A humidity-sensitive color-changing film of vanadium oxide and a preparation method and application thereof

Abstract

This invention belongs to the field of functional thin films and sensing technology, specifically relating to a vanadium oxide humidity-sensitive color-changing thin film, its preparation method, and its application. The vanadium oxide humidity-sensitive color-changing thin film is an amorphous vanadium oxide (VxOy) thin film, prepared by reactive magnetron sputtering. The ratio of V to O elements in the amorphous vanadium oxide (VxOy) thin film is 1:1.8~2.4. The surface color of the humidity-sensitive color-changing thin film changes reversibly with humidity within 0.1 s. The thickness of the humidity-sensitive color-changing thin film is 250 nm~500 nm. The humidity-sensitive color-changing thin film of this invention has a response speed of <0.03 s, high visibility, and a simple preparation process.

Description

Technical Field

[0001] This invention belongs to the field of functional thin films and sensing technology, specifically relating to a vanadium oxide humidity-sensitive color-changing thin film, its preparation method, and its application. Background Technology

[0002] Humidity detection is crucial in many fields. Optical humidity sensors have attracted attention due to their advantages such as resistance to electromagnetic interference and fast response, and their core lies in humidity-sensitive materials. Currently, some polymer or nanoporous materials, such as graphene, graphene oxide, carbon nanotubes, and nano-anatase TiO2, are used for optical humidity sensing. Lim W, Yap Y, Chong W, et al. All-Optical Graphene Oxide Humidity Sensors[J]. Sensors, 2014, 14(12):24329-24337.DOI:10.3390 / s141224329 reported that the optical sensor based on graphene oxide nanosheets has a response time of less than 1 second. Existing humidity-sensitive materials have a slow response speed to humidity and low color contrast. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a vanadium oxide humidity-sensitive color-changing thin film, its preparation method, and its application.

[0004] The first objective of this invention is to provide a humidity-sensitive color-changing thin film of vanadium oxide, wherein the humidity-sensitive color-changing thin film is an amorphous vanadium oxide VxOy thin film, which is prepared by reactive magnetron sputtering.

[0005] The ratio of V to O elements in the amorphous vanadium oxide (VxOy) thin film is 1:1.8~2.4. The vanadium oxide in the amorphous VxOy thin film contains four valence states: +2, +3, +4, and +5, corresponding to VO, VO2, V2O3, and V2O5. During the reaction of metallic vanadium with oxygen, a higher amount of oxygen results in a higher valence state for vanadium; it is not a fixed value. Therefore, the state of the vanadium oxide in the VxOy thin film is represented by the ratio of V to O elements.

[0006] The surface color of the humidity-sensitive color-changing film changes reversibly with humidity within 0.1 seconds.

[0007] The thickness of the humidity-sensitive color-changing film is 250nm~500nm.

[0008] The VxOy thin film is a two-dimensional sheet structure of metal-oxygen octahedral chain layers with periodic repeating units, formed by vanadium atoms and oxygen atoms bonded by covalent bonds or ionic bonds. The layers of the VxOy thin film two-dimensional sheet structure are bonded to each other by van der Waals forces, hydrogen bonds or physical adsorption, allowing water molecules to reversibly insert and escape.

[0009] When the ambient humidity increases, water molecules will insert into the gaps between the film layers, and when the ambient humidity decreases, water molecules will escape from the gaps between the film layers. The insertion or overflow of water molecules will cause the optical path of light refracted on the surface of the humidity-sensitive color-changing film to change, thus causing the color of the light to change, thereby exhibiting the function of humidity sensitivity.

[0010] A water molecule has a diameter of 0.3 nm. When water molecules insert into the VxOy thin film layers of a humidity-sensitive color-changing film, the interlayer spacing increases. As humidity increases and more water molecules are inserted, the interlayer spacing can reversibly expand to 0.6 nm to 1.2 nm. This variable gap on the nm scale is the physical basis for the change in light interference conditions, which leads to color changes.

[0011] Preferably, the surface color of the humidity-sensitive color-changing film changes reversibly with humidity within 0.03s.

