A method for regulating two-dimensional magnetic materials through small molecule chemisorption

Abstract

The present invention belongs to the technical field of two-dimensional magnetic materials, and relates to a method for regulating two-dimensional magnetic materials through small molecule chemical adsorption, including the following steps; Step 1, exfoliation and transfer of two-dimensional magnetic materials; Step 2, preparation of a solution of 7,7,8,8-tetracyanoquinodimethane (TCNQ); Step 3, surface spreading of TCNQ molecules. The present invention utilizes the adsorption of organic small molecules on the surface of two-dimensional materials to form an organic-inorganic hybrid composite, improving the comprehensive magnetic properties of the composite, solving the disadvantages of low Curie temperature and poor controllability of magnetic regulation of two-dimensional materials. The formed composite has a high Curie temperature and has broad application prospects in the field of spintronics.

Description

Technical Field

[0001] The present invention relates to a method for regulating two-dimensional magnetic materials through small molecule chemisorption, which can be used in the application of room-temperature spintronic devices. It belongs to the technical field of two-dimensional magnetic materials. Background Art

[0002] Two-dimensional materials are a general term for a large class of materials, whose material size is reduced to the limit atomic size in one dimension, while the other two dimension sizes are relatively large. Benefiting from the quantum confinement effect in the atomic layer thickness direction, two-dimensional materials exhibit properties quite different from those of their parent materials, such as the ultra-high electron mobility of graphene. In addition, two-dimensional materials also exhibit excellent flexibility and have great potential in the application of wearable flexible electronic devices. Moreover, the band changes induced by the stacking method greatly enrich the material properties and application scope.

[0003] As a kind of two-dimensional materials, two-dimensional magnetic materials have immediately received extensive attention since their discovery. The discovery of two-dimensional magnetic materials provides a new opportunity for the preparation of spintronic devices with high information storage density, ultrafast response, high integration, and low power consumption. At present, the phase transition temperature of the discovered two-dimensional magnetic materials is much lower than room temperature, and many of them are even lower than the liquid nitrogen temperature. Therefore, there is an urgent need for magnetic two-dimensional materials with high phase transition temperature. Currently, the magnetic properties can be changed by means such as applying an external magnetic field, electric field, stacking method, electrostatic doping, ion intercalation, strain, and proximity effect, which are finally reflected in the changes of properties such as magnetization direction, Curie temperature, coercivity, magnetic anisotropy, and magnetization intensity.

[0004] Among the currently discovered two-dimensional magnetic materials, the two-dimensional iron germanium telluride material has the highest Curie temperature. The Curie temperature of bulk iron germanium telluride is about 230 Kelvin, and as the thickness decreases, the Curie temperature will drop to 130 Kelvin for the single layer. Compared with other two-dimensional magnetic materials, two-dimensional iron germanium telluride has better stability, stronger out-of-plane magnetic anisotropy, and is a typical itinerant ferromagnetic material. Currently, the magnetic properties of few-layer iron germanium telluride are mainly optimized by methods such as electrostatic doping, proximity effect, and adjusting the stoichiometry ratio. However, the repeatability of magnetic regulation and the enhanced level have not yet met the requirements of spintronic devices. At the same time, compared with other magnetic materials, the regulation means are relatively scarce, and there is an urgent need to develop new regulation means to obtain stable two-dimensional magnetic order with a high Curie temperature.

[0005] Molecular chemisorption is a highly extensible method that can generate tunable charge transfer effects in two-dimensional materials and has potential applications in low-dimensional electronics. Different from defect or impurity doping methods, molecular adsorption can regulate the electronic structure without destroying the crystal structure. Among adsorbates, organic molecules have great advantages and can be designed with various functional groups for different conditions. For example, the commonly used electron acceptor molecule TCNQ and the electron donor molecule tetrathiafulvalene (TTF) can regulate the ferromagnetic properties of two-dimensional materials by adjusting the Fermi level. Summary of the Invention

[0006] The present invention proposes a simple and efficient method of molecular surface chemisorption to effectively regulate the ferromagnetic properties of two-dimensional ferromagnetic material iron germanium telluride. By forming an organic-inorganic hybrid complex through the adsorption of organic small molecules on the surface of two-dimensional materials, the comprehensive magnetic properties of the complex are improved, solving the problems of low Curie temperature and poor controllability of magnetic regulation in two-dimensional materials. The formed complex has a high Curie temperature and has broad application prospects in the field of spintronics.

