JP3646134B2 - Photoelectron spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectron spectrometer.
[0002]
[Prior art]
In the conventional photoelectron spectrometer, the characteristic X-ray generated from the target material when the electron beam collides with the solid target material is used as the X-ray irradiated to the sample (use of an X-ray tube for electron beam excitation). ).
For example, aluminum or magnesium is used as a target substance, and X-rays having wavelengths of 0.83 nm (photon energy 1487 eV) and 0.99 nm (photon energy 1254 eV), which are Kα characteristic X-rays thereof, have been used.
[0003]
[Problems to be solved by the invention]
In the conventional techniques as described above, since the wavelength of X-rays is short (photon energy is large), it is difficult to manufacture a mirror that can efficiently reflect these X-rays and can focus on a minute region. There was a problem.
Further, since the brightness of the electron beam-excited X-ray tube is small, there is a problem that the number of photoelectrons emitted from a minute X-ray irradiation region is small and it takes a long time to obtain a photoelectron spectrum.
Due to such circumstances, it has been difficult to realize a micro region analysis with a photoelectron spectrometer using an electron beam excitation X-ray tube.
[0004]
Therefore, in order to analyze a minute region, experiments using undulator light (radiated light) with high brightness have been carried out, but such facilities of radiated light are huge and expensive, and general analysis engineers have Since it cannot be used easily, there is a problem that it is not a general analyzer.
[0005]
The present invention has been made in view of such problems of the prior art. 1. Miniaturization and high brightness of X-ray source 2. Easy production of X-ray optical element to be used; 3. High energy resolution and high spatial resolution. 4. Reduction of measurement time An object of the present invention is to provide a photoelectron spectrometer capable of realizing all or some of the downsizing of the entire apparatus.
[0006]
[Means for Solving the Problems]
Therefore, identified by the present invention is to analyze the energy of photoelectrons emitted from the sample surface upon irradiation of X-rays to "sample First, atoms constituting the sample, the type and chemical bonding state of the molecules In the photoelectron spectrometer, the X-ray generation source is a laser plasma X-ray source that collects and irradiates the target material with pulsed laser light to form plasma, and extracts X-rays from the plasma, and the target material Is a boron or a compound containing boron, and provides a photoelectron spectrometer (claim 1).
The present invention is also characterized in that “the X-ray irradiated to the sample is monochromatic to X-rays (center wavelength: 4.86 nm) emitted by 1s-2p transition of hydrogen-like boron ions (B ⁴⁺ )”. A photoelectron spectrometer (claim 2) according to claim 1 is provided.
The third aspect of the present invention is that “the X-ray irradiated to the sample is monochromatized into an X-ray (center wavelength: 6.03 nm) emitted by a 1s ² −1s2p transition of a helium-like boron ion (B ³⁺ ). A photoelectron spectrometer (claim 3) according to claim 1 is provided.
According to a fourth aspect of the present invention, the photoelectron spectroscopy according to any one of claims 1 to 3 , wherein the boron-containing compound is boron nitride (BN) or boron carbide (B ₄ C). An apparatus (Claim 4) "is provided.
According to a fifth aspect of the present invention, there is provided a photoelectron spectrometer according to claim 2 or 4, wherein a thin film of carbon or a substance containing carbon is disposed between the X-ray source and the sample. 5) ".
According to a sixth aspect of the present invention, the photoelectron spectrometer according to claim 3 or 4, wherein a molybdenum thin film or a thin film of a substance containing molybdenum is disposed between the X-ray source and the sample. (Claim 6) "is provided.
In addition, the present invention is seventhly an optical element for condensing X-rays emitted from the X-ray source between the X-ray source and the sample, and wavelength selectivity with respect to the X-ray used. The photoelectron spectrometer (Claim 7) according to any one of Claims 1 to 6, wherein one or two or more optical elements having the above are arranged.
In addition, according to an eighth aspect of the present invention, “X-rays (central wavelength: 4.86 nm) emitted by 1s-2p transition of hydrogen-like boron ions (B ⁴⁺ ) between the X-ray source and the sample, or helium One or more optical elements that selectively reflect or condense X-rays (center wavelength: 6.03 nm) emitted by 1s ² -1 s 2p transition of boron-like ions (B ³⁺ ) are arranged. Item 8. A photoelectron spectrometer according to any one of Items 1 to 7 (Claim 8).
