CN105022106A - Absorber of ultra wide band of visible and near-infrared band and preparation method thereof - Google Patents

Abstract

The invention discloses an ultra-broadband absorber in the visible-near-infrared band and a preparation method thereof, comprising: the ultra-broadband absorber in the visible-near-infrared band is composed of a substrate and five layers of optical films, the bottom film is a metal absorbing layer, Above the metal absorption layer is a germanium layer, and above the germanium layer are the remaining three layers, and the refractive index of the material decreases gradually from bottom to top. Based on the incident blocking effect of the metal absorption layer combined with the wide-band anti-reflection film layer of the germanium layer, the invention constructs a wide-band non-transmission anti-reflection structure, and realizes high-efficiency, angle-insensitive ultra-broadband absorption in the visible-near-infrared band , completely surpassing the traditional absorber in performance. The absorber of the present invention is a compact multi-layer thin film structure. Compared with the traditional broadband absorber and the artificial electromagnetic absorber proposed in recent years, the structure is simpler, the complex nano-processing technology is avoided, and the production cost is significantly reduced. The cycle is significantly shortened, which is convenient for large-scale and batch production.

Description

An ultra-broadband absorber in the visible-near-infrared band and its preparation method

technical field

The invention belongs to the fields of stray light elimination, space detection, imaging, light-to-heat conversion, electromagnetic absorption, etc., and specifically relates to an ultra-broadband absorber in the visible-near-infrared band.

Background technique

Since the visible-infrared broadband absorber can play an important role in many different new fields, the visible-infrared broadband absorber has been extensively studied in recent years, so that more and more broadband absorbers have been prepared. In recent years, researchers have proposed various near-infrared absorbers for electromagnetic waves with artificial electromagnetic structures. Among them, Chen et al. used the method of droplet evaporation to form randomly arranged gold nanorods on a metal substrate coated with a dielectric layer to achieve high absorption in the near-infrared 900nm-1600nm band (Near-infrared broadband absorber with film-coupled multilayernanorods, Optics Lett.38,2247-2249(2013)); Zhou et al. used the characteristics of lateral deposition to prepare a multi-layer alternating dielectric/metal cone structure to achieve higher absorption in the near-infrared broadband (Experiment and Theory of the Broadband Absorption by a Tapered Hyperbolic Metamaterial Array, ACS Photonics 1,618-624(2014)); Ji et al proposed a structure in which metal particles and silicon oxide films are alternately stacked on the surface of a silver mirror, so as to achieve an average of more than 96% in the 300nm-1100nm band High absorption (Plasmonic broadband absorber by stacking multiple metallic nanoparticle layers, Appl. Phys. Lett. 106, 161107 (2015)).

However, the preparation process of the above method is relatively complicated, takes a long time, and the preparation cost is high, which is not conducive to large-scale quantitative production.

The current relevant literature reports mainly include:

The Chinese patent document with the application number 201510163240.8 discloses an ultra-broadband absorber based on cascaded metamaterials. The absorber consists of 9 dielectric layers and 9 metal layers. The first to third dielectric layers and metal layers are diameters For the same cylinder, the 4th to 6th dielectric layers and metal layers are cylinders with the same diameter, and the 7th to 9th dielectric layers and metal layers are cylinders with the same diameter.

The Chinese patent document with the application number 201410020841.9 discloses a structure based on absorbing films in the visible to near-infrared bands, which uses vapor deposition and liquid deposition to sequentially grow a metal thin film layer and a dielectric thin film layer on any substrate, wherein the metal thin film layer The thickness is 80nm-1μm, the thickness of the dielectric film layer is 1nm-200nm, the average height of the equivalent film layer in the metal particle disorder distribution layer is 5nm-100nm, the average particle size is 10nm-200nm, and the surface coverage of metal particles is 3%-90 %. The structure is relatively simple, but its absorption rate is not good.

The Chinese patent document with application number 201110410712.7 discloses a solar selective absorption coating, which consists of a double-layer or three-layer structure: the first layer is a polished stainless steel substrate, and the second layer is Cu1.5Mn1.5O4 Composite oxide absorption layer, the third layer is composed of TiO2 thin film anti-reflection layer, arranged from bottom to top. The absorptivity of the coating is lower than 0.9, and the preparation process is complicated.

Contents of the invention

The invention provides an ultra-broadband absorber in the visible-near-infrared band. The absorber can cover a wider absorption band, has better absorption performance, and has better incident angle insensitivity.

The invention also provides a method for preparing an ultra-broadband absorber in the visible-near-infrared band, which is convenient for preparation, low in cost, and convenient for large-scale and batch production.

