A method for manufacturing a neutron absorption grating

Abstract

The present application relates to a kind of neutron absorption grating manufacturing method, using the way of changing grating surface particle layer manufacturing and realizes, (1) using carrier solution to soak grating, so that wetting layer is formed in grating;(2) select the particle containing gadolinium element as neutron absorption material, particle is uniformly dispersed in carrier solution, excess particle solution is injected into grating, so that particle free deposition fills grating;(3) after carrier solution volatilizes, directly on the surface of grating, realize the pressure of particle filling grating;(4) remove the excess particle on the surface of grating after filling, high concentration particle solution is uniformly spin-coated on the surface of grating, carrier solution volatilizes and deposits a layer of excess particle on the surface of grating, again on the surface of grating pressurization;(5) repeat step (3) and (4), gradually increase the filling rate of particle, until the filling rate of particle is constant to reach maximum filling.The present application improves the manufacturing efficiency of the whole pressure absorption grating manufacturing.

Description

Technical Field

[0001] This invention relates to a method for fabricating neutron absorption gratings, belonging to the fields of neutron phase-contrast imaging, neutron absorption gratings, and micro / nano fabrication technology. Background Technology

[0002] Neutron absorption gratings are key optical components in neutron phase-contrast imaging systems. Because gadolinium has a high absorption coefficient for neutrons, gadolinium or gadolinium oxides are typically chosen as the neutron-absorbing material for fabricating absorption gratings. Currently, methods for fabricating neutron absorption gratings based on gadolinium or gadolinium oxide include: tilted evaporation of pure gadolinium metal, gadolinium or gadolinium oxide particle filling, and gadolinium alloy metal-glass imprinting. The tilted evaporation method produces absorption gratings with high gadolinium density in the grooves, but the filling cross-section has an irregular shape and cannot completely fill the grating grooves, making it suitable for low aspect ratio absorption gratings. The metal-glass imprinting method offers advantages such as high throughput, low cost, and high efficiency; however, under rapid heating conditions, the silicon grating structure is prone to collapse during imprinting, causing damage to the grating structure. The particle filling method achieves this through free deposition of particles, a simple process. Typically, a low-concentration particle solution is used to cover the grating surface, allowing the particles to freely deposit into the grating grooves. However, this method results in large particle gaps and low filling rates in the absorption grating grooves.

[0003] Existing pressurized particle filling methods are based on free particle deposition (e.g., Chinese patent application No. 202310129799.3), which can improve the particle filling rate in grating grooves and are suitable for fabricating large-size, long-period absorption gratings. This method involves depositing a particle layer on the grating surface using free particle deposition, followed by covering the grating surface with a soft material. Pressure is applied to the soft material surface to deform it, causing the particles in the groove to rearrange under force. Multiple pressurized fillings reduce the gaps between particles in the groove, increasing the filling rate. However, this method requires free particle deposition to create a particle layer on the grating surface before each pressurized filling. Limited by the time required for free particle deposition and the natural evaporation of the particle carrier solution, the pressurized particle filling interval is typically 3 to 10 hours, and approximately 10 pressurized fillings are needed to reach the maximum filling rate. Using this method to fabricate neutron absorption gratings results in a relatively long cycle and low efficiency. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a method for fabricating neutron absorption gratings. This method changes the fabrication method of the particle layer on the grating surface, improves the efficiency of fabricating absorption gratings by pressurized particle filling, thereby improving the overall fabrication efficiency of pressurized absorption gratings and achieving high-efficiency fabrication of neutron absorption gratings.

[0005] Technical solution of the present invention:

[0006] This invention provides a method for fabricating a neutron absorption grating, which is achieved by changing the fabrication method of the grating surface particle layer, as detailed below:

[0007] (1) The grating is wetted with a carrier solution to form a wetting layer inside the grating;

[0008] (2) Select gadolinium-containing particles as neutron absorbing materials, disperse the particles evenly in a carrier solution to form a particle solution, and then inject excess particle solution into the grating to allow the particles to freely deposit and fill the grating.

