Fabrication And Application Of Controlled Microstructural Tips Based On 3D Direct Laser Writing

The structural constructions in the micro/nano scale have played an important role in developing novel functional material possessing exotic properties,which remains the hotspot of current science and technology.Rapid advances of the three-dimensional additive manufacturing field in recent years enable the extension of the microarchitectures from two dimensions to three dimensions,which attracts extensive research interests of customized microstructural morphology and thereby tailored properties.The main topic of this thesis is centered on the controllable characteristics of microstructural architectural(CMA)tip fabricated by three-dimensional direct laser writing(3D DLW),detailing microstructural fabrication processes,morphology-dependent controllable properties,and inherent relations of the both,based on the combined considerations of ‘constructive methods' and “constructive morphology”.Three studies concerning the applications of controllable microstructural tips have been fully addressed,i.e.,microstructural nanofocusing,morphologically interfacial microscopy and near-field optical imaging.The detailed research contents are listed as follows:1.The design and fabrication of 3D asymmetric structure for plasmonic nanofocusing.The plasmonic nanofocusing possesses two complementary aspects that affect the focusing performance,i.e.,polarization dependency and structure dependency.In order to physically realize the focusing at the incidence of a linearly polarized beam with increased efficiency,the waveguide structure should be specially designed such that the enhancement of structure dependency could reduce the critical requirement on polarization dependency.Therefore,assisted by finite element methods(FEM),we analyzed the physical mechanism of plasmonic nanofocusing theoretically,compared the focusing performances of structures with different symmetric degrees and proposed a 3D asymmetric structural design for plasmonic nanofocusing in light of the symmetry-breaking guideline.The surface-enhanced Raman scattering(SERS)tests explicitly exhibited a 400-fold enhancement of Raman characteristic peak intensity compared to contrast results from the flat silver surface.The enhancement factor of internal illumination is 19 times more than that of an external incidence while the signal-tonoise ratio(SNR)is 3.5 times as much,which strongly proves the excellent performance of plasmonic nanofocusing afforded by asymmetric microstructure realizable via direct laser printing.2.The design and fabrication of cellular microstructural scanning-tips for interfacial microscopy.In the scanning course,the apex of the tip frequently impacts the sample surface.In order to reduce the interfacial deformation caused by the impulsive load from tip to the substrate surface during this approaching process,we designed and fabricated a cellular microstructural tip with 3D direct laser writing technique.The kinetic energy of the mechanical impact can be stored and dissipated through the structural deformation of the tip,reducing the energy transferred towards the sample,in which case,the sample can be mechanically protected and imaging can be improved.The written tips have an apex radius of 47-77 nm with an imaging error of less than 4%.The tip stiffness can be flexibly tailored within a wide range of 4.2-199.75N/m by adjusting its geometrical parameters,correspondingly leading to a peak stress of 0.23-0.72 MPa,a plateau stress of 0.1-0.54 MPa,and an energy-absorbing efficiency of 0.55-0.69.Calculated from experimental results,the stress exerted by the CMA tip is approximately 0.07 MPa,which is about 9.8%-18.3% compared to stress produced by the solid tip,greatly mitigating the mechanical tip-sample interactions and improving overall imaging quality.3.The design and fabrication of apertured near-field scanning tips for near-field optical imaging.Conventional manufacturing technique barely provides effective control of tip construction,rendering performance restrictions of near-field optical imaging.We developed a tilted manufacturing process for the fabrication of apertured tip based on direct laser writing,addressing the control of tip bending and aperture size in tip machining,to realize near-field optical imaging of micropatterns.The experiment outcome shows a controllable tip-bending range of 0-60°as well as a variable aperture size of 50-500 nm by changing the mounting location of optical fiber,and precisely regulating the power and scan speed of laser direct writing,effectively contributing to the near-field optical imaging.The study sheds light on an exotic application instance in building micro/nano optical devices using 3D printing.