Research On The Super Absorption Of Nano Structure Based On Surface Plasmons

The super absorption of electromagnetic wave means that the incoming electromagnetic energy can be effectively absorbed in a designed band,and then converted to Ohmic heat or other forms of energy.Therefore,when the electromagnetic wave passes through the absorber,it does not produce transmission and reflection.The traditional absorbing layer is usually made by high loss materials,which cannot achieve controllable super absorption or is also not conducive to integration and miniaturization of the devices.With the improvement of micro-nano processing,the fabrication of micro-nano structures becomes a reality.The free electrons in the metal can couple with the electromagnetic wave leading to the formation of surface plasmon polaritons(SPPs)propagating at the interface of the metal and dielectric,which has strong local and controlled characteristic.The SPPs has potential application value in many field such as super absorption material,biological and chemical sensors,nonlinear optics,super resolution,and photo detectors.Super absorption based on the SPPs takes the advantages of high controlled absorption,miniaturization and integration,which can greatly improve the performance of traditional devices,such as light-emitting devices,solar cells,sensors,et al.All of the superiority above make the super absorber based on surface plasmon become a hot research topic in recent years in the field of nano photonics.Therefore,in this work,a series of research has been carried out on the super absorption properties of nanostructured thin films based on the surface plasmon polaritons.In the first place,the research on the development of super absorber based on surface plasmon has been deeply studied.The development history and the latest research progress at home and abroad are introduced in details.The theory of surface plasmon,the design method of microstructure and the fabrication technology are investigated and summarized in details.Then based on the Maxwell's equations and its boundary conditions,the conditions of SPPs excitation are theoretically discussed.The physics mechanism of the super absorption is also studied.The main contents of the thesis are listed as follows:1.A three-layer metal-insulator-metal(MIM)asymmetric Fabry-Perot narrowband super absorber film structure is designed to achieve narrowband tunable super absorption in the visible and near infrared bands.In this structure,the selected two layers of metallic silver film are separated by a layer of lossless silicon oxide film to form a resonant cavity.The thickness of the bottom Ag film is 100 nm,ensuring that all incident light cannot pass through.The top silver film has only an ultra-thin 30 nm thickness,which is optimized for the best absorption.The relationship between the thickness of the middle silicon oxide layer and the wavelength of the resonance absorption peak was studied in detail by using the FDTD and transmission matrix algorithm.After confirming the best parameters by simulation,the three-layer thin film structure is successfully prepared by magnetron sputtering.The maximum absorption is up to 99.4% and the narrowest half-wave width is 20 nm.We profoundly analyzed the physical mechanism of super absorption: incident light at the resonance wavelength resonates between two layers of metal and is constantly lost in the form of Ohmic losses by two layers of metallic Ag film.2.Based on the previous work,we fabricate a three-layer MIM structure with nano hole array.FDTD algorithm is used to simulate the influence of the period and radius of the nano hole on the absorption peak position and confirmed the SPPs and LSPR modes in the structure by the simulated electromagnetic field distribution,which lead to optical extraordinary transmission and super absorption.At the same time,a theoretical model is established,the surface plasmons resonances in single-layer and multi-layer structures are analyzed.The theoretical calculation is in good agreement with the simulation results.Experimentally,we obtain the surface plasmon resonance absorption up to 90%,and the absorption peaks are in good agreement with the theoretical calculation and numerical simulation,further verifying the correctness of our theoretical model.3.We use microspheres self-assembly and combined with reactive ion beam etching technology to produce a large area of nanocone array on the silicon wafer,which effectively reduces the surface reflection of the silicon wafer to improve the utilization of visible light.Further by sputtering ultrathin gold film(13 nm)on the surface of the nanocone,the absorption of silicon in the near infrared band(> 1100 nm)is effectively increased by the excitation of SPPs,LSPR and cavity modes,overcoming the limitation of the band gap.This work will lay the foundation for the future application of silicon in the near infrared band.In addition,a new type of gold-silicon multilayer microstructures is proposed.By using the new dielectric constants constructed by the equivalent medium theory,the super absorption with a wide spectrum(800 nm-2000 nm),large-angle,and insensitive polarization is achieved.In addition,the physical mechanism of broadband super absorption is analyzed in detail by using waveguide theory and numerical simulation.4.In the fabrication of micro-nano structures,we discuss the development status and advantages as well as disadvantages of the micro/nano processing methods in the mainstream.In this thesis,we choose the microsphere self-assembly method in combination with our own conditions and also find out all the fabrication process successfully.The nano hole array and nano cone array are successfully fabricated.This kind of method of making a micro or nano structure has the advantages of simple operation,low cost,high efficiency,and large area.