A cold electron neutral post-ionization device

Abstract

The present invention relates to the technical field of mass spectrometers, and more specifically, to a cold electron neutral post-ionization device comprising a laser sputtering cavity, a laser light source, a vacuum ultraviolet light source, a photocathode, a horseshoe magnet, a sample target, an annular focusing electrode A, an annular focusing electrode B, an extraction electrode, and a mass spectrometer. The present invention utilizes a vacuum ultraviolet light source to irradiate the photocathode to generate a high-intensity photoelectron stream. The photoelectrons are accelerated under the action of magnetic and electric fields to obtain higher energy. The photoelectron stream is then used to ionize the neutral particle plume generated by laser sputtering, thereby improving the sensitivity of laser sputtering ionization and significantly reducing the matrix effect of laser sputtering. The electrons generated by the vacuum ultraviolet light source irradiating the photocathode are cold electrons, which not only solves the problem of difficulty in introducing hot electrons as a post-ionization method, but also allows the introduction of inert gas to adjust the pressure of the ionization zone, thereby improving ionization efficiency.

Description

Technical Field

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

[0002] During laser desorption and ionization, ions constitute only a small fraction of the desorbed particles compared to neutrals; over 99.9% are neutral species. Ionizing these neutrals significantly improves instrument sensitivity. In addition to improving sensitivity, post-ionization techniques can separate the desorption and ionization processes in time and space, allowing for optimized control of each process. Therefore, developing neutral particle post-ionization techniques has become an effective solution for reducing matrix effects and improving ionization efficiency.

[0003] Photoelectron ionization occurs when vacuum ultraviolet light photons strike a metal electrode, generating photoelectrons that are accelerated by an electric field and then collide with sample molecules, producing a spectrum similar to electron ionization. Compared to thermionic emission in electron ionization, electrons generated by the photoelectric effect do not require heating and are a cold electron source. This patented invention applies photoelectron ionization to laser desorption postionization, proposing a novel laser desorption postionization technique. 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 cold electron neutral post-ionization device.

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

[0006] A cold electron neutral post-ionization device, comprising a laser sputtering cavity, a laser light source, a vacuum ultraviolet light source, a photocathode, a horseshoe magnet, a sample target, an annular focusing electrode A, an annular focusing electrode B, an extraction electrode and a mass spectrometer;

[0007] The extraction electrode is insulated and mounted on the laser sputtering chamber. The mass spectrometer is connected to the portion of the extraction electrode located outside the laser sputtering chamber. A conical channel is provided on the extraction electrode. 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 chamber.

[0008] The horseshoe magnet is installed inside the laser sputtering chamber, and the horseshoe magnet is divided into two horizontal parts and a vertical part connected together to form a U-shaped opening. The photocathode is arranged on one horizontal part of the horseshoe magnet and is located in the U-shaped opening of the horseshoe magnet. The vacuum ultraviolet light source is arranged on the outside of the other horizontal part of the horseshoe magnet. The light emitted by the vacuum ultraviolet light source is irradiated on the photocathode. The annular focusing electrode A and the annular focusing electrode B are respectively arranged in the U-shaped opening of the horseshoe magnet and are respectively located on both sides of the light emitted by the vacuum ultraviolet light source. The annular focusing electrode A is located on the side away from the extraction electrode, and the annular focusing electrode B is located on the side close to the extraction electrode. The annular focusing electrode A and the annular focusing electrode B are both provided with a through hole A corresponding to the opening at the end with a smaller diameter of the tapered channel;

[0009] The sample target is arranged inside the laser sputtering cavity near the annular focusing electrode A, the laser emitted by the laser light source irradiates the sample target, and the focal position of the laser emitted by the laser light source on the sample target is collinear with the axial center line of the through hole A of the annular focusing electrode A, the axial center line of the through hole A of the annular focusing electrode B and the axial center line of the tapered channel.

[0010] The laser sputtering cavity is provided with an air extraction port and an injection pipeline, the injection 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.

