Photoelectric effect ion source and ionization method of sample to be detected

Abstract

The invention relates to the technical field of detection, and provides a photoelectric effect ion source and an ionization method of a to-be-detected sample, and the method comprises the steps: a metal silver layer, the bottom of which is provided with a reflection increasing film, and the bottom of the reflection increasing film is provided with a substrate; the ultraviolet light-emitting diode is opposite to the metal silver layer, and a channel through which a sample to be detected passes is reserved between the ultraviolet light-emitting diode and the metal silver layer; the ultraviolet light-emitting diode irradiates the metal silver layer, electrons on the surface of the metal silver layer are excited to escape, molecules of the sample to be detected capture the escaped electrons, reactant negative ions are generated, and generation of ions is achieved; the heating device is arranged at the bottom of the substrate and used for heating the metal silver layer in the electron escape process; the ultraviolet light emitting diode is arranged on the inner top surface of the shell; the heating device is installed on the inner bottom face of the shell. The ionization efficiency of the photoelectric effect ion source on the sample can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of detection technology, and in particular relates to a photoelectric effect ion source and an ionization method for a sample to be detected. Background Art

[0002] The ion source is a device that ionizes the neutral molecules of the sample to be tested into ions. The type and performance of the ion source directly affect the sensitivity and resolution of the analyzer, and is a key component to ensure efficient analysis and reliable detection of the system.

[0003] Radioactive sources have been used for a long time, but their use has been strictly restricted due to safety issues. When the corona discharge ion source uses gas discharge ionization, the discharge will be unstable and require high voltage support. At the same time, byproduct ions will be produced, which will affect the experimental results. Ultraviolet light ionization sources are expensive and large in size, which limits their application in miniaturized equipment. Photoelectric effect ion sources use light to irradiate the surface of metals or other materials, generate electrons and ionize highly electronegative substances. They are clean, safe, simple and efficient. However, common photoelectric effect ion sources have problems such as large light source volume, poor heat dissipation performance, easy attenuation of the emission electrode, and low light utilization efficiency.

[0004] Patent CN101667518A discloses a photoemission ionization source and describes its application in mass spectrometry or ion mobility spectrometry. The device includes: an ultraviolet light source; a metal mesh or a metal ring; and a carrier gas. However, the metal has a high reflectivity to light, which reduces the light absorption efficiency. In addition, the metal surface is susceptible to contamination and oxidation, which reduces the photoelectron emission efficiency.

[0005] Patent CN108109892B discloses an ion source device based on the photoelectric effect of graphene electrodes. The ultraviolet rays emitted by the light source used in the device must pass through a transparent support body to irradiate the graphene layer, causing a large amount of attenuation of the ultraviolet rays during the transmission process, so the utilization efficiency of the light source is low. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a photoelectric effect ion source and a method for ionizing a sample to be tested, wherein heating is used to decompose the oxidized silver oxide of the photoelectric effect emission electrode into silver, which can effectively avoid the attenuation problem of the metal caused by oxidation. At the same time, the present invention adds an anti-reflection film at the bottom of the metal silver layer to significantly improve the light absorption efficiency, which can improve the ionization efficiency of the sample to be tested.

[0007] The following are technical details of the present invention:

[0008] A photoelectric effect ion source, characterized in that it comprises:

[0009] The metal silver layer has a reflection enhancement film at the bottom, and a substrate at the bottom of the reflection enhancement film;

[0010] An ultraviolet light emitting diode is opposite to the metallic silver layer, and a channel is left between the ultraviolet light emitting diode and the metallic silver layer for the sample to be tested to pass through; the ultraviolet light emitting diode irradiates the metallic silver layer to stimulate the electrons on the surface of the metallic silver layer to escape, and the molecules of the sample to be tested capture the escaped electrons to generate reactant negative ions, thereby realizing the generation of ions;

[0011] A heating device, disposed at the bottom of the substrate, for heating the metal silver layer during the electron escape process;

[0012] The housing is provided with the ultraviolet light emitting diode mounted on the inner top surface of the housing; and the heating device is mounted on the inner bottom surface of the housing.

[0013] Further,

[0014] A counter electrode is also installed on the inner top surface of the shell, and the counter electrode is opposite to the metal silver layer;

[0015] The positive electrode of a DC voltage source is connected to the counter electrode, and the negative electrode is connected to the metal silver layer.

