CN114231922B

CN114231922B - VO (volatile organic compound) 2 Method for preparing base multilayer film structure and product thereof

Info

Publication number: CN114231922B
Application number: CN202111441667.1A
Authority: CN
Inventors: 金海波; 凌晨; 李静波; 王晓乾; 赵政晶; 李东来
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2022-09-02
Anticipated expiration: 2041-11-30
Also published as: CN114231922A

Abstract

The invention discloses a VO ₂ A preparation method of a base multilayer thin film structure and a product thereof relates to the technical field of spacecraft thermal control. The invention uses magnetron sputtering method, takes monocrystalline silicon piece in (100) direction as substrate, and adopts metal titanium target, metal silver target, metal aluminum target and metal vanadium target to prepare VO ₂ Based on a multilayer film structure. VO prepared by the invention ₂ The multilayer film structure enables the intelligent thermal control radiation device to realize low-temperature low-heat conductivity, high-temperature high-heat conductivity and low solar absorptivity, has good thermal control performance and thermal shock resistance, has the solar absorptivity of 27.5 percent, has the integrated emissivity of 0.26 and 0.91 at room temperature and 100 ℃ within the range of 5-15 mu m, and has the emissivity modulation amplitude of 0.65.

Description

VO (volatile organic compound) 2 Method for preparing base multilayer film structure and product thereof

Technical Field

The invention relates to the technical field of thermal control of spacecrafts, in particular to a VO ₂ Methods for making the base multilayer film structures and products thereof.

Background

With the continuous development of aerospace technology, the microminiaturization of spacecrafts poses challenges to the thermal control technology. An intelligent radio Device (SRD) is an important spacecraft thermal control technology, and has important significance for reducing the volume and load of a spacecraft and adapting to severe and complex orbital space environments. Thermotropic phase change material vanadium dioxide (VO) ₂ ) The material has the advantages of high thermochromic modulation efficiency, high response speed, phase change temperature close to room temperature and adjustability and the like, and becomes the most potential SRD functional material at present.

When the spacecraft executes a space orbit task, the external environment temperature can be changed violently along with the movement of the spacecraft, and the temperature change range can reach-150 ℃. Good control of the temperature inside the spacecraft is required in order to achieve optimum performance of its load system and to extend the service life of the components. In an orbital space environment, thermal radiation is the only way for a spacecraft to transfer heat to an external space environment, and the radiation intensity is mainly concentrated in a middle infrared band with the wavelength range of 5-15 mu m. Therefore, the variable emissivity thermal control device becomes an important component of a spacecraft thermal control system, the emissivity of the variable emissivity thermal control device can be changed along with control signals such as voltage and temperature, low-temperature low-emissivity and high-temperature high-emissivity are realized, and the thermal control efficiency of the thermal management system is greatly improved. At present, the spacecraft has the development trend of microminiature, has the characteristics of high load integration level, high power density and the like, and puts higher requirements on the thermal control technology. However, the existing thermal control device for the spacecraft has the problems of complex structure and preparation process, high energy consumption, high manufacturing and emission cost and the like.

VO based on thermotropic phase change material ₂ The intelligent radiation Device (SRD) of (1) provides a passive thermal management method with a simple structure. The SRD device can adjust emissivity according to the ambient temperature, plays a role in intelligently adjusting and controlling the internal temperature of the spacecraft, and does not need components such as a control circuit, a driver and energy supply and complex structures. VO using thermochromism ₂ VO (volatile organic compound) with material as functional layer for designing intelligent thermal control radiation device ₂ The multi-layer thin film structure realizes low-temperature low thermal conductivity, high-temperature high thermal conductivity and low solar absorptivity, improves intelligent thermal control performance, and has important significance for aerospace vehicles with extremely limited space and energy.

Disclosure of Invention

The invention aims to provide a VO ₂ Based multilayer thin film structure and preparation method of product thereof, VO prepared by the invention solves the problems in the prior art ₂ The multilayer film structure enables the intelligent thermal control radiation device to realize low-temperature low-heat conductivity, high-temperature high-heat conductivity and low solar absorptivity, and has good thermal control performance and thermal shock resistance.

In order to achieve the purpose, the invention provides the following scheme:

the invention provides a VO ₂ The preparation method of the multi-layer thin film structure comprises the steps of preparing the VO by using a magnetron sputtering method and using a monocrystalline silicon wafer in the (100) direction as a substrate and sequentially adopting a metal titanium target, a metal silver target, a metal aluminum target and a metal vanadium target ₂ The multilayer film structure specifically includes:

(1) taking a monocrystalline silicon wafer in the (100) direction as a substrate, and performing radio frequency sputtering deposition on a transition layer Ti film to obtain a Ti film;

(2) depositing a reflecting layer Ag film on the surface of the Ti film by direct current sputtering to obtain a Ti/Ag film;

(3) depositing a light medium layer Al on the surface of the Ti/Ag film by direct current sputtering ₂ O ₃ Film to obtain Ti/Ag/Al ₂ O ₃ A film;

(4) in the presence of Ti/Ag/Al ₂ O ₃ Functional layer VO deposited by direct current reactive sputtering on surface of thin film ₂ Film to obtain Ti/Ag/Al ₂ O ₃ /VO ₂ A film;

(5) for Ti/Ag/Al ₂ O ₃ /VO ₂ Carrying out heat treatment on the film to obtain the VO ₂ Based on a multilayer film structure.

Further, in the step (1), before sputtering and depositing a transition layer Ti thin film, the monocrystalline silicon wafer in the (100) direction is further subjected to pretreatment, specifically including: and (2) ultrasonically cleaning the monocrystalline silicon wafer in the (100) direction by acetone, absolute ethyl alcohol and deionized water in sequence, and then drying by using nitrogen.

Further, the specific operation of the step (1) is as follows: the monocrystalline silicon piece in the (100) direction is used as a substrate, a metal Ti target is used as a target material, the substrate temperature is kept at 100 ℃, and the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa, the argon flow is 49sccm, the working pressure is 1Pa, the sputtering power is 80W, and the sputtering time is 10 min.

Further, the specific operation of the step (2) is as follows: depositing an Ag film on the surface of the Ti film by taking a metal Ag target as a target material, keeping the substrate temperature at 100 ℃, and controlling the vacuum degree of the magnetron sputtering base to be 1 multiplied by 10 ^-4 Pa, the argon flow is 49sccm, the working pressure is 1Pa, the sputtering power is 40W, and the sputtering time is 15 min.

Further, the specific operation of step (3) is: depositing Al on the surface of the Ti/Ag film by taking a metal Al target as a target material ₂ O ₃ The temperature of the film and the substrate is kept at 200 ℃, the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa, argon flow of 49sccm, oxygen flow of 0.6sccm, working pressure of 2Pa, sputtering power of 120W, sputtering time of 4h, stopping sputtering every 30min in the process of reactively sputtering the alumina film, closing a substrate baffle, and continuing sputtering after waiting for 10 min.

