Method for preparing aluminum-doped vanadium trioxide film by sol-gel method

Abstract

The invention discloses a method for preparing an aluminum-doped vanadium trioxide film by a sol-gel method, which comprises the following steps: dissolving vanadium isopropoxide and an aluminum isopropoxide solution in isopropanol, adding acetic acid, and fully and uniformly mixing to obtain sol; the sol is dropwise coated on the surface of an aluminum oxide substrate to form a film, one drop is dropped after each drop is dried, and the relative thickness of the film is controlled through different drop numbers. Putting the obtained film into a graphite boat, putting vanadium dioxide powder around the graphite boat, putting the graphite boat into an aluminum oxide square crucible, then putting the crucible into a tubular furnace, reducing the crucible into vanadium dioxide at a relatively low temperature, and then continuously heating and annealing in a reducing atmosphere to obtain the doped vanadium trioxide film. The obtained finished product is a polycrystalline film, the obtained film is uniform, the high-temperature phase change of the film ranges from 250 K to 380 K, and the resistance change is 2-20 times after phase change.

Description

Technical Field

[0001] The invention relates to a method for preparing a vanadium trioxide material, in particular to a method for preparing an aluminum-doped vanadium trioxide film by a sol-gel method. Background Art

[0002] Vanadium trioxide (V 2 O 3 ) is a classic material with metal-insulation transition. It is a paramagnetic metal phase (PM) at room temperature and pressure, but it will become an antiferromagnetic insulating phase (AFI) when the temperature is very low. This temperature is around 160K, and the resistance changes by about 4 to 6 orders of magnitude. At room temperature, the crystal structure is a corundum structure, which belongs to the hexagonal crystal system. When the low-temperature insulating metal phase transition occurs, the corundum structure changes to a monoclinic structure. However, when doped with a small amount of aluminum, its resistance characteristics show a positive temperature coefficient characteristic. The doped vanadium trioxide will undergo a new phase transition, that is, it will undergo a transition from a paramagnetic metal phase to a paramagnetic insulating phase (PI) when the temperature rises. Moreover, the metal-insulating transition temperature of the doped vanadium trioxide will decrease with the increase of aluminum content, and the phase transition temperature tends to room temperature, and a transition between the metal phase and the insulating phase occurs. This phase transition is related to temperature, electric field, pressure, magnetic field, etc., and is usually accompanied by significant changes in electrical and optical properties. Therefore, it is widely used in electronic components.

[0003] There are many common processes for preparing thin films, including magnetron sputtering, chemical vapor deposition, etc. The thin films obtained by sputtering have high purity, good density, and good film uniformity, but this method is not easy to control the valence state of vanadium, and the equipment and operation of chemical vapor deposition are relatively complicated. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing aluminum-doped vanadium trioxide thin film by a sol-gel method. The method is simple to operate, the obtained thin film is uniform and has low requirements on equipment.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing aluminum-doped vanadium trioxide thin film by a sol-gel method, comprising: Step 1: Prepare aluminum isopropoxide solution Dissolving aluminum isopropoxide powder in isopropanol, and stirring to fully dissolve the powder to obtain an aluminum isopropoxide solution; Step 2: Preparation of doped sol Dissolving vanadium isopropoxide and aluminum isopropoxide solutions in isopropanol, adding acetic acid and mixing thoroughly to obtain a sol; Step three, thin film coating, the sol obtained in step two is drop by drop applied onto the surface of the aluminum oxide substrate to form a thin film, and after each drop is dried, another drop is added, and the relative thickness of the film is controlled by different numbers of drops.

[0006] Step 4: annealing treatment. Place the obtained film in a graphite boat, and place vanadium dioxide powder around it. Place the graphite boat in an alumina square crucible, and then place the crucible in a tube furnace. Heat it to 60°C and keep it for 10 min to 30 min. Continue to heat it to 400°C and keep it for 15 to 30 min. Then evacuate the tube furnace to a vacuum, and then introduce H 2 The mixed gas is returned to normal pressure, and then the temperature is continued to be raised to an annealing temperature of 800°C~880°C, the annealing time is 40min~3h, and after the annealing is completed, the temperature is returned to room temperature to obtain an aluminum-doped vanadium trioxide film.

[0007] As a preferred embodiment, in step 1, a magnetic stirrer is used for stirring at a rotation speed of 1000-1200 revolutions per minute.

[0008] As a preferred embodiment, in step 1, the concentration of the aluminum isopropoxide solution is 1.7-2 mg / ml.

