JP2000249655A - Laser-excitaed plasma emission spectrophotometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a high-accuracy analysis by preventing a contamination inside an analytical chamber. SOLUTION: In a main chamber 20, a sample opening 21 is formed in the opposite position of a window plate 23 for laser transmission, and a sample 5 is pressed by a pressure body 31 so at to be brought into close contact in such a way that a sample face is exposed in the opening 21. In addition, an auxiliary chamber 27 is brought into close contact with the main chamber 20 so as to surround the sample 5. The inside of the main chamber 20 and the inside of the auxiliary chamber 27 are kept independently airtight by keeping a gap from the sample 5. Since only a part of the sample 5 is exposed inside the main chamber 20, a contamination due to an undesired component which sticks to the sample 5 can be suppressed to a minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser-excited plasma emission spectrometer using a laser as an energy source for emitting light from a solid sample.

[0002]

2. Description of the Related Art As one method of emission spectroscopy, there is known a method of irradiating a solid sample with a laser under reduced pressure conditions, taking out emission light of plasma generated from the irradiated area, and performing spectral analysis (refer to ""). Emission Spectroscopy Using N2 Laser Excited Plasma ", see Kiichiro Kagawa et al., Spectroscopic Research, Vol. 34, No. 5, (1985)).

FIG. 6 is a schematic configuration diagram of a light emitting unit in the emission spectrometer described in the above-mentioned document. A high-power N2 laser emitted from a laser light source (not shown) is condensed by a lens 40 and introduced into a chamber 41 evacuated to about 1 Torr by a vacuum pump (not shown). Chamber 4
A sample 42 is rotatably accommodated in the motor 1 by a motor 43. When the sample 42 is irradiated with the laser, a small-diameter white plasma (primary plasma) is generated near the upper portion of the irradiation region. Subsequently, the secondary plasma 44 spreads hemispherically so as to surround the primary plasma. Since the secondary plasma 44 emits an emission line of a color (wavelength) corresponding to the constituent elements of the sample 42, the emission line is taken out of the chamber 41 and introduced into the spectral analysis unit 45.

If the same area of the sample 42 is continuously irradiated with the laser, the sample near the irradiation position becomes liquefied, causing a depression, and the emission intensity of the plasma decreases. Therefore, the sample 42 is slowly rotated by the motor 43 so that the laser irradiation position is formed in a ring shape. This makes it possible to obtain plasma having a stable shape and emission intensity over a long period of time.

[0005] As another emission spectroscopy technique, inductively coupled plasma (Inductively coupled plasma) by laser excitation is used.
Plazma = ICP) Emission spectroscopy is well known,
In this analysis method, fine particles of a sample are introduced into an argon plasma to emit light. Therefore, various kinds of hydrocarbons (CnHm) contained in argon gas, carbon monoxide contained in residual air, and carbon dioxide are contained in steel. Measurement accuracy of trace carbon is not high enough. In addition, measurement of nitrogen and oxygen contained in the metal cannot be performed. On the other hand, the laser-excited plasma emission spectroscopy has the advantage that it is possible to analyze a wide range of elements including these elements and elements that cannot be analyzed by other methods.

[0006]

However, the conventional laser-excited plasma emission spectroscopy analyzer has several problems as described below, and has not been put into practical use at present. (1) The above-described configuration in which the sample itself is rotated has many problems, such as having to penetrate an axis through the wall surface of the chamber 41. Therefore, as an alternative method, it is conceivable to optically change the laser irradiation position. However, in this case, since the position where the plasma is generated moves in the horizontal direction, the optical axis of the light introduced into the spectroscope changes and causes an error. (2) The secondary plasma, which is the object of the side light, is generated following the primary plasma, but the primary plasma does not emit light peculiar to the element and thus contributes to background noise. (3) To perform high-precision analysis in the above spectroscopic analysis,
It is preferable that the spatial distribution of the emitted light of the plasma is stable, but in practice, the distribution is affected by the pressure in the chamber 41, so that the results obtained when the laser is irradiated a plurality of times may vary. There is. (4) Assuming that the sample is accommodated in the chamber 41,
Because the surface area of the sample exposed in the chamber 41 is large,
Atmospheric components and the like adhering to this surface are removed from the chamber 4
1 to cause contamination, resulting in a decrease in accuracy.