Further, the present invention according to any one of claims 1 to 8, characterized in that as an analysis mechanism for performing energy analysis of "the optoelectronic Ninth, provided an analysis mechanism according to time-of-flight method A photoelectron spectrometer (claim 9) "is provided.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the photoelectron spectrometer according to the present invention (claims 1 to 9), an X-ray generation source for irradiating a sample is focused and irradiated with pulsed laser light on a target material to form plasma, and X-rays are extracted from the plasma. A laser plasma X-ray source (LPX) was used.
LPX is an X-ray source with a high brightness even though it is small in size, has a brightness comparable to or higher than synchrotron radiation, and is about 10 ⁸ times higher in peak value than an X-ray tube excited by an electron beam. Has brightness. The average luminance can be increased by about 10 ² to 10 ³ times higher than that of the X-ray tube by using high repetition laser light.
For this reason, when LPX is used as an X-ray source of a photoelectron spectrometer, it is possible to irradiate a sample with high-intensity X-rays and increase the X-ray dose to the irradiation region (sample). The number of photoelectrons emitted from the sample) increases, and as a result, the photoelectron spectrometer of the present invention (claims 1 to 9) can shorten the measurement time.
[0008]
Furthermore, in the photoelectron spectrometer of the present invention (claims 1 to 9), boron or a boron compound, which is a light element, is used as a target substance for LPX.
When a light element such as boron is used as a target material for LPX, the X-ray spectrum emitted from the plasma becomes several discrete line spectra, and the line width δλ satisfies λ / δλ> 1000. .
By selecting one line spectrum (X-ray) in such a line spectrum group and irradiating the sample, the photoelectron spectrometer of the present invention (Claims 1 to 9) can improve the energy resolution of photoelectrons conventionally. (For example, 0.5 eV or less) (higher energy resolution).
[0009]
In addition, when the boron line spectrum (X-ray) is used, the wavelength is in the soft X-ray region, which is longer than that of the X-ray generated from the above-mentioned X-ray tube. A low-aberration X-ray optical element can be easily manufactured. Therefore, in the photoelectron spectrometer according to the present invention (claims 1 to 9), an X-ray optical element having a high reflectance and low aberration can be used, and the irradiated X-ray is condensed with high accuracy on a minute region of the sample. (High spatial resolution).
[0010]
Therefore, according to the photoelectron spectrometer of the present invention (claims 1 to 9), 1. Miniaturization and high brightness of X-ray source 2. Easy production of X-ray optical element to be used; 3. High energy resolution and high spatial resolution. 4. Reduction of measurement time All or some of the miniaturization of the entire device can be realized.
[0011]
In particular, the line spectrum of the soft X-ray region (wavelength 4.86 nm) emitted by the 1s-2p transition of hydrogen-like boron ion (B ⁴⁺ ) or the 1s ² -1s2p transition of helium-like boron ion (B ³⁺ ) The line spectrum (wavelength 6.03 nm) in the soft X-ray region has a wavelength region in the soft X-ray region and a high X-ray intensity.
Therefore, when these X-rays are used, the X-rays can be condensed with high intensity in a minute region on the sample, and the measurement time can be shortened (claim 2 or 3).
[0012]
As a target substance for LPX, boron nitride (BN) or boron carbide (B ₄ C), which is easily available and can be used in various shapes, is preferred (Claim 4).
It should be noted that some discrete line spectra are also emitted from nitrogen or carbon contained in the target substance, but these X-ray wavelengths are far away from the X-ray wavelengths emitted from the boron ions described above. Therefore, for example, by using a multilayer mirror, a diffraction grating, an X-ray transmission filter, or the like, only X-rays from boron ions to be used can be extracted.
[0013]
When the X-rays irradiated to the sample are monochromatic or nearly monochromatic to X-rays (center wavelength: 4.86 nm) emitted by the 1s-2p transition of hydrogen-like boron ions (B ⁴⁺ ), the X-ray source It is preferable to arrange a thin film of carbon or a substance containing carbon between the sample and the sample.
That is, such a thin film has a high transmittance for X-rays emitted by a 1s-2p transition slightly longer than the wavelength of 4.4 nm, which is the absorption edge of carbon, and further has a shorter wavelength than the longer wavelength region and absorption edge. In this region, since the transmittance is low, unnecessary X-rays can be removed, and the sample can be selectively irradiated with X-rays emitted by the 1s-2p transition of boron ions (claimed). Item 5).