Further, the specific operation of step (4) is: using a metal V target as a target material, wherein the Ti/Ag/Al is ₂ O ₃ Surface direct current reactive sputtering deposition VO of film ₂ The temperature of the film and the substrate is kept at 200 ℃, the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^- ⁴ Pa, the flow of argon gas is 49sccm, the flow of oxygen is 0.5sccm, the working pressure is 1Pa, the sputtering power is 80W, and the sputtering time is 10 min.

Further, the specific operation of step (5) is: mixing the Ti/Ag/Al ₂ O ₃ /VO ₂ The film is heat treated in air atmosphere, the pressure is 1kPa, the temperature is raised to 480 ℃ at the speed of 120 ℃/min, and then the temperature is maintained at 480 ℃ for 800 s.

The invention also provides a VO ₂ Preparation method of intelligent thermal control radiation device based on multilayer thin film structure, VO of intelligent thermal control radiation device ₂ The multi-layer thin film structure is prepared according to the preparation method.

The invention discloses the following technical effects:

VO ₂ undergoes metal-insulator transition (MIT) before and after 341K at room temperature, and changes from a low-temperature monoclinic insulating phase (M) ₁ Phase) to a high temperature rutile phase (R phase). VO at low temperature ₂ The infrared band high-transmittance characteristic is presented, and the infrared band strong-reflection characteristic is presented under the high-temperature condition; and for the visible light wave band, the transmittance before and after the phase change is basically unchanged. VO due to its unique infrared thermochromic properties ₂ The intelligent infrared response to the environmental temperature self-adaptation can be realized, and the higher visible light transmittance can be maintained. The invention is based on an asymmetric clothVO is prepared based on the structural principle of a Lily-Perot (F-P) resonant cavity ₂ Base multilayer thin film structure and having VO ₂ An intelligent radiation device based on a multilayer thin film structure. The result shows that the intelligent radiation device can realize the characteristics of low temperature, low emissivity, high temperature, high emissivity, low solar absorptivity and the like. VO prepared by the invention ₂ The intelligent radiation device based on the multilayer film structure has good thermal control performance and thermal shock resistance, the sunlight absorption rate can reach 27.5%, the integral emissivity in the range of 5-15 mu m is 0.26 and 0.91 at room temperature and 100 ℃, respectively, and the emissivity modulation amplitude can reach 0.65.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 shows VO at different temperatures ₂ The SRD multilayer film structure is shown in the figure, (a) is a low-temperature insulating state M ₁ Phase VO ₂ (b) is high-temperature metallic R phase VO ₂ ；

FIG. 2 is a schematic view of an air/media/metal multilayer film structure;

FIG. 3 is a schematic diagram of an optical path of an emissivity testing device;

FIG. 4 is a schematic diagram of an SRD device with or without a dielectric layer, where (a) is Ag/VO ₂ A double-layer film structure, wherein (b) is Ag/Al ₂ O _3/ VO ₂ A three-layer film structure;

FIG. 5 illustrates the effect of a layer with and without a dielectric layer on the infrared absorption of an SRD device;

FIG. 6 is a graph of the effect of different optical media materials on the infrared absorption of an SRD device;

FIG. 7 shows the immobilization of VO ₂ Thickness (50nm), different Al ₂ O ₃ The effect of layer thickness on the infrared absorption rate of the SRD device;

FIG. 8 shows fixed Al ₂ O ₃ Thickness (1500nm), different VO ₂ Layer thicknessInfluence on the infrared absorption rate of the SRD device;

fig. 9 is a schematic diagram of the SRD protective layer film structure, (a) is a single-layer protective film structure, and (b) is a multi-layer protective film structure with n ═ 1;

FIG. 10 shows the calculation results of the solar absorptance of the SRD single-layer structure protective film made of different materials, (a) is a low-temperature visible light band, (b) is a low-temperature near-infrared band, (c) is a high-temperature visible light band, and (d) is a high-temperature near-infrared band;

FIG. 11 shows the results of the calculation of the solar absorptance of the SRD multilayer LH structural protective film, wherein (a) is a low-temperature visible light band, (b) is a low-temperature near-infrared band, (c) is a high-temperature visible light band, and (d) is a high-temperature near-infrared band;

FIG. 12 is a SEM image showing the effect of the presence or absence of a transition layer on the adhesion of an Ag thin film, (a) shows an Ag film without a transition layer, and (b) shows a silver film with a Ti/Ag transition layer;

FIG. 13 shows XRD results of Ag films prepared at different substrate temperatures;

FIG. 14 is SEM pictures of Ag film surfaces and sample objects, (a-e) SEM pictures of Ag film surfaces at different substrate temperatures, and (f) pictures of sample objects deposited at a substrate temperature of 200 ℃;

FIG. 15 shows the relationship between the total reflectance of Ag films at different substrate temperatures and the total reflectance of solar spectrum as a function of the substrate temperature, wherein (a) shows the UV-visible-near-IR reflectance of Ag films at different substrate temperatures, and (b) shows the relationship between the total reflectance of solar spectrum as a function of the substrate temperature;

FIG. 16 shows different sputtering times of Al ₂ O ₃ SEM sectional view of the thin film, wherein (a)3h, (b)4h, (c)5h, and (d) are Al ₂ O ₃ Layer sputtering time versus thickness;

FIG. 17 shows different Al ₂ O ₃ Ag/Al for film sputtering time ₂ O ₃ A solar reflection spectrum and a solar total reflectance, wherein (a) is the solar reflection spectrum and (b) is the solar total reflectance;

FIG. 18 is an SEM image of SRD multilayer film structure samples prepared at different sputtering times, wherein (a)5min, (b) 10min, (c)15min, (d)30 min;

FIG. 19 shows Si/Ag/Al ₂ O ₃ /VO ₂ The result of multilayer film structure XRD;

FIG. 20 shows VO at different sputtering times (5min, 10min, 15min and 30min) ₂ The analysis result of the multilayer film structure performance is shown in the specification, wherein (a) is a solar light reflection spectrum, (b) is solar light absorptivity change, (c) is a variable temperature emissivity spectral line, and (d) is total emissivity modulation comparison;

FIG. 21 shows VO ₂ Infrared emissivity spectral lines of the multilayer film SRD device with the sputtering time of 10min at different temperatures;

FIG. 22 shows the thermal shock test results of the SRD device, (a) is a physical test diagram of the thermal shock test, (b, c) is physical diagrams before and after the thermal shock test of the SRD device, and (d, e) is a surface SEM diagram before and after the thermal shock test of the SRD device;

FIG. 23 shows the change in the reflection spectrum of an SRD device before and after thermal shock;

FIG. 24 is a diagram of an atomic oxygen simulation scenario;

FIG. 25 shows the comparison of solar spectral reflectance of SRD devices before and after the atomic oxygen space environment simulation experiment, wherein (a) is no protective film and (b) is Al ₂ O ₃ A protective film, (c) is TiO ₂ Protective film, (d) is total reflectance contrast;