[0012] The second objective of this invention is to provide a method for preparing a vanadium oxide moisture-sensitive color-changing thin film, comprising the following steps: Using metallic vanadium as the target material, amorphous vanadium oxide VxOy is deposited on the substrate by reactive magnetron sputtering at 200W~400W and working pressure of 0.5Pa~2.0Pa in an atmosphere of argon and oxygen, without heating the substrate; after the deposition is completed, the substrate is cooled to obtain a moisture-sensitive color-changing film.

[0013] The substrate is silicon, ceramic, glass, quartz, mica, or sapphire.

[0014] Preferably, the flow rate ratio of argon to oxygen is 100~150:8~30.

[0015] Preferably, the flow rate ratio of argon to oxygen is 120:12.4, 120:8.4, 120:24.4, 100:100.5, 120:16, or 121:31.

[0016] Preferably, the reactive magnetron sputtering method has a sputtering power of 300W and a working gas pressure of 1.5Pa; the substrate is not heated.

[0017] A third objective of this invention is to provide an application of a vanadium oxide humidity-sensitive color-changing thin film in the fabrication of a humidity sensor or humidity-sensitive indicator element.

[0018] Preferably, the humidity sensor or humidity-sensitive indicator element comprises a substrate, electrodes, and a humidity-sensitive color-changing film. The electrodes are distributed on the surface of the substrate, and the humidity-sensitive color-changing film covers the surfaces of both the electrodes and the substrate. After encapsulation and protection, the electrodes are led out to form the humidity sensor.

[0019] A humidity-sensitive indicator element consists of a substrate and a humidity-sensitive color-changing film, with the film located on the substrate surface. Ambient humidity is qualitatively or semi-quantitatively determined by observing the color change of the humidity-sensitive indicator element.

[0020] Preferably, the humidity sensor or humidity-sensitive indicator element is used for environmental humidity monitoring, food packaging preservation indication, and medical disinfection process indication.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The vanadium oxide humidity-sensitive color-changing film of the present invention is formed by stacking amorphous VxOy films. The humidity-sensitive color-changing film of the present invention exhibits obvious color changes, such as red, green, yellow, and purple, which are visible to the naked eye, eliminating the need for complex electrical reading devices and facilitating intuitive indication of humidity status. The vanadium oxide humidity-sensitive color-changing film of the present invention has an extremely fast response. Due to the abundant surface states and diffusion channels of the amorphous film, the adsorption or desorption process of water molecules is rapid, and the color-changing response time can reach the millisecond level, less than 30 ms, far exceeding most traditional humidity-sensitive materials. The humidity-sensitive color-changing film of the present invention exhibits stable performance and good stability in dry environments.

[0022] The humidity-sensitive color-changing film of this invention has a layered crystal structure. The ratio of x to y in the VxOy film is 1:1.8~2.4. The VxOy film is a two-dimensional sheet structure of metal-oxygen octahedral chains with periodic repeating units, formed by vanadium and oxygen atoms bonded by covalent or ionic bonds, with a thickness of one atom. The layers of the VxOy film are bonded together by van der Waals forces, hydrogen bonds, or physical adsorption, allowing water molecules to reversibly insert and escape. When the ambient humidity increases, water molecules insert into the interlayer gaps of the film; when the ambient humidity decreases, water molecules escape from the interlayer gaps. The insertion or escape of water molecules causes a change in the optical path of light refracted on the surface of the humidity-sensitive color-changing film, resulting in a change in the color of the light, thus exhibiting a humidity-sensitive function. The surface color of the humidity-sensitive color-changing film changes reversibly with humidity within 0.1s. The thickness of the humidity-sensitive color-changing film is 250nm~500nm. The diameter of a water molecule is 0.3nm. When water molecules insert into the VxOy thin film layers of a humidity-sensitive color-changing film, the interlayer spacing increases. As humidity increases and more water molecules are inserted, the interlayer spacing can reversibly expand to 0.6 nm to 1.2 nm. This nanoscale, variable gap is the physical basis for the change in light interference conditions, which leads to color changes.

