Strain-induced ferromagnetic Mn-doped MoS2 thin film material and preparation method thereof

Abstract

The invention relates to a strain-induced ferromagnetic Mn-doped MoS2 film material and a preparation method thereof, and belongs to the technical field of two-dimensional magnetic semiconductor materials, the technical key points are as follows: the chemical formula of the material is Mo (1-x) MnxS2, and stable biaxial tensile strain is formed by depositing a MoSe2 buffer layer on a Si (100) substrate and introducing lattice mismatch with the Mo (1-x) MnxS2; the ferromagnetic coupling effect between Mn atoms can be enhanced through strain regulation and control, and room-temperature intrinsic ferromagnetism is achieved; moSe2 and Mo (1-x) MnxS2 films are sequentially deposited in a magnetron co-sputtering mode, and a crystal structure and magnetic response performance are optimized through high vacuum annealing; the thickness of the obtained film is 15-25 nm, the saturation magnetization reaches 0.011 emu / g, and the Curie temperature is higher than 315 K. The method is stable in preparation process and adjustable in parameter, and the obtained material is suitable for the fields of spintronics, magnetic sensors and the like.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional magnetic semiconductor materials technology, and more specifically, to a strain-induced ferromagnetic Mn-doped MoS2 thin film material and its preparation method. Background Technology

[0002] With the rapid development of two-dimensional materials research, transition metal dichalcogenides (TMDs) have shown broad application prospects in next-generation electronic devices, optoelectronic devices, and flexible wearable devices due to their unique layered structure and excellent electronic and optical properties. MoS2, as a representative TMD material, has seen extensive research and partial applications in field-effect transistors, photodetectors, and catalysis. However, MoS2 itself is a non-magnetic material, limiting its functional applications in spintronics. Achieving its ferromagnetism, especially intrinsic ferromagnetism stable at room temperature, is one of the key technological bottlenecks for improving its device integration capabilities and functional diversity.

[0003] Current research on introducing magnetism into the MoS2 system mainly focuses on transition metal doping (such as Mn, Fe, and Co), edge modification, and defect engineering. Among these, Mn doping is considered a relatively stable and tunable magnetization pathway. Theoretical calculations and some experiments have shown that Mn atoms can substitute for Mo sites and form localized magnetic moments under certain conditions, thereby generating ferromagnetic coupling. However, in actual fabrication processes, due to factors such as poor lattice matching, inhomogeneous doping, and insufficient thermal stability, the resulting MoS2 magnetic films often exhibit weak magnetism, low Curie temperatures, and unstable magnetic responses, making it difficult to meet the basic magnetic performance requirements of room-temperature spintronic devices.

[0004] In recent years, strain engineering has gradually become an important means of controlling the properties of low-dimensional materials. By adjusting the lattice strain, the band structure, magnetic coupling behavior, and electronic state distribution of materials can be effectively altered. In the MoS2 system, theoretical studies have shown that applying biaxial tensile strain can significantly enhance the ferromagnetic coupling strength between Mn atoms and raise the Curie temperature to above room temperature, offering new possibilities for achieving intrinsic ferromagnetism. However, there is currently a lack of experimental schemes based on strain control to stably introduce strain into the MoS2 system and obtain high-quality thin film materials with room-temperature ferromagnetism. In particular, how to precisely control the strain source, stabilize the doped state, and maintain structural integrity during the thin film deposition process remains a key challenge in this research direction.

[0005] Therefore, developing a strain-controlled mechanism to realize room-temperature ferromagnetic Mn-doped MoS2 thin film materials and constructing a controllable and repeatable fabrication process not only fills the gap in existing experimental research, but also provides an important theoretical foundation and technical support for the practical application of two-dimensional magnetic semiconductor materials in the field of spin devices. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems mentioned in the background section and to provide a method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film materials.