FIG. 26 shows the emissivity test results of SRD devices with protective layers made of different materials before and after an atomic oxygen space environment simulation experiment, wherein (a) is an emissivity spectral line, and a solid line and a dotted line in the graph are 90 ℃ and 30 ℃ spectral lines respectively; (b) the total emissivity is compared.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. It is intended that the specification and examples be considered as exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

Simulation design principle of SRD device:

VO ₂ the low-temperature high-transmittance high-reflection infrared radiation film has the characteristics of low temperature high transmittance and high temperature high reflection in an infrared band, and the emissivity of the film is just opposite to the thermal control requirement of a spacecraft along with the temperature change. Single layer VO ₂ The film cannot realize the infrared emissivity adjusting function required by the spacecraft thermal control. Therefore, to realize VO ₂ For application in thermal control of spacecraft, a reasonable design of the thin film structure is required. The invention adopts a high-reflection metal film/an infrared light-transmitting dielectric film/VO ₂ The multilayer film structure of the film forms an asymmetric Fabry-Perot resonant cavity (F-P), and the thermal control function of low-temperature low emissivity and high-temperature high emissivity is realized through coherent extinction. VO designed by the invention ₂ A schematic of the multiple layer film structure is shown in fig. 1. The multilayer film structure selects a metal silver film as a reflecting layer to realize sunlight and mid-infrared raysHigh reflection of light. The material of the dielectric layer is selected from Al with higher refractive index ₂ O ₃ (n ═ 1.62), the phase of the lightwave is adjusted. VO (vacuum vapor volume) ₂ As a functional layer, the emissivity change of the SRD device is adjusted.

According to the theory of wave optics, the reflection coefficient r of electromagnetic waves when reflected at the interface of two media _ij Can be expressed as

In the formula N _i And N _j Is the refractive index of optical media i and j.

For a multilayer film structure, an incident wave is first reflected at the surface, the rest enters the film layer, and then is reflected successively in the film system, and a part of the wave is transmitted through a corresponding interface in each reflection. Fig. 2 is a schematic view of an air/media/metal multilayer film structure for a single layer optical media. The film layer structure has 3 kinds of

media

0, 1 and 2 with different optical constants, and the corresponding complex refractive indexes are N respectively ₀ 、N ₁ 、N ₂ The reflection coefficient of each interface is r ₀₁ And r ₁₂ 。

For such a simple single layer film structure, the overall reflectance can be expressed as:

wherein

Is the effective phase thickness of the selected layer. When the number of layers in the entire thin film system is increased, such as the composition of 4 media with different optical constants in fig. 1, the interface 12 and the interface 23 are represented by an equivalent interface 123 using an effective interface processing method. The final overall reflection coefficient can be expressed as:

then for the total film structure, the total reflectivity is:

according to Kirchhoff's law, the emissivity of any object under thermal equilibrium conditions is equal to the absorptivity of the object at the same temperature. When the multilayer film structure total reflectance R is 0, complete absorption can be achieved. It can thus be derived from equation (1.4),

i.e. the vector r ₀₁ And r ₁₂₃ It should satisfy the length equality, opposite direction:

|r ₀₁ | ² -|r ₁₂₃ | ² e ^-4nd/λ ＝0 (1.7)

for the asymmetric F-P cavity shown in FIG. 1, the optical thickness of the middle dielectric layer should satisfy 1/4 times of the set waveband, that is, interference extinction is realized, the reflectivity is lowest, and the absorptivity (emissivity) is highest.

In the design and optimization work of the multilayer film structure, a large number of calculation and optimization solving processes are involved, and the calculation and optimization solving processes are usually completed by the aid of computers. The invention adopts TFcalc software, starts from Maxwell equation, and carries out simulation calculation on the designed film structure in the electromagnetic field environment, thereby completing the performance analysis and optimization work of the film system.

The test characterization methods used in the following examples are as follows:

the phase composition of the sample was characterized by means of X-ray diffraction (XRD). The X-ray diffractometer used was the Bruker-AXS Model D8 ANVANCE, and the test employed a Cu target.

And observing the microscopic morphology of the sample by using a Scanning Electron Microscope (SEM), wherein the model of the used SEM is Hitachi S-4800.

The solar reflectance spectrum of the sample was tested using an ultraviolet-visible-near infrared spectrophotometer (UV-VIS-NIR) in combination with a 110mm aperture integrating sphere accessory. Integrating the reflectivity spectrum data obtained by the test with reference to equation (1), and finally calculating the solar reflectivity (delta R) of the sample _sol ，200～2600nm)：

Wherein R (lambda) is the transmittance at a wavelength of lambda,

the spectrum of solar radiation is when the atmospheric mass is 1.5. The solar absorptance (A) is obtained by using the relation of the formula (2.2),

A＝1-ΔR (2.2)

and (3) representing the phase change performance of the vanadium oxide film by adopting a temperature-variable resistance test method. The temperature-changing resistance testing system is formed by taking an Agilent U3606A universal meter and a Linkam196 temperature-changing table as cores and automatically building. Through software integration, the temperature of the temperature changing table can be controlled by a program, and resistance-temperature data can be synchronously obtained.

Emissivity is a physical quantity that characterizes the radiation power of a material surface, and is related not only to the composition of the material but also to the surface condition of the material, as well as to the temperature of the material and the wavelength under investigation. The emissivity is thus a multivariate function of the above parameters. Therefore, a device for measuring the spectral emissivity of the thin film material is developed on the basis of a Fourier transform infrared spectrometer (FTIR). The optical path of the emissivity measuring device is shown in figure 3.

The FTIR spectrometer has a linear response to incident spectral radiation, and when measuring a sample at a temperature T, the output of the spectrometer at wavelength λ is V (λ, T):

V(λ,T)＝R(λ,T)·L(λ,T)+S(λ,T) (2.3)

in the formula (2.3)R (lambda, T) is a spectrometer spectral response function; s (lambda, T) is a spectrometer background function; l (λ, T) is the spectral radiance of the sample. For black bodies and samples, L _b (lambda) and L _s (λ) can be expressed as:

L _b (λ,T)＝ε _b ·L _b '(λ,T)+L _e (λ,T _e ) (2.4)

L _s (λ,T)＝ε _s ·L _b '(λ,T)+L _e (λ,T _e ) (2.5)

in the formula L _b ' (λ, T) is the true spectral radiance of the blackbody at temperature T; l is _s (λ, T) is the spectral radiance of the sample; l is _e (lambda, T) is the ambient temperature T _e The introduced spectral radiance; epsilon _b And ε _s Emissivity for the reference black body sample and the sample, respectively. The formula (2.4) and the formula (2.5) are substituted into the formula (3) to obtain:

wherein

In the formula (2.6), a background function S (lambda, T) of the FTIR spectrometer exists, in order to eliminate the influence of the background function of the spectrometer on the measurement result, the linear response of the spectrometer to the incident spectral radiation is utilized, R (lambda, T) and S (lambda, T) of the spectrometer are calibrated by adopting a multi-temperature method, namely the spectral radiation brightness L (lambda, T) of a black body is taken as a variable, the slope of the formula (2.3) is R (lambda, T), and the longitudinal intercept is S (lambda, T), namely

