In this introductory paper, my primary concern will be in identifying
and outlining the various types of inelastic processes resulting from the
interaction of electrons with matter. Elastic processes are understood
reasonably well at the present experimental level and can be regarded as
giving information on spatial arrangements. We need not consider them here.
Inelastic processes do contain information of considerable value which
reflect the electronic and chemical structure of the sample. In combination
with the spatial resolution of the electron microscope, a unique probe of
materials is finally emerging (Hillier 1943, Watanabe 1955, Castaing and
Henri 1962, Crewe 1966, Wittry, Ferrier and Cosslett 1969, Isaacson and
Johnson 1975, Egerton, Rossouw and Whelan 1976, Kokubo and Iwatsuki 1976,
Colliex, Cosslett, Leapman and Trebbia 1977). We first review some
scattering terminology by way of background and to identify some of the more
interesting and significant features of energy loss electrons and then go on
to discuss examples of studies of the type of phenomena encountered. Finally
we will comment on some of the experimental factors encountered.