A multi-level infrared laser modulation structure based on vanadium dioxide thin film and its preparation method

Abstract

This invention discloses a multi-level infrared laser modulation structure based on vanadium dioxide thin films and its preparation method, relating to the field of laser protection technology. By rationally controlling the thin film structure, an absorption layer is added to lower the laser power threshold for exciting the vanadium dioxide phase transition. The phase transition functional layer improves the modulation effect of the laser, exhibiting multi-level modulation effects under different laser powers. The protective layer allows the sample to operate in air for extended periods, making it suitable for various applications. The prepared thin film is epitaxially grown, exhibits excellent photoelectric properties, and the entire preparation method is low-cost and non-toxic.

Description

Technical Field

[0001] This invention relates to the field of laser protection technology, specifically to a vanadium dioxide thin film junction with multi-level infrared laser modulation and its preparation method. Background Technology

[0002] Electro-optical detection equipment is one of the key sensing devices in integrated avionics systems. Many aircraft, both domestically and internationally, are equipped with advanced tracking and targeting pods or airborne infrared search and track (IRST) systems, as well as electro-optical surveillance and reconnaissance equipment. However, without protection, these electro-optical detection devices are highly vulnerable to damage from modern blinding laser weapons, leading to functional failure. Blinding lasers can damage the structural materials, optical components, and sensor films of electro-optical equipment, damaging the entire component and system. They can even raise the temperature of the equipment's casing or critical components to their melting point, causing ablation or reaching the structural failure temperature, thus threatening the aircraft's survivability.

[0003] VO2 undergoes a phase transition under certain external stimuli (including lasers, heat, and electric fields), changing from high infrared transmittance to low transmittance. When normal low-energy signal light enters the detection device, the VO2 film maintains high transmittance, ensuring normal signal transmission. When a strong blinding laser strikes, the phase transition occurs, reducing transmittance and preventing damage to internal components. Furthermore, VO2 has a low phase transition threshold and can undergo phase transition within femtoseconds, meaning it can be induced by both continuous and pulsed lasers, providing effective protection and making it considered an excellent laser protection material.

[0004] Different ion doping methods have varying effects on vanadium dioxide, specifically influencing crystal structure and grain size. These effects directly impact the phase transition temperature, resistivity, hysteresis loop width, transmittance, and reflectivity of the thin film. Therefore, selecting appropriate elements for doping VO2 thin films is crucial for understanding the phase transition mechanism of vanadium dioxide and expanding its practical applications. Among numerous doping elements, tungsten doping significantly reduces the phase transition temperature of VO2 thin films.

[0005] However, single-layer vanadium dioxide has high infrared transmittance and low absorptivity, making it difficult to induce phase transitions at low laser power, resulting in slow response time and poor modulation. Furthermore, vanadium dioxide is easily oxidized to vanadium pentoxide and becomes ineffective when exposed to air for extended periods. Therefore, the optical structure of vanadium dioxide thin films is of great significance for their application in laser protection. Summary of the Invention

[0006] To address the problems of poor modulation effect and easy oxidation leading to failure in single-layer vanadium dioxide films, the present invention aims to provide a vanadium dioxide thin film structure with multi-level infrared laser modulation and its preparation method. The present invention designs a vanadium dioxide thin film structure with multi-level infrared laser modulation, which reduces the laser power threshold for exciting the vanadium dioxide phase transition, improves the modulation effect of the laser, and exhibits multi-level modulation effect under different laser powers.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: a multi-level infrared laser modulation structure based on vanadium dioxide thin film, wherein the structure is stacked sequentially from bottom to top as follows: a first vanadium dioxide thin film layer, a sapphire substrate, a second vanadium dioxide thin film layer, a vanadium dioxide thin film layer doped with tungsten, and a PMMA layer; the PMMA layer is a protective layer; the vanadium dioxide thin film layer doped with tungsten is an absorption layer; and the first vanadium dioxide thin film layer and the second vanadium dioxide thin film layer are phase change functional layers.

