JP2014025793A - Method and apparatus for evaluating crystalline samples - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for evaluating crystalline samples, which enable evaluation based on changes in intensity of an optical spectrum of a sample without moving the sample.SOLUTION: A crystalline sample evaluation apparatus includes; an irradiator section which irradiates a crystalline sample S with light from a light source 10 via a 1/2 wavelength plate 20; a spectroscope 40 and a photodetector 42 which disperse scattered light from the crystalline sample S that passes through the 1/2 wavelength plate 20 and acquire an optical spectrum of the scattered light; and an arithmetic processing unit 50 which evaluates the crystalline sample S on the basis of the acquired optical spectrum. The 1/2 wavelength plate 20 is rotatably configured around an optical path OA. The arithmetic processing unit 50 performs a process for deriving magnitude of the Raman tensor component of the crystalline sample S on the basis of changes in intensity of the optical spectrum acquired while rotating the 1/2 wavelength plate 20.

Description

  The present invention relates to a crystal sample evaluation method and an evaluation apparatus.

  Conventionally, a confocal microspectroscopic device that detects Raman scattered light generated when a sample is irradiated with excitation laser light is known (for example, Patent Document 1). Analyzing the spectrum of scattered light measured with different polarization arrangements using the above confocal microspectrophotometer and determining the presence or absence of a Raman peak, thereby determining the symmetry of the crystal and the symmetry of the vibration mode Can do.

JP 2008-299146 A

  Furthermore, the Raman tensor component is quantitatively determined by analyzing the intensity change of the spectral spectrum of the scattered light measured while rotating the crystal sample around the measurement point using the confocal microspectroscopic device. It becomes possible.

  However, in the above-described method of rotating the sample, for example, it is necessary to rotate the sample while finely adjusting the wound around the measurement point as a mark so that they move on a concentric circle centered on the measurement point. At the same time, it is necessary to rotate an apparatus for controlling the temperature of the sample and applying an external field such as an electric field, which makes the measurement procedure complicated. Further, the above method has a problem that measurement cannot be performed when there is no mark or the like on the surface of the sample. Further, depending on the external field application device, rotation itself may be impossible.

  The present invention has been made in view of the problems as described above, and an object of the present invention is to provide a crystal sample evaluation method capable of performing an evaluation based on a change in the intensity of a spectral spectrum without rotating the sample. And providing an evaluation apparatus.

(1) The present invention provides a crystal sample evaluation method,
Irradiating the crystal sample with light from a light source via a half-wave plate;
An acquisition procedure for separating scattered light generated from the crystal sample and transmitted through the half-wave plate to obtain a spectral spectrum of the scattered light;
An evaluation procedure for evaluating the crystal sample based on the acquired spectral spectrum,
The half-wave plate is configured to be rotatable,
In the evaluation procedure,
The crystal sample is evaluated based on a change in the intensity of the spectrum obtained when the half-wave plate is rotated.

The present invention also provides a crystal sample evaluation apparatus,
An irradiation unit for irradiating the crystal sample with light from the light source via a half-wave plate;
A spectral spectrum acquisition unit that splits scattered light generated from the crystal sample and transmitted through the half-wave plate, and acquires a spectral spectrum of the scattered light;
An evaluation unit that evaluates the crystal sample based on the acquired spectral spectrum,
The half-wave plate is configured to be rotatable,
The evaluation unit is
The crystal sample is evaluated based on a change in the intensity of the spectrum obtained when the half-wave plate is rotated.

  According to the present invention, the light from the light source is transmitted through the rotatable half-wave plate, and the scattered light from the crystal sample is again transmitted through the half-wave plate. The crystal sample is evaluated based on the intensity change of the spectrum obtained by rotating the half-wave plate, thereby evaluating the crystal sample based on the intensity change of the spectrum without rotating the sample. be able to.

