JP7344832B2 - Measurement method using cantilever and scanning probe microscopes and scanning probe microscopes - Google Patents

Description

The present invention relates to cantilever and scanning probe microscopes and measurement techniques using scanning probe microscopes, and is used, for example, in spectroscopic probe microscopes typified by near-field optical probe microscopes and tip-enhanced Raman scattering (TERS) microscopes. This article relates to techniques that are effective when applied to cantilevers.

A scanning near-field optical microscope (SNOM) is known as a means for measuring optical properties and physical property information on the surface of an object (sample) with high resolution. In recent years, as one application of SNOM technology, a scanning probe microscope has been developed that enables nano-resolution Raman spectroscopy using the local enhancement effect of near-field light.

For example, Japanese Patent Application Laid-Open No. 2019-7756 (Patent Document 1) describes a scanning probe microscope that can improve the spatial resolution and reproducibility of measurements, using FIB processing technology to introduce a thin film at the tip of a cantilever (probe, tip). A technique is described in which a waveguide is formed and near-field light is generated at the tip of a cantilever by making light incident on the thin film waveguide at a plasmon resonance angle.

In this technique, a noble metal film is formed on the cantilever so that tip-enhanced Raman spectroscopy can be performed, and measurement is performed by indirect light incident on the tip.

JP 2019-7756 Publication

The technique described in Patent Document 1 mentioned above aims to improve the intensity of near-field light at the tip of a cantilever by generating surface plasmon and propagating it to the tip of the cantilever. However, it has become clear that as a result of the long propagation distance of surface plasmons, the intensity of near-field light cannot be sufficiently improved by surface plasmons. That is, the technique described in Patent Document 1 mentioned above has room for improvement, for example, from the viewpoint of improving the measurement sensitivity of probe-enhanced Raman spectroscopy using a scanning probe microscope.

Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

The cantilever in one embodiment is used in a scanning probe microscope. In a cross-sectional view, the cantilever is a part that can be brought close to the sample, and is connected to the apex part covered with the metal film, and is connected to the ridge line covered with the metal film. It has an upper corner part. Here, the part of the ridgeline and the upper corner portion are the portions that are irradiated with excitation light emitted from the excitation light source installed in the scanning probe microscope system.

A scanning probe microscope in one embodiment includes a sample holder that holds a sample, a light source that emits excitation light, and a cantilever that is irradiated with excitation light. Here, the cantilever included in the scanning probe microscope has the structure described above.

A cantilever in one embodiment includes a probe section and a beam section that connects to the probe section from the bottom surface and holds the probe section. In a cross-sectional view, the probe portion includes a vertex portion covered with a metal film, a first line connecting the vertex portion and the beam portion, and a ridge line connected to the vertex portion and covered with a metal film. , an upper corner portion connected to the ridgeline, and a second line connecting the upper corner portion and the beam portion. At this time, the second line has either the first configuration or the second configuration. Here, in the first configuration, each of the first line and the second line includes a straight part directly connected to the beam part, and the distance between the straight part of the first line and the straight part of the second line is at the vertex. The structure is the same or narrows as it approaches the site. On the other hand, the second configuration is a configuration in which the second line includes an extension line portion located on an extension of the ridgeline, and a recessed portion connected to the upper corner portion and the extension line portion and recessed toward the first line side. .

A measurement method using a scanning probe microscope in one embodiment includes (a) irradiating a cantilever with excitation light emitted from a light source, and (b) detecting scattered light from a sample placed opposite to the cantilever. and a process. Here, the cantilever is a part that can be brought close to the sample and has an apex part covered with a metal film, a ridgeline connected to the apex part and covered with a metal film, and an upper corner part connected to the ridgeline. and has. At this time, the part of the ridgeline and the upper corner portion are the portions that are irradiated with excitation light emitted from the light source of the scanning probe microscope.

According to one embodiment, the measurement sensitivity of a scanning probe microscope can be improved.

FIG. 1 is a diagram showing a schematic configuration of a scanning probe microscope in an embodiment. 3 is a diagram showing a schematic configuration of a scanning probe microscope in Modification 1. FIG. 7 is a diagram showing a schematic configuration of a scanning probe microscope in Modification 2. FIG. It is a perspective view showing a typical composition of a cantilever in an embodiment. 5 is a cross-sectional view taken along line AA in FIG. 4. FIG. 7 is a perspective view showing a schematic configuration of a cantilever in Modification 1. FIG. 7 is a cross-sectional view taken along line AA in FIG. 6. FIG. 7 is a perspective view showing a schematic configuration of a cantilever in Modification 2. FIG. 9 is a cross-sectional view taken along line AA in FIG. 8. FIG. FIG. 7 is a perspective view showing a schematic configuration of a cantilever in Modification 3. FIG. 11 is a sectional view taken along line AA in FIG. 10. FIG. FIG. 7 is a perspective view showing a schematic configuration of a cantilever in Modification 4. FIG. 13 is a cross-sectional view taken along line AA in FIG. 12. FIG. FIG. 3 is a diagram schematically showing a simulation calculation model for verifying the effects of the embodiment. These are simulation results for the entire probe section. This is a simulation result with an enlarged view of the vicinity of the tip of the probe. These are simulation results that have been image-processed to make it easier to understand the electric field strength near the tip of the probe. It is a diagram showing that the electric field distribution caused by surface plasmons formed on the ridge line differs depending on the length of the ridge line in the probe part. (b) is a diagram showing the electric field distribution in the case where the length of the ridgeline is L=4820 nm. (a) is a diagram showing the tip structure of the probe, and (b) is a diagram showing the prerequisite configuration for performing the first simulation. It is a graph showing the results of the first simulation. FIG. 3 is a diagram showing a prerequisite configuration for performing a second simulation. It is a graph showing the results of a second simulation. 7 is a graph showing the relationship between electric field strength and ridge length when the incident angle is fixed at 60° in the first simulation. It is a graph showing the relationship between the electric field strength and the length of the ridge line when the incident angle is fixed at 60° in the second simulation. FIG. 2 is a diagram schematically showing an incident optical system included in a scanning probe microscope that can change the incident angle. (a) to (c) are diagrams illustrating that the incident angle of excitation light to the cantilever can be changed by changing the optical path configuration. FIG. 7 is a diagram illustrating an example in which a lens is used to also configure the optical path of the optical lever detection section. FIG. 3 is a diagram showing a cantilever included in a scanning probe microscope that can change the incident angle. (a) is a diagram showing a reflective objective lens, (b) is a diagram showing a parabolic mirror, and (c) is a diagram showing an integrating mirror. FIG. 7 is a diagram illustrating an example in which the optical path of the optical lever detection section is also configured using a condensing optical component.

In the following embodiments, when necessary for convenience, the explanation will be divided into multiple sections or embodiments, but unless otherwise specified, they are not unrelated to each other, and one does not differ from the other. This is related to variations, details, supplementary explanations, etc. of some or all of the above.

In addition, in the following embodiments, when referring to the number of elements (including numbers, numerical values, amounts, ranges, etc.), we also refer to cases where it is specifically specified or where it is clearly limited to a specific number in principle. However, it is not limited to the specific number, and may be greater than or less than the specific number.

Furthermore, in the embodiments described below, the constituent elements (including elemental steps, etc.) are not necessarily essential, unless explicitly stated or when they are considered to be clearly essential in principle. Needless to say.

Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of components, etc., the references are substantially the same, unless explicitly stated or when it is considered that it is clearly not possible in principle. It shall include things that approximate or are similar in shape, etc. This also applies to the above numerical values and ranges.

Furthermore, in all the drawings for explaining the embodiments, the same members are designated by the same reference numerals in principle, and repeated explanation thereof will be omitted. Note that, in order to make the drawings easier to understand, hatching may be added even in a plan view.

<Overview of scanning probe microscope>
A scanning probe microscope (SPM) is a general term for microscopes typified by scanning tunneling microscopes and atomic force microscopes. This scanning probe microscope is a microscope that scans a sample with a minute probe to observe the shape and properties of the sample. In particular, in a scanning probe microscope, the tip of the probe is brought close to the surface of the sample and scanned while detecting the mechanical and electromagnetic interactions between the sample and the probe, allowing for an enlarged image of the sample surface and information on physical properties. can be obtained. For example, a scanning probe microscope has atomic-level or molecular-level resolution for a sample. In recent years, scanning probe microscopes having atomic-level resolution have been used to examine physical property information such as optical properties of samples. Specifically, by irradiating excitation light from a light source to the tip of the probe, near-field light (local electric field concentration) is formed at the tip of the probe, and the light emitted from the sample due to this near-field light is Detect scattered light. By analyzing this scattered light, information on the physical properties of the sample is obtained.

For example, when Rayleigh scattered light is detected as the scattered light, physical property information such as reflectance and surface roughness of the surface of the sample can be acquired. On the other hand, when detecting Raman scattered light, it is possible to identify the types of chemical bonds and the substances constituting the sample.

