A high-performance adaptive radiative cooler comprising a multilayer-filter VO_(2)-based Fabry-Pérot(FP)cavity is proposed.The bottom FP cavity has four layers,VO_(2)/NaCl/PVC/Ag.Based on the phase transition of ...A high-performance adaptive radiative cooler comprising a multilayer-filter VO_(2)-based Fabry-Pérot(FP)cavity is proposed.The bottom FP cavity has four layers,VO_(2)/NaCl/PVC/Ag.Based on the phase transition of VO_(2),the average emissivity in the transparent window can be switched from 3.7%to 96.3%.Additionally,the average emissivity can also be adjusted with external strain to the PVC layer,providing another way to attain the desired cooling effect.An upper filter is included to block most of the solar radiation and provide a transmittance of 96.7% in the atmospheric window.At high temperature,the adaptive emitter automatically activates radiative cooling.The net cooling power is up to 156.4 W·m^(-2)at an ambient temperature of 303 K.Our adaptive emitter still exhibits stable selective emissivity at different incident angles and heat transfer coefficients.At low temperature,the radiative cooling automatically deactivates,and the average emissivity decreases to only 3.8%.Therefore,our work not only provides new insights into the design of high-performance adaptive radiative coolers but also advances the development of intelligent thermal management.展开更多
We theoretically investigate the photonic band gap in one-dimensional photonic crystals with a graded multilayer structure. The proposed structure constitutes an alternating composite layer （metallic nanoparticles em...We theoretically investigate the photonic band gap in one-dimensional photonic crystals with a graded multilayer structure. The proposed structure constitutes an alternating composite layer （metallic nanoparticles embedded in TiO2 film） and an air layer. Regarding the multilayer as a series of capacitance, effective optical properties are derived. The dispersion relation is obtained with the solution of the transfer matrix equation. With a graded structure in the composite layer, numerical results show that the position and width of the photonic band gap can be effectively modulated by varying the number of the graded composite layers, the volume fraction of nanoparticles and the external stimuli.展开更多
Composite nanoparticles （NPs） have the ability of combining materials with different properties together, thus receiving extensive attention in many fields. Here we theoretically investigate the electric field distr...Composite nanoparticles （NPs） have the ability of combining materials with different properties together, thus receiving extensive attention in many fields. Here we theoretically investigate the electric field distribution around core/shell NPs （a type of composite NPs） in ferrofluids under the influence of an external magnetic field. The NPs are made of cobalt （ferromagnetic） coated with gold （metallic）. Under the influence of the external magnetic field, these NPs will align along the direction of this field, thus forming a chain of NPs. According to Laplace＇s equations, we obtain electric fields inside and outside the NPs as a function of the incident wavelength by taking into account the mutual interaction between the polarized NPs. Our calculation results show that the electric field distribution is closely related to the resonant incident wavelength, the metallic shell thickness, and the inter-particle distance. These analytical calculations agree well with our numerical simulation results. This kind of field-induced anisotropic soft-matter systems offers the possibility of obtaining an enhanced Raman scattering substrate due to enhanced electric fields.展开更多
A dualband terahertz(THz) absorber including periodically distributed cross-shaped graphene arrays and a gold layer spaced by a thin dielectric layer is investigated.Numerical results reveal that the THz absorber disp...A dualband terahertz(THz) absorber including periodically distributed cross-shaped graphene arrays and a gold layer spaced by a thin dielectric layer is investigated.Numerical results reveal that the THz absorber displays two perfect absorption peaks.To elucidate the resonant behavior, the LC model is introduced to fit the spectra.Moreover, the strength and linewidth of the absorption peak can be effectively tuned with structural parameters and the relaxation time of graphene.Owing to its rotational symmetry, this THz absorber exhibits polarization insensitivity.Our designed absorber is a promising candidate in applications of tunable optical sensors and optical filters.展开更多
