CN116815122A - Method for effectively improving superconducting critical magnetic field - Google Patents
Method for effectively improving superconducting critical magnetic field Download PDFInfo
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- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
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Abstract
The invention belongs to the technical field of superconducting materials, and particularly relates to a method for effectively improving a superconducting critical magnetic field. Sputtering a single-metal superconducting target material to a substrate in a cluster mode by using a low-energy deposition method to prepare a clustered metal film, wherein the low energy refers to the landing energy of the metal cluster being less than 10meV/atom. The single-metal superconducting target can be a Pb target. The invention prepares the superconductive single metal into the clustered metal film by utilizing the low-energy cluster beam deposition technology, thereby realizing the great improvement of the superconductive critical magnetic field and showing a novel method and a novel way for regulating the superconductive critical magnetic field on the nanometer scale. The superconducting metal film prepared by the method is loose and porous, and fusion phenomenon does not occur among metal clusters, so that the sizes of all clusters in the film are very consistent, and the property of the film is ensured not to be interfered by the averaging effect of broad particle size distribution.
Description
Technical Field
The invention belongs to the technical field of superconducting materials, and particularly relates to a method for effectively improving a superconducting critical magnetic field.
Background
The superconducting material can show zero resistance and complete diamagnetism below the characteristic temperature, and the singular electromagnetic property enables the superconducting material to be always in the front of basic scientific research and interdisciplinary development. In recent years, with the continuous development and maturation of nanotechnology and micro-nano technology, superconducting wires and devices have shown wide application prospects in various fields of military, medical treatment, communication, energy, transportation and the like (E.A.G.D, M.J.Deen, C.Claeys, lowtemperature electronics: physics, devices, circles, and applications, academic Press, san diego, USA, 2001.). Meanwhile, the regulation and control of the superconducting critical parameters and the exploration of the superconducting mechanism also enter a brand-new stage. Increasing the critical temperature of superconducting materials is a very intense research direction for researchers because it can be effectively increased by changing the preparation methods such as pulse laser deposition, magnetron sputtering, chemical vapor deposition, sol-gel, hydrothermal methods, etc. However, the critical magnetic field of the superconducting material is difficult to be strongly controlled by the method. The research thinking for improving the property is through multiple chemical element doping, high-pressure (more than hundreds of thousands of atmospheres) environment and other means. This results in very complex chemical compositions of superconducting materials with good properties, and slight loss of stoichiometry during the preparation process can significantly reduce the properties of these materials, making mass production and application difficult. Meanwhile, because no extremely high pressure exists in daily application, the critical magnetic field can be lifted by the method only stay in the basic theory exploration stage and cannot be applied (K.Y.Chen, N.N.Wang, Q.W.Yin, Y.H.Gu, K.Jiang, Z.J.Tu, C.S.Gong, Y.Uwatoko, J.P.Sun, H.C.Lei, J.P.Hu, andJ.G.Cheng, double superconducting dome andtriple enhancement ofT c intheKagome superconductorCsV 3 Sb 5 unrerhaghpressure. Phys. Rev. Lett.126,247001 (2021). Therefore, the research on critical magnetic fields of superconducting materials in complex electromagnetic environments is relatively lacking. It is noted that the above method and the control concept are based on the bloch periodic structure and neglect the contribution of the aperiodic atomic structure in the superconductivity, so the improvement of the critical magnetic field is very limited. Thus, in view of the current challenges encountered with superconducting material regulation, it is necessary to find new methods that can effectively raise the critical magnetic field, which must be simple and have significant success. Particularly, if the novel method can greatly improve the superconducting critical magnetic field of simple metal, the difficult problem of mass production caused by complex preparation can be avoided, and a novel regulating thought is provided to replace the current extreme modes, so that the research interest of the masses is promoted.
Disclosure of Invention
The invention provides a method for improving a superconductive critical magnetic field, which aims to solve the problems of complex regulation means and weak regulation effect of the current superconductive critical magnetic field.