The scanning probe microscope in this embodiment can be widely applied to techniques for detecting Rayleigh scattered light and Raman scattered light, but in particular, in this embodiment, the scanning probe microscope is used to detect Raman scattered light. We are focusing on spectroscopic measurement technology. That is, the scanning probe microscope in this embodiment is a microscope that realizes tip-enhanced Raman spectrometry using near-field light formed at the tip of the probe. Efforts have been made to improve detection sensitivity. Specifically, this embodiment focuses on improving the intensity of near-field light at the tip of the probe in order to improve the detection sensitivity of Raman scattered light. This is because while the intensity of Raman scattered light is extremely weak compared to the intensity of Rayleigh scattered light, it increases in proportion to the intensity of near-field light. This is because if it can be made stronger, the detection sensitivity of Raman scattered light can be improved.

Regarding this point, in this embodiment, the shape of the tip of the cantilever, which is a component of the scanning probe microscope, and the method of irradiating the excitation light to the tip of the cantilever are devised. The strength of the near field formed at the tip of the part is increased. Below, before explaining the points regarding the shape of the probe portion of the cantilever, first, the configuration and operation of a scanning probe microscope equipped with this cantilever will be briefly explained.

<Scanning probe microscope configuration>
FIG. 1 is a diagram showing a schematic configuration of a scanning probe microscope in this embodiment.

The scanning probe microscope 100 shown in FIG. 1 is, for example, a microscope called a near-field optical scanning probe microscope or a scanning probe microscope for tip-enhanced Raman spectroscopy.

In FIG. 1, a scanning probe microscope 100 according to the present embodiment includes a sample holder 20 on which a sample 10 is mounted, a piezoelectric element stage 30 on which the sample holder 20 is placed, a probe portion 40a, a beam portion 40b, and a held portion 40c. It has a cantilever 40 including. Here, the beam portion 40b may have a structure that plays the role of a leaf spring. The piezoelectric element stage 30 is configured to be able to scan the sample 10 in the x and y directions relative to the probe portion 40a of the cantilever 40. The cantilever 40 is made of, for example, silicon, silicon oxide, or silicon nitride.

Next, the scanning probe microscope 100 in this embodiment includes a piezoelectric element stage 50 that scans the cantilever 40 relative to the sample 10, a piezoelectric element actuator 51, and a piezoelectric element stage 50 and a piezoelectric element actuator 51. It has a head 52 that holds the cantilever 40. In other words, the cantilever 40 has the held portion 40c held by the head 52 via the piezoelectric element stage 50 and the piezoelectric element actuator 51. However, if the cantilever 40 does not require vibration by the piezoelectric actuator 51 (for example, if the base material is a cantilever with self-detection performance), the piezoelectric actuator 51 is not necessarily required.

Next, the scanning probe microscope 100 in this embodiment includes an optical lever detection section 60. This optical lever detection unit 60 is configured to detect deformation of the beam portion 40b of the cantilever 40. Specifically, the optical lever detection section 60 includes a light source 61 and a photodetector 63. The optical lever detection unit 60 is configured to emit light 62 from a light source 61 toward the beam portion 40b of the cantilever 40, and detects the light 62 (reflected light) reflected by the beam portion 40b of the cantilever 40. The detector 63 is configured to receive the light. At this time, the optical lever detection unit 60 is configured to detect a position change of the light 62 (reflected light) caused by the deformation of the cantilever 40 using a photodetector 63.

Next, the scanning probe microscope 100 in this embodiment has an entrance/detection optical system 70. The entrance/detection optical system 70 includes, for example, a light source 71 that emits laser light (excitation light), a lens 72 that focuses the laser light, and a light receiving optical system 73 that receives Raman scattered light from the sample 10. ing. By using a spectrometer, it becomes possible to perform spectroscopic measurements. The excitation light emitted from the light source 71 can be, for example, a single wavelength laser beam, but is not limited to this, and the excitation light can also be composed of laser beams with multiple wavelengths.

Furthermore, the scanning probe microscope 100 in this embodiment includes a spectrometer 80 that is optically connected to the light receiving optical system 73 via an optical fiber 75, and a control section 90 that is electrically connected to the spectrometer 80. have. Here, the spectrometer 80 is configured to input Raman scattered light from the light receiving optical system 73 via the optical fiber 75 and separate each Raman spectrum component of the Raman scattered light. On the other hand, the control unit 90 is configured to control the piezoelectric element stage 30 and the piezoelectric element stage 50. Further, the control section 90 is connected to the optical lever detection section 60 and determines the distance between the probe section 40a of the cantilever 40 and the sample 10 based on the amount of deformation of the cantilever 40 detected by the optical lever detection section 60. It is configured to detect the applied force and distance. Then, the control unit 90 controls the piezoelectric element stage 30 and the piezoelectric element stage 50 so that the amount of deformation of the cantilever 40 is constant, so that the probe part 40a of the cantilever 40 scans over the entire surface of the sample 10. It is composed of Further, the control unit 90 generates a Raman spectrum image, which is a near-field optical image, and a surface unevenness image, based on the xyz displacement signals for controlling the piezoelectric element stage 30 and the piezoelectric element stage 50, and the output signal from the spectrometer 80. It is configured to generate and output.

In the scanning probe microscope 100 according to the present embodiment configured as described above, the lens 72 is shared in the entrance/detection optical system 70, so that the configuration of the scanning probe microscope 100 can be simplified.

Next, the operation of scanning probe microscope 100 in this embodiment will be briefly described. First, in FIG. 1, the control section 90 controls the piezoelectric element stage 30 and the piezoelectric element stage 50 to bring the probe part 40a of the cantilever 40 close to the sample 10 and arrange it at a predetermined position. Thereafter, the probe portion 40a of the cantilever 40 is irradiated with excitation light emitted from the light source 71. Then, near-field light is generated at the tip of the probe portion 40a, and as a result, scattered light including Raman scattered light is emitted from the sample 10 placed opposite to the cantilever 40. This scattered light passes through a lens 72 and a light receiving optical system 73, and then is detected by a spectrometer 80 via an optical fiber 75. The Raman scattered light incident on the spectroscope 80 is separated into Raman spectral components by the spectroscope 80. Thereafter, signals corresponding to each Raman spectrum component are output from the spectrometer 80 to the control section 90. Such an operation is repeated while scanning the probe portion 40a of the cantilever 40 over the surface of the sample 10. Specifically, the control unit 90 scans the probe portion 40a of the cantilever 40 over the entire surface of the sample 10 by controlling the piezoelectric element stage 30 and the piezoelectric element stage 50 so that the amount of deformation of the cantilever 40 is constant. do. As a result, the control unit 90 generates a Raman spectral image and a surface unevenness image.

<Modification example 1 of scanning probe microscope>
FIG. 2 is a diagram showing a schematic configuration of a scanning probe microscope in Modification 1.

In the scanning probe microscope 200 according to Modification 1 shown in FIG. 2, among the Raman scattered light emitted from the sample 10, the Raman scattered light that has passed through the sample 10 is detected.

Specifically, in the scanning probe microscope 200 in Modification 1, near-field light is applied to the tip of the probe 40a by irradiating excitation light from the light source 71 of the input optical system 74 to the probe 40a of the cantilever 40. generate. Then, among the Raman scattered light emitted from the sample 10 placed opposite to the cantilever 40 , the Raman scattered light that has passed through the sample 10 passes through the light receiving optical system 73 and the optical fiber 75 and is focused on the spectroscope 80 . and the Raman spectra are detected. Here, as shown in FIG. 2, in this modification 1, the piezoelectric element stage 30 that scans the sample 10 placed on the sample holder 20 in the x and y directions passes the Raman scattered light that has passed through the sample 10. There is a need. Therefore, as shown in FIG. 2, the piezoelectric element stage 30 is provided with an opening 31, and the Raman scattered light that has passed through the sample 10 passes through this opening 31 and enters the light receiving optical system 73. It is configured as follows. Note that the other configurations are the same as those of the scanning probe microscope 100 shown in FIG. 1, so the explanation will be omitted.

According to the scanning probe microscope 200 in the present modification 1, the Raman scattered light is not easily blocked by the cantilever 40 or the piezoelectric element stage 30, so that a large detection solid angle can be obtained. As a result, it is possible to obtain a near-field optical image or a Raman spectroscopic image with high sensitivity and high contrast. That is, according to the scanning probe microscope 200 in the present modification 1, it is possible to improve the S/N ratio and measurement reproducibility of a near-field optical image or a Raman spectroscopy spectrum image.

<Modification 2 of scanning probe microscope>
FIG. 3 is a diagram showing a schematic configuration of a scanning probe microscope in Modification 2.