[0023] 2. The method for preparing the vanadium oxide moisture-sensitive color-changing thin film of the present invention comprises the following steps: using a vanadium metal target as the target material and a silicon wafer as the substrate, in an atmosphere of argon and oxygen, amorphous VxOy is deposited on the substrate by reactive magnetron sputtering at a power of 200W~400W, a working pressure of 0.5Pa~2.0Pa, and a substrate temperature of 25℃~200℃. After the deposition is completed, the thin film is cooled in a vacuum or inert atmosphere without high-temperature crystallization annealing treatment to obtain the moisture-sensitive color-changing thin film.

[0024] Heating a vanadium oxide film in a humidity-sensitive color-changing film will cause further crystallization, altering the multilayer structure and resulting in the loss of its color-changing properties. Therefore, the sputtering parameters of the humidity-sensitive color-changing film are crucial; substrate heating is prohibited, and high-temperature heat treatment annealing should be avoided after film deposition. The oxygen content of the humidity-sensitive color-changing film should be above 5%. Increasing the oxygen content raises the valence state of the vanadium oxide, further increasing the layered structure and thus enhancing the color-changing ability of the film. More oxygen leads to more complete vanadium oxide formation from the metallic vanadium reaction, resulting in more pronounced color-changing properties due to water molecule insertion and extraction. Less oxygen results in more metallic vanadium, fewer multilayer structures, and poorer color-changing performance. However, the argon-oxygen ratio must be above 20:1; otherwise, excessive vanadium content in the film will render it colorless. The humidity-sensitive color-changing film is a multilayered vanadium oxide film, facilitating the entry and exit of water molecules, which is beneficial for the humidity-sensitive color-changing reaction.

[0025] 3. The method for preparing the vanadium oxide moisture-sensitive color-changing thin film of the present invention adopts mature magnetron sputtering technology, which forms a film in one step without the need for subsequent complex annealing. The process has good repeatability, is easy to integrate with microelectronic processes, and is simple, stable, and suitable for large-scale production. Attached Figure Description

[0026] Figure 1 This is a color change diagram of the vanadium oxide humidity-sensitive color-changing film prepared in Example 1 of the present invention. In the diagram, A represents the color change of the humidity-sensitive color-changing film during the first cooling. B represents the color change of the humidity-sensitive color-changing film during natural temperature recovery. C represents the color change of the humidity-sensitive color-changing film during the second cooling.

[0027] Figure 2 This is a color change diagram of the vanadium oxide humidity-sensitive color-changing film prepared in Example 2 of the present invention. In the diagram, A represents the color change of the humidity-sensitive color-changing film during cooling; B represents the color change of the humidity-sensitive color-changing film during natural temperature recovery; and C represents the color change of the humidity-sensitive color-changing film during heating.

[0028] Figure 3 This is a color change diagram of the vanadium oxide humidity-sensitive color-changing film prepared in Example 3 of the present invention. In the diagram, A represents the color change of the humidity-sensitive color-changing film during heating, and B represents the color change of the humidity-sensitive color-changing film during natural temperature recovery after heating.

[0029] Figure 4 These are scanning electron microscope (SEM) images of the vanadium oxide moisture-sensitive color-changing films prepared in Examples 2 and 3 of the present invention. In the images, A represents Example 2, and B represents Example 3.

[0030] Figure 5 This is a schematic diagram of the XRD pattern of the vanadium oxide humidity-sensitive color-changing film prepared in Examples 5 and 6 of the present invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the following detailed description, in conjunction with preferred embodiments and accompanying drawings, provides a clear and complete account of the technical solutions of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1 A method for preparing a vanadium oxide moisture-sensitive color-changing thin film includes the following steps: A 1cm square silicon wafer was first ultrasonically cleaned with deionized water for 15 minutes, then ultrasonically cleaned with anhydrous ethanol for 10 minutes, and finally ultrasonically cleaned with acetone for 20 minutes to remove surface impurities. The sample was then dried with a hair dryer and placed into the target. The target material was a square metal sheet with a side length of 2 inches and a vanadium content of 99.99%.