[0014]
In addition, when the X-rays irradiated to the sample are monochromatic or substantially monochromatic to X-rays (center wavelength: 6.03 nm) emitted by the 1s ² -1 s 2p transition of boron ions, between the X-ray source and the sample It is preferable to dispose a molybdenum thin film or a thin film of a substance containing molybdenum.
That is, a molybdenum thin film or a thin film of a substance containing molybdenum has a high transmittance for X-rays emitted by a 1s ² -1 s 2p transition having a wavelength slightly longer than the vicinity of 5.4 nm, which is the M absorption edge of molybdenum. Furthermore, since the transmittance is low in the long wavelength region and the short wavelength region from the absorption edge, unnecessary X-rays can be removed, and the X-rays emitted by the 1s ² -1s 2p transition of boron ions are selectively used. It is preferable that the sample can be irradiated to the sample (claim 6).
[0015]
In addition, an optical element that collects X-rays emitted from the X-ray source on the sample between the X-ray source and the sample, and one or more optical elements having wavelength selectivity with respect to the used X-rays When arranged, it is preferable because a more monochromatic X-ray can be irradiated onto a minute region of the sample (claim 7).
[0016]
Also, X-rays (center wavelength: 4.86 nm) emitted by 1s-2p transition of hydrogen-like boron ions (B ⁴⁺ ) or 1s ^{2 of} helium-like boron ions (B ³⁺ ) between the X-ray source and the sample. If one or more optical elements that selectively reflect or condense X-rays (center wavelength: 6.03 nm) emitted by the -1s2p transition are placed in other X-rays and target substances emitted from boron ions other can be removed X-rays from ions, since X-rays by 1s-2p transition or 1s ² -1s2p transition of boron ions alone (more monochromatic X-ray) can be irradiated to the specimen preferred ( Claim 8).
[0017]
Furthermore, it is preferable to provide an analysis mechanism according to the time-of-flight method as an analysis mechanism for performing the energy analysis of the photoelectrons.
That is, in the photoelectron spectrometer of the present invention (Claims 1 to 8), since LPX which is a pulse X-ray source is used as the X-ray source, an analysis mechanism for performing energy analysis of photoelectrons emitted from the sample surface. By using the time-of-flight method, which provides an analysis mechanism related to the time-of-flight method and can take a large solid angle of photoelectrons, it is possible to efficiently detect photoelectrons emitted from a minute region and reduce the measurement time. This is preferable because it can be further shortened (claim 9).
[0018]
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
[0019]
[Example 1]
FIG. 1 is a schematic configuration diagram of the photoelectron spectrometer of the present embodiment.
When the laser beam 102 emitted from the pulse laser device is focused and irradiated by the lens 103 onto the target material 105 made of boron nitride (BN) disposed in the vacuum vessel 101, the target material 105 is turned into plasma and X The line is radiated.
The vacuum vessel 101 is evacuated in advance by an exhaust device (not shown) to a pressure at which the generated X-rays are sufficiently transmitted.
X-rays emitted from the plasma 106 pass through the carbon film and mylar film (organic film) used as the X-ray transmission filter 107 and are then irradiated onto the sample 108 disposed in the flight tube 110. .
[0020]
The carbon film is used as a filter that removes visible light and ultraviolet light radiated from plasma and transmits X-rays, and the Mylar film is not only used as an X-ray transmission filter but also has a relatively low vacuum. It also serves as a pressure partition that separates the vacuum vessel 101 and the high-vacuum flight tube 110. As an example, FIG. 2 shows the wavelength dependence of the transmittance of a Mylar film having a thickness of 2.4 μm.
The carbon film and mylar film used as filters are X-rays emitted by the 1s-2p transition of boron ions slightly longer than the K absorption edge (wavelength 4.4 nm) of carbon contained in these filters. The transmittance is high with respect to (wavelength 4.8 nm), and the transmittance is low with respect to X-rays in the longer wavelength region and shorter X-rays than the K absorption edge of carbon.
Therefore, the X-rays that have passed through the filter are almost monochromatic to X-rays (center wavelength: 4.86 nm) emitted by the 1s-2p transition of boron ions.
[0021]
FIG. 3 shows an X-ray spectrum (a) emitted from boron nitride and an X-ray spectrum (b) after passing through the Mylar film.
While boron nitride is some discrete line spectrum caused by boron (B) and nitrogen (N) ions are released, in which, due to the 1s-2p transition and 1s ² -1s2p transition boron ions Since the intensity of X-rays is high and these are separated from the X-rays caused by nitrogen ions, unnecessary X-rays from nitrogen ions can be easily removed.
