CN111830761A

CN111830761A - Plasma induction transparent resonator based on graphene in intermediate infrared band

Info

Publication number: CN111830761A
Application number: CN201910317027.6A
Authority: CN
Inventors: 肖丙刚; 宫绍康; 蔡万钧
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2019-04-19
Filing date: 2019-04-19
Publication date: 2020-10-27

Abstract

The invention discloses a plasma induced transparent resonator based on graphene in a middle infrared band, belongs to a resonance device in the technical field of middle infrared, and utilizes the characteristics of graphene surface plasmas and a plasma induced transparent theory. The resonance device is a three-dimensional periodic structure, and the structure of the resonance device comprises the following components: the top layer is a graphene ring and a graphene symmetrical fan-shaped disc, the middle layer is a calcium fluoride medium, and the bottom layer is a doped silicon substrate layer which is stacked from top to bottom to form a three-layer structure. The invention mainly calculates and simulates the resonance spectrum of the intermediate infrared band resonator by a finite element method, optimizes the structure of the resonator, has the capability of exciting the plasma-induced transparent resonance in the intermediate infrared band, and can effectively tune the linear and resonant frequency of the plasma-induced transparent resonance. The invention has simple, compact and reasonable structure and is convenient to process.

Description

Plasma induction transparent resonator based on graphene in intermediate infrared band

Technical Field

The invention relates to a plasma induced transparent resonator based on graphene in a middle infrared band, and belongs to the field of application of graphene materials in middle infrared band resonators.

Background

Electromagnetic Induced Transparency (EIT) is a phenomenon of enhanced absorption and transmission caused by quantum interference, and can be implemented to control the optical response of a material with an electromagnetic field. This phenomenon was first observed in the original system, which can be implemented in a three-level system. The atomic EIT effect is widely applied to the fields of slow light, nonlinear optics and the like. However, the implementation of atomic EIT effect is difficult, requiring very harsh environmental and operating conditions, which greatly limits the application and development of traditional atomic EIT. To overcome these problems, new systems similar to the atomic EIT system have been developed. Plasma Induced Transparency (PIT) is a kind of EIT effect, has attracted people's attention, and is applied in the fields of sensing, slow light, optical storage, etc. The implementation of the PIT effect typically uses bright-dark mode coupling, i.e. generated by direct destructive interference between the bright and dark state modes.

The frequency of the mid-infrared is mainly a spectrum in the range of 15-150 THz (2-20 μm), and the mid-infrared spectrum has a great potential in various fields such as environmental monitoring, sensing and astronomical detection, because fingerprints of many materials fall in the spectral region. Especially in the sensing field, many molecular fingerprints are distributed in the mid-infrared band, and the molecular fingerprints can be very accurately judged by the sensor, so that the mid-infrared band sensor has attracted much attention in recent years. However, conventional sensors generally use metal and semiconductor materials, have large ohmic and radiation losses, suffer from serious performance loss, and generally have low quality factor and sensitivity. For reduced losses in the mid-infrared region, the plasmon resonance (PFR) should exhibit a high quality factor. This feature has a strong effect on surface enhanced infrared absorption (SEIRA), which can provide molecular information due to material specific vibration absorption in the mid-infrared fingerprint region. The plasma induced transparency phenomenon is used as a resonance form in the plasmon, and the ultrahigh quality factor and the high sensitivity are shown in the mid-infrared band, which shows that the transparent material has great potential in the fields of sensing and the like.

In consideration of the requirements of difficulty and easiness of the structure and the like, the invention provides a graphene-based plasma-induced transparent resonator, which can provide important preconditions for the adjustable mechanism of a graphene plasma excimer structure and the design of high-sensitivity devices (such as a sensor, a modulator and an antenna).