The invention adopts the following technical scheme:
sputtering a single-metal superconducting target material to a substrate in a cluster beam mode by utilizing a low-energy deposition method to prepare a clustered metal film; the low energy means that the landing energy of the metal clusters to the substrate is <10meV/atom. The single-metal superconducting target can be a Pb target.
The method comprises the following specific steps:
(1) The Pb target was cleaned and mounted in a sputtering zone, specifically, a Pb target having a purity of 99.9% was polished with 2000-mesh sand paper, and then put into absolute ethyl alcohol for ultrasonic cleaning for 30 minutes, followed by mounting in a sputtering zone of a cluster beam deposition apparatus. The thickness of the Pb target is 3mm, and the radius is 25mm.
(2) The substrate is cleaned and installed in a deposition area, wherein the substrate is a high-resistance insulating substrate, and specifically, the substrate is placed in absolute ethyl alcohol for ultrasonic cleaning for 20 minutes and then is installed on a sample holder of the deposition area of the cluster beam deposition equipment.
The substrate can be specifically prepared from SiO with thickness of 300nm 2 Si sheet with insulating SiO 2 The Si sheet of the layer is used for preventing current from flowing into the Si sheet in the superconducting critical magnetic field test process, so that the test result can be ensured to be the pure cluster Pb film performance. Other high resistance insulating substrates, such as Al, can thus also be selected 2 O 3 AlN, etc.
(3) Sputtering deposition of Pb in protective gas with sputtering power of 40-50W and sputtering air pressure of 50-60Pa, and sputtering deposition rate ofThe sputtering time is 2-3 hours, and the deposition distance between the target and the substrate is 525-600mm. The shielding gas is 99.99% Ar. The atomic number and the size of the non-periodic structure Pb clusters in the film can be obviously controlled by changing the deposition distance.
Specifically, firstly, a mechanical pump and a molecular pump group are utilized to pump air from a cavity of the cluster beam deposition equipment, and meanwhile, a cooling water circulation system is started to maintain the temperature of the system at 18 ℃ so as to avoid overhigh temperature of the molecular pump group, the air pumping time is standard-free, and the back bottom air pressure of the cavity is required to be ensured to be lower than 5 multiplied by 10 -5 Pa. And after the air extraction is finished, sputtering gas (namely shielding gas) with the pressure of 10Pa is introduced to perform impurity gas removal treatment on the cavity of the deposition equipment for 15 minutes. Then adjusting the cavity of the deposition equipment to form multistage differential pressure state, such as 55Pa in sputtering zone and 1×10 in screening zone -1 Pa, screening zone two 3×10 -3 Pa, deposition area 5X 10 -5 Pa. In this multistage differential pressure state, the gas generated by sputtering flies forward and collides with the shielding gas to start growing gradually, thereby forming an initial Pb cluster in the sputtering zone.
And then adjusting a proper deposition distance, starting a sputtering direct current power supply, closing the sputtering power supply after sputtering, and setting the sputtering air pressure to be 8-10Pa. The deposition rate is maintained atThe method aims to ensure uniform growth speed of Pb non-periodic structure clusters.
(4) And carrying out in-situ annealing on the deposited Pb cluster film for 20-30 minutes in the atmosphere of protective gas, wherein the annealing temperature is 270-320 ℃. After the annealing was completed, the sputtering apparatus was turned off after waiting for 2 hours to completely cool the film to prevent the film from being oxidized.
The reason for carrying out in-situ annealing is not only to enable Pb clusters with non-periodic structures in the film to be better crystallized, but also to enable the Pb clusters to be subjected to secondary reconstruction, so that cluster growth occurs to ensure extremely narrow particle size distribution and enhance the performance of the film.
