An ultra-smooth nickel (100) single crystal thin film and a preparation method thereof

Abstract

This invention relates to an ultra-flat nickel (100) single-crystal thin film and its preparation method. The method involves depositing a nickel thin film on the surface of an A-plane single-crystal sapphire substrate using physical vapor deposition. The nickel thin film is then subjected to high-temperature annealing in a reducing protective atmosphere to obtain a single-crystal nickel thin film with a (100) orientation. By selecting an A-plane single-crystal sapphire with a (11-20) crystal orientation as the epitaxial substrate, it exhibits excellent lattice matching with the Ni (100) plane (mismatch <5%), effectively inducing the epitaxial growth of the nickel thin film along the [100] direction and suppressing the nucleation and growth of grains with other orientations. Furthermore, the prepared nickel (100) single-crystal thin film possesses advantages such as atomic-level surface flatness (Ra < 1 nm), absence of twin defects, and high crystal orientation consistency, meeting the stringent material quality requirements of high-end devices.

Description

Technical Field

[0001] This invention relates to the field of single-crystal thin film material preparation technology, specifically to an ultra-flat nickel (100) single-crystal thin film and its preparation method. Background Technology

[0002] Nickel single-crystal thin films have shown significant application value in spintronic devices, catalytic electrodes, and epitaxial growth substrates for two-dimensional materials due to their excellent magnetic properties, catalytic activity, and good lattice matching. In particular, the Ni(100) crystal plane has fourfold symmetry and high lattice matching with various functional materials, such as ferroelectrics, superconducting thin films, and two-dimensional magnetic materials, making it an ideal template for preparing high-quality heterojunction structures.

[0003] However, the following technical bottlenecks still exist in the preparation of high-quality, ultra-flat nickel single-crystal thin films:

[0004] 1) Difficulty in controlling lattice orientation: When nickel thin films are grown on conventional substrates, such as SiO2 / Si and glass substrates, due to the large differences in lattice mismatch and thermal expansion coefficients, polycrystalline or twinned structures are easily formed, making it difficult to obtain single-crystal thin films with a single orientation. 2) Insufficient surface smoothness: The nickel thin film obtained by traditional preparation methods has a high surface roughness Ra>5 nm, such as electrochemical deposition and electron beam evaporation, which is difficult to meet the interface smoothness requirements of high-end devices; 3) Twin defects are difficult to eliminate: During the high-temperature annealing process of nickel thin films, due to the low stacking fault energy of the face-centered cubic structure, Σ3-type twin boundaries are easily formed, which seriously affects the single crystal quality of the thin film and the device performance. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-flat nickel (100) single crystal thin film and its preparation method. By selecting A-side single crystal sapphire as the epitaxial substrate and combining optimized physical vapor deposition process and high-temperature annealing treatment, high-quality, twin-free, atomically flat nickel (100) single crystal thin film can be prepared in a controllable manner.

[0006] The present invention discloses a method for preparing an ultra-flat nickel (100) single crystal thin film, comprising the following steps: S1: A nickel film is deposited on the surface of a single-crystal sapphire substrate on side A using physical vapor deposition. S2: The nickel film is subjected to high-temperature annealing in a reducing protective atmosphere to obtain a single-crystal nickel film with (100) orientation.

[0007] Furthermore, the A-side single-crystal sapphire substrate is a (11-20) crystal plane single-crystal sapphire.

[0008] Furthermore, the surface roughness Ra of the single-crystal nickel film is less than 1 nm.

[0009] Furthermore, the thickness of the single-crystal nickel film is 10nm~2000nm.

[0010] Furthermore, the physical vapor deposition method includes: DC sputtering, radio frequency sputtering, and magnetron sputtering in sputtering deposition methods; electron beam evaporation and molecular beam epitaxy in vacuum evaporation methods; and arc ion plating and magnetron sputtering ion plating in ion plating methods.

[0011] Furthermore, the deposition rate of the physical vapor deposition method is controlled at (1~5) nm / min.

[0012] Furthermore, the reducing protective atmosphere is a mixture of Ar and H2, or a mixture of N2 and H2; and the pressure of the reducing protective atmosphere is continuously maintained at 0.1 Pa to 2.0 Pa.

[0013] Furthermore, the high-temperature annealing conditions are as follows: heating rate is (5~40)℃ / min; annealing temperature is 800℃~1200℃, holding time is 10 minutes~40 minutes; annealing cooling rate is (1~20)℃ / min, and then cooled to room temperature.