V _b (λ,T ₁ )＝R(λ,T ₁ )·L _b (λ,T ₁ )+S(λ,T ₁ ) (2.8)

V _b (λ,T ₂ )＝R(λ,T ₂ )·L _b (λ,T ₂ )+S(λ,T ₂ ) (2.9)

Finishing to obtain:

the emissivity test experiment uses a temperature-changing emissivity test system which IS independently built by taking a Saimer fly IS50 Fourier infrared spectrometer as a core and combining a Harrick emissivity temperature-changing accessory. In order to reduce the infrared noise interference generated by the ambient temperature, the ambient temperature is kept stable at 16 ℃ in the testing process. Through software integration, the temperature of the sample cabin can be controlled by a program, and V (lambda, T) -T temperature data can be synchronously obtained. The test temperature range is: 30-100 ℃ and a measurement interval of 2 ℃. Three groups of data of a sample, a high emissivity blackbody material and an environment are respectively tested, and the data are processed by a Matlab software program to obtain an emissivity-temperature relation curve and a thermal control response temperature. Integrating the spectral data of the emissivity obtained by the test by reference equation (2.11), and finally calculating the total emissivity (epsilon) of the sample at different temperatures _total (T)，5～15μm)：

Example 1

VO is prepared by adopting JGP450 magnetron sputtering deposition system in the embodiment ₂ A multilayer film structure. In an experiment, a monocrystalline silicon wafer in the (100) direction is used as a substrate, and a high-purity metal target titanium target (with the purity of 99.99%), a high-purity metal silver target (with the purity of 99.99%), a high-purity metal aluminum target (with the purity of 99.999%) and a high-purity metal vanadium target (with the purity of 99.9%) are respectively adopted to prepare a multilayer film structure. Ag/Al ₂ O ₃ /VO ₂ The preparation process of the SRD device with the thin film structure comprises the following steps: (1) depositing a transition layer Ti film by radio frequency sputtering; (2) depositing a reflecting layer Ag film by direct current sputtering; (3) depositing optical medium layer Al by direct current reactive sputtering ₂ O ₃ A film; (4) functional layer VO deposited by direct current reactive sputtering ₂ A film; (5) VO (vacuum vapor volume) ₂ And (4) carrying out subsequent heat treatment on the film. The specific experimental process for preparing the film by the magnetron sputtering method comprises the following steps:

firstly, a monocrystalline silicon substrate is respectively processed by acetone, absolute ethyl alcohol and deionized waterAnd after ultrasonic cleaning is carried out for 15min in sequence, the substrate is dried by a nitrogen gun, and the existence of dust and drying traces on the surface of the substrate is observed in a backlight mode. And then fixing the cleaned substrate on a sample table, and placing the sample table in magnetron sputtering equipment. Opening the magnetron sputtering deposition system, and vacuumizing to 1 × 10 ^-4 Pa, introducing argon gas and maintaining proper pressure. And slowly increasing the power of a power supply to the power required by sputtering deposition according to the gradient, and pre-sputtering for 15 min. And introducing gas according to an experimental scheme, adjusting the pressure intensity and raising the temperature of the substrate. And after the sputtering is finished, opening the sputtering chamber after the substrate is cooled to the room temperature, and taking out the film sample. The specific preparation process parameters are as follows:

(1) preparing a transition layer Ti film:

in the experiment, a monocrystalline silicon wafer in the (100) direction is used as a substrate, a high-purity metal Ti target is used as a target material, the substrate temperature is kept at 100 ℃, and the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa. The argon flow is 49sccm, the working pressure is 1Pa, the sputtering power is 80W, and the sputtering time is 10 min.

(2) Preparing a reflecting layer Ag film:

depositing an Ag film on the surface of the Ti film, taking a high-purity metal Ag target as a target material, keeping the substrate temperature at 100 ℃, and controlling the vacuum degree of the magnetron sputtering base to be 1 multiplied by 10 ^-4 Pa. The argon flow is 49sccm, the working pressure is 1Pa, the sputtering power is 40W, and the sputtering time is 15 min.

(3) Optical medium layer Al ₂ O ₃ Preparing a film:

depositing Al on the surface of Ti/Ag film ₂ O ₃ The film takes a high-purity metal Al target as a target material, the substrate temperature is kept at 200 ℃, the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa. The argon flow is 49sccm, the oxygen flow is 0.6sccm, the working pressure is 2Pa, the sputtering power is 120W, and the sputtering time is 4 h. In the process of reactively sputtering an alumina film, in order to prevent the reduction of the deposition rate caused by target poisoning, sputtering is stopped every 30min in the sputtering process, and the sputtering is continued after closing a substrate baffle for 10 min.

(4) Functional layer VO ₂ Preparation of the film:

in the presence of Ti/Ag/Al ₂ O ₃ VO deposited on the surface of the film ₂ The film takes a high-purity metal V target as a target material, the substrate temperature is kept at 200 ℃, the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa. The argon flow is 49sccm, the oxygen flow is 0.5sccm, the working pressure is 1Pa, the sputtering power is 80W, and the sputtering time is 10 min.

(5)VO ₂ And (3) subsequent heat treatment of the film:

preparing VO according to laboratory prophase magnetron sputtering ₂ Working of the film, the film deposited by the process is oxygen-deficient VO with non-stoichiometric ratio ₂ The film is subjected to oxygen supplementation by rapid thermal treatment during subsequent temperature-pressure-control to obtain stoichiometric VO ₂ A film. The heat treatment method comprises the following steps of placing a film sample in the middle position in a chamber of a rapid annealing furnace, adjusting heat treatment process parameters, carrying out heat treatment in an air atmosphere, adjusting the pressure in the furnace to be 1kPa under no special condition, rapidly heating to 480 ℃ at a speed of 120 ℃/min, and keeping the temperature for 800s to obtain a final experimental sample.

Comparative example 1

The difference from example 1 is only that the film prepared in this comparative example has a structure of Ag/VO ₂ The preparation process of the SRD device comprises the following steps: (1) depositing a transition layer Ti film by radio frequency sputtering; (2) depositing a reflecting layer Ag film by direct current sputtering; (3) functional layer VO deposited by direct current reactive sputtering ₂ A film; (4) VO (vacuum vapor volume) ₂ And (4) carrying out subsequent heat treatment on the film. The preparation of each layer was the same as in example 1.

