Rate of formation of silicon dioxide; Semiconducting ruthenium silicide

Abstract

The rate of oxide formation over Ru2Si3, a semiconductor with a band gap of about 1 eV, is about as slow as that for Ir3Si5, another semiconducting silicide, and comparable to the rate observed over silicon itself. This is in opposition to what one obtains over metallic silicides where the linear term of oxidation kinetics is at least an order of magnitude greater than that for silicon. Analysis of these contrasting results leads to the conclusion that the enhanced rate over metallic silicides is due to the greater density of states at the Fermi level which facilitates charge transfer between the oxygen atoms and the oxidizing material. The possibility that the rate of oxidation should depend strongly on the metallic or covalent character of the Si bonding appears to be excluded by the fast oxidation rate observed over NiSi2 and CoSi2.