Accelerator neutron source target composite transition layer and its hydrothermal-magnetron sputtering preparation method

Abstract

The present invention relates to the field of neutron source targets, and discloses an accelerator neutron source target composite transition layer and a hydrothermal-magnetron sputtering preparation method thereof. The composite transition layer is located between the substrate and the target layer, and includes a TiO₂ layer deposited by a hydrothermal method and attached to the surface of the substrate through pickling and roasting, and a tantalum layer deposited on the surface of the TiO₂ layer. In the present invention, a TiO₂ layer with a specific morphology is first deposited on the surface of the substrate by a hydrothermal method, and then a tantalum layer is deposited by magnetron sputtering. On the one hand, the TiO₂ layer can reduce the stress generated between the substrate and the tantalum layer due to the mismatch of the thermal expansion coefficients through its own deformation, thereby playing a buffering role; on the other hand, the present invention also finds that the lattice structure of the TiO₂ with a specific morphology can also induce the deposition of tantalum atoms in a specific direction during the growth process, avoiding the stress generated due to the disordered arrangement of atoms inside the tantalum layer, and finally improving the bonding force between the tantalum layer and the substrate and reducing the risk of cracking of the tantalum layer.

Description

Technical Field

[0001] The present invention relates to the field of neutron source targets, and particularly relates to a composite transition layer of an accelerator neutron source target and a hydrothermal-magnetron sputtering preparation method thereof. Background Art

[0002] Boron neutron capture therapy (BNCT) is a tumor treatment method with broad prospects, especially having significant advantages for tumors that are difficult to cure by traditional radiotherapy. Through the targeted delivery of boron drugs and neutron capture reactions, BNCT can kill tumor cells to the greatest extent and reduce damage to normal tissues. As a core element of BNCT, the neutron source must efficiently provide a neutron beam to react with the boron drug. Currently, there are two main sources for generating neutron beams internationally. One is to generate neutron beams through a nuclear reactor, and the other is to generate neutron beams through an accelerator. The accelerator neutron source generates a neutron beam by accelerating particles (such as protons or deuterons) to contact with the target material to undergo a nuclear reaction. Compared with traditional nuclear reactors, it has higher flexibility and precision, and can provide a more controllable and more directional neutron beam. And due to its advantages in aspects such as radiation safety, operation flexibility, and operation and maintenance costs, the accelerator neutron source has shown extensive application potential in the fields of materials science, irradiation research, especially clinical medicine.

[0003] The target material plays a core role in the accelerator neutron source. The selection and design of the neutron source target material directly affect the quality, energy distribution, output flux of the neutron beam, and the durability of the equipment. During long-term operation, the target material will be affected by radiation damage and material fatigue. Therefore, optimizing the target material and structural design is of great significance for improving the generation efficiency, precision, and treatment effect of the neutron beam. The neutron source target system generally uses lithium or beryllium as the main nuclear reaction layer (i.e., the target material layer, usually deposited on the surface of the substrate) to generate neutrons. At the same time, the target system needs to have good radiation resistance, thermal stability, and mechanical properties to withstand the heat and stress generated by a large number of high-energy particle impacts. Most protons generate bubbles when passing through the target material layer and depositing on the surface of the substrate, thereby triggering hydrogen embrittlement and affecting the service life of the target material.

[0004] Tantalum is considered an ideal material for the transition layer (located between the substrate and the target layer) of the target system in accelerator-based boron neutron capture therapy (AB-BNCT) due to its relatively high hydrogen diffusion coefficient. It can effectively prevent the migration of hydrogen, reduce hydrogen embrittlement, and protect the substrate material under proton beam bombardment. There are various methods for preparing tantalum films, commonly including vacuum plasma spraying (VPS), chemical vapor deposition (CVD), physical vapor deposition (PVD), and magnetron sputtering. Among them, magnetron sputtering has become the best choice due to its significant advantages such as fast sputtering speed, large deposition area, dense and uniform thin film, and strong adhesion. However, the disadvantage of using tantalum as the transition layer is that it is required to reach a thickness of 20 μm to effectively block the proton current, reduce hydrogen diffusion, and thus improve the stability and durability of the system. However, there are significant differences in the physical properties between tantalum and the substrate material (usually copper). When the magnetron sputtering-deposited tantalum film reaches a certain thickness, due to factors such as temperature change and stress accumulation, significant stress concentration will occur inside the film layer, which may lead to cracking and peeling of the thin film.

[0005] Therefore, the current solution mainly involves surface roughening treatment of the target substrate, such as using surface treatment techniques like etching, sandblasting, and polishing to increase the surface roughness of the substrate (CN110914922A). Although the above methods can improve the bonding force between the tantalum film and the substrate to a certain extent, on the one hand, the effect is not ideal enough, and on the other hand, it is difficult to achieve uniform treatment on the surface of substrates with relatively complex shapes. For example, when treating the surface of an irregular substrate by methods such as sandblasting and mechanical polishing, only the contacted surface can be roughened, and it is difficult to take into account local areas with tiny fine structures such as via structures. Summary of the Invention[[ID=⑥]] [[ID=⑦]]

