Halide adsorption influences snapback distance in Scanning Tunnelling Microscope break junctions

• Snapback method as a tool for studying electrochemical surface processes. • Significant reduction in snapback distance of Au break junctions in halide electrolytes. • Electrochemical potential control confirms snapback distance reduction due to halide adsorption. ‘Snapback distance’ refers to the rapid increase in the size of the gap formed immediately after breaking an atomic-scale metallic contact. It is a commonly observed phenomenon in Scanning Tunnelling Microscope break junction (STM-BJ) and mechanically controlled break junction (MCBJ) experiments. Here, we show that the snapback distance measured for a gold break junction in pure water was significantly reduced in an electrolyte containing halide anions. In the case of Br − , experiments under electrochemical control provided clear evidence that this reduction was caused by halide adsorption on the surface of the gold.