[0007] The above-mentioned objective of the present invention is achieved as follows:

[0008] A strain-induced ferromagnetic Mn-doped MoS2 thin film material, the chemical formula of the thin film material being Mo1-xMn x S2, where x represents the doping ratio of Mn, satisfying 0 <x<0.3;

[0009] The thin film is deposited on a MoSe2 substrate, utilizing the reaction of MoSe2 and Mo1-xMn. x The lattice constant mismatch between S2 introduces biaxial tensile strain, which enhances the ferromagnetic coupling effect between Mn atoms, enabling the thin film material to exhibit stable intrinsic ferromagnetism at room temperature, with a Curie temperature above 315K.

[0010] As a preferred technical solution of the present invention, the Mo1-xMn x The molar ratio of Mo, Mn, and S in the S2 thin film is approximately 4:1:10, and the film thickness is controlled between 15-25 nm to ensure magnetic uniformity and structural integrity.

[0011] As a preferred technical solution of the present invention, the MoSe2 substrate has a thickness of 5-10nm and is formed by magnetron sputtering. The substrate is deposited on a cleaned Si(100) crystalline silicon substrate to improve adhesion and film flatness.

[0012] This invention also provides a method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film materials, comprising the following steps:

[0013] (1) A MoSe2 buffer layer was deposited on a Si(100) substrate by magnetron sputtering to construct a strain-controlled substrate structure;

[0014] (2) Mo, Mn and S are deposited on the MoSe2 substrate by magnetron co-sputtering to form Mo1-xMn. x The S2 thin film layer utilizes the lattice mismatch between the substrate and the film layer to introduce biaxial tensile strain;

[0015] (3) Regarding the Mo1-xMn x The S2 thin film was subjected to high-vacuum annealing to promote crystal growth, stabilize the Mn doped state, and optimize its magnetic properties.

[0016] As a preferred technical solution of the present invention, the deposition of the MoSe2 buffer layer in step (1) uses a Mo target and a Se target, both of which are 3-inch diameter disk-shaped targets. Radio frequency power of 35W and 65W are applied respectively. The deposition atmosphere is Ar, the gas flow rate is 24 SCCM, the cavity deposition pressure is 4 mTorr, and the background vacuum of the main chamber is better than 5.5 × 10⁻⁶ m / s². -8 Torr.

[0017] As a preferred technical solution of the present invention, the Mo1-xMn in step (2) x The deposition of the S2 thin film employed a combination of Mn, Mo, and S targets for sputtering. The Mn and Mo targets used DC powers of 20 W and 35 W, respectively, while the S target used an RF power of 60 W. During deposition, the background vacuum in the main chamber was better than 6.0 × 10⁻⁶. -8 Torr, deposition pressure 4 mTorr, Ar flow maintained at 24 SCCM.

[0018] As a preferred technical solution of the present invention, in step (2), an external magnetic field with a magnetic field strength of 650 Oe and a direction parallel to the thin film surface is applied during the thin film deposition process to induce in-plane uniaxial magnetic anisotropy and enhance the magnetic anisotropic response of the thin film.

[0019] As a preferred embodiment of the present invention, the annealing temperature in step (3) is set to 600-700℃, the annealing duration is 10-30 minutes, and the annealing environment is under high vacuum conditions with a gas pressure better than 7.5×10⁻⁶. -7 Torr is used to promote crystal reconstruction and uniform strain diffusion.

[0020] As a preferred technical solution of the present invention, the substrate temperature in the deposition process in step (2) is controlled between 200-500℃ to improve the crystal quality of the film and the effectiveness of Mn doping, and to prevent the formation of a non-magnetic intermediate phase.

