On-chip synthesis of niobium diselenide superconducting nanowires and applications thereof

Abstract

The application discloses an on-chip synthesis method of niobium diselenide superconducting nanowires and application thereof. The application forms a micron-level confined cavity by face-to-face buckling of a substrate loaded with a niobium precursor and a substrate coated with elemental selenium powder, and high-crystalline-quality niobium diselenide van der Waals superconducting nanowires can be grown on various microelectronic substrates through reduction atmosphere high-temperature annealing treatment. The whole process does not need photolithography patterning process, and the closed melting confined system eliminates the generation of oxidation impurities from the source; the geometric size of the nanowires can be accurately controlled through the concentration of the precursor solution, and various device substrates are compatible; the prepared product has high residual resistance ratio, narrow superconducting transition interval, super-high in-plane upper critical magnetic field, and simultaneously supports controllable heteroatomic doping modification, effectively overcomes the technical shortcomings of oxidation defects, poor controllability, dependence on photolithography and difficulty in scaling of traditional etching and pre-patterned selenization process, and is suitable for low-dimensional superconducting functional devices such as superconducting single-photon detectors and quantum phase slip devices.

Description

Technical Field

[0001] This invention relates to an on-chip synthesis method for preparing high-purity niobium diselenide van der Waals superconducting nanowires using photolithography-free, melt-confined topological transformation and its application. Background Technology

[0002] Superconducting nanowires are core functional units in superconducting electronics and quantum detection. Superconducting single-photon detectors based on superconducting nanowires possess key advantages such as high detection efficiency, fast response speed, and extremely low dark count, making them crucial components for quantum communication, deep-space weak light detection, and single-photon imaging systems. The transition metal chalcogenide NbSe2 possesses a natural van der Waals layered crystal structure, exhibiting superconductivity with adjustable layer thickness, strong anisotropic thermal conductivity, and atomic-level structural homogeneity, making it an ideal material for fabricating high-performance one-dimensional superconducting nanowires. Currently, there are two main process routes for the fabrication of NbSe2 van der Waals superconducting nanowires, but both suffer from insurmountable technical drawbacks:

[0003] (1) Top-down stripping etching process: First, mechanical stripping is used to obtain single-crystal NbSe2 thin films, and then the nanowires are patterned by electron beam lithography + reactive ion etching. This process introduces a large number of surface oxidation defects during the entire process of photolithography and plasma etching, which seriously degrades the intrinsic superconducting performance; at the same time, the nanowire size and composition control window is narrow, making it impossible to achieve large-area array fabrication and resulting in poor mass production adaptability.

[0004] (2) Pre-patterned precursor topological selenization process: Niobium-based precursor nanowires are first prepared by photolithography, and then converted into NbSe2 nanowires by high-temperature selenization reaction. Niobium oxides remaining in the precursor film will remain as impurities inside the finished nanowires after selenization, causing the superconducting transition range to widen, the upper critical magnetic field to drop significantly, and the long-term stability of the material to be poor; moreover, the whole process depends on high-precision photolithography equipment, the process flow is long and the production cost is high.

[0005] Neither of the two traditional processes mentioned above can achieve direct on-chip in-situ growth of NbSe2 superconducting nanowires that are oxidation-free, have high-precision tunable dimensions, and are compatible with multiple substrates, severely restricting the engineering development of high-performance superconducting quantum detection devices. Therefore, there is an urgent need in the industry to develop a new method for the in-situ synthesis of NbSe2 van der Waals superconducting nanowires that is photolithography-free, has low defects, is scalable, and has universal substrate compatibility. Summary of the Invention

[0006] Objective of this invention: Addressing the technical bottlenecks of existing etching and pre-patterned selenization methods for preparing NbSe2 superconducting nanowires, including oxidation contamination, weak size control, reliance on photolithography, and difficulty in large-scale fabrication, the core objective of this invention is to provide an on-chip synthesis method using melt-confined topological deselenization conversion. This method eliminates the need for photolithography patterning throughout the process, enabling in-situ growth of oxygen-free, high-crystallinity, and precisely tunable NbSe2 superconducting nanowires on various commonly used microelectronic substrates. The resulting products exhibit excellent superconductivity and support directional array fabrication and controllable heteroatom doping modification. Another objective of this invention is to provide applications for the niobium diselenide superconducting nanowires obtained by this synthesis method in the fabrication of superconducting single-photon detectors or low-dimensional superconducting quantum devices.

