Method for preparing single crystal manganese nitride thin film
By combining molecular beam epitaxy and radio frequency plasma pyrolysis, the problem of preparing single-crystal manganese nitride thin films was solved by controlling the nitrogen partial pressure and radio frequency power, resulting in high-quality single-crystal manganese nitride thin films suitable for antiferromagnetic spintronics research.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INSTITUTE OF PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2024-11-05
- Publication Date
- 2026-05-08
AI Technical Summary
Existing technologies make it difficult to prepare high-quality single-crystal manganese nitride films without impurities, which limits their application in antiferromagnetic memory materials.
A single-crystal manganese nitride thin film was prepared by using molecular beam epitaxy combined with a radio frequency plasma pyrolysis source, strictly controlling the nitrogen partial pressure and radio frequency power, and pre-treating the substrate, including annealing under high vacuum and in-situ annealing.
High-quality single-crystal manganese nitride thin films with uniform composition and precisely controllable thickness were obtained. These films exhibit good single-crystal properties, stability, and antiferromagnetic properties, making them suitable for antiferromagnetic spintronics research.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of materials. Specifically, this invention relates to a method for preparing single-crystal manganese nitride thin films. Background Technology
[0002] With the development of the Internet of Things and the rapid advancement of artificial intelligence applications, human society is constantly placing higher demands on the application areas and scope of computers. The traditional von Neumann computer architecture relies on linear logic communication between the arithmetic control unit and various memory units. The massive data access, transmission, and computation result in limitations imposed by the "memory wall" and "power wall." To meet the demands of today's data-intensive applications, next-generation logic storage devices need to consider the following characteristics: 1. Non-volatility: The device must be able to handle unexpected situations and prevent data loss due to unforeseen circumstances; 2. Low power consumption: Massive data computation requires very low power consumption to avoid unnecessary energy waste and interference with device operation; 3. Large storage capacity: Capable of handling and storing massive amounts of data.
[0003] Magnetic random access memory (MRAM) has the potential to be a next-generation logic memory device. It represents the logical relationship of "0" and "1" through two different states of a ferromagnetic layer. Compared to traditional charge storage, MRAM devices exhibit excellent non-volatility and near-zero static power consumption, and also boast high storage density, meeting the demands for large-scale data storage and computation. After many years of research and development, MRAM has gradually entered commercial use, from the first-generation Toggle-MRAM based on strong external magnetic field manipulation of the magnetic moment to the new generation of STT and SOT-MRAM devices based on spin-polarized current manipulation of the magnetic moment. However, these devices still face some unavoidable problems, such as data loss caused by strong external magnetic field interference, power consumption due to large manipulation current, and limitations on device miniaturization due to the involvement of auxiliary external fields. These issues require further research and improvement of current MRAM devices.
[0004] One approach to solving the aforementioned problems is further research into antiferromagnetic materials. The crystal lattice of antiferromagnetic materials consists of alternating magnetic atoms with opposite magnetic moments. Overall, antiferromagnetic materials do not exhibit outward magnetism and are not sensitive to external perturbed magnetic fields. Furthermore, they possess terahertz-level spin response speeds, making them potential cores for next-generation logic memory devices. On one hand, by manipulating the direction of the Nell vector in antiferromagnetic materials, the changes in high and low resistance states can be electrically controlled, providing an important approach for using antiferromagnetic materials as magnetic storage materials. On the other hand, it has been discovered that the exchange bias at the interface between antiferromagnetic and ferromagnetic materials can act as an effective field to assist in the decisive flipping of the magnetic moment in MRAM devices. Moreover, under a certain write current, this exchange bias field itself also flips, providing new insights for the application of antiferromagnetic materials in MRAM devices.