The beneficial effects of the invention are as follows:
the invention prepares the superconductive single metal (such as Pb) into the clustered metal film by utilizing the low-energy cluster beam deposition technology, thereby realizing the great improvement of the superconductive critical magnetic field and showing a novel method and a novel way for regulating the superconductive critical magnetic field on the nanometer scale. The superconducting metal (such as Pb) film prepared by the method is loose and porous, and the metal clusters are not fused, so that the sizes of all clusters in the film are very consistent, the property of the film is ensured not to be interfered by the averaging effect of wide particle size distribution, and the size characteristics and the limited atomic number characteristics of the nanoclusters can be brought into full play. While the low-energy soft landing (< 10 meV/atom) is capable of well retaining the original structure and properties of the clusters, so that the excellent properties of Pb particles in the clustered state at the characteristic size do not disappear.
The embodiment of the invention prepares the cluster Pb assembled film with four scales for effect display and comparison, and when the particle scale is 9.24nm, the superconductive critical magnetic field of the Pb film is 800Oe at 4K, which is higher than the results of the current theory and other methods; when the cluster size reaches 17.69nm, the critical magnetic field reaches 1600Oe, which has been improved by 2 times over conventional cognition; when the size reaches 24.03nm, the superconducting critical magnetic field reaches 3600Oe, which is 4.5 times higher than the conventional cognition; when the cluster size reached 31.49nm, the critical magnetic field was 2600Oe, which was 3.25 times higher than conventional cognition, but decreased compared to 24.03nm. It should be noted that the test apparatus in this embodiment can only be lowered to 4K, so that the superconducting critical magnetic field at 4K is tested, and the superconducting temperature is 803Oe for the recognized Pb metal at a theoretical value close to absolute zero. Therefore, the improvement factor of the superconducting critical magnetic field of the clustered Pb film is calculated by comparing the accepted value of absolute zero with the experimental value of the embodiment at 4K. Thus, in fact, the fold improvement of clustered Pb films over conventional cognition should be much greater than the results currently calculated in this example.
In summary, in the characteristic cluster size range, the cluster Pb assembled film shows a significant improvement in the superconducting critical magnetic field, and there is a very high point, which represents an absolute advantage of this preparation method and the non-periodic structure cluster species.
Drawings
Fig. 1 is a schematic diagram of the present invention for preparing assembled films of different sizes of clustered Pb using a low energy cluster beam deposition apparatus.
In the figure, (1) is a target holder, (2) is a sample holder, (3) is an inflation valve, (4) is a mechanical pump, (5) is a Roots pump, (6) (7) (8) is a molecular pump, (9) is a shielding cover, 3 is a nozzle, and A and B are separators.
Fig. 2 is a transmission electron microscope image of the assembled film of clustered Pb prepared in example 1.
Fig. 3 (a) - (d) are scanning electron microscope images of the assembled films of clustered Pb of examples 1-4, respectively.
Fig. 4 (a) - (d) are graphs of resistance versus temperature for the clustered Pb assembled films of examples 1-4, respectively, under different magnetic fields.
Detailed Description
In order to more directly demonstrate the objects, technical processes and advantages of the present invention, the thin film fabrication process and the corresponding superconducting critical magnetic field results are described in detail below by describing examples 1 to 4 in conjunction with fig. 1 to 4.
Example 1
Fig. 1 shows a schematic diagram of the present invention for preparing different-sized cluster Pb assembled films using a low-energy cluster beam deposition apparatus divided into a sputtering zone, a screening zone, and a deposition zone.
The preparation process of the cluster Pb assembled film specifically comprises the following steps:
first, a Pb (thickness 3mm, radius 25 mm) target having a purity of 99.9% was sanded and ultrasonically cleaned, and then mounted on the sputtering region at the position of the backing plate (1). Will carry 300nm thick SiO 2 The Si substrate of the layer was put in absolute ethanol for ultrasonic cleaning for 20 minutes and then mounted on a sample holder (2) of a deposition area. Before the cavity of the cluster beam deposition equipment is vacuumized, an inflation valve (3) of the deposition equipment is screwed to a sealing state, so that the optimal exhausting efficiency is ensured. And then starting a cooling water circulation system, and maintaining the water temperature at 18 ℃ to ensure that the air pump set cannot be overhigh in the operation process. Then the mechanical pump (4) is opened to suck air, when the cavity air pressure is 1.013X10 from the atmospheric pressure 5 Pa is reduced to 1X 10 2 The Roots pump (5) is automatically started when Pa, and the pressure is lower than 1×10 -1 At Pa, three molecular pumps (6) (7) (8) are turned on. When the back pressure of the cavity is lower than 5 multiplied by 10 -5 After Pa, sputtering gas Ar gas of 10Pa is introduced to carry out impurity removal treatment on the equipment cavity for 15 minutes.