[0014] Furthermore, when preparing the material using magnetron sputtering, the following steps are included: Using A-side single-crystal sapphire as the epitaxial substrate and high-purity nickel target as the sputtering source, the epitaxial substrate and the target are placed in the vacuum cavity of a magnetron sputtering equipment. After the vacuum chamber is evacuated to a base vacuum, a reducing protective atmosphere is introduced as the sputtering gas; the temperature of the sputtering substrate is room temperature to 600°C. A plasma-bombarded sputtering source is used within a vacuum chamber to sputter and deposit nickel atoms or ions onto the substrate surface, forming a nickel thin film.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, A-plane single crystal sapphire with crystal orientation (11-20) is selected as epitaxial substrate. It has excellent lattice matching with Ni (100) plane (mismatch degree <5%), which can effectively induce the epitaxial growth of nickel film along the

[100] direction and inhibit the nucleation and growth of other orientation grains. (2) The present invention adopts a two-step process of "deposition followed by annealing". By optimizing the deposition parameters, a dense and uniform nickel film precursor is obtained. Then, high-temperature annealing is used to promote grain recrystallization and grain boundary migration, resulting in a high-quality, ultra-flat nickel (100) single crystal film with high lattice matching. (3) The present invention performs annealing in a reducing protective atmosphere (a mixture of Ar / H2). H2 can effectively reduce nickel oxide impurities and clean grain boundaries, while inhibiting nickel oxidation at high temperatures, thus ensuring the high purity and single crystal quality of the film. (4) By precisely controlling the annealing temperature (800℃-1200℃) and the heating rate (5-40)℃ / min, the present invention achieves controllable grain growth and avoids thermal stress cracking caused by excessive heating or incomplete recrystallization caused by insufficient temperature. (5) The nickel (100) single crystal thin film prepared by the present invention has the advantages of atomic-level surface flatness (Ra<1 nm), no twin defects, and high crystal orientation consistency, which meet the stringent requirements of high-end devices for material quality.

[0016] Meanwhile, the present invention proposes an ultra-flat nickel (100) single crystal thin film, which is prepared according to the preparation method of the ultra-flat nickel (100) single crystal thin film described in any of the above claims.

[0017] Compared with existing technologies, the ultra-flat nickel (100) single crystal thin film proposed in this invention has advantages such as atomic-level surface flatness (Ra<1 nm), no twin defects, and high crystal orientation consistency, which meet the stringent requirements of high-end devices for material quality. Attached Figure Description

[0018] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings.

[0019] Figure 1 This is a schematic diagram of the method process of the present invention; Figure 2 X-ray diffraction (XRD) pattern of the ultra-flat nickel (100) single crystal thin film prepared in Example 2; Figure 3 XRD pattern of the nickel thin film prepared for comparison; Figure 4 An optical microscope image of the ultra-flat nickel (100) single crystal thin film prepared in Example 2; Figure 5 An optical microscope image of a nickel thin film prepared for comparison. Figure 6 The electron backscattering diffraction (EBSD) inverse pole figure of the ultraflat nickel (100) single crystal thin film prepared in Example 2 includes... Figure 6 a's IPF X, Figure 6 b's IPF Y, Figure 6 c's IPF Z, Figure 6 'a' represents the direction parallel to the surface of the nickel (100) single crystal thin film. Figure 6 b represents direction 2, which is parallel to the surface of the nickel (100) single crystal thin film and perpendicular to direction 1. Figure 6c represents the direction perpendicular to the surface of the nickel (100) single crystal thin film; Figure 7 The EBSD inverse pole figure of the nickel thin film prepared for comparison includes three directions: IPF-X, IPF-Y, and IPF-Z. Figure 7 a's IPF X, Figure 7 b's IPF Y, Figure 7 c's IPF Z, Figure 7 'a' represents a direction parallel to the surface of the nickel film. Figure 7 b represents direction 2, which is parallel to the surface of the nickel film and perpendicular to direction 1. Figure 7 c represents the direction perpendicular to the surface of the nickel film; 3; Figure 8 XRD-rocking curve test image of the ultra-flat nickel (100) single crystal thin film prepared in Example 2; Figure 9 XRD-rocking curve test image of the nickel thin film prepared for comparison; Figure 10 Atomic force microscopy (AFM) characterization of the ultra-flat nickel (100) single crystal thin film prepared in Example 2; Figure 11 Atomic force microscopy (AFM) characterization of the nickel thin film prepared for comparison. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more comprehensive and detailed description of the present invention will be provided below, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention are well known in the art and can be obtained commercially, but this does not limit the implementation of this invention. Other reagents and equipment well known in the art can also be used in the implementation of the following embodiments of this invention. In the quantitative experiments of this invention, three repeated experiments are set up, and the results are averaged.