[0034] Sand the removable parts of the vacuum chamber with sandpaper, wipe the chamber and the removable parts with anhydrous ethanol, dry them with a blower, and then install them.

[0035] Turn on the mechanical pump, preheat it, then open the valve to begin vacuuming until the vacuum level reaches 5.5 × 10⁻⁶. -4Argon gas was introduced at 120 sccm, and after purging for 10 minutes, the RF power supply was turned on for ignition. After ignition, oxygen was introduced at 12.4 sccm. Once the oxygen level was adjusted, the power was adjusted as needed, and then pre-sputtering was started for 5 minutes to prevent impurities introduced into the chamber during the cleaning step from affecting the film. During pre-sputtering, the spinneret was turned on and set to a speed of 30 r / min to ensure the uniformity of the film deposition and avoid errors caused by differences in substrate placement.

[0036] After pre-sputtering, sputtering was performed at 300W, a working gas pressure of 1.5Pa, and a substrate temperature of 25℃ for 30 min. After sputtering, the film was cooled in the furnace for 24 h to obtain a moisture-sensitive color-changing film. The ratio of V to O in the moisture-sensitive color-changing film was 1:2.2, and the vanadium oxide content was VO. 2.2 The thickness of the humidity-sensitive color-changing film is 400 nm, and the surface color changes reversibly with humidity within 0.04 s.

[0037] Example 2 A method for preparing a vanadium oxide moisture-sensitive color-changing thin film includes the following steps: A 1cm square silicon wafer was first ultrasonically cleaned with deionized water for 15 minutes, then ultrasonically cleaned with anhydrous ethanol for 10 minutes, and finally ultrasonically cleaned with acetone for 20 minutes to remove surface impurities. The sample was then dried with a hair dryer and placed into the target. The target material was a square metal sheet with a side length of 2 inches and a vanadium content of 99.99%.

[0038] Sand the removable parts of the vacuum chamber with sandpaper, wipe the chamber and the removable parts with anhydrous ethanol, dry them with a blower, and then install them.

[0039] Turn on the mechanical pump, preheat it, then open the valve to begin vacuuming until the vacuum level reaches 5.5 × 10⁻⁶. -4 At 120 sccm, argon gas was introduced and purged for 10 minutes before ignition. After ignition, oxygen was introduced at 8.4 sccm. Once the oxygen level was adjusted, the power was adjusted to the required level, followed by 5 minutes of pre-sputtering to prevent impurities introduced into the cavity during the cleaning process from affecting the film. During pre-sputtering, the spindle was activated at a speed of 30 r / min to ensure uniform film deposition and avoid errors caused by differences in substrate placement.

[0040] After pre-sputtering, sputtering was performed at 200W, a working gas pressure of 0.5Pa, and a substrate temperature of 25℃ for 30 minutes. After sputtering, the film was cooled in the furnace for 24 hours to obtain a moisture-sensitive color-changing film. The ratio of V to O in the moisture-sensitive color-changing film was 1:1.8, and the vanadium oxide content was VO. 1.8 The thickness of the humidity-sensitive color-changing film is 250 nm, and the surface color changes reversibly with humidity within 0.1 s.

[0041] Example 3 A method for preparing a vanadium oxide moisture-sensitive color-changing thin film includes the following steps: A 1cm square silicon wafer was first ultrasonically cleaned with deionized water for 15 minutes, then ultrasonically cleaned with anhydrous ethanol for 10 minutes, and finally ultrasonically cleaned with acetone for 20 minutes to remove surface impurities. The sample was then dried with a hair dryer and placed into the target. The target material was a square metal sheet with a side length of 2 inches and a vanadium content of 99.99%.

[0042] Sand the removable parts of the vacuum chamber with sandpaper, wipe the chamber and the removable parts with anhydrous ethanol, dry them with a blower, and then install them.

