Low energy electron-excited nanoscale (LEEN) luminescence spectroscopy and secondary ion mass spectrometry have been used to probe the defect states and chemical composition in as-deposited relatively thick (similar to 100 nm) HfO2 films and in SiO2/HfO2/SiO2/Si (5 nm/15 nm/5 nm) heterojunction stacks grown by plasma enhanced chemical vapor deposition including as well changes in bonding and defects after high temperature (900 degrees C) annealing. LEEN measurements of optical transitions in the thicker HfO2 films are assigned to defect-associated radiative transitions centered at approximately 2.7, 3.4, 4.2 and 5.5 eV. These spectra exhibited significant changes in as-deposited films (300 degrees C) and after a 900 degrees C anneal in forming gas (N-2/H-2). Qualitative differences in LEEN spectra of stacked films are correlated with (i) formation of Hf silicate during deposition of the HfO2 film onto the SiO2 substrates in the as-deposited films, and (ii) a chemical phase separation of these Hf silicates into a heterogeneous mixture SiO2 and HfO2 nanocrystallites after the 900 degrees C anneal. (c) 2008 American Vacuum Society.