Microfocus x-ray source cathode structure and method of making

Abstract

The application provides a micro-focus X-ray source cathode structure and a preparation method thereof. The method forms a secondary zone-fused LaB6 single crystal with a [100] crystal direction, the electron emission stability of the single crystal is good, the brightness is higher and the service life is longer than that of a tungsten wire under the same current density; the single crystal LaB6 tip is prepared by using an electrochemical corrosion method, the curvature radius of the single crystal LaB6 tip is about 1 mu m, a high-brightness electron beam can be generated, so that the emission performance of the secondary zone-fused LaB6 single crystal is more than dozens of times higher than that of a tungsten wire cathode, the generated X-ray intensity and imaging quality are higher than those of the tungsten wire cathode; the secondary zone-fused LaB6 single crystal is applied to an X-ray source of a Micro-CT, the original tungsten wire cathode electron gun structure and power supply do not need to be changed, the performance of a Micro-CT system is not limited by the defects of a hot tungsten wire cathode, such as small emission current, low brightness and short service life, so that the overall performance of the Micro-CT is improved.

Description

Technical Field

[0001] This invention relates to the field of electronic source technology, and more specifically, to a microfocus X-ray source cathode structure and its preparation method, particularly to a microfocus X-ray source cathode structure for Micro-CT and its preparation method. Background Technology

[0002] X-ray sources have long been widely used in production and medicine. The penetrating power of X-rays enables non-destructive testing, the fluorescence effect of X-rays enables trace analysis of materials, and the denaturation of proteins by X-rays enables radiotherapy of tumors. The basic characteristic of the currently used X-ray sources is that they adopt thermionic emission, that is, they use a heated filament as the electron emission source, and X-rays are generated by bombarding the anode under high voltage acceleration. However, such light sources are large in size, require a power supply to heat the cathode, and have a slow frequency response.

[0003] Micro-computed tomography (Micro-CT) is a non-destructive 3D imaging technique that can clearly understand the internal microstructure of a sample without damaging it. It has developed rapidly and been widely used in the field of non-destructive testing. Focused electron beam target shooting is the simplest and most practical method to output micro-spot X-rays with sufficient intensity. The emission performance of its electron source is one of the key factors affecting the stability of the emitted X-rays.

[0004] Currently, the three main methods for cathode-emitting electron beams are thermionic emission, field emission, and thermo-field emission. However, thermionic emission cathodes have disadvantages such as low efficiency, low emission, low brightness, and short lifespan, which cannot meet the requirements of microfocus X-ray sources. Field emission cathodes, on the other hand, require relatively harsh operating conditions. Therefore, microfocus X-ray sources generally use thermo-field emission cathodes, which have stable performance and high efficiency. Single-crystal LaB6 cathodes are considered ideal microfocus X-ray source cathodes due to their advantages such as high emission current density, low emission, good stability, and long lifespan.

[0005] Therefore, given the shortage of long-lifetime, high-brightness single-crystal LaB6 cathodes required for microfocus X-ray sources and the technical challenges in their fabrication, researching electron sources capable of generating high-quality electron beams is of paramount importance in the development of microfocus X-ray sources and Micro-CT, and has always been a goal and hot topic pursued by many researchers. Summary of the Invention

[0006] In view of this, to solve the above problems, the present invention provides a microfocus X-ray source cathode structure and its preparation method, the technical solution of which is as follows:

[0007] A method for fabricating a microfocus X-ray source cathode structure, the method comprising:

[0008] Preparation of LaB6 sintered polycrystalline rods;

[0009] The LaB6 sintered polycrystalline rod is used as the first feeding rod, and a LaB6 single crystal with the same diameter as the LaB6 sintered polycrystalline rod is used as the first seed crystal. The first zone melting is performed to obtain the LaB6 single crystal after the first zone melting, wherein the first seed crystal is fixed to the lower end shaft of the first feeding rod.

[0010] The LaB6 single crystal after the first zone melting is used as the second feeding rod, and the LaB6 single crystal with the

[100] crystal orientation is used as the second seed crystal. The second zone melting is performed to obtain the LaB6 single crystal after the second zone melting. The second seed crystal is fixed at the lower end of the second feeding rod, and the LaB6 single crystal after the second zone melting has the

[100] crystal orientation.

[0011] The LaB6 single crystal after secondary zone melting is treated by electrochemical corrosion to form a single crystal LaB6 tip;

[0012] The LaB6 single crystal after secondary zone melting, which has the tip of the single crystal LaB6, is fixed on a support to form a microfocus X-ray source cathode structure.

[0013] Preferably, in the above-mentioned method for preparing the microfocus X-ray source cathode structure, the preparation of the LaB6 sintered polycrystalline rod includes:

[0014] LaB6 powder is sintered in a sintering furnace to obtain the LaB6 sintered polycrystalline rod. The purity of the LaB6 powder is greater than or equal to 99.9%, and the particle size of the LaB6 powder is in the range of 300 mesh to 400 mesh.

