex tip T1 of the rough surface formed in a part of the base material 21 (the region including the protruding tip) are formed. By arranging the metal nanoparticles 22 in close proximity to or in contact with the sample S, the surface plasmon P can be excited on the surface of the metal nanoparticles 22 in close proximity to or in contact with the sample S, and the surface plasmon P excited in the sample surface S1 or the sample S can be excited. As a result, the surface-enhanced Raman scattered light L3 in which the intensity of the Raman scattered light is increased by several orders of magnitude can be obtained, so that the sensitivity of the surface-enhanced Raman scattered light L3 can be increased in the imaging means 16.

Further, in the optical device 7 according to the present embodiment provided with the metal nanoparticles 22, when the sample surface S1 and the surface of the optical device 7 are placed near the focal point, the metal nanoparticles 22 on the surface of the optical device 7 (for example, Ag) field gradient of the excitation light field in the vicinity is increased by the electric field enhancing effect of surface plasmon P from 0.1 [nm] per 10 ³ to 10 ^4. Since it is known that the intensity of surface-enhanced Raman scattered light L3 (Raman intensity) is proportional to the fourth power of the electric field, it is possible to sensitively capture changes in Raman intensity at a distance difference of about 0.1 [nm]. It will be possible. In the analyzer 1 according to the present embodiment, the base 12 on which the sample S is placed is moved, or the objective lens 6 is moved by the piezo actuator 5, so that the depth direction is z (focus direction). Changes in Raman intensity can be measured.

In this analyzer 1, for example, when the excitation light wavelength is 532 [nm], the electric field of the surface plasmon P generated on the surface of the optical device 7 is rapidly attenuated when the surface is separated from the surface, so that the electric field is rapidly attenuated in the depth direction z. There is an advantage that the influence of signals from other than the measurement points of can be reduced. Here, at a location separated from the surface of the optical device 7 by a predetermined distance or more, the sensitivity of the surface-enhanced Raman scattered light L3 by the imaging means 16 decreases, so that the enhancement of the Raman spectrum can be obtained from the surface of the optical device 7. It can be up to about 100 [nm] in the depth direction z.

Incidentally, the excitation light electric field enhanced by the electric field of the surface plasmon P becomes maximum at the focal position of the excitation light L1 focused by the objective lens 6, and becomes a steep electric field gradient around the focal position, and the electric field before and after the focal point. High depth resolution is obtained because the intensity decreases sharply.
When the focal position coincides with the interface between the optical device 7 and the sample S, the intensity of the excitation light electric field becomes maximum (that is, the intensity of the surface-enhanced Raman scattered light L3 becomes maximum). On the other hand, when the focal position moves to the inside of the sample S, the effect of enhancing the surface plasmon P by the electric field weakens, and the intensity of the excitation light electric field at the focal position decreases (that is, surface-enhanced Raman scattering). The intensity of light L3 decreases). However, since the change in the electric field gradient is small, high depth resolution is maintained.

The analyzer 1 moves the focal position in the depth direction z in this way, and obtains a Raman spectrum of surface-enhanced Raman scattered light L3 obtained based on a high-gradient intensity change of the excitation photoelectric field generated in the vicinity of the focal point. By the measurement, the change in the molecular structure of the sample S in the depth direction z can be specified based on the change in the intensity of the Raman spectrum obtained along the depth direction z.

Next, the configuration of the optical device 7 according to the present embodiment will be described in detail.
As described above, the base material 21 constituting the optical device 7 is made of a transparent member capable of transmitting light, and is formed of, for example, quartz, glass, sapphire, diamond, CaF _2, or SiO ₂ having excellent workability. The base material 21 is preferably formed of quartz or sapphire because of its optical properties and ease of rough surface processing due to its hardness. The base material 21 is formed to have dimensions according to the sample to be measured, for example, having a thickness of 0.1 [mm] to 10 [mm] and a diameter of 5 [mm] to 100 [mm], in one example. , The thickness is 1 [mm] and the diameter is 20 [mm].