As shown in FIG. 4, this comparative example designed Ag/VO ₂ The film structure is used for researching the function of the F-P resonant cavity by an asymmetric method by comparing the infrared modulation performance of an SRD device with or without a dielectric layer. Table 1 shows simulation parameters related to the multilayer film structure of the SRD device with and without the dielectric layer. The calculation results are shown in FIG. 5, and it can be observed that Ag/Al is used ₂ O ₃ /VO ₂ Multilayer film structure of the film at VO ₂ The change of the absorptivity of the middle infrared band is obvious before and after the conversion of the thin film metal-insulator. When the ambient temperature is less than the phase transition temperature (T < T) _MIT ) Time, VO ₂ In an insulating state M ₁ Phase, multilayer film structure exhibits lowerThe absorptivity (13.7 percent), namely the infrared emissivity is low. When the ambient temperature is higher than the phase transition temperature (T > T) _MIT ) Time, VO ₂ And the transition is carried out to a metallic state R phase, and the whole film structure shows the performance of the asymmetric F-P resonant microcavity. By coherent extinction, a high absorption rate (-88.9%) for a specific wavelength band is achieved. From the simulation calculation result, for the light beam in the middle infrared band, Ag/VO ₂ The structure cannot realize a remarkable infrared emissivity modulation function.

TABLE 1 calculation parameters for thin film structures with and without dielectric layer

Experimental example 1

After the thin film structure is determined to be an F-P resonant cavity, a proper thin film material needs to be searched for as an optical medium layer. By changing the material of the optical medium layer, Al is simulated respectively ₂ O ₃ 、SiO ₂ 、TiO ₂ And HfO ₂ The influence of the optical medium material on the thermal control performance of the SRD device. According to the previous derivation, the thickness of the F-P cavity optical medium layer and the designed specific wave band should satisfy lambda/4 n, namely the optical thickness (qw). The thickness parameters for each material were selected as shown in table 2 for a 10 μm wavelength design thickness. Figure 6 is a graph of the effect of different optical media materials on the infrared absorption of an SRD device. It can be seen that for the F-P cavity, different optical dielectric materials have no significant effect on the infrared absorption performance of the SRD. However, in order to meet the requirement of emissivity modulation, the different optical constants n between various materials can affect the thickness of the optical medium layer. Viewed in entirety with TiO ₂ And HfO ₂ In contrast, Al ₂ O ₃ And SiO ₂ The material has wider infrared absorption band and infrared modulation amplitude when being used as an optical medium layer. However, it should be noted that the selection of the material of the optical medium layer not only considers the infrared modulation performance, but also needs to consider the difficulty of the subsequent experimental preparation and the problems of film falling caused by an excessively thick film. Due to SiO ₂ Too small refractive index (-1.43) resulting in SiO ₂ Is relatively large. If SiO is selected ₂ As an optical medium layer, the optical medium layer has the problems of too low growth speed, too high overall thickness, easy falling off and the like. Therefore, the selection of Al is decided by comprehensive consideration ₂ O ₃ As the optical medium layer of the SRD device.

TABLE 2 optical thickness of dielectric layers of different materials

Experimental example 2

When Al is present ₂ O ₃ After the material is selected as the optical medium layer, the thickness of the optical medium layer needs to be determined. Selecting VO ₂ The thickness of the functional layer (50nm) simulates the thickness Al of 900nm, 1200nm, 1500nm and 1700nm respectively ₂ O ₃ The effect of the film on the infrared absorption capability of the SRD device. FIG. 7 shows the infrared absorption rate with Al of an SRD device ₂ O ₃ Profile of layer thickness variation. As can be seen, Al ₂ O ₃ The thickness of the film determines the position of the absorption peak of the F-P resonant cavity. Al (Al) ₂ O ₃ The thickness of the layer can adjust the propagation phase of light waves in the thin film structure, and coherent extinction is realized on light beams meeting the lambda/4 n optical thickness wave band. It can be seen that when Al is used ₂ O ₃ When the thickness of the layer is increased, the position of the absorption peak of the device in a high temperature state is shifted to a long wave direction, and the absorption intensity is slightly increased. For infrared band beam of 10 μm wavelength, Al ₂ O ₃ When the thickness of the device is 1500nm, the infrared absorption performance of the device is strongest, and the device has wider absorption bandwidth. Therefore, in combination, Al with a thickness of 1500nm is finally selected ₂ O ₃ A film.

Experimental example 3

When the parameters of the optical medium layer are selected, the functional layer VO needs to be determined ₂ Is measured. FIG. 8 shows the infrared absorption rate of an SRD device with VO ₂ And (3) a layer. Selecting Al ₂ O ₃ The thickness of the optical medium layer (1500nm) simulates VO with the thickness of 20nm, 50nm, 80nm, 110nm and 140nm respectively ₂ The effect of the film on the infrared absorption capability of the film structure. It can be observed that VO ₂ The thickness of the film directly determines the infrared absorption of the deviceRadiation performance. At high temperature, VO ₂ The whole infrared absorption capability of the SRD device is strongest when the thickness of the film is 20 nm. Following VO ₂ The infrared absorption capability of the SRD device is obviously reduced due to the increase of the thickness. This is due to metallic R phase VO ₂ Has the characteristics of infrared high reflection and appropriate thickness of R-phase VO ₂ The film can be combined with Ag/Al ₂ O ₃ The effect of F-P resonance absorption is generated. But following VO ₂ The further increase of the film thickness, the coherent extinction effect of the film structure is gradually weakened, the infrared reflectivity of the device is increased, and the infrared absorption effect is obviously reduced. Corresponding to VO at low temperature ₂ The infrared absorption ability of the SRD is weakest when the thickness of the film is 20nm, and the infrared absorption ability is gradually enhanced along with the increase of the thickness. The result shows that the multilayer film structure shows the performances of low-temperature low emissivity and high-temperature high emissivity, and VO ₂ The thinner the film thickness, the better the emissivity modulation performance. However, it is considered that the difficulty of controlling the film thickness increases as the film thickness decreases. At the same time, VO is generated under the action of surface stress ₂ The infrared modulation capability itself will be degraded. Considering comprehensively, VO with the thickness of 50nm is finally selected ₂ A film.

Experimental example 4

The intelligent radiation device for the spacecraft needs to have good infrared absorption modulation capability and also needs to meet the requirements that the device has reliable service performance and lower sunlight absorption rate in an orbit space environment. Therefore, it is required to design a protective layer in a thin film structure while reducing the solar light absorption rate. For this purpose, a low refractive index/high refractive index (LH) multilayer dielectric high reflection film is designed. Respectively using Al ₂ O ₃ As a low refractive index material (-1.63), TiO ₂ As a high index material (-2.38). For a specific wavelength of 550nm, the optical thicknesses of the two materials are respectively: 84.4nm (Al) ₂ O ₃ ) And 57.6nm (TiO) ₂ )。Al ₂ O ₃ Or TiO ₂ As a commonly used atomic oxygen protective material, Al ₂ O ₃ And TiO ₂ Not only can play a role of increasing the reaction, but also can effectively protect the surface material of the spacecraft. The designed multilayer protective film structure is composed of n repeated film periodsIn which a single layer of "L" film (Al) ₂ O ₃ ) And a single layer of "H" film (TiO) ₂ ) Stacking in the manner of "LH" constitutes one membrane cycle. Fig. 9 is a schematic diagram of a designed single-layer protective film structure and a designed multilayer protective film structure, wherein (a) is a comparative single-layer protective film structure, and (b) is a multilayer protective film structure when n is 1.

