On Laser Direct Writing Graphene And Its Process For Micro/Nano Functional Devices

The micro-nano structure represented by graphene has been widely used in gas sensing,energy storage devices and other fields for its excellent specific surface area and conductivity.Conventional graphene manufacturing methods such as mechanical stripping,vapor deposition,epitaxial growth and reduction methods,etc have many problems,such as high equipment environment requirements,difficulty in patterning and complex processes.The manufacturing method of laser-induced direct writing on polyimide can obtain high-precision macro-patterned units in one step,and at the same time,its rapid manufacturing,low cost and other characteristics can meet the demand of numerous industrial production.In order to further explore and improve the conductive properties and specific surface area of graphene,the thesis mainly study on:?the specific process of laser direct writing polyimide(PI)to prepare graphene;?prepare and analyse the graphene NH3 sensor by laser direct writing;?electrodeposition of polyaniline on graphene skeleton to construct composite materials,in order to increase the performance of supercapacitors with specific surface area.(1)The mechanism of laser-induced polyimide grapheneization was analyzed,and the effect of photon and thermal action on grapheneization was determined.In order to obtain better graphene quality and pattern line width,the optimized laser power density,platform moving speed and laser pulse width and other conditions were selected 7.27 kw/cm2?1.6 mm/s?357 ?s,respectively.(2)Based on the specific surface area and electrical conductivity of graphene,the graphene NH3 sensor by laser direct writing was studied.Firstly we analyzed the effect of graphene line width on the NH3 detection sensitivity,detection time.The results shown that there is NH3 residue on the graphene gas-sensor.In order to solve this problem,we placed a graphene heating unit on both sides of the gas sensing unit by laser direct writing and used its auxiliary heating method to promote better desorption of NH3 gas sensor.Finally,under the desorption temperature of 70?,we make graphene gas sensor for 10 cycles test in 235 ppm NH3 concentration,the results show that the temperature can effectively promote the desorption of NH3,the resistance can return to initial value.(3)We choose the electrochemical method to deposit polyaniline inside the graphene skeleton.The polyaniline deposition process was optimized by electrochemical,and the deposition time of 15 minutes was selected.The contact resistance can be reduced by the overlap of polyaniline which at the same time can improve the specific surface area of electrode materials.The graphene supercapacitors with interdigitated electrodes by laser direct writing is verified by typical applications.The pore diameter and specific surface area of the composite electrode are mainly about 3 nm and 113.8 m2/g,respectively.The pore diameter is reduced by nearly 7 times and the specific surface area is increased by nearly 6.8 times.The polyaniline/graphene composite electrode has a specific capacitance value of 202.83 Fcm-3 and an energy density of about 22.42 mWh cm-3 at a current density of 0.75 Acm-3.The capacitance and energy density of the composite electrode are much larger than those of laser direct writing graphene electrode.The composite process can solve the problems of large pore diameter,low specific surface area and large contact resistance of graphene materials prepared by laser direct writing.In this thesis,the process optimization was optimized for laser direct writing graphene,sensors detection.and electrodeposition of polyaniline to construct the composite electrode to enhance the specific surface area,which will deeply furthered the recognition of laser direct writing graphene.It can lay the foundation for the future apply in actual situation.