  Epitaxial silicene, which is one single layer of silicon atoms packed in a
honeycomb structure, demonstrates a strong interaction with the substrate that
dramatically affects its electronic structure. The role of electronic coupling
in the chemical reactivity between the silicene and the substrate is still
unclear so far, which is of great importance for functionalization of silicene
layers. Here, we report the reconstructions and hybridized electronic
structures of epitaxial 4x4 silicene on Ag(111), which are revealed by scanning
tunneling microscopy and angle-resolved photoemission spectroscopy. The
hybridization between Si and Ag results in a metallic surface state, which can
gradually decay due to oxygen adsorption. X-ray photoemission spectroscopy
confirms the decoupling of Si-Ag bonds after oxygen treatment as well as the
relatively oxygen resistance of Ag(111) surface, in contrast to 4x4 silicene
[with respect to Ag(111)]. First-principles calculations have confirmed the
evolution of the electronic structure of silicene during oxidation. It has been
verified experimentally and theoretically that the high chemical activity of
4x4 silicene is attributable to the Si pz state, while the Ag(111) substrate
exhibits relatively inert chemical behavior.
