WO2014097886A1

WO2014097886A1 - Optical device and analysis apparatus

Info

Publication number: WO2014097886A1
Application number: PCT/JP2013/082578
Authority: WO
Inventors: 本間　敬之; 雅広柳沢; 美紀子齋藤
Original assignee: 学校法人早稲田大学
Priority date: 2012-12-18
Filing date: 2013-12-04
Publication date: 2014-06-26
Also published as: JPWO2014097886A1; JP6179905B2

Abstract

Proposed are an optical device and an analysis apparatus which are capable of reliably enhancing Raman scattered light from a sample by a surface plasmon and improving the sensitivity of surface enhanced Raman scattered light compared to conventional ones. In this optical device (5), a surface plasmon (P) can be excited on the proximity surface in proximity to a sample (S) of a metallic nanoparticle (9) by forming a flat surface in the metallic nanoparticle (9), thereby making it possible to reliably enhance Raman scattered light from the sample (S) by the surface plasmon (P) and improve the sensitivity of surface enhanced Raman scattered light (L3) compared to conventional ones. Further, the molecular structure in the depth direction (z) of the sample (S) can be measured with high depth resolution by providing the focus of excitation light (L1) in the vicinity of an interface between the metallic nanoparticle (9) and the sample (S) by an objective lens (4).

Description

Optical device and analyzer

The present invention relates to an optical device and an analysis apparatus, and is suitable for application to an analysis apparatus that performs sample analysis by measuring surface-enhanced Raman scattered light, for example.

Surface-enhanced Raman scattering (hereinafter referred to as SERS (Surface Enhanced Raman Scattering)) is a phenomenon in which the intensity of Raman scattered light of molecules existing on a metal surface is enhanced by several orders of magnitude by an electric field generated by surface plasmons excited on the metal surface. is there. The surface plasmon is a close-packed wave of free electrons in the metal that is excited when the metal is irradiated with light. Such SERS has been applied to a measurement method in the vicinity of a sample surface, and has been proposed as a surface-enhanced Raman spectroscopy that can increase the measurement sensitivity of Raman scattered light by about two orders of magnitude or more.

An analyzer using such surface-enhanced Raman spectroscopy is disclosed in Japanese Patent Application Laid-Open No. 2008-281530 (Patent Document 1). In Patent Document 1, a plurality of metal particles formed in a spherical shape 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 makes incident light incident on the probe with the probe tip close to the sample, and excites the electric field of the surface plasmon by the incident light to cause surface-enhanced Raman scattering from the sample. It can measure light.

JP 2008-281530 A

However, the conventional analyzer having such a configuration has a problem that although the surface plasmon is excited on the probe, the Raman scattered light from the sample cannot be sufficiently enhanced by the surface plasmon.

Therefore, the present invention has been made in consideration of the above points, and an object of the present invention is to propose an optical device and an analysis apparatus that can surely enhance Raman scattered light from a sample by surface plasmons as compared with the conventional case.

An optical device according to claim 1 of the present invention includes a device body that is capable of transmitting excitation light, and one or more metal nanoparticles having a surface exposed on one surface of the device body and having a flat surface formed thereon, When the metal nanoparticles are brought close to a sample and the excitation light is incident from the other surface of the device body, surface plasmons are excited on the proximity surface of the metal nanoparticles that are brought close to the sample, and the surface plasmons The surface-enhanced Raman scattered light is generated by enhancing the Raman scattered light from the sample.

In the analyzer according to claim 14 of the present invention, the sample is irradiated with the optical device according to any one of claims 1 to 13 and the excitation light emitted from the light source via the optical device, and the excitation light is applied to the sample. And a light guide unit that guides the surface-enhanced Raman scattered light emitted from the sample to the imaging unit by irradiating the sample.

The analyzer according to claim 15 further includes an objective lens that collects the excitation light emitted from the light source and irradiates the sample through the optical device, and the electric field gradient in the vicinity of the focal point of the objective lens is the surface plasmon. It is characterized by strengthening.

According to the optical device according to claim 1 and the analyzer according to claim 14 of the present invention, surface plasmons are excited on a proximity surface close to the sample of metal nanoparticles by forming a flat surface on the metal nanoparticles. Thus, the Raman scattered light from the sample can be surely enhanced by the surface plasmon, and the sensitivity of the surface enhanced Raman scattered light can be improved as compared with the prior art.

Further, according to the analyzer of the fifteenth aspect, the electric field gradient near the focal point of the objective lens can be enhanced by the surface plasmon, and the depth resolution in the depth direction of the sample can be improved.

It is the schematic which shows the whole structure of the analyzer of this invention. It is the schematic which shows the detailed structure of an optical device. It is the photograph which shows the structure of the optical device actually produced, and the SEM image which shows the structure of the one surface of a metal nanoparticle installation part. FIG. 4A is a schematic diagram showing an excited state of surface plasmons when hemispherical metal nanoparticles are brought into point contact with the sample surface, and FIG. 4B shows surface plasmons when spherical metal nanoparticles are used. It is the schematic which shows the excited state of. It is the schematic which shows the excitation state of a surface plasmon when hemispherical metal nanoparticles are surface-contacted with the sample surface. It is a graph which shows the relationship between the diameter of a metal nanoparticle, and the Raman intensity of surface enhancement Raman scattered light. FIG. 7A is a schematic diagram for explaining the principle that the depth resolution is improved when the optical device is applied, and FIG. 7B is a graph showing the electric field gradient of the surface plasmon from the surface of the optical device. It is the schematic which shows the excitation light electric field enhanced by the electric field of surface plasmon, and the excitation light electric field before enhancement. It is the schematic which shows the excitation light electric field at the time of moving the focus position of excitation light. It is the schematic where it uses for description when the molecular structure of HOPG is analyzed using the analyzer. It is a graph which shows the measurement result of the G band intensity of the HOPG obtained along the photograph of the cross-sectional profile along the depth direction of the peak intensity of the HOPG G band. It is the schematic which shows the structure of the metal nanoparticle which the curved surface swelled from the metal nanoparticle installation part, and the metal nanoparticle embedded in the metal nanoparticle installation part. It is the schematic which shows the structure by which the several metal nanoparticle which becomes hemispherical or conical shape was embedded in the metal nanoparticle installation part. It is the schematic which shows the structure by which the metal nanoparticle was covered with the coating film. It is the schematic which shows the structure which covered the hemispherical or conical metal nanoparticle with the coating film. It is the photograph and graph which show the Raman intensity | strength of an adhesion spherical particle. It is the photograph and graph which show the Raman intensity | strength of an embedding spherical particle. It is the photograph and graph which show the Raman intensity of an embedding hemisphere particle. It is the photograph and graph which show the Raman intensity | strength of an embedded cone particle. It is the photograph and graph which show the Raman intensity | strength of the conical particle embedded in a high refractive index material. It is the schematic which shows the structure of the analyzer by other embodiment. It is the schematic which shows the structure of the optical device by other embodiment. It is various graphs which show the analysis result of the protective film of a magnetic disc medium.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(1) Analytical apparatus of the present invention In FIG. 1, reference numeral 1 denotes an analytical apparatus according to the present invention, which has a light source 2 that emits excitation light L1, and the excitation light L1 emitted from the light source 2 is a half mirror 3 and an objective lens 4. And it is comprised so that it can inject into the sample S through the optical device 5 sequentially. The optical device 5 has a device body 6 that can transmit light, and one surface of the device body 6 is close to (in contact with and close to) the surface S1 of the sample S to be analyzed (also simply referred to as the sample surface). In an arranged state, the excitation light L1 can be incident from the other surface of the device body 6.

