JP7565906B2 - Laser Raman spectroscopy and manufacturing method of ceramic products using the results obtained - Google Patents

Description

The present invention relates to a laser Raman spectroscopy method and a method for manufacturing ceramic products by feeding back the results obtained therefrom, and in particular to a laser Raman spectroscopy method suitable for analyzing opaque bodies and a method for manufacturing ceramic products by feeding back the results obtained therefrom.

When electromagnetic waves such as visible light are irradiated onto a substance, Rayleigh scattered light with the same frequency as the irradiated electromagnetic wave and Raman scattered light with a different frequency are generated. Raman scattered light appears shifted from the frequency of the irradiated electromagnetic wave based on the vibration and rotation of the bond state that constitutes the substance. The frequency shift of this Raman scattered light (Raman shift) depends on the bond energy between atoms. Therefore, by creating a spectrum with this frequency shift on the horizontal axis, laser Raman spectroscopy can be widely used for qualitative and quantitative analysis of molecules, bond states, functional groups, etc.
Furthermore, laser Raman spectroscopy uses laser light as the incident light, and the wavelength of the incident light can be narrowed down to about 1 μm, making it a useful measurement method even for microscopic areas.

In laser Raman spectroscopy, angles of 90° and 180° are primarily used as detection angles for scattered light relative to incident light.
In the case of a detection angle of 180°, the incident light and the scattered light are coaxial, so for example, a microscope lens can be placed on the optical axis, and the incident light can be irradiated and the scattered light can be detected through this microscope lens. This is widely used in microscopic Raman spectroscopic analysis devices that can measure microscopic areas of 10 μm or less.

However, when measuring discoloration or foreign matter that can be seen with the naked eye, or other objects larger than a microscopic area (10 to 1000 μm level) at a detection angle of 180°, the focus of the microscope lens must be widened, resulting in an unavoidable decrease in sensitivity, which is a technical challenge.

On the other hand, when the detection angle is 90°, when measuring discoloration or foreign matter that can be seen with the naked eye, or other areas larger than a microscopic area (10 to 1000 μm level), the incident light and scattered light are not coaxial, so the incident light can be set to a stronger output, achieving even higher sensitivity.

Furthermore, when the detection angle is 90°, if the sample is a transparent material such as glass, the incident light can pass through the sample, making this a particularly useful technique.
However, if the sample is opaque, it cannot transmit the incident light, so the analytical surface of the sample must be tilted at an appropriate angle to the incident light to avoid detecting the reflection (reflected light) of the incident light.
Regarding sensitivity, as shown in FIG. 10( a), when the inclination angle of the analytical surface W1 of the sample W with respect to the optical axis of the incident light L1 is reduced, the irradiated area on the analytical surface W1 becomes larger, and the area of the scattered light that can pass through the aperture 14 becomes smaller compared to the irradiated area, resulting in a decrease in sensitivity.

On the other hand, as shown in FIG. 10( b ), when the inclination angle of the analytical surface W1 of the sample W with respect to the optical axis of the incident light L1 is increased, the irradiation area on the analytical surface W1 becomes smaller, and the area of scattered light that can pass through the aperture 14 occupies a larger area relative to the irradiation area, resulting in higher sensitivity.
That is, the closer the inclination angle of the analytical surface W1 of the sample W is to the vertical, the larger the area through which scattered light passes relative to the area irradiated with the incident light, and therefore, highly sensitive detection and analysis can be expected.

However, as shown in FIG. 10(b), when the inclination angle of the analysis surface W1 of the sample W is brought closer to perpendicular to the optical axis of the incident light, the shape becomes elliptical rather than circular when viewed from the aperture 14, and the area to be measured becomes larger than expected, which may result in the detection of unnecessary information. In such a case, the diameter of the aperture 14 can be made smaller to prevent the area of the measurement area from increasing, and only the information of the required analysis area can be detected.

As described above, when the sample W is opaque and the detection angle of the scattered light is 90° with respect to the incident light L1, the closer the inclination angle of the analysis surface W1 of the sample W to the optical axis of the incident light L1 is to perpendicular, the higher the sensitivity can be expected.
10(b), when the analytical surface W1 of the sample W is brought closer to being perpendicular to the incident light L1, the incident light reflected from the sample (reflected light L2) is incident on the condenser lens 13 on the detection side, and is condensed by the condenser lens 13 together with the scattered light that should be detected, passes through the aperture 14, and is dispersed and detected, which causes the problem of stray light (unnecessary reflection and scattering of light occurring within the optical system). The presence of this stray light causes the detection of peaks that should not have been detected and deformation of the spectrum, and these phenomena lead to erroneous judgment of the measurement results.

