Design and analysis for roll-to-roll graphene transfer

Graphene as the first 2D material ever discovered has attracted tremendous attention worldwide since its discovery in 2004. One of the goals of graphene research is to implement this wonder material into industrial applications, e.g., flexible transparent electrode. Chemical vapor deposition (CVD) was proven to be a viable method for growing large-scale, electronics-grade graphene on transition metal substrates. The next critical step is to transfer as-grown graphene from its growth substrate to a target for device fabrication. In this study, a roll-to-roll (R2R) system was developed to transfer as-grown graphene from copper foil to flexible polymer film by mechanical dry peeling. With the proposed R2R design, high-purity copper foil can be recycled for future graphene growth. This approach could considerably reduce graphene production cost. Furthermore, the high transfer speed and efficiency of R2R graphene dry peeling is superior to the traditional wet etching and the recently reported R2R electrochemical delamination method. The process parameters for R2R dry peeling were investigated in detail, and their individual effects on transferred graphene quality were quantified for process optimization. The success of R2R graphene dry peeling is dependent on the understanding of interfacial property of as-grown graphene on copper. A blister test was used to measure the interfacial adhesion energy of CVD graphene on copper foil. Prior to CVD graphene growth, acetic acid was used to remove surface oxidation on copper. Different treatment time was used to generate three levels of surface roughness. It was found that higher copper surface roughness led to increased interfacial adhesion energy. To find its root cause, the surface of as-grown graphene samples were characterized with atomic force microscope (AFM), scanning electron microscope (SEM), and optical profilometer to identify the surface morphology on various length scales. Additionally, an analytical model was developed to describe the interfacial adhesion using both global mode mixity and local kinking angle at the interfacial delamination front. The analytical model was validated by experimental dataMechanical Engineerin