CN113249700A

CN113249700A - Metamaterial with infrared high refractive index and low dispersion and preparation method thereof

Info

Publication number: CN113249700A
Application number: CN202110591053.5A
Authority: CN
Inventors: 高俊华; 王鑫鹏; 曹鸿涛; 胡海搏; 汪湾
Original assignee: Ningbo Institute of Material Technology and Engineering of CAS
Current assignee: Ningbo Institute of Material Technology and Engineering of CAS
Priority date: 2021-05-28
Filing date: 2021-05-28
Publication date: 2021-08-13
Anticipated expiration: 2041-05-28
Also published as: CN113249700B

Abstract

The invention discloses a metamaterial with infrared high refractive index and low dispersion, which comprises a metal nanowire array and a dielectric layer, wherein the metal nanowire array is vertically embedded into the dielectric layer; the metal nanowire array is composed of a plurality of metal nanowires, the diameter of each metal nanowire is not less than 2nm, the length of each metal nanowire is equal to the thickness of the dielectric layer, and the distance between every two metal nanowires is 1-6 nm; the volume percentage of the metal nanowires in the metamaterial is 5% -50%; the dielectric layer is a semiconductor or ceramic dielectric. The metamaterial has higher refractive index and lower dispersion, and the invention also discloses a preparation method of the metamaterial with infrared high refractive index and low dispersion, which comprises the following steps: pretreating a substrate; and respectively selecting metal, ceramic or semiconductor as co-sputtering target materials, carrying out multi-target magnetron co-sputtering, and simultaneously applying plasma bombardment assistance to prepare the metal nanowire array-ceramic or semiconductor composite layer metamaterial. The preparation method is simple and efficient.

Description

Metamaterial with infrared high refractive index and low dispersion and preparation method thereof

Technical Field

The invention belongs to the field of optical films (nano materials), and particularly relates to an infrared metamaterial with high refractive index and low dispersion and a preparation method thereof.

Background

The refractive index is closely related to the electromagnetic property of the material, and particularly for the high refractive index material, the material plays a key role in the aspects of miniaturization of devices, improvement of imaging resolution and the like, however, the refractive index of the natural transparent material is generally limited within 4 in the range from visible light to near infrared, which greatly limits the application of the material in the novel optical fields of nano imaging, integrated optics and the like. On the other hand, the refractive index of common materials varies with the wavelength of incident light, and the generated chromatic dispersion causes the problem of residual chromatic aberration which is difficult to eliminate, thereby bringing about very adverse effects on the design of optical elements such as lenses. Therefore, there is a strong need for obtaining a material with high refractive index and low dispersion for nano-optics, super-resolution imaging, and miniaturization of optical components.

Since the beginning of the twenty-first century, the rapid development of metamaterials has given researchers a new idea of freely regulating and controlling the optical properties of materials, and becomes an optimal way for crossing the limit of refractive index. The key to obtaining high refractive index is to increase the dielectric constant epsilon and the magnetic permeability mu and inhibit the diamagnetic response of the material. The metamaterial is an artificial periodic structure with a sub-wavelength scale, the refractive index of the metamaterial can be conveniently regulated, and meanwhile, outside a resonance waveband, the scale of a metamaterial unit is far smaller than the skin depth of metal, so that the absorption of the metamaterial can be ignored at the moment, and the dispersion effect is greatly reduced. The high-refractive-index characteristic can be obtained in the terahertz waveband by densely arranging the periodic I-shaped metal arrays (the two metal planes are connected through a straight line passing through the mass center). The principle is that when electromagnetic wave interacts with periodic structure, equal amount of charges with different polarities are excited on the surface of adjacent unit structure to induce capacitive coupling effect and increase local polarizationP(ε＝1+P/ε₀E) And finally, the dielectric constant of the material is improved. On the other hand, it is necessary to reduce the thickness of a certain dimension to suppress the diamagnetic effect caused by the cyclic displacement current in the cell structure, and the permeability μ is as close to 1 as possible. Obtaining the metamaterial with high refractive index needs to consider both strong capacitive coupling between units and optimization of a unit structure, which brings challenges to large-area controllable preparation of the metamaterial.