It can also be seen that only the X-rays resulting from the 1s-2p transition of boron ions are monochromatized by passing through the Mylar film. In general, since the line width [delta] [lambda] of these lines spectra satisfies λ / δλ> 1000, the line width of the X-rays due to the 1s-2p transition ^{δλ <4.8 × 10 - 3 nm} , in terms of energy &Dgr; E <0.26 eV It is monochromatic.
Since this energy width is smaller than 0.8 eV, which is the energy width of the X-ray tube that has been used conventionally, a photoelectron spectrometer with high energy resolution can be easily realized (in FIG. 3, the line resolution depends on the resolution of the spectrometer. Width is limited).
[0022]
As described above, the X-rays monochromated by the filter are irradiated onto the sample 108, and photoelectrons 109 are emitted from the sample surface. The energy of the emitted photoelectrons 109 is analyzed by the time-of-flight method.
That is, the photoelectrons 109 emitted from the sample surface pass through the flight tube 110 covered with the magnetic shielding material 111, and then detected by the microchannel plate (MCP) 112, which is a photoelectron detector. The output signal is taken in as a digital signal by a high-speed digital oscilloscope (not shown), and the kinetic energy of photoelectrons is obtained from the arrival time at the MCP by an arithmetic unit (not shown).
According to the photoelectron spectrometer of the present embodiment, the X-ray source can be reduced in size and brightness, increased in energy resolution, reduced in measurement time, and reduced in size of the entire apparatus.
[0023]
[Example 2]
FIG. 4 is a schematic configuration diagram of the photoelectron spectrometer of the present embodiment.
In this example, as in Example 1, boron nitride is used as the target material.
The X-ray 408 emitted from the plasma 407 passes through the X-ray filter 409 and is then collected on the sample 411 by the Schwarzschild mirror 410.
Molybdenum (Mo) foil is used for the X-ray filter 409 and cuts visible light and ultraviolet light emitted from the plasma 407.
[0024]
Also, by using the M absorption edge (near 5.4 nm) of molybdenum, the transmittance for X-rays (center wavelength 6.03 nm) due to the 1s ² -1 s 2p transition of boron, which is slightly longer than the absorption edge, is obtained. The X-ray filter has a high transmittance with respect to X-rays longer than that and X-rays shorter than the M absorption edge of molybdenum.
Therefore, the X-rays that have passed through the filter are almost monochromatized into X-rays (center wavelength 6.03 nm) emitted by the 1s ² -1s2p transition of boron ions.
The filter also serves as a pressure partition for the vacuum vessels 401 and 402.
[0025]
On the Schwarzschild mirror 410, by forming a multilayer film that matches the center wavelength with the X-rays (wavelength 6.03 nm) emitted by the 1s ² -1 s 2p transition of boron ions, the spectral characteristics of the multilayer film are utilized. Since it is possible to eliminate weak satellite lines existing in the vicinity of the 1s ² -1 s 2p transition of boron ions, the monochromaticity of the irradiated X-rays can be further increased.
[0026]
In addition, a Schwarzschild mirror (an example of an X-ray optical element) has a small aberration with respect to the X-ray used and can be manufactured relatively easily with a high magnification (100 to 200 times). Therefore, if the size of the plasma 407 is about 50 μm, it can be easily condensed to about submicron using a Schwarzschild mirror.
[0027]
The photoelectrons 412 emitted from the sample 411 are analyzed for photoelectron energy by the time-of-flight method as described above.
That is, after the photoelectron 412 passes through the magnetically shielded flight tube 413, it is detected by a microchannel plate (MCP) 414, and its output signal is converted into a digital signal by a high-speed digital oscilloscope (not shown). It is captured. And the kinetic energy of a photoelectron is calculated | required from the arrival time to MCP with an arithmetic unit (not shown).
[0028]
According to the photoelectron spectrometer of the present embodiment, 1. Miniaturization and high brightness of X-ray source 2. Easy production of X-ray optical element to be used; 3. High energy resolution and high spatial resolution. 4. Reduction of measurement time Miniaturization of the entire apparatus can be realized.
[0029]
In the above embodiment, boron nitride (BN) is used as the LPX target material, but boron carbide (B ₄ C) may be used. In addition, the target substance has a plate shape, but may be a columnar shape, a cylindrical shape, a disc shape, a tape shape, or a linear shape.