Table 3 and fig. 10 show the calculated results of the absorption rate of the SRD single-layered structure protective film, where the solid line shows the high temperature state HT and the dotted line shows the low temperature state LT. Here the thicknesses of the two materials are set to two qws: 168.8nm (Al) ₂ O ₃ ) And 115.2nm (TiO) ₂ ). It can be seen that the SRD device has a high solar absorption: 42.3% (low temperature) and 40.4% (high temperature). The single protective layer has limited effect of reducing the solar absorption rate of the SRD device at low temperature, even if TiO is used ₂ The film has higher refractive index, is very suitable to be used as an antireflection film, but the absorption rate reduction effect is still very limited and is only reduced to 39.7 percent. And a single layer of Al ₂ O ₃ Even the solar absorption rate (-45.5%) is improved due to the lower refractive index. VO in R phase under high temperature condition ₂ High refractive index, single layer of Al ₂ O ₃ And TiO ₂ The film cannot play a role in increasing the reflection, and the sunlight absorption rate of the SRD device is improved. Therefore, the single-layer protective layer only can realize the function of track space protection and cannot meet the requirement of reducing the sunlight absorption rate.

TABLE 3 solar absorptivity of SRD single-layer structure protective film

TABLE 4 solar absorptivity of SRD multilayer "LH" structure protective film

Table 4 and fig. 11 show the results of the solar spectrum absorptance of SRD devices simulated by the protective layer of the multilayer "LH" thin film structure. Under low temperature conditions, as shown in table 4, the absorption rate of the SRD device in the solar band is significantly reduced as the number n of periods of the multilayer protective film is increased. This is due to the fact that the "LH" multilayer protective film designed for 550nm band beams produces up-and-down modulation in the wavelength range of 500nm to 625 nm. The adverse effect becomes more remarkable as the number n of cycles increases. However, for the SRD device under the high-temperature condition, when the film period is 1-4, the solar spectrum absorption of the SRD is improved along with the increase of the period number. This is because the "LH" structured film enhances absorption in the near infrared band of the SRD device, as shown in fig. 11 (d). In the visible band, the LH structural film produces similar synergistic effect to that of SRD devices under high temperature condition.

The protective layer film added on the surface of the SRD device can change the propagation phase of an incident beam and influence the overall performance of the device. Therefore, the influence of protective layers with different structures on the infrared radiation performance of the SRD device is simulated. The single-layer structure protective film has only dozens of nanometers of thickness, and has small influence on light beams in the middle infrared band. For the multilayer structure protective film, when the film period n is 1-6, the absorption band can be widened by properly increasing the film period number, and the infrared absorption effect is enhanced. However, when the period n reaches 8, the reflectivity thereof starts to increase and the coherent extinction effect is weakened.

Experimental example 5 preparation of optical reflective layer Ag film

Ag is widely used in optical film design due to its high reflectance properties in the visible and infrared wavelength ranges. As a metal reflective layer for the F-P resonator in SRD devices, Ag films need to maintain extremely high reflectivity after subsequent deposition and thermal processing steps. However, the Ag film has poor adhesion to the substrate Si surface, and is very easy to fall off in subsequent experiments, which seriously affects the overall thermal control performance of the film device. FIG. 12 shows the effect of the presence or absence of a transition layer on the adhesion of Ag films. It can be seen that the Ag film is very easy to fall off on the Si substrate surface. It is therefore contemplated to pre-deposit a transition layer between the substrate and the metal film to improve the bonding strength. The film adhesion is mainly generated by the actions of chemical bonds, van der waals force, diffusion adhesion, mechanical locking, electrostatic adsorption and the like. The interface between the Ag film prepared based on magnetron sputtering and the substrate is a diffusion-like interface, and the adhesion force mainly comes from diffusion adhesion and mechanical locking, because Ag particles with certain energy enter the substrate during sputtering to generate. Because the bonding force between Ag and Si is smaller than the bonding force inside the silicon wafer, Ag particles diffusing into the silicon wafer still exist in the form of atoms, which can cause the Ag film to easily fall off from the silicon wafer. The bonding force between Ti atoms and a silicon wafer is large, the Ti atoms and the silicon wafer are easy to oxidize to form chemical bonds with the surface of Si, meanwhile, Ti and Ag are well diffused and combined, and the adhesive force between the Ag film and the substrate is enhanced. Therefore, it was decided in the experiment to sputter a transition layer Ti film in advance and then sputter a metal Ag film. FIG. 12(b) shows a metallic Ag film of pre-sputtered transition layer Ti, which is strongly adhered to the surface of single crystal Si.

The film adhesion was measured by a peel test using a Scotch 3M tape applied to the surface of the film and observed whether the film remained on the substrate or peeled from the substrate after peeling, from which the magnitude of adhesion was inferred. Experiments show that the samples plated with the transition layer in advance begin to peel off after nearly 20 experiments. The result shows that the adhesion between the Ag film and the substrate can be effectively enhanced by plating the transition layer Ti film with the thickness of 10-30nm on the single crystal Si substrate in advance.

The substrate temperature has a significant effect on the quality of the deposited Ag film. The Ag film is easy to agglomerate when being heated, so that the overall thermal control performance of the device can be influenced. By properly raising the substrate temperature, the crystallinity of the film is improved, and the thermal stability of the Ag film can be improved. Fig. 13 is XRD results of Ag thin film samples deposited at different substrate temperatures. The diffraction peak positions are basically the same under different substrate temperatures, and diffraction peaks exist at 38.1 degrees, 44.3 degrees, 64.4 degrees and 77.4 degrees and respectively correspond to the (111), (200), (220) and (311) crystal planes of Ag (PDF card 4-0783). Wherein the sample at room temperature, 100 ℃ has a diffraction peak at 32.9 ℃ which is analyzed as the extinction peak of the substrate silicon wafer (200). The diffraction peak intensity is gradually enhanced along with the increase of the substrate temperature, which shows that the crystallinity of the film is improved.

As shown in fig. 14, the particles on the surface of the sample deposited on the substrate at room temperature exhibit a loose and porous orange peel texture. As the temperature of the substrate rises to 100 ℃, the crystal grains grow, the holes gradually disappear, and the film structure is compact. The temperature of the substrate is increased, Ag atoms in the film obtain energy to migrate, crystal grains are promoted to grow, cavities among the crystal grains are reduced, and the compactness of the film is obviously improved. However, as the substrate temperature further rises, the Ag film surface particles agglomerate to precipitate and form metal globules dispersed on the film surface. When the substrate temperature reached 400 ℃, cracks appeared on the surface of the film. Unlike the metallic Ag film deposited at room temperature, when the temperature exceeds 100 ℃, the surface of the deposited Ag film becomes white, probably due to the scattering effect of Ag particles on the surface of the film. Fig. 15 shows the solar reflectance of the Ag film prepared under different substrate temperature conditions, and it can be seen that the solar spectral reflectance of the prepared film is the highest, which can reach-99%, when the substrate temperature is 100 ℃.