Chinese patent publication No. CN209249703U discloses a microwave high refractive index metamaterial based on a ring structure and a double-letter-shaped structure. The unit described in this patent consists of two vertically distributed i-shaped copper metals separated by a dielectric layer. Through numerical simulation and electromagnetic parameter extraction, the calculated equivalent refractive index value is about 27 in the frequency band of 6.55 GHz-10.32 GHz, and the low dispersion is shown. Chinese patent publication No. CN103941316A discloses a polarization-insensitive terahertz high refractive index metamaterial and a preparation method thereof. The metamaterial structure unit prepared by the method utilizes an electron beam vacuum evaporation method and a photoetching method and is two I-shaped metal materials which are vertically and symmetrically arranged and embedded in a medium material. The units are periodically arranged on a plane to form a single-layer two-dimensional metamaterial. The refractive index peak value of the obtained metamaterial at 1THz is 60, and the refractive index is kept at about 20 when the refractive index peak value is higher than 2 THz. Although the I-shaped metamaterials can obtain very high refractive index in microwave and terahertz wave bands, the I-shaped metamaterials are difficult to be applied to shorter wavelengths from visible to near infrared and the like, mainly because the size of a structural unit is too large, and simultaneously, a nanometer-scale gap is difficult to realize by a top-down photoetching process, and the expansion of the high refractive index characteristic of the metamaterials to the visible and near infrared wave bands still faces a huge obstacle.

In recent years, researches on the high refractive index of materials by preparing metal nano cubic or granular metamaterial arrays by a colloidal solution self-assembly method (Huh J H, Kim K, et al. explicit colloidal metals for high-frequency and infrared bands, adv. Mater.,2020,32: 2001806; Doyle D, Charopar N, Argyrolours C, et al. tunable submicron meter Gap plasma metals, 2017,5:1012) have attracted much attention. The method can realize the particle gap of nanometer level, greatly enhances the capacitive coupling effect among metal nanometer units, and the maximum value of the effective refractive index of the obtained metamaterial structure can reach more than 6, and the effective refractive index is more than 4.3 in middle and far infrared, keeps the low dispersion characteristic and is higher than 4.0 of infrared high refractive index material germanium. Large-scale preparation is difficult and the process is complex.

Therefore, how to simply and efficiently obtain the high-frequency-band (visible-infrared) high-refractive-index low-dispersion metamaterial becomes a problem to be solved urgently at present.

Disclosure of Invention

The invention provides a metamaterial with infrared high refractive index and low dispersion and a preparation method of the metamaterial with infrared high refractive index and low dispersion.

A metamaterial with infrared high refractive index and low dispersion comprises a metal nanowire array and a dielectric layer, wherein the metal nanowire array is vertically embedded into the dielectric layer;

the metal nanowire array is composed of a plurality of metal nanowires, the diameter of each metal nanowire is not less than 2nm, the length of each metal nanowire is equal to the thickness of the dielectric layer, and the distance between every two metal nanowires is 1-6 nm;

the dielectric layer is a semiconductor or ceramic transparent medium;

the volume percentage of the metal nanowire in the metamaterial is 5% -50%.

The diameter and the length of the metal nanowires in the metamaterial and the distance between the nanowires can be regulated and controlled by adjusting experimental conditions. From the theory of effective media, it is known that the optical properties of the composite structure are the average effect of the collection of individual microscopic media. For the electromagnetic waves incident along the normal, the polarization directions of the electromagnetic waves are all vertical to the axial direction of the nanowires, the isotropic property is shown, in addition, the proper distance between the metal nanowires is adopted, the stronger capacitive coupling effect is generated, the higher polarization strength is obtained, and the promotion of the dielectric constant of the material is obvious. Meanwhile, as the scale of the metal nanowire array structure is in the nanometer level, the diamagnetic response can be effectively inhibited, and the regulation and control capability of the refractive index of the material is further enhanced.

