Investigation Of Functional Silicon Micro And Nanostructures Fabricated By Femtosecond Laser

Silicon,a very important semiconductor material,is widely applied in photoelectric detection and semiconductor integrated circuits due to its excellent thermal conductivity,mechanical strength and infrared transmittance.The reasonable design and fabrication of the surface structures can manipulate the optical characteristics and surface properties of silicon,which makes structured silicon attract more attention in the fields of solar cells,microelectronics,micro-optics,etc.At present,there are many methods for processing micro-nano structures on silicon,mainly including mechanical processing,chemical etching and laser fabrication.In recent years,with the rapid development of femtosecond laser,the micro/nano processing technology becomes a potential tool for high precision fabrication and modification of material surface because of its low cost,flexible operation and large-area processing.On the one hand,femtosecond laser has ultra-high peak power and ultra-short pulse width,which can fabricate functional structures by laser direct writing ablation on silicon.However,their practical applications are still insufficient and more various functional structures need to be further developed.On the other hand,although femtosecond laser-induced periodic surface structures can break through the optical diffraction limit,it is still a great challenge to flexibly fabricate high-quality and diversified nanostructures on silicon.In order to solve the above problems,this thesis focuses on the fabrication and application of functionalized silicon micro/nanostructures based on femtosecond laser.The self-driven microchannels and self-driven microfluidic surface-enhanced Raman scattering（SERS）chips are fabricated by femtosecond laser,which can promote the practical application of microstructures in microfluidic field.A novel approach of secondary laser spatial-selective amorphization combined with chemical etching was proposed to realize the fabrication of extra-uniform deep gratings and diversified two-dimensional（2D）nanostructures.The method not only enriches the types of functionalized micro/nanostructures on silicon but also provides a new view for femtosecond laser micro/nano processing.The main research contents of this thesis are summarized as follows:1.To solve the problem of insufficient functionalized micro/nano structures,we fabricated the microchannels on silicon and investigated their self-driven properties based on unique advantages of femtosecond laser.Combined the knowledge of capillary dynamics with the morphology of microchannels,the intrinsic mechanism of self-driven property was clarified and the fluid dynamics model related with flow velocity was established.By the guidance of this model,the microchannels,with stable self-driven properties and controllable flow velocities,were successfully fabricated by femtosecond laser.2.Combined the self-driven channel with surface-enhanced Raman scattering（SERS）detection technology,the self-driven microfluidic SERS chip was further designed and processed by femtosecond laser on silicon,which promotes the application of functional structures in microfluidic field.The SERS substrate was prepared by femtosecond laser-induced periodic structures deposited with Ag film.The relationship between the structure morphology and the SERS activity of the substrates was investigated by optimizing femtosecond laser parameters.Using R6G as probe molecules,the quantitative analysis of Hg²⁺by the self-driven microfluidic SERS chip was further investigated with a detection limited up to 10^-9M,and the detection mechanism was elucidated.3.In order to improve the quality and variety of periodic nanostructures fabricated by femtosecond laser,a novel strategy of secondary laser spatial-selective amorphization combined with HF etching was proposed.First,based on a new concept of spatial-selective amorphization,the morphology evolution with various laser parameters and the corresponding formation mechanisms were explored.With futher secondary laser spatial-selective amorphization,the deepening of grating nanostructures is realized.The mechanism of deepening structures by femtosecond laser with etching was clarified and the depth of structure is finally deepened up to three times.In addition,under the influence of overlapping effect and light field enhanced effect,the various uniform 2D nanostructures were fabricated by changing laser polarization directions.4.The optical properties and potential application in structural color field of periodic nanostructures were explored.The results indicated that the deep grating structures fabricated by secondary laser spatial-selective amorphization exhibited superior antireflection and SERS performance.Furthermore,it was found that the antireflection and SERS properties of deep grating structures shown stronger polarization sensitivity.For the deep grating structures,the anisotropy properties of SERS were explored under different wavelengths and analyzed by theoretical simulation and experiment.The patterned structural colors of gratings and structural colors of 2D structures with multi-angle visual were explored.And the results demonstrated the potential application of periodic structures on silicon in the field of color display.