[0021] As a preferred technical solution of the present invention, in step (2), the S element is introduced by using H2S gas as the sulfur source, which is mixed with Ar and injected into the reaction chamber through a preset flow rate ratio; in order to ensure operational safety, the system is equipped with a dedicated gas cabinet, a toxic gas leak alarm and a positive pressure gas mask, and the operation is completed in a fume hood or a closed reaction platform.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention designs MoSe2 and Mo1-xMnx The lattice mismatch between S2 atoms introduces stable biaxial tensile strain within the material, effectively enhancing the ferromagnetic coupling between Mn atoms, thus achieving intrinsic ferromagnetism at room temperature. Compared to traditional strain-uncontrolled MoS2 magnetic thin film materials, this invention provides a structurally stable two-dimensional magnetic semiconductor material with significantly enhanced magnetic response, effectively overcoming the technical bottleneck of existing systems with Curie temperatures below 300K.

[0024] 2. This invention uses magnetron co-sputtering to prepare Mo1-xMn. x The S2 thin film, combined with high-vacuum annealing and external magnetic field induction, produces a uniform and dense structure with high Mn doping efficiency and excellent crystal quality. The saturation magnetization of the material reaches 0.011 emu / g, and the coercivity is close to 100 Oe. It is superior to existing similar experimental systems in terms of structural stability and magnetic property uniformity, and has the potential for industrial scale-up with strong repeatability and adjustable parameters.

[0025] 3. This invention is the first to realize a synergistic control mechanism of "doping + strain" in the field of magnetic control of two-dimensional materials, which expands the application boundary of strain engineering in magnetic semiconductor materials, enriches the magnetic tuning path of MoS2 system, and also provides a replicable experimental strategy for other two-dimensional material systems to achieve room temperature ferromagnetism. It has important theoretical guiding significance and practical application prospects, and is particularly suitable for the key material design of novel spintronic devices such as spin injectors, magnetic channels, and spin logic gates. Attached Figure Description

[0026] Figure 1 This is a hysteresis loop diagram of the Mn-doped MoS2 thin film material prepared in the embodiments of the present invention at room temperature (300K) (the horizontal axis is the applied magnetic field H, unit: Oe; the vertical axis is the mass magnetization σ, unit: emu / g). Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0029] Example: This invention provides a method for preparing a Mn-doped MoS2 thin film material with room-temperature ferromagnetism achieved through tensile strain control. The purpose of this invention is to address the problems of weak magnetism and low Curie temperature in traditional doped MoS2 magnetic thin films. Specifically, this method utilizes a lattice mismatch strategy to introduce controllable biaxial tensile strain into Mn-doped MoS2, enhancing the magnetic moment coupling strength and thus achieving stable room-temperature ferromagnetism. This method is suitable for cutting-edge fields such as magnetic storage and spintronics.

[0030] In the specific implementation of the invention, a Si(100) single-crystal silicon substrate is first selected as the support substrate. After removing surface contaminants using standardized chemical cleaning, the substrate is dried with nitrogen and immediately fed into a magnetron sputtering system. A MoSe2 buffer layer is used to construct a strain-controlled structure. Mo and Se are deposited sequentially by magnetron sputtering to form a MoSe2 layer. In this step, the Mo and Se targets are 3-inch diameter metal disk targets, with RF sputtering powers of 35W and 65W applied respectively. The working atmosphere is pure Ar, the flow rate is set to 24 SCCM, the system deposition pressure is controlled at 4 mTorr, and the main cavity vacuum is maintained at 5.5 × 10⁻⁶ m / s². -8 The deposition temperature was kept below Torr to ensure film density and interface cleanliness. The deposition temperature was controlled between 200-500K, which facilitated the formation of the MoSe2 crystal structure and subsequent film adhesion. The final MoSe2 buffer layer was approximately 6 nm thick, providing a lattice constant basis for introducing biaxial tensile strain into the subsequent film.