The control of the refractive index mainly comes from the geometrical parameters of the microstructure in the metamaterial, namely the size and the gap of the metal nanowire and the dielectric constant of the semiconductor or ceramic dielectric material. The volume percentage of the metal nanowires in the composite layer is the key point for establishing and regulating the capacitive coupling among the nanowires, the larger the volume percentage is, the smaller the wire spacing is, the stronger the capacitive coupling is, the higher the corresponding refractive index is, and the dielectric constant of the semiconductor or ceramic medium determines the initial value of the refractive index of the composite film, and more importantly, the capacitive coupling effect among the nanowires can be further remarkably improved. On the other hand, the diameter of the metal nanowire is far smaller than the skin depth of the bulk metal, so that the loss of the system under non-resonance is almost negligible under incidence of micron-sized infrared light, and meanwhile, the system can have the advantage of broadband low dispersion due to the large size difference between the incident wavelength and the nano-structure unit. In particular, in order to weaken the mismatch problem of the high-refractive-index metamaterial and the substrate and more conveniently detect the spectral signals of the materials, the volume percentage of the metal nanowires in the selected sample is limited to a certain extent, and further, the spacing between the metal nanowires is 1-5nm, the diameter is 3-7nm, and the volume percentage of the metal nanowires in the metamaterial is 10% -30%. The length of the metal nanowire is 150-300 nm.

The metamaterial is wide in material selection, the metal nanowire is any one of gold, silver, platinum, copper and aluminum, the semiconductor transparent medium is any one of silicon, germanium, zinc sulfide, zinc selenide and silicon carbide, and the ceramic transparent medium is any one of oxide, nitride and carbide

The high refractive index property of the metamaterial provided by the invention is closely related to the material and the structural characteristics thereof, namely, the metamaterial with high refractive index and low dispersion needs to meet the following requirements: firstly, the gaps among the unit structures are in a nanometer scale, so that the capacitive coupling degree among the unit structures is enhanced; secondly, the size of the structure is small, so that the area of a current loop is reduced, and diamagnetic response is inhibited; and thirdly, the degree of capacitive coupling between the structures is further regulated and controlled by changing the dielectric environment. Further, the metal nanowires are any one of gold, silver and platinum, the semiconductor transparent medium is any one of silicon, germanium and zinc selenide, the ceramic transparent medium is any one of silicon dioxide, silicon carbide and aluminum oxide, the spacing between the metal nanowires is 2-5nm, and the diameter is 3-6 nm.

The low-resistance metals such as gold, silver, platinum and the like are selected as the nanowire materials, so that the nanowire materials have great advantages, and firstly, the absorption of a metamaterial system is greatly reduced due to the low ohmic loss of the nanowire materials. In addition, the nanowires can grow vertically and densely in a self-organized ordered manner in the preparation process, the consistency of the size of cavities among the nanowires is realized, the wire spacing is controlled within the range of 2-5nm, and the necessary condition for generating strong capacitive coupling is met, on the other hand, the diameter of the metal nanowires prepared by the method is 3-6nm, a current loop is difficult to form on the surface of the wires under the size, the generation of the diamagnetic effect is effectively inhibited, the wavelength difference with infrared waves is large, and the low dispersion characteristic is favorably obtained.

In addition, the method is different from the traditional method for preparing the high-refractive-index metamaterial by using a solution self-organization method, and has the advantage that the dielectric environment is adjustable and controllable, so that the refractive index of the whole metamaterial structure can be effectively regulated and controlled, and when the volume percentage of the silver nanowires is 10-35%, the refractive index of the silver nanowires is between 5-10 in the middle and far infrared wave bands by taking the combination of the silver nanowires and a germanium medium as an example.

The invention also provides a preparation method of the metamaterial with the infrared high refractive index and low dispersion, which comprises the following steps:

(1) pretreating a substrate;

(2) and (2) selecting metal, ceramic or semiconductor as co-sputtering targets respectively, performing multi-target magnetron co-sputtering on the substrate pretreated in the step (1) under the argon atmosphere at the sputtering pressure of 0.15-0.6Pa, and simultaneously applying plasma bombardment assistance to prepare the metal nanowire array-ceramic or semiconductor composite layer metamaterial.