In the scanning probe microscope 300 according to the second modification shown in FIG. 3, among the Raman scattered light emitted from the sample 10, Raman scattered light scattered in the side direction of the cantilever 40 is detected. Specifically, in the scanning probe microscope 300 according to the second modification, near-field light is applied to the tip of the probe 40a by irradiating excitation light from the light source 71 of the input optical system 74 to the probe 40a of the cantilever 40. generate. Then, among the Raman scattered light emitted from the sample 10 placed opposite to the cantilever 40, the Raman scattered light scattered in the side direction of the cantilever 40 passes through the light receiving optical system 73 and the optical fiber 75 and is sent to the spectroscope. 80, and a Raman spectroscopic spectrum is detected. Note that the other configurations are the same as those of the scanning probe microscope 100 shown in FIG. 1, so the explanation will be omitted.

According to the scanning probe microscope 300 in the second modification, scattered light can be collected from multiple directions, and therefore measurements can be performed that are not easily affected by the shape of the sample 10.

<Configuration of cantilever in embodiment>
While the intensity of Raman scattered light is extremely weak compared to the intensity of Rayleigh scattered light, it increases in proportion to the intensity of near-field light. Therefore, from the perspective of improving the detection sensitivity of Raman scattered light, it is necessary to It is important to increase the intensity of the near-field light formed at the tip of the part.

Regarding this point, in this embodiment, the shape of the tip of the cantilever, which is a component of the scanning probe microscope, and the method of irradiating the excitation light to the tip of the cantilever are devised. This increases the strength of the near field formed at the tip of the In the following, the configuration of the cantilever in this embodiment in which this idea is applied will be explained.

FIG. 4 is a perspective view showing a schematic configuration of a cantilever in this embodiment.

In FIG. 4, a cantilever 40 in this embodiment is used, for example, in the scanning probe microscope shown in FIGS. 1 to 3. This cantilever 40 includes a held part 40c held by the head of a scanning probe microscope, a beam part 40b integrally formed with the held part 40c, and a probe part 40a supported by the beam part 40b. ing. The beam portion 40b extends in the x direction and is configured to be deformable. On the other hand, the probe portion 40a has, for example, a substantially triangular pyramid shape that protrudes in the z direction. However, the shape of the probe portion 40a is not limited to a substantially triangular pyramid shape, but may also be, for example, a substantially quadrangular pyramid shape.

When the probe section 40a of the cantilever 40 configured in this manner is irradiated with the excitation light 8, near-field light 8a is generated at the tip of the probe section 40a.

Here, in FIG. 4, the x-axis is defined as an axis parallel to the extending direction of the beam portion 40b. On the other hand, the y-axis is defined as an axis that is an imaginary plane that includes the x-axis and is parallel to the normal line of the imaginary plane in which the cantilever 40 is plane symmetrical. Additionally, the z-axis is defined as an axis perpendicular to both the x-axis and y-axis defined above.

Next, FIG. 5 is a cross-sectional view taken along line AA in FIG. 4. That is, FIG. 5 can also be said to be a cross-sectional view taken along a virtual plane that includes the ridge line that constitutes a part of the probe portion 40a of the cantilever 40 and is orthogonal to the upper surface of the beam portion 40b of the cantilever 40.

In FIG. 5, the probe part 40a of the cantilever 40 in this embodiment is a part that can be brought close to the sample, and is connected to the apex part 2 covered with the metal film 7, and is connected to the apex part 2 and is connected to the apex part 2 and is 7 and an upper corner portion 5 connected to the ridge line 4. In particular, at least one ridge line 4 exists at the tip of the probe portion 40a. Further, the cantilever 40 in this embodiment includes a beam portion 40b that connects to the probe portion 40a from the lower surface 1 and holds the probe portion 40a. Here, in FIG. 5, the probe part 40a connects a first line 3 connecting the apex part 2 and the beam part 40b, and a second line 6 connecting the upper corner part 5 and the upper surface of the beam part 40b. have. At this time, as shown in FIG. 5, the first line 3 is composed of a straight portion directly connected to the beam portion 40b. On the other hand, the second line 6 includes an inclined portion 6a directly connected to the upper corner portion 5, and a straight portion 6b connecting the inclined portion 6a and the upper surface of the beam portion 40b. In the cantilever 40 of this embodiment configured in this way, as shown in FIG. 5, the excitation light 8 focused by the lens 72 is irradiated obliquely to the ridgeline 4. A part of the ridgeline 4 and the upper corner portion 5 of the probe portion 40a are irradiated with excitation light 8 emitted from an excitation light source mounted on the scanning probe microscope system. That is, in the cantilever 40 according to the present embodiment, the ridge line 4 and the upper corner portion 5, which constitute a part of the probe portion 40a, are the portions to which the excitation light 8 is irradiated. In other words, in the cantilever 40 according to the present embodiment, at least a part of the ridgeline 4 and the upper corner portion 5 are included in the irradiation spot of the excitation light 8 focused by the lens 72.

Here, the material of the probe part 40a of the cantilever 40 is generally silicon (Si), but _the material of the probe part 40a is silicon oxide ( _SiO2 ), silicon nitride ( _Si3N4 ), carbon ( C) etc.

Further, the metal film 7 covering the apex portion 2 and the ridge line 4 of the probe portion 40a is formed from a metal film such as a gold film, a silver film, a platinum film, or an aluminum film, an alloy film, or a multilayer film of multiple metals. be able to. Although the thickness of the metal film 7 is not fundamentally limited, it is desirable that it be 0.1 times or more the wavelength of the excitation light 8, for example. However, in order to ensure the intensity of the near-field light 8a excited at the tip, it is desirable to keep the diameter of the tip of the probe part 40a small, so the thickness of the metal film 7 should not be too thick. do not have. Therefore, the thickness of the metal film 7 may be set depending on the purpose of measurement.

Next, in FIG. 5, the probe portion 40a has an upper corner portion 5 and a second line 6 formed by FIB (Focused Ion Beam) processing. At this time, silicon, which is the constituent material of the probe portion 40a, is exposed at the upper corner portion 5. In the cantilever 40 in this embodiment, the length of the ridge line 4 is extremely short. For example, the length of the ridgeline 4 is 10 times or less the wavelength of the excitation light 8 that is incident on the probe portion 40a of the cantilever 40. To give a specific example, when the wavelength of the excitation light 8 is 660 nm, the length of the ridge line 4 is 6.6 μm or less. Expressed in another way, the beam spot diameter of the excitation light 8 irradiated onto the probe portion 40 a is larger than the length of the ridge line 4 . In other words, the length of the ridgeline 4 is smaller than the beam spot diameter of the excitation light 8 irradiated onto the probe portion 40a.

When the cantilever 40 in this embodiment is used in a scanning probe microscope, as shown in FIG. be done. At this time, if the incident angle of the excitation light 8 with respect to the ridgeline 4 is θ, θ is greater than 0 degrees and smaller than 90 degrees. To give a specific example, θ is 45 degrees.

<Features of the embodiment>
Next, the feature points in this embodiment will be explained.

The first characteristic point of this embodiment is that, as shown in FIG. It is in. In other words, the first feature of this embodiment is the improvement in the shape of the probe portion 40a of the cantilever 40, in which the upper corner portion 5 is placed close to the apex portion 2 so that the length of the ridgeline 4 is shortened. The point is that the shape of the probe portion 40a is processed so that the probe portion 40a is arranged.

As shown in FIG. Collective oscillations of free electrons constituting the film 7 are excited. Then, the excited surface plasmons 8b propagate toward the apex portion 2 of the probe portion 40a, but in this embodiment, since the length of the ridge line 4 is short, the surface plasmons 8b do not decrease and are efficiently propagated. Surface plasmons 8b can be propagated to the vertex portion 2. As a result, local electric field concentration occurs at the apex portion 2 of the probe portion 40a, and extremely strong near-field light 8a is generated. That is, in this embodiment, as a result of the excitation light being irradiated onto the tip of the cantilever by the light source of the measurement device in which the cantilever is installed, free electrons move from the upper corner portion 5 to the vertex portion 2 along the ridge line 4. However, electric field concentration occurs at the vertex portion 2. At this time, in order to strengthen the coupling between the excitation light 8 and the surface plasmon 8b and concentrate the surface plasmon 8b on the vertex portion 2, the polarization direction of the excitation light 8 is changed so that the component parallel to the ridge line 4 (p-polarized component) is A large number is desirable.

Next, the second feature of this embodiment is that, for example, as shown in FIG. 5, the cantilever 40 is irradiated with excitation light 8 from an oblique direction with respect to the ridgeline 4 of the probe portion 40a. In this case, very strong surface plasmons 8b can be excited on the surface of the metal film 7 covering the ridgeline 4. That is, when the excitation light 8 is irradiated to the ridgeline 4 from an oblique direction, very strong surface plasmons 8b are excited on the surface of the metal film 7 covering the ridgeline 4. As a result, the energy carried by the surface plasmons 8b to the apex site 2 increases, thereby making it possible to generate very strong near-field light 8a in a region near the apex site 2. From the above, by combining the first feature point and the second feature point described above, surface plasmons 8b having very strong energy can be excited on the surface of the metal film 7 covering the ridgeline 4. As a result, due to the synergistic effect of the first feature point and the second feature point, very strong near-field light 8a can be generated near the apex portion 2 of the probe portion 40a. This means that the intensity of the Raman scattered light from the sample can be increased, so the scanning probe microscope using the cantilever 40 in this embodiment can significantly improve the measurement sensitivity of the Raman scattered light. Remarkable effects can be obtained.

