An actinide iron toroid thin film material, its preparation method and application

Abstract

The present invention discloses an actinide ferrocenium thin film material, a preparation method thereof and an application thereof, belonging to the technical field of ferromagnetic materials. The actinide ferrocenium thin film material is a crystalline thin film prepared by a spin coating method, and its chemical components include cyclodextrin, actinyl ions and alkali metal ions. First, an actinyl cyclodextrin crystalline thin film is prepared on a substrate by a spin coating method, and the thin film has good denseness and controllable thickness; then, through two ways of radiation reduction or LED light reduction, efficient and controllable reduction of the crystalline thin film is realized to obtain a ferrocenium thin film. The actinide ferrocenium thin film material of the present invention has the basic properties of ferrocenium, laying an important foundation for the development of ferrocenium devices.

Description

Technical Field

[0001] The present invention relates to toroidal materials, in particular to an actinide toroidal thin film material, a preparation method and an application thereof, belonging to the technical field of ferroic materials. Background Art

[0002] Ferroic materials refer to a class of materials that can be polarized under an external field and whose polarization properties will flip with the external field and produce a hysteresis effect. The three common ferroic properties at present include ferromagnetism (spontaneous magnetization), ferroelectricity (spontaneous polarization) and ferroelasticity (spontaneous strain), which are polarized under the action of an external magnetic field, electric field and stress field respectively and flip with the change of the external field (A. Zimmermann, D. Meier & M. Fiebig. Ferroic nature of magnetic toroidal order. [J]. Nature Communications 2014, 5, 4796). Ferromagnetism and ferroelectricity break the time-reversal symmetry and space-inversion symmetry respectively, while the time-reversal symmetry and space-inversion symmetry of ferroelasticity remain unchanged. According to theoretical speculation, there should exist a material with a single order parameter that breaks both space-inversion symmetry and time-reversal symmetry, which scientists call ferrotoroidic materials (G. T. Rado. Observation and Possible Mechanisms of Magnetoelectric Effects in a Ferromagnet [J]. Physical Review Letters 1964, 13, 335 - 337).

[0003] Theoretical physicists have made great contributions to the prediction of the properties of ferrotoroidic materials, mainly including: (1) proving that the prerequisite for the formation of ferrotoroidicity is the formation of antiferromagnetic coupling between magnetic ions; (2) proposing 31 magnetic point groups that can satisfy ferrotoroidicity, revealing the symmetry of ferrotoroidic materials; (3) proposing four criteria for ferrotoroidic materials: i. long-range order below a specific temperature; ii. the existence of ferrotoroid domains; iii. the existence of a phase transition temperature; iv. a significant increase in the macroscopic magnetic susceptibility near the transition temperature (S. Gnewuch, E. E. Rodriguez. The fourth ferroic order: Current status on ferrotoroidic materials [J]. J. Solid State Chem. 2019, 271: 175 - 190). There have been many studies exploring the synthesis of ferrotoroidic materials, but currently, examples that fully prove ferrotoroidicity (such as LiCoPO4 Few (S.Gnewuch, E. E. Rodriguez. The fourth ferroic order: Current status on ferrotoroidic materials [J]. J. Solid State Chem. 2019, 271: 175-190). This is mainly due to two reasons: (1) Difficult synthesis. It is very difficult to construct a toroidal magnetic moment and keep it in long-range order; (2) Difficult characterization. For traditional hard toroid materials, to prove long-range order, second harmonic generation spectroscopy (SHG) or spherical neutron polarization analysis (SNP) is required, and millimeter-sized single crystals needed for these experiments are very difficult to grow (S.Gnewuch, E. E. Rodriguez. The fourth ferroic order: Current status on ferrotoroidic materials [J]. J. Solid State Chem. 2019, 271: 175-190).

