Amorphous substrate VO2 single crystal thin film and preparation method thereof

Abstract

The present invention discloses a VO2 single crystal thin film grown on an amorphous substrate. The specific preparation steps include: 1) using vanadium oxide as a target, magnetron sputtering is performed in an inert atmosphere to form a disordered vanadium oxide thin film on the surface of the amorphous substrate; 2) the resulting disordered vanadium oxide film is placed in a reaction vessel, oxygen is introduced, and the pressure is adjusted, followed by heating for annealing and oxidation to obtain the VO2 single crystal thin film. This invention proposes for the first time the construction of high-quality VO2 single crystal thin films on amorphous substrates such as glass. The VO2 single crystal thin film exhibits a resistance change ratio of more than three orders of magnitude before and after phase transition, achieving both good electrical and optical properties. The preparation method is relatively simple and easy to operate, providing a new approach for the preparation of high-quality single crystal VO2 thin films.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film materials and preparation processes thereof, and in particular relates to a VO2 single crystal thin film based on an amorphous substrate and a preparation method thereof. Background Art

[0002] Window glass typically has high thermal conductivity, making it a weak link in building energy efficiency. Nearly half of a building's energy consumption is lost through glass. Smart window glass can reduce solar transmittance at high temperatures, lowering indoor temperatures, while increasing solar transmittance at room temperature, raising indoor temperatures, making it suitable for use in high-rise buildings. VO2 can transition from an insulating state to a metallic state at a critical temperature. Under ideal conditions, VO2 thin films exhibit excellent thermochromic properties, solar modulation efficiency, and electrical performance, making them suitable for applications in smart windows and other fields.

[0003] VO2 thin films can be synthesized through methods such as magnetron sputtering, chemical vapor deposition, hydrothermal deposition, and sol-gel deposition. During the actual preparation process, VO2 thin films are susceptible to oxidation and reduction, which can lead to defects and impurities in the film, affecting its physical and chemical properties. Conventional VO2 thin films have average crystallization quality and lattice matching, poor directionality and uniformity, and thus poor film performance. Single-crystal VO2 thin films exhibit superior crystallization quality, a complete lattice structure, and few defects and impurities during crystal growth, resulting in excellent crystallization quality and physical and chemical properties. By controlling the crystal growth direction and morphology, single-crystal VO2 thin films can achieve excellent directionality and uniformity, improving the performance and stability of VO2 thin films during application. These thin films also exhibit low thermal hysteresis loop width, good visible light transmittance, and solar modulation efficiency.

[0004] Vanadium has multiple valence states, making it difficult to fully control them. Existing methods for preparing single-crystal VO2 thin films primarily use sapphire as the substrate. Growing single-crystal VO2 thin films directly on quartz glass substrates presents the following challenges: 1) Surface defects such as grains and cracks are easily formed on the quartz glass substrate, which reduces the quality and performance of the VO2 film. 2) The lattice mismatch between quartz glass and VO2 leads to lattice mismatch and stress accumulation during film growth, resulting in unstable film morphology and structure. 3) Preparation of single-crystal VO2 thin films requires high-temperature annealing to grow the crystal on the quartz glass substrate. The different thermal expansion coefficients of the quartz glass substrate and VO2 easily induce stress and cracks between the crystal and the glass substrate during temperature fluctuations. 4) VO2 itself has weak crystallinity and small grain size, making it difficult to form large-area single-crystal VO2 thin films on quartz glass substrates. Therefore, growing single-crystal VO2 thin films on glass substrates is difficult. Currently, single-crystal VO2 thin films are primarily grown on sapphire substrates, which results in high production costs. Summary of the Invention

[0005] The purpose of the present invention is to address the problems and shortcomings of the above-mentioned prior art and provide a method for preparing a single-crystal VO2 thin film based on an amorphous substrate, in which a single-crystal structure VO2 thin film is grown on an amorphous substrate; and the preparation cost involved is low, the process flow is simple, the film quality and performance are excellent, and when doped with other elements, a single-crystal structure VO2 thin film with better performance can still be prepared.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] The invention discloses a VO2 single crystal thin film on an amorphous substrate, which is a VO2 single crystal thin film grown on an amorphous substrate.