For example, in a measurement technique in which only the tip of the probe portion 40a is irradiated with excitation light 8, only a portion of excitation light 8 can be converted into near-field light 8a. For this reason, it is difficult to utilize the maximum energy of the excitation light 8 for generating the near-field light 8a. Furthermore, if the length of the ridgeline 4 is too long, the propagation distance of the surface plasmon 8b excited on the surface of the metal film 7 covering the ridgeline 4 becomes long, and as a result, the surface plasmon 8b decreases due to the long propagation distance. It does not lead to improvement in sensitivity. On the other hand, in the present embodiment, as shown in FIG. The surface plasmons 8b are excited by the excitation light 8. The intensity of the near-field light 8a generated near the apex portion 2 is increased by the propagation of energy by the surface plasmon 8b. At this time, in this embodiment, since the length of the ridge line 4 is short, the surface plasmon 8b is less likely to decrease, and the intensity of the near-field light 8a can be efficiently improved. In other words, in this embodiment, the energy of the excitation light 8 can be utilized to the maximum through the propagation of energy by the surface plasmon 8b, so a very strong near-field light 8a is generated at the apex portion 2 of the probe portion 40a. can do. Therefore, according to the present embodiment, the intensity of the near-field light 8a generated near the vertex portion 2 of the probe portion 40a can be improved, so that the measurement sensitivity can be improved.

Furthermore, it is known that the measurement sensitivity of typical cantilevers used in scanning probe microscopes rapidly decreases due to, for example, dirt or oxidation on the surface of the metal film covering the tip of the probe. . For example, the lifespan of a typical cantilever is several weeks at most. In contrast, in the configuration of the present invention, the area of the metal film that can excite surface plasmons is large, and it is extremely unlikely that the entire excitation area becomes contaminated, so the cantilever 40 in this embodiment can realize a long life. Confirmed. Therefore, it can be said that the cantilever 40 according to the present embodiment is not only useful in that it can significantly improve measurement sensitivity, but also very excellent in that it can provide a highly reliable and long-life cantilever. .

<Modified example>
<<Modification 1>>
FIG. 6 is a perspective view showing a schematic configuration of a cantilever in Modification 1.

In FIG. 6, the cantilever 40-1 in Modification 1 is also used, for example, in the scanning probe microscope shown in FIGS. 1 to 3. This cantilever 40-1 includes a held part 40c held by the head of a scanning probe microscope, a beam part 40b integrally formed with the held part 40c, and a probe part 40a supported by the beam part 40. It is equipped with The beam portion 40b extends in the x direction and is configured to be deformable. On the other hand, the probe portion 40a has, for example, a substantially triangular pyramid shape that protrudes in the z direction. However, the shape of the probe portion 40a is not limited to a substantially triangular pyramid shape, but may also be, for example, a substantially quadrangular pyramid shape.

When the probe section 40a of the cantilever 40-1 configured in this manner is irradiated with the excitation light 8, near-field light 8a is generated at the tip of the probe section 40a.

FIG. 7 is a cross-sectional view taken along line AA in FIG.

In FIG. 7, the probe part 40a has a first line 3 that connects the apex part 2 and the beam part 40b, and a second line 6 that connects the upper corner part 5 and the upper surface of the beam part 40b. There is. At this time, as shown in FIG. 7, the first line 3 is composed of a straight portion directly connected to the beam portion 40b. On the other hand, the second line 6 includes a horizontal straight portion 6c directly connected to the upper corner portion 5, and a straight portion 6b connecting the horizontal straight portion 6c and the upper surface of the beam portion 40b.

Also in the cantilever 40-1 of the present modification 1 configured in this way, as shown in FIG. 7, the excitation light 8 focused by the lens 72 is irradiated obliquely to the ridge line 4. A part of the ridgeline 4 and the upper corner portion 5 of the probe portion 40a are irradiated with excitation light 8 emitted from the light source of the scanning probe microscope. Thereby, the cantilever 40-1 in the present modification 1 can also improve the intensity of the near-field light 8a generated near the vertex portion 2 of the probe portion 40a, similarly to the cantilever 40 in the embodiment.

<<Modification 2>>
FIG. 8 is a perspective view showing a schematic configuration of a cantilever in Modification 2. FIG.

In FIG. 8, the cantilever 40-2 in Modification 2 is also used, for example, in the scanning probe microscope shown in FIGS. 1 to 3. This cantilever 40-2 includes a held part 40c held by the head of the scanning probe microscope, a beam part 40b integrally formed with the held part 40c, and a probe part 40a supported by the beam part 40. It is equipped with The beam portion 40b extends in the x direction and is configured to be deformable. On the other hand, the probe portion 40a has, for example, a substantially triangular pyramid shape that protrudes in the z direction. However, the shape of the probe portion 40a is not limited to a substantially triangular pyramid shape, but may also be, for example, a substantially quadrangular pyramid shape.

When the probe section 40a of the cantilever 40-2 configured in this manner is irradiated with the excitation light 8, near-field light 8a is generated at the tip of the probe section 40a.

FIG. 9 is a cross-sectional view taken along line AA in FIG.

In FIG. 9, the probe part 40a has a first line 3 that connects the apex part 2 and the beam part 40b, and a second line 6 that connects the upper corner part 5 and the upper surface of the beam part 40b. There is. At this time, as shown in FIG. 9, the first line 3 is composed of a straight portion directly connected to the beam portion 40b. On the other hand, the second line 6 includes an inclined straight portion 6d that is directly connected to both the upper corner portion 5 and the upper surface of the beam portion 40b.

Also in the cantilever 40-2 in the second modified example configured in this way, as shown in FIG. 9, the excitation light 8 focused by the lens 72 is irradiated obliquely to the ridge line 4. A part of the ridgeline 4 and the upper corner portion 5 of the probe portion 40a are irradiated with excitation light 8 emitted from the light source of the scanning probe microscope. Thereby, the cantilever 40-2 in the present modification 2 can also improve the intensity of the near-field light 8a generated near the apex portion 2 of the probe portion 40a, similarly to the cantilever 40 in the embodiment.

In particular, the cantilever 40-2 in the present modification 2 has the advantage that it is easy to perform FIB processing because the second line 6 is composed only of the inclined straight portion 6d having a constant inclination.

<<Modification 3>>
FIG. 10 is a perspective view showing a schematic configuration of a cantilever in Modified Example 3.

In FIG. 10, the cantilever 40-3 in the present modification 3 is also used, for example, in the scanning probe microscope shown in FIGS. 1 to 3. This cantilever 40-3 includes a held part 40c held by the head of the scanning probe microscope, a beam part 40b integrally formed with the held part 40c, and a probe part 40a supported by the beam part 40. It is equipped with The beam portion 40b extends in the x direction and is configured to be deformable. On the other hand, the probe portion 40a has, for example, a substantially triangular pyramid shape that protrudes in the z direction. However, the shape of the probe portion 40a is not limited to a substantially triangular pyramid shape, but may also be, for example, a substantially quadrangular pyramid shape.

When the probe section 40a of the cantilever 40-3 configured in this manner is irradiated with the excitation light 8, near-field light 8a is generated at the tip of the probe section 40a.

FIG. 11 is a cross-sectional view taken along line AA in FIG. 10.

In FIG. 11, the probe part 40a has a first line 3 that connects the apex part 2 and the beam part 40b, and a second line 6 that connects the upper corner part 5 and the upper surface of the beam part 40b. There is. At this time, as shown in FIG. 11, the first line 3 is composed of a straight portion directly connected to the beam portion 40b. On the other hand, the second line 6 connects to the extension line part 9 located on the extension of the ridge line 4, the upper corner part 5 and the extension line part 9, and is recessed toward the first line 3 side. It consists of

Also in the cantilever 40-3 in the third modified example configured in this way, as shown in FIG. 11, the excitation light 8 focused by the lens 72 is irradiated obliquely to the ridge line 4. A part of the ridgeline 4 and the upper corner portion 5 of the probe portion 40a are irradiated with excitation light 8 emitted from the light source of the scanning probe microscope. Thereby, the cantilever 40-3 in the present modification 3 can also improve the intensity of the near-field light 8a generated near the apex portion 2 of the probe portion 40a, similarly to the cantilever 40 in the embodiment.

In particular, in the cantilever 40-3 according to the third modification, since the volume of the first recess 6e formed by FIB processing is small, the time required for FIB processing can be shortened.

<<Modification 4>>
FIG. 12 is a perspective view showing a schematic configuration of a cantilever in Modification 4. FIG.

