Targeted modification of interfacial structure in epitaxially-strained rare-earth nickelate heterostructure

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Interface-engineering, controlled at the level of the unit-cell can exhibit unconventional magnetic, electric, even superconductivity and/or catalytic properties of artificial rare-earth nickelates superlattice- and multilayer heterostructures opening the route towards new electronic devices. As their properties cannot be explained as sum of each constitu-ent, it is required to unravel on the atomic scale the interconnection of the heteroepitaxial interfacial design and the properties of the underlying crystal structure. With our 2-years project we intend to make an essential contribution to this topic by determining - for selected heterostructures - the atomic structure of the interfaces and its chemical and electronic properties. The prerequisites for the successful completion of this task are very good, because the key problem, the successful sample preparation strategy for imaging the individual atomic columns that build the interface were solved in the past 2-years funding period. Moreover, we elucidated the necessary material combi-nations and individual layer thicknesses that can effectively influence the epitaxial inter-facial tension, the deformation of the functional octahedra, the chemical nature of the interface, the valence states and the defect structure. We thus gained the knowledge necessary to successfully investigate the new heterostructures. The application-determining key questions to be solved within the next two-years period are: (1) how does epitaxial strain, interfacial lattice-and symmetry mismatch as well as defects affect the octahedral networkat the interface and in the individual layer stacks and (2) how chemically sharp are the hetero-interfaces, what is the degree of chemical intermixing and/or interface roughness and (3) how structural modifications in-fluence the electronic properties, such as the charge and bonding state locally and those of the entire heterostructure? The heterostructures are produced by our cooperation partner Dr. Benckiser, MPI / FKF Stuttgart using laser-assisted atomic layer deposition (ALD). To answer the above-mentioned questions, we will employ aberration-corrected high-resolution TEM, density functional theory calculations, and, moreover, methods of scanning TEM (partly in coop-eration with the Ernst Ruska Centre) in connection with local spectroscopy (EELS and EDX).