Multifunctional
molecules have been important for being building
blocks of interesting molecular systems. A combination of these multifunctional
molecules with conventional semiconductor surfaces has been utilized
in designing new materials for different electronic and optical applications.
Metalloles, as a group of multifunctional molecules, have unique electronic
and photophysical properties. In this study, density functional theory
calculations were performed to examine the structural and electronic
properties of metallole (MC4H6; M = Si, Ge,
and Sn)-decorated Si(001)-(2 × 2) surfaces. After determining
the structural parameters of single isolated metallole molecules,
eight different adsorption configurations on the silicon surface were
proposed to find out the most stable binding model for each. The self-dissociation
of H atoms in the stannole [4 + 2]-(II) model during these calculations
led to three different dissociation models (including M–H and
C–H dissociation) to be considered for all M atoms. As a result
of total and adsorption energy calculations, the bridge-(I) model
was found to be the most stable configuration for nondissociated molecules,
whereas M–H dissociation was the most stable for dissociated
configurations. The reaction paths of structural transitions between
the proposed models were also plotted to compare the energy barriers.
The highest barrier was seen for the [2 + 2]-(I) to bridge-(II) transition.
Dimerization of these metallole molecules was also studied. The exo
model dimer adsorption on the Si(001)-(2 × 2) surface was found
to be the most stable one. According to the electronic structure calculations,
the energy band gap of the clean (2 × 2) silicon surface widens
from ∼0.05 to ∼0.9 eV (direct) and ∼0.6 eV (indirect)
upon the adsorption of metallole monomers and dimers, respectively.