In FIG. 12, the cantilever 40-4 in Modification 4 is also used, for example, in the scanning probe microscope shown in FIGS. 1 to 3. This cantilever 40-4 includes a held part 40c held by the head of the scanning probe microscope, a beam part 40b integrally formed with the held part 40c, and a probe part 40a supported by the beam part 40. It is equipped with The beam portion 40b extends in the x direction and is configured to be deformable. On the other hand, the probe portion 40a has, for example, a substantially triangular pyramid shape that protrudes in the z direction. However, the shape of the probe portion 40a is not limited to a substantially triangular pyramid shape, but may also be, for example, a substantially quadrangular pyramid shape.

When the probe section 40a of the cantilever 40-4 configured in this manner is irradiated with the excitation light 8, near-field light 8a is generated at the tip of the probe section 40a.

FIG. 13 is a cross-sectional view taken along line AA in FIG. 12.

In FIG. 13, the probe portion 40a has a first line 3 connecting the vertex portion 2 and the beam portion 40b, and a second line 6 connecting the upper corner portion 5 and the upper surface of the beam portion 40b. There is. At this time, as shown in FIG. 13, the first line 3 is composed of a straight portion directly connected to the beam portion 40b. On the other hand, the second line 6 is connected to an extension line part 9 located on an extension of the ridge line 4, the upper corner part 5 and the extension line part 9, and a second recessed part curved toward the first line 3 side. Consists of 6f.

Also in the cantilever 40-4 of the present modification 4 configured in this manner, as shown in FIG. 13, the excitation light 8 focused by the lens 72 is irradiated obliquely to the ridge line 4. A part of the ridgeline 4 and the upper corner portion 5 of the probe portion 40a are irradiated with excitation light 8 emitted from the light source of the scanning probe microscope. Thereby, the cantilever 40-4 in the present modification 4 can also improve the intensity of the near-field light 8a generated near the apex portion 2 of the probe portion 40a, similarly to the cantilever 40 in the embodiment.

In particular, in the cantilever 40-4 in the fourth modification, the volume of the second recess 6f formed by FIB processing is small, so that the time required for FIB processing can be shortened.

<High-level conceptualization of cantilever>
As described above, the configurations of the cantilever that embody the technical idea of this embodiment include, for example, the configuration shown in FIG. 5, the configuration shown in FIG. 7, the configuration shown in FIG. 9, and the configuration shown in FIG. configuration and the configuration shown in FIG. 13. Here, for example, if a configuration including the configuration shown in FIG. 5, the configuration shown in FIG. 7, and the configuration shown in FIG. 9 is called the first configuration, this first configuration can be understood as the configuration shown below. be able to. That is, in the first configuration, in FIG. 5, FIG. 7, and FIG. On the premise that the second line 6 includes a straight part (straight part 6b, inclined straight part 6d) that is directly connected to the upper surface of the beam part 40b, the straight part of the first line 3 and the second line 6 (straight part 6b, It can be said that the configuration is such that as the distance from the inclined straight portion 6d) approaches the apex portion 2, the distance remains the same or becomes narrower. Thereby, the first configuration can be said to be a higher-level configuration that includes the configuration shown in FIG. 5, the configuration shown in FIG. 7, and the configuration shown in FIG. 9. According to such a first configuration, the rigidity of the cantilever around the y-axis can be increased. From this, the first configuration can suppress vibrations caused by the shape of the cantilever.

Next, for example, if a configuration including the configuration shown in FIG. 11 and the configuration shown in FIG. 13 is called a second configuration, this second configuration can be understood as the configuration shown below. That is, the second configuration is based on the premise that the probe portion 40a includes the apex portion 2, the first line 3, the ridge line 4, the upper corner portion 5, and the second line 6 in FIGS. An extension line part 9 where the line 6 is located on an extension of the ridge line 4, and a recess part (first recess part 6e, second It can be said that the configuration includes a recessed portion 6f). Thereby, the second configuration can be said to be a higher-level configuration that includes the configuration shown in FIG. 11 and the configuration shown in FIG. 13. According to such a second configuration, the technical idea of this embodiment can be more easily realized. Furthermore, according to the second configuration, the positions where the recesses (first recess 6e, second recess 6f) are formed can be easily adjusted in accordance with the focusing characteristics of the excitation light lens of the scanning probe microscope. This provides versatility in that it can be applied to a wide variety of cantilevers for scanning probe microscopes. Additionally, since the processed part is extremely small, there is little effect on the vibration characteristics of the cantilever, and it can be used as is.

<Verification of effectiveness>
According to this embodiment, it is possible to obtain the effect of improving the intensity of near-field light generated at the tip of the probe, and below, the verification results of this effect will be explained.

FIG. 14 is a diagram schematically showing a simulation calculation model for verifying the effects of this embodiment. FIG. 14 shows a schematic probe section 1000 used in the simulation calculation model. This probe portion 1000 includes an apex portion 1001, a ridgeline 1002, an upper corner portion 1003, and a first line 1004. In FIG. 14, "(1)" indicates a case in which excitation light is irradiated from below to the apex region 1001 (downward irradiation), and "(2)" indicates a case in which excitation light is irradiated to the vertex region 1001 from the side. The figure shows the case of irradiation (lateral irradiation). In addition, in FIG. 14, "(3)" indicates the case where the excitation light is irradiated from the back side of the first line 1004 (backside irradiation), and "(4)" indicates the case where the excitation light is irradiated from the back side of the first line 1004, and "(4)" indicates the case where the excitation light is irradiated from the back side of the first line 1004. This shows the case where excitation light is irradiated from the front (oblique irradiation). Here, the case "(4)" corresponds to the proposed method in this embodiment. In the simulation calculation, the excitation light irradiated to the probe section 1000 is a Gaussian beam with a diameter of 3 μm, the polarization is P polarization, and the incident power is set to 1W. Further, the base material of the probe portion 1000 is silicon, and the thickness of the metal film 1005 is set to be about 100 nm on the edge line 1002 side and about 45 nm on the first line 1004 side.

Below, the generation situation of near-field light calculated using the above-mentioned simulation calculation model will be explained. FIG. 15 shows the simulation results for the entire probe section. On the other hand, FIG. 16 is a simulation result in which the vicinity of the tip of the probe is enlarged, and FIG. 17 is a simulation result in which the image is processed so that the electric field strength near the tip of the probe can be clearly understood. In FIGS. 15 and 16, the darker the area, the higher the electric field strength. In FIG. 17, focusing on the tip of the probe, it is shown that the electric field strength increases in the order of "white" → "black" → "gray". In each of FIGS. 15 to 17, "(1)" indicates downward illumination, and "(2)" indicates sideward illumination. Furthermore, in each of FIGS. 15 to 17, "(3)" indicates backside illumination, and "(4)" indicates oblique illumination. For example, as shown in FIG. 17, in oblique irradiation corresponding to the method proposed in this embodiment, the maximum electric field strength of near-field light in the region near the tip of the probe is 15.8 (V/m) ² It can be seen that the maximum electric field strength is more than twice that of the downward irradiation shown in (1), the side irradiation shown in (2), and the back irradiation shown in (3). . Therefore, for example, since the signal intensity of Raman spectroscopy is proportional to the fourth power of the intensity of near-field light, when performing tip-enhanced Raman spectroscopy with near-field light generated by oblique irradiation (4), other irradiation methods may be used. It can be estimated that an amplification of 4 times higher than the measurement sensitivity can be obtained. In this way, considering the verification results using the simulation calculation model described above, according to the present embodiment, as a result of being able to improve the intensity of the near-field light generated at the tip of the probe, for example, tip-enhanced Raman spectroscopy is possible. This proves that the measurement sensitivity can be improved.

<Considerations regarding the length of the ridge line>
Next, consideration regarding the length of the ridgeline will be explained.

FIG. 18 is a diagram showing that the electric field distribution caused by surface plasmons formed on the ridgeline differs depending on the length of the ridgeline in the probe section. For example, FIG. 18A shows the electric field distribution when the length L of the ridge line is L=1028 nm. On the other hand, FIG. 18(b) shows the electric field distribution when the ridge length L=4820 nm.

From this simulation result, it is possible to understand the necessity of specifying the length of the ridgeline. That is, in FIG. 18A, surface plasmons are excited and confined on the surface of the metal film covering the ridgeline, and as a result, a standing wave is generated by the surface plasmons. As a result, local electric field concentration occurs at the apex portion of the probe, and extremely strong near-field light is generated. For example, in FIG. 18A, the electric field strength of near-field light generated at the apex portion of the probe is 21.5 (V/m). On the other hand, if the length of the ridge line becomes too long as shown in FIG. 18(b), the surface plasmon confinement effect weakens. As a result, the electric field intensity of the generated near-field light becomes relatively weak at the apex portion of the probe. For example, in FIG. 18(b), the electric field strength of the near-field light generated at the apex portion of the probe portion is 13.9 (V/m). Note that the incident electric field strength during simulation calculation is 1 (V/m).

