A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure

A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength.The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method.Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure.Subsequently,one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte.After optimizing the grating geometric variables of the structure,the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit(nm/RIU)and the figure of merit of 409 RIU^(-1).The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.

Efficient manipulation of terahertz waves by multi-bit coding metasurfaces and further applications of such metasurfaces

Benefiting from the unprecedented superiority of coding metasurfaces at manipulating electromagnetic waves in the microwave band,in this paper,we use the Pancharatnam-Berry(PB)phase concept to propose a high-efficiency reflectivetype coding metasurface that can arbitrarily manipulate the scattering pattern of terahertz waves and implement many novel functionalities.By optimizing the coding sequences,we demonstrate that the designed 1-,2-,and 3-bit coding metasurfaces with specific coding sequences have the strong ability to control reflected terahertz waves.The two proposed1-bit coding metasurfaces demonstrate that the reflected terahertz beam can be redirected and arbitrarily controlled.For normally incident x-and y-polarized waves,a 10 d B radar cross-section(RCS)reduction can be achieved from 2.1 THz to5.2 THz using the designed 2-bit coding metasurface.Moreover,two kinds of orbital angular momentum(OAM)vortex beams with different moduli are generated by a coding metasurface using different coding sequences.Our research provides a new degree of freedom for the sophisticated manipulation of terahertz waves,and contributes to the development of metasurfaces towards practical applications.

A multi-band and polarization-independent perfect absorber based on Dirac semimetals circles and semi-ellipses array

We design a four-band terahertz metamaterial absorber that relied on the block Dirac semi-metal(BDS).It is composed of a Dirac material layer,a gold reflecting layer,and a photonic crystal slab(PCS)medium layer.This structure achieved perfect absorption of over 97%at 4.06 THz,6.15 THz,and 8.16 THz.The high absorption can be explained by the localized surface plasmon resonance(LSPR).And this conclusion can be proved by the detailed design of the surface structure.Moreover,the resonant frequency of the device can be dynamically tuned by changing the Fermi energy of the BDS.Due to the advantages such as high absorption,adjustable resonance,and anti-interference of incident angle and polarization mode,the Dirac semi-metal perfect absorber(DSPA)has great potential value in fields such as biochemical sensing,information communication,and nondestructive detection.

Refractive index sensing of double Fano resonance excited by nano-cube array coupled with multilayer all-dielectric film

We propose a hybrid structure of a nano-cube array coupled with multilayer full-dielectric thin films for refractive index sensing.In this structure,discrete states generated by two-dimensional grating and continuous states generated by a photonic crystal were coupled at a specific wavelength to form two Fano resonances.The transmission spectra and electric field distributions of the structure were obtained via the finite-difference time-domain method.We obtained the optimal structural parameters after optimizing the geometrical parameters.Under the optimal parameters,the figure of merit(FOM)values of the two Fano resonances reached 1.7×10^(4)and 3.9×10^(3),respectively.These results indicate that the proposed structure can achieve high FOM refractive index sensing,thus offering extensive application prospects in the biological and chemical fields.

A high-quality-factor ultra-narrowband perfect metamaterial absorber based on monolayer molybdenum disulfide

In order to significantly improve the absorption efficiency of monolayer molybdenum disulfide(M-MoS_(2)), an ultranarrowband M-MoS_(2)metamaterial absorber was obtained through theoretical analysis and numerical calculation using the finite difference time domain method. The physical mechanism can be better analyzed through critical coupling and guided mode resonance. Its absorption rate at λ = 806.41 nm is as high as 99.8%, which is more than 12 times that of bare MMoS_(2). From the simulation results, adjusting the geometric parameters of the structure can control the resonant wavelength range of the M-MoS_(2). In addition, we also found that the maximum quality factor is 1256.8. The numerical result shows that the design provides new possibilities for ultra-narrowband M-MoS_(2) perfect absorbers in the near-infrared spectrum.The results of this work indicate that the designed structure has excellent prospects for application in wavelength-selective photoluminescence and photodetection.

