Partial coherence of inelastically scattered electrons in transmission electron microscopy

Coherence of electron waves is central to transmission electron microscopy. However, the mechanism underlying partial loss of coherence during inelastic scattering has been a perplexing problem for many decades. Here we show that the inelastic collision time is the key parameter governing coherence. Large energy transfers have short collision times and an inversely decaying coherence length. It is also shown that the inelastic coherence volume is highly elongated along the electron beam direction. Plasmon excitation and inter-band transition events therefore have only a minor effect on dynamical diffraction, a fact confirmed by energy filtered measurements on [001]-oriented SrTiO3.