We have measured the energy bandgaps of thermally evaporated ZrO2 on Si(1 0 0) and a very-thin interfacial silicate (SiOx:Zr) layer formed by 500 degreesC annealing in dry O-2 from the onset of the energy loss spectra of O 1s photoelectrons. The valence band lineups at the interfaces among ZrO2, SiOx:Zr and Si(1 0 0) have also been evaluated by analyzing the valence band spectra of thin heterostructures. By combination of the measured energy bandgaps and valence band lineups, we have determined the energy band alignments of as-evaporated ZrO2/Si(1 0 0) and annealed ZrO2/SiOx:Zr/Si(1 0 0) systems. The influence of 300-500 degreesC O-2-annealing on the energy distribution of electronic defect states in the films and at the interfaces has been demonstrated by total photoelectron yield measurements. (C) 2002 Elsevier Science Ltd. All rights reserved.