[0015] Preferably, in the above-mentioned method for preparing the microfocus X-ray source cathode structure, the environmental conditions for sintering the LaB6 powder in a sintering furnace to obtain the LaB6 sintered polycrystalline rod include:

[0016] The sintering temperature is 1000℃-1500℃, the sintering pressure is 10MPa-50MPa, the sintering holding time is 5min-30min, and the sintering heating rate is 100℃ / min-200℃ / min.

[0017] Preferably, in the above-mentioned method for preparing the microfocus X-ray source cathode structure, a first zone melting is performed in a quartz tube, wherein the first zone melting to obtain a LaB6 single crystal after the first zone melting includes:

[0018] Argon gas is introduced into the quartz tube, and the first feeding rod and the first seed crystal are rotated in opposite directions to obtain the LaB6 single crystal after the first zone melting. The speed of the first reverse rotation is 15rpm-30rpm, and the speed of the first zone melting is 20mm / h-30mm / h.

[0019] Preferably, in the above-mentioned method for preparing the microfocus X-ray source cathode structure, a second zone melting is performed in a quartz tube, wherein the second zone melting to obtain the LaB6 single crystal after secondary zone melting includes:

[0020] Argon gas is introduced into the quartz tube, and the second feeding rod and the second seed crystal are rotated in opposite directions to obtain the LaB6 single crystal after secondary zone melting. The speed of the second reverse rotation is 15rpm-30rpm, and the speed of the second zone melting is 5mm / h-15mm / h.

[0021] Preferably, in the above-described method for fabricating a microfocus X-ray source cathode structure, before forming the single-crystal LaB6 tip, the formation method further includes:

[0022] The LaB6 single crystal after secondary zone melting is cut into LaB6 single crystal rods, and one end of the LaB6 single crystal rod is covered with paraffin wax. The dimensions of the LaB6 single crystal rod are Φ1mm*5mm.

[0023] Preferably, in the above-mentioned method for preparing the microfocus X-ray source cathode structure, the step of treating the LaB6 single crystal after secondary zone melting with an electrochemical etching method to form a single-crystal LaB6 tip includes:

[0024] A voltage and a first current are applied to insert one end of the LaB6 single crystal rod covered with paraffin into the electrolyte and keep the LaB6 single crystal rod moving up and down.

[0025] After the portion of the LaB6 single crystal rod inserted into the electrolyte and not covered by the paraffin is sharpened, a second current is applied to keep the LaB6 single crystal rod in a static state for electrochemical corrosion. The power is turned off at the moment the LaB6 single crystal rod breaks to form the tip of the single crystal LaB6.

[0026] The value of the first current ranges from 0.02mA to 0.17mA.

[0027] Preferably, in the above-mentioned method for fabricating the microfocus X-ray source cathode structure, the electrochemical etching method is based on an electrochemical etching apparatus, which includes:

[0028] The LaB6 single crystal rod, the electrolyte, the power supply, the stainless steel ring, the beaker, the support stage, the displacement device, the sample clip, and the resistor;

[0029] The displacement device is connected to the sample clamp and the support stage respectively, and the sample clamp is used to fix the LaB6 single crystal rod.

[0030] One end of the LaB6 single crystal rod covering the paraffin is located in the central region of the stainless steel ring;

[0031] The volume ratio of the electrolyte is:

[0032] V(HCl):V(C2H5OH):V(H2O)=1mL:10mL~20mL:10mL~20mL;

[0033] The LaB6 single crystal rod covering one end of the paraffin, the stainless steel ring, and the electrolyte are placed in the beaker;

[0034] The positive terminal of the power supply is connected to the LaB6 single crystal rod through a resistor, and the negative terminal of the power supply is connected to the stainless steel ring.

[0035] A microfocus X-ray source cathode structure, wherein the microfocus X-ray source cathode structure is prepared based on the preparation method described in any one of the above-mentioned methods, and the microfocus X-ray source cathode structure comprises:

[0036] LaB6 single crystal and support after secondary zone melting;

[0037] The LaB6 single crystal after secondary zone melting has a (100) crystal plane and a single crystal LaB6 tip;

[0038] The LaB6 single crystal after secondary zone melting is fixed on the support.

[0039] Preferably, in the above-described microfocus X-ray source cathode structure, the support further includes:

[0040] Support rod, ceramic base, and distributor;

[0041] One end of the support rod is inverted V-shaped and is used to fix the LaB6 single crystal after secondary zone melting;

[0042] The other end of the support rod is fixed to the ceramic base;

[0043] The distributor is connected to the support rod.