[0006] [[ID=⑧]]To solve the above technical problems, the present invention provides an accelerator neutron source target composite transition layer and its hydrothermal-magnetron sputtering preparation method. The present invention first deposits a TiO2 layer with a specific morphology on the surface of the substrate by the hydrothermal method, and then deposits a tantalum layer by magnetron sputtering. On the one hand, the TiO2 layer can reduce the stress generated between the substrate and the tantalum layer due to the mismatch of thermal expansion coefficients through its own deformation, thus playing a buffering role; on the other hand, the present invention also discovers that the TiO2 lattice structure with a specific morphology can also induce tantalum atoms to deposit in a specific direction during the growth process, avoiding the generation of stress due to the disordered arrangement of atoms inside the tantalum layer, and ultimately improving the bonding force between the tantalum layer and the substrate and reducing the risk of cracking of the tantalum layer. [[ID=⑨]] [[ID=⑩]]

[0007] [[ID=⑪]]The specific technical solution of the present invention is as follows: [[ID=⑫]] [[ID=⑬]]

[0008] [[ID=⑭]]In the first aspect, the present invention provides an accelerator neutron source target composite transition layer, which is located between the substrate and the target layer, and includes a TiO2 layer deposited on the surface of the substrate by the hydrothermal method and calcined and adhered thereto, and a tantalum layer deposited on the surface of the TiO2 layer. [[ID=⑮]]

[0009] In the present invention, a TiO2 layer with a specific morphology is first deposited on the surface of a substrate by a hydrothermal method, and then a tantalum layer is deposited by magnetron sputtering. On the one hand, the TiO2 layer can reduce the stress generated between the substrate and the tantalum layer due to the mismatch of thermal expansion coefficients through its own deformation, thus playing a buffering role. On the other hand, the present invention also finds that the lattice structure of the TiO2 with a specific morphology can also induce tantalum atoms to deposit in a specific direction during the growth process, avoiding the stress generated due to the disordered arrangement of atoms inside the tantalum layer. According to the previous research of the present invention, the microstructure characteristics such as the grain size and orientation of the tantalum layer have an important influence on the stress. The thin film with smaller grains has more grain boundaries, which cannot effectively conduct heat diffusion during the deposition process, and the grain boundaries will block the stress transmission, making the stress more concentrated. Especially during the growth of the thin film, the strongly oriented thin film usually has smaller internal stress because the orientation of the grains can effectively reduce the lattice mismatch and stress transmission; while when the grain orientation is uneven or random, the internal stress of the thin film is larger. Specifically, the lattice structure of titanium dioxide has a good match with some crystal planes of tantalum, thus promoting the growth of tantalum on its surface in an orderly manner. At the same time, titanium dioxide has various nanostructures (such as nanotubes, nanowires, nanospheres, etc.), and these structures can be used as templates or substrates to induce tantalum to self-assemble in a specific manner. In summary, the TiO2 layer with a specific morphology in the present invention can reduce the stress by inducing the orderly growth of tantalum atoms, providing nucleation sites for tantalum atoms, and alleviating the lattice mismatch between the tantalum layer and the substrate, thereby promoting the growth of high-quality tantalum thin films and ultimately achieving the purpose of enhancing the bonding force with the surface of the substrate.

[0010] Specifically, the microstructure of the TiO2 layer includes at least one of the following:

[0011] (a) A stacked nanotube structure;

[0012] (b) A stacked nanosheet structure;

[0013] (c) A nano-networked porous structure;

[0014] (d) A stacked nanosphere structure;

[0015] (e) A stacked nanoneedle-like protrusion structure.

[0016] In the present invention, the effect order of the above several TiO2 layer morphologies is: (a) > (b) > (c) > (d) > (e). The nanosheet and nanotube morphologies have relatively flat surfaces and low lattice defects, and can effectively alleviate the lattice mismatch. The nanosphere morphology has a large surface area, but due to the large particle spacing and the surface structure being less uniform than that of the nanosheet, the stress improvement result is inferior to that of the nanosheet. Compared with the nanosphere, the nano-networked porous structure has better stress dispersion ability. And the nanoneedle-like protrusion structure will cause partial stress concentration due to the spike structure during the subsequent coating process, so the effect is the worst.

[0017] Preferably, the TiO2 layer is formed by hydrothermal reaction of an alkaline deposition solution containing a titanium source to deposit titanate on the surface of a substrate and then through pickling and calcination.

[0018] The above reaction principle is as follows: taking TiO2 powder as the titanium source as an example, first add TiO2 powder to an alkaline solution (taking NaOH as an example). Hydroxylation and partial dissolution occur on the surface of TiO2 to generate soluble titanate ions. The reaction formula is:

[0019] TiO2 (solid) + 2OH − + 2H2O → [Ti(OH)6] 2- ;

[0020] After immersing the substrate in the alkaline deposition solution, under hydrothermal conditions, the dissolved [Ti(OH)6] 2- combines with Na + in the solution to form a layered titanate solid, and a carbonate skeleton layer will nucleate and form on the surface of the substrate. The reaction formula is:

[0021] 3[Ti(OH)6] 2- + 2Na + → Na2Ti3O7 (solid) + 7H2O;

[0022] With the completion of the hydrothermal reaction, transfer the substrate to an acidic solution. The H + participates in dynamic ion exchange to displace the cations in the titanate system, and the titanate is converted into H2Ti3O7 titanic acid, exposing more active sites. The reaction formula is:

[0023] Na2Ti3O7 + 2H2O → H2Ti3O7 (solid) + 2NaOH;

[0024] During the calcination process, the O-H bonds of two adjacent –OH groups (Ti-OH) in the titanium-oxygen skeleton break under high temperature, releasing H2O molecules, and continuous Ti-O-Ti bonds form a three-dimensional network structure, finally generating a crystalline TiO2 layer. The reaction formula is:

[0025] H2Ti3O7 → 3TiO2 + H2O.

