Investigate The Fabrication Technology Of TiO₂ Nanocomposites Via Direct Laser Writing

Direct laser writing(DLW)is a kind of maskless processing technology which can realize real three-dimensional structure based on two-photon polymerization effect.Two-photon polymerization uses ultrafast laser to make materials produce two-photon absorption and induce photochemical reactions to polymerize.Two-photon absorption is a third-order nonlinear effect whose occurrence range is limited to the spatial region of?³ and two-photon polymerization only occurs at the focal point of the laser.The resolution can break through the optical diffraction limit determined by the Rayleigh criterion and reach hundred nanometer scale.In order to get the fabrication structure with functional characteristics,such as conductivity,magnetism,high mechanical strength and high refractive index,researchers often use special functional materials and mix them into the photoresist to get the composite photoresist system with corresponding special properties.When the material size is small enough to the nanometer scale,it often has quantum size effect and small size effect.These effects can make materials excellent properties,such as mechanics,optics,electricity and magnetism.Therefore,nanomaterials are widely used in the field of functionalized micro-nano devices based on direct laser writing technology.However,there are many problems in the doping process because of the large surface energy of the nanoparticles,such as uneven dispersion,irregular processing structure,bubbles and shrinkage,which destroy the integrity of the structure.In this paper,we proposed a kind of modification method that we used silane coupling agent KH-570 in the treatment of Ti O₂ nanoparticles surface.This method can make Ti O₂ nanoparticles better disperse in the photoresist and obtain an adjustable photoresist material with an effective refractive index.Meanwhile,Ti O₂ nanoparticles can be an inorganic photoinitiator in polymerization,which can greatly reduce the photopolymerization threshold power of the composite photoresist(40%reduction).At the same time,the line width is reduced from 103 nm to 70 nm.It can improve the effective refractive index of polymer structure.This method of combining the direct laser writing one-time molding technology can directly pattern nanomaterials with special properties become specific functional micro-nano structures,which reduces the complexity of the device processing technology,and these micro-nano structures has potential application prospects in the fields of optical devices,microelectronic devices and biomedicine.The main work of this thesis can be summarized into the following aspects:(1)The applicability of direct laser writing technology of nanomaterials and the principle of direct laser writing technology are discussed.Firstly,we introduced the functional characteristics of the structure produced by the nano materials doped photoresist with the aid of direct laser writing technology,which include mechanical strength,magnetism,electrical and optical properties;Secondly,the principle of direct laser writing technology and the processing characteristics of laser direct writing technology at present stage are introduced.(2)We researched the surface modification scheme of Ti O₂ nanoparticles,and a composite photoresist based on Ti O₂ nanoparticles was obtained.Firstly,comparison of in situ and ex situ methods for synthesis of two-photon polymerization polymer nanocomposites and their advantages and disadvantages are analyzed.Subsequently,the silane coupling agent KH-570 was used to modify the Ti O₂ nanoparticles,and a series of characterization of the modified Ti O₂nanoparticles were carried out.Finally,the preparation process of the composite photoresist was introduced.(3)We explored the processing characteristics and optical properties of the composite photoresist with different content of Ti O₂ nanoparticles.Firstly,it is proved that Ti O₂ nanoparticles can participate in the polymerization reaction as an inorganic photoinitiator.The photoresist doped with Ti O₂ nanoparticles can be achieved arbitrary structure by direct laser writing,and the Ti element inside the structure is characterized.We designed and processed micro-nano hemispheres,and explored the changes of forward scattering of micro-nano hemispheres with different Ti O₂concentrations in the dark field.We proved that doping Ti O₂ nanoparticles can increase the effective refractive index of the structure through the theoretical analysis and test.