Next, the thin film preparation process is entered. Firstly, a direct-current power supply of a sputtering instrument is started, the sputtering power is set to be 45W, and the sputtering air pressure is set to be 55Pa. When the sputtering power is turned on, a high voltage exists in the gap between the shielding cover (9) and the target, so that Ar gas entering the gap through the annular air pipe of the shielding cover can be ionized into Ar + The surface of the Pb target is then bombarded, which in turn generates a large amount of atomic and ionic gas. Because the rotation speeds of the three molecular pumps are obviously different, the pressures of the sputtering area, the screening area I, the screening area II and the deposition area are sequentially reduced to 55Pa (sputtering area) and 1 multiplied by 10 respectively -1 Pa (screening area one), 3×10 -3 Pa (screening region two) and 5×10 -5 Pa (deposition area) to form a multi-stage differential pressure state. In this case, pb atoms generated by sputtering fly forward and collide with Ar gas to start growing gradually, thereby forming primary particles in the sputtering regionInitial Pb clusters. The Pb clusters then isentropically expand through the nozzles into the screening zone where they collide with each other and grow gradually and pass through the two separators (A and B) under differential pressure. Because of the taper of the nozzle and separator, it can act to screen the cluster size, and eventually form a collimated and very uniform size cluster beam stream in the deposition zone. It is noted that the method for preparing non-periodic structure cluster Pb film is a low energy deposition method, so that the cluster beam reaches Si/SiO in a soft landing manner 2 A substrate. Due to the landing energy of Pb clusters<10 meV/atom) is extremely small, so that clusters are not broken or reflected back, and are not migrated and fused on the surface of the substrate, and therefore, the clustered Pb assembled film with extremely narrow size distribution can be finally prepared. During the preparation process, the deposition rate is maintained as much as possibleThe Pb cluster growth speed is ensured to be uniform, and the sputtering deposition time is 2.5 hours. The precondition for preparing the cluster film is that the landing energy is smaller than the bonding energy among atoms, and the deposition distance of more than 500mm ensures that the landing energy is smaller than 10meV/atom, so that the monodisperse cluster film can be prepared.
And after the uniform film is prepared, a sputtering power supply is turned off, the sputtering air pressure is set to 8Pa, then a substrate heating device is turned on, the temperature is raised to 280 ℃ to enable the film to be annealed in situ under the atmosphere of protective gas Ar for 30 minutes. To prevent the film from being oxidized, it is necessary to wait 2 hours after the end of annealing to completely cool the film. When the equipment is closed, the switch of the molecular pump is firstly clicked to reduce the speed, when the speed is reduced to a certain degree to enable the equipment to resonate, the mechanical pump is closed to protect the machine, finally, the power switch of the cluster instrument is closed, and a film sample in the deposition area is taken out.
FIG. 2 shows the microstructure of the clustered Pb film tested by high resolution transmission electron microscopy, and shows that the interplanar spacing d of the two types of stripes is respectively 0.301nm and 0.269nm after being measured by using Digital Micrograph software, and the corresponding crystal face indexes are [100] and [101] of a Pb standard card (PDF#44-0872), so that the accuracy of the clustered Pb prepared by the embodiment is demonstrated.