[0004] LiCoPO 4 As the most studied ferrotoroidic material at present, it meets the above four criteria. LiCoPO 4 The method to form a toroidal moment is through the tilting of spin electrons in the unit cell to form a large toroidal moment and a small toroidal moment, presenting a net toroidal moment as a whole. Although this method can form a toroidal moment, the net value of the toroidal moment is very low, and the toroidicity of the formed material is not strong. At the same time, there is no super-exchange interaction between the magnetic ions Co 2+ that form the toroidal moment, and the formed toroidicity is not stable enough. More importantly, the LiCoPO 4 material based on the inorganic framework itself has no scalability and is not easy to be functionalized and modified for subsequent application transformation. Another type of material with toroidicity that has received wide attention is single-molecule toroids. It itself has the advantages of super-exchange and easy modification of the organic framework (X. Li, J. Wu, J. Tang, B. L. Guennic, W. Shi, P. Cheng. A planar triangular Dy 3 + Dy 3A single-molecule magnet with a toroidal magnetic moment [J]. Chem.Commun. 2016, 52: 9570-9573), but its disadvantage is that it does not have long-range order of the toroidal moment, so it does not meet all the criteria of toroidal materials and does not belong to a true toroid. Since it does not exhibit toroidicity in the long range, its device applications are very limited.

[0005] Actinides, especially actinyl ions (UO 2 + , NpO 2 2+ , PuO 2 2+ , AmO 2 2+ , CmO 2 2+ ) have strong spin-orbit coupling effects (Meihaus, K. R. & Long, J. R. Actinide-based single-molecule magnets[J]. Dalton Trans. 2015, 44: 2517-2528) and strong superexchange effects (Belkhiri, L., Guennic, B. L. & Boucekkine, A. DFT investigations of the magnetic properties of actinide complexes [J]. Magnetochemistry 2019, 5:15), and it is easier to construct long-range magnetic ordered structures compared with transition metals and lanthanide metals.

[0006] CN116836406A successfully constructed an actinide soft toroidal material based on actinides and cyclodextrin. This actinide soft toroidal supramolecular crystal material has more strict and stronger toroidicity compared with the LiCoPO 4 material mentioned above, and has the following six characteristics of a toroid: (1) long-range order below a specific temperature; (2) existence of toroidal domains; (3) existence of a phase transition temperature; (4) significant enhancement of the macroscopic magnetic susceptibility near the transition temperature; (5) truly geometric circular arrangement of magnetic moments; (6) existence of superexchange interactions between magnetic ions.

[0007] The applications of toroidal materials are mainly reflected in two aspects: (1) Information storage. The inherent electromagnetic coupling effect of toroidal materials makes them have great potential applications in the field of information storage. Due to the characteristics of spontaneous magnetization and electric polarization, toroidal materials can achieve electric field control of magnetic field. Compared with the working mode of changing the magnetic field by changing the current to change the stored information, the working mode of electric field control of magnetic field can greatly reduce energy consumption and improve the reading and writing speed. The storage device developed based on this system can achieve fast information storage, reading and writing with low power consumption. (2) Quantum computing. Toroidal materials have the property of long-range magnetic order and can be used to create stable quantum states. The magnetic ions in toroids have the quantum Hall effect, which means they can exhibit fractional spin currents and other interesting phenomena. This makes them very suitable for quantum spintronic devices, which use spins instead of electrons to store and process information.

[0008] At present, the toroid field still remains in the stage of material preparation and basic property research, and there is no research exploring the thin film preparation and device processing technology of toroids. Although the previously prepared actinide soft toroid supramolecular crystals have excellent toroid properties, to truly achieve applications such as information storage or quantum computing, they must be processed into electronic devices. However, the crystal powder belongs to bulk material, and there are still problems such as insufficient crystal size and difficulty in processing the crystal. The development from bulk material to thin film material can achieve the planarization of the material, which can largely solve the above problems, realize micro-nano processing and device manufacturing, and can be said to be an essential step towards practical applications in the future (J. Ma, J. M. Hu, Z. Li, & C. W. Nan. Recent progress in multiferroic magnetoelectric composites: from bulk to thin Films. [J]. Adv. Mater. 2021, 23: 1062-1087).

[0009] For the thin film preparation of inorganic crystals, it is often achieved through techniques such as physical vapor deposition, chemical vapor deposition, and atomic layer deposition, which have problems of complex preparation processes and high manufacturing costs. For organic crystals, due to their strong solubility, good volatility, and flexible structure, they are particularly suitable for using the spin-coating method to prepare thin films. At the same time, by controlling the spin-coating parameters, such as spin-coating speed, drying temperature, etc., the structure of the thin film can be regulated, thereby changing the performance. Summary of the Invention

[0010] The object of the present invention is to provide an actinide toroid thin film material and a preparation method thereof. This material has the basic properties of toroid crystals, has long-range toroidal moments and superexchange ability between magnetic ions, and the thin film size reaches the millimeter level, which is sufficient to be processed into electronic devices, laying a foundation for the development of toroid devices.