Based on Dirac semimetal metamaterials,the tunable plasmon induced transparency(PIT)is investigated elaborately in this work.The designed unit cell consists of a strip and a square bracket,which is periodically aligne...Based on Dirac semimetal metamaterials,the tunable plasmon induced transparency(PIT)is investigated elaborately in this work.The designed unit cell consists of a strip and a square bracket,which is periodically aligned on the dielectric substrate.Our numerical results illustrate that a pronounced transparency window exists due to near field coupling between two bright modes,which can be dynamically tuned with Fermi energy.Namely,the transparency window demonstrates a distinct blue shift with a larger Fermi energy.Moreover,an on-to-off switch of the PIT transparency window is realized with different polarization angles.In addition,the accompanied slow light property is examined with the calculation of phase and group delay.Finally,a small variation of the refractive index of the substrate can induce a clear movement of the PIT transparency window which delivers a guidance in the application of optical sensing.Thus,this work provides us a new strategy to design compact and adjustable PIT devices and has potential applications in highly tunable optical switchers,sensors,and slow light devices.展开更多
A novel thermal emitter with metal-insulator-metal design is proposed to realize efficient daytime radiative cooling.It can achieve ultrahigh absorption of 99.67%in the first atmospheric window and strong reflection o...A novel thermal emitter with metal-insulator-metal design is proposed to realize efficient daytime radiative cooling.It can achieve ultrahigh absorption of 99.67%in the first atmospheric window and strong reflection of94.86%in solar band.Analysis on the cooling performance with different real and imaginary parts of refractive index is carried out to provide a guide line in the material choice.As a case study,three inorganic materials are substituted to get enhanced absorption and it is verified that the refractive index matching is desirable to obtain high absorption.In addition,such high emissivity persists under different incident angles in both TE and TM modes.A net cooling power of 96.39 W/m^(2)is achieved in the daytime with the incorporation of convection coefficients.Finally,this thermal emitter achieves an average temperature drop of 5.1℃based on the solution of conduction equation at 300 K.Therefore,our design with an excellent cooling ability can further bolster development in managements of radiative cooling or thermal radiation.展开更多
We propose and numerically demonstrate a tunable plasmon-induced transparency(PIT) phenomenon based on asymmetric H-shaped graphene metamaterials. The tunable PIT effect is realized through varying the applied polariz...We propose and numerically demonstrate a tunable plasmon-induced transparency(PIT) phenomenon based on asymmetric H-shaped graphene metamaterials. The tunable PIT effect is realized through varying the applied polarization angles rather than changing the structure geometry. By simply adjusting the polarization angle, the transmission spectra can be controlled between the switch-on state and switch-off state. The physical mechanism of the induced transparency is revealed from magnetic dipole inductive coupling and phase coupling. Importantly, by varying the Fermi energy of the graphene or the refractive index of the substrate, the resonant position of the PIT can be dynamically controlled and the maximum modulation depths can reach up to 60.7%. The sensitivity(nm/RIU) of the graphene structure, which is the shift of resonance wavelength per unit change of refractive index, is 5619.56 nm/RIU. Moreover, we also extend our research to the x-axis symmetric H-shaped structure, and the tunable PIT transmission window can also be realized. The physical mechanism of the induced transparency is revealed from the electric dipole hybridization coupling. Our designed H-shaped graphene-based structures is a promising candidate for compact elements such as tunable sensors, switches and slow-light devices.展开更多