[0007] Technical solution: The present invention provides a method for on-sheet synthesis of niobium diselenide superconducting nanowires, comprising the following steps:

[0008] (1) Prepare niobium precursor support substrate and selenium source substrate respectively;

[0009] (2) The niobium precursor substrate and the selenium source substrate are fastened face to face to form a closed confined cavity. The fastened bilayer substrate is placed in a tube furnace and Ar / H2 mixed reducing protective gas is continuously introduced.

[0010] (3) High temperature treatment: molten selenium is used to construct a selenium-rich reducing environment in a confined cavity, and single-crystal Nb2Se9 one-dimensional nanowire intermediates are grown in situ on the surface of the niobium precursor substrate.

[0011] (4) Continue heating treatment, and the Nb2Se9 one-dimensional nanowires undergo in-situ topological deselenization lattice reconstruction, transforming into layered 2H phase NbSe2 superconducting nanowires;

[0012] (5) Natural cooling under a protective atmosphere yields NbSe2 van der Waals superconducting nanowires grown in situ on the substrate.

[0013] In step (1), when preparing the niobium precursor substrate, the niobium precursor solution used is an aqueous solution of ammonium niobate oxalate, with a concentration of 1~80 mM. As the precursor concentration increases, the length, width, thickness, and cross-sectional area of ​​the nanowires increase linearly. However, when the precursor solution concentration exceeds 80 mM, the nanowire growth density increases significantly, and the geometric dimensions of a single nanowire tend to stabilize. The niobium precursor solution is spin-coated onto the substrate at a speed of 1000 rpm or more and a spin-coating time of 30 s or more. By controlling the concentration of ammonium niobate oxalate solution from 1~80 mM, the length, width, and thickness of the NbSe2 superconducting nanowires are precisely controlled. When the solute concentration is greater than 80 mM, the nanowire growth density increases, and the size of a single nanowire tends to stabilize. The preparation of the selenium source substrate includes coating the substrate with elemental selenium powder.

[0014] The aforementioned substrate must possess the following physical properties:

[0015] 1) The surface roughness of the substrate is ≤0.5 nm;

[0016] 2) The substrate is not easily hydrolyzed;

[0017] 3) The substrate will not change during any of the processes, nor will it affect the physical and chemical properties of the thin film.

[0018] The substrate can be selected from any one of Si substrate, Si / SiO2 substrate, Si3N4 substrate, Al2O3 substrate, MgO substrate, mica substrate or quartz substrate.

[0019] In step (2), the Ar / H2 mixed protective gas flow ratio is argon:hydrogen = 4:1~1:1. The niobium precursor substrate is placed on top, and the selenium source substrate is placed below. In step (3), the high-temperature treatment is carried out at a heating rate of 20~50 ℃ / min to 350~450 ℃ and held for 10~60 min. In step (4), the heating treatment is continued at a heating rate of 20~50 ℃ / min to 600~800 ℃ and held for 5~10 min.

[0020] Alternatively, vanadium salts can be added to the niobium precursor solution to prepare vanadium-doped modified NbSe2 superconducting nanowires.

[0021] The application of niobium diselenide superconducting nanowires prepared by the method described in this invention in the preparation of superconducting single-photon detectors or low-dimensional superconducting quantum devices.

