阅读说明：本技术 可调控的近红外超薄宽带完美吸收器及其制备方法 (Adjustable near-infrared ultrathin broadband perfect absorber and preparation method thereof ) 是由 章俞之 郭云峰 柴忻 吴岭南 马佳玉 曹韫真 宋力昕 于 2019-09-10 设计创作，主要内容包括：本发明公开一种可调控的近红外超薄宽带完美吸收器及其制备方法,所述吸收器包括衬底、位于衬底上的背反射层、位于背反射层上的介质层,以及位于介质层上的二氧化钒层；所述吸收器的膜层总厚度小于工作波长的四分之一。本发明的吸收器是超薄的多层薄膜结构,相比于传统的四分之一波长厚度吸收器以及近年提出的超材料吸收器,该吸收器可通过外场控制二氧化钒薄膜的介电函数,从而调控吸收器在近红外波段的吸收带宽及吸收效率,且结构厚度明显降低,避免使用复杂的光刻加工技术,使生产周期显著缩短,生产成本显著下降,便于大规模、批量化制备。(The invention discloses an adjustable near-infrared ultrathin broadband perfect absorber and a preparation method thereof, wherein the absorber comprises a substrate, a back reflecting layer positioned on the substrate, a dielectric layer positioned on the back reflecting layer and a vanadium dioxide layer positioned on the dielectric layer; the total thickness of the films of the absorber is less than one quarter of the operating wavelength. Compared with the traditional quarter-wavelength thickness absorber and the metamaterial absorber which is proposed in recent years, the absorber disclosed by the invention has an ultrathin multilayer film structure, can control the dielectric function of the vanadium dioxide film through an external field, so that the absorption bandwidth and the absorption efficiency of the absorber in a near-infrared band are regulated and controlled, the structure thickness is obviously reduced, the use of a complex photoetching technology is avoided, the production period is obviously shortened, the production cost is obviously reduced, and the large-scale and batch preparation is facilitated.)

1. The adjustable near-infrared ultrathin broadband perfect absorber is characterized by comprising a substrate, a back reflecting layer positioned on the substrate, a dielectric layer positioned on the back reflecting layer and a vanadium dioxide layer positioned on the dielectric layer; the total thickness of the films of the absorber is less than one quarter of the operating wavelength.

2. The near-infrared ultrathin broadband perfect absorber of claim 1, characterized in that the absorber has an average absorption rate at 1.6-2.4 μm of up to 95% and an average absorption rate at 1.2-1.5 μm of 74% without excitation by an external field; under the excitation action of an external field, the absorption intensity distribution wavelength of the absorber is adjusted, the average absorption rate at the position of 1.2-1.5 mu m is more than or equal to 90%, and the average absorption rate at the position of 1.6-2.4 mu m is 78%.

3. The near-infrared ultrathin broadband perfect absorber of claim 1 or 2, characterized in that the dielectric layer is 50-80 nm thick.

4. The near-infrared ultrathin broadband perfect absorber of any one of claims 1 to 3, characterized in that the vanadium dioxide layer is 30 to 50nm thick.

5. The near-infrared ultra-thin broadband perfect absorber of any of claims 1-4, wherein the substrate material comprises at least one of fused silica, sapphire, and single crystal silicon.

6. The near-infrared ultrathin broadband perfect absorber of any one of claims 1 to 5, wherein the back reflecting layer material comprises at least one of noble metal, AZO and ITO, and the thickness of the back reflecting layer is 100 to 500 nm.

7. The near-infrared ultrathin broadband perfect absorber of any one of claims 1-6, wherein the dielectric layer material comprises Al₂O₃、SiO₂At least one of them.

8. The near-infrared ultrathin broadband perfect absorber as claimed in any one of claims 1 to 7, wherein the vanadium dioxide layer is obtained by vacuum evaporation coating, sputtering coating or sol-gel coating.

9. A method for regulating and controlling a near-infrared ultrathin broadband perfect absorber as claimed in any one of claims 1 to 8, characterized by comprising the following steps:

(1) the absorption rate of the absorber is improved by changing the vanadium dioxide layer in an insulating phase through an external field;

(2) the absorption rate and the bandwidth of the absorber are regulated and controlled by changing the vanadium dioxide layer in a metal phase through an external field.