[0016] Further,

[0017] The material of the shell is PCB, ceramic or glass.

[0018] Further,

[0019] The thickness of the metallic silver layer is 5 nm.

[0020] Further,

[0021] The heating device is a polyimide heating film.

[0022] Further,

[0023] The anti-reflection film is a mirror-surface polymer reflective film.

[0024] Further,

[0025] It also includes: a constant current source, which is electrically connected to the ultraviolet light emitting diode and is used to supply power to the ultraviolet light emitting diode.

[0026] A method for ionizing a sample to be tested, characterized by comprising:

[0027] Utilizing the ultraviolet light emitting diode to irradiate the metallic silver layer, thereby stimulating the electrons on the surface of the metallic silver layer to escape;

[0028] The sample to be tested is transported to the channel between the ultraviolet light-emitting diode and the metal silver layer, and the molecules of the sample to be tested capture the escaped electrons to generate reactant negative ions, thereby achieving ionization of the sample to be tested;

[0029] The metallic silver layer is heated by a heating device during the electron escape process.

[0030] Further,

[0031] When the ultraviolet light emitting diode irradiates the metallic silver layer, an electric field directed toward the metallic silver layer is applied between the metallic silver layer and the inner top surface of the shell, pushing electrons to escape from the silver metal surface.

[0032] Further,

[0033] When an electric field directed toward the metal silver layer is applied between the metal silver layer and the inner top surface of the shell, the cutoff frequency of the photoelectric effect generated by the metal silver layer is:

[0034] ν0'=ν0-bE 1 / 2

[0035] Among them, ν0' is the cutoff frequency of the photoelectric effect of the metallic silver layer in the presence of an external electric field, ν0 is the cutoff frequency when the external electric field is 0V, E is the electric field strength applied to the metal surface, and b is a constant.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] The present invention utilizes a housing (3) to mount an ultraviolet light emitting diode (2) on the inner top surface and a heating device (9) on the inner bottom surface, which not only provides stable structural support but also serves as a substrate for the ultraviolet light emitting diode, thereby achieving highly integrated photoelectric effect ion source, giving the system a miniaturized advantage and improving the integration level.

[0038] The heating device (9) heats the metal silver layer (6) during the electron escape process, so that the silver oxide can be thermally decomposed into silver metal, thereby preventing the emission electrode from decaying due to oxidation. According to the formula, the increase in temperature will reduce the metal work function, improve the photoelectric emission efficiency, and further improve the ionization efficiency. The high reflectivity of the anti-reflection film (8) at the bottom of the metal silver layer (6) can reflect photons back to the metal, achieving a photon radiation effect of nearly twice, thereby improving the metal's light absorption efficiency, greatly improving the ultraviolet light utilization rate, and further improving the photoelectric emission efficiency, thereby significantly improving the ionization efficiency.

[0039] In conclusion, the present invention can significantly improve the ionization efficiency while increasing the device integration.

[0040] Other features and advantages of the present disclosure will be described in the following description, and partly become apparent from the description, or be understood by implementing the present disclosure. The purpose and other advantages of the present disclosure can be realized and obtained by the structures indicated in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 A schematic diagram of an ion source of the present invention is shown;

[0043] Figure 2 A schematic diagram of a sample detection system according to an embodiment of the present invention is shown.

[0044] Reference numerals:

[0045] Constant current source-1; UV light emitting diode-2; shell-3; counter electrode-4; DC voltage source-5; metallic silver-6; substrate-7; anti-reflection film-8; polyimide heating film-9; sample molecule-10; sample inlet-11; sample molecule-12; mass flow meter-13; air inlet-14; UV-LED photoelectric effect ion source system-15; scanning voltage source-16; separation voltage source-17; deflection voltage source-18; repulsion voltage source-19; upper and lower separation electrodes-20, 21; upper and lower detection electrodes-20, 23; shielding electrode-24; air outlet-25; air pump-26; weak current detector-27; host computer-28. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the embodiments of the present disclosure clearer, the technical scheme in the embodiments of the present disclosure will be clearly described in combination with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0047] Figure 1 A schematic diagram of the device according to the present invention is shown, and the specific implementation details of the present invention include:

[0048] A photoelectric effect ion source:

[0049] It includes:

[0050] A metallic silver layer (6);

[0051] An ultraviolet light emitting diode (2) is opposite to the metal silver layer (6), and a channel is left between the ultraviolet light emitting diode (2) and the metal silver layer (6) for allowing the sample to be tested to pass through; the ultraviolet light emitting diode (2) irradiates the metal silver layer (6) to stimulate the electrons of the metal silver layer (6) to escape; the molecules of the sample to be tested capture the escaped electrons to generate reactant negative ions, thereby achieving ion generation; and a constant current source (1) is used to supply power to the ultraviolet light emitting diode (2).

