DFT Characterization of Metallole-Decorated Silicon (001) Surface

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.