In order to prevent the stray light in laser Raman spectroscopy, Patent Document 1 discloses a configuration in which two to eight dichroic mirrors that transmit Raman scattered light are installed to attenuate reflected light and remove the stray light.
Furthermore, Japanese Patent Laid-Open No. 2003-233693 discloses a configuration in which an aperture is provided on the detection optical path of near-field light, and stray light is eliminated as much as possible by this aperture.

Japanese Patent Application Publication No. 1-287448 JP 2004-37158 A

However, the configuration disclosed in Patent Document 1 has a problem in that the device configuration is large-scale and the cost of the equipment is high, so that it cannot be easily applied.
Furthermore, the configuration disclosed in Patent Document 2 cannot prevent the occurrence of stray light itself, and there is a problem that even if the stray light is eliminated as much as possible, a stray light component is included in the detection light path.

The present invention was made under the above circumstances, and its purpose is to provide a laser Raman spectroscopy method that can prevent the generation of stray light and perform highly sensitive analysis when detecting and analyzing an opaque sample at an angle of 90° to the incident laser light, and a manufacturing method for ceramic products that utilizes the results obtained therein.

The laser Raman spectroscopy method according to the present invention, which has been made to solve the above-mentioned problems, is a laser Raman spectroscopy method in which laser light is irradiated as incident light onto an analysis surface formed on a flat surface of a sample which is an opaque body, and scattered light generated from the sample is passed through a collecting lens whose main surface is arranged parallel to the optical axis of the incident light in a direction at an angle of 90° to the optical axis of the incident light, and then dispersed, detected, and spectrally analyzed, wherein the inclination angle of the analysis surface of the sample with respect to the incident light is less than ½ of the angle formed by a line connecting the center of the main surface of the collecting lens to an end of the main surface of the collecting lens, and a line connecting the intersection of the analysis surface of the sample and the optical axis of the incident light to the end of the main surface of the collecting lens.
It is preferable that the inclination angle of the analysis surface of the sample with respect to the incident light is 15° or more.
It is also preferable that the sample used has a visible light transmittance of 10 ⁻⁴ % or less.
It is also preferable that the diameter of the incident light is set to be 10 μm or more and 100 μm or less.

As described above, in the laser Raman spectroscopy according to the present invention, the inclination angle of the analysis surface of the sample with respect to the incident laser light is set to be less than half the angle formed by the line connecting the center of the main surface of the focusing lens to the end of the main surface of the focusing lens and the line connecting the intersection of the analysis surface of the sample with the optical axis of the incident light to the line connecting the end of the main surface of the focusing lens, so that the reflected light does not pass through the focusing lens and the generation of stray light can be prevented.
Furthermore, by setting the inclination angle of the analytical surface of the sample with respect to the incident light to 15° or more, a sufficient amount of light per unit area on the analytical surface can be obtained, enabling stable, highly sensitive measurements.

The method for manufacturing a ceramic product according to the present invention, which has been developed to solve the above problems, is characterized by feeding back the analysis results obtained by the laser Raman spectroscopy analysis method.

In this way, by using the present invention to evaluate opaque ceramic materials such as alumina, yttria, silicon carbide, carbon, and other materials, it is possible to perform highly sensitive evaluations that are free from the effects of stray light, making it possible to develop and provide higher quality ceramic products.
Furthermore, by feeding back the measurement results of the laser Raman spectroscopy of the present invention to the manufacturing conditions, it becomes possible to manufacture higher quality ceramic products.

The present invention provides a laser Raman spectroscopic analysis method that can prevent the generation of stray light and perform highly sensitive analysis when detecting and analyzing an opaque sample at an angle of 90° to the incident laser light, and a manufacturing method for ceramic products that feeds back the results obtained therefrom.