[0008] In the above solution, the amorphous substrate can be a glass substrate, an amorphous titanium dioxide substrate, etc.

[0009] In the above scheme, the area of ​​the VO2 single crystal film can reach 100cm 2 above.

[0010] In the above solution, the resistance change ratio of the VO2 single crystal thin film before and after the phase transition can reach more than 1000 (more than three orders of magnitude).

[0011] The above-mentioned method for preparing a VO2 single crystal thin film on an amorphous substrate comprises the following steps:

[0012] 1) Using vanadium oxide as a target, magnetron sputtering is performed in an inert atmosphere to form a disordered vanadium oxide film on the surface of an amorphous substrate;

[0013] 2) placing the obtained disordered vanadium oxide film into a reaction vessel (after evacuation), introducing oxygen to adjust the pressure, and then heating to perform annealing and oxidation to obtain the VO2 single crystal thin film.

[0014] In the above solution, the vanadium oxide is an oxide of the vanadium series such as vanadium trioxide, vanadium dioxide or vanadium pentoxide.

[0015] In the above scheme, the magnetron sputtering step adopts an inert gas flow rate of 10-20 sccm, a sputtering working pressure of 2-10 mtorr, a vanadium oxide target sputtering power of 30-100 W, a substrate temperature of room temperature, and a sputtering time of 100-140 min.

[0016] Furthermore, pre-sputtering is performed before the magnetron sputtering (process parameters are the same as the magnetron sputtering step), and the sputtering time is 5-15 minutes.

[0017] In the above solution, the inert atmosphere can be nitrogen or argon.

[0018] In the above scheme, the flow rate of oxygen in step 2) is 2-10 sccm, and the gas pressure is 50-250 mTorr.

[0019] In the above scheme, the temperature used in the annealing and oxidation step is 480-550° C. and the time is 30-60 minutes.

[0020] Furthermore, the heating rate used in the annealing and oxidation step is 20-50° C. / min.

[0021] Furthermore, the vanadium oxide target material also contains doping elements, specifically one or more of W, V, etc., with a doping ratio of 0-5at%.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) This invention proposes for the first time the construction of high-quality VO2 single-crystal thin films on amorphous substrates such as glass. The resistance change ratio of the VO2 single-crystal thin films before and after the phase transition reaches more than three orders of magnitude, achieving both good electrical and optical properties, and providing a new approach for the preparation of high-quality single-crystal VO2 thin films.

[0024] 2) The preparation method of the present invention is simple to operate, and the subsequent annealing process is simple. No other gases other than oxygen need to be introduced, which is convenient for large-scale production. The substrate material used can be an amorphous substrate such as ordinary quartz glass, and other substrates such as sapphire and epitaxial thin films are not required, which is suitable for popularization and application.

[0025] 3) When doped with other elements, single-crystal VO2-based thin films can still be prepared, which have a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the deposition process of a VO2 single crystal thin film according to one embodiment of the present invention;

[0027] Figure 2 TEM lattice fringe image of the VO2 single crystal thin film obtained in Example 1;

[0028] Figure 3 is a TEM lattice fringe image of the VO2 single crystal thin film obtained in Example 2;

[0029] Figure 4 is a TEM lattice fringe image of the VO2 single crystal thin film obtained in Example 3;

[0030] Figure 5 TEM electron diffraction pattern of the VO2 single crystal thin film obtained in Example 1;

[0031] Figure 6 TEM electron diffraction pattern of the VO2 single crystal thin film obtained in Example 2;

[0032] Figure 7TEM electron diffraction pattern of the VO2 single crystal thin film obtained in Example 3;

[0033] Figure 8 Graphs showing resistance changes before and after complete phase transition of the single-crystal vanadium dioxide thin film obtained in Example 1, the tungsten-doped single-crystal vanadium dioxide thin film obtained in Example 4, the niobium-doped single-crystal vanadium dioxide thin film obtained in Example 5, and the polycrystalline vanadium dioxide thin film obtained in Comparative Example 4;

