Surface phenomena atom scattering

For crystals which have flat faces which extend for a fraction of 1 ym, a new type of phenomenon may be observed. Electrons incident at the edge of the crystal parallel to the surface may be channelled along the surface. The potential field of the crystal extending into the vacuum deflects the electrons so that they tend to enter the surface but they are scattered out of the crystal by the surface atoms or by diffraction from the crystal lattice planes parallel to the surface. If the scattering angle is less than the critical angle for total external reflection, the scattered electrons can not surmount the external potential barrier and are deflected back into the crystal (figure 4 (a)). 

The strong Raman signals for the atomic oxygen species dissolved in the metallic silver phase are due to a phenomenon known as surface-enhanced Raman scattering... 

Two rather different techniques that exploit the same underlying phenomenon of coherent interference of elastically scattered low energy electrons are photoelectron diffraction [5] and surface extended X-ray absorption fine structure (SEXAFS) [6,7]. Figure 1.1. shows schematically a comparison of the electron interference paths in LEED and in these two techniques. In both photoelectron diffraction and SEXAFS the source of electrons is not an electron beam from outside the surface, as in LEED, but photoelectrons emitted from a core level of an atom within the adsorbate. In photoelectron diffraction one detects the photoelectrons directly, outside the surface, as a function of direction or photoelectron energy (or both). The detected angle-resolved photoemission signal comprises a coherent sum of the directly emitted component of the outgoing photoelectron wavefield and other components of the same wavefield elastically scattered by atoms (especially in the substrate) close... 

Adsorption of mercury atoms onto thin gold film leads to scattering of conduction electrons at the gold surface resulting in an increase of surface electrical resistance. This phenomenon is used for preparation... 

Fundamentals. The scattered X-ray from crystal planes or a thin metal film can interfere coherently with scattered X-rays from an adsorbate layer. This phenomenon is called surface differential X-ray diffraction (SDD) or Bragg peak interference. The theory has been described elsewhere in detail [43,44], Information on the relative amount of material in the adsorbate layer (coverage) and the distance between atoms in the top layer of the substrate and in the adsorbate layer as a function of electrode potential can be derived from SDD measurements. 

Sputtering When a solid surface is bombarded with energetic particles such as accelerated ions, surface atoms of the solid are scattered backward due to collisions between the surface atoms and the energetic particles. This phenomenon is called back-sputtering, or simply sputtering. 

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