[0026] Preferably, the substrate is a flat or irregular surface; for example, a surface with a grid-like structure.

[0027] Compared with traditional processes such as sandblasting and polishing, which are only applicable to flat substrate surfaces, the present invention can form a transition layer with an ideal morphology on the surface of an irregular substrate through hydrothermal-magnetron sputtering technology.

[0028] Preferably, it is characterized in that the thickness range of the TiO2 layer is 200 - 800 nm.

[0029] Preferably, the thickness range of the tantalum layer is 1 - 20 μm.

[0030] Preferably, the substrate is a copper substrate; the target is a lithium target or a beryllium target.

[0031] In a second aspect, the present invention provides a method for preparing the above accelerator neutron source target composite transition layer, which includes the following steps:

[0032] 1) Place the substrate in an alkaline deposition solution containing TiO2 for hydrothermal reaction. TiO2 undergoes hydroxylation and gradually dissolves to form soluble titanate ions. The titanate ions combine with cations in the solution (such as Na + / K + ) to nucleate and form a solid titanate layer on the surface of the substrate.

[0033] 2) Immerse the substrate in an acidic solution. The cations in the titanate are replaced by H + to form titanic acid. Further ion exchange occurs on the surface of the substrate through pickling to form a titanic acid skeleton with more active sites, and then continue to rinse with water until neutral.

[0034] 3) Through calcination, the titanic acid layer on the surface of the substrate undergoes dehydroxylation condensation (Ti - OH + HO - Ti → Ti - O - Ti + H2O) at high temperature to form a crystalline TiO2 layer with different morphologies, and at the same time release the internal participation stress.

[0035] 4) Deposit a tantalum layer on the surface of the TiO2 layer by magnetron sputtering.

[0036] In addition, the present invention can also adjust the microscopic morphology of the TiO2 layer by controlling the conditions of the hydrothermal reaction. When the reaction temperature is relatively low (100 - 110 °C), the solubility of titanate ions is relatively low. In the case of high alkali concentration, the supersaturation of titanate ions increases, and the nucleation rate of titanate on the surface of the substrate is much higher than the growth rate. Therefore, the particles cannot preferentially grow along a specific crystal plane and can only form fine spherical structures by minimizing the surface energy. In the case of low alkali concentration, the supersaturation decreases, the nucleation rate slows down, and it is more inclined to form larger nanospheres, and secondary aggregation occurs due to van der Waals forces to form a cluster network structure. When the reaction temperature rises (130 - 140 °C), the solubility of titanate ions increases. When the alkali concentration is relatively low, nano - needle - like structures with smaller sizes are preferentially formed on the surface of the substrate. As the alkali concentration increases, the concentration of titanate ions increases, and there is sufficient diffusion energy and sufficient diffusion space in the vertical direction at high temperature. The hydrothermal products on the surface of the substrate grow along the axial direction, so nano - sheet shapes are formed. When the hydrothermal time is extended, the nano - sheets have enough time to curl to form nanotubes. Specifically as follows:

[0037] Preferably, the TiO2 layer has a stacked nanotube structure; the alkali concentration in the alkaline deposition solution is 9 - 11 mol / L, and the TiO2 content is 0.4 - 0.5 g / L; the hydrothermal reaction temperature is 130 - 140 °C, and the time is 22 - 24 h.

[0038] Preferably, the TiO2 layer has a stacked nanosheet structure; the alkali concentration in the alkaline deposition solution is 9 - 11 mol / L; the TiO2 content is 0.4 - 0.5 g / L; the hydrothermal reaction temperature is 130 - 140 °C, and the time is 10 - 12 h.

[0039] Preferably, the TiO2 layer has a nano-network porous structure; the alkali concentration in the alkaline deposition solution is 5 - 7 mol / L; the TiO2 content is 0.4 - 0.5 g / L; the hydrothermal reaction temperature is 100 - 110 °C, and the time is 10 - 12 h.

[0040] Preferably, the TiO2 layer has a stacked nanosphere structure; the alkali concentration in the alkaline deposition solution is 9 - 11 mol / L; the TiO2 content is 0.4 - 0.5 g / L; the hydrothermal reaction temperature is 100 - 110 °C, and the time is 10 - 12 h.

[0041] Preferably, the TiO2 layer has a stacked nanoneedle-like protrusion structure; the alkali concentration in the alkaline deposition solution is 5 - 7 mol / L; the TiO2 content is 0.4 - 0.5 g / L; the hydrothermal reaction temperature is 130 - 140 °C, and the time is 10 - 12 h.

[0042] Preferably, in step 1), the alkali in the alkaline deposition solution is NaOH or KOH.

[0043] Preferably, in step 1), the substrate is pre-treated by grinding, polishing, cleaning, and drying.

[0044] Preferably, in step 2), the acidic solution is a 0.1 - 0.5 mol / L hydrochloric acid solution.

