Preparation method of diffused island distribution vanadium dioxide thermochromic film

Abstract

The application relates to a preparation method of a diffused island-shaped vanadium dioxide thermochromic film. The preparation method comprises the following steps: a precursor forming step: forming a vanadium oxide film with a thickness of 20-100 nm as a precursor on the surface of a substrate by a magnetron sputtering method, a thermal deposition method or a laser-induced vapor deposition method; a pretreatment step: heating the film to 600-950 DEG C at a temperature increasing rate of more than 80 DEG C / min in an annealing furnace with a pressure of 50 mTorr or less, then keeping the temperature for 5-30 min, and then cooling the film to 300-450 DEG C in the furnace to form the film into a diffused island shape; and an oxidation step: introducing oxygen into the annealing furnace to oxidize the film to obtain a vanadium dioxide film. The film prepared by the preparation method of the vanadium dioxide thermochromic film has good sunlight modulation efficiency and good light transmittance.

Description

Technical Field

[0001] This application relates to the field of thin film materials technology, specifically to a method for preparing a diffusely distributed island-shaped vanadium dioxide thermochromic thin film. Background Technology

[0002] Reducing building energy consumption while ensuring living comfort is a hot research topic today. Windows are recognized as one of the highest energy-consuming components in buildings, and it has been found that controlling the heat exchange between indoors and outdoors through windows can significantly reduce building energy consumption.

[0003] In summer, reducing the transmission of sunlight can lower the indoor temperature to some extent and reduce the energy consumption of air conditioning. In winter, increasing the transmittance of sunlight can raise the indoor temperature to some extent and reduce the energy consumption of heating equipment such as air conditioners.

[0004] Existing energy-saving windows can be divided into two categories: thermochromic energy-saving windows and electrochromic energy-saving windows. Electrochromic energy-saving windows have a complex structure and high manufacturing costs. In contrast, thermochromic energy-saving windows are lower in cost, more convenient to use, and can intelligently adjust their light transmittance according to atmospheric temperature.

[0005] Vanadium dioxide exists in nature as various oxides of the transition metal vanadium. Vanadium dioxide exhibits four different crystal structures: below its critical temperature, it exists as a monoclinic crystal (M1 phase); above its critical temperature, it becomes a stable tetragonal crystal (R phase); and in the temperature range between these two, it exists as a metastable monoclinic phase (B) and a metastable tetragonal phase (A). Around 340K, vanadium dioxide undergoes a phase transition, transforming from a semiconductor monoclinic crystal (M1 phase) to a body-centered tetragonal crystal (R phase). While the transmittance of vanadium dioxide in the monoclinic (M1 phase) and tetragonal (R phase) phases is similar in the visible light range, their transmittance in the infrared range differs significantly. This difference in transmittance can be used to regulate indoor temperature, making it an ideal material for smart windows.

[0006] In existing technologies, there are reports of improving the optical properties of vanadium dioxide by designing multilayer film structures. However, multilayer film structures lead to a decrease in its transmittance in the visible light region. How to simultaneously achieve both solar light modulation efficiency and visible light transmittance in vanadium dioxide thin films is currently a hot research topic. Summary of the Invention

[0007] After in-depth research, the inventors discovered that by adopting the preparation method of the vanadium dioxide thermochromic thin film of this application, the problem that pure vanadium dioxide thin films in the prior art are difficult to balance sunlight modulation efficiency and visible light transmittance is solved, thus completing this invention.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a diffusely distributed island-shaped vanadium dioxide thermochromic thin film. The aforementioned diffusely distributed island-shaped vanadium dioxide thermochromic thin film has a substrate and a functional layer. The aforementioned functional layer is formed by diffusely distributed island-shaped vanadium dioxide particles. The thickness of the aforementioned functional layer is 20-100 nm, and the volume content of the vanadium dioxide phase in the aforementioned functional layer is 0.4-0.9%.

[0009] The aforementioned preparation method includes the following steps:

[0010] Precursor formation step: A vanadium oxide thin film with a thickness of 20 nm to 100 nm as a precursor is formed on the surface of the substrate by magnetron sputtering, thermal deposition or laser-induced vapor deposition.

