阅读说明：本技术 一种基于氮氢混合气产生装置的二氧化钒薄膜的制备方法 (Preparation method of vanadium dioxide film based on nitrogen-hydrogen mixed gas generation device ) 是由 高敏 徐晨曦 林媛 路畅 杨帆 于 2021-08-11 设计创作，主要内容包括：本发明提供一种基于氮氢混合气产生装置的二氧化钒薄膜的制备方法,属于二氧化钒薄膜制备技术领域。本发明采用PAD法制备二氧化钒薄膜,针对热处理过程中还原气氛容易发生波动从而影响制备二氧化钒薄膜质量的问题,一套还原气氛产生装置,使得能够在稳定的还原气氛下还原得到高质量的二氧化钒薄膜。本申请通过在管式炉管口处设置氢气浓度检测计,并与氢气产生装置的电压源相连,可以在热处理过程中通过浓度数值变化自动调节电压源的电压大小,从而调控氢气产生速度以控制氢气浓度在外界环境变化时,炉管内氢气浓度在较小范围内波动,从而提供稳定的热处理气氛,从而控制氧化钒的化学计量比,制备出可重复性高、质量高的二氧化钒薄膜。(The invention provides a preparation method of a vanadium dioxide film based on a nitrogen-hydrogen mixed gas generation device, belonging to the technical field of preparation of vanadium dioxide films. According to the invention, the PAD method is adopted to prepare the vanadium dioxide film, and a set of reducing atmosphere generating device is provided to reduce the vanadium dioxide film in a stable reducing atmosphere to obtain the high-quality vanadium dioxide film aiming at the problem that the quality of the prepared vanadium dioxide film is influenced because the reducing atmosphere is easy to fluctuate in the heat treatment process. According to the method, the hydrogen concentration detector is arranged at the opening of the tubular furnace tube and is connected with the voltage source of the hydrogen generation device, the voltage of the voltage source can be automatically adjusted through the change of the concentration value in the heat treatment process, so that the hydrogen generation speed is regulated and controlled to control the hydrogen concentration when the external environment changes, the hydrogen concentration in the furnace tube fluctuates in a small range, a stable heat treatment atmosphere is provided, the stoichiometric ratio of vanadium oxide is controlled, and the vanadium dioxide film with high repeatability and high quality is prepared.)

1. A nitrogen-hydrogen mixed gas generating device is characterized by comprising a hydrogen generating device, a gas conveying device and a hydrogen concentration detection sensor;

the hydrogen generating device comprises a U-shaped pipe, a voltage source, a control device and two electrodes; the U-shaped pipe is filled with conductive solution, two electrodes are respectively connected with the positive electrode and the negative electrode of a voltage source and placed in the conductive solution, a branch pipe port of a hydrogen generation end of the U-shaped pipe is sealed, and a branch pipe port of an oxygen generation end is connected with an adjustable knob, so that the oxygen overflow rate can be conveniently adjusted; the control device is connected with a voltage source;

the gas conveying device comprises a gas washing bottle, a flow meter and two gas guide pipes; one of the gas conduits is a three-port gas conduit, and the first port is connected with the hydrogen generation end of the U-shaped pipe and is used for conveying hydrogen generated by the hydrogen generation device; the second port is connected with a nitrogen cylinder, and a flow meter is arranged on the gas guide pipe and used for detecting the nitrogen flow rate; the third port is arranged below the liquid level of the gas washing bottle and is used for conveying the nitrogen-hydrogen mixed gas; one end of the second gas guide pipe is arranged on the liquid level of the gas washing bottle, and the other end of the second gas guide pipe is arranged at the inlet of the tubular furnace and used for conveying nitrogen-hydrogen mixed gas into the tubular furnace;

the hydrogen concentration detection sensor is arranged at an inlet of the tubular furnace and used for detecting the actual concentration of hydrogen in the nitrogen-hydrogen mixed gas conveyed by the second gas guide tube and transmitting a detection result to the control device, and the control device regulates and controls the size of the voltage source according to the detection result so as to control the hydrogen generation rate.

