CN114498070A

CN114498070A - Terahertz double-band adjustable absorber based on graphene-medium-metal structure

Info

Publication number: CN114498070A
Application number: CN202210255602.6A
Authority: CN
Inventors: 付麦霞; 王金义; 杨鹏须; 夏娜; 叶玉超
Original assignee: Henan University of Technology
Current assignee: Henan University of Technology
Priority date: 2022-03-16
Filing date: 2022-03-16
Publication date: 2022-05-13

Abstract

The invention provides a terahertz double-band adjustable absorber based on a graphene-medium-metal structure. The absorber is composed of a metal layer, a middle medium layer and a top layer U-shaped graphene pattern from bottom to top in sequence, the upper layer U-shaped graphene pattern is periodically arranged in the x and y directions, and a bottom layer metal film, the middle medium layer and the top layer U-shaped graphene are attached to each other. The absorption spectrum of the terahertz waveband absorber is calculated and simulated mainly through a time domain finite difference method, the structure of the absorber is optimized, absorption of a broadband and a single band is realized in the terahertz waveband, and the amplitude of the absorption rate can be effectively tuned by adjusting an external voltage under the condition of not changing the structure of a device. In addition, the invention has compact structure and simple manufacture, can be manufactured by a conventional method, and avoids the defects of complex process, large geometric dimension and the like.

Description

Terahertz double-band adjustable absorber based on graphene-medium-metal structure

Technical Field

The invention belongs to the technical field of terahertz wave application. In particular to a terahertz double-band adjustable absorber based on a graphene-medium-metal structure.

Background

Graphene is a single layer of carbon atoms with a hexagonal lattice, and is considered as a functional optical material for adjusting terahertz wave propagation characteristics due to its remarkable photoelectric characteristics, such as an abnormal quantum hall effect, high carrier mobility, and adjustable conductivity. In addition, the graphene surface plasmon can greatly enhance the interaction between light and graphene, compared to the conventional noble metal surface plasmon. Therefore, the structure based on the graphene surface plasmon has the advantages of tunability, extremely strong constraint, low loss, adjustable conductivity through chemical doping or bias voltage and the like.

The absorber refers to a device capable of absorbing incident electromagnetic waves, but the conventional absorber formed by natural materials needs the size of the structure to be in proportion to the wavelength of the incident waves, which causes the defect that the designed device has large thickness, and limits the progress of miniaturization. However, for graphene, the wavelength of the graphene is far smaller than that of electromagnetic waves with the same frequency in a free space, and by utilizing the characteristic, some sub-wavelength structures can be designed, and the graphene is processed into a metamaterial in a terahertz waveband, so that miniaturization and integration of devices are realized. Based on these advantages, many perfect absorbers based on graphene metamaterials have been widely studied and successfully applied, such as chemical and biomedical sensors, photodetectors, imaging and solar cells, etc.

A terahertz double-band adjustable absorber with a graphene-dielectric-metal structure is characterized in that substantially U-shaped patterned graphene unit structures are periodically arranged on a dielectric layer polyimide-metal reflector combined substrate. This design mainly changes its chemical formula through the opening distance of U-shaped graphite alkene and adjusts graphite alkene voltage and realizes absorbing horizontal regulation, and then realizes the design and the research of graphite alkene double-band adjustable absorber.

According to research, the conventional dual-band absorber studied at present is found to be mainly realized by combining a plurality of microstructures into a large coplanar single-layer structural unit or a stack of multi-layer metal microstructures, which leads to the bulky structural unit of the device and is not beneficial to the miniaturization development of the device. In addition, the complicated structure or the stack of the multi-layer structure increases the difficulty and the accuracy of the device preparation, and is not beneficial to the practicability and the commercialization of the device. Once the device is manufactured, the absorption performance of the device is difficult to change, and the application requirements cannot be met. Therefore, the design of the absorber which is miniaturized, has multiple frequency bands, obvious absorption and simple structure has very important practical significance.

Disclosure of Invention

The invention aims to provide a terahertz double-band adjustable absorber based on a graphene-medium-metal structure, and solves the technical problems that the conventional wave absorber cannot achieve the effects of high absorption and high modulation depth and can only achieve the absorption of double single frequency points. Meanwhile, the coupling device is small in size, thin in thickness, simple in structure and easy to integrate and manufacture.