[0011] Pretreatment steps: In an annealing furnace with a pressure of less than 50 mTorr, the film is heated to 600℃~950℃ at a heating rate of more than 80℃ / min, then held at that temperature for 5min~30min, and then cooled in the furnace to 300℃~450℃, so that the film forms a diffuse island shape.

[0012] Oxidation step: Oxygen is introduced into the annealing furnace to oxidize the film and obtain a vanadium dioxide film.

[0013] Beneficial effects of the present invention

[0014] Compared with existing technologies, the thin film prepared by the method of the present invention for preparing diffuse island-distributed vanadium dioxide thermochromic thin films exhibits both good solar light modulation efficiency and good light transmittance. Furthermore, the preparation method of the present invention can use sputtering with different vanadium source targets, is simple to operate, and the subsequent annealing process is straightforward. No other gases besides argon and oxygen are required, facilitating large-scale production. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application 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 of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a field emission scanning electron microscope (FE-SEM) image of the surface morphology of the diffuse island-distributed vanadium dioxide thermochromic thin film prepared in Example 1.

[0017] Figure 2 These are FE-SEM images of the surface morphology of the diffuse island-distributed vanadium dioxide thermochromic thin film prepared in Example 2.

[0018] Figure 3 These are FE-SEM images of the surface morphology of the diffuse island-shaped vanadium dioxide thermochromic thin film prepared in Example 3.

[0019] Figure 4 This is an FE-SEM image of the surface morphology of the diffuse island-shaped vanadium dioxide thermochromic thin film prepared in Comparative Example 1.

[0020] Figure 5 This is an FE-SEM cross-sectional image of the diffuse island-distributed vanadium dioxide thermochromic thin film prepared in Example 2.

[0021] Figure 6 This is an FE-SEM cross-sectional image of the diffuse island-distributed vanadium dioxide thermochromic thin film prepared in Example 3.

[0022] Figure 7 The optical transmittance spectra of the diffuse island-distributed vanadium dioxide thin films prepared in Example 3 and Comparative Example 1 were measured in hot (90°C) and cold (25°C) conditions, respectively. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] In some embodiments of the preparation method of the diffuse island-shaped distributed vanadium dioxide thermochromic thin film, the aforementioned diffuse island-shaped distributed vanadium dioxide thermochromic thin film has a substrate and a functional layer. The aforementioned functional layer is formed by diffuse island-shaped distributed vanadium dioxide particles, the thickness of the aforementioned functional layer is 20~100 nm, and the volume content of the vanadium dioxide phase in the aforementioned functional layer is 0.4~0.9.

[0025] The aforementioned preparation method includes the following steps:

[0026] Precursor formation step: A vanadium oxide thin film with a thickness of 20 nm to 100 nm as a precursor is formed on the surface of the substrate by magnetron sputtering, thermal deposition, or laser-induced vapor deposition.

[0027] Pretreatment steps: In an annealing furnace with a pressure of less than 50 mTorr, the film is heated to 600℃~950℃ at a heating rate of more than 80℃ / min, then held at that temperature for 5min~30min, and then cooled in the furnace to 300℃~450℃, so that the film forms a diffuse island shape.

[0028] Oxidation step: Oxygen is introduced into the annealing furnace to oxidize the film and obtain a vanadium dioxide film.

[0029] By employing this method of preparing a diffusely distributed vanadium dioxide thermochromic thin film, vanadium dioxide particles with a volume fraction of 0.4–0.9 are formed as the functional layer of the vanadium dioxide thermochromic thin film. Compared to thin films formed from continuously distributed vanadium dioxide particles, this method achieves a combination of visible light transmittance and solar light modulation efficiency. Here, "visible light" refers to light in the wavelength range of 400–800 nm. The inventors of this application hypothesize that by forming such diffusely distributed vanadium dioxide particles with a volume fraction of 0.4–0.9, air is present between the vanadium dioxide particles, resulting in a dielectric constant of the thin film that differs from that of the continuous state, thus improving transmittance to a certain extent. Simultaneously, the presence of vanadium dioxide particles causes localized plasmon resonance in the wavelength range of 1200 nm–1600 nm in the hot state, forming a plasmon resonance absorption peak. The proportion of solar spectral irradiance in this region is much greater than that in the 1600 nm–2500 nm region, thus resulting in higher solar light modulation efficiency.

