Application Of Laser Interference And Laser Direct Writing Technology For The Preparation Of Controllable Micro/nano- Structures

With the increasing demand of micro/nano-structures for high-performance devices,the study on how to fabricate controlled micro/nano-structures has become one of hot topics in the field of scientific research.Ordered micro/nano-structures show some excellent physical and chemical properties.Therefore,they have potential applications in microelectronics,sensing and biochemical detection.In addition,specific patterns of material are effective to achieve some unique functions.The development of micro/nano processing technology for controlled micro/nano-structures is thus focused on a simplified and low cost process with high repeatability.Laser micro/nano processing has been widely used due to various advantages of the laser,such as high energy density,high precision,fast processing speed and non-mechanical contact processing.Especially,laser interference processing and laser direct writing technology improve the processing efficiency and repeatability without using a mask.In this thesis,the periodic structure of silver nanoparticles was prepared by using355 nm pulsed laser interference from the silver ion film.The periodic structure of silver nanoparticles is further turned to the periodic structure of silver nanowires through low temperature sintering.The length of silver nanowires can reach 2.8?m by annealing at 250 ~oC for 1h.In order to further improve the length of silver nanowires,we used silver nanospheres or silver nanosheets produced by photo-reduction with two kinds of wavelength to fill in the gaps between short silver bars.The continuity of silver nanowires in the long direction is improved after the secondary sintering.365 nm ultraviolet light induced the growth of silver nanospheres,and the length of silver nanowires can be increased to 3.0?m after the secondary sintering.615 nm LED light induced the growth of silver nanosheets,and the length of silver nanowires can be increased to 3.2?m after the secondary sintering.The flexible conductive lines were fabricated on high insulating polyimide(PI)films by laser induced carbonization via a direct writing technique.The effects of laser power and scanning speed on the conductivity were studied.When the scanning speed is constant,a linear relationship is built between conductivity and laser power within the appropriate laser power range.The conductivity of conductive lines developed in PI can be up to 9.2 S/cm.We propose doping and surface modification to further improve the conductivity of PI conductive lines.The conductivity is increased by 2.9times in a silver nano-plates-carbon composite.Laser reduction graphene oxide can also increase the conductivity(about 4 times).Silver nanoparticles through photo-reduction attached on the skeleton of carbonization can significantly increase the conductivity in two order of magnitude.The interdigitated electrodes on PI film produced by laser direct writing can be used for gas sensors due to the high temperature resistant property of PI film.ZnO nanowire arrays are produced by a hydrothermal method on PI substrate with the interdigitated electrode,and the gas sensitivity of ZnO nanowires array is studied for acetone and ethanol sensing.