[0034] Figure 9 Graphs showing the transmittance changes before and after complete phase transition of the single crystal vanadium dioxide thin film obtained in Example 1, the tungsten-doped single crystal vanadium dioxide thin film obtained in Example 4, and the niobium-doped single crystal vanadium dioxide thin film obtained in Example 5;

[0035] Figure 10 This is a graph showing the resistance change of the film obtained in Comparative Example 1 before and after the complete phase change;

[0036] Figure 11 This is a graph showing the resistance change of the film obtained in Comparative Example 2 before and after the complete phase change;

[0037] Figure 12 This is a graph showing the resistance change of the film obtained in Comparative Example 2 before and after the complete phase change. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0039] In the following examples, the vanadium dioxide target material or composite target material used is provided by Zhongnuo New Materials.

[0040] In the following embodiments, the method for preparing the vanadium dioxide single crystal thin film comprises the following steps:

[0041] S1: Sputtering disordered vanadium dioxide thin film on the surface of quartz glass substrate using magnetron sputtering;

[0042] S2: placing the disordered vanadium oxide film in a tubular annealing furnace, introducing 2-10 sccm of oxygen, and adjusting the internal pressure of the tubular furnace to 200 mTorr;

[0043] S3: Control the temperature of the tube furnace and perform annealing to obtain a vanadium dioxide film with a single crystal structure.

[0044] In the present invention, a single-crystal vanadium dioxide film is obtained by annealing a disordered oxide film. Therefore, the oxygen flow rate introduced during the annealing process is relatively small, and the oxygen flow rate accuracy requirement is relatively high. The specific oxygen introduction amount is mainly controlled by the internal pressure of the tube furnace displayed by an electronic vacuum gauge.

[0045] The specific experimental process is as follows: a cleaned quartz glass sheet is placed on the sample stage of a magnetron sputtering apparatus, argon gas is introduced, and the vanadium oxide target is pre-sputtered and sputtered to obtain a disordered vanadium oxide film. The disordered vanadium oxide film is annealed to obtain a single crystal vanadium dioxide film.

[0046] Furthermore, the mass purity of the argon gas is 99.99%, and the mass purity of the vanadium oxide target is 99.9%.

[0047] Furthermore, during the pre-sputtering and sputtering process, the vacuum degree of the magnetron sputtering instrument was 5.0×10 -6 Torr, the flow rate of the high-purity argon gas is 15 sccm, and the sputtering working pressure is 2.8 mTorr.

[0048] Furthermore, during the magnetron sputtering process, the substrate temperature is room temperature.

[0049] Furthermore, during the annealing process, the temperature was maintained at 500° C. for 30 minutes, and the flow rate of oxygen introduced was such that the pressure inside the tube furnace chamber was maintained at 120 mTorr.

[0050] Example 1

[0051] A VO2 single crystal thin film on an amorphous substrate, the preparation method of which comprises the following steps:

[0052] 1) First, clean the quartz glass surface with a surfactant. After rinsing, ultrasonically clean it in deionized water for 30 minutes. Then, ultrasonically clean it in an ethanol solution for 30 minutes to clean both sides. Finally, place the cleaned quartz glass substrate in anhydrous ethanol and seal it to prevent dust from entering. Dry the ethanol before use.

[0053] 2) The quartz glass substrate obtained by the treatment in step 1) was fixed on the sample stage base of the magnetron sputtering instrument, and a vanadium dioxide target was used as the target material, and the vacuum was evacuated to 5.0×10 -6 Torr, the argon flow rate was controlled at 15 sccm and the sputtering working pressure was 2.8 mTorr, and argon with a mass purity of 99.99% was used as the working gas to sputter the target material; wherein, the target material sputtering power was 40 W, and the pre-sputtering time was 5 minutes; then, the back plate under the sample stage was opened and sputtering was carried out at a sputtering power of 50 W. After sputtering for 120 minutes, a disordered vanadium oxide film was obtained;

[0054] 3) placing the disordered vanadium oxide film in a tubular annealing furnace, using a mechanical pump to pump the internal air pressure of the tubular furnace to below 10 mTorr, introducing oxygen to stabilize the internal pressure of the tubular furnace to 200 mTorr, then heating the film to 500°C at a rate of 50°C / min, keeping the temperature for 30 minutes, and cooling the film to below 30°C with the furnace to obtain the glass-based VO2 single crystal film with an area of ​​2.5×2.5 cm.