As described above, at least a part of the region (the region including the protruding tip) is a rough surface on the second surface 21b of the base material 21. The rough surface has an arithmetic mean roughness Ra measured in accordance with ISO 25178 of more than 0.1 [μm], preferably 0.25 [μm] or more and 1.0 [μm] or less. It is more preferably 0.4 [μm] or more and 0.7 [μm] or less. The arithmetic mean roughness Ra can be measured by a laser microscope or an atomic force microscope (AFM).

The metal nanoparticles 22 contain either Ag, Au, Cu, Pd, Pt, Al, or a metal having a negative real part of the dielectric constant, preferably Ag. The metal nanoparticles 22 have a diameter of 5 [nm] to 100 [nm] and a distance between the metal nanoparticles of 1 [nm] to 100 [nm] to enhance the electric field of the surface plasmon. Can be done. In particular, by setting the diameter of the metal nanoparticles to 10 [nm] to 60 [nm], the electric field of the surface plasmon can be further increased 1000 times or more, and the corresponding intensity of Raman scattered light is remarkably amplified. can do. The metal nanoparticles 22 are provided with the metal nanoparticles 22 on the rough surface of a part of the region (the region including the tip of the convex portion of the second surface 21b) so that the metal nanoparticles 22 can be reliably approached to the sample S. It is desirable to fix it in an island shape.

The shape of the metal nanoparticles 22 is not limited to the hemisphere shown in FIG. 3A, and may be various shapes such as a conical shape, a spherical shape, a pyramidal shape, a semi-elliptical shape, a rectangular parallelepiped shape, and an indefinite shape. , These metal nanoparticles 22 may be embedded in the second surface 21b of the base material 21.

Next, the manufacturing method of the optical device 7 according to the present embodiment will be described in detail.
First, it has a first surface 21a and a second surface 21b which is a surface opposite to the first surface 21a and is curved in a convex shape toward the direction opposite to the first surface 21a side, for example, light. Prepare a base material 21 that allows light to pass through.

Next, at least a part of the second surface 21b of the base material 21 (the region including the protruding tip) is subjected to a roughening treatment such as sandblasting or mechanical polishing to form a roughened surface. The roughening treatment is applied to, for example, the entire surface of the second surface 21b of the base material 21, and a rough surface is formed on the entire surface of the second surface 21b of the base material 21. The roughening treatment is preferably a sandblasting treatment because a roughened surface can be easily formed even if the second surface 21b is a curved surface.

The abrasive used in the sandblasting treatment is not particularly limited, and is based on, for example, ceramic materials such as alumina, glass and silicon carbide, metal materials such as steel, zinc, stainless steel, iron and copper, and fine particles of synthetic resin. It can be used depending on the hardness of the material 21. When quartz or sapphire is used as the base material 21, it is preferable to perform sandblasting using an abrasive containing fine particles of silicon carbide having a hardness higher than that of the base material 21. The arithmetic mean roughness Ra of the rough surface can be adjusted, for example, by adjusting the time for sandblasting, the type of abrasive, or the particle size.

Next, the metal is sputtered onto the rough surface to fix the metal nanoparticles to at least the tip of the convex portion of the rough surface. Sputtering of the metal is performed, for example, on the entire surface of the second surface 21b of the base material 21. According to metal sputtering, metal nanoparticles can be easily formed in an island shape even if the second surface 21b is a curved surface. The diameter of the metal nanoparticles 22 and the distance between the particles can be adjusted, for example, by adjusting the time and number of times the metal is sputtered.

In the optical device 7 according to the embodiment described above, a part of the region (the region including at least the protruding tip of the second surface 21b of the base material 21 having a convex shape) is a rough surface, and at least the convex portion of the rough surface. Metal nanoparticles 22 are fixed to the tip. Therefore, the excitation light L1 can be focused and irradiated on the metal nanoparticles 22 fixed to the tip of the convex portion, and the surface plasmon P can be excited on the surface of the metal nanoparticles 22 in close proximity to or in contact with the sample S. Since the analyzer provided with such an optical device 7 can excite the surface plasmon P more reliably, the Raman scattered light can be further enhanced, and the surface-enhanced Raman scattered light L3 can be measured with higher sensitivity than before. If the surface-enhanced Raman scattered light L3 can be measured with higher sensitivity than before, various sample analyzes can be performed and the versatility can be improved as compared with the conventional one. Further, since the optical device 7 has a simple structure composed of the base material 21 and the metal nanoparticles 22, it can be manufactured inexpensively and with good reproducibility.