2. The apparatus for generating an N-H mixture as defined in claim 1, wherein the conductive solution contained in the U-shaped tube is NaOH solution, KOH solution, or,HCl solution, H₂SO₄The concentration of the solution is 0-2 mol/L.

3. The apparatus for generating a nitrogen-hydrogen mixture gas as claimed in claim 1, wherein the electrode is a platinum electrode or a gold electrode.

4. The apparatus for generating an N-H mixture gas as defined in claim 1, wherein the voltage value of the voltage source is adjusted to be in the range of 0-5V.

5. The method for preparing a vanadium dioxide thin film based on the device according to any one of claims 1 to 4, comprising the following steps:

step 1, preparing a vanadium ion-containing polymer precursor solution by adopting a PAD method;

step 2, spin-coating the polymer precursor solution prepared in the step 1 on the surface of the cleaned substrate;

step 3, placing the substrate spin-coated with the polymer precursor liquid in the step 2 in the middle of a tube, uniformly distributing the temperature at the middle, performing heat treatment in a nitrogen-hydrogen mixed atmosphere generated by the device, and naturally cooling to room temperature to obtain a vanadium dioxide film on the substrate; the ratio of the nitrogen to the hydrogen flow of the nitrogen-hydrogen mixed gas can be dynamically adjusted in real time, the detection data of the hydrogen concentration detection sensor is fed back to the control device in real time, the voltage value of the voltage source is automatically regulated and controlled by the control device, and the hydrogen generation rate is changed, so that the ratio of the nitrogen flow to the hydrogen flow is changed, and the hydrogen concentration at the gas inlet of the tube furnace tube of the tube furnace is kept in dynamic balance.

6. The method for preparing a vanadium dioxide film according to claim 5, wherein the PAD method adopted in the step 1 is used for preparing the vanadium ion-containing polymer precursor solution by the following specific steps: dissolving polyetherimide or polyethylene glycol in water, adding ethylene diamine tetraacetic acid after stirring, continuing stirring until a uniform solution is formed, then adding ammonium metavanadate into the solution, stirring to form a transparent solution, finally transferring the solution into an ultrafiltration device, pressurizing during filtering, carrying out magnetic stirring, and removing water in the solution.

7. The method for preparing the vanadium dioxide thin film according to claim 5, wherein the specific parameters of the spin coating in the step 2 are as follows: firstly rotating at the rotation speed of 600-650r/min for 10s, and then rotating at the rotation speed of 6000-7000r/min for 40 s.

8. The method for preparing the vanadium dioxide film according to claim 5, wherein the heat treatment in the step 3 comprises the following specific steps: firstly, the temperature is raised to 100-plus-120 ℃ and is preserved for 20-30min, then the temperature is raised to 430-plus-450 ℃ and is preserved for 140min, and then the temperature is raised to 490-plus-550 ℃ and is preserved for 2-2.5 h; the nitrogen in the nitrogen-hydrogen mixed gas is 99.999 percent pure nitrogen, and the flow rate is 0.2-0.5L/min; the hydrogen is supplied by a hydrogen generating device, and the flow rate is controlled by the power supply voltage.

9. The method for preparing a vanadium dioxide film according to claim 5, wherein the concentration of hydrogen at the gas inlet of the tube furnace is 2.5% to 3.5%.

Technical Field

The invention belongs to the technical field of preparation of vanadium dioxide films, and particularly relates to a preparation method of a vanadium dioxide film based on a nitrogen-hydrogen mixed gas generation device.

