Study On The Mechanism Of The Electrochemical Bubbling Delamination Of Chemical Vapor Deposited Graphene

Graphene is a new two-dimensional material which have great potential in many fields, has been research extensively in various fields like optoelectronics, materials science and microbiology when it is found in 2004 due to its excellent features. Currently, a thorny problem restricting the development of graphene is how to transfer chemical vapor deposition(CVD) graphene to target substrate but reduce the damage in maximum degree. Traditional substrate-etched transfer method has a high cost, and it is unfriendly for environment, besides, graphene may induce defects by the etchant. Although a new transfer method, electrochemical bubbling, have avoided the metal catalysts be etched away, but the integrity of graphene transferred is worse than this transferred by substrate-etched method, because the microscopic mechanism of electrochemical bubbling method has not been studied. This paper is based on the former, the large area graphene is synthesized in Pt by CVD and transferred to foreign substrate by use optimized electrochemical bubbling method. The graphene after transferred shows high quality and then we propose the microscopic mechanism of electrochemical bubbling method first time. The main works in this paper are as follows:1.Optimized the CVD graphene synthesis conditions, such as growth temperature?annealing rate and flow ratio of gases, and synthesized the large area monolayer graphene.2. According to preliminary speculation, the scheme of using polytetrafluoroethylene(PTFE) film as a stopping layer to avoid the water and H~+ permeate PMMA has been designed, compared with the scheme which only use polyethylene terephthalate(PET) frame as the graphene's support layer, the quality of graphene transferred by PTFE-assisted is better obviously.3. Analysis the reason of tear traces in graphene transferred by PTFE-assisted: the PTFE film itself is easy tear in one direction. In order to reduce the stress of the graphene's stopping layer, the scheme of using a polymer support with encapsulated air gap as permeation stopping layer has been designed. The graphene shows high quality by optical micrographs image.4. Comprehensive analysis the impact of water and H~+ permeate PMMA for transfer process. Water and H~+ can penetrate PMMA reach the graphene-PMMA interface, and then part of these particles penetrate graphene reach the graphene-Pt interface when just use a simple PMMA as the supporting layer. These particles can arrive at the interface much earlier than those come from the edges along the graphenePt interface, leading to trapped H2 bubbles in the center. Without any supporting layer, the strain therein make the graphene cracking and then caused the broken holes and wrinkles. By compared of if there trapped H2 bubbles in the sample's center when transferred by air-gap-assisted and air-gap-free techniques, the corollary has been verified.5. Scanning electron microscopy(SEM)?atomic force microscopy(AFM)?Raman spectrum?Raman mapping and the field effect mobility of graphene transistor have been detected, the results indicated the graphene transferred by air-gap-assisted technique have a high quality.6. As the part of application of graphene, a process method for preparing a nanometer electromechanical system(NEMS) based on a vertically suspended graphene, and a micro-environment chambers for microorganism based on perpendicular graphene have been introduced.