Further, in the optical device 7, since at least a part of the second surface 21b (the region including the protruding tip) is a rough surface, the metal nanoparticles 22 can be spatially arranged at high density and are adjacent to each other. The plasmon resonance generated in the gap between the metal nanoparticles 22 can more reliably enhance the surface plasmon P excited to the close surface of the metal nanoparticles 22 close to the sample S.

Further, in the optical device 7, by forming a flat surface on the metal nanoparticles 22, the surface plasmon P is excited on a close surface close to the sample S of the metal nanoparticles 22 as compared with a simple spherical metal nanoparticles 22. The Raman scattered light from the sample S can be reliably enhanced by the surface plasmon P.

Further, in the optical device 7, since the second surface 21b of the base material 21 has a protruding tip, positioning the protruding tip with respect to the sample surface S1 ensures that the metal nanoparticles 22 near the protruding tip are secured. And can easily approach the sample surface S1.

In the case of mere spherical metal nanoparticles, another metal nanoparticles must be present next to each other in order to cause plasmon resonance, but in the case of metal nanoparticles 22 having a flat surface, adjacent metal nanoparticles are required. Since 22 is unnecessary, surface-enhanced Raman scattered light L3 from sample S can be obtained even with isolated metal nanoparticles 22. Therefore, a high spatial resolution corresponding to the diameter of the metal nanoparticles 22 can be realized.

In the method for manufacturing an optical device according to the above-described embodiment, a step of sandblasting the second surface 21b of the base material 21 to form a rough surface and a step of sputtering a metal on the rough surface to fix metal nanoparticles. Including the step of causing. Therefore, it is possible to manufacture an optical device 7 that can realize the measurement of surface-enhanced Raman scattered light with high sensitivity at low cost and with good reproducibility without using complicated microfabrication technology.

Further, the analyzer 1 is configured so that the optical device 7 is irradiated with the excitation light L1 and the focal position of the excitation light L1 can be adjusted in the depth direction z of the sample S, so that the analysis device 1 is steep with respect to the focal position. The sample analysis can be performed from the change in Raman intensity that changes along the depth direction z by moving the excitation optical electric field that has a stable electric field gradient in the depth direction z of the sample S. At this time, in this analyzer 1, since the excitation light electric field has a steep electric field gradient around the focal position and the Raman scattered light from before and after the focal point is reduced, high depth resolution can be obtained.

The analyzer 1 and the optical device 7 according to the present embodiment can adopt various forms described below in addition to the above-described configuration.
In the analyzer 1 shown in FIG. 1, an example in which the optical device 7 is arranged on the upper side of the sample surface S1 (the side on which the excitation light L1 is incident) is shown, but the arrangement of the optical device 7 and the sample S is limited to this. Not done. As in the analyzer shown in FIG. 4, the sample surface S1 may be arranged on the upper side of the optical device 7 (the side on which the excitation light L1 is incident). In FIG. 4, the second surface 21b of the optical device 7 is arranged so as to face upward, and the sample S is arranged so that the sample surface S1 comes into contact with the protruding tip thereof. In this case, the sample S is configured to be capable of transmitting light, for example, a thin film to be measured is formed on the sample surface S1 on a substrate such as a glass substrate through which light can be transmitted. Further, in this case, the base material 21 may be formed of the above-mentioned transparent member capable of transmitting light, and may be a metal material such as Fe, Ni, Zn, Ti, or a semiconductor material such as Si, Ge, C, or them. It may be formed from an alloy material of the above, or a conductive material such as ITO. Further, in this case, the focal position of the excitation light L1 is used, for example, in accordance with the contact surface between the sample surface S1 and the optical device 7.