[0045] Preferably, in step 3), the calcination temperature is 300 - 500 °C, and the time is 1 - 3 h.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] (1) In the present invention, a TiO2 layer with a specific morphology is first deposited on the surface of the substrate by the hydrothermal method, and then a tantalum layer is deposited by magnetron sputtering. On the one hand, the TiO2 layer can reduce the stress generated between the substrate and the tantalum layer due to the mismatch of thermal expansion coefficients through its own deformation, thus playing a buffering role; on the other hand, the present invention also finds that the lattice structure of the TiO2 with a specific morphology can also induce the tantalum atoms to deposit in a specific direction during the growth process, avoiding the stress generated due to the disordered arrangement of atoms inside the tantalum layer, and finally improving the bonding force between the tantalum layer and the substrate and reducing the risk of cracking of the tantalum layer.

[0048] (2) By controlling the conditions of the hydrothermal reaction, the present invention obtains TiO2 layers with different micro-morphologies.

[0049] (3) Compared with the traditional processes such as sandblasting and polishing which are only applicable to the flat surface of the substrate, the present invention can form a transition layer with an ideal morphology on the surface of the irregular substrate through the hydrothermal-magnetron sputtering technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a scanning picture of the Cu substrate after cleaning in Example 1.

[0051] Figure 2 It is a scanning picture of Cu / TiO2 obtained after roasting the Cu substrate in Example 1.

[0052] Figure 3 It is a scanning picture of Cu / TiO2 obtained after roasting the Cu substrate in Example 2.

[0053] Figure 4 It is a scanning picture of Cu / TiO2 obtained after roasting the Cu substrate in Example 3.

[0054] Figure 5 It is a scanning picture of Cu / TiO2 obtained after roasting the Cu substrate in Example 4.

[0055] Figure 6 It is a scanning picture of Cu / TiO2 obtained after roasting the Cu substrate in Example 5.

[0056] Figure 7 It is a scanning picture of preparing a 20-μm Ta layer by magnetron sputtering on the original Cu substrate in Comparative Example 1.

[0057] Figure 8 It is a scanning picture of preparing a 20-μm Ta layer by magnetron sputtering after the hydrothermal deposition pretreatment in Examples 1-5.

[0058] Figure 9 It is an LSCM picture of Cu / TiO2 obtained after the hydrothermal deposition pretreatment in Example 5.

[0059] Figure 10 LSCM image of the 20-μm Ta layer prepared by magnetron sputtering after hydrothermal deposition pretreatment in Example 5.

[0060] Figure 11 Physical diagram of the sample obtained by plating a 20-μm Ta layer on the original copper substrate in Comparative Example 1 and plating a 20-μm Ta layer after hydrothermal deposition pretreatment in Examples 1-5. Detailed implementation manners

[0061] The present invention will be further described below in conjunction with embodiments.

[0062] In a first aspect, the present invention provides an accelerator neutron source target composite transition layer, which is located between a substrate and a target layer, and includes a TiO2 layer deposited by a hydrothermal method and attached to the surface of the substrate after calcination, and a tantalum layer deposited on the surface of the TiO2 layer. Specifically, the microscopic morphology of the TiO2 layer includes at least one of the following:

[0063] (a) Stacked nanotube structure;

[0064] (b) Stacked nanosheet structure;

[0065] (c) Nanonetwork-like porous structure;

[0066] (d) Stacked nanosphere structure;

[0067] (e) Stacked nanoneedle-like protrusion structure.

[0068] Preferably, the TiO2 layer is formed by a hydrothermal reaction of an alkaline deposition solution containing titanate ions to deposit titanate on the surface of the substrate and then pickling and calcination to form the TiO2 layer.

[0069] The above reaction principle is as follows: First, TiO2 powder is added to an alkaline solution (taking NaOH as an example). Hydroxylation and partial dissolution occur on the surface of TiO2 to generate soluble titanate ions. The reaction formula is:

[0070] TiO2 (solid) + 2OH − + 2H2O → [Ti(OH)6] 2- ;

[0071] After the substrate is immersed in the alkaline deposition solution, under hydrothermal conditions, the dissolved [Ti(OH)6] 2- combines with Na + in the solution to form a layered titanate solid, which nucleates on the surface of the substrate. The reaction formula is:

[0072] 3[Ti(OH)6] 2- + 2Na + → Na2Ti3O7 (solid) + 7H2O;

[0073] After the completion of the hydrothermal reaction, the substrate is transferred to an acidic solution, where H + participates in dynamic ion exchange, replacing the cations in the titanate system. The titanate is converted into H2Ti3O7, exposing more active sites. The reaction formula is:

[0074] Na2Ti3O7 + 2H2O → H2Ti3O7 (solid) + 2NaOH;

[0075] After washing with deionized water, during the calcination process, two adjacent –OH groups (Ti-OH) in the titanium-oxygen framework break the O-H bond under high temperature, releasing H2O molecules, and continuous Ti-O-Ti bonds form a three-dimensional network structure, finally generating a crystalline TiO2 layer. The reaction formula is:

[0076] H2Ti3O7 → 3TiO2 + H2O.

[0077] Preferably, the substrate is a flat or irregular surface; for example, a surface with a grid-like structure.