[0011] To achieve the above technical object, the present invention adopts the following technical solutions:

[0012] An actinide toroid thin film material is a crystalline thin film prepared by a spin coating method. Its chemical components include cyclodextrin, actinyl ions and alkali metal ions. Among them, cyclodextrin can be α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, macrocyclodextrin and other cyclodextrins; the actinyl ions are selected from UO 2 + , NpO 2 2+ ,NpO 2 + ,PuO 2 2+ , AmO 2 2+ , CmO 2 2+ one or more of them; the alkali metal ions are selected from Li + , Na + , K + , Rb + , Cs + one or more of them.

[0013] First, a well-uniform actinyl cyclodextrin crystalline thin film is prepared by a spin coating method. Among them, the uranyl cyclodextrin crystalline thin film must be reduced by irradiation reduction or photoreduction to reduce hexavalent uranyl to pentavalent, and then a toroid thin film is obtained. For other actinyl cyclodextrin crystalline thin films, toroidity can be obtained without reduction.

[0014] Due to the strong superexchange ability of actinides and the annular molecular skeleton, high electron density and confinement coordination effect of cyclodextrin, the obtained actinide toroids have stronger toroid order, and the order transition temperature (Curie temperature, T c ) is above room temperature, which has great practical application value.

[0015] In the preparation method of the actinide toroid thin film material of the present invention, the first step is to prepare an actinide cyclodextrin crystalline thin film by spin coating a mother liquor containing actinyl nitrate, cyclodextrin and alkali metal hydroxide on a substrate. Among them, the mother liquor solvent is ultrapure water, and the molar ratio range of actinyl nitrate:cyclodextrin:alkali metal hydroxide in the composition is 1:2:10 to 1:2:50, and the concentration range of actinyl nitrate is preferably 10-80 mM.

[0016] The growth of the crystal thin film can be affected by adjusting the spin-coating conditions, and the structural information such as the thickness and the dominant crystal plane of this type of crystal thin film can be changed, thereby realizing the regulation of the performance of the crystal thin film. The adjustment parameters of the spin-coating method mainly include substrate selection, sample addition method, spin-coating speed, spin-coating time, and drying method. The substrate can be selected from single-crystalline silicon wafers, quartz glass, sapphire, metal substrates, etc. The static sample addition method is adopted for the sample addition method, and the sample addition amount should preferably cover 1 / 3 to 1 / 2 of the substrate area. When using a silicon wafer as the spin-coating substrate, preferably, the silicon wafer is chemically cleaned with piranha solution before spin-coating. The spin-coating speed affects the film thickness, and the preferred spin-coating speed is 1000 - 10000 rpm, and the spin-coating time is 0.5 - 10 min. The drying method is natural drying or heating drying (<100 °C). After drying, the film exhibits colorful diffraction fringes.

[0017] In the preparation method of the actinide iron cyclide thin film material of the present invention, the second step is the reduction of the actinyl cyclodextrin crystal thin film. The uranyl cyclodextrin crystal thin film must be reduced, while other actinyl cyclodextrin crystal thin films can be reduced or not. There are two reduction methods, including radiation reduction method and LED light reduction method.

[0018] The radiation reduction method uses γ-rays as the emitted rays, and the radiation source can be 60 Co. The radiation dose affects the reduction degree. The radiation dose range used in the present invention is 100 - 800 kGy, and the radiation dose rate is 100 - 800 Gy / min.

[0019] The LED light reduction method uses white light LED as the light source, and the light wavelength range is between 400 - 700 nm, with two peaks, which are 480 nm and 550 nm respectively. During the irradiation process, the light source is close to the sample thin film, the light source power selection range is 10 - 100 mW, and the irradiation time range is 1 - 100 h.

[0020] The present invention has studied the basic properties of the actinide iron cyclide thin film material prepared, such as time-reversal symmetry breaking and space-inversion symmetry breaking.