[0043] Turn on the mechanical pump, preheat it, then open the valve to begin vacuuming until the vacuum level reaches 5.5 × 10⁻⁶. -4 Argon gas was introduced at 120 sccm, and after purging for 10 minutes, the RF power supply was turned on for ignition. After ignition, oxygen was introduced at 24.4 sccm. After adjusting the oxygen level, the required power was adjusted, and then pre-sputtering was started for 5 minutes to prevent impurities introduced into the chamber during the cleaning step from affecting the film. During pre-sputtering, the spin was turned on and the spin speed was set to 30 r / min to ensure the uniformity of the film deposition and avoid errors caused by differences in substrate placement.

[0044] After pre-sputtering, sputtering was performed at 400W, a working gas pressure of 2Pa, and a substrate temperature of 25℃ for 30 minutes. After sputtering, the film was cooled in the furnace for 24 hours to obtain a moisture-sensitive color-changing film. The ratio of V to O in the moisture-sensitive color-changing film was 1:2.2, and the vanadium oxide content was VO. 2.2 The thickness of the moisture-sensitive color-changing film is 500 nm, and the surface color changes reversibly with humidity within 0.03 s.

[0045] Example 4 A method for preparing a vanadium oxide moisture-sensitive color-changing thin film includes the following steps: The argon-oxygen partial pressure ratio in Example 1 was adjusted to 100:100.5, while all other conditions remained the same as in Example 1, resulting in a humidity-sensitive color-changing film. The ratio of V to O elements in the humidity-sensitive color-changing film was 1:2.4, and the vanadium oxide was VO₂O₃. 2.4 The thickness of the humidity-sensitive color-changing film is 400 nm, and the surface color changes reversibly with humidity within 0.06 s.

[0046] Example 5 A method for preparing a vanadium oxide moisture-sensitive color-changing thin film includes the following steps: The argon-oxygen partial pressure ratio in Example 1 was adjusted to 120:16, while all other conditions remained the same as in Example 1, resulting in a humidity-sensitive color-changing film. The ratio of V to O elements in the humidity-sensitive color-changing film was 1:2.2, and the vanadium oxide was V₂O₃. 2.2 The thickness of the humidity-sensitive color-changing film is 400 nm, and the surface color changes reversibly with humidity within 0.03 s.

[0047] Example 6 A method for preparing a vanadium oxide moisture-sensitive color-changing thin film includes the following steps: The argon-oxygen partial pressure ratio in Example 1 was adjusted to 121:31, while all other conditions remained the same as in Example 1, resulting in a humidity-sensitive color-changing film. The ratio of V to O elements in the humidity-sensitive color-changing film was 1:2.3, and the vanadium oxide was V₂O₃. 2.3 The thickness of the humidity-sensitive color-changing film is 400 nm, and the surface color changes reversibly with humidity within 0.04 s.

[0048] Comparative Example 1 A method for preparing a vanadium oxide moisture-sensitive color-changing thin film includes the following steps: The cooling time of 24 hours in Example 2 was adjusted to an annealing temperature of 500°C and an annealing time of 180 minutes to prepare a vanadium oxide moisture-sensitive color-changing film. The obtained vanadium oxide moisture-sensitive color-changing film exhibited poor reversible color-changing properties; moisture easily damaged the film after cooling and color change, and the film adhesion weakened. After storing the vanadium oxide moisture-sensitive color-changing film in a vacuum drying oven for 16 hours, its color changed to red, a mixture of red and yellow, or a mixture of red and green. At this time, the temperature of the vanadium oxide moisture-sensitive color-changing film was 24°C. After annealing, the vanadium oxide moisture-sensitive color-changing film turned gray and lost its color-changing properties.

[0049] To illustrate the beneficial effects of the present invention, the following experiments were also conducted: 1. Analysis of the color-changing properties of moisture-sensitive color-changing films The humidity-sensitive color-changing film is a multilayered film of mixed oxides with multiple valence states. Its layered structure allows water molecules to reversibly intercalate and deintercalate. The intercalation and deintercalation of water molecules directly change the optical thickness and dielectric environment of the film. The change in the optical thickness of the film causes a change in the spectral color of the reflected light, thereby enabling humidity visualization. Therefore, the vanadium oxide humidity-sensitive color-changing films prepared in Examples 1 to 6 of this invention have sensitive optical response characteristics to ambient humidity. The preparation process conditions of Examples 1 to 6 are shown in Table 1.

