Copper Oxidation-Induced Nanoscale Deformation of Electromechanical, Laminate Polymer/Graphene Thin Films during Thermal Annealing: Implications for Flexible, Transparent, and Conductive Electrodes.

The transfer of large-area, continuous, chemical vapor deposition (CVD)-grown graphene without introducing defects remains a challenge for fabricating graphene-based electronics. Polymer thin films are commonly used as supports for transferring graphene, but they typically require thermal annealing before transfer. However, little work has been done to thoroughly investigate how thermal annealing affects the polymer/graphene thin film when directly annealed on the growth substrate. In this work, we demonstrate that under improper annealing conditions, thermal annealing of poly(ether imide)/single-layer graphene (PEI/SLG) thin films on Cu causes detrimental nanoscale structural deformations, which permanently degrade the mechanical properties. Furthermore, we elucidate the mechanisms of PEI/SLG deformation during thermal annealing and find that permanent deformations and cracking are caused by Cu substrate oxidation. This study provides an understanding of annealing-induced deformation in polymer/graphene thin films. We anticipate that this knowledge will be useful for further developing defect-free, graphene-based thin film electronics.