An ultra-broadband absorber in the visible-near-infrared band, including a base, on which a metal absorption layer, a germanium layer, and three layers of wide-band anti-reflection coatings are sequentially arranged; the three-layer wide-band anti-reflection coatings are respectively It includes a bottom layer, a middle layer and an outermost layer sequentially arranged on the germanium layer, and the refractive indexes of the bottom layer, the middle layer and the outermost layer gradually decrease.

Below is the preferred scheme based on the above-mentioned scheme:

The substrate material is not limited, and preferably, the substrate can be selected from glass materials such as K9, fused silica, float glass, or semiconductor materials such as silicon and gallium arsenide. More preferably, it is a silicon wafer.

Preferably, the metal absorption layer can be selected from chromium, titanium, iridium, tungsten, nickel and alloys of the above materials; as a further preference, the metal absorption layer can be selected from chromium. The thickness of the metal absorption layer should be greater than 100 nm; more preferably 100-500 nm; and more preferably 150-300 nm.

Preferably, the germanium layer is 10nm-40nm;

Preferably, the refractive index of the three-layer broadband anti-reflection film layer gradually decreases from bottom to top, and the bottom film material close to the germanium layer is selected from silicon, with a thickness of 10nm-40nm, and a further preferred thickness of 15nm-35nm; the middle layer The film material can be selected from titanium dioxide, hafnium oxide, tantalum oxide, silicon nitride and other high-refractive index dielectric materials, with a thickness of 30nm-80nm, and a further preferred thickness of 35nm-60nm; the outermost film material can be selected from magnesium fluoride, Low refractive index dielectric materials such as silicon dioxide and yttrium fluoride have a thickness of 70nm-130nm, and a further preferred thickness is 80nm-120m. The three-layer broadband anti-reflection film layer of the present invention is preferably silicon, titanium dioxide, and magnesium fluoride from bottom to top.

The present invention also provides a preparation method of an ultra-broadband absorber in the visible-near-infrared band, comprising the following steps:

(1) According to the required absorber bandwidth requirements and absorption rate requirements, by optimizing the thickness of each layer of film, design a film system that meets the requirements; this step can use existing software to achieve optimization operations;

(2) Put the substrate in acetone solution for ultrasonication, then wash the substrate with ethanol; then put the substrate in ethanol solution for ultrasonication, then wash the substrate with deionized water; finally put the substrate in deionized water for ultrasonication, and then wash it with deionized water Water washes the substrate again;

(3) Each film layer is sequentially deposited by vacuum coating to obtain an ultra-broadband absorber in the visible-near infrared band.

As a preference, in step (2), the time for each ultrasound is generally 5-30 minutes; more preferably 5-10 minutes.

Compared with the traditional absorber, the visible-near-infrared ultra-broadband absorber of the present invention can cover a wider absorption band, have better absorption performance, and have better incident angle insensitivity. Therefore, the ultra-wide band absorption performance of the visible-near-infrared band of the present invention completely surpasses the traditional absorber. Since the structure of the ultra-broadband absorber in the visible-near-infrared band of the present invention is a compact multi-layer film structure, the structure is simpler than the traditional broadband absorber and the artificial electromagnetic absorber proposed in recent years. Just because of its compact multi-layer film structure, the ultra-broadband absorber in the visible-near-infrared band of the present invention avoids complex nano-processing technologies, such as electron beam processing technology, focused ion beam etching technology, reactive ion etching technology, Photolithography technology, etc., so that the production cost is significantly reduced, and the production cycle is significantly shortened, thereby facilitating large-scale and batch production.

The present invention is based on the incident blocking effect of the metal absorption layer combined with the wide-band anti-reflection film layer of the germanium layer, thereby constructing a wide-band non-transmission anti-reflection structure, thereby realizing a high-efficiency, angle-insensitive visible-near-infrared band ultra- broadband absorption. The visible-near-infrared band ultra-broadband absorber of the present invention has simple structure, convenient preparation, low cost, and is suitable for large-area batch production, thereby greatly reducing the preparation cost of the visible-near-infrared band ultra-broadband absorber. Therefore, this invention is expected to be widely used in light-to-heat conversion, electromagnetic absorption, detection, and imaging, and contribute to the fields of national economy, social development, science and technology, and national defense construction in our country.