[0008] Furthermore, the thickness of the first vanadium dioxide thin film layer and the second vanadium dioxide thin film layer is 100-200 nm.

[0009] Furthermore, the PMMA layer has a thickness of 300-500 nm; the sapphire substrate has a thickness of 0.5 mm.

[0010] Furthermore, the thickness of the vanadium dioxide thin film layer doped with tungsten is 30 nm.

[0011] Furthermore, the tungsten doping concentration of the vanadium dioxide thin film layer doped with tungsten is 0.3-0.5% atomic concentration.

[0012] A method for fabricating a multi-level infrared laser modulation structure based on vanadium dioxide thin film, the method comprising:

[0013] Step 1: Prepare vanadium-containing precursor solution and tungsten-doped precursor solution;

[0014] The specific method for preparing the vanadium ion-containing precursor solution is as follows: Weigh ammonium metavanadate and polyethyleneimine in a molar ratio of 1:1, add them to deionized water, and stir until the reagents are completely dissolved; finally, transfer the solution to an ultrafiltration device, apply 0.2 atmospheres of pressure and perform magnetic stirring during filtration to remove water from the solution; during the preparation process, pressure ultrafiltration needs to be repeated at least three times, with the same amount of deionized water added each time, until the last ultrafiltration is completed; a stabilizing gas needs to be introduced during pressure ultrafiltration; the purpose of pressure ultrafiltration is to remove residual small molecules in the solution, further improve the stability of the precursor solution, and finally obtain a vanadium ion precursor solution with a concentration of 0.471 mmol / mL;

[0015] Step 2: Polish and clean the sapphire substrate on both sides, and then dry it with nitrogen gas;

[0016] Step 3: Spin-coat one side of the sapphire substrate with a vanadium ion-containing precursor solution and sinter it in a nitrogen and water vapor mixed atmosphere to prepare a vanadium dioxide thin film layer;

[0017] Step 4: Using the same method as in Step 3, a vanadium dioxide thin film layer is prepared on the other side of the sapphire substrate;

[0018] Step 5: Spin-coat a tungsten-doped precursor solution onto one side of the vanadium dioxide thin film layer, and sinter it under a nitrogen and water vapor mixed atmosphere to obtain a tungsten-doped vanadium dioxide thin film layer.

[0019] Step 6: Spin-coat PMMA solution onto the vanadium dioxide thin film layer doped with tungsten, and then cure it.

[0020] Furthermore, the concentration of tungsten in the tungsten-doped precursor solution is 0.3%-0.5% atomic concentration.

[0021] Furthermore, the substrate is double-polished sapphire with an orientation of (10-10), and the specific cleaning process is as follows: ultrasonic cleaning is performed sequentially with acetone, anhydrous ethanol, and deionized water.

[0022] Furthermore, the sintering method in step 3 is as follows:

[0023] First, heat to 100℃ and hold for 30 minutes to remove water from the precursor solution; then heat to 450℃ and hold for 240 minutes to remove colloids; then heat to 495℃ and hold for 240 minutes to nucleate; after the reaction is complete, allow it to cool naturally to room temperature.

[0024] Furthermore, the specific parameters of the spin coating method in steps 3 and 6 are as follows: first, rotate at a lower speed of 900-1000 r / min for 10 seconds, and then rotate at a higher speed of 6000-7000 r / min for 40 seconds.

[0025] Furthermore, the specific parameters for curing in step 6 are: temperature of 180-200℃ and time of 40-60min.

[0026] Furthermore, the modulated infrared laser has a wavelength of 1550nm and a power of 0-1100mW.

[0027] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] This invention presents a vanadium dioxide thin film structure with multi-level infrared laser modulation. By rationally controlling the film structure, an absorption layer is added to reduce the laser power threshold for exciting the phase transition of vanadium dioxide. The phase transition functional layer improves the modulation effect of the laser, exhibiting multi-level modulation effects under different laser powers. The protective layer allows the sample to be used in air for a long time, making it suitable for various applications. The prepared film is epitaxially grown, has excellent photoelectric properties, and the entire preparation method is low-cost and non-toxic. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the vanadium dioxide thin film structure of the present invention.