[0031] Subsequently, Mo1-xMn was produced on a MoSe2 substrate. x Deposition of the S2 thin film. This step employed a three-target co-sputtering method using Mn, Mo, and S targets, with applied power levels of 20 W (Mn), 35 W (Mo), and 60 W (S), respectively. DC sputtering was used for the Mn and Mo targets, while RF sputtering was used for the S target. The deposition gas pressure was maintained at 4 mTorr, and the main cavity vacuum was better than 6.0 × 10⁻⁶. -8 The Torr and Ar flow rate remained at 24 SCCM. During the deposition process, H2S gas with a controlled dilution ratio was injected into the chamber as a sulfur source gas to regulate the S content and promote the formation of Mo–S and Mn–S bonds. Considering the toxicity of H2S, the system was equipped with a dedicated gas cabinet, a toxic gas alarm, and a positive-pressure gas mask, and was operated in a well-ventilated closed system.

[0032] During thin film deposition, to improve magnetic anisotropy, a constant magnetic field with a strength of 650 Oe is applied parallel to the film plane along the target-substrate plane, which helps induce uniaxial in-plane magnetic anisotropy. The deposition temperature is maintained at the same level as the previous stage, controlled between 200-500 K to promote the doping efficiency of Mn atoms and suppress the formation of amorphous structures. The final obtained Mo1-xMn... xThe S2 thin film thickness is controlled in the range of 15-25 nm. It has a dense structure, uniform element doping, and a molar ratio of Mn:Mo:S of about 1:4:10, which meets the electronic structure distribution required for magnetic control.

[0033] After deposition, the prepared film was annealed under high vacuum to further optimize its crystal structure and magnetic properties. Annealing was performed in a vacuum furnace with a vacuum level better than 7.5 × 10⁻⁶. -7 Torr annealing was performed at temperatures between 600-700 K for 10-30 minutes. This treatment facilitates the stabilization of Mn doping, defect repair, and uniform strain propagation within the film. After annealing and cooling to room temperature, the samples were removed. The sample surface showed uniform color, no obvious cracks, and a dense film structure.

[0034] Phase structure and crystallinity analysis were performed using X-ray diffraction (XRD) to confirm Mo1-xMn x The S2 thin film exhibits a layered 2H-MoS2 crystal structure with no obvious impurity phases. Energy dispersive spectroscopy (EDS) analysis confirmed that the atomic ratios of Mo, Mn, and S were close to the target molar ratio, indicating successful and uniform doping. Hysteresis loop measurements at room temperature using a vibrating sample magnetometer (VSM) revealed a clearly open hysteresis loop with saturation magnetization between 0.009 and 0.012 emu / g. Stable residual magnetism and coercivity confirmed typical room-temperature ferromagnetism. Further calculations using mean-field theory showed that the Curie temperature of the material is above 315 K, meeting the requirements for spintronics applications under practical room-temperature conditions.

[0035] The Mn-doped MoS2 thin film material prepared by the above-described embodiments of the present invention utilizes lattice mismatch to introduce biaxial tensile strain. Combined with a reasonable sputtering ratio, magnetic field-induced direction control, and vacuum heat treatment, the magnetic moment coupling of Mn atoms is transformed from an antiferromagnetic state to a ferromagnetic coupling, forming a stable two-dimensional magnetic state. While ensuring the electrical properties of the material, the magnetic response characteristics are significantly enhanced. Furthermore, the preparation process of the present invention is simple, the process parameters are controllable, and the repeatability is good, making it suitable for widespread application in fields such as magnetic control of two-dimensional materials, novel magnetic sensors, and spin logic devices.

[0036] This embodiment also provides a specific method for preparing room-temperature ferromagnetic Mn-doped MoS2 thin film materials by magnetron sputtering under laboratory conditions, in order to verify the feasibility and superiority of the technical solution of the present invention.

[0037] The magnetron sputtering equipment used in the experiment was the Kurt J. Lesker PVD75PRO-Line magnetron sputtering system, which has a three-target co-sputtering function, a programmable substrate heating and external magnetic field control module, and is suitable for high-precision thin film deposition experiments.

[0038] First, a 2-inch Si(100) single-crystal silicon substrate was selected, ultrasonically cleaned with acetone and anhydrous ethanol for 10 minutes, dried with nitrogen, and immediately placed in the sputtering chamber for pre-drying and dehumidification. The system was evacuated to a baseline vacuum level better than 5.5 × 10⁻⁶. - 8 Torr.