[0007] To achieve the above object, the technical solution of the present invention is: select a suitable electron acceptor molecule, namely TCNQ, for surface chemisorption of two-dimensional iron germanium telluride material, and realize the efficient regulation of the magnetism of the organic-inorganic complex by optimizing the solvent type, molecular concentration, and drying conditions.

[0008] A method for regulating two-dimensional magnetic materials by small molecule chemisorption includes the following steps;

[0009] Step 1, exfoliation and transfer of two-dimensional magnetic materials: Wash the single crystal of two-dimensional magnetic materials thoroughly to remove impurities, thin the above single crystal by mechanical exfoliation or liquid phase exfoliation method, transfer the obtained nanosheets to a silicon substrate with an oxide layer, and measure the thickness of the nanosheets by atomic force microscopy (AFM).

[0010] Step 2, preparation of TCNQ solution: Dissolve TCNQ powder in N,N-dimethylformamide (DMF) or tetrahydrofuran (THF) solvent to prepare a TCNQ solution with a concentration of 10 -6 ~10 -3 mol / L for use. Pipette the TCNQ solution and slowly drop it on the silicon oxide substrate transferred with nanosheets to ensure that the nanosheets on the substrate are in full contact with the solution and remain in the impregnated state for a certain time.

[0011] Step 3, surface spreading of TCNQ molecules: Immerse the nanosheets in the TCNQ solution, and use an ear syringe to concentrate the surface droplets; dry the surface droplets of the silicon oxide substrate in a vacuum drying oven to remove the residual solvent and accelerate the spreading of TCNQ molecules. The drying temperature is 50-180 degrees Celsius, and the drying time is 2-10 hours.

[0012] The two-dimensional magnetic material is a two-dimensional iron germanium telluride material.

[0013] The first step is to fully wash the single crystal of the two-dimensional magnetic material with ethanol, then perform exfoliation by mechanical exfoliation or liquid-phase exfoliation method, and transfer the exfoliated nanosheets to a silicon oxide substrate.

[0014] The second step is to dissolve TCNQ powder into DMF solvent with ultrasonic oscillation to prepare a TCNQ solution for use. Use a pipette to suck 1 ml of the TCNQ solution and slowly drop it on the silicon oxide substrate transferred with nanosheets. The substrate is covered with the TCNQ solution and the nanosheets are in full contact with the TCNQ solution.

[0015] The third step is to immerse the nanosheets in the TCNQ solution for 5 - 3600 seconds, and use an ear bulb to concentrate the surface droplets; use a vacuum drying oven to dry the surface droplets of the silicon oxide substrate to remove the DMF solvent and accelerate the spreading of TCNQ molecules. The drying temperature is 50 - 180 °C and the drying time is 2 - 10 hours.

[0016] In the second step, the purity of the TCNQ powder is 99.0% and the purity of the DMF solvent is analytical pure. The concentration of the prepared solution is 10 -6 ~10 -3 mol / L.

[0017] In the first step, the thickness of the silicon oxide substrate is 50 - 300 nanometers.

[0018] In the first step, the thickness of the exfoliated nanosheets is all below 200 nanometers and the lateral size is all below 50 micrometers.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The present invention selects TCNQ as an electron acceptor. TCNQ is a strong electron acceptor and can form a charge transfer pair with an electron donor. At the same time, TCNQ is a planar molecule. When it forms a complex with a two-dimensional material, theoretically, good spreading can be formed. Since the intermolecular distance is small enough, a considerable degree of π-electron cloud overlap can be formed, ultimately changing the conductivity of the two-dimensional material.