[0030] The aforementioned "dispersed island-like distribution" refers to the discontinuous distribution of vanadium dioxide particles on the high-temperature resistant substrate, with certain gaps between the particles, exhibiting a dispersed distribution. The volume content of the vanadium dioxide phase in this film is 0.4~0.9. The aforementioned "volume content" refers to the volume ratio of the vanadium dioxide film to the total volume of the composite film. The preferred volume content of the vanadium dioxide phase in the aforementioned functional layer is 0.4~0.8.

[0031] The substrate for the vanadium dioxide thermochromic thin film can be a high-temperature resistant substrate such as quartz glass or sapphire, preferably quartz glass. This allows it to withstand the high temperatures used in subsequent steps.

[0032] The magnetron sputtering, thermal deposition, or laser-induced vapor deposition methods used in the aforementioned precursor formation steps are all commonly used techniques in the field. Those skilled in the art can select appropriate methods as needed and set specific conditions according to actual circumstances.

[0033] For example, in one embodiment, magnetron sputtering is used. The aforementioned substrate is placed in the sputtering chamber of a magnetron sputtering instrument, and a vanadium source is sputtered onto the substrate using a vanadium metal target, V₂O₃, or V₂O₅ as the target material. When using argon as the atmosphere, preferably, the argon gas used has a purity of 99.99% or higher. Preferably, the vanadium source used has a purity of 99.9% or higher.

[0034] Preferably, a pre-sputtering process is performed before the formal sputtering of the precursor film using a magnetron sputtering apparatus. Pre-sputtering removes nitrides, oxides, and other contaminants from the target surface, thereby preventing surface impurities from affecting the subsequent vanadium dioxide film quality and increasing the sputtering rate of the target. During this process, it is preferable to close the baffle to prevent pre-sputtered material from depositing on the substrate and affecting the subsequent vanadium dioxide film quality.

[0035] Preferably, during the pre-sputtering process, the vacuum level of the sputtering chamber is 1.0 × 10⁻⁶. -5 Torr~1.0×10 -6 Torr, argon flow rate is 10 sccm~18 sccm, pre-sputtering working pressure is 2 mTorr~6 mTorr, vanadium target pre-sputtering power is 50~80 W, and pre-sputtering time is 180s~600s.

[0036] In another embodiment, in the aforementioned precursor formation step, magnetron sputtering is used, wherein the argon gas flow rate is 10 sccm to 18 sccm, the sputtering working pressure is 2 mTorr to 6 mTorr, the sputtering power of the vanadium target is 90 W to 120 W, the substrate rotation speed is fixed, and the sputtering time is 120 s to 600 s.

[0037] In some embodiments of the preparation method, the aforementioned pressure is further preferably 30 mTorr or less in the aforementioned pretreatment step.

[0038] In some embodiments of the preparation method, in the aforementioned pretreatment step, the vacuum degree in the tubular annealing furnace is evacuated to below 30 mTorr using a mechanical pump, and the temperature is increased to 600°C to 950°C, preferably 700°C to 900°C, at a heating rate of 80°C / min or higher, held at this temperature for 5 min to 30 min, and then cooled in the furnace to 300°C to 450°C, preferably 400°C to 450°C. Further, the aforementioned heating rate is preferably 80°C / min to 150°C / min.

[0039] In some embodiments of the preparation method, during the aforementioned oxidation step, the oxygen flow rate is controlled at 30 sccm to 120 sccm, the temperature is increased to 420°C to 460°C at a heating rate of 10°C / min to 50°C / min, held at that temperature for 50 to 100 minutes, and then cooled in the furnace to 20°C to 30°C to obtain a vanadium dioxide thin film. The aforementioned oxygen flow rate is preferably controlled by a mass flow meter, thereby ensuring a stable oxygen content during the annealing process. Furthermore, controlling the oxygen flow rate using the pressure value displayed by an electronic vacuum gauge is not preferred, because the pressure value displayed by the electronic vacuum gauge changes with temperature, leading to a difference between the actual and displayed oxygen content.