[0005] However, while traditional antiferromagnetic metallic materials such as IrMn and PtMn have mature manufacturing processes and are suitable for the industrial production of current GMR and TMR devices, their use still faces numerous challenges. For example, the large-scale use of rare and expensive metals hinders cost reduction, and the high formation temperature of the antiferromagnetic ordered structure impedes practical industrial preparation and application. There is a need to find suitable material systems for antiferromagnetic spintronics research and application, and to conduct fundamental property studies to develop them as the core of next-generation logic memory devices. Among the many antiferromagnetic material systems, manganese nitride (MnN) is a potential candidate for magnetic storage, and there are already some reports on its antiferromagnetic spintronic applications. In conclusion, antiferromagnetic manganese nitride has the potential for research and application as a next-generation antiferromagnetic spintronic device; however, the preparation of its thin films still faces challenges such as impurities or poor crystal quality, limiting further research on this material.
[0006] In existing technologies, magnetron sputtering or molecular beam epitaxy are commonly used to prepare manganese nitride thin films. However, the preparation of high-quality single-crystal manganese nitride materials still faces some challenges. For example, the existing technology (Large exchange bias in polycrystalline MnN / CoFe bilayers at room temperature, Markus Meinert, PHYSICALREVIEW B, VOLUME 92, ISSUE 14) discloses a method for preparing manganese nitride thin films using magnetron sputtering, but the sample prepared is a polycrystalline structure. The existing technology (Crystalline phase and orientation control of manganese nitride grown on MgO(001) by molecular beam epitaxy, Haiqiang Yang, JOURNAL OF APPLIED PHYSICS, VOLUME 91, NUMBER 3) discloses a method for preparing manganese nitride thin films. Although it also uses molecular beam epitaxy, the crystal growth quality is poor, it is not single-crystal, and other phases appear.
[0007] Therefore, there is an urgent need for a method to prepare single-crystal manganese nitride thin films that can obtain impurity-free and high-quality single-crystal thin films. Summary of the Invention
[0008] The purpose of this invention is to provide a method for preparing single-crystal manganese nitride thin films, which can obtain high-quality single-crystal thin films free of impurities. The method of this invention can produce single-crystal thin films with uniform composition, precise and controllable thickness, and high quality, thus providing a reliable foundation for the application of single-crystal manganese nitride materials as antiferromagnetic storage materials.
[0009] The above-mentioned objective of the present invention is achieved through the following technical solution.
[0010] This invention provides a method for preparing single-crystal manganese nitride thin films, comprising the following steps:
[0011] (1) Pre-treat the substrate to remove impurities adsorbed on the substrate surface;
[0012] (2) Using a manganese source as the evaporation source and a radio frequency plasma pyrolysis source, nitrogen molecules were pyrolyzed into more chemically reactive nitrogen atoms, and a single-crystal manganese nitride thin film was prepared by molecular beam epitaxy; wherein the nitrogen partial pressure was 2 × 10⁻⁶. -5 -4×10 -5 Millibar, RF power is 200-300W.
[0013] The inventors of this application unexpectedly discovered that when preparing single-crystal manganese nitride thin films using molecular beam epitaxy, it is necessary to strictly control the nitrogen partial pressure and radio frequency power in order to obtain high-quality single-crystal manganese nitride thin films.
[0014] If the partial pressure of nitrogen is less than 2 × 10 -5 At millibars, due to the low partial pressure of nitrogen, there are not enough nitrogen atoms to participate in the synthesis of substances, ultimately forming substances with even lower nitrogen content, such as trimanganese dinitride or tetramanganese nitride; if the partial pressure of nitrogen is greater than 4 × 10⁻⁶, ... -5 The presence of domain structures in the material due to excessive nitrogen partial pressure (mbar) may indicate that the material is no longer a rock salt mineral structure, but has formed structures such as sphalerite.
[0015] If the radio frequency power is less than 200W, the radio frequency plasma pyrolysis source cannot be effectively used to pyrolyze nitrogen molecules to form nitrogen atoms. If the radio frequency power is greater than 300W, although the effective nitrogen atoms produced will increase significantly, the energy transferred to the nitrogen atoms will also be greater due to the excessive radio frequency power, which is not conducive to the growth kinetics of Mn atoms and nitrogen atoms on the substrate surface.