[0023] Based on the problems of insufficient surface flatness and low lattice matching in existing nickel single-crystal thin film preparation methods, this invention studies a method for preparing ultra-flat nickel (100) single-crystal thin films. The preparation method uses physical vapor deposition to deposit a nickel thin film on the surface of a single-crystal sapphire substrate with a crystal orientation of (11-20) on the A-plane. The nickel thin film is then subjected to high-temperature annealing in a reducing protective atmosphere to obtain a single-crystal nickel thin film with (100) orientation and a surface roughness Ra of less than 1 nm. The thickness of the single-crystal nickel thin film is prepared by controlling the deposition time. This method uses A-plane single-crystal sapphire with crystal orientation (11-20) as epitaxial substrate, which has excellent lattice matching with Ni (100) plane (mismatch degree <5%), and can effectively induce the epitaxial growth of nickel film along the

[100] direction; at the same time, a two-step process of "deposition first and annealing" is adopted. By optimizing the deposition parameters, a dense and uniform nickel film precursor is obtained. Then, high-temperature annealing is used to promote grain recrystallization and grain boundary migration, resulting in a high-quality, ultra-flat nickel (100) single-crystal film with high lattice matching degree.

[0024] The physical vapor deposition methods described in this invention include, but are not limited to: DC sputtering, radio frequency sputtering, and magnetron sputtering in sputtering deposition methods; electron beam evaporation and molecular beam epitaxy in vacuum evaporation methods; and arc ion plating and magnetron sputtering ion plating in ion plating methods.

[0025] The deposition rate of the physical vapor deposition method is controlled at (1~5) nm / min.

[0026] The reducing protective atmosphere described in this invention is a mixture of Ar and H2, or a mixture of N2 and H2; and the pressure of the reducing protective atmosphere is continuously maintained at 0.1 Pa to 2.0 Pa.

[0027] The high-temperature annealing conditions described in this invention include: The annealing heating rate is (5~40)℃ / min; The annealing temperature is 800℃~1200℃, and the holding time is 10 minutes~40 minutes; The annealing cooling rate is (1~20)℃ / min, and the temperature is cooled to room temperature.

[0028] Example 1 Ultra-flat nickel (100) single crystal thin films were prepared by magnetron sputtering.

[0029] S10: Select a wafer-level A-side single-crystal sapphire with a crystal orientation of (11-20) and a size of 4 inches as the epitaxial substrate, and select a nickel target with a purity of 99.99% as the sputtering source. Place the epitaxial substrate and the sputtering source in the corresponding positions in the vacuum chamber of the magnetron sputtering equipment. S20: Heat the epitaxial substrate to 500℃ and deposit nickel atoms on the epitaxial substrate at a deposition rate of 2nm / min until the film thickness reaches 500nm to obtain a nickel film; S30: The nickel film is annealed in an Ar / H2 mixed atmosphere, heated to an annealing temperature of 800°C at a heating rate of 15°C / min, held at that temperature for 40 minutes, and cooled to room temperature at a cooling rate of 10°C / min; wherein the flow rate of Ar is controlled at 500 sccm and the flow rate of H2 is controlled at 30 sccm.

[0030] Example 2 The preparation method in this embodiment is basically the same as that in Example 1, except for step S30, which is as follows: S30: The nickel film is annealed in an Ar / H2 mixed atmosphere, heated to an annealing temperature of 1000°C at a heating rate of 15°C / min, held for 25 minutes, and cooled to room temperature at a cooling rate of 10°C / min; wherein the flow rate of Ar is controlled at 500 sccm and the flow rate of H2 is controlled at 30 sccm.

[0031] Example 3 The preparation method in this embodiment is basically the same as that in Example 1, except for step S30, which is as follows: S30: The nickel film is annealed in an Ar / H2 mixed atmosphere, heated to an annealing temperature of 1200°C at a heating rate of 15°C / min, held for 10 minutes, and cooled to room temperature at a cooling rate of 10°C / min; wherein the flow rate of Ar is controlled at 500 sccm and the flow rate of H2 is controlled at 30 sccm.

[0032] Comparative Example Nickel thin films were prepared by magnetron sputtering.