Background

The vanadium dioxide has the phase change characteristics of ultra-fast, reversible and multi-stimulus response, and can be completed by various stimuli from a monoclinic tetragonal phase to a metal phase, wherein the stimuli comprise electric, thermal, optical, electrochemical, mechanical and magnetic disturbances and the like. A reversible metal-insulator (MIT) transition occurs at a critical temperature of 340K, and the resistance changes by 4 to 5 orders of magnitude during the transition, which is an oxide having a strong electron-related characteristic. Below the transition temperature, VO₂Is of monoclinic structure And above the transition temperature, VO₂Is a tetragonal rutile structureDue to the unique phase change characteristic, the vanadium dioxide film can be widely applied to the fields of intelligent windows, memristors, switches, terahertz modulators and the like.

At present, the preparation of vanadium dioxide films with high repeatability and high quality is still a difficult task because the stability of vanadium dioxide relative to the oxidation-reduction process is very low and vanadium ions can be in V²⁺，V³⁺，V⁴⁺And V⁵⁺Will form non-stoichiometric vanadium oxides with variable oxygen content. The existing preparation methods of the vanadium dioxide film comprise magnetron sputtering and pulsed laserDeposition, chemical vapor deposition, molecular beam epitaxy, sol-gel methods, and the like. The advantage of preparing vanadium dioxide by magnetron sputtering is that the film has good uniformity, is suitable for large-area preparation and has high deposition efficiency, but the process parameters such as oxygen partial pressure, temperature and the like need to be accurately controlled, so the prepared vanadium dioxide film has poor repeatability; the pulsed laser deposition usually needs 450 ℃ to obtain a vanadium dioxide thin film with good performance, but the extremely high temperature brings huge energy consumption, so how to synthesize the vanadium dioxide thin film at low temperature is a big difficulty, and the oxygen partial pressure, the distance between a target and a substrate and the laser energy need to be accurately controlled; the chemical vapor deposition can obtain a dense and uniform vanadium dioxide film with high growth speed, but the temperature and the oxygen partial pressure of the substrate in the preparation process can influence the V: o stoichiometry, which in turn affects its phase purity and physical properties; molecular beam epitaxy can produce high-quality and homogeneous epitaxial vanadium dioxide films, but due to the high melting point and low saturated vapor pressure, controllable vanadium evaporation is not easy, so that the prepared vanadium oxide shows multiple valence states; the sol-gel method is widely used for depositing vanadium dioxide thin films due to its low cost, suitability for large-area deposition and suitability for metal doping, but toxic reagents are generally used in the preparation process to pollute the environment, and the solution needs to be prepared in situ.

Polymer Assisted Deposition (PAD) is another chemical solution process than sol-gel, which requires very inexpensive reagents to prepare the precursor and annealing to produce VO with high performance₂The film has high solution stability, and after the solution is prepared, the solution can still be used after being stored in a refrigerator for half a year, so that the preparation is more convenient. But the key step in the PAD method preparation process is to anneal the precursor film to obtain the vanadium dioxide film, and the annealing needs to be carried out in a nitrogen-hydrogen mixed atmosphere. At present, commonly used nitrogen-hydrogen mixed gas is generally provided by a gas cylinder, but the actual precision of the mixed gas in the gas cylinder can not better accord with the standard; in addition, the change of the environment during the preparation process can cause the fluctuation of the atmosphere in the tube furnace, thereby influencing VO₂The quality of the film.

Therefore, the development of a simple preparation method of the vanadium dioxide film with low cost, high repeatability and high quality has very important significance for the practical application of vanadium dioxide.

Disclosure of Invention

Aiming at the problem that the quality of the prepared vanadium dioxide film is affected because the reducing atmosphere is easy to fluctuate in the heat treatment process when the vanadium dioxide film is prepared by adopting the PAD method in the background art, the invention aims to provide the preparation method of the vanadium dioxide film based on the nitrogen-hydrogen mixed gas generation device. The invention designs a set of reducing atmosphere generating device, which controls the fluctuation of the hydrogen concentration in the device in a small range when the hydrogen concentration changes in the external environment by detecting the hydrogen concentration in the heat treatment device in real time and adjusting the hydrogen generating speed according to the hydrogen concentration, thereby providing stable heat treatment atmosphere and obtaining a high-quality vanadium dioxide film.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a nitrogen-hydrogen mixed gas generating device comprises a hydrogen generating device, a gas conveying device and a hydrogen concentration detection sensor;

