Dynamically tunable dual-function devices based on graphene and vanadium dioxide metamaterials

Abstract

The invention discloses a dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials, belonging to the field of mid-infrared technology, and a wave absorbing and reflecting device, which utilizes the surface plasma characteristics of graphene and the phase change characteristics of vanadium dioxide. The device is a three-dimensional periodic structure, and its structural composition is: a metal substrate (1) composed of gold, a vanadium dioxide layer (2), and a cross-star graphene layer (3). The invention mainly calculates and simulates the absorption spectrum of graphene to electromagnetic waves through the finite element method, optimizes the structure of the wave absorbing device, and obtains an ideal broadband wave absorbing effect. At the same time, the phase change characteristics of vanadium dioxide are utilized to dynamically change the function of the device. The invention has a simple structure and is easy to process. By simply superimposing a layer of cross-shaped graphene on the vanadium dioxide material, a wave absorbing device with an absorption efficiency of more than 90% and a bandwidth of 2.9THz can be realized. In addition, a reflecting device with a reflectivity of more than 99% can be obtained within the full frequency range.

Description

Technical Field

[0001] The invention relates to a dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials, belonging to the application field of metamaterials in the mid-infrared band. Background Art

[0002] Metamaterials have gradually come into the field of vision of researchers due to their special properties that many natural materials do not have, such as negative refractive index, complex dielectric constant, inverse Doppler effect, etc. Metamaterials, as a special subtype of material, can be used as ideal absorbing materials to obtain near-perfect absorption characteristics in a narrow or wide frequency band.

[0003] Absorbing materials are a type of material that can convert electromagnetic waves incident on the surface of the material into heat or other forms of energy, which can reduce the transmission and reflection of electromagnetic waves, thereby absorbing electromagnetic waves. At present, the typical structure of absorbing devices is a sandwich type: the top layer is a periodic metamaterial pattern, the middle layer is a layer of non-metallic dielectric material, and the bottom layer is an opaque metal plane. The position of the absorption peak and the absorption efficiency are adjusted by adjusting the size of the unit structure, so once it is fixed in the experiment, it is difficult to achieve adjustability.

[0004] Since it was discovered that graphene can exist stably in nature, it has become a research hotspot in the field of nanomaterials due to its many excellent optical and electronic properties. As a new type of two-dimensional material, graphene is one of the strongest materials known and has good toughness. In the optical frequency band, it has an absorption rate of only 2.3% and a transmittance of 97.7%. That is, for visible light, graphene is basically transparent, and when the incident light intensity reaches a certain threshold, its absorption will reach a saturation state. Due to its unique optical and electronic properties, such as high carrier mobility, zero-gap bandgap structure, and tunability of changing conductivity by applying bias voltage or chemical doping, graphene has become one of the main materials for making absorbers.

[0005] In addition to graphene, the phase change material vanadium dioxide has gradually entered the field of vision of researchers. People have found that the optical properties of vanadium dioxide change with temperature. Therefore, vanadium dioxide materials are gradually used to realize optical devices and radio frequency electronic devices. The phase change of vanadium dioxide occurs between dielectric and metal. When the temperature is at room temperature, vanadium dioxide is in the dielectric state; when the temperature exceeds 340K, vanadium dioxide exhibits the properties of metal.

[0006] Compared with traditional metal absorbers, the absorber based on graphene and vanadium dioxide proposed in the present invention has a simple structure and is easy to process. The properties of graphene can also be adjusted by applying an external voltage, and the properties of vanadium dioxide can also be adjusted by changing the temperature. In addition, when the temperature exceeds 340K, the device proposed in the present invention can work as a reflector to completely reflect the incident electromagnetic waves. Summary of the invention

[0007] The present invention designs a dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials, providing a dual-function device with simple structure and easy adjustment.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials. The device is a two-dimensional periodic three-layer structure, which consists of: a layer of cross-graphene, a layer of vanadium dioxide, and a bottom metal reflective layer from top to bottom.

[0010] The dynamically adjustable dual-function device of graphene and vanadium dioxide metamaterial in the technical solution is based on graphene material and can be made by graphite oxide reduction method, and the processing of the device also includes photolithography and etching technology. The present invention uses graphene material as an absorption medium.

[0011] The beneficial effects of the present invention are:

[0012] 1. It can achieve efficient absorption of terahertz waves, and the absorption efficiency of a single band is close to 100%.

[0013] 2. By adjusting the chemical potential of graphene, the absorption bandwidth can be dynamically adjusted, and the absorption efficiency is above 90%.

[0014] 3. By adjusting the external temperature, the properties of vanadium dioxide can be dynamically changed, thereby adjusting the absorption bandwidth, and the absorption efficiency is above 90%.

