Phonon Scattering in High-Resolution Electron Microscopy

Abstract

It is generally accepted that the lattice fringe contrast in experimental high-resolution electron microscope (HREM) images is lower than that in image simulations by a factor of between 2 and 6 [1]. One likely reason for this discrepancy is the contribution phonon, or thermal diffuse, scattering makes to lattice images. Electrons scattered by phonons are visible as diffuse scattering between the Bragg spots in the diffraction pattern and the loss in intensity of the Bragg spots is modeled by the Debye-Waller factor in image simulations. However, the additive effect of this diffuse scattering on images is not taken into account by image simulations. The amount of phonon scattering as a function of specimen thickness has been measured both for Si by convergent beam diffraction [2] and for ZrB12 by electron holography [3] and in both cases found to contribute about 10% of the total intensity at a thickness typically used in high resolution imaging.