[0007] The present invention has been made to solve these problems, and has as its main object to improve the analysis accuracy in a laser-excited plasma emission spectrometer.

[0008]

According to a first aspect of the present invention, a solid sample is irradiated with a laser under reduced pressure, and light emitted from plasma generated by the laser is spectrally analyzed. In a laser-excited plasma emission spectrometer, a) an elongated aperture that is placed in close proximity to the laser irradiation position and is approximately parallel to the sample surface to remove light emitted from the center and top of the hemispherical plasma. B) light collecting means for condensing the light passing through the opening of the incident light limiting means, and c) the light dispersion direction is the same as the extending direction of the opening. Light dispersing means including an arranged concave diffraction grating.

A second aspect of the present invention has been made to solve the above-mentioned problems. In the second aspect, a solid sample is irradiated with a laser under reduced pressure conditions, and light emitted from plasma generated by the solid sample is detected by a detector to perform spectral analysis. In the laser-excited plasma emission spectrometer, a) a signal generating means for generating a signal of a predetermined time width after a predetermined delay time has elapsed from the laser irradiation time, and b) during a period of the signal of the predetermined time width. And integrating means for integrating the light receiving signal by the light that has reached the detector.

A third aspect of the present invention has been made to solve the above-mentioned problems, and comprises irradiating a solid sample with a laser under reduced pressure conditions.
In a laser-excited plasma emission spectrometer that disperses the wavelength of light emitted from the generated plasma with a spectroscope and simultaneously detects a plurality of dispersed lights with a plurality of detectors, a) a main component obtained at a predetermined wavelength Calculation means for calculating the ratio between the elemental spectrum intensity and the other elemental spectrum intensities; andb) analysis processing means for executing an analysis based on the ratio of each spectrum intensity calculated by the calculation means during a plurality of laser irradiations. , Are provided. Here, the analysis processing means may perform processing such as qualitative analysis or quantitative analysis.

A fourth aspect of the present invention for solving the above-mentioned problem is to irradiate a solid sample placed in a chamber in a reduced-pressure atmosphere with a laser and to separate light emitted from plasma generated by the laser. In the laser-excited plasma emission spectrometer for analysis, the chamber includes: a) a main chamber having an opening formed at a laser irradiation position; and b) a main chamber having a sample closed so as to close the opening from outside the main chamber. And c) a sub-chamber surrounding the sample in close contact with the outer wall of the main chamber and being disposed in close contact with the main chamber.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Among the plasmas that spread in a hemispherical shape from the laser irradiation area, the primary plasma existing near the center of the plasma does not emit light peculiar to the elements contained in the sample. Light emission tends to be unstable near the top of the head. Therefore, in the laser-excited plasma emission spectrometer according to the first invention, the light emitted from those portions is removed by the incident light restricting means, and only the light having a stable large emission intensity is collected by the focusing means. Collected and introduced into light dispersion means. Therefore, the light peculiar to the element generated from the plasma can be reliably and stably analyzed.

Further, since the aperture of the incident light restricting means is elongated in a direction parallel to the sample surface, the irradiation position of the laser moves in the horizontal direction on the sample surface, and the plasma generation position moves accordingly. Even so, the necessary light is introduced into the light condensing means with almost no loss. Further, since the dispersion direction of the concave diffraction grating coincides with the extension direction of the aperture, even if the plasma generation position moves horizontally, light having the same wavelength always reaches the same detector. Therefore, even if the irradiation position of the laser changes, stable analysis can be performed without being affected by the change.

In the laser-excited plasma emission spectrometer according to the second aspect of the present invention, the signal generation means may be configured to stop the emission of the primary plasma generated immediately after the laser irradiation or to reduce the emission intensity. And generating a signal having a time width until the emission of the secondary plasma ends or the emission intensity decreases. The integrating means integrates the received light signal only during the period of this signal.
It is hardly affected by the emission of the secondary plasma. That is, according to the laser-excited plasma emission spectrometer according to the second aspect of the invention, it is possible to eliminate background noise caused by the primary plasma and obtain a more accurate signal.

In the laser-excited plasma emission spectrometer according to the third aspect of the present invention, the data obtained each time a plurality of laser irradiations are performed is not used as it is, but the spectral intensity of the main component element obtained at a predetermined wavelength is obtained. Calculate the ratio between the intensity and the intensity of other elemental spectra, and perform qualitative analysis or quantitative analysis based on the ratio. Therefore, even when unexpected fluctuations occur in the analysis conditions at the time of laser irradiation, for example, gas pressure in the chamber, laser intensity, etc., the effects of such fluctuations are suppressed and highly accurate analysis is performed. It can be carried out.

