JPH0654652B2 - Photoionization mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention irradiates a sample, which is an analyte, with an ion beam or a laser beam, and ionizes neutral particles generated from the sample surface by the impact with the laser beam. Then, the present invention relates to a photoionization mass spectrometer that performs mass analysis of a sample by measuring a mass spectrum of photoexcited ions that have been generated.

[Prior Art] Conventionally, there has been a mass spectrometer as a measuring instrument used for precise measurement of atomic mass, chemical analysis, and measurement of atomic composition (molecular formula), in which a sample as an analyte is sputtered. Ionized neutral particles with laser light and measuring the mass spectrum of the photoexcited ions generated,
A photoionization mass spectrometer that performs mass spectrometry of a sample is known. When the sample is irradiated with an ion beam or a laser beam, neutral particles having no charge and charged secondary ions are generated from the surface of the sample due to the impact. The amount of neutral particles is larger than that of secondary ions. Therefore, the photoionization mass spectrometry method for detecting neutral particles is advantageous in obtaining sensitivity as compared with other mass spectrometry methods for measuring secondary ions.

FIG. 5 is a principle configurational diagram of a conventional photoionization mass spectrometer using an ion beam as a sample sputtering means.
In FIG. 5, reference numeral 1 is a primary ion generator, which supplies a gas such as argon or oxygen to ionize it to generate a primary ion beam 2. Then, the primary ion beam 2 is focused by using the electron lens 3, and then pulsed by the electrode 4 to impact the surface of the sample 5. The impact of the primary ion beam 2 causes the neutral particles 6 to fly out to the ionization region 7. In the ionization region 7, the neutral particles 6 are ionized by the ultraviolet laser beam 11 emitted from the semi-transmissive mirror 10 of the laser resonator configured by the total reflection mirror 8, the laser medium 9, and the semi-transmissive mirror 10 to photoexcited ions 1
It becomes 2. Here, ultraviolet laser beam 1 by photoionization
There is almost no intensity decay of 1. The photoexcited ions 12 thus generated are extracted to the mass spectrometer 15 by the extraction electrode 13 and the converging lens 14 and analyzed by the ion detector 61. In the above description, there are only two types of laser light sources, that is, an excimer laser and a pulse YAG laser, which are high-power ultraviolet lasers, as a light source of laser light having an intensity capable of ionizing the neutral particles 6 sputtered from the sample 5. It was a pulsed laser.

[Problems to be Solved by the Invention] However, in the photoionization mass spectrometer in the above-mentioned conventional technique, it has been a problem to be solved to improve the sensitivity as described below.

The ultraviolet laser beam 11 used for ionizing the neutral particles 6 in the conventional photoionization mass spectrometer is a YAG laser or an excimer laser, and the laser beam emits light in pulses. This emission time is 10 to 30 ns per pulse
ec, the repetition rate of the pulse is 1 kHz or less, so the effective time of irradiating the ionization region 7 with the laser is 1
This is a very small value of 30 μsec or less per second.
Photoexcited ions are generated only when the ionized region 7 is irradiated with a laser. If the effective light irradiation time is extremely short as described above, it is disadvantageous in that sensitivity is obtained. Further, in general, it is possible to lengthen the pulse width and extend the effective light irradiation time by changing the resonance condition of the laser, but in this case, the laser generation efficiency is deteriorated, so that sufficient laser intensity can be obtained. However, it is difficult to increase the sensitivity in the conventional example.

The present invention was devised to solve the above-described problems, and a photoionization mass spectrometer capable of increasing the photoionization efficiency and the light irradiation time to achieve high sensitivity for photoexcited ion detection. The purpose is to provide.

[Means for Solving the Problems] The configuration of the photoionization mass spectrometer of the present invention for achieving the above object is to irradiate the surface of a sample as an analyte with an ion beam or a first laser beam, Thereby, the neutral particles emitted from the sample are irradiated with the second laser beam to generate photoexcited ions that ionize the neutral particles, and the mass of the photoexcited ions is analyzed by the mass spectrometric means. In the analyzer, the neutral particles are added to the second
The region which is ionized by the laser beam is placed between one of the resonator mirrors for generating the second laser beam and the laser medium, and the two resonator mirrors for generating the second laser beam are totally reflected. It is characterized by being a mirror.