The preparation method provided by the invention is characterized in that metal, ceramic or semiconductor is used as a target material and is co-sputtered into a pretreated substrate, and the vertical orientation self-organization growth of nanowires is realized under the assistance of plasma bombardment, so that the metal nanowire array-ceramic or semiconductor composite layer metamaterial is formed.

In the step (1), the substrate comprises an inorganic non-metallic material, a flexible material or a semiconductor material.

Further, the inorganic non-metallic material comprises any one of glass, ceramic, oxide and carbide; the flexible material is PET or PP; the semiconductor material is any one of silicon, germanium, zinc sulfide, zinc selenide and silicon carbide.

Further preferably, the substrate is any one of a quartz wafer, sapphire and a double polished silicon wafer. To facilitate optical testing.

In the step (1), the substrate is pretreated by the following specific steps:

the substrate is sequentially cleaned by acetone, alcohol and deionized water, ultrasonic action is simultaneously carried out in the cleaning process, and then heating desorption and plasma sputtering cleaning are carried out.

The processed substrate has higher cleanliness and provides conditions for better growth of a metal nanowire-semiconductor or ceramic composite structure.

In the step (2), the metal target is driven by a pulse, radio frequency or direct current power supply, the semiconductor target is driven by a pulse, radio frequency or direct current power supply, and the ceramic target is driven by a radio frequency power supply.

In the step (2), the adopted power range of the metal target material is 0.5-2W/cm²The adopted power range of the semiconductor target material is 2-8W/cm²The adopted power range of the ceramic target material is 4-12W/cm²Furthermore, the distance of the target from the substrate is 75-90 mm.

Furthermore, when the copper and aluminum active metal is used as the nanowire metal material, the adopted power is 0.8-2W/cm²(ii) a The power of the semiconductor target is 2-7W/cm²。

Further, the substrate is silicon dioxide, silicon, sapphire or zinc selenide, the metal target is gold or silver, and the adopted power range is 0.5-2.5W/cm²(ii) a The semiconductor target material is silicon, germanium or zinc selenide, and the adopted power range is 2-7W/cm²(ii) a The ceramic target material is silicon dioxide, silicon carbide or aluminum oxide, and the adopted power range is 2-10W/cm²。

The growth of metal nanowires by co-sputtering with a medium is carried out by suitably combining the substrate, the metal target, the semiconductor target or the ceramic target, and the respectively applied power ranges, such as silver and silicon, gold and silicon carbide. The obtained metamaterial structure is that vertically grown metal nanowires are embedded in corresponding media, wherein the spacing between the nanowires is usually 3-4nm, the capacitive coupling effect between the nanowires is greatly enhanced, the dielectric constant is obviously improved, on the other hand, the diameters of the nanowires are commonly 3-5nm, the nanometer size enables a current loop to be difficult to form in the nanowire structure, the diamagnetic response is further reduced, the dielectric environment where the nanowires are located is improved through the high-refractive-index media, the refractive index value is greatly improved, and the improvement range is 1-5.

Compared with the prior art, the invention has the following advantages:

(1) for the incident condition vertical to the surface of the material, the peak value of the refractive index of the material in the near infrared band can be up to more than 7, and the refractive index in the middle and far infrared bands can be kept constant at a certain value between 4.3 and 10, so that the requirement of broadband low dispersion and high refractive index can be effectively met. In addition, the results of calculation and simulation show that the metamaterial has a low extinction coefficient, and is expected to bring new application in the fields of infrared transparent media and the like.

(2) Compared with the traditional micro-nano structure preparation method, such as photoetching, a solution self-assembly growth method and the like, the method for growing the metal nanowire metamaterial by the magnetron sputtering method has the advantages of simple process, low cost, convenient parameter regulation and control, and great benefit to large-area production, and in addition, the obtained composite structure is uniform and stable in property.

