The application of spectroscopic ellipsometry to the oxidation of magnesium

The interaction of oxygen with the Mg(001) surface has been studied under UHV conditions using automatic spectroscopic ellipsometry in the energy range 1.8-5.2 eV. The first stage of oxidation can be described in terms of the growth of a surface layer consisting of a mixture of Mg and MgO with a composition up to 70% MgO and a thickness of ∼4 Å. After a phase transition, where part of this mixed layer is converted into a three-dimensional MgO film, further oxidation proceeds via layer growth of the pure oxide. In order to calculate the dielectric properties of the mixed phase, the effective medium models of Maxwell-Garnett, Lorentz-Lorenz and Bruggeman are compared. It is shown that only the approach of Bruggeman is capable of describing the experimental results.