A. Marvin

Theory of Brillouin scattering from surface acoustic phonons in supported films

The theory of the Brillouin scattering from the surface of a semi-infinite medium, developed previously, is extended to coated surfaces of cubic materials. The Brillouin cross section is obtained for any scattering geometry and for p and s polarisation of the incident and scattered light. The formulae for the cross section contain contributions from the ripple and the elasto-optic scattering mechanisms for the film as well as for the substrate. The theory is applied to a silica film deposited on crystalline silicon and the behaviour of the cross section against the film thickness is investigated. The authors find that there are strong interference effects among the various contributions to the cross-section, so that the intensity of the spectral lines dramatically oscillates by changing the thickness. Although in general the ripple scattering mechanism is the dominant one it is found that the elasto-optic coupling in the silica film is not negligible and sometimes is even prevailing. The discrete phonon spectrum (Rayleigh, Sezawa, Lamb modes) and the continuous spectrum (resonances, mixed modes) are both studied.

Surface Brillouin scattering from acoustic phonons. II. Application to semiconductors

The theory of Brillouin scattering from corrugated surfaces developed previously has been applied to semiconductors. The available spectra measured with 5145 AA light has been used for evaluating the elasto-optic constants (k11, k12, k44) of the medium. For GaAs k11=42.5, k12=51 and k44=25.5. This is the first determination of these constants in GaAs at this wavelength, where other techniques are not applicable. For silicon k11=53, k12=25 and k44=23. It is also shown that in opaque semiconductors the elasto-optic coupling depends strongly on the surface orientation.

General relation between surface impedance and surface curvature

We relate in a general way the surface impedance of a metal to the local curvature of the surface. We obtain the corrections to the flat-surface impedance formula up to second order in dΔ, where d is the penetration depth of the electromagnetic field and Δ is the difference between maximum and minimum curvature. We give explicit expressions relating to each other the electric and magnetic fields parallel to the surface, E|| and H||, respectively. We show that the terms neglected in the surface impedance approximation contain only the second derivatives of these fields in the plane tangent to the surface.

Theory of the three-wave mixing of volume EM, surface polaritons and surface acoustic waves

This paper deals with the theory of light scattering from a thin metallic film where corrugations exists at both surfaces. The scattering cross section for backward and forward diffraction is computed by solving perturbatively the Maxwell equations to first order in the corrugation amplitude. A comparison is made with the experimental results presented in the preceding paper where the corrugations are of dynamic character (surface elastic waves). The different behaviour of the backward and forward cross sections is explained in terms of interference effects.

Debye-Waller factor in atom-surface scattering: Elastic and inelastic channels

Abstract Explicit expressions for the Debye-Waller factor for the elastic and one-phonon channels are presented to lowest order in the phonon displacement, using a hard wall model to represent the atom-surface interaction. The periodicity of the crystal is accounted for; thus we explicitly generalize to all elastic channels the reflectance result found by Garcia et al. within the plane-surface model, and we include the contribution of the umklapp processes to the inelastic channels. We show how for high incident energy of the atom all Debye-Waller factors reduce to the standard result.