Enhanced Absorption And Transmission Based On Metal-dielectric-metal Nanostructure

Physics behind the interaction between light and medium under micron-scale and submicron-scale have been in pursuit by the scientists recently.It is well known that dielectric materials are low loss and optically transparent over broadband.Meanwhile,light confinement effect of dielectric materials are weak compared to metals.Quite the contrary,metals can transform light into surface plasmonic waves on the metal surface to realize extreme light concentration.However,its large ohmic loss and light dissipation would induce much signal damping and thermal generation.Combination of these two materials has became a key point to manipulate photonic devices for light emitters,detectors,solar cells etc.In this dissertation,we aim to devise broadband absorber and transmission enhanced device based on metal-dielectric-metal nano structure toward electromagnetic resonance enhanced optical characteristics mechanism.COMSOL Multiphysics and FDTD software are used for numerical simulation.Focused ion beam and electron beam lithography are used for sample preparation.Reflection and transmisstion property of these devices are tested by a fourier transform infrared spectroscopy(FTIR)and a homemade optical path.We mainly design broadband absorbers and antireflective films.The former uses tungsten material with high refractive index and high intrinsic loss,so that the incident light in the visible and near infrared wavelengths is confined within the structure,absorbed by the material and transformed as heat loss.Theoretical calculation and experimental results are consistent with each other.The average absorption from 400 nm to 1700 nm is up to 80%.The structure of this device is simple and easy to fabricate.Its thickness of the whole device is only 215 nm.In the simulation of this absorber,gold,silver,titanium and nickel are used to substitute tungsten to understand the physics behind the broadband absorptive effect.It was found that the absorption bandwidth of the high refractive index material is wider than that of the low refractive index materials,although the electric field intensity in the low refractive index materials is higher than that in the high refractive index material.We believe that the refractive index plays a decisive role in the bandwidth of absorbers.In addition,we designed a variable broadband absorber by the temperature-dependent phase-change VO2 material.The absorber has strong absorption characteristics only at 85?when VO2 phase changes to the metallic material.With its temperature dropping,its absorption gradually decreases.In the case of a resonance-enhanced transmission device,we still use a metal-dielectric-metal micro/nano structure to achieve an antireflective device that is polarization-sensitive and has wide-angle operating characteristics in the visible and near-infrared wavelength bands.The device is designed for applications where conductive properties are required,and a seamless continuous metal film are contained in the the inside of the device.The simulation and experimental results show that the structure can obtain more than 40%transmission in the near-infrared band(930 nm).And the enhancement of transmittance is twice and 8 times,compared to the single-layer gold film and the continuous metal-dielectric-metal layer structure,respectively.In general,the electromagnetic absorption and transmission characteristics of the micro/nano structure are enhanced for the applications of micro/nano photonic devices in the fields of thermal radiation,optical filtering,optical sensing,and solar energy.The effective combination of dielectric materials and metals is utilized to design different devices to meet different needs.