(3) From the microstructure, the distance between the metal nanowires reaches the nanometer level, so that the capacitive coupling effect between the nanowires is greatly improved, and the refractive index of a near-infrared band can be greatly improved. Compared with a solution self-assembly method, the metal nanowire provided by the invention has the advantages of uniform size, few defects, high quality of vertically and densely grown nanowires, and no need of further etching correction.

(4) The invention has loose selection on metal and semiconductor or ceramic matrixes, and can select proper materials for preparation according to different refractive index requirements, namely the broadband high-refractive index low-dispersion property of the nanowire metamaterial mainly comes from the coupling property among micro-nano structures.

(5) The invention has wide selection range of substrate materials, and the selectable materials are not limited to rigidity, flexibility, semiconductors, metals and the like, and have positive effect on the application of the metamaterial with high refractive index and low dispersion.

(6) The method is different from other metamaterial preparation methods, can regulate and control the dielectric environment among the micro-nano structures, namely a semiconductor or ceramic mother phase with high refractive index, and further improves the capacitive coupling effect among the metal nano wires, so that higher refractive index and low dispersion are obtained.

Drawings

FIG. 1 is a schematic structural diagram of a metamaterial having high infrared refractive index and low dispersion provided by the present invention;

FIG. 2 is a TEM image of a cross-section of the silver nanowire-silicon dielectric composite structure prepared in example 1;

FIG. 3 is an infrared transmission spectrum corresponding to the silver nanowire-silicon dielectric composite structure prepared in example 1;

FIG. 4 is a comparison of the refractive index of the silver nanowire-silicon dielectric composite structure prepared in example 1 with that of pure silicon;

FIG. 5 is an infrared transmission spectrum corresponding to the silver nanowire-silicon dielectric composite structure prepared in example 2;

FIG. 6 is a comparison of the refractive index of the silver nanowire-silicon dielectric composite structure prepared in example 2 with that of pure silicon;

FIG. 7 is an infrared transmission spectrum corresponding to the silver nanowire-germanium dielectric composite structure prepared in example 3;

FIG. 8 is a comparison of the refractive index of the silver nanowire-germanium dielectric composite structure prepared in example 3 with that of pure germanium;

FIG. 9 is a comparison of the refractive index of the gold nanowire-silicon carbide composite structure prepared in example 4 with that of pure silicon carbide;

Detailed Description

The following detailed description of the present invention is provided in conjunction with the accompanying drawings and the embodiments, which are meant to be exemplary only and not limiting.

Example 1

Firstly, cleaning a substrate, and respectively ultrasonically cleaning a double-polished silicon wafer, a single-polished silicon wafer, a quartz wafer and sapphire for 10min by using acetone, ethanol and deionized water in sequence to remove surface pollutants; drying the cleaned substrate by using nitrogen, and fixing the substrate on a substrate tray; loading the tray into a preparation chamber of a magnetron sputtering device, and vacuumizing the preparation chamber to 10 by using a mechanical pump and a molecular pump in sequence^-4Pa below; opening an argon gas path, introducing argon gas flow to keep the pressure of a deposition chamber at 0.35-0.6 Pa, cleaning a silver target by radio frequency sputtering and a silicon target by a direct current power supply for 10min, and applying bias voltage to clean the substrate for 10 min; after the cleaning is finished, the air pressure of the deposition chamber is adjusted to 0.3Pa, and the sputtering power density of the silver target material is controlled to be 0.75W/cm²The sputtering power of the silicon target material is 6W/cm²With the additional assistance of plasma bombardment, the power density of the power supply is 2W/cm²And simultaneously opening a baffle plate in front of the silver target and the silicon target to start sputtering, wherein the deposition time is 3h10 min. After the time is over, the silver target, the silicon target and the bias driving power supply are closed, so that the metal nanowire metamaterial film with high refractive index and low dispersion can be obtained, and the schematic diagram of the obtained composite structure is shown in fig. 1.

