Nanocarbon-assisted chemical etching of Ge(100) in H2O2

•A monolayer nanocarbon enhances the reduction of oxidants in solution.•Different oxidants used bring huge differences in etch morphology.•The addition of H2O2 to the etching solution provides rapid hole diffusion.•The mechanism of etching involves hole injection and diffusion via nanocarbons. We utilized graphene oxide (GO) flakes as a starting material to conduct nanocarbon (NC)-assisted chemical etching of Ge(100) surfaces in H2O2 solutions. Upon initial etching in H2O2, a pitted morphology formed beneath the loaded nanocarbon. The etch pits exhibited a tendency to expand, with edges assuming square-like shapes in H2O2 solutions. This phenomenon is reminiscent of an inverted pyramidal structure observed during enhanced etching of a Ge surface loaded with metallic particles, exposing (111) microfacets. As the etching progressed, noticeable lateral etching occurred on the Ge surface. Consequently, the small pits merged to form larger hollows, potentially exceeding the size of the initial GO flake. These etching properties were analyzed based on electrochemical reactions there, or the injection of holes created by the enhanced reduction of H2O2 molecules on nanocarbons, which were compared to those observed when using O2-dissolved water as an etchant. Additionally, we provide guidelines for achieving more homogeneous and deeper etch structures using a loaded nanocarbon catalyst in H2O2.