[0050] Table 1. Preparation processes of Examples 1-6 Existing common knowledge, such as P. HMA. Thermal Physics of the Atmosphere [M]. John Wiley & Sons, Ltd.: 2010-04-09: DOI: 10.1002 / 9780470710364, indicates that under the condition of constant moisture content in the air, the higher the temperature, the lower the relative humidity. Based on this theory, the adsorption / desorption kinetics of water molecules in the thin film were accelerated by changing the ambient temperature. Humidity response experiments under varying temperature conditions were conducted on the thin films of Examples 1 to 6, and color changes were recorded. The specific experimental procedures are as follows.

[0051] During the experiment, the indoor temperature was 25℃ and the humidity was 70%. In an open environment, atmospheric pressure and absolute humidity are stable values, meaning the partial pressure of water vapor remains constant. When the temperature changes, the relative humidity is equal to the percentage of the partial pressure of water vapor to the saturated vapor pressure at the corresponding temperature. The saturated vapor pressure is calculated using the Magnus-Tetens formula, as shown in formula (1). Therefore, the relationship between relative humidity and temperature is shown in Table 2.

[0052] Formula (1): .

[0053] In the formula, P is the saturated vapor pressure. T is the temperature, in °C.

[0054] Table 2. Relative humidity and temperature of the experiment The moisture-sensitive color-changing film prepared in Example 1 was green immediately after sputtering and when it was removed from the chamber. The color change of the moisture-sensitive color-changing film prepared in Example 1 is as follows: Figure 1 As shown in the figure. The results show that after the vanadium oxide moisture-sensitive color-changing film prepared in Example 1 was placed in a vacuum drying oven for 16 hours, the color changed to a mixture of red and yellow.

[0055] When the lower edge of the moisture-sensitive color-changing film prepared in Example 1 contacts an ice pack, the color of the moisture-sensitive color-changing film prepared in Example 1 changes rapidly from a vertical viewing angle. The upper edge of the vanadium oxide moisture-sensitive color-changing film prepared in Example 1 begins to turn red away from the edge of the ice pack, and the red color deepens while transitioning downwards. Simultaneously, the upper edge turns green and continues to transition downwards, then becomes light red again and continues to transition downwards, creating a phenomenon where red and green colors alternate continuously from the upper edge to the lower edge. This change process, from the placement of the ice pack to the cessation of the color change, takes 1.5 seconds. The color change is as follows: Figure 1 As shown in A in the diagram.

[0056] The moisture-sensitive color-changing film prepared in Example 1, after being removed from the ice pack, rapidly warmed up and the relative humidity decreased. The periphery of the film first changed color, from light green to dark green. Then, the center changed color, forming a light green from the bottom edge and transitioning upwards, while simultaneously forming a light red from the bottom edge and transitioning upwards. Next, the bottom edge formed a dark green and transitioned upwards, finally forming a dark red from the bottom edge and gradually transitioning upwards until it filled the center of the moisture-sensitive color-changing film. Ultimately, the moisture-sensitive color-changing film presented a dark green border and a dark red center, and the color no longer changed. This color change process took 5 seconds. Figure 1 As shown in B in the diagram.

[0057] After the vanadium oxide humidity-sensitive film prepared in Example 1 was restored to room temperature, it was cooled again to increase the relative humidity. At this time, the color of the humidity-sensitive film from a vertical viewing angle was green around the edges and light red in the center. Then, the humidity-sensitive film was held with tweezers, and the lower edge of the film was placed in contact with an ice pack. It was obvious that the color of the humidity-sensitive film from a vertical viewing angle changed rapidly: the middle part of the film turned dark red, while the upper edge turned green and continuously transitioned to the lower edge, forming a phenomenon of red and green colors constantly alternating from the upper edge to the lower edge, and the colors gradually faded until finally yellow appeared. The time from the placement of the ice pack to the cessation of the color change was 2 seconds. Figure 1 As shown in C.

