Boronene-based and strain-tunable broadband terahertz absorber and design method thereof

Abstract

The application discloses a kind of based on boronene and its strain regulation and control broadband terahertz wave absorber and its design method, the designed wave absorber includes metal bottom plate and dielectric substrate silicon, sheet boronene is arranged on the surface of silicon lining, and thin dielectric layer silicon is arranged above boronene.The optical conductivity of boronene in terahertz frequency band is calculated by first principle, and then through design and simulation by finite-difference time-domain method, a broadband terahertz wave absorber is obtained.The boronene based on different uniaxial tensile strain is calculated, the designed wave absorber under different polarization directions, the working bandwidth of wave absorber is widened or reduced respectively, the wave absorber changes from isotropic to anisotropic, solves the problem that existing broadband terahertz wave absorber is difficult to actively control, simultaneously expands the terahertz working bandwidth of wave absorber, realizes the characteristics of active control in broadband terahertz wave absorption work.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing materials, and particularly to a wideband terahertz wave-absorbing device based on boronene and its strain regulation and a design method thereof. BACKGROUND

[0002] Boronene is a two-dimensional material composed of boron atoms, which has good thermal stability and high electron velocity, exhibits metallic electron transport characteristics, and exhibits unique anisotropy in photons and electrons. At the same time, the intrinsic metallic properties and high carrier concentration of boronene make it have great potential in future nanophotonic electronics.

[0003] A metamaterial wave-absorbing device is a device that binds incident electromagnetic waves through surface plasmons excited by periodic patterning, thereby causing dielectric loss or ohmic loss to absorb electromagnetic waves, and ultimately achieving high absorption or even perfect absorption. Terahertz waves, as electromagnetic radiation waves with a frequency range of 0.1 THz to 10 THz, have important application value in military and civilian fields, but their electromagnetic radiation characteristics have not been fully understood and developed. Therefore, the research on wideband terahertz wave-absorbing devices has extremely important role and significance. With the emergence of two-dimensional materials, terahertz wave-absorbing devices have good wave-absorbing ability by utilizing their excellent optoelectronic properties. However, their wave-absorbing bandwidth and active tunability are still not satisfactory. For example, Cheng et al. published "Broadband Terahertz Near-Perfect Absorbers" in the ACS Applied Materials & Interfaces journal in 2020, in which patterned metal was used as a metamaterial surface structure to make the wave-absorbing device have a wideband wave-absorbing effect. However, the wave-absorbing device lacks active regulation performance. In addition, Qing et al. published "Tailoring anisotropic perfect absorption in monolayer black phosphorus by critical coupling at terahertz frequencies" in the Optical Express journal, in which a single-layer black phosphorus and a dielectric layer were coupled to realize the active tuning of the wave-absorbing device. However, the wave-absorbing device lacks wideband wave-absorbing performance, and it is difficult to change the carrier concentration and has a great impact on the wave-absorbing ability, which limits the practical application of the wave-absorbing device.

[0004] Due to the important role of wideband wave-absorbing devices in terahertz technology, the devices not only need to have high wave-absorbing ability and high working bandwidth, but also need to have sufficient active coordination performance. However, the existing technology has insufficient wave-absorbing bandwidth and complex structure on the one hand, and lacks sufficient active tuning on the other hand. SUMMARY

[0005] The present application aims at overcoming the deficiencies in the prior art, and provides a terahertz broadband wave absorber which can be actively tuned and has excellent wave absorbing performance.

[0006] The present application provides a design method of a broadband terahertz wave absorber based on boronene and strain regulation, comprising the following steps:

[0007] Step 1: establishing a crystal structure of boronene from an atomic level;

[0008] Step 2: based on the obtained crystal structure of boronene, using a first-principle calculation software package, calculating optical conductivity of the obtained boronene in a terahertz frequency band under no strain and uniaxial tensile strain;

[0009] Step 3: based on the boronene under no strain, designing a broadband terahertz wave absorber, using a finite-difference time-domain method to simulate and calculate broadband wave absorbing efficiency of the boronene under no strain in the absorber in a terahertz frequency band;

[0010] Step 4: by changing a strain rate of the boronene, the wave absorbing bandwidth of the absorber is widened or reduced, so that the absorber obtains an active tuning characteristic.