[0055] Example 2

[0056] A VO2 single crystal thin film on an amorphous substrate, the preparation method of which comprises the following steps:

[0057] 1) First, clean the quartz glass surface with a surfactant. After rinsing, ultrasonically clean it in deionized water for 30 minutes. Then, ultrasonically clean it in an ethanol solution for 30 minutes to clean both sides. Finally, place the cleaned quartz glass substrate in anhydrous ethanol and seal it to prevent dust from entering. Dry the ethanol before use.

[0058] 2) The quartz glass substrate obtained by the treatment in step 1) was fixed on the sample stage base of the magnetron sputtering instrument, and a vanadium dioxide target was used as the target material, and the vacuum was evacuated to 5.0×10 -6 Torr, the argon flow rate was controlled at 15 sccm and the sputtering working pressure was 2.8 mTorr, and argon with a mass purity of 99.99% was used as the working gas to sputter the target material; wherein, the target material sputtering power was 40 W, and the pre-sputtering time was 5 minutes; then, the back plate under the sample stage was opened and sputtering was carried out at a sputtering power of 40 W. After sputtering for 134 minutes, a disordered vanadium oxide film was obtained;

[0059] 3) placing the disordered vanadium oxide film in a tubular annealing furnace, using a mechanical pump to pump the internal air pressure of the tubular furnace to below 10 mTorr, introducing oxygen to stabilize the internal pressure of the tubular furnace to 150 mTorr, then heating the furnace to 520°C at a rate of 50°C / min, keeping the temperature for 40 minutes, and cooling the furnace to below 30°C to obtain the glass-based VO2 single crystal film with an area of ​​2.5×2.5 cm.

[0060] Example 3

[0061] A VO2 single crystal thin film on an amorphous substrate, the preparation method of which comprises the following steps:

[0062] 1) First, clean the quartz glass surface with a surfactant. After rinsing, ultrasonically clean it in deionized water for 30 minutes. Then, ultrasonically clean it in an ethanol solution for 30 minutes to clean both sides. Finally, place the cleaned quartz glass substrate in anhydrous ethanol and seal it to prevent dust from entering. Dry the ethanol before use.

[0063] 2) The quartz glass substrate obtained by the treatment in step 1) was fixed on the sample stage base of the magnetron sputtering instrument, and a vanadium dioxide target was used as the target material, and the vacuum was evacuated to 5.0×10 -6 Torr, the argon flow rate was controlled to be 15 sccm and the sputtering working pressure was 2.8 mTorr, and the target material was sputtered using argon with a mass purity of 99.99% as the working gas; the target material sputtering power was 40 W, and the pre-sputtering time was 5 minutes; then the back plate under the sample stage was opened for sputtering, and the sputtering power was 70 W. After sputtering for 100 minutes, a disordered vanadium oxide film was obtained;

[0064] 3) placing the disordered vanadium oxide film in a tubular annealing furnace, using a mechanical pump to pump the internal air pressure of the tubular furnace to below 10 mTorr, introducing oxygen to stabilize the internal pressure of the tubular furnace to 120 mTorr, then heating the furnace to 530°C at a rate of 50°C / min, keeping the temperature for 50 minutes, and cooling the furnace to below 30°C to obtain the glass-based VO2 single crystal film with an area of ​​2.5×2.5 cm.

[0065] Example 4

[0066] A tungsten-doped VO2 single crystal thin film on an amorphous substrate, the preparation method of which comprises the following steps:

[0067] 1) First, clean the quartz glass surface with a surfactant. After rinsing, ultrasonically clean it in deionized water for 30 minutes. Then, ultrasonically clean it in an ethanol solution for 30 minutes to clean both sides. Finally, place the cleaned quartz glass substrate in anhydrous ethanol and seal it to prevent dust from entering. Dry the ethanol before use.

