Investigation On Direct Transfer Method Of Graphene Film

Graphene is a two-dimensional material with excellent properties,such as high light transmittance,electrical conductivity,mechanical strength and thermal conductivity,which has broad application prospects.Chemical vapor deposition(CVD)method based on copper substrate is main method for preparation of high quality,large area monolayer continuous graphene films.However,graphene films grown on copper substrates usually need to be transferred to target substrate for subsequent application,thus how to achieve clean and efficient non-destructive transfer of graphene films is an important topic.The transfer methods of graphene film can be divided into direct transfer and indirect transfer according to transfer process.Indirect transfer method refers to the transfer process in which graphene transferred from the growth substrate to the target by using a carrier material as a support layer,which can be physically or chemically removed eventually.Direct transfer method involves gluing graphene directly totarget substrate and then removing growth substrate.While fewer steps needed and less secondary transfer damages to graphene occurred compared with the indirect transfer method,its application is limited by the use of adhesives between graphene andsubstrate.To address such problem,research on direct transfer of graphene to target substrate without the use of adhesives is carried out,mainly including:1.Graphene is transferred directly at room temperature.Graphene is attached directly to the surface of substrate,and copper foil is then chemically or electrochemically etched,leaving graphene on substrate.For a rigid substrate,because the surface of copper foil is not atomically smooth,graphene cannot form a good fit with the smooth surface of substrate,so van der Waals forces cannot be used effectively.After removing copper foil,graphene film is easy to fall off and lead to fracture,which cannot meet the requirements of the application.The porous flexible polymer film substrate can be conformal with copper foil substrate easily,and the siphon effect of the porous structure can further increase the binding force between film and graphene,so as to realize complete transfer of graphene film.2.High-temperature evaporation method of copper is employed to transfer graphene directly to rigid substrate.The copper foil with graphene is evaporated at high temperature after placing on target substrate,while graphene left.The effects of temperature(equal to or lower than the melting point of copper),loading way(graphene copper foil placed directly on the substrate or sandwiched between two substrates)and substrate materials(Si O₂/Si substrate or quartz substrate)were investigated.The results show that sandwich structure can inhibit damage of graphene film caused by molten copper,keep graphene film in good contact with quartz,and transfer graphene film to target substrate in a very short time(3 min).3.Further,growth and transfer of graphene are achieved simultaneously by placing copper foil between two substrates to grow graphene on copper foil substrate first,and thencopper is in situ removed by evaporation.