[0030] Figure 2 The image shows the near-infrared transmission spectrum of the vanadium dioxide thin film prepared in Example 1.

[0031] Figure 3 The image shows the near-infrared transmission spectrum of the vanadium dioxide thin film prepared in Comparative Example 1.

[0032] Figure 4 This is a 1550nm infrared laser modulation image of the vanadium dioxide thin film prepared in Example 1.

[0033] Figure 5 The image shows the 1550nm infrared laser modulation pattern of the vanadium dioxide thin film prepared in Comparative Example 1. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0035] A vanadium dioxide thin film structure with multi-level infrared laser modulation includes a phase change layer disposed on both sides of a substrate and a protective layer disposed on the phase change layer. The phase change layer consists of an absorption layer and a phase change functional layer. The absorption layer is a tungsten-doped vanadium dioxide thin film, the phase change functional layer is a high-quality vanadium dioxide thin film, and the protective layer is a high infrared transmittance material.

[0036] The above-described method for preparing vanadium dioxide thin films includes the following steps:

[0037] A vanadium-containing polymer precursor solution and a tungsten-doped precursor solution were prepared using a polymer-assisted deposition method. Vanadium dioxide thin film phase change functional layers were grown on both sides of a cleaned double-polished sapphire substrate. Then, a tungsten-doped vanadium dioxide thin film absorption layer was deposited on the sample with the vanadium dioxide thin film. Finally, a layer of PMMA was spin-coated on the surface of the absorption layer, and the cured PMMA served as a protective layer.

[0038] Example 1

[0039] The above-described method for preparing vanadium dioxide thin films includes the following steps:

[0040] Step 1: Prepare vanadium ion precursor solution and tungsten-doped precursor solution according to polymer-assisted deposition. The specific method for preparing the vanadium ion-containing precursor solution is as follows: Weigh ammonium metavanadate and polyethyleneimine in a 1:1 molar ratio, add them to deionized water, and stir until the reagents are completely dissolved. Finally, transfer the solution to an ultrafiltration device, apply 0.2 atmospheres of pressure during filtration, and perform magnetic stirring to remove water from the solution. During the preparation process, pressure ultrafiltration needs to be repeated at least three times, adding the same amount of deionized water each time, until the final ultrafiltration is completed. A stabilizing gas, argon or nitrogen, needs to be introduced during pressure ultrafiltration. The purpose of pressure ultrafiltration is to remove residual small molecules in the solution, further improve the stability of the precursor solution, and finally obtain a vanadium ion precursor solution with a concentration of 0.471 mmol / mL.

[0041] Step 2: Clean the Al2O3 substrate. The substrate is ultrasonically cleaned sequentially with acetone, anhydrous ethanol and deionized water, and then dried with nitrogen gas for later use.

[0042] Step 3: The vanadium ion precursor solution prepared in Step 1 is spin-coated onto one side of the cleaned sapphire substrate using a spin-coating method. The spin-coating is carried out at a low speed of 1000 r / min for 10 s, and then at a high speed of 6000 r / min for 40 s.

[0043] Step 4: Install the heat-insulating furnace plug at the gas inlet of the tube furnace, place the substrate coated with the precursor solution in Step 3 on an inverted quartz ceramic boat and place it in the center of the tube furnace, seal it with a flange, place the gas conduit in a beaker filled with water, and sinter under a mixed atmosphere of nitrogen and water vapor. Observe the bubbling in the beaker to check the sealing effect; start the set tube furnace program: heat up to 100℃ and hold for 30 min to remove water from the precursor solution, heat up to 450℃ and hold for 240 min to remove the binder, then heat up to 495℃ and hold for 240 min for nucleation, and after the reaction is completed, allow it to cool naturally to room temperature to obtain the VO2 / Al2O3 sample;

[0044] Step 5: Repeat the above steps to deposit VO2 on the other side of Al2O3 to obtain a VO2 / Al2O3 / VO2 sample;

[0045] Step 6: Spin-coating the tungsten-doped precursor solution prepared in Step 1 onto the sample prepared in Step 5 using the spin-coating method. Spin-coating is performed according to the parameters in Step 3, and Step 4 is repeated to obtain the W-VO2 / VO2 / Al2O3 / VO2 sample.