[0033] The preparation method in this embodiment is basically the same as that in Example 1, except for step S10, which is as follows: S10: Select a wafer-level C-plane single-crystal sapphire with a crystal orientation of (0001) and a size of 4 inches as the epitaxial substrate, and select a nickel target with a purity of 99.99% as the sputtering source. Place the epitaxial substrate and the sputtering source in the corresponding positions in the vacuum chamber of the magnetron sputtering equipment.

[0034] Results Test Analysis The test results for Example 2 and the comparative example are as follows.

[0035] 1. Structural characterization comparison Please see Figure 2 The structure of the nickel (100) single crystal thin film of Example 2 was characterized using X-ray diffraction. Figure 2As can be seen from the data, in addition to the same diffraction peaks as those on the single-crystal sapphire substrate on the A-side, a Ni(200) diffraction peak also appears. This peak corresponds to the second-order diffraction of the Ni(100) crystal plane, indicating that the obtained nickel film is a single-crystal nickel film with a nickel(100) orientation.

[0036] Please see Figure 3 The structure of the comparative nickel thin film was characterized using X-ray diffraction. Figure 3 As can be seen from the diffraction pattern, in addition to the same diffraction peaks as the C-plane single-crystal sapphire substrate, Ni(111) and Ni(222) diffraction peaks also appeared. These two peaks correspond to the first and second order diffractions of the Ni(111) crystal plane, respectively. This indicates that the obtained nickel film is a Ni(111) oriented twinned nickel film.

[0037] 2. Comparison of crystal plane quality Please see Figure 4 The surface of the nickel (100) single crystal thin film of Example 2 was observed using an optical microscope. The film surface was uniform in color and no twins or obvious defects were observed, indicating that the film had good uniformity.

[0038] Please see Figure 5 The surface of the comparative nickel film was observed using an optical microscope. Obvious grain boundaries were visible on the surface of the film, indicating the presence of twins in the film.

[0039] Please see Figure 6 The inverse pole figure of the nickel (100) single crystal thin film of Example 2 was analyzed by electron backscatter diffraction (EBSD), including... Figure 6 a's IPF X, Figure 6 b's IPF Y, Figure 6 c's IPF Z, Figure 6 'a' represents the direction parallel to the surface of the nickel (100) single crystal thin film. Figure 6 b represents direction 2, which is parallel to the surface of the nickel (100) single crystal thin film and perpendicular to direction 1. Figure 6 c represents direction 3 perpendicular to the surface of the nickel (100) single crystal film. No grain boundaries were observed in any of the three inverse pole figures, further proving that the nickel (100) single crystal film is a twin-free single crystal film.

[0040] Please see Figure 7 Electron backscatter diffraction (EBSD) was used to analyze the inverse pole figures of the comparative nickel thin films, including... Figure 7 a's IPF X, Figure 7 b's IPF Y, Figure 7 The IPF Z of c shows clear grain boundaries in all three inverse pole figures, further confirming that the nickel film has a twinned structure.

[0041] Please see Figure 8The nickel (100) single crystal thin film of Example 2 was subjected to XRD rocking curve test using an X-ray diffractometer. The calculated full width at half maximum (FWHM) was 0.1429°, indicating that the nickel (100) single crystal thin film has excellent single crystal quality.

[0042] Please see Figure 9 The comparative nickel film was tested by XRD rocking curve test using an X-ray diffractometer. The calculated full width at half maximum (FWHM) was 0.73°, which is much higher than the corresponding value of 0.1429° of the nickel (100) single crystal film prepared in Example 2, indicating that the crystal quality of the twinned nickel film is poor.

[0043] 3. Surface flatness measurement Please see Figure 10 The surface smoothness of the nickel (100) single crystal thin film of Example 2 was characterized by atomic force microscopy. According to the software analysis, its average surface roughness RMS=0.38 nm, indicating that the film has extremely high surface smoothness.

[0044] Please see Figure 11 The surface smoothness of the comparative nickel film was characterized by atomic force microscopy. According to the software analysis, its average surface roughness RMS=4.97nm, which is much higher than the corresponding value of 0.38nm of the nickel (100) single crystal film prepared in Example 2, indicating that the surface smoothness of the twinned nickel film is low.