Experimental example 6 optical medium layer Al ₂ O ₃ Preparation of films

Al ₂ O ₃ The film has good physical and chemical properties, high mechanical strength, stable chemical properties, high wear resistance, good insulation property and good optical characteristics, so the film is widely applied to the field of optical films. The absorption effect in the F-P cavity structure is related to the phase delay caused by multiple round trips of the electromagnetic wave inside the cavity. Experimental study of various Al ₂ O ₃ The effect of film thickness on the performance of the thermal control device. FIG. 16 shows different Al ₂ O ₃ And (3) a cross-section SEM topography of the multilayer film structure device with the film thickness. The thickness of the multilayer film was measured by SEM for 3h, 4h and 5h of Al ₂ O ₃ The film thicknesses were-1.02 μm, -1.46 μm, and-1.72 μm, respectively. FIG. 17(a) shows different thicknesses of Al ₂ O ₃ The solar spectrum reflectivity curve of (1) shows that with Al ₂ O ₃ Increase in thickness, Ag/Al ₂ O ₃ The sunlight reflection performance of the multilayer film structure is gradually weakened, and particularly the reflection performance of a visible light wave band is obviously weakened. As shown in FIG. 17(b), Al of different thicknesses ₂ O ₃ The solar reflectance of the multilayer film structure is respectively as follows: 98.5% (3h), 95.3%, (4h) And 92.7% (5 h). According to the simulation results of Experimental example 2, Al with a thickness of 1500nm should be selected ₂ O ₃ A film.

Experimental example 7Si/Ag/Al ₂ O ₃ /VO ₂ Multilayer film and VO ₂ Effect of thickness on its Properties

According to the research work before the subject group, a direct current reactive sputtering method is adopted to combine with a rapid heat treatment process to form Si/Ag/Al ₂ O ₃ Preparation of VO on the surface of multilayer film ₂ Thin film, different VOs were studied experimentally ₂ The effect of film thickness on the performance of the thermal device, VO in FIG. 18 ₂ And (4) a cross-sectional SEM topography of the multilayer film structure device. VO with sputtering time of 5min, 10min, 15min, 30min ₂ The film thicknesses are respectively 27nm, 59nm, 73nm and 130 nm. The sputtering rate was consistent with the results of previous experimental studies on the subject group.

FIG. 19 shows Si/Ag/Al ₂ O ₃ /VO ₂ XRD test data for multilayer film structures. An insulating state M appears at the position of 28 DEG ₁ Phase VO ₂ (011) The diffraction peaks in the directions and those of Ag at (111) and (200) at-38.2 ℃ and-44.4 ℃ illustrate VO ₂ And the Ag layer is a crystalline film. However, no Al is observed in the XRD spectrum ₂ O ₃ The diffraction peak of (1) is only an obvious bulge existing between 15 and 30 degrees, and Al can be considered to be ₂ O ₃ The film did not crystallize.

FIG. 20(a) shows VO having different thicknesses ₂ The solar spectrum reflectivity curve of the multilayer film structure can be seen along with VO ₂ The solar reflection performance of the device gradually weakens due to the increased thickness of the VO ₂ Has stronger sunlight absorption capacity. As shown in FIG. 20(b), VO of different thicknesses ₂ The solar absorptivity of the multilayer film structure is respectively as follows: 19.1% (5min), 27.5% (10min), 42.9% (15min) and 46.3% (30 min). FIG. 20(c, d) shows VO of different thicknesses ₂ Influence on the modulation of the variable temperature emissivity spectral line and the emissivity of the SRD device. It can be seen that VO ₂ When the thickness is less than 50nm, the emissivity modulation amplitude delta epsilon of the SRD is along with VO ₂ Is increased by increasing the thickness of (a). Increase VO properly ₂ Can be made thickTo improve the absorption of the light beam in the F-P cavity. VO (vacuum vapor volume) ₂ When the thickness is more than 50nm, Delta epsilon is along with VO ₂ Increases and decreases in thickness. Metallic R phase VO under high temperature condition ₂ The infrared high-reflection type F-P cavity has the characteristic of infrared high reflection, the coherent extinction effect of the F-P cavity is weakened, and the absorption rate is reduced. When VO is present ₂ When the thickness reaches 59nm, the maximum value of Delta epsilon reaches about-0.65.

FIG. 21 shows VO ₂ The infrared emissivity line of the multilayer film structure sputtered for 10min as a function of temperature corresponds to the SEM image in fig. 18 (b) and the emissivity data for the sputtered sample in fig. 20 (c). It can be observed that the emissivity of the SRD device increases rapidly in the 60-70 c range, and does not change substantially after temperatures above 75 c. The high-temperature emissivity of the film reaches 0.91 (the emissivity of a reference blackbody is not lower than 0.9), the low-temperature emissivity is 0.26, the emissivity modulation reaches 0.65, and the film shows good thermal control performance.

Space service performance verification of SRD device

(1) Space thermal environment simulation experiment

The spacecraft repeatedly enters and exits the earth shadow during the operation of the orbit space environment, and the environment temperature is changed alternately. The temperature variation range has great difference along with the difference of the height of the track, the season and the heat insulation measure, and generally changes alternately in the range of-150 to 150 ℃. The long-term thermal shock action can generate thermal stress in the structure of the thermal control device of the spacecraft, so that the material is fatigued. For a multilayer film structure applied to a device, the thermal stress value increases with the use temperature and the temperature difference value due to the linear expansion coefficient difference between the thin films. When the thermal stress is at its maximum, the device may develop microcracks. Therefore, the ability of the sample to resist cyclic thermal shock needs to be observed.

FIG. 22(a) is a set-up for cyclic thermal shock experiments: a heating platform and a liquid nitrogen heat preservation tank. In the experiment, the alloy prepared in example 1 has Ag/Al ₂ O ₃ /VO ₂ And (3) putting the SRD device with the thin film structure into liquid nitrogen, rapidly cooling to-196 ℃ and keeping the temperature for 30s, taking out a sample, rapidly putting the sample on a heating table heated to 150 ℃, and rapidly heating. Fig. 22(b, c) shows the sample after 20 thermal shock cycles, and no significant change was observed on the surface of the sample by naked eye. FIG. 22And (d, e) SEM images of the surfaces of the SRD devices before and after the thermal shock experiment, and the surface of the film can be observed to generate a plurality of micro cracks after the sample is subjected to thermal shock treatment. This is due to thermal stress generated by the films of each layer during rapid temperature changes. Fig. 23 is solar spectrum reflectance spectra of the SRD device before and after the thermal shock experiment, and it can be observed that there is no significant change in the solar spectrum reflectance properties of the SRD device before and after the thermal shock experiment. The result shows that the SRD device has no shedding phenomenon through a thermal shock experiment, basically has no influence on the performance of the device, and has good thermal shock resistance.