Technical Field

The invention relates to design and optimization of a multilayer absorption structure, in particular to an adjustable near-infrared ultrathin broadband perfect absorber and a preparation method thereof.

Background

Light absorption is a physical process by which light (electromagnetic waves) passes through a material, interacting with the material, and the energy of the electromagnetic radiation is partially converted into other forms of energy. Light is generally arranged from low to high in frequency and can be classified into radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, gamma rays and the like. The absorption performance of the regulating material in near infrared is very important to be applied to the aspects of target identification, thermophotovoltaic cells, energy storage, inductive components, stealth and the like.

The absorption process of light satisfies A ═ 1-R-T, where R is the reflection coefficient and T is the transmission coefficient. The critical coupling condition can be achieved through the design of a multilayer structure, and the high absorption performance of the material can be realized. The F-P resonant cavity structure based on metal-dielectric-metal (MIM) generally requires the thickness of the middle dielectric film to be at least a quarter wavelength, and for infrared and longer wave bands, requires the thickness of the film layer to be increased, and is difficult to prepare. Although the top metal layer can be replaced by a sub-wavelength patterned structure, such a metamaterial or super-surface structure can greatly reduce the thickness of the thin film, more elaborate lithography and other technical means are required, so that the preparation cost is high and the sample size is limited.

Absorbent structures are generally limited by construction parameters, material parameters, and arrangements that, once established, are difficult to alter in their absorbent properties. In the application scenes of modern energy, communication, military and the like, the absorption of materials is required to make timely response and adjustment to variable environments, and adjustable infrared absorption becomes an important research direction. If in the multi-layer absorbent structure, leadAn adjustable optical material is introduced, so that the material can reversibly change the optical properties under the action of an external field (temperature, magnetic field, electric field, stress and the like), and an intelligent adjustable absorption structure can be formed. VO (vacuum vapor volume)₂As a thermotropic phase change material, the transformation from a low-temperature semiconductor monoclinic phase to a high-temperature metal rutile phase occurs at the temperature of about 68 ℃, and meanwhile, the appearance of metal nanoclusters in a phase change intermediate state can be regarded as a natural and disordered metamaterial.

Disclosure of Invention

The invention provides an adjustable near-infrared ultrathin broadband perfect absorber, which is thinner in thickness and wider in absorption range compared with the traditional absorber, and solves the problem that the existing absorber cannot adjust the absorption rate of the absorber.

In a first aspect, the absorber comprises a substrate, a back reflector layer on the substrate, a dielectric layer on the back reflector layer, and a vanadium dioxide layer on the dielectric layer; the thickness of the film layer of the absorber is less than one quarter of the working wavelength.

The film thickness of the absorber is the thickness of all films except the substrate, including the back reflecting layer, the dielectric layer and the vanadium dioxide layer. Preferably, the total thickness of the film layers of the absorber is less than 200-600 nm. Further, the total thickness of the film layers of the absorber is 380-530 nm.

According to the invention, the adjustable and controllable ultrathin multilayer absorption structure is constructed by using the strong interference effect of the absorption film and the phase change characteristic of the vanadium dioxide film through the optimized substrate, so that the adjustable absorption of the near-infrared band ultra-wide band with high efficiency and wide absorption angle is realized, and the performance of the adjustable and controllable ultrathin multilayer absorption structure is completely superior to that of the traditional absorber. Compared with the traditional quarter-wavelength thickness absorber and the metamaterial absorber which is proposed in recent years, the absorber disclosed by the invention has an ultrathin multilayer film structure, can control the dielectric function of the vanadium dioxide film through an external field, so that the absorption bandwidth and the absorption efficiency of the absorber in a near-infrared band are regulated and controlled, the structure thickness is obviously reduced, the use of a complex photoetching technology is avoided, the production period is obviously shortened, the production cost is obviously reduced, and the large-scale and batch preparation is facilitated.

Preferably, under the condition of no excitation of an external field, the average absorption rate of the absorber at the position of 1.6-2.4 μm is up to 95%, and the average absorption rate at the position of 1.2-1.5 μm is 74%; under the excitation action of an external field, the absorption intensity distribution wavelength of the absorber is adjusted, the average absorption rate at the position of 1.2-1.5 mu m is more than or equal to 90%, and the average absorption rate at the position of 1.6-2.4 mu m is 78%.

