Heterostructures Assembly Of Two-Dimensional Materials And The Study On Their Sensing Mechanisms

As one of the "three cornerstones" for establishing an environmental monitoring system,gas sensors have become more and more important to the country.Gas sensors with excellent performance generally need to have good conductivities,huge specific surface areas,and orderly structures.With the rapid development of nanotechnology,many nanomaterials with such characteristics have attracted great interest from researchers in the field of gas sensing,such as graphene two-dimensional materials and silicon nanowire arrays,which have high carrier mobility and huge specific surface areas.However,the recovery time of traditional graphene gas sensors are very long,and some even up to several hours.The bare silicon nanowire arrays are extremely unstable and easily oxidized by air.Especially in corrosive atmosphere,the detection environment is fatal to the destruction of bare silicon nanowire arrays.In view of the above problems,we proposed a two-pronged approach in this thesis.On the one hand,the graphene materials were prepared into graphene quantum dots by controlling the shape and size of the materials;on the other hand,the graphene quantum dots and silicon nanowire arrays were assembled into a heterostructure.In addition,PEDOT:PSS was introduced in order to simplify the device preparation on the basis of graphene quantum dots/silicon nanowire arrays.The main research results of this study are as follows:Firstly,silicon nanowire arrays were used as skeletons and the graphene quantum dots were modified externally by vacuum-assisted method to assemble graphene quantum dots/silicon nanowire arrays heterostructures.Compared to the bare silicon nanowire arrays sensor,graphene quantum dots/silicon nanowire arrays sensor has nearly 10 times higher sensitivity to low-concentration NO2(lOppm)response.Besides,the reasons for the improvement of the sensor performance from the interface point of view were studied and the mechanism explanation was given in this thesis.In addition,under the protection of the graphene quantum dots layer,the silicon nanowire arrays were prevented from being oxidized,which is of great significance for extending the service life of the devices.Secondly,in order to solve the problem that the fabrication process is time-consuming and cumbersome,we improve the structure of graphene quantum dots/silicon nanowire arrays heterostructures.The conductive polymer PEDOT:PSS was introduced into the sensing system to assemble graphene quantum dots/PEDOT:PSS/silicon nanowire arrays.While maintaining device sensing performance,the preparation time was reduced by nearly 2/3.Meanwhile,the reason for PEDOT:PSS improving the sensing performance of graphene quantum dots/silicon nanowire arrays was analyzed.