From the above, it can be seen that in order to increase the electric field strength of near-field light at the apex of the probe, it is desirable to limit the length of the ridgeline at the probe to a predetermined first specified value or less. . In other words, in order to effectively utilize local electric field concentration due to surface plasmons, there is an upper limit to the length of the ridgeline. On the other hand, if the length of the ridgeline is too short, it is thought that standing waves cannot be generated by surface plasmons. Therefore, in order to effectively utilize the local electric field concentration caused by surface plasmons, the length of the ridgeline must be set to a predetermined second value. It can be seen that it is desirable to limit the value to a specified value or more. In other words, in order to effectively utilize local electric field concentration due to surface plasmons, there is a lower limit to the length of the ridgeline. In this way, the electric field strength of the near-field light at the apex of the probe qualitatively depends on the length of the ridgeline, and from the viewpoint of increasing the electric field strength of the near-field light, the length of the ridgeline is set within a predetermined range ( It can be seen that it is desirable to limit the value to a value greater than or equal to the second specified value and less than or equal to the first specified value.

Therefore, the following describes simulation results in which changes in the electric field intensity of near-field light are calculated when the length of the ridge line is changed. For example, FIG. 19 is a diagram illustrating the preconditions in the first simulation for calculating the change in the electric field intensity of near-field light when the length of the ridgeline is changed. FIG. 19(a) shows the tip structure of the probe portion 40a. In FIG. 19(a), a line connecting the apex portion 8a and the upper corner portion 5 is a ridgeline 4, and the length of this ridgeline 4 is indicated by “L”. In the first simulation, this "L" is changed.

FIG. 19(b) is a diagram showing a prerequisite configuration for performing the first simulation. As shown in FIG. 19(b), the excitation light 8 is irradiated onto the apex portion 8a of the probe portion 40a. At this time, the wavelength of the excitation light 8 is 660 nm. This excitation light 8 is focused into a spot shape and irradiated onto the apex portion 8a of the probe portion 40a. Specifically, the center of the spot shape is irradiated onto the apex portion 8a, and the range of the spot shape includes the ridgeline 4 and the upper corner portion 5. In FIG. 19(b), in the first simulation, the angle between the horizontal line HL1 passing through the vertex portion 8a and the incident direction of the excitation light 8 is defined as the incident angle θ. Further, the electric field strength of the near-field light calculated in the first simulation is the electric field strength at the position indicated by "P" in FIG. 19(b). That is, in the first simulation, the gold substrate 10A is placed below the probe portion 40a, and a gap of 2 nm exists between the vertex portion 8a of the probe portion 40a and the surface of the gold substrate 10A. Here, the midpoint between the vertex portion 8a and the surface of the gold substrate 10A is "P", and the distance between "P" and the gold substrate 10 is 1 nm.

In addition, in the first simulation, since the configuration is such that the excitation light 8 is irradiated to the vertex portion 8a, the incident angle θ cannot be greater than 90°. Considering this, the range of the incident angle θ is 0° or greater. It is 90° or less. However, in an actual scanning probe microscope, the incident angle θ is limited to 15° or more and 90° or less in order to avoid physical interference between the gold substrate 10A and the incident optical system that focuses the excitation light 8 into a spot shape. That will happen.

FIG. 20 is a graph showing the results of the first simulation. In FIG. 20, the vertical axis represents the electric field strength (V/m), while the horizontal axis represents the incident angle θ (°). FIG. 20 shows the incident angle θ and the electric field strength when the length L of the ridge line 4 is λ/2 (=330 nm) or more and 5λ (=3300 nm) or less, when the wavelength of the excitation light is λ (=660 nm). The relationship between As shown in FIG. 20, in any case where the length L of the ridgeline 4 is λ/2 or more and 5λ or less, there is an incident angle θ at which the electric field strength takes a maximum value of, for example, 16 (V/m) or more. I understand that. Therefore, when the length L of the ridge line 4 is in the range of λ/2 or more and 5λ or less, the electric field strength of the near-field light can be increased by determining the incident angle that maximizes the electric field strength with reference to FIG. can do. In other words, based on the results of the first simulation, the electric field strength of near-field light depends on both the length L of the ridge line 4 and the incident angle θ, and when the length L of the ridge line 4 is λ/2 or more and 5λ or less, By selecting an appropriate incident angle θ based on the graph shown in FIG. 20, the electric field strength of the near-field light can be increased. That is, for example, by adjusting the incident angle θ depending on the difference in length L of the ridge line 4, the electric field strength of the near-field light can be increased. In other words, based on the results of the first simulation, the electric field strength of the near-field light depends on both the length L of the ridge line 4 and the incident angle θ, and for example, when the incident angle θ is determined, By selecting an appropriate length L of the ridge line 4 in the range from λ/2 to 5λ based on the graph, the electric field strength of the near-field light can be increased. In this way, by adjusting the incident angle θ depending on the length L of the ridge line 4 or selecting an appropriate length L of the ridge line 4 based on the incident angle θ, for example, the measurement sensitivity of tip-enhanced Raman spectroscopy can be improved. be able to.

Next, the results of the second simulation will be explained.

FIG. 21 is a diagram showing the prerequisite configuration for performing the second simulation. As shown in FIG. 21, excitation light 8 is irradiated onto the upper corner portion 5 of the probe portion 40a. At this time, the wavelength of the excitation light 8 is 660 nm. This excitation light 8 is focused into a spot shape and irradiated onto the upper corner portion 5 of the probe portion 40a. Specifically, the center of the spot shape is irradiated onto the upper corner portion 5, and the range of the spot shape includes the ridgeline 4 and the apex portion 8a. In FIG. 21, in the second simulation, the angle formed by the horizontal line HL2 passing through the upper corner portion 5 and the incident direction of the excitation light 8 is defined as the incident angle θ. Further, the electric field strength of the near-field light calculated in the second simulation is the electric field strength at the position indicated by "P" in FIG. That is, in the second simulation, the gold substrate 10A is placed below the probe part 40a, and a gap of 2 nm exists between the upper corner part 5 of the probe part 40a and the surface of the gold substrate 10A. . Here, the midpoint between the upper corner portion 5 and the surface of the gold substrate 10A is "P", and the distance between "P" and the gold substrate 10 is 1 nm.

In addition, in the second simulation, since the upper corner portion 5 is irradiated with the excitation light 8, considering that the incident angle θ may be 90° or more, the range of the incident angle θ is, for example, 0° or more. The angle can be set to 130° or less. However, in an actual scanning probe microscope, in order to avoid physical interference between the incident optical system that focuses the excitation light 8 into a spot shape and the gold substrate 10A, the incident angle θ is set to, for example, 15° or more and 130° or less. It will be limited.

FIG. 22 is a graph showing the results of the second simulation. In FIG. 22, the vertical axis represents the electric field strength (V/m), while the horizontal axis represents the incident angle θ (°). FIG. 22 shows the incident angle θ and the electric field strength when the length L of the ridge line 4 is λ/2 (=330 nm) or more and 3λ (=1980 nm) or less, when the wavelength of the excitation light is λ (=660 nm). The relationship between As shown in FIG. 22, in any case where the length L of the ridgeline 4 is λ/2 or more and 3λ or less, there is an incident angle θ at which the electric field strength takes a maximum value of, for example, 16 (V/m) or more. I understand that. Therefore, when the length L of the ridge line 4 is in the range of λ/2 or more and 3λ or less, the electric field strength of the near-field light can be increased by determining the incident angle that maximizes the electric field strength with reference to FIG. can do. In other words, based on the results of the second simulation, the electric field strength of near-field light depends on both the length L of the ridge line 4 and the incident angle θ, and when the length L of the ridge line 4 is λ/2 or more and 3λ or less, By selecting an appropriate incident angle θ based on the graph shown in FIG. 22, the electric field strength of the near-field light can be increased. That is, for example, by adjusting the incident angle θ depending on the difference in length L of the ridge line 4, the electric field strength of the near-field light can be increased. In other words, based on the results of the second simulation, the electric field strength of the near-field light depends on both the length L of the ridgeline 4 and the incident angle θ, and for example, when the incident angle θ is determined, By selecting an appropriate length L of the ridge line 4 in the range from λ/2 to 3λ based on the graph, the electric field strength of the near-field light can be increased. In this way, by adjusting the incident angle θ depending on the length L of the ridge line 4 or selecting an appropriate length L of the ridge line 4 based on the incident angle θ, for example, the measurement sensitivity of tip-enhanced Raman spectroscopy can be improved. be able to.

In the first and second simulations described above, the wavelength λ of the excitation light 8 was explained using λ = 660 nm as an example, but the results of the first simulation and the results of the second simulation show that, for example, λ is visible light. It can be applied to a range of wavelengths. However, the wavelength λ of the excitation light 8 is not limited to a wavelength in the visible light region, and the material of the metal film 7 covering the probe portion 40a may be changed from a gold film (Au film) to a silver film (Ag film). By replacing it with an aluminum film (Al film), it can be applied to a wide range of wavelengths from the near-ultraviolet region to the infrared region.

For example, when using a wavelength in the infrared region as the excitation light 8, in addition to measurements of SNOM and TERS, the sample surface expands due to irradiation with the excitation light 8 or near-field light generated by irradiation with the excitation light 8. The measurement sensitivity of infrared (IR) spectroscopy can also be made high by measuring either the change in reflectance or the photo-induced force at a nano-resolution level.