In the optical device 5, the excitation light L1 incident from the other surface of the device body 6 is transmitted, and the sample S can be irradiated and condensed with the excitation light L1. In the optical device 5, a plurality of metal nanoparticles (described later) are arranged on one surface of the device body 6, and surface plasmons can be excited on a proximity surface of the metal nanoparticles close to the sample surface S 1. At this time, Raman scattered light is generated from the sample S by the excitation light L1, and the intensity of the Raman scattered light of 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 5. SERS (surface enhanced Raman scattering) occurs, and surface enhanced Raman scattered light L3 is emitted.

Here, the analyzer 1 is provided with an imaging optical system of a pinhole 13, an optical filter 14, and an imaging means 15, and the imaging optical system and the light source 2 are orthogonal to each other about the half mirror 3. Are arranged. The analyzer 1 irradiates the half mirror 3 through the objective lens 4 with the reflected light L2 including the surface enhanced Raman scattered light L3 generated in the sample S, and reflects the surface enhanced Raman scattered light L3 by the half mirror 3. Thus, it can be guided to the pinhole 13 and can reach the imaging means 15 such as a CCD via the optical filter 14. In the imaging optical system, the light that has passed through the pinhole 13 can be filtered by the optical filter 14 so that only the surface-enhanced Raman scattered light L3 from the reflected light L2 can reach the imaging means 15. In this way, the analyzing apparatus 1 is capable of spectroscopically measuring the Raman spectrum from the image obtained by the imaging means 15 and specifying the molecular structure of the sample S from the intensity of the Raman spectrum.

In addition to this configuration, the analyzer 1 includes a base 12 on which the sample S is placed, and excitation light irradiated on the sample S when the base 12 moves in three axial directions. The focal point F of L1 can be adjusted in the depth direction z and the surface direction of the sample S (the x-axis direction and the y-axis direction orthogonal to the depth direction z). In practice, the base 12 includes 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 orthogonal to the x-axis direction, and in the x-axis direction and the y-axis direction. A second piezo stage 11 that moves in the orthogonal depth direction z, and the first and second

piezo stages

10 and 11 position the focal position in angstroms in the surface direction and the depth direction z. It can be adjusted.

In the case of this embodiment, the focal point F of the excitation light L1 collected by the objective lens 4 is changed in the plane direction of the sample S by moving the base 12 on which the sample S is placed in three axes. Although the present invention is not limited to this, the base on which the sample S is placed is fixed, and the objective lens 4 is moved in the surface direction and the depth direction z. It may be configured to be movable, and the focal point F of the excitation light L1 collected by the objective lens 4 may be moved in the surface direction and the depth direction z of the sample S.

Here, the electric field of the excitation light L1 narrowed down by the objective lens 4 (hereinafter referred to as the excitation light electric field) is enhanced by the surface plasmon P. For example, when the focal point F is in the sample S, the electric field becomes maximum at the focal position. In addition, a steep electric field gradient centering on the focal position can be obtained (described later). 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 aligned with the predetermined interface S2 in the sample S, for example, to the focal position (interface S2). The largest 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 can be identified from the intensity of the Raman spectrum. It is made like that.

Actually, the device main body 6 constituting the optical device 5 includes a base body 7 on which the other surface is irradiated with the excitation light L1, and a metal nanoparticle installation portion 8 disposed on one surface of the base body 7. The substrate 7 is made of, for example, a transparent member such as quartz and has a structure formed in a disk shape having a thickness, and has a metal nanoparticle installation portion 8 made of a transparent member such as quartz on a flat surface.

As shown in FIG. 2, the metal nanoparticle installation part 8 has a surface 8b facing the other surface 8a formed in a curved shape, and a plurality of metal nanoparticles 9 are installed along the surface 8b. The metal nanoparticles 9 swelled from can be arranged so as to be close to the sample surface S1. In practice, the metal nanoparticles 9 are made of any of Ag, Au, Cu, Pd, and Pt, and are formed in a hemispherical shape having a curved surface. The metal nanoparticles 9 can be arranged such that a flat surface is fixed to the one surface 8b of the metal nanoparticle placement portion 8 by surface contact and a curved surface is close to the sample surface S1. As a result, when the metal nanoparticle 9 is irradiated with the excitation light L1 from the other surface 8a side to the one surface 8b side of the metal nanoparticle installation portion 8, the surface plasmon is excited in the vicinity of the sample surface S1, and this surface plasmon Surface-enhanced Raman scattered light L3 is obtained from the sample S by the electric field (also simply referred to as plasmon electric field).