FIG. 1 is a block diagram of a laser Raman spectroscopic analysis apparatus to which the laser Raman spectroscopic analysis method of the present invention can be applied. FIG. 2 is a schematic side view for explaining the inclination angle of the analysis surface in the laser Raman spectroscopy of the present invention. FIG. 3 is a block diagram of the laser Raman spectroscopy method of the present invention. 4(a) and (b) are graphs showing the results of Experiment 1 in the embodiment. FIG. 5 is another graph showing the results of Experiment 1 in the example. FIG. 6 is a graph showing the results of Experiment 2 in the embodiment. 7A and 7B are schematic side views for explaining Experiment 2 in Example 2. FIG. 8(a) and (b) are graphs showing the results of Experiment 3 in the embodiment. FIG. 9 is a graph showing the results of Experiment 4 in the embodiment. 10A and 10B are side views showing the relationship between the inclination angle of the analysis surface of the sample with respect to the incident light and the irradiation area.

Hereinafter, an embodiment of the laser Raman spectroscopy method according to the present invention and a manufacturing method for a ceramic product that utilizes the results obtained therein will be described. The laser Raman spectroscopy method according to the present invention is a method for analyzing an opaque sample, in which a laser beam is irradiated onto the sample as incident light, and scattered light generated from the sample is detected in a direction at 90° to the optical axis of the incident light. In this embodiment, an opaque sample is a sample that does not transmit light, and specifically, a material with a visible light (380 to 780 mm) transmittance of 10 ^-4 % or less.
In addition, the scattered light generated from the sample is detected from a direction at 90° to the optical axis of the incident light because the incident light and scattered light are not coaxial as in the case where the detection angle is 180°, and therefore it is possible to avoid detecting reflection (reflected light) of the incident light, thereby enabling more sensitive analysis.

Figure 1 is a block diagram of a laser Raman spectroscopic analysis device to which the laser Raman spectroscopic analysis method of the present invention can be applied. The laser Raman spectroscopic analysis method of the present invention is performed by a laser Raman spectroscopic analysis device 11 as shown in Figure 1. As shown in the figure, the laser Raman spectroscopic analysis device 11 includes an optical system 12 of incident light including a laser having a specific wavelength by irradiating a sample W with laser light, a focusing lens 13 that focuses Raman scattered light from the sample W, an aperture 14 that adjusts the amount of light that passes through the focusing lens 13, a spectrometer 15 that separates the light that passes through the aperture 14 into wavelengths, and a detector 16 that detects the light separated by the spectrometer 15.

The focusing lens 13 is formed to have a diameter of, for example, 4 cm, and is arranged so that its principal surface (the surface including the line EF in FIG. 2) is parallel to the optical axis of the incident light L1 from the incident light optical system 12, and is arranged so as to detect scattered light L3 in a direction at 90° to the incident light L1.
Furthermore, the analytical surface W1 of the sample W onto which the laser light is incident is disposed so as to be inclined at an angle θ with respect to the incident light. This angle θ is determined as follows. As shown in Fig. 2, if the laser optical axis on the laser device 12 side is A, the intersection point between the analytical surface W1 of the sample W and the optical axis of the incident light L1 is B, and the lower end of the inclination of the analytical surface W1 of the sample W is C, then the inclination angle θ of the analytical surface W1 of the sample W with respect to the incident light L1 is ∠ABC. If the upper end of the inclination of the analytical surface W1 of the sample W is D and the front of the laser optical axis is H, then ∠DBH is the apex angle of ∠ABC, and its magnitude is the angle θ.

If the perpendicular direction of the analysis surface W1 of the sample W is I and the tip of the optical axis of the reflected light L2 is G, then the angle of incidence and the angle of reflection are equal, so ∠ABI = ∠GBI. Furthermore, since ∠CBI = ∠DBI = 90°, ∠ABC = ∠DBG = θ. Therefore, ∠HBG = 2θ.

