Degradation Protection of Color Dyes Encapsulated by Graphene Barrier Films

The decolorization of paintings, photographs, and artworks is a common phenomenon related to the oxidative degradation of color dyes reacting with oxygen or water molecules, which also causes a critical problem in organic light-emitting diodes (OLEDs). It is expected that the gas-impermeable property of graphene and h-BN can be utilized to protect the color dyes from degradation. However, the transfer method has been limited to a polymer with high glass transition temperature (T-g) or a glass substrate due to hot or wet transfer conditions. Here, we report the dry transfer coating of the graphene barrier films on flexible substrates at room temperature using a roll-to-roll process to prevent the bleaching of color dyes, which can be widely used to protect various colorization and light-emitting materials for sustainable printing and display technologies in the future.

Tension-controlled single-crystallization of copper foils for roll-to-roll synthesis of high-quality graphene films

It has been known that the crystalline orientation of Cu substrates plays a crucial role in chemical vapor deposition (CVD) synthesis of high-quality graphene. In particular, Cu (1 1 1) surface showing the minimum lattice mismatch with graphene is expected to provide an ideal catalytic reactivity that can minimize the formation of defects, which also induces larger single-crystalline domain sizes of graphene. Usually, the Cu (1 1 1) substrates can be epitaxially grown on single-crystalline inorganic substrates or can be recrystallized by annealing for more than 12 h, which limits the cost and time-effective synthesis of graphene. Here, we demonstrate a new method to optimize the crystalline orientations of vertically suspended Cu foils by tension control during graphene growth, resulting in large-area recrystallization into Cu (1 1 1) surface as the applied tension activates the grain boundary energy of Cu and promotes its abnormal grain growth to single crystals. In addition, we found a clue that the formation of graphene cooperatively assists the recrystallization into Cu (1 1 1) by minimizing the surface energy of Cu. The domain sizes and charge carrier mobility of graphene grown on the single-crystalline Cu (1 1 1) are 5 times and similar to 50% increased, respectively, in comparison with those of graphene from Cu (1 0 0), indicating that the less lattice mismatch and the lower interaction energy between Cu (1 1 1) and graphene allows the growth of larger single-crystalline graphene with higher charge carrier mobility. Thus, we believe that our finding provides a crucial idea to design a roll-to-roll (R2R) graphene synthesis system where the tension control is inevitably involved, which would be of great importance for the continuous production of high-quality graphene in the future.