Resonant guided elastic waves in an adsorbed slab: theoretical analysis of the density of states
Résumé
An isolated elastic slab presents an infinite number of guided vibrational modes. Upon its adsorption oil a semi-infinite substrate some of them become resonant with the bulk modes of the subsme. Such resonances were initially studied by Brillouin and by inelastic helium-atom scattering. We present here an exact method fdt obtaining the total vibrational density of states of the adsorbed slab. This method is then applied IO isotropic elastic media and gives a semi-analytical expression fof the vibratibnal density of states. Derailed analysis for an AI slab on a W substrate and vice v m a shows that the resonant modes appear in general as well defined peaks in the total density of sram. The position of these peaks enables us to study the speed of the resonant modes as a function of the thickness of the slab or of rhe propagation vector p@lel to the surface.