[0046] Step 7: Spin-coat PMMA solution onto the sample prepared in Step 6, maintain a low speed of 1000 r / min for 10 s, then maintain a high speed of 6000 r / min for 40 s, and place the sample on a 180℃ hot stage to cure for 30 min to obtain PMMA / W-VO2 / VO2 / Al2O3 / VO2 sample.

[0047] The near-infrared transmission spectrum of the vanadium dioxide thin film prepared in this embodiment is shown below. Figure 2 As shown, the blue line represents the near-infrared transmittance curve of the sample before the phase transition (30℃), and the red line represents the near-infrared transmittance curve of the sample after the phase transition (90℃). The specific expression for the infrared modulation depth is as follows:

[0048]

[0049] Where M is the modulation depth of the sample, T1 is the transmittance of the sample before phase transition (30℃), and T2 is the transmittance of the sample after phase transition (90℃).

[0050] The sample exhibits a transmittance of 40.07% before the phase transition and 4.88% after the phase transition at 1550 nm, with a modulation depth of 87.82% at 1550 nm. Similarly, the sample shows a transmittance of 59.06% before the phase transition and 2.74% after the phase transition at 2500 nm, with a modulation depth of 95.37% at 2500 nm.

[0051] Figure 4 The image shows the modulation pattern of a 1550nm continuous laser beam on the sample. At lower laser power, no phase transition occurs. The power is increased by 100mW every 20 seconds and maintained for 20 seconds, and the power waveform is observed to determine if a phase transition occurs. When the laser power reaches 800mW, a significant phase transition occurs. At this point, the power is increased by 50mW every 20 seconds and maintained for 20 seconds. Analysis Figure 4 It can be seen that under a laser power of 700mW, the sample underwent a phase transition after 18.7s, at which point the modulation depth was 26.13%. As the laser power increased further, the phase transition time gradually shortened, and different modulation effects were observed under different laser powers. When the laser power increased to 1000mW, the sample underwent a phase transition after 2.1s, at which point the modulation depth was 48.17%. When the laser power increased to 1100mW, the VO2 in the upper layer of the substrate underwent a phase transition after 0.1s, at which point the modulation depth was 48.88%. After 4.9s, the VO2 in the lower layer of the substrate underwent a phase transition, achieving second-order modulation, at which point the modulation depth reached 75.24%.

[0052] Comparative Example 1

[0053] Prepare VO2 / Al2O3 samples according to the steps in Example 1, repeating only steps 1 to 4.

[0054] The sample exhibits a transmittance of 63.11% before the phase transition and 33.07% after the phase transition at 1550 nm, with a modulation depth of 47.60% at 1550 nm. Similarly, the sample shows a transmittance of 80.56% before the phase transition and 22.05% after the phase transition at 2500 nm, with a modulation depth of 72.63% at 2500 nm.

[0055] Figure 4 The image shows the modulation pattern of a 1550nm continuous laser beam on the sample. At lower laser power, no phase transition occurs. The power is increased by 100mW every 20 seconds and maintained for 20 seconds, and the power waveform is observed to determine if a phase transition occurs. When the laser power reaches 1000mW, the sample undergoes a phase transition after 9.3 seconds, with a modulation depth of 36.83%. When the laser power reaches 1100mW, the sample undergoes a phase transition after 3.4 seconds, with a modulation depth of 45.30%.

[0056] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A multi-level infrared laser modulation structure based on vanadium dioxide thin film, wherein the structure is stacked sequentially from bottom to top as follows: a first vanadium dioxide thin film layer, a sapphire substrate, a second vanadium dioxide thin film layer, a vanadium dioxide thin film layer doped with tungsten, and a PMMA layer; wherein the PMMA layer is a protective layer; the vanadium dioxide thin film layer doped with tungsten is an absorption layer; and the first vanadium dioxide thin film layer and the second vanadium dioxide thin film layer are phase change functional layers.