(2) Space atomic oxygen environment simulation experiment

In the Low Earth Orbit (LEO) with the height of 180-650 km, the probability of the oxygen atoms to react with other particles is extremely low due to the high vacuum state, so that the spacecraft can maintain the atomic oxygen with higher concentration. Atomic oxygen content as high as 80% is the main component of LEO ambient gas. Molecular oxygen (O) ₂ ) Two independent oxygen atoms (O) are formed under solar ultraviolet irradiation conditions:

atomic oxygen is one of the most reactive gas particles, and since spacecraft often fly at 8km/s in an atomic oxygen environment, the particles bombard the spacecraft surface at high speed. This can cause severe erosion effects on the thermal control material on the surface of the spacecraft. For a spacecraft which works on a low orbit for a long time, due to the fact that the spacecraft is close to the atmosphere of the earth and the atomic oxygen concentration of the space is high, special attention needs to be paid to the service capacity of a surface thermal control material in an atomic oxygen environment. VO (vacuum vapor volume) ₂ The vanadium ion is +4 valence and is easily oxidized into +5 valence ion to form V ₂ O ₅ 。V ₂ O ₅ The absence of thermochromic properties can lead to device failure. Thus, the atomic oxygen pair VO was studied ₂ The stability of atomic oxygen resistance of smart-based radiating devices is critical to their application in aerospace thermal control devices. In addition, atomic oxygen also has a great influence on the solar light absorption rate of the entire device. Therefore, the method is combined with the Chinese space technology research instituteExperiments for simulating the atomic oxygen environment on the ground are carried out. Atomic oxygen simulation experiments were performed according to the GJB 2502.9-2015 Standard, part 9 of the spacecraft thermal control coating test method: atomic oxygen experiments. Atomic oxygen energy of 5eV + -0.5 eV, atomic oxygen flux of 5.0 × 10 ¹⁵ atom/cm ² Total dose of s-atomic oxygen: 3.6-3.9X 10 ²¹ atom/cm ² . FIG. 24 is a diagram of atomic oxygen environment simulation.

FIG. 25(a) is a comparison of solar spectrum reflectivity of an SRD device without a protective layer before and after an atomic oxygen space environment simulation experiment, and it can be seen that in a space atomic oxygen simulation environment, the intelligent bolometric control device without a protective film (i.e., the SRD device with Ag/Al prepared in example 1) is provided ₂ O ₃ /VO ₂ SRD device with thin film structure) from 0.705 to 0.595, the results show that atomic oxygen has strong damage capability to the overall reflective performance of the device. As shown in FIG. 25(b, c), the alloy prepared in example 1 has Ag/Al ₂ O ₃ /VO ₂ The surface of the film structure is respectively prepared with Al ₂ O ₃ Protective film and TiO ₂ The solar reflectance of the sample of the protective film before atomic oxygen irradiation was 0.74 and 0.78, respectively, and the reflectance after irradiation was 0.67 and 0.72, respectively. The results show that by preparing a protective material with a suitable thickness on the surface of the device, both the enhancement effect and the device protection can be achieved, as shown in fig. 25 (d).

FIG. 26 is a comparison of the emissivity of an SRD device with and without a protective film before and after an atomic oxygen space simulation experiment. It can be seen that the SRD device without protection treatment has emissivity of 0.51 and 0.59 at room temperature and 90 ℃ in the range of 5-15 μm after atomic oxygen experiment, and almost completely loses the infrared emissivity modulation performance. The deposition protective layer plays a good role in protecting the SRD device from atomic oxygen. Wherein the TiO is ₂ The film has better protective effect on SRD devices than Al ₂ O ₃ . After atomic oxygen simulation experiment, the alloy has TiO ₂ The SRD device of the protective film has emissivity modulation of 0.36 in the range of 5-15 μm and has Al ₂ O ₃ The SRD device of the guard film becomes-0.17.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims

1. VO (volatile organic compound) ₂ The preparation method of the multi-layer thin film structure is characterized in that a magnetron sputtering method is utilized, a monocrystalline silicon wafer in the (100) direction is taken as a substrate, and a metal titanium target, a metal silver target, a metal aluminum target and a metal vanadium target are sequentially adopted to prepare the VO ₂ The multilayer film structure specifically includes:

(5) for Ti/Ag/Al ₂ O ₃ /VO ₂ Carrying out heat treatment on the film to obtain the VO ₂ A base multilayer thin film structure;

the specific operation of the step (1) is as follows: the monocrystalline silicon piece in the (100) direction is used as a substrate, a metal Ti target is used as a target material, the substrate temperature is kept at 100 ℃, the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa, argon flow of 49sccm, working pressure of 1Pa, sputtering power of 80W and sputtering time of 10 min;

the specific operation of the step (2) is as follows: depositing an Ag film on the surface of the Ti film by taking a metal Ag target as a target material, keeping the substrate temperature at 100 ℃, and controlling the vacuum degree of the magnetron sputtering base to be 1 multiplied by 10 ^-4 Pa, argon flow of 49sccm, working pressure1Pa, sputtering power of 40W and sputtering time of 15 min;

the specific operation of the step (3) is as follows: depositing Al on the surface of the Ti/Ag film by taking a metal Al target as a target material ₂ O ₃ The temperature of the film and the substrate is kept at 200 ℃, the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa, argon flow of 49sccm, oxygen flow of 0.6sccm, working pressure of 2Pa, sputtering power of 120W, sputtering time of 4h, stopping sputtering every 30min in the process of reactively sputtering the alumina film, closing a substrate baffle, and continuing sputtering after waiting for 10 min;

the specific operation of the step (4) is as follows: using a metal V target as a target material, wherein the Ti/Ag/Al is ₂ O ₃ Surface direct current reactive sputtering deposition VO of film ₂ The temperature of the film and the substrate is kept at 200 ℃, the background vacuum degree of magnetron sputtering is 1 multiplied by 10 ^-4 Pa, the flow of argon gas is 49sccm, the flow of oxygen is 0.5sccm, the working pressure is 1Pa, the sputtering power is 80W, and the sputtering time is 10 min.

2. The preparation method according to claim 1, wherein in the step (1), the monocrystalline silicon wafer in the (100) direction is further subjected to pretreatment before sputtering deposition of the transition layer Ti film, and specifically comprises the following steps: and (3) ultrasonically cleaning the monocrystalline silicon wafer in the (100) direction by acetone, absolute ethyl alcohol and deionized water in sequence, and then drying by using nitrogen.

3. The preparation method according to claim 1, wherein the specific operation of step (5) is: mixing the Ti/Ag/Al ₂ O ₃ /VO ₂ The film is heat treated in air atmosphere, the pressure is 1kPa, the temperature is raised to 480 ℃ at the speed of 120 ℃/min, and then the temperature is maintained at 480 ℃ for 800 s.

4. Has VO ₂ The preparation method of the intelligent thermal control radiation device based on the multilayer thin film structure is characterized in that VO of the intelligent thermal control radiation device ₂ A multi-layered thin film structure prepared according to the preparation method of any one of claims 1 to 3.