Fabrication And Assembly Of Metal Oxide Micro/Nano Structures By Femtosecond Laser Direct Writing

Metal oxide as a binary or multicomponent compound that consists of oxygen and one or more metallic chemical elements,has stable properties and is widely distributed on the earth.Its excellent characteristics,including high carrier mobility,wide band gap,and controllable doping,etc.,endow it a wide application prospect in the thin film transistors,photodetectors,biochemical sensors,supercapacitors,piezoelectric generators,solar cells,catalytic degradation and other fields.At present,the preparation of metal oxide nanomaterials has become increasingly mature,but its flexible patterning and efficient assembly are faced with many problems,including low fabrication precision,complicated steps and the great difficulty in achieving the true three-dimensional（3D）assembly.The femtosecond laser direct writing technology can realize the polymerization,modification and forming of materials by focusing high-energy pulses into the material,and it has the merits of high precision,high orientation,wide applicability of materials and true 3D manufacturing capability.This dissertation aims at the problems existing in the fabrication and assembly of metal oxide nanomaterials,studied the patterning,directional assembly and device integration of metal oxide nanomaterials by femtosecond laser direct writing technique,and the mechanism of preparation and assembly were analyzed and discussed at the same time.The main results and conclusions are as follows:（1）The high precision Sn O₂ micro-nano crystal structures were prepared by combining the femtosecond laser direct writing technique with the traditional sol-gel method.The fabricated micro/nano structures have satisfactory morphology and crystal structure,their line width can reach 1μm,and the grain size is about 135 nm.Moreover,the process of fabricating Sn O₂ micro/nano structures using femtosecond laser direct writing,nanosecond laser and picosecond laser was compared and analyzed.The tight focus unit and ultrashort pulse duration of femtosecond laser direct writing system endow the fabricated Sn O₂micro/nano structures with high resolution.Furthermore,the simulation results based on two-temperature diffusion model reveal that:when the femtosecond laser pulse is focus on the Sn O₂ micro-nano structures,the rapid rising and cooling process does not cause the macroscopic rise of the crystal temperature.The electron and lattice temperatures decay significantly faster in the direction perpendicular to the substrate than in the direction parallel to the substrate.（2）The highly doped and uniformly dispersed zinc oxide nanowires（Zn O NWs）composite acrylic resin was prepared by silane coupling agent modification.The directional assembly Zn O NWs via femtosecond laser direct writing was investigated.Through ultrafast nonlinear spectroscopy and other characterization techniqures,it is confirmed that3D highly directional assembly of Zn O NWs can achieved by femtosecond laser direct writing with the accuracy up to 300 nm.（3）The mechanism of the laser assembly Zn O NWs was studied.The effects of different material properties and laser parameters on Zn O NWS assembly were investigated.It is revealed that,after the silane modification,the highly oriented assembly of Zn O NWs can be obtained under the conditions that the laser power,scanning speed and hatching distance were 10 m W,50μm/s and 400 nm,respectively.Based on simulation results and the analysis of the forces on Zn O NW during the assembly process,it is found that the non-optical forces,including shear force,volume shrinkage and spatial confinement,are the main factors that induce the directional distribution of Zn O NWs.（4）The Sn O₂ micro-nano crystal structures and the highly directional assembled Zn O NWs were integrated into the functional devices by femtosecond laser direct writing respectively.The gas sensing and ultraviolet（UV）response properties of the devices above were characterized and analyzed.The results show that the Sn O₂ micro/nano crystal structures are sensitive to hydrogen sulfide（H₂S）and nitrogen dioxide（NO₂）gas at room temperature.The detection limit for NO₂ gas is only 0.25 ppm.And the Sn O₂ based photodetector has good response to UV light.Under the UV light irradiation,the ratio of UV current and dark current of Zn O NWs based photodetector can reach 300,and its responsivity is calculated to be as high as 4×10⁴ A/W.Moreover,it is sensitive to the polarization of UV light,so it can be used in the field of polarization UV detection.This dissertation used the femtosecond laser direct writing method to realize the patterning of high-quality Sn O₂ micro-nano crystal structures and the high-precision and high-directional assembly of Zn O NW_S in 3D space.The mechanism of patterning of Sn O₂and assembly of Zn O NW_S were respectively simulated and analyzed.Moreover,the assembly and integration of gas sensor and UV detector were realized.The results not only deepen the understanding of the process and mechanism of fabrication and assembly via laser direct writing,but also provide guidance for the future integration of metal oxide functional devices on chip,which has a positive research significance.