Metamaterial terahertz device with temperature regulation function that can achieve perfect absorption and complete reflection conversion of ultrawideband

The field of terahertz devices is important in terahertz technology.However,most of the current devices have limited functionality and poor performance.To improve device performance and achieve multifunctionality,we designed a terahertz device based on a combination of VO_(2)and metamaterials.This device can be tuned using the phase-transition characteristics of VO_(2),which is included in the triple-layer structure of the device,along with SiO_(2)and Au.The terahertz device exhibits various advantageous features,including broadband coverage,high absorption capability,dynamic tunability,simple structural design,polarization insensitivity,and incidentangle insensitivity.The simulation results showed that by controlling the temperature,the terahertz device achieved a thermal modulation range of spectral absorption from 0 to 0.99.At 313 K,the device exhibited complete reflection of terahertz waves.As the temperature increased,the absorption rate also increased.When the temperature reached 353 K,the device absorption rate exceeded 97.7%in the range of 5-8.55 THz.This study used the effective medium theory to elucidate the correlation between conductivity and temperature during the phase transition of VO_(2).Simultaneously,the variation in device performance was further elucidated by analyzing and depicting the intensity distribution of the electric field on the device surface at different temperatures.Furthermore,the impact of various structural parameters on device performance was examined,offering valuable insights and suggestions for selecting suitable parameter values in real-world applications.These characteristics render the device highly promising for applications in stealth technology,energy harvesting,modulation,and other related fields,thus showcasing its significant potential.

Multi-functional metasurface:ultra-wideband/multi-band absorption switching by adjusting guided-mode resonance and local surface plasmon resonance effects

This study introduces an innovative dual-tunable absorption film with the capability to switch between ultra-wideband and narrowband absorption.By manipulating the temperature,the film can achieve multi-band absorption within the 30-45 THz range or ultra-wideband absorption spanning 30-130 THz,with an absorption rate exceeding 0.9.Furthermore,the structural parameters of the absorption film are optimized using the particle swarm optimization(PSO)algorithm to ensure the optimal absorption response.The absorption response of the film is primarily attributed to the coupling of guided-mode resonance and local surface plasmon resonance effects.The film's symmetric structure enables polarization incoherence and allows for tuning through various means such as doping/voltage,temperature and structural parameters.In the case of a multi-band absorption response,the film exhibits good sensitivity to refractive index changes in multiple absorption modes.Additionally,the absorption spectrum of the film remains effective even at large incidence angles,making it highly promising for applications in fields such as biosensing and infrared stealth.

Simulation study of multi-layer titanium nitride nanodisk broadband solar absorber and thermal emitter

Solar energy has always been a kind of energy with large reserves and wide application.It is well utilized through solar absorbers.In our study,the finite difference time domain method(FDTD)is used to simulate the absorber composed of refractory metal materials,and its absorption performance and thermal emission performance are obtained.The ultra-wide band of 200 nm-3000 nm reaches 95.93%absorption efficiency,of which the bandwidth absorption efficiency of2533 nm(200 nm-2733 nm)is greater than 90%.The absorption efficiency in the whole spectrum range(200 nm-2733 nm)is 97.17%on average.The multilayer nanodisk structure of the absorber allows it to undergo strong surface plasmon resonance and near-field coupling when irradiated by incident light.The thermal emission performance of the absorber enables it to also be applied to the thermal emitter.The thermal emission efficiency of 95.37%can be achieved at a high temperature of up to 1500 K.Moreover,the changes of polarization and incident angle do not cause significant changes in absorption.Under the gradual change of polarization angle(0°-90°),the absorption spectrum maintains a high degree of consistency.As the incident angle increases from 0°to 60°,there is still 85%absorption efficiency.The high absorption efficiency and excellent thermal radiation intensity of ultra-wideband enable it to be deeply used in energy absorption and conversion applications.