the hydrogen generating device comprises a U-shaped pipe, a voltage source, a control device and two electrodes; the U-shaped pipe is filled with conductive solution, two electrodes are respectively connected with the positive electrode and the negative electrode of a voltage source and placed in the conductive solution, a branch pipe port of a hydrogen generation end of the U-shaped pipe is sealed, and a branch pipe port of an oxygen generation end is connected with an adjustable knob, so that the oxygen overflow rate can be conveniently adjusted; the control device is connected with a voltage source;

the gas conveying device comprises a gas washing bottle, a flow meter and two gas guide pipes; one of the gas conduits is a three-port gas conduit, and the first port is connected with the hydrogen generation end of the U-shaped pipe and is used for conveying hydrogen generated by the hydrogen generation device; the second port is connected with a nitrogen cylinder, and a flow meter is arranged on the gas guide pipe and used for detecting the nitrogen flow rate; the third port is arranged below the liquid level of the gas washing bottle and is used for conveying the nitrogen-hydrogen mixed gas; one end of the second gas guide pipe is arranged on the liquid level of the gas washing bottle, and the other end of the second gas guide pipe is arranged at the inlet of the tubular furnace and used for conveying nitrogen-hydrogen mixed gas into the tubular furnace;

the hydrogen concentration detection sensor is arranged at an inlet of the tubular furnace and used for detecting the actual concentration of hydrogen in the nitrogen-hydrogen mixed gas conveyed by the second gas guide tube and transmitting a detection result to the control device, and the control device regulates and controls the size of the voltage source according to the detection result so as to control the hydrogen generation rate.

Further, the conductive solution carried in the U-shaped tube can be NaOH solution, KOH solution, HCl solution, H solution₂SO₄The solution, preferably KOH solution, has the concentration of 0-2mol/L, preferably 1 mol/L;

further, the electrode may be a platinum electrode, a gold electrode, preferably a gold electrode.

Further, according to calculation, the voltage value of the voltage source can be adjusted within the range of 0-5V.

The preparation method of the vanadium dioxide film based on the device comprises the following steps:

step 1, preparing a vanadium ion-containing polymer precursor solution by adopting a PAD method;

step 2, spin-coating the polymer precursor solution prepared in the step 1 on the surface of the cleaned substrate;

step 3, placing the substrate spin-coated with the polymer precursor liquid in the step 2 in the middle of a tube, uniformly distributing the temperature at the middle, performing heat treatment in a nitrogen-hydrogen mixed atmosphere generated by the device, and naturally cooling to room temperature to obtain a vanadium dioxide film on the substrate; the ratio of the nitrogen to the hydrogen flow of the nitrogen-hydrogen mixed gas can be dynamically adjusted in real time, the detection data of the hydrogen concentration detection sensor is fed back to the control device in real time, the voltage value of the voltage source is automatically regulated and controlled by the control device, and the hydrogen generation rate is changed, so that the ratio of the nitrogen flow to the hydrogen flow is changed, and the hydrogen concentration at the gas inlet of the tube furnace tube of the tube furnace is kept in dynamic balance.

Further, the specific process of preparing the vanadium ion-containing polymer precursor solution by using the PAD method in the step 1 is as follows: dissolving 0.001-0.002mol of Polyetherimide (PEI) or polyethylene glycol (PEG) in 60-120ml of water, adding 0.001-0.002mol of Ethylene Diamine Tetraacetic Acid (EDTA) after stirring, continuously stirring until a uniform solution is formed, then adding 0.001-0.002mol of ammonium metavanadate in the solution, stirring to form a transparent solution, finally transferring the solution into an ultrafiltration device, adding 0.2 atmosphere during filtering, carrying out magnetic stirring, and removing water in the solution.

