Catalytic Properties of Chemically Modified Graphene Sheets to Enhance Etching of Ge Surface in Water

We examined chemical etching of the Ge surface assisted by single sheets of chemically modified graphene in O₂-containing water. Three types of graphene sheets were used: graphene oxide (GO), hydrazine-reduced GO (hyd-rGO), and hydrothermally treated GO in an ammonia solution (amm-rGO). amm-rGO possessing pyridinic-N atoms produced the highest etching rates of the graphene used for all water temperatures tested. We propose that graphene sheets catalyze Ge oxidation underneath the sheets and that this phenomenon probably originates from the enhanced adsorption of O₂ molecules in water at local defects, such as graphene edges and carbon atoms next to pyridinic-N, in the sheets. Because O₂ adsorption is the initial step of either the oxygen reduction reaction or direct oxidation, it results in the formation of soluble GeO₂ at the graphene/Ge interface, leaving etched hollows under the sheets. In addition, we combined graphene-assisted chemical etching with lithography by using photoresist to fabricate a trench pattern on Ge.