Assessing the mechanical strength of interfacial atomic bonds by quantitative high-resolution transmission electron microscopy

Abstract

A method is presented for quantitatively assessing the strength of interatomic bonding forces across interfaces between two dissimilar crystalline materials. At such interfaces, the mismatch of corresponding lattice parameters gives rise to a periodic pattern of linear regions of poor match, denoted as ‘misfit dislocations’. The atom displacements that occur in these regions constitute an ‘image’ of the bonding forces across the interface. By fitting a model of the displacement field to experimentally determined atom positions at misfit dislocation cores, therefore, it should be possible to assess the mechanical strength of the interatomic bonds across the interface. The feasibility of this approach is demonstrated for the cube-on-cube interface between a SrTiO₃(001) substrate and an epitaxial layer of SrZrO₃. The atom positions at the misfit dislocations in this interface were determined with small error limits (0.03 nm) by quantitative high-resolution transmission electron microscopy. By fitting a continuum model describing the displacement field of misfit dislocations as a function of elasticity parameters of the interfacial bond layer and the two juxtaposed crystals, it is possible to determine the shear stiffness of the interatomic bonds across this interface quantitatively and with well-defined error limits (30%). Moreover, the analysis enables determining Poisson's ratio and the shear modulus of epitaxial layers, in this case SrZrO₃. The method introduced here has a broad range of applications.