In addition, although the Schwarzschild mirror is used as the X-ray condensing optical element, other than this, a multilayer elliptical mirror, a total reflection mirror such as a Walter mirror, or a zone plate that can be manufactured or is relatively easy to manufacture May be used.
By adding a divergent magnetic field (P. Kruit and FHRead, J. Phys. E, 16, 1983, p313) as reported by P. Kruit and FHRead to the sample and flight tube mentioned above, Most of the photoelectrons emitted from the sample can be captured, and the measurement time can be greatly shortened.
In addition, by arranging an electrode for reducing the speed of photoelectrons in the flight tube section, it is possible to increase the energy resolution by extending the arrival time of the photoelectrons to the detector.
[0030]
【The invention's effect】
As described above, according to the photoelectron spectrometer of the present invention, 1. Miniaturization and high brightness of X-ray source 2. Easy production of X-ray optical element to be used; 3. High energy resolution and high spatial resolution. 4. Reduction of measurement time All or some of the miniaturization of the entire device can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a photoelectron spectrometer according to a first embodiment.
FIG. 2 is a data diagram showing the wavelength dependence of the transmittance of a Mylar film having a thickness of 2.4 μm.
FIG. 3 is a data diagram showing an X-ray spectrum (a) emitted from boron nitride and an X-ray spectrum (b) after passing through a Mylar film.
FIG. 4 is a schematic configuration diagram of a photoelectron spectrometer according to the second embodiment.
[Explanation of main part codes]
101 ·· Vacuum container 102 · · Laser beam 103 · · Lens 104 · · Window 105 · · Target material (for example, boron nitride)
106 .. Plasma 107 .. X-ray transmission filter 108 .. Sample 109 .. Photoelectron 110 .. Flight tube 111 .. Magnetic shielding material 112 .. Microchannel plate 401, 402 .. Vacuum vessel 403 .. Laser beam 404 · · Lens 405 · · Window 406 · · Target substance (for example, boron nitride)
407 ··· Plasma 408 · · X-ray 409 · · X-ray transmission filter 410 · · Schwarzschild mirror (an example of an X-ray optical element)
411 ··· Sample 412 · · Photoelectron 413 · · Flight tube 414 · · Microchannel plate

Claims (9)

In a photoelectron spectrometer that identifies the types of atoms, molecules, and chemical bonds constituting the sample by analyzing the energy of photoelectrons emitted from the sample surface when the sample is irradiated with X-rays.
The X-ray generation source is a laser plasma X-ray source that collects and irradiates a target material with pulsed laser light to form plasma and extracts X-rays from the plasma, and the target material contains boron or boron A photoelectron spectrometer characterized by being a compound. 2. The photoelectron spectroscopy according to claim 1, wherein X-rays irradiated to the sample are monochromatized into X-rays (center wavelength: 4.86 nm) emitted by 1s-2p transition of hydrogen-like boron ions (B ⁴⁺ ). apparatus. ^{2. The} photoelectron according to claim 1, wherein X-rays irradiated to the sample are monochromatized into X-rays (center wavelength: 6.03 nm) emitted by a 1s ² −1 s 2p transition of helium-like boron ions (B ³⁺ ). Spectrometer. The photoelectron spectrometer according to claim 1 , wherein the boron-containing compound is boron nitride (BN) or boron carbide (B ₄ C).   5. The photoelectron spectrometer according to claim 2, wherein a thin film of carbon or a substance containing carbon is disposed between the X-ray source and the sample.   5. The photoelectron spectrometer according to claim 3, wherein a molybdenum thin film or a thin film of a substance containing molybdenum is disposed between the X-ray source and the sample. An optical element that collects X-rays emitted from the X-ray source on the sample between the X-ray source and the sample, and one or more optical elements having wavelength selectivity with respect to the used X-rays The photoelectron spectrometer according to claim 1 , wherein the photoelectron spectrometer is arranged. X-rays (center wavelength: 4.86 nm) emitted by 1s-2p transition of hydrogen-like boron ions (B ⁴⁺ ) or 1s ^{2 of} helium-like boron ions (B ³⁺ ) between the X-ray source and the sample -1s2p transition X-rays emitted by the (center wavelength 6.03Nm) selectively reflected or focused optical elements one or more, in any one of claims 1 to 7, characterized in that arranged The photoelectron spectrometer as described. As an analysis mechanism for performing energy analysis of the optoelectronic photoelectron spectrometer according to any one of claims 1-8, characterized in that a analysis mechanism according to time-of-flight method.

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