[0078] Preferably, it is characterized in that: the thickness range of the TiO2 layer is 200 - 800 nm.

[0079] Preferably, the thickness range of the tantalum layer is 1 - 20 μm.

[0080] Preferably, the substrate is a copper substrate; the target is a lithium target or a beryllium target.

[0081] In a second aspect, the present invention provides a method for preparing the above accelerator neutron source target composite transition layer, which includes the following steps:

[0082] 1) Place the substrate in an alkaline deposition solution containing a titanium source (TiO2 powder) for hydrothermal reaction. The TiO2 powder undergoes hydroxylation and gradually dissolves to form soluble titanate ions. The titanate ions combine with the cations in the solution to nucleate on the substrate surface to form a solid titanate layer;

[0083] 2) Immerse the hydrothermal product in a weakly acidic solution. The cations in the titanate will be replaced by H + in the pickling solution to form titanic acid. After pickling, wash the substrate with deionized water to remove excess HCl;

[0084] 3) Calcinate. The titanium-oxygen framework contains Ti-OH groups, which form a three-dimensional crystalline TiO2 layer with different morphologies through dehydroxylation condensation at high temperature, and at the same time remove the residual stress in the film;

[0085] 4) Deposit a tantalum layer on the surface of the TiO2 layer by magnetron sputtering.

[0086] ​Preferably, the TiO2 layer has a stacked nanotube structure; the alkali concentration in the alkaline deposition solution is 9-11 mol / L, and the TiO2 addition amount is 0.4-0.5 g / L; the hydrothermal reaction temperature is 130-140 °C, and the time is 22-24 h.

[0087] Preferably, the TiO2 layer has a stacked nanosheet structure; the alkali concentration in the alkaline deposition solution is 9-11 mol / L; the TiO2 addition amount is 0.4-0.5 g / L; the hydrothermal reaction temperature is 130-140 °C, and the time is 10-12 h.

[0088] Preferably, the TiO2 layer has a nano-network porous structure; the alkali concentration in the alkaline deposition solution is 5-7 mol / L; the TiO2 addition amount is 0.4-0.5 g / L; the hydrothermal reaction temperature is 100-110 °C, and the time is 10-12 h.

[0089] Preferably, the TiO2 layer has a stacked nanosphere structure; the alkali concentration in the alkaline deposition solution is 9-11 mol / L; the TiO2 addition amount is 0.4-0.5 g / L; the hydrothermal reaction temperature is 100-110 °C, and the time is 10-12 h.

[0090] Preferably, the TiO2 layer has a stacked nano-needle-like protrusion structure; the alkali concentration in the alkaline deposition solution is 5-7 mol / L; the TiO2 addition amount is 0.4-0.5 g / L; the hydrothermal reaction temperature is 130-140 °C, and the time is 10-12 h.

[0091] Preferably, in step 1), the alkali in the alkaline deposition solution is NaOH or KOH.

[0092] Preferably, in step 1), the substrate is pre-treated by polishing, cleaning, and drying.

[0093] Preferably, in step 2), the acidic solution is a 0.1-0.5 mol / L hydrochloric acid solution.

[0094] Preferably, in step 3), the calcination temperature is 300-500 °C, and the time is 1-3 h. Specific Examples

[0095] Example 1 (Nanotube Structure Morphology)

[0096] (1) Add 0.4 g·L -1 TiO2 powder to 10 mol·L -1 NaOH aqueous solution to form a deposition solution for standby, and prepare 0.1 mol·L -1 HCl solution as an acid cleaning solution for standby:

[0097] (2) The Cu substrate is polished, buffed, cleaned, and dried for standby, as Figure 1 shown;

[0098] (3) The Cu substrate and the deposition solution are placed together in a polytetrafluoroethylene reaction kettle, the hydrothermal temperature is set at 130 °C, and the hydrothermal time is 24 h for hydrothermal deposition reaction to form a titanate layer;

[0099] (4) The deposited Cu substrate is cleaned with an acid cleaning solution to remove Na + and then rinsed thoroughly with deionized water, and placed in a muffle furnace for calcination at 400 °C for 2 h to obtain Cu / TiO2. The surface morphology is as Figure 2 shown. The hydrothermal reaction temperature in this process is relatively high, and the high-temperature environment and long reaction time provide sufficient energy for the construction of the titanate skeleton. After pickling and calcination, a curly nanotube morphology is formed;

[0100] (5) Target pretreatment: Install the Ta target at the first target position of the magnetron sputtering coating machine; fix the Cu substrate treated in step (4) on the substrate table, and then fix them together on the sample trolley. Close the sputtering chamber, first extract low vacuum. When the air pressure in the sputtering chamber cavity reaches below 10 Pa, then start the molecular pump to extract high vacuum; when the vacuum degree in the sputtering chamber reaches 8×10 -5 Pa, introduce argon for pre-sputtering to remove contaminants on the target surface;

[0101] (6) Coating: Adjust the air pressure in the sputtering chamber to 0.5 Pa, adjust the sputtering power of the Ta target to 500 W, and the duty cycle to 90% for sputtering coating; after sputtering is completed, turn off the magnetron and take out the substrate table to obtain a Cu substrate deposited with a TiO2 layer of about 590 nm and a tantalum layer of 20 μm.