Description of drawings

Fig. 1 is the structural representation of the ultra-broadband absorber of visible-near-infrared band of the present invention;

Fig. 2 is the preparation flowchart of the ultra-broadband absorber of visible-near infrared band of the present invention;

Fig. 3 is the analysis diagram of the ultra-broadband absorption mechanism of the ultra-broadband absorber in the visible-near-infrared band of the present invention;

Figure 4 is the absorption spectrum diagram of samples with different absorption bandwidth requirements and absorptivity requirements:

Fig. 4 (a) is the absorption spectrum of the absorber sample prepared in embodiment 1, 400nm-1200nm band, the average absorption rate is more than 98.75%;

Fig. 4 (b) is the absorption spectrum of the absorber sample prepared in embodiment 2, 400nm-2000nm band, the average absorption rate is more than 97.75%;

Fig. 4 (c) is the absorption spectrum of the absorber sample prepared in embodiment 3, 400nm-1200nm band, the average absorption rate is more than 99%;

Fig. 4 (d) is the absorption spectrum of the absorber sample prepared in embodiment 4, 400nm-2000nm band, the average absorption rate is more than 96.2%;

Fig. 4 (e) is the absorption spectrum of the absorber sample prepared in embodiment 5, 400nm-1200nm band, average absorption rate is more than 98.8%;

Fig. 4(f) is the absorption spectrum of the absorber sample prepared in Example 6, 400nm-2000nm, the average absorption rate is above 95.2%.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, an ultra-broadband absorber in the visible-near infrared band consists of a substrate 1 and five layers of thin films. The material of the substrate 1 is not limited, glass materials such as K9, fused silica, and float glass can be selected, and semiconductor materials such as silicon and gallium arsenide can also be selected. The bottom film is a metal absorption layer 2, and the thickness of this layer should be greater than 100nm to prevent incident light from entering the substrate; above the metal absorption layer is a germanium layer 3, with a thickness of 10nm-40nm, and above the germanium layer is a three-layer thin film (4 -6), the refractive index of the material decreases gradually from bottom to top, and the three layers can be regarded as a wide-band anti-reflection coating layer of germanium. The metal absorption layer 2 can be selected from chromium, titanium, iridium, tungsten, nickel and alloys of the above materials, and the metal absorption layer 2 of the present invention is preferably chromium. The three-layer broadband anti-reflection film (4-6) gradually reduces the refractive index from bottom to top. The film material of the film layer 4 close to the germanium layer 3 is silicon, and the thickness is 10nm-40nm. The film material of the middle layer 5 can be titanium dioxide. , hafnium oxide, tantalum oxide, silicon nitride and other high refractive index dielectric materials, the thickness is 30nm-80nm, the outermost layer 6 thin film materials can choose magnesium fluoride, silicon dioxide, yttrium fluoride and other low refractive index dielectric materials, the thickness It is 70nm-130nm. The three-layer broadband anti-reflection film layer of the present invention is preferably silicon, titanium dioxide, and magnesium fluoride from bottom to top.

A preparation method of an ultra-broadband absorber in the visible-near-infrared band, comprising the following steps, as shown in Figure 2:

1) According to the required absorber bandwidth requirements and absorption rate requirements, by optimizing the thickness of each layer of film, design a film system that meets the requirements;

2) put the substrate into the acetone solution for 8 minutes, then clean the substrate with ethanol; then put the substrate (substrate) into the ethanol solution for 8 minutes, then clean the substrate with deionized water; finally clean the substrate Put it in deionized water for 8 minutes, and then wash the substrate again with deionized water;

3) Vacuum coating technology is used to deposit each film layer in sequence to obtain an ultra-broadband absorber in the visible-near infrared band;

The ultra-broadband absorption of the ultra-broadband absorber in the visible-near-infrared band of the present invention is based on the mechanism that multiple resonances are formed simultaneously by stacking graded refractive index materials. As shown in Figure 3, with the accumulation of the film layers, the resonant reflection valleys that originally appeared are translated to the long-wave direction, and at the same time, the resonant reflection valleys corresponding to the film layer appear in the short-wave direction. In addition, with the accumulation of the film layers, the refractive index of the outermost layer gradually decreases, forming a graded refractive index film system with anti-reflection properties, which makes the overall reflectivity decrease continuously, thereby increasing the absorption. Therefore, the structure of an ultra-broadband absorber in the visible-near-infrared band of the present invention is the most important reason for forming the ultra-broadband absorption.

Specific embodiment mode:

Embodiment 1: Visible-near-infrared band ultra-broadband absorber, the expected absorption bandwidth is 400nm-1200nm, and the average absorption rate is above 98%. The absorption spectrum of the absorber sample prepared by the present invention is as shown in Figure 4 (a), The average absorption rate is above 98.75%. The corresponding substrate material is silicon wafer, and the corresponding film layer materials are sequentially chromium, germanium, silicon, titanium dioxide, magnesium fluoride, and the film thickness corresponding to each film layer is 200nm (chromium ), 18nm (germanium), 19nm (silicon), 35nm (titanium dioxide), 80nm (magnesium fluoride).

Embodiment 2: Visible-near-infrared band ultra-broadband absorber, the expected absorption bandwidth is 400nm-2000nm, and the absorption rate of each wavelength is above 90%. The absorption spectrum of the absorber sample prepared by the present invention is shown in Figure 4 (b) , the average absorption rate is above 97.75%, the corresponding substrate material is silicon wafer, and the corresponding film layer materials are chromium, germanium, silicon, titanium dioxide, magnesium fluoride in sequence, and the film thickness corresponding to each film layer is 200nm (chromium), 33nm (germanium), 32nm (silicon), 56nm (titanium dioxide), 118nm (magnesium fluoride).

