Electron-scattering

SEM Scanning electron microscopy [7, 10, 14] A beam of electrons scattered from a surface is focused Surface morphology... 

Electrons interact with solid surfaces by elastic and inelastic scattering, and these interactions are employed in electron spectroscopy. For example, electrons that elastically scatter will diffract from a single-crystal lattice. The diffraction pattern can be used as a means of stnictural detenuination, as in FEED. Electrons scatter inelastically by inducing electronic and vibrational excitations in the surface region. These losses fonu the basis of electron energy loss spectroscopy (EELS). An incident electron can also knock out an iimer-shell, or core, electron from an atom in the solid that will, in turn, initiate an Auger process. Electrons can also be used to induce stimulated desorption, as described in section Al.7.5.6. 

B1.6.2.1 BETHE-BORN THEORY FOR HIGH-ENERGY ELECTRON SCATTERING... 

A succinct picture of the nature of high-energy electron scattering is provided by the Bethe surface [4], a tlnee-dimensional plot of the generalized oscillator strength as a fiinction of the logaritlnn of the square of the... 

Figure Bl.6.8 Energy-loss spectra of 200 eV electrons scattered from chlorine at scattering angles of 3° and 9° [10]. Optically forbidden transitions are responsible for the intensity in the 9° spectrum that does not appear in the 3 ° spectrum.

Bonham R A and Fink M 1974 High Energy Electron Scattering (ACS Monograph 169) (New York Van Nostrand Reinhold) oh 5... 

This text covers quantitative analysis by electron energy-loss spectroscopy in the electron microscope along with instrumentation and applicable electron-scattering theory. 

The atomic scattering factor for electrons is somewhat more complicated. It is again a Fourier transfonn of a density of scattering matter, but, because the electron is a charged particle, it interacts with the nucleus as well as with the electron cloud. Thus p(r) in equation (B1.8.2h) is replaced by (p(r), the electrostatic potential of an electron situated at radius r from the nucleus. Under a range of conditions the electron scattering factor, y (0, can be represented in temis... 

Figure Bl.25.12 illustrates the two scattering modes for a hypothetical adsorption system consisting of an atom on a metal [3]. The stretch vibration of the atom perpendicular to the surface is accompanied by a change m dipole moment the bending mode parallel to the surface is not. As explained above, the EELS spectrum of electrons scattered in the specular direction detects only the dipole-active vibration. The more isotropically scattered electrons, however, undergo impact scattering and excite both vibrational modes. Note that the comparison of EELS spectra recorded in specular and off-specular direction yields infomiation about the orientation of an adsorbed molecule.

In an electron scattering or recombination process, the free center of the incoming electron has the functions Wi = ui U u, and the initial state of the free elechon is some function v/ the width of which is chosen on the basis of the electron momentum and the time it takes the electron to aiTive at the target. Such choice is important in order to avoid nonphysical behavior due to the natural spreading of the wavepacket. 

Example 3. The mean free path of electrons scattered by a crystal lattice is known to iavolve temperature 9, energy E, the elastic constant C, the Planck s constant the Boltzmann constant and the electron mass M. (see, for example, (25)). The problem is to derive a general equation among these variables. 

EXAFS Spectroscopy Techniques and Applications. (B. K. Teo and D. C. Joy, eds.) Plenum, New York, 1981. Contains historical items and treatments of EXELFS, the electron-scattering counterpart of EXAFS. 

When an electron scatters from an atom, its phase is changed so that the reflected wave is not in phase with the incoming wave. This changes the interference pattern and hence the apparent distance between the two atoms. Knowledge of this phase shift is the key to getting precise bond lengths from SEXAFS. Phase shifts depend mainly on which atoms are involved, not on their detailed chemical environment, and should therefore be transferable from a known system to unknown systems. The phase shifts may be obtained ftom theoretical calculations, and there are published tabulations, but practically it is desirable to check the phase shifts using... 

Figure 5 (a) Schematic of inelastic electron scattering occurring as a photoelectron, ini-... 

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