(2) In the crystal sample evaluation method according to the present invention,
In the acquisition procedure,
Obtaining a spectral spectrum of the scattered light whose polarization direction is parallel to the incident light from the light source incident on the half-wave plate, and a spectral spectrum of the scattered light whose polarization direction is orthogonal to the incident light,
In the evaluation procedure,
The crystal sample is evaluated based on the intensity change of the spectrum of the scattered light whose polarization direction is parallel to the incident light and the intensity change of the spectrum of the scattered light whose polarization direction is orthogonal to the incident light. Also good.

In the crystal sample evaluation apparatus according to the present invention,
The spectrum acquisition unit
Obtaining a spectral spectrum of the scattered light whose polarization direction is parallel to the incident light from the light source incident on the half-wave plate, and a spectral spectrum of the scattered light whose polarization direction is orthogonal to the incident light,
The evaluation unit is
The crystal sample is evaluated based on the intensity change of the spectrum of the scattered light whose polarization direction is parallel to the incident light and the intensity change of the spectrum of the scattered light whose polarization direction is orthogonal to the incident light. Also good.

  According to the present invention, it is possible to evaluate a crystal sample based on a change in intensity of a spectral spectrum without rotating the sample.

(3) In the crystal sample evaluation method and evaluation apparatus according to the present invention,
The scattered light may be Raman scattered light.

The figure which shows an example of a structure of the measuring apparatus (evaluation apparatus) of this embodiment. The figure for demonstrating the polarization state of incident light and a scattered light when a half-wave plate is rotated. The figure which shows the intensity | strength change of the spectral spectrum and Raman peak of the Raman scattered light of PT crystal | crystallization according to the rotation angle of the polarization direction of the incident light around the z-axis of the crystal | crystallization measured by the method of this embodiment. In accordance with a rotation angle of the polarization direction of the x-axis of the crystal (or y axis) of the incident light, it shows a change in intensity of the Raman peak of A ₁ mode PbTiO ₃ crystals (PT crystals). The spectral change of the Raman scattered light of the PT crystal and the intensity change of the Raman peak according to the rotation angle of the polarization direction of the incident light around the z axis of the crystal measured by the method of rotating the crystal sample S around the measurement point. Comparative example shown. The case in accordance with the rotation angle of the polarization direction of the z axis of the incident light of the crystal, a change in intensity of the Raman peak of A ₁ Mode PT crystal in the parallel Nicols, obtained by the method of Comparative Example, the method of this embodiment The figure for comparing with the case where it acquires with.

  Hereinafter, this embodiment will be described. In addition, this embodiment demonstrated below does not unduly limit the content of this invention described in the claim. In addition, all the configurations described in the present embodiment are not necessarily essential configuration requirements of the present invention.

1. Configuration FIG. 1 is a diagram illustrating an example of a configuration of a measurement apparatus (evaluation apparatus) according to the present embodiment. The measuring apparatus 1 of the present embodiment is configured as an apparatus that performs Raman spectroscopic measurement of the crystal sample S. The measuring apparatus 1 includes a light source 10 such as a laser light source, a beam expander 12, a half mirror 14 (beam splitter), an objective lens 16, a half-wave plate 20, a polarizing plate 22 (analyzer), Depolarization plate 24, lenses 30, 32, and 34, aperture 36 (confocal pinhole), spectroscope 40 and photodetector 42 functioning as a spectrum acquisition unit, and arithmetic processing unit 50 functioning as an evaluation unit Including. The crystal sample S is supported by a stage device (not shown) and configured to be movable in an arbitrary direction. Further, an achromatic wave plate is used as the half-wave plate 20. Further, instead of the depolarizing plate 24, a quarter wavelength plate or a half wavelength plate may be used.

