Ultra-thin high-k layers based on HfO2, or Hf-silicates in combination with sub-nanometer SiO2, show muchpromise in their use as Si-compatible gate dielectrics. XPS has been applied on a range of HfO2/SiO2and HfSiOx(60%Hf)/SiO2films on Si(100), before and after decoupled plasma nitridation (DPN) at 1073 K. The treatment of the data was optimized in order to determine individual layer thicknesses of the multilayer stack taking into account the measured nitrogen content of the nitrided films. The procedure adhered to the prescriptions of ISO18118:2004(E) for the calculations of inelastic mean free paths (IMFP) and elastic corrections thereof, using film material properties, like densities and band gaps. Effective attenuation lengths (EAL) were taken throughout as 90% of the respective IMFP, whereas an appropriate set of empirical relative sensitivity factors (RSF) was used. The XPS-derived thicknesses were compared with corresponding values obtained from medium-energy ion scattering (MEIS) measurements on the same series of specimens in combination with energy spectrum simulation to provide quantitative layer information with sub-nanometer resolution. The XPS and MEIS results exhibit very good agreement on the deduced layer structures within the respective experimental uncertainty, and both sets are consistent with the grown nominal layer parameters of the high-k nanofilms.