Iron adsorption on SiO₂/Si(111)

The adsorption of ferric and ferrous iron onto the native oxide of the SiO₂/Si(111) surface has been evaluated using X-ray photoelectron spectroscopy (XPS). Through a series of immersion experiments, performed at room temperature and pH 1, it has been shown that the ferric species is strongly adsorbed onto the hydrophilic surface, while ferrous iron remains in solution. Dehydroxylation of the silica surface by etching with hydrofluoric acid reduces the concentration of receptive Si-OH groups, thereby limiting iron adsorption. The experiments were reproduced in a combined ultrahigh vacuum-electrochemical system (UHV-EC), which allowed a carbon-free surface to be prepared before contacting the iron solutions, and confirmed the strong affinity of ferric iron towards the SiO₂/Si(111) surface.