The technical scheme adopted by the invention is as follows: a terahertz double-band adjustable absorber based on a graphene-medium-metal structure is composed of a plurality of absorber units, wherein the absorber units are sequentially provided with a bottom metal layer, a middle dielectric layer and an upper U-shaped graphene layer from bottom to top. The bottom metal, the middle dielectric layer and the upper U-shaped graphene are attached to each other. The bottom layer metal is an all-metal film, and the upper layer U-shaped graphene structure is opened at the same horizontal position to form a symmetrical U-shaped graphene pattern structure.

The invention has the characteristics that:

each unit structure is opened at the same horizontal position, and the symmetrical U-shaped graphene pattern structures are the same. The length of the U-shaped ring is 15 μm, the width is 1.5 μm, the opening distance of the symmetrical U-shaped graphene is 2 μm, and the openings are in the same direction.

The middle dielectric layer is made of polyimide, and the thickness h = 16-17.5 μm of the dielectric layer.

The lower layer is a metal layer, and the thickness of the lower layer is 0.6 mu m.

The period of each unit structure is 15 × 15 μm.

The Fermi level of the graphene is 0.1-0.6 eV.

The U-shaped graphene is manufactured by a chemical vapor phase method, and the distance between openings in the U-shaped graphene (2) is manufactured by laser etching.

The U-shaped graphene is of a single-layer atomic arrangement structure.

The bottom layer metal is used for preventing terahertz waves from penetrating.

The invention has the beneficial effects that:

(1) the terahertz double-band tunable absorber based on the graphene-medium-metal structure changes the Fermi level of the terahertz double-band tunable absorber by utilizing the semimetal property of graphene and externally applying voltage, so that the frequency and the amplitude of the terahertz double-band tunable absorber are effectively regulated and controlled, and the development of terahertz waveband tunable devices is promoted.

(2) The terahertz double-band adjustable absorber based on the graphene-medium-metal structure realizes double-band super absorption with both a wide band and a single band, solves the problem of small application range of the wave absorber in the prior art, and can be widely applied to the fields of sensors, optical detectors, stealths, solar cells and the like.

The terahertz double-band adjustable absorber based on the graphene-medium-metal structure overcomes the defect that the design structure of the absorber in the prior art is complex. The graphene metamaterial is selected, so that the preparation technology is mature and the graphene metamaterial is easy to manufacture.

Drawings

FIG. 1: the invention is a schematic diagram of a unit structure.

FIG. 2: the invention is a top view of the cell structure.

FIG. 3: the absorption rate profile of the absorber of the present invention.

FIG. 4: the absorption curve diagram of different Fermi energy levels of 0.1-0.6 eV is disclosed.

FIG. 5: the absorption rate profile of the absorber of the invention at different opening distances.

Detailed Description

(1) The description is further explained in conjunction with the figures and the examples.

(2) As shown in fig. 1 and 2, the invention relates to a terahertz double-band tunable absorber based on a graphene-dielectric-metal structure, wherein the absorber is a periodic structure, each basic unit structure is the same and is arranged along the same direction on an xy plane, an upper layer is a graphene layer, a middle layer is a polyimide layer, and a bottom layer is a metal layer.

(3) The U-shaped ring unit structure of the upper graphene layer corresponds to a serial number 1, the middle medium layer is a polyimide layer corresponding to a serial number 2, and the bottom layer metal corresponds to a serial number 3.

(4) The terahertz plane wave light source vertically irradiates on the patterned graphene structure to obtain a section of absorption bandwidth, double-band absorption is achieved, the Fermi level of graphene in the structure is adjusted by changing side end gate voltage, the Fermi level of the graphene is changed under the condition that the side end gate voltage is electrified, and dynamic adjustment of the absorption level based on the graphene broadband absorber is achieved.

(5) In this example, the upper U-shaped graphene ring pattern had a length of 15 μm and a width of 1.5 μm, and the symmetrical U-shaped graphene had an opening pitch of 2 μm and openings in the same direction. The middle dielectric layer is made of polyimide, and the thickness h = 16-17.5 μm. The lower layer is a metal layer, and the thickness of the lower layer is 0.6 mu m. The period of each unit structure is 15 × 15 μm. The Fermi level of graphene is varied from 0.1eV to 0.6 eV.

(6) The working principle of the invention is as follows: a beam of plane wave is vertically incident on the designed super surface, and local surface plasma resonance is excited at the opening of the U-shaped ring due to different structures of metamaterials, so that first broadband near-perfect absorption is formed. While a second peak is formed due to the interaction between the U-shaped bands. In addition, a time-domain finite difference method is adopted, a three-dimensional model is established in FDTD solution software, and terahertz plane waves vertically incident along the z axis are used. Periodic boundary conditions are used in the x and y directions and metallic boundary conditions are used in the z direction. In the calculation, a suitable non-uniform grid may be used to satisfy the condition of good convergence results.

