CN108646325A - A kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency - Google Patents

Abstract

A frequency-tunable graphene wide-angle terahertz absorber relates to terahertz absorbing. It is a 5-layer structure device, from top to bottom: upper graphene strip layer, upper dielectric layer, lower graphene strip layer, lower dielectric layer and metal substrate layer; it is periodic in the xoy plane, so The upper graphene strip layer is composed of rectangular strip graphene; the upper dielectric layer is composed of low dielectric constant material, and the lower graphene strip layer is composed of rectangular strip graphene; the lower dielectric layer is composed of low dielectric constant material Composition; the thickness of the metal substrate layer is greater than the skin depth of the incident wave; the lower graphene strip layer and the upper graphene strip layer are vertically placed and separated by the upper dielectric layer.

Description

A frequency-tunable graphene wide-angle terahertz absorber

technical field

The invention relates to terahertz absorbers, in particular to a graphene wide-angle terahertz absorber with adjustable frequency.

Background technique

Terahertz waves generally refer to electromagnetic waves with a frequency of 0.1-10THz, and the corresponding wavelength range is 3-0.03mm[1-2]. Broad application prospects. Since Landy et al. proposed a perfect metamaterial absorber in 2008 (Phys.Rev.Lett., vol.100, pp.207402, 2008), the research on terahertz metamaterial absorber has attracted people's attention. great concern. The sub-wavelength metal microstructure array layer-dielectric layer-metal layer sandwich structure is a typical structure of metamaterial absorbers, which can suppress the transmission and reflection channels by utilizing the subwavelength metal array layer structure, the ohmic loss of the metal layer and the Dielectric absorption achieves perfect absorption of incident electromagnetic waves. However, due to the use of conventional metal and dielectric materials for this type of absorber, the adjustment of the absorbing frequency of this type of metamaterial absorber can only be realized by changing the geometric structure size under normal circumstances. Once the device is prepared, The structure size is fixed, and its absorption characteristics are not adjustable. Therefore, in order to realize the adjustment of the terahertz absorption frequency without changing the geometric structure, it has become an important research direction in the field of terahertz absorbers to conduct in-depth research on new absorbers with materials with adjustable electromagnetic parameters. .

Graphene is a honeycomb two-dimensional carbon atom material. Due to its special electronic band structure, graphene exhibits excellent performance characteristics such as unique electrical tunability, low intrinsic loss, and high optical field localization. extensive attention. In particular, graphene has become an electromagnetic film material with excellent performance and is widely used in various surface plasmon devices due to its ability to support surface plasmon polaritons (SPPs) transmission in terahertz, infrared and visible bands. The new metamaterial absorber based on graphene material can not only achieve extremely high absorption rate, but also adjust the conductivity of graphene through external bias voltage, and then realize the adjustment of its absorbing characteristics. At present, people have proposed various forms of graphene absorbers. For example, Ning Renxia et al. proposed a broadband absorber based on hyperbolic graphene metamaterials, and its absorption rate is 70%. The relative absorption bandwidth is 45% (Eur.Phys.J.Appl.Phys.,68(2):20401,2014); YayingNing et al proposed a graphene-based metal nanostructure tunable absorber when the frequency of the absorber is graphene chemistry When the potential changes from 0.2eV to 0.8eV, the central absorption frequency of the absorber will increase from 30.1THz to 32.2THz, and the fractional frequency modulation range relative to the lowest absorption frequency is only 6.97%, and the incident wave angle-independent range is only -12° to 12° (Optics Express, 25(26), 2017). However, many current graphene absorbers still have problems such as complex device structure, angle dependence, and small adjustment range of absorbing frequency and absorption rate for incident waves. In view of the fact that frequency-tunable wide-angle terahertz absorbers have important application prospects in the fields of detectors, sensors, sensors, electromagnetic wave detection and control, and stealth, the research has the advantages of simple structure and wide-range adjustable absorbing frequency The graphene wide-angle terahertz absorber is of great significance.

Contents of the invention

The purpose of the present invention is to solve the problem of the graphene wave absorber in the prior art that the frequency and angle adjustment range of the absorption rate is small, and to provide a large-scale adjustment of the absorption frequency of the wide-angle incident terahertz wave Frequency-tunable graphene wide-angle terahertz absorber.

