scattering contrast

Incident electrons are scattered by constituent atoms in a specimen. When scattered electrons are stopped by the objective aperture, those scattered electrons act as if there arises electron absorption in the specimen. This is expressed as scattering absorption. The scattering cross section of the electron becomes larger as the mass of the atom is larger, and then image contrast produced by differences in scattering amount is termed “scattering contrast.” Since the scattering cross section for electrons is large for the atom with a large mass, the scattering contrast is sometimes called “mass contrast.” The contrast of a TEM image taken from a non-crystalline specimen is explained by the scattering contrast. In the case of a crystalline specimen, elastically scattered waves behave as diffracted waves. Thus, this image contrast is interpreted by the behavior of the diffracted waves.


TEM image of kidney tubules of a mouse taken at an accelerating voltage of 120 kV.

The specimen was chemically fixed using gultaraldehyde and osmium tetroxide and then, subjected to electron staining by uranium acetate and lead citrate. The parts containing heavy elements (osmium, uranium and lead) scatter more electrons at large angles (than the areas containing light elements), and such electrons are intercepted by the objective aperture. As a result, the parts are observed with low intensity (as dark).

Related Term(s)