The HfO2/Si(001) interfaces formed by reactive dc sputter deposition of Hf buffer layer followed by HfO2 stacking were analyzed by high-resolution transmission electron microscopy, medium energy ion scattering (MEIS), and photoelectron spectroscopy using synchrotron-radiation lights. The present MEIS analysis determined the elemental depth profiles and revealed that no Hf buffer layer resulted in growth of SiO2 at the interface, and that the presence of the Hf layer led to the formation of Si-rich silicate-like interlayers. The binding energy shifts of Si-2p3/2 identified the chemical bonds of the interfacial layers and confirmed the formation of SiO2 (no buffer layer) and silicate layers (presence of the buffer layers) at the interfaces. The Hf-buffer layer suppresses the O diffusion toward the interface and thus the thicker the buffer layer, the thinner the Hf-silicate interlayer. The deposition condition of HfO2 (1.3 nm)/Hf (1.3 nm) has achieved the highest permittivity of 28 for HfO2 (3.6 nm) and 8 for the silicate layer (1.7 nm). © 2002 American Institute of Physics.