Preparation method of two-dimensional metal oxide film

Abstract

The invention discloses a preparation method of a two-dimensional metal oxide film. The preparation method comprises the following steps: providing a growth substrate; growing an initial thin film on the growth substrate by using a molecular beam epitaxy process, wherein metal ions which are not completely oxidized exist in the initial thin film; the initial thin film is heated and oxidized to obtain a two-dimensional metal oxide thin film, metal ions in the two-dimensional metal oxide thin film are completely oxidized, and the two-dimensional metal oxide thin film is a two-dimensional tin oxide thin film, a two-dimensional molybdenum oxide thin film or a two-dimensional nickel oxide thin film. The molecular beam epitaxy technology is utilized to grow the initial thin film, the initial thin film is heated and oxidized, and the surface chemical state of the two-dimensional metal oxide thin film can be accurately regulated and controlled.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials technology, and specifically relates to a method for preparing two-dimensional metal oxide thin films. Background Technology

[0002] Metal oxides are important materials exhibiting diverse properties in various applications. Two-dimensional (2D) metal oxide thin films, as a novel nanomaterial, demonstrate significant application value in multiple fields due to their unique structure and superior performance. Compared to traditional bulk materials, 2D metal oxide thin films possess atomic-level thickness and extremely high specific surface area, which not only significantly enhances the exposure of surface active sites but also optimizes carrier transport paths, thereby significantly improving electrical performance. In the optoelectronic field, the ultrathin 2D structure endows 2D metal oxide thin films with higher visible light transmittance and tunable wide bandgap characteristics, making them an ideal choice for flexible transparent conductive electrodes, which can be widely used in devices such as flexible displays, touch screens, and perovskite solar cells.

[0003] Tin oxide (SnO2) is an important n-type wide-bandgap (~3.6 eV) semiconductor material among metal oxides. It possesses high light transmittance, excellent chemical stability, and electrical properties, making it irreplaceable in numerous fields such as transparent conductive electrodes, solid-state gas sensors, optoelectronic devices, lithium-ion battery anodes, and photocatalysis. Structurally, tin oxide exhibits a typical tetragonal rutile crystal structure at room temperature and pressure, where each tin atom (Sn...)... 4+ ) and six oxygen atoms (O 2- The coordination of tin oxide forms [SnO6] octahedral basic units, which are connected by sharing edges and corners to form a three-dimensional network, endowing the material with excellent thermal stability and mechanical strength. The close-packed structure of tin oxide gives it a high melting point of approximately 1630℃. Simultaneously, its excellent chemical stability allows it to withstand most acid and alkali corrosion (except hydrofluoric acid and hot concentrated sulfuric acid), maintaining stable performance even in harsh environments. Furthermore, the surface of tin oxide is rich in chemically adsorbed oxygen species (O2). - O 2- SnO2 exhibits a sensitive resistive response to reducing gases such as CO and H2, making it highly sought after in the field of gas sensors. Compared to bulk tin oxide, two-dimensional SnO2 thin films have a higher density of surface-adsorbed oxygen active sites, resulting in better resistance to CO and NO. x The detection sensitivity for gases is higher and the response time is shorter. More importantly, through existing advanced preparation techniques, the controllable preparation of single-layer or few-layer SnO2 thin films can be achieved, and the thickness-related performance regulation provides the possibility for on-demand design of functional devices.

[0004] However, in existing technologies, two-dimensional metal oxide films prepared using molecular beam epitaxy contain incompletely oxidized metal ions. For example, in existing two-dimensional tin oxide films, Sn is also present. 2+ Ions and Sn 4+ The valence state of tin ions in the thin film cannot be precisely controlled. Furthermore, existing preparation methods cannot precisely control the oxygen vacancy concentration in the prepared two-dimensional metal oxide thin films, and are easily affected by air, introducing impurities and making it difficult to guarantee the purity of the prepared two-dimensional metal oxide thin films.

[0005] Therefore, in order to address the above-mentioned technical problems, it is necessary to provide a method for preparing two-dimensional metal oxide thin films. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing two-dimensional metal oxide thin films, which can precisely control the valence state of metal ions in the two-dimensional oxide thin films.

[0007] To achieve the above objectives, an embodiment of the present invention provides the following technical solution:

[0008] A method for preparing a two-dimensional metal oxide thin film, the method comprising the following steps:

[0009] Provide growth substrate;

[0010] An initial thin film is grown on a growth substrate using molecular beam epitaxy, wherein the initial thin film contains incompletely oxidized metal ions;

[0011] The initial thin film is heated and oxidized to obtain a two-dimensional metal oxide thin film, in which the metal ions are completely oxidized. The two-dimensional metal oxide thin film is a two-dimensional tin oxide thin film, a two-dimensional molybdenum oxide thin film, or a two-dimensional nickel oxide thin film.