The present invention is a device with a 5-layer structure. From top to bottom, it is: upper graphene strip layer, upper dielectric layer, lower graphene strip layer, lower dielectric layer and metal substrate layer; it has periodicity in the xoy plane , the upper graphene strip layer is composed of rectangular strip graphene; the upper dielectric layer is composed of low dielectric constant material, and the lower graphene strip layer is composed of rectangular strip graphene; the lower dielectric layer is composed of low dielectric constant Composed of constant materials; the thickness of the metal substrate layer is greater than the skin depth of the incident wave; the lower graphene strip layer and the upper graphene strip layer are vertically placed and separated by the upper dielectric layer.

The period lengths of the periodic unit structure in the xoy plane in the x and y directions are L _x =L _y =4 μm respectively; the upper graphene strip layer has a width of W _u =0.9 μm and a length of L _x = 4 μm rectangular ribbon-shaped graphene; the upper dielectric layer is made of low dielectric constant material with a thickness of h ₁ = 1 μm, and the lower graphene strip layer is composed of a width of W _d = 0.9 μm and a length of L _y = 4μm rectangular striped graphene; the thickness of the lower dielectric layer is h ₂ =4μm low dielectric constant material; the thickness of the metal substrate layer is h ₃ =1μm greater than the skin depth of the incident wave.

The low dielectric constant material can be one of Sio ₂ , Topas, Zro ₂ , etc.; the metal substrate layer can be made of good conductor materials such as gold or silver.

The working principle of the present invention is as follows:

The invention is a periodic graphene strip layer-dielectric layer-graphene strip layer-dielectric layer-metal layer 5-layer structure device, the thick metal layer in the design structure is equivalent to mirror reflection to suppress the transmission of electromagnetic waves when electromagnetic waves are incident At the same time, by rationally designing the structural dimensions of the upper and lower graphene layers and the upper and lower dielectric layers, the electromagnetic wave reflection can be effectively suppressed, and the mutually coupled terahertz localized surface plasmon resonance can be excited by the upper and lower graphene layers at the same time. Perfect absorption of Hertzian waves; using the electrical tunability of graphene, the binding properties of excitons such as the graphene surface can be changed by adjusting the chemical potential of the graphene layer, so as to achieve a wide range of adjustment of the center frequency of the incident terahertz wave.

The beneficial effects of the present invention are:

1) The present invention has a periodic graphene strip layer structure, can excite local surface plasmons, and has a very high absorption rate for narrow-band incident terahertz waves, and the present invention can achieve 100% perfect absorption by setting parameters reasonably.

2) The present invention has the characteristic that the absorption rate of the incident terahertz wave is angle-independent. When the chemical potential of graphene is 0.5eV, when the angle of the incident terahertz wave changes in the range of 0°～85°, the absorption The absorption rate of the wave filter can be kept above 80%.

3) The present invention has electrical adjustability. By changing the bias voltage of the upper and lower graphene strip layers, the absorption frequency of the terahertz wave can be adjusted in a large range. When the graphene chemical potential changes from 0.2eV to 0.9eV, the absorption The central absorption frequency of the oscilloscope for terahertz waves will increase from 5.4THz to 12THz, and the fractional frequency modulation range relative to the lowest frequency will reach 122.2%.

4) The present invention has a simple structure, is easy to apply a bias, and can be used for electromagnetic wave absorption in the infrared region, visible light region or other frequency bands through scale transformation.

Description of drawings

FIG. 1 is a schematic diagram of the structural composition of an embodiment of the present invention.

Fig. 2 is a top view of the unit structure of the embodiment of the present invention.

Fig. 3 is a diagram of absorption curves at different incident angles from 0° to 85° according to an embodiment of the present invention.

Fig. 4 is a curve diagram of the absorption rate of the embodiment of the present invention under different chemical potentials such as 0.2-0.9eV.

Detailed ways

The present invention will be further elaborated below in conjunction with the accompanying drawings and specific examples.