Here, FIG. 3A is a photograph showing the optical device 5 made of quartz actually produced, and FIG. 3B is an SEM image of one surface 8b of the metal nanoparticle installation portion 8 in the optical device 5. As shown in FIG. 3B, a plurality of fine metal nanoparticles 9 can be arranged on the one surface 8b of the metal nanoparticle installation portion 8 at predetermined intervals as needed. The metal nanoparticles 9 as shown in FIG. 3B are formed on one surface 8b of the metal nanoparticle installation portion 8 made of a transparent member such as quartz by, for example, sputtering, metal plating, vapor deposition, CVD (Chemical Vapor Deposition), or the like. More than one can be formed.

Next, the excitation of surface plasmons will be described in comparison with the case of using hemispherical metal nanoparticles 9 as shown in FIG. 4A and the case of using spherical metal nanoparticles 100 as shown in FIG. 4B. . As shown in FIG. 4A, the metal nanoparticle 9 provided in the optical device 5 of the present invention has a hemispherical shape obtained by cutting off a spherical base portion, and a flat flat surface is one surface 8b of the metal nanoparticle installation portion 8. It is fixed to. When the metal nanoparticle 9 is perpendicularly incident with excitation light L1 that vibrates in the direction of electric field oscillation from the other surface 8a side of the metal nanoparticle installation portion 8 toward the sample S in a state where the curved surface is close to the sample surface S1 Then, surface plasmon P is excited in a proximity surface close to sample surface S1, and SERS (surface enhanced Raman scattering) in which the intensity of Raman scattered light from molecules of sample S is enhanced by several orders of magnitude by the electric field of surface plasmon P. And surface enhanced Raman scattered light L3 is obtained.

On the other hand, in the spherical metal nanoparticle 100 as a comparative example as shown in FIG. 4B, the excitation light L1 is directed toward the sample S from the other surface side of the metal nanoparticle installation portion (not shown) as in FIG. 4A. Even if is incident perpendicularly, the surface plasmon P is not excited on the adjacent surface close to the sample surface S1, and the surface plasmon P is excited on both side surfaces of the metal nanoparticle 100 corresponding to the electric field vibration direction. The surface-enhanced Raman scattering light cannot be obtained without enhancing the Raman scattering light from the molecules. In the case of the metal nanoparticles 100, it is necessary to have another metal nanoparticle 100 next to cause plasmon resonance, but the metal nanoparticle 9 of the present invention does not require the adjacent metal nanoparticle 9, Even with the isolated metal nanoparticles 9, surface enhanced Raman scattered light L3 from the sample S can be obtained. Accordingly, a high spatial resolution corresponding to the diameter of the metal nanoparticles 9 can be realized.

Thus, in the optical device 5 according to the present invention, the hemispherical metal nanoparticles 9 having a flat surface are provided on the one surface 8b of the metal nanoparticle installation portion 8 so as to bulge from the one surface 8b. Surface plasmon P can be surely excited at the apex of the curved surface (proximity surface) close to sample S of metal nanoparticle 9 and thus Raman scattered light is excited by sample surface S1 and surface plasmon P excited in sample S. Surface-enhanced Raman scattered light L3 having an intensity increased by several orders of magnitude is obtained, and the sensitivity of the surface-enhanced Raman scattered light L3 can be increased in the imaging means 15.

Further, as shown in FIG. 5, the bulging-type metal nanoparticle 9 having a flat surface fixed to one surface 8b of the metal nanoparticle installation portion 8 has a curved surface vertex that is a proximity surface in a plane with respect to the sample surface S1. Even in the case of contact (proximity), the plasmon electric field P is excited in the vicinity of the sample surface S1, and strong surface-enhanced Raman light L3 from the sample S can be obtained. When the metal nanoparticles 9 are brought into surface contact with the sample surface S1 in this way (FIG. 5), the intensity of the plasmon electric field is such that the metal nanoparticles 9 are spotted on the sample surface S1, as shown in FIG. 4A. It was found to be about 3 times as compared with the case of contact.

Next, when the relationship between the diameter of the bulging-type metal nanoparticles 9 shown in FIGS. 4A and 5 and the electric field of the surface plasmon P was examined, the results shown in FIG. 6 were obtained. Here, the diameter of the hemispherical metal nanoparticles 9 is a diameter when assuming a spherical shape, and the measurement position of the electric field of the surface plasmon P is the apex of the curved surface of the metal nanoparticles 9. Therefore, the metal nanoparticles 9 can enhance the electric field of the surface plasmon by selecting the diameter of 5 to 100 [nm], and in particular, the surface can be further increased by selecting the diameter of 16 to 60 [nm]. The electric field of plasmon can be increased 1000 times or more, and the corresponding Raman scattered light intensity is amplified 10 ¹² times or more, which is a great practical advantage. In the metal nanoparticle placement unit 8, it is desirable to arrange such fine metal nanoparticles 9 in an island shape.

Next, the principle of improving the resolution in the depth direction z (hereinafter also referred to as depth resolution) when the optical device 5 of the present invention is applied will be described below with reference to FIG. 7A. In FIG. 7A, the magnitude of the electric field of the excitation light L1 (excitation light electric field) with respect to the distance from the surface of the optical device 5 is calculated, and the magnitude of this excitation light electric field and the positional relationship between the optical device 5 and the sample S are calculated. It is the shown schematic.

Normally, the excitation light electric field is maximized at the focal position narrowed down by the objective lens 4, but when the excitation light L1 is irradiated to the sample S without passing through the optical device 5 of the present invention, the focal position is centered. The gradient of the excitation electric field is very small (4 × 10 ⁻⁸ per 0.1 [nm]), and the depth resolution is about a micron.

On the other hand, as shown in FIG. 7A, in the optical device 5 of the present invention provided with the metal nanoparticles 9, when the sample surface S1 and the surface of the optical device 5 are installed in the vicinity of the focal point, the surface of the optical device 5 The electric field gradient of the excitation light electric field E1 near the metal nanoparticles 9 (for example, Ag) increases from 10 ⁻⁴ to 10 ⁻³ per 0.1 [nm] due to the electric field enhancement effect of the surface plasmon. Since it is known that the intensity of the surface-enhanced Raman scattered light L3 (Raman intensity) is proportional to the fourth power of the electric field, it is possible to capture changes in Raman intensity with a difference of about 0.1 [nm] with high sensitivity. Become. In the analyzer 1 of the present invention, the change in Raman intensity in the depth direction z (focal direction) can be measured by moving the base 12 on which the sample S is placed.

