Low-noise and high-sensitivity mass spectrometer Faraday cup

Abstract

The invention relates to the field of mass spectrum equipment, in particular to a low-noise and high-sensitivity mass spectrometer Faraday cup. The Faraday cup comprises a rectangular housing, one side of which is open; the suppression grid is arranged in the shell and is close to the opening; the collector is arranged in the shell and is adjacent to the suppression grid; a slit baffle is arranged at the opening of the shell; the collector is fixed through the insulating lining, insulated from the shell, and used for receiving the ion beam and generating current; the suppression grid electrode is fixed through an insulating lining and a metal positioning block, and negative bias voltage is applied to suppress escape of secondary electrons; the top cover is assembled on the shell to form a sealed whole; the collector connecting piece is arranged on the lower portion of the collector, one end of the Faraday cup outgoing line is welded to the collector connecting piece, and the other end of the Faraday cup outgoing line is led out of the shell. Noise is remarkably reduced, and the detection sensitivity of a mass spectrometer is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of mass spectrometry equipment, and particularly relates to a low-noise and high-sensitivity mass spectrometer Faraday cup. BACKGROUND

[0002] As a core equipment of modern analytical chemistry, the performance of the ion detection system of a mass spectrometer directly determines the detection limit, accuracy and precision of the instrument. In the process of mass spectrometric analysis, the ion beam current after separation by a mass analyzer is extremely weak (typically in the range of 10 -9 ~ 10 -18 A), and the traditional Faraday cup faces significant technical bottlenecks when detecting a current below 10 -14 A. On the one hand, the ion flow signal is easily disturbed by the secondary electron emission effect, and even if a suppression electrode is used, there is still an electron escape rate of about 5-10%; on the other hand, there is an assembly gap between the shield structure and the receiver of the discrete design, which increases the stray ion interference noise by about 20-30%, seriously restricting the detection sensitivity (usually only about 6x10 -15 A). In addition, the movable multi-cup system in the prior art generally adopts a split assembly, and the cumulative tolerance of each component can be more than 0.1 mm, which not only reduces the ion transmission efficiency, but also introduces mechanical vibration noise.

[0003] Taking a single ion receiver principle as an example, as shown in Figure 1 , the Faraday cup is a rectangular bucket installed behind the ion outlet slit. It can receive all the ions entering it and transmit the current flowing through the high resistance to the electrostatic amplifier to record the ion current. A negative voltage is applied to the electrode on the cup to balance the charge carried by the positive ions. This electrode is usually installed near the cup opening. Positive ions hit the surface of the Faraday cup obliquely, and electrons pass through the high resistance from the electrode surface to the positive ions to neutralize them, forming a current. However, the presence of extra positive ions will cause some secondary electrons to be emitted from the surface of the Faraday cup. In order to suppress the escape of secondary electrons, a secondary electron suppression electrode with a negative voltage is designed on the cup to suppress the escape of secondary electrons. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a low-noise and high-sensitivity mass spectrometer Faraday cup, which significantly reduces noise and improves the detection sensitivity of the mass spectrometer.

[0005] The present application provides a low-noise and high-sensitivity mass spectrometer Faraday cup, comprising:

[0006] a rectangular housing with an opening on one side;

[0007] a suppression grid disposed in the housing near the opening;

[0008] The collector is disposed within the housing and adjacent to the suppression gate;

[0009] A slit baffle is provided at the opening of the outer casing;

[0010] The collector is fixed by an insulating liner, is insulated from the outer shell, receives the ion beam and generates an electric current;

[0011] The suppression gate is fixed by an insulating liner and a metal positioning block, and a negative bias voltage is applied to suppress the escape of secondary electrons.

[0012] The top cover is fitted onto the outer casing to form a sealed unit.

[0013] The collector connector is located at the bottom of the collector. One end of the Faraday cup lead wire is soldered to the collector connector, and the other end is led out of the outer casing.

[0014] In one specific embodiment of the present invention, the insulating liner includes a short insulator and a long insulator; the short insulator is interference-fitted between the suppression gate and the housing.

[0015] Long insulators fill the gap between the collector and the housing.

[0016] In one specific embodiment of the present invention, the insulating liner is made of ceramic.

[0017] In one specific embodiment of the present invention, the output wire of the suppression gate is led out from the housing.

[0018] In one specific embodiment of the present invention, a base is also included, which is installed on the lower part of the outer casing.

[0019] In one specific embodiment of the present invention, a polytetrafluoroethylene gasket is provided between the outer shell and the metal positioning block.

[0020] In one specific embodiment of the present invention, a positioning block is further provided between the collector and the suppression gate, and one end of the positioning block is welded to the inner wall of the housing.