[0011] Further, in Step 1, the crystal structure of boronene is established from an atomic level, and the boronene is selected from β 12 -type boronene or χ3-type boronene.

[0012] Further, in Step 2, the calculation of the optical conductivity of the boronene under no strain and uniaxial tensile strain comprises the following contents:

[0013] (2.1) performing relaxation and self-consistent calculation on the obtained boronene crystal structure to obtain Fermi energy E F ;

[0014] (2.2) performing optical parameter calculation on the self-consistently optimized crystal structure, and establishing plasmon frequency ω n,k by obtaining wave vector k of the boronene, volume V of the boronene, energy E p of a k point on the nth energy band, and expression:

[0015]

[0016] wherein x i i=1 represents an x component, x i i=2 represents a y component, is a reduced Planck constant, e is an electron charge amount, is a unit vector in the i-th direction;

[0017] (2.3) Calculate the optical conductivity of the obtained boronene based on the Drude model using the plasma frequency expression:

[0018]

[0019] Where ω is the working frequency, and the relaxation time τ is 65 fs.

[0020] Further, step 3 designs and calculates the broadband terahertz wave absorber, wherein, under no strain, the absorption calculation expression is:

[0021] A = 1 - R - T

[0022] Where A is the absorption power, R is the reflectivity, and T is the transmissivity.

[0023] Further, in step 4, the uniaxial tensile strain regulation of boronene is carried out to obtain the active regulation characteristics of the broadband terahertz wave absorber.

[0024] The application also provides a broadband terahertz wave absorber based on boronene and its strain regulation, which comprises a metal bottom plate, a dielectric substrate, the obtained boronene, and a dielectric plate; wherein the metal bottom plate is located at the bottom region of the absorber, the dielectric substrate is located above the metal bottom plate, the obtained boronene is located between the dielectric plate and the dielectric substrate, the dielectric plate is located above the obtained boronene, and the dielectric substrate and the dielectric plate form a dielectric layer, and the dielectric substrate and the dielectric plate are both silicon materials.

[0025] Advantages: Compared with the prior art, the application has the following significant features: the crystal structure of boronene is established from the atomic level, the optical conductivity of boronene in the terahertz frequency band under no strain and uniaxial tensile strain is calculated, the metamaterial wave absorber is designed, the broadband absorption efficiency of the metamaterial wave absorber is calculated, the broadband absorption of the wave absorber in the terahertz frequency band is realized, and the dynamic adjustment characteristics in the wave absorption process are realized by changing the strain rate of boronene and using the strain regulation method. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the atomic structure diagram of the β 12 type boronene in the application;

[0027] Figure 2 is the real part optical conductivity distribution diagram of the β 12 type boronene under no strain and different strains in the application;

[0028] Figure 3 is a schematic diagram of the metamaterial wave absorber in the application;

[0029] Figure 4 is the broadband terahertz wave absorber based on the β 12The terahertz wave absorber of the β

[0030] Figure 5 is based on strain regulation β 12 The absorption rate distribution diagram of the metamaterial wave absorber of the β

[0031] Figure 6 is based on strain regulation β 12 The absorption rate distribution diagram of the metamaterial wave absorber of the β Specific implementation method

[0032] The application will be further described in detail below with reference to the drawings and specific embodiments.

[0033] Embodiment 1

[0034] The application provides a broadband terahertz wave absorber design method based on boronene and strain regulation thereof, the boronene is selected from β 12 type boronene or χ3 type boronene, wherein β 12 type boronene a1=0.292 nm, a2=0.508 nm; χ3 type boronene a1=a2=0.455 nm, the angle between a1 and a2 is 141.7°. In this embodiment, β 12 type boronene is taken as an example, comprising the following steps:

[0035] Step 1: establishing the crystal structure of boronene from the atomic level;

[0036] As Figure 1 shown is the atomic structure diagram of β 12 type boronene, the lattice constant is a1=0.292 nm, a2=0.508 nm.