In example 1, the deposition distance between the target and the substrate is required to be L 1 The cluster size is known to be larger as the deposition distance is longer according to the principle of preparing clusters by a deposition apparatus, =525 mm, so that a cluster Pb thin film having the smallest size can be prepared under this condition. The film was subjected to microscopic morphological characterization using a scanning electron microscope, and the result is shown in fig. 3 (a). The Pb clusters in the film can be found to be monodisperse uniform spheres, and most importantly, the size distribution is extremely narrow, so that the size dependence characteristic and the limited atomic number characteristic of the cluster-state substance can be well reflected. Comprehensive statistics using Nano measure software showed that the average size of Pb clusters was 9.24nm. The superconducting property of the film is characterized by combining a four-probe method with a comprehensive physical property measuring system, and attention is paid to the fact that a lead bonding instrument is needed to be used for connecting a sample and a test support so as to ensure good contact, thereby ensuring accurate test results. The resistance-temperature curves of the samples prepared in example 1 under different magnetic fields are shown in fig. 4 (a), and in order to more directly show the data result, the resistance is normalized, which does not have any influence on the theory, and it can be found that the superconducting critical magnetic field of the film under 4K is 800Oe.
Example 2
In this embodiment, except that the deposition distance between the target and the substrate is set to L 2 Except for 550mm, the rest of the operation methods (details of operation of the cluster beam deposition apparatus) and the settings of all parameters (chamber gettering time, sputtering power, sputtering gas pressure, sputtering deposition rate, sputtering deposition duration, annealing temperature, annealing time, etc.) were the same as those of example 1. The microscopic morphology of the film sample was also characterized using a scanning electron microscope, and as shown in fig. 3 (b), it was found that the film was still assembled from spherical Pb clusters with a very uniform size distribution. Since the deposition distance was increased, the growth time of Pb clusters was also increased, and thus the statistical result showed that the average size of Pb clusters at this time was 17.69nm. FIG. 4 (b) shows the resistance-temperature curve of the film under different magnetic fields, and the result showsThe superconducting critical magnetic field is 1600Oe, which has been improved by 2 times over conventional cognition, demonstrating the unique charm of clustered Pb films at feature sizes.
Example 3
In this embodiment, except that the deposition distance between the target and the substrate is set to L 3 Except for 570mm, the rest of the operation methods (details of operation of the cluster beam deposition apparatus) and the settings of all parameters (chamber gettering time, sputtering power, sputtering gas pressure, sputtering deposition rate, sputtering deposition duration, annealing temperature, annealing time, etc.) were the same as those of example 1. The microscopic morphology of the film sample was characterized using a scanning electron microscope, and as shown in fig. 3 (c), it was found that the film was assembled from spherical Pb clusters having a very uniform size distribution. Since the deposition distance continues to increase, the growth time of Pb clusters also increases, and thus the statistical result shows that the average size of Pb clusters at this time is 24.03nm. Fig. 4 (c) shows the resistance-temperature curve of the film under different magnetic fields, and shows that the superconducting critical magnetic field is 3600Oe, which has been improved by 4.5 times over the conventional cognition, showing the unique charm of clustered Pb film under characteristic dimensions.
Example 4
In this embodiment, except that the deposition distance between the target and the substrate is set to L 4 Except for 600mm, the rest of the operation methods (details of operation of the cluster beam deposition apparatus) and the settings of all parameters (chamber gettering time, sputtering power, sputtering gas pressure, sputtering deposition rate, sputtering deposition duration, annealing temperature, annealing time, etc.) were the same as those of example 1. The microscopic morphology of the film sample was characterized using a scanning electron microscope, and as a result, as shown in fig. 3 (d), it was found that the film was assembled from spherical Pb clusters having a very uniform size distribution. Since the deposition distance was the farthest, the growth time of Pb clusters was also the longest, and thus the statistical result showed that the average size of Pb clusters at this time was 31.49nm. FIG. 4 (d) shows the resistance-temperature curve of the film under different magnetic fields, showing that the superconducting critical magnetic field is 2600Oe, which has been improved 3.25 times over conventional cognition, showing clustered Pb films at characteristic dimensionsUnique charm.