Further, the specific parameters of the spin coating in the step 2 are as follows: firstly rotate at the lower speed of 600-650r/min for 10s, and then rotate at the higher speed of 6000-7000r/min for 40 s.

Further, the substrate is preferably sapphire (Al) having a crystal plane orientation of (10-10)₂O₃) The specific cleaning process comprises the following steps: sequentially and respectively ultrasonically cleaning the glass substrate by acetone, absolute ethyl alcohol and deionized water.

Further, the specific process of the heat treatment in the step 3 is as follows: the temperature is raised to 100-plus-one temperature of 120 ℃ and is preserved for 20-30min, the residual water in the solution is removed, the temperature is raised to 430-plus-one temperature of 450 ℃ and is preserved for 140min, the organic matter is removed, and then the temperature is raised to 490-plus-one temperature of 550 ℃ and is preserved for 2-2.5h, and the vanadium dioxide film is obtained.

Further, the nitrogen in the nitrogen-hydrogen mixed gas in the step 3 is 99.999 percent pure nitrogen, and the flow rate is 0.2-0.5L/min; the hydrogen is supplied by a hydrogen generating device, and the flow rate is controlled by the power supply voltage.

Further, the hydrogen concentration at the gas inlet of the tube furnace tube of the tube furnace is preferably 2.5-3.5%.

The mechanism of the invention is as follows: preparing a vanadium ion polymer precursor solution by a PAD method, spin-coating the precursor solution on a substrate, and finally carrying out heat treatment on a sample; during the heat treatment, a reducing atmosphere is provided by a mixed gas of nitrogen and hydrogen passing through water. Because the humidity and temperature of the external environment are interfered, the concentration of the reducing hydrogen in the furnace tube is easy to fluctuate, therefore, the hydrogen concentration detector is arranged at the inlet of the tubular furnace and is connected with a voltage source of the hydrogen generating device, the voltage of the voltage source can be automatically adjusted through the change of concentration numerical values in the heat treatment process, the hydrogen generating speed is regulated and controlled to control the fluctuation of the concentration of the hydrogen in a smaller range when the external environment changes, so that the stable heat treatment atmosphere is provided, the stoichiometric ratio of vanadium oxide is controlled, and the vanadium dioxide film with high repeatability and high quality is prepared. Meanwhile, the mixed gas of hydrogen and nitrogen firstly passes through the gas washing bottle and then is input into the tube furnace, and the introduction of moisture into the growth environment of the moisture gas establishes a self-regulation process for oxygen partial pressure when the growth temperature changes, so that the preparation of the high-quality vanadium dioxide film is facilitated.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

the invention provides a simple device, which improves the repeatability of the vanadium dioxide film prepared by the PAD method, the quality of the prepared film is good, the film has resistance change of four orders of magnitude before and after phase change, and the device is suitable for various applications; the whole preparation method has low cost and no toxicity.

Drawings

FIG. 1 is a schematic diagram of a nitrogen-hydrogen mixed gas generating device for preparing a vanadium dioxide film according to the present invention.

FIG. 2 is an XRD pattern of the vanadium dioxide film obtained in example 1.

FIG. 3 is a temperature resistance curve of the vanadium dioxide thin film obtained in example 1.

FIG. 4 is a graph showing the resistance temperature of the vanadium dioxide thin film obtained in comparative example 1.

FIG. 5 is a graph showing the resistance temperature of the vanadium dioxide thin film obtained in comparative example 2.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings.

The method adopts a simple PAD method to prepare the high-molecular precursor liquid, the precursor liquid is coated on a substrate in a spinning mode, the substrate is placed in a tube furnace to carry out heat treatment on a sample, and mixed reducing gas of nitrogen and hydrogen is introduced in the heat treatment process to reduce the mixture to obtain the vanadium dioxide film.

