Electrical and structural properties of metal-oxide-semiconductor capacitors having as dielectric nanoscopic LaAlO3 or HfAlOx films deposited on nitrided or nonnitrided Si substrates were investigated. The electrical superiority of RuO2/HfAlOx/SiON/Si stacks was evidenced by a dielectric constant of 19 and a leakage current density of 67 mA/cm(2) at a gate voltage of -1 V, for a capacitance equivalent to silicon oxide thickness of 1.1 nm. Morphology, composition, and structure of the stacks were accessed by X-ray diffraction and reflectometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and narrow resonant nuclear reaction profiling with isotopic substitution. In spite of presenting crystalline phases associated with HfO2, the HfAlOx dielectric layers led to a smoother and thinner interfacial layer, improved by the thermal nitridation of the Si substrate prior to high-kappa deposition. This SiON-like interlayer thickness is self-limited even after postdeposition annealing owing to the formation of an effective diffusion barrier by the strong N-Si-N and N-Si-O-N bonds, which is also effective in preventing substrate oxidation. (C) 2008 The Electrochemical Society.