  The electronic structure, specific heat, and thermal conductivity of silicon
embedded in a monolayer graphene nanosheet are studied using Density Functional
Theory. Two different shapes of the substitutional Si doping in the graphene
are studied, a triangular and a dot shape. The silicon doping of a graphene
nanosheet, with the silicon atoms arranged in a triangular configuration in
ortho- and para-positions, opens up a band gap transforming the sheet to a
semiconducting material. The opening of the band gap is caused by the presence
of the repulsion force between the silicon and carbon atoms decreasing the
density of states around the Fermi energy. Consequently, the specific heat and
the thermal conductivity of the system are suppressed. For graphene nanosheet
doped with a dot-like configuration of silicon atoms, at the ortho-, meta-, and
para-positions, the valence band crosses the Fermi level. This doping
configuration increases the density of state at the Fermi level, but mobile
charge are delocalized and diminished around the silicon atoms. As a result,
the specific heat and the thermal conductivity are enhanced. Silicon
substitutionally doped graphene nanosheets may be beneficial for photovoltaics
and can further improve solar cell devices by controlling the geometrical
configuration of the underlying atomic systems.
