Reliable Fabrication Of Symmetry-breaking Plasmonic Micro-nanostructures And Their Anomalous Optical Properties

Many unique micro-nanostructures in nature often exhibit abnormal functional properties,such as the hydrophobicity and self-cleaning ability of the surface of the lotus leaf,the colors of butterfly wings and bird feathers,etc.all of which come from the unique micronanostructure on the surface.These phenomena have also promoted people’s research on functional micro-nanostructures with special functions.In recent years,they have developed into new research hotspots in many fields,and have been widely used in important fields such as information,medical treatment,and energy.The characteristics of the micro-nanostructure depend on its morphology and the materials that make up the structure.In order to achieve special performance,it is necessary to design and optimize the morphology and materials of the structure.In some scenarios,to achieve the required performance,the designing structures with extremely small feature sizes or relatively complex shape is required,and brings many challenges in design and preparation of micro-nanostructures.The research content in this thesis focuses on the design and fabrication of metal micro/nanostructures with abnormal optical response.Light has great advantages in power consumption,information transmission,etc.It has been widely used in the fields of information,instrumentation,aerospace,etc.The metal micro-nanostructure can generate localized surface plasmon resonance under the excitation of light,which has a strong ability to control light.In this thesis,by designing and preparing symmetry-breaking metal micronanostructures with extremely small feature sizes,the abnormal optical response is obtained,and the optical properties of these structures are studied.By investigating the influence of symmetry breaking on optical properties,provide a deeper understanding of the physical nature of the unique optical behavior of metal micro-nanostructures,and they also provide more control methods in applications.Although the small feature size of the structure bringing superior near-field characteristics,it is also a great challenge to fabricate these structures by using the traditional photolithography or high-energy beam exposure process.This type of structure can be accurately and stably prepared by using the developed "sketch and peel" process.In addition,using the near field electromagnetic hot spots brought about by the extremely small feature size of the structure and the high-precision multi-dimensional control of the far field optical response of the structures,it is used in the fields of sensing,nonlinear optics,and chiral optics.The main innovative content and research results in this thesis are as follows:(1)A simple split-disk structure by introducing a nano-gap in the gold nano-disk was designed,which can support unique Fano resonance.The optical response of a nano-gold split-disk structure with a very small gap is prepared by using the focused electron beam "sketch and peel" lithography process based on negative HSQ resist.The minimum feature size is only 15 nm,and its special optical response is verified.The intensity of Fano resonance can be modulated by changing the geometric parameters of the structure,such as the length of the nanogap,and with the change of the length of the nanogap,the resonance mode of the structure will also change.In addition,the strong near-field enhancement generated by the extremely small gap can greatly improve the sensitivity of refractive index sensing,which makes the structure have a wide range of application prospects in the optical field.(2)A series of evenly divided disk(EDD)plasmonic nanostructures by uniformly dividing a complete disk was successfully designed and fabricated,and systematically studied the optical behavior of the designed structure.Author also use "sketch and peel" lithography process based on negative HSQ resist to prepare the structure,with a gap width of about 20 nm and excellent repeatability over a larger area.It is found that the EDD structure also support Fano resonance.By increasing the number of segments N of the equally divided structures,the position and depth of the Fano dip can be modulated.The designed EDD structure improves the flexibility of plasmon resonance modulation.In addition,the highly localized energy in the tiny gap of the EDD may have great application potential in practical applications,such as surface enhanced spectroscopy,refractive index sensing,and enhanced nonlinear optics.(3)An inverse split disk structure composed of nanopores and nanorods was designed and fabricated.Using PMMA-based "sketch and peel" lithography method,the structure can be fabricated with high precision.The width of the nanorods in the structure is around 30 nm,which has a strong electric field focusing effect.Under the excitation of linearly polarized incident light whose polarization direction is parallel to the nanorods,the resonance mode in the structure can generate strong electromagnetic hot spots,and the position of the resonance can be adjusted by adjusting the length of the nanorods.We have also studied the application of this structure in enhancing the second harmonic effect.The strong electromagnetic hot spot in this structure can significantly increases the intensity of second harmonic signal,which shows that this structure has great application potential in related fields.(4)A quasi-three-dimensional complementary chiral plasmonic nanostructure with stack of solid and inverse structures was designed and fabricated using traditional electron beam processing methods,and the origin of the chiral response were analyzed by simulation.Compared with a single-layer chiral metal structure,this structure has a stronger chiral optical response.The strong chiral optical response in the structure comes from the F-P resonance between the two layers of the structure.The influence of each parameter in the structure on the chiral response was discussed and investigated.In addition,the structure has the advantages of strong optical chirality and simple processing,and the method can also be extended to other processing techniques such as photolithography and nanoimprinting,which is a great promotion for the practical application of chiral optical detection.