[0037] Step 2: based on the obtained crystal structure of boronene, the optical conductivity of the obtained boronene in the terahertz frequency band under no strain and uniaxial tensile strain is calculated by using a first-principle calculation software package.

[0038] (2.1) performing relaxation and self-consistent calculation on the boronene crystal structure to obtain the Fermi energy E F of the boronene.

[0039] (2.2) performing optical parameter calculation on the self-consistently optimized crystal structure, obtaining the wave vector k of the boronene, the volume V of the boronene, the energy E n,k of the k point on the nth energy band, and establishing the expression of the plasma frequency ω p :

[0040]

[0041] wherein xi In this context, i = 1 represents the x component, and i = 2 represents the y component. Here, e is the reduced Planck constant, and e is the electron charge. Let be the unit vector in the i-th direction;

[0042] (2.3) The optical conductivity based on the Drude model was calculated using the plasma frequency expression:

[0043]

[0044] Where ω is the operating frequency and the relaxation time τ is 65fs.

[0045] like Figure 2 The image shows the optical conductivity distribution, β. 12 Boronene exhibits near-isotropic properties with similar optical conductivity along the x and y axes under unstrained conditions. As the uniaxial strain rate gradually increases, β... 12 The optical conductivity of boroene gradually increases along the x-axis, while the optical conductivity along the y-axis gradually decreases with increasing strain rate. Therefore, the optical anisotropy gradually increases with increasing strain rate.

[0046] Step 3: Design a broadband terahertz absorber based on a boronene crystal structure, and use the finite-difference time-domain method to perform simulation in the terahertz band to calculate the bandwidth absorption efficiency of the boronene in the absorber.

[0047] like Figure 3 As shown, this embodiment provides a method based on β 12 A broadband terahertz absorber of boronene includes a metal substrate 1, a dielectric substrate 2 on top of the metal substrate 1, and a sheet-like β-type absorber. 12 Type 3 and β-boronene 12 The dielectric plate 4 is an upper layer of boronene. The metal substrate 1 has the same length as the period p, p = 2.1 μm, and a thickness d3 = 0.5 μm; the dielectric substrate 2 has a thickness d2 = 3.1 μm, and the dielectric plate has a thickness d1 = 0.5 μm. Both the dielectric substrate 2 and the dielectric plate 4 are made of silicon with a refractive index n = 3.4, and are sheet-like β-type. 12 The width of type borone 3 is w = 1.3 μm.

[0048] like Figure 4 As shown, the results obtained from simulation using the finite-difference time-domain method are based on unstrained β. 12 The absorption effect of the terahertz absorber of boronene. In the range of 4.56THz to 7.74THz, the absorption rate is above 90%, the bandwidth is 3.18THz, the average absorption rate is 94.8%, and the absorption capacity of the absorber is similar when the electromagnetic wave electric field direction is along the x and y directions, respectively, exhibiting isotropic characteristics.

[0049] The working principle of the microwave absorber is as follows: The absorption rate of the microwave absorber is calculated using the formula A = 1 – R – T, where A is the absorbed power, R is the reflectivity, and T is the transmittance. Since the metal base plate 1 is sufficiently thick, the transmittance T = 0. Therefore, the absorption formula can be expressed as: A = 1 – R. When a terahertz wave is incident perpendicularly into the absorbing material, it excites the sheet-like β... 12 Localized surface plasmon polaritons (LSPPs) of boronene 3. Here, the excited local electric field energy is distributed along the electric field polarization direction in the terahertz band on the sheet-like β... 12 The edges and four peaks of the boronene lead to enhanced resonant absorption at two terahertz frequencies, and the superposition of the two resonant peaks results in a broadband absorption effect.

[0050] Step 4: By changing the strain rate of the boronene, the absorption bandwidth of the absorber can be widened or reduced, thereby enabling the absorber to obtain active tuning characteristics.