[0016] In this invention, the purpose of pretreating the substrate is to remove impurities adsorbed on the surface and obtain a smooth surface.
[0017] Preferably, in the method of the present invention, the pretreatment of the substrate in step (1) is performed by a method including the following steps:
[0018] The substrate is placed in the molecular beam epitaxy chamber, and the substrate is less than or equal to 10. -10 Anneal at 900-1000℃ for 0.5-2 hours under a vacuum of millibars.
[0019] Preferably, in the method described in this invention, the substrate is selected from magnesium oxide and / or strontium titanate.
[0020] Preferably, in the method described in this invention, the purity of the manganese source is greater than or equal to 99.9998% by weight.
[0021] Preferably, in the method described in this invention, the purity of the nitrogen gas is greater than or equal to 99.9999% by weight.
[0022] Preferably, in the method described in this invention, the temperature of the evaporation source is set to 730-770°C.
[0023] Preferably, in the method described in this invention, the preparation of single-crystal manganese nitride thin films by molecular beam epitaxy in step (2) is carried out under the following conditions:
[0024] The growth temperature is 300-350℃, and the growth time is 15-120 minutes.
[0025] Preferably, in the method described in this invention, the method further includes the following steps after step (2):
[0026] The monocrystalline manganese nitride film obtained in step (2) is subjected to in-situ annealing to obtain a higher quality monocrystalline manganese nitride film.
[0027] Preferably, in the method described in this invention, the in-situ annealing treatment is performed under the following conditions:
[0028] The annealing temperature is 300-350℃, and the nitrogen partial pressure is 2×10⁻⁶. -5 -4×10 -5 Millibars, annealing time is 25 minutes to 1 hour.
[0029] This invention provides a method for preparing a single-crystal manganese nitride thin film, namely, a high-quality single-crystal manganese nitride thin film with a thickness of 5-40 nanometers is epitaxially grown on a magnesium oxide (MgO) substrate using molecular beam epitaxy. Throughout the growth process, reflective high-energy electron diffraction (RHEED) is used to characterize the film growth in situ and monitor the film growth quality. The growth time is 15-120 minutes, and different thicknesses of manganese nitride films can be obtained by controlling the growth time. After growth, the sample is annealed in situ within a chamber to improve the growth quality of the manganese nitride thin film. After annealing, the heating stage is cooled and the sample is removed, yielding a high-quality epitaxial single-crystal manganese nitride (MnN) thin film sample.
[0030] The present invention has the following beneficial effects:
[0031] (1) The high-quality single-crystal manganese nitride thin film of the present invention was prepared by molecular beam epitaxy and has good single-crystal properties. X-ray diffraction scans of the film at 10-110° were performed. The results showed that the single peak appearing at 43.65° corresponds to the (002) peak of the MnN material. Laue oscillations on both sides of the main peak indicate its high crystal quality and good interface with the substrate. The out-of-plane lattice constant of the single-crystal thin film was calculated to be 4.148 Å, which is consistent with the scanning results of in-plane reciprocal space imaging. In addition, the in-plane lattice constant was also calibrated to be 4.206 Å by reciprocal space imaging. Combined with the φ scan results of the (204) asymmetric crystal plane, the results of the in-plane tetragonal symmetric lattice structure were obtained, confirming that the grown film is a high-quality epitaxially oriented single-crystal manganese nitride (MnN) material.
[0032] (2) The single-crystal manganese nitride thin film prepared by this invention exhibits excellent atmospheric stability. Specifically, it retains its good single-crystal properties even after being placed in the atmosphere for 120 days; no significant changes were observed in the X-ray diffraction results, and electron energy loss spectroscopy measurements revealed no significant oxidation within the film's growth range. The single-crystal manganese nitride thin film grown by this invention also exhibits good structural stability in water; prolonged immersion does not alter its material structure. Specifically, after being placed in water for 24 hours, the X-ray diffraction peak positions of the film showed no significant change. This excellent structural stability demonstrates the wide applicability of the single-crystal manganese nitride thin film.