[0039] Subsequently, a MoSe2 buffer layer was formed by sputtering using a 3-inch Mo and Se metal target. RF sputtering powers of 35W and 65W were applied, respectively. The working atmosphere was high-purity Ar gas with a flow rate of 24 SCCM, a working pressure of 4 mTorr, and a substrate temperature of 300 K. This deposition process lasted for 15 minutes, resulting in a MoSe2 layer approximately 6 nm thick. Since the lattice constant of MoSe2 is greater than that of MoS2, subsequent material growth will introduce approximately 2.5% biaxial tensile strain into the thin film layer.

[0040] Then Mo1-xMn x Deposition of S2 magnetic thin films. Co-sputtering was employed, using Mn (99.9%), Mo (99.99%), and S (ternary compound MoS2 ceramic target) targets for deposition. DC power of 20 W and 35 W was applied to the Mn and Mo targets, respectively, while RF power of 60 W was applied to the S target. The main cavity floor vacuum was better than 6.0 × 10⁻⁶. -8 The working pressure was maintained at 4 mTorr, the gas flow rate was 24 SCCM, and a 1% volume fraction of H2S / Ar mixed gas was introduced to supplement the sulfur element. To ensure operational safety, the H2S gas cylinder was placed in a dedicated gas cabinet and equipped with a toxic gas alarm and a negative pressure exhaust system. The deposition time was set to 40 minutes, and the film thickness was controlled to be approximately 22 nm.

[0041] Throughout the thin film deposition process, a constant magnetic field of 650 Oe was applied, with the magnetic field direction parallel to the film plane, to induce in-plane uniaxial magnetic anisotropy. The substrate temperature was maintained at 350 K to improve crystallinity and stabilize Mn substitution doping.

[0042] After deposition, the sample was post-treated in a vacuum annealing furnace at a temperature of 650 K for 20 minutes, with a vacuum level better than 7.5 × 10⁻⁶. -8 Torr is used to further promote grain rearrangement, enhance Mn doping uniformity, and release residual stress.

[0043] After annealing and cooling to room temperature, the sample was removed and its crystal structure was tested by X-ray diffraction (XRD). The crystal structure of the film was confirmed to be 2H-MoS2, and no obvious Mn or MnS phase separation was observed. The elemental ratio of the film was tested by energy dispersive spectroscopy (EDS), and the results showed that Mo:Mn:S was about 4:1:10, which met the target ratio.

[0044] Furthermore, to verify the room-temperature magnetic response performance of the prepared thin film material, a vibrating sample magnetometer (VSM) was used to perform hysteresis loop tests on the Mn-doped MoS2 thin film obtained in this embodiment at 300 K. The test results are as follows: Figure 1 As shown in the figure, the horizontal axis represents the applied magnetic field strength H (unit: Oe), ranging from -2000 Oe to +2000 Oe, and the vertical axis represents the mass magnetization σ (unit: emu / g), ranging from -0.010 emu / g to +0.010 emu / g. The results indicate that the Mn-doped MoS2 film still possesses a certain remanent magnetization under zero magnetic field, exhibiting significant hysteresis without hysteresis closure or sharp reversal characteristics, suggesting that it is not paramagnetic or superparamagnetic, but rather possesses stable intrinsic ferromagnetism. The saturation magnetization of this sample reaches 0.011 emu / g, and the coercivity is approximately 98 Oe, further confirming that the biaxial tensile strain introduced through the substrate significantly enhances the magnetic moment coupling. Figure 1 The hysteresis loop curve shown is stable and symmetrical, which is highly consistent with the room temperature magnetic control effect expected by this invention.