In this analyzer 1, as shown in FIG. 7B, the electric field of the surface plasmon P from the surface of the optical device 5 at the excitation light wavelength of 532 nm (simply expressed as “electric field” in FIG. 7B) is rapidly attenuated. There is an advantage that the influence of signals from other than the measurement points in the depth direction z can be reduced. In FIG. 7B, the distance at which the intensity of the electric field of the surface plasmon P is reduced to 1 / e is about 3 [nm], but this also varies depending on the shape of the optical device 5, and therefore the optical device 5 For example, the detection region of the surface-enhanced Raman scattered light L3 in the depth direction z can be widened by increasing the particle size or by forming a structure having a large plasmon electric field at the interface such as an inverted conical shape. Further, the excitation light may be a long wavelength (for example, 532 [nm] to 1500 [nm], preferably 785 [nm] or 1060 [nm]), or the plasmon wavelength may be increased from Ag to Au having a different dielectric constant. In addition, the detection region of the surface enhanced Raman scattered light L3 in the depth direction z can be expanded.

However, since the sensitivity of the surface-enhanced Raman scattered light L3 by the imaging means 15 is lowered at a location away from the surface of the optical device 5 by a predetermined distance or more, the enhancement of the Raman spectrum can be obtained from the surface of the optical device 5. Up to about 100 [nm] in the depth direction z is preferable.

In FIG. 7B, the electric field gradient of the surface plasmon P is maximized at a position close to the surface of the optical device 5, and this is assumed that one metal nanoparticle 9 is in point contact with the sample surface S1. When calculated. Actually, the electric field of the surface plasmon P is gentle due to variations in the particle size of the plurality of metal nanoparticles 9 formed on the surface of the optical device 5 and variations in the contact gap between the metal nanoparticles 9 and the sample surface S1. It is presumed that the slope is a simple gradient (indicated by a dotted line in FIG. 7B).

Here, FIG. 8 shows an excitation light electric field (indicated as “enhanced electric field (Raman intensity)” in FIG. 8) E1 enhanced by the electric field of the surface plasmon P excited by the optical device 5 of the present invention, The electric field E2 before the enhancement is schematically shown. The excitation light electric field E1 becomes maximum at the focal position of the excitation light L1 collected by the objective lens 4 (indicated as “0” on the horizontal axis in FIG. 8), and becomes a steep electric field gradient around the focal position. Since the electric field strength before and after F decreases rapidly, a high depth resolution can be obtained.

9A to 9C are schematic diagrams showing the positional relationship between the interface between the optical device 5 and the sample S and the focal position of the excitation light L1, and the enhanced excitation light electric field distribution. As shown in FIG. 9B, when the focal position coincides with the interface between the optical device 5 and the sample S, the intensity of the excitation light electric field E1 becomes maximum (that is, the intensity of the surface enhanced Raman scattered light L3 becomes maximum). ).

On the other hand, as shown in FIG. 9A, when the focal position moves outside the sample S, the enhancement effect by the electric field of the surface plasmon P is weakened, and the intensity of the excitation light electric field E1 is reduced (that is, the surface enhanced Raman scattered light L3 Decreases in strength). Further, as shown in FIG. 9C, as the position of the focal point F moves into the sample S, the enhancement effect due to the electric field of the surface plasmon P is weakened, and the intensity of the excitation light electric field E1 at the focal point decreases. (That is, the intensity of the surface-enhanced Raman scattered light L3 decreases). However, since the change in the electric field gradient is small, a high depth resolution is maintained.

The analyzer 1 thus moves the focal position in the depth direction z, and the Raman spectrum of the surface-enhanced Raman scattered light L3 obtained based on the high gradient intensity change of the excitation light electric field E1 generated in the vicinity of the focal point. Can be measured. Then, the analyzer 1 can specify the change in the molecular structure in the depth direction z of the sample S based on the change in the intensity of the Raman spectrum obtained along the depth direction z.

Next, highly oriented pyrolytic graphite (Highly Oriented Pyrolytic Graphite: HOPG) is prepared as a sample S, and the molecular structure of the HOPG in the depth direction z is actually measured using the analyzer 1 of the present invention shown in FIG. Analysis was carried out. Actually, in this verification test, as shown in FIG. 10, the metal nanoparticle installation part 8 is arranged so that the metal nanoparticle 9 comes into contact with the surface of the sample S (HOPG), and the excitation light L1 is installed on the metal nanoparticle. The sample 8 was irradiated from the other surface 8a side of the part 8 toward the sample S. Note that the HOPG used as the sample S has a structure in which a plurality of crystal structure A layers and B layers are alternately stacked one after another (in FIG. 10, only the crystal structure A layer, the B layer, and the A layer are briefly described. The lattice constant indicating the distance between the crystal structure A layer and the B layer is about 0.7 [nm].

At this time, by moving the base 12 in the depth direction z, the focal position of the excitation light L1 along the depth direction z from the outside to the inside of the sample S is set to, for example, 0.05 [nm] (stage drift correction). The correction value was corrected by one). At this time, the surface-enhanced Raman scattered light L3 emitted from the HOPG is imaged by the imaging means 15 of the analyzer 1, and the cross-sectional profile along the depth direction z of the peak intensity (1582 [cm ⁻¹ ]) of the HOPG G band. Was measured, and the result as shown in FIG. 11A was obtained. FIG. 11B is a graph showing a result of measuring the G band intensity of HOPG from the surface enhanced Raman scattered light L3 obtained along the depth direction z.

11A and 11B, (a) shows the external position of the sample S, (b) shows the surface (outermost surface) position of the sample S, and (c) shows the internal position of the sample S. In FIG. 11A and FIG. 11B, the crystal structure A layer and the B layer in HOPG appear as a periodic change in the depth direction z, and the distance between the peaks of the A layer or the B layer is HOPG lattice constant 0.7 [nm]. Therefore, it was confirmed that the molecular structure in the depth direction z of HOPG could be specified.

