JP4401828B2 - Glow discharge optical emission spectrometer - Google Patents

Description

  The present invention relates to a glow discharge emission spectroscopic analysis apparatus, and more particularly to a high-precision glow discharge emission spectroscopic analysis apparatus that prevents intrusion of outside air and air into a glow discharge section.

  A glow discharge is generated in an inert gas atmosphere such as argon at a pressure of about 500 to 1300 Pa, and atoms on the surface of the sample are knocked out by a sputtering phenomenon caused by colliding the generated ions with the surface of the sample, which is a cathode. An analysis method for identifying an element by spectroscopically diffusing the light inherent to the element that is excited when it returns to the ground state with a spectroscope is called glow discharge emission spectroscopy. This method is widely used for analyzing the depth direction of the sample surface.

  This glow discharge emission spectroscopic analysis is typically performed by an apparatus having a Grimm discharge tube shown in FIG. However, for example, when trying to quantitatively analyze trace oxygen or nitrogen of 100 mass ppm or less in a sample, the background intensity of these elements is high, and there is a problem that accurate analysis cannot be performed. In the apparatus shown in FIG. 6, the problem is that the atmosphere enters the glow discharge portion through a slight gap between the O-ring 8 for keeping the surface of the sample S and the support block 4 holding the sample S airtight. This is because the background intensity of elements such as nitrogen (N) and oxygen (O) increases. In particular, when the sample is polished with an abrasive having good workability (eg, coarser than P220 of JIS R6010: 2000), the above problem is unavoidable.

  In order to avoid this problem, Patent Document 1 discloses a technique for preventing the atmosphere from being mixed into the plasma by making the seal (O-ring) of the sample stage double and reducing the pressure between them or sealing the discharge gas. It is disclosed. Patent Document 2 discloses a technique for preventing the atmosphere from being mixed into the plasma by flowing a discharge gas around the O-ring to bring it into a pressurized state. Furthermore, in Patent Document 3, as a countermeasure when atmospheric components enter the discharge tube from the O-ring seal part because the surface of the sample is uneven or curved, the vacuum in the discharge tube cannot be maintained. An apparatus is disclosed that uses a sample mounting device that shuts off the entire sample from outside air and exhausts the interior of the sample mounting device.

JP-A-1-206237 JP-A-8-338761 JP-A-7-225187

  However, with the means disclosed in Patent Document 1, since the seal portion is further overlapped on the outside of the conventional seal portion, the minimum diameter of the sample has to be approximately twice as large as that of the conventional sample (area ratio is approximately four times). When only a small sample can be prepared, the glow discharge emission spectroscopic analysis must be abandoned. In addition, when reducing the pressure between the double O-rings, an exhaust facility such as a vacuum pump is required. On the other hand, when gas is sealed between the double O-rings, mixing of atmospheric air into the plasma cannot be completely suppressed. There is a problem. The means disclosed in Patent Document 2 has no problem due to the increase in size of such an apparatus. However, it is difficult to allow the discharge gas to flow uniformly around the O-ring seal portion, and therefore, it is inevitable that air enters from a part around the O-ring. The means disclosed in Patent Document 3 can suppress the influence of the atmosphere, but it takes time to evacuate the inside of the sample mounting portion, and intake / exhaust for maintaining the pressure inside the mounting device at an optimum value. There is a problem that equipment is required and the cost of the apparatus increases.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a high-precision glow discharge emission spectroscopic analysis apparatus that can quickly and surely prevent air from entering without enlarging the size of the apparatus or sample. .

A glow discharge emission spectroscopic analysis apparatus according to the present invention has an anode tube, a cathode, and a support block that is interposed between the anode tube and the cathode and contacts the sample. In a glow discharge optical emission spectrometer comprising a power supply means for sputtering a sample by applying a high-frequency voltage, an inner O-ring and an outer O-ring having a diameter larger than that of the inner O-ring are provided on a sample contact surface of the support block. An opening that opens from the support block side between the inner O-ring and the outer O-ring, in order to allow argon gas having the same pressure as the outer pressure to flow between the inner O-ring and the outer O-ring; The apparatus is configured to be provided with an argon gas continuous supply means composed of a gas passage communicating with the gas and a gas flow rate control means.

