Polymer-Free Gradient-Etching Transfer of Freestanding Monolayer Graphene.

A polymer-free graphene transfer method based on a gradient-etching strategy is reported, allowing the fabrication of centimeter-scale, substrate-free monolayer graphene. Through unidirectional etching of the Cu substrate, the graphene layer is progressively released to float freely on the liquid surface, thereby eliminating tearing and fragmentation arising from random copper dissolution in conventional isotropic etching. The gradient etching can be realized through either electrochemically assisted etching, where the enhanced edge field near the counter electrode accelerates the local corrosion, or flow-assisted etching, where fluid motion promotes faster mass transport at the advancing reaction front. The resulting freestanding graphene serves as a transparent, gate-tunable electrode, ideally suited for spectroscopic studies of the intrinsic carbon-water interface. Its electrical and catalytic properties can be further tailored via in situ electrochemical deposition of catalyst nanoparticles. This method offers a highly flexible and versatile experimental platform for both fundamental investigations and high-performance device fabrication based on cleanly transferred graphene.