In the above configuration, the optical device 5 has a configuration in which a plurality of metal nanoparticles 9 having a flat surface are exposed on one surface of the device body 6, the metal nanoparticles 9 are brought close to the sample S, and the device body 6 When the excitation light L1 is incident from the other surface, the surface plasmon P is excited on the near surface of the metal nanoparticle 9 close to the sample S, and this surface plasmon P enhances the Raman scattered light from the sample S. Thus, the surface enhanced Raman scattered light L3 was obtained.

As described above, in the optical device 5, by forming a flat surface on the metal nanoparticle 9, the surface plasmon P can be excited on a surface close to the sample S of the metal nanoparticle 9, and thus the Raman from the sample S can be excited. The scattered light can be surely enhanced by the surface plasmon P as compared with the conventional case. In addition, the optical device 5 can improve the sensitivity of the surface-enhanced Raman scattered light L3 as much as the Raman scattered light can be enhanced. Can also improve.

In addition, the analyzer 1 is configured so that the optical device 5 is irradiated with the excitation light L1 and the focal position can be adjusted in the depth direction z of the sample S of the excitation light L1, so that the steepness is focused on the focal position. A sample analysis can be performed from a change in Raman intensity that varies along the depth direction z by moving the excitation light electric field E1 that has an 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 E1 has a steep electric field gradient centered on the focal position and the Raman scattered light from before and after the focal point F is reduced, a high depth resolution can be obtained. it can.

In the optical device 5 according to the present invention, the case where a plurality of metal nanoparticles 9 having a flat surface are provided on one surface of the device body 6 has been mainly described. As shown in FIG. 4A, it is not necessary to enhance the electric field by resonance between adjacent metal nanoparticles 100 as in the case of a spherical metal nanoparticle 100, and as shown in FIG. 4A, the surface plasmon can be reliably generated on the sample surface S1. Thus, the surface-enhanced Raman scattered light L3 can be reliably obtained.

Incidentally, when the excitation light is incident on the sample S from an oblique direction, the surface plasmon P is difficult to excite on the adjacent surface of the metal nanoparticle 9 close to the sample S, and the Raman scattered light from the sample S is The surface plasmon P cannot be sufficiently enhanced, and the sensitivity of the surface-enhanced Raman scattered light is lowered. On the other hand, in the optical device 5 according to this embodiment, the excitation light L1 that vibrates in the direction of electric field oscillation toward the sample S is incident on the sample S perpendicularly via the metal nanoparticles 9. Thus, the surface plasmon P can be reliably excited on the proximity surface of the metal nanoparticle 9 close to the sample S, and thus the Raman scattered light from the sample S can be surely enhanced by the surface plasmon P, and the surface-enhanced Raman The sensitivity of the scattered light L3 can be improved.

(2) Other Embodiments (2-1) Other Embodiments Related to Shape of Optical Device and Arrangement Mode of Metal Nanoparticles on Metal Nanoparticle Placement Section The present invention is not limited to the above-described embodiments. The present invention is not limited, and various modifications can be made within the scope of the present invention. In the above-described embodiment, as shown in FIG. 12A, the flat surface of the hemispherical metal nanoparticles 9 is arranged in surface contact on the one surface 8b of the metal nanoparticle installation portion 8, and the metal nanoparticles 9 are formed from the one surface 8b. However, the present invention is not limited to this, and the present invention is not limited to this, and the proximity of the surface of the metal nanoparticles close to the sample surface S1 is described. If the surface plasmon P can be excited, the shape of the metal nanoparticles may be conical, pyramidal, semi-elliptical, and other various shapes, and these metal nanoparticles are embedded in the metal nanoparticle installation part. May be.

Here, FIG. 12 is a schematic diagram showing the result of calculating the position where the surface plasmon is excited by changing the shape of the metal nanoparticle and the arrangement form of the metal nanoparticle on the metal nanoparticle installation portion. It is. For example, as shown in FIG. 12B, the buried metal nanoparticles 9a have a hemispherical shape obtained by cutting off a spherical base portion, and a flat surface extends along one surface 8b of the metal nanoparticle installation portion 8. Alternatively, the curved surface may be embedded in the metal nanoparticle installation part 8 and only a flat surface may be exposed from the one surface 8b of the metal nanoparticle installation part 8. In this case, when the excitation light L1 corresponding to the electric field oscillation direction is irradiated from the other surface side of the metal nanoparticle installation portion 8 to the one surface 8b, the flat surface (proximal surface) close to the sample S in the metal nanoparticle 9a is irradiated. The surface plasmon P can be excited, and thus the Raman scattered light from the sample S can be enhanced by the surface plasmon P. Therefore, as shown in FIG. 13A, as another optical device 5a, such buried hemispherical metal nanoparticles 9a may be arranged at a predetermined interval. The intervals between the metal nanoparticles 9a may be regular.

Further, as shown in FIG. 12C, the other buried metal nanoparticles 9b are arranged so that the shape thereof is conical and the flat surface is exposed along one surface 8b of the metal nanoparticle installation portion 8. Alternatively, the apex may be embedded in the metal nanoparticle installation part 8, and only the flat surface may be exposed from the one surface 8b of the metal nanoparticle installation part 8. Even in this case, when the excitation light L1 is irradiated from the other surface side of the metal nanoparticle installation part 8 to the one surface 8b, the surface plasmon P is excited on the flat surface (proximal surface) close to the sample S in the metal nanoparticle 9b. Thus, the surface plasmon P can enhance the Raman scattered light from the sample S. Therefore, as shown in FIG. 13B, as another optical device 5b, such buried conical metal nanoparticles 9b may be arranged at a predetermined interval. The intervals between the metal nanoparticles 9b may be regular. Furthermore, since the adjacent metal nanoparticles 9b are unnecessary, a single particle can be obtained with high resolution. However, since the intensity of the Raman scattered light becomes weaker as the density of the metal nanoparticles is smaller, the intensity of the Raman scattered light is related to the SN of the signal.