[0022] This invention involves bonding a substrate loaded with niobium precursor face-to-face with a substrate coated with elemental selenium powder to form a micrometer-scale confined cavity. After high-temperature annealing in a reducing atmosphere, high-crystallinity niobium diselenide van der Waals superconducting nanowires can be grown on various microelectronic substrates. The entire process eliminates the need for photolithography patterning, and the closed-loop molten confinement system prevents the generation of oxidation impurities at the source. The nanowire geometry can be precisely controlled by the precursor solution concentration, making it compatible with various device substrates. The prepared product exhibits a high residual resistivity, a narrow superconducting transition range, and an ultra-high in-plane upper critical magnetic field. It also supports controllable heteroatom doping modification, effectively overcoming the technical shortcomings of traditional etching and pre-patterned selenization processes, such as oxidation defects, poor controllability, reliance on photolithography, and difficulty in large-scale production. This method is suitable for low-dimensional superconducting functional devices such as superconducting single-photon detectors and quantum phase-slip devices. This invention proposes an on-chip synthesis method for NbSe2 superconducting nanowires based on a molten confinement topological chemical transformation strategy. A molten confined selenium-rich oxygen-free reaction environment was constructed to suppress the generation of oxidation impurities in nanowires. One-dimensional Nb2Se9 nanowire intermediate states were formed at low temperature. Atomic-level topological lattice reconstruction was achieved through mild deselenization. The one-dimensional linear morphology of the nanowires was completely preserved throughout the entire conversion process, without any breakage, damage, or agglomeration.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The reducing atmosphere and molten selenium closed confinement system proposed in the method of the present invention can completely contain Nb in the precursor. 5+ Restored to Nb 4+ The finished nanowires are free of Nb2O5 oxide impurities. The prepared NbSe2 superconducting nanowires have a residual resistivity of up to 3.7, a superconducting transition temperature of 6.71 K, and a superconducting transition width of only 0.51 K; the in-plane upper critical magnetic field is as high as 24.87 T, which is far higher than the Pauli paramagnetic limit, and they have strong spin-orbit coupling induced Ising superconductivity; (2) The method of the present invention does not require patterning processes such as electron beam lithography and laser direct writing lithography, avoiding oxidation damage and lattice defects caused by lithography and etching, greatly reducing equipment investment, shortening the preparation cycle, and reducing production costs. It can be directly grown on various commonly used microelectronic substrates such as Si, Si / SiO2, Si3N4, Al2O3, MgO, mica, and quartz, perfectly adapting to the existing micro-nano fabrication device substrate system; (3) The method of the present invention can precisely control the length, width, and thickness of the nanowires by simply adjusting the concentration of the precursor solution; the solution-based precursor system can conveniently introduce heteroatoms such as vanadium to achieve quantitative and controllable doping, precisely control the crystal stacking structure and superconducting physical properties, and expand the research and development space of new superconducting functional devices. Attached Figure Description

[0024] Figure 1 Schematic diagrams and performance radar comparisons of three NbSe2 superconducting nanowire fabrication routes are shown. In particular, a) is a schematic diagram of the top-down etching method for fabricating NbSe2 nanowires, where a continuous thin film is patterned into NbSe2 nanowires through a top-down etching process; b) is a schematic diagram of the topological chemistry method, where NbO with a predetermined one-dimensional morphology is first prepared. X Nanowires are then transformed into NbSe2 nanowires by selenization while maintaining their overall morphology. c is a schematic diagram of melt-confined topological transformation growth of NbSe2 nanowires. First, Nb2Se9 nanowires are directly formed on the target substrate using melt confinement growth, and then Nb2Se9 is transformed into NbSe2 nanowires through topological deselelation. d is a comparison of the comprehensive performance of the three preparation methods. The radar chart compares the three routes—downward etching, topological chemical preparation, and melt confinement growth—in terms of material quality, tunability, and scalability.

[0025] Figure 2 This is a schematic diagram of melt-confined topological transformation growth;

[0026] Figure 3High-resolution transmission electron microscopy (TEM) images of NbSe2 superconducting nanowires prepared in Example 1; where a is a high-resolution TEM image of the NbSe2 nanowire in-plane; b is a high-resolution TEM image of the cross-section of the NbSe2 nanowire and a magnified view of its atomic structure.

[0027] Figure 4 The figures show the low-temperature electrical transport characteristics of the NbSe2 nanowire device prepared in Example 1. Figure a shows the resistance-temperature characteristics of the NbSe2 nanowire device, with the main plot displaying the RT curves from low temperature to room temperature. The resistance in the normal state increases approximately monotonically with increasing temperature, exhibiting metallic conductivity. Around 7K, the resistance rapidly decreases to near zero, indicating a superconducting transition. The upper left inset shows an optical micrograph of the device, and the lower right inset magnifies the superconducting transition process in the low-temperature region. Figure b shows the superconducting transition curves under different magnetic fields.