[0021] In one specific embodiment of the present invention, the slit on the slit baffle has a height of 12-14 mm and a width of 8-10 mm.

[0022] The present invention provides a Faraday cup assembly, comprising several Faraday cups as described in the above technical solutions.

[0023] The present invention provides a mass spectrometer comprising one or more Faraday cups stacked as described in the above technical solutions. Each Faraday cup is fixed to an independent slide plate by a base, and the guide rod rotates to move the slide plate along the focal plane.

[0024] Compared with the prior art, the low-noise, high-sensitivity Faraday cup of the mass spectrometer of the present invention has the following beneficial effects:

[0025] (1) By integrating the ion inlet with the suppression gate through the slit baffle, a dual effect of physical barrier and electric field shielding is formed to reduce stray ion interference;

[0026] (2) The rectangular box-shaped sealing structure (opening only on one side) combined with an integrated slit baffle can reduce external electromagnetic interference to below 0.1μV. Experimental data shows that at 10 -15 When detecting weak current, the signal-to-noise ratio (SNR) is improved from 15dB in the traditional scheme to 28dB, which is close to the level of SEM detection, while avoiding the signal drift problem of secondary electron multipliers.

[0027] (3) By pre-grinding the ceramic insulator with interference fit (tolerance controlled within ±0.002mm) and dynamically adjusting the polytetrafluoroethylene gasket, multiple insulation barriers are formed, and the leakage current fluctuation is less than 5% under the working conditions of -40~80℃.

[0028] (4) Multiple components can move along the focal plane to match ion beams with different mass-to-charge ratios for testing multiple samples, avoiding the cumbersome operation of disassembling and assembling the entire detector required by traditional methods.

[0029] Using the Faraday cup mass spectrometer described in this invention, measurement noise is significantly reduced, and the detection sensitivity is increased from 6 × 10⁻⁶. -15 A has been increased to 2×10 -15 A. Attached Figure Description

[0030] Figure 1 This diagram illustrates the working principle of a Faraday cup receiver.

[0031] Figure 2 A schematic diagram showing the structure of the Faraday cup;

[0032] Figure 3 A schematic diagram showing the structure of the back of the Faraday Cup;

[0033] Figure 4 This diagram shows the structure of an insulator.

[0034] Figure 5 A schematic diagram showing the bottom surface of the Faraday cup;

[0035] Figure 6 This shows the external view of the Faraday Cup.

[0036] Figure 7 A cross-sectional view of the Faraday cup;

[0037] Figure 8 This represents a side view of the Faraday Cup.

[0038] Figure 9 This diagram shows a design for a movable multi-cup combination.

[0039] In the diagram, 1-slit, 2-suppression gate, 3-Faraday cup, 4-high voltage resistor, 5-amplifier, 6-electrostatic amplifier, 7-casing, 8-collector, 9-insulating liner, 10-slit baffle, 11-suppression gate lead, 12-base, 13-short insulator, 14-long insulator, 15-positioning block, 16-PTFE gasket, 17-collector contact, 18-metal positioning block, 19-top cover, 20-slide plate, 21-guide rod, 22-output lead of suppression gate, 23-Faraday cup lead. Detailed Implementation

[0040] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0041] Embodiments of the present invention disclose a low-noise, high-sensitivity Faraday cup for mass spectrometry, such as... Figures 2 to 8 As shown, it includes:

[0042] The rectangular outer shell 7 has an opening on one side; except for the ion beam inlet, the other sides are completely sealed, effectively shielding external electromagnetic interference and reducing noise.

[0043] The suppression gate 2 is disposed inside the housing 7, near the opening;

[0044] Collector 8 is disposed inside housing 7 and adjacent to suppression gate 2;

[0045] A slit baffle 10 is provided at the opening of the outer casing 7; the slit on the slit baffle 10 has a height of 12-14 mm and a width of 8-10 mm. The slit baffle 10 is used to collimate the ion beam, reduce stray ion interference, and improve the signal-to-noise ratio.

[0046] The collector 8 is fixed by an insulating liner 9, is insulated from the outer shell 7, receives the ion beam and generates current;

[0047] The suppression gate 2 is fixed by an insulating liner 9 and a metal positioning block 18, and a negative bias voltage is applied to suppress the escape of secondary electrons.

[0048] The insulating liner 9 is made of pre-ground ceramic.

[0049] The insulating liner 9 includes a short insulator 13 and a long insulator 14;

[0050] The short insulator 13 is interference-fitted between the suppression gate 2 and the housing 7, providing high insulation and fixing the electrode;

[0051] The long insulator 14 fills the gap between the collector 8 and the housing 7 to prevent leakage and signal crosstalk.