[0015] 4. The absorption peak position of the device can be adjusted not only by geometric parameters but also by applying external voltage and changing the external temperature.

[0016] 5. The dual-function device adopts a two-dimensional periodic structure, which is simple and compact, and is easy to integrate on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structural unit of the present invention.

[0018] Figure 2 This is an absorption diagram with l=5.0um, w=2um, and μ varying from 0.1eV to 0.3eV.

[0019] Figure 3 It is an absorption diagram with l=5.0um, w=2um, and σ varying from 100S / m to 10000S / m.

[0020] Figure 4 It is the reflection spectrum when l=5.0um, w=2um, σ=200000S / m.

[0021] The above pictures contain: 1: metal material gold; 2: vanadium dioxide; 3 graphene DETAILED DESCRIPTION

[0022] Figure 1 It is a dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials. It is composed of gold with a period of p = 6.0um and a thickness of t = 0.2um as the reflective bottom layer; a layer of vanadium dioxide with a thickness of d = 0.5um is superimposed on the gold, and its conductivity can change dynamically with the change of temperature, reflecting the properties of the medium at room temperature and the properties of the metal when the temperature exceeds 340K; a layer of cross-shaped graphene with a thickness of g = 0.001um is superimposed on the vanadium dioxide. Among them, the thickness of gold is much greater than the skin depth of gold in the mid-infrared band, so the gold substrate of the material can be regarded as a perfect electrical conductor (PEC).

[0023] The working principle of the dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials can be explained as follows. When at room temperature, vanadium dioxide exhibits the properties of a medium, and at this time, the present invention can be used as an absorber. Figure 1 As shown, due to the cross-shaped graphene structure, when the electromagnetic wave is incident on the graphene surface, the resonance condition is met, and the resonance condition can be expressed by the formula 2ksppL+2δ=2pπ, where kspp is the graphene surface plasma wave vector, L is the resonance cavity length, δ is the phase change at both ends of the resonance cavity, and p is an integer. In addition, the resonance frequency of the trapezoidal graphene array can be expressed by the formula ω=1.0 / (LC) 1 / 2 To describe, L and C in the formula are the inductance and capacitance of the resonator respectively. The total inductance of the resonator is the dynamic inductance L k And the ordinary inductor L g The dynamic inductance can be calculated by the formula L k =α(m e / (N d e 2 )) to estimate, where α is a parameter related to the structural unit, e is the electron charge, m e is the mass of the electron, N dis the carrier concentration. When the Fermi level of graphene increases, its dynamic inductance decreases, resulting in a decrease in the total inductance, so the resonant frequency increases. Here we can change the carrier concentration of graphene by applying a bias voltage between the graphene strip and the metal substrate, thereby achieving the purpose of adjusting the chemical potential of graphene. Figure 2 As shown, when μ=0.1eV, the absorption bandwidth range of the absorber above 90% is 56.1THz-59.0THz, and the maximum absorption rate exceeds 99.5%; when μ=0.3eV, the absorption bandwidth range of the absorber above 90% is 57.1THz-59.6THz, and the maximum absorption rate exceeds 99.9%.

[0024] When the external temperature changes, the conductivity of vanadium dioxide also changes. As the temperature gradually increases, the conductivity of vanadium dioxide gradually increases. When the temperature exceeds 340K, vanadium dioxide fully reflects the properties of metal. Figure 3 We can see that as the conductivity of vanadium dioxide increases, the position of the absorption peak and the absorption bandwidth of the absorber change. When σ = 100S / m, more than 90% of the absorption bandwidth is 54.6THz-58.6THz, and the maximum absorption rate exceeds 99.7%; when σ = 10000S / m, the absorption rate near 50THz decreases, and more than 90% of the absorption peak is near 90THz. The absorption bandwidth of more than 90% is 90.1THz-91.1THz, and the maximum absorption rate exceeds 97.8%. From Figure 3 It can be seen that with the increase of the conductivity of vanadium dioxide, the low-frequency band absorption peak gradually decreases, and the high-frequency band absorption peak gradually increases.

[0025] As the temperature rises further, vanadium dioxide exhibits metallic properties, and at this point, the dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials can be used as a reflector. Figure 4 As shown, the present invention has a reflectivity of more than 99% in the entire frequency band.

Claims

1. A dynamically adjustable dual-function device based on graphene and vanadium dioxide metamaterials. The device adopts a two-dimensional periodic three-layer structure, which includes: A layer of cross-shaped graphene, a layer of vanadium dioxide, and a bottom layer with gold as a reflective base; wherein the thicknesses of the bottom gold reflective base layer, the vanadium dioxide layer, and the top graphene layer are 0.2um, 0.5um, and 0.001um, respectively, the period P=6um, and the length l of the cross arm of the cross-shaped graphene is 5um, and the width w is 2um.

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