[0021] Time-reversal symmetry breaking is mainly verified by magnetic measurements. The temperature-dependent magnetic susceptibility and the hysteresis loop are measured using a standard comprehensive magnetic measurement system (PPMS). Space-inversion symmetry breaking is verified by second-harmonic generation spectroscopy (SHG) tests. The SHG signal under variable power tests is used to illustrate the non-centrosymmetric structure of the crystal, and thus infer the property of space-inversion symmetry breaking. The magnetic data show that this type of actinide ferrotoroid thin film material has ferromagnetic characteristics at room temperature, and the zero-field-cooled (ZFC) and field-cooled (FC) curves are significantly separated, indicating the existence of strong magnetic coupling interactions in the material. The transition temperature under an external field of 2000 Oe is approximately 280 K. The SHG results show that the crystal exhibits a significant non-centrosymmetric structure, and combined with the crystal chirality, it can be proved that the crystal has the property of space symmetry breaking. This actinide ferrotoroid thin film material exhibits the basic properties of ferrotoroids, with long-range ferrotoroid moments and the ability of super-exchange between magnetic ions; the film size reaches the millimeter level, which is sufficient for processing into electronic devices; at the same time, due to the adjustable composition and thickness, its structure can be regulated according to different application requirements to achieve better performance.

[0022] Advantages of the present invention:

[0023] The present invention provides an actinide ferrotoroid supramolecular thin film and a preparation method thereof. The present invention first prepares an actinyl cyclodextrin crystal thin film with a millimeter size by a spin-coating method, and the film thickness can be changed and the performance can be regulated by adjusting the mother liquor concentration and the spin-coating speed, opening up a new idea for the preparation of cyclodextrin supramolecular materials. At the same time, by using the high electron density and confined coordination environment of cyclodextrin, the present invention can achieve the efficient reduction of uranyl and stabilize it to the pentavalent state, thereby obtaining a ferrotoroid thin film. For other actinyl cyclodextrin materials, ferrotoroid thin films with specific magnetism can be obtained without reduction. The preparation method has mild conditions, and compared with the xenon lamp reduction, the irradiation reduction method and the LED light reduction method have the advantage of non-destructiveness, and can better maintain the structure of the crystal thin film. In addition, the present invention solves the following technical problems and achieves the following beneficial effects:

[0024] 1) Preparation of large-sized ferrocene thin films based on substrates. Previously, ferrocenes were mostly concentrated in the field of inorganic crystals, lacking research on thin film preparation and properties. The planar structure is the basis for integrated addition and device manufacturing. Preparing ferrocene thin film structures, especially ferrocene thin films based on silicon substrates, is of great practical significance for realizing the application of ferrocenes in the field of electronic devices. Since the raw materials for the thin films are organic molecules and metal ions, the rapid growth and preparation of crystal thin films can be achieved by spin coating, which is an advantage not possessed by inorganic crystals. For silicon substrates, since cyclodextrin and metal ions are hydrophilic while silicon substrates are hydrophobic, spin coating directly on silicon substrates cannot form films. In this invention, piranha solution is used to chemically clean the silicon wafers, enabling a thin layer of silicon dioxide molecules to form on the surface of the silicon wafers. Due to the hydrogen bond interaction between hydroxyl groups and water molecules, the silicon wafers change from hydrophobic to hydrophilic, thus solving the problem of difficult film growth on silicon wafers.

[0025] 2) The spin coating method used in this invention has the following characteristics and advantages: (a) By screening parameters such as substrate selection, mother liquor dropping method, spin coating speed, spin coating time, and drying temperature, the optimal conditions for film growth are obtained, forming an optimal method for the preparation of this type of actinide ferrocene thin films; (b) The crystals grown from the thin films have better crystallinity, and the dominant crystal planes can be adjusted by changing the spin coating speed and time, that is, the crystal growth direction can be controlled, thereby realizing performance regulation; (c) From the perspective of application, the preparation of thin film materials has achieved the planarization of ferrocene materials, laying an important foundation for device processing and large-scale integration.