In the analyzer shown in FIG. 4, the excitation light L1 is transmitted through the sample S toward the sample surface S1 by the light guide means, and then is irradiated and focused on the contact surfaces of the metal nanoparticles 22 and the sample surface S1, for example. .. At this time, Raman scattered light is emitted from the sample S by the excitation light L1, and the intensity of the Raman scattered light of the molecules existing in the sample S is increased by several orders of magnitude due to the electric field generated by the surface plasmon P excited by the optical device 7. SERS (surface-enhanced Raman scattering) occurs and emits surface-enhanced Raman scattered light L3. Even with such a configuration, the same effect as that of the analyzer 1 according to the above-described embodiment can be obtained.

Further, in the analyzer 1 shown in FIG. 1, an example in which the second surface 21b of the optical device 7 has a convex shape has been described, but the structure of the optical device 7 is not limited to this. In the optical device, the base material 21'may have a flat plate shape as in the optical device 7'shown in FIG. The optical device 7'has the same configuration as the optical device 7 except that the second surface 21b'is a flat surface and the base material 21'is a flat plate. Specifically, the optical device 7'has the rough surface in a part of the second surface 21b', and the plurality of metal nanoparticles 22 are fixed to the tip of the convex portion of the rough surface. .. Here, the partial region is a region that is close to or in contact with the sample surface S1 and is transmitted or irradiated with the excitation light L1, for example, the central region of the second surface 21b'. The optical device 7'can be manufactured in the same manner as the above-described method for manufacturing the optical device 7 except that the base material 21'is used instead of the base material 21. Even with such a configuration, the same effect as that of the optical device 7 according to the above-described embodiment can be obtained.

Further, in the analyzer 1 shown in FIG. 1, an example in which the sample surface S1 is flat has been described, but the shape of the sample surface S1 is not limited to this. The sample surface S1 may have a rough surface (for example, a rough surface having an arithmetic mean roughness Ra of 0.1 [μm] or more). Further, as shown in FIG. 6, the sample surface S1 may be the sample surface S1'curved in a convex shape toward the optical device 7'. Further, the fact that the shape of the sample surface is a smooth surface or a rough surface and a flat surface or a curved surface may be applied in an appropriate combination. As shown in FIG. 6, when the optical device 7'is a flat plate, if the shape of the sample surface S1 is curved, the positional resolution of the sample surface S1 can be improved in the same manner as the optical device 7. It is preferable because it can be done. Further, the sample S is not limited to a solid state and may be a liquid state. For example, a liquid layer to be measured may be formed on a substrate such as a glass substrate through which light can be transmitted.

The arrangement of the optical device and the sample, the shape of the optical device, and the shape of the sample described above are not limited to the above-mentioned examples, and may be applied in an appropriate combination. Even with a configuration composed of such a combination, the same effect as that of the analyzer according to the above-described embodiment can be obtained.

Next, the optical device according to the present embodiment will be described in more detail with reference to Examples and Comparative Examples.
(Example 1 and Comparative Example 1)
The optical device according to Example 1 was manufactured by the method shown below.
First, a base material made of quartz having a thickness of 1 [mm] and a diameter of 20 [mm] was prepared. This base material has a first surface and a second surface which is a surface opposite to the first surface and is curved in a convex shape toward the direction opposite to the first surface side.

Next, the entire surface of the second surface of the base material was sandblasted using an abrasive made of silicon carbide to form a rough surface having an arithmetic average roughness Ra of 0.46 [μm]. The arithmetic mean roughness Ra was measured according to ISO25178.

FIG. 7 is a scanning electron micrograph showing a rough surface of the second surface of the base material of the optical device according to the first embodiment. From the results of FIG. 7, it can be seen that a rough surface composed of an uneven structure is formed on the second surface of the base material of the optical device of Example 1.

Next, Ag was sputtered onto the rough surface of the second surface of the base material to roughen the Ag nanoparticles and fixed them in an island shape on the tip of the convex portion of the second surface and the wall surface of the convex portion. The metal nanoparticles had a diameter of 5 [nm] to 100 [nm] and a distance between the metal nanoparticles was 1 [nm] to 100 [nm].