[0021] The present invention is applicable to multiple types of two-dimensional magnetic materials, not limited to two-dimensional itinerant ferromagnetic iron germanium telluride, and is also applicable to two-dimensional semiconductor magnetic materials. Similarly, the single crystal thinning method is applicable to methods such as mechanical exfoliation and liquid-phase exfoliation. Through a simple solution immersion and drying process, the organic molecules can be spread on the surface, improving the magnetic properties of the two-dimensional material to meet the requirements of spin electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is a flowchart for preparing the two-dimensional TCNQ / iron germanium telluride composite of the present invention;

[0024] Figure 2 It is a statistical chart of magnetic properties under different impregnation times of the present invention;

[0025] Figure 3 It is a comparison between the atomic force microscope (AFM) and the corresponding magnetic force microscope (MFM) of the original iron germanium telluride nanosheets and the TCNQ / iron germanium telluride composite thin sheets of the present invention;

[0026] Figure 4 It is a comparison of the magnetization intensity-temperature curves of the original iron germanium telluride and the composite in the optimal magnetization state of the present invention. Detailed Embodiments

[0027] The following further describes the detailed embodiments of the present invention in conjunction with the drawings. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Example 1:

[0029] A method for regulating two-dimensional magnetic materials through small molecule chemical adsorption, comprising the following steps;

[0030] Step 1, exfoliation and transfer of two-dimensional magnetic materials: Thoroughly wash the two-dimensional magnetic material single crystal to remove impurities, thin the single crystal by mechanical exfoliation or liquid phase exfoliation method, transfer the obtained nanosheets to a silicon substrate with an oxide layer, and measure the thickness of the nanosheets by atomic force microscope (AFM);

[0031] Step 2, preparation of TCNQ solution: Dissolve TCNQ powder in N,N-dimethylformamide (DMF) or tetrahydrofuran (THF) solvent to prepare a TCNQ solution with a concentration of 10 -6 ~10 -3 mol / L for standby. Pipette the TCNQ solution and slowly drop it on the silicon oxide substrate transferred with nanosheets to ensure that the nanosheets on the substrate are in full contact with the solution and remain in the impregnated state for a certain time;

[0032] Step 3, surface spreading of TCNQ molecules: The nanosheets are immersed in the TCNQ solution, and an ear pipette is used to concentrate the surface droplets; a vacuum drying oven is used to dry the surface droplets of the silicon oxide substrate to remove the residual solvent and accelerate the spreading of TCNQ molecules. The drying temperature is 50-180 °C, and the drying time is 2-10 hours.

[0033] The two-dimensional magnetic material is a two-dimensional iron germanium tellurium material. In Step 1, the two-dimensional magnetic material single crystal is thoroughly washed with ethanol, and then peeled by mechanical peeling or liquid-phase peeling methods, and the peeled nanosheets are transferred onto a silicon oxide substrate. In Step 2, the TCNQ powder is dissolved in the DMF solvent with ultrasonic oscillation to prepare a TCNQ solution for use. 1 ml of the TCNQ solution is aspirated with a pipette and slowly dropped onto the silicon oxide substrate transferred with nanosheets, and the substrate is covered with the TCNQ solution and the nanosheets are fully contacted with the TCNQ solution.

[0034] In Step 3, the nanosheets are immersed in the TCNQ solution, and the solution immersion time is 5-3600 seconds. An ear pipette is used to concentrate the surface droplets; a vacuum drying oven is used to dry the surface droplets of the silicon oxide substrate to remove the DMF solvent and accelerate the spreading of TCNQ molecules. The drying temperature is 50-180 °C, and the drying time is 2-10 hours. The purity of the TCNQ powder in Step 2 is 99.0%, and the purity of the DMF solvent is analytical grade. The concentration of the prepared solution is 10 -6 ~10 -3 mol / L. The thickness of the silicon oxide substrate in Step 1 is 50-300 nm. The thickness of the peeled nanosheets in Step 1 is all below 200 nm, and the lateral dimension is all below 50 μm.