The cross-sectional morphology of the thin film sample is observed and analyzed by a Transmission Electron Microscope (TEM). Fig. 2 shows a TEM morphology of a cross section of the metal nanowire metamaterial thin film in example 1, and as can be clearly seen from the figure, the cross section includes a substrate and a metal nanowire-semiconductor composite structure, wherein the thickness of the metal nanowire-semiconductor composite layer is 200-210 nm. The silver nanowires are vertically and periodically arranged and embedded in a silicon medium, wherein the average diameter of the silver nanowires is 3.5nm, the spacing between the nanowires is 2.5nm, and the volume percentage of the metal nanowires is 15%.

FIG. 3 is a Fourier transform infrared spectrum of the metal nanowire metamaterial in example 1. The substrate selected by the sample is a double-polished silicon wafer, and the infrared spectrum obtained by the sample is compared with the infrared transmission spectrum of a pure double-polished silicon substrate, so that the transmittance of the sample obtained in the embodiment 1 is obviously reduced at about 2 microns, because the refractive index reaches the peak value under the strong coupling resonance effect among the metal nanowires, and the refractive index mismatch degree between the silver nanowire-silicon composite layer and the air and the substrate is improved. Meanwhile, in the middle and far infrared wave bands, the transmittance curve obtained by the sample keeps consistent with the transmittance curve trend of the double-polished silicon substrate, and is only reduced in numerical value, so that the obtained silver nanowire-silicon composite layer is proved to have low dispersion characteristic similar to pure silicon and refractive index larger than that of silicon.

Theoretical calculation is carried out on the refractive index of the silver nanowire-silicon composite layer of example 1, and as a result, as shown in fig. 4, the refractive index of the composite structure is greatly improved compared with that of pure silicon, and at the filling rate, the obtained refractive index has a maximum value of 5.8 at 1.4 μm and remains 4.3 at more than 1.4 μm.

Example 2

Firstly, cleaning a substrate, and respectively ultrasonically cleaning a double-polished silicon wafer, a single-polished silicon wafer, a quartz wafer and sapphire for 10min by using acetone, ethanol and deionized water in sequence to remove surface pollutants; drying the cleaned substrate by using nitrogen, and fixing the substrate on a substrate tray; loading the tray into a preparation chamber of a magnetron sputtering device, and vacuumizing the preparation chamber to 10 by using a mechanical pump and a molecular pump in sequence^-4Pa below; opening an argon gas path, and introducing argon gas flow to keep the pressure of the deposition chamber at 0.5-0.7Pa, cleaning the silver target material by radio frequency sputtering, cleaning the silicon target material by a direct current power supply for 10min, and applying bias voltage to clean the substrate for 10 min; after the cleaning is finished, the air pressure of the deposition chamber is adjusted to 0.3Pa, and the sputtering power density of the silver target material is controlled to be 1.25W/cm²The sputtering power of the silicon target material is 7W/cm²With the additional assistance of plasma bombardment, the power density of the power supply is 2W/cm²And simultaneously opening a baffle plate in front of the silver target and the silicon target to start sputtering, wherein the deposition time is 3 h. And after the time is over, closing the silver target, the silicon target and the bias driving power supply to obtain the metal nanowire metamaterial film with high refractive index and low dispersion.

The average diameter of the obtained silver nanowires is 6nm, the space between the nanowires is 2.5nm, and the volume percentage of the metal nanowires is obviously increased to 25% compared with the sample obtained in example 1. FIG. 5 is a Fourier transform infrared spectrum of a metal nanowire metamaterial in example 2. The substrate selected by the sample is a double-polished silicon wafer, and the infrared spectrum obtained by the sample is compared with the infrared transmission spectrum of a pure double-polished silicon substrate, so that the transmittance of the sample in the embodiment 2 is still remarkably reduced at about 2 micrometers, which is similar to that of the sample in the embodiment 1. Meanwhile, in the middle and far infrared wave bands, the transmittance curve obtained by the sample keeps consistent with the transmittance curve trend of the double-polished silicon substrate, and is reduced in value compared with that of the example 1, which shows that the silver nanowire-silicon composite layer obtained in the example 2 has low dispersion characteristic similar to that of pure silicon, and the refractive index is larger than that of the sample in the example 1.

