Solitary acoustic pulses can propagate along the surface of a coated homogeneous and inhomogeneous medium. It is shown how these nonlinear surface acoustic waves evolve out of initial pulselike conditions generated by pulsed laser excitation and how they can be monitored by optical detection. The solitary pulse shapes at the surface are computed on the basis of an evolution equation with nonlocal nonlinearity. They depend on the anisotropy of the substrate. Various approaches for the derivation of the evolution equation from nonlinear elasticity theory are critically compared. The behavior of the solitary pulses in collisions is investigated and is found to strongly depend on the linear dispersion law. The nontrivial depth dependence of these solitary pulses is also analyzed.

The nonlinear dynamics of elastic shear waves is investigated taking into account the interaction of the shear component of the displacements with low-amplitude sagittal components. Nonlinear evolutionary equations are derived for the shear-displacement field. These equations contain additional nonlinear dispersion terms due to the interaction with displacements in the sagittal plane. The soliton solutions of the equations obtained are studied and the possibility of the existence of exotic solitons—compactons and peakons—is discussed.

The propagation of Rayleigh waves is investigated in a solid substrate of linear material covered by a film consisting of a material with large nonlinear elastic moduli. For this system, a nonlinear evolution equation is derived that may be regarded as a special case in a wider class of evolution equations with a specific type of nonlocal nonlinearity. Periodic pulse train solutions are computed. For a certain member of the class of nonlinear evolution equations, several families of solitary wave solutions and their associated periodic stationary wave solutions are derived analytically.

Coating a planar surface of a homogeneous elastic halfspace by a thin film gives rise to dispersion of Rayleigh waves that, together with the second-order nonlinearity of the substrate or surface nonlinearities, leads to the existence of surface acoustic solitary pulses. Their shapes are computed and their stability with respect to small changes of their initial conditions and partly to collisions with each other is analyzed numerically. The existence of gap solitary waves in the case of a periodically structured film is demonstrated, and periodic solitary pulse train solutions on a small oscillatory background are found. Their stability is investigated by means of a Floquet analysis.

The attenuation and frequency shift of surface acoustic waves of Rayleigh and Sezawa types are calculated, which propagate in a layered semiconductor heterostructure containing an embedded spatially modulated two-dimensional electron gas (2DEG). The surface waves couple to the 2DEG via the piezoelectric effect. The electron gas is subjected to a static magnetic field directed normal to the interfaces of the levered system. The one- and two-dimensional periodic spatial modulations are due either to an electrostatic external potential or to a spatially varying magnetic field. The effects of the anisotropy of the elastic media as well as the two-dimensionally modulated electron gas are studied on the Weiss oscillations occurring in this system.

Surface-phonon-dispersion curves of the (001) surfaces of the GaSe and InSe films epitaxially grown on the hydrogen-terminated Si(111)(1 x 1) surface have been investigated by high-resolution inelastic helium-atom scattering. The phonon-dispersion curves of the GaSe(001) thin epitaxial films are very similar to those of the single crystals investigated previously. For comparison with the experiments, density-functional theory based on the plane-wave pseudopotential method has been used to determine the phonon-dispersion curves of bulk GaSe and InSe in a consistent formalism. No difference is found between the surface and bulk phonons of these two layered compounds, as expected due to weak interlayer interaction forces. The high quality of the time-of-flight spectra presented here together with the ab initio calculations provide insight into the phonon dynamics of GaSe(001), and a characterization of the phonon modes of InSe(001).

We present the results from density-functional calculations of the phonon dispersion of adsorbate-covered semiconductor surfaces. The plane-wave method is used together with the slab-supercell description for the surfaces. We focus on vibrational states that characterize the chemisorption site of the adsorbed atoms and phonon modes of the interface. By comparing the vibrational states in the presence of the adsorbates with those of the clean surfaces, adsorption-induced changes of the surface geometry and force constants can be identified. We study the chemisorption of hydrogen, antimony, and group-III elements on the (110) surfaces of III–V compounds, as well as on the (001) and (111) surfaces of silicon.

Nonlinear Rayleigh waves are considered that propagate along the surface of a homogeneous solid medium covered by a thin film. Their dynamics is described by an evolution equation containing dispersion of the Benjamin-Ono type and a nonlocal nonlinearity. Periodic nonlinear wave solutions are found which become solitary waves in the limit of infinite periodicity. It is shown that these solitary solutions are stable, but unlike the Korteweg-de Vries solitons, they do not survive collisions with each other and therefore are no real solitons.

The plane-wave pseudopotential approach based on the density-functional theory together with the slab supercell method has been applied to determine the surface phonons of GaP(110) and InAs(110). We have calculated and analyzed the phonon dispersion curves along high-symmetry lines of the surface Brillouin zone by means of an ab initio linear-response formalism. The obtained phonon spectra are in excellent agreement with the results of previous theoretical studies and with data from high-resolution electron-energy-loss spectroscopy and inelastic He-atom scattering. Furthermore, we work out chemical trends concerning the dynamical properties of several III-V(110) surfaces. (C) 1997 Elsevier Science B.V.

In the context of an ab initio linear-response approach we have applied the density-functional theory to the investigations of structural and dynamical properties of semiconductor surfaces. The relaxation geometry was found by minimizing the total energy with the help of the Hellmann-Feynman forces. We present the full phonon dispersion of GaAs (1 1 0) and InP (1 1 0) along high symmetry lines of the surface Brillouin zone and the bond-stretching frequencies of these surfaces covered with one monolayer hydrogen. All calculated frequencies compare very well with all available experimental data from HREELS and He atom scattering.