[0045] The final results show that the embodiments of the present invention successfully prepared Mn-doped MoS2 thin film materials with ferromagnetism at room temperature. The crystal structure is complete, the strain is effectively regulated, and the magnetic response is obvious. This verifies the theoretical path of introducing strain regulation of Mn magnetic moment coupling through MoSe2 lattice mismatch, which has good industrial application potential and academic research value.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A strain-induced ferromagnetic Mn-doped MoS2 thin film material, characterized in that, The chemical formula of the thin film material is Mo. 1-x Mn x S2, where x represents the doping ratio of Mn, satisfying 0 <x<0.3; The thin film is deposited on a MoSe2 substrate, utilizing the reaction between MoSe2 and Mo... 1-x Mn x The lattice constant mismatch between S2 introduces biaxial tensile strain, which enhances the ferromagnetic coupling effect between Mn atoms, enabling the thin film material to exhibit stable intrinsic ferromagnetism at room temperature, with a Curie temperature above 315K.

2. The strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 1, characterized in that, The Mo 1- x Mn x The molar ratio of Mo, Mn, and S in the S2 thin film is 4:1:10, and the film thickness is controlled between 15-25 nm.

3. The strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 1, characterized in that, The MoSe2 substrate has a thickness of 5-10 nm and is formed by magnetron sputtering. The substrate is deposited on a cleaned Si(100) crystalline silicon substrate.

4. A method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) A MoSe2 buffer layer was deposited on a Si(100) substrate by magnetron sputtering to construct a strain-controlled substrate structure; (2) Mo, Mn and S are deposited on the MoSe2 substrate by magnetron co-sputtering to form Mo 1-x Mn x The S2 thin film layer utilizes the lattice mismatch between the substrate and the film layer to introduce biaxial tensile strain; (3) For the Mo 1-x Mn x The S2 thin film was subjected to high-vacuum annealing to promote crystal growth, stabilize the Mn doped state, and optimize its magnetic properties.

5. The method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 4, characterized in that, The deposition of the MoSe2 buffer layer in step (1) uses Mo and Se targets, both of which are 3-inch diameter disk-shaped targets. RF powers of 35W and 65W are applied respectively. The deposition atmosphere is Ar, the gas flow rate is 24 SCCM, the cavity deposition pressure is 4 mTorr, and the base vacuum of the main chamber is better than 5.5 × 10⁻⁶. -8 Torr.

6. The method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 4, characterized in that, The Mo1-xMn mentioned in step (2) x The deposition of the S2 thin film employed a combination of Mn, Mo, and S targets for sputtering. The Mn and Mo targets used DC powers of 20 W and 35 W, respectively, while the S target used an RF power of 60 W. During deposition, the background vacuum in the main chamber was better than 6.0 × 10⁻⁶. -8 Torr, deposition pressure 4 mTorr, Ar flow maintained at 24 SCCM.

7. The method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 4, characterized in that, In step (2), an external magnetic field with a strength of 650 Oe and a direction parallel to the film surface is applied during the film deposition process to induce in-plane uniaxial magnetic anisotropy and enhance the magnetic anisotropic response of the film.

8. The method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 4, characterized in that, The annealing temperature in step (3) is set to 600-700℃, the annealing duration is 10-30 minutes, and the annealing environment is under high vacuum conditions with a gas pressure better than 7.5×10⁻⁶. -7 Torr.

9. The method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 4, characterized in that, In step (2), the substrate temperature during the deposition process is controlled between 200-500℃ to improve the crystal quality of the film and the effectiveness of Mn doping, and to prevent the formation of a non-magnetic intermediate phase.

10. The method for preparing strain-induced ferromagnetic Mn-doped MoS2 thin film material according to claim 4, characterized in that, In step (2), the sulfur element is introduced by using H2S gas as the sulfur source, which is mixed with Ar and injected into the reaction chamber through a preset flow ratio. The system is equipped with a dedicated gas cabinet, a toxic gas leak alarm and a positive pressure gas mask, and the operation is completed in a fume hood or a closed reaction platform.

Images