Further, in the laser-excited plasma emission spectrometer according to the fourth aspect of the invention, only a very small portion of the sample is exposed in the main chamber, and the other surface is exposed in the sub-chamber. ing. Therefore, the possibility that the inside of the main chamber that emits light is contaminated is greatly reduced as compared with the related art, and highly accurate analysis becomes possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser-excited plasma emission spectrometer according to one embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a main part of the laser-excited plasma emission spectroscopy analyzer. A laser emitted from a laser light source 1 is condensed by a lens 3 via a galvano scanning unit 2,
The sample 5 provided in the chamber 4 is irradiated. The galvano scanning section 2 is configured to include a galvanometer mirror driven by a piezoelectric coil or the like, so that the irradiation position of the laser can be scanned in the X-axis and Y-axis directions. When the sample 5 is disposed in the chamber 4, the sample 5 can be mounted at an arbitrary position within a predetermined range in the X-axis and Y-axis directions.

Light emitted from the plasma generated above the sample 5 by the laser irradiation is taken out of the chamber 4 and introduced into the spectroscope 8 through the lens 7. The spectroscope 8 includes an entrance slit 9, a concave diffraction grating 10, a plurality of exit slits 11, and a photodetector 1 on the circumference of the Rowland circle.
2 are arranged side by side, that is, a so-called Paschen-Runge type spectroscope, in which light whose wavelength is dispersed and focused by the concave diffraction grating 10 reaches each photodetector 12. The exit slit 11 and the photodetector 12 are arranged at positions where light having a specific wavelength can be detected, respectively, and the received light signal is sent to the signal acquisition unit 13. In FIG. 1, only three sets of the exit slit 11 and the photodetector 12 are described. However, in actuality, the exit slits 11 and the photodetectors 12 are provided in a number corresponding to the wavelength to be measured.

The signal acquiring section 13 accumulates (accumulates) the electric charge of each light receiving signal for a predetermined time to obtain a detection signal, converts the signal into a digital signal, and sends it to the data processing section 14 as described later. The data processing unit 14 performs qualitative or quantitative analysis of the sample by receiving the data and performing arithmetic processing according to a predetermined algorithm.
The control unit 15 has a function of controlling the operation of each unit. Many of the functions of the control unit 15 and the data processing unit 14 are achieved by executing predetermined programs on a personal computer.

FIG. 2 is a longitudinal sectional view showing the detailed structure of the chamber 4. The chamber 4 includes a main chamber 20 having an internal space for generating plasma, and a sub-chamber 27 which is detachably provided in the main chamber 20 and has an internal space for storing the sample 5. Main chamber 20
Is a sample opening 21 from which the measurement surface of the sample 5 is viewed, and an O-ring 22 for maintaining airtightness provided around the outer wall of the sample opening 21.
And an optically transparent window plate 23 provided at a position facing the sample opening 21, an inert gas introduction passage 24 and an exhaust passage 25 communicating with the internal space, and taking out light emitted from the plasma to the outside. And a light lead-out path 26.

On the other hand, the sub-chamber 27 has an O-ring 28 for maintaining airtightness on a surface in close contact with the main chamber 20, and has an inert gas introduction passage 29 and an exhaust passage 30 on the wall surface. Further, a pressing body 31 for pressing the sample 5 against the outer wall surface of the main chamber 20 is slidably provided through a wall surface provided with an O-ring 32 for maintaining airtightness. Further, the sub-chamber 27 is provided outside the sub-chamber 27 with the main chamber 2.
A pressing body 33 for pressing against zero is provided.

The procedure for mounting the sample 5 in the chamber 4 is as follows. Before the sample is mounted, the pressing by the pressing body 33 is released, and the sub-chamber 27 is
Away from zero. In this state, the sample 5 is pressed by the pressing body 31 so that the measurement surface is exposed to the sample opening 21 as shown in FIG. The gap between the sample 5 and the outer edge of the sample opening 21 is sealed by an O-ring 22. Sample 5
The sub-chamber 27 is attached so as to cover the whole,
Press firmly on 1. The gap between the outer wall surface of the main chamber 20 and the contact surface of the sub-chamber 27 is sealed by an O-ring 28. Then, an exhaust pump (not shown) is driven to suck the residual air in the main chamber 20 and the sub-chamber 27 through the exhaust paths 25 and 30, and Ar at a small flow rate through the inert gas introduction paths 24 and 29. Pour the gas. As a result, the undesired gas in the main chamber 20 and the sub chamber 27 is exhausted, and a low-pressure Ar gas atmosphere is obtained.