The optical device of Comparative Example 1 was manufactured by the same method as in Example 1 except that the second surface of the base material was not sandblasted. The arithmetic mean roughness Ra of the second surface of the base material of Comparative Example 1 was a smooth surface of 0.00 [μm] when measured in the same manner as in Example 1.

Next, a glass substrate on which a zinc dialkylthiophosphate (ZDTP) thin film (Sample S) was formed was prepared. In the analyzer shown in FIG. 1, the second surface of the optical device according to Example 1 and Comparative Example 1 is arranged on the ZDTP thin film of the glass substrate so that the Ag nanoparticles fixed to the second surface come into contact with each other. Raman spectra were measured. The contact between the Ag nanoparticles and the sample surface S1 was performed by applying a load of 1 [mN] in the vertical direction toward the sample surface S1 with each optical device. FIG. 8 is a graph showing the Raman spectrum of the surface of the ZDTP thin film measured using the optical devices according to Example 1 and Comparative Example 1.

As is clear from FIG. 8, the analyzer incorporating the optical device of Example 1 has about 10 times the CH ₂ peak of the lubricating film of ZDTP as compared with the analyzer incorporating the optical device of Comparative Example 1. It was confirmed that it can be obtained with strength. Therefore, by incorporating the optical device of Example 1 in the analyzer using surface-enhanced Raman scattered light, the Raman scattered light from the sample can be reliably enhanced by the surface plasmon, and the molecular structure of the sample can be analyzed with high sensitivity. I was able to confirm that it could be done.

(Examples 2 to 4 and Comparative Examples 2 and 3)
The optical devices according to Examples 2 to 4 and Comparative Examples 2 and 3 were manufactured by the methods shown below.
First, a base material made of sapphire having a thickness of 1 [mm] and a diameter of 20 [mm] was prepared. This base material has a first surface and a second surface opposite to the first surface, and has a flat plate shape. That is, the optical devices according to Examples 2 to 4 and Comparative Examples 2 and 3 have a structure as shown in FIG.

Next, the entire second surface of the base material of the optical devices of Comparative Examples 3, 2, 3 and 4 is sandblasted in the same manner as in Example 1, and the arithmetic mean roughness Ra is 0, respectively. .1 [μm] smooth surface, 0.3 [μm], 0.5 [μm] and 0.65 [μm] rough surfaces. Here, the arithmetic mean roughness Ra was changed by adjusting the time for performing the sandblasting treatment.

Next, Ag is sputtered over the entire surface of the second surface of the base material of the optical device according to Examples 2 to 4 and Comparative Examples 2 and 3 by the same method as in Example 1, and a plurality of metal nanoparticles composed of Ag. Was fixed.

The optical device of Comparative Example 2 was manufactured by the same method as in Examples 2 to 4 and Comparative Example 2 except that the second surface of the base material was not sandblasted. The arithmetic mean roughness Ra of the second surface of the base material of Comparative Example 2 was 0.00 [μm] smooth surface when measured in the same manner as in Example 1.

Here, FIG. 9 shows a metal on the rough surface of the second surface of the base material of the optical device according to the fourth embodiment (the region where the arithmetic mean roughness Ra is 0.65 [μm] and includes the protruding tip). It is a scanning electron micrograph which shows a state that nanoparticles were fixed. From this result, the metal nanoparticles 22 are arranged in an island shape in which the diameter of the metal nanoparticles is 5 [nm] to 20 [nm] and the distance between the metal nanoparticles is 1 [nm] to 20 [nm]. It was confirmed that it was done.

Next, a glass substrate on which a thin film of Fe ₂ O ₃ (Sample S) was formed was prepared. In the analyzer shown in FIG. 1, Ag nanoparticles having the second surface of the optical device according to Examples 2 to 4 and Comparative Examples 2 and ₃ fixed to the second surface on a thin film of Fe ₂ O ₃ on a glass substrate. The Raman spectrum was measured by arranging them in contact with each other. The contact between the Ag nanoparticles and the sample surface S1 was performed by applying a load of 1 [mN] in the vertical direction toward the sample surface S1 with each optical device. FIG. 10 is a graph showing a Raman spectrum on the surface of a thin film of Fe ₂ O ₃ measured using the optical device according to Example 2.