[0033] (3) The manganese nitride thin film prepared by the present invention has very good metallic and antiferromagnetic properties, and is suitable for the study of antiferromagnetic spintronics. Attached Figure Description
[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:
[0035] Figure 1 A schematic diagram of a molecular beam epitaxy apparatus according to a specific embodiment of the present invention;
[0036] Figure 2 A spectrum characterizing the single-crystallinity and structural properties of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention; wherein Figure 2 a represents a large-scale X-ray diffraction pattern. Figure 2 b is a small-range X-ray diffraction pattern, specifically the reciprocal space imaging pattern. Figure 2 c represents the X-ray reflectance spectrum, and Figure 2 d represents the asymmetric plane φ scan pattern. Figure 2 e represents the reciprocal space imaging map;
[0037] Figure 3 X-ray diffraction patterns characterizing the stability of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention; wherein the upper left image is the X-ray diffraction pattern characterizing the stability of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention in water; the upper right image is the X-ray diffraction pattern characterizing the stability of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention in the atmosphere; the lower left image is an electron microscope image of the single-crystal manganese nitride thin film; and the lower right image is the electron energy loss spectrum of the thin film.
[0038] Figure 4 The graphs are used to characterize the electrical conductivity and antiferromagnetic properties of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention; the left graph is the resistivity of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention as a function of temperature; the right graph is the magnetic test curve of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention.
[0039] Figure 5X-ray diffraction pattern for characterizing the structure of the epitaxial thin film prepared in Comparative Example 1 of the present invention;
[0040] Figure 6 X-ray diffraction pattern for characterizing the structure of the epitaxial thin film prepared in Comparative Example 2 of the present invention;
[0041] Figure 7 X-ray diffraction pattern and reciprocal space imaging pattern characterizing the structure of the epitaxial thin film prepared in Comparative Example 3 of the present invention. Detailed Implementation
[0042] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.
[0043] The manganese nitride thin film prepared in the embodiments of the present invention is fabricated on a molecular beam epitaxy (MBE) apparatus. The apparatus includes a sample inlet chamber, a main chamber, a reflective high-energy electron diffraction (HEAD) system, a radio frequency plasma pyrolysis source, and five evaporation sources. One of the low-temperature furnaces is selected to hold manganese powder with a purity of 99.9998%. Nitrogen gas with a purity of 99.9999% is used as the nitrogen atom source, and the nitrogen atoms are pyrolyzed using the radio frequency plasma pyrolysis source. The heating stage allows for five-dimensional operation, and the substrate is heated using resistance heating with thermocouples for temperature monitoring. Specific embodiments are shown below.
[0044] Example 1
[0045] (1) Substrate pretreatment
[0046] like Figure 1 As shown, a magnesium oxide (MgO) substrate is fed into the molecular beam epitaxy chamber. The background vacuum is 10... -10 At the millibar level, the heating stage is heated, and the substrate is annealed at 900°C for 1 hour to remove surface-adsorbed impurities and obtain a smooth surface.
[0047] (2) Preparation of single-crystal manganese nitride thin films using molecular beam epitaxy
[0048] A manganese (Mn) source with a purity of 99.9998% was used as the evaporation source, and the evaporation source temperature was set to 750℃. A radio frequency plasma pyrolysis source was used to pyrolyze high-purity (99.9999%) nitrogen molecules (N2) into nitrogen atoms; the radio frequency power was 200W, and the nitrogen partial pressure was controlled at 3×10⁻⁶. -5 The substrate surface temperature (i.e., growth temperature) was controlled at 300℃, and the film growth time was controlled at 75 minutes, resulting in a manganese nitride film with a thickness of 24 nm. After growth, the sample was subjected to in-situ cavity annealing at 300℃ for 25 minutes, with a nitrogen partial pressure of 3 × 10⁻⁶ during annealing. -5A millibar (mbar) was applied to improve the growth quality of the manganese nitride thin film. After annealing, the heating stage was cooled and the sample was removed, yielding a high-quality epitaxial single-crystal manganese nitride (MnN) thin film. The sample surface exhibited a good metallic luster.