[0052] A polytetrafluoroethylene (PTFE) gasket 16 is disposed between the outer casing 7 and the metal positioning block 18. The function of the PTFE gasket 16 is to avoid direct contact, maintain insulation, and adjust the position of the suppression gate 2.

[0053] A positioning block 15 is also provided between the collector 8 and the suppression gate 2, and one end of the positioning block 15 is welded to the inner wall of the outer casing 7.

[0054] Specifically, the positioning block 15 is welded to the inner wall of the outer shell 7 using plasma welding.

[0055] Top cover 19 is assembled onto outer shell 1 to form a sealed whole;

[0056] Collector connector 17 is located at the lower part of collector 8. One end of Faraday cup lead wire 23 is soldered to collector connector 17, and the other end is led out of housing 1.

[0057] The Faraday cup lead 23 is a nickel-based metal wire, which is sheathed with a polytetrafluoroethylene tube for insulation.

[0058] The output wire 22 of the suppression gate is led out from the housing 7.

[0059] It also includes a base 12, which is mounted on the lower part of the housing 7.

[0060] The assembly process of the Faraday cup assembly described in this invention is as follows:

[0061] The collector 8 is assembled onto the housing 7, and the long insulator 14 is interference-fitted together with the housing 7.

[0062] The nickel-based metal wire of collector contact 17 needs to be welded and then fitted with an insulating tube to avoid short circuit with the outer casing 7;

[0063] By increasing or decreasing the number of polytetrafluoroethylene gaskets 16, the position of the metal positioning block 18 is finely adjusted to suppress the gate 2, ensuring that the ion beam is aligned with the center of the collector 8.

[0064] The top cover 19 is locked to the outer casing 7 by bolts and double-ended bolts, and a gasket prevents vacuum leakage.

[0065] An embodiment of the present invention discloses a Faraday cup assembly, comprising several Faraday cups as described in the above technical solutions.

[0066] Embodiments of the present invention also disclose a mass spectrometer, such as Figure 9As shown, it includes one or more Faraday cups stacked as described in the above technical solutions. Each Faraday cup is fixed on an independent slide plate 20 by a base 12. The guide rod 21 rotates to drive the slide plate 20 to move along the focal plane.

[0067] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0068] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low-noise, high-sensitivity Faraday cup for a mass spectrometer, characterized in that, include: A rectangular shell with an opening on one side; The suppression gate is located inside the housing, near the opening; The collector is disposed within the housing and adjacent to the suppression gate; A slit baffle is provided at the opening of the outer casing; The collector is fixed by an insulating liner, is insulated from the outer shell, receives the ion beam and generates an electric current; The suppression gate is fixed by an insulating liner and a metal positioning block, and a negative bias voltage is applied to suppress the escape of secondary electrons. The top cover is fitted onto the outer casing to form a sealed unit. The collector connector is located at the bottom of the collector. One end of the Faraday cup lead wire is soldered to the collector connector, and the other end is led out of the outer casing.

2. The low-noise, high-sensitivity mass spectrometer Faraday cup according to claim 1, characterized in that, The insulating liner includes short insulators and long insulators; A short insulator is interference-fitted between the suppression gate and the case. Long insulators fill the gap between the collector and the housing.

3. The low-noise, high-sensitivity mass spectrometer Faraday cup according to claim 2, characterized in that, The insulating liner is made of ceramic.

4. The low-noise, high-sensitivity mass spectrometer Faraday cup according to claim 1, characterized in that, The output wire of the suppression gate is led out from the housing.

5. The low-noise, high-sensitivity mass spectrometer Faraday cup according to claim 1, characterized in that, It also includes a base, which is mounted on the lower part of the housing.

6. The low-noise, high-sensitivity mass spectrometer Faraday cup according to claim 1, characterized in that, A polytetrafluoroethylene gasket is provided between the outer shell and the metal positioning block.

7. The low-noise, high-sensitivity mass spectrometer Faraday cup according to claim 1, characterized in that, A positioning block is also provided between the collector and the suppression gate, and one end of the positioning block is welded to the inner wall of the housing.

8. The low-noise, high-sensitivity mass spectrometer Faraday cup according to claim 1, characterized in that, The slit on the slit baffle has a height of 12-14 mm and a width of 8-10 mm.

9. A Faraday cup assembly, characterized in that, It includes several Faraday cups as described in any one of claims 1 to 8.

10. A mass spectrometer, characterized in that, It includes one or more Faraday cups stacked as described in any one of claims 1 to 8, each Faraday cup being fixed to an independent slide plate by a base, and the guide rod rotating to drive the slide plate to move along the focal plane.

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