FIG. 3 is a diagram showing the state of light emission from the plasma light emitting unit, and FIG. 4 is a configuration diagram showing an optical path from the light emitting unit to the concave diffraction grating. The opening 26a of the light guide path 26 extending from the internal space of the main chamber 20 to the lens 7 has a rectangular shape elongated in a direction parallel to the upper surface of the sample 5, as shown in FIG. That is, the opening 26a itself has a light shielding function, and the secondary plasmas P12 and P2 which spread in a hemispherical shape.
2. Light emitted from the vicinity of the center and the top of P32 is shielded, and light from the center of the plasma is led out.

As shown in FIG. 3, the entrance slit 9 disposed between the lens 7 and the concave diffraction grating 10 also has a slit opening 9a in a direction parallel to the upper surface of the sample 5, that is, the opening 2
6a is provided so as to extend in the same direction as 6a. Also,
As shown in FIG. 4, the concave diffraction grating 10 is arranged such that the dispersion direction of the wavelength coincides with the sample surface.

When the laser is scanned by the galvano scanning unit 2 and the irradiation position moves in the horizontal direction as shown in FIG. 3 (irradiation positions S1, S2, S3), secondary plasmas P12, P22 generated above the irradiation position. , P32 are shifted in the horizontal direction. However, since the opening 26a is elongated so as to cover the moving range of the secondary plasmas P12, P22, and P32, a sufficient amount of light is emitted no matter where the secondary plasma exists within the range. The light passes through 26a and reaches the lens 7. Further, even if the position of the secondary plasma is shifted in the horizontal direction, since the dispersion directions of the wavelengths of the concave diffraction grating 10 match, light having a specific wavelength reflected on the grating surface reaches a specific photodetector. , Wavelength shift can be suppressed.

Next, the operation of the apparatus of this embodiment at the time of analysis will be described with reference to FIG. After the preparation in the chamber 4 is completed as described above, when a laser irradiation trigger signal is given to the laser light source 1 by the control unit 15 (see FIG. 5A), the sample 5 has a pulse shape having an output of 5 mJ or more. Is irradiated. Then, a part of the sample 5 is separated into fine particles, and a plasma that emits an atomic spectrum is generated by collision of the fine particles with each other and surrounding Ar gas molecules. This plasma is generated immediately after laser irradiation (several n
Second period), a small white primary plasma P1 in the center
1, P21 and P31 occur, and the light emission ends in about 20 nsec to about one hundred and several tens nsec (see FIG. 5B). From the site where the primary plasmas P11, P21 and P31 are generated, the secondary plasma P1
2, P22 and P32 are generated, spread in a hemispherical shape with the lapse of time, and the light emission is continuously continued for several tens of nanoseconds to several microseconds (see FIG. 5C).

The control unit 15 generates a charge accumulation signal that is at a high level only during a period from the time when a predetermined time T1 elapses to the time when a predetermined time T2 elapses from the time when the pulse of the laser irradiation trigger signal is generated (FIG. 5 (d)). )), Signal acquisition unit 1
Send to 3. The predetermined times T1 and T2 may be set automatically or may be set appropriately according to an instruction of the operator. In any case, by appropriately setting the times T1 and T2, it is possible to obtain the charge accumulation signal only during the period in which the secondary plasma is generated. The signal acquisition unit 13 includes, for each photodetector 12, an integration circuit that integrates an input signal only during a period when the charge accumulation signal is at a high level, for example. Therefore, the signal acquisition unit 13 can obtain a detection signal based on only the light emitted from the secondary plasma while excluding the light emitted from the primary plasma.