(2-2) Optical Device Provided with Coating Film As another embodiment, one surface 8b of the metal nanoparticle installation portion 8 provided with the metal nanoparticles 9 as in the optical device 17 shown in FIG. Alternatively, a coating film 18 made of a material different from that of the metal nanoparticle placement part 8 may be formed, and the metal nanoparticles 9 may be covered with the coating film 18. Further, as shown in FIG. 15A, another optical device 5c has a configuration in which the flat surface of the hemispherical metal nanoparticles 9a is arranged on the surface of the coating film 18 and the curved surface is buried in the coating film 18. Only the flat surfaces of the metal nanoparticles 9a may be exposed from the surface of the coating film 18. Even in this case, when the coating film 18 is irradiated with the excitation light L1 from the other surface side of the metal nanoparticle installation part 8, the surface plasmon P is applied to the flat surface (proximal surface) close to the sample S in the metal nanoparticle 9a. Thus, the Raman scattered light from the sample S can be enhanced by the surface plasmon P.

Further, as shown in FIG. 15B, another optical device 5d has a configuration in which the flat surface of the conical metal nanoparticles 9b is arranged on the surface of the coating film 18 and the apex is buried in the coating film 18. Only the flat surface of the metal nanoparticles 9b may be exposed from the surface of the coating film 18. Even in this case, when the coating film 18 is irradiated with the excitation light L1 from the other surface side of the metal nanoparticle installation part 8, the surface plasmon P is applied to the flat surface (proximal surface) close to the sample S in the metal nanoparticle 9b. Thus, the Raman scattered light from the sample S can be enhanced by the surface plasmon P.

Here, the coating film 18 described above is preferably formed of diamond having higher wear resistance and higher refractive index than the metal nanoparticle installation portion 8 made of, for example, quartz. Other materials for forming the coating film 18 may be formed of TiO ₂ , Si, Ge, or the like having a higher refractive index than that of the metal nanoparticle placement portion 8, and further formed of a transparent conductive film (ITO). May be.

In the

optical device

17, 5c, 5d in which the

metal nanoparticles

9, 9a, 9b are buried in such a coating film 18, the coating film 18 is formed of a material having higher wear resistance than the metal nanoparticle installation portion 8. As a result, even if the surfaces of the

optical devices

17, 5c, 5d are brought into contact with the sample S, they are not easily worn and durability can be improved. Further, in the

optical device

17, 5c, 5d in which the

metal nanoparticles

9, 9a, 9b are buried in the coating film 18, the coating film 18 is formed of a material having a higher refractive index than the metal nanoparticle installation portion 8. The enhancement rate of Raman scattered light can be improved, high sensitivity can be obtained, and electric field distribution can be easily controlled.

Incidentally, as a method of manufacturing an optical device in which metal nanoparticles are embedded in the device main body or the coating film 18, for example, nanoimprint or EB exposure and etching etc. Then, a metal thin film is formed on the recess by plating filling or the like, and the metal thin film other than the recess is removed by a CMP method, ion etching, or the like, so that metal nanoparticles can be formed only in the recess. Further, after the metal nanoparticles are deposited on the surface of the device body by vapor deposition or sputtering, a coating film 18 is formed, and the coating film 18 is polished to expose the metal nanoparticles from the coating film 18. Alternatively, a flat surface of the metal nanoparticles may be formed on the surface of the coating film 18.

(2-3) Raman intensity when the shape or the like of the metal nanoparticles is changed Here, when the shape or the like of the metal nanoparticles is changed, the Raman intensity is changed by simulation. A result as shown in FIG. 20 was obtained. The maximum electric field on the analysis surface was determined by FDTD (Finite Difference Time Domain method) (a method for calculating the electromagnetic field of light based on Maxwell's equations).

16A and 16B are Comparative Example 1, and spherical metal nanoparticles 100 formed of Ag were attached to one surface of a metal nanoparticle installation portion 8 (denoted as a lens in FIG. 16A) made of SiO ₂ . The composition (denoted as adherent spherical particles) was used, and the Raman intensity at this time was examined. As shown in FIGS. 16A and 16B, when the spherical metal nanoparticles 100 were attached to one surface of the metal nanoparticle installation portion 8, the maximum electric field on the analysis surface was 0.7. In Comparative Example 1, it was confirmed that the sensitivity of Raman intensity was low.

FIG. 17A and FIG. 17B are comparative examples 2 in which spherical metal nanoparticles 100 formed of Ag are embedded in a metal nanoparticle installation portion 8 (denoted as a lens in FIG. 17A) made of SiO ₂ ( It is expressed as embedded spherical particles), and the Raman intensity at this time was examined. As shown in FIGS. 17A and 17B, when the entire spherical metal nanoparticle 100 was embedded in the metal nanoparticle installation part 8, the maximum electric field on the analysis surface was 0.8. It was confirmed that even in Comparative Example 2 as described above, the sensitivity of the Raman intensity was lowered.

18A and 18B show Example 1, in which the flat surface of the hemispherical metal nanoparticles 9a formed of Ag is one surface of the metal nanoparticle installation portion 8 (referred to as a lens in FIG. 18A) made of SiO ₂ . Accordingly, the structure in which the metal nanoparticles 9a are embedded in the metal nanoparticle installation portion 8 (denoted as embedded hemispherical particles) is used, and the Raman intensity at this time is examined. As shown in FIGS. 18A and 18B, when the flat surface of the hemispherical metal nanoparticles 9a was embedded in one surface of the metal nanoparticle installation portion 8, the maximum electric field on the analysis surface was 2.0. In Example 1, it was confirmed that the sensitivity of Raman intensity was increased.

19A and 19B are Example 2, in which the flat surface of the conical metal nanoparticles 9b formed of Ag is the one surface of the metal nanoparticle installation portion 8 (denoted as a lens in FIG. 19A) made of SiO ₂ . Accordingly, the structure in which the metal nanoparticles 9b are embedded in the metal nanoparticle installation portion 8 (denoted as embedded cone particles) is examined, and the Raman intensity at this time is examined. As shown in FIGS. 19A and 19B, when the flat surface of the conical metal nanoparticle 9b was embedded in one surface of the metal nanoparticle installation portion 8, the maximum electric field on the analysis surface was 8.0. In Example 2, it was confirmed that the sensitivity of Raman intensity was further increased.

20A and 20B show Example 3, in which a flat surface of conical metal nanoparticles 9b formed of Ag is formed on a coating film 18 (denoted as a lens in FIG. 20A) made of high refractive index diamond. In accordance with one surface, the metal nanoparticles 9b are embedded in the coating film 18 (denoted as embedded cone particles in a high refractive index material), and the Raman intensity at this time was examined. As shown in FIG. 20A and FIG. 20B, when the flat surface of the conical metal nanoparticles 9b was embedded in one surface of the coating film 18, the maximum electric field on the analysis surface was 10.3. In such Example 3, it was confirmed that the sensitivity of the Raman intensity was further increased.