We experimentally fabricate a non-spherical Ag and Co surface-enhanced Raman scattering（SERS） substrate, which not only retains the metallic plasmon resonant effect, but also possesses the magnetic field controllabl...We experimentally fabricate a non-spherical Ag and Co surface-enhanced Raman scattering（SERS） substrate, which not only retains the metallic plasmon resonant effect, but also possesses the magnetic field controllable characteristics.Raman detections are carried out with the test crystal violet（CV） and rhodamine 6G（R6G） molecules with the initiation of different magnitudes of external magnetic field. Experimental results indicate that our prepared substrate shows a higher SERS activity and magnetic controllability, where non-spherical Ag nanoparticles are driven to aggregate effectively by the magnetized Co and plenty of hot-spots are built around the metallic Ag nanoparticles, thereby leading to the enhancement of local electromagnetic field. Moreover, when the external magnetic field is increased, our prepared substrate demonstrates excellent SERS enhancement. With the 2500 Gs and 3500 Gs（1 Gs = 10^（-4）T） magnetic fields, SERS signal can also be obtained with the detection limit lowering down to 10^（-9）M. These results indicate that our proposed magnetic field controlled substrate enables us to freely achieve the enhanced and controllable SERS effect, which can be widely used in the optical sensing, single molecule detection and bio-medical applications.展开更多
Two-dimensional double nanoparticle （DNP） arrays are demonstrated theoretically, supporting the interaction between out-of-plane magnetic plasmons and in-plane lattice resonances, which can be achieved by tuning the...Two-dimensional double nanoparticle （DNP） arrays are demonstrated theoretically, supporting the interaction between out-of-plane magnetic plasmons and in-plane lattice resonances, which can be achieved by tuning the nanoparticle height or the array period due to the height-dependent magnetic resonance and the periodicity-dependent lattice resonance. The interplay between the two plasmon modes can lead to a remarkable change in resonance lineshape and an improvement on magnetic field enhancement. Simultaneous electric field and magnetic field enhancement can be obtained in the gap region between neighboring particles at two resonance frequencies as the interplay occurs, which presents “open” cavities as electromagnetic field hot spots for potential applications on detection and sensing. The results not only offer an attractive way to tune the optical responses of plasmonic nanostructure, but also provide further insight into the plasmon interactions in periodic nanostructure or metamaterials comprising multiple elements.展开更多
基金supported by the Natural Science Foundation of Henan Province(Grant No.232102231023)。
文摘A high-performance adaptive radiative cooler comprising a multilayer-filter VO_(2)-based Fabry-Pérot(FP)cavity is proposed.The bottom FP cavity has four layers,VO_(2)/NaCl/PVC/Ag.Based on the phase transition of VO_(2),the average emissivity in the transparent window can be switched from 3.7%to 96.3%.Additionally,the average emissivity can also be adjusted with external strain to the PVC layer,providing another way to attain the desired cooling effect.An upper filter is included to block most of the solar radiation and provide a transmittance of 96.7% in the atmospheric window.At high temperature,the adaptive emitter automatically activates radiative cooling.The net cooling power is up to 156.4 W·m^(-2)at an ambient temperature of 303 K.Our adaptive emitter still exhibits stable selective emissivity at different incident angles and heat transfer coefficients.At low temperature,the radiative cooling automatically deactivates,and the average emissivity decreases to only 3.8%.Therefore,our work not only provides new insights into the design of high-performance adaptive radiative coolers but also advances the development of intelligent thermal management.
基金the National Natural Science Foundation of China(Grant Nos.10974183 and 11104252)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20114101110003)+4 种基金the Fund for Science and Technology Innovation Team of Zhengzhou(2011-03)the Aeronautical Science Foundation of China(Grant No.2011ZF55015)the Basic and Frontier Technology Research Program of Henan Province,China(Grant Nos.112300410264 and 122300410162)the Cooperation Fund with Fudan University,China(Grant No.KL2011-01)the National Basic Research Program of China(Grant No.2011CB922004)
文摘We theoretically investigate the photonic band gap in one-dimensional photonic crystals with a graded multilayer structure. The proposed structure constitutes an alternating composite layer （metallic nanoparticles embedded in TiO2 film） and an air layer. Regarding the multilayer as a series of capacitance, effective optical properties are derived. The dispersion relation is obtained with the solution of the transfer matrix equation. With a graded structure in the composite layer, numerical results show that the position and width of the photonic band gap can be effectively modulated by varying the number of the graded composite layers, the volume fraction of nanoparticles and the external stimuli.
