Direct measurement of local lattice distortions in strained layer structures by HREM

Abstract

We present a method which allows the direct measurement of local displacements within a crystal lattice by high-resolution electron microscopy (HREM). The basic idea of this method is the formation of moiré structures when two two-dimensional lattices are superimposed. The first lattice is given by the experimental micrograph and the second one is calculated from an undisturbed area of the first. From the analysis of the resulting moiré structure the local displacements of the crystal lattice with respect to the calculated lattice are deduced. We thus measure strain (which is characteristic for each element embedded in the host lattice) and thickness of the strained layers independently. Simultaneously, the positions of the interfaces are identified, without relying on the contrast difference between the constituent materials. Therefore, this novel method represents a chemical mapping which is inherently free of contrast interpretations.