[0068] 2) The quartz glass substrate obtained by the treatment in step 1) was fixed on the sample stage base of the magnetron sputtering apparatus, and a VO2-WO3 composite target material was used as the target material, wherein the atomic ratio of W element to V element was 1:99, and the vacuum degree was 5.0×10 - 6 The target was sputtered using 99.99% pure argon at a controlled argon flow rate of 15 sccm and a sputtering pressure of 2.8 mTorr. The target sputtering power was 40 W, and the pre-sputtering time was 300 seconds. The backplate below the sample stage was then opened for sputtering at a power of 50 W. After 7200 seconds of sputtering, a disordered tungsten-doped vanadium oxide film was obtained.

[0069] 3) placing the disordered tungsten-doped vanadium oxide film in a tubular annealing furnace, using a mechanical pump to pump the internal air pressure of the tubular furnace to below 10 mTorr, introducing oxygen to stabilize the internal pressure of the tubular furnace to 200 mTorr, then heating the film to 500°C at a rate of 50°C / min, keeping the temperature for 30 minutes, and cooling the film to below 30°C with the furnace; thus, the glass-based VO2 single crystal film having an area of ​​2.5 cm×2.5 cm was obtained.

[0070] Example 5

[0071] A large-area glass-based tungsten-doped VO2 single crystal thin film, the preparation method of which comprises the following steps:

[0072] 1) First, clean the quartz glass surface with a surfactant. After rinsing, ultrasonically clean it in deionized water for 30 minutes. Then, ultrasonically clean it in an ethanol solution for 30 minutes to clean both sides. Finally, place the cleaned quartz glass substrate in anhydrous ethanol and seal it to prevent dust from entering. Dry the ethanol before use.

[0073] 2) The quartz glass substrate obtained by the treatment in step 1) was fixed on the sample stage base of the magnetron sputtering apparatus, and a VO2-Nb2O composite target was used as the target material, wherein the atomic ratio of Nb element to V element was 2:98, and the vacuum degree was 5.0×10 - 6 The target was sputtered using 99.99% pure argon at a controlled argon flow rate of 15 sccm and a sputtering pressure of 2.8 mTorr. The target was sputtered at a power of 40 W and a pre-sputtering time of 300 seconds. The backplate below the sample stage was then opened for sputtering at a power of 50 W. After 7200 seconds of sputtering, a disordered niobium-doped vanadium oxide film was obtained.

[0074] 3) placing the disordered niobium-doped vanadium oxide film in a tubular annealing furnace, using a mechanical pump to pump the internal pressure of the tubular furnace to below 10 mTorr, introducing oxygen to stabilize the internal pressure of the tubular furnace to 200 mTorr, then raising the temperature to 500°C at 50°C / min, holding for 30 minutes, and cooling to below 30°C with the furnace; thus, the glass-based VO2 single crystal film having an area of ​​10×10 cm was obtained.

[0075] Comparative Example 1

[0076] A VO2 thin film, the preparation method of which is substantially the same as that of Example 1, except that the oxidation annealing temperature is 560°C, and the color of the obtained vanadium dioxide thin film is uneven (polycrystalline VO2 thin film).

[0077] Comparative Example 2

[0078] A VO2 thin film, the preparation method of which is substantially the same as that of Example 1, except that: when oxygen is introduced during oxidation annealing, the internal pressure of the tube furnace is 300 mtorr, and the obtained vanadium dioxide film is bluish in color (polycrystalline VO2 thin film).

[0079] Comparative Example 3

[0080] A VO2 thin film is prepared by a method substantially the same as that of Example 1, except that the oxygen is introduced for 20 minutes during oxidation annealing, and the color of the resulting vanadium dioxide film is close to blue (polycrystalline VO2 thin film).

[0081] Comparative Example 4

[0082] A VO2 thin film (polycrystalline VO2 thin film) is prepared by a method substantially the same as that in Example 1, except that the time for introducing oxygen during oxidation annealing is 70 minutes.