[0102] Example 2 (nanosheet structure morphology)

[0103] (1) Add 0.4 g·L -1 TiO2 powder to 10 mol·L -1 NaOH aqueous solution to prepare the deposition solution for standby, and prepare 0.1 mol·L -1 HCl solution as the acid cleaning solution for standby:

[0104] (2) The Cu substrate is polished, buffed, cleaned, and dried for standby;

[0105] (3) The Cu substrate and the deposition solution are placed together in a polytetrafluoroethylene reaction kettle, the hydrothermal temperature is set at 130 °C, and the hydrothermal time is 12 h for hydrothermal deposition reaction to form a titanate layer;

[0106] (4) The deposited Cu substrate is cleaned with an acid cleaning solution to remove Na+ Then it was rinsed thoroughly with deionized water and calcined in a muffle furnace at 400 °C for 2 h to obtain Cu / TiO2. The surface morphology is as follows Figure 3 shown. At a relatively high reaction temperature, the solubility of titanate ions increases, and there is sufficient diffusion energy at high temperatures and sufficient diffusion space in the vertical direction. The hydrothermal products on the substrate surface grow along the axis, so a nanosheet structure morphology is formed;

[0107] (5) Target pretreatment: Install the Ta target on the first target position of the magnetron sputtering coating machine; Fix the Cu substrate treated in step (4) on the substrate table, and then fix them together on the sample trolley. Close the sputtering chamber, first perform low-vacuum pumping. When the air pressure in the sputtering chamber cavity reaches below 10 Pa, then start the molecular pump for high-vacuum pumping; When the vacuum degree in the sputtering chamber reaches 8×10 -5 Pa, introduce argon gas and perform pre-sputtering to remove contaminants on the target surface;

[0108] (6) Coating: Adjust the air pressure in the sputtering chamber to 0.5 Pa, adjust the sputtering power of the Ta target to 500 W, and the duty cycle to 90%, and perform sputtering coating; After the sputtering is completed, turn off the magnetron and take out the substrate table to obtain a Cu substrate deposited with a TiO2 layer of about 530 nm and a tantalum layer of 20 μm.

[0109] Example 3 (nanosphere structure morphology)

[0110] (1) Add 0.4 g·L -1 TiO2 powder to 10 mol·L -1 NaOH aqueous solution to form a deposition solution for standby, and prepare 0.1 mol·L -1 HCl solution as an acid cleaning solution for standby:

[0111] (2) The Cu substrate was polished, cleaned, and dried for standby;

[0112] (3) Place the Cu substrate and the deposition solution together in a polytetrafluoroethylene reaction kettle, set the hydrothermal temperature to 100 °C, and the hydrothermal time to 12 h to carry out the hydrothermal deposition reaction to form a titanate layer;

[0113] (4) Wash the deposited Cu substrate with the acid cleaning solution to remove Na + Then it was rinsed thoroughly with deionized water and calcined in a muffle furnace at 400 °C for 2 h to obtain Cu / TiO2. The surface morphology is as follows Figure 4 shown. In this process, the reaction temperature is relatively low, the solubility of titanate ions is low, and in the case of high alkali concentration, the supersaturation of titanate ions increases. The nucleation rate of titanate on the substrate surface is much higher than the growth rate, so the particles cannot grow preferentially along a specific crystal plane and can only form a fine nanospherical structure by minimizing the surface energy;

[0114] (5) Target pre-treatment: Install the Ta target on the first target position of the magnetron sputtering coating machine; fix the Cu substrate processed in step (4) on the substrate table, and then fix them together on the sample trolley. Close the sputtering chamber, first perform low-vacuum pumping. When the air pressure in the sputtering chamber cavity reaches below 10 Pa, then start the molecular pump for high-vacuum pumping; when the vacuum degree in the sputtering chamber reaches 8×10 -5 Pa, introduce argon gas and perform pre-sputtering to remove contaminants on the target surface;

[0115] (6) Coating: Adjust the air pressure in the sputtering chamber to 0.5 Pa, adjust the sputtering power of the Ta target to 500 W, and the duty cycle to 90%, and perform sputtering coating; after the sputtering is completed, turn off the magnetron and take out the substrate table to obtain a Cu substrate deposited with a TiO2 layer of about 480 nm and a tantalum layer of 20 μm.

[0116] Example 4 (Nanoscale network-like porous structure morphology)

[0117] (1) Add 0.4 g·L -1 TiO2 powder to 5 mol·L -1 NaOH aqueous solution to form a deposition solution for standby, and prepare 0.1 mol·L -1 HCl solution as an acid cleaning solution for standby:

[0118] (2) The Cu substrate is polished, buffed, cleaned, and dried for standby;

[0119] (3) Place the Cu substrate and the deposition solution together in a polytetrafluoroethylene reaction kettle, set the hydrothermal temperature to 100 °C, and the hydrothermal time to 12 h to perform hydrothermal deposition reaction to form a titanate layer;

[0120] (4) Wash the deposited Cu substrate with the acid cleaning solution to remove Na + and then rinse it thoroughly with deionized water, and place it in a muffle furnace for calcination at 400 °C for 2 h to obtain Cu / TiO2. The surface morphology is as Figure 5 shown. When the reaction temperature is relatively low and the alkali concentration is relatively low, the supersaturation of titanate ions decreases, the nucleation rate slows down, and it is more inclined to form larger nanospheres. Due to van der Waals forces, secondary aggregation occurs, forming a cluster-like nanoscale network-like porous structure;

[0121] (5) Target pre-treatment: Install the Ta target on the first target position of the magnetron sputtering coating machine; fix the Cu substrate processed in step (4) on the substrate table, and then fix them together on the sample trolley. Close the sputtering chamber, first perform low-vacuum pumping. When the air pressure in the sputtering chamber cavity reaches below 10 Pa, then start the molecular pump for high-vacuum pumping; when the vacuum degree in the sputtering chamber reaches 8×10 -5After reaching 10 Pa, argon gas is introduced for pre-sputtering to remove contaminants on the surface of the target.