Next, based on the results of the first simulation and the second simulation, we will discuss the advantages of the configuration in which the spot center of the excitation light 8 is irradiated onto the apex portion 8a of the probe portion 40a, and the upper corner portion 5 of the probe portion 40a. The advantage of the configuration in which the spot center of the excitation light 8 is irradiated will be explained.

The results of the first simulation are for a configuration in which the spot center of the excitation light 8 is irradiated onto the apex portion 8a of the probe portion 40a. For example, as can be seen by comparing FIG. 20 and FIG. 22, the electric field intensity of the near-field light in the first simulation is generally higher than the electric field intensity of the near-field light in the second simulation. In particular, in the first simulation, when the length L of the ridgeline 4 is L=1028 nm and the incident angle θ is θ=65°, the electric field strength of the near-field light is 21 (V/m), which is the maximum value. . Therefore, the configuration in which the spot center of the excitation light 8 is irradiated onto the vertex portion 8a corresponding to the first simulation has the advantage that the magnitude of the electric field strength can be increased. Furthermore, based on the results of the first simulation, in the configuration in which the spot center of the excitation light 8 is irradiated onto the apex portion 8a, the length L of the ridge line 4 can be adjusted in the range from λ/2 to 5λ. The degree of freedom in designing the length L can be increased.

On the other hand, the results of the second simulation are for a configuration in which the spot center of the excitation light 8 is irradiated onto the upper corner portion 8a of the probe portion 40a. For example, as can be seen by comparing FIG. 19(b) and FIG. 21, in the configuration corresponding to the second simulation, the excitation light is directed not to the vertex region 8a near the gold substrate 10A but to the upper corner region 5 far from the gold substrate 10A. The center of spot number 8 is irradiated. This means that in the configuration in which the spot center of the excitation light 8 is irradiated onto the upper corner portion 5, the excitation light 8 is irradiated on areas other than the measurement target area of the sample than in the configuration in which the spot center of the excitation light 8 is irradiated on the apex portion 8a. This means that it is possible to reduce the amount of damage caused by That is, in the configuration in which the spot center of the excitation light 8 is irradiated onto the upper corner portion 5, the excitation light 8 is irradiated onto areas other than the measurement target area of the sample than in the configuration in which the spot center of the excitation light 8 is irradiated on the vertex portion 8a. This has the advantage of reducing background noise caused by this. Furthermore, in a configuration in which the spot center of the excitation light 8 is irradiated onto the upper corner portion 5, an incident angle θ of 90° or more is acceptable, which is better than in a configuration in which the spot center of the excitation light 8 is irradiated onto the apex portion 8a. The degree of freedom can be increased.

The electric field strength of the near-field light depends on the length L of the ridgeline 4 of the probe portion 40a and the incident angle θ. Therefore, in order to increase the electric field strength of the near-field light, two methods can be considered for determining the parameters, the length L of the ridge line 4 and the incident angle θ. That is, the first method determines the length L of the ridge line 4 that maximizes the electric field strength of the near-field light after determining the incident angle θ, and the first method determines the length L of the ridge line 4 that maximizes the electric field strength of the near-field light after determining the length L of the ridge line 4. This is the second method of determining the maximum incident angle θ.

<First method>
The first method is effective when, for example, the incident angle θ is fixed in a scanning probe microscope. For example, FIG. 23 shows the length L of the ridge line 4 and the electric field strength of the near-field light when the incident angle θ is fixed at θ=60°, assuming a configuration in which the spot center of the excitation light is irradiated to the apex region. It is a graph showing the relationship. This FIG. 23 can be calculated based on the graph shown in FIG. 20, for example. In FIG. 23, when the incident angle θ is fixed at θ=60°, the length of the ridge line 4 where the electric field strength is the largest is L=1λ. Therefore, in a scanning probe microscope in which the incident angle θ is fixed at θ=60°, it is sufficient to employ a cantilever in which the length L of the ridge line 4 of the probe portion 40a is L=λ.

Similarly, for example, FIG. 24 shows the length L of the ridgeline 4 and the near-field light when the incident angle θ is fixed at θ=60°, assuming a configuration in which the spot center of the excitation light is irradiated to the upper corner part. It is a graph showing the relationship between the electric field strength and the electric field strength. This FIG. 24 can be calculated based on the graph shown in FIG. 22, for example. In FIG. 24, when the incident angle θ is fixed at θ=60°, the length of the ridge line 4 where the electric field strength is the largest is L=1λ. Therefore, in a scanning probe microscope in which the incident angle θ is fixed at θ=60°, it is sufficient to employ a cantilever in which the length L of the ridge line 4 of the probe portion 40a is L=λ.

<Second method>
The second method is effective, for example, when a cantilever is manufactured in which the length L of the ridgeline 4 is determined in advance. In order to realize this second method, the scanning probe microscope needs to be configured so that the incident angle θ can be changed.

Below, an example of the configuration of a scanning probe microscope that can change the incident angle θ will be described.

FIG. 25 is a diagram schematically showing an incident optical system included in a scanning probe microscope that can change the incident angle. In FIG. 25, the incident optical system 74 is an optical system that focuses excitation light into a spot shape and irradiates the cantilever 40, and the incident optical system 74 adjusts the incident angle to the cantilever 40, for example, from 15 degrees to 135 It is configured so that it can be changed within the following range. Specifically, for example, when the center of the spot shape is irradiated onto the apex region, the incident optical system 74 sets the incident angle between the horizontal line passing through the apex region and the center line of the incident optical system 74 from 15 degrees to 90 degrees. Includes an angle adjustment mechanism that can be set to In addition, when the incident optical system 74 irradiates the upper corner part with the center of the spot shape, the incident angle between the horizontal line passing through the upper corner part and the center line of the incident optical system 74 is set to 15 degrees or more and 135 degrees or less. Including possible angle adjustment mechanism. This makes it possible to realize a scanning probe microscope that can change the incident angle.

FIG. 26 is a diagram showing a lens 72 that is a condensing lens included in a scanning probe microscope that can change the incident angle. In FIG. 26, by increasing the aperture (NA) of the lens 72, for example, as shown in FIGS. 72 (see FIGS. 26(a) and 26(c)) and an optical path configuration in which the center of the excitation light 8 coincides with the center line CL of the lens 72 (see FIG. 26(b)). )) is configured to include an optical path adjustment mechanism that allows changing the optical path configuration between the two. Thereby, the angle of incidence of the excitation light 8 on the cantilever 40 can be changed as shown in FIGS. 26(a) to 26(c).

Note that, as shown in FIG. 27, the lens 72 can also be placed above the cantilever 40. In this case, the lens 72 can be used to change the angle of incidence of the excitation light 8 onto the cantilever 40, and the lens 72 can also be used to configure the optical path of the optical lever detection section 60. Specifically, after the light 62 emitted from the light source 61 is irradiated onto the beam portion 40b of the cantilever 40 via the lens 72, the light 62 (reflected light) reflected by the beam portion 40b of the cantilever 40 is reflected by the lens 72. The light is received by the photodetector 63 via the light beam. In this way, the optical path of the optical lever detection section 60 can also be configured by the lens 72 disposed above the cantilever 40. As a result, according to the configuration shown in FIG. 27, the difficulty in spatial arrangement of the optical lever detection section 60 can be solved.

FIG. 28 is a diagram showing a cantilever included in a scanning probe microscope that can change the incident angle. In FIG. 28, the scanning probe microscope has an adjustment unit that adjusts the position of the cantilever 40 so as to change the incident angle of the excitation light 8 irradiated onto the cantilever 40. Thereby, for example, as shown in FIG. 28, as a result of adjusting the position of the cantilever 40, the angle of incidence of the excitation light 8 on the cantilever 40 can be changed. Therefore, also with the configuration shown in FIG. 28, it is possible to realize a scanning probe microscope in which the incident angle can be changed.

<Modified example>
In the scanning probe microscope according to the present embodiment, for example, as shown in FIG. 1, a lens 72, which is a transmission type objective lens, is used as a condensing optical component that condenses the excitation light 8 into a spot shape and irradiates the cantilever 40. I am using it. However, the condensing optical component is not limited to the lens 72, and includes, for example, a reflective objective lens 72A shown in FIG. 29(a), a parabolic mirror 72B shown in FIG. 29(b), and a parabolic mirror 72B shown in FIG. 29(c). Any optical component of integrating mirror 72C may be used.

Note that, as shown in FIG. 30, when a parabolic mirror 72D is used as a condensing optical component that condenses excitation light into a spot shape and irradiates it onto the cantilever 40, this parabolic mirror 72D is used. The optical path of the optical lever detection section 60 can also be configured. For example, as shown in FIG. 30, light 62 emitted from the light source 61 is reflected by a parabolic mirror 72D and then irradiated onto the cantilever 40. Thereafter, the light 62 irradiated onto the cantilever 40 is reflected by the cantilever 40, further reflected by the parabolic mirror 72D, and received by the photodetector 63. In this way, the parabolic mirror 72D can also configure the optical path of the optical lever detection section 60. As a result, according to the configuration shown in FIG. 30, the difficulty in spatial arrangement of the optical lever detection section 60 can be solved.

