JP2004333131A - Total reflection fluorescence xafs measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make parallel X rays applied to a sample and to fully secure the X-ray intensity by irradiating the sample with dispersion X rays coming out of a light reception slit after condensation by a curved crystal monochromator after turning the dispersion X rays into parallel beams by a parabolic multilayer mirror. <P>SOLUTION: The wavelength of the X rays 22 coming out of the light reception slit 14 can be changed by changing the relative position relationship among an X ray source 10, the light reception slit 14, and the curved crystal monochromator 12. The X rays 22 are reflected by the parabolic multilayer film mirror 24 to become parallel beams 26. The parallel beams 26 are transmitted through a transmission type X-ray detector 28 and enter the surface of the sample 30 under total reflection conditions. Fluorescent X rays 36 coming out of the sample 30 are detected by a fluorescent X-ray detector 38. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an XAFS measuring apparatus, and more particularly to a total reflection fluorescent XAFS measuring apparatus which irradiates a surface of a sample with X-rays under a condition of total reflection and detects fluorescence generated therefrom.
[0002]
[Prior art]
The documents cited as the prior art in this specification are as follows.
[0003]
[Patent Document 1]
JP 2001-66268 A [Patent Document 2]
Japanese Patent Application Laid-Open No. Hei 5-196585 [Patent Document 3]
JP 2001-21507 [Patent Document 4]
JP-A-11-352297
Patent Document 1 discloses a laboratory-specific XAFS measurement device using an X-ray tube and a curved crystal monochromator. Patent Literature 2 discloses a total reflection fluorescent XAFS measurement device using synchrotron radiation light. Patent Document 3 discloses an XAFS measurement device using a parallel beam. Patent Document 4 discloses a parabolic multilayer mirror for X-rays.
[0005]
An XAFS (X-ray Absorption Fine Structure: X-ray absorption fine structure) measuring device is a device for measuring a fine X-ray absorption spectrum near an X-ray absorption edge of a sample. XAFS includes EXAFS (Extended X-ray Absorption Fine Structure) and XANES (Zenes, X-ray Absorption Near Edge and fine structure, which are classified as X-ray absorption near-edge structure). EXAFS is an absorption fine structure that can be seen over a wide range of about 1 keV toward higher energy than the X-ray absorption edge of a sample, and is well known in the art. On the other hand, XANES is an absorption edge fine structure that appears in a narrow region near the X-ray absorption edge (about ± 50 eV at the absorption edge), and has recently attracted attention. Since XANES can be measured with the same configuration as the EXAFS measurement device, recently, as a device capable of performing both XANES measurement and EXAFS measurement, the name of the conventional EXAFS measurement device has been replaced by the name of the XAFS measurement device. It has become to.
[0006]
The XAFS measurement apparatus can separate continuous X-rays with a crystal monochromator to take out monochromatic X-rays of an arbitrary wavelength, and can irradiate the sample with X-rays by changing this wavelength. As the X-ray source of the XAFS measurement apparatus, it is common to use synchrotron radiation light that is continuous X-rays and has high intensity, but an X-ray tube is used in a laboratory specification. An XAFS device using an X-ray tube often uses a curved crystal monochromator as a crystal monochromator for separating X-rays to increase the intensity. A laboratory-specific XAFS measurement apparatus using an X-ray tube and a curved crystal monochromator is described in the above-mentioned Patent Document 1.
[0007]
The present invention relates to a total reflection fluorescent XAFS measurement device among XAFS measurement devices. That is, this is an XAFS measurement device that irradiates the surface of the sample with X-rays under the condition of total reflection and detects fluorescence generated therefrom. When the sample is irradiated with X-rays under the condition of total reflection, (1) the amount of scattered X-rays from the sample is reduced and the S / N ratio is improved, and (2) only information near the sample surface can be obtained. , There is an advantage. Such a total reflection X-ray fluorescence spectrometer is described in Patent Document 2 mentioned above. The total reflection X-ray fluorescence spectrometer disclosed in Patent Document 2 uses synchrotron radiation as an X-ray source, and monochromatizes it to a desired wavelength by a two-crystal monochromator. The light is condensed on the light receiving slit to extract X-rays.