[0009] (3) After the carrier solution evaporates, apply a uniform downward force directly to the grating surface to achieve pressurized particle filling of the grating;

[0010] (4) Remove excess particles from the grating surface after pressurization and filling, uniformly spin-coat the high-concentration particle solution onto the grating surface, allow the carrier solution to evaporate and deposit an excess of particles on the grating surface, and pressurize the grating surface again.

[0011] (5) Repeat steps (3) and (4) to gradually increase the particle filling rate until the particle filling rate remains unchanged and reaches the maximum filling.

[0012] Optionally, in step (4), the high-concentration particle solution is prepared by mixing particles and carrier solution in a ratio of 1:4 to 1:20.

[0013] Optionally, in step (4), the uniform spin coating refers to the uniform distribution of a high-concentration particle solution on the grating surface. The spin coating is performed using a spin coater, and the thickness of the excess particle layer is at least 30 micrometers.

[0014] Optionally, in step (2), the gadolinium-containing particles include gadolinium metal particles, gadolinium oxide particles, and gadolinium oxysulfide particles.

[0015] Optionally, in step (2), the particle solution is prepared by mixing particles and carrier solution at a mass ratio of 1:50 to 1:200, and the particles are evenly dispersed in the carrier solution using an ultrasonic machine.

[0016] Optionally, in step (4), the excess means ensuring that the entire pressurized part of the grating can form a uniform particle layer and that there are still excess particles on the surface after pressurization.

[0017] Optionally, in step (2), the excess particle solution refers to a solution in which the particles can be freely deposited to fill the grating and form a uniform particle layer on the grating surface, and there are still excess particles on the grating surface after pressure is applied.

[0018] The advantages of this invention compared to the prior art are:

[0019] (1) The present invention can significantly improve the fabrication efficiency of absorption gratings, and can repeatedly pressurize and fill particles to fabricate absorption gratings in a short time. The existing pressurized particle filling method for fabricating absorption gratings is limited by the free deposition of particles and the solvent evaporation time. The interval between each pressurized particle filling is 3 to 10 hours, resulting in a long fabrication cycle and low efficiency.

[0020] This invention changes the method of fabricating the particle layer on the grating surface, using a spin coater and a high-concentration particle solution to cover the grating surface with a uniform particle layer, shortening the particle filling time for each pressurization, and completing the particle filling for each pressurization within 1 hour, which greatly improves the overall fabrication efficiency of the pressurized absorption grating.

[0021] (2) This invention is applicable to the fabrication of large-size, large-period, and small-period absorption gratings. The process involved in this invention is suitable for the fabrication of large-size absorption gratings and is effective for both large and small periods, such as large-size absorption gratings of 80 mm * 80 mm, 100 mm * 100 mm, etc., with periods ranging from a few micrometers to several hundred micrometers. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the implementation of the method of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some embodiments of the present invention, but not all embodiments.

[0024] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0025] The main purpose of this invention to improve the efficiency of particle-filled absorption grating fabrication is to address the issue of particle deposition efficiency on the grating. In the particle pressurized filling process, effective particle filling into the grating grooves is typically ensured by the long-term free deposition of a low-concentration particle solution. If an excess of particles is naturally deposited, not only will the particles fully fill the grating grooves, but a complete particle layer will also form on the grating surface, and the integrity of this particle layer will not change after pressurization. Thus, in subsequent pressurized filling processes, only a uniform particle layer needs to be deposited on the grating surface. Correspondingly, the natural deposition of particles is no longer necessary; instead, a high-concentration particle solution can be used with rapid film-forming methods such as spin-coating to obtain a uniform particle layer, significantly improving the particle deposition efficiency on the grating and achieving highly efficient fabrication of neutron absorption gratings.