[0009] As a preferred embodiment, in step 2, the volume ratio of the vanadium isopropoxide, isopropanol, acetic acid and aluminum isopropoxide solution is 1:20:1:(4.8-9.72).

[0010] As a preferred embodiment, in step three, the ambient humidity during film coating is 35% to 80%.

[0011] As a preferred embodiment, in step three, the volume of each drop during thin film coating is 50 μl.

[0012] As a preferred embodiment, in step 4, a hole is opened at the front and rear positions of the graphite boat respectively.

[0013] As a preferred embodiment, the substrate is cleaned before the film coating, the substrate is ultrasonically cleaned in dilute nitric acid, and then the dilute nitric acid on the surface is rinsed clean with anhydrous ethanol and wiped dry.

[0014] As a preferred embodiment, the concentration of the dilute nitric acid is 31.68%.

[0015] As a preferred embodiment, the mass proportion of aluminum in the obtained aluminum-doped vanadium trioxide film is 1% to 2%.

[0016] The invention adopts a sol-gel method, uses isopropanol as a solvent, adds a small amount of acetic acid, and undergoes hydrolysis and polycondensation to obtain an aluminum-doped sol, drops the sol on a substrate, and then dries to obtain a dry gel, and finally undergoes a step-by-step annealing treatment with a reducing gas, firstly reduces the vanadium dioxide at a relatively low temperature, and then continues to anneal at a high temperature in a reducing atmosphere to obtain a doped vanadium trioxide film. The operation is simple, the obtained film is uniform, the equipment requirement is low, and the cost is more saved, and the invention is suitable for industrial production and application.

[0017] In practical applications, thin films are more widely used rather than crystals. The finished product obtained by the present invention is a polycrystalline film, and the obtained thin film has a high-temperature phase transition between 250K and 380K, and the resistance changes by 8 to 10 times after the phase transition. In the application process, it is easier to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope image of the aluminum-doped vanadium trioxide film obtained in Example 1.

[0019] Figure 2 This is a high temperature resistance-temperature curve of the aluminum-doped vanadium trioxide film obtained in Example 1.

[0020] Figure 3 This is a low-temperature resistance-temperature curve of the aluminum-doped vanadium trioxide film obtained in Example 1.

[0021] Figure 4 This is a differential curve of the relationship between the resistance and temperature of the aluminum-doped vanadium trioxide film obtained in Example 1.

[0022] Figure 5 This is the XRD pattern of the aluminum-doped vanadium trioxide film obtained in Example 3.

[0023] Figure 6 This is the macroscopic morphology of the aluminum-doped vanadium trioxide film obtained in Example 3. DETAILED DESCRIPTION

[0024] A typical embodiment of the present invention provides a method for preparing an aluminum-doped vanadium trioxide film by a sol-gel method, which includes the following steps 1 to 4.

[0025] Step 1: Prepare aluminum isopropoxide solution Aluminum isopropoxide powder is dissolved in isopropanol and stirred to fully dissolve to obtain an aluminum isopropoxide solution.

[0026] In this step, a magnetic stirrer is used for stirring, the speed of the magnetic stirrer is 1000-1200 revolutions per minute, and the stirring time is 1 hour. The preferred concentration of the aluminum isopropoxide solution is 1.7-2 mg / ml.

[0027] Step 2: Preparation of doped sol The vanadium isopropoxide and aluminum isopropoxide solutions are dissolved in isopropanol, and acetic acid is added and mixed thoroughly to obtain a sol.

[0028] In this step, the volume ratio of the vanadium isopropoxide, isopropanol, acetic acid and aluminum isopropoxide solution is 1:20:1:(4.8-9.72), wherein vanadium isopropoxide is the main raw material to obtain the vanadium trioxide film, isopropanol is the solvent and no other impurities are introduced, acetic acid is used as a catalyst, and the addition of aluminum isopropoxide causes the vanadium trioxide film to be doped with aluminum element to cause a phase change.

[0029] Step three, thin film coating, the sol obtained in step two is drop by drop applied onto the surface of the aluminum oxide substrate to form a thin film, and after each drop is dried, another drop is added, and the relative thickness of the film is controlled by different numbers of drops.

[0030] Before film coating, the substrate is cleaned by ultrasonic cleaning in dilute nitric acid, and then the dilute nitric acid on the surface is rinsed clean with anhydrous ethanol and wiped dry. The preferred concentration of dilute nitric acid is 31.68%.

[0031] The above-mentioned thin film coating is dripped in an environment with a certain humidity, and the drying speed is controlled by different humidity environments. The preferred environmental humidity is 35% to 80%, and the drying temperature is room temperature. If the environmental humidity is too low, cracks will appear during the drying process.