[0049] Figure 2 A spectrum characterizing the single-crystallinity and structural properties of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention; wherein Figure 2 a represents a large-scale X-ray diffraction pattern. Figure 2 b is a small-range X-ray diffraction pattern. Figure 2 c represents the X-ray reflectance spectrum. Figure 2 d represents the asymmetric plane φ scan pattern. Figure 2 e represents the reciprocal space imaging map. For example... Figure 2 As shown, X-ray diffraction of the prepared thin film showed only a single peak at 43.6°, corresponding to the (002) peak of the MnN material. Laue oscillations on both sides of the main peak indicate a good single-crystal structure. The out-of-plane lattice constant of the single-crystal thin film was calculated to be 4.148 Å, consistent with the scanning results of in-plane reciprocal space imaging. The in-plane lattice constant obtained through reciprocal space imaging was 4.206 Å. Combined with φ scanning of the (204) asymmetric crystal plane, the result showed an in-plane tetragonal symmetric lattice structure. Therefore, it can be seen that the thin film grown in Example 1 is a high-quality single-crystal manganese nitride (MnN) thin film.
[0050] Figure 3 X-ray diffraction (XRD) patterns characterizing the stability of the single-crystal manganese nitride thin film prepared in Example 1 of this invention are shown below. The upper left image is an XRD pattern characterizing the water stability of the single-crystal manganese nitride thin film prepared in Example 1 of this invention; the upper right image is an XRD pattern characterizing the atmospheric stability of the single-crystal manganese nitride thin film prepared in Example 1 of this invention; the lower left image is an electron micrograph of the single-crystal manganese nitride thin film; and the lower right image is an electron energy loss spectrum of the material. The grown single-crystal manganese nitride thin film exhibits good atmospheric stability, maintaining good single-crystal properties even after being placed in the atmosphere for 120 days. No significant changes were observed in the XRD results, and electron energy loss spectroscopy characterization confirmed that the chemical valence state of the material was not oxidized. Furthermore, prolonged immersion in water did not alter its material structure. Specifically, after 24 hours in water, the XRD peak positions of the film did not change significantly.
[0051] Figure 4The graphs characterize the electrical conductivity and antiferromagnetic properties of the single-crystal manganese nitride thin film prepared in Example 1 of the present invention; the left graph shows the resistivity of the single-crystal manganese nitride thin film prepared in Example 1 as a function of temperature; the right graph shows the magnetic properties of the single-crystal manganese nitride thin film prepared in Example 1. The resistivity curve of the thin film prepared in Example 1 as a function of temperature shows its good metallic properties. The magnetic test of the thin film did not show any magnetism, which is consistent with the property of MnN as an antiferromagnetic material, where the internal magnetic moment does not respond to the external magnetic field.
[0052] Example 2
[0053] (1) Substrate pretreatment
[0054] like Figure 1 As shown, a magnesium oxide (MgO) substrate is fed into the molecular beam epitaxy chamber. The background vacuum is 10... -10 At the millibar level, the heating stage is heated, and the substrate is annealed at 1000°C for 2 hours to remove surface-adsorbed impurities and obtain a smooth surface.
[0055] (2) Preparation of single-crystal manganese nitride thin films using molecular beam epitaxy
[0056] A manganese (Mn) source with a purity of 99.9998% was used as the evaporation source, and the evaporation source temperature was set to 730℃. A radio frequency plasma pyrolysis source was used to pyrolyze high-purity (99.9999%) nitrogen molecules (N2) into nitrogen atoms; the radio frequency power was 300W, and the nitrogen partial pressure was controlled at 2×10⁻⁶. -5 The substrate surface temperature (i.e., growth temperature) was controlled at 330℃, and the film growth time was controlled at 120 minutes to obtain a manganese nitride film with a thickness of 40 nm. After growth, the sample was subjected to in-situ cavity annealing at 330℃ for 1 hour, with a nitrogen partial pressure of 2 × 10⁻⁶ mbar. -5 A millibar (mbar) was applied to improve the growth quality of the manganese nitride thin film. After annealing, the heating stage was cooled and the sample was removed, yielding a high-quality epitaxial single-crystal manganese nitride (MnN) thin film. The sample surface exhibited a good metallic luster.