[0122] (6)Coating: Adjust the air pressure in the sputtering chamber to 0.5 Pa, adjust the sputtering power of the Ta target to 500 W, and the duty cycle to 90%, and perform sputtering coating; after sputtering is completed, turn off the magnetron and take out the substrate table to obtain a Cu substrate deposited with a TiO2 layer of about 450 nm and a tantalum layer of 20 μm.

[0123] Example 5 (Morphology of nano-needle-like protrusion structure)

[0124] (1)Add 0.4 g·L -1 TiO2 powder to 5 mol·L -1 NaOH aqueous solution to form a deposition solution for standby, and prepare 0.1 mol·L -1 HCl solution as an acid cleaning solution for standby:

[0125] (2)The Cu substrate is polished, cleaned, and dried for standby;

[0126] (3)Place the Cu substrate and the deposition solution together in a polytetrafluoroethylene reaction kettle, set the hydrothermal temperature to 130 °C, and the hydrothermal time to 12 h for hydrothermal deposition reaction to form a titanate layer;

[0127] (4)Clean the deposited Cu substrate with the acid cleaning solution to remove Na + and then rinse it thoroughly with deionized water, and place it in a muffle furnace for calcination at 400 °C for 2 h to obtain Cu / TiO2. The surface morphology is as Figure 6 shown. When the reaction temperature is relatively high and the alkali concentration is relatively low, nano-needle-like protrusion structures with smaller sizes are preferentially formed on the surface of the substrate;

[0128] (5)Target pretreatment: Install the Ta target in the first target position of the magnetron sputtering coating machine; fix the Cu substrate processed in step (4) on the substrate table, and then fix them together on the sample trolley. Close the sputtering chamber, first perform low-vacuum pumping. When the air pressure in the sputtering chamber cavity reaches below 10 Pa, then start the molecular pump for high-vacuum pumping; when the vacuum degree in the sputtering chamber reaches 8×10 -5 Pa, introduce argon gas for pre-sputtering to remove contaminants on the surface of the target.

[0129] (6)Coating: Adjust the air pressure in the sputtering chamber to 0.5 Pa, adjust the sputtering power of the Ta target to 500 W, and the duty cycle to 90%, and perform sputtering coating; after sputtering is completed, turn off the magnetron and take out the substrate table to obtain a Cu substrate deposited with a TiO2 layer of about 420 nm and a tantalum layer of 20 μm.

[0130] Comparative Example 1 (Without TiO2 layer)

[0131] (1)The Cu substrate is polished, buffed, cleaned, and dried for later use;

[0132] (2)Target pre-treatment: Install the Ta target on the first target position of the magnetron sputtering coating machine; Fix the Cu substrate treated in step (1) on the substrate table, and then fix them together on the sample trolley. Close the sputtering chamber, first extract low vacuum. When the air pressure in the sputtering chamber cavity reaches below 10 Pa, then start the molecular pump to extract high vacuum; When the vacuum degree in the sputtering chamber reaches 8×10 -5 Pa, introduce argon gas for pre-sputtering to remove contaminants on the target surface;

[0133] (3)Coating: Adjust the air pressure in the sputtering chamber to 0.5 Pa, adjust the sputtering power of the Ta target to 500 W, and the duty cycle to 90% for sputtering coating; After the sputtering is completed, turn off the magnetron and take out the substrate table to obtain a Cu substrate deposited with a 20-μm tantalum layer (as Figure 7 shown). Cracking occurs on the surface of the 20-μm tantalum layer obtained by magnetron sputtering on the copper substrate without the TiO2 layer under the action of stress.

[0134] Performance testing

[0135] Figure 7 This is a scanning picture of the 20-μm Ta layer prepared by magnetron sputtering on the original Cu substrate in Comparative Example 1. Figure 8 This is a scanning picture of the 20-μm Ta layer prepared by magnetron sputtering after hydrothermal deposition pretreatment in Examples 1-5. By comparison, Figure 7 obvious local cracking and peeling phenomena occur in the Ta layer.

[0136] Figure 9 This is the LSCM diagram of Cu / TiO2 obtained after hydrothermal deposition pretreatment in Example 5, and it can be seen that the surface roughness of the substrate is large at this time. Figure 10 This is the LSCM diagram of the 20-μm Ta layer prepared by magnetron sputtering after hydrothermal deposition pretreatment in Example 5. The tantalum atoms fully fill the Figure 9 voids in it. The film has a stronger bonding force, and the internal stress can be released along the rough surface. Finally, the surface roughness of the obtained Cu / TiO2 / Ta decreases, and the surface height difference reduces.