[0008]
[Problems to be solved by the invention]
In the total reflection fluorescent XAFS measuring apparatus, it is necessary to irradiate the surface of the sample with X-rays in order to satisfy the total reflection condition. Therefore, when the sample is irradiated with X-rays that spread at a predetermined divergence angle, a problem is likely to occur in that only a part of the X-rays hits the sample surface and the remaining X-rays do not hit the sample surface. In the fluorescent XAFS measuring device, the ratio of the intensity of the X-rays incident on the sample to the intensity of the fluorescent X-rays generated from the sample is measured. Therefore, even if the intensity of the incident X-rays is measured in front of the sample. If the part does not hit the sample, the above ratio cannot be calculated correctly. In addition, when X-rays hit the side surface of the sample or the sample holder, scattered X-rays are generated from the X-rays, which greatly affects measurement accuracy. Furthermore, when the sample is irradiated with divergent X-rays, the incident angle of the incident X-rays differs depending on the position on the sample, and all positions on the sample do not always satisfy the condition of total reflection.
[0009]
Therefore, in Patent Document 2 described above, in order to reduce the angle fluctuation of the X-ray irradiated on the sample (that is, to reduce the divergence angle), the distance from the total reflection type condenser mirror to the sample is set to 11 m. I've been taking it for a long time.
[0010]
On the other hand, it is desired to be able to measure the total reflection fluorescence XAFS at the laboratory level without using the above-mentioned synchrotron radiation, but in that case, a curved crystal monochromator that can increase the intensity is desired. Is assumed to be used for a spectrometer. However, measuring "total reflection" fluorescence has the following problems. When spectrally separated by a curved crystal monochromator, X-rays of a desired wavelength are condensed on a light receiving slit, and the X-rays emitted from the light receiving slit spread with a predetermined divergence angle. When such a divergent X-ray is irradiated on a sample, as described above, a problem that some X-rays do not hit the sample surface and a problem that the incident angle of the X-ray varies depending on a position on the sample occur. Such a problem is caused by divergent X-rays coming out of the light receiving slit, and if this becomes a parallel beam, the problem should be solved.
[0011]
Further, in order to irradiate the sample with all the X-rays that spread at a predetermined divergence angle, it is necessary to prepare a large-sized sample or to bring the sample closer to the light receiving slit. In the case of a small sample, the sample needs to be very close to the light receiving slit. However, since there is a transmission type X-ray detector for detecting the intensity of incident X-rays between the light receiving slit and the sample, there is a limit in bringing the sample closer to the light receiving slit. Therefore, from such a viewpoint, it is desirable to use a parallel beam instead of a diverging beam.
[0012]
Meanwhile, as an XAFS measuring apparatus using a parallel beam, an apparatus described in Patent Document 3 is known. In this XAFS measuring apparatus, a total reflection parabolic mirror is arranged between an X-ray source and a sample, and the parabolic mirror parallelizes the X-rays. Then, the obtained parallel beam is made incident on a plate crystal monochromator to monochromaticize X-rays, and the parallel beam reflected by the plate crystal monochromator is irradiated on the sample. As the parabolic mirror, a mirror having a gold vapor-deposited film formed on a glass surface is used.
[0013]
Therefore, in the total reflection fluorescent XAFS measuring apparatus, if a parallel beam is obtained by this method, the above-mentioned various problems caused by divergent X-rays should be solved. However, another problem arises as follows. In Patent Document 3 described above, since a parabolic mirror of the total reflection type is arranged between the X-ray source and the flat crystal monochromator, of the X-rays emitted from the X-ray source, the parabolic mirror is used. Only X-rays within a small divergence angle satisfying the condition of total reflection will be used. Therefore, using a spectroscope that combines a total reflection parabolic mirror and a flat crystal monochromator, the intensity of X-rays incident on the sample is much higher than when condensing using a curved crystal monochromator. It becomes weak.
[0014]
In the case of a combination of a total reflection type parabolic mirror and a flat crystal monochromator, monochromaticity of X-rays incident on the sample is not always sufficient, and X-rays having slightly different wavelengths are mixed.
[0015]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an X-ray which can irradiate a sample with a parallel beam and sufficiently secure the X-ray intensity. It is an object of the present invention to provide a reflection fluorescence XAFS measurement device.