[0083] Figures 2-4 TEM lattice fringe images of the thin film products obtained in Examples 1, 4, and 5, respectively; Figures 5-7 The TEM lattice fringe images and TEM electron diffraction pattern images of the thin film products obtained in Examples 1, 4 and 5 respectively show that the crystal structure of the thin film product obtained in the present invention is a single crystal structure; different from the traditional polycrystalline vanadium dioxide thin film, its electron diffraction pattern is a series of regularly arranged spots (the electron diffraction of the polycrystalline structure is composed of a series of concentric circles of different radii).

[0084] Figure 8 The resistance change diagrams before and after the complete phase transition of the single-crystalline vanadium dioxide thin films obtained in Examples 1, 3, and 4 and the polycrystalline vanadium dioxide thin film obtained in Comparative Example 4 are respectively shown. It can be seen that the resistance change of the pure vanadium dioxide single-crystalline thin film (Example 1) obtained in the present invention before and after the phase transition reaches more than three orders of magnitude. Doping with other elements will affect the electrical properties of the vanadium dioxide thin film to a certain extent. However, the resistance change of the single-crystalline vanadium dioxide thin film doped with other elements in the present invention before and after the phase transition also reaches more than two orders of magnitude; the resistance change of the polycrystalline vanadium dioxide thin film described in Comparative Example 4 before and after the phase transition is generally only more than one order of magnitude.

[0085] Figure 9 The transmittance change diagrams of the single-crystal vanadium dioxide thin films obtained in Examples 1 to 3 are respectively obtained after complete phase change. It can be seen that the visible light transmittance and solar energy modulation efficiency of the single-crystal vanadium dioxide thin films of the present invention are relatively excellent; and after doping with other elements, the optical properties of the prepared films are still relatively excellent and are not greatly affected.

[0086] Figures 10-12The resistance change diagrams of the thin film products obtained in comparative examples 1 to 3 before and after complete phase change are shown. It can be seen that the electrical properties of the thin films obtained in the comparative examples are poor, which are quite different from the electrical properties of single crystal structure films, and are similar to the electrical properties of ordinary vanadium dioxide films. The resistance change before and after the phase change is only about one order of magnitude.

[0087] The present invention is not limited to the above-described embodiments. Persons skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are deemed to be within the scope of protection of the present invention. Any matters not described in detail in this specification constitute prior art known to those skilled in the art.

Claims

1. A method for preparing a VO2 single crystal thin film on an amorphous substrate, characterized in that: The following steps are involved: 1) Using vanadium oxide as a target, magnetron sputtering is performed in an inert atmosphere to form a disordered vanadium oxide film on the surface of an amorphous substrate; 2) placing the obtained disordered vanadium oxide film into a reaction vessel, introducing oxygen to adjust the pressure, and then heating to perform annealing and oxidation to obtain the VO2 single crystal thin film; The magnetron sputtering step adopts an inert gas flow rate of 10-20 sccm, a sputtering working pressure of 3-10 mtorr, a vanadium oxide target sputtering power of 50-100 W, a substrate temperature of room temperature, and a sputtering time of 100-140 min; In step 2), the oxygen flow rate is 2-10 sccm and the pressure is 50-250 mTorr; The annealing and oxidation step adopts a temperature of 480-550° C. and a time of 30-60 minutes.

2. The preparation method according to claim 1, characterized in that The vanadium oxide is vanadium trioxide, vanadium dioxide or vanadium pentoxide.

3. The preparation method according to claim 1, characterized in that The heating rate used in the annealing and oxidation step is 20-50°C / min.

4. The preparation method according to claim 1, characterized in that The vanadium oxide target also contains doping elements with a doping ratio of 0~5at%.

5. A VO2 single crystal thin film on an amorphous substrate prepared by the preparation method according to any one of claims 1 to 4, characterized in that: It is a VO2 single crystal thin film grown on an amorphous substrate.

6. The VO2 single crystal thin film on an amorphous substrate according to claim 5, characterized in that The amorphous substrate is a glass substrate or an amorphous titanium dioxide substrate.

7. The VO2 single crystal thin film on an amorphous substrate according to claim 5, characterized in that The area of ​​the VO2 single crystal thin film is up to 100 cm 2 above.

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