  The deposition of one silicon monolayer on Ag(111) gives rise to a set of
superstructures depending on growth conditions. These superstructures are
correlated to the epitaxy between the honeycomb structure of silicon (so called
silicene) and the silver substrate. In this paper, from a detailed re-analysis
of experimental results, obtained by Scanning Tunneling Microscopy and by Low
Energy Electron Diffraction on the (2R3x2R3)R30 structure, we propose a new
atomic model of the silicene layer based on periodic arrangements of perfect
areas of (2R3x2R3)R30 surrounded by defect areas. A generalization of this
model explains the main experimental observations: deviation of the average
direction, Moire patterns and apparent global disorder. In the frame of the
proposed model, the apparent disorders observed on the STM images, would be
topological effects, i.e. the silicene would keep a quasi-perfect honeycomb
structure.