[0044] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0045] This invention provides a method for preparing a microfocus X-ray source cathode structure. The method includes: preparing a LaB6 sintered polycrystalline rod; using the LaB6 sintered polycrystalline rod as a first feeding rod, and using a LaB6 single crystal with the same diameter as the LaB6 sintered polycrystalline rod as a first seed crystal, performing a first zone melting to obtain a LaB6 single crystal after one zone melting, wherein the first seed crystal is fixed to the lower end axis of the first feeding rod; using the LaB6 single crystal after one zone melting as a second feeding rod, and using a LaB6 single crystal with the

[100] crystal orientation as a second seed crystal, performing a second zone melting to obtain a LaB6 single crystal after two zone meltings, wherein the second seed crystal is fixed to the lower end axis of the second feeding rod, and the LaB6 single crystal after two zone meltings has the

[100] crystal orientation; treating the LaB6 single crystal after two zone meltings using an electrochemical etching method to form a single-crystal LaB6 tip; fixing the LaB6 single crystal after two zone meltings with the single-crystal LaB6 tip on a support to form a microfocus X-ray source cathode structure. The LaB6 single crystal formed by the present invention after secondary zone melting with

[100] crystal orientation has good electron emission stability. Compared with tungsten wire, the LaB6 single crystal after secondary zone melting has higher brightness and longer lifespan under the same current density. The LaB6 single crystal tip is prepared by electrochemical etching, so that the radius of curvature of the LaB6 single crystal tip is about 1 μm. The cathode tip with a small radius of curvature can generate a high-brightness electron beam, so that the emission performance of the LaB6 single crystal after secondary zone melting is more than 10 times higher than that of the hot tungsten wire cathode. The X-ray intensity generated by the LaB6 single crystal after secondary zone melting is higher than that of the tungsten wire cathode, and the X-ray imaging quality of the LaB6 single crystal after secondary zone melting is better than that of the tungsten wire cathode. When the LaB6 single crystal after secondary zone melting is applied to the X-ray source of Micro-CT, it can overcome the limitations of the hot tungsten wire cathode in Micro-CT system performance due to its small emission current, low brightness and short lifespan without changing the original tungsten wire cathode electron gun structure and power supply, thereby improving the overall performance of Micro-CT. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0047] Figure 1 A schematic flowchart illustrating a method for fabricating a microfocus X-ray source cathode structure according to an embodiment of the present invention;

[0048] Figure 2A schematic diagram illustrating the principle of zone melting provided in an embodiment of the present invention;

[0049] Figure 3 A schematic diagram illustrating another principle of zone melting provided in an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram illustrating an embodiment of the present invention where one end of a LaB6 single crystal rod is covered with paraffin wax.

[0051] Figure 5 This is a schematic diagram of a process for forming a single-crystal LaB6 tip by treating the LaB6 single crystal after secondary zone melting using an electrochemical etching method, as provided in an embodiment of the present invention.

[0052] Figure 6 An electron microscope image of a single-crystal LaB6 tip provided for an embodiment of the present invention;

[0053] Figure 7 This is a schematic diagram of an electrochemical etching apparatus provided in an embodiment of the present invention;

[0054] Figure 8 This is a schematic diagram of a microfocus X-ray source cathode structure provided in an embodiment of the present invention. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] This invention provides a method for fabricating a microfocus X-ray source cathode structure, referring to... Figure 1 , Figure 1 This is a schematic flowchart illustrating a method for fabricating a microfocus X-ray source cathode structure according to an embodiment of the present invention, combined with... Figure 1 The preparation method includes:

[0058] S100: Preparation of LaB6 sintered polycrystalline rods.

[0059] S200: Using the LaB6 sintered polycrystalline rod as the first feeding rod, and using a LaB6 single crystal with the same diameter as the LaB6 sintered polycrystalline rod as the first seed crystal, perform the first zone melting to obtain a LaB6 single crystal after one zone melting, wherein the first seed crystal is fixed to the lower end shaft of the first feeding rod.

[0060] S300: The LaB6 single crystal after the first zone melting is used as the second feeding rod, and the LaB6 single crystal with the

[100] crystal orientation is used as the second seed crystal. The second zone melting is performed to obtain the LaB6 single crystal after the second zone melting. The second seed crystal is fixed on the lower end axis of the second feeding rod, and the LaB6 single crystal after the second zone melting has the

[100] crystal orientation.

[0061] Specifically, in step S300, the LaB6 single crystal after the first zone melting is used as the second feed rod, that is, the product of the first zone melting in step S200 is used as the second feed rod in step S300; in the second zone melting process, the LaB6 single crystal with the

[100] crystal orientation is used as the second seed crystal, which can guide the second feed rod to grow along the

[100] crystal orientation, thereby obtaining the LaB6 single crystal after the second zone melting with the

[100] crystal orientation; the work function of each crystal plane of the LaB6 single crystal is different, among which the (100) crystal plane has the best electron emission stability and the best electron emission performance; the work function of the (100) crystal plane of the LaB6 single crystal is about 2.40eV, which is lower than that of tungsten wire. Therefore, under the same current density, the LaB6 single crystal emitter can reach the lower temperature, and the temperature is brighter and the service life is longer than that of tungsten wire. Therefore, in this embodiment of the invention, the LaB6 single crystal after the second zone melting with the (100) crystal plane is preferably used as the electron source emitter.

[0062] S400: The LaB6 single crystal after secondary zone melting is treated by electrochemical etching to form a single crystal LaB6 tip.

[0063] S500: The LaB6 single crystal after secondary zone melting with the tip of the single crystal LaB6 is fixed on the support to form a microfocus X-ray source cathode structure.