[0040] Example 1

[0041] Using 10 mm thick quartz glass as a substrate, the surface of the quartz substrate was first cleaned with a surfactant, then ultrasonically cleaned in deionized water for 30 min, and then ultrasonically cleaned in anhydrous ethanol for 30 min. Finally, the cleaned quartz glass substrate was placed in anhydrous ethanol for storage until use. When using, it was taken out and dried.

[0042] The cleaned and dried quartz glass substrate was fixed onto the sputtering substrate. The substrate was then placed in the magnetron sputtering chamber, using a vanadium target with a purity of 99.9% as the target material, and the vacuum level was evacuated to 5.0 × 10⁻⁶. -6 Torr was used to control the argon gas flow rate at 15 sccm and the pre-sputtering working pressure at 0.3 Pa. Argon gas with a purity of 99.99% was used as the working gas for pre-sputtering the vanadium target. The pre-sputtering power of the vanadium target was 70 W, and the pre-sputtering time was 360 s. Subsequently, the sputtering power of the vanadium target was adjusted to 100 W, and after 180 s of sputtering, the precursor film was obtained.

[0043] The obtained precursor film was placed in a tubular vacuum annealing furnace, and a mechanical pump was used to evacuate the furnace to 10 mTorr. Then, the temperature was rapidly increased to 900℃ at a heating rate of 300℃ / min, and held at 900℃ for 30 min.

[0044] After the heat preservation is completed, wait for the temperature inside the furnace to cool to 430℃, control the oxygen flow rate to 60 sccm with the mass flow meter, and raise the temperature to 450℃ at a heating rate of 30℃ / min. Hold the temperature for 80 minutes, and then cool the furnace to room temperature. Figure 1 The surface morphology image of the obtained diffuse island-shaped vanadium dioxide thermochromic thin film is shown by field emission scanning electron microscopy (FE-SEM).

[0045] Example 2

[0046] In the pretreatment step, the furnace temperature was cooled to 430°C. Then, in the oxidation step, the oxygen flow rate was controlled at 80 sccm using a mass flow meter, and the temperature was increased to 450°C at a rate of 30°C / min, held for 80 min, and then cooled to room temperature with the furnace. Otherwise, the preparation of the vanadium dioxide thermochromic film was carried out in the same manner as in Example 1. Figure 2 , Figure 5 The surface morphology image and cross-sectional image of the diffuse island-distributed vanadium dioxide thermochromic thin film prepared in Example 2 are shown respectively.

[0047] Example 3

[0048] In the precursor formation step, the vanadium target was sputtered at a power of 100W for 300 s. In the pretreatment step, a mechanical pump was used to evacuate to 12 mTorr, followed by a heating rate of 300°C / min to 900°C, holding at 900°C for 30 min, and then cooling with the furnace to 420°C. In the oxidation step, the oxygen flow rate was controlled at 60 sccm using a mass flow meter, and the temperature was raised to 450°C at a rate of 30°C / min, held for 80 min, and then cooled with the furnace to room temperature. Otherwise, the process was the same as in Example 1. Figure 3 , Figure 6 The surface morphology image and cross-sectional image of the diffuse island-distributed vanadium dioxide thermochromic thin film prepared in Example 3 are shown respectively.

[0049] Comparative Example 1

[0050] Similar to Example 3, quartz glass was used as the substrate, and the precursor formation step was performed in the same manner. Then, without any pretreatment step, the obtained precursor film was directly placed in a tube annealing furnace, with the oxygen flow rate controlled at 60 sccm. Subsequently, the temperature was rapidly increased to 430 ℃ at a heating rate of 30 ℃ / min, and held at 430 ℃ for 80 min. Figure 4 The surface morphology image of the diffuse island-distributed vanadium dioxide thermochromic thin film prepared in Comparative Example 1 is shown by field emission scanning electron microscopy (FE-SEM).