A nitrogen-hydrogen mixed gas generating device is shown in figure 1, the gas flow rate of the device can be automatically regulated and controlled, and the device comprises a hydrogen generating device, a gas conveying device and a hydrogen concentration detection sensor;

because the electrolyzed water simultaneously generates hydrogen and oxygen, in order to enable the two gases to be generated at different places, the hydrogen generating device adopts a U-shaped pipe, the reduction reaction and the oxidation reaction are separately generated on two electrodes, and one end of the U-shaped pipe generates the hydrogen and the other end generates the oxygen. Accordingly, an apparatus for producing hydrogen by electrolysis of water comprises: the device comprises a U-shaped pipe (divided into a hydrogen end and an oxygen end), two gold electrodes, a gas conduit, a control device and a voltage source; the U-shaped pipe is filled with a conductive solution KOH with the concentration of 1mol/L, two electrodes are respectively connected with the positive electrode and the negative electrode of a voltage source and are placed in the conductive solution, two ports of the U-shaped pipe are sealed, meanwhile, a branch pipe port of a hydrogen generation end is sealed, and a branch pipe port of an oxygen generation end is connected by an adjustable knob, so that the oxygen overflow rate can be conveniently adjusted; the control device is connected with a voltage source;

the gas conveying device comprises a gas washing bottle, a flow meter and two gas guide pipes; one of the gas conduits is a three-port gas conduit, the first port is connected with the hydrogen generation end of the U-shaped pipe and used for conveying hydrogen generated by the hydrogen generation device, the second port is connected with a nitrogen cylinder, a flow meter is arranged on the gas conduit and used for detecting the flow rate of nitrogen, and the third port is arranged below the liquid level of the gas washing cylinder and used for conveying nitrogen-hydrogen mixed gas; one end of the second gas guide pipe is arranged on the liquid level of the gas washing bottle, and the other end of the second gas guide pipe is arranged at the inlet of the tubular furnace and used for conveying nitrogen-hydrogen mixed gas into the tubular furnace; sealing two ends of the tube furnace;

the hydrogen concentration detection sensor is arranged at an inlet of the tubular furnace and used for detecting the actual concentration of hydrogen in the nitrogen-hydrogen mixed gas conveyed by the second gas guide pipe and transmitting a detection result to the control device, and the control device adjusts the size of the voltage source according to the detection result so as to control the hydrogen generation rate. The inlet of the tube furnace is sealed, so that the detection of hydrogen is convenient, the outlet is not sealed, so that oxygen in the air participates in the annealing process of the vanadium dioxide film, namely the oxygen is used for oxidizing carbon in the precursor film which is coated by spinning to form CO₂And (4) discharging.

Example 1

The preparation method of the vanadium dioxide film based on the device comprises the following steps:

step 1, adopting a PAD method to prepare a vanadium ion-containing polymer precursor solution, and the specific process comprises the following steps: dissolving 3.0g of Polyetherimide (PEI) in 60ml of water, stirring for 30min, adding 3.0g of Ethylene Diamine Tetraacetic Acid (EDTA), continuing stirring until a uniform solution is formed, then adding 1.2g of ammonium metavanadate into the solution, stirring for 30min to form a transparent solution, finally transferring the solution into an ultrafiltration device, and adding 0.2 atmosphere during filtration and carrying out magnetic stirring to obtain a polymer precursor solution;

step 2, spin-coating the polymer precursor solution prepared in the step 1 on the surface of the substrate, and the specific process is as follows; selecting sapphire (Al) with crystal face orientation of (10-10) and 1cm x 1cm₂O₃) As a substrate, sequentially and respectively ultrasonically cleaning the substrate for 10 minutes by acetone, absolute ethyl alcohol and deionized water, then drying the substrate by using a nitrogen gun, placing the cleaned substrate on a spin coater, and spin-coating the polymer precursor solution prepared in the step 1 on the surface of the substrate, wherein the substrate is firstly rotated at a low speed of 600r/min for 10 seconds and then rotated at a high speed of 6500r/min for 40 seconds in the spin coating process;