Theoretical calculation was carried out on the refractive index of the silver nanowire-silicon composite layer of example 2, and as a result, as shown in fig. 6, the refractive index of the composite structure was greatly improved compared to that of pure silicon, and at this filling rate, the obtained refractive index had a maximum value of 7 at 2.1 μm and remained unchanged at 5.8 at more than 2.7 μm.

By changing experimental parameters, the microstructure of the metal nanowire-semiconductor composite layer can be effectively regulated and controlled, so that a series of gradient high-refractive-index low-dispersion metamaterial optical films are obtained.

Example 3

Firstly, cleaning a substrate, and respectively ultrasonically cleaning the substrate with acetone, ethanol and deionized water in sequencePolishing silicon wafers, single polishing silicon wafers, quartz wafers and sapphire for 10min to remove surface pollutants; drying the cleaned substrate by using nitrogen, and fixing the substrate on a substrate tray; loading the tray into a preparation chamber of a magnetron sputtering device, and vacuumizing the preparation chamber to 10 by using a mechanical pump and a molecular pump in sequence^-4Pa below; opening an argon gas path, introducing argon gas flow to keep the pressure of a deposition chamber at 0.35-0.6 Pa, cleaning the silver target material by radio frequency sputtering and the germanium target material by a direct current power supply for 10min, and applying bias voltage to clean the substrate for 10 min; after the cleaning is finished, the air pressure of the deposition chamber is adjusted to 0.3Pa, and the sputtering power density of the silver target material is controlled to be 0.70W/cm²The sputtering power of the germanium target material is 7W/cm²With the additional assistance of plasma bombardment, the power density of the power supply is 2W/cm²And simultaneously opening a baffle plate in front of the silver target and the germanium target to start sputtering, wherein the deposition time is 3h50 min. And after the time is over, closing the silver target, the germanium target and the bias driving power supply to obtain the metal nanowire metamaterial film with high refractive index and low dispersion.

FIG. 7 is a Fourier transform infrared spectrum of a metal nanowire metamaterial in example 3. The substrate selected by the sample is a double-polished silicon wafer, the infrared spectrum obtained by the sample is compared with the infrared transmission spectrum of a pure double-polished silicon substrate, and the result shows that the transmittance curve obtained by the sample keeps consistent with the transmittance curve trend of the double-polished silicon substrate in the middle and far infrared wave bands, and the transmittance is reduced by 30% compared with the transmittance of the double-polished silicon substrate in numerical value, which indicates that the silver nanowire-germanium composite layer obtained in the embodiment 3 has the low dispersion characteristic similar to pure silicon and has a larger effective refractive index.

Theoretical calculation is carried out on the refractive index of the silver nanowire-germanium composite layer in example 3, and as a result, as shown in fig. 8, the refractive index of the composite structure is greatly improved compared with that of infrared high-refractive-index material germanium, and at the filling rate, the obtained refractive index has a maximum value of 8.9 at 2.5 μm and is kept constant at 7.9 at more than 2.5 μm.

Example 3 shows that the refractive index of the system can be effectively controlled by controlling the semiconductor/ceramic medium in the metal nanowire-semiconductor/ceramic medium, so that the material selection and the range of the refractive index are greatly improved.

Example 4

Firstly, cleaning a substrate, and respectively ultrasonically cleaning a double-polished silicon wafer, a single-polished silicon wafer, a quartz wafer and sapphire for 10min by using acetone, ethanol and deionized water in sequence to remove surface pollutants; drying the cleaned substrate by using nitrogen, and fixing the substrate on a substrate tray; loading the tray into a preparation chamber of a magnetron sputtering device, and vacuumizing the preparation chamber to 10 by using a mechanical pump and a molecular pump in sequence^-4Pa below; opening an argon gas path, introducing argon gas flow to keep the pressure of a deposition chamber at 0.5-0.7 Pa, cleaning the gold target material by radio frequency sputtering and the silicon carbide target material by a direct current power supply for 10min, and applying bias voltage to clean the substrate for 10 min; after the cleaning is finished, the air pressure of the deposition chamber is adjusted to 0.3Pa, and the sputtering power density of the gold target material is controlled to be 0.75W/cm²The sputtering power of the silicon carbide target is 10W/cm²With the additional assistance of plasma bombardment, the power density of the power supply is 2W/cm²And simultaneously opening a baffle plate in front of the gold target and the silicon carbide target, and starting sputtering, wherein the deposition time is 3h and 10 min. And after the time is over, closing the gold target, the silicon carbide target and the bias driving power supply to obtain the metal nanowire metamaterial film with high refractive index and low dispersion.

