EELS study of oxygen superstructure in epitaxial Y2O3 layers

The superstructure found in epitaxial Y2O3 layers on (0 0 1)Si is examined by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The oxygen K-edge is measured by EELS both on the superstructure and a defect-free region of the Y2O3 layers and they are compared to EELS spectra obtained from bulk stoichiometric and reduced Y2O3. It is shown that during epitaxial growth of Y2O3 on (0 0 1)Si in UHV, oxygen vacancies order into a superstructure creating non-stoichiometric regions in an otherwise stoichiometric Y2O3 layer. Furthermore it is shown that oxygen deficiency introduces a change of the density of states of the lower conduction band of Y2O3 and a decrease of its electronic gap by 0.8 eV.