[0064] This invention provides a method for preparing a microfocus X-ray source cathode structure. The method includes: preparing a LaB6 sintered polycrystalline rod; using the LaB6 sintered polycrystalline rod as a first feeding rod, and using a LaB6 single crystal with the same diameter as the LaB6 sintered polycrystalline rod as a first seed crystal, performing a first zone melting to obtain a LaB6 single crystal after one zone melting, wherein the first seed crystal is fixed to the lower end axis of the first feeding rod; using the LaB6 single crystal after one zone melting as a second feeding rod, and using a LaB6 single crystal with the

[100] crystal orientation as a second seed crystal, performing a second zone melting to obtain a LaB6 single crystal after two zone meltings, wherein the second seed crystal is fixed to the lower end axis of the second feeding rod, and the LaB6 single crystal after two zone meltings has the

[100] crystal orientation; treating the LaB6 single crystal after two zone meltings using an electrochemical etching method to form a single-crystal LaB6 tip; fixing the LaB6 single crystal after two zone meltings with the single-crystal LaB6 tip on a support to form a microfocus X-ray source cathode structure. The LaB6 single crystal formed by the present invention after secondary zone melting with

[100] crystal orientation has good electron emission stability. Compared with tungsten wire, the LaB6 single crystal after secondary zone melting has higher brightness and longer lifespan under the same current density. The LaB6 single crystal tip is prepared by electrochemical etching, so that the radius of curvature of the LaB6 single crystal tip is about 1 μm. The cathode tip with a small radius of curvature can generate a high-brightness electron beam, so that the emission performance of the LaB6 single crystal after secondary zone melting is more than 10 times higher than that of the hot tungsten wire cathode. The X-ray intensity generated by the LaB6 single crystal after secondary zone melting is higher than that of the tungsten wire cathode, and the X-ray imaging quality of the LaB6 single crystal after secondary zone melting is better than that of the tungsten wire cathode. When the LaB6 single crystal after secondary zone melting is applied to the X-ray source of Micro-CT, it can overcome the limitations of the hot tungsten wire cathode in Micro-CT system performance due to its small emission current, low brightness and short lifespan without changing the original tungsten wire cathode electron gun structure and power supply, thereby improving the overall performance of Micro-CT.

[0065] Furthermore, the reason why LaB6 material is used as the cathode material for the microfocus X-ray source in this embodiment of the invention is that with the introduction of the field electron emission theory, the field emission characteristics of LaB6 material have gradually attracted attention. Since the work function of LaB6 material is very low, only about half that of metallic Mo, the emission current of the field emission cathode made of LaB6 material will be several orders of magnitude larger than that of metallic Mo. Therefore, the external electric field strength required to obtain the same field emission current will be greatly reduced. This not only reduces the difficulty of engineering design, but also reduces the energy carried by positive ions back-bombarding the cathode during operation. At the same time, LaB6 material itself has extremely high resistance to ion bombardment and conductivity, which can fundamentally prevent the cathode from being damaged by back-bombarded positive ions or poisoned, extend the cathode's service life, and improve the stability of the device. In addition, LaB6's high melting point, high chemical stability, low evaporation rate, and strong replenishment ability all demonstrate its emission potential.

[0066] Optionally, in another embodiment of the present invention, the process of preparing the LaB6 sintered polycrystalline rod in step S100 of the above-described method for preparing the microfocus X-ray source cathode structure is further illustrated in detail below:

[0067] LaB6 powder is sintered in a sintering furnace to obtain the LaB6 sintered polycrystalline rod. The purity of the LaB6 powder is greater than or equal to 99.9%, and the particle size of the LaB6 powder is in the range of 300 mesh to 400 mesh.

[0068] Specifically, in this embodiment of the invention, the particle size of the LaB6 powder can be any value within the range of 300 mesh to 400 mesh. For example, the particle size of the LaB6 powder can be 300 mesh, 350 mesh, 400 mesh, etc. In addition, before placing the LaB6 powder in the sintering furnace, the LaB6 powder needs to be ball-milled in an argon atmosphere for a time of not less than 2 hours. The purpose of this is to homogenize the LaB6 powder. Then, the LaB6 powder is placed in the sintering furnace for sintering in an environment of 5 Pa to 10 Pa.

[0069] The sintering temperature is 1000℃-1500℃, the sintering pressure is 10MPa-50MPa, the sintering holding time is 5min-30min, and the sintering heating rate is 100℃ / min-200℃ / min.

[0070] Specifically, in this embodiment of the invention, the sintering temperature is preferably any value within the range of 1100℃-1300℃, for example, the sintering temperature can be 1100℃, 1200℃, 1300℃, etc.; the sintering pressure is preferably any value within the range of 20MPa-40MPa, for example, the sintering pressure can be 20MPa, 35MPa, 40MPa, etc.; the sintering holding time is preferably any value within the range of 5min-20min, for example, the sintering holding time can be 5min, 15min, 20min, etc.; the sintering heating rate is preferably any value within the range of 120℃ / min-180℃ / min, for example, the sintering heating rate can be 120℃ / min, 150℃ / min, 180℃ / min, etc.

