Origin and quantification of anomalous behaviour in velocity dispersion curves of stiffening layer/substrate configurations

Layer stiffening effects are studied via positive dispersion curves calculated for several layer/substrate configurations. The investigated layers (ZnO, Al, SiO2, Cr, Si, SiC, AlN, Si3N4 and Al2O3) deposited on Cu and/or Si substrates, showed two types of anomalous behaviour: velocities greater than the layer Rayleigh velocity and those smaller that the substrate Rayleigh velocity. The appearance and disappearance of these phenomena are analysed and quantified in terms of a suggested elastic parameter, ξ, which shows that their origin is due the combined effect of the velocities and densities of both the layer and the substrate. To cite this article: Z. Hadjoub et al., C. R. Physique 8 (2007). © 2007 Académie des sciences.