[0026] 3) Development of mild and controllable reduction methods. In previous studies, pentavalent uranyl crystal thin films were prepared by xenon lamp reduction, but this method still has problems such as insufficient penetration depth, thermal damage to the crystals, and low reduction ratio. This invention has developed two novel reduction methods, irradiation reduction and LED light reduction methods, enriching the reduction methods. Among them, irradiation reduction has advantages such as high penetration depth, small thermal effect, and high reduction ratio; while the LED light reduction method has advantages such as no thermal effect damage, easy regulation of reduction ratio, and easy scale-up. The two new reduction methods have their own advantages and disadvantages, and can well solve several problems of previous xenon lamp reduction, and have greater application potential in future applications. Description of the Drawings

[0027] Figure 1 Optical micrograph of the uranyl cyclodextrin crystal thin film prepared in Example 1.

[0028] Figure 2 Electron micrograph of the uranyl cyclodextrin crystal thin film prepared in Example 1.

[0029] Figure 3Scanning electron microscope (SEM) photographs and energy-dispersive X-ray spectroscopy (EDS spectra) of the uranyl cyclodextrin crystal film prepared in Example 1. Among them, (a) SEM photograph; (b) C element spectrum; (c) O element spectrum; (d) Cs element spectrum; (e) U element spectrum; (f) Si element spectrum.

[0030] Figure 4 Thickness curves of the uranyl cyclodextrin crystal film at different spin-coating speeds in Example 1.

[0031] Figure 5 XRD patterns of the uranyl cyclodextrin crystal film at different spin-coating speeds in Example 1. Among them, (a) XRD pattern of the film prepared at 8000 rpm; (b) XRD pattern of the film prepared at 2000 rpm.

[0032] Figure 6 EPR spectra of the film samples with different LED photoreduction times in Example 1. Among them, (a) EPR spectrum of the sample irradiated with LED light for 3 h; (b) EPR spectrum of the sample irradiated with LED light for 6 h; (c) EPR spectrum of the sample irradiated with LED light for 9 h.

[0033] Figure 7 XPS spectra of the film samples with different LED photoreduction times in Example 1. Among them, (a) XPS U4f fine spectrum of the sample irradiated with LED light for 3 h; (b) XPS U4f fine spectrum of the sample irradiated with LED light for 6 h; (c) XPS U4f fine spectrum of the sample irradiated with LED light for 9 h.

[0034] Figure 8 Temperature-dependent magnetic susceptibility curve of the ferricyclophane film prepared in Example 1 (external magnetic field is 400 Oe, temperature range is 4 K - 300 K).

[0035] Figure 9 Hysteresis loop of the ferricyclophane film prepared in Example 1 (temperature is 4 K, scanning range is -1 T - 1 T).

[0036] Figure 10 SHG spectra of the ferricyclophane film prepared in Example 1. Among them, (a) Variable-power SHG spectrum; (b) Plot of SHG signal intensity vs. power (the signal intensity and power are plotted after taking the logarithm, and the slope is about 2, which conforms to the characteristics of the SHG signal). Detailed implementation method

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present invention belong to the scope of protection of the present invention.

[0038] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present invention. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0039] Materials and methods:

[0040] 1. Experimental materials

[0041] Cesium hydroxide (50% wt, Aladdin); γ-cyclodextrin (>99%, InnoChem); uranyl nitrate (used after recrystallization purification). The experimental water is ultrapure water.

[0042] 2. Experimental methods

[0043] The spin coating experiment uses an EZ4-S-PP small spin coater; the film thickness is measured using a step profiler (DektakXT, Bruker) on the micro-nano platform of Peking University; the photoreduction experiment uses an LED light source (Zhongke Jinyuan) and 60 a Co radiation source (Peking University); X-ray photoelectron spectroscopy (XPS) is detected and data is collected using Al-Kα rays (λ = 1.3371 Å) on an ESCALAB250Xi spectrometer; electron paramagnetic resonance (EPR) is tested and data is collected on a Magnettech ESR5000 instrument produced by Bruker; the DC susceptibility, AC susceptibility and hysteresis loop effect are tested and data is collected on an MPMS-3 produced by Quantum Design. The SHG data is measured using a Raman microscopy measurement system (WITec alpha 300R).