[0035] Example 2:

[0036] A method for regulating two-dimensional magnetic materials by small molecule chemisorption, comprising the following steps;

[0037] Step 1, peeling and transfer of two-dimensional magnetic materials: The iron germanium tellurium single crystal is thoroughly washed to remove impurities, and then peeled by mechanical peeling or liquid-phase peeling methods. The thickness of the nanosheets is preliminarily estimated by an optical microscope and the peeled nanosheets are transferred onto a silicon oxide substrate that has been cleaned in advance; the thickness of the silicon oxide substrate in Step 1 is 200 nm. The thickness of the peeled nanosheets in Step 1 is all below 200 nm, and the average lateral dimension is 25 μm.

[0038] Step 2, preparation of TCNQ solution: The TCNQ powder is dissolved in the DMF solvent to prepare a solution with a concentration of 1×10 -6The TCNQ solution of [[mol / L]] is ready for use. Use a pipette to aspirate the TCNQ solution and slowly drop it onto the silicon oxide substrate transferred with nanosheets, ensuring that the nanosheets on the substrate are in full contact with the solution and maintaining the impregnation state for a certain period of time;

[0039] Step 3, surface spreading of TCNQ molecules: After the nanosheets are impregnated for 30 seconds, use an ear bulb to concentrate the surface droplets; use a vacuum drying oven to dry the surface droplets of the silicon oxide substrate, remove the residual DMF solvent and accelerate the spreading of TCNQ molecules. The drying temperature is 50 °C and the drying time is 2 hours.

[0040] Example 3:

[0041] The difference from Example 2 is that in Step 3, the solution of the two-dimensional iron germanium telluride flakes obtained by mechanical exfoliation is impregnated for 5 minutes, the drying temperature is 55 °C, and the drying time is 5 hours.

[0042] In Step 2, prepare a TCNQ solution with a concentration of 5×10 -5 [[mol / L]] for use.

[0043] Example 4:

[0044] The difference from Example 2 is that in Step 2, the solution is THF. In Step 3, the solution of the two-dimensional iron germanium telluride flakes obtained by mechanical exfoliation is impregnated for 10 minutes, and the drying temperature is 60 °C.

[0045] In Step 2, prepare a TCNQ solution with a concentration of 1×10 -4 [[mol / L]] for use.

[0046] Example 5:

[0047] The difference from Example 2 is that in Step 2, the solution is THF. In Step 3, the solution of the two-dimensional iron germanium telluride flakes obtained by mechanical exfoliation is impregnated for 30 minutes, and the drying temperature is 60 °C.

[0048] In Step 2, prepare a TCNQ solution with a concentration of 1×10 -3 [[mol / L]] for use.

[0049] Use AFM and MFM to statistically analyze the magnetic properties of the samples in Examples 1-5 above, and the results are as Figure 2 shown. Among them, Δphase represents the magnetic-related phase difference in MFM, and its value is negative, that is, the sample exhibits ferromagnetism, and the absolute value of it represents the strength of the magnetic property.

[0050] From Figure 2It can be seen that when the impregnation time is 10 minutes and the thickness of the nanosheets is 120 nm, the magnetization effect is the best. Among them, the impregnation time affects the uniformity of molecular spreading. When the impregnation time is too short or too long, organic molecules will form clusters more or less, resulting in uneven spreading. Similarly, the sample thickness affects the effective depth of magnetization. When the sample is too thin, the overall magnetic moment is small, resulting in weak magnetism. When the sample thickness is large, the magnetization depth does not meet the requirements of the sample thickness, resulting in a decrease in the overall magnetization effect.

[0051] We also compared the atomic force microscopy and magnetic force microscopy images of the original iron germanium telluride thin flakes and the TCNQ / iron germanium telluride composite thin flakes, and the results are as Figure 3 shown. Compared with the original iron germanium telluride thin flakes, the TCNQ / iron germanium telluride composite thin flakes exhibit significant room-temperature ferromagnetic properties.

[0052] Figure 4 For the comparison of the magnetization intensity-temperature curves of the original iron germanium telluride and the sample in Example 4, it can be seen from the curves that compared with the original iron germanium telluride, the sample in Example 4 exhibits a Curie temperature much higher than room temperature.