[0071] Furthermore, to facilitate subsequent processing, after obtaining the LaB6 sintered polycrystalline ingot, it is necessary to cut it into cylinders with a diameter ranging from 2mm to 10mm. Then, the cylinders are polished with sandpaper to remove impurities, and subsequently cleaned in a dilute nitric acid solution. Next, they are cleaned sequentially with anhydrous ethanol and acetone solutions for 20-30 minutes each to remove oxides, oil stains, and other impurities from the surface of the LaB6 sintered polycrystalline ingot, resulting in the final LaB6 sintered polycrystalline ingot. The diameter of the LaB6 sintered polycrystalline ingot can be any value within the range of 2mm to 10mm, for example, 2mm, 5mm, or 10mm. The cleaning time can also be any value within the range of 20-30 minutes, for example, 20 minutes, 25 minutes, or 30 minutes.

[0072] Optionally, in another embodiment of the present invention, the implementation process of performing a first zone melting in step S200 of the above-mentioned method for preparing a microfocus X-ray source cathode structure to obtain a LaB6 single crystal after a first zone melting is further illustrated in detail below:

[0073] The process of obtaining the LaB6 single crystal after the first zone melting is carried out in a quartz tube. Argon gas is introduced into the quartz tube, and the first feeding rod and the first seed crystal are rotated in opposite directions to obtain the LaB6 single crystal after the first zone melting. The speed of the first reverse rotation is 15rpm-30rpm, and the speed of the first zone melting is 20mm / h-30mm / h.

[0074] Specifically, in the embodiments of the present invention, such as Figure 2 As shown, Figure 2 This is a schematic diagram illustrating the principle of zone melting according to an embodiment of the present invention. Figure 2The first feeding bar 1 is shown in the figure. Figure 2 The first seed crystal, indicated by number 2, is the first feed bar. Figure 2 The symbol 3 indicates the melting zone 3. Figure 2 The heater 4 is shown in reference numeral 4. The LaB6 sintered polycrystalline rod is used as the first feeding rod 1, and the LaB6 single crystal with the same diameter as the LaB6 sintered polycrystalline rod is used as the first seed crystal 2. They are added to the optical zone melting furnace for the first zone melting. The heater 4 is placed in the area where the melting zone 3 is located. The first feeding rod 1 and the first seed crystal 2 are rotated in opposite directions to obtain the LaB6 single crystal after the first zone melting. The speed of the first reverse rotation can be any value in the range of 15rpm-30rpm. For example, the speed of the first reverse rotation can be 15rpm, 20rpm, 30rpm, etc. The speed of the first zone melting can be any value in the range of 20mm / h-30mm / h. For example, the speed of the first zone melting can be 20mm / h, 25mm / h, 30mm / h, etc.

[0075] Optionally, in another embodiment of the present invention, the implementation process of performing a second zone melting in step S300 of the above-mentioned method for preparing a microfocus X-ray source cathode structure to obtain a LaB6 single crystal after secondary zone melting is further illustrated in detail below:

[0076] The process of obtaining the LaB6 single crystal after the second zone melting is carried out in a quartz tube. Argon gas is introduced into the quartz tube, and the second feeding rod and the second seed crystal are rotated in opposite directions to obtain the LaB6 single crystal after the second zone melting. The speed of the second reverse rotation is 15rpm-30rpm, and the speed of the second zone melting is 5mm / h-15mm / h.

[0077] Specifically, in the embodiments of the present invention, such as Figure 3 As shown, Figure 3 This is a schematic diagram illustrating another principle of zone melting provided in an embodiment of the present invention. Figure 3 The number 5 indicates the second feeding bar 5. Figure 3 The number 6 indicates the second seed crystal, which is the second feed bar. Figure 3 The symbol 7 indicates the melting zone 7. Figure 3The heater 8 is shown in the reference numeral 8. The LaB6 single crystal after the first zone melting is used as the second feeding rod 5, and the LaB6 single crystal with the

[100] crystal orientation is used as the second seed crystal 6. They are added to the optical zone melting furnace for the second zone melting. The heater 8 is placed in the area where the melting zone 7 is located. The second feeding rod 5 and the second seed crystal 6 are rotated in opposite directions to obtain the LaB6 single crystal after the second zone melting. The speed of the second reverse rotation can be any value in the range of 15rpm-30rpm. For example, the speed of the second reverse rotation can be 15rpm, 20rpm, 30rpm, etc. The speed of the second zone melting can be any value in the range of 5mm / h-15mm / h. For example, the speed of the second zone melting can be 5mm / h, 10mm / h, 15mm / h, etc.

[0078] Optionally, in another embodiment of the present invention, the process of using an electrochemical etching method to treat the LaB6 single crystal after secondary zone melting to form a single-crystal LaB6 tip in step S400 of the above-mentioned method for preparing the microfocus X-ray source cathode structure is further illustrated in detail below:

[0079] Before forming the single-crystal LaB6 tip, the forming method further includes: cutting the LaB6 single crystal after secondary zone melting into a LaB6 single crystal rod, and covering one end of the LaB6 single crystal rod with paraffin wax. The LaB6 single crystal rod has a size of Φ1mm*5mm, a diameter of 1mm, and a length of 5mm.

