Spontaneous dissociation of Co ₂(CO) ₈ and autocatalytic growth of Co on sio _2: A combined experimental and theoretical investigation

We present experimental results and theoretical simulations of the adsorption behavior of the metal-organic precursor Co ₂(CO) ₈ on SiO ₂ surfaces after application of two different pretreatment steps, namely by air plasma cleaning or a focused electron beam pre-irradiation. We observe a spontaneous dissociation of the precursor molecules as well as autodeposition of cobalt on the pretreated SiO ₂ surfaces. We also find that the differences in metal content and relative stability of these deposits depend on the pretreatment conditions of the substrate. Transport measurements of these deposits are also presented. We are led to assume that the degree of passivation of the SiO ₂ surface by hydroxyl groups is an important controlling factor in the dissociation process. Our calculations of various slab settings, using dispersion-corrected density functional theory, support this assumption. We observe physisorption of the precursor molecule on a fully hydroxylated SiO ₂ surface (untreated surface) and chemisorption on a partially hydroxylated SiO ₂ surface (pretreated surface) with a spontaneous dissociation of the precursor molecule. In view of these calculations, we discuss the origin of this dissociation and the subsequent autocatalysis.