[0051] Thermochromic performance test :

[0052] The optical transmittance spectra of the diffuse island-distributed vanadium dioxide thermochromic films prepared in Example 3 and Comparative Example 1 were measured in the range of 350 nm to 2500 nm using a UV spectrophotometer (UV-3600, Shimadzu, Japan) under cold (25°C) and hot (90°C) conditions. The results are shown in the figure. Figure 7 middle. Figure 7 In the diagram, the solid line represents the optical transmittance spectrum of the thin film in its cold state, and the dashed line represents the optical transmittance spectrum of the thin film in its hot state. Figure 7 The curve with a triangular tip represents the vacuum-pretreated film of Example 3, while the curve with dots represents the unpretreated film of Comparative Example 1.

[0053] Using the optical transmittance spectrum obtained from the above measurements, the solar modulation efficiency T in the hot and cold states can be calculated based on the following formula. sol and visible light transmittance (T lum ):

[0054]

[0055]

[0056] Among them, T sol (λ) represents the solar radiation transmittance. T represents solar spectral irradiance. lum Visible light transmittance φ lum (λ) represents the standard luminous efficacy indicated by the human eye, with a wavelength range of 380 nm to 780 nm.

[0057] Furthermore, the solar modulation efficiency T under hot and cold states was analyzed. sol The difference ∆T between the solar modulation efficiency in the hot state and the solar modulation efficiency in the cold state can be obtained. sol .

[0058] from Figure 7 It can be seen that the transmittance of the film in Example 3 after vacuum pretreatment is 52.5% (cold state) and 55.8% (hot state) in the visible light band, respectively. In contrast, the transmittance of the film in Comparative Example 1 without vacuum pretreatment is 48.1% (cold state) and 51.9% (hot state) in the visible light band, respectively. Using the above formula, the solar modulation efficiency of the film in Example 3 is calculated to be 5.4%, while the solar modulation efficiency of the film in Comparative Example 1 is 4.5%. Therefore, the film prepared in Example 3 shows an improvement of nearly 20% in solar modulation efficiency compared to the film prepared in Comparative Example 1.

[0059] The foregoing description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a diffusely distributed island-shaped vanadium dioxide thermochromic thin film, wherein the diffusely distributed island-shaped vanadium dioxide thermochromic thin film has a substrate and a functional layer, wherein the functional layer is formed by diffusely distributed island-shaped vanadium dioxide particles, the thickness of the functional layer is 20~100 nm, and the volume content of the vanadium dioxide phase in the functional layer is 0.4~0.

9. The preparation method includes: Precursor formation steps: The substrate is placed in the sputtering chamber of a magnetron sputtering instrument by magnetron sputtering, and a vanadium source is sputtered onto the substrate. A vanadium metal target is used as the target material to form a vanadium oxide thin film with a thickness of 20nm~100nm as a precursor on the surface of the substrate. Pretreatment steps: In an annealing furnace with a pressure of less than 30 mTorr, the film is heated to 600℃~950℃ at a heating rate of 80℃ / min~150℃ / min, then held at that temperature for 5min~30min, and then cooled in the furnace to 300℃~450℃, so that the film forms a diffuse island shape. Oxidation step: Oxygen is introduced into the annealing furnace to oxidize the film. The oxygen flow rate is 30 sccm to 120 sccm. The temperature is increased to 420°C to 460°C at a heating rate of 10°C to 50°C to 50°C to 120°C. The temperature is held for 50 to 100 minutes and then cooled to 20°C to 30°C in the furnace to obtain a vanadium dioxide film.

2. The method for preparing a diffusely distributed island-shaped vanadium dioxide thermochromic thin film according to claim 1, wherein, The volume content of vanadium dioxide phase in the functional layer is 0.4~0.8%.

3. The method for preparing a diffusely distributed island-like vanadium dioxide thermochromic thin film according to claim 1 or 2, wherein, The substrate is quartz glass.

4. The method for preparing a diffusely distributed island-shaped vanadium dioxide thermochromic thin film according to claim 1 or 2, wherein, In the precursor formation step, the temperature of the substrate is 20~100℃.

Images