[0080] Specifically, in this embodiment of the invention, the method includes, but is not limited to, using wire cutting to cut the LaB6 single crystal after secondary zone melting into LaB6 single crystal rods; the dimensions of the LaB6 single crystal rod are Φ1mm*5mm, which can be understood as the diameter of the LaB6 single crystal rod being 1mm and the length of the LaB6 single crystal rod being 5mm; additionally, as... Figure 4 As shown, Figure 4 This is a schematic diagram illustrating an embodiment of the present invention where one end of a LaB6 single crystal rod is covered with paraffin wax. Figure 4 The figure number 9 shows a LaB6 single crystal rod. Figure 4 The symbol 10 indicates paraffin wax 10. The purpose of covering one end of the LaB6 single crystal rod 9 with paraffin wax 10 is to protect the area of ​​the LaB6 single crystal rod 9 covered by paraffin wax from electrochemical corrosion. Figure 4 The reference numeral 18 is the sample clip 18, which is a needle gauge used to hold the LaB6 single crystal rod 9 during electrochemical etching.

[0081] The process of treating the LaB6 single crystal after secondary zone melting using an electrochemical etching method to form a single-crystal LaB6 tip includes:

[0082] A voltage and a first current are applied to insert one end of the LaB6 single crystal rod 9, which is covered by the paraffin wax 10, into the electrolyte while keeping the LaB6 single crystal rod 9 moving up and down. After the portion of the LaB6 single crystal rod 9 that is inserted into the electrolyte and not covered by the paraffin wax 10 is sharpened, a second current is applied to keep the LaB6 single crystal rod 9 in a static state for electrochemical corrosion. The power is turned off at the moment the LaB6 single crystal rod 9 breaks, forming the tip of the single crystal LaB6. The value of the first current ranges from 0.02mA to 0.17mA.

[0083] Specifically, in this embodiment of the invention, the first current can take any value within the range of 0.02mA-0.17mA, for example, the first current can be 0.02mA, 0.10mA, 0.17mA, etc.; the second current is preferably 0.01mA, the voltage is preferably 3V, and the electrochemical etching time is preferably 1 hour. Figure 5 As shown, Figure 5 This is a schematic diagram illustrating a process for forming a single-crystal LaB6 tip by treating the LaB6 single crystal after secondary zone melting using an electrochemical etching method, as provided in an embodiment of the present invention. Figure 5 Figure a shows a LaB6 single crystal rod 9 cut from the LaB6 single crystal after secondary zone melting. The bottom of the rod is covered with paraffin wax 10. One end of the LaB6 single crystal rod 9 covered with paraffin wax 10 is inserted into the electrolyte. The portion protected by paraffin wax 10 is not corroded by the electrolyte, while the remaining portion inserted into the solution gradually tapers until it is finally broken off by gravity, forming the tip of the single crystal LaB6. Figure 6 As shown, Figure 6 An electron microscope image of a single-crystal LaB6 tip provided in an embodiment of the present invention, by... Figure 6 As can be seen, the surface of the formed single-crystal LaB6 tip 11 is smooth, and the presence of crystal edges can be seen in the tip, indicating that this electrochemical etching method has a certain anisotropy in the crystal plane etching rate. In addition, since the performance of the microfocus X-ray source depends on the high brightness of the electron beam, a cathode tip with a small radius of curvature is necessary to obtain a high brightness electron beam. Currently, most commercial single-crystal LaB6 tips are prepared by grinding, and the radius of curvature is generally around 10 μm. This is because the brightness of the electron beam depends on the field strength distribution of the cathode tip, which in turn depends on the geometry and size of the cathode tip. In the embodiment of this invention, the radius of curvature of the single-crystal LaB6 tip 11 formed by the electrochemical etching method is about 1 μm.

[0084] According to the preparation method described above, the electrochemical etching method is based on an electrochemical etching apparatus, as referenced. Figure 7 , Figure 7This is a schematic diagram of an electrochemical etching apparatus provided in an embodiment of the present invention, as shown below. Figure 7 As shown, the electrochemical etching apparatus includes:

[0085] The LaB6 single crystal rod 9, the electrolyte 12, the power supply 13, the stainless steel ring 14, the beaker 15, the support stage 16, the displacement device 17, the sample holder 18, and the resistor 19.

[0086] The displacement device 17 is connected to the sample clamp 18 and the support stage 16 respectively. The sample clamp 18 is used to fix the LaB6 single crystal rod 9.

[0087] Specifically, in this embodiment of the invention, the beaker 15 is placed on the support platform 16, and the sample 18 is placed above the beaker 15.

[0088] The end of the LaB6 single crystal rod 9 covering the paraffin wax 10 is located in the central region of the stainless steel ring 14; the end of the LaB6 single crystal rod 9 covering the paraffin wax, the stainless steel ring 14, and the electrolyte 12 are placed in the beaker 15; the volume ratio of the electrolyte 12 is V(HCl):V(C2H5OH):V(H2O) = 1mL:10mL~20mL:10mL~20mL.

