Dynamical diffraction effects of inhomogeneous strain fields investigated by scanning convergent electron beam diffraction and dark field electron holography

Abstract

Many material properties can be tuned by strain fields within the specimen. Examples range from mechanical properties of alloy hardening to electro-optical properties like emission wavelengths in semiconductor heterostructure quantum wells. While several transmission electron microscopy techniques for the measurements of these strain fields exists, these techniques typically neglect strain variations along the electron beam or try to mitigate their effects. Here we investigated the effects of these strain inhomogeneities along the beam direction under dynamical diffraction conditions. We performed scanning convergent beam electron diffraction and tilt series of dark-field electron holography measurements on an inclined layer structure, which exhibits a known 3D strain field. These measurements are compared with numerical multi-beam calculations, which allows to identify the depth of the strain inhomogeneity from the measured data. However, we observed a ambiguity of diffracted intensities stemming from a strain inhomogeneity which is symmetric with respect to the specimens mid-plane. The phases of the diffracted beams do not exhibit this symmetry. Furthermore, we also investigate the influence of experimental parameters like defocus and specimen curvature as well as relaxation effects on the measurements. We anticipate that the reported systematical investigations will form a starting point for the use of dynamical diffraction effects for more thorough measurements of 3D strain fields.