The magnitude of the interaction of the electrons with a material scales as 2 π π m ∗ ∗ h 2 k = 2 π π m ∗ ∗ λ λ h 2 = π π h c 2 m 0 c 2 E + 1 . While the wavevector increases as the energy increases, the change in the effective mass compensates this so even at the very high energies used in electron diffraction there are still significant interactions.