[0044] Example 1

[0045] (1) Preparation of uranyl cyclodextrin crystal film

[0046] Mother liquor preparation

[0047] Weigh UO 2 (NO 3 ) 2 ∙6H 2O (0.251 g, 0.5 mmol) and γ-cyclodextrin (1.297 g, 1 mmol) were dissolved in 5.0 mL of ultrapure water. 50 wt% CsOH (2.998 g, 10 mmol) was quickly added, and the mixture was shaken well to disperse. Then, ultrapure water was added to make the volume up to 10.0 mL, and it was stored in the dark at a cool place.

[0048] Preparation of thin films by spin coating

[0049] Use a pipette to transfer 2 - 3 drops of the mother liquor and drop it onto a 10 * 10 mm polished silicon wafer (cleaned with piranha solution at 100 °C). Set the spin-coating speed to 4000 rpm, the spin-coating time to 120 s, and the acceleration to 100 rpm / s.

[0050] After spin-coating, heat and dry the silicon wafer on a hot plate to completely evaporate the solvent and obtain a crystal film.

[0051] (2)Characterization of the uranyl cyclodextrin crystal film

[0052] Observation of crystal morphology

[0053] As Figure 1 shown, the optical micrograph shows that the film has good compactness, large size (millimeter scale) and is relatively uniform. At the same time, small crystal samples are dispersed on the surface of the crystal film.

[0054] As Figure 2 shown, the electron micrograph shows that the film is actually a polycrystalline film, and countless small crystals are stacked together to form a large polycrystalline film. As Figure 3 can be seen, the crystal contains C, O, U, Cs elements and is evenly distributed, indicating the successful preparation of the crystal film.

[0055] Thin film thickness - spin coating speed curve

[0056] Films with different thicknesses were prepared by controlling the spin-coating speed, and the film thickness was measured by a profilometer. For each sample, the film thickness was measured in three different regions, and the average value and standard deviation of the film thickness were calculated to establish a film thickness - spin-coating speed curve, as Figure 4 shown.

[0057] Crystal plane characterization and dominant crystal plane regulation

[0058] As Figure 5As shown, the crystal thin film quality, dominant crystal planes and other structural information were analyzed by powder XRD. It can be seen that compared with the powder crystal, the diffraction peak intensity of the thin film crystal is significantly increased, that is, the crystallinity is greatly improved. At the same time, at low rotation speeds such as 2000 rpm, the dominant crystal plane is near 28.5°. At high rotation speeds, the 28.5° crystal plane disappears, and the growth crystal plane tilts towards the low diffraction angle. This example shows that the crystal growth direction can be controlled by adjusting the spin-coating speed, which will ultimately affect the performance of the ferricyclopentadiene thin film.

[0059] (3)Preparation of ferricyclopentadiene thin film by reduction of uranyl cyclodextrin crystal thin film

[0060] Irradiation reduction

[0061] The uranyl cyclodextrin crystal thin film was placed in a sample tube protected by nitrogen and placed 60 under a Co radiation source for irradiation. The irradiation dose rate was 100 Gy / min and the irradiation dose was 600 kGy. Compared with the reduction by xenon lamp, the reduction rate of the crystal can be increased from about 70% to nearly 90% by irradiation reduction, and the reduction ratio is greatly increased. Moreover, the reduction degree of the sample can be controlled by changing the irradiation dose. After irradiation, the thin film sample became dark brown under the microscope.

[0062] LED light reduction

[0063] The uranyl cyclodextrin crystal thin film was placed in a light protector to isolate water and oxygen. The light protector containing the sample thin film was placed under an LED light source for irradiation. The irradiation power was 100 W and the irradiation time was 6 h. Among them, by controlling the irradiation time, the reduction degree of the crystal can be controlled to obtain ferricyclopentadiene thin films with different reduction ratios. From Figure 6 it can be seen that as the reduction time increases, the EPR signal of the thin film is continuously enhanced. From Figure 7 it can be seen that as the reduction time increases, the reduction ratio is continuously increased.