[0053] In summary, the present invention provides an effective method for enhancing two-dimensional magnetism by small molecule adsorption. The present invention uses the method of surface adsorption of the electron acceptor molecule TCNQ to transfer electrons in the two-dimensional iron germanium telluride thin flakes. By changing the solution impregnation time, the spreading effect of the molecules can be optimized, so as to achieve the best magnetization state. The method for enhancing the magnetism of two-dimensional iron germanium telluride thin flakes provided by the present invention has remarkable effects, is simple to operate, and effectively expands the application prospects of two-dimensional iron germanium telluride in spin electronic devices.

[0054] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principles and spirits of the present invention, various changes, modifications, substitutions and variations to these embodiments still fall within the protection scope of the present invention.

Claims

1. A method for regulating two-dimensional magnetic materials through small molecule chemisorption, characterized in that: Including the following steps; Step 1, exfoliation and transfer of two-dimensional magnetic material: Thoroughly wash the single crystal of two-dimensional magnetic material to remove impurities, then exfoliate it by mechanical exfoliation or liquid-phase exfoliation method, and transfer the exfoliated nanosheets onto a silicon substrate with an oxide layer; Step 2, preparation of TCNQ solution: Dissolve TCNQ powder in N,N-dimethylformamide or tetrahydrofuran solvent for later use. Use a pipette to suck up the TCNQ solution and slowly drip it onto the silicon oxide substrate transferred with nanosheets to make the nanosheets fully contact with the TCNQ solution; Step 3, surface spreading of TCNQ molecules: Immerse the nanosheets in the TCNQ solution, and use an ear bulb to concentrate the surface droplets; Use a vacuum drying oven to dry the surface droplets of the silicon oxide substrate to remove the residual solvent and accelerate the spreading of TCNQ molecules. The two-dimensional magnetic material is two-dimensional iron germanium telluride material.

2. The method for regulating two-dimensional magnetic materials by small molecule chemical adsorption according to claim 1, wherein: In Step 1, the single crystal of two-dimensional magnetic material is thoroughly washed with ethanol, then exfoliated by mechanical exfoliation or liquid-phase exfoliation method, and the exfoliated nanosheets are transferred onto a silicon substrate with an oxide layer.

3. A method for regulating two-dimensional magnetic materials by small molecule chemical adsorption according to claim 1, characterized in that: In Step 2, TCNQ powder is dissolved in N,N-dimethylformamide or tetrahydrofuran solvent with ultrasonic oscillation to prepare the TCNQ solution for later use. Use a pipette to suck up 1 ml of TCNQ solution and slowly drip it onto the silicon oxide substrate transferred with nanosheets. The substrate is covered with the TCNQ solution and the nanosheets are fully in contact with the TCNQ solution.

4. A method for regulating two-dimensional magnetic materials through small molecule chemisorption according to claim 1, characterized in that: In Step 3, the nanosheets are immersed in the TCNQ solution for 5 - 3600 seconds, and use an ear bulb to concentrate the surface droplets; Use a vacuum drying oven to dry the surface droplets of the silicon oxide substrate to remove the residual solvent and accelerate the spreading of TCNQ molecules. The drying temperature is 50 - 180 °C and the drying time is 2 - 10 hours.

5. A method for regulating two-dimensional magnetic materials by small molecule chemisorption according to claim 1 or 3, characterized in that: In the second step, the purity of the TCNQ powder is 99.0%, the purity of the N,N-dimethylformamide or tetrahydrofuran solvent solution is of analytical reagent grade, and the concentration of the prepared TCNQ solution is 10 -6 ~10 -3 mol / L.

6. A method for regulating two-dimensional magnetic materials by small molecule chemisorption according to claim 1, characterized in that: In Step 1, the thickness of the silicon oxide substrate is 50 - 300 nanometers.

7. A method for regulating two-dimensional magnetic materials by small molecule chemical adsorption according to claim 1, characterized in that: In Step 1, the thickness of the exfoliated nanosheets is less than 200 nanometers and the lateral size is less than 50 micrometers.

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