[0032] When controlling the film thickness, half a drop, one drop, two drops or more than two drops of sol are dripped according to the size of the substrate, the volume of each drop is 50 microliters, and the half drop is controlled within the range of 20-30 microliters.

[0033] Step 4: annealing treatment. Place the obtained film in a graphite boat, and place vanadium dioxide powder around it. Place the graphite boat in an alumina square crucible, and then place the crucible in a tube furnace. Heat it to 60°C and keep it for 10 min to 30 min. Continue to heat it to 400°C and keep it for 15 to 30 min. Then evacuate the tube furnace to a vacuum, and then introduce H 2 The mixed gas is returned to normal pressure, and then the temperature is continued to be raised to an annealing temperature of 800°C~880°C, the annealing time is 40min~3h, and after the annealing is completed, the temperature is returned to room temperature to obtain an aluminum-doped vanadium trioxide film.

[0034] During the annealing process, vanadium dioxide powder is added to provide a vanadium-containing annealing atmosphere for the film, which is beneficial to reduce the loss of vanadium in the film. The amount of vanadium dioxide powder should occupy half of the space in the graphite boat.

[0035] The graphite boat is placed in an alumina square crucible to reduce the contamination of the tube furnace wall by vanadium-containing vapor during annealing. A hole is opened at the front and back of the graphite boat to facilitate the circulation of reducing gas and give full play to its function.

[0036] After the temperature is raised to 60°C and kept warm to fully volatilize the residual organic solvent, the temperature is raised to 400°C and kept to evacuate the vacuum to significantly reduce the oxygen content and introduce reducing gas for reduction, and the temperature is raised to the annealing temperature for reduction to obtain the doped vanadium trioxide film.

[0037] In a preferred embodiment, the gas introduced is 5% H 2 and 95% Ar mixed gas.

[0038] The method for preparing aluminum-doped vanadium trioxide thin film by sol-gel method provided in this embodiment is simple to operate, the obtained thin film is uniform, the equipment requirements are low, and it is more cost-effective, and it is suitable for industrial production applications. The obtained finished product is a polycrystalline film, and in practical applications, thin films are more widely used, rather than crystals. The phase transition temperature is near room temperature, and it is easier to operate during the application process.

[0039] The technical scheme claimed in the present invention is further described below by some examples. However, the examples and comparative examples are used to explain the embodiments of the present invention and do not exceed the scope of the subject matter of the present invention. The protection scope of the present invention is not limited by the examples. Unless otherwise specified, the materials and reagents used in the present invention can be obtained from commercial products in the art. Example

[0040] (1) Preparation of aluminum isopropoxide solution: add an excess amount of aluminum isopropoxide to 20 ml of isopropanol, stir with a magnetic stirrer at 1125 revolutions per minute for 1 hour, let stand for three days and collect the supernatant to obtain an isopropanol solution of aluminum isopropoxide.

[0041] (2) Preparation of sol: 200 μL of vanadium isopropoxide, 4000 μL of isopropanol, 200 μL of acetic acid, and 1058.69 μL of aluminum isopropoxide solution were mixed and stirred at 1125 rpm for 30 min using a magnetic stirrer.

[0042] (3) Prepare the substrate: Ultrasonic clean the aluminum oxide substrate in dilute nitric acid for 10 minutes, take it out and rinse it with anhydrous ethanol, then wipe it dry for later use.

[0043] (4) Thin film coating: Use a humidifier to adjust the humidity to 47%, drop a drop of the prepared sol on the substrate, dry it for 12 minutes, then drop the second drop, dry the second drop for 12.5 minutes, and then dry it in the air for 15 minutes.

[0044] (5) Annealing treatment: Place the sample in a graphite boat and place vanadium dioxide powder around it. Place the graphite boat in an alumina square crucible. Then place the crucible in a tube furnace. Heat from room temperature to 60°C over 10 minutes and keep warm for 30 minutes. Heat to 400°C over 15 minutes and keep warm for 15 minutes. Vacuum to 2.1 Pa. At 400°C, introduce 5% H 2 and 95% Ar mixed gas, and heated to 520℃ after 10 minutes, kept warm for 30 minutes, heated to 620℃ after 10 minutes, kept warm for 20 minutes, heated to 850℃ after 20 minutes, kept warm for 60 minutes, cooled to 600℃ after 20 minutes, and then cooled naturally to room temperature to obtain (V 0.989 Al 0.011 ) 2 O 3 The surface of the film is smooth and black similar to that of Example 3. Figure 2 This is the resistance change of the sample during the high-temperature phase change. The resistance changes 8.5 times before and after the phase change. Example

[0045] (1) Preparation of aluminum isopropoxide solution: Add an excess of aluminum isopropoxide to 20 ml of isopropanol and stir at 1125 revolutions per minute using a magnetic stirrer for 1 hour. After standing for three days, take the supernatant to obtain an isopropanol solution of aluminum isopropoxide.