[0051] β 12 The absorptivity distribution of the absorbing sorbent under different uniaxial tensile strain rate modulations is as follows: Figure 5 As shown. When the strain rates are 2%, 4%, and 6%, and the electromagnetic wave electric field polarization direction is along the y-axis, the absorption rate is also above 85%, and the absorption bandwidth is 2.75 THz, 3.1 THz, 3.25 THz, and 3.4 THz, respectively. Conversely, as... Figure 6 As shown, when the polarization direction of the electromagnetic wave's electric field is along the x-axis, the absorption rate decreases, but the absorption bandwidth gradually expands with increasing tensile strain rate. Simultaneously, the anisotropy of the absorber gradually strengthens with increasing strain rate. Therefore, based on the β... 12 By controlling the strain of boronene, the terahertz absorber can be actively and dynamically adjusted, expanding its application range.

[0052] The above is based solely on β. 12 The dimensional parameters involved in this invention are also applicable to broadband absorbers based on χ3-type borene and its strain-controlled properties.

[0053] In summary, absorbers based on borophene and its strain-tunable structure can achieve broadband absorption in the terahertz band, and active tuning characteristics can be achieved by applying strain to borophene to tune the absorption bandwidth. The absorber described in this invention has a simple structure and can be used in terahertz technology and novel optoelectronic devices.

Claims

1. A method for designing a borophene-based and strain-tunable broadband terahertz absorber, characterized in that, Comprising the following steps: Step 1: Establishing the crystal structure of boronene from the atomic level; Step 2: Based on the obtained crystal structure of boronene, using the first-principles calculation software package, the optical conductivity of the obtained boronene in the terahertz frequency band under unstrained and uniaxial tensile strain is calculated, specifically including: (2.1) Relaxing and self-consistent calculation are performed on the obtained boronene crystal structure to obtain its Fermi energy ; (2.2) Optical parameter calculation is performed on the self-consistent optimized crystal structure, and the wave vector k of boronene, the volume V of boronene, and the energy of the k point on the nth energy band are obtained , the plasma frequency Expression: where x i represents the x component, i = 2 represents the y component, is the reduced Planck constant, is the elementary charge, is the unit vector in the i th direction; (2.3) Calculate the optical conductivity of the obtained boronene based on the Drude model using the plasma frequency expression: wherein is the operating frequency, and the relaxation time τ is 65 fs; Step 3: Based on the boronene under unstrained, design a broadband terahertz wave absorber, use the finite difference time domain method to simulate in the terahertz frequency band, calculate the broadband wave absorption efficiency of the boronene under unstrained in the absorber; Step 4: By changing the strain rate of boronene, the absorption bandwidth of the absorber is widened or reduced, so that the absorber obtains the active tuning characteristics.

2. The borophene and its strain-tunable based broadband terahertz absorber design method according to claim 1, wherein, In step 1, the crystal structure of boronene is constructed at the atomic level, and boronene is selected as β 12 type boronene or χ3type boronene.

3. The borophene and its strain tuning based broadband terahertz absorber design method according to claim 1, wherein, Step 3 designs and calculates the broadband terahertz wave absorber, wherein under unstrained, the absorption calculation expression is: Where A is the absorption power, R is the reflectivity, and T is the transmissivity.

4. The borophene and its strain tuning based broadband terahertz absorber design method according to claim 1, wherein, In step 4, the boronene is uniaxially stretched and strained to obtain the active tuning characteristics of the broadband terahertz wave absorber.

5. A broadband terahertz wave absorber implementing the boronene-based and strain-regulated broadband terahertz wave absorber design method of claims 1-4, comprising a metal bottom plate, a dielectric substrate, the obtained boronene, and a dielectric plate; wherein the metal bottom plate is located at the bottom area of the absorber, the dielectric substrate is located above the metal bottom plate, the obtained boronene is located between the dielectric plate and the dielectric substrate, the dielectric plate is located above the obtained boronene, the dielectric substrate and the dielectric plate form a dielectric layer, and the dielectric substrate and the dielectric plate are both made of silicon material.

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