Although the invention made by the present inventor has been specifically explained based on the embodiments thereof, the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, the probe portion 40a and the beam portion 40b do not need to be separated by a clear external feature. Therefore, the probe portion 40a, the beam portion 40b, and the held portion 40c may be referred to as the first portion (40a), second portion (40b), and third portion (40c) of the cantilever 40, respectively. good.

1 Lower surface 2 Vertex part 3 First line 4 Edge line 5 Upper corner part 6 Second line 6a Slanted part 6b Straight part 6c Horizontal straight part 6d Slanted straight part 6e First recessed part 6f Second recessed part 7 Metal film 8 Excitation light 8a Near field Light 8b Surface plasmon 10 Sample 10A Gold substrate 20 Sample holder 30 Piezoelectric stage 40 Cantilever 40-1 Cantilever 40-2 Cantilever 40-3 Cantilever 40-4 Cantilever 40a Probe section 40b Beam section 40c Holding section 50 Piezoelectric stage 51 Piezoelectric element actuator 52 Head 60 Optical lever detection unit 61 Light source 62 Light 63 Photodetector 70 Incident/detection optical system 71 Light source 72 Lens 72A Reflective objective lens 72B Parabolic mirror 72C Integrating mirror 72D Parabolic mirror 73 Light receiving optical system 74 Input optical system 80 Spectrometer 90 Control part 100 Scanning probe microscope 200 Scanning probe microscope 300 Scanning probe microscope 1000 Probe part 1001 Vertex part 1002 Ridge line 1003 Upper corner part 1004 First line 1005 Metal film CL Center line HL1 Horizontal line HL2 Horizontal line

Claims (17)

A cantilever used in a scanning probe microscope,
In cross-sectional view,
The cantilever is
a vertex part that is a part that can be brought close to the sample and is covered with a metal film;
a ridge line connected to the apex portion and covered with the metal film;
an upper corner part connected to the ridge line;
has
The cantilever is
A probe part;
a beam part connected to the probe part from the bottom surface and for holding the probe part;
has
In a cross-sectional view, the probe part is
The apex portion;
a first line connecting the vertex portion and the beam portion;
the ridge line;
the upper corner part;
a second line connecting the upper corner portion and the beam portion;
has
Each of the first line and the second line includes a straight part directly connected to the beam part,
In the cantilever, the distance between the linear portion of the first line and the linear portion of the second line becomes narrower as it approaches the apex portion. A cantilever used in a scanning probe microscope,
In cross-sectional view,
The cantilever is
a vertex part that is a part that can be brought close to the sample and is covered with a metal film;
a ridge line connected to the apex portion and covered with the metal film;
an upper corner part connected to the ridge line;
has
The cantilever is
A probe part;
a beam part connected to the probe part from the bottom surface and for holding the probe part;
has
In a cross-sectional view, the probe part is
The apex portion;
a first line connecting the vertex portion and the beam portion;
the ridge line;
the upper corner part;
a second line connecting the upper corner portion and the beam portion;
has
The second line is
an extension line portion located on an extension of the ridge line;
a recessed portion connected to the upper corner portion and the extension line portion and recessed toward the first line side;
including cantilever. The cantilever according to claim 1 or 2,
The metal film is a metal film, an alloy film, or a multilayer film of multiple metals, such as a gold film, a silver film, a platinum film, or an aluminum film,
The material of the cantilever is silicon, silicon oxide, or silicon nitride. a sample holder that holds the sample;
a light source that emits excitation light;
a cantilever that is irradiated with the excitation light;
A scanning probe microscope comprising:
In cross-sectional view,
The cantilever is
a vertex portion that is a portion that can be brought close to the sample and is covered with a metal film;
a ridge line connected to the apex portion and covered with the metal film;
an upper corner part connected to the ridge line;
has
The part of the ridgeline and the upper corner part are parts to which excitation light emitted from the light source of the scanning probe microscope is irradiated. The scanning probe microscope according to claim 4 ,
A scanning probe microscope in which the excitation light is irradiated obliquely to the ridgeline. The scanning probe microscope according to claim 4 ,
A scanning probe microscope configured to be able to adjust the direction in which the cantilever is irradiated with the excitation light depending on the length of the ridgeline of the cantilever used. The scanning probe microscope according to claim 4 ,
When the wavelength of the excitation light is λ, the length of the ridge is λ/2 or more and 5λ or less,
The scanning probe microscope has an entrance optical system that focuses the excitation light into a spot shape and irradiates the cantilever,
The incidence optical system can set an incident angle between a horizontal line passing through the vertex region and a center line of the incidence optical system to be 15 degrees or more and 90 degrees or less when irradiating the center of the spot shape to the vertex region. A scanning probe microscope that includes an adjustable angle mechanism. The scanning probe microscope according to claim 4 ,
When the wavelength of the excitation light is λ, the length of the ridge is λ/2 or more and 3λ or less,
The scanning probe microscope has an entrance optical system that focuses the excitation light into a spot shape and irradiates the cantilever,
When the incident optical system irradiates the upper corner portion with the center of the spot shape, the incident angle between a horizontal line passing through the upper corner portion and a center line of the incident optical system is 15 degrees or more and 135 degrees or less. Scanning probe microscope, including a configurable angle adjustment mechanism. The scanning probe microscope according to claim 4 ,
When the wavelength of the excitation light is λ, the length of the ridge is λ/2 or more and 5λ or less,
The scanning probe microscope has an entrance optical system including a condensing lens that condenses the excitation light into a spot shape and irradiates the cantilever with the excitation light,
The input optical system has a first optical path configuration in which the center of the excitation light coincides with the center of the condenser lens, and a second optical path configuration in which the center of the excitation light passes through a position offset from the center of the condenser lens. A scanning probe microscope that includes an optical path adjustment mechanism that can be changed between The scanning probe microscope according to claim 9 ,
Deformation of the cantilever is performed by detecting reflected light from the beam portion of the cantilever of light irradiated onto the beam portion of the cantilever via the condensing lens with a photodetector via the condensing lens. A scanning probe microscope that has an optical lever detection section that detects. The scanning probe microscope according to claim 4 ,
When the wavelength of the excitation light is λ, the length of the ridge is λ/2 or more and 5λ or less,
The scanning probe microscope includes an adjustment unit that adjusts the position of the cantilever so as to change the angle of incidence of the excitation light irradiated onto the cantilever. The scanning probe microscope according to claim 4 ,
The scanning probe microscope includes a condensing optical component that condenses the excitation light into a spot shape and irradiates the cantilever,
A scanning probe microscope in which the condensing optical component is comprised of any one of a transmission objective lens, a reflection objective lens, a parabolic mirror, or an integrating mirror. The scanning probe microscope according to claim 12 ,
By detecting the reflected light from the beam part of the cantilever of the light irradiated onto the beam part of the cantilever via the condensing optical part with a photodetector, the cantilever is A scanning probe microscope that has an optical lever detection section that detects deformation of. The scanning probe microscope according to claim 4 ,
The excitation light has a wavelength in the infrared region,
The scanning probe microscope measures at a nano-resolution level any of the expansion of the sample surface, changes in reflectance, and optical induced force due to irradiation with the excitation light or irradiation with near-field light generated by irradiation with the excitation light. scanning probe microscope. (a) A step of irradiating the cantilever with excitation light emitted from a light source,
(b) detecting scattered light from a sample placed opposite to the cantilever;
A measurement method using a scanning probe microscope, comprising:
The cantilever is
a vertex portion that is a portion that can be brought close to the sample and is covered with a metal film;
a ridge line connected to the apex portion and covered with the metal film;
an upper corner part connected to the ridge line;
has
A measuring method using a scanning probe microscope, wherein the part of the ridgeline and the upper corner portion are areas to which the excitation light emitted from the light source of the scanning probe microscope is irradiated. In the measurement method using a scanning probe microscope according to claim 15 ,
A measurement method using a scanning probe microscope, in which the excitation light is irradiated obliquely to the ridgeline. A probe part;
a beam part connected to the probe part from the bottom surface and for holding the probe part;
A cantilever comprising:
In a cross-sectional view, the probe part is
An apex part covered with a metal film,
a first line connecting the vertex portion and the beam portion;
a ridge line connected to the apex portion and covered with the metal film;
an upper corner part connected to the ridge line;
a second line connecting the upper corner portion and the beam portion;
has
The second line has either a first configuration or a second configuration,
The first configuration is
Each of the first line and the second line includes a straight part directly connected to the beam part,
The distance between the straight part of the first line and the straight part of the second line is configured to become narrower as it approaches the apex part,
The second configuration is
The second line is
an extension line portion located on an extension of the ridge line;
a recessed portion connected to the upper corner portion and the extension line portion and recessed toward the first line side;
A cantilever, which is a configuration that includes.

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