[0052] A heating device (9), disposed at the bottom of the metal silver layer (6), for heating the metal silver layer (6) during the photoelectric effect process;

[0053] The housing (3) is provided with the ultraviolet light emitting diode (2) mounted on the inner top surface of the housing (3); and the heating device (9) is mounted on the inner bottom surface of the housing (3).

[0054] The shell (3) not only provides stable structural support as a photoelectric effect shell, but also serves as a substrate for the ultraviolet light-emitting diode, successfully realizing the highly integrated integration of the photoelectric effect ion source, thereby giving the system the advantage of miniaturization. The shell material can be selected from PCB; ceramics; glass, etc., and the specific material can be flexibly adjusted according to needs. This design not only meets the requirements of high integration, but also takes into account the requirements of efficient heat dissipation, ensuring that the system can maintain a stable working state when operating at high power.

[0055] The heating device (9) can be used for heating, so that the silver oxide formed by the oxidation of silver in the air during the operation of the photoelectric effect ion source is converted into silver metal through thermal decomposition, thereby effectively preventing the attenuation problem of the emission electrode caused by oxidation. Heating not only solves the problem of photoelectric emission attenuation, but also improves the ionization efficiency. The relationship between metal escape and metal work function can be described by the following formula:

[0056] φ(T)=φ o -γ((K B T) 2 / φ o )

[0057] where φ o is the work function of the metal at T = 0K, T is the temperature of the metal photoemission electrode, γ is the crystal structure coefficient, K B is the Boltzmann constant. From the formula, we can see that when the photoelectric emission electrode material is constant, γ is a constant. When the temperature rises, the work function of the metal will decrease, resulting in an increase in the photoelectric emission efficiency.

[0058] Specifically, the heating device (9) may optionally use a polyimide heating film.

[0059] Specifically, it also includes:

[0060] The counter electrode (4) is opposite to the metal silver layer (6); the positive electrode of a DC voltage source (5) is connected to the counter electrode (4), and the negative electrode is connected to the metal silver layer (6); the ultraviolet light-emitting diode (2) is arranged in the middle of the counter electrode (4); and the counter electrode (4) is installed on the inner top surface of the shell (3).

[0061] Under the action of the DC voltage source (5), the repulsion voltage applied to the silver metal will affect the photoemission process. The effect of the external electric field on photoemission can be described by the following formula:

[0062] ν0'=ν0-bE 1 / 2

[0063] Wherein, ν0' is the cutoff frequency when the external electric field is 0V, ν0 is the cutoff frequency after the electric field is added, E is the electric field strength applied to the metal surface, and b is a constant. It can be seen from the formula that when the external electric field increases, the cutoff frequency decreases with the increase of the accelerating potential, thereby reducing the metal work function and increasing the photoelectric emission efficiency. The sample molecule (11) is a substance with strong electronegativity, which can combine with electrons or O2(H2O)n to generate reactant ions (M-; MO2-(H2O)nm) for instrument detection.

[0064] Specifically, it also includes:

[0065] A substrate (7) is arranged on top of the polyimide heating film (9);

[0066] an anti-reflection film (8) disposed between the substrate (7) and the metal silver layer (6);

[0067] The anti-reflection film (8) can be a high-efficiency multilayer mirror-reflective polymer film, such as 3M ESR 65Auto or 3M ESR80v2 Auto. The anti-reflection film (8) has a reflectivity of more than 98%. The depth of photons entering the metal can be calculated according to the following formula: I = I0e (-(4pi / λ)kr)), where I is the intensity of the transmitted light, I0 is the initial intensity of the incident light, λ is the wavelength of the incident light, k is the extinction coefficient of the metal at this wavelength, and r is the incident depth of the photon on the metal surface.

