A wafer-level ferromagnetic metal-organic thin film and its preparation method

Abstract

This invention discloses a wafer-level ferromagnetic metal-organic thin film and its preparation method, belonging to the field of carbon metal-organic thin film preparation. The method includes the following steps: using low-pressure chemical vapor deposition (LPCVD), with metal phthalocyanine as the molecular precursor and copper foil as the growth substrate, the reaction is carried out under heating in a hydrogen-argon mixed atmosphere, followed by rapid cooling after growth. The prepared monolayer metal-organic thin film exhibits strong in-plane ferromagnetism and certain mechanical properties, and can be directly transferred without a polymer protective film. The grown ferromagnetic metal-organic thin film is transferred to any desired substrate by wet transfer etching of the copper foil. This invention proposes for the first time a bottom-up one-step method for synthesizing wafer-scale air-stable ferromagnetic metal-organic thin films. The controllable preparation and transfer process of this ferromagnetic metal-organic thin film has significant implications for applications such as electromagnetic transport.

Description

Technical Field

[0001] This invention belongs to the field of carbon metal-organic thin film preparation, specifically relating to a wafer-level ferromagnetic metal-organic thin film and its preparation method. Background Technology

[0002] Achieving long-range ordered ferromagnetic coupling in two-dimensional systems not only advances our understanding of fundamental physics but also effectively promotes the development of various quantum technologies, such as magnetoelectronic devices. Currently, two-dimensional ferromagnetic systems are mainly divided into two categories: intrinsically magnetic materials, such as Fe3GeTe2 and CrX3 (X=I, Br, Cl), and intrinsically magnetic materials, such as dilute magnetic semiconductors (DMSs). Intrinsically magnetic materials typically require mechanical exfoliation to obtain single-layer or few-layer samples, which results in very limited sample sizes. Furthermore, intrinsically magnetic materials generally have low magnetic transition temperatures (Curie temperatures), and are often air-sensitive after exfoliation to single or few layers. These problems significantly limit subsequent processing and device fabrication. Compared to intrinsically magnetic materials, preparing intrinsically magnetic materials through magnetic metal doping is a widely studied and promising method for achieving large-area ferromagnetic thin films. However, effectively doping magnetic atoms into non-magnetic materials is challenging, and overcoming air instability requires further research. Summary of the Invention

[0003] This invention provides a wafer-level ferromagnetic metal-organic thin film and its preparation method, which allows for the controlled growth of a large-area monolayer ferromagnetic thin film on a copper sheet, which can then be transferred to any substrate via a wet process for device fabrication and testing.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing a wafer-level ferromagnetic metal-organic thin film includes the following steps:

[0006] 1) Place 10 mg ~ 50 mg of the precursor in a quartz boat and place it in the temperature zone of a CVD tube furnace;

[0007] 2) The growth substrate is etched and cleaned to remove the oxide layer and then placed in the lower temperature zone of the CVD tube furnace;

[0008] 3) The tubular furnace is evacuated and cleaned with argon gas in a circulating process.

[0009] 4) While maintaining continuous operation of the vacuum pump, introduce a hydrogen-argon mixture and control the partial pressure of the tubular furnace at 4 torr using a valve;

[0010] 5) Heat the lower temperature zone containing the substrate to 900℃ and maintain for 30 minutes to perform annealing treatment;

[0011] 6) Cool the lower temperature zone where the substrate is located to 700℃ in preparation for growth;

[0012] 7) Slowly heat the upper temperature zone where the precursor is located to 360-400℃; once the upper temperature zone reaches the specified temperature, start growth, and after 10 minutes of growth, rapidly cool down to form a completely covered metal-organic film.

[0013] In the above steps, step 4) specifically involves: after the vacuum pump evacuates to 0.1 mtorr, a hydrogen-argon mixture (500 sccm of argon and 50 sccm of hydrogen) is introduced, and the tube furnace pressure is set at 4 torr. The tube furnace pressure is precisely and in real time controlled by an electric regulating valve.

[0014] In step 5), the heating rate is 20°C / min, and 500 sccm of argon and 100 sccm of hydrogen are introduced during the heating and maintenance process for annealing.

[0015] Step 6) The cooling rate is 20℃ / minute;

[0016] In step 7), the temperature is raised to 360°C when the precursor is nickel phthalocyanine, to 380°C when the precursor is cobalt phthalocyanine, and to 400°C when the precursor is iron phthalocyanine. The heating rate is 30°C / min, and the rapid cooling rate is 50°C / min.