On the other hand, if the center of the principal surface of the focusing lens 13 is E, the end of the principal surface of the focusing lens 13 is F, and the angle γ is ∠EFB formed by the line EF connecting E and F and the line BF connecting B and F, then since the straight line AH (incident optical axis) and the straight line EF are parallel, ∠HBF is an alternate angle of ∠EFB, and its magnitude is the angle γ.
Therefore, if γ>2θ (i.e., θ is less than 1/2γ) is satisfied, the reflected light L2 will not be incident on the condenser lens on the detection side, and the reflected light L2 will not be condensed together with the scattered light L3 by the condenser lens 13. In other words, unnecessary light will not pass through the aperture 14 and be detected by the spectroscope 15 and the detector 16, and the occurrence of stray light (reflection or scattering of unnecessary light) can be prevented.
Specifically, in this embodiment, the angle θ is set to be equal to or greater than 15° and less than ½γ. This is because, when the tilt angle θ is smaller than 15°, the irradiation area of the incident light L1 on the sample W becomes large, resulting in low analytical sensitivity. On the other hand, when the tilt angle θ is equal to or greater than 15°, sufficient analytical sensitivity can be ensured.

In the laser Raman spectroscopic analysis apparatus 11 configured in this manner, the incident light optical system 12 generates laser incident light having a diameter of, for example, 10 μm or more and 100 μm or less (step S1 in FIG. 3), and the laser light having a wavelength of, for example, 532 nm is incident on the analysis surface W1 of the sample W (step S2 in FIG. 3).
The laser light (incident light L1) incident on the analytical surface W1 of the sample W is split into reflected light L2 and scattered light L3, and the scattered light L3 emitted from the sample W passes through the condenser lens 13. Here, the inclination angle θ of the analytical surface W1 of the sample W with respect to the incident laser light is set to be less than 1/2 of ∠EFB defined by the center E of the principal surface of the condenser lens 13 on the detection side, the end F of the principal surface of the condenser lens 13 on the detection side, and the intersection B between the analytical surface W1 of the sample W and the optical axis of the incident light. As a result, the reflected light L2 of the incident laser light L1 does not pass through the condenser lens 13, preventing the generation of stray light.
The inclination angle θ is set to 15° or more, so that the irradiation area of the incident light L1 on the single sample W is small, and a sufficient amount of light can be obtained to analyze an opaque sample, thereby ensuring sufficient analytical sensitivity.

The Raman scattered light L3, which has a wavelength different from that of the laser light and has passed through the condenser lens 13, passes only information about the location to be measured through the aperture 14. The Raman scattered light which has passed through the aperture 14 is sent to the spectrometer 15, which separates the Raman scattered light into wavelengths (step S3 in FIG. 3).
The Raman scattered light for each wavelength separated by the spectrometer 15 is detected as a signal by the detector 16 (step S4 in FIG. 3), and is converted into a spectrum by the computer (step S5 in FIG. 3).

As described above, according to the embodiment of the present invention, by setting the inclination angle of the analytical surface W1 of the sample W with respect to the incident laser light L1 to be less than ½ of ∠EFB defined by the center E of the focusing lens 13 on the detection side, the end F of the focusing lens 13 on the detection side, and the intersection B of the analytical surface W1 of the sample W and the optical axis of the incident light L1, the reflected light L2 does not pass through the focusing lens 13, and the generation of stray light can be prevented.
Furthermore, by setting the inclination angle of the analysis surface W1 of the sample W with respect to the incident light to 15° or more, stable and highly sensitive measurements can be made possible.

Furthermore, by using the laser Raman spectroscopy analysis method of the present invention to evaluate opaque ceramic materials such as alumina, yttria, silicon carbide, carbon, and other materials, it is possible to perform highly sensitive evaluations that are free from the effects of stray light, making it possible to develop and provide higher quality ceramic products.
Furthermore, by feeding back the measurement results of the present invention to the manufacturing conditions, it becomes possible to manufacture higher quality ceramic products.

The laser Raman spectroscopy according to the present invention will be further described with reference to examples.
[Experiment 1]
In experiment 1, in the device configuration shown in FIG. 1, the diameter of the focusing lens 13 on the detection side was set to 4 cm, and an optical system was configured in which the distance between the incident light irradiated point B on the sample W shown in FIG. 2 and the center E of the focusing lens 13 on the detection side was 4 cm (angle γ = 60°).
In this configuration, the inclination angle θ of the analysis surface W1 of the sample W with respect to the incident light was changed, and the S/N ratio (ratio of peak height to noise) and changes in the Raman spectrum at the analysis points (analysis point 1, analysis point 2) were measured.