[0026] The present invention is implemented as follows: First, a silicon grating is fabricated using wet etching or dry etching, or other processes. A volatile solvent is selected as the particle carrier solution, and the grating is wetted with the carrier solution to form a wetting layer within the grating. Gadolinium-containing particles, including metallic gadolinium particles, gadolinium oxide particles, and gadolinium oxysulfide particles, are selected as neutron absorbing materials, and the particles are uniformly dispersed in the carrier solution using an ultrasonic machine. An excess of the uniformly dispersed particle solution is injected into a container containing the grating, allowing the particles to freely deposit and fill the grating. After particle deposition, excess carrier solution is removed from the surface to shorten the solvent evaporation time. After the carrier solution evaporates, pressure is applied to the grating surface using a pressurizing device. Excess particles on the surface are removed, and a high-concentration particle solution is uniformly spin-coated onto the grating surface using a spin coater. The carrier solution evaporates quickly, covering the grating surface with an excess of particles, and then pressure is applied again for filling. The above spin-coating method is repeated to cover the grating surface with excess particles and apply pressure until the particle filling rate remains constant.

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] like Figure 1 As shown, the process flow of this embodiment of the invention is as follows:

[0029] 1. Fabrication of silicon gratings

[0030] Silicon gratings can be fabricated using processes such as dry etching, wet anisotropic etching, and photo-assisted electrochemical etching, with the crystal orientation of the silicon substrate selected according to the fabrication process.

[0031] 2. Create a wetting layer

[0032] Choose a volatile solvent as the particle carrier solution (usually ethanol), inject the carrier solution into a container containing a grating, and let it stand for a period of time.

[0033] 3. Particle free deposition filling grating

[0034] A particle solution is prepared by mixing gadolinium-containing particles and a carrier solution at a specific mass ratio (1:50-1:200). The particles are then uniformly dispersed in the carrier solution using an ultrasonic machine. An excess of the particle suspension is injected into a container equipped with a grating and allowed to stand at room temperature and pressure, allowing the particles to freely deposit into the grating groove. After particle deposition, the excess carrier solution above the particle layer is removed.

[0035] 4. Pressurized granule filling

[0036] After the carrier solution has evaporated, a uniform downward force is applied directly to the grating surface using a pressurizing device. Figure 1 F in the figure represents the pressure applied to the grating surface. The particles on the grating surface and in the grating groove are rearranged in the grating groove under the action of force, the gap between the particles decreases and the filling rate in the grating groove increases.

[0037] 5. Excessive particle deposition

[0038] A high-concentration particle solution was prepared by mixing the particles and carrier solution in a certain ratio (1:4-1:20), and the particles were dispersed evenly using an ultrasonic machine. Excess particles were removed from the grating surface after pressurization and filling. The high-concentration particle solution was then added dropwise to the grating surface, and a spin coater was used to distribute the solution evenly on the grating surface at a certain speed and time. Finally, the grating was placed on a horizontal experimental table and allowed to stand for a period of time.

[0039] 6. Repeated pressure filling

[0040] Repeat steps 4 and 5, gradually increasing the particle filling rate until the particle filling rate remains constant and reaches maximum filling.

[0041] The specific implementation method is as follows:

[0042] Example 1: A method for fabricating a neutron absorption grating, the specific steps of which are as follows:

[0043] Step 1: Select a silicon wafer with a (110) crystal orientation. Use AZ1500 photoresist for UV exposure and development to obtain a photoresist grating mask. Obtain a silicon nitride grating mask by dry etching. Place it in a 50% KOH solution for wet etching at room temperature. Add an appropriate amount of anhydrous ethanol to ensure uniform etching of the grating grooves. Finally, obtain a silicon grating structure with a period of 40 micrometers, a duty cycle of 1:1, a depth of 70 micrometers, and an area of ​​80 mm × 80 mm.