(7) The absorption rate of the terahertz dual-band tunable absorber based on the graphene-dielectric-metal structure is defined as a =1-R-T, where R is a reflection rate and T is a transmission rate. In order to maximize the absorption, it is desirable that the reflectance and transmittance be as small as possible over the entire frequency range. The bottom metal of the absorption unit designed by the invention is an all-metal film, electromagnetic waves cannot be transmitted, and the transmissivity approaches to zero, so that the calculation formula of the absorptivity can be simplified to be A-1-R.

(8) Fig. 3 is a graph of the absorption rate of the absorber calculated by simulation. Here, the chemical potential of graphene is set to 0.6eV and the relaxation time is set to 1 ps. It can be seen that the absorber structure of the invention has strong absorption characteristics for incident terahertz waves, nearly perfect absorption of the absorption rate is realized in the frequency range of 2.26-3.2THz, and the absorption rate is close to 90% in the frequency range of 8 THz.

(9) Fig. 4 shows that when the geometrical parameters of the invention are fixed, the fermi level of graphene is increased from 0.1eV to 0.6eV, the absorption rate of the absorber can be adjusted within the range of 6% -100%, and the larger the fermi level is, the larger the absorption rate of the absorber is, so that the absorber is a novel adjustable dual-band absorber with good performance.

(10) Fig. 5 is a graph showing the absorption rate of the absorber at different opening distances, which still can achieve absorption rates of not less than 90% in both the frequency ranges 2.26-3.2THz and 8THz at an opening distance of 4 μm.

(11) Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. It will be understood by those skilled in the art that various changes, substitutions of equivalents, and improvements made based on the present invention are intended to be included within the scope of the present invention.

Claims

1. The terahertz double-band adjustable absorber based on the graphene-medium-metal structure is composed of a periodic structure and is characterized by comprising a plurality of basic units which are periodically arranged on a plane along the same direction; each basic unit comprises three layers: the upper layer is a U-shaped pattern graphene layer, the middle layer is a dielectric polyimide layer, and the lower layer is a metal layer;

the actual processing process comprises the following steps: firstly, forming a dielectric layer film on a substrate, plating a graphene film layer on the dielectric layer by adopting a chemical method or a physical method to form a graphene layer, etching graphene by photoetching or electron beam exposure according to a set period and the number of basic units, removing redundant graphene films, and forming symmetrical U-shaped graphene patterns at the same horizontal position to form the graphene layer with a periodic structure; after all graphene layers are etched at one time, a layer of conductive adhesive needs to be plated on the graphene layers.

2. The terahertz dual-band tunable absorber based on the graphene-dielectric-metal structure as claimed in claim 1, wherein the openings corresponding to each basic unit in the same horizontal position form the same symmetrical U-shaped graphene pattern structure, and the specific structural shape is as follows: the length of the U-shaped ring is 15 μm, the width is 1.5 μm, the opening distance of the symmetrical U-shaped graphene is 2 μm, and the openings are in the same direction.

3. The terahertz double-band tunable absorber based on the graphene-dielectric-metal structure as claimed in claim 1, wherein the material of the middle dielectric layer is polyimide, and the thickness h = 16-17.5 μm of the dielectric layer.

4. The terahertz dual-band tunable absorber based on a graphene-dielectric-metal structure as claimed in claim 1, wherein the lower layer is a metal layer with a thickness of 0.6 μm.

5. The graphene-dielectric-metal structure based terahertz dual-band tunable absorber of claim 1, wherein the period of each unit structure is 15 x 15 μ ι η.

6. The terahertz dual-band tunable absorber based on a graphene-dielectric-metal structure as claimed in claim 1, wherein the graphene has a fermi level of 0.1eV to 0.6 eV.

7. The terahertz dual-band tunable absorber based on a graphene-dielectric-metal structure as claimed in claim 1, wherein: the U-shaped graphene (2) is manufactured by a chemical vapor phase method, and the distance between openings in the U-shaped graphene (2) is manufactured by laser etching.

8. The terahertz dual-band tunable absorber based on a graphene-dielectric-metal structure as claimed in claim 1, wherein: the U-shaped graphene (2) is of a single-layer atomic arrangement structure.

9. The terahertz dual-band tunable absorber based on a graphene-dielectric-metal structure as claimed in claim 1, wherein: the bottom layer metal (4) is used for preventing terahertz waves from penetrating.