Preferably, the thickness of the dielectric layer is 50 to 80 nm.

Preferably, the thickness of the vanadium dioxide layer is 30-50 nm.

Preferably, the substrate material comprises at least one of fused silica, sapphire, and single crystal silicon.

Preferably, the material of the back reflecting layer comprises at least one of noble metal, AZO and ITO, and the thickness of the back reflecting layer is more than 100 nm.

Preferably, the dielectric layer material comprises Al₂O₃、SiO₂At least one of them.

Preferably, the vanadium dioxide layer is obtained by vacuum evaporation coating, sputtering coating or sol-gel coating.

Compared with the traditional absorber, the near-infrared ultrathin broadband perfect absorber has the advantages of thinner thickness, wider absorption range and better incident angle insensitivity, and solves the problem that the existing absorber cannot adjust the absorption rate. Therefore, the near-infrared ultrathin broadband perfect absorber completely surpasses the traditional absorber in absorption performance. Because the near-infrared ultrathin broadband perfect absorber structure is an ultrathin multilayer film structure, compared with the traditional broadband absorber and a metamaterial absorber proposed in recent years, the structure is simpler. Due to the ultrathin multilayer film structure, the near-infrared ultrathin broadband perfect absorber can avoid complex photoetching technology, so that the production period is obviously shortened, the production cost is obviously reduced, and large-scale and batch production and preparation are facilitated.

The invention is based on the strong interference effect of the absorption film, thereby constructing the absorber which can realize the ultra-thin perfect absorption even if the thickness is far less than the lambda/4 wavelength, and having the near-perfect absorption performance of the near-infrared ultra-thin broadband with high efficiency, adjustability and angle insensitivity. The near-infrared ultrathin broadband perfect absorber has the advantages of simple structure, no need of complex photoetching technology, low cost and suitability for large-area batch production, thereby greatly reducing the preparation cost of the near-infrared ultrathin broadband perfect absorber. The invention is expected to be widely applied in the aspects of target identification, thermophotovoltaic batteries, energy storage, induction components, stealth and the like, and makes a contribution to the fields of scientific technology, national defense construction and the like in China.

The invention also provides a regulating and controlling method of the adjustable and controllable near-infrared ultrathin broadband perfect absorber, which comprises the following steps:

(1) the absorption rate of the absorber is improved by changing the vanadium dioxide layer in an insulating phase through an external field;

(2) the absorption rate and the bandwidth of the absorber are regulated and controlled by changing the vanadium dioxide layer in a metal phase through an external field.

The invention realizes the regulation and control of the near-infrared band absorption rate of the absorber by changing the dielectric function of the vanadium dioxide film.

The invention also provides a preparation method of the adjustable near-infrared ultrathin broadband perfect absorber, which comprises the following steps:

(1) according to the bandwidth requirement and the absorption rate requirement of the absorber, the thickness of each layer of film is obtained through optimization design, and a film system meeting the requirement is determined;

(2) and sequentially depositing each layer of film on the substrate to obtain the near-infrared ultrathin broadband perfect absorber.

The preparation method of the adjustable near-infrared ultrathin broadband perfect absorber is simple in preparation, low in cost and easy for large-scale production and batch preparation.

Drawings

FIG. 1 is a schematic structural diagram of a near-infrared ultra-thin broadband perfect absorber prepared according to an embodiment of the present invention;

FIG. 2 shows ITO/Al for absorber prepared according to the embodiment of the present invention₂O₃/VO₂An absorption spectrum of the thin film structure;

FIG. 3 is a flow chart of the preparation of a near infrared ultra-thin broadband perfect absorber prepared according to an embodiment of the present invention.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

The present invention will be described in detail with reference to the accompanying drawings.

As shown in fig. 1, a tunable near-infrared ultrathin broadband perfect absorber is composed of a substrate 1, a back reflector 2 on the substrate, a dielectric layer 3 on the back reflector, and a vanadium dioxide layer 4 on the dielectric layer. The near-infrared ultrathin broadband perfect absorber is thinner than the traditional absorber, the thickness of a film layer is less than one fourth of the working wavelength, and the size of a single-layer film is in the nanometer level.