  The light from the light source 10 is incident on the half mirror 14 after the beam diameter is expanded by the beam expander 12. The light reflected by the half mirror 14 enters the half-wave plate 20, passes through the half-wave plate 20, and is condensed and irradiated on the measurement site on the crystal sample S by the objective lens 16. . At this time, light having a different energy from the light from the light source 10 (incident light) is emitted from the crystal sample S as Raman scattered light (an example of inelastically scattered light). The Raman scattered light generated from the crystal sample S enters the half-wave plate 20 through the objective lens 16, passes through the half-wave plate 20, and enters the half mirror 14. The Raman scattered light that has passed through the half mirror 14 passes through the polarizing plate 22 and the depolarizing plate 24, and enters the spectroscope 40 through the lens 30, the aperture 36, the lens 32, and the lens 34.

  The Raman scattered light that has entered the spectroscope 40 is split by a diffraction grating or the like that constitutes the spectroscope 40, and enters a photodetector 42 that is configured by a line sensor camera or the like. A detection signal (intensity signal for each wavelength of Raman scattered light) detected by the photodetector 42 is output to the arithmetic processing unit 50.

  Here, the half-wave plate 20 is configured to be rotatable around an optical path OA (an axis parallel to the optical path OA, a Z axis) by a rotation mechanism (not shown). This rotation mechanism is controlled by a control signal from the arithmetic processing unit 50.

In the present embodiment, instead of measuring the spectral spectrum of the Raman scattered light while rotating the crystal sample S, the spectral spectrum of the Raman scattered light is measured while rotating the half-wave plate 20. Yes. As shown in FIG. 2A, when the half-wave plate 20 is rotated by an angle θ _r / 2, the polarization direction of incident light transmitted downward through the half-wave plate 20 is rotated by an angle θ _r . . On the other hand, the polarization direction of the Raman scattered light that is transmitted upward through the half-wave plate 20 is rotated by an angle −θ _r . That is, by rotating the half-wave plate 20 by the angle θ _r / 2 while fixing the crystal sample S, the crystal sample S is rotated by the angle θ _r while fixing the polarization direction of the incident light (FIG. 2). (See (B)). That is, in the measurement apparatus 1 of the present embodiment, it is possible to measure the change in the intensity of the spectral spectrum of Raman scattered light with a simple apparatus configuration and a simple measurement procedure without rotating the crystal sample S and its associated apparatus. .

  Referring to FIG. 1 again, the arithmetic processing unit 50 (computer) acquires a spectrum of Raman scattered light based on the detection signal from the photodetector 42. Further, the arithmetic processing unit 50 performs a process of quantitatively determining the Raman tensor component of the crystal sample S based on the intensity change of the spectral spectrum acquired when the half-wave plate 20 is rotated. . Specifically, processing for obtaining the ratio of the magnitudes of the Raman tensor components is performed by function fitting the intensity change (Raman peak intensity change) in a given wavenumber band in the spectrum.

  In addition, the arithmetic processing unit 50 changes the intensity of the spectral spectrum (first spectral spectrum) of the Raman scattered light whose polarization direction is parallel to the incident light incident on the half-wave plate 20 and the half-wave plate 20. The Raman tensor component of the crystal sample S is determined based on the intensity change of the spectral spectrum (second spectral spectrum) of the Raman scattered light whose polarization direction is orthogonal to the incident incident light. When acquiring the first spectral spectrum, the orientation of the polarizing plate 22 is adjusted so that the transmission axis of the polarizing plate 22 is parallel to the polarization direction of the incident light (parallel Nicol state), and the second spectral spectrum is obtained. When acquiring a spectrum, the orientation of the polarizing plate 22 is adjusted so that the transmission axis of the polarizing plate 22 is perpendicular to the polarization direction of the incident light (in a state of orthogonal Nicols).

  Here, the Raman tensor T is expressed by the following equation.

For example, the A ₁ mode Raman tensor T of a tetragonal PbTiO ₃ crystal (PT crystal) is expressed by the following equation.

Further, the Raman tensor T of B ₁ mode PT crystal is expressed by the following equation.