A Si wafer was used as the sample W (the size of the sample W was 1 cm square, and the visible light transmittance was ^10-4 % or less). The reason why a Si wafer was used as the sample W is that it has high crystallinity, which gives a sharp peak and makes it easy to evaluate the S/N ratio, which is an index of analytical sensitivity, the analytical surface is flat, and handling and sample placement are easy.
The device used was an iRHR320 manufactured by Horiba, Ltd. The laser device used was a diode-pumped solid-state laser (DPSS), and the incident light was a laser beam with a wavelength of 532 nm, an output of 400 mW, and a diameter of 100 μm. The integration time per time was 30 seconds, and the number of integrations was 8.

The S/N ratio was measured for each of the tilt angles θ of 5°, 10°, 15°, 20°, 25°, 30°, 35°, and 40°.
The measurement area on the analytical surface was measured in two cases: when the angle with respect to the incident light was 0°, the diameter was 100 μm, and when the diameter was 3 mm.

As the results of Experiment 1, FIG. 4(a) shows a graph in which the diameter of the measurement region is 100 μm, and FIG. 4(b) shows a graph in which the diameter of the measurement region is 3 mm (in both cases, the analysis points are two locations within the measurement region).
In the graphs of FIGS. 4(a) and 4(b), the vertical axis represents the S/N ratio (au) and the horizontal axis represents the inclination angle (°) of the analytical surface with respect to the incident light.
The S/N ratio was calculated as the standard deviation of the background signal (cps/s) at 30 cm ^-1 min on both sides of the Si peak in the graph of the Raman spectrum for each inclination angle (°) of the analysis surface shown in FIG. 5 (vertical axis: Raman scattered light intensity (cps/s), horizontal axis: Raman shift (cm- ¹ )), where signal S is the height (cps/s) of the Si peak.
As shown in the graphs of Figures 4(a) and (b), it was confirmed that the S/N ratio tended to increase up to an analytical surface angle of 15°. In addition, the S/N ratio remained roughly constant when the analytical surface angle was between 15° and 25°. In addition, when the analytical surface angle was greater than 25° and up to 30°, both increases and decreases occurred. In addition, when the analytical surface angle was greater than 30°, the S/N ratio significantly decreased.

In addition, as shown in Fig. 5, it was confirmed that the spectrum was significantly distorted due to the influence of stray light when the angle of the analytical surface was 35° and 40°. It is considered that this influence caused a significant decrease in the S/N ratio when the angle of the analytical surface was larger than 30°.
As a result of the above experiment 1, it was confirmed that the angle of the analysis surface which can prevent the generation of stray light and enable measurement with good sensitivity is 15° to 25°.
It was also confirmed that when the angle is greater than 30°, which corresponds to half the angle γ (60° in this experiment) shown in FIG. 2, the sensitivity is significantly reduced due to the influence of stray light.

Therefore, in order to verify the lower limit threshold of the inclination angle of the analytical surface at which measurements can be made stably and with high sensitivity, we calculated how the size of the area where scattered light is generated changes depending on the angle of the scattered light relative to the incident light.
The results are shown in the graph of Figure 6. The vertical axis of the graph in Figure 6 represents the size of the scattered light generating region, and the horizontal axis represents the inclination angle (°) of the analytical surface with respect to the incident light.

As shown in FIG. 6, it was confirmed that by increasing the inclination angle of the analysis surface with respect to the incident light, the area on the sample where scattered light occurs (the area irradiated with the laser light) becomes smaller (i.e., the amount of light per unit area increases).
The scattered light that can pass through the aperture becomes part of the scattered light generation area, but for example, the scattered light generation area at angles of 5° and 10° is roughly half that of an angle of 5°, so the amount of light per unit area is thought to be more than double. Similarly, at an angle of 10°, the amount of light per unit area is roughly 2/3 that of an angle of 15°, so the amount of light per unit area is thought to be roughly 1.5 times.

That is, an increase in the amount of light per unit area means that the amount of scattered light that can pass through the aperture increases, and so an increase in sensitivity can be expected. However, as the angle is further increased, the reduction in the area where scattered light occurs decreases (the increase in the amount of light per unit area decreases), so at angles of 15° or more, the S/N ratio is considered to be close to a constant, as shown in Figures 4(a) and 4(b).
From the calculation results, it was confirmed that a tilt angle of 15° of the analytical surface with respect to the incident light is the lower limit threshold at which measurements can be performed stably and with high sensitivity.