(2-4) Other Analyzing Apparatus (2-4-1) Cantilever Analyzing Apparatus In the case of the above-described embodiment, the convex lens-shaped optical device 5 is provided, and the piezo control analyzing apparatus 1 Although the present invention is not limited to this, the optical device 25 having the configuration of the present invention may be applied to a cantilever type analyzer 21 as shown in FIG. 21A. In practice, this analyzer 21 includes an optical device 25 in which a triangular pyramid-shaped device body 6 whose apex protrudes toward the sample S is supported by a cantilever 26 (denoted as Si cantilever in FIG. 21A). The excitation light L1 can be irradiated from the other surface of the device body 6 toward the apex.

In addition, the analyzer 21 irradiates the other surface of the device body 6 with control light (gap control light) from an LD (laser diode) 22 disposed obliquely above the optical device 25 and reflects it on the device body 6. The control light is detected by a four-divided PD (photodiode) 23, and the light detection outputs from the four light-receiving portions of the four-divided PD 23 are compared, and these are kept in a constant state. It is comprised so that the space | interval between S may be kept constant.

Even in this case, in the optical device 25, one or a plurality of hemispherical metal nanoparticles 9 bulge the curved surface at the apex and the side facing the sample S of the device main body 6 with a predetermined interval. The surface plasmon P can be excited on the proximity surface adjacent to the sample S of the metal nanoparticles 9 by being irradiated with the excitation light L1. Thus, in this analyzer 21 as well, the surface plasmon P is excited on the proximity surface close to the sample S of the metal nanoparticle 9 by forming a flat surface on the metal nanoparticle 9 as in the above-described embodiment. Thus, the Raman scattered light from the sample S can be surely enhanced by the surface plasmon P, and the sensitivity of the surface enhanced Raman scattered light L3 can be improved as compared with the prior art. In addition, even in such a cantilever type analyzer 21, the molecular structure in the depth direction z of the sample S can be obtained by focusing the excitation light L1 near the interface between the metal nanoparticle 9 and the sample S by the objective lens 4. It can be measured with high depth resolution.

22A is a schematic view showing an optical device 25a according to another embodiment provided with a cantilever 26. FIG. As shown in FIG. 22A, this optical device 25a has a device main body 28 formed in a trapezoidal cross section, and has a configuration in which conical metal nanoparticles 9a are buried on one surface close to the sample S. In this case, the metal nanoparticle 9a is embedded in the device body 28 with a flat surface coinciding with one surface of the device body 28, and the flat surface exposed from one surface of the device body 28 becomes a proximity surface close to the sample S. obtain. Even in such an optical device 25a, the surface plasmon P is excited on the flat surface of the metal nanoparticle 9a, and the Raman scattered light of the sample S can be enhanced by the electric field enhancement effect of the surface plasmon P. Also in such an optical device 25a, the objective lens 4 is used to focus the excitation light L1 in the vicinity of the interface between the metal nanoparticles 9a and the sample S, thereby increasing the molecular structure in the depth direction z of the sample S to a high depth. It can be measured with resolution.

(2-4-2) Tuning Fork Type Analyzing Device Using Fiber-Shaped Optical Device FIG. 21B shows a tuning fork type analyzing device 31 according to another embodiment, which is an optical device comprising a fiber-like device body. Using the device 33, the optical device 33 is fixed to the tuning fork 32. The analyzer 31 can control the interval between the one end surface of the optical device 33 and the sample S to a constant interval of 1 [nm] or less by maintaining the vibration frequency of the tuning fork 32 at the resonance frequency. Further, even in such a tuning fork type analyzer 31, the excitation light L1 is placed near the interface between the metal nanoparticles placed at the tip of the device body and the sample S by the objective lens 4 installed in the fiber-like device body. The molecular structure in the depth direction z of the sample S can be measured with high depth resolution.

Also in this optical device 33, as described above, for example, hemispherical single or a plurality of metal nanoparticles 9 (not shown) are regularly arranged on one end face as necessary, and the excitation light L1 from the other end face. , The surface plasmon P is excited on the proximity surface of the metal nanoparticle 9 that is close to the sample S, and the Raman scattered light of the sample S can be enhanced, and the same effect as in the above-described embodiment can be obtained. be able to.

Here, FIG. 22B is a schematic view showing a fiber-like optical device 33 provided with buried metal nanoparticles 9a. As shown in FIG. 22B, this fiber-shaped optical device 33 is formed in a columnar shape, has a device body with an objective lens 4 inside, and has conical metal nanoparticles 9a on one surface close to the sample S. The configuration is provided. In this case, the metal nanoparticles 9a are embedded in the device body such that the flat surface coincides with one surface of the device body, and the exposed flat surface can be a proximity surface close to the sample S. Even in such a fiber-like optical device 33, the surface plasmon P is excited on the flat surface of the metal nanoparticle 9a, and the Raman scattered light of the sample S can be enhanced by the electric field enhancement effect of the surface plasmon P.

(2-4-3) Tuning Fork Type Analyzing Apparatus with Optical Device in Waveguide FIG. 21C shows a tuning fork type analyzing apparatus 41 according to another embodiment. A convex lens-shaped optical device 43 is provided, and a waveguide 42 is fixed to the tuning fork 32. The analyzer 41 maintains the vibration frequency of the tuning fork 32 at the resonance frequency, thereby reducing the distance between one end surface of the optical device 43 provided at the tip of the waveguide 42 and the sample S to 1 [nm] or less. Can be controlled at regular intervals. Also, in such a tuning fork type analyzer 41, the shape of the optical device 43 is a convex lens shape at the tip, and the excitation light L1 is focused in the vicinity of the interface between the metal nanoparticles and the sample S. The molecular structure in the depth direction z can be measured with high depth resolution.

