Study On Directly Patterned Graphene Growth And Flexible Transparent Graphene Sensing Network

Due to its excellent properties,the preparation methods and sensing applications of graphene have been widely studied in recent years.However,a series of scientific and technological problems are still unsolved.For example,how to realize the low temperature controllable preparation of graphene?How to obtain high-quality graphene directly on a non-metallic substrate?How can graphene be patterned and functionalized directly?How to apply the graphene strain sensors from the laboratory to the real life?In this thesis,we perform several low temperature growth strategies for graphene and directly prepare patterned graphene on various insulating substrates using our developed gallium-tungsten-assisted-chemical-vapor-deposition?CVD?method.We fabricate three-dimensional graphene network?3DGN?strain sensor using this method and the sensor exhibits outstanding flexibility and strain sensing performance.The main research results are as follows:We explore several low temperature growth methods for graphene.Using liquid metal gallium as catalyst,we obtain graphene crystal grains with microns in diameter,these grains can continue to grow and expand into graphene flakes under 150?.We also prepare uniformly distributed,micrometer-sized graphene crystal seeds on copper foil and then grow a graphene layer starting from these seeds on sapphire substrates at 250?with the assistance of liquid gallium.The obtained graphene film has a surface coverage⁷0%.We try the method of forming graphene by diffusion of graphite particles in nano-nickel film at lower temperature,only observe a small amount of graphene flakes.We modify the chemical vapor deposition method using gallium-tungsten as an auxiliary catalyst,and successfully realized the growth of graphene and its patterned structures on non-metallic substrates.In this method,we can carry the liquid gallium on the tungsten foil,expand the liquid gallium at high temperature to obtain a uniformly distributed catalytic vapor.We design a special chemical vapor deposition device to directly grow the nano-graphene film on insulating substrates such as quartz,sapphire,silicon wafer et al.The thickness and quality of the nanographene film can be further adjusted by controlling the conditions such as growth time and pressure.A typical nanographene film grown for15 minutes has a corresponding square resistance of 19.15 k?sq^-1 and the transmittance of 95.5%in the visible region.More convenient,we could transfer the pattern of a pre-designed mask directly onto the graphene film if the mask was introduced between the liquid catalyst and substrate during the growth process.Using the above method we successfully prepare three-dimensional graphene network with a transparency of up to 83%.We fabricate this graphene network into flexible strain sensor.The sensor shows wide measurement range?0.15%-3.5%?,high gauge factor?²5?,fast response time?<220 ms?,good linearity and high cycle stability.The zero point drift of the sensor is negligible after 5000 stretch-release cycles.We demonstrate scanning electron microscopy characterization and show that the strain-resistance response of the graphene network is mainly caused by recoverable microcracks generated on the graphene surface during the stretching process.