  The glow discharge optical emission spectrometer of the present invention has double O-rings with different outer diameters arranged on the sample contact surface of a support block that has been used in the past, and is not inserted between the double O-rings. Since it has a simple configuration of supplying an active gas, it prevents air from being mixed into the plasma of the glow discharge tube without changing the restrictions on the shape of the sample that can be measured. It has become possible to greatly reduce the background such as, and to greatly improve the quantitative accuracy of these elements present in the material.

  FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is an AA sectional view thereof. As shown here, in the present invention, an inner O-ring 8 and an outer O-ring 9 having a diameter larger than that of the inner O-ring 8 are provided on the sample abutting surface of the support block 4 that abuts the sample, and the inner O-ring is provided. An opening 11 is provided between 8 and the outer O-ring 9.

  The glow discharge emission spectrometer is configured as a typical grim glow discharge tube. In the apparatus shown here, a support block 4 also serving as a cathode plate and an anode block 2 are joined via an insulating material 5. An anode tube 26 is formed integrally with the anode block 2, and the anode tube 21 is inserted into the support block 4 and faces the analysis surface of the sample S in the vicinity.

  An inner O-ring 8 and the aforementioned outer O-ring 9 are provided on the sample contact surface of the support block 4, and an annular opening 11 is provided between these O-rings. The annular opening 11 is connected to a gas passage 12, and is further connected to a gas flow rate control means 13 including a control valve or the like provided outside the system of the glow discharge emission spectrometer. The gas flow rate control means 13 is further connected to an inert gas supply means (not shown) to constitute an inert gas supply means. Therefore, in the present invention, the flow rate of an inert gas, for example, argon gas, can be controlled and fed to the opening 11 between the double O-rings (8, 9) provided in the support block 4.

  Since the glow discharge optical emission spectrometer according to the present invention is configured as described above, after evacuating the system as usual, a predetermined flow rate of argon gas is introduced, and a predetermined power source is connected between the anode tube and the cathode. When a voltage (DC voltage or high-frequency voltage) is applied, glow discharge occurs, and the generated argon gas ions are accelerated by a high electric field and collide with the sample surface, which is a cathode, to eject analytical sample component atoms by sputtering. The ejected component atoms are further excited and emit light L specific to the element when it returns to the ground state. The light L is guided to the spectroscope 25 through the window plate 21, and the intensity of the light L is measured.

  In general, the sample is in a state of being polished by the above-mentioned P220 abrasive, and therefore there is a slight gap between the sample S and the support block 4, and as described with respect to the prior art, air is passed through the slight gap. Intrudes and interferes with accurate analysis. On the other hand, in the present invention, the inert gas having a controlled flow rate is supplied to the opening portion 11 opened between the double O-rings (8, 9) provided in the support block 4. New inert gas constantly circulates in the gap, and the atmosphere does not enter from outside.

  FIG. 3 is a graph showing the relationship between the flow rate of the inert gas (argon) supplied to the opening between the inner O-ring and the outer O-ring and the variation in the emission intensity of nitrogen. Here, the variation in emission intensity is represented by a variation coefficient σ / x, where x is an average value of analysis values of a specific element, and σ is a standard deviation thereof. Therefore, the relative variation coefficient σ / x (%) with respect to the average value x of the standard deviation σ is an indicator of variation.

  The same argon as the discharge gas was used as the inert gas, the glow discharge conditions were DC 800V, and argon at a pressure of 300 Pa as the discharge gas. As shown in the figure, when the inert gas (argon) is not supplied to the opening between the inner O-ring and the outer O-ring, the emission intensity of nitrogen (N) varies greatly, but the atmospheric pressure is used as the inert gas. It can be seen that when the argon gas having the same pressure is supplied at 100 ml / min or more, the variation in emission intensity of nitrogen (N) becomes as small as about 10%, and the influence of the background is eliminated.