[0044] Step 2: Select anhydrous ethanol as the carrier solution to wet the grating. Place the cleaned and dried silicon grating under negative pressure, remove the air from the grating groove, and then inject anhydrous ethanol. Let it stand for 20 minutes at room temperature and pressure.

[0045] Step 3: Prepare a particle solution by mixing gadolinium oxide particles and anhydrous ethanol at a mass ratio of 1:100. The average particle size of the gadolinium oxide is 2 micrometers. The solution is then sonicated at 720W for 15 minutes to obtain a uniformly dispersed particle solution. Excess particle solution is injected into a container equipped with a grating and allowed to stand at room temperature and pressure for 5 hours to allow complete sedimentation of the particles. Excess ethanol is removed using a pipette, and the solution is then allowed to stand for 2 hours to allow the ethanol on the grating surface to completely evaporate.

[0046] Step 4: Apply a uniform downward pressure of 10 MPa directly to the grating surface using a pressurizing device and maintain it for 10 minutes.

[0047] Step 5: Prepare a high-concentration particle solution by mixing gadolinium oxide particles and anhydrous ethanol at a mass ratio of 1:5. Use an ultrasonic machine at 720W power for 45 minutes to disperse the particles evenly. Remove excess particles from the pressurized and filled grating surface. Drop the high-concentration particle solution onto the surface and use a spin coater at 80 rpm for 10 seconds to evenly distribute the solution on the grating surface. Then, place the grating on a horizontal experimental platform and let it stand for 30 minutes to deposit a 120-micrometer-thick particle layer on the grating surface.

[0048] Step 6: Repeat steps 4 and 5, gradually increasing the particle filling rate until the particle filling rate remains constant and reaches maximum filling.

[0049] In this embodiment, the maximum filling rate of the pressurized particles is achieved after 8 pressurizations, with a maximum filling rate of 35%, which is 40% higher than the natural filling rate. This is consistent with the results of existing pressurized particle filling methods. In this embodiment, the interval between each pressurization is 1 hour, while existing pressurized particle filling methods require 10 pressurizations to achieve the maximum filling rate, with an interval of at least 3 hours between each pressurization. This embodiment significantly improves the fabrication efficiency of the absorption grating by pressurization.

[0050] Example 2: A method for fabricating a neutron absorption grating, the specific steps of which are as follows:

[0051] Step 1: Select a silicon wafer with a (110) crystal orientation. Use AZ1500 photoresist for UV exposure and development to obtain a photoresist grating mask. Obtain a silicon nitride grating mask by dry etching. Place it in a 50% KOH solution for wet etching at room temperature. Add an appropriate amount of anhydrous ethanol to ensure uniform etching of the grating grooves. Finally, a silicon grating structure with a period of 4 micrometers, a duty cycle of 1:1, a depth of 20 micrometers, and an area of ​​100 mm × 100 mm can be obtained.

[0052] Step 2: Select anhydrous ethanol as the carrier solution to wet the grating. Place the cleaned and dried silicon grating under negative pressure to remove air from the grating groove, then inject anhydrous ethanol and let it stand for 20 minutes at room temperature and pressure.

[0053] Step 3: Prepare a particle solution by mixing gadolinium oxide particles and anhydrous ethanol at a mass ratio of 1:150, wherein the average particle size of gadolinium oxide is 100 nanometers. The solution is then sonicated at 720W for 10 minutes to obtain a uniformly dispersed particle solution. Excess particle solution is injected into a container equipped with a grating and allowed to stand at room temperature and pressure for 5 hours to allow complete sedimentation of the particles. Excess ethanol is removed using a pipette, and the solution is then allowed to stand for 2 hours to allow complete evaporation of the ethanol from the grating surface.

[0054] Step 4: Apply a uniform downward pressure of 10 MPa directly to the grating surface using a pressurizing device and maintain it for 10 minutes.