[0012] In one embodiment, the initial thin film is SnO. x Thin film, the initial thin film containing Sn 2+ Ions and Sn 4+ The two-dimensional metal oxide film is a SnO2 film, and the two-dimensional metal oxide film contains only Sn. 4+ ion.

[0013] In one embodiment, in the step of heating and oxidizing the initial thin film to obtain a two-dimensional metal oxide thin film, the heating power is 1W to 20W.

[0014] In one embodiment, in the step of heating and oxidizing the initial film to obtain a two-dimensional metal oxide film, the pressure of the oxygen introduced is 0.1 mbar to 0.3 mbar.

[0015] In one embodiment, prior to the step of growing an initial thin film on a growth substrate using molecular beam epitaxy, the method further includes:

[0016] The growth substrate is annealed.

[0017] In one embodiment, the growth substrate is annealed in an annealing furnace, an initial thin film is grown in a molecular beam epitaxy (MBE) apparatus, and the initial thin film is heated and oxidized in a near-atmospheric pressure X-ray photoelectron spectroscopy (NAPX) apparatus. The annealing furnace and the MBE apparatus are connected via a first vacuum interconnect pipe, and the MBE apparatus and the NAPX apparatus are connected via a second vacuum interconnect pipe.

[0018] In one embodiment, the vacuum level of the first vacuum interconnection pipe is not less than 1×10⁻⁶. -10 mbar, the vacuum level of the molecular beam epitaxy equipment is 1×10⁻⁶ mbar. -8 mbar~1×10 -10 mbar.

[0019] In one embodiment, growing an initial thin film on a growth substrate using molecular beam epitaxy includes the following steps:

[0020] The growth substrate is placed on the sample stage in the molecular beam epitaxy equipment, and the sample stage is heated.

[0021] The evaporation source is heated and evaporated;

[0022] An initial thin film is grown on a growth substrate.

[0023] In one embodiment, the evaporation source is a metal oxide powder.

[0024] In one embodiment, the growth substrate is an Al2O3(0001) substrate.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention utilizes molecular beam epitaxy to grow initial thin films and then heats and oxidizes these initial films, enabling precise control of the surface chemical state of two-dimensional metal oxide thin films.

[0027] This invention uses vacuum interconnection technology to connect the annealing furnace, MBE equipment, NAP-XPS equipment and SEM equipment, which can efficiently and conveniently process samples. At the same time, it can isolate air pollution, ensure the purity of the grown two-dimensional metal oxide film, and achieve in-situ characterization of the film and precisely control the oxygen vacancy filling in the film. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic flowchart of the two-dimensional metal oxide thin film preparation method in Embodiment 1 of the present invention;

[0030] Figure 2a and 2b AFM images of the Al2O3(0001) substrate after high-temperature annealing in Example 1 of this invention at different magnifications;

[0031] Figure 3a and 3b SEM images of the initial thin film grown by the MBE process in Example 1 of the present invention at different magnifications;

[0032] Figure 4a and 4b AFM images of the initial thin film grown by the MBE process in Example 1 of this invention at different magnifications;

[0033] Figure 5 XPS spectra of tin in the initial thin film and two-dimensional tin oxide thin films prepared under different heating powers in this invention;

[0034] Figure 6 XPS spectra of oxygen in the initial thin film and two-dimensional tin oxide thin films prepared under different heating powers in this invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0036] This invention discloses a method for preparing two-dimensional metal oxide thin films, comprising the following steps:

[0037] Provide growth substrate;

[0038] An initial thin film is grown on a growth substrate using molecular beam epitaxy, and the initial thin film contains incompletely oxidized metal ions;

[0039] The initial thin film is heated and oxidized to obtain a two-dimensional metal oxide thin film. The metal ions in the two-dimensional metal oxide thin film are completely oxidized. The two-dimensional metal oxide thin film is a two-dimensional tin oxide thin film, a two-dimensional molybdenum oxide thin film or a two-dimensional nickel oxide thin film.

[0040] The present invention will be further described below in conjunction with specific examples.

[0041] Example 1:

[0042] See Figure 1 As shown, the preparation method of the two-dimensional metal oxide thin film in this example includes the following steps:

[0043] S1. Provide a growth substrate.

