[18a-F210-1~13] 6.6 Probe Microscopy

△ [18a-F210-3] Graphene-assisted Chemical Etching of Ge Surfaces in Water
~In situ AFM Observations of the Etching Process~

〇(M1)Shaoxian Li¹, Tomoki Hirano¹, Kentaro Kawai¹, Kazuya Yamamura¹, Kenta Arima¹ (1.Osaka Univ.)

Keywords:graphene, AFM, semiconductor

Wet etching is a promising method for fabricating diverse nanostructures on a semiconductor surface, such as nanowires, nanorods, nanopores and so on. The great advantage of this surface treatment is its simplicity. Noble metal is usually used as the catalyst in a conventional wet etching process to enhance an etching rate. Although a noble metal exhibits a high performance as a catalyst, we found that contamination of noble metals on a processed surface can be fatal during metal-assisted chemical etching. In order to solve this problem, a non-metallic material is demanded to replace a noble metal as the catalyst.In our work, we pay attention to a two-dimensional material-graphene, which is studied extensively currently due to its excellent properties. We employed reduced graphene oxide (rGO) as a chemical tool for nano-machining of a Ge surface in water. Comprehending the reaction mechanism at the interface between a catalyst and a semiconductor surface is essential for realizing catalyst-assisted machining.This study mainly focuses on the chemical etching effect mediated by the diffusion and intercalation of H₂O molecules at the interface between an rGO sheet and a Ge surface. Namely, in situ atomic force microscopy (in-situ AFM) was employed for observing etching of a Ge surface in water assisted by reduced graphene oxide. We found that H₂O molecules are intercalated at the rGO/Ge interface during the etching processe, which was revealed by the difference in rGO thicknesses in air and in water. By analyzing the cross-sectional profiles, we found that enhanced etching of Ge first occurs at the edge of an rGO sheet, then a Ge surface beneath the entire rGO sheet is etched. Local defects such as vacancies and tears probably determine the etch rate. Furthermore, the morphology change of an rGO sheet during etching affects an etch rate especially with a large sheet.We expect that our results contribute to grasp the basics of graphene-assisted chemical etching, and to utilize it in practical applications such as nano-scale fabrication and flattening of a semiconductor surface.