Helium atom scattering surface dynamics

D. D. Koleske, Studies of surface vibrations and structure using molecular dynamics simulations, lattice dynamics calculations, and helium atom scattering, 1992)... 

It is intended for this chapter to be a brief introduction to surface lattice dynamics and to some of the kinds of information that one is able to obtain about the electronic and vibrational properties of surfaces through high-resolution helium atom scattering. Such information is critical to the understanding of many aspects of surface chemistry and to the design of novel materials with specifically desired properties. 

The next phase for the theorists in connection with this work lies in predictions of helium atom scattering intensities associated with surface phonon creation and annihilation for each variety of vibrational motion. In trying to understand why certain vibrational modes in these similar materials appear so much more prominently in some salts than others, one is always led back to the guiding principle that the vibrational motion has to perturb the surface electronic structure so that the static atom-surface potential is modulated by the vibration. Although the polarizabilities of the ions may contribute far less to the overall binding energies of alkali halide crystals than the Coulombic forces do, they seem to play a critical role in the vibrational dynamics of these materials. 

Graham, A.P. The low energy dynamics of adsorbates on metal surfaces investigated with helium atom scattering. Surf. Sci. Rep. 2003, 49,115. 

ElHs, J., Graham, A.P., Hofmann, R, Toennies, J.P. Coverage dependence of the microscopic diffusion of Na atoms on the Cu(OOl) surface A combined helium atom scattering experiment and molecular dynamics study, Phys. Rev. B 2001, 63,195408. 

Elastic and inelastic colUsions of atoms and molecules at surfaces are also of importance. The scattering of hydrogen and helium from surfaces leads to diffraction patterns in the same manner as with LEED, but since the atoms penetrate the surface far less deeply than even low-energy electrons, the structures obtained reflect the very surface of the sample. The inelastic surface scattering of molecules can be examined in detail using laser and mass spectromet-ric detection for the scattered molecules. Such measurements can be used to model the form of the gas-surface interaction potential, knowledge of which is a prerequisite for any detailed picture of gas-surface reaction dynamics. 

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