The substrate 1 is not limited to a material, and may be selected from, but not limited to, fused silica, sapphire, and silicon. Fused silica is more preferable.

The material of the back reflector 2 over the substrate may be selected from, and is not limited to, noble metals, ITO, or AZO. ITO is further preferred, and the ITO film has very low absorption in an infrared band and has very high reflection characteristic, so that the absorption efficiency of the multilayer structure can be improved.

The thickness of the back reflection layer is 100nm or more, and more preferably 200 to 500 nm. More preferably 300 to 400 nm. The thickness of the vanadium dioxide layer is more than 100nm, so that incident light can be prevented from entering the back reflection layer, light can be reflected to enter the vanadium dioxide layer, light transmission is avoided, and absorption is greatly increased.

The material of the dielectric layer 3 on the back reflection layer can be selected from and is not limited to Al₂O₃Or SiO₂More preferably, Al₂O₃，Al₂O₃Has good infrared transmittance and environmental stability. The thickness of the dielectric layer is 50-80 nm, preferably 60-80 nm, and more preferably 65-75 nm.

The thickness of the vanadium dioxide layer 4 on the reflected layer is 30 to 50nm, preferably 30 to 40nm, and more preferably 35 to 40 nm. The vanadium dioxide layer can be obtained by a method without limitation of vacuum evaporation coating, sputtering coating or sol-gel coating.

In the whole structure, only the vanadium dioxide layer positioned at the top layer has good infrared absorption characteristics, and the thickness of the vanadium dioxide layer determines the position of an absorption peak, so that the position of the absorption peak can be changed by changing the thickness of the vanadium dioxide layer at the top layer. The invention can be used as a supplement of the existing adjustable near-infrared ultrathin broadband perfect absorber, and has potential application value.

The invention also provides a regulating and controlling method of the adjustable and controllable near-infrared ultrathin broadband perfect absorber, which comprises the following steps:

(1) the absorption rate of the absorber is improved by changing the vanadium dioxide layer in an insulating phase through an external field;

(2) the absorption rate and the bandwidth of the absorber are regulated and controlled by changing the vanadium dioxide layer in a metal phase through an external field.

Such external fields include, but are not limited to, temperature, light, magnetic fields, electric fields, stress, and the like. For example, the phase change of vanadium dioxide can be controlled by changing the temperature field.

The vanadium dioxide has the characteristic of controlling phase change through external field changes such as heat, light or electric field, and has the advantages of adjustable phase change temperature, high phase change speed and large conductivity change before and after phase change, so the vanadium dioxide has a wide application prospect in the field of infrared detection. Among them, vanadium dioxide is a 3d transition metal oxide, has a characteristic of MIT phase transition under external field excitation, and has a great change in dielectric function after transition from an insulating (I) phase to a metallic (M) phase. The absorber adopting vanadium dioxide can achieve control on absorption peak position and absorption rate through external field excitation, and the excitation can be heat, light and electricity, so that the application range of the absorber is wider.

The invention also provides a preparation method of the adjustable near-infrared ultrathin broadband perfect absorber.

Firstly, according to the required bandwidth requirement and the absorption rate requirement of the absorber, the thickness of each layer of thin film is obtained through optimization design, and a film system meeting the requirement is determined. This step can be implemented by existing emulation software.

The high broadband absorption of the adjustable near-infrared ultrathin broadband perfect absorber is designed based on an interference stacking multilayer film absorption theory, the phase difference of main reflected light and partial reflected light of a multilayer film structure is pi through film system design, so that the main reflected light and the partial reflected light generate destructive interference at an air/vanadium dioxide layer interface, high absorption is realized, and the absorber has good angle compatibility due to the thin film thickness.