[0068] According to the formula, the radiation intensity of light is almost attenuated when the thickness of the film is generally in the range of 0.5nm to 100nm. The present invention prefers a silver metal film with a thickness of about 5nm as the photoelectric emission material. The anti-reflection film is placed directly below the silver metal film, and the light reaching the anti-reflection film is reflected back to the metal from its surface, thereby achieving a photon radiation effect of nearly twice.

[0069] The use of the anti-reflection film (8) achieves a photon radiation effect that is nearly doubled, greatly improves the utilization rate of ultraviolet light, and further enhances the efficiency of photoelectric emission.

[0070] A method for ionizing neutral molecules of a sample to be tested:

[0071] 1) When the instrument is started, the ultraviolet light emitting diode (2) light source is turned on under the action of the constant current source (1), and the ultraviolet light irradiates the surface of the silver metal (6) emission electrode to produce a photoelectric effect, which stimulates electrons to escape;

[0072] 2) The sample to be tested (10) is introduced into the ionization zone by the carrier gas. Under the action of the photoelectric effect ion source of the ultraviolet light emitting diode (2), the sample to be tested (10) captures the escaped electrons or combines with oxygen molecule clusters (such as O2(H2O)n) to generate reactant negative ions (M-; MO2-(H2O)nm). In this process, only negative ions are generated, and no positive ions are generated, thereby avoiding the loss of positive and negative ion combination.

[0073] Further:

[0074] During the photoelectric effect, silver metal is oxidized. The polyimide heating film (9) is opened to decompose the silver oxide into silver metal (6), thereby avoiding the attenuation of the emission electrode and increasing the photoelectric emission efficiency.

[0075] Further:

[0076] Increasing the voltage of the DC voltage source voltage (5) increases the photo-emission effect.

[0077] The following is an embodiment of the present invention:

[0078] like Figure 2 As shown: After the gas sample enters the high-field asymmetric waveform ion mobility spectrometer (FAIMS) device through the air inlet (14), it is excited by the ultraviolet light-emitting diode photoelectric effect ion source (15) and ionized to generate negative ions. The negative ions are separated and screened under the combined action of the separation voltage source (17) and the compensation voltage source (16). At the same time, the deflection voltage source (18) is applied to the lower detection electrode (23), and the trajectory of the negative ions is adjusted so that they are finally captured by the lower detection electrode (23). After the signal is amplified by the weak current detector (27), it is finally transmitted to the host computer (28) through the current signal, thereby obtaining the FAIMS spectrum.

[0079] Adjusting the size of the DC repulsion voltage source (19) will affect the number of electrons escaping per unit time, thereby indirectly changing the ionization efficiency. The DC repulsion voltage (19) has an optimal value. If the voltage continues to increase, the negative ions will move toward the counter electrode, making it impossible to enter the separation zone, thereby affecting the subsequent detection effect. To this end, the temperature of the silver metal (6) emission electrode is adjusted by a polyimide heating film (9) to improve the electron emission efficiency, and a reflection enhancement film (8) is used to improve the utilization rate of light. The shell (3) solves the integration and heat dissipation problems of the ultraviolet light-emitting diode and FAIMS.

[0080] In summary, the following are the technical effects of the present invention:

[0081] 1) By integrating the ultraviolet light-emitting diode directly with the shell, a high degree of integration of the photoelectric effect ion source is achieved.

[0082] The present invention significantly improves the integration of the photoelectric effect ion source. The integrated structure tightly combines the ultraviolet light-emitting diode and the components of the photoelectric effect ion source in one module, simplifies the overall structural design, improves the reliability and compactness of the equipment, and effectively reduces the space occupation and solves the problem of heat dissipation of the light source while ensuring high electron emission performance.

[0083] 2) The method of decomposing silver oxide into silver by heating solves the attenuation problem of the emission electrode of the photoelectric effect ion source during operation.

[0084] In a conventional photoelectric effect ion source, the long-term operation of the emission electrode may lead to a decrease in ionization efficiency due to the accumulation of oxides or the degradation of the electrode material. The present invention proposes to convert silver oxide (Ag2O) into silver metal by thermal decomposition, thereby solving the problem of performance degradation caused by attenuation of conventional electrode materials during use.

[0085] 3) The use of anti-reflection film is used to improve the light absorption efficiency of metal materials, achieving nearly twice the photon radiation effect.