[0058] The humidity-sensitive color-changing film prepared in Example 2 was dark green when it was first removed from the chamber after sputtering. After heating and reducing relative humidity, the color turned light red. Then, the temperature was lowered and the relative humidity increased. The film was then placed in contact with an aluminum nitride sheet, which was placed on an ice pack. It was observed that the color of the film changed to red due to the increased relative humidity. A corner furthest from the ice pack began to turn green, spreading towards the center of the film until a large area was green with a light red edge. The color change was observed from the initial point... The color continues to turn red and diffuses towards the center of the moisture-sensitive film until a large area of ​​the film turns red. A green border forms within the previously red border, and the color continues to turn green from the previous area, repeating this process. A red border forms within the previous two borders, and the color turns yellow from the previous area, repeating this process to form a red border. Subsequently, the green and yellow colors alternate, but each alternation lasts longer and the color change range becomes smaller, until the moisture-sensitive film returns to room temperature. The entire process takes 3 seconds. Figure 2 As shown in A in the diagram.

[0059] As the relative humidity decreased after the moisture-sensitive color-changing film prepared in Example 2 was removed from the ice pack, its color gradually changed in the opposite direction of the cooling process: alternating between green and yellow, then between green and red, until the film turned red. The entire process took 6 seconds. Figure 2 As shown in B in the diagram. Then, a hot air blower is used to accelerate the decrease in relative humidity of the moisture-sensitive color-changing film, causing the film to change color again: alternating between red and green. The entire change process takes 0.5 seconds, as shown in the diagram. Figure 2 As shown in Figure C. After the cooling experiment of the moisture-sensitive color-changing film prepared in Example 2, the film was left to stand, and its color eventually returned to green.

[0060] The moisture-sensitive color-changing film prepared in Example 3 was red when it first came out of the warehouse, but its color changed sequentially from red to purple, blue, and green within 5 minutes of exposure to air. Heating the moisture-sensitive color-changing film prepared in Example 3 with a hair dryer to reduce relative humidity resulted in the following color changes: Figure 3 As shown in Figure A, the change time is 2 seconds. After the humidity-sensitive color-changing film turns red, the color no longer changes. The humidity-sensitive color-changing film prepared in Example 3 undergoes natural cooling, and the color change is as follows... Figure 3 As shown in B, the change time is 10s.

[0061] In summary, the vanadium oxide humidity-sensitive color-changing film of the present invention possesses the ability to change color with varying humidity, and this color change is repeatable and reversible. The film prepared in this invention undergoes reversible color changes with both increases and decreases in relative humidity, and the color change is more uniform when the relative humidity decreases. The higher the relative humidity, the more sensitive the color-changing performance of the film and the richer the range of colors.

[0062] 2. Morphological analysis of the color-changing film The argon-oxygen partial pressure ratios in Examples 2 and 3 of this invention were 120:8.4 and 120:24.4, respectively. The humidity-sensitive color-changing films of vanadium oxide prepared in Examples 2 and 3 were examined using a field emission scanning electron microscope, and the results are as follows: Figure 4 As shown in the figure, the surface morphology of the humidity-sensitive color-changing film does not change significantly with different oxygen-argon partial pressure ratios. Magnification to 200,000 times reveals that the film particles have a diameter of 20 nm, and the film is relatively uniform and smooth. Furthermore, the deposition amount of vanadium oxide particles increases slightly with increasing oxygen-argon partial pressure ratio. Therefore, changes in oxygen partial pressure affect the crystal structure of the film, ultimately influencing its phase transition characteristics.