From this result, it was confirmed that when the optical device according to Example 2 was used, a peak of Fe ₂ O _{3 and} a peak corresponding to the excitation light having a wavelength of 532 [nm] could be obtained. At this time, the intensity of the peak corresponding to Fe ₂ O ₃ and the excitation light is read as I (Fe ₂ O ₃ ) and I (532 [nm]), and the intensity ratio is calculated by the following equation (1). did.
Intensity ratio [-] = I (Fe ₂ O ₃ ) / I (532 [nm]) ... (1)

For each of the optical devices according to Examples 2 to 4 and Comparative Examples 2 and 3, the intensity ratio was calculated by the equation (1), and the result is shown in FIG. FIG. 11 is a graph showing the relationship between the arithmetic mean roughness Ra of the second surface of the base material of the optical device according to Examples 2 to 4 and Comparative Examples 2 and 3 and the intensity ratio. The intensity ratio indicates the high detection sensitivity of the surface-enhanced Raman scattered light enhanced by each optical device.

From this result, when the optical device according to Examples 2 to 4 in which the second surface of the base material is a rough surface is used, the intensity ratio indicating the high detection sensitivity is as high as 0.95 or more, and Raman scattering from the sample. It was confirmed that the light can be further enhanced by the surface plasmon, and the surface-enhanced Raman scattered light can be measured with higher sensitivity. Furthermore, by comparing the results of Examples 2 to 4, it was confirmed that the higher the arithmetic mean roughness Ra of the second surface of the base material, the more sensitive the optical device capable of measuring the surface-enhanced Raman scattered light can be obtained. ..

1 ... Analyzer, 2 ... Light source, 4 ... Half mirror (light guide means), 5 ... Piezo actuator (focus moving means), 6 ... Objective lens, 7 ... Optical device, 12 ... Base (focus moving means), 16 ... Imaging means, 21 ... Base material, 21a ... First surface, 21b ... Second surface, 22 ... Metal nanoparticles, S ... Sample, P ... Surface plasmon

Claims (9)

Used in analyzers that measure surface-enhanced Raman scattered light for sample analysis
A base material having a first surface and a second surface opposite to the first surface is provided.
An optical device in which at least a part of the second surface is a rough surface, and a plurality of metal nanoparticles are fixed to at least the tip of a convex portion of the rough surface. The optical device according to claim 1, wherein the base material is formed of a material capable of transmitting light. The second surface is curved in a convex shape facing in the direction opposite to the first surface side, and at least a part of the region is a region including a protruding tip of the convex shape, according to claim 1 or 2. The optical device described. The optical device according to claim 1 or 2, wherein the base material is a flat plate. The optical device according to any one of claims 1 to 4, wherein the arithmetic average roughness Ra of the rough surface is 0.25 [μm] or more and 1.0 [μm] or less. The optical device according to any one of claims 1 to 5, wherein the base material is formed of quartz or sapphire. The optical device according to any one of claims 1 to 6, wherein the metal nanoparticles include any of Ag, Au, Cu, Pd, Pt, Al and a metal having a negative real part of the dielectric constant. The optical device according to any one of claims 1 to 7.
A light source that emits excitation light and
Imaging means and
The excitation light is transmitted to the sample after being transmitted through the optical device, or the optical device is irradiated with the excitation light after being transmitted through the sample, and the surface-enhanced Raman scattered light emitted from the sample is guided to the imaging means. Light means and
An analyzer equipped with. A base material having a first surface and a second surface opposite to the first surface is provided, the second surface has at least a part of a rough surface, and the rough surface has a plurality of metals. A method for manufacturing an optical device used in an analyzer that measures surface-enhanced Raman scattered light to which nanoparticles are fixed and performs sample analysis.
A step of sandblasting a region including a part of the second surface of the base material to form the rough surface.
A step of sputtering a metal on the rough surface to fix the metal nanoparticles on the rough surface, and
A method of manufacturing an optical device including.

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