In recent years, with the research on graphene by researchers, the plasma-induced transparency effect based on graphene attracts much attention. It is well known that the plasma transparency effect based on the excitation of conventional metallic metamaterials has a serious drawback in that the operating wavelength of the transparent window is fixed once the structure is fabricated. The transparent window can be controlled by regulating the Fermi level of the graphene based on the plasma induced transparency effect of the graphene, so that the transparent window has great application potential in the fields of slow light devices, sensors and the like. The resonator can realize dynamic tuning of the resonance spectrum by adjusting the Fermi level of the single-layer graphene in a biased mode, so that optical resonance can be overlapped with molecular vibration fingerprints. As a new graphene material, the processing technology thereof is being researched by a great number of researchers and becomes mature day by day, and the most common processing technology is the CVD method. Therefore, the invention has important scientific significance and practical application value and has certain prospect in the practical application of the middle infrared resonance field.

Disclosure of Invention

The invention aims to provide a graphene-based plasma-induced transparent resonator which is simple in structure and can conveniently excite high-performance plasma-induced transparency in a mid-infrared band.

In consideration of the requirements of difficulty and easiness in structure and the like, the invention provides the graphene-based plasma-induced transparent resonator, and provides important help for the development of the graphene-based plasma excimer structure high-adjustability resonator.

In order to achieve the purpose, the invention adopts the technical scheme that: a plasma induction transparent resonator based on graphene is of a three-dimensional periodic structure, and adopts a graphene ring and graphene symmetrical fan-shaped disc structure to excite plasma induction transparent resonance; the method is characterized in that: the structure comprises a doped silicon substrate layer, a calcium fluoride medium layer and a graphene ring and graphene symmetrical fan-shaped disc structure from bottom to top.

The intermediate infrared band plasma induced transparent resonator in the technical scheme is based on a graphene material and can be manufactured by a graphite oxide reduction method, and the device processing further comprises photoetching and etching technologies. The Fermi level of the graphene material is between 0.5eV and 1.0eV, and the doping is easily realized experimentally.

The effective gain of the invention is:

(1) the resonator has simple and compact structure, and can excite high-performance plasma-induced transparent resonance in the mid-infrared band.

(2) The transparent window of the plasma induction transparent excited by the resonator is very sharp, and the excitation of the plasma induction transparent resonance with excellent performance is proved.

(3) Destructive interference between the graphene symmetrical fan-shaped disc as a bright state mode and the graphene circular ring as a dark state mode is utilized, so that high-performance plasma-induced transparent resonance is excited.

(4) The Fermi level of graphene can be adjusted by adding a polarization voltage mode to the excited plasma-induced transparent resonance of the resonator, so that the resonant frequency and the resonant strength of the plasma-induced transparent resonance are changed, and different requirements of the resonator are met.

Drawings

FIG. 1 is a schematic diagram of the resonator unit structure;

FIG. 2 is a structural diagram of the graphene on the top of the resonator;

FIG. 3 is a transmission spectrum of a plasma-induced transparent resonance of the resonator at different graphene Fermi levels;

FIG. 4 is a transmission spectrum of a plasmon induced transparent resonance of the resonator at different material refractive indices;

the above pictures contain: px is 100nm, r1 is 25nm, r2 is 40nm, w is 10nm, θ is 150 °, d is 20nm, and h is 20 nm.

Description of reference numerals: 1-doped silicon base layer; 2-a calcium fluoride dielectric layer; 3-a graphene ring; 4-graphene symmetric sector disks.

Detailed Description

The following is a specific embodiment of the present invention and is further described with reference to the accompanying drawings, but the present invention is not limited to the embodiment.

Fig. 1 is a schematic diagram of a unit structure of a graphene-based plasma-induced transparent resonator device. The length and width of the structural unit are px and py, the thickness of the doped silicon substrate layer is h, the thickness of the calcium fluoride dielectric layer is d, the thicknesses of the graphene ring and the graphene symmetrical sector disc are 1nm, the radius length of the graphene symmetrical sector disc is r1, the radius length of the graphene ring is r2, the width of the graphene ring is w, and the structure of the graphene ring-symmetrical sector disc is shown in figure 2.