[0028] Figure 5 Optical microscope images of niobium precursor nanowires with a concentration of 1-200 mM in Example 2;

[0029] Figure 6 The image shows a scanning electron microscope image of nanowires with a niobium precursor concentration of 1-80 mM in Example 2.

[0030] Figure 7 These are atomic force microscope images of nanowires with niobium precursor concentrations of 1-80 mM in Example 2.

[0031] Figure 8 The diagram shows the relationship between niobium precursor concentration and the length, width, thickness, and cross-sectional area of ​​NbSe2 superconducting nanowires in Example 2, along with a scatter plot. In this diagram, a represents the relationship between the thickness and cross-sectional area of ​​the NbSe2 nanowires and the Nb precursor concentration (where d represents thickness, A represents cross-sectional area, and w represents width); b represents the variation of the length and width of the NbSe2 nanowires with the Nb precursor concentration.

[0032] Figure 9 The image shows the Raman spectrum of the vanadium-doped NbSe2 superconducting nanowires prepared by doping V in Example 3.

[0033] Figure 10 Optical microscope images of NbSe2 nanowires prepared on different substrates in Example 4. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Example 1: Preparation of pure-phase NbSe2 superconducting nanowires on Si / SiO2 substrate

[0036] A 20 mM niobium ammonium oxalate aqueous solution was prepared and spin-coated onto a 10 × 10 mm Si / SiO2 substrate with a 265 nm SiO2 layer. The spin-coating parameters were 3000 rpm and 30 s. This substrate served as the niobium precursor substrate. A separate Si / SiO2 substrate of the same specifications was prepared, with 2 mg of elemental selenium powder uniformly deposited on its surface as the selenium source substrate. The niobium precursor substrate was placed on top, and the selenium source substrate on the bottom. The two substrates were sealed face-to-face and placed in a tube furnace. An Ar / H2 mixed protective gas was continuously introduced, with a gas flow rate of Ar (20 sccm) + H2 (5 sccm). The temperature was increased to 400 °C at a rate of 50 °C / min and held at this temperature for 30 min. Single-crystal Nb2Se9 nanowire intermediates were formed on the surface of the niobium precursor substrate. The temperature was then increased to 600 °C at a rate of 50 °C / min and held at this temperature for 5 min to complete the topological transformation of Nb2Se9 to 2H-NbSe2 (e.g., Figure 2 (As shown). Heating was stopped, and the tube furnace was allowed to cool naturally to room temperature under a protective atmosphere. The substrate was then removed. Uniformly sized, oxide-free NbSe2 superconducting nanowires were directly grown on the Si / SiO2 substrate surface (the NbSe2 superconducting nanowires were measured to be 25.4 nm thick, 300 nm wide, and 28.5 μm long). The fabrication process is as follows. Figure 1 As shown.

[0037] The NbSe2 nanowires prepared in this embodiment were analyzed by high-resolution transmission electron microscopy, and the results are as follows: Figure 3 As shown, a) is a high-resolution transmission electron microscopy image of NbSe2 nanowires. Continuous, regularly arranged lattice fringes can be observed in the image, and the interplanar spacing is measured to be approximately 0.29 nm, which is basically consistent with the (100) interplanar spacing of hexagonal NbSe2. b) shows the cross-sectional atomic structure of the NbSe2 nanowires. The low-magnification image on the left shows a multi-layered, parallel-arranged layered structure, while the magnified image on the right further reveals a clear atomic arrangement. The lattice maintains good continuity within the observation area, indicating that the obtained NbSe2 has high crystallinity.