  Here, when the polarization direction of incident light is rotated around the z-axis of the crystal sample S (that is, the crystal sample S is arranged so that the optical path OA (Z-axis) and the z-axis of the crystal sample S are parallel to each other). / 2 When the wavelength plate 20 is rotated around the optical path OA), the equation (3) changes as the following equation (5) by the rotation matrix R of the following equation (4). Equation (5) represents the laboratory Raman tensor observed when the polarization direction of incident light is rotated about the z-axis of the crystal. In addition, about Formula (2), it does not change with the rotation matrix R of following Formula (4).

  Here, θ is the rotation angle of the half-wave plate 20.

When the optical path OA is parallel to the z-axis of the crystal sample S and the polarization direction of the incident light is parallel to the x-axis of the crystal sample S, the intensity I of the Raman scattered light whose incident light and the polarization direction are parallel is the Raman tensor component The intensity I of the Raman scattered light that is proportional to the square of T _{xx and} whose polarization direction is orthogonal to the incident light is proportional to the square of the Raman tensor component T _yx . Therefore, when rotating the polarization direction of the incident light on the z axis of the crystal sample S, from equation (2), for the mode A _1, the intensity I of the incident light and the polarization direction parallel to the Raman scattered light to a ² The intensity I of the Raman scattered light that is proportional to the incident light and whose polarization direction is orthogonal is zero. Further, from equation (5), for the mode B _1, the intensity I of the incident light and the polarization direction parallel to the Raman scattered light is proportional to c ² cos ² 2 [Theta], the Raman scattered light incident light and the polarization directions are orthogonal Intensity I is proportional to c ² sin ² 2θ. That is, the intensity of the Raman scattered light, for mode B ₁ varies depending on the rotation angle of the half wave plate 20 theta (rotation angle of the polarization direction of the z axis of the incident light crystal theta), Mode A _It can be seen that 1 does not depend on the rotation angle θ around the z axis.

  3A and 3B show a spectrum of Raman scattered light measured by the measuring apparatus 1 of the present embodiment using a PT crystal as the crystal sample S. FIG. FIG. 3A shows a spectrum of Raman scattered light whose incident light and polarization direction are parallel, and FIG. 3B shows a spectrum of Raman scattered light whose incident light and polarization direction are orthogonal. 3A and 3B, the horizontal axis represents the relative wave number (Raman shift), and the vertical axis represents the intensity of the scattered light. In this measurement, a spectroscopic spectrum was acquired every time the rotation angle θ of the half-wave plate 20 was changed in increments of 20 ° in the range of 0 ° to 180 °. In this measurement, an Ar ion laser (wavelength 514.5 nm) was used as the light source 10.

FIG. 3 (A), the as shown in FIG. 3 (B), in the vicinity of 288cm ^-1, appears Raman peak of _{B 1} mode, in the vicinity of 350 cm ^-1, _{A 1} mode Raman peak (parallel Nicol only) Appears. Further, the Raman peak of B ₁ mode changes according to the rotation angle theta, the Raman peak of A ₁ mode is found to be constant independently of the rotational angle theta.

FIG. 3C shows a change in the intensity of the Raman peak in the B ₁ mode in accordance with the rotation angle θ obtained from the spectrums shown in FIGS. 3A and 3B. When obtaining the change in the intensity of the Raman peak, it is desirable to obtain the difference from the Raman peak intensity at each rotation angle θ with reference to the Raman peak intensity at an arbitrary rotation angle θ. In this way, the influence of the background component that does not depend on the rotation angle θ can be eliminated.

As shown in FIG. 3C, the Raman peak of the B ₁ mode in parallel Nicol indicated by a circular point changes according to a theoretical curve (a function proportional to c ² cos ² 2θ) indicated by a solid line. Further, the Raman peak of the B ₁ mode in orthogonal Nicol indicated by a rectangular point also changes according to a theoretical curve (a function proportional to c ² sin ² 2θ) indicated by a solid line.