基金supported by the National Natural Science Foundation of China(Grant Nos.11104252 and 11222544)the Science Fund of the Ministry of Education of China(Grant No.20114101110003)+6 种基金the Fund for Science and Technology Innovation Team of Zhengzhou City(2011-03)the Aeronautical Science Foundation of China(Grant No.2011ZF55015)the Basic and Frontier Technology Research Program of Henan Province,China(Grant Nos.112300410264 and 122300410162)the Cooperation Fund with Fudan University,China(Grant No.KL2011-01)the Fok Ying Tung Education Foundation,China(GrantNo.131008)the Program for New Century Excellent Talents in University(Grant No.NCET-12-0121)the National Key Basic Research Program of China(Grant No.2011CB922004)
文摘Composite nanoparticles （NPs） have the ability of combining materials with different properties together, thus receiving extensive attention in many fields. Here we theoretically investigate the electric field distribution around core/shell NPs （a type of composite NPs） in ferrofluids under the influence of an external magnetic field. The NPs are made of cobalt （ferromagnetic） coated with gold （metallic）. Under the influence of the external magnetic field, these NPs will align along the direction of this field, thus forming a chain of NPs. According to Laplace＇s equations, we obtain electric fields inside and outside the NPs as a function of the incident wavelength by taking into account the mutual interaction between the polarized NPs. Our calculation results show that the electric field distribution is closely related to the resonant incident wavelength, the metallic shell thickness, and the inter-particle distance. These analytical calculations agree well with our numerical simulation results. This kind of field-induced anisotropic soft-matter systems offers the possibility of obtaining an enhanced Raman scattering substrate due to enhanced electric fields.
基金Project supported by the Key Science and Technology Research Project of Henan Province,China(Grant Nos.162102210164 and 1721023100107)the Natural Science Foundation of Henan Educational Committee,China(Grant No.17A140002)
文摘A dualband terahertz(THz) absorber including periodically distributed cross-shaped graphene arrays and a gold layer spaced by a thin dielectric layer is investigated.Numerical results reveal that the THz absorber displays two perfect absorption peaks.To elucidate the resonant behavior, the LC model is introduced to fit the spectra.Moreover, the strength and linewidth of the absorption peak can be effectively tuned with structural parameters and the relaxation time of graphene.Owing to its rotational symmetry, this THz absorber exhibits polarization insensitivity.Our designed absorber is a promising candidate in applications of tunable optical sensors and optical filters.
基金Project supported by the Natural Science Foundation of Henan Provincial Educational Committee,China(Grant No.21A140026).
文摘Based on Dirac semimetal metamaterials,the tunable plasmon induced transparency(PIT)is investigated elaborately in this work.The designed unit cell consists of a strip and a square bracket,which is periodically aligned on the dielectric substrate.Our numerical results illustrate that a pronounced transparency window exists due to near field coupling between two bright modes,which can be dynamically tuned with Fermi energy.Namely,the transparency window demonstrates a distinct blue shift with a larger Fermi energy.Moreover,an on-to-off switch of the PIT transparency window is realized with different polarization angles.In addition,the accompanied slow light property is examined with the calculation of phase and group delay.Finally,a small variation of the refractive index of the substrate can induce a clear movement of the PIT transparency window which delivers a guidance in the application of optical sensing.Thus,this work provides us a new strategy to design compact and adjustable PIT devices and has potential applications in highly tunable optical switchers,sensors,and slow light devices.
基金supported by the Natural Science Foundation of Henan Educational Committee(Grant No.21A140026)the Natural Science Foundation of Henan Province(Grant Nos.212300410411 and 232102231023)+1 种基金the National Natural Science Foundation of China(Grant No.12174351)the Fund from Zhengzhou University(Grant No.JC22149003)。
文摘A novel thermal emitter with metal-insulator-metal design is proposed to realize efficient daytime radiative cooling.It can achieve ultrahigh absorption of 99.67%in the first atmospheric window and strong reflection of94.86%in solar band.Analysis on the cooling performance with different real and imaginary parts of refractive index is carried out to provide a guide line in the material choice.As a case study,three inorganic materials are substituted to get enhanced absorption and it is verified that the refractive index matching is desirable to obtain high absorption.In addition,such high emissivity persists under different incident angles in both TE and TM modes.A net cooling power of 96.39 W/m^(2)is achieved in the daytime with the incorporation of convection coefficients.Finally,this thermal emitter achieves an average temperature drop of 5.1℃based on the solution of conduction equation at 300 K.Therefore,our design with an excellent cooling ability can further bolster development in managements of radiative cooling or thermal radiation.