[0055] Step 5: Prepare a high-concentration particle solution by mixing gadolinium oxide particles and anhydrous ethanol at a mass ratio of 2:8. Disperse the particles evenly using an ultrasonic machine at 720W power for 45 minutes. Remove excess particles from the pressurized and filled grating surface, drop the high-concentration particle solution onto the surface, and then use a spin coater at 100 rpm for 10 seconds to evenly distribute the solution on the grating surface. Then, place the grating on a horizontal experimental platform and let it stand for 30 minutes to deposit a particle layer with a thickness of 110 micrometers on the grating surface.

[0056] Step 6: Repeat steps 4 and 5, gradually increasing the particle filling rate until the particle filling rate remains constant and reaches maximum filling.

[0057] In this embodiment, the maximum filling rate is achieved by pressurizing the particles 10 times, which increases the particle filling rate by 60% compared to the natural deposition filling method.

[0058] The advantages of this invention compared to the prior art are explained below through comparison.

[0059] Table 1. Comparison of Production Efficiency Improvements Using Pressurization Methods

[0060] There are existing pressurized particle filling methods 3 10 This invention 1 8

[0061] As can be seen from the above, the absorption gratings produced by the embodiments of the present invention have improved efficiency compared with the existing pressurized particle filling method for producing absorption gratings. In the examples, absorption gratings with periods of 4 micrometers and 40 micrometers and sizes of 80 mm × 80 mm and 100 mm × 100 mm have been produced. Absorption gratings with larger periods and larger sizes can also be produced by the same method as the above embodiments.

[0062] The above embodiments are provided merely for the purpose of describing the present invention and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within the scope of the invention.

Claims

1. A method for fabricating a neutron absorption grating, characterized in that: This is achieved by changing the fabrication method of the grating surface grain layer and applying pressure, as detailed below: (1) The grating is wetted with a carrier solution to form a wetting layer inside the grating; (2) Select gadolinium-containing particles as neutron absorbing materials, disperse the particles evenly in a carrier solution to form a particle solution, and then inject an excess of the particle solution into the grating to allow the particles to freely deposit and fill the grating. (3) After the carrier solution evaporates, apply a uniform downward force directly to the grating surface to achieve pressurized particle filling of the grating; (4) Remove excess particles from the grating surface after pressurization and filling, uniformly spin-coat the high-concentration particle solution onto the grating surface, allow the carrier solution to evaporate and deposit an excess of particles on the grating surface, and pressurize the grating surface again. (5) Repeat steps (3) and (4) to gradually increase the particle filling rate until the particle filling rate remains unchanged and reaches the maximum filling rate; In step (4), the high-concentration particle solution is prepared by mixing particles and carrier solution in a ratio of 1:4 to 1:

20.

2. The method for fabricating a neutron absorption grating according to claim 1, characterized in that: In step (4), uniform spin coating refers to the uniform distribution of a high-concentration particle solution on the grating surface. Spin coating is performed using a spin coater, and the thickness of the excess particle layer is at least 30 micrometers.

3. The method for fabricating a neutron absorption grating according to claim 1, characterized in that: In step (2), the gadolinium-containing particles include gadolinium metal particles, gadolinium oxide particles, and gadolinium oxysulfide particles.

4. The method for fabricating a neutron absorption grating according to claim 1, characterized in that: In step (2), the particle solution is prepared by mixing particles and carrier solution at a mass ratio of 1:50-1:200, and the particles are evenly dispersed in the carrier solution using an ultrasonic machine.

5. The method for fabricating a neutron absorption grating according to claim 1, characterized in that: In step (4), the excess means ensuring that the entire grating pressurized part can form a uniform particle layer and that there are still excess particles on the surface after pressurization.

6. The method for fabricating a neutron absorption grating according to claim 1, characterized in that: In step (2), the excess particle solution refers to the particle free deposition that can fill the grating and form a uniform particle layer on the grating surface, and there are still excess particles on the grating surface after pressure is applied.

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