Also in this optical device 43, as described above, for example, hemispherical single or plural metal nanoparticles 9 (not shown) are regularly arranged on one side as necessary, and from the waveguide 42 to the other side. When the excitation light L1 is incident toward the side, the surface plasmon P is excited on the proximity surface of the metal nanoparticle 9 that is close to the sample S, and the Raman scattered light of the sample S can be enhanced. The same effect as the form can be obtained.

Here, FIG. 22C is a schematic diagram showing a waveguide thin film type optical device 44 having another configuration. As shown in FIG. 22C, this waveguide thin film type optical device 44 has a device body formed in a columnar shape, and has a configuration in which conical metal nanoparticles 9a are provided on one surface close to the sample S. In this case, the metal nanoparticles 9a are embedded in the device body so that the flat surface coincides with one surface of the device body, and the exposed flat surface can be a proximity surface close to the sample S. Even in such a waveguide thin film type optical device 44, the surface plasmon P is excited on the flat surface of the metal nanoparticle 9a, and the Raman scattered light of the sample S can be enhanced by the electric field of the surface plasmon P. Further, in such an optical device 44, the molecular structure in the depth direction z of the sample S is obtained by focusing the excitation light L1 near the interface between the metal nanoparticle 9a and the sample S by the objective lens 4 provided outside. Can be measured with high depth resolution.

The above-mentioned “(2-4-1) cantilever type analyzer”, “(2-4-2) Tuning fork type analyzer using fiber optical device” and “(2-4-3 In the “tuned fork type analyzer provided with an optical device in a waveguide”, the configuration of each optical device may be a configuration in which a coating film is provided as in the configuration of FIG.

In FIGS. 21A, 21B, and 22A to 22C described above, the case where the fixed objective lens 4 is applied has been described. However, the present invention is not limited to this, and the objective lens 4 is provided by providing a focus moving means. The focal point of the objective lens 4 may be freely moved in the depth direction z of the sample S by moving the sample S.

(2-4-4) Analysis of protective film of magnetic disk medium by analyzer of the present invention The analyzer 1 of the present invention as shown in FIG. 1 is used for a catalytic reaction used in fuel cells, Li ion batteries, plating, etc. It can also be used for analysis. Further, the analyzer 1 can also be used for structural analysis of thin film devices such as solar cells, EL elements, and liquid crystal displays. Further, the analyzer 1 can measure the molecular structure and distribution of a thin film having a sub-nanometer thickness, and can be used, for example, for analysis of a protective film or a lubricating film of a magnetic disk medium (HDD: Hard Disc Drive). Can do.

For example, FIG. 23 is a graph showing an analysis result obtained by analyzing a protective film of a magnetic disk medium using the analyzer 1 of the present invention shown in FIG. When the protective film (diamond-like carbon (DLC) film) having a thickness of 2 [nm] of the magnetic disk medium is analyzed by the analyzer 1 of the present invention, as shown in FIG. The Raman spectrum of was observed well. FIG. 23C shows a histogram of the G band intensity that can be measured by the analyzer 1. FIG. 23B is a Raman spectrum observed by an analyzer that does not have the optical device of the present invention, and it can be confirmed that the D band and G band cannot be specified as in the case of using the analyzer 1 of the present invention. It was.

1,21,31,41 Analyzer 3 Half mirror (light guide)
4

Objective lens

5,17,5a, 5b, 5c, 5d, 25a, 33,43,44 Optical device 6

Device body

9,9a, 9b Metal nanoparticle 12 base (focus moving means)
18 Coating film

Claims

A device body capable of transmitting excitation light; and
One or more metal nanoparticles having a surface exposed on one surface of the device body and a flat surface formed thereon,
When the metal nanoparticles are brought close to a sample and the excitation light is incident from the other surface of the device body, surface plasmons are excited on the proximity surface of the metal nanoparticles that are brought close to the sample, and the surface plasmons A surface-enhanced Raman scattered light is generated by enhancing the Raman scattered light from the sample.
The said metal nanoparticle has the said flat surface arrange | positioned along one surface of the said device main body, it swells from one surface of the said device main body, or is embedded in the said device main body. The optical device described.
The optical device according to claim 2, wherein the flat surface of the metal nanoparticles bulging from one surface of the device body is in surface contact with one surface of the device body.
The optical device according to claim 2, wherein the metal nanoparticle embedded in the device body has the flat surface exposed along one surface of the device body.
When the metal nanoparticles are assumed to be spherical, the diameter is 5 to 100 [nm],
The optical device according to claim 3, wherein the flat surface is formed on the metal nanoparticle so that a part of the spherical metal nanoparticle is cut off.
The optical device according to any one of claims 1 to 4, wherein the metal nanoparticles are hemispherical or conical.
The optical device according to any one of claims 1 to 6, wherein the metal nanoparticles are any one of Ag, Au, Cu, Pd, and Pt.
The optical device according to any one of claims 1 to 6, wherein the device main body has a convex lens shape that bulges toward the sample side.
The optical device according to any one of claims 1 to 7, wherein the device body has a weight shape protruding toward the sample side and is supported by a cantilever.
The optical device according to any one of claims 1 to 7, wherein the device body is formed in a fiber shape.
The metal nanoparticles are
The optical device according to any one of claims 1 to 10, wherein the optical device is covered with a coating film formed of a material having higher wear resistance than that of the device body.
The metal nanoparticles are
The optical device according to any one of claims 1 to 10, wherein the optical device is covered with a coating film formed of a material having a refractive index higher than that of the device body.
The optical device according to claim 11 or 12, wherein the metal nanoparticle has the flat surface disposed on a surface of the coating film, and the flat surface is exposed to the outside.
An optical device according to any one of claims 1 to 13;
A light guide means for irradiating the sample with excitation light emitted from a light source and guiding the surface-enhanced Raman scattered light emitted from the sample to the imaging means by irradiating the sample with the excitation light. An analyzer characterized by that.
An objective lens that collects excitation light emitted from the light source and irradiates the sample through the optical device;
The analyzer according to claim 14, wherein the electric field gradient near the focal point of the objective lens is enhanced by surface plasmon.
A focal point moving means for moving the focal point of the objective lens in the depth direction of the sample;
The analyzer according to claim 15, wherein the electric field gradient enhanced by the surface plasmon is moved in a depth direction of the sample by moving the focus within the sample by the focus moving unit. .