[Experiment 2]
In experiment 2, the change in peak height of scattered light intensity with respect to angle was measured to verify what angle should be set within the range of 15° to 25° when actually making measurements with this optical system.
The experimental conditions were as follows: in the device configuration shown in FIG. 1, the diameter of the condenser lens 13 on the detection side was 4 cm, and an optical system was configured in which the distance between the incident light irradiated point B on the sample W shown in FIG. 2 and the center E of the condenser lens 13 on the detection side was 4 cm (angle γ=60°).
In this configuration, the inclination angle θ of the analysis surface W1 of the sample W with respect to the incident light was changed, and the peak heights at the analysis points (analysis point 1, analysis point 2) were measured.

A Si wafer was used as the sample W (the size of the sample W was the same as in Experiment 1).
The device used was an iRHR320 manufactured by Horiba, Ltd. The laser device used was a diode-pumped solid-state laser (DPSS), and the incident light was a laser beam with a wavelength of 532 nm, an output of 400 mW, and a diameter of 100 μm. The integration time per time was 30 seconds, and the number of integrations was 8.

The peak height (cps/s) of the scattered light intensity was measured for each of the tilt angles θ of 5°, 10°, 15°, 20°, 25°, 30°, 35°, and 40°.
The measurement area on the analytical surface was measured in two cases: when the angle with respect to the incident light was 0°, the diameter was 100 μm, and when the diameter was 3 mm.
The graph in Figure 8 shows the results of Experiment 3. The vertical axis of the graphs in Figures 8(a) and (b) represents the scattered light peak height (cps/s), and the horizontal axis represents the inclination angle (°) of the analysis surface with respect to the incident light.
As shown in the graph of FIG. 8, it was confirmed that in all cases, the peak height increased up to an inclination angle of 25° of the analysis surface, and the peak height at an inclination angle of 25° was maximum within the range of 15° to 25°.

Therefore, since the area of the measurement region on the analytical surface (the region on the sample through which scattered light can pass through the aperture) increases as the inclination angle of the analytical surface increases (possibly obtaining information that is not actually required), we calculated the specific increase in area within the angle range of 15° to 25°.
The calculation results are shown in the graph of Fig. 9. In the graph of Fig. 9, the vertical axis represents the increase in area (%) when the angle with respect to the incident light is set to 1 when the angle is 0°, and the horizontal axis represents the inclination angle (°) of the analysis surface with respect to the incident light.

As shown in the graph of FIG. 9, the increase in area is about 0.2% at an angle of 15° and about 0.6% at an angle of 25°, and there is a slight increase in the angle range of 15° to 25°.
Therefore, it was confirmed that within the angle range of 15° or more and 25° or less, a smaller inclination angle is preferable if one wishes to minimize the effect of the increase in area even if only slightly, and that if one wishes to increase the scattered light intensity by increasing the inclination angle (i.e., to further improve sensitivity), it is necessary to take measures to suppress the increase in the area of the measurement region by reducing the diameter of the aperture 14 in the configuration of Figure 1.

Claims (4)

A laser Raman spectroscopic analysis method in which a laser beam is irradiated as incident light onto an analysis surface formed on a flat surface of an opaque sample, and scattered light generated from the sample is passed through a condenser lens arranged with a main surface parallel to the optical axis of the incident light in a direction at an angle of 90° to the optical axis of the incident light, and then the scattered light is dispersed and detected, followed by spectrometry, for analysis,
The inclination angle of the analysis surface of the sample with respect to the incident light is
a line connecting a center of a main surface of the condenser lens and an end of the main surface of the condenser lens;
is less than ½ of the angle formed by a line connecting an intersection point between the analysis surface of the sample and the optical axis of the incident light and an end of the principal surface of the condenser lens ;
A laser Raman spectroscopic analysis method characterized in that the angle is 15° or more and 25° or less . 2. The laser Raman spectroscopic analysis method according to claim 1 , wherein a sample having a visible light transmittance of 10 ⁻⁴ % or less is used as the sample. 3. The laser Raman spectroscopic analysis method according to claim 1, wherein the diameter of the incident light is set to be 10 μm or more and 100 μm or less. A method for manufacturing a ceramic product, comprising: feeding back results obtained from an analysis by the laser Raman spectroscopy method according to any one of claims 1 to 3 .

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