Fabrication Of Monocrystalline Silicon Metasurfaces For A Preliminary Investigation In Application

In recent years,as an artificial structure that arranges the order in accordance with certain rules on the two-dimensional plane,metasurfaces can regulate the amplitude,phase,and polarization of light waves on subwavelengths.It has shown great application potential in virtual displays,visible light communication,solid-state lighting and other fields.Compared with metasurfaces made of metal materials,dielectric metasurfaces prepared by dielectric materials such as silicon and titaniumdioxide have become a new research popularity because they do not have ohmic losses and show a richer optical resonance model.Among them,monocrystalline silicon(c-Si)has a higher refractive index and a lower absorption coefficient,but because the application of commercial c-Si is more difficult,it has not been widely used.At the same time,combining the metasurface with specific light response characteristics with the active emitting materials can make the radiation rate,direction and polarization characteristics of the optical field realize new light-emitting and high performance devices.This thesis will perform a series of studies on the preparation and application of c-Si metasurfaces with high craft thresholds and cumbersome craftsmanship.It includes three kinds of fabrication techniques for c-Si metasurfaces and an investigation of the application of light-emitting metasurfaces to control the directional light emission of single-layer two-dimensional materials.The main research results of this thesis are as follows:(1)Prepare three c-Si metasurfaces with excellent optical properties:The idea of preparing a structure and then moving it to the substrate.Giving up the method of transferring the structure of the c-Si thin film first and then preparing the structure.The parameter exploration was based on two light engraving methods based on positive glue PMMA and negative glue HSQ,as well as a c-Si etching rate with a minimum of 0.53 nm/s.At the same time,through the innovative ’float off’ method transfer process,the metasurface can be achieved on a substrate that is insoluble in water.Through this method,we have prepared a low loss metasurface with a quality factor of 450.Then,by high-temperature heating of the metasurface,the adsorption of dangling bonds achieved the fixation of nanoparticle arrays(NPAs)on the surface of the substrate.It has been applied to the preparation of light-emitting metasurfaces.Then,c-Si NPAs and a superflat gold film were prepared through the ’template stripping’ method,a～3 nm optical resonance cavity was built between the structures,with a perfect absorption band at 750 nm.At the same time,it implemented approximately 60 times enhancement in the near-field by the dielectric-metal composite metasurface.In addition,in the overall preparation process,the device is characterized by a variety of representation methods on the macro-and microscale,ensuring that the metasurface has excellent optical performance while maintaining a high level of preparation.(2)Preliminary exploration of the directional light emission of single layer twodimensional materials:We solved the problem of rupture between the single-layer twodimensional material and metasurface by the flipping process during the fabrication process of wet-transfer.We find that the directional emission of a WS2 monolayer can be enhanced as a factor of 3 assisted by a NPA with a large diameter of 170 nm.And the beaming angles of emission can be tuned by engineering the geometries of the individual nanoparticle.Additionally,we tried to avoid the quenching of the light-emitting laser by adding a PMMA layer,but the unexpected air layer increased the enhancement of the directional light emission to nearly 10 times.After removing the air layer,the enhancement factor of directional light emission was finally determined at 4 times.Finally,a simulation of directional emission was implemented based on the reciprocity theorem,verifying the spatial distribution of fluorescence intensity measured through back-focal plane imaging technology in the experiment.The physical mechanism for achieving directional emission was discussed through theoretical analysis of the phased array.