The interaction of β-FeSi 2 with atomic hydrogen, carbon monoxide and oxygen

Abstract

Using static and time dependent HREELS the influence of hydrogen, CO and oxygen on the formation of β-FeSi 2 as well as the adsorption of these gases on Fe-films grown on Si(111) has been studied as function of annealing temperature. The saturation of a Fe-film with atomic hydrogen had no measurable effect on its transformation to β-FeSi 2. On β-FeSi 2 films atomic hydrogen occupies silan-like states which are characterized by losses at h ̵ ω = 260 and 108 meV , and states which are associated with FeH as characterized by a loss at 160 meV. The desorption temperature for both states is about 330 K. CO adsorbed on Fe-films is characterized by losses at 250, 194, 68 and 43 meV and a combination loss with h ̵ ω = 68 + 250 meV . These losses unambiguously demonstrate that on evaporated iron films CO simultaneously occupies at least two different sites in upright position, at low temperature. On Fe-films part of CO dissociates before it can desorb. This process starts at 300 K. The remaining carbon and oxygen have a strong effect on the formation of β-FeSi 2. In particular we could observe a strong long term corrosive action. A direct signal of carbon could not be observed in the present study probably due to bulk diffusion. The adsorption of oxygen on Fe-films is characterized by two losses at 56 and 133 meV, respectively. Upon formation to β-FeSi 2 the 133 meV loss shifts to 143 meV. This loss can be associated with the v 3 vibration of SiO 2. The intensity of this loss increases with time at 300 K due to segregation of oxygen towards the surface.