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

Abstract

Layer stiffening effects are studied via positive dispersion curves calculated for several layer/substrate configurations. The investigated layers (ZnO, Al, SiO 2 , Cr, Si, SiC, AlN, Si 3 N 4 and Al 2 O 3 ) 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.