Active tunable terahertz bandwidth absorber based on single layer graphene

In this paper,an active tunable terahertz bandwidth absorber based on single-layer graphene is proposed,which consists of a graphene layer,a photo crystal plate,and a gold substrate.When the Fermi energy(Ef)of graphene is 1.5 eV,the absorber shows high absorption in the range of 3.7 THz–8 THz,and the total absorption rate is 96.8%.By exploring the absorption mechanism of the absorber,the absorber shows excellent physical regulation.The absorber also shows good adjustability by changing the Efof graphene.This means that the absorber exhibits excellent tunability by adjusting the physical parameters and Efof the absorber.Meanwhile,the absorber is polarization independent and insensitive to the incident angle.The fine characteristics of the absorber mean that the absorber has superior application value in many fields such as biotechnology and space exploration.

High-sensitive refractive index sensing and excellent slow light based on tunable triple plasmon-induced transparency in monolayer graphene based metamaterial

A patterned monolayer graphene metamaterial structure consisting of six graphene blocks and two graphene strips is proposed to generate triple plasmon-induced transparency(PIT).TriplePIT can be effectively modulated by Fermi levels of graphene.The theoretically calculated results by coupled mode theory show a high matching degree with the numerically simulated results by finite-difference time-domain.Intriguingly,the high-sensitive refractive index sensing and excellent slow-light performance can be realized in the proposed graphene metamaterial structure.The sensitivity(S)and figure of merit can reach up to 5.7115 THz RIU^(-1)and 116.32,respectively.Moreover,the maximum group refractive index is 1036.Hence,these results may provide a new idea for designing graphene-based sensors and slow light devices.

Alkali-metal(Li, Na, and K)-adsorbed MoSi_(2)N_(4) monolayer: an investigation of its outstanding electronic, optical, and photocatalytic properties

Single-layer MoSi_(2)N_(4),a high-quality two-dimensional material,has recently been fabricated by chemical vapor deposition.Motivated by this latest experimental work,herein,we apply first principles calculations to investigate the electronic,optical,and photocatalytic properties of alkali-metal(Li,Na,and K)-adsorbed MoSi_(2)N_(4) monolayer.The electronic structure analysis shows that pristine MoSi_(2)N_(4) monolayer exhibits an indirect bandgap(E_(g)=1.89 eV).By contrast,the bandgaps of one Li-,Na-,and K-adsorbed MoSi_(2)N_(4) monolayer are 1.73 eV,1.61 eV,and 1.75 eV,respectively.Moreover,the work function of MoSi_(2)N_(4) monolayer(4.80 eV)is significantly reduced after the adsorption of alkali metal atoms.The work functions of one Li-,Na-,and K-adsorbed MoSi_(2)N_(4) monolayer are 1.50 eV,1.43 eV,and 2.03 eV,respectively.Then,optical investigations indicate that alkali metal adsorption processes substantially increase the visible light absorption range and coefficient of MoSi_(2)N_(4) monolayer.Furthermore,based on redox potential variations after alkali metals are adsorbed,Li-and Na-adsorbed MoSi_(2)N_(4) monolayers are more suitable for the water splitting photocatalytic process,and the Li-adsorbed case shows the highest potential application for CO_(2) reduction.In conclusion,alkali-metal-adsorbed MoSi_(2)N_(4) monolayer exhibits promising applications as novel optoelectronic devices and photocatalytic materials due to its unique physical and chemical properties.

Multi-frequency switch and excellent slow light based on tunable triple plasmon-induced transparency in bilayer graphene metamaterial

We propose a novel bilayer graphene terahertz metamaterial composed of double graphene ribbons and double graphene rings to excite a dynamically adjustable triple plasma-induced transparency(PIT)effect.The coupled mode theory(CMT)is used to explain the PIT phenomenon,and the results of the CMT and the finite-difference time-domain simulation show high matching degree.By adjusting the Fermi levels of graphene,we have realized a pentafrequency asynchronous optical switch.The performance of this switch,which is mainly manifested in the maximum modulation depth(MD=99.97%)and the minimum insertion loss(IL=0.33 dB),is excellent.In addition,we have studied the slow-light effect of this triple-PIT and found that when the Fermi level of graphene reaches 1.2 eV,the time delay can reach 0.848ps.Therefore,this metamaterial provides a foundation for the research of multi-frequency optical switches and excellent slow-light devices in the terahertz band.