[0016]
[Means for Solving the Problems]
The total reflection fluorescent XAFS measuring apparatus of the present invention includes a spectroscope, a parabolic multilayer mirror, a transmission X-ray detector, a sample holding device, and a fluorescent X-ray detector. The spectrometer includes an X-ray source, a light receiving slit, and a curved crystal monochromator. The curved crystal monochromator reflects the X-rays emitted from the X-ray source and focuses the X-rays on a light receiving slit. Then, by changing the relative positional relationship between the X-ray source, the light receiving slit, and the curved crystal monochromator, the wavelength of the X-ray emitted from the light receiving slit can be changed. The parabolic multilayer mirror reflects the X-ray coming out of the light receiving slit and converts it into a parallel beam. The transmission X-ray detector is disposed between the parabolic multilayer mirror and the sample, and detects the intensity of the X-ray before entering the sample. The sample holding device holds the sample so that X-rays emitted from the transmission X-ray detector can be incident on the surface of the sample under the condition of total reflection. The fluorescent X-ray detector detects fluorescent X-rays emitted from the sample.
[0017]
According to the present invention, since the X-rays coming out of the light receiving slit are made into a parallel beam by a parabolic multilayer mirror and then irradiated to the sample, the divergent beam is irradiated to the sample in the total reflection fluorescent XAFS measuring apparatus. The various problems caused by the above are eliminated.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the total reflection fluorescent XAFS measurement device of the present invention. The X-rays 18 emitted from the X-ray source 10 are divergent X-rays, which are reflected by the curved crystal monochromator 12 to be monochromatic, and the reflected X-rays 20 are condensed on the light receiving slit 14. The reflection surface of the curved crystal monochromator 12 is curved in an arc shape along the Rowland circle 16. The reflection surface of the X-ray source 10, the curved crystal monochromator 12, and the light receiving slit 14 are placed on a Rowland circle 16. By changing the relative positional relationship between the X-ray source 10, the curved crystal monochromator 12, and the light receiving slit 14, the wavelength of the X-ray 22 coming out of the light receiving slit 14 can be changed. For example, if the position of the X-ray source 10 is changed on the Roland circle 16, the incident angle of the X-rays 18 on the curved crystal monochromator 12 changes, and accordingly, the wavelength of the X-rays that can be reflected by the curved crystal monochromator 12 Changes. The position where the reflected X-rays 20 converge is a position symmetrical to the X-ray source 10 about the curved crystal monochromator 12. The light receiving slit 14 is brought to that position. The angle of the reflected X-ray 20 with respect to the incident X-ray 18 in the curved crystal monochromator 12 is 2θ, and the wavelength of the X-ray 22 coming out of the light receiving slit 14 changes by changing 2θ.
[0019]
As the X-ray source 10, for example, an X-ray tube of a molybdenum target can be used. Of the generated X-rays, a wavelength portion that is a continuous X-ray is used for XAFS.
[0020]
The light receiving slit 14 has a slit width of about 0.1 to 0.2 mm, and cuts scattered X-rays by the light receiving slit.
[0021]
The X-ray 22 coming out of the light receiving slit 14 spreads at a predetermined divergence angle. The X-rays 22 are reflected by the parabolic multilayer mirror 24 and become parallel beams 26. The reflection surface of the parabolic multilayer mirror 24 is a paraboloid, and the light receiving slit 14 is located at the focal point of the paraboloid. Therefore, the parallel beam 26 is obtained as described above. After passing through the transmission type X-ray detector 28, the parallel beam 26 is incident on the surface of the sample 30 at a small incident angle α (that is, under the condition of total reflection). The sample 30 is held by the sample holding device 31, and the holding angle of the sample 30 can be adjusted so that the parallel beam 26 is incident on the sample 30 under the condition of total reflection. X-rays 34 totally reflected on the surface of the sample 30 are detected by the reflected X-ray detector 32. On the other hand, the fluorescent X-rays 36 generated on the surface of the sample 30 are detected by the fluorescent X-ray detector 38.
