Reza Mahjoub

Direct Evidence for Cation Non‐Stoichiometry and Cottrell Atmospheres Around Dislocation Cores in Functional Oxide Interfaces

Perovskite oxides are a ubiquitous class of functional oxide materials that are used in a variety of nanoscale functional applications. In order to exploit their properties, these materials are often deposited on a dissimilar underlying substrate. A critical consequence of this process is the formation of misfit dislocation arrays at the film-substrate interface as a mechanism to release the lattice mismatch strain. Although dislocation cores are only a few angstroms wide, the associated strain-fields are often significant and long-range. Theoretical computations of the strain-field for metals reveal that the stress due to the local strain around the core can be equal to or even higher, than the yield stress. Concurrently, the trend of aggressive downsizing has resulted in functional materials being confined to nanometric volumes. The presence of even a single defect, and its associated long-range field, could adversely affect device performance. Such longrange strain fields are known to affect both the microstructure and electronic states. More recently the detrimental effect of this strain field on the polarization and electromechanical

Ferroelastic domains in bilayered ferroelectric thin films

We investigate theoretically ferroelastic domain fractions in a heteroepitaxial bilayer consisting of (001) tetragonal PbZrxTi1−xO3 and (001) rhombohedral PbZr1−xTixO3 on a thick (001) passive substrate as a function of the lattice misfit strain between layers and the substrate. By considering the self-strain in each layer and the indirect elastic interaction between the layers, we provide a numerical analysis of the relative domain fractions in the tetragonal layer of a (001)PbZr0.2Ti0.8O3/(001)PbZr0.8Ti0.2O3 and (001)PbZr0.4Ti0.6O3/(001)PbZr0.6Ti0.4O3 bilayer structure as a function of the tetragonal layer thickness on (001)LaAlO3, (001)SrTiO3, and (001) MgO. It is found that the elastic coupling between the tetragonal and rhombohedral layers leads to an excess elastic energy in the tetragonal layer, resulting in a two to three times increase in the ferroelastic domain volume fraction of the tetragonal layer compared to single-layer films of similar thickness. These results show alternate ways of engine...

Analytical Aberration-Corrected STEM of Ferroelectric Functional Interfaces

SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane, Daresbury WA4 4AD, U.K. School of Mat. Sci. and Engineering, U. of New South Wales, Sydney NSW 2052, Australia. Monash Centre for Electron Microscopy, Monash University, Victoria 3800, Australia. Max Planck Institute for Microsctructural Physics, Weinberg 2, D-06120 Halle, Germany Dept. of Chem. Eng. and Mat. Sci., University of California-Davis, Davis CA 95616 Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore CA 94550