[0046] (2) Preparation of sol: 200 μL of vanadium isopropoxide, 4000 μL of isopropanol, 200 μL of acetic acid, and 1037 μL of aluminum isopropoxide solution were mixed and stirred at 1125 rpm using a magnetic stirrer for 30 min.

[0047] (3) Prepare the substrate: Ultrasonic clean the aluminum oxide substrate in dilute nitric acid for 10 minutes, take it out and rinse it with anhydrous ethanol, then wipe it dry for later use.

[0048] (4) Thin film coating: Use a humidifier to adjust the humidity to 40%, drip a drop of the prepared sol on the substrate, dry it for 6 minutes, then drip the second drop. After the second drop has dried for 4 minutes, adjust the humidity to 66%, and continue drying for 10 minutes.

[0049] (5) Annealing treatment: Place the sample in a graphite boat and place vanadium dioxide powder around it. Place the graphite boat in an alumina square crucible. Then place the crucible in a tube furnace. Heat from room temperature to 60°C over 10 minutes and keep it warm for 10 minutes. Heat to 400°C over 20 minutes and keep it warm for 25 minutes. Vacuum to 2 Pa. At 400°C, introduce 5% H 2and 95% Ar mixed gas, and heated to 520℃ after 10 minutes, kept warm for 40 minutes, heated to 620℃ after 10 minutes, kept warm for 40 minutes, heated to 800℃ after 20 minutes, kept warm for 40 minutes, cooled to 600℃ after 40 minutes, and then cooled naturally to room temperature to obtain (V 0.9893 Al 0.0107 ) 2 O 3 The surface of the film is smooth and black similar to that of Example 3, and the resistance change trend during the high-temperature phase change is similar to that of Example 1, with the maximum and minimum resistance changing 15 times before and after the phase change. Example

[0050] (1) Preparation of aluminum isopropoxide solution: add an excess amount of aluminum isopropoxide to 20 ml of isopropanol, stir with a magnetic stirrer at 1125 revolutions per minute for 1 hour, let stand for three days and collect the supernatant to obtain an isopropanol solution of aluminum isopropoxide.

[0051] (2) Preparation of sol: 200 μL of vanadium isopropoxide, 4000 μL of isopropanol, 200 μL of acetic acid, and 961.47 μL of aluminum isopropoxide solution were mixed and stirred at 1125 rpm using a magnetic stirrer for 30 min.

[0052] (3) Prepare the substrate: Ultrasonic clean the aluminum oxide substrate in dilute nitric acid for 10 minutes, take it out and rinse it with anhydrous ethanol, then wipe it dry for later use.

[0053] (4) Thin film coating: Use a humidifier to adjust the humidity to 41%, drip a drop of the prepared sol on the substrate, dry it for 10.5 minutes, adjust the humidity to 39%, and then drip the second drop. The drying time for the second drop is 12.5 minutes.

[0054] (5) Annealing treatment: Place the sample in a graphite boat and place vanadium dioxide powder around it. Place the graphite boat in an alumina square crucible. Then place the crucible in a tube furnace. Heat from room temperature to 60°C over 10 minutes and keep warm for 20 minutes. Heat to 400°C over 20 minutes and keep warm for 20 minutes. During the warming process, continue to evacuate. At 400°C, introduce 5% H 2 and 95% Ar mixed gas, and heated to 520℃ after 10 minutes, kept warm for 30 minutes, heated to 620℃ after 10 minutes, kept warm for 20 minutes, heated to 880℃ after 20 minutes, kept warm for 60 minutes, cooled to 600℃ after 20 minutes, and then cooled naturally to room temperature to obtain (V 0.99 Al 0.01 ) 2 O 3 film. Figure 6The surface morphology of the display film is smooth and black, and the resistance change trend during the high-temperature phase change is similar to that of Example 1, and the resistance changes by 7.7 times before and after the phase change. Example

[0055] (1) Preparation of aluminum isopropoxide solution: Add an excess of aluminum isopropoxide to 20 ml of isopropanol and stir at 1200 rpm for 1 hour using a magnetic stirrer. After three days of settling, take the supernatant to obtain an isopropanol solution of aluminum isopropoxide.