In addition, as another configuration, in the above configuration, a semi-transmissive mirror or a total transmissive window is provided between a region where the neutral particles are ionized by the second laser beam and the laser medium. And

[Operation] The present invention installs the ionization region of the neutral particles between the two resonator mirrors of the second laser beam, that is, inside the resonator. Ionize with a laser beam to improve photoionization efficiency. Also, since it is not necessary to emit laser light to the outside of the resonator, both resonator mirrors are total reflection mirrors, so that the laser pulse width can be expanded and the light irradiation time can be expanded by preventing a decrease in laser energy. To

EXAMPLES Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a device configuration diagram of a photoionization mass spectrometer showing a first embodiment of the present invention. 1 is a sample 5 which is an analyte
This is a primary ion generator that is the sputtering means, and after the primary ion beam 2 generated from the primary ion generator 1 is converged by using the converging lens 3, it is pulsed by the electrode 4 to impact the surface of the sample 5. The impact of the primary ion beam 2 causes the neutral particles 6 to fly out to the ionization region 7. In this embodiment, the ionization region 7 is installed inside the laser resonator which is the laser light source for ionization. That is, the laser medium 1
The ionization region 7 is sandwiched between the one end of 8 and the total reflection mirror 19. Another total reflection mirror is arranged opposite to the other end of the laser medium 18, and the total reflection mirror 17, the laser medium 18, and the total reflection mirror 19 form a laser resonator. The ultraviolet laser beam 2 generated between the total reflection mirrors 17 and 19 inside the laser resonator
At 0, the neutral particles 6 become photoexcited ions 12 that are photoionized. Since the density of the neutral particles 6 is sufficiently small, the existence of the neutral particles 6 does not disturb the laser resonance. The photoexcited ions 12 thus generated are extracted to the mass spectrometer 15 by the extraction electrode 13 and the converging lens 14 and analyzed by the ion detector 16.

The operation of the first embodiment constructed as above will be described. In a conventional laser resonator for ionizing neutral particles, one mirror is a total reflection and the other is a semi-transmissive mirror, and a part of the laser generated inside the resonator emitted from this semi-transmissive mirror is ionized. Is used as a laser beam. With this method, it was not possible to irradiate the ionized region with the highest intensity laser generated inside the resonator. Further, the laser beam once emitted to the outside and passing through the ionization region could not be reused although it has the ability to perform photoionization. On the other hand, in the present embodiment, since the ionization region 7 is installed inside the laser resonator, it is possible to irradiate the ionization region 7 with the laser having the highest intensity. Moreover, since it is not necessary to emit the ultraviolet laser beam 20 to the outside, the resonance mirrors 17 and 19 can be total reflection mirrors, and the strength can be further improved. That is, the ultraviolet laser beam 20 repeats resonance between the mirror 17 having a reflectance close to perfect reflection and the mirror 19.
Since the laser intensity is hardly attenuated by ionizing the neutral particles 6, the mirrors 17, 19 and the laser medium 1
The ultraviolet laser beam 20 passes through the ionization region 7 until the laser intensity is attenuated by absorption by 8. For example,
When the distance between the mirrors 17 and 19 is set to about 2 m, lights having a pulse width of about 10 nsec overlap each other, and as a result, the intensity of the laser beam 20 passing through the ionization region 7 is improved, and the photoionization efficiency is improved. The sensitivity can be improved.

FIGS. 2A and 2B are diagrams showing the laser pulse (a) according to the present embodiment and the laser pulse (b) according to the conventional example for showing the effect of the present embodiment. In the conventional example, since the energy loss due to the laser emission is severe, the pulse intensity is rapidly attenuated over time, whereas in the present example, since the laser is not emitted to the outside, the energy loss is caused by the mirror 17, The degree of attenuation is small because only 19 and the laser medium 18 are absorbed. Thereby, the pulse width can be expanded and the effective light irradiation time can be expanded. That is, it is possible to increase the amount of the photoexcited ions 12 and increase the sensitivity of the detection.