[0089] Specifically, in this embodiment of the invention, in order to ensure that the LaB6 single crystal rod 9 is uniformly corroded, the stainless steel ring 14 is made into a circle with a diameter of about 3 cm, and the LaB6 single crystal rod 9 is placed in the center of the circle; anhydrous ethanol is used as a buffer in the electrolyte 12, which can make the surface of the single crystal LaB6 tip 11 formed after electrochemical corrosion smooth; in addition, the volume ratio of the electrolyte 12 can also be prepared by using V(phosphoric acid):V(ethanol):V(deionized water) = 1 mL: 20 mL ~ 30 mL: 20 mL ~ 30 mL.

[0090] The positive terminal of the power supply 13 is connected to the LaB6 single crystal rod 9 through a resistor 19, and the negative terminal of the power supply 13 is connected to the stainless steel ring 14.

[0091] Specifically, in this embodiment of the invention, the resistor 19 is preferably a megohm resistor; the positive terminal of the power supply 13 is connected to the LaB6 single crystal rod 9 through the resistor 19 by a wire, and the negative terminal of the power supply 13 is also connected to the stainless steel ring 14 by a wire.

[0092] Optionally, based on the above embodiments of the present invention, another embodiment of the present invention also provides a microfocus X-ray source cathode structure, which is prepared based on the preparation method described in the above embodiments, with reference to... Figure 8 , Figure 8 This is a schematic diagram of a microfocus X-ray source cathode structure provided in an embodiment of the present invention, combined with... Figure 8 The microfocus X-ray source cathode structure includes:

[0093] The LaB6 single crystal 20 after secondary zone melting and the support 22; the LaB6 single crystal 20 after secondary zone melting has a (100) crystal plane and a single crystal LaB6 tip 11; the LaB6 single crystal 20 after secondary zone melting is fixed on the support 22.

[0094] Specifically, in this embodiment of the invention, the bracket 22 includes, but is not limited to, a mini Vogel bracket, which is capable of withstanding reasonable impacts without deviating from its structural specifications.

[0095] The microfocus X-ray source cathode structure provided by this invention has the advantages of simplicity, durability, and precision. It can resist any movement of the crystal even under high operating temperatures and is easy to install and align. In addition, since the pyrolytic graphite block 21 pad shields the evaporation of the LaB6 single crystal 20 after secondary zone melting in the direction of the clamping force, the LaB6 single crystal 20 after secondary zone melting can be fully utilized without causing degradation of the support 22. When the cathode operates within the correct temperature and pressure range, there will be no serious structural failure of the support 22.

[0096] Optionally, in another embodiment of the present invention, the structure of the support 22 in the microfocus X-ray source cathode structure described above is further illustrated, such as... Figure 8 As shown, the bracket 22 also includes:

[0097] The support rod 23, the ceramic base 24, and the shunt 25 are provided. One end of the support rod 23 is inverted V-shaped and is used to fix the LaB6 single crystal 20 after secondary zone melting. The other end of the support rod 23 is fixed to the ceramic base 24. The shunt 25 is connected to the support rod 23.

[0098] Specifically, in this embodiment of the invention, the support rod 23 is made of molybdenum-rhenium alloy, which allows the support rod 23 to maintain a high elastic modulus even at high temperatures. Additionally, the bracket 22 includes a pyrolytic graphite block 21, which is placed between the secondary-melted LaB6 single crystal 20 and the support rod 23. The pyrolytic graphite block 21 can act as a resistance heater, helping to thermally insulate the hot, secondary-melted LaB6 single crystal 20 from the highly conductive support rod 23. When the compressive force of the support rod 23 is released, the secondary-melted LaB6 single crystal 20 is forcefully and precisely clamped, which is beneficial for the use of the cathode. The clamping force of the support rod 23 is maintained at around 5000 psi throughout its lifespan; the shunt 25 is made of rhenium sheet; typically, the beam stability of the mini Vogel support cathode exceeds the specifications of the system it operates on, and the 0.001mm thick shunt resistance allows the cathode to better match the temperature and resistance profile of the tungsten filament; the current takes the path of least resistance through the shunt, bypassing the external pyrolytic graphite block 21, and all heating is generated by the internal pyrolytic graphite block 21. This design utilizes the anisotropic properties of the pyrolytic graphite block 21 to define a differential heat conduction plane in the direction between the shunt 25 and the support rod 23.

