  Silicene, a counterpart of graphene, has achieved rapid development due to
its exotic electronic properties and excellent compatibility with the mature
silicon-based semiconductor technology. Its low room-temperature mobility of
about 100 cm2V-1s-1, however, inhibits device applications such as in
field-effect transistors. Generally, defects and grain boundaries would act as
scattering centers and thus reduce the carrier mobility. In this paper, the
morphologies of various point defects in epitaxial silicene on Ag(111) surfaces
have been systematically investigated using first-principles calculations
combined with experimental scanning tunneling microscope (STM) observations.
The STM signatures for various defects in epitaxial silicene on Ag(111) surface
are identified. In particular, the formation energies of point defects in
Ag(111)-supported silicene sheets show an interesting dependence on the
superstructures, which, in turn, may have implications for controlling the
defect density during the synthesis of silicene. Through estimating the
concentrations of various point defects in different silicene superstructures,
the mystery of the defective appearance of v13*v13 silicene in experiments is
revealed, and 4*4 silicene sheet is thought to be the most suitable structure
for future device applications.