基金Project supported by the Key Science and Technology Research Project of Henan Province,China(Grant Nos.162102210164 and 1721023100107)the Natural Science Foundation of Henan Educational Committee,China(Grant No.17A140002)
文摘We propose and numerically demonstrate a tunable plasmon-induced transparency(PIT) phenomenon based on asymmetric H-shaped graphene metamaterials. The tunable PIT effect is realized through varying the applied polarization angles rather than changing the structure geometry. By simply adjusting the polarization angle, the transmission spectra can be controlled between the switch-on state and switch-off state. The physical mechanism of the induced transparency is revealed from magnetic dipole inductive coupling and phase coupling. Importantly, by varying the Fermi energy of the graphene or the refractive index of the substrate, the resonant position of the PIT can be dynamically controlled and the maximum modulation depths can reach up to 60.7%. The sensitivity(nm/RIU) of the graphene structure, which is the shift of resonance wavelength per unit change of refractive index, is 5619.56 nm/RIU. Moreover, we also extend our research to the x-axis symmetric H-shaped structure, and the tunable PIT transmission window can also be realized. The physical mechanism of the induced transparency is revealed from the electric dipole hybridization coupling. Our designed H-shaped graphene-based structures is a promising candidate for compact elements such as tunable sensors, switches and slow-light devices.
基金Project supported by the Key Science and Technology Research Project of Henan Province,China(Grant No.162102210164)the Natural Science Foundation of Henan Educational Committee,China(Grant No.17A140002)+1 种基金the National Natural Science Foundations of China(Grant Nos.11574276,11404291,and11604079)the Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.17HASTIT0)
文摘We experimentally fabricate a non-spherical Ag and Co surface-enhanced Raman scattering（SERS） substrate, which not only retains the metallic plasmon resonant effect, but also possesses the magnetic field controllable characteristics.Raman detections are carried out with the test crystal violet（CV） and rhodamine 6G（R6G） molecules with the initiation of different magnitudes of external magnetic field. Experimental results indicate that our prepared substrate shows a higher SERS activity and magnetic controllability, where non-spherical Ag nanoparticles are driven to aggregate effectively by the magnetized Co and plenty of hot-spots are built around the metallic Ag nanoparticles, thereby leading to the enhancement of local electromagnetic field. Moreover, when the external magnetic field is increased, our prepared substrate demonstrates excellent SERS enhancement. With the 2500 Gs and 3500 Gs（1 Gs = 10^（-4）T） magnetic fields, SERS signal can also be obtained with the detection limit lowering down to 10^（-9）M. These results indicate that our proposed magnetic field controlled substrate enables us to freely achieve the enhanced and controllable SERS effect, which can be widely used in the optical sensing, single molecule detection and bio-medical applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10974183,11104252,61274012,and 51072184)the Specialized Re-search Fund for the Doctoral Program of Higher Education of China(Grant No.20114101110003)+4 种基金the Aeronautical Science Foundation of China(Grant No.2011ZF55015)the Basic and Frontier Technology Research Program of Henan Province,China(Grant Nos.112300410264 and 122300410162)the Foundation of University Young Key Teacher from Henan Province,China(Grant No.2012GGJS-146)the Key Program of Science and Technology of Henan Education Department,China(Grant Nos.12A140014 and 13A140693)the Postdoctoral Research Sponsorship of Henan Province,China(Grant No.2011002)
文摘Two-dimensional double nanoparticle （DNP） arrays are demonstrated theoretically, supporting the interaction between out-of-plane magnetic plasmons and in-plane lattice resonances, which can be achieved by tuning the nanoparticle height or the array period due to the height-dependent magnetic resonance and the periodicity-dependent lattice resonance. The interplay between the two plasmon modes can lead to a remarkable change in resonance lineshape and an improvement on magnetic field enhancement. Simultaneous electric field and magnetic field enhancement can be obtained in the gap region between neighboring particles at two resonance frequencies as the interplay occurs, which presents “open” cavities as electromagnetic field hot spots for potential applications on detection and sensing. The results not only offer an attractive way to tune the optical responses of plasmonic nanostructure, but also provide further insight into the plasmon interactions in periodic nanostructure or metamaterials comprising multiple elements.
