Scanning Microscopy


A survey of electron scattering from a free atom or molecule by incident electrons with energies below 10 keV is best accomplished by viewing a Bethe surface. This surface presents a global picture of nearly all observable phenomena obtained from the investigation of the angular and energy dependence of scattered electrons. An absolute, comprehensive and accurate surface for molecular nitrogen, obtained from electron energy loss spectroscopic experiments, illustrates the major points to be made. Two general uses of such scattering information are: (i) the inference of various aspects of the electronic structure of the target through the observation of spectral features and (ii) the measurement of absolute values of the various cross sections, elastic and inelastic.

The lack of availability of cross section data is currently a stumbling block to understanding radiation physics in the gas and condensed phases. The use of gas phase cross sections for modeling condensed phase phenomena has certain limitations imposed by the existence of strong collective excitation peaks in the valence or band spectra of solids. On the other hand the absolute gas phase cross sections for inner shell excitation may be of use in modeling solid state radiation processes.

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