The detection signals thus obtained for each wavelength are converted into digital signals and processed by the data processing unit 14. The data processing unit 14 performs the following process in order to eliminate the influence of the variation in the data obtained for each of the plurality of laser irradiations. That is, among the signals obtained for each wavelength, the component whose spectrum appears very strongly compared to the maximum or the other components is used as a reference. Then, the spectrum intensity of each of the other components is represented by a ratio to the reference spectrum. In a plurality of laser irradiations performed on the same sample, the spectral intensities of the other components are standardized, so to speak, by using the same principal component as a reference. At the same time, the analysis conditions (such as the pressure in the chamber 4 and the laser intensity) in the signals obtained by the plurality of photodetectors 12 can be considered to be the same. The difference in the analysis conditions for each can be eliminated. By executing arithmetic processing such as quantitative analysis thereafter using such standardized data, analysis with less error can be performed.

The above embodiment is merely an example, and it is apparent that changes and modifications can be made within the spirit of the present invention.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a laser-excited plasma emission spectroscopy analyzer according to one embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a detailed structure of a chamber of the present embodiment.

FIG. 3 is a diagram showing a state in which light is emitted from a plasma light emitting unit in the embodiment.

FIG. 4 is a configuration diagram showing an optical path from a light emitting unit to a diffraction grating in the present embodiment.

FIG. 5 is a timing chart for explaining the operation in the embodiment.

FIG. 6 is a configuration diagram of a light emitting unit of a conventional laser-excited plasma emission spectrometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Galvano scanning part 3, 7 ... Lens 4 ... Chamber 5 ... Sample 8 ... Spectroscope 9 ... Incident slit 9a ... Slit opening 10 ... Concave diffraction grating 11 ... Outgoing slit 12 ... Photodetector 13 ... Signal acquisition Unit 14 Data processing unit 20 Main chamber 21 Sample opening 22, 28, 3
2 O-ring 23 Window plate 24, 29 Inert gas introduction path 25, 30 Exhaust path 26 Light extraction path 26a Opening 27 Sub-chamber 31, 33 Pressing body

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G020 BA02 CA01 CB03 CB23 CB54 CC05 CC42 CC46 CD03 CD06 CD11 CD22 DA12 2G043 AA01 CA02 CA05 DA06 DA08 EA10 FA01 FA03 GA02 GA08 GB05 GB17 GB21 HA01 HA05 JA04 KA09 LA01 MA01 NA01 NA06

Claims (4)

[Claims] 1. A laser-excited plasma emission spectrometer for irradiating a solid sample with a laser under reduced pressure and spectrally analyzing light emitted from plasma generated by the laser. An incident light restricting means which is disposed and has an elongated opening substantially parallel to the sample surface to remove light emitted from the central portion and the top of the plasma expanding in a hemispherical shape; b) passing through the opening of the incident light restricting means Light condensing means for condensing the light, and c) light dispersing means including a concave diffraction grating arranged so that the light is dispersed in the same direction as the direction in which the aperture extends. Laser-excited plasma emission spectroscopy analyzer. 2. A laser-excited plasma emission spectrometer for irradiating a solid sample with a laser under reduced pressure, detecting light emitted from a plasma generated thereby by a detector, and performing spectral analysis. Signal generating means for generating a signal of a predetermined time width after a predetermined delay time has elapsed from the irradiation time; andb) integrating a light receiving signal by light reaching the detector during the signal of the predetermined time width. A laser-excited plasma emission spectroscopy analyzer comprising: an integrating means. 3. Laser excitation for irradiating a solid sample with a laser under reduced pressure conditions, dispersing light emitted from plasma generated by the laser with a spectroscope, and simultaneously detecting a plurality of dispersed lights with a plurality of detectors. In the plasma emission spectrometer, a) calculating means for calculating the ratio between the main component element spectral intensity obtained at a predetermined wavelength and the other element spectral intensity, and b) calculating by the calculating means upon a plurality of laser irradiations. Analysis processing means for performing an analysis based on the ratio of the respective spectral intensities, and a laser-excited plasma emission spectroscopy analyzer. 4. A laser-excited plasma emission spectrometer for irradiating a solid sample placed in a chamber in a reduced-pressure atmosphere with a laser and performing spectral analysis of light emitted from plasma generated by the laser, wherein the chamber comprises: a) a main chamber having an opening formed at a laser irradiation position; b) sample holding means for pressing a sample against an outer wall of the main chamber so as to close the opening from outside the main chamber; c) an outer wall of the main chamber. And a sub-chamber which is disposed in close contact with the main chamber surrounding the sample which is in close contact with the laser-excited plasma emission spectroscopy analyzer.