Laminar Flow-Assisted Metal Etching for the Preparation of High-Quality Transfer-Free Graphene

The synthesis of transfer-free graphene at metal–substrate interfaces using a sacrificial metal film deposited on dielectric substrates is promising for producing graphene for industrial applications. However, although no complex transfer process is used in the aforementioned method, an etching process is required to remove the overlying sacrificial metal to expose the interfacial transfer-free graphene. The conventional etching method, which involves immersing metal-covered, transfer-free graphene into an etchant solution for metal removal, has been extensively applied while it is highly dependent on individual handling skills. Thus, this method does not provide suitable reproducibility and scalability. In this study, we designed a laminar flow-assisted etching method by using a microfluidic system to remove the metal film on graphene in a well-controlled and smooth manner. The coverage of transfer-free graphene retained on a silica substrate after using the designed etching method (95%) was considerably higher than that of transfer-free graphene produced by the conventional etching process (64%). The produced graphene contained uniform monolayers with few defects and decent field-effect mobility of 1665 cm2 V–1 s–1. In addition, this microfluidic etching method is highly compatible with automatic operation and thus provides advantages such as labor economization as well as high reproducibility, throughput, and scalability.