Cold electron neutral post-ionization device

Abstract

The invention relates to the technical field of mass spectrum analyzers, in particular to a cold electron neutral post-ionization device which comprises a laser sputtering cavity, a laser light source, a vacuum ultraviolet light source, a photoelectric cathode, a horseshoe-shaped magnet, a sample target, an annular focusing electrode A, an annular focusing electrode B, an extraction electrode and a mass spectrometer. A vacuum ultraviolet light source is utilized to irradiate a photoelectric cathode to generate high-intensity photoelectron current, photoelectrons are accelerated under the action of a magnetic field and an electric field to obtain higher energy, and the photoelectron current is utilized to ionize neutral particle plume generated by laser sputtering, so that the sensitivity of laser sputtering ionization is improved, and the matrix effect of laser sputtering is greatly reduced; electrons generated when the vacuum ultraviolet light source irradiates the photoelectric cathode are cold electrons, the problem that it is difficult to introduce hot electrons as a post-ionization method is solved, inert gas can be introduced to adjust the air pressure of an ionization area, and the ionization efficiency is improved.

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] In the laser desorption ionization process, ions only account for a small part of the desorbed particles relative to neutral particles, and more than 99.9% are neutral species. Ionizing these neutral particles can greatly improve the sensitivity of the instrument. In addition to improving sensitivity, post-ionization technology can also achieve the separation of desorption and ionization processes in time and space, and optimize and control the two processes respectively. Therefore, the development of neutral particle post-ionization technology has become an effective solution to reduce the influence of matrix effects and improve ionization efficiency.

[0003] Photoelectron ionization is a process in which photoelectrons generated by vacuum ultraviolet light photons shining on metal electrodes collide with sample molecules after being accelerated by an electric field, thereby producing a spectrum similar to electron ionization. Compared with the thermal electron emission in electron ionization, the electrons generated by the photoelectric effect do not need to be heated and are a cold electron source. 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 cold electron neutral post-ionization device.

[0005] The objective 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 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 horseshoe magnet is installed inside the laser sputtering cavity, 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 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 irradiates 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, the annular focusing electrode B is located on the side close to the extraction electrode, and the annular focusing electrode A and the annular focusing electrode B are both provided with a through hole A corresponding to the opening at one end with a smaller diameter of the conical 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 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.

[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 emitted by 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 the light emitted by the vacuum ultraviolet light source to pass through is formed on the other horizontal part of the horseshoe magnet.

[0016] The sample target, annular focusing electrode A, annular focusing electrode B, and extraction electrode are respectively applied with axial voltage 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.

[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 and is not limited by the working gas pressure. It effectively combines the advantages of vacuum ultraviolet light and electron ionization, and 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 a laser sputtering chamber, 2 is a vacuum ultraviolet light source, 3 is a photocathode, 4 is a horseshoe magnet, 5 is a sample target, 6 is an annular focusing electrode A, 7 is an annular focusing electrode B, 8 is an extraction electrode, 9 is a sample injection pipeline, 10 is a molecular pump, 11 is a vacuum gauge, and 12 is a three-dimensional moving platform; 001 is a laser. DETAILED DESCRIPTION

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

[0022] A cold electron neutral postionization device, such as Figure 1 As shown, the present embodiment includes 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. 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 direction indicated by the middle arrow is the position of the mass spectrometer. In this embodiment, the photocathode 3 uses various metal, graphene or carbon nanotube materials of the prior art. In this embodiment, the laser light source is a commercial product, and the laser light source is installed on the laser sputtering cavity 1. The installation and setting structure of the laser light source is the prior art.

[0023] The extraction electrode 8 is insulated and installed on the laser sputtering cavity 1. The mass spectrometer is connected to the extraction electrode 8 located outside the laser sputtering cavity 1. A conical channel is provided on the extraction electrode 8. 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 8 and the mass spectrometer in this embodiment is the prior art.

[0024] The horseshoe magnet 4 is installed inside the laser sputtering chamber 1. The horseshoe magnet 4 is divided into two horizontal parts and a vertical part connected together to form a U-shaped opening. The two horizontal parts are respectively the N pole and the S pole of the horseshoe magnet 4. The photocathode 3 is arranged on a horizontal part of the horseshoe magnet 4 and 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. The light emitted by the vacuum ultraviolet light source 2 irradiates 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. 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 one end with a smaller diameter of the tapered channel.

[0025] The sample target 5 is arranged inside the laser sputtering chamber 1 near the annular focusing electrode A 6, and the laser light 001 emitted by the laser light source is irradiated on the sample target 5, and the focal position of the laser light 001 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. In this embodiment, the annular focusing electrode A 6 and the annular focusing electrode B 7 are both circular flat plate electrodes with a through hole A in the center, and the extraction electrode 6 is an annular metal electrode with a tapered channel in the center.

[0026] Specifically, in the present embodiment, a vacuum port and a sampling line 9 are provided on the laser sputtering chamber 1, the sampling line 9 is connected to an external inert gas source, a molecular pump 10 is provided on the vacuum port, and a vacuum gauge 11 is also provided on the laser sputtering chamber 1. In the present embodiment, the molecular pump 10 and the vacuum gauge 11 are both commercially available products. In the present embodiment, the sampling 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 0.001-1000Pa by controlling the inert gas flow rate and adjusting the molecular pump 10 switch. In the present embodiment, the internal air pressure of the entire laser sputtering chamber 1 is controlled at 0.3Pa. The internal air pressure of the laser sputtering chamber 1 is detected by a 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 commercially available 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 mobile platform 12. The three-dimensional mobile platform 12 can move the position of the sample target 5 in the three directions of X, Y, and Z with a moving accuracy of 1 μm, which is convenient for adjusting the position of the sample target 5 irradiated by the laser 001.

[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 part 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, which is 45 degrees in this embodiment 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, the sample target 5, the annular focusing electrode A 6, the annular focusing electrode B 7, and the extraction electrode 8 are respectively applied with axial voltages from high to low, and form an axial excitation electric field of 5V / cm from left to right. In this embodiment, a negative voltage of 10V is applied to the surface of the photocathode 3 relative to the ground.

[0030] Working principle:

[0031] The laser light source 001 irradiates the sample target 5 and then sputters to generate a neutral plume. The vacuum ultraviolet light source 2 irradiates the photocathode 3 and generates photoelectrons, which ionize the neutral plume under the action of the electric field and magnetic field between the horseshoe magnet 4, the annular focusing electrode A 6, and the annular focusing electrode B 7 to generate high-intensity sample ions, which are transmitted to the mass spectrometer for detection through the 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 flow, and the photoelectrons are accelerated under the action of the magnetic field and the electric field to obtain higher energy. The photoelectron flow 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 as a post-ionization method using hot electrons, but also can introduce inert gas to adjust the gas pressure of 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 installed 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); the horseshoe magnet (4) is divided into two horizontal parts and a vertical part connected together to form a U-shaped opening; the photocathode (3) is arranged on one horizontal part of the horseshoe magnet (4) and 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); 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 of the end with a smaller diameter of the conical channel; The sample target (5) is arranged inside the laser sputtering chamber (1) near the annular focusing electrode A (6), the laser light source emits laser light that irradiates the sample target (5), and the focal 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. A 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 sample injection pipeline (9), the sample injection pipeline (9) is connected to an external inert gas source, and a molecular pump (10) is provided on the air extraction port.

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

4. A cold electron neutral 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.

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. A 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 the laser light emitted by the laser light source to pass through, and 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 fixed value.

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

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, respectively, 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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