Electrochemistry in nano-hole formation on gold surface with a scanning tunnelling microscope

By increasing the interaction strength between the tip and the sample in a controllable and reproducible manner, scanning tunnelling microscopy has been used to produce nanometre scale structures. Two types of modifications could be realised: holes or mounds. In this paper we focus on the understanding of the mechanism responsible for nano-hole formation. The smallest stable nano-hole formed is 3 nm in diameter and 0.24 nm in depth, which represents the loss of ca 100 gold atoms. The writing process has an unitary rate in nitrogen gas with the presence of water vapour. The chemical composition of the tip-sample interface is important in nano-hole formation. The etching mechanism seems to be electrochemical in origin, where water or more precisely oxygen atoms could have a predominant play. A place-exchange mechanism between gold surface atoms and oxygen atoms adsorbed on surface seems to be the crucial point of this reaction. (C) 1997 Elsevier Science B.V.