Atomic-Layer Etching and Electron-Stimulated Desorption of Br-Chemisorbed Si(111) Surfaces

Abstract

Atomic-layer etching and electron-stimulated desorption of Br-chemisorbed Si(111)-7×7 surfaces were investigated by scanning tunneling microscope. In a Br₂ dose of 100 L, most of the Si adatoms are saturated with Br atoms, while the 7×7 structure is completely retained. In further Br₂ doses up to 400 L, most of the Si adatoms are etched, and the underlying rest-atom layer is imaged during the tip scanning at a sample bias of +3 V. Irradiating Br-chemisorbed surfaces with the field-emitted electrons from an STM tip, which was farther away from the sample than at usual observation, induced various desorption behavior depending on the initial Br coverage and electron energy. At low Br coverage, Br atoms desorb but no atomical changes on the Si surface occur. At saturation coverage, Si adatoms as well as Br atoms desorb remarkably. The cross section of Br atom desorption first increases near 15 eV and then increases by orders of magnitude with an electron energy up to 150 eV. The cross section of adatom desorption, in contrast, is much less dependent on the electron energy in the above energy region. The desorption behavior is discussed in terms of electronic excitation at the Br-chemisorbed Si(111) surface.