[0017] Beneficial Effects: This invention provides a wafer-level ferromagnetic metal-organic thin film and its preparation method. The method employs a bottom-up, one-step synthesis of monodisperse ferromagnetic metal-organic thin films, unlike traditional top-down methods for metal doping organic carbon materials. This effectively avoids the formation of doped metal clusters and significantly improves the air stability of the metal-organic thin film. The monodisperse metal doping method of this invention enables the monolayer metal-organic thin film to exhibit strong in-plane ferromagnetism, and the prepared monolayer metal-organic thin film possesses certain mechanical properties, allowing for direct transfer without a polymer protective film. The air-stable ferromagnetic metal-organic thin film growth and transfer process provided by this invention can be directly integrated into the mature graphene two-dimensional material industry, effectively promoting the development of spin quantum devices and electromagnetic transport applications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation process of metal-organic thin films in an embodiment of the present invention;

[0019] Figure 2 This is an atomic-resolution scanning transmission microscope image of the metal-organic thin film in an embodiment of the present invention;

[0020] Figure 3These are optical microscope images and corresponding Raman spectra of metal-organic thin films with different metal doping in the embodiments of the present invention.

[0021] Figure 4 These are atomic force microscope images of metal-organic thin films in embodiments of the present invention;

[0022] Figure 5 The X-ray photoelectron spectroscopy (XPS) of metal-organic thin films with different metal doping in the embodiments of the present invention is shown, where ab is the N1s peak and cd is the 3d peak.

[0023] Figure 6 The superconducting quantum interference (SQUID) spectra of metal-organic thin films with different metal doping in the embodiments of the present invention are shown.

[0024] Figure 7 These are optical photographs of the transfer of metal-organic thin films without a polymer protective layer in an embodiment of the present invention, where a is a metal-organic thin film grown on a copper foil floating on an etching solution, and b is a metal-organic thin film floating after the substrate is etched.

[0025] Figure 8 Figure 1 shows the measurement results of the mechanical properties of the metal-organic thin film in the embodiment of the present invention. Figure 2a is a curve showing the relationship between force and displacement of the metal-organic thin film. Figure 3b is a statistical analysis of the effective Young's modulus extracted from Figure 2a. Figure 4cd is an atomic force microscope image showing the morphology of the metal-organic thin film before and after being punctured by the tip of an atomic force microscope. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0027] The following embodiments require the following materials and instruments:

[0028] Copper foil: 0.025 mm (0.001 in) thick, annealed, 99.8%, purchased from Thermo Fisher.

[0029] Metal phthalocyanine molecules: cobalt phthalocyanine β-form, purity 97%; iron phthalocyanine, purity 98%; nickel phthalocyanine, purity 90%, purchased from Sigma Aldrich;

[0030] Silicon oxide wafers: The silicon oxide thickness is 285 nanometers, and the silicon wafer thickness is 535 micrometers. They were purchased from Suzhou Jingxi Electronics Technology Co., Ltd.

[0031] CVD tube furnace.

[0032] like Figure 1 As shown, a method for preparing wafer-sized air-stabilized ferromagnetic metal-organic thin films includes the following specific steps:

[0033] 1) Place the precursor molecules in a quartz boat and put it in the upper temperature zone of a CVD tube furnace.

[0034] 2) The copper substrate is etched and cleaned to remove the oxide layer and then placed in the lower temperature zone of the CVD tube furnace;

[0035] 3) The tubular furnace is evacuated and cleaned with argon gas in a circulating process.

[0036] 4) After the vacuum pump evacuates to 0.1 mtorr, a hydrogen-argon mixture (500 sccm of argon and 50 sccm of hydrogen) is introduced, and the tube furnace pressure is set to 4 torr. The tube furnace pressure is precisely and in real-time controlled by an electrically operated regulating valve.

[0037] 5) Heat the lower temperature zone containing the copper substrate to 900℃ at a rate of 20℃ / min. After reaching the specified temperature, maintain it for 30 minutes. During the heating and maintenance process, introduce 500 sccm of argon and 100 sccm of hydrogen for annealing.

[0038] 6) Heat the lower temperature zone containing the substrate to 700℃ to prepare for growth;

[0039] 7) Slowly heat the upper temperature zone where the molecular precursor is located to 360-400℃ (360℃ for nickel phthalocyanine, 380℃ for cobalt phthalocyanine, and 400℃ for iron phthalocyanine) at a heating rate of 30℃ / min. After reaching the specified temperature, hold it for 10 minutes, then remove the heating furnace and quickly cool it to room temperature and take it out to obtain a large-area ferromagnetic metal-organic thin film.

[0040] 8) The grown metal-organic thin film is then transferred to any substrate, such as a wafer-sized silicon wafer, using a wet transfer method.

[0041] Figure 2 This is an atomic-resolution scanning transmission microscope image of a cobalt metal-organic thin film, which shows good metal monodispersity.

[0042] Figure 3 Optical microscope images and corresponding Raman spectra of metal-organic thin films with different metal dopants are shown. The optical microscope images shown in ab indicate that the metal-organic thin film has good film formation and good uniformity. The Raman spectrum shown in cd shows broad D and G peaks, indicating that the metal-organic thin film contains a large number of metal dopants and structural defects.

[0043] Figure 4 The image shows an atomic force microscopy (AFM) image of a metal-organic thin film with a thickness of approximately 0.7 nm. After being exposed to air for 180 days, the AFM image showed no significant changes in morphology, demonstrating its excellent air stability.