The working principle or working process of the resonator can be explained as follows. Due to the fact that the graphene material has very high electron mobility, the Fermi level of the graphene is adjusted by adding bias voltage to the graphene, the conductivity of the graphene layer is enhanced, the graphene layer presents the property of metal, and surface plasma resonance is excited under the action of a calcium fluoride medium and an air medium. A graphene film with the thickness of 1nm can be manufactured by adopting a graphite oxide reduction method, then the graphene film is transferred to a calcium fluoride dielectric layer, and a graphene ring-symmetrical fan-shaped disc array is obtained by a mask photoetching method. In order to tune the Fermi level of graphene, an ion gel layer is spin-coated on the graphene layer, and a polarization voltage is added together with the doped silicon substrate layer, so that the Fermi level of graphene can be conveniently adjusted by the top gating method. In the middle infrared band, when middle infrared electromagnetic waves vertically enter the surface of the graphene circular ring-symmetrical fan-shaped disc, surface plasmons (SPPs) in the graphene symmetrical fan-shaped disc can be directly excited, and dipole resonance is generated near 49.2 THz. And the graphene ring cannot directly excite resonance near 49.2THz, but the six-order resonance of the graphene ring can be indirectly excited at the frequency point by utilizing the dipole resonance of the graphene symmetrical fan-shaped disc. At the moment, destructive interference is generated between the graphene symmetrical sector disc and the graphene circular ring, so that the transparent resonance induced by the plasma is excited. And the transparent window of the plasma-induced transparent resonance has the characteristics of high sensitivity and quality factor, and can realize high-performance sensing application. When different gases or different liquids are introduced above the resonator, the resonant excitation frequency of the resonator at the mid-infrared frequency band shifts due to different refractive indexes of the gases or the liquids, so that the gases or the liquids can be detected, and finally, the sensing application is realized.

FIG. 3 shows the Fermi level E of different graphene_FThe following graphene-based plasma induces the transmission spectrum of the transparent resonator. The characteristic feature of the plasmon-induced transparent resonance is an asymmetric line type, i.e. two resonance valleys and a transparent window in the middle in the figure indicate that the typical plasmon-induced transparent resonance is excited. In the transmission spectrum, the narrower the transparent window of the plasmon-induced transparent resonance is, the better the excited resonance is, so that the sharp transparent window in the figure proves that the plasmon-induced transparent resonance with excellent performance is excited. The Fermi level of the graphene is adjusted by adding the polarization voltage, as the Fermi level of the graphene is increased from 0.5eV (0.5 electron volt) to 0.9eV (0.9 electron volt), the intensity of the transparent resonance induced by the plasma is enhanced, namely the transmittance change at the resonance is increased, the resonance frequency is gradually increased along with the increase of the Fermi level, and the resonance frequency is moved from 38-40THz to 52-54THz, so that the excitation frequency in the middle infrared band is further increased.

Fig. 4 shows the change of the transmission curve of the resonator caused by the change of the refractive index of the substance when the substance above the resonator is changed when the graphene fermi level is 0.7eV (0.7 electron volt), and when the refractive index n is changed from 1 to 1.4, the position of the transparent window of the plasma-induced transparent resonance shifts from 46.1THz to 39.1THz, so that the substance component of the gas or liquid to be measured can be judged from the change of the position of the transparent window.

Claims

1. A middle infrared band is based on induced transparent resonator of plasma of graphite alkene which characterized in that: the structure comprises a doped silicon substrate layer, a calcium fluoride medium layer and a graphene ring and graphene symmetrical fan-shaped disc structure from bottom to top.

2. The mid-infrared band graphene-based plasma-induced transparent resonator of claim 1, wherein: the thickness h of the doped silicon substrate is 20nm, and the thickness d of the calcium fluoride dielectric layer is 20 nm.

3. The mid-infrared band graphene-based plasma-induced transparent resonator of claim 1, wherein: the radius of the graphene symmetrical fan-shaped disc is 25nm, the radius of the graphene circular ring is 40nm, and the width of the graphene circular ring is 10 nm.