[0038] Fabrication of NbSe2 nanowire devices: Standard micro / nano fabrication processes were employed. The devices were fabricated directly on a Si / SiO2 substrate on which NbSe2 nanowires were grown. First, LOR10B and AZ1500 double-layer photoresist were spin-coated sequentially onto the NbSe2 superconducting nanowires. A four-probe electrode pattern was then defined on both sides of the NbSe2 superconducting nanowires using UV exposure and development. After development, Ti and Au were sequentially deposited using electron beam evaporation, with Ti serving as the adhesion layer and Au as the conductive electrode. Finally, the sample was immersed in a photoresist stripping solvent to remove the photoresist and excess metal, retaining the four metal electrodes in contact with the nanowires, thus obtaining the desired NbSe2 nanowire device. Figure 4The four-terminal NbSe2 nanowire device is shown in the upper left inset of figure a. Electrical tests were performed in a physical property measurement system, using the four-probe method to measure the resistance-temperature curves in the range of 2-300 K. Furthermore, magnetic fields perpendicular and parallel to the sample plane were applied, and the superconducting transition curves under different magnetic fields were recorded. The upper critical magnetic field H in both directions was extracted based on the transition temperature. c2 .

[0039] Electrical tests were performed on the NbSe2 superconducting nanowires. First, the resistance-temperature (RT) curves of the NbSe2 nanowire device from low temperature to room temperature were measured using the four-probe method. A schematic diagram of the NbSe2 nanowire device is shown below. Figure 4 As shown in the upper left corner illustration of section a. Figure 4 It can be seen that the resistance of the NbSe2 nanowire device decreases with decreasing temperature, exhibiting metallic transport characteristics. Its residual resistivity ratio (RRR) is 3.7, indicating good conductivity and crystal quality. The superconducting transition temperature is 6.71 K, and the superconducting transition width is 0.51 K; the narrow transition range indicates good uniformity of the superconducting properties of the nanowire. Subsequently, in-plane and out-of-plane magnetic fields were applied, and the RT curves at 0-9 T were measured to extract the upper critical magnetic field H at each temperature. c2 And then fit H c2 The -T phase diagram yields an in-plane upper critical magnetic field of 24.87 T.

[0040] Example 2

[0041] The experimental procedure was the same as in Example 1, except that the concentration of the niobium ammonium oxalate precursor aqueous solution was changed to 1 mM, 2 mM, 5 mM, 10 mM, 20 mM, 40 mM, 80 mM, 100 mM, and 200 mM, respectively, to obtain a series of NbSe2 superconducting nanowires. Their optical microscope, scanning electron microscope, and atomic force microscope images are shown below. Figure 5-7 As shown, the length of NbSe2 superconducting nanowires increases with increasing niobium precursor solution concentration, but when the concentration exceeds 80 mM, the nanowires exhibit stacking and aggregation, and the length change is not significant (e.g., ...). Figure 5 (As shown). The width of the NbSe2 nanowires varies with the concentration of the niobium precursor solution as follows: Figure 6 As shown, it is evident that the nanowire width gradually increases with increasing concentration from 1 mM to 80 mM. The thickness of the NbSe2 nanowires varies with solution concentration as follows: Figure 7 As shown, the left side displays atomic force microscope images of NbSe2 nanowires with different concentrations, and the right side displays the corresponding cross-sectional height curves. The distance between the upper and lower dashed lines in the height curve is taken as the nanowire thickness, and the area of ​​the trapezoid is taken as the cross-sectional area of ​​the nanowire. The results show that both the nanowire thickness and cross-sectional area increase.

[0042] Further statistical analysis was conducted on 50 nanowires selected from concentrations of 1-80 mM, systematically analyzing the variations in length, width, thickness, and cross-sectional area of ​​the NbSe2 nanowires with the concentration of the precursor solution. The changes in thickness and cross-sectional area of ​​the NbSe2 nanowires with the Nb precursor concentration are shown below. Figure 8 As shown in Figure a, with the increase of niobium precursor concentration, the nanowires exhibit a significant positive correlation between thickness and cross-sectional area. The changes in length and width of NbSe2 nanowires with Nb precursor concentration are shown in Figure a. Figure 8 As shown in Figure b, the length and width of the nanowires generally increase with increasing solution concentration, but the growth rate gradually slows down, exhibiting a nonlinear positive correlation. The results indicate that increasing the precursor solution concentration can simultaneously promote the three-dimensional growth of the nanowires in the transverse, longitudinal, and thickness directions. In summary, by statistically analyzing the geometric dimensions (length, width, thickness, and cross-sectional area) of NbSe2 nanowires at different niobium precursor concentrations, fitting curves between the nanowire geometric dimensions and the niobium precursor concentration were obtained, demonstrating that precise control of the nanowire size can be achieved by adjusting the concentration of the niobium precursor solution.

