Surface Energy Engineered, High‐Resolution Micropatterning of Solution‐Processed Reduced Graphene Oxide Thin Films

Graphene, an atomically thin layer of two-dimensional carbon nanostructure, has received intense attention in recent years because of its extraordinary optoelectronic properties and potential applications in microelectronics. [ 1–4 ] While high-quality graphene has been produced by chemical vapor deposition (CVD) on metallic surfaces [ 5 , 6 ] and graphitization of a single crystal SiC, [ 7 ] reduced graphene oxide (rGO) is also considered as a promising electronic nanomaterial because of its solution processability, residual chemically active sites, and high-volume production at low cost. [ 4 , 8 , 9 ] In the form of a single-layer sheet or fi lms of a few layers, rGO has been employed in various electronic devices including chemical/biological sensors, [ 10 , 11 ] fi eldeffect transistors (FETs), [ 8 , 12 ] transparent electrodes, [ 13 , 14 ] and photovoltaics. [ 15 ] However, previous studies have largely focused on a single electronic device or sensor. To fabricate practical and reproducible rGO-based microelectronics, a scalable and effective method for high-resolution rGO micropatterns on various substrates is highly desirable. Top-down lithographic techniques have been widely used to create rGO micropatterns by selectively etching parts of rGO thin fi lms. [ 12 , 16–18 ] Although a variety of well-defi ned rGO patterns can be obtained from such lithographic methods, they are time-consuming, involve complex procedures, and give rise to undesirable contamination of the patterned surface from contact with sacrifi cial masks. Alternatively, rGO patterning has been explored with nonlithographic routes such as micromolding in capillaries [ 19 , 20 ] and solvent evaporation-driven self-assembly process. [ 21 ] These methods, however, are often limited to simple patterned structures such as stripes, because the assembly of GO fl akes occurs in a restricted geometry. In addition, although various printing techniques including inkjet printing, [ 22 , 23 ] transfer printing [ 24 , 25 ] and imprinting [ 26 ] have also been applied for rGO patterning, the production of highresolution and reproducible rGO micropatterns on a large scale still remains a challenging task.