Atomic-Layer Etching of a Br-Saturated Si(111)-7×7 Surface by Using Scanning Tunneling Microscope

Atomic-layer etching of Br-saturated Si(111) surfaces has been achieved by using scanning tunneling microscope at room temperature. At a Br2 dose of 100 L, most of the Si adatoms are saturated with Br atoms, while the 7×7 structure is completely retained. At further Br2 doses up to 400 L, most of the Si adatoms are removed during the tip scanning at a sample bias of +3 V, and the underlying rest-atom layer is imaged. The adatoms remaining on the scanned surface are dominantly SiBr and SiBr2 species, suggesting that highly brominated adatoms like SiBr3 or SiBr4 are more likely etched away during the tip scanning. These highly brominated silicon adatoms are not volatile at room temperature, but easily desorb through the field evaporation under the usual scan mode.