Interaction of W(CO)₆ with SiO₂ surfaces: A density functional study

The interaction of tungsten hexacarbonyl [W(CO)₆] precursor molecules with SiO₂ substrates is investigated by means of density functional theory calculations with and without inclusion of long-range van der Waals interactions. We consider two different surface models, a fully hydroxylated and a partially hydroxylated SiO₂ surface, corresponding to substrates under different experimental conditions. For the fully hydroxylated surface, we observe only a weak interaction between the precursor molecule and the substrate, with physisorption of W(CO)₆. Inclusion of van der Waals corrections results in a stabilization of the molecules on this surface, but does not lead to significant changes in the chemical bonding. In contrast, we find a spontaneous dissociation of the precursor molecule on the partially hydroxylated SiO₂ surface, where chemisorption of a W(CO)₅ fragment is observed upon removal of one of the CO ligands from the precursor molecule. Irrespective of the hydroxylation, the precursor molecule prefers binding of more than one of its CO ligands. In light of these results, implications for the initial growth stage of tungsten nanodeposits on SiO₂ in an electron-beam-induced deposition process are discussed.