[0064] (4)Characterization of the properties of ferricyclopentadiene thin film

[0065] Magnetic research

[0066] A MPMS-3 instrument was used to measure the variable-temperature DC magnetic susceptibility and the hysteresis loop. From Figure 8 it can be seen that the thin film exhibits characteristic ferromagnetic signals, and the field-cooled (FC) and zero-field-cooled (ZFC) curves are separated, indicating that there is magnetic coupling in the ferricyclopentadiene thin film and the transition temperature is above 250 K. From Figure 9 it can be seen that the ferricyclopentadiene has an obvious hysteresis loop, which conforms to the characteristics of soft ferromagnetic signals. Magnetic research proves that there is time-reversal symmetry breaking in the ferricyclopentadiene thin film.

[0067] SHG characterization

[0068] The variable-power SHG data was measured using a WITec 300R Raman measurement system, as Figure 10 shown. Under the excitation of the 1064 nm wavelength, the thin film can emit a second-harmonic peak at 532 nm, and although the power changes, the signal intensity increases significantly. By confirming that the net signal intensity is proportional to the square of the power, it can be confirmed that the signal is an SHG signal. And only non-centrosymmetric structures have SHG signals, which indicates that there is a spatial inversion symmetry breaking in the toroid thin film.

[0069] In summary, the present invention provides an actinide toroid thin film, its preparation method and property research. Two reduction methods for uranyl cyclodextrin thin films were developed for the first time: irradiation reduction and LED light reduction, realizing the efficient reduction and stable retention of uranyl. By measuring magnetism and SHG, it was proved that the crystal thin film has the characteristics of time reflection and spatial inversion symmetry breaking, meeting the basic property requirements of toroids, and is a potential toroid thin film material.

[0070] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention. Those skilled in the art should understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection claimed by the present invention is subject to the scope defined by the claims.

Claims

1. A method for preparing an actinide iron ring thin film material, wherein the chemical components of the actinide iron ring thin film material include cyclodextrin, actinyl ions and alkali metal ions, wherein: The actinyl ion is selected from UO2 + 、NpO2 2+ 、NpO2 + 、PuO2 2+ 、AmO2 2+ 、CmO2 2+ One or more of, the alkali metal ion is selected from Li + 、Na + , K + , Rb + , Cs + One or more of the above, characterized in that, first, a mother solution containing actinyl nitrate, cyclodextrin and alkali metal hydroxide is spin-coated on a substrate at a spin-coating speed of 1000 to 10000 rpm for a spin-coating time of 0.5 to 10 min, and then the substrate is dried naturally or heated at a temperature of <100°C to obtain an actinyl cyclodextrin crystal film, wherein the solvent of the mother solution is ultrapure water, the molar ratio of actinyl nitrate: cyclodextrin: alkali metal hydroxide is in the range of 1:2:10 to 1:2:50, and the concentration of actinyl nitrate is 10-80 mM; then the actinyl cyclodextrin crystal film is treated by irradiation reduction or LED light reduction, or no reduction is required to obtain an ferric ring film; wherein, for the uranyl cyclodextrin crystal film, hexavalent uranyl is reduced to pentavalent uranyl by irradiation or LED light to obtain an ferric ring film; and for other actinyl cyclodextrin crystal films, no reduction is required to obtain an ferric ring film, or actinyl ions are reduced by irradiation or LED light to obtain a stable ferric ring film.

2. The preparation method according to claim 1, characterized in that The substrate is a single crystal silicon wafer, quartz glass, sapphire or a metal substrate.

3. The preparation method according to claim 2, characterized in that: A single crystal silicon wafer is used as the spin coating substrate, and the silicon wafer is chemically cleaned with piranha solution before spin coating.

4. The preparation method according to claim 1, characterized in that: The radiation reduction method uses γ-rays as the emission rays, the irradiation dose is 100 to 800 kGy, and the irradiation dose rate is 100 to 800 Gy / min; the photoreduction method uses white light LED as the light source, the light wavelength range is between 400 and 700 nm, the light source power is 10 to 100 mW, and the irradiation time is 1 to 100 h.

5. The preparation method according to claim 1, characterized in that: The cyclodextrin is α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin or macrocyclodextrin.

6. The actinide iron ring thin film material obtained by the preparation method according to any one of claims 1 to 5, characterized in that: The actinide iron ring film material has strong iron ring order, and the order transition temperature is above room temperature.

7. Use of the actinide iron ring thin film material according to claim 6 in the preparation of electronic devices.

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