Fig. 1 Solid electrochemical reaction process. (a) Schematic illustration of the process. The process is categorized into five regions. 1) STM observation using a bias which does not cause the solid electrochemical reaction. 2) Electron injection into the ionic material by changing the bias polarity. 3) Precipitation of atoms starts after a certain time. 4) Precipitated atoms form a bridge connected to the counter electrode. 5) The bridge thickens due to the further precipitation of atoms. (b) Experimental result. Change in the applied bias (green) and the measured current (black). The number of precipitated atoms can be estimated from the change in the current.