Here, by fitting the peak intensity indicated by a circular point to a function proportional to c ² cos ² 2θ (or fitting the peak intensity indicated by a rectangular point to a function proportional to c ² sin ² 2θ), it is possible to obtain the amplitude component c ^2, it is possible to determine the magnitude of the Raman tensor of component c B ₁ mode. Similarly, the intensity of the Raman peak of A ₁ mode is proportional to the square of the Raman tensor component a of A ₁ mode, the intensity of the Raman peak of A ₁ mode shown in FIG. 3 (A), the Raman tensor component a The size can be determined.

  Thus, the magnitude of the Raman tensor component (for example, the ratio of each Raman tensor component) can be quantitatively determined from the shape and amplitude of the intensity change of the Raman peak according to the rotation angle θ. By quantitatively determining the Raman tensor component of the crystal sample, it is possible to acquire information on macroscopic physical property quantities such as the dielectric constant and piezoelectricity of the crystal sample.

  In the above description, when the polarization direction of the incident light is rotated around the z axis of the crystal sample S (that is, the crystal sample S is arranged so that the optical path OA (Z axis) and the z axis of the crystal sample S are parallel). The case where the half-wave plate 20 is rotated around the optical path OA has been described, but the case where the polarization direction of the incident light is rotated around the x-axis of the crystal sample S (that is, x between the optical path OA and the crystal sample S). When the crystal sample S is arranged so that the axes are parallel and the half-wave plate 20 is rotated about the optical path OA), the equation (2) is expressed by the rotation matrix R of the following equation (6). It changes like (7) and Formula (3) changes like Formula (8). The same applies to the case where the polarization direction of the incident light is rotated around the y-axis of the crystal sample S.

When the optical path OA is parallel to the x-axis of the crystal sample S and the polarization direction of the incident light is parallel to the y-axis (or z-axis) of the crystal sample S, the intensity I of the Raman scattered light with the incident light and the polarization direction parallel. Is proportional to the square of the Raman tensor component T _yy (or T _zz ), and the intensity I of the Raman scattered light whose polarization direction is orthogonal to the incident light is proportional to the square of the Raman tensor component T _zy (or T _yz ). Therefore, when the polarization direction of the incident light is rotated about the x-axis of the crystal sample S, the Raman scattered light intensity I also changes depending on the rotation angle θ in the mode A ₁ from the equation (7). Namely, the Raman peak of A ₁ Mode PT crystals, according to the rotation angle of the polarization direction of the x-axis theta, indicating the change as shown in FIG. 4 (A) or FIG. 4 (B). Incidentally, FIG. 4 (A), _{A 1} mode of the Raman tensor components a, relationship b is <shows the intensity variation of 0, FIG. 4 (B), a × b> a × b where a 0 Indicates intensity change.

As described above, by analyzing the intensity change pattern of the Raman peak according to the rotation angle θ around each axis of the crystal sample S, mode candidates are determined, and the symmetry (point group) of the crystal sample S is determined. It becomes possible. It is also possible to determine the ratio of each Raman tensor component. For example, the PT crystal, x-axis of the intensity variation of the Raman peak of A ₁ mode obtained by rotating the polarization direction of the incident light on the z axis of the crystal, the polarization direction of the incident light crystals (or y axis) a change in intensity of a ₁ mode of the Raman peaks obtained by rotating by analyzing the Raman tensor components a of a ₁ mode, it is possible to find the ratio of b to.