[0086] In order to further improve the performance of the photoelectric effect ion source, the present invention introduces a reflection enhancement film (such as 3M ESR 65Auto or 3M ESR 80v2 Auto film) to enhance the light absorption efficiency. The reflection enhancement film enhances the light reflection, thereby improving the light absorption efficiency of the emitting electrode, significantly improving the utilization rate of the UV light source, and nearly doubling the photon radiation effect. This not only improves the ionization efficiency of the photoelectric effect ion source, but also achieves higher electron generation with lower power consumption.

[0087] In summary, the present invention realizes high integration of other components of the ion source with other components of the ion source through the shell, forming an integrated structural design; metallic silver with low work function is selected as the photoelectric emission material, and the oxidized silver oxide of the photoelectric effect emission electrode is decomposed into silver by heating, thereby effectively avoiding the attenuation problem of the metal caused by oxidation. At the same time, the present invention adds an anti-reflection film at the bottom of the metallic silver layer, which significantly improves the light absorption efficiency, thereby improving the ionization efficiency of the sample to be tested.

[0088] Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A photoelectric effect ion source, characterized in that: include: A metallic silver layer (6) having a reflection enhancement film (8) at its bottom, and a substrate (7) at the bottom of the reflection enhancement film (8); The ultraviolet light emitting diode (2) is opposite to the metal silver layer (6), and a channel is left between the ultraviolet light emitting diode (2) and the metal silver layer (6) for the sample to be tested to pass through; the ultraviolet light emitting diode (2) irradiates the metal silver layer (6), thereby stimulating the electrons on the surface of the metal silver layer (6) to escape, and the molecules of the sample to be tested capture the escaped electrons to generate reactant negative ions, thereby achieving ion generation; A heating device (9), arranged at the bottom of the substrate (7), used for heating the metal silver layer (6) during the electron escape process; The housing (3) is provided with the ultraviolet light emitting diode (2) mounted on the inner top surface of the housing (3); and the heating device (9) is mounted on the inner bottom surface of the housing (3).

2. A photoelectric effect ion source according to claim 1, characterized in that: A counter electrode (4) is also mounted on the inner top surface of the housing (3), and the counter electrode (4) is opposite to the metal silver layer (6); A positive electrode of a DC voltage source (5) is connected to the counter electrode (4), and a negative electrode is connected to the metal silver layer (6).

3. A photoelectric effect ion source according to claim 1, characterized in that: The material of the housing (3) is PCB, ceramic or glass.

4. A photoelectric effect ion source according to claim 1, characterized in that: The thickness of the metallic silver layer (6) is 5 nm.

5. A photoelectric effect ion source according to claim 1, characterized in that: The heating device (9) is a polyimide heating film.

6. A photoelectric effect ion source according to claim 1, characterized in that: The anti-reflection film (8) is a mirror-surface polymer reflective film (8).

7. A photoelectric effect ion source according to claim 1, characterized in that: Also includes: A constant current source (1) is electrically connected to the ultraviolet light emitting diode (2) and is used to supply power to the ultraviolet light emitting diode (2).

8. A method for ionizing a sample to be tested based on the photoelectric effect ion source according to claim 1, characterized in that: include: Utilizing the ultraviolet light emitting diode (2) to irradiate the metallic silver layer (6) to stimulate electrons on the surface of the metallic silver layer (6) to escape; The sample to be tested is transported to the channel between the ultraviolet light emitting diode (2) and the metal silver layer (6), and the molecules of the sample to be tested capture the escaped electrons to generate reactant negative ions, thereby achieving ion generation; The metal silver layer (6) is heated by a heating device (9) during the electron escape process.

9. The method for ionizing a sample to be tested according to claim 8, characterized in that: When the ultraviolet light-emitting diode (2) irradiates the metallic silver layer (6), an electric field directed toward the metallic silver layer (6) is applied between the metallic silver layer (6) and the inner top surface of the shell (3), thereby driving electrons to escape from the silver metal surface.

10. The method for ionizing a sample to be tested according to claim 9, characterized in that: When an electric field directed toward the metal silver layer (6) is applied between the metal silver layer (6) and the inner top surface of the housing (3), the cutoff frequency at which the metal silver layer (6) generates a photoelectric effect is: ν0'=ν0-bE 1 / 2 Wherein, ν0' is the cutoff frequency of the photoelectric effect generated by the metal silver layer (6) when an external electric field exists, ν0 is the cutoff frequency when the external electric field is 0V, E is the electric field strength applied to the metal surface, and b is a constant.

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