The Fabrication,Characterization And Application Ultrathin Of Graphene Strain Sensor

With the development of science and technology,the demand of wearable device is stronger.Flexible strain sensor can be used in many areas,such as wearable devices,medical monitor and electronic skin,and so on.Graphene has attracted the attention of researchers for its advantages and is used to make flexible strain sensors.However,the graphene used in most of these researches is acquired by liquid-phase exploited method,which has many disadvantages,such as inconvenient preparation,uncontrollable layers and size of graphene.It brings difficulties to explore the working mechanism of graphene flexible strain sensor.The advantage of chemical vapor deposition for the growth of graphene is that the size,layers and distribution of graphene are controllable.Therefore,we aims to obtain monolayer graphene crystal by controlling the growth the condition of graphene,and then stack monolayer graphene crystal up to form a two-layer stacking structure.The two layers are connected by van der Waals force and the effect of vertical tunneling assures conductivity.This structure is the thinnest flexible strain detection device of utilizing the vertical tunneling effect between graphene sheets.Therefore,the working mechanism of graphene flexible strain sensor can be studied through its deformation state in the stretching process.About best condition of preparing monolayer small graphene crystal by chemical vapor deposition,we found that electrochemical polishing copper foil could significantly remove the rolling marks of copper foil and facilitate the uniform nucleation and growth of small graphene crystal on the surface of copper foil.It was found that when the growth gas flow rate of hydrogen was at 10 sccm(standard cube centimeter per minute),the growth gas flow rate of methane was 1 sccm,and the growth time was 32 s,we could acquire the appropriate size and distribution density of monolayer small graphene crystal.About fabrication of two-layer graphene stacking structure,we successfully fabricated it by transferring monolayer small graphene crystal to another monolayer small graphene crystal through the method of corrosion.The two-layer graphene stacking structure was confirmed by Electron Microscopy and Raman spectroscopy.The light transmittance was 96.74%at 550 nm,showing its excellent light transmittance.And we transferred the two-layer stacking structure to the flexible substrate for stretching experiment for Raman mapping test,to explore its motion process.Finally,the flexible strain sensor was fabricated by using the two-layer stacking structure.The performance of the sensor was tested.Gauge factor was as high as 2290 when the substrate strain was 6.64%_The sensor presented excellent cycling performance.We explored its working mechanism.When the substrate strain was 2%,the ripples or folds stored in small graphene crystals were released,but the deformation is less than the substrate's deformation.Therefore,with the increase of the substrate strain,the resistance of the sensor increased.When the substrate strain was 7%,the substrate's deformation was large and the small graphene crystal's deformation was extremely small.Therefore,with the increase of the substrate strain,the resistance of the sensor increased significantly,and the amplitude was much larger than that of the last progress.In addition,we have tested the sensor on human body,revealing a huge application prospect in the future.