An embodiment of the present invention is shown in Figures 1 and 2. A frequency-tunable graphene wide-angle terahertz absorber is a five-layer structure device, from top to bottom: the upper graphene strip layer 1 , an upper dielectric layer 2, a lower graphene strip layer 3, a lower dielectric layer 4, and a metal substrate layer 5; the frequency-tunable graphene wide-angle terahertz absorber has a periodic unit structure in the xoy plane The period lengths in the x and y directions are L _x and _{Ly y} respectively, wherein: the upper graphene strip layer 1 is composed of rectangular ribbon graphene with a width of Wu _u and a length of L _x ; the upper dielectric layer 2 is Thickness h ₁ low dielectric constant material, such as: Sio ₂ , Topas, Zro ₂ , etc.; the lower graphene strip layer 3 is also composed of rectangular strips of graphene with a width of W _d and a length of _Ly ; The dielectric layer ₄ is made of a low dielectric constant material with a thickness of h2, such as: Sio2, Topas, _Zro2 , etc.; the material of the metal substrate layer ₅ is a good conductor material such as gold or silver, and its thickness is h3 greater _than that of the incident wave skin depth; the structure of the wide-angle terahertz wave absorber of a frequency-tunable graphene is characterized in that the graphene strip 3 and the graphene strip 1 are placed perpendicularly to each other in the structure of the wave absorber. Dielectric layer 2 isolation. The size parameters of the unit structure are set as: L _x =L _y =4 μm, Wu _u =W _d =0.9 μm, h ₁ =1 μm, h ₂ =4 μm, h ₃ =1 μm. Since the upper and lower graphene strip layers of the absorber can excite mutually coupled terahertz surface plasmons, it can have a very high absorption rate for narrow-band terahertz waves incident in a wide range of angles. When the chemical potential When 0.5eV is taken, the electromagnetic simulation obtained the absorption rate curves of this embodiment for different angles of incident terahertz waves, as shown in Figure 3. It can be seen that when the incident TM polarized terahertz waves have an angle in the range of 0° to 85° When changing, the absorption rate of this embodiment can be kept above 80%, and has good angle-independent absorption characteristics. The chemical potential of graphene can be changed by changing the bias voltage loaded on the graphene layer, and then the adjustment of the absorptivity can be realized. The absorptivity curves of this embodiment for vertically incident terahertz waves under different chemical potential conditions are as follows As shown in Figure 4, it can be seen that when the chemical potential is 0.3eV and 0.5eV, the absorption rate of this embodiment can reach 100%. This embodiment has electrical adjustability. When the geometric parameters of this embodiment are kept constant Under the premise that the chemical potential of graphene changes from 0.2eV to 0.9eV, the central absorption frequency of the terahertz wave in this embodiment will increase from 5.4THz to 12THz, that is, the range of fractional frequency modulation relative to the lowest frequency can reach 122.2%, which is a A novel wide-angle terahertz absorber with adjustable center frequency and good performance.

The invention is a device with a 5-layer structure, which is graphene strip layer-dielectric layer-graphene strip layer-dielectric layer-metal layer from top to bottom, wherein the graphene strip layer is composed of periodic rectangular strips Composed of graphene, two layers of graphene strips are placed perpendicular to each other and separated by a dielectric layer. The invention can achieve strong absorption of terahertz waves and has angle-independent characteristics for terahertz waves. When the incident angle increases to 85°, its absorption rate can still be maintained above 80%. When the chemical potential of graphene changes from 0.2eV Increase to 0.9eV, its absorbing frequency increases from 5.4THz to 12THz, and the corresponding fractional frequency modulation range reaches 122.2%. The invention can realize the large-range adjustment of the absorption rate and center frequency of the terahertz wave, and is a novel wide-angle terahertz wave absorber with great potential for frequency adjustment.

Claims (9)

1. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency, it is characterised in that be a kind of 5 layers of structure devices, from upper It is followed successively by under：Upper graphene strips belt, upper dielectric layer, lower graphene strips belt, lower dielectric layer and metallic substrate layer；In xoy Have in plane periodically, the upper graphene strips belt is made of rectangular strip shape graphene；Upper dielectric layer is by low-k Material is constituted, and lower graphene strips belt is made of the band-like graphene of rectangular strip；Lower dielectric layer is made of advanced low-k materials；Gold The thickness for belonging to substrate layer is more than the skin depth of incidence wave；The lower graphene strips belt is mutually perpendicular to upper graphene strips belt It places and is isolated by upper dielectric layer.

2. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that it is described It is respectively L to have the cycle length of periodic cellular construction in the x and y direction in xoy planes_x=L_y=4 μm.

3. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that on described Graphene strips belt is W by width_u=0.9 μm, length L_x=4 μm of rectangular strip shape graphene composition.

4. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that on described The thickness of dielectric layer is h₁=1 μm of advanced low-k materials are constituted.

5. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that under described Graphene strips belt is W by width_d=0.9 μm, length L_y=4 μm of the band-like graphene composition of rectangular strip.

6. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that under described The thickness of dielectric layer is h₂=4 μm of advanced low-k materials are constituted.

7. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that the gold The thickness for belonging to substrate layer is h₃=1 μm of skin depth for being more than incidence wave.

8. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that described low Dielectric constant material is Sio₂、Topas、Zro₂In one kind.

9. a kind of adjustable graphene wide angle Terahertz wave absorbing device of frequency as described in claim 1, it is characterised in that the gold Belong to substrate layer using gold or silver-colored good conductor material.