[0045] The above comparative analysis shows that, compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, A-plane single crystal sapphire with crystal orientation (11-20) is selected as epitaxial substrate. It has excellent lattice matching with Ni (100) plane (mismatch degree <5%), which can effectively induce the epitaxial growth of nickel film along the

[100] direction and inhibit the nucleation and growth of other orientation grains. (2) The present invention adopts a two-step process of "deposition followed by annealing". By optimizing the deposition parameters, a dense and uniform nickel film precursor is obtained. Then, high-temperature annealing is used to promote grain recrystallization and grain boundary migration, resulting in a high-quality, ultra-flat nickel (100) single crystal film with high lattice matching. (3) The present invention performs annealing in a reducing protective atmosphere (a mixture of Ar / H2). H2 can effectively reduce nickel oxide impurities and clean grain boundaries, while inhibiting nickel oxidation at high temperatures, thus ensuring the high purity and single crystal quality of the film. (4) By precisely controlling the annealing temperature (800℃-1200℃) and the heating rate (5-40)℃ / min, the present invention achieves controllable grain growth and avoids thermal stress cracking caused by excessive heating or incomplete recrystallization caused by insufficient temperature. (5) The nickel (100) single crystal thin film prepared by the present invention has the advantages of atomic-level surface flatness (Ra<1 nm), no twin defects, and high crystal orientation consistency, which meets the stringent requirements of high-end devices for material quality.

[0046] This invention is not limited to the above-described embodiments. If any modifications or variations to this invention do not depart from the spirit and scope of this invention, and if such modifications and variations fall within the scope of the claims and equivalent technologies of this invention, then this invention also intends to include such modifications and variations.

Claims

1. A method for preparing an ultra-flat nickel (100) single crystal thin film, characterized in that: A nickel film was deposited on the surface of a single-crystal sapphire substrate on side A using physical vapor deposition. The nickel film is subjected to high-temperature annealing in a reducing protective atmosphere to obtain a single-crystal nickel film with (100) orientation.

2. The method for preparing an ultra-flat nickel (100) single crystal thin film according to claim 1, characterized in that, The A-side single-crystal sapphire substrate is a single-crystal sapphire with a crystal orientation of (11-20).

3. The method for preparing an ultra-flat nickel (100) single crystal thin film according to claim 1, characterized in that, The surface roughness Ra of the single-crystal nickel film is less than 1 nm.

4. The method for preparing an ultra-flat nickel (100) single crystal thin film according to any one of claims 1 to 3, characterized in that, The thickness of the single-crystal nickel film is 10nm~2000nm.

5. The method for preparing an ultra-flat nickel (100) single crystal thin film according to claim 1, characterized in that, The physical vapor deposition methods include: DC sputtering, radio frequency sputtering, and magnetron sputtering in sputtering deposition methods; electron beam evaporation and molecular beam epitaxy in vacuum evaporation methods; and arc ion plating and magnetron sputtering ion plating in ion plating methods.

6. The method for preparing an ultra-flat nickel (100) single crystal thin film according to claim 1, characterized in that, The deposition rate of the physical vapor deposition method is controlled at (1~5) nm / min.

7. The method for preparing an ultra-flat nickel (100) single crystal thin film according to claim 1, characterized in that, The reducing protective atmosphere is a mixture of Ar and H2, or a mixture of N2 and H2; and the pressure of the reducing protective atmosphere is continuously maintained at 0.1 Pa to 2.0 Pa.

8. The method for preparing an ultra-flat nickel (100) single crystal thin film according to claim 1, characterized in that, The high-temperature annealing conditions are as follows: heating rate is (5~40)℃ / min; annealing temperature is 800℃~1200℃, holding time is 10 minutes~40 minutes; annealing cooling rate is (1~20)℃ / min, and cooling to room temperature.

9. The method for preparing an ultra-flat nickel (100) single crystal thin film according to claim 5, characterized in that, When preparing the material using magnetron sputtering, the following steps are included: Using A-side single-crystal sapphire as the epitaxial substrate and high-purity nickel target as the sputtering source, the epitaxial substrate and the target are placed in the vacuum cavity of a magnetron sputtering equipment. After the vacuum chamber is evacuated to a base vacuum, a reducing protective atmosphere is introduced as the sputtering gas; the temperature of the sputtering substrate is room temperature to 600°C. A plasma bombardment sputtering source is used in a vacuum chamber to sputter and deposit nickel atoms or ions onto the substrate surface to form a nickel thin film.

10. An ultra-flat nickel (100) single crystal thin film, characterized in that: It is prepared by the method for preparing ultra-flat nickel (100) single crystal thin film according to any one of claims 1 to 8.

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