[0043] Example 3: Preparation of 10 at.% vanadium-doped modified NbSe2 superconducting nanowires

[0044] Vanadium salt was quantitatively added to a 20 mM niobium ammonium oxalate precursor aqueous solution to control the V / Nb atomic ratio in the solution to 10%; the entire process parameters of spin coating, heating, holding, and cooling were completely consistent with those in Example 1; vanadium-doped NbSe2 superconducting nanowires were prepared, and Raman spectroscopy characterization confirmed uniform vanadium doping (e.g., ...). Figure 9 As shown in the figure, this preparation method has the scalability of the material system.

[0045] Example 4: Fabrication of NbSe2 nanowires on different substrates

[0046] The preparation process is the same as in Example 1, except that Si, SiO2, Si3N4, Al2O3, mica, MgO, or quartz substrates are selected as the niobium precursor carrier substrates, and a 20 mM niobium ammonium oxalate aqueous solution is used for spin-coating. The remaining heat treatment process is consistent with Example 1. The prepared NbSe2 nanowires are as follows: Figure 10 As shown, the nanowires maintained a relatively uniform morphology on all substrates, indicating that melt-confined growth of NbSe2 superconducting nanowires has good substrate scalability and universality.

Claims

1. A method for on-sheet synthesis of niobium diselenide superconducting nanowires, characterized in that, Includes the following steps: (1) Prepare niobium precursor support substrate and selenium source substrate respectively; (2) The niobium precursor substrate and the selenium source substrate are fastened face to face to form a closed confined cavity. The fastened bilayer substrate is placed in a tube furnace and Ar / H2 mixed protective gas is continuously introduced. (3) High temperature treatment to grow single-crystal Nb2Se9 one-dimensional nanowire intermediates in situ on the surface of niobium precursor substrate; (4) Continue heating treatment to transform Nb2Se9 one-dimensional nanowires into layered 2H phase NbSe2 superconducting nanowires; (5) Natural cooling under a protective atmosphere yields NbSe2 van der Waals superconducting nanowires grown in situ on the substrate.

2. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 1, characterized in that, In step (1), when preparing the niobium precursor carrier substrate, the niobium precursor solution used is an aqueous solution of ammonium niobate oxalate, and the concentration of the niobium precursor solution is 1~80 mM; the niobium precursor solution is spin-coated onto the substrate at a speed of more than 1000 rpm and a spin-coating time of more than 30 s.

3. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 1, characterized in that, In step (1), the preparation of the selenium source substrate includes coating the substrate with elemental selenium powder.

4. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 2 or 3, characterized in that, The substrate has a surface roughness of ≤0.5 nm, is resistant to hydrolysis, and does not undergo deformation during high-temperature heat treatment.

5. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 4, characterized in that, The substrate can be selected from any one of the following: Si substrate, Si / SiO2 substrate, Si3N4 substrate, Al2O3 substrate, MgO substrate, mica substrate or quartz substrate.

6. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 1, characterized in that, In step (2), the flow ratio of the Ar / H2 mixed protective gas is: argon:hydrogen = 4:1~1:

1.

7. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 1, characterized in that, In step (3), the high-temperature treatment involves raising the temperature to 350-450 ℃ at a rate of 20-50 ℃ / min and holding it at that temperature for 10-60 min.

8. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 1, characterized in that, In step (4), the temperature is raised to 600-800℃ at a rate of 20-50℃ / min and held for 5-10 min.

9. The method for on-sheet synthesis of niobium diselenide superconducting nanowires according to claim 1, characterized in that, Vanadium salts can also be added to niobium precursor solutions to prepare vanadium-doped modified NbSe2 superconducting nanowires.

10. The application of niobium diselenide superconducting nanowires obtained by the preparation method according to any one of claims 1 to 9 in the preparation of superconducting single-photon detectors or low-dimensional superconducting quantum devices.

Images