[0044] Figure 5 The X-ray photoelectron spectroscopy (XPS) of metal-organic films doped with different metals is shown. The ab peak represents the N1s peak, indicating that the nitrogen element is mainly composed of six-membered ring pyridine nitrogen, which is similar to the coordination environment of nitrogen atoms in the precursor center structure. The cd peak represents the 3d peak of different metals, indicating that the metals mainly exist in the +2 valence form, which is consistent with the valence state of the precursor metal center. The above results indicate that the metals in the metal-organic films exist in a metal nitrogen 4 structure similar to the precursor center structure.

[0045] Figure 6 Superconducting quantum interference (SQUID) spectra of metal-organic thin films doped with different metals are used to characterize the magnetic properties of metal-organic films. The figures show a distinct hysteresis loop and temperature-dependent changes in the saturation magnetic moment, indicating that the metal-organic films exhibit significant ferromagnetic properties with a high ferromagnetic transition temperature. It can be seen that the magnitude of the saturation magnetic moment decreases with increasing temperature, which differs from the ferromagnetic properties of typical metal particles, which usually exhibit a saturation magnetic moment that hardly changes with temperature. This result indicates that the ferromagnetism in metal-organic films is caused by monodisperse metal single atoms; compared to metal particles, metal single atoms have better stability, reflected in the good air stability of metal-organic films.

[0046] Figure 7 Optical images of the metal-organic thin film transferred without a polymer protective layer are shown. Image a shows the metal-organic thin film grown on a copper foil before etching, and image b shows the floating metal-organic thin film after substrate etching. This result indicates that the metal-organic thin film possesses certain tensile strength and ductility, which differs from common two-dimensional carbon materials such as graphene. Furthermore, the transfer without a polymer protective layer helps prevent contamination of the metal-organic thin film surface by residual polymeric organic solvents.

[0047] Figure 8 The mechanical properties of metal-organic thin films were measured. Figure a shows the force-displacement relationship curve of the metal-organic thin film, figure b shows the statistical analysis of the effective Young's modulus extracted from figure a, and figures cd show the atomic force microscope morphology before and after the metal-organic thin film was punctured by the tip of an atomic force microscope. This result shows that the metal-organic thin film has certain mechanical strength and ductility.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a wafer-level ferromagnetic metal-organic thin film, characterized in that, A bottom-up, one-step method for preparing atomically thin films includes the following steps: (1) The copper foil substrate is surface treated to remove the oxide layer and placed in the lower temperature zone of the CVD tube furnace, while the single metal phthalocyanine precursor is placed in the upper temperature zone of the CVD tube furnace. (2) Evacuate the CVD tube furnace and clean it with argon gas; (3) Introduce a hydrogen-argon mixture, control the pressure, and maintain a low-pressure environment at 4 torr; (4) The lower temperature zone where the copper foil substrate is located is heated to 900°C at a heating rate of 20°C / min, and annealed for 30 minutes. During the heating and annealing process, 500 sccm of argon and 100 sccm of hydrogen are introduced. After the annealing process, the lower temperature zone where the substrate is located is heated and cooled to 700°C to prepare for growth. (5) The temperature of the upper temperature zone containing the single metal phthalocyanine precursor is raised to 360-400℃; growth begins when the upper temperature zone reaches the specified temperature, and the temperature is rapidly reduced to room temperature after growth is completed to form a completely covered metal-organic film.

2. The method for preparing wafer-level ferromagnetic metal-organic thin films according to claim 1, characterized in that, Before introducing the hydrogen-argon mixture in step (2), the reactor is evacuated and purged with argon gas.

3. The method for preparing wafer-level ferromagnetic metal-organic thin films according to claim 1 or 2, characterized in that, The hydrogen-argon mixture is introduced at 500 sccm of argon and 50 sccm of hydrogen.

4. The method for preparing wafer-level ferromagnetic metal-organic thin films according to claim 1, characterized in that, The cooling rate in step (4) is 20℃ / minute.

5. The method for preparing wafer-level ferromagnetic metal-organic thin films according to claim 1, characterized in that, In step (5), the heating rate is 30℃ / min and the growth time is 10 minutes.

6. The method for preparing wafer-level ferromagnetic metal-organic thin films according to claim 1 or 5, characterized in that, In step (5), the temperature is raised to 360°C when the precursor is nickel phthalocyanine, to 380°C when the precursor is cobalt phthalocyanine, and to 400°C when the precursor is iron phthalocyanine.

7. The wafer-level ferromagnetic metal-organic thin film prepared by the method according to any one of claims 1-6, characterized in that, The organic film is a monodisperse ferromagnetic metal-organic film with atomic-level thickness and in-plane ferromagnetism.

8. The wafer-level ferromagnetic metal-organic thin film according to claim 7, characterized in that, The thickness of the monodisperse ferromagnetic metal-organic thin film is less than 1 nanometer.

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