[0137] Figure 11 This is the physical picture of the sample obtained by plating a 20-μm Ta layer on the original copper substrate in Comparative Example 1 and plating a 20-μm Ta layer after hydrothermal deposition pretreatment in Examples 1-5 (arranged from left to right). After coating the original copper substrate, almost the entire surface cracks and exposes the copper substrate, while the sample morphology obtained by first hydrothermally depositing to construct the microstructure morphology and then magnetron sputtering coating is smoother and more uniform, without cracking and peeling phenomena.

[0138] Stress tests were conducted on the samples obtained from each example and comparative example, and the results are shown in the following table:

[0139]

[0140] During the cooling process, since the thermal expansion coefficients of copper and tantalum are 16.5 µm·m -1 ·K -1 and 6.3 µm·m -1 ·K -1 respectively, the large difference will cause the copper substrate to shrink more than the tantalum layer, resulting in more internal stress accumulation in the tantalum layer on the substrate (Comparative Example 1). When the TiO2 layer is introduced, TiO2 varies according to different crystal structures, and the average thermal expansion coefficient is about 8 - 8.5 µm·m -1 ·K -1 , which is between copper and tantalum, and can relieve the stress problem caused by the mismatch of thermal expansion coefficients between the substrate and the tantalum film. Although the roughness of the copper substrate surface will also cause stress concentration, it also provides a path and way for stress release, making the stress in Examples 1 - 5 lower than that of the original copper. At the same time, the lattice structure of titanium dioxide has a good match with some crystal planes of tantalum, thus promoting the growth of tantalum on its surface in an orderly manner. At the same time, various nanostructured morphologies of titanium dioxide (such as nanotubes, nanosheets, nanospheres, etc.) can induce the self-assembly of tantalum in a specific way. Among them, the ranking in terms of effectiveness is: nanotube structure > nanosheet structure > nano-networked porous structure > nanosphere structure > nano-needle-like protrusion structure.

[0141] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0142] The above are only preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. An accelerator neutron source target, comprising a substrate and a target material layer, characterized in that: A composite transition layer is provided between the substrate and the target layer, including a TiO2 layer attached to the surface of the substrate and a tantalum layer deposited on the surface of the TiO2 layer; The TiO2 layer is formed by hydrothermal reaction of an alkaline deposition solution containing TiO2 to deposit titanate on the surface of the substrate and then formed after pickling and calcination; The microscopic morphology of the TiO2 layer includes at least one of the following: a) A stacked nanotube structure: the alkali concentration in the alkaline deposition solution is 9-11 mol / L, TiO2 is 0.4-0.5 g / L; the hydrothermal reaction temperature is 130-140 °C, and the time is 22-24 h; b) A stacked nanosheet structure: the alkali concentration in the alkaline deposition solution is 9-11 mol / L; TiO2 is 0.4-0.5 g / L; the hydrothermal reaction temperature is 130-140 °C, and the time is 10-12 h; c) A nano-network porous structure: the alkali concentration in the alkaline deposition solution is 5-7 mol / L; TiO2 is 0.4-0.5 g / L; the hydrothermal reaction temperature is 100-110 °C, and the time is 10-12 h; d) A stacked nanosphere structure: the alkali concentration in the alkaline deposition solution is 9-11 mol / L; TiO2 is 0.4-0.5 g / L; the hydrothermal reaction temperature is 100-110 °C, and the time is 10-12 h; e) A stacked nanoneedle-like protrusion structure: the alkali concentration in the alkaline deposition solution is 5-7 mol / L; TiO2 is 0.4-0.5 g / L; the hydrothermal reaction temperature is 130-140 °C, and the time is 10-12 h.

2. The accelerator neutron source target according to claim 1, wherein: The substrate is a flat or irregular surface.

3. The accelerator neutron source target according to claim 1 or as described above, characterized in that: The thickness range of the TiO2 layer is 200-800 nm.

4. The accelerator neutron source target according to claim 1 or 3, characterized in that: The thickness range of the tantalum layer is 1-20 μm.

5. The accelerator neutron source target according to claim 1, wherein: The substrate is a copper substrate; the target is a lithium target or a beryllium target.

6. A method for preparing an accelerator neutron source target according to any one of claims 1-5, characterized in that: The preparation of the composite transition layer includes: 1) Placing the substrate in an alkaline deposition solution containing TiO2 for hydrothermal reaction to nucleate and form a titanate layer on the surface of the substrate; 2) Immersing the substrate in an acidic solution to convert the titanate layer into a titanic acid layer, and then washing with water; 3) Calcining to convert the titanic acid layer into a TiO2 layer; 4) Depositing a tantalum layer on the surface of the TiO2 layer by magnetron sputtering.

7. The preparation method according to claim 6, characterized in that: In step 1), the substrate is pre-treated by grinding, polishing, cleaning, and drying.

8. The preparation method according to claim 6, characterized in that: In step 1), the alkali in the alkaline deposition solution is NaOH or KOH.

9. The preparation method according to claim 6, characterized in that: In step 2), the acidic solution is a 0.1-0.5 mol / L hydrochloric acid solution.

10. The preparation method according to claim 6, characterized in that: In step 3), the calcination temperature is 300-500 °C, and the time is 1-3 h.

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