step 3, placing the substrate spin-coated with the polymer precursor liquid in the step 2 in an alumina crucible, then placing the crucible in the center of a corundum tube type furnace, opening a voltage source of a nitrogen-hydrogen mixed gas generation device, setting a voltage value to be 2.3V, generating hydrogen, simultaneously opening a nitrogen cylinder, inputting nitrogen, introducing hydrogen and high-purity nitrogen (with the purity of 99.999%) into the tube type furnace together with water vapor after passing through a gas washing cylinder, wherein the nitrogen flow rate is 0.36/min, so that the substrate is subjected to heat treatment in a nitrogen-hydrogen mixed atmosphere, firstly raising the temperature to 100 ℃, preserving the heat for 25min, then raising the temperature to 450 ℃, preserving the heat for 120min, then raising the temperature to 505 ℃, preserving the heat for 2h, reducing the substrate spin-coated with the precursor liquid in a nitrogen-hydrogen reducing atmosphere, and taking out the alumina crucible when the temperature in a furnace tube is reduced to room temperature, so as to obtain a vanadium dioxide film with the thickness of 25.5 nm; the data of a sensor for detecting the hydrogen concentration at the tail of the corundum tube is fed back to the nitrogen-hydrogen mixed gas generation device in real time, the control device automatically regulates and controls the power supply voltage value of the hydrogen generation device according to the hydrogen concentration value, and the hydrogen generation speed is changed, so that the ratio of nitrogen to hydrogen is changed, and the hydrogen concentration at the inlet of the corundum tube is maintained at about 3.5% when the external environment fluctuates.

The XRD spectrum of the vanadium dioxide film prepared in the example is shown in FIG. 2, and the substrate Al is at 68 DEG₂O₃The peak of (30-30) is that of vanadium dioxide (-402) at around 65 degrees, and it can be seen that the film produced is a vanadium dioxide film and the film is epitaxial. The resistance temperature curve is shown in FIG. 3, and the high resistance can reach 10⁵Omega, low resistance of only 15 omega, resistance variation up to 10⁴Thus indicating that the high-quality vanadium dioxide film is successfully prepared.

Comparative example 1

A vanadium dioxide film was prepared by following the procedure of example 1, with only the hydrogen concentration at the outlet of the end of the corundum tube in step 3 set to 2%, and the other steps were not changed.

The resistance temperature curve of the vanadium dioxide thin film prepared in the embodiment is shown in FIG. 4, and it can be seen from the graph that the thin film prepared under 2% hydrogen content has a high resistance of 10⁶But the low resistance is up to 8000 omega, and the resistance change is 10²The film quality was inferior to the vanadium dioxide film prepared in example 1. Because the vanadium in the ammonium metavanadate in the precursor raw material is +5 valent and the vanadium in the vanadium dioxide film is +4 valent, the whole preparation process is a reduction process. If the hydrogen concentration in the nitrogen-hydrogen mixed atmosphere is too high, the vanadium ions can be excessively reduced; and the hydrogen concentration is too low, so that the reduction is insufficient, and finally pure vanadium dioxide cannot be prepared.

Comparative example 2

A vanadium dioxide thin film was produced by following the procedure of example 1, and the nitrogen-hydrogen mixture gas in step 3 was replaced with a commercially available nitrogen gas containing 3.5% hydrogen gas, without adding a control device. The resistance temperature curve of the vanadium dioxide film prepared in this comparative example is shown in FIG. 5, and it can be seen that the film prepared in a commercially available nitrogen atmosphere containing 3.5% hydrogen has a high resistance of 10⁵Low resistance of 65 omega and resistance variation of 10³The film quality did not achieve the effect prepared in example 1.

While the invention has been described with reference to specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise; all of the disclosed features, or all of the method or process steps, may be combined in any combination, except mutually exclusive features and/or steps.