2. The multi-level infrared laser modulation structure based on vanadium dioxide thin film as described in claim 1, characterized in that, The thicknesses of the first and second vanadium dioxide thin films are 100-200 nm.

3. The multi-level infrared laser modulation structure based on vanadium dioxide thin film as described in claim 1, characterized in that, The PMMA layer has a thickness of 300-500 nm; the sapphire substrate has a thickness of 0.5 mm.

4. The multi-level infrared laser modulation structure based on vanadium dioxide thin film as described in claim 1, characterized in that, The thickness of the vanadium dioxide thin film doped with tungsten is 30 nm.

5. The multi-level infrared laser modulation structure based on vanadium dioxide thin film as described in claim 1, characterized in that, The tungsten doping concentration of the vanadium dioxide thin film layer is 0.3-0.5% atomic concentration.

6. A method for fabricating a multi-level infrared laser modulation structure based on a vanadium dioxide thin film, the method comprising: Step 1: Prepare vanadium-containing precursor solution and tungsten-doped precursor solution; The specific method for preparing the vanadium ion-containing precursor solution is as follows: Weigh ammonium metavanadate and polyethyleneimine in a molar ratio of 1:1, add them to deionized water, and stir until the reagents are completely dissolved; finally, transfer the solution to an ultrafiltration device, apply 0.2 atmospheres of pressure and perform magnetic stirring during filtration to remove water from the solution; during the preparation process, pressure ultrafiltration needs to be repeated at least three times, with the same amount of deionized water added each time, until the last ultrafiltration is completed; a stabilizing gas needs to be introduced during pressure ultrafiltration; the purpose of pressure ultrafiltration is to remove residual small molecules in the solution, further improve the stability of the precursor solution, and finally obtain a vanadium ion precursor solution with a concentration of 0.471 mmol / mL; Step 2: Polish and clean the sapphire substrate on both sides, and then dry it with nitrogen gas; Step 3: Spin-coat one side of the sapphire substrate with a vanadium ion-containing precursor solution and sinter it in a nitrogen and water vapor mixed atmosphere to prepare a vanadium dioxide thin film layer; Step 4: Using the same method as in Step 3, a vanadium dioxide thin film layer is prepared on the other side of the sapphire substrate; Step 5: Spin-coat a tungsten-doped precursor solution onto one side of the vanadium dioxide thin film layer, and sinter it under a nitrogen and water vapor mixed atmosphere to obtain a tungsten-doped vanadium dioxide thin film layer. Step 6: Spin-coat PMMA solution onto the vanadium dioxide thin film layer doped with tungsten, and then cure it.

7. The method for preparing a multi-level infrared laser modulation structure based on a vanadium dioxide thin film as described in claim 6, characterized in that, The substrate is double-polished sapphire with an orientation of (10-10). The cleaning process is as follows: ultrasonic cleaning is performed sequentially with acetone, anhydrous ethanol and deionized water.

8. The method for preparing a multi-level infrared laser modulation structure based on a vanadium dioxide thin film as described in claim 6, characterized in that, The sintering method in step 3 is as follows: First, heat to 100℃ and hold for 30 minutes to remove water from the precursor solution; then heat to 450℃ and hold for 240 minutes to remove colloids; then heat to 495℃ and hold for 240 minutes to nucleate; after the reaction is complete, allow it to cool naturally to room temperature.

9. The method for preparing a multi-level infrared laser modulation structure based on a vanadium dioxide thin film as described in claim 6, characterized in that, The specific parameters for the spin coating method in steps 3 and 6 are as follows: first, rotate at a lower speed of 900-1000 r / min for 10 seconds, and then rotate at a higher speed of 6000-7000 r / min for 40 seconds.

10. The method for preparing a multi-level infrared laser modulation structure based on a vanadium dioxide thin film as described in claim 6, characterized in that, The specific parameters for curing in step 6 are: temperature 180-200℃, time 40-60min.

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