[0022]
As an example of a detector, a transmission type proportional counter can be used as the transmission X-ray detector 28, a scintillation detector can be used as the reflection X-ray detector 32, and a fluorescent X-ray detector can be used. As the detector 38, a semiconductor detector having a high energy resolution can be used. However, the type of the detector is not limited to these.
[0023]
In order to set the X-ray incident angle α to the sample 30, first, the reflectance is measured. That is, by comparing the incident X-ray intensity detected by the transmission X-ray detector 28 and the reflected X-ray intensity detected by the reflected X-ray detector 32, the X-ray reflectivity on the surface of the sample 30 is obtained. be able to. By referring to this X-ray reflectivity, the incident angle α can be correctly adjusted so as to satisfy the total reflection condition. The maximum incident angle (critical incident angle) that satisfies the condition for total reflection depends on the X-ray wavelength, but is about 0.2 to 0.6 °, and the incident angle α is set to a smaller value. There is a need to.
[0024]
When the incident angle α can be set as described above, the total reflection fluorescence XAFS is measured as follows. The intensity of the X-ray 26 incident on the sample 30 can be detected by a transmission X-ray detector 28. The intensity of the fluorescent X-ray 36 coming out of the sample 30 can be detected by the fluorescent X-ray detector 38 for each energy. Then, by changing the wavelength of the X-ray 26 and plotting the ratio between the intensity of the incident X-ray and the intensity of the fluorescent X-ray, a total reflection fluorescent XAFS can be obtained.
[0025]
In the total reflection fluorescent XAFS measuring apparatus of the present invention, since the parallel beam 26 is formed by the parabolic multilayer mirror 24, even if the position of the sample 30 is far from the parabolic multilayer mirror 24, the divergent X-ray There are no such problems.
[0026]
Next, the parabolic multilayer mirror 24 will be described. The reflection surface of the parabolic multilayer mirror 24 is made of an artificial multilayer film. This artificial multilayer film is obtained by alternately stacking layers made of heavy elements and layers made of light elements. The stacking cycle corresponds to the lattice spacing of the single crystal. And this lamination cycle changes continuously along the paraboloid. Thus, if the light receiving slit 14 is arranged on the focal point of the parabolic surface, the X-rays 22 that spread at a predetermined divergence angle from the light receiving slit 14 can be projected at any position on the reflecting surface of the parabolic multilayer mirror 24. The beam becomes a parallel beam 26 that satisfies the Bragg diffraction condition. Such a parabolic multilayer mirror is described in the above-mentioned Patent Document 4 and the references cited therein.
[0027]
To design this parabolic multilayer mirror, it is necessary to determine the wavelength of the X-ray to be used. On the other hand, in the total reflection fluorescent XAFS measuring device, it is necessary to perform measurement while changing the wavelength of the X-ray. Therefore, in practice, the wavelength range of the X-ray to be used is determined, and the parabolic multilayer mirror is designed with reference to the wavelength in the center of the range. In this case, if the wavelength range is widened, whether the parabolic multilayer mirror functions normally within that range (ie, whether or not X-rays are reflected) becomes a problem. The same parabolic multilayer mirror can be used as it is within a predetermined wavelength range.
[0028]
Next, numerical values are used to verify within what wavelength range the same parabolic multilayer mirror functions. It is assumed that the element to be measured is cobalt, and the center value of the X-ray energy used for the measurement is 8 keV (corresponding to CuKα ray). The currently manufactured multilayer mirror has a half width of about 0.1 to 0.2 degrees in 2θ in rocking curve measurement. Assuming that a multilayer mirror having a lattice spacing (stacking period) of 4 nm is to be produced, 2θ that satisfies Bragg's diffraction condition is 2.20 degrees for incident X-ray energy of 8 keV. In consideration of the above half width, even if 2θ changes within a range of about ± 0.05 degrees, it is possible to reflect X-rays with this multilayer mirror. Therefore, the parabolic multilayer mirror functions sufficiently within the range of 2θ = 2.15 to 2.25 degrees. When this is converted into an X-ray energy value, it becomes 7.72 to 8.46 keV. That is, the same parabolic multilayer mirror functions within the energy range of about 700 eV, and a parallel beam can be obtained even if the wavelength of X-rays is changed within this range of energy.