[0057] The monocrystalline manganese nitride thin film prepared in this embodiment exhibits the same monocrystalline properties and structural characteristics as in Example 1. Furthermore, the monocrystalline manganese nitride thin film prepared in this embodiment, like that in Example 1, possesses atmospheric and water stability. Simultaneously, the electrical conductivity and antiferromagnetic properties of the monocrystalline manganese nitride thin film prepared in this embodiment are similar to those in Example 1. The resistivity curve of the thin film as a function of temperature demonstrates its excellent metallic properties. Magnetic testing of the thin film did not reveal any magnetism, consistent with the property of MnN as an antiferromagnetic material, where the internal magnetic moment does not respond to an external magnetic field.
[0058] Example 3
[0059] (1) Substrate pretreatment
[0060] like Figure 1 As shown, a magnesium oxide (MgO) substrate is fed into the molecular beam epitaxy chamber. The background vacuum is 10... -10 At the millibar level, the heating stage is heated, and the substrate is annealed at 950°C for 0.5 hours to remove surface-adsorbed impurities and obtain a smooth surface.
[0061] (2) Preparation of single-crystal manganese nitride thin films using molecular beam epitaxy
[0062] A manganese (Mn) source with a purity of 99.9998% was used as the evaporation source, and the evaporation source temperature was set to 770℃. A radio frequency plasma pyrolysis source was used to pyrolyze high-purity (99.9999%) nitrogen (N2) into nitrogen atoms; the radio frequency power was 250W, and the nitrogen partial pressure was controlled at 4 × 10⁻⁶. -5 The substrate surface temperature (i.e., growth temperature) was controlled at 350℃, and the film growth time was controlled at 15 minutes to obtain a manganese nitride film with a thickness of 5 nm. After growth, the sample was subjected to in-situ cavity annealing at 350℃ for 50 minutes, with a nitrogen partial pressure of 4 × 10⁻⁶ mbar. -5 A millibar (mbar) was applied to improve the growth quality of the manganese nitride thin film. After annealing, the heating stage was cooled and the sample was removed, yielding a high-quality epitaxial single-crystal manganese nitride (MnN) thin film. The sample surface exhibited a good metallic luster.
[0063] The monocrystalline manganese nitride thin film prepared in this embodiment exhibits the same monocrystalline properties and structural characteristics as in Example 1. Furthermore, the monocrystalline manganese nitride thin film prepared in this embodiment, like that in Example 1, possesses atmospheric and water stability. Simultaneously, the electrical conductivity and antiferromagnetic properties of the monocrystalline manganese nitride thin film prepared in this embodiment are similar to those in Example 1. The resistivity curve of the thin film as a function of temperature demonstrates its excellent metallic properties. Magnetic testing of the thin film did not reveal any magnetism, consistent with the property of MnN as an antiferromagnetic material, where the internal magnetic moment does not respond to an external magnetic field.
[0064] Comparative Example 1
[0065] The preparation steps of this comparative example are the same as those of Example 1, except that the radio frequency power in step (2) is changed. Specifically, the radio frequency power in step (2) is changed to 350W.
[0066] Figure 5The X-ray diffraction pattern characterizes the structure of the epitaxial thin film prepared in Comparative Example 1 of this invention. As can be seen from the figure, when the radio frequency power is too high, the peak position of the prepared thin film is closer to the magnesium oxide substrate, and the out-of-plane lattice constant of the thin film is larger. Compared with the manganese nitride thin film prepared in Example 1, the thin film prepared in this comparative example has a larger lattice constant. However, compared with the manganese nitride thin film obtained in Example 1, the epitaxial quality of the manganese nitride prepared in this comparative example is significantly lower. Higher radio frequency power introduces more effective nitrogen atoms and transfers more energy to the nitrogen atoms, which may affect the growth kinetics of the thin film and thus affect the epitaxial quality of the film.