  This is considered to be because air intrusion into the discharge region is almost completely suppressed by the continuous flow of new inert gas between the two O-rings. In addition, being able to suppress the influence of atmospheric contamination in the plasma almost completely contributes to the stabilization of glow discharge plasma. This contributes to the improvement of the analysis accuracy of not only nitrogen and oxygen but also other elements.

  As the inert gas, argon, helium, neon, or a mixed gas thereof can be used, but it is desirable to use argon which is generally used for a discharge gas. In addition to the direct current power source, a high frequency power source can be used as the discharge power source. In the latter case, analysis of non-conductive substances is possible.

  In the example shown in FIG. 3, the opening between the inner O-ring and the outer O-ring has an annular slit shape. However, the opening is not necessarily limited thereto. It can depend on what was arranged above. The point is that any inert gas can be supplied to the opening between the inner O-ring and the outer O-ring.

  Using the glow discharge optical emission spectrometer of the structure illustrated in FIG. 1, after mounting the sample, argon gas of the same pressure as the external pressure is continuously supplied between the O-rings at a rate of 200 ml / min. The nitrogen and oxygen contents in the steel samples were analyzed under the condition of the argon gas pressure of 300 Pa at the time. The obtained calibration curves of nitrogen and oxygen are shown in FIG. 4 (in the case of oxygen) and FIG. 5 (in the case of nitrogen). For comparison, an analysis using a conventional example having the structure shown in FIG. 6 was performed.

  In the case of the present invention, the background of nitrogen and oxygen was lowered, and the lower limit of quantification (the concentration at which the variation σ / x was 10%) could be improved to 30 mass ppm and 20 mass ppm, respectively. On the other hand, in the case of the conventional example, since the atmosphere entered the glow discharge region, the background of nitrogen and oxygen was high, and the lower limit of quantification was 100 mass ppm and 70 mass ppm, respectively.

It is sectional drawing which shows schematic structure of the glow discharge emission-spectral-analysis apparatus of this invention. It is AA sectional drawing of FIG. It is a graph which shows the relationship between the flow volume of the inert gas (argon) supplied to the opening part between an inner side O-ring and an outer side O-ring, and the dispersion | variation in the emitted light intensity of nitrogen. It is an example of the calibration curve of oxygen (O) by this invention shown in contrast with the prior art example. (a) When applying the present invention, (b) When applying a conventional example It is an example of the calibration curve of nitrogen (N) by this invention shown in contrast with the prior art example. (a) When applying the present invention, (b) When applying a conventional example It is sectional drawing which shows schematic structure of the conventional glow discharge emission-spectral-analysis apparatus.

Explanation of symbols

2: Anode block
3: Cathode (sample hold down)
4: Support block
5: Insulation material
8: Inner O-ring
9: Outer O-ring
11: Opening
12: Gas passage
13: Gas flow control means
21: Window plate
22: Argon supply hole
23: Exhaust hole
25: Spectrometer
26: Anode tube
S: Sample
L: Light path

Claims (1)

Power supply means having an anode tube, a cathode, a support block interposed between the anode tube and the cathode and in contact with the sample, and applying a DC voltage or a high frequency voltage between the anode tube and the cathode to sputter the sample In a glow discharge optical emission spectrometer comprising:
An inner O-ring and an outer O-ring having a diameter larger than that of the inner O-ring are provided on the sample contact surface of the support block, and argon gas having the same pressure as the outer air pressure is provided between the inner O-ring and the outer O-ring. In order to circulate, an argon gas continuous supply means comprising an opening opening from the support block side, a gas passage leading to the opening and a gas flow rate control means is provided between the inner O-ring and the outer O-ring. Glow discharge optical emission spectrometer.

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