[0029]
When the EXAFS measurement of the XAFS measurement is performed, the range of about 700 eV described above is somewhat narrow as an energy scan range. However, this is an energy range that is too large as an energy scan range for performing XANES measurement.
[0030]
If the element to be measured is different, the energy of the X-ray used for the measurement is different. Therefore, it is necessary to prepare a different multilayer mirror in accordance with the energy.
[0031]
Next, a preferred spectroscopic device will be described. FIG. 2 shows a spectrometer from the X-ray source to the light receiving slit. As described above, this spectroscopic apparatus changes the wavelength of the X-rays 22 emitted from the light receiving slit 14 by changing the relative positional relationship between the X-ray source 10a, the curved crystal monochromator 12a, and the light receiving slit 14. be able to. In the total reflection fluorescent XAFS measuring apparatus of the present invention of the type using the parabolic multilayer mirror 24, the position of the light receiving slit 14 and the position of the optical axis 40 of the X-ray 20 traveling therethrough do not change even if the wavelength changes. It is preferred to use a type of spectrometer. When such a spectroscopic device is used, when the diffraction angle at the curved crystal monochromator 12a is changed from 2θa to 2θb, the position of the Rowland circle moves from 16a to 16b (that is, the center position moves from Oa to Ob). , X-ray source moves from 10a to 10b, and the position of the curved crystal monochromator moves from 12a to 12b. At this time, the curved crystal monochromator 12a moves on the optical axis 40. Even if such a movement due to the wavelength change occurs, the position of the light receiving slit 14 and the position of the optical axis 40 do not change. A specific mechanism for realizing such a spectroscopic device is known, and such a mechanism is described in Patent Document 1 described above.
[0032]
When such a spectroscopic device is used, the position of the light receiving slit 14 and the direction of the X-rays 22 emitted therefrom do not change at all even if the measurement wavelength is changed. Total reflection fluorescent XAFS measurement can be performed while keeping the arrangement of the subsequent measurement system the same.
[0033]
【The invention's effect】
The total reflection fluorescent XAFS measurement apparatus of the present invention irradiates the sample with the X-rays coming out of the light receiving slit after being converted into a parallel beam by the parabolic multilayer mirror. The incident angle does not change depending on the position on the sample, (2) the incident X-ray does not hit the place other than the sample surface, and the scattered X-ray does not increase, (3) the light receiving slit even if the sample size is small. The effect is that there is no need to shorten the distance from the sample to the sample.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing one embodiment of a total reflection fluorescent XAFS measurement device of the present invention.
FIG. 2 is a configuration diagram showing a spectroscopic device from an X-ray source to a light receiving slit.
[Explanation of symbols]
Reference Signs List 10 X-ray source 12 Curved crystal monochromator 14 Receiving slit 16 Roland circle 24 Parabolic multilayer mirror 26 Parallel beam 28 Transmission X-ray detector 30 Sample 31 Sample holder 32 Reflected X-ray detector 38 Fluorescent X-ray detector

Claims (2)

A total reflection fluorescent XAFS measurement device having the following configuration.
(A) an X-ray source, a light-receiving slit, and a curved crystal monochromator that reflects the X-rays emitted from the X-ray source and condenses the light on the light-receiving slit; A spectroscope capable of changing the wavelength of X-rays emitted from the light receiving slit by changing the relative positional relationship between the slit and the curved crystal monochromator. (B) A parabolic multilayer mirror that reflects the X-rays coming out of the light receiving slit and converts it into a parallel beam.
(C) A transmission X-ray detector that is arranged between the parabolic multilayer mirror and the sample and detects the intensity of X-rays before entering the sample.
(D) A sample holding device capable of holding the sample so that X-rays emitted from the transmission type X-ray detector can be incident on the surface of the sample under the condition of total reflection.
(E) An X-ray fluorescence detector for detecting X-ray fluorescence emitted from the sample. 2. The total reflection fluorescent XAFS measuring apparatus according to claim 1, wherein the position of the light receiving slit and the direction of the X-ray coming out of the light receiving slit are changed even when the wavelength of the X-ray coming out of the light receiving slit is changed. A total reflection fluorescent XAFS measuring device characterized by not changing.

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