[0044] Among them, the growth substrate is an Al2O3(0001) substrate.

[0045] Specifically, before placing the growth substrate in a Molecular Beam Epitaxy (MBE) device for thin film growth, the growth substrate needs to be annealed.

[0046] See Figure 2a and 2b As shown, in this example, the Al2O3(0001) substrate is placed in an annealing furnace and annealed at a temperature of 800 °C for 4 h, and then annealed at a temperature of 1200 °C for 4 h to obtain a flat Al2O3(0001) substrate. After the high-temperature annealing treatment, a highly flat morphology is formed on the surface of the Al2O3(0001) substrate, presenting a uniform atomic-scale step structure, indicating that the annealing process effectively eliminates the scratches and defects remaining from mechanical polishing, providing an ideal growth substrate for the subsequent epitaxial growth of the two-dimensional metal oxide thin film.

[0047] S2. Use the molecular beam epitaxy process to grow an initial thin film on the growth substrate. There are incompletely oxidized metal ions in the initial thin film.

[0048] In existing technologies, various preparation methods are used to prepare tin oxide thin films. Magnetron sputtering is currently the most commonly used preparation technique due to its mature process and good film uniformity. By adjusting the sputtering power (50W~300W), oxygen partial pressure (5%~30%), and substrate temperature (room temperature~400℃), tin oxide thin films with different crystal qualities and electrical properties can be obtained. Chemical vapor deposition (CVD) performs well in tin oxide thin film preparation, using SnCl4 or organotin as precursors, and can achieve thickness control at 500℃~800℃. The sol-gel method has attracted widespread attention due to its simple equipment and low cost. Porous tin oxide thin films are prepared through the hydrolysis-condensation process of SnCl2·2H2O or tin alkoxides, combined with subsequent heat treatment (400℃~600℃), and is particularly suitable for gas sensors.

[0049] Compared with the above preparation methods, the use of molecular beam epitaxy for the preparation of initial thin films has many advantages:

[0050] 1. MBE process can achieve atomic-level precision thin film growth in an ultra-high vacuum environment. By precisely controlling the temperature and evaporation rate of the evaporation source, a highly accurate initial thin film with stoichiometry can be obtained, effectively reducing intrinsic defects such as oxygen vacancies.

[0051] 2. The growth temperature of the MBE process is relatively low, much lower than that of traditional vapor deposition methods. This not only reduces energy consumption but also avoids the interface diffusion problem caused by high temperature.

[0052] 3. The MBE process has excellent thickness control capabilities. The growth rate can be determined by a film thickness gauge, thereby determining the initial film thickness.

[0053] 4. The initial thin films grown by the MBE process have extremely high crystal quality, which has significant advantages in high-end electronic device applications.

[0054] In this embodiment, the two-dimensional metal oxide film is a two-dimensional tin oxide film, and the initial film grown using molecular beam epitaxy is SnO. x Thin film, SnO x The thin film contains Sn 2+ Ions and Sn 4+ ion.

[0055] Specifically, this step includes:

[0056] 1. Place the growth substrate on the sample stage in the molecular beam epitaxy equipment and heat the sample stage.

[0057] Specifically, the molecular beam epitaxy equipment and the annealing furnace are connected via a first vacuum interconnection pipe, the vacuum level of which is not less than 1×10⁻⁶. -10 mbar, the vacuum level of the molecular beam epitaxy equipment is not less than 1×10-8 mbar, preferably 1×10 -9 mbar. The grown substrate after high-temperature annealing treatment is transferred from the annealing furnace to the growth chamber of the molecular beam epitaxy equipment through the first vacuum interconnection pipeline, effectively avoiding air pollution, ensuring interface quality, and being conducive to precisely regulating the oxygen vacancy concentration.

[0058] More specifically, the sample stage is heated to 500 °C, and the Al2O3(0001) substrate is placed on the sample stage for annealing for 1 h.

[0059] 2. Heat and evaporate the evaporation source.

[0060] Specifically, metal oxide powder is used as the evaporation source. An independent beam source is formed by heating and evaporation, and the beam current intensities of different elements are respectively controlled by the independent beam source, enabling precise regulation of the stoichiometric ratio.

[0061] More specifically, in this embodiment, SnO2 powder is used as the evaporation source, which can precisely control the beam current intensities of oxygen and tin elements. The Sn / O ratio error is <1%, and the evaporation temperature is set to 750 °C.

[0062] 3. Grow an initial thin film on the grown substrate.