The average diameter of the obtained gold nano-wires is 3.5nm, the space between the nano-wires is 3nm, and the volume percentage of the metal nano-wires is 22.7 percent. Theoretical calculation is carried out on the refractive index of the gold nanowire-silicon carbide composite layer in example 4, and as a result, as shown in fig. 9, the refractive index of the composite structure is greatly improved compared with that of pure silicon carbide, and under the filling rate, the average refractive index value is 5.8, and the maximum value is 6.2.

Example 4 demonstrates that high index low dispersion metamaterial optical films can also be conveniently obtained using different metals in combination with ceramics to form nanowires.

The above-mentioned embodiments are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only the most preferred embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions, equivalents, etc. made within the scope of the principles of the present invention should be included in the scope of the present invention.

Claims

1. The metamaterial with the infrared high refractive index and low dispersion is characterized by comprising a metal nanowire array and a dielectric layer, wherein the metal nanowire array is vertically embedded into the dielectric layer;

the dielectric layer is a semiconductor or ceramic transparent medium;

the volume percentage of the metal nanowire in the metamaterial is 5% -50%.

2. A metamaterial with infrared high refractive index and low dispersion as claimed in claim 1, wherein the metal nanowires have a pitch of 1-5nm, a diameter of 3-7nm, and a volume percentage of metal nanowires in the metamaterial is 10% -30%.

3. The metamaterial with high infrared refractive index and low dispersion as claimed in claim 1 or 2, wherein the length of the metal nanowire is 150-300 nm.

4. A metamaterial with infrared high refractive index and low dispersion as claimed in claim 2, wherein the metal nanowire is any one of gold, silver, platinum, copper and aluminum, the semiconductor transparent medium is any one of silicon, germanium, zinc sulfide, zinc selenide and silicon carbide, and the ceramic transparent medium is any one of oxide, nitride and carbide.

5. A metamaterial with infrared high refractive index and low dispersion as claimed in claim 4, wherein the metal nanowires are preferably gold, silver or platinum, the metal nanowires have a pitch of 2-5nm and a diameter of 3-6 nm.

6. A metamaterial with infrared high refractive index and low dispersion as claimed in claim 5, wherein the semiconductor transparent medium is silicon, germanium or zinc selenide, and the ceramic transparent medium is silicon dioxide, aluminum oxide, silicon carbide or silicon nitride.

7. A method of making a metamaterial having high refractive index and low dispersion in the infrared as claimed in any one of claims 1 to 6, comprising:

(1) pretreating a substrate;

8. The metamaterial with high infrared refractive index and low dispersion as claimed in claim 7, wherein in the step (1), the substrate is pre-treated by the following specific steps:

9. The metamaterial according to claim 7, wherein in step (2), the metal target is applied at a power in the range of 0.5-3W/cm²The adopted power range of the semiconductor target material is 2-8W/cm²The adopted power range of the ceramic target material is 4-12W/cm²。

10. A metamaterial with high infrared refractive index and low dispersion as in claim 9, wherein the substrate is silicon dioxide, silicon, sapphire or zinc selenide, the metal target is silver or platinum, and the power range used is 0.5-2.5W/cm²(ii) a The semiconductor target material is silicon, germanium or zinc selenide, and the adopted power range is 2-7W/cm²(ii) a The ceramic target material is silicon dioxide, silicon carbide or aluminum oxide, and the adopted power range is 2-10W/cm²。