Investigation of reaction sequence occurring in graphene-assisted chemical etching of Ge surfaces in water

This study aims to elucidate the reaction sequence of enhanced etching of Ge surfaces in water with the assistance of reduced graphene oxide (rGO) sheets. For this purpose, we performed in situ atomic force microscopy observations. After the immersion of a Ge surface loaded with dispersed rGO sheets into water, a water film was promptly intercalated at the rGO/Ge interface. First, the Ge surface along the outer edges of the rGO sheets was etched. Then, an etched hollow was formed beneath the entire rGO sheet. This is probably due to the chemical activity at not only the outer edges but also at the local edges of the small holes in rGO sheets. As etching of the Ge surface proceeded, the rGO sheet covering the etched bottom of a hollow was physically bent. We point out that the contact area between the wrinkled sheet and the Ge surface may decrease, affecting the etching rate.