[0056] (2) Preparation of sol: 200 μL of vanadium isopropoxide, 4000 μL of isopropanol, 200 μL of acetic acid, and 1942.3 μL of aluminum isopropoxide solution were mixed and stirred at 1200 rpm using a magnetic stirrer for 30 min.

[0057] (3) Prepare the substrate: Ultrasonic clean the aluminum oxide substrate in dilute nitric acid for 10 minutes, take it out and rinse it with anhydrous ethanol, then wipe it dry for later use.

[0058] (4) Thin film coating: Use a humidifier to adjust the humidity to 40%, drip a drop of the prepared sol on the substrate, dry it for 6 minutes, then drip the second drop. After the second drop has dried for 4 minutes, adjust the humidity to 66%, and continue drying for 10 minutes.

[0059] (5) Annealing treatment: Place the sample in a graphite boat and place vanadium dioxide powder around it. Place the graphite boat in an alumina square crucible. Then place the crucible in a tube furnace. Heat from room temperature to 60°C over 10 minutes and keep warm for 30 minutes. Heat to 400°C over 20 minutes and keep warm for 30 minutes. Vacuum to 2 Pa. At 400°C, introduce 5% H 2 and 95% Ar mixed gas, and heated to 520℃ after 10 minutes, kept warm for 40 minutes, heated to 620℃ after 10 minutes, kept warm for 40 minutes, heated to 800℃ after 20 minutes, kept warm for 3 hours, cooled to 600℃ after 40 minutes, and then cooled naturally to room temperature to obtain (V 0.98 Al 0.02 ) 2 O 3 The film surface is smooth and black similar to Example 3. Figure 2 The resistance change of the sample during the high-temperature phase transition is 3.8 times. The film thickness is 1.983 nanometers.

[0060] The scope of protection claimed by the present invention is not limited to the above specific embodiments. For those skilled in the art, the present invention may have various deformations and changes. Any modifications, improvements and equivalent substitutions made within the concept and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing aluminum-doped vanadium trioxide thin film by a sol-gel method, characterized in that: include: Step 1: Prepare aluminum isopropoxide solution Dissolving aluminum isopropoxide powder in isopropanol, and stirring to fully dissolve the powder to obtain an aluminum isopropoxide solution; Step 2: Preparation of doped sol Dissolving vanadium isopropoxide and aluminum isopropoxide solutions in isopropanol, adding acetic acid and mixing thoroughly to obtain a sol; Step 3, thin film coating, drop by drop the sol obtained in step 2 onto the surface of the aluminum oxide substrate to form a thin film, and after each drop is dried, another drop is dropped, and the relative thickness of the film is controlled by different numbers of drops; Step four, annealing treatment, placing the obtained film in a graphite boat, and placing vanadium dioxide powder around it, placing the graphite boat in an alumina square crucible, and then placing the crucible in a tubular furnace, heating to 60°C and keeping warm for 10min~30min, continuing to heat to 400°C and keeping warm for 15~30min and evacuating the tubular furnace to vacuum, and then introducing a mixed gas of H2 and Ar to restore to normal pressure, and then continuing to heat to an annealing temperature of 800°C~880°C, the annealing time is 40min~3h, and after annealing is completed, returning to room temperature to obtain an aluminum-doped vanadium trioxide film.

2. The method according to claim 1, characterized in that: In step 1, a magnetic stirrer is used for stirring at a speed of 1000-1200 revolutions per minute.

3. The method according to claim 1 or 2, characterized in that: In step 1, the concentration of the aluminum isopropoxide solution is 1.5-2 mg / ml.

4. The method according to claim 3, characterized in that: In step 2, the volume ratio of the vanadium isopropoxide, isopropanol, acetic acid and aluminum isopropoxide solution is 1:20:1:(4.8-9.72).

5. The method according to claim 1 or 4, characterized in that: In step 3, the ambient humidity during film coating is 35% to 80%.

6. The method according to claim 5, characterized in that: In step 3, the volume of each droplet during film coating was 50 μl.

7. The method according to claim 1 or 6, characterized in that: In step 4, a hole is opened at the front and rear positions of the graphite boat.

8. The method according to claim 7, characterized in that: Before film coating, the substrate is cleaned by ultrasonic cleaning in dilute nitric acid, and then the dilute nitric acid on the surface is rinsed clean with anhydrous ethanol and wiped dry.

9. The method according to claim 8, characterized in that: The concentration of the dilute nitric acid is 31.68%.

10. The method according to claims 1 to 9, wherein: In the obtained aluminum-doped vanadium trioxide film, the mass proportion of aluminum is 1%~2%.

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