Then, ITO and Al are deposited on the substrate in sequence₂O₃、VO₂And obtaining the near-infrared ultrathin broadband perfect absorber. The film layers may be deposited, for example, using vacuum deposition. In some embodiments, before the film layer is deposited, the substrate is respectively placed into acetone, ethanol and deionized water for ultrasonic cleaning, and finally the substrate is blown dry by nitrogen. Each ultrasonic treatment time can be 5-25 min, more preferably 5-15 min, and still more preferably 10 min.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

The adjustable near-infrared ultrathin broadband perfect absorber provided by the embodiment of the invention comprises a fused quartz substrate, an ITO (indium tin oxide) layer positioned on the fused quartz substrate, and Al positioned on the ITO layer₂O₃A dielectric layer and Al₂O₃And the vanadium dioxide layer is arranged on the dielectric layer. Among them, the fused silica substrate was purchased from Nantong Zhenhua photoelectricity, Inc. and had a thickness of 0.5 μm.

FIG. 3 shows an adjustable near-infrared ultra-thin broadband provided by an embodiment of the inventionA method of making a perfect absorber comprising the steps of: (1) obtaining the thickness of each layer of thin film through optimization design according to the required bandwidth requirement and the absorption rate requirement of the absorber, and determining a film system meeting the requirement; wherein the thickness of the ITO layer is 350nm, and Al₂O₃The thickness of the dielectric layer is 70nm, and the thickness of the vanadium dioxide layer is 35 nm; (2) putting a fused quartz substrate into acetone for ultrasonic treatment for 10 minutes, then putting the fused quartz substrate into ethanol for ultrasonic treatment for 10 minutes, then cleaning the fused quartz substrate with deionized water for 10 minutes, and finally blowing the substrate with nitrogen; (3) sequentially depositing ITO film and Al₂O₃Thin film and VO₂The film is prepared by adopting a direct current magnetron sputtering mode, wherein the target material is an ITO target, the sputtering power is 120W, the Ar gas flow during sputtering is 100sccm, and the sputtering time is 20 min; al (Al)₂O₃The preparation of the thin film adopts an Atomic Layer Deposition (ALD) method, trimethylaluminum and water are used as precursors, the temperature of a reaction chamber in the deposition process is 175 ℃, and the deposition rate isThe number of cycles is 645; VO (vacuum vapor volume)₂The film deposition adopts a radio frequency magnetron sputtering method, the flow rate of Ar is set to be 100sccm, the pressure of a reaction chamber is set to be 0.5Pa, the radio frequency power is 300W, and O is adopted₂The flow is controlled by a PEM system, the formal sputtering time is 40min, and the near-infrared ultrathin broadband perfect absorber is obtained.

The absorption spectrum of the near-infrared ultrathin broadband perfect absorber sample prepared by the embodiment of the invention is shown in fig. 2, and the more detailed change relationship between the vanadium dioxide dielectric function and the absorber absorption rate is as follows: when the vanadium dioxide is in the insulating phase without the action of an external field (the temperature is at room temperature), the real part epsilon of the dielectric function of the vanadium dioxide₁And imaginary part ε₂When the infrared band is close to the zero point, the average absorption rate of the absorber at the position of 1.6-2.4 mu m reaches 95% (the highest absorption rate reaches 97.6% when no external field exists in figure 2), and the average absorption rate at the position of 1.2-1.5 mu m is only 74%; under the excitation of external field (at 80 deg.C), vanadium dioxide is in metal phase, and in infrared band, the real part epsilon of dielectric function₁Decreasing to negative value, the imaginary part epsilon of the dielectric function₂Increase and follow waveThe length is increased and linearly increased, the absorption intensity of the absorber at the position of 1.6-2.4 mu m is reduced, the average absorption rate is only 78%, and the average absorption rate in the range of 1.2-1.5 mu m is more than 90%.

The control method of the adjustable near-infrared ultrathin broadband perfect absorber provided by the embodiment of the invention is realized by controlling the phase change of vanadium dioxide by changing a temperature field, and specifically comprises the following steps: (1) the absorption rate of the absorber is improved by adjusting the temperature of the temperature field to room temperature to change the vanadium dioxide layer to be in an insulating phase; (2) the absorption rate and the bandwidth of the absorber are regulated and controlled by adjusting the temperature of the temperature field to 80 ℃ and changing the vanadium dioxide layer to be in a metal phase.

When the vanadium dioxide layer is changed from an insulating phase to a metal phase, namely the vanadium dioxide layer has MIT phase transition, the absorption rate of the absorber is changed along with the change of the dielectric function of the vanadium dioxide layer, and the operation of regulating the absorption rate of the absorber under a specific frequency is realized.