Adsorption of LiF on Si(111)-7×7 surface studied by scanning tunneling microscopy and low energy electron diffraction

Modification of the Si(111)-7×7 surface by LiF adsorbates and its annealing behavior are investigated using Scanning Tunneling Microscopy and Low Energy Electron Diffraction. The preferred adsorption sites are found to be the center adatom sites. Whereas, at the coverage higher than 0.4 monolayer, the 7×7 structure disappears. One monolayer (ML) is referred to as the site density of the unreconstructed surface. For the LiF-covered surface (0.4 ML), the 7×7 structure begins to recover at an annealing temperature of 325°C, and at 800°C it reconstructs into the 7×7 structure. In the temperature range of 300 ∼ 800°C, the Si(111) surface and LiF adsorbates are suggested to undergo the processes including dissociation of LiF adsobates, fluorination of Si atoms, desorption of the fluorides, etching of the surface and reconstruction of the etched surface.