Fabrication Of Flexible Micro/Nano-structures And Devices By Laser Direct Writing

Nowdays micro-nano processing and manufacturing technologies have become one of the important science and technology topics.With the trend of micro manufacturing being more flexible,customized,integrated,flexible sensors have great potential applications in the field of medicine and entertainment,especially in health monitoring and wearable electronics devices.The development and application of flexible electronics will be one of the main directions of health monitoring and treatment in the future.For flexible sensors,the products and relevant preparation processes are relatively abundant.So far,the traditional processing method has been mainly used,however,it cannot satisfy the micromanufacturing features of high flexibility and high precision.In this project we proposed a method for flexible sensor devices with laser direct writing.Micro-nano structure and sensors were prepared in a transparent flexible plastic or paper substrate using laser direct writing technology combined with other chemical physics technology.In the early stage of this thesis,the preparation and properties of silver nano materials were studied.The method of chemical synthesis was used to prepare the silver nanoparticle solution.In the experiment,the coffee ring effect was found,which could be controlled through a deposition method with a small tilting angle.The thin film assembled with silver nanoparticles at a high concentration was achieved with the surface roughness at a nanometer level.The surface Raman spectroscopic properties of silver nanoparticle film were studied for the detection of drugs.The ordered silver nanowire films were also fabricated through controlling the coffee ring effect.The anisotropic optical properties of ordered silver nanowire films were studied.Our results show that Raman enhancement changed regularly with the angles between the directions of laser polarization and silver nanowires.The strongest Raman signal is obtained when the laser polarization direction perpendicular to the the nanowires,the weakest signal is obtained when the polarization direction is parallel to the the nanowires.The silver nanoparticles were further treated by laser irradiation.After laser irradiation,nanoparticle with the size about 133.57 nm,and the middle neck width about 148.07 nm were generated.These sizes are suitable for the excitation with 532 nm wavelength laser.It can obtain an outstanding Raman enhancement effect.A new method was invented for the rapid preparation of silver nanoparticles with high bonding strength on PC flexible substrate by 405 nm continuous laser.A new formulated paste was developed to prepare of silver ink for laser direct writing.The silver paste mainly contains silver nitrate,three sodium citric acid and PVP.The addition of PVP with the mass ratio of 5% plays a very important role.At first,PVP was able to improve the absorption of silver ink under the 405 nm laser irradiation.It can improve the hydrophilicity of silver paste on the substrate,and improve the adhesion properties at the same time.In this research,an innovative way is unveiled to improve the adhesion between the silver particles and the polymer substrate.Silver electrodes are written by focusing the laser beam to the interface between the PC film and the silver ink layer through the transparent PC film.The laser beam causes some microscale damage of PC films when writing through the PC film on the interface between the PC film and the silver ink layer.These treatments can increase the adhesion strength of the electrode and the substrate.Through these improvements,the silver electrode with very high adhesion strength was prepared.The adhesive force was tested by 3M tape.After more than fifty tests,there is no shedding phenomenon.The prepared electrode can be used for flexible electronic devices,such as flexible display.Based on the aforementioned research,flexible waterproof force sensors were studied using laser direct writing.At first,PDMS 184 and the curing agent were mixed in the mass ratio of 10:1.Bubbles were removed by vacuum pumping.Then the PDMS flexible substrate was prepared by a spin coating method.Silver ink was coating on the substrate.Silver micro nano structure was prepared by laser direct writing using 405 nm laser.After cleaning the unreacted silver ink,the PDMS was coating on the prepared silver electrode.The silver micro nano structure is prepared in the PDMS film to form a waterproof force sensor.The force sensor can detect the finger bending.The response time of the force sensor is 0.3 seconds;the recovery time is 0.45 seconds.The response rate is ten times as fast as that reported result.Meanwhile,it can operate normally under water.This method can be used for preparing a waterproof sensor.Paper based graphene oxide thick film materials were prepared.The graphene oxide was reducd by laser direct writing.Reduced graphene oxide nanostructures were prepared on the substrate surface.Based on this structure,the paper based photosensitive sensor was prepared.The performance of the sensor is examined.The test results show that the photosensitive sensor has a good response to 405 nm and 808 nm laser.It can be used to detect the laser power.And the sensor has a good sensitivity to the tensile deformation at the same time.