FIG. 3 is a partial block diagram showing a second embodiment of the present invention. This embodiment is basically the same as the first embodiment, but is different in that the two total reflection mirrors forming the laser resonator are a combination of spherical mirrors 21 and 23 having an appropriate curvature. To do. In this embodiment, the spherical mirror 21,
By combining 23, the laser medium 23 and the spherical mirror 2
The laser beam 24 oscillating between 1 and 22 is focused in the photoionization region 7. By condensing the laser beam 24, the photon density in the photoionization region 7 can be improved. As a result, the photoionization efficiency of the neutral particles 6 sputtered from the sample 5 is improved, and more sensitive measurement can be performed.

FIG. 4 is a partial block diagram showing a third embodiment of the present invention. This embodiment basically has the same configuration as that of the first embodiment, but corresponds to the case where the laser medium 25 that cannot be evacuated is used because the ionization region 7 is evacuated.
In this case, as a partition between the ionization region 7 of the neutral particles 6 sputtered from the sample 5 and the laser medium 25, the light transmission window 2 is provided between the ionization region 7 and the laser medium 25.
6 should be installed. The light transmission window 26 may be a total transmission window that transmits most of the laser or a semi-transmission mirror. The reason is that in any case, since the laser beam 29 is not emitted to the outside from between the total reflection mirrors 27 and 28, the laser beam between the light transmission window 26 and the total reflection mirror 27 and between the light transmission window 26 and the total reflection mirror 28 is laser. This is because the strengths are the same. The present embodiment is slightly inferior because the light transmission window 26 absorbs light, but it is possible to obtain an effect that is substantially the same as that of the configuration of the first embodiment.

The primary ion generator that is the sample sputtering means shown in the first embodiment may be a laser oscillator. As described above, the present invention has various applications in line with its gist,
Various embodiments are possible.

[Effects of the Invention] As is clear from the above description, according to the photoion mass spectrometer of the present invention, it is possible to increase the intensity and pulse width of the ultraviolet laser that photoionizes the neutral particles that have sputtered from the sample by sputtering. Therefore, the photoionization efficiency of neutral particles can be increased, and the analysis sensitivity in photoionization mass spectrometry can be improved.

[Brief description of drawings]

FIG. 1 is a device configuration diagram showing a first embodiment of the present invention, and FIG.
FIGS. 3A and 3B are diagrams showing laser pulses of this embodiment and a conventional example showing the effect of this embodiment, and FIG.
FIG. 4 is a partial block diagram showing an embodiment of the present invention, FIG. 4 is a partial block diagram showing a third embodiment of the present invention, and FIG. 5 is a principle block diagram of a conventional example. 1 ... Primary ion generator, 2 ... Primary ion beam,
3 ... Converging lens, 4 ... Electrode, 5 ... Sample, 6 ... Neutral particle, 7 ... Ionization region, 12 ... Photoexcited ion,
13 ... Extraction electrode, 14 ... Converging lens, 15 ...
Mass spectrometer, 16 ... Ion detector, 17 ... Total reflection mirror, 18 ... Laser medium, 19 ... Total reflection mirror, 2
0 ... UV laser beam, 21 ... Spherical mirror, 22 ...
... Spherical mirror, 23 ... laser medium, 24 ... ultraviolet laser beam, 25 ... laser medium, 26 ... light transmitting window, 2
7 ... Total reflection mirror, 28 ... Total reflection mirror, 29 ...
UV laser beam.

Claims (2)

[Claims] 1. A surface of a sample, which is an analyte, is irradiated with an ion beam or a first laser beam, and thereby neutral particles emitted from the sample are irradiated with a second laser beam. In a photoionization mass spectrometer that generates photoexcited ions that ionize neutral particles and analyzes the mass of the photoexcited ions by mass analysis means, a region in which the neutral particles are ionized by the second laser beam is defined as the second region. Photoionization mass spectrometry, characterized in that it is installed between one of the resonator mirrors that generate a laser beam and a laser medium, and that the two resonator mirrors that generate the second laser beam are total reflection mirrors. apparatus. 2. The photoionization mass spectrometer according to claim 1, wherein a semitransparent mirror or a total transmission window is provided between a region where the neutral particles are ionized by the second laser beam and the laser medium. A photoionization mass spectrometer characterized by comprising: