Ultrathin high-k layers such as hafnium oxide (HfO2) in combination with a subnanometer SiO2 or Hf silicate have emerged as Si compatible gate dielectric materials. Medium energy ion scattering (MEIS) analysis has been carried out on a range of such metal oxide chemical vapor deposition grown HfO2/SiO2 and HfSiOx(60%Hf)/SiO2 gate oxide films of thickness between 1 and 2 nm on Si(100), before and after decoupled plasma nitridation (DPN). The ability of MEIS in combination with energy spectrum simulation to provide quantitative layer information with subnanometer resolution is illustrated and the effect of the DPN process is shown. Excellent agreement on the deduced layer structures and atomic composition with the as grown layer parameters, as well as with those obtained from cross section electron microscopy and other studies, is demonstrated. MEIS analysis of a high-k, metal gate TiN/Al2O3/HfO2/SiO2/Si stack shows the interdiffusion, after thermal treatment, of Hf and Al from the caplayer, inserted to modify the metal gate workfunction.