Embodiment 3: basically the same as Embodiment 1, the difference is that chromium is replaced by titanium, all the other conditions are the same as in Embodiment 1, the absorption spectrum designed by the present invention is shown in Figure 4 (c), and the average absorption rate is more than 99% , the film thickness corresponding to each film layer is 200nm (titanium), 12nm (germanium), 17nm (silicon), 38nm (titanium dioxide), 89nm (magnesium fluoride).

Embodiment 4: basically the same as Embodiment 2, the difference is that chromium is replaced by titanium, all the other conditions are the same as in Embodiment 2, the absorption spectrum designed by the present invention is shown in Figure 4 (d), and the average absorption rate is more than 96.2% , the film thickness corresponding to each film layer is 200nm (titanium), 23nm (germanium), 31nm (silicon), 55nm (titanium dioxide), 119nm (magnesium fluoride).

Embodiment 5: basically the same as Embodiment 1, the difference is that titanium dioxide is replaced by tantalum oxide, all the other conditions are the same as in Embodiment 1, the absorption spectrum designed by the present invention is shown in Figure 4 (e), and the average absorption rate is 98.8% Above, the film thickness corresponding to each film layer is 200nm (titanium), 18nm (germanium), 21nm (silicon), 48nm (tantalum oxide), and 101nm (magnesium fluoride).

Embodiment 6: basically the same as Embodiment 2, the difference is that magnesium fluoride is replaced by silicon dioxide, all the other conditions are the same as in Embodiment 2, the absorption spectrum designed by the present invention is as shown in Figure 4 (f), and the average absorption The ratio is above 95.2%, and the corresponding film thicknesses of each film layer are 200nm (titanium), 32nm (germanium), 33nm (silicon), 56nm (titanium dioxide), and 111nm (magnesium fluoride).

Claims (10)

1. A kind of ultra-broadband absorber of visible-near-infrared band, comprises substrate, it is characterized in that, described substrate is successively provided with metal absorption layer, germanium layer and three-layer wide-band anti-reflection film layer; The band anti-reflection coating layer respectively includes a bottom layer, a middle layer and an outermost layer which are sequentially arranged on the germanium layer, and the refractive index of the bottom layer, the middle layer and the outermost layer gradually decreases. 2. The ultra-broadband absorber in the visible-near-infrared band according to claim 1, wherein the base material is selected from K9, fused silica, float glass, silicon, and gallium arsenide. 3. The ultra-broadband absorber in the visible-near-infrared band according to claim 1, wherein the material of the metal absorbing layer is selected from the group consisting of chromium, titanium, iridium, tungsten, nickel and alloys of the above materials. 4. The ultra-broadband absorber in the visible-near infrared band according to claim 1 or 3, characterized in that the thickness of the metal absorbing layer is greater than 100 nm. 5. The ultra-broadband absorber in the visible-near infrared band according to claim 1 or 3, characterized in that the germanium layer is 10nm-40nm. 6. The ultra-broadband absorber in the visible-near infrared band according to claim 1, wherein the bottom layer material is silicon; the middle layer material is selected from titanium dioxide, hafnium oxide, tantalum oxide, and silicon nitride; The material of the outermost layer is selected from magnesium fluoride, silicon dioxide, and yttrium fluoride. 7. the ultra-broadband absorber of visible-near infrared band according to claim 6 is characterized in that, described bottom layer thickness is 10nm-40nm; Described middle layer thickness is 30nm-80nm; Described outermost layer thickness is 70nm—130nm. 8. The ultra-broadband absorber of the visible-near-infrared band according to claim 6 or 7, wherein the bottom layer material is silicon, the middle layer material is titanium dioxide, and the outermost layer material is fluorinated magnesium. 9. A preparation method of an ultra-broadband absorber in the visible-near-infrared band according to any one of claims 1-8, characterized in that, comprising the steps of: (1) According to the required absorber bandwidth requirements and absorption rate requirements, the thickness of each layer of film is obtained through optimal design, and the film system that meets the requirements is determined; (2) Put the substrate in acetone for ultrasonication, wash the substrate with ethanol; then put the substrate in ethanol for ultrasonication, wash the substrate with deionized water; finally put the substrate in deionized water for ultrasonication, and then wash the substrate again with deionized water ; (3) Each film layer is sequentially deposited by vacuum coating to obtain an ultra-broadband absorber in the visible-near infrared band. 10. The preparation method of the ultra-broadband absorber in the visible-near-infrared band according to claim 9, characterized in that, in step (2), the time of each ultrasonic wave is 5-30min.