In summary, it can be found that when Pb metal is prepared into a non-periodic structure cluster Pb film with extremely narrow size distribution by using the low energy cluster beam deposition technique, the superconducting critical magnetic field is greatly improved. In particular, when the cluster size is 24.03nm, the superconducting critical magnetic field of the cluster Pb film is 3600Oe, which is 4.5 times higher than the theoretical value 800Oe at the absolute zero degree at present, and the size characteristic and the limited atomic number characteristic of the cluster Pb film under the characteristic size are shown.
Therefore, the technology and the thought for preparing the non-periodic structure cluster film provide a new mode for improving the superconducting critical magnetic field, and the technology and the thought are simpler to operate and have obvious effect than the traditional regulation and control technology through multiple element doping, extremely high voltage and the like. The practical technology and thought can promote the research of the current superconducting critical magnetic field, solve the problems that the current regulation and control means are complex, the effect is weak and mass production cannot be realized, and promote the research interest of the masses.
The above description is only a detailed description of the invention in connection with the specific preferred embodiments, but the invention is not limited thereto. Various simple modifications, such as a few simple deductions or substitutions, can be made to the technical solution of the present invention without departing from the technical concept of the present invention, including that the technical features are combined in any other suitable manner, and these simple modifications and combinations should also be regarded as the disclosure of the present invention, which is also within the scope of the present invention.
Claims (10)
1. A method for effectively improving a superconductive critical magnetic field is characterized in that a low-energy deposition method is utilized to sputter a single-metal superconductive target material to a substrate in a cluster beam mode to prepare a clustered metal film; the low energy means that the landing energy of the metal clusters to the substrate is <10meV/atom.
2. The method of claim 1, wherein the single-metal superconducting target is a Pb target.
3. A method of effectively increasing a superconducting critical magnetic field according to claim 2, comprising the steps of:
(1) Cleaning a Pb target and a substrate;
(2) Sputtering deposition of Pb in a mode of cluster beam flow in a protective gas, wherein the sputtering power is 40-50W, the sputtering air pressure is 50-60Pa, and the sputtering deposition rate isThe sputtering time is 2-3 hours, and the deposition distance between the target material and the substrate is 525-600mm; setting the sputtering air pressure to 8-10Pa after sputtering;
(3) And (3) carrying out in-situ annealing on the deposited Pb cluster film under the protection gas for 20-30 minutes at 270-320 ℃.
4. A method for effectively increasing a superconducting critical magnetic field according to claim 3, wherein the thickness of the Pb target in step (1) is 3mm, the radius is 25mm, and the purity of the Pb target is 99.9%.
5. A method for effectively increasing a superconducting critical magnetic field according to claim 3, wherein the specific operation of cleaning Pb target in step (1) is as follows: and polishing the Pb target material by using 2000-mesh sand paper, and then putting the Pb target material into absolute ethyl alcohol for ultrasonic cleaning for 30 minutes.
6. A method for effectively increasing a superconducting critical magnetic field as claimed in claim 3 wherein said substrate in step (1) is a high resistance insulating substrate employing a substrate with 300nm thick SiO 2 Si sheet, al of (C) 2 O 3 Or AlN.
7. A method for effectively increasing a superconducting critical magnetic field according to claim 3, wherein the cleaning of the substrate in step (1) is performed as follows: the substrate was placed in absolute ethanol and ultrasonically cleaned for 20 minutes.
8. A method of effectively increasing a superconducting critical magnetic field according to claim 3 wherein the shielding gas in steps (2) and (3) is 99.99% Ar.
9. The method of claim 3, wherein in step (2), the deposition apparatus is pumped down before sputter deposition to ensure that the back pressure in the chamber of the deposition apparatus is less than 5 x 10 -5 Pa, then introducing 10Pa of protective gas to perform impurity gas removal treatment, and then adjusting the gas pressure to form a multistage differential pressure state in the cavity of the deposition equipment.
10. The method for effectively increasing a superconducting critical magnetic field according to claim 9, wherein the multi-stage differential pressure state is specifically: sputtering area 55Pa, screening area 1×10 -1 Pa, screening zone two 3×10 -3 Pa, deposition area 5X 10 - 5 Pa。
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