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

[0014] The annular focusing electrode A is provided with a through hole B for the laser light source to pass through. The laser light emitted by the laser light source and irradiated on the sample target intersects with the axial center line of the through hole A of the annular focusing electrode A at a fixed angle.

[0015] A through hole C for allowing light emitted by the vacuum ultraviolet light source to pass through is formed on the other horizontal portion of the horseshoe magnet.

[0016] Axial voltages are applied to the sample target, annular focusing electrode A, annular focusing electrode B, and extraction electrode from high to low, forming an axial excitation electric field of 1-500V / cm; a negative voltage of 0-300V relative to the ground is applied to the surface of the photocathode.

[0017] The advantages and positive effects of the present invention are:

[0018] The present invention is based on neutral post-ionization technology. This method introduces electric and magnetic fields to control the energy of photoelectrons. It is not limited by the working gas pressure and effectively combines the advantages of vacuum ultraviolet light and electron ionization. It can effectively solve the problems of matrix effect and low ionization efficiency in the laser desorption ionization process. It is a novel neutral post-ionization technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention.

[0020] In the figure: 1 is the laser sputtering chamber, 2 is the vacuum ultraviolet light source, 3 is the photocathode, 4 is the horseshoe magnet, 5 is the sample target, 6 is the annular focusing electrode A, 7 is the annular focusing electrode B, 8 is the extraction electrode, 9 is the sample injection pipeline, 10 is the molecular pump, 11 is the vacuum gauge, and 12 is the three-dimensional moving platform; 001 is the laser. DETAILED DESCRIPTION

[0021] The following is combined with Figure 1 The present invention is described in further detail.

[0022] A cold electron neutral postionization device, such as Figure 1 As shown, this embodiment includes a laser sputtering chamber 1, a laser light source, a vacuum ultraviolet light source 2, a photocathode 3, a horseshoe magnet 4, a sample target 5, an annular focusing electrode A 6, an annular focusing electrode B 7, an extraction electrode 8, and a mass spectrometer. In this embodiment, the vacuum ultraviolet light source 2 is a deuterium lamp. The mass spectrometer can be a time-of-flight mass spectrometer, a quadrupole mass spectrometer, or an ion trap mass spectrometer. In this embodiment, the mass spectrometer is a time-of-flight mass spectrometer. Figure 1 The arrow in the middle indicates the location of the mass spectrometer. In this embodiment, the photocathode 3 is constructed from various conventional metal, graphene, or carbon nanotube materials. The laser light source in this embodiment is a commercially available product, mounted on the laser sputtering chamber 1, using a conventional mounting structure.

[0023] Extraction electrode 8 is insulated and mounted on laser sputtering chamber 1. The mass spectrometer is connected to the portion of extraction electrode 8 located outside of the laser sputtering chamber 1. Extraction electrode 8 has a tapered channel, with the larger end of the channel facing the sample input of the mass spectrometer and the smaller end of the channel located within the laser sputtering chamber 1. The connection structure between extraction electrode 8 and the mass spectrometer in this embodiment is conventional.

[0024] A horseshoe magnet 4 is mounted within the laser sputtering chamber 1. The horseshoe magnet 4 is comprised of two horizontal portions connected together to form a U-shaped opening, and a vertical portion. The two horizontal portions serve as the north and south poles of the horseshoe magnet 4, respectively. A photocathode 3 is disposed on one horizontal portion of the horseshoe magnet 4 and within the U-shaped opening. A vacuum ultraviolet light source 2 is disposed outside the other horizontal portion of the horseshoe magnet 4. Light emitted by the vacuum ultraviolet light source 2 irradiates the photocathode 3. An annular focusing electrode A6 and an annular focusing electrode B7 are disposed within the U-shaped opening of the horseshoe magnet 4 and on either side of the light emitted by the vacuum ultraviolet light source 2. The annular focusing electrode A6 is located away from the extraction electrode 8, while the annular focusing electrode B7 is located closer to the extraction electrode 8. Both the annular focusing electrodes A6 and B7 have through-holes A corresponding to the opening at the smaller end of the tapered channel.