FIGS. 5A and 5B show Raman scattered light measured for a PT crystal by a method (see FIG. 2B) in which the crystal sample S is rotated around the measurement point around the z axis of the crystal. It is a comparative example which shows the spectrum of these. FIG. 5A shows a spectrum of Raman scattered light whose incident light and polarization direction are parallel, and FIG. 5B shows a spectrum of Raman scattered light whose incident light and polarization direction are orthogonal. FIG. 5 (C) FIG. 5 (A), the obtained from spectrum of FIG. 5 (B), is a diagram illustrating a change in intensity of the Raman peak of B ₁ mode. As shown in FIG. 5 (C), in the comparative example, the variation of the measured values of the intensity change of B ₁ mode Raman peak is large, it deviates from the theoretical value indicated by the solid line. Further, as shown in FIG. 5 (A), FIG. 5 (B), the in the comparative example, the Raman peak of A ₁ mode should not depend on the rotation angle of the z axis of the crystal θ is, depending on the rotation angle θ Has changed. Therefore, when a spectrum as shown in FIGS. 5A and 5B is acquired, it cannot be determined whether or not the peak appearing at 350 cm ⁻¹ is an A ₁ mode Raman peak. . The measurement error in these comparative examples is considered to be caused by variations in measurement points and the like when the crystal sample S is rotated.

FIG. 6 is a diagram for comparing the intensity change of the A ₁ mode Raman peak in parallel Nicol with respect to the PT crystal between the case of being obtained by the method of the comparative example and the case of being obtained by the method of the present embodiment. . Turning to FIG. 6, the Raman peak obtained by the method of comparative example shown by a rectangle point, the error between the theoretical straight line (function proportional to a ²⁾ is varied greatly by the θ rotation angle around the z-axis of the crystal On the other hand, it can be seen that the Raman peak obtained by the method of the present embodiment indicated by a circular point has a small error from the theoretical value regardless of the rotation angle θ.

  As described above, according to the measurement apparatus and the measurement method of the present embodiment, it is possible to measure the intensity change of the Raman peak with higher accuracy than the method of rotating the crystal sample S around the measurement point. It becomes possible to quantitatively measure the Raman tensor component of.

  The technical scope of the present invention is not limited to the above-described embodiment, and appropriate modifications can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the case of measuring Raman scattered light as scattered light has been described. However, the present invention may be applied to measuring Brillouin scattered light that is inelastic scattering.

DESCRIPTION OF SYMBOLS 1 Measurement apparatus (evaluation apparatus), 10 light source, 12 beam expander, 14 half mirror, 16 objective lens, 20 1/2 wavelength plate, 22 polarizing plate, 24 depolarization plate, 30, 32, 34 lens, 36 aperture, 40 spectroscope, 42 photodetector, 50 arithmetic processing unit (evaluation unit), S crystal sample

Claims (4)

Irradiating the crystal sample with light from a light source via a half-wave plate;
An acquisition procedure for separating scattered light generated from the crystal sample and transmitted through the half-wave plate to obtain a spectral spectrum of the scattered light;
An evaluation procedure for evaluating the crystal sample based on the acquired spectral spectrum,
The half-wave plate is configured to be rotatable,
In the evaluation procedure,
A method for evaluating a crystal sample, comprising: evaluating the crystal sample based on an intensity change of the spectral spectrum acquired when the half-wave plate is rotated. In claim 1,
In the acquisition procedure,
Obtaining a spectral spectrum of the scattered light whose polarization direction is parallel to the incident light from the light source incident on the half-wave plate, and a spectral spectrum of the scattered light whose polarization direction is orthogonal to the incident light,
In the evaluation procedure,
Evaluating the crystal sample on the basis of a change in intensity of a spectrum of the scattered light whose polarization direction is parallel to the incident light and a change in intensity of the spectrum of the scattered light whose polarization direction is orthogonal to the incident light. A method for evaluating a crystal sample characterized by In claim 1 or 2,
The method for evaluating a crystal sample, wherein the scattered light is Raman scattered light. An irradiation unit for irradiating the crystal sample with light from the light source via a half-wave plate;
A spectral spectrum acquisition unit that splits scattered light generated from the crystal sample and transmitted through the half-wave plate, and acquires a spectral spectrum of the scattered light;
An evaluation unit that evaluates the crystal sample based on the acquired spectral spectrum,
The half-wave plate is configured to be rotatable,
The evaluation unit is
An apparatus for evaluating a crystal sample, wherein the crystal sample is evaluated based on a change in intensity of the spectral spectrum acquired when the half-wave plate is rotated.