Ionization device after laser desorption

Abstract

The invention relates to the technical field of mass spectrum analyzers, in particular to a laser desorption post-ionization device which comprises a laser sputtering cavity, a laser light source assembly, a vacuum ultraviolet light source, a repulsion electrode, a photoelectric cathode, an annular magnet, a sample target, an extraction electrode and a mass spectrometer. According to the invention, the photoelectric cathode is irradiated by adopting the vacuum ultraviolet light source, photoelectrons generated on the surface of the photoelectric cathode due to a photoelectric effect obtain relatively high energy under the action of a magnetic field and an electric field and are used for ionizing a large amount of neutral particle plume generated by laser desorption, a serious matrix effect existing in laser ionization is solved, and the ionization sensitivity is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of mass spectrometers, in particular to a laser desorption and post-ionization device. Background Art

[0002] The absolute ionization efficiency of samples in the limited sampling volume during laser sputtering ionization is insufficient, more than 99.9% of them are neutral species, and the matrix effect interferes seriously. The development of neutral particle post-ionization technology has become an effective solution to reduce the influence of matrix effect and improve ionization efficiency.

[0003] Photoelectron ionization is the process of photoelectrons generated by vacuum ultraviolet light photons shining on metal electrodes, which are accelerated by electric fields and collide with sample molecules to produce a spectrum similar to electron ionization. This patent applies photoelectron ionization technology to laser desorption post-ionization, and proposes a novel laser desorption post-ionization technology. Summary of the invention

[0004] In view of the problems of insufficient laser desorption ionization efficiency and serious matrix effect, the present invention aims to provide a laser desorption and post-ionization device.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A laser desorption and post-ionization device comprises a laser sputtering cavity, a laser light source assembly, a vacuum ultraviolet light source, a repeller electrode, a photocathode, a ring magnet, a sample target, an extraction electrode and a mass spectrometer;

[0007] The extraction electrode is insulated and installed on the laser sputtering cavity, the mass spectrometer is connected to the extraction electrode located outside the laser sputtering cavity, a conical channel is provided on the extraction electrode, the opening of the end with a larger diameter of the conical channel is opposite to the sample input end of the mass spectrometer, and the opening of the end with a smaller diameter of the conical channel is located inside the laser sputtering cavity;

[0008] The repelling electrode and the photocathode are respectively installed inside the laser sputtering chamber, the photocathode and the repelling electrode are parallel to each other, the repelling electrode is located on the side away from the extraction electrode, a through hole A is provided on the repelling electrode, the photocathode is located on the side close to the extraction electrode, a through hole B is provided on the photocathode, the annular magnet is installed on the side surface of the photocathode close to the repelling electrode and a through hole C is provided, the aperture of the through hole C is larger than the aperture of the through hole B, there is a gap between the repelling electrode and the annular magnet, the vacuum ultraviolet light source is installed on the side of the repelling electrode away from the photocathode, the axial center line of the through hole A of the repelling electrode, the axial center line of the through hole B of the photocathode, the axial center line of the through hole C of the annular magnet and the axial center line of the tapered hole of the extraction electrode are all collinear, and the light emitted by the vacuum ultraviolet light source passes through the through hole A and the through hole C and irradiates on the surface of the photocathode;

[0009] The sample target is arranged inside the laser sputtering cavity, the laser light emitted by the laser light source assembly irradiates the sample target, and the focal position of the laser light emitted by the laser light source assembly on the sample target corresponds to the gap position between the repeller electrode and the annular magnet.

[0010] The laser sputtering cavity is provided with an air extraction port and a sampling pipeline, the sampling pipeline is connected to an external inert gas source, and the air extraction port is provided with a molecular pump.

[0011] A vacuum gauge is also provided on the laser sputtering cavity.

[0012] The vacuum ultraviolet light source adopts a gas discharge lamp light source or a laser light source.

[0013] The sample target is installed in the laser sputtering cavity through a three-dimensional moving platform.

[0014] The laser light source assembly includes a laser, a reflector, a lens and a quartz window. The laser, the reflector and the lens are respectively arranged on the outside of the laser sputtering cavity. The quartz window is arranged on the laser sputtering cavity at a position corresponding to the sample target. The laser emitted by the laser is reflected by the reflector and sequentially passes through the lens and the quartz window to irradiate the sample target.

[0015] The advantages and positive effects of the present invention are:

[0016] The present invention is based on the efficient secondary ionization of neutral gas phase plume by photoelectrons, decoupling the sputtering process from the ionization process, effectively eliminating the matrix effect and improving the ionization efficiency. The method is not limited by the working gas pressure, is easy to control, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the present invention.

[0018] In the figure: 1 is a laser sputtering chamber, 2 is a vacuum ultraviolet light source, 3 is a repeller electrode, 4 is a photocathode, 5 is a ring magnet, 6 is a sample target, 7 is an extraction electrode, 8 is a sample injection pipeline, 9 is a molecular pump, 10 is a vacuum gauge, 11 is a three-dimensional moving platform, 12 is a laser, 13 is a reflector, 14 is a lens, and 15 is a quartz window. DETAILED DESCRIPTION

[0019] The following is combined with Figure 1 The present invention is further described in detail.

[0020] A laser desorption and subsequent ionization device, such as Figure 1 As shown, the present embodiment includes a laser sputtering chamber 1, a laser light source assembly, a vacuum ultraviolet light source 2, a repelling electrode 3, a photocathode 4, a ring magnet 5, a sample target 6, an extraction electrode 7 and a mass spectrometer. In the present embodiment, the vacuum ultraviolet light source 2 uses a deuterium lamp. The mass spectrometer can use a time-of-flight mass spectrometer, a quadrupole mass spectrometer or an ion trap mass spectrometer. In the present embodiment, the mass spectrometer uses a time-of-flight mass spectrometer. Figure 1 The arrow in the middle indicates the direction of the mass spectrometer.

[0021] The extraction electrode 7 is insulated and installed on the laser sputtering cavity 1. The mass spectrometer is connected to the extraction electrode 7 located outside the laser sputtering cavity 1. A conical channel is provided on the extraction electrode 7. The opening at one end with a larger diameter of the conical channel is opposite to the sample input end of the mass spectrometer, and the opening at one end with a smaller diameter of the conical channel is located inside the laser sputtering cavity 1. The connection structure between the extraction electrode 7 and the mass spectrometer in this embodiment is the prior art.

[0022] The repelling electrode 3 and the photocathode 4 are respectively installed inside the laser sputtering chamber 1, the photocathode 4 and the repelling electrode 3 are parallel to each other, the repelling electrode 3 is located on the side away from the extraction electrode 7, and a through hole A is provided on the repelling electrode 3. The photocathode 4 is located on the side close to the extraction electrode 7, and a through hole B is provided on the photocathode 4. The annular magnet 5 is installed on the side surface of the photocathode 4 close to the repelling electrode 3 and a through hole C is provided. The annular magnet 5 is also parallel to the repelling electrode 3, the aperture of the through hole C is larger than the aperture of the through hole B, and there is a gap between the repelling electrode 3 and the annular magnet 5. The vacuum ultraviolet light source 2 is installed on the side of the repelling electrode 3 away from the photocathode 4, the axial center line of the through hole A of the repelling electrode 3, the axial center line of the through hole B of the photocathode 4, the axial center line of the through hole C of the annular magnet 5 and the axial center line of the tapered channel of the extraction electrode 7 are all collinear, and the light emitted by the vacuum ultraviolet light source 2 passes through the through hole A and the through hole C and irradiates on the surface of the photocathode 4. The repelling electrode 3 is a circular flat electrode, and the central aperture of the through hole A can be 2-15 mm. In this embodiment, the central aperture of the through hole A is 6 mm. The photocathode 4 is a circular flat electrode, and the central aperture of the through hole B can be 2-15 mm. In this embodiment, the central aperture of the through hole B is 3 mm. The annular magnet 5 is an annular flat magnet.

[0023] The sample target 6 is arranged inside the laser sputtering chamber 1, and the laser light emitted by the laser light source assembly irradiates the sample target 6, and the focal position of the laser light emitted by the laser light source assembly on the sample target 6 corresponds to the gap position between the repeller electrode 3 and the annular magnet 5. In this embodiment, the sample target 6 is placed vertically to the repeller electrode 3.

[0024] Specifically, in this embodiment, the laser sputtering chamber 1 is provided with an air pump and a sampling line 8, the sampling line 8 is connected to an external inert gas source, a molecular pump 9 is provided on the air pump, and a vacuum gauge 10 is provided on the laser sputtering chamber 1. In this embodiment, the molecular pump 9 and the vacuum gauge 10 are both commercially available products. In this embodiment, the sampling line 8 is connected to an external inert gas source to introduce an inert gas such as helium. The internal pressure of the entire laser sputtering chamber 1 is controlled at 10 by controlling the inert gas flow rate and adjusting the molecular pump 9 switch. -4 -1000 Pa. In this embodiment, the internal pressure of the entire laser sputtering chamber 1 is controlled at 0.3 Pa. The internal pressure of the laser sputtering chamber 1 is detected by a vacuum gauge 10 .

[0025] Specifically, in this embodiment, the sample target 6 is installed in the laser sputtering chamber 1 through a three-dimensional moving platform 11. In this embodiment, the three-dimensional moving platform 11 is a commercially available product, and its movement is controlled by an external controller. Figure 1As shown, the sample target 6 is fixed on the surface of the three-dimensional mobile platform 11. The three-dimensional mobile platform 1 can move the position of the sample target 6 in the X, Y, and Z directions with a moving accuracy of 1 μm, which is convenient for adjusting the position of the sample target 6 irradiated by the laser.

[0026] Specifically, in this embodiment, the laser light source assembly includes a laser 12, a reflector 13, a lens 14 and a quartz window 15. The laser 12, the reflector 13 and the lens 14 are respectively arranged outside the laser sputtering cavity 1, and the quartz window 15 is arranged on the laser sputtering cavity 1 at a position corresponding to the sample target 6. The laser emitted by the laser 12 is reflected by the reflector 13, and sequentially passes through the lens 14 and the quartz window 15 to irradiate the sample target 6. In this embodiment, the laser 12, the reflector 13 and the lens 14 are all commercially available products, and the arrangement structure of the quartz window 15 is also an existing technology, which is convenient for adjustment according to the experimental site.

[0027] Working principle:

[0028] The laser light emitted by the laser light source assembly irradiates the sample target 6 and then sputters to generate a neutral plume. The vacuum ultraviolet light emitted by the vacuum ultraviolet light source 2 irradiates the photocathode 4 and then generates photoelectrons, which ionize the neutral plume under the action of the electric field and the magnetic field between the repeller electrode 3 and the photocathode 4 to generate high-intensity sample ions, which are then transmitted to the mass spectrometer for detection through the extraction electrode 7 under the action of the electric field. The present invention uses the vacuum ultraviolet light source 2 to irradiate the photocathode 4. The photoelectrons generated on the surface of the photocathode 4 due to the photoelectric effect obtain higher energy under the action of the magnetic field and the electric field, and are used to ionize a large number of neutral particle plumes generated by laser desorption, thereby solving the serious matrix effect existing in laser ionization and greatly improving the sensitivity of ionization.

Claims

1. A laser desorption and post-ionization device, characterized in that: It comprises a laser sputtering cavity (1), a laser light source assembly, a vacuum ultraviolet light source (2), a repelling electrode (3), a photocathode (4), a ring magnet (5), a sample target (6), an extraction electrode (7) and a mass spectrometer; The extraction electrode (7) is insulated and mounted on the laser sputtering cavity (1); the mass spectrometer is connected to the portion of the extraction electrode (7) located outside the laser sputtering cavity (1); a conical channel is provided on the extraction electrode (7); an opening at one end with a larger diameter of the conical channel is opposite to a sample input end of the mass spectrometer; and an opening at one end with a smaller diameter of the conical channel is located inside the laser sputtering cavity (1); The repelling electrode (3) and the photocathode (4) are respectively installed inside the laser sputtering chamber (1); the photocathode (4) and the repelling electrode (3) are parallel to each other; the repelling electrode (3) is located on a side away from the extraction electrode (7); a through hole A is provided on the repelling electrode (3); the photocathode (4) is located on a side close to the extraction electrode (7); a through hole B is provided on the photocathode (4); the annular magnet (5) is installed on a side surface of the photocathode (4) close to the repelling electrode (3) and a through hole C is provided; the aperture of the through hole C is larger than the aperture of the extraction electrode (7); The aperture of the through hole B is such that there is a gap between the repelling electrode (3) and the annular magnet (5); the vacuum ultraviolet light source (2) is installed on a side of the repelling electrode (3) away from the photocathode (4); the axial center line of the through hole A of the repelling electrode (3), the axial center line of the through hole B of the photocathode (4), the axial center line of the through hole C of the annular magnet (5) and the axial center line of the tapered hole of the extraction electrode (7) are all collinear; the light emitted by the vacuum ultraviolet light source (2) passes through the through hole A and the through hole C and is irradiated on the surface of the photocathode (4); The sample target (6) is arranged inside the laser sputtering chamber (1), the laser light emitted by the laser light source assembly irradiates the sample target (6), and the focal position of the laser light emitted by the laser light source assembly on the sample target (6) corresponds to the position of the gap between the repelling electrode (3) and the annular magnet (5).

2. A laser desorption and post-ionization device according to claim 1, characterized in that: The laser sputtering chamber (1) is provided with an air extraction port and a sample injection pipeline (8), the sample injection pipeline (8) is connected to an external inert gas source, and a molecular pump (9) is provided on the air extraction port.

3. The laser desorption and post-ionization device according to claim 1, characterized in that: The laser sputtering chamber (1) is also provided with a vacuum gauge (10).

4. The laser desorption and post-ionization device according to claim 1, characterized in that: The vacuum ultraviolet light source (2) is a gas discharge lamp light source or a laser light source.

5. The laser desorption and post-ionization device according to claim 1, characterized in that: The sample target (6) is installed in the laser sputtering chamber (1) via a three-dimensional moving platform (11).

6. The laser desorption and post-ionization device according to claim 1, characterized in that: The laser light source assembly comprises a laser (12), a reflector (13), a lens (14) and a quartz window (15); the laser (12), the reflector (13) and the lens (14) are respectively arranged outside the laser sputtering cavity (1); the quartz window (15) is arranged at a position on the laser sputtering cavity (1) corresponding to the sample target (6); laser light emitted by the laser (12) is reflected by the reflector (13), and sequentially passes through the lens (14) and the quartz window (15) to irradiate the sample target (6).

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