[0099] The present invention provides a detailed description of a microfocus X-ray source cathode structure and its preparation method. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

[0100] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0101] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that elements inherent to a process, method, article, or apparatus that comprises a list of elements, or elements inherent to such processes, methods, articles, or apparatus, are also included. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0102] 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 method for fabricating a microfocus X-ray source cathode structure, characterized in that, The preparation method includes: Preparation of LaB6 sintered polycrystalline rods; The LaB6 sintered polycrystalline rod is used as the first feeding rod, and a LaB6 single crystal with the same diameter as the LaB6 sintered polycrystalline rod is used as the first seed crystal. The first zone melting is performed to obtain the LaB6 single crystal after the first zone melting, wherein the first seed crystal is fixed to the lower end shaft of the first feeding rod. The LaB6 single crystal after the first zone melting is used as the second feeding rod, and the LaB6 single crystal with the [100] crystal orientation is used as the second seed crystal. The second zone melting is performed to obtain the LaB6 single crystal after the second zone melting. The second seed crystal is fixed at the lower end of the second feeding rod, and the LaB6 single crystal after the second zone melting has the [100] crystal orientation. The LaB6 single crystal after secondary zone melting is cut into LaB6 single crystal rods, and one end of the LaB6 single crystal rod is covered with paraffin wax. The LaB6 single crystal after secondary zone melting is treated by electrochemical etching to form a single crystal LaB6 tip, including: applying voltage and a first current to insert the end of the LaB6 single crystal rod covered with paraffin into an electrolyte while keeping the LaB6 single crystal rod moving up and down; after the part of the LaB6 single crystal rod inserted into the electrolyte and not covered with paraffin is sharpened, a second current is applied to keep the LaB6 single crystal rod in a static state for electrochemical etching; and the power is turned off at the moment the LaB6 single crystal rod breaks to form the single crystal LaB6 tip. The LaB6 single crystal after secondary zone melting, which has the tip of the single crystal LaB6, is fixed on a support to form a microfocus X-ray source cathode structure.

2. The preparation method according to claim 1, characterized in that, The preparation of the LaB6 sintered polycrystalline rod includes: LaB6 powder is sintered in a sintering furnace to obtain the LaB6 sintered polycrystalline rod. The purity of the LaB6 powder is greater than or equal to 99.9%, and the particle size of the LaB6 powder is in the range of 300 mesh to 400 mesh.

3. The preparation method according to claim 2, characterized in that, The environmental conditions for sintering LaB6 powder in a sintering furnace to obtain the LaB6 sintered polycrystalline rod include: The sintering temperature is 1000℃-1500℃, the sintering pressure is 10MPa-50MPa, the sintering holding time is 5min-30min, and the sintering heating rate is 100℃ / min-200℃ / min.

4. The preparation method according to claim 1, characterized in that, The process involves a first zone melting in a quartz tube to obtain a LaB6 single crystal after the first zone melting, comprising: Argon gas is introduced into the quartz tube, and the first feeding rod and the first seed crystal are rotated in opposite directions to obtain the LaB6 single crystal after the first zone melting. The speed of the first seed crystal rotating in opposite directions is 15rpm-30rpm, and the speed of the first zone melting is 20mm / h-30mm / h.

5. The preparation method according to claim 1, characterized in that, A second zone melting process is performed in a quartz tube to obtain a LaB6 single crystal after the second zone melting, comprising: Argon gas is introduced into the quartz tube, and the second feeding rod and the second seed crystal are rotated in opposite directions to obtain the LaB6 single crystal after the second zone melting. The speed of the second seed crystal in the opposite direction is 15rpm-30rpm, and the speed of the second zone melting is 5mm / h-15mm / h.

6. The preparation method according to claim 1, characterized in that, The dimensions of the LaB6 single crystal rod are Φ1mm*5mm.

7. The preparation method according to claim 6, characterized in that, The value of the first current ranges from 0.02mA to 0.17mA.

8. The preparation method according to claim 7, characterized in that, The electrochemical etching method is based on an electrochemical etching apparatus, which includes: The LaB6 single crystal rod, the electrolyte, the power supply, the stainless steel ring, the beaker, the support stage, the displacement device, the sample clip, and the resistor; The displacement device is connected to the sample clamp and the support stage respectively, and the sample clamp is used to fix the LaB6 single crystal rod. One end of the LaB6 single crystal rod covering the paraffin is located in the central region of the stainless steel ring; The volume ratio of the electrolyte is: V(HCl):V(C2H5OH):V(H2O)=1mL:10mL~20mL:10ml~20mL; The LaB6 single crystal rod covering one end of the paraffin, the stainless steel ring, and the electrolyte are placed in the beaker; The positive terminal of the power supply is connected to the LaB6 single crystal rod through a resistor, and the negative terminal of the power supply is connected to the stainless steel ring.

9. A microfocus X-ray source cathode structure, characterized in that, The microfocus X-ray source cathode structure is prepared according to the preparation method of any one of claims 1-8, and the microfocus X-ray source cathode structure comprises: LaB6 single crystal and support after secondary zone melting; The LaB6 single crystal after secondary zone melting has a (100) crystal plane and a single crystal LaB6 tip; The LaB6 single crystal after secondary zone melting is fixed on the support.

10. The microfocus X-ray source cathode structure according to claim 9, characterized in that, The support also includes: Support rod, ceramic base, and distributor; One end of the support rod is inverted V-shaped and is used to fix the LaB6 single crystal after secondary zone melting; The other end of the support rod is fixed to the ceramic base; The distributor is connected to the support rod.

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