[0067] Comparative Example 2
[0068] The preparation steps for this comparative example are the same as in Example 1, except that the nitrogen partial pressure in step (2) is changed. Specifically, the nitrogen partial pressure in step (2) is changed to 1×10⁻⁶. -5 millibar.
[0069] Figure 6 The X-ray diffraction pattern is used to characterize the structure of the epitaxial thin film prepared in Comparative Example 2 of the present invention. As can be seen from the figure, in addition to the obvious shift of the peak position away from the substrate, an additional manganese dinitride peak is also generated in the prepared thin film. This indicates that in this comparative example, reducing the nitrogen partial pressure will significantly reduce the nitrogen content of the prepared thin film and will lead to the appearance of impurity phases with lower nitrogen content.
[0070] Comparative Example 3
[0071] The preparation steps for this comparative example are the same as in Example 1, except that the nitrogen partial pressure in step (2) is changed. Specifically, the nitrogen partial pressure in step (2) is changed to 6 × 10⁻⁶. -5 millibar.
[0072] Figure 7 X-ray diffraction patterns and reciprocal space imaging diagrams characterizing the structure of the epitaxial thin film prepared in Comparative Example 3 of the present invention are shown. As can be seen from the figures, when the nitrogen partial pressure is too high, domain structures appear in the material, indicating a change in the atomic arrangement within the material, not just in the high-quality single-crystal epitaxial manganese nitride thin film required for preparation. Compared to Example 1, increasing the nitrogen partial pressure significantly alters the internal structure of the film, forming domain structures, possibly indicating that the material is no longer a rock salt mineral structure, but rather a zincblende or similar structure.
Claims
1. A method for preparing single-crystal manganese nitride thin films, comprising the following steps: (1) Pre-treat the substrate to remove impurities adsorbed on the substrate surface; (2) Using a manganese source as the evaporation source and a radio frequency plasma pyrolysis source, nitrogen molecules were pyrolyzed into more chemically reactive nitrogen atoms, and a single-crystal manganese nitride thin film was prepared by molecular beam epitaxy; wherein the nitrogen partial pressure was 2 × 10⁻⁶. -5 -4×10 -5 Millibar, RF power is 200-300W.
2. The method according to claim 1, wherein, The substrate pretreatment in step (1) is performed by a method including the following steps: The substrate is placed in the molecular beam epitaxy chamber, and the substrate is less than or equal to 10. -10 Anneal at 900-1000℃ for 0.5-2 hours under a vacuum of millibars.
3. The method according to claim 1, wherein, The substrate is selected from magnesium oxide and / or strontium titanate.
4. The method according to claim 1, wherein, The purity of the manganese source is greater than or equal to 99.9998% by weight.
5. The method according to claim 1, wherein, The purity of the nitrogen gas is greater than or equal to 99.9999% by weight.
6. The method according to claim 1, wherein, The temperature of the evaporation source is set to 730-770℃.
7. The method according to claim 1, wherein, The preparation of single-crystal manganese nitride thin films by molecular beam epitaxy in step (2) is carried out under the following conditions: The growth temperature is 300-350℃, and the growth time is 15-120 minutes.
8. The method according to claim 1, wherein, The method further includes the following steps after step (2): The monocrystalline manganese nitride film obtained in step (2) is subjected to in-situ annealing to obtain a higher quality monocrystalline manganese nitride film.
9. The method according to claim 9, wherein, The in-situ annealing process is performed under the following conditions: The annealing temperature is 300-350℃, and the nitrogen partial pressure is 2×10⁻⁶. -5 -4×10 -5 Millibars, annealing time is 25 minutes to 1 hour.