[0063] Specifically, a 100-nm-thick SnO x thin film is grown on the Al2O3(0001) substrate at a growth rate of 0.23 Å / s.

[0064] Refer Figure 3a and 3b As shown, the grown initial thin film is characterized by a scanning electron microscope (Scanning Electron Microscope, SEM). The SEM characterization results show that the initial thin film is composed of uniformly distributed nanosheets with clear edges, an average particle size of 100 nm - 140 nm, and no macroscopic defects such as cracks or holes.

[0065] Refer Figure 4a and 4b As shown, the grown initial thin film is characterized by an atomic force microscope (Atomic Force Microscope, AFM). The AFM characterization results show that the surface of the initial thin film is flat and the undulation of the nanosheets is small.

[0066] It is worth noting that in this embodiment, the SEM equipment and the MBE equipment are connected via a third vacuum interconnection channel. The growth substrate with the initial thin film can be transferred to the SEM for characterization via this third vacuum interconnection channel. Simultaneously, the SEM equipment is connected to a glove box via a fourth vacuum interconnection channel. The sample, after SEM characterization, is first transferred to the glove box, and then placed in a portable vacuum sample transfer container for transfer to the AFM equipment for characterization. This vacuum interconnection technology connects the MBE equipment and the characterization equipment, isolating them from external air interference.

[0067] S3. The initial film is heated and oxidized to obtain a two-dimensional metal oxide film. The metal ions in the two-dimensional metal oxide film are completely oxidized. The two-dimensional metal oxide film is a two-dimensional tin oxide film, a two-dimensional molybdenum oxide film, or a two-dimensional nickel oxide film.

[0068] In this embodiment, the two-dimensional metal oxide film is a SnO2 film, which contains only Sn. 4+ ion.

[0069] Specifically, in this embodiment, the initial thin film is heated and oxidized in a near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) device.

[0070] X-ray photoelectron spectroscopy (XPS) is one of the core technologies for materials surface analysis. By measuring the energy distribution of photoelectrons emitted by materials excited by X-rays, rich information about the surface chemistry can be obtained. XPS can analyze the elements on the material surface (detection depth 2 nm ~ 10 nm) and determine the chemical state of elements through high-resolution narrow scans, such as distinguishing Sn. 0 / Sn 2+ / Sn 4+ The NAP-XPS system offers high resolution and sensitivity in quantitative and qualitative analysis of material surface elements by determining the bonding environment through chemical shift, obtaining the depth distribution of layered structural components through Ar⁺ sputtering, and calculating the relative content of each element through peak area. Compared with traditional ultra-high vacuum XPS, the NAP-XPS system overcomes pressure limitations, allowing direct study of gas-solid interface reactions (such as catalysis and corrosion), real-time observation of the elemental composition, chemical state changes, and adsorption behavior of samples in a real reaction environment, and in-situ monitoring of the dynamic changes of the Sn 3d peak during heating and oxidation.

[0071] In addition, in this embodiment, the NAP-XPS device and the MBE device are connected through a second vacuum interconnection pipeline. After the preparation of the initial thin film, the growth substrate with the initial thin film is transferred to the NAP-XPS device through the second vacuum interconnection pipeline for heating oxidation, while monitoring the oxidation process of Sn 2+ converted to Sn 4+ .

[0072] More specifically, the heating power is 1W to 20W, preferably 15W, and the pressure of oxygen introduced is 0.1 mbar to 0.3 mbar, preferably 0.2 mbar.

[0073] Example 2:

[0074] The preparation method of the two-dimensional metal oxide thin film in this embodiment is substantially the same as that in Example 1, except that the heating power is 1W.

[0075] Example 3:

[0076] The preparation method of the two-dimensional metal oxide thin film in this embodiment is substantially the same as that in Example 1, except that the heating power is 4W.

[0077] Example 4:

[0078] The preparation method of the two-dimensional metal oxide thin film in this embodiment is substantially the same as that in Example 1, except that the heating power is 10W.

[0079] Example 5:

[0080] The preparation method of the two-dimensional metal oxide thin film in this embodiment is substantially the same as that in Example 1, except that the heating power is 15W.

[0081] Refer Figure 5 As shown, in the heating oxidation step, there is an oxidation process in which the initial Sn 2+ (485.5 eV) is converted to Sn 4 (486.7 eV). In this embodiment, the initial thin film uses tin oxide powder as the evaporation source during the preparation process, and certain decomposition will occur in the ultra-high vacuum environment, so the prepared initial thin film is a SnO x thin film, which contains both Sn2+ ions and Sn4+ ions. By comparing the thin film samples in Example 1, Example 2, Example 3, Example 4, and Example 5, it shows that under the same oxidation time, the higher the heating power, the easier it is to convert the initial Sn 2+ (485.5 eV) to Sn 4 (486.7 eV).

