Excitation Of Surface Modes Research Articles

Low Energy Electron Spectroscopy—a Tool for Studies of Surface Vibrations

Surface vibrations are investigated with a high resolution electron spectrometer (ΔE≈10 meV). For sufficiently low electron energies the electrons are scattered mainly by the extended electric dipole field associated with certain types of surface vibrations. The excitation of Fuchs-Kliewer surface modes in infrared-active materials is illustrated in zinc oxide. On the cleaved (111) silicon surface a surface phonon of ℏω=56 meV is found. Furthermore, the localized modes of oxygen adsorbed on a (111) silicon surface are discussed. The sensitivity of electron spectroscopy is several orders of magnitude higher than light spectroscopy.

Spin-dependent effects in proton inelastic scattering

Proton inelastic collisions leading to the excitation of surface modes in even target nuclei are considered. An extension of the phenomenological optical model is made in which both the spin-independent and spin-dependent potentials contain terms linear in the nuclear collective surface coordinates. The spin-dependent part has the full Thomas form. The T-matrix element is derived in the DWBA approximation, and expressions for inelastic observables such as cross section, polarization, asymmetry and spin flip probability are given. The theory is applied to the analysis of the inelastic scattering of protons in the energy range 29–50 MeV by several nuclei. Special attention is paid to the deformed spin-dependent interaction, where we compare the full Thomas form with a previously proposed simplified form. It is found that the use of the full Thomas form substantially improves the fit to the observed asymmetries, especially at forward scattering angles. Moreover, certain features of the measured spin-flip probabilities are reproduced only when the deformed spin-dependent interaction is of the full Thomas form.

Solution to the Phenomenological Problem of a Magnetic Line Source Above a Plane Structure that SupportsN-Excited Modes

The phenomenological theory of multimode surface wave excitation is applied to the problem of a line source above an infinite plane exciting surface. Mathematically, this involves solving the reduced wave equation subject to an Nth order differential boundary condition, constructed to allow for the excitation of surface and leaky wave modes. The results of this paper show that the response of any plane surface that is Characterizable by such a boundary condition exhibits certain characteristic phenomena. Namely, the far field is composed of a radiated field and excited modes and there exist sectors where the excited modes disappear. Also, it is possible for energy to be transported to infinity along the surface. These phenomena are familiar in the case of a dielectric slab. The solution is obtained by introducing a suitable auxiliary operator which is then inverted. This allows the determination of the radiated far field by elementary algebraic techniques. Then the result is transformed into a contour integral and the excited modes and high frequency approximation are discussed.

Excitation of surface modes along a semi-infinite dielectric cylinder

Expressions for the amplitude and power of surface-waveguide modes excited by a plane wave along a semi-infinite dielectric cylinder are presented. Approximations for small dielectric differences are given, which result in a simple expression for the power of the modes. Application of these results to light propagating along the human retinal receptors is discussed.

Alpha-particle excitation of quadrupole and octupole surface modes in Ti, Fe, Ni, Zn and Sr

Angular distributions were obtained for elastic and inelastic scattering of 41 MeV alpha particles by Ti 48, Fe, Ni, Zn, Zn 64 and Sr. In all targets excitation by inelastic scattering is strongest for the low-lying 2 + levels, usually described in terms of quadrupole surface vibrations, and for the “anomalous” levels of somewhat higher excitation. The results for both elastic and inelastic scattering are analyzed in terms of a strong absorption diffraction scattering model. Parameters associated with collective interpretations of both types of levels are estimated and compared with values of the corresponding quantities derived from Coulomb excitation and electron scattering experiments. Reasonable agreement is obtained in the quadrupole excitation analyses. Strong support is given for 3 − assignments for the anomalous levels and for their interpretation in terms of surface octupole vibrations.