Composite gate dielectrics for advanced Si devices that include high-k dielectrics have two interfaces that determine performance and reliability: (i) the Si-SiO2, interface, and (ii) the internal interface between SiO2, and the high-k dielectric. Spectroscopic studies combined with ab initio electronic structure calculations and bond constraint theory (BCT) identify quantitative relationships between electronic and/or mechanical strain and densities of defects and defect precursors at these interfaces. Discontinuities in the number of bonds/atom, N-av at these dielectric interfaces introduce high densities of defects that scale as the square of N-av. BCT also explains the driving force for nano-scale self-organizations at these interfaces, and the effect this has on defect densities, and other interfacial properties. (c) 2004 Elsevier B.V. All rights reserved.