Broadband Perfect Absorption Characteristics Based On Titanium Nitride Metasurface

Metamaterials are materials composed of artificially constructed subwavelength structural units that can produce extraordinary optical properties and modulate the amplitude,phase,and polarization of incident electromagnetic waves in unprecedented ways.Their applications include negative refractive index,artificial magnetism,superlens,perfect absorption,and nano-lasing,et al.In particular,the metasurface perfect absorption has attracted widespread attention in recent years,and it is very important in solar-related applications,stealth,and sensing applications.The covering bands for metasurface perfect absorption include ultraviolet,visible,infrared to terahertz regimes,and even expanded down to low-frequency acoustic waves.Although metasurface perfect absorbers exhibit impressive optical properties,they always suffer from high temperatures due to the photothermal effect,especially in solar thermal energy harvesting applications.In order to achieve broadband perfect absorption and high-temperature durability,refractory materials should be involved to design metasurfaces.The transition metal nitride titanium nitride(Ti N)exhibits plasmonic responses at visible and near-infrared wavelengths.Titanium nitride is also refractory,with a melting point as high as 2930°C,which makes it a suitable material for designing refractory metasurface perfect absorbers.Moreover,the physical properties of titanium nitride are more stable,biocompatible,more abundant,and cheaper.In addition,titanium nitride has a strong hot carrier generation ability.Therefore,it is very valuable to conduct research on the metasurface perfect absorbers based on refractory titanium nitride.Therefore,this thesis will study the metasurface perfect absorber in the ultraviolet,visible,and near-infrared bands based on titanium nitride.In summary,the main research contents of this thesis are as the followings:First,a four-layer titanium nitride/dielectric stack structure is used to explore the interaction between light and matter in the stack structure.Using the film stack structure,the mode coupling behavior is observed.By adjusting the mode coupling,the near-perfect absorption in the visible regime can be achieved.The titanium nitride film is further patterned into a nanodisk array to form a metasurface,and the size parameters of the structure are adjusted.The superposition of three resonant absorption peaks in the structure achieves a wide and high absorption band,as a result,an average absorption rate of 95% is obtained in the 400?2000 nm band.Then,the traditional three-layer metasurface structure is adopted,the titanium nitride nanodisk array is used,and monolayer molybdenum disulfide,a twodimensional material,is introduced into the structure.Utilizing the plasmonic resonance absorption in the titanium nitride nanodisk array and the absorption in the single-layer molybdenum disulfide,the near-perfect absorption in the visible-to-nearinfrared regime from 400 to 850 nm is achieved,and the average absorption rate is as high as 98.1%.At the same time,the absorption enhancement in monolayer molybdenum disulfide is explored.The device can be as thin as 120 nm,which is conducive to the miniaturization of the device.Next,a special metasurface structure unit is designed using a three-layer metasurface structure containing a titanium nitride nanocone array.Based on the electric field resonance and gap surface plasmon resonance in the structure,the average broadband perfect absorption is 99.5% in the 300?1500 nm band.By adjusting the size of the nanocone,the perfect absorption bandwidth of the Ti N nanocone array can be increased.The equivalent circuit model is used to explain the influence of the nanocone size on the absorption spectra of the metasurface,and the applicability of the nanocone metasurface to other materials is also explored.Finally,the metasurface with a double-layer structure is used,and the intermediate dielectric layer of the traditional metal/dielectric/metal structure is discarded to reduce the preparation steps.The optical responses of Ti N nanopillars,nanocones,and truncated cone metasurfaces were studied respectively.The cavity resonance mode is observed in the Ti N nanopillar array structure,and the optical response of the structure is modulated by using a thin layer of the dielectric coating.Using the gap surface plasmon resonance between the titanium nitride nanocones,the average absorption rate as high as 99.5% is finally achieved.The truncated cone metasurface is further used to reduce the height of the cone to 400 nm,and at the same time,when it is coated by a dielectric layer of alumina,a near-perfect absorption rate of 97.5% is achieved in the entire solar radiation spectrum range(300?2500 nm).The dissertation's research content and designed structures broaden the horizons of the research field of metasurface perfect absorbers based on refractory materials and provide systematic explanations of the physical connotation.At the same time,the metasurface perfect absorber structure in this dissertation can be extended to other refractory materials,such as metal materials with high melting points.It has huge potential for solar energy absorption,sensing,and other related applications.In addition,the related structures and results in this thesis are expected to be extended to the study of metasurface perfect absorbers in other wavebands and can be referenced for related research works.