[0063] 3. XRD analysis of the color-changing film The argon-oxygen partial pressure ratios of the vanadium oxide humidity-sensitive films prepared in Examples 5 and 6 were 120:16 and 121:31, respectively. The vanadium oxide humidity-sensitive film prepared in Example 6 was annealed at 500°C for 1 hour in a vacuum atmosphere. X-ray diffraction tests were then performed on both humidity-sensitive films, and the results are as follows. Figure 5 As shown in the figure, a comparison reveals that the unannealed color-changing film exhibits no diffraction peaks other than the silicon substrate peak, indicating that it is a typical amorphous film. In contrast, the annealed vanadium oxide film shows strong diffraction peaks on the (011) crystal plane, indicating that vanadium dioxide crystals were formed after annealing. Furthermore, the resistance-temperature experiment demonstrates a phase transition and almost no color-changing properties. Therefore, it can be concluded that the vanadium oxide in the color-changing film primarily exists in an amorphous state.

[0064] By controlling the composition ratio of different oxides in the vanadium oxide thin film, an amorphous functional thin film with a fast response time and obvious color change phenomenon to water molecules in humidity or ambient atmosphere was prepared. Experimental results show that the color of the vanadium oxide thin film exhibits periodic changes during heating or cooling, and the process is reversible, exhibiting characteristics of a thermosensitive material. The film color also shows regular and reversible changes with changes in vacuum level. The fastest color change time is less than 0.03 s.

[0065] Conclusion The humidity-sensitive color-changing film of this invention changes color when humidity changes. The adsorption and embedding of water molecules in the environment on the surface of the vanadium oxide film increases the film's optical thickness, leading to a change in the color of the reflectance spectrum and exhibiting a regular color transition, thus achieving a visual response to humidity—making it a thermochromic film. On the other hand, temperature and vacuum levels can affect the bonding between water and the humidity-sensitive color-changing film, thereby influencing its color.

[0066] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the inventive concept of this invention, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0067] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention is also intended to include such modifications and variations.

Claims

1. A vanadium oxide moisture-sensitive color-changing thin film, characterized in that, The humidity-sensitive color-changing film is an amorphous vanadium oxide VxOy film, which is prepared by reactive magnetron sputtering. The ratio of V to O elements in the amorphous vanadium oxide VxOy thin film is 1:1.8~2.4; The surface color of the humidity-sensitive color-changing film changes reversibly with humidity within 0.1s; The thickness of the humidity-sensitive color-changing film is 250nm~500nm.

2. The vanadium oxide moisture-sensitive color-changing film according to claim 1, characterized in that, The surface color of the humidity-sensitive color-changing film changes reversibly with humidity within 0.03s.

3. The method for preparing a vanadium oxide moisture-sensitive color-changing thin film according to claim 1, characterized in that, Includes the following steps: Using metallic vanadium as the target material, amorphous vanadium oxide VxOy is deposited on the substrate by reactive magnetron sputtering at 200W~400W and working pressure of 0.5Pa~2.0Pa in an atmosphere of argon and oxygen, without heating the substrate; after the deposition is completed, it is cooled to obtain a humidity-sensitive color-changing film. The substrate is silicon, ceramic, glass, quartz, mica, or sapphire.

4. The method for preparing a vanadium oxide moisture-sensitive color-changing thin film according to claim 3, characterized in that, The flow rate ratio of argon to oxygen is 100~150:8~30.

5. The method for preparing a vanadium oxide moisture-sensitive color-changing thin film according to claim 4, characterized in that, The flow ratio of argon to oxygen is 120:12.4, 120:8.4, 120:24.4, 100:100.5, 120:16, or 121:

31.

6. The method for preparing a vanadium oxide moisture-sensitive color-changing thin film according to claim 3, characterized in that, The reactive magnetron sputtering method has a sputtering power of 300W and a working gas pressure of 1.5Pa; the substrate is not heated.

7. The application of the vanadium oxide humidity-sensitive color-changing thin film according to claim 1 in the preparation of humidity sensors or humidity-sensitive indicator elements.

8. The application of the vanadium oxide humidity-sensitive color-changing thin film according to claim 7 in the preparation of humidity sensors or humidity-sensitive indicator elements, characterized in that, The humidity sensor or humidity-sensitive indicator element is used for environmental humidity monitoring, food packaging preservation indication, and medical disinfection process indication.

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