Inelastic scattering

Scattering with significant loss of energy. See also [animation]

The term inelastic scattering refers to a process by which the primary electron loses a significant amount of energy. Among these processes are:

• The excitation of a plasmon (a collective oscillation of the valence electrons).
• The excitation of one or more phonons (quanta of lattice vibration) and thus heat.
• The ejection of an inner-shell electron (in this simulation a K-shell or 1s electron).
• The ejection of an outer shell electron (in this simulation an L-shell electron, 2s or 2p).
• Interaction with a single electron in the valence band.

Electron trajectories in the vicinity of the specimen electrons are determined by forces of repulsion. The closer the approach, the larger is the deviation of the electron trajectory. In the case of electrostatic interactions and collisions between the beam electrons and the electrons surrounding the atomic nucleus, the deflected electrons are likely to undergo a loss of energy (i.e. shift to longer wavelength and lower velocity). The energy loss is generally on the order of 10-20 eV for thin specimens (<100 nm) where there is generally only one scattering event as the electron passes through the specimen. The beam electrons suffering such an energy loss are deflected through very small angles (~10-4 radians), thus nearly all of them pass through the objective aperture. The proportional energy loss due to inelastic collisions corresponds to fluctuations in the accelerating voltage of the order one part in 104-105. Thus, the change in wavelength produced by a single electron scattering event is relatively insignificant. However, multiple scattering, which can occur in relatively thick specimens, can be a serious source of chromatic aberration in the image.