[0082] It should be understood that during the actual preparation process, the heating power and heating time should be reasonably controlled so that the metal ions in the initial thin film are completely oxidized.

[0083] As shown Figure 6 By adjusting the heating power, the ratio of lattice oxygen (530.2 eV) to adsorbed oxygen (531.8 eV) in the O 1s peak can be adjusted.

[0084] In summary, the present invention has the following beneficial effects:

[0085] The present invention uses molecular beam epitaxy technology to grow an initial thin film and heats and oxidizes the initial thin film, capable of precisely controlling the surface chemical state of the two-dimensional metal oxide thin film;

[0086] The present invention uses a vacuum interconnection technology to connect an annealing furnace, MBE equipment, NAP-XPS equipment, and SEM equipment, capable of efficiently and conveniently processing samples, and while isolating air pollution and ensuring the purity of the grown two-dimensional metal oxide thin film, realizing in-situ characterization of the thin film and precisely controlling the oxygen vacancy filling in the thin film.

[0087] For those skilled in the art, it is obvious that the present disclosure is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present disclosure, the present disclosure can be implemented in other specific forms. Therefore, in any aspect, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present disclosure is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present disclosure. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0088] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a two-dimensional metal oxide thin film, characterized in that, The preparation method includes the following steps: Provide growth substrate; An initial thin film is grown on a growth substrate using molecular beam epitaxy, wherein the initial thin film contains incompletely oxidized metal ions; The initial thin film is heated and oxidized to obtain a two-dimensional metal oxide thin film, in which the metal ions are completely oxidized. The two-dimensional metal oxide thin film is a two-dimensional tin oxide thin film, a two-dimensional molybdenum oxide thin film, or a two-dimensional nickel oxide thin film.

2. The method for preparing a two-dimensional metal oxide thin film according to claim 1, characterized in that, The initial thin film is SnO. x Thin film, the initial thin film containing Sn 2+ Ions and Sn 4+ The two-dimensional metal oxide film is a SnO2 film, and the two-dimensional metal oxide film contains only Sn. 4+ ion.

3. The method for preparing a two-dimensional metal oxide thin film according to claim 1, characterized in that, In the step of heating and oxidizing the initial thin film to obtain a two-dimensional metal oxide thin film, the heating power is 1W to 20W.

4. The method for preparing a two-dimensional metal oxide thin film according to claim 1, characterized in that, In the step of heating and oxidizing the initial thin film to obtain a two-dimensional metal oxide thin film, the pressure of the oxygen introduced is 0.1 mbar ~ 0.3 mbar.

5. The method for preparing a two-dimensional metal oxide thin film according to claim 1, characterized in that, Before the step of growing an initial thin film on a growth substrate using molecular beam epitaxy, the process also includes: The growth substrate is annealed.

6. The method for preparing a two-dimensional metal oxide thin film according to claim 5, characterized in that, The growth substrate is annealed in an annealing furnace, an initial thin film is grown in a molecular beam epitaxy (MBE) device, and the initial thin film is heated and oxidized in a near-atmospheric pressure X-ray photoelectron spectroscopy (NAPX) device. The annealing furnace and the MBE device are connected through a first vacuum interconnect pipe, and the MBE device and the NAPX device are connected through a second vacuum interconnect pipe.

7. The method for preparing a two-dimensional metal oxide thin film according to claim 6, characterized in that, The vacuum level of the first vacuum interconnection pipe is not less than 1×10 -10 mbar, the vacuum level of the molecular beam epitaxy equipment is 1×10⁻⁶ mbar. -8 mbar~1×10 -10 mbar.

8. The method for preparing a two-dimensional metal oxide thin film according to claim 1, characterized in that, The initial thin film grown on a growth substrate using molecular beam epitaxy includes the following steps: The growth substrate is placed on the sample stage in the molecular beam epitaxy equipment, and the sample stage is heated. The evaporation source is heated and evaporated; An initial thin film is grown on a growth substrate.

9. The method for preparing a two-dimensional metal oxide thin film according to claim 8, characterized in that, The evaporation source is metal oxide powder.

10. The method for preparing a two-dimensional metal oxide thin film according to claim 1, characterized in that, The growth substrate is an Al2O3(0001) substrate.

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