[0025] The sample target 5 is positioned within the laser sputtering chamber 1 near the annular focusing electrode A6. Laser light 001 emitted by the laser light source irradiates the sample target 5, and the focal position of the laser light 001 on the sample target 5 is collinear with the axial centerline of through-hole A of the annular focusing electrode A6, the axial centerline of through-hole A of the annular focusing electrode B7, and the axial centerline of the tapered channel. In this embodiment, both the annular focusing electrode A6 and the annular focusing electrode B7 are circular, flat plate electrodes with through-hole A in their centers, while the extraction electrode 6 is an annular metal electrode with a tapered channel in its center.

[0026] Specifically, in this embodiment, the laser sputtering chamber 1 is provided with an air extraction port and an injection line 9, the injection line 9 is connected to an external inert gas source, a molecular pump 10 is provided on the air extraction port, and a vacuum gauge 11 is also provided on the laser sputtering chamber 1. In this embodiment, the molecular pump 10 and the vacuum gauge 11 are both commercially available products. In this embodiment, the injection line 9 is connected to an external inert gas source to introduce an inert gas such as helium. The internal air pressure of the entire laser sputtering chamber 1 is controlled between 0.001-1000 Pa by controlling the inert gas flow rate and adjusting the molecular pump 10 switch. In this embodiment, the internal air pressure of the entire laser sputtering chamber 1 is controlled at 0.3 Pa. The internal air pressure of the laser sputtering chamber 1 is detected by the vacuum gauge 11.

[0027] Specifically, in this embodiment, the sample target 5 is installed in the laser sputtering chamber 1 through a three-dimensional moving platform 12. In this embodiment, the three-dimensional moving platform 12 is a commercial product, and its movement is controlled by an external controller. Figure 1 As shown, the sample target 5 is fixed on the surface of the three-dimensional moving platform 12. The three-dimensional moving platform 12 can move the position of the sample target 5 in the X, Y, and Z directions with a moving accuracy of 1 μm, which is convenient for adjusting the position of the laser 001 irradiating the sample target 5.

[0028] Specifically, in this embodiment, a through hole B is provided on the annular focusing electrode A6 for allowing the laser light 001 emitted by the laser light source to pass through, and a through hole C with a diameter of 6 mm is provided on the other horizontal portion of the horseshoe magnet 4 for allowing the light emitted by the vacuum ultraviolet light source 2 to pass through. The laser light 001 emitted by the laser light source and irradiated on the sample target 5 intersects with the axial center line of the through hole A of the annular focusing electrode A6 at a fixed angle. In this embodiment, the angle is 45 degrees to avoid interference between the laser light 001 and the light emitted by the vacuum ultraviolet light source 2.

[0029] Specifically, if Figure 1 As shown, in this embodiment, axial voltages are applied to the sample target 5, annular focusing electrode A 6, annular focusing electrode B 7, and extraction electrode 8, respectively, from high to low, forming an axial excitation electric field of 5 V / cm from left to right. In this embodiment, a negative voltage of 10 V relative to ground is applied to the surface of the photocathode 3.

[0030] Working principle:

[0031] Laser light 001 emitted by a laser light source irradiates a sample target 5 and sputters to produce a neutral plume. Photoelectrons generated by a vacuum ultraviolet light source 2 irradiating a photocathode 3 ionize the neutral plume under the action of the electric and magnetic fields between a horseshoe magnet 4, annular focusing electrode A 6, and annular focusing electrode B 7, generating high-intensity sample ions. The ions are then transmitted to a mass spectrometer for detection via an extraction electrode 8 under the action of the electric field. The present invention utilizes the vacuum ultraviolet light source 2 to irradiate the photocathode 3 to generate a high-intensity photoelectron stream. The photoelectrons are accelerated to obtain higher energy under the action of the magnetic and electric fields. The photoelectron stream is used to ionize the neutral particle plume generated by laser sputtering, thereby improving the sensitivity of laser sputtering ionization and greatly reducing the matrix effect of laser sputtering. The electrons generated by the vacuum ultraviolet light source 2 irradiating the photocathode 3 are cold electrons, which not only solves the problem of difficulty in introducing electrons using hot electrons as a post-ionization method, but also allows the introduction of inert gas to adjust the gas pressure in the ionization zone, thereby improving the ionization efficiency.

Claims

1. A cold electron neutral post-ionization device, characterized in that: It comprises a laser sputtering cavity (1), a laser light source, a vacuum ultraviolet light source (2), a photocathode (3), a horseshoe magnet (4), a sample target (5), an annular focusing electrode A (6), an annular focusing electrode B (7), an extraction electrode (8) and a mass spectrometer; The extraction electrode (8) is insulated and mounted on the laser sputtering cavity (1); the mass spectrometer is connected to the portion of the extraction electrode (8) located outside the laser sputtering cavity (1); a conical channel is provided on the extraction electrode (8); 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 horseshoe magnet (4) is installed inside the laser sputtering chamber (1), and the horseshoe magnet (4) is divided into two horizontal parts and a vertical part that are connected together to form a U-shaped opening. The photocathode (3) is arranged on one horizontal part of the horseshoe magnet (4) and is located in the U-shaped opening of the horseshoe magnet (4). The vacuum ultraviolet light source (2) is arranged outside the other horizontal part of the horseshoe magnet (4), and the light emitted by the vacuum ultraviolet light source (2) is irradiated on the photocathode (3). The annular focusing electrode A (6) and the annular focusing electrode B (7) are respectively arranged in the U-shaped opening of the horseshoe magnet (4) and are respectively located on both sides of the light emitted by the vacuum ultraviolet light source (2), the annular focusing electrode A (6) is located on the side away from the extraction electrode (8), and the annular focusing electrode B (7) is located on the side close to the extraction electrode (8), and the annular focusing electrode A (6) and the annular focusing electrode B (7) are both provided with a through hole A corresponding to the opening at the end with a smaller diameter of the tapered channel; The sample target (5) is arranged inside the laser sputtering cavity (1) near the annular focusing electrode A (6), the laser light source emits laser light on the sample target (5), and the focus position of the laser light emitted by the laser light source on the sample target (5) is collinear with the axial center line of the through hole A of the annular focusing electrode A (6), the axial center line of the through hole A of the annular focusing electrode B (7), and the axial center line of the tapered channel.

2. The cold electron neutral post-ionization device according to claim 1, characterized in that: The laser sputtering chamber (1) is provided with an air extraction port and a sampling pipeline (9), the sampling pipeline (9) is connected to an external inert gas source, and a molecular pump (10) is provided on the air extraction port.

3. The cold electron neutral post-ionization device according to claim 1, characterized in that: The laser sputtering cavity (1) is also provided with a vacuum gauge (11).

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

5. The cold electron neutral post-ionization device according to claim 1, characterized in that: The sample target (5) is installed in the laser sputtering chamber (1) via a three-dimensional moving platform (12).

6. The cold electron neutral post-ionization device according to claim 1, characterized in that: The annular focusing electrode A (6) is provided with a through hole B for allowing the laser light emitted by the laser light source to pass through. The laser light emitted by the laser light source and irradiated on the sample target (5) intersects with the axial center line of the through hole A of the annular focusing electrode A (6) to form an angle of a fixed value.

7. The cold electron neutral post-ionization device according to claim 1, characterized in that: A through hole C for allowing light emitted by the vacuum ultraviolet light source (2) to pass through is provided on the other horizontal portion of the horseshoe-shaped magnet (4).

8. The cold electron neutral post-ionization device according to claim 1, characterized in that: The sample target (5), annular focusing electrode A (6), annular focusing electrode B (7), and extraction electrode (8